Дисертації: "Mechanism impact model"

1

Valacchi, Giulia. "An intertemporal pricing model for CO2 allowances: The impact of the clean development mechanism." Master's thesis, NSBE - UNL, 2013. http://hdl.handle.net/10362/11603.

Повний текст джерела

Анотація:

A Work Project, presented as part of the requirements for the Award of a Masters Degree in Finance from the NOVA – School of Business and Economics
The increasing global attention to greenhouse emissions and the recent creation of EU Emission Trading Scheme has clearly suggested the need of consistent methods to value projects aimed to reduce gases. This need particularly concerns companies that have to find a way to both remain profitable and conform to new legal requirements. Multiple ways of cutting emission costs are available nowadays: short term abatement measures, which primary involve switching production machinery from coal to gas; long term abatement measures, which envisage the implementation of new types of projects .e.g Clean Development Mechanism or Joint Implementation Mechanism suggested by Kyoto Protocol -. In this work we study the impact of the introduction of both kinds of policy in a pricing model for CO2 allowances.

Стилі APA, Harvard, Vancouver, ISO та ін.

2

Vignotto, Davide. "Analysis of the in-Flight Performance of a Critical Space Mechanism." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/323575.

Повний текст джерела

Анотація:

Gravitational waves detection is a challenging scientific objective, faced by scientist in the last 100 years, when Einstein theorized their existence. Despite multiple attempts, it was only in 2016 that the first observation of a gravitational wave was officially announced. The observation, worth a Nobel Prize, was made possible thanks to a worldwide collaboration of three large ground-based detectors. When detecting gravitational waves from ground, the noisy environment limits the frequency bandwidth of the measurement. Thus, the type of cosmic events that are observable is also limited. For this reason, scientists are developing the first gravitational waves detector based in space, which is a much quieter environment, especially in the sub-Hertz bandwidth. The space-based detector is named laser interferometer space antenna (LISA) and its launch is planned for 2034. Due to the extreme complexity of the mission, involving several new technologies, a demonstrator of LISA was launched and operated between 2015 and 2017. The demonstrator mission, called LISA Pathfinder (LPF), had the objective to show the feasibility of the gravitational waves observation directly from space, by characterizing the noise affecting the relative acceleration of two free falling bodies in the milli-Hertz bandwidth. The mission was a success, proving the expected noise level is well below the minimum requirement. The free-falling bodies of LPF, called test masses (TMs), were hosted inside dedicated electrode housings (EH), located approximately 30 cm apart inside the spacecraft. When free falling, each TM stays approximately in the center of the EH, thus having milli-meter wide gaps within the housing walls. Due to the presence of such large gaps, the TMs were mechanically constrained by dedicated mechanisms (named CVM and GPRM) in order to avoid damaging the payload during the launch phase and were released into free fall once the spacecraft was in orbit. Prior to the start of the science phase, the injection procedure of the TMs into free-fall was started. Such a procedure brought each TM from being mechanically constrained to a state where it was electro-statically controlled in the center of the EH. Surprisingly, the mechanical separation of the release mechanism from the TM caused unexpected residual velocities, which were not controllable by the electrostatic control force responsible for capturing the TM once released. Therefore, both the TMs collided with either the surrounding housing walls or the release mechanism end effectors. It was possible to start the science phase by manually controlling the release mechanism adopting non-nominal injection strategies, which should not be applicable in LISA, due to the larger time lag. So, since any release mechanism malfunctioning may preclude the initialization of LISA science phase, the GPRM was extensively tested at the end of LPF, by means of a dedicated campaign of releases, involving several modifications to the nominal injection procedure. The data of the extended campaign are analyzed in this work and the main conclusion is that no optimal automated release strategy is found for the GPRM flight model as-built configuration that works reliably for both the TMs producing a nominal injection procedure. The analysis of the in-flight data is difficult since the gravitational referencesensor of LPF is not designed for such type of analysis. In particular, the low sampling frequency (i.e., 10 Hz) constitutes a limiting factor when detecting instantaneous events such as collisions of the TM. Despite the difficulties of extracting useful information on the TM residual velocity from the in-flight data, it is found that the main cause of the uncontrollable state of the released TM is the collision of the TM with the plunger, i.e., one of the end-effectors of the GPRM. It is shown that the impact is caused by the oscillation of the plunger or by the elastic relaxation of the initial preload force that holds the TM. At the end of the analysis, some improvements to the design of the release mechanism are brie y discussed, aimed at maximizing the probability of performing a successful injection procedure for the six TMs that will be used as sensing bodies in the LISA experiment.

Стилі APA, Harvard, Vancouver, ISO та ін.

3

Griffiths, Genevieve S. "Investigating the impact and mechanism of vesicular and non-vesicular mediated GPI-linked protein transfer from reproductive luminal fluids to sperm, using SPAM1 as a model." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 119 p, 2007. http://proquest.umi.com/pqdweb?did=1397900391&sid=22&Fmt=2&clientId=8331&RQT=309&VName=PQD.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

4

Maire, du Poset Aline. "Hydrogels de polygalacturonate réticulés par les ions Fe2+ : impact du mode d'association local sur les mécanismes de gélification, contrôle de la structure multi-échelle et des propriétés mécaniques." Thesis, Bourgogne Franche-Comté, 2018. http://www.theses.fr/2018UBFCK029/document.

Повний текст джерела

Анотація:

Ce travail de thèse décrit la formulation d'hydrogels de polygalacturonate (polyGal) réticulés par les cations Fe2+, ainsi que leur caractérisation expérimentale depuis les échelles moléculaires jusqu'aux échelles macroscopiques, en utilisant notamment la spectroscopie d'absorption X (EXAFS), la diffusion de neutrons aux petits angles (DNPA) ainsi que des mesures de rhéologie. Nous avons élaboré un protocole de gélification robuste permettant d'obtenir des gels cylindriques reproductibles qui présentent des gradients de concentrations contrôlés depuis leur partie basale jusqu'à leur partie apicale. Le rapport R = [Fe]/[Gal] a une valeur constante de 0,25 tout au long du gel, ce qui prouve que les cations Fe2+ s'associent avec 4 unités galacturonate. La confrontation des résultats d’EXAFS et de dynamique moléculaire a démontré que ces associations se font via le modèle ''egg-box''. Les mécanismes de réticulation qui contrôlent la structure du réseau formée par les chaînes aux échelles locales sont donc les mêmes dans l'ensemble du gel, ce qui est confirmé par les mesures de DNPA. La formation des gradients de concentration macroscopiques provient des mécanismes de diffusion des cations à travers le gel lors de sa formation. Ces gradients de concentration contrôlent les propriétés mécaniques des gels. En outre, nous avons prouvé que le mode d'association "egg-box" permettait la protection des ions Fe2+ contre l'oxydation, ce qui confère à ces hydrogels un potentiel applicatif pour soigner l'anémie car ils pourraient permettre la vectorisation du fer sous cette forme réduite biodisponible jusqu’à l’intestin.Nous avons étendu notre étude à la formulation d'hydrogels avec d'autres cations (Ca2+ et Zn2+). Ces hydrogels présentent des propriétés macroscopiques proches de celles des hydrogels Fe2+-polyGal car les mécanismes de diffusion des cations régissant la formation des gradients macroscopiques lors de la formation des gels sont similaires. Les hydrogels présentent cependant des structures locales différentes car les modes d'associations locaux varient d"un cation à l’autre. L’ensemble de ces résultats nous a permis de proposer un mécanisme généralisé permettant de décrire les mécanismes de formation d"hydrogels de polygalacturonate pour les cations divalents, et ainsi de moduler finement leur structure sur plusieurs échelles. Ces hydrogels pourraient donc être des outils de choix pour la vectorisation de molécules actives et le contrôle de leur relargage
This pHD thesis describes the design of polygalacturonate hydrogels (polyGal) cross-linked by the Fe2+ cations, and their experimental characterization from the molecular scales up to the macroscopic scales, by combining EXAFS spectroscopy, Small Angle Neutron Scattering (SANS) and rheological measurements. We designed a robust gelling protocol that allowed to obtain reproducible cylindrical gels with controlled concentration gradients from the lower side to the upper side of the gel. The ratio [Fe]/[Gal] has a constant value all along the gel, which demonstrate that the Fe2+ cations are associated with 4 galacturonate units. The comparison of EXAFS measurements and molecular dynamics simulation has shown that these associations followed the "egg-box" model. The crosslinking mechanisms that control the structure of the network made by the chains at local scale is therefore the same throughout the whole gel, which is confirmed by SANS measurements. The formation of the macroscopic concentration gradients comes from the mechanisms that drive the cations diffusion through the gel during the gelation process. These gradients control the gels mechanical properties. Besides, we proved that the “egg-box" association enables to protect Fe2+ against oxidation, which gives to these hydrogels an applicative potential to cure anemia as they could allow to target iron under its bioavailable form up to the gut.We have extended the study to the design of hydrogels with other cations (Ca2+ et Zn2+). The macroscopic properties of these hydrogels are very close to that of the Fe2+-polyGal hydrogels because the cation diffusion that govern the formation of macroscopic gradients during the gelationg process are similar. The hydrogels have however different local structures because the cation- polyGal local association varies from one cation to another. All these results allowed us to propose a generalized mechanism that describes the polygalacturonate hydrogels formation for divalent cations, and thus to tune their structure over several scales. These hydrogels could therefore be some promising tools for the vectorization of active molecules and the control of their release

Стилі APA, Harvard, Vancouver, ISO та ін.

5

Gutierrez, Acebo Ester. "Impact of the topology of the zeolite structure on the mechanism and selectivity of ethylcyclohexane bifunctional isomerization : experiments, ab initio calculations and multi-scale kinetic modelling." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1240/document.

Повний текст джерела

Анотація:

Le paraxylène (pX), utilisé dans la fabrication de l'acide téréphtalique pour la production de nylon, est principalement produit par isomérisation de la coupe aromatique C8. Cette dernière est principalement composée des trois isomères du xylènes (para, ortho et méta) et de l'éthylbenzène (EB). L’EB est transformé en xylènes grâce à un catalyseur bifonctionnel comprenant à la fois une fonction acide comme la zéolithe EU-1 et une fonction hydro-déshydrogénante (HD/DHD) comme le platine. L’hydrogénation de l’EB conduit également à la production d’éthylcyclohexane, qui peut subir des réactions non désirées d’ouverture de cycle et de craquage sur la fonction acide du catalyseur. Au cours de ce travail, nous avons cherché à comprendre les facteurs influant sur la sélectivité du catalyseur bifonctionnel en hydroconversion de l’éthylcyclohexane (ECH), et à identifier des phases acides zéolithiques très sélectives. L’effet de paramètres tels que le ratio et la proximité entre sites acides et sites HD/DHD, la localisation des sites acides au sein du réseau zéolithique, et la topologie de ce réseau zéolithique, a été examiné. Des études catalytiques ont été mises en œuvre sur des séries de catalyseurs bifonctionnels à base de zéolithe EU-1, et interprétées à la lueur de calculs ab initio focalisés sur les mécanismes d’isomérisation et d’ouverture de cycle de l’ECH sur la phase acide EU-1. L’intégration de données thermocinétiques déterminées ab initio dans un modèle cinétique en champ moyen a permis de valider l’approche et d’identifier les étapes réactionnelles clés dictant la sélectivité. Un criblage rationnel de structures zéolithes a ensuite été proposé pour identifier les paramètres topologiques influant
The paraxylene (pX), used in the manufacture of terephtalic acid for the production of nylon, is mainly produced by isomerization of the C8 aromatic cut. The latter is mainly composed of the three xylene isomers (para, ortho and meta) and ethylbenzene (EB). EB is converted into xylenes by mean of a bifunctional catalyst comprising both an acid function, such as EU-1 zeolite, and a hydro-dehydrogenating function (HD / DHD), such as platinum. The hydrogenation of EB also leads to the production of ethylcyclohexane, which can undergo undesired ring-opening and cracking reactions on the acid function of the catalyst. In this work, we tried to understand the factors influencing the selectivity of the bifunctional catalyst in the hydroconversion of ethylcyclohexane (ECH), and to identify very selective zeolitic acid phases. The effect of parameters such as the ratio and proximity between acid and HD / DHD sites, the location of acid sites within the zeolite network, and the topology of this zeolite network, was evaluated. Catalytic studies have been carried out over bifunctional catalysts series based on the EU-1 zeolite, and interpreted considering ab initio calculations focused on the isomerization and ring-opening mechanisms of ECH on the EU-1 acid phase. The integration of thermokinetic data (determined by ab initio calculations) in a mean field kinetic model made it possible to validate the approach and to identify the key reaction steps dictating the selectivity. A rational screening of zeolite structures was then proposed to identify the influential topological parameters

Стилі APA, Harvard, Vancouver, ISO та ін.

6

Dabke, Partha [Verfasser], Anibh Martin [Akademischer Betreuer] Das, Wolfgang [Akademischer Betreuer] Löscher, and Karin [Akademischer Betreuer] Weißenborn. "Mechanism of Ketogenic Diet: Impact of Beta – Hydroxybutyrate and Decanoic Acid on Sirtuins, Energy Metabolism and Cellular Lipids in a Murine Hippocampal Neuronal Cell Model / Partha Dabke ; Anibh Martin Das, Wolfgang Löscher, Karin Weißenborn." Hannover : Stiftung Tierärztliche Hochschule Hannover, 2020. http://d-nb.info/1224883012/34.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

7

Modarres, Najafabadi Seyed Ali. "Dynamics modelling and analysis of impact in multibody systems." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115886.

Повний текст джерела

Анотація:

In this thesis, we discuss a novel approach to the dynamics modelling and analysis of impact in unilaterally constrained multibody systems. This approach is based on an analysis of energy absorption and restitution during impact, using a decomposition technique, which decouples the kinetic energy associated with the spaces of admissible and constrained motions of unilateral contacts. This is done based on the decomposition of the tangent space of the configuration manifold at the pre-impact instant. The decomposition of the kinetic energy can provide a picture of how the energy absorption and dissipation during impact is related to the variation of the generalized velocities and the configuration of multibody systems.
Further, based on the above analysis approach, we introduce a new interpretation of the energetic coefficient of restitution, specially applicable to contact involving multibody systems. This interpretation generalizes the concept of the energetic coefficient of restitution and allows for consideration of simultaneous multiple-point contact scenarios. Moreover, based on the concept of the generalized energetic coefficient of restitution, the contact modes and the post-impact state of planar single-point impact are determined. Further, the problem of simultaneous multiple-point impact is considered, where it is shown that our approach can also be advantageous to characterize the dynamics of interaction in such systems.
The use and applicability of the approach reported are further investigated by conducting an experimental study on a robotic testbed. The open architecture of the testbed allows us to perform various contact experiments, such as single- and multiple-point impact scenarios, with different pre-impact configurations and velocities. The kinematic and dynamic models of the system have been developed and implemented for real-time analysis. It is shown that impact between multibody systems is considerably affected by not only the local dynamics characteristics of the interacting bodies, but also the (global) configuration of the interacting multibody systems. The reported results suggest that the material presented herein offers a useful means to characterize impact in complex systems.

Стилі APA, Harvard, Vancouver, ISO та ін.

8

Zeng, Ning. "Climatic impact of Amazon deforestation: A study of underlying mechanism through simple modeling." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186999.

Повний текст джерела

Анотація:

An intermediate level model for tropical climatology including atmosphere-land-ocean interaction is developed. The model contains basically linearized steady state primitive equations with simplified thermodynamics. A simple hydrological cycle is also included. Special attention has been paid to land surface processes in attempting to study climate change caused by Amazon deforestation. In comparison with previous simple modeling work on tropical climatology or anomaly, the present model is more sophisticated in the sense that it predicts all the important meteorological variables with little input, while being computationally simple. The modeled tropical climatology appears to be realistic. The model generally better simulates the ENSO anomaly compared to many previous simple model simulations. We provide analysis of model results and discuss model deficiencies and possible improvements of the model. The climatic impact of Amazon deforestation is studied in the context of this model. Model results show a much weakened Atlantic Walker/Hadley circulation as a result of the existence of a strong positive feedback loop in the atmospheric circulation system and the hydrological cycle. The regional climate is very sensitive to albedo change and sensitive to evapotranspiration change. The pure dynamical effect of surface roughness on convergence is small, but the surface flow anomaly displays intriguing features. Analysis of the thermodynamic equation reveals the balance among convective heating, adiabatic cooling and radiation largely determines the deforestation response. The model provides a plausible mechanism for the common results of many GCM simulations. Studies of the consequences of hypothetical continuous deforestation suggest that the replacement of forest by desert may be able to sustain a desert-like climate. When a simple mixed layer ocean model is coupled with the atmospheric model, the results suggest a 1 °C decrease in SST gradient across the equatorial Atlantic ocean in response to Amazon deforestation. The magnitude of the decrease depends on the coupling strength.

Стилі APA, Harvard, Vancouver, ISO та ін.

9

Sirivolu, Dushyanth. "An Analytical Model for High-Velocity Impact of Composite Sandwich Panels." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1227548412.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

10

Silvestri, Chiara. "Development and validation of a knee-thigh-hip LSDYNA model of a 50th percentile male." Worcester, Mass. : Worcester Polytechnic Institute, 2008. http://www.wpi.edu/Pubs/ETD/Available/etd-042908-144927/.

Повний текст джерела

Анотація:

Dissertation (Ph.D.)--Worcester Polytechnic Institute.
Keywords: active muscles, out-of-position, fracture mechanisms, impacts, KTH, dynamic ligament failure model. Includes bibliographical references (leaves 353-365).

Стилі APA, Harvard, Vancouver, ISO та ін.

11

Zitzman, Spencer T. "Pornography viewing as attachment trauma in pair-bond relationships : a theoretical model of mechanisms /." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2148.pdf.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

12

Jiang, Tianci. "Impact & penetration studies simplified models and and materials design from AB initio methods /." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10443.

Повний текст джерела

Анотація:

In recent impact and penetration mechanical tests, steel projectiles (AISI4340) were impacted into targets like concrete with striking velocities (1200 m/s to 1500 m/s). Results indicated a material removal from the nose of the projectile, phase changes of the projectile materials, a reduction in the length of the projectile, and a blunting of the nose shape. These observations cannot be explained by current theories and numerical integration code that are used to study impact and penetration mechanics. Thus, the objectives of the thesis research are to (a) formulate and characterize the mechanisms responsible for the material erosion of the impacting projectile and the mass loss from the nose region; and (b) to determine the physical properties of alloy steels that are important to penetration mechanics from ab initio methods. The results can be used to design new projectile materials that can provide the desired penetration characteristics. These objectives are accomplished by investigating two related problems. The first problem is to formulate simplified models that can explain the penetration mechanics. The new models include the varying cross-section nose, changes of yield stress behind the shock wave and high strain rate phase transitions. Nose erosion effects, and time-dependent penetration path can be determined by integrating ODEs. A cavity expansion theory model is used to obtain the target resistance that is responsible slowing and deforming the penetrating projectile. The second problem concerns the determination of the constitutive relations from ab initio methods. The equation of state (EOS) and magnetic moments for alloy steels are investigated by using a special quasirandom structure technique and ab initio methods. Specifically, EOS for an interstitial disordered alloy Fe1-x-yNixCy is developed. First, the EOS of iron and phase transition of iron are studied and validated. Second, Nickel is considered to investigate the substitutional disordered alloy Fe1-x-yNixCy. Third, Carbon is placed at an interstitial position in the substitutional disordered alloy. These investigations will form foundation for future work involving new projectile with steel nose and shank made of multifunctional structural energetic materials.

Стилі APA, Harvard, Vancouver, ISO та ін.

13

Fievisohn, Elizabeth Mary. "Traumatic Brain Injury Mechanisms in the Gottingen Minipig in Response to Two Unique Input Modes." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64280.

Повний текст джерела

Анотація:

Traumatic brain injury (TBI) continues to be a widespread problem in the United States with approximately 1.7 million occurrences annually [1]. Current automotive crash test standards use the Head Injury Criterion (HIC) [2] to assess head injury potential, but this metric does not relate an impact to underlying damage. For an injury metric to effectively predict TBI, it is crucial to relate level of impact to resulting injury. The research presented in this dissertation explains the development and repeatability of two novel injury devices, impact response characterization over the course of 24 hours in the Gottingen minipig and the relationships between metabolite changes, underlying disruption, and impact kinematics, and the characterization of impact response over the course of 72 hours. The translation-input and combined translation and rotation-input injury devices were shown to be repeatable, minimizing the number of animals needed for testing. Impact response over the course of 24 hours showed axonal disruption through immunostaining and proton magnetic resonance spectroscopy. The translation-input injury group metabolite analyses revealed the initial stages of glutamate excitotoxicity while the combined-input injury group showed a clear pathway for glutamate excitotoxicity. Numerous correlative relationships and potential underlying disruption predictors were found between metabolites, immunostaining, and kinematics. The most promising predictor combination for the translation-input injury device was N-acetylaspartylglutamate/Scyllo at 24 hours compared to 1 hour and linear speed for predicting underlying light neurofilament disruption. For the combined-input injury device, the strongest predictor combination was Glutamine/N-acetylaspartylglutamate at 24 hours compared to baseline and angular acceleration for predicting underlying light neurofilament disruption. Statistically significant predictors were found between Glutamate+Glutamine/Total Creatine at 24 hours compared to baseline and all kinematics and injury metrics with an angular component for predicting heavy neurofilament disruption. Analyses over the course of 72 hours revealed persistent axonal disruption and metabolite perturbations. Overall, this dissertation and the complementary parts of this project have many societal implications. Due to the high incidence of traumatic brain injury, there is a need for prevention, mitigation, and treatment strategies. Developing a new injury metric will help improve prevention strategies, especially in the automotive, sporting, and military environments. 1 Faul, M., Xu, L., Wald, M. M., and Coronado, V. G. (2010). Traumatic Brain Injury in the United States. Atlanta, GA: Centers for Disease Control and Prevention, National Center for Injury Prevention and Control. 2 Versace, J. (1971). A Review of the Severity Index. SAE Technical Paper. No. 710881
Ph. D.

Стилі APA, Harvard, Vancouver, ISO та ін.

14

Signetti, Stefano. "Computational models for impact mechanics and related protective materials and structures." Doctoral thesis, Università degli studi di Trento, 2017. https://hdl.handle.net/11572/368874.

Повний текст джерела

Анотація:

The mechanics of impacts is not yet well understood due to the complexity of materials behaviour under extreme stress and strain conditions and is thus of challenge for fundamental research, as well as relevant in several areas of applied sciences and engineering. The involved complex contact and strain-rate dependent phenomena include geometrical and materials non-linearities, such as wave and fracture propagation, plasticity, buckling, and friction. The theoretical description of such non-linearities has reached a level of advance maturity only singularly, but when coupled -due to the severe mathematical complexity- remains limited. Moreover, related experimental tests are difficult and expensive, and usually not able to quantify and discriminate between the phenomena involved. In this scenario, computational simulation emerges as a fundamental and complementary tool for the investigation of such otherwise intractable problems. The aim of this PhD research was the development and use of computational models to investigate the behaviour of materials and structures undergoing simultaneously extreme contact stresses and strain-rates, and at different size and time scales. We focused on basic concepts not yet understood, studying both engineering and bio-inspired solutions. In particular, the developed models were applied to the analysis and optimization of macroscopic composite and of 2D-materials-based multilayer armours, to the buckling-governed behaviour of aerographite tetrapods and of the related networks, and to the crushing behaviour under compression of modified honeycomb structures. As validation of the used approaches, numerical-experimental-analytical comparisons are also proposed for each case.

Стилі APA, Harvard, Vancouver, ISO та ін.

15

Moore, Matthew Richard. "New mathematical models for splash dynamics." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:c94ff7f2-296a-4f13-b04b-e9696eda9047.

Повний текст джерела

Анотація:

In this thesis, we derive, extend and generalise various aspects of impact theory and splash dynamics. Our methods throughout will involve isolating small parameters in our models, which we can utilise using the language of matched asymptotics. In Chapter 1 we briefly motivate the field of impact theory and outline the structure of the thesis. In Chapter 2, we give a detailed review of classical small-deadrise water entry, Wagner theory, in both two and three dimensions, highlighting the key results that we will use in our extensions of the theory. We study oblique water entry in Chapter 3, in which we use a novel transformation to relate an oblique impact with its normal-impact counterpart. This allows us to derive a wide range of solutions to both two- and three-dimensional oblique impacts, as well as discuss the limitations and breakdown of Wagner theory. We return to vertical water-entry in Chapter 4, but introduce the air layer trapped between the impacting body and the liquid it is entering. We extend the classical theory to include this air layer and in the limit in which the density ratio between the air and liquid is sufficiently small, we derive the first-order correction to the Wagner solution due to the presence of the surrounding air. The model is presented in both two dimensions and axisymmetric geometries. In Chapter 5 we move away from Wagner theory and systematically derive a series of splash jet models in order to find possible mechanisms for phenomena seen in droplet impact and droplet spreading experiments. Our canonical model is a thin jet of liquid shot over a substrate with a thin air layer trapped between the jet and the substrate. We consider a variety of parameter regimes and investigate the stability of the jet in each regime. We then use this model as part of a growing-jet problem, in which we attempt to include effects due to the jet tip. In the final chapter we summarise the main results of the thesis and outline directions for future work.

Стилі APA, Harvard, Vancouver, ISO та ін.

16

Lee, Jong Wook. "Development of a numerical model of rock failure mechanisms associated with the impact of lateral displacement." Access electronically, 2005. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20051110.162002/index.html.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

17

McTaggart, Kevin Andrew. "Hydrodynamics and risk analysis of iceberg impacts with offshore structures." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/30733.

Повний текст джерела

Анотація:

The evaluation of design iceberg impact loads for offshore structures and the influence of hydrodynamic effects on impact loads are examined. Important hydrodynamic effects include iceberg added mass, wave-induced oscillatory iceberg motions, and the influence of a large structure on the surrounding flow field and subsequent velocities of approaching icebergs. The significance of these phenomena has been investigated using a two-body numerical diffraction model and through a series of experiments modelling the drift of various sized icebergs driven by waves and currents approaching a large offshore structure. Relevant findings from the hydrodynamic studies have been incorporated into two probabilistic models which can be used to determine design iceberg collision events with a structure based on either iceberg kinetic energy upon impact or global sliding force acting on the structure. Load exceedence probabilities from the kinetic energy and sliding force models are evaluated using the second-order reliability method. Output from the probabilistic models can be used to determine design collision parameters and to assess whether more sophisticated modelling of various impact processes is required. The influence of the structure on velocities of approaching icebergs is shown to be significant when the structure horizontal dimension is greater than twice the iceberg dimension. As expected, wave-induced oscillatory motions dominate the collision velocity for smaller icebergs but have a negligible effect on velocity for larger icebergs.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

Стилі APA, Harvard, Vancouver, ISO та ін.

18

Parrinello, Antonino. "A rate-pressure-dependent thermodynamically-consistent phase field model for the description of failure patterns in dynamic brittle fracture." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:c6590f4f-f4e2-40e3-ada1-49ba35c2a594.

Повний текст джерела

Анотація:

The investigation of failure in brittle materials, subjected to dynamic transient loading conditions, represents one of the ongoing challenges in the mechanics community. Progresses on this front are required to support the design of engineering components which are employed in applications involving extreme operational regimes. To this purpose, this thesis is devoted to the development of a framework which provides the capabilities to model how crack patterns form and evolve in brittle materials and how they affect the quantitative description of failure. The proposed model is developed within the context of diffusive interfaces which are at the basis of a new class of theories named phase field models. In this work, a set of additional features is proposed to expand their domain of applicability to the modelling of (i) rate and (ii) pressure dependent effects. The path towards the achievement of the first goal has been traced on the desire to account for micro-inertia effects associated with high rates of loading. Pressure dependency has been addressed by postulating a mode-of-failure transition law whose scaling depends upon the local material triaxiality. The governing equations have been derived within a thermodynamically-consistent framework supplemented by the employment of a micro-forces balance approach. The numerical implementation has been carried out within an updated lagrangian finite element scheme with explicit time integration. A series of benchmarks will be provided to appraise the model capabilities in predicting rate-pressure-dependent crack initiation and propagation. Results will be compared against experimental evidences which closely resemble the boundary value problems examined in this work. Concurrently, the design and optimization of a complimentary, improved, experimental characterization platform, based on the split Hopkinson pressure bar, will be presented as a mean for further validation and calibration.

Стилі APA, Harvard, Vancouver, ISO та ін.

19

Bowman, Adam. "Toward a Rigorous Justification of the Three-Body Impact Parameter Approximation." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/56623.

Повний текст джерела

Анотація:

The impact parameter (IP) approximation is a semiclassical model in quantum scattering theory wherein N large masses interact with one small mass. We study this model in one spatial dimension using the tools of time-dependent scattering theory, considering a system of two large-mass particles and one small-mass particle. We demonstrate that the model's predictive power becomes arbitrarily good as the masses of the two heavy particles are made larger by studying the S-matrix for a particular scattering channel. We also show that the IP wave functions can be made arbitrarily close to the full three-body solution, uniformly in time, provided one of the large masses is fixed in place, and that such a result probably will not hold if we allow all the masses to move.
Ph. D.

Стилі APA, Harvard, Vancouver, ISO та ін.

20

Buyuk, Murat. "Development of A Tabulated Thermo-Viscoplastic Material Model with Regularized Failure for Dynamic Ductile Failure Prediction of Structures under Impact Loading." Thesis, The George Washington University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3597748.

Повний текст джерела

Анотація:

It is important to understand the dynamic failure behavior of structures subjected to impact loading in order to improve the survivability. Materials under impact are utterly affected by large deformations, high strain-rates, temperature softening and varying stress-states, which finally may lead to failure. It is shown that the impact characteristics are prone to change with several independent factors such as; impact speed, material thickness, and shape and orientation of the impacting object. Validated numerical simulations of impact tests reveal that the failure on ductile metals occur at certain locations of the failure locus that is constructed on a space as a function of all three stress invariants, which indicates that the failure depends profoundly on the state-of-stress. It is shown that existing material models are not always successful enough to cover the whole range of the failure locus and predict the failure. Therefore, it is a common practice to use different sets of material model parameters tuned or calibrated to cover a specific region of the failure loci in an ad hoc manner for practical reasons to match particular test results. Even in that case, specially tuned material properties are not capable of predicting these limited cases if differences in the mesh size and pattern need to be considered.

In this dissertation a new, generic, thermo-elastic/viscoplastic material model with regularized failure is introduced. The new material model is implemented into a non-linear, explicit dynamics finite element code, LS-DYNA. A von Mises type isotropic, isochoric plasticity is utilized, where isotropic hardening, strain-rate hardening and temperature softening is considered. The model takes adiabatic heating and softening into account due to the plastic work. The constitutive relation is coupled with a new regularized accumulated failure law that is specifically developed to cover a large extent of the failure locus as a function of state-of-stress, strain-rate and temperature. Regularization treatment is implemented to reduce mesh size dependency especially for the problems where softening and failure is involved for the failure prediction.

Ductile deformation and failure mechanism of 2024-T3/T351 aluminum alloy is investigated experimentally and numerically for quasi-static and dynamic conditions at various temperatures and stress-states. An intelligently contrived test matrix is developed by designing specific test specimens with different geometries that can construct a failure locus as a function of state-of-stress, strain-rate and temperature. An inverse material characterization algorithm is then introduced to generate input data for the new material model. Tabulated inputs of characterized material test results are directly used for both the constitutive and failure treatment of the new material model. Component based specimen tests that are used to characterize the material input properties and full-scale impact tests that are performed at different target thicknesses and impact speeds are used to validate and show the robustness, accuracy and efficiency of the new material model.

It is shown that the new material model is capable of predicting ballistic limit and failure modes accurately for structures under impact even if the failure mode changes drastically. It is also shown that the new regularization model provides less mesh size dependency. These associated features of the model suggest that the new material model can be used as a promising generic tool for diverse applications of dynamic ductile deformation and failure phenomenon.

Стилі APA, Harvard, Vancouver, ISO та ін.

21

Ahmed, Lamis. "Models for analysis of young cast and sprayed concrete subjected to impact-type loads." Doctoral thesis, KTH, Betongbyggnad, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-168211.

Повний текст джерела

Анотація:

The strive for a time-efficient construction process naturally put focus on the possibility of reducing the time of waiting between stages of construction, thereby minimizing the construction cost. If recently placed concrete, cast or sprayed, is exposed to impact vibrations at an early age while still in the process of hardening, damage that threatens the function of the hard concrete may occur. A waiting time when the concrete remains undisturbed, or a safe distance to the vibration source, is therefore needed. However, there is little, or no, fully proven knowledge of the length of this distance or time and there are no established guidelines for practical use. Therefore, conservative vibration limits are used for young and hardening concrete exposed to vibrations from e.g. blasting. As a first step in the dynamic analysis of a structure, the dynamic loads should always be identified and characterized. Here it is concluded that impact-type loads are the most dangerous of possible dynamic loads on young and hardening concrete. Shotcrete (sprayed concrete) on hard rock exposed to blasting and cast laboratory specimens subjected to direct mechanical impact loads have been investigated using finite element models based on the same analysis principles. Stress wave propagation is described in the same way whether it is through hard rock towards a shotcrete lining or through an element of young concrete. However, the failure modes differ for the two cases where shotcrete usually is damaged through loss of bond, partly or over larger sections that may result in shotcrete downfall. Cracking in shotcrete due to vibrations only is unusual and has not been observed during previous in situ tests. The study of shotcrete is included to demonstrate the need of specialized guidelines for cases other than for mass concrete, i.e. structural elements or concrete volumes with large dimensions in all directions. Within this project, work on evaluating and proposing analytical models are made in several steps, first with a focus on describing the behaviour of shotcrete on hard rock. It is demonstrated that wave propagation through rock towards shotcrete can be described using two-dimensional elastic finite element models in a dynamic analysis. The models must include the material properties of the rock and the accuracy of these parameters will greatly affect the results. It is possible to follow the propagation of stress waves through the rock mass, from the centre of blasting to the reflection at the shotcrete-rock interface. It is acceptable to use elastic material formulations until the strains are outside the elastic range, which thus indicates imminent material failure. The higher complexity of this type of model, compared with mechanical models using mass and spring elements, makes it possible to analyse more sophisticated geometries. Comparisons are made between numerical results and measurements from experiments in mining tunnels with ejected rock mass and shotcrete bond failure, and with measurements made during blasting for tunnel construction where rock and shotcrete remained intact. The calculated results are in good correspondence with the in situ observations and measurements, and with previous numerical modelling results. Examples of preliminary recommendations for practical use are given and it is demonstrated how the developed models and suggested analytical technique can be used for further detailed investigations. The modelling concept has also been used for analysis of impact loaded beams and concrete prisms modelled with 3D solid elements. As a first analysis step, an elastic material model was used to validate laboratory experiments with hammer-loaded concrete beams. The laboratory beam remained un-cracked during the experiments, and thus it was possible to achieve a good agreement using a linear elastic material model for fully hardened concrete. The model was further developed to enable modelling of cracked specimens. For verification of the numerical results, earlier laboratory experiments with hammer impacted smaller prisms of young concrete were chosen. A comparison between results showed that the laboratory tests can be reproduced numerically and those free vibration modes and natural frequencies of the test prisms contributed to the strain concentrations that gave cracking at high loads. Furthermore, it was investigated how a test prism modified with notches at the middle section would behave during laboratory testing. Calculated results showed that all cracking would be concentrated to one crack with a width equal to the sum of the multiple cracks that develop in un-notched prisms. In laboratory testing, the modified prism will provide a more reliable indication of when the critical load level is reached. This project has been interdisciplinary, combining structural dynamics, finite element modelling, concrete material technology, construction technology and rock support technology. It is a continuation from previous investigations of the effect on young shotcrete from blasting vibrations but this perspective has been widened to also include young, cast concrete. The outcome is a recommendation for how dynamic analysis of young concrete, cast and sprayed, can be carried out with an accurate description of the effect from impact-type loads. The type of numerical models presented and evaluated will provide an important tool for the work towards guidelines for practical use in civil engineering and concrete construction work. Some recommendations on safe distances and concrete ages are given, for newly cast concrete elements or mass concrete and for newly sprayed shotcrete on hard rock.

QC 20150529

Стилі APA, Harvard, Vancouver, ISO та ін.

22

Diangha, Maurice Nkinyam Boh. "Punching shear modes of failure in impacted reinforced concrete beams." Thesis, University of Sheffield, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245559.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

23

Khan, Md Mahfujul H. "IMPACT PERFORMANCE AND BENDING BEHAVIOR OF COMPOSITESANDWICH STRUCTURES IN COLD TEMPERATURE ARCTIC CONDITION." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1580471034677078.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

24

Sellayah, Dyan. "Mechanisms underlying developmental induction of energy homeostasis and cardiovascular function in a mouse model : impact of pre- and post-natal nutritional mismatch." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/375583/.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

25

Blaker, Carina Louise. "THE IMPACT OF JOINT INJURY Understanding the Role of Injury Mechanism in the Structural and Symptomatic Progression of Osteoarthritis Using Mouse Models of Knee Injury." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/19983.

Повний текст джерела

Анотація:

Post-traumatic osteoarthritis (PTOA) accounts for approximately 12% of all lower limb OA. Compared to other OA-phenotypes PTOA has the advantage of a known initiating event/time, enabling early identification of at-risk patients. However, with only ~50% of those with apparently similar joint injuries progressing to PTOA, one of the challenges in the field is defining the factors which separate progressors from non-progressors. Do these factors involve tissue-specific injury; biomechanical instability; or the impact trauma at the time of injury? The aims of this thesis were to investigate the role of injury mechanism on the progression of PTOA through the assessment of structural, symptomatic and biomechanical changes in three mouse models of knee injury: (1) surgical ACL transection (ACLT: joint instability, no impact trauma), (2) mechanical ACL rupture (ACLR: joint instability plus a single impact trauma) and (3) sub-critical knee injury (no joint instability, single impact trauma). The two mouse models of ACL injury (ACLT, ACLR) replicated variable PTOA risk seen in patients. Similar to ACL injured patients, joint instability and symptoms (pain/sensitization) were not related to tissue-specific pathologies or structural PTOA progression. Specific tissue pathologies and their associations were identified in the more progressive ACLR model, aligning with OA-cartilage risk factors in patients: synovial inflammation, subchondral bone remodelling, and meniscal pathology. The interaction of OA pathology both within and between knee compartments was found to be dependent on injury mechanism, but not instability or pain. The role and consequences of loading history in joint degeneration was explored in the sub-critical joint injury model. While a single loading event did not induce PTOA, it resulted in focal osteochondral lesions, reduced ACL strength, and altered joint sensitisation. The results of this thesis highlight the importance of joint injury mechanism on PTOA risk, defining key injury- and compartment-specific joint tissue pathology associations, and identifying sub-critical injuries as risk factors for both critical injury and subsequent PTOA.

Стилі APA, Harvard, Vancouver, ISO та ін.

26

Vu, Xuan Dung. "Vulnérabilité des dalles en béton sous impact : caractérisation, modélisation et validation." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENI028/document.

Повний текст джерела

Анотація:

Le béton est un matériau dont le comportement est complexe, notamment dans le cas de sollicitations extrêmes. L’objectif de cette thèse est de caractériser expérimentalement le comportement du béton lorsque celui-ci est soumis à des sollicitations générées par un impact (compression confinée et traction dynamique) ; et de développer un outil numérique robuste permettant de modéliser son comportement de manière fiable. Dans la partie expérimentale, on a étudié des échantillons de béton provenant du centre de VTT (Centre de recherche technique en Finlande). Dans un premier temps, des essais statiques de compression triaxiale dont le confinement varie de 0 MPa (compression simple) à 600 MPa ont été réalisés. On observe que, sous l’effet de confinement la rigidité du béton devient plus importante à cause de la réduction de la porosité. Par conséquent, la résistance maximale au cisaillement du béton est augmentée. La présence d’eau joue un rôle important lorsque le degré de saturation est élevé et le béton est soumis à un fort confinement. Au delà d’un certain seuil de confinement, la résistance maximale au cisaillement diminue avec l’augmentation de la teneur en eau. L’eau influence également le comportement volumique du béton. Lorsque tous les pores libres du béton sont fermés sous l’effet de la compaction, la faible compressibilité de l’eau s’oppose à la déformation du béton, de sorte que le béton humide est moins déformé que le béton sec pour une même contrainte moyenne. Le deuxième volet du programme expérimental concerne des essais de traction dynamique à différentes vitesses de chargement, et à différents états d’humidité du béton. Les résultats obtenus montrent que la résistance en traction du béton C50 peut augmenter jusqu’à 5 fois par rapport à sa résistance statique pour une vitesse de déformation de l’ordre de 100 s-1. Dans la partie numérique, on s’intéresse à développer le modèle de comportement du béton PRM couplé (Pontiroli-Rouquand-Mazars) capable de prédire le comportement du béton sous impact. Ce modèle repose sur un couplage entre un modèle d’endommagement capable de décrire des mécanismes de dégradation et de fissuration du béton à faible confinement et un modèle de plasticité permettant de simuler le comportement du béton sous très fort confinement. L’identification du modèle a été réalisée avec les résultats des essais expérimentaux. L’amélioration du modèle, notamment sur le modèle de plasticité, porte sur trois points principaux : prise en compte de l’effet de la contrainte déviatoire dans le calcul de la contrainte moyenne ; de l’effet de l’eau avec la loi poro-mécanique au lieu de la loi des mélanges ; amélioration de la variable de couplage entre le modèle d’endommagment et le modèle élastoplastique avec une prise en compte de l’angle de Lode. Ces améliorations ont ensuite été validées par une confrontation des résultats numériques obtenus et des essais de type impact qui démontrent la fiabilité de la prédiction du modèle. Le modèle amélioré est capable de reproduire le comportement du béton sous différents trajets de chargement et à différents niveaux de confinement tout en tenant compte du degré de saturation du béton
Concrete is a material whose behavior is complex, especially in cases of extreme loads. The objective of this thesis is to carry out an experimental characterization of the behavior of concrete under impact-generated stresses (confined compression and dynamic traction) and to develop a robust numerical tool to reliably model this behavior. In the experimental part, we have studied concrete samples from the VTT center (Technical Research Center of Finland). At first, quasi-static triaxial compressions with the confinement varies from 0 MPa (unconfined compression test) to 600 MPa were realized. The stiffness of the concrete increases with confinement pressure because of the reduction of porosity. Therefore, the maximum shear strength of the concrete is increased. The presence of water plays an important role when the degree of saturation is high and the concrete is subjected to high confinement pressure. Beyond a certain level of confinement pressure, the maximum shear strength of concrete decreases with increasing water content. The effect of water also influences the volumic behavior of concrete. When all free pores are closed as a result of compaction, the low compressibility of the water prevents the deformation of the concrete, whereby the wet concrete is less deformed than the dry concrete for the same mean stress. The second part of the experimental program concerns dynamic tensile tests at different loading velocities, and different moisture conditions of concrete. The results show that the tensile strength of concrete C50 may increase up to 5 times compared to its static strength for a strain rate of about 100 s-1. In the numerical part, we are interested in improving an existing constitutive coupled model of concrete behavior called PRM (Pontiroli-Rouquand-Mazars) to predict the concrete behavior under impact. This model is based on a coupling between a damage model which is able to describe the degradation mechanisms and cracking of the concrete at weak confinement pressure and a plasticity model which allows to reproduce the concrete behavior under strong confinement pressure. The identification of the model was done using the results of experimental tests. The improvement of this model, especially the plasticity part, focuses on three main points : taking into account the effect of the deviatoric stress in the calculation of the mean stress; better accounting for the effect of water using poromechanical law instead of mixing law, improvement of the coupling variable between the damage model and the elastoplastic model with consideration of the Lode angle. These improvements were then validated by comparing numerical results and impact tests. The improved model is capable of reproducing the behavior of concrete under different loading paths and at different levels of confinement pressure while taking into account the degree of saturation of concrete

Стилі APA, Harvard, Vancouver, ISO та ін.

27

Krantz, Dino. "Methodology and vibrational analysis for measurements on a VTOL RAPS." Thesis, Linköpings universitet, Fluida och mekatroniska system, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-142928.

Повний текст джерела

Анотація:

In this thesis a methodology for measuring vibrations has been produced andinvestigated for APID 60, a rotorcraft in a Vertical Take-off and landing remotelypiloted aircraft system (VTOL RPAS). A comparative study was carried out forthe purpose of identifying the methodology with respect to design modificationscommon to the APID 60. The pilot-study identified experimental modal analysis(EMA) as a feasible part of the methodology for experimentally extracting themodal parameters of a structure. The EMA was performed on the main frameof the APID 60 where an impact hammer test was chosen as the technique forextracting the response data. As a comparison a point mass was added to thestructure to alter the dynamic properties and the test was repeated.The results from the EMA was compared with a modal analysis performednumerically with a calculation software. Comparison of the results from EMAwith the modal analysis performed numerically indicates consistency. This confirmsa good reliability of the methodology produced. However, the structure onwhich the test were preformed is simple in terms of constant structural properties.Further work should therefore investigate whether this methodology of measuringvibrations could be successfully applied to a structure with higher complexity.

Стилі APA, Harvard, Vancouver, ISO та ін.

28

Kinnaert, Xavier. "Data processing of induced seismicity : estimation of errors and of their impact on geothermal reservoir models." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAH013/document.

Повний текст джерела

Анотація:

La localisation de séismes induits ainsi que les mécanismes au foyer associés sont des outils fréquemment utilisés afin, entre autres, d’imager la structure d’un réservoir. Cette thèse présente une technique permettant de quantifier les erreurs associées à ces deux paramètres. Par cette méthode, incertitudes et imprécisions sont distinguées. La méthode a été appliquée aux sites de Soultz et de Rittershoffen pour étudier l’impact de plusieurs critères sur la localisation de la sismicité induite. Ainsi, il a été montré que l’utilisation de capteurs installés profondément dans des puits et qu’une bonne couverture sismique azimutale réduit sérieusement les incertitudes de localisation. Les incertitudes du modèle de vitesse, représentées par une distribution gaussienne des modèles avec un écart de 5% autour du modèle de référence, multiplient les incertitudes de localisation par un facteur 2 à 3. Des simplifications utilisées pour le calcul ou une mauvaise connaissance du milieu peuvent mener à des imprécisions de l’ordre de 10% spatialement non isotropes. Ainsi, les structures du sous-sol peuvent être déformées dans les interprétations. L’application d’un tir de calibration peut néanmoins corriger ce fait en grande partie. L’étude d’erreurs associées aux mécanismes au foyer ne semble cependant pas conduire aux mêmes conclusions. Le biais angulaire peut certes être augmenté par l’omission de la faille dans le modèle de vitesse, mais dans plusieurs cas il est le même que dans le cas idéal voire diminué. En outre, une meilleure couverture sismique améliorerait toujours le mécanisme au foyer obtenu. Ainsi, il n’est pas conseillé d’imager un réservoir en n’utilisant que la localisation de séismes, mais une combinaison de plusieurs paramètres sismiques pourrait s’avérer efficace. La méthode appliquée dans le cadre de cette thèse pourra servir pour d’autres sites à condition d’en avoir une bonne connaissance a priori
Induced seismicity location and focal mechanisms are commonly used to image the sub-surface designin reservoirs among other tasks. In this Ph.D. the inaccuracies and uncertainties on earthquake location and focal mechanisms are quantified using a three-step method. The technique is applied to the geothermal sites of Soultz and Rittershoffen to investigate the effect of several criteria on thee arthquake location. A good azimuthal seismic coverage and the use of seismic down-hole sensors seriously decrease the location uncertainty. On the contrary, velocity model uncertainties, represented by a 5% Gaussian distribution of the velocity model around the reference model, will multiply location uncertainties by a factor of 2 to 3. An incorrect knowledge of the sub-surface or the simplifications performed before the earthquake location can lead to biases of 10% of the vertical distance separating the source and the stations with a non-isotropic spatial distribution. Hence the sub-surface design maybe distorted in the interpretations. To prevent from that fact, the calibration shot method was proved to be efficient. The study on focal mechanism errors seems to lead to different conclusions. Obviously, the angular bias may be increased by neglecting the fault in the velocity. But, it may also be the same as or even smaller than the bias calculated for the case simulating a perfect knowledge of the medium of propagation. Furthermore a better seismic coverage always leads to smaller angular biases. Hence,it is worth advising to use more than only earthquake location in order to image a reservoir. Other geothermal sites and reservoirs may benefit from the method developed here
Die korrekte Lokalisierung von induzierter Seismizität und den dazugehörigen Herdflächenlösungensind sehr wichtige Parameter. So werden zum Beispiel die Verteilung der Erdbeben und die Orientierung ihrer Herdflächenlösungen dazu benutzt um in der Tiefe liegende Reservoirs zulokalisieren und abzubilden. In dieser Doktorarbeit wird eine Technik vorgeschlagen um diemethodisch bedingten Fehler zu quantifizieren. Mit dieser Methode werden die verschiedenen Fehlerquellen, die Unsicherheiten und die Fehler im Modell getrennt. Die Technik wird für die geothermischen Felder in Soultz und in Rittershoffen benutzt um den Einfluss verschiedener Parameter (Annahmen) auf die Lokalisierung der induzierten Seismizität zu bestimmen. Es wurde festgestellt, dass Bohrlochseismometer und eine gute azimutale Verteilung der seismischen Stationen die Unbestimmtheiten verkleinern. Die Geschwindigkeitsunbestimmheiten, die durch eine Gauss-Verteilung mit 5% Fehler dargestellt werden, vervielfachen die Lokalisierungsungenauigkeiten um einen Faktor 2 bis 3. Eine ungenaue Kenntnis des Untergrunds oder die verwendete vereinfachte Darstellung der Geschwindigkeitsverhältnisse im Untergrund (notwendig um die synthetischen Rechnungen durchführen zu können) führen zu anisotropen Abweichungen und Fehlern in der Herdtiefe von bis zu 10%. Diese können die Interpretationen des Untergrunds deutlich verfälschen. Ein “calibration shot” kann diese Fehler korrigieren. Leider können die Fehler für die Herdflächenlösungen nicht in derselben Weise korrigiert werden. Es erscheint daher als keine gute Idee, ein Reservoir nur über die Lokalisierung von Erdbeben zu bestimmen. Eine Kombination mehrerer seismischer Methoden scheint angezeigt. Die hier besprochene Methode kann als Grundlage dienen für die Erkundung anderer (geothermischer)

Стилі APA, Harvard, Vancouver, ISO та ін.

29

Conroy, William John. "A coupled upland-erosion, instream hydrodynamic-sediment transport model for assessing primary impacts of forest management practices on sediment yield and delivery." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Dissertations/Spring2005/w%5Fconroy%5F041505.pdf.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

30

Dincã, Diana Mihaela. "Mechanisms of brain dysfunction in myotonic dystrophy type 1 : impact of the CTG expansion on neuronal and astroglial physiology." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCB054/document.

Повний текст джерела

Анотація:

La dystrophie myotonique de type 1 (DM1), ou maladie de Steinert, est une maladie qui touche plusieurs tissus, dont le système nerveux central (SNC). L’atteinte neurologique est variable et inclut des troubles de la fonction exécutive, des changements de comportement et une hypersomnolence dans la forme adulte, ainsi qu’une déficience intellectuelle marquée dans la forme congénitale. Dans leur ensemble, les symptômes neurologiques ont un fort impact sur le parcours académique, professionnel et les interactions sociales. Aujourd’hui aucune thérapie n’existe pour cette maladie. La DM1 est due à une expansion anormale d’un triplet CTG non-codant dans le gène DMPK. Les ARN messagers DMPK, porteurs de l’expansion, s’accumulent dans le noyau des cellules (sous forme de foci) et perturbent la localisation et la fonction de protéines de liaison à l’ARN, notamment des familles MBNL et CELF, ce qui entraîne des défauts d’épissage alternatif, d’expression, de polyadenylation et de localisation d’autres ARN cibles. Malgré le progrès récent dans la compréhension des mécanismes de la maladie, les aspects cellulaires et moléculaires de l’atteinte neurologique restent méconnus: nous ne connaissons ni la contribution de chaque type cellulaire du cerveau, ni les voies moléculaires spécifiquement dérégulées dans chaque type cellulaire. L’objectif de ma thèse a été de répondre à ces deux questions importantes en utilisant un modèle de souris transgéniques et des cellules primaires dérivées de celui-ci. Pour mon projet, j’ai utilisé les souris DMSXL générées par mon laboratoire. Ces souris reproduisent des caractéristiques importantes de la DM1, notamment l’accumulation des ARN toxiques et la dérégulation de l’épissage alternatif dans plusieurs tissus. L’impacte fonctionnel des transcrits DMPK toxiques dans le SNC des souris DMSXL se traduit par des problèmes comportementaux et cognitifs et par des défauts de la plasticité synaptique. Afin d’identifier les mécanismes moléculaires associés à ces anomalies, une étude protéomique globale a montré une dérégulation de protéines neuronales et astrocytaires dans le cerveau des souris DMSXL. De plus, l’étude de la distribution des foci d’ARN dans les cerveaux des souris et des patients a montré un contenu plus élevé dans les astrocytes par rapport aux neurones. Ensemble, ces résultats suggèrent une contribution à la fois neuronale et gliale dans la neuropathogenèse de la DM1. L’étude protéomique globale des cerveaux des souris DMSXL, a aussi montré des défauts de protéines synaptiques spécifiques des neurones, que nous avons par la suite validés dans le cerveau des patients. SYN1 est hyperphosphorylée d’une façon CELF-dépendante et RAB3A est surexprimé en réponse à l’inactivation de MBNL1. Les protéines MBNL et CELF régulent l’épissage alternatif d’un groupe de transcrits au cours du développement, et leur dérégulation dans la DM1 entraîne l’expression anormale d’isoformes d’épissage embryonnaires dans le tissu adulte. Dans ce contexte, j’ai étudié si les défauts des protéines RAB3A et SYN1 sont associés à une dérégulation d’épissage, et si les anomalies des protéines synaptiques identifiées dans la DM1 reproduisent des évènements embryonnaires de la régulation de RAB3A et SYN1. Mes résultats indiquent que les défauts de ces protéines dans les cerveaux adultes ne sont pas dus à une altération de l’épissage alternatif des transcrits et ne recréent pas des évènements embryonnaires. La neuropathogenèse de la DM1 va, donc, au delà de la dérégulation de l’épissage et d’autres voies moléculaires restent à explorer dans les cerveaux DM1. Afin d’identifier des sous-populations cellulaires susceptibles à l’accumulation des ARN toxiques, nous avons étudié la distribution des foci dans plusieurs régions cérébrales. (...)
Myotonic dystrophy type 1 (DM1) is a severe disorder that affects many tissues, including the central nervous system (CNS). The degree of brain impairment ranges from executive dysfunction, attention deficits, low processing speed, behavioural changes and hypersomnia in the adult form, to pronounced intellectual disability in the congenital cases. The neurological manifestations have a tremendous impact on the academic, professional, social and emotional aspects of daily life. Today there is no cure for this devastating condition. DM1 is caused by the abnormal expansion of a CTG trinucleotide repeat in the 3’UTR of the DMPK gene. Expanded DMPK transcripts accumulate in RNA aggregates (or foci) in the nucleus of DM1 cells, disrupting the activity of important RNA-binding proteins, like the MBNL and CELF families, and leading to abnormalities in alternative splicing, gene expression, RNA polyadenylation, localisation and translation. In spite of recent progress, fundamental gaps in our understanding of the molecular and cellular mechanisms behind the neurological manifestations still exist: we do not know the contribution of each cell type of the CNS to brain dysfunction, or the molecular pathways specifically deregulated in response to the CTG expansion. The aim of my PhD project has been to gain insight into these two important questions using a relevant transgenic mouse model of DM1 and cell cultures derived thereof. In my studies I used the DMSXL mice, previously generated in my host laboratory. The DMSXL mice express expanded DMPK mRNA with more than 1,000 CTG repeats. They recreate relevant DM1 features, such as RNA foci and missplicing in multiple tissues. The functional impact of expanded DMPK transcripts in the CNS of DMSXL mice translates into behavioural and cognitive abnormalities and defective synaptic plasticity. To identify the molecular mechanisms behind these abnormalities, a global proteomics analysis revealed changes in both neuron-specific and glial-specific proteins in DMSXL brain. We also investigated RNA foci in DMSXL and human DM1 brains and found non-homogenous distribution between cell types, with a higher foci content in astrocytes relative to neurons. Together these results suggest that both neuronal and glial defects contribute to DM1 neuropathogenesis. The global proteomics analysis of DMSXL brains also identified abnormalities in neuronal synaptic proteins that we have validated in human brain samples. SYN1 is hyperphosphorilated in a CELF-dependent manner while RAB3A is upregulated in association with MBNL1 depletion. CELF and MBNL proteins regulate the alternative splicing of a subset of transcripts throughout development, and their deregulation in DM1 leads to abnormal expression of fetal splicing isoforms in adult DM1 brains. In this context, I have studied if RAB3A and SYN1 deregulations observed in adult brains are associated with splicing abnormalities or if they recreated embryonic expression and phosphorylation events. My results indicate that the synaptic proteins abnormalities observed in adult DMSXL brains are not caused by defective alternative splicing and do not recreate embryonic events. Thus, DM1 neuropathogenesis goes beyond missplicing and other molecular pathways must be explored in DM1 brains. To better understand the cellular sub-populations susceptible of accumulating toxic RNA foci we have studied foci distribution in different brain regions. We identified pronounced accumulation of toxic RNAs in Bergman astrocytes of DMSXL mice cerebellum and DM1 patients, associated with neuronal hyperactivity of Purkinje cells. A quantitative proteomics analysis revealed a significant downregulation of GLT1 – a glial glutamate transporter expressed by the Bergmann cell in the cerebellum. I have confirmed the GLT1 downregulation in other brain regions of mouse and human brain. (...)

Стилі APA, Harvard, Vancouver, ISO та ін.

31

Zuanetti, Bryan. "Characterization of Polyetherimide Under Static, Dynamic, and Multiple Impact Conditions." Honors in the Major Thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1569.

Повний текст джерела

Анотація:

The application of polymers in robust engineering designs is on the rise due to their excellent mechanical properties such as high fracture toughness, specific strength, durability, as well as, thermal and chemical resistances. Implementation of some advanced polymeric solids is limited due to the lack of available mechanical properties. In order for these materials to endure strenuous engineering designs it is vital to investigate their response in multiple loading rates and conditions. In this thesis, the mechanical response of polyethermide (PEI) is characterized under quasi-static, high strain rate, and multiple impact conditions. Standard tension, torsion, and compression experiments are performed in order to distinguish the multi-regime response of PEI. The effects of physical ageing and rejuvenation on the quasi-static mechanical response are investigated. The strain softening regime resulting from strain localization is eliminated by thermal and mechanical rejuvenation, and the advantages of these processes are discussed. The dynamic fracture toughness of the material in response to notched impact via Charpy impact test is evaluated. The high strain-rate response of PEI to uniaxial compression is evaluated at rates exceeding 104/s via miniaturized Split Hopkinson Pressure Bar (MSHPB), and compared to the quasi-static case to determine strain-rate sensitivity. The elastic response of the aged material to multiple loading conditions are correlated using the Ramberg-Osgood equation, while the elastoplastic response of rejuvenated PEI is correlated using a both the Ramberg-Osgood equation and a novel model. The strain-rate sensitivity of the strength is found to be nominally bilinear and transition strains are modeled using the Ree-Erying formulation. Finally, multiple impact experiments are performed on PEI using the MSHPB and a model is proposed to quantify damage as a result of collision.
B.S.M.E.
Bachelors
Engineering and Computer Science
Mechanical and Aerospace Engineering

Стилі APA, Harvard, Vancouver, ISO та ін.

32

Profizi, Paul. "Development of a numerical model of single particle impact with adhesion for simulation of the Cold Spray process." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI088/document.

Повний текст джерела

Анотація:

Dans le cadre du procédé de revêtement de surface Cold Spray, un modèle numérique d’impact de particule sur substrat à haute vitesse est créé, ainsi qu’une nouvelle interaction adhésive, dans le logiciel de dynamique explicite du CEA Europlexus. Le modèle utilise des Éléments Finis et la méthode sans maillage SPH (Smoothed Particle Hydrodynamics) avec la loi matériau de Johnson-Cook, couramment utilisée pour modéliser les métaux à des vitesses de déformation élevées et prenant en compte le durcissement plastique, le durcissement en vitesse de déformation, et l’assouplissement thermique. L’interaction adhésive est basée sur les modèles de zone cohésive de Dugdale-Barenblatt et Griffith, avec une limite sur la contrainte cohésive et la rupture de l’adhésion dictée par l’énergie dissipée. L’étude de cette interaction dans le cas des corps déformables à haute vitesse de déformation montre que le type de modèle cohésif utilisé impacte directement et de façon très prononcée les résultats du calcul. L’interaction adhésive est ensuite liée à un mécanisme physique connu pour être la raison majeure de l’adhésion entre métaux lors du procédé Cold Spray : l’instabilité en cisaillement à l’interface de contact (présente dans la simulation grâce à une loi d’endommagement). Pour ce faire, un critère d’activation de l’adhésion est créé, basé sur une chute de la valeur locale de limite élastique du matériau. Ce critère permet de retrouver le phénomène de vitesse critique nécessaire pour l’adhésion de la particule lors du procédé. Un critère de rupture de l’adhésion supplémentaire est ajouté, basé sur la valeur de l’endommagement dans les éléments collés, et permet de retrouver le phénomène de vitesse maximale pour l’adhésion de la particule. Le modèle complet, construit sur des principes physiques, est ainsi capable de simuler le phénomène d’adhésion Cold Spray. Des tests de dureté et images EBSD sont aussi présentés et comparés aux résultats numériques
In the context of the Cold Spray process, a numerical model of a single particle impact is developed. The point of interest is the adhesion of the particle to the substrate, thus an adhesive interaction model is also created. The impact model uses the Smooth Particle Hydrodynamics and/or the Finite Elements methods, with a Johnson-Cook material law, commonly used for metals at high strain rates, which takes into account strain hardening, strain rate hardening and thermal softening. The adhesive interaction is a Griffith and Dugdale-Barenblatt cohesive model with energy dissipation and a limit on the cohesive stress. Using this model it is shown that in the case of fast dynamics and deformable bodies, not only the adhesion parameters but also the type of model has an influence on the results. The adhesion model is also, contrary to previous works, linked with an actual physical mechanism known to induce adhesion in Cold Spray: a shear stress instability at the interface. This is done by adding an activation criterion to the cohesive model. This criterion is defined as a local drop in yield strength on either element in contact. Only when this criterion is locally met are the cohesive stresses applied and cohesive energy dissipated. The result is the apparition of a critical velocity, under which adhesion cannot occur due to either not enough initial kinetic energy to create an instability at the interface, or not enough adhesive surface created to keep the particle from rebounding. For the model to localize and undergo shear banding/shear instability, a damage value is added to the material law. An erosion criterion is then implemented in the cohesive model to remove the cohesive stresses from highly damaged parts of the adhesive surface. This results at high impact speeds in a maximal velocity above which the interfacial material is too damaged to sustain adhesion and prevent the particle from rebounding. A deposition behavior similar to the Cold Spray process is then observed, with a range of low velocities without any adhesion of the particle, then a critical speed initiating a velocity range of adhesion of the particle, and finally a maximum speed above which the interface is too damaged to sustain the adhesion. A set of experimental observations is also carried out to better understand the actual microstructural dynamics and changes at the interface of 1 mm copper particles impacted on copper. The results are compared to simulations and the use of the macroscopic Johnson-Cook law at a microscopic level is validated

Стилі APA, Harvard, Vancouver, ISO та ін.

33

Kadel, Sabita. "Impact of physicochemical properties of filtration membranes on peptide migration and selectivity during electrodialysis with filtration membranes : development of predictive statistical models and understanding of mechanisms involved." Doctoral thesis, Université Laval, 2020. http://hdl.handle.net/20.500.11794/66602.

Повний текст джерела

Анотація:

Au cours du procédé d'électrodialyse avec membrane de filtration (EDMF), les peptides chargés migrent sélectivement à travers des membranes de filtration (MFs) dans les compartiments respectifs de récupération des peptides anioniques (ARC) ou cationiques (C+ RC). Par conséquent, le type d'interaction entre les peptides et l'interface de la MF, en raison de ses propriétés physicochimiques, doit avoir un impact significatif sur la performance globale de l’EDMF (migration et sélectivité des peptides). Donc, l'objectif principal de cette thèse de doctorat était d'étudier les propriétés physicochimiques principales des MFs qui contribuent aux interactions interfaciales peptide-membrane facilitant ou entravant la migration globale et la séparation sélective des peptides pendant l’EDMF, et de comprendre les mécanismes impliqués dans ces interactions. Ainsi, dans cette étude, 16 MFs, caractérisées en termes de propriétés physicochimiques (potentiel zêta, conductivité, nature hydrophile/hydrophobe de la surface et des pores, épaisseur, rugosité, porosité et pourcentage de distribution des macropores dans la couche filtrante), ont été testées lors de l'EDMF pour séparer simultanément les peptides anioniques et cationiques d'un hydrolysat de protéines de lactosérum complexe et bien caractérisé. Dans la première étude, 6 MFs, différentes en termes de matériau, ont été testées incluant une membrane d’ultrafiltration (polyéthersulfone (PES)) comme contrôle et cinq membranes de microfiltration (fluorure de polyvinylidène (PVDF) et chlorure de polyvinyle (PVC-silice, fonctionnalisée (sulfopropyle ou amine quaternaire) ou non)). Les analyses de redondance (RDA) et de régression multivariées ont démontré qu’au moins deux des quatre propriétés suivantes des MF avaient un impact significatif sur la migration de tout peptide chargé ; le potentiel zêta, l’hydrophilie de surface/des pores, la porosité et la rugosité. De plus, l'effet important de la taille des pores sur la sélectivité des peptides a également été rapportée dans cette étude. Enfin, des modèles statistiques prédictifs qui relient la migration des peptides avec les propriétés de MF significatives ont été proposés. Dans la deuxième étude, réalisée sur des membranes de PES avec une large gamme de seuils de coupure (MWCO) de (5 à 300 kDa), une relation linéaire a été observée entre le MWCO et la migration globale des peptides (MGP) pour les deux compartiments de récupération. iii Cependant, la migration sélective des peptides vers ARC ou C+ RC s'est révélée être influencée par le MWCO des MFs ainsi que par les propriétés physicochimiques (charge et poids moléculaire (PM)) des peptides ; la migration d'un peptide ayant un faible PM et une faible charge (positive ou négative) était favorisée lorsqu’une MF ayant un petit MWCO était utilisée, tandis que l’inverse se produisait pour un peptide ayant un PM élevé et une charge élevée. Dans la troisième étude, l'effet de la combinaison du matériau de la membrane (polyacrylonitrile (PAN), PES et PVDF) /MWCO (30 et 50 kDa) sur la migration et la sélectivité des peptides, a tout d’abord été étudié. Les effets simples du matériau membranaire et du MWCO sur la MGP vers C+ RC, de même que l'effet combiné des matériaux membranaires/MWCO sur la MGP vers ARC et la migration sélective des peptides vers les deux compartiments de récupération ont été observés. Deuxièmement, une RDA réalisée sur l’ensemble des données obtenues pour les MFs sélectives testées dans cette recherche doctorale, a démontré l'impact significatif du potentiel zêta, de la conductivité, de la rugosité et du pourcentage de distribution des macropores dans la couche filtrante des MFs sur la MGP. Concernant la migration sélective des peptides, en plus des propriétés des MFs susmentionnées, l'impact significatif de l'angle de contact a été démontré pour au moins la migration d’un peptide anionique et/ou cationique vers leurs compartiments de récupération respectifs. Ces propriétés significatives ont favorisé différentes interactions telles qu’électrostatique, exclusion de taille et hydrophile/hydrophobe entre l’interface de la MF et le peptide, ce qui a eu pour effet de, soit faciliter, soit inhiber la migration de ce peptide. Enfin, des modèles statistiques prédictifs globaux ont été développés pour la MGP et pour la migration de chaque peptide individuel vers ARC et/ou C+ RC en fonction des propriétés importantes de la MF utilisée. Ces modèles permettent ainsi l'estimation du comportement de migration de ces peptides lorsque les MFs, sur une large gamme de propriétés physicochimiques, sont utilisées en EDMF. Les résultats obtenus dans cette thèse ont démontré, pour la première fois, la corrélation significative entre les propriétés physicochimiques des MFs, et la migration et la sélectivité des peptides pendant l'EDMF. Cependant, les modèles prédictifs développés dans cette étude iv peuvent être utilisés pour la gamme de peptides et les propriétés physicochimiques des MFs testées. Par contre, les mécanismes et explications proposés dans cette étude, concernant les interactions MF/peptide, peuvent être généralisés afin de comprendre tous les types d'interactions peptide/membrane. Comme perspectives à ce travail, l’étude de différentes sources d'hydrolysats, d’autres MFs et d’un hydrolysat produit par d’autres enzymes permettra la validation de ces modèles statistiques et leur généralisation.
During electrodialysis with filtration membranes (EDFM), charged peptides selectively migrate through filtration membranes (FMs) to their respective anionic (ARC) or cationic (C + RC) peptide recovery compartments. Consequently, the type of interactions occurring between FM and peptide at the interface, due to their physicochemical properties, must have significant impact on overall EDFM performances (peptide migration and selectivity). Therefore, the main objective of this doctoral thesis was to investigate the major FM properties that contribute to peptide-membrane interactions at the interface, which either facilitates or hinders global migration and selective separation of peptides during EDFM, and to understand the mechanisms involved behind those interactions. Thus, in this study, 16 FMs, characterized in terms of their physicochemical properties (zeta potential, conductivity, hydrophilic/hydrophobic nature of the surface and pores, thickness, roughness, porosity and percentage of macropores distribution in filtrating layer) were tested during EDFM to simultaneously separate anionic and cationic peptides from a well-characterized complex whey protein hydrolysate. In the first study, 6 FMs were tested, differing in terms of membrane materials, including one ultrafiltration (polyethersulfone (PES)) as a control and 5 microfiltration ( one polyvinylidene fluoride (PVDF) and four polyvinyl chloride (PVC)-silica: two functionalized (sulfonyl or amino) or two non-functionalized). Redundancy analysis (RDA) and multivariate regression analysis demonstrated that at least two FM properties among zeta potential, pore/surface hydrophilicity, porosity and roughness significantly impacted the migration of any charged peptide. In addition, the important effect of pore size on peptide selectivity was also reported. Finally, predictive statistical models that link each peptide migration with significant FM properties were proposed. In the second study, which was carried out on PES membranes with a wide range of molecular weight cut-offs (MWCOs) (5 kDa to 300 kDa), a linear relation was noticed between MWCO and global peptide migration (GPM) to both recovery compartments. However, the selective peptide migration to A - RC or C + RC was found to be influenced by the vi MWCO of FMs as well as physicochemical properties (charge and molecular weight (MW)) of peptides. For instance, the migration of a peptide having low MW and low charge (positive or negative) was favored when a FM with small MWCO was used, while the opposite was observed for a peptide having high MW and high charge. In the third study, the effect of combination of membrane material (PAN, PES and PVDF)/MWCO (30 and 50 kDa) on peptide migration and selectivity was first studied. The simple effect of membrane material and MWCO on GPM to C+ RC was observed, while the combined effect of membrane materials/MWCO on GPM to A - RC and selective peptide migration to both recovery compartments was observed. Secondly, a RDA was performed on the data obtained for all the selective FMs tested in this doctoral research, which demonstrated the significant impact of zeta potential, conductivity, roughness and percentage of macropores distribution in the filtrating layer of FMs on GPM. Concerning selective peptide migration, in addition to the aforementioned FM properties, the significant impact of contact angle was noticed for at least one anionic and/or cationic peptide migration to their respective recovery compartments. These significant FM properties were found to trigger different interactions such as electrostatic, size exclusion and hydrophilic/hydrophobic between FM and peptide at the interface resulting in either facilitation or inhibition of peptide migration. Finally, global predictive statistical models were developed for GPM and each individual peptide migration to ARC and/or C+ RC based on these significant FM properties, which allow the estimation of their migration behavior when FMs having a wide range of physicochemical properties are used during EDFM. The results obtained in this Ph.D. thesis demonstrated, for the first time, the significant correlation between physicochemical properties of FMs, and peptide migration and selectivity during EDFM. The predictive models developed in this study can be used for the range of peptides and FMs tested. Moreover, the types of interactions occurring between FMs and peptide at the interface, and mechanisms and explanations proposed in this study can be applied to understand all types of peptide/membrane interactions. Validation of such models vii by using different sources of hydrolysates or different FMs or a hydrolysate produced by other enzymes will be the main perspectives of this research work.

Стилі APA, Harvard, Vancouver, ISO та ін.

34

Oudich, Hamza. "Analytical Investigation of Planetary Gears Instabilities and the Impact of Micro-Macro Geometry Modifications." Thesis, KTH, Farkostteknik och Solidmekanik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-276775.

Повний текст джерела

Анотація:

Due to their large torque-speed ratio and transmission efficiency, planetary gears are widely used in the automotive industry. However, high amplitude vibrations remain their critical weakness, which limits their usage especially when new strict noise legislations come into action. A new approach to handle the instability problems of planetary gears encountered in real industrial context is presented in this work. First, the dynamic response of a planetary gear failing to pass the noise regulations is theoretically investigated through an analytical model. The equations of motion were solved using the Spectral Iterative Method. The observed experimental results correlated well with those from the developed model. In order to limit the resonance phenomena, impacts of different macro and micro-geometry modifications were analytically investigated: quadratic teeth profile, different planets positioning, different number of teeth and number of planets. Optimum modifications were retrieved and are expected to be tested experimentally on a test bench and on the truck. Finally, the analytical model’s limits and sensitivity to different parameters were investigated in order to certify its reliability, and suggestions for improvements were presented.

Стилі APA, Harvard, Vancouver, ISO та ін.

35

Mendes, Sebastian B. "The Development of an Improved Finite Element Muscle Model and the Investigation of the Pre-loading Effects of Active Muscle on the Femur During Frontal Crashes." Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-theses/1007.

Повний текст джерела

Анотація:

"Mammalian skeletal muscle is a very complicated biological structure to model due to its non-homogeneous and non-linear material properties as well as its complex geometry. Finite element discrete one-dimensional Hill-based elements are largely used to simulate muscles in both passive and active states. There are, however, several shortfalls to utilizing one-dimensional elements, such as the impossibility to represent muscle physical mass and complex lines of action. Additionally, the use of one-dimensional elements restricts muscle insertion sites to a limited number of nodes causing unrealistic loading distributions in the bones. The behavior of various finite element muscle models was investigated and compared to manually calculated muscle behavior. An improved finite element muscle model consisting of shell elements and Hill-based contractile truss elements in series and parallel was ultimately developed. The muscles of the thigh were then modeled and integrated into an existing 50th percentile musculo-skeletal model of the knee-thigh-hip complex. Impact simulations representing full frontal car crashes were then conducted on the model and the pre-loading effects from active thigh muscles on the femur were investigated and compared to cadaver sled test data. It was found that the active muscles produced a pre-load femoral axial force that acted to slightly stabilize the rate of stress intensification on critical stress areas on the femur. Additionally, the active muscles served to direct the distribution of stress to more concentrated areas on the femoral neck. Furthermore, the pre-load femoral axial force suggests that a higher percentage of injuries to the knee-thigh-hip complex may be due to the effects of active muscles on the femur. "

Стилі APA, Harvard, Vancouver, ISO та ін.

36

Medina, Camila, and Monika Miljanovic. "EXPLORING DIGITALIZATION AND VALUE CO-CREATION IN THE FOOD INDUSTRY : Study on challenges and opportunities for digitalization and the impact on the customer offering." Thesis, Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-36032.

Повний текст джерела

Анотація:

The purpose of this study is to identify the challenges and opportunities for digitalization within the food industry, and give suggestions on how to co-create value through digitalization. This qualitative study is based on data collected from scientific articles, reports and books about digitalization and value co-creation in the food industry. The primary data collection was carried out by twelve semi-structured interviews and a complementary food industry study with eleven respondents. The collected data was handled in thematic analysis and inspired by coding. The study’s main conclusion was the discovering of a new value co- creation mechanism defined as relationship and learning.

Стилі APA, Harvard, Vancouver, ISO та ін.

37

Grégoire, David. "Initiation, propagation, arrêt et redémarrage de fissures sous impact." Phd thesis, INSA de Lyon, 2008. http://tel.archives-ouvertes.fr/tel-00418626.

Повний текст джерела

Анотація:

Les risques liés à la propagation de fissures sous impact sont encore très difficiles à estimer. La détermination de critères de rupture dynamique uniquement à partir de résultats expérimentaux reste délicate. Ainsi la première étape pour valider des lois de propagation de fissures sous impact passe par le développement d'outils de simulation numérique. Depuis les années 1970, de nombreux codes de calcul mécanique ont été dédiés à l'étude de la propagation de fissures, notamment dans le cas du phénomène de fatigue. La principale difficulté consiste dans la nécessité de suivre la géométrie de la fissure au cours du temps. Ces dernières années, des méthodes alternatives basées sur la partition de l'unité ont permis une description implicite des discontinuités mobiles. C'est le cas de la méthode des éléments finis étendue (X-FEM) qui paraît particulièrement adaptée à la simulation de la propagation dynamique de fissures sous chargement mixte où les trajets de fissures ne sont pas connus a priori. Si ces outils numériques permettent maintenant de représenter l'avancée dynamique d'une fissure, les résultats numériques doivent être comparés à des résultats expérimentaux pour s'assurer que les lois introduites sont physiquement fondées. Notre objectif est donc de développer conjointement des techniques expérimentales fiables et un outil de simulation numérique robuste pour l'étude des phénomènes hautement transitoires que sont l'initiation, la propagation, l'arrêt et le redémarrage de fissures sous impact.
Des expériences de rupture dynamique ont donc été réalisées sur du Polyméthacrylate de méthyle (PMMA) durant lesquelles la mixité du chargement varie et des arrêts et redémarrages de fissures se produisent. Deux bancs d'essais différents ont été utilisé, le premier basé sur la technique des barres de Hopkinson (ou barres de Kolsky), le second mettant en jeu un vérin rapide. Le PMMA étant transparent, la position de la fissure au cours de l'essai a été acquise grâce à des caméras rapides mais aussi en utilisant un extensomètre optique (Zimmer), habituellement dédié à la mesure de déplacements macroscopiques d'un contraste noir/blanc. L'utilisation de cet extensomètre pour suivre la fissure au cours de l'essai a permis d'obtenir une localisation très précise de la pointe de la fissure en continu, permettant ainsi l'étude des phases transitoires de propagation. Afin d'étudier le même phénomène dans des matériaux opaques comme les aluminiums aéronautiques (Al 7075), des techniques de corrélation d'images numériques ont été employées en mouchetant les éprouvettes impactées. De nouveaux algorithmes ont été développés afin de traiter les images issues d'une caméra ultra-rapide (jusqu'à 400 000 images par seconde).
Plusieurs géométries ont été envisagées afin d'étudier différents cas de propagation dynamique : initiation en mode I pur, initiation en mode mixte, propagation, arrêt, redémarrage, interaction entre deux fissures, influence d'un trou sur le trajet d'une fissure, branchement dynamique de fissures. Ces expériences ont ensuite été reproduites numériquement afin de valider les algorithmes et les critères de rupture choisis.

Стилі APA, Harvard, Vancouver, ISO та ін.

38

Delille, Rémi. "Contribution à la compréhension du comportement mécanique de l'os du crâne humain sous différents moyens de conservation et de sollicitation." Phd thesis, Université de Valenciennes et du Hainaut-Cambresis, 2007. http://tel.archives-ouvertes.fr/tel-00270740.

Повний текст джерела

Анотація:

Les études statistiques d'accidents montrent que la tête est le segment corporel le plus vulnérable lors d'un accident (chocs piétons, chocs deux-roues et chocs latéraux). Pour enrichir les modèles virtuels d'être humain et développer de nouveaux outils de prédictions lésionnelles, ce travail propose une série d'expérimentations afin d'obtenir les propriétés mécaniques homogénéisées de l'os du crâne humain (pas de distinction entre l'os cortical et spongieux).
Des essais ont été réalisés sur 20 SHPM (Sujet Humain Post Mortem) « frais ». Un protocole spécifique a été développé afin de prélever 19 éprouvettes par crâne. Au total, 380 échantillons ont été testés en flexion trois points. Les courbes effort/déplacement ont servi de référence pour l'identification du comportement élastique. De nombreuses relations par zones et orientations osseuses ont été obtenues.
Des essais de cyclage dans la zone élastique ont été réalisés sur 105 échantillons prélevés sur 7 SHPM congelés. L'effet de la vitesse de sollicitation a été étudié. Cette seconde campagne permet de comparer les éprouvettes en fonction de leur mode de conservation. Une corrélation a été mise en évidence et a permis d'extrapoler le module d'élasticité à l'état « frais » d'un SHPM testé congelé.
Ces deux campagnes d'essais ont permis d'aboutir à une corrélation entre le module d'élasticité équivalent et les propriétés géométriques (épaisseur et densité) d'un SHPM « frais ».
Les derniers travaux ont porté sur le développement d'un nouveau prototype de tête. Pour cela, 7 calottes, provenant de SHPM congelés, ont été testées en compression. Les propriétés élastiques du prototype sont issues des campagnes expérimentales précédentes et présentent une distinction entre chaque zone. Ce prototype a été validé par des essais statiques et dynamiques en compression dans différentes zones osseuses.

Стилі APA, Harvard, Vancouver, ISO та ін.

39

Chen, Zengshi. "Dynamics and control of collision of multi-link humanoid robots with a rigid or elastic object." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1158442034.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

40

Thomas, Amandine. "Hypoxie intermittente et homéostasie glucidique : étude des mécanismes d'action cellulaire A hybrid model to study pathological mutations of the human ADP/ATP carriers Visceral white fat remodeling contributes to intermittent hypoxia-induced atherogenesis The insulin sensitizing effect of topiramate involves KATP channel activation in the central nervous system The Impact of Sleep Disorders on Glucose Metabolism: Endocrine and Molecular Mechanisms Endoplasmic reticulum stress as a novel inducer of hypoxia inducible factor-1 activity: its role in the susceptibility to myocardial ischemia-reperfusion induced by chronic intermittent hypoxia Chronic intermittent hypoxia improves whole-body glucose tolerance by activating skeletal muscle AMP-activated protein kinase in mice Prolyl-4-hydroxylase 1 (PHD1) deficiency impairs whole-body glucose tolerance and insulin sensitivity in mice but does not worsen high-fat diet-induced metabolic dysfunctions Specific transcriptomic signature in response to intermittent hypoxia exposure in liver and fat tissue." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAV044.

Повний текст джерела

Анотація:

L'hypoxie intermittente (HI), induite par les apnées du sommeil, conduit à des altérations de la sensibilité à l'insuline et de l'homéostasie glucidique mais les mécanismes impliqués restent mal connus. L'objectif de ce travail était d'étudier les effets et les mécanismes sous jacents d'une exposition chronique à l'HI sur l'homéostasie glucidique. L'HI induit une résistance à l'insuline à la fois systémique et tissulaire, ainsi qu'une amélioration de la tolérance au glucose associée à une activation de l'AMPK musculaire. L'HI cause également des altérations du foie et du tissu adipeux associées à un changement du pattern d'expression des gènes dans ces tissus et à un risque accru de développement de pathologies vasculaires comme l'athérosclérose. Enfin, la délétion de PHD1, une des protéines régulatrices de HIF-1, entraîne une résistance à l'insuline associée une stéatose hépatique, faisant de HIF-1 une cible potentielle impliquée dans les altérations metaboliques induites par l'HI
Intermittent hypoxia (IH), induced by sleep apnea, leads to alterations in insulin sensitivity and glucose homeostasis but the mechanisms involved remains poorly understood. The objective of this work was to study the effects and the underlying mechanisms of chronic exposure to IH on glucose homeostasis. IH induces both systemic and tissue-specific insulin resistance , as well as improved glucose tolerance associated with an activation of muscle AMPK. IH also causes a change in the pattern of gene expression in liver and adipose tissue and an increased risk of vascular pathologies such as atherosclerosis development. Finally, the deletion of PHD1, a regulatory protein of HIF-1, leads to insulin resistance associated with hepatic steatosis, making HIF-1 a possible target involved in the metabolic changes induced by IH

Стилі APA, Harvard, Vancouver, ISO та ін.

41

Biswas, Subhankar. "Development of a constitutive model for energy factors in erosive wear models to predict the service life of ductile metals." Thesis, 2016. http://hdl.handle.net/1959.13/1317966.

Повний текст джерела

Анотація:

Research Doctorate - Doctor of Philosophy (PhD)
To gain a better understanding of the surface behaviour and its influence on erosion mechanisms, erosion tests were performed using a micro-sandblaster under a constant particle flux with a range of impact velocities and angles. Two different sizes of angular SiC and Al₂O₃ particles were entrained into a stream of compressed air to impact on commercial grade mild steel and aluminium surfaces. Both the surface materials were ductile with the erodents hard and angular. The erosion rates for different impact angles and particle velocities were determined following the experimental methodology outlined in the ASTM G76 standard procedure. It was found that impact velocity, angle, as well as particle size, reflected the severity of erosion. The particle flux effect on the scar area revealed that the particle flux increased as impact angle increased. Erosion testing events were further analysed to study the different mechanisms of material removal and to examine the characteristics of surface and subsurface wear in ductile materials. Scanning electron microscopy results confirmed that at shallow impact angles, erosion was dominated by the cutting wear mechanism; however, at higher angles, erosion was dominated by the deformation wear mechanism. At shallow impact angles, materials were removed through cutting, ploughing and the formation of lips. Surface analysis also showed that at higher impact angles, the ductile material surfaces underwent severe deformation. It was also evident that surface deformation was accompanied by substantial heat affects that modified the surface and altered the material removal mechanism. Additionally, investigated impact angles (from 15° to 90°) also confirmed that material was removed through surface and subsurface cracking and damage. These subsurface cracking and damage were observed up to a certain depth from the worn surface. It was also apparent that both the depth of subsurface cracking and subsurface damages increased when impact velocity increased. The variation was consistent with an increase in surface and subsurface temperature (heating) at higher velocities. With increased temperature, the depth of the heat affected zone increased and the work hardening layer thickness also increased. It was also evident that the subsurface microstructure of the material plays a significant role in the erosion process. Subsurface microstructural damage was consistent with attainment of higher temperature and can be explained by the high strain-rate deformation and thermo-physical properties of the surface. A comprehensive study on erosion in ductile surfaces and their affects on the surface and subsurface were shown that there are some satisfactory predictive models developed for erosion. However, there are still many unknown factors that contribute to the erosion process; for example, in many instances even the mechanisms of material removal is unclear and the manner in which energy factors are involved in the wear system has not been adequately described. Further, the influence of the dissipation of kinetic energy to the surface at different impact angles was not apparent in the described models. Thus, there was a gap in the literature in relation to the dissipation of kinetic energy to the surface material during erosion and a need to study the relevant surface parameters such as coefficient of restitution, elastic-plastic properties, microstructure and surface heating. In this thesis, a new empirical erosion model was developed based on surface material properties, impact parameters and energy factors as described below: [formula could not be replicated] In which W is the erosion rate in units of mass loss, ϕ is the cutting energy factor, ε is the deformation energy factor, α is impact angle and KE_pd is the dissipated kinetic energy in the surface material as is expressed below: [formula could not be replicated] Where, m is the total mass of impacting particles, v_i is impact velocity, p_d is dynamic pressure during impact, E₁ and E₂ are the elastic modulus of impacting particle and surface material respectively, γ₁ and γ₂ are the Poisson’s ratio for impacting particle and surface material as well as R is the radius of the impacting particle. This study has shown that the erosion model can be used successfully at various impact conditions. Validation studies on a larger scale were also performed for independent validation. It was shown that the erosion rate is independent of a certain velocity and impact angles. The model was also able to determine the dynamic pressure, strain rate and coefficient of restitution and the useful parameters for determining erosion mechanism.

Стилі APA, Harvard, Vancouver, ISO та ін.

42

Yen, Shih-ying, and 顏詩穎. "Social Impact Bond Finance Model and Payment Mechanism-The Application of SROI Analysis." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/398a33.

Повний текст джерела

Анотація:

碩士
國立中山大學
財務管理學系研究所
103
Failures of government, market and voluntary sector appeared in 1970s and negatively affected the capability of solving social problems. Since then, the way of ‘impact investing’ or ‘social investment’ has been introduced. Along with this trend, Social impact bond(SIB) was discussed after 2008 global financial crisis. It advocates two key concepts: ‘impact-initiated’ and ‘public-private partnership(PPP).’ It is organized by multi-stakeholder partnership and evident-based preventative intervention. Under SIB mechanism, short-term capital can be poured in and investors wish to get reimbursement in the future. Government only has to pay when final outcomes meet predetermined targets. To strengthen this mechanism and make it work, there’s much effort to do. Base on this cognition, this research contains two parts: (1)designing of SIB financial model and (2)applying SIB to ‘forecasting’ SROI analysis. SIB finance model will discuss: multi-stakeholder partnership, outcome metrics and payment schedule. The next step is applying SROI analysis: it is an economic evaluating method, which values the material costs and benefits to all key stakeholders on a single monetary scale. The outcome of SROI analysis provides the commissioners and social investors a reference to make decision. The findings of this research are: (1) the suggested financial model with the issue of short supply of labor force in long-term care; (2) the presentation of SROI analysis process and pro forma SROI: 2.782.

Стилі APA, Harvard, Vancouver, ISO та ін.

43

Aum, Ho Sung. "Parameters affecting mechanical collisions." Thesis, 1992. http://hdl.handle.net/1957/35770.

Повний текст джерела

Анотація:

Even though the elastic deformations that occur during the impact of colliding bodies may be small in comparison to their actual dimensions, they play an important role in mechanical collisions. During the time the bodies are in contact, elastic, friction, and inertia properties combine to produce a complex variation of sliding and sticking throughout the contact surface. Detailed analysis of this interaction is quite tedious, but would seem to be necessary for accurately predicting the impulse and velocity changes that occur during contact. However, a considerably-simplified model captures the essential characteristics of the elastic-friction interaction during contact, leading to predictions of impulse and velocity changes that agree well with those of more detailed analyses of a number of different collisions. The model's simplicity enables an examination of parameters that affect a general class of collisions. For planar collisions, the model contains five dimensionless parameters; the effects of four of these on the rebound velocity are examined here. In addition, comparisons are made with a previously-used, somewhat simpler model, which neglects the tangential compliance in the region of contact.
Graduation date: 1993

Стилі APA, Harvard, Vancouver, ISO та ін.

44

Dreke, Linda L. "A Conceptual Model of the Mechanisms by which Ego Resiliency Impacts Academic Engagement and Achievement: Social Relatedness as a Mediator." 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-12-7286.

Повний текст джерела

Анотація:

The current study tested the effect of ego resilience on engagement and achievement as mediated by social relatedness, using three waves of data and controlling for the stability of each construct as well as within wave correlations among study variables. Using structural equation modeling, we were able to control for the stability of each construct as well as the within wave correlations of residual error variances between constructs. The model also took into account the transactional properties of academic engagement and academic achievement. Furthermore, the study tested the moderation effects of gender on each theoretically-significant path. Despite the models having adequate fit indices, in the larger context of the model the hypothesis that ego resiliency predicts subsequent social relatedness was not supported in either reading or math revised models. Because of this, the overall study hypothesis that social relatedness would mediate the relationship between ego resiliency and subsequent academic engagement and achievement was not supported. However, there were several findings of interest. The results of this study were consistent with the reasoning that social relatedness helps children feel more accepted and supported by peers and teachers, therefore promoting more classroom engagement. Findings suggested that, while social interactions seem to impact students? academic engagement across in the subsequent year, their level of ego resilience at school entry appears to be an important long-term contributor to math achievement two years later. The moderation analyses indicated that ego resilience had more effect on boys? reading achievement and academic engagement two years later. Study limitations and implications were also discussed.

Стилі APA, Harvard, Vancouver, ISO та ін.

45

Bann, Glen Robert. "Apparent dryland salinity on the uplands of southeastern Australia; quantification of biotic and abiotic indicators, causes, mechanisms, processes and effects." Phd thesis, 2014. http://hdl.handle.net/1885/101934.

Повний текст джерела

Анотація:

Secondary dryland salinity in Australia has been a major environmental concern for a number of decades, yet aspects remain controversial. These include the processes which induce salinised soils, the environmental impacts of salinity, and the way in which it is mapped and managed. Dryland salinity has been almost universally attributed to rising saline groundwater caused by excess water accumulation in the landscape following European settlement and tree clearing. However, there is a body of evidence that instead suggests increased soil salinisation in SE Australia is attributable to localized surface water problems associated with soil and vegetation degradation. The ‘Rising Groundwater Model’ has been widely accepted as the paradigm for understanding, mapping and monitoring dryland salinity. However, little quantitative research has been undertaken to understand the mechanisms and processes that cause secondary dryland salinity in the uplands of south eastern Australia. Further, there is little research that demonstrates adverse impacts of secondary salinity on terrestrial endemic biota even though it is listed as a threatening process to biodiversity. This research tested the applicability of an alternative ‘Surface Water Model’ to explain outbreaks of salinity or soil surface degradation in this region. This research investigated the effects of the joint phenomenon of soil and vegetation degradation and elevated salinity levels on soil biotic and abiotic parameters. Field research was conducted at ten box/gum grassy woodland sites in the agricultural zone of the Southern Tablelands of NSW. A holistic suite of metrics, including soil physical, chemical, hydrological and biological attributes, were assessed in the field and laboratory; geophysical surveys (EM31/EM38) and various fauna and flora surveys were performed. Results indicated that degraded soil surfaces were generally small in area and localized. These surfaces had highly variable soil EC levels (often very low), and were associated with in situ synergistic factors related to in situ soil and vegetation degradation. Some surfaces had accumulated NaCl, but many also had other, both toxic and low cation and anion levels particularly reduced levels of Ca, Fe, N, SOM and SOC. Extreme pH levels and other soil physical, chemical and biological impacts were also common. It is concluded that elevated soil salinity levels are a symptom of soil and vegetation degradation, not the cause. It was found that the predominant water movement in these landscapes occurred as overland runoff and surficial lateral interflow above the clay-dominant B horizon. There was no biological, pedological, geophysical or hydrological evidence of groundwater being a major factor for elevated soil surface salinity levels. Evidence suggests that these degraded ecosystems are relatively stable but urgently require nutrient/SOM input. Many endemic fauna and flora species flourish at highly degraded and salinised sites; tolerating elevated and fluctuating salinity levels, at all life cycle stages, which may effectively increase the gamma biodiversity in these grassy woodlands. No evidence was found to suggest that biodiversity is suffering from rising saline groundwater or elevated soil salinity levels per se, or that elevated salinity levels favour exotic species. It is therefore problematical to directly link soil salinity per se with ecological stress, as many other synergistic factors are involved and are more significant for degraded soils. Management decisions based on reducing the soil surface evaporation potential on site is the most coherent approach. Management activities should focus on stock grazing exclusion, soil amelioration and revegetation activities using endemic species, rather than focusing on excess deep landscape water management with hybrids and exotic plants. The present use of AEM for mapping dryland salinity in upland environments is therefore questionable.

Стилі APA, Harvard, Vancouver, ISO та ін.

Дисертації з теми "Mechanism impact model"

Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями