Letteratura scientifica selezionata sul tema "Non regular contact dynamics"
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Articoli di riviste sul tema "Non regular contact dynamics"
1
Caux, S., e R. Zapata. "Modeling and control of biped robot dynamics". Robotica 17, n. 4 (luglio 1999): 413–26. http://dx.doi.org/10.1017/s0263574799001411.
Testo completoAbstract (sommario):
This paper addresses the problem of modeling biped dynamics and the use of such models for the control of walking, running and jumping robots. We describe two approaches to dynamic modeling: the basic Lagrange approach and the non-regular dynamic approach. The new non-regular dynamic approach takes into account discontinuities due to rigid contact between punctual feet and the ground without computing the exact impact time. The contact is close to the physical situation given by non-linear laws (impenetrability, non-smooth contact and real friction cone). Contact dynamics can be well managed with an accurate dynamic model that respects energy consistency during all the phases encountered during a step (0, 1 or 2 contacts). With this model, we can first study the equilibrum of a biped standing on one foot by a linearisation method. In the second stage, the unified modelized equation is used to establish a general control frame based on non-regular dynamical decoupling. A comparison is made and some simulation results are given with a two degree of freedom planar biped robot.
2
Jelbart, S., e C. Kuehn. "Extending discrete geometric singular perturbation theory to non-hyperbolic points". Nonlinearity 37, n. 10 (2 settembre 2024): 105006. http://dx.doi.org/10.1088/1361-6544/ad72c5.
Testo completoAbstract (sommario):
Abstract We extend the recently developed discrete geometric singular perturbation theory to the non-normally hyperbolic regime. Our primary tool is the Takens embedding theorem, which provides a means of approximating the dynamics of particular maps with the time-1 map of a formal vector field. First, we show that the so-called reduced map, which governs the slow dynamics near slow manifolds in the normally hyperbolic regime, can be locally approximated by the time-1 map of the reduced vector field which appears in continuous-time geometric singular perturbation theory. In the non-normally hyperbolic regime, we show that the dynamics of fast-slow maps with a unipotent linear part can be locally approximated by the time-1 map induced by a fast-slow vector field in the same dimension, which has a nilpotent singularity of the corresponding type. The latter result is used to describe (i) the local dynamics of two-dimensional fast-slow maps with non-normally singularities of regular fold, transcritical and pitchfork type, and (ii) dynamics on a (potentially high-dimensional) local center manifold in n-dimensional fast-slow maps with regular contact or fold submanifolds of the critical manifold. In general, our results show that the dynamics near a large and important class of singularities in fast-slow maps can be described via the use of formal embedding theorems which allow for their approximation by the time-1 map of a fast-slow vector field featuring a loss of normal hyperbolicity.
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Whitfield, Carl A., Martie van Tongeren, Yang Han, Hua Wei, Sarah Daniels, Martyn Regan, David W. Denning, Arpana Verma, Lorenzo Pellis e Ian Hall. "Modelling the impact of non-pharmaceutical interventions on workplace transmission of SARS-CoV-2 in the home-delivery sector". PLOS ONE 18, n. 5 (5 maggio 2023): e0284805. http://dx.doi.org/10.1371/journal.pone.0284805.
Testo completoAbstract (sommario):
Objective We aimed to use mathematical models of SARS-COV-2 to assess the potential efficacy of non-pharmaceutical interventions on transmission in the parcel delivery and logistics sector. Methods We devloped a network-based model of workplace contacts based on data and consultations from companies in the parcel delivery and logistics sectors. We used these in stochastic simulations of disease transmission to predict the probability of workplace outbreaks in this settings. Individuals in the model have different viral load trajectories based on SARS-CoV-2 in-host dynamics, which couple to their infectiousness and test positive probability over time, in order to determine the impact of testing and isolation measures. Results The baseline model (without any interventions) showed different workplace infection rates for staff in different job roles. Based on our assumptions of contact patterns in the parcel delivery work setting we found that when a delivery driver was the index case, on average they infect only 0.14 other employees, while for warehouse and office workers this went up to 0.65 and 2.24 respectively. In the LIDD setting this was predicted to be 1.40, 0.98, and 1.34 respectively. Nonetheless, the vast majority of simulations resulted in 0 secondary cases among customers (even without contact-free delivery). Our results showed that a combination of social distancing, office staff working from home, and fixed driver pairings (all interventions carried out by the companies we consulted) reduce the risk of workplace outbreaks by 3-4 times. Conclusion This work suggests that, without interventions, significant transmission could have occured in these workplaces, but that these posed minimal risk to customers. We found that identifying and isolating regular close-contacts of infectious individuals (i.e. house-share, carpools, or delivery pairs) is an efficient measure for stopping workplace outbreaks. Regular testing can make these isolation measures even more effective but also increases the number of staff isolating at one time. It is therefore more efficient to use these isolation measures in addition to social distancing and contact reduction interventions, rather than instead of, as these reduce both transmission and the number of people needing to isolate at one time.
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Fricke, Mathis, e Dieter Bothe. "Boundary conditions for dynamic wetting - A mathematical analysis". European Physical Journal Special Topics 229, n. 10 (settembre 2020): 1849–65. http://dx.doi.org/10.1140/epjst/e2020-900249-7.
Testo completoAbstract (sommario):
Abstract The moving contact line paradox discussed in the famous paper by Huh and Scriven has lead to an extensive scientific discussion about singularities in continuum mechanical models of dynamic wetting in the framework of the two-phase Navier–Stokes equations. Since the no-slip condition introduces a non-integrable and therefore unphysical singularity into the model, various models to relax the singularity have been proposed. Many of the relaxation mechanisms still retain a weak (integrable) singularity, while other approaches look for completely regular solutions with finite curvature and pressure at the moving contact line. In particular, the model introduced recently in [A.V. Lukyanov, T. Pryer, Langmuir 33, 8582 (2017)] aims for regular solutions through modified boundary conditions. The present work applies the mathematical tool of compatibility analysis to continuum models of dynamic wetting. The basic idea is that the boundary conditions have to be compatible at the contact line in order to allow for regular solutions. Remarkably, the method allows to compute explicit expressions for the pressure and the curvature locally at the moving contact line for regular solutions to the model of Lukyanov and Pryer. It is found that solutions may still be singular for the latter model.
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Kovačič, Boštjan, Tomaž Motoh e Samo Lubej. "Experimental analysis of the dynamic responses of bridging objects with alternative non-contact method". E3S Web of Conferences 110 (2019): 01028. http://dx.doi.org/10.1051/e3sconf/201911001028.
Testo completoAbstract (sommario):
Structure objects are exposed to different natural influences resulting in long-term and catastrophic outcomes. In order to avoid them, regular monitoring is needed. Various approaches to control condition of a structure can be considered, one of them is the measurement by means of monitoring which can be performed in different ways, depending on responses – static or dynamic, or both simultaneously. Specifically, technological development has enabled to monitor not only static but also dynamic responses by non-contact geodetic methods. Due to their simplicity and reliability of results, geodetic methods are more and more useful in this area. Moreover, state-of-art instruments and additional programme equipment allows up to 100 readings per second with an almost constant frequency of sampling, which is a condition for calculation of a dynamic response according to Fourier’s transformation. The article presents non-contact geodetic method of RTS on a bridging object.
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Mohajeri, Mohammad Javad, Mehdi Shafieefar e Soheil Radfar. "NUMERICAL MODELING OF NON-COHESIVE CONTACT IN MULTI-BODY HYDRODYNAMIC SYSTEMS WITH SPH". Coastal Engineering Proceedings, n. 35 (23 giugno 2017): 49. http://dx.doi.org/10.9753/icce.v35.structures.49.
Testo completoAbstract (sommario):
Enforcing solid boundary conditions is one of the most challenging parts of the Smoothed Particle Hydrodynamics (SPH) method and many different approaches have been recently developed. Better understanding of interaction forces between solid bodies is of great importance in the investigation of structural stability and armor layer displacement in breakwaters. In this study, performance of repulsive force and dynamic boundary conditions have been investigated and showed that non-physical results are presented in non-cohesive contact. In this paper, a non-cohesive contact model in multi-body hydrodynamic systems has been developed and validated against other common boundary conditions. Using the developed contact model, the effect of regular and irregular placement of cubic concrete armors has been investigated. Also, comparison has been made with Van Buchem (2009) experimental results and concluded that in the irregular case it is more possible that a unit moves toward instability.
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DUROG, Mark Ronie O., e Pamela F. RESURRECCION. "Organizational Identification as a Mediator of Organizational Support, Employee Engagement, and Commitment: The Case of Non-Teaching Employees in the Mindanao State University-Iligan Institute of Technology (MSU-IIT)". Journal of Human Resource Management - HR Advances and Developments 2024, n. 2 (24 novembre 2024): 34–51. http://dx.doi.org/10.46287/uwwt1370.
Testo completoAbstract (sommario):
Purpose – The primary objective of this study is to assess and compare the levels of organizational identification, employee engagement, organizational commitment, and perceptions of organizational support between contract-of-service and regular non-teaching employees in a state university in Iligan City. Aims(s) – This study investigates whether OI among contract-of-service and regular non-teaching employees mediates the relationships between OS, EE, and OC. Design/methodology/approach – This study used a cross-sectional quantitative research design. The respondents comprised 81 contract-of-service and 91 regular non-teaching employees from different offices in MSU-IIT using an online survey form. The collected data was analyzed using SmartPLS4 and Partial Least Square of Structural Equation Modeling (PLS-SEM) to test the hypotheses. Findings – The findings show that Organizational Identification (OI) significantly mediates the relationship between Organizational Support and Affective Commitment (AC), with stronger effects for contract-of-service employees. For contract-of-service and regular employees, OI is crucial in linking support and commitment. Regular non-teaching employees show stronger OI than temporary workers, enhancing their engagement and commitment. Limitations of the study and practical implications – Future research can also be conducted on a larger sample size, including other government higher educational institutions in Mindanao, to generalize the findings. One such limitation is the scope of this study, which is limited to a state university in Iligan City only. This work is limited to the MSU-IIT non-teaching employees; a cross-cultural study may be conducted to see if any variations occur in other cultural settings. A comparative study among the non-teaching employees of government and private higher educational institutions is also suggested. Originality - This research contributes to the broader understanding of employee dynamics, especially the non-teaching employees within the academic sector, specifically in the Philippine context, with implications for improving institutional performance and employee well-being.
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Al-Ghurabi, Ebrahim H., Mohammad Asif, Nadavala Siva Kumar e Sher Afghan Khan. "Fluidization Dynamics of Hydrophobic Nanosilica with Velocity Step Changes". Applied Sciences 10, n. 22 (17 novembre 2020): 8127. http://dx.doi.org/10.3390/app10228127.
Testo completoAbstract (sommario):
Nanosilica is widely used in various applications, with its market expected to grow over USD 5 billion by 2025. The fluidized bed technology, owing to its intimate contact and efficient mixing of phases, is ideally suited for the large scale processing of powders. However, the bulk processing and dispersion of ultrafine nanosilica using the fluidized bed technology are critically affected by the interparticle forces, such that the hydrophilic nanosilica shows agglomerate bubbling fluidization (ABF), while the hydrophobic nanosilica undergoes agglomerate particulate fluidization (APF). This study carried out a detailed investigation into the fluidization hydrodynamic of the hydrophobic nanosilica by monitoring the region-wise dynamics of the fluidized bed subjected to a regular step change of fixed duration in the gas velocity. The gas flow was controlled using a mass controller operated with an analog output signal from a data acquisition system. The analog input data were acquired at the sampling rate of 100 Hz and analyzed in both time and temporal frequency domains. The effect of velocity transients on the bed dynamics was quickly mitigated and appeared as lower frequency events, especially in regions away from the distributor. Despite the apparent particulate nature of the fluidization, strong hysteresis was observed in both pressure drop and bed expansion. Moreover, the fully fluidized bed’s pressure drop was less than 75% of the theoretical value even though the bed appeared to free from non-homogeneities. Key fluidization parameters, e.g., minimum fluidization velocity (Umf) and the agglomerate size, were evaluated, which can be readily used in the large scale processing of nanosilica powders using fluidized bed technology.
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Ghaychi Afrouz, Setareh, Mohammad Reza Razavi, Ashkan Pourkand e Claudia Mara Dias Wilson. "Dynamic Displacement of an Aluminum Frame Using Close Range Photogrammetry". Buildings 9, n. 8 (29 luglio 2019): 176. http://dx.doi.org/10.3390/buildings9080176.
Testo completoAbstract (sommario):
Dynamic displacement measurement of objects can be challenging due to the limitations of conventional methods and pricey instrumentation of unconventional methods, such as laser scanners. In this research, Close Range Photogrammetry (CRP) is used as an affordable non-contact method to measure 3D dynamic displacements. It is proposed as a reliable alternative to traditional dynamic deformation measurement methods such as displacement sensors or accelerometers. For this purpose, dynamic displacements of a three-dimensional one-story building frame model on a one-dimensional shake table are determined by using the traditional method of attached accelerometer and CRP. The results of the CRP method are compared with the results of the traditional methods as well as numerical models. The results show a good agreement which evidences the reliability of the CRP with regular cameras.
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Legarreta, Carmen, Manuel De la Sen e Santiago Alonso-Quesada. "On the Properties of a Newly Susceptible, Non-Seriously Infected, Hospitalized, and Recovered Subpopulation Epidemic Model". Mathematics 12, n. 2 (11 gennaio 2024): 245. http://dx.doi.org/10.3390/math12020245.
Testo completoAbstract (sommario):
The COVID-19 outbreak has brought to the forefront the importance of predicting and controlling an epidemic outbreak with policies such as vaccination or reducing social contacts. This paper studies an SIHR epidemic model characterized by susceptible (S), non-seriously infected (I), hospitalized (H), and recovered (R) subpopulations, and dynamic vaccination; vaccination itself and H are fed back, and its dynamics are also determined by a free-design time-dependent function and parameters. From a theoretical analysis, the well-posedness of the model is demonstrated; positivity and the disease-free (Pdf) and endemic (Pee) equilibrium points are analyzed. The controlled reproduction number (Rc) is proved to be a threshold for the local asymptotic stability of Pdf and the existence Pee; when Rc<1 (Rc>1), then Pdf is (not) locally asymptotically stable and Pee does not (does) exist. Simulations have been carried out with data concerning COVID-19 where the importance of keeping Rc<1 to prevent the disease spreading and future deaths is highlighted. We design the control input, since it can be easily adapted to match the user specification, to obtain impulsive and regular vaccination and fulfill the condition Rc<1.
Tesi sul tema "Non regular contact dynamics"
1
Larousse, Paul. "Modélisation d'interface endommageable en dynamique explicite dédiée au démoulage de pneumatiques". Electronic Thesis or Diss., Lyon, INSA, 2024. http://www.theses.fr/2024ISAL0098.
Testo completoAbstract (sommario):
Le pneumatique est un produit complexe soumis à de nombreuses contraintes. Il doit répondre à un compromis entre coût, performance, sécurité et recyclabilité. Il est formé d'une multitude de couches composées de différents matériaux entraînant des comportements complexes à étudier. Ainsi, le choix de la simulation numérique s’impose, permettant notamment l’étude de nombreux scénarios. Elle permet d'étudier l'impact de chaque étape de fabrication, et notamment celle du démoulage, qui a inspiré cette thèse. Ce problème non-régulier est associé à du contact et de l'endommagement, modélisés à l’aide de modèle de zones cohésives, et à de la dynamique rapide, phénomènes rarement combinés ensemble en simulation. Le problème à résoudre étant en dynamique transitoire, le choix d’un intégrateur temporel explicite s’impose. L'idée ici est d'utiliser un schéma explicite symplectique possédant ainsi de bonnes propriétés énergétiques en vérifiant les équations de conservation discrètes. Basé sur des travaux antérieurs, le choix est porté sur le schéma explicite CD-Lagrange. Ainsi, l'étude se concentre sur l'interface de contact entre un solide déformable, et un solide rigide. Une méthode pour résoudre en dynamique des problèmes d’interface est présentée. Un cadre thermodynamique et explicite de résolution est alors proposé, avec un traitement local des non-linéarités et des non-régularités conduisant à un algorithme de résolution "matrix-free". Les formulations sont basées sur le cadre thermodynamique des matériaux standards généralisés et de la mécanique non régulière. Ensuite, l'accent est mis sur les lois d'évolution thermodynamique en étudiant la non-localité temporelle pour limiter la localisation de l’endommagement sur l’interface. Des modèles à effet retard sont alors introduits. L'aspect modulaire de la résolution proposée est montré, avec l’application de plusieurs lois d’interface et de comportement volumique. L'application à des problèmes en grandes transformations est également fournie. Enfin, la faisabilité de l'approche est mise en évidence par son intégration dans un code semi-industriel, MEF++The tire is a complex product subjected to numerous constraints, and the designer must find a compromise between cost, performance, safety and recyclability. It is composed of a multitude of overlayed layers of different materials, resulting in complex behaviors. Thus, numerical simulation is an obvious choice by allowing the study of a wide range of scenarios. It enables to study the impact of each manufacturing step, and in particular the unmolding tire process, which inspired this thesis. This non-regular problem is associated to contact and damage, described by a cohesive zone model, with fast dynamics phenomena, rarely combined together in simulation. Since the problem is a transient dynamics one, the choice of an explicit time integrator is natural. The proposed idea here is the use of an explicit symplectic scheme providing by definition good energy properties and discrete equations conservation. Based on previous work, the explicit CD-Lagrange scheme is chosen. Thus, the study is focused on the contact interface between a deformable solid and a rigid one. A method for solving interface problems in dynamics is presented. A thermodynamic and explicit resolution framework is then proposed, with local treatment of non-linearities and non-regularities leading to a matrix-free resolution algorithm. Formulations are based on the thermodynamic framework of generalized standard materials and non-regular mechanics. Next, the focus is set on the thermodynamic evolution laws by studying temporal non-locality in order to limit the damage localization on the interface. Delayed-effect models are then introduced. The modular aspect of the proposed resolution is shown, with application of several interface laws and bulk behaviors. Application to large transformation contact problems is also provided. Finally, the feasibility of the approach is demonstrated by its integration into a semi-industrial code, MEF++
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Wang, Zhaoxin. "Dynamics of Mechanical System Involving Conformal and Non-conformal Contact". OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/222.
Testo completoAbstract (sommario):
Effective prediction of mechanical system response containing rough surface contact requires a multi-scale modeling approach. A mechanical system model may involve a Finite Element (FE) or Lumped Parameter (LP) method. In either case the model must be capable of accounting for at least two scales. The macro-scale behavior, including metric or sub-metric, such as centimeter and millimeter scales, and micron-scale accounting for the surface roughness effects must be included simultaneously. It is the objective of this research to facilitate the multi-scale modeling of mechanical system containing rough surface contact, by developing approximate equation for contact of rough surfaces and demonstrating the inclusion of the approximate equations in FE and LP models of mechanical systems. The Approximate equations for conformal and non-conformal rough surfaces in contact are derived. The approximate equations constitute contact force-displacement equations based on statistical account of interaction between rough surfaces. The force-displacement relations are implemented in an FE model of a circular washer in a bolted joint, including the surface roughness effects. The equations also serve to account for the effect of roughness in the vibration interaction of a wavy surface with a nominally flat surface.
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Shahzamanian, Sichani Matin. "Wheel-rail contact modelling in vehicle dynamics simulation". Licentiate thesis, KTH, Spårfordon, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-127949.
Testo completoAbstract (sommario):
The wheel-rail contact is at the core of all research related to vehicle-track interaction. This tiny interface governs the dynamic performance of rail vehicles through the loads it transmits and, like any high stress concentration zone, it is subjected to serious damage phenomena. Thus, a clear understanding of the rolling contact between wheel and rail is key to realistic vehicle dynamic simulation and damage analyses. In a multi-body-system simulation package, the essentially demanding contact problem should be evaluated in about every millisecond. Hence, a rigorous treatment of the contact is highly time consuming. Simplifying assumptions are, therefore, made to accelerate the simulation process. This gives rise to a trade-off between accuracy and computational efficiency of the contact models in use. Historically, Hertz contact solution is used since it is of closed-form. However, some of its underlying assumptions may be violated quite often in wheel-rail contact. The assumption of constant relative curvature which leads to an elliptic contact patch is of this kind. Fast non-elliptic contact models are proposed by others to lift this assumption while avoiding the tedious numerical procedures. These models are accompanied by a simplified approach to treat tangential tractions arising from creepages and spin. In this thesis, in addition to a literature survey presented, three of these fast non-elliptic contact models are evaluated and compared to each other in terms of contact patch, pressure and traction distributions as well as the creep forces. Based on the conclusions drawn from this evaluation, a new method is proposed which results in more accurate contact patch and pressure distribution estimation while maintaining the same computational efficiency. The experience gained through this Licentiate work illuminates future research directions among which, improving tangential contact results and treating conformal contacts are given higher priority.QC 20130911
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Shahzamanian, Sichani Matin. "On Efficient Modelling of Wheel-Rail Contact in Vehicle Dynamics Simulation". Doctoral thesis, KTH, Spårfordon, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-181691.
Testo completoAbstract (sommario):
The wheel-rail contact is at the core of all research related to vehicletrackinteraction. This tiny interface governs the dynamic performanceof rail vehicles through the forces it transmits and, like any high stressconcentration zone, it is subjected to serious damage phenomena. Thus,a clear understanding of the rolling contact between wheel and rail is keyto realistic vehicle dynamics simulation and damage analysis. In a multi-body dynamics simulation, the demanding contact problemshould be evaluated at about every millisecond for several wheel-rail pairs.Hence, a rigorous treatment of the contact is highly time-consuming.Simplifying assumptions are therefore made to accelerate the simulationprocess. This gives rise to a trade-o between the accuracy and computationaleciency of the contact model in use. Conventionally, Hertz+FASTSIM is used for calculation of the contactforces thanks to its low computational cost. However, the elliptic patchand pressure distribution obtained by Hertz' theory is often not realisticin wheel-rail contact. Moreover, the use of parabolic traction bound inFASTSIM causes considerable error in the tangential stress estimation.This combination leads to inaccurate damage predictions. Fast non-elliptic contact models are proposed by others to tacklethis issue while avoiding the tedious numerical procedures. The studiesconducted in the present work show that the accuracy of these models iscase-dependent. To improve the accuracy of non-elliptic patch and pressure estimation,a new method is proposed. The method is implemented in an algorithmnamed ANALYN. Comparisons show improvements in patch and, particularly,pressure estimations using ANALYN. In addition, an alternative to the widely-used FASTSIM is developed, named FaStrip. Unlike FASTSIM, it employs an elliptic traction boundand is able to estimate the non-linear characteristic of tangential stressdistribution. Comparisons show more accurate estimation of tangentialstress and slip velocity distribution as well as creep forces with FaStrip. Ultimately, an ecient non-elliptic wheel-rail contact model consistingof ANALYN and FaStrip is proposed. The reasonable computationalcost of the model enables it to be used on-line in dynamics simulationand its accuracy can improve the damage predictions.QC 20160202
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Votsios, Vasilis. "Contact mechanics and impact dynamics of non-conforming elastic and viscoelastic semi-infinite or thin bonded layered solids". Thesis, Loughborough University, 2003. https://dspace.lboro.ac.uk/2134/11815.
Testo completoAbstract (sommario):
The thesis is concerned with the contact mechanics behaviour of non-conforming solids. The geometry of the solids considered gives rise to various contact configurations, from concentrated contacts with circular and elliptical configuration to those of finite line nature, as well as those of less concentrated form such as circular flat punches. The radii of curvature of mating bodies in contact or impact give rise to these various nonconforming contact configurations and affect their contact characteristics, from those considered as semi-infinite solids in accord with the classical Hertzian theory to those that deviate from it. Furthermore, layered solids have been considered, some with higher elastic modulus than that of the substrate material (such as hard protective coatings) and some with low elastic moduli, often employed as tribological coatings (such as solid lubricants). Other bonded layered solids behave in viscoelastic manner, with creep relaxation behaviour under load, and are often used to dampen structural vibration upon impact. Analytic models have been developed for all these solids to predict their contact and impact behaviour and obtain pressure distribution, footprint shape and deformation under both elastostatic and transient dynamic conditions. Only few solutions for thin bonded layered elastic solids have been reported for elastostatic analysis. The analytical model developed in this thesis is in accord with those reported in the literature and is extended to the case of impact of balls, and employed for a number of practical applications. The elastostatic impact of a roller against a semi-infinite elastic half-space is also treated by analytic means, which has not been reported in literature. Two and three-dimensional finite element models have been developed and compared with all the derived analytic methods, and good agreement found in all cases. The finite element approach used has been made into a generic tool for all the contact configurations, elastic and viscoelastic. The physics of the contact mechanical problems is fully explained by analytic, numerical and supporting experimentation and agreement found between all these approaches to a high level of conformance. This level of agreement, the development of various analytical impact models for layered solids and finite line configuration, and the development of a multi-layered viscoelastic transducer with agreed numerical predictions account for the main contributions to knowledge. There are a significant number of findings within the thesis, but the major findings relate to the protective nature of hard coatings and high modulus bonded layered solids, and the verified viscoelastic behaviour of low elastic modulus compressible thin bonded layers. Most importantly, the thesis has created a rational framework for contact/impact of solids of low contact contiguity.
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Hedman, Stefan. "Smooth and non-smooth approaches to simulation of granular matter". Thesis, Umeå universitet, Institutionen för fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-50584.
Testo completoAbstract (sommario):
Granular matter is defined as a collection of particle grains, such as sand.This type of matter have different characteristics (solid, liquid and gas) depending on the energy level per grain. There are several approaches to modeling and numerical simulations of granular matter. They are used by different groups for different purposes, and the choice between the approaches is based on knowledge and tradition rather than what might be best for the purpose. The key questions are when to use what method and what physical quality is lost depending on the choice.Two regimes of discrete element granular simulations emerge: smooth and non-smooth. To compare the efficiency and physical quality of the two approaches, four physics softwares are examined including Bullet Physics, LMGC90, AgX and LIGGGHTS. Test scenes are setup in each software and the results are compared to each other or to the results of other work.The thesis is performed at UMIT Research Lab at Umeå University.
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Diallo, Moustapha. "Wetting on heterogeneous metal-oxides regular patterned surfaces by a non-reactive liquid metal". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC004/document.
Testo completoAbstract (sommario):
Dans la galvanisation à chaud, les aciers sont protégés contre la corrosion par une mince couche de zinc obtenue par immersion dans un bain d’alliage de zinc. Avant ce processus, les tôles d'acier subissent un recuit de recristallisation afin d'éliminer l’écrouissage après laminage à froid. Les conditions de recuit utilisées réduisent le film d'oxyde de fer natif, ce qui favorise la mouillabilité de la surface de l'acier par le zinc liquide. Cependant, les nouveaux aciers à haute résistance contiennent des quantités importantes d'éléments d’addition, tels que le silicium et le manganèse. Ces élements diffusent à la surface de l'acier pendant le recuit de recristallisation et forment des particules ou des films d'oxyde par oxydation sélective externe. Si le fer pur est bien mouillé par le zinc liquide, ces oxydes ne le sont pas et leur présence à la surface peut entraîner des défauts dans le revêtement final.Pour étudier l'influence de la taille et de la distribution des oxydes sur le mouillage par le métal liquide, nous avons étudié un mouillage non réactif du plomb liquide sur une surface hétérogène texturée Fe / silice en utilisant la technique de chute de goutte.Ces surfaces ont été conçues par dépôt chimique en phase vapeur assisté par plasma, suivi d'un procédé photolithographique.Après l'impact, la goutte s'étend jusqu'à son diamètre d'étalement maximal. S’ensuit une phase de recule de la goutte. Pendant son recul, la goutte est plus ou moins retenue, en fonction du taux de couverture de silice, sur le fer pur: phénomène d’accrochage-glissement. Sur les surfaces à faible teneur en silice, ce phénomène entraîne une déformation de la forme de la goutte qui est plus allongée dans un sens et quelquefois à la division de la goutte.Il a été démontré que le mouillage est affecté principalement par la fraction de surface de la silice.Enfin, nous avons modélisé les différentes phases de l'étalement de la goutte sur ces surfaces hétérogènes. Des modèles de littérature ont été revus et adaptés et nous avons proposé des modèles macroscopiques de l'oscillation de la goutte pendant son étalementIn hot-dip galvanizing, steel sheets are protected against corrosion by a thin layer of zinc obtained by immersion in a zinc alloy bath. Before this process, the steel sheets undergo recrystallization annealing to eliminate stresses after cold-rolling. The annealing conditions used reduce the native iron oxide film, which promotes the wettability of the steel surface with liquid zinc. However, new high-strength steels contain significant quantities of addition elements, such as silicon and manganese. These elements diffuse on the surface of the steel sheets during recrystallization annealing and form oxide particles or films by selective external oxidation. If pure iron is well wet with liquid zinc, these oxides are not and their presence on the surface can lead to defects in the final coating.To study the influence of oxide size and their distribution on liquid metal wetting, we studied a non-reactive wetting of liquid lead on a heterogeneous Fe / silica textured surface using the dispensed technique.These surfaces were designed by plasma-assisted chemical vapour deposition followed by a photolithographic process.After impact, the drop extends to its maximum spreading diameter. This is followed by a phase of drop receding. During this, the drop is more or less retained, depending on the silica coverage rate, on the pure iron: stick-slip motion. On surfaces with low silica content, this phenomenon causes a deformation of the drop shape which is more elongated in one direction and sometimes at the division of the drop.We showed that wetting is mainly affected by the surface fraction of silica.Finally, we modelled the different phases of drop spreading on these heterogeneous surfaces. Literature models were reviewed and adapted and macroscopic models of the oscillation of the drop during its spreading were proposed
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Dia, Seydou. "Modélisation d'un contact dynamique non-linéaire : application au développement et à l'optimisation de modalsens". Phd thesis, Université de Haute Alsace - Mulhouse, 2010. http://tel.archives-ouvertes.fr/tel-00683067.
Testo completoAbstract (sommario):
La tribologie et l'analyse non-linéaire du signal est le sujet de mon travail de thèse. Dans la nature, les phénomènes linéaires sont l'exception ; rares sont les systèmes réels qui obéissent exclusivement à des lois linéaires. A l'opposée, les non-linéarités sont impliquées dans tous les processus naturels (réactions chimiques, mécanique, économie, etc.). Les systèmes frottant en sont un des exemples les plus courants, avec des applications très variées. Dans les systèmes de freinage, le frottement se trouve être à l'origine de nombreux problèmes d'instabilités. Les types d'instabilités auxquelles on a affaire dans ce cas sont celles des vibrations induites par le frottement. C'est justement sur ces instabilités que repose le principe Modalsens; un capteur- une lamelle- vient frotter sur un échantillon et ce frottement génère la vibration de celui-ci : le post-traitement par analyse de Fourier du signal vibratoire permet de distinguer des composantes liées au relief, au frottement et à la compressibilité des aspérités. Dans le cas de la méthode Modalsens, l'analyse de Fourier, qui est un outil linéaire, agit comme des lunettes aux travers desquelles est observé le signal et qui filtrerait toutes les composantes non-linéaires. Notre contribution s'inscrit dans cette optique: mettre en place une méthode performante d'analyse non-linéaire pour permettre de mieux appréhender l'analyse du comportement dynamique de Modalsens et de dégager de nouveaux estimateurs pour la caractérisation des surfaces textiles. Partant de là, les résultats obtenus nous serviront à proposer une modélisation du contact sur matériaux fibreux.
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Sundar, Sriram. "Impact damping and friction in non-linear mechanical systems with combined rolling-sliding contact". The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1386245045.
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AHMED, RIZWAN. "Experimental Investigation Of Non-Linear Structural Dynamics of Shrouded Turbine Blade". Doctoral thesis, Politecnico di Torino, 2022. https://hdl.handle.net/11583/2972153.
Testo completoLibri sul tema "Non regular contact dynamics"
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Friedrich, Pfeiffer, Wriggers Peter e SpringerLink (Online service), a cura di. Numerics of Unilateral Contacts and Friction: Modeling and Numerical Time Integration in Non-Smooth Dynamics. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009.
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Studer, Christian. Numerics of Unilateral Contacts and Friction: Modeling and Numerical Time Integration in Non-Smooth Dynamics. Springer, 2010.
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Mercati, Flavio. Solutions of Shape Dynamics. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198789475.003.0013.
Testo completoAbstract (sommario):
This chapter deals with the most important results in SD, namely, the classical solutions of the theory in which the equivalence with (GR) breaks down. Firstly, I study the case of homogeneous but not isotropic cosmologies, known as ‘Bianchi IX’ universes in detail. In this case, each solution that reaches the big bang singularity can be continued uniquely through it, just by requiring continuity of the conformally- and scale-invariant degrees of freedom. The result is a couple of cosmological solutions with opposite orientation glued at the big bang. This result is more general than the homogeneous case, and can be extended to a large class of solutions if the BKL conjecture is valid. In the case of spherically symmetric solutions one has to couple gravity to some form of matter in order to have dynamically non-trivial degrees of freedom. The simplest case is a series of concentric infinitely thin shells of dust in a universe with the topology of a three-sphere. In this case too a departure from the dynamics of (GR) is seen, that manifests itself in a failure of the CMC slicing when one of the shells collapses (no spacetime corresponding to that solution of SD exists). The conformally invariant degrees of freedom, again, seem to still be regular when this happens. In the last part of the chapter I will discuss the sense in which one can talk about asymptotically flat solutions of SD, and past results in this regime.
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Timmins, Bryan. Non-prescription drugs. A cura di Patrick Davey e David Sprigings. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780199568741.003.0342.
Testo completoAbstract (sommario):
The use of non-prescription drugs is widespread and has a major impact on the health of the individual user and society. In 2006, the British Crime Survey reported that 10% of adults had used one or more illicit drugs in the preceding year, with 3% reporting using a Class A drug. Over 11 million people in the UK are estimated to have used an illicit drug at least once in their lifetime (35%). Drugs abused vary in their intrinsic potential to cause addiction and, with it, more regular and harmful use. Drug users are influenced by trends and fashions, adopting new compounds such as crack cocaine and experimenting with routes of ingestion. Some drugs may become less popular over time, such as LSD, while others, such as cannabis, experience a revival as more potent strains (e.g. Skunk) are developed. A problem drug user is best defined as a person whose drug taking is no longer controlled or undertaken for recreational purposes and where drugs have become a more essential element of the individual’s life. The true economic and social cost of drug use is likely to be substantially greater than the published figures, which are derived from a variety of health and crime surveys which may overlook vulnerable groups such as the homeless. The majority of non-prescription drugs used in the UK are illegal and covered by the Misuse of Drugs Act 1971. The drugs most commonly abused gave rise in 2003–4 to an estimated financial cost in England and Wales of 15.4 billion pounds to the economy, with Class A drugs such as heroin and cocaine accounting for the majority of this. Some 90% of the cost is due to drug-related crime, with only 3% (£488 million) due to health service expenditure, which is mainly spent on inpatient care episodes. This still represents a major health pressure, which in 2006–7 amounted to 38 000 admissions, in England, for primary and secondary drug-related mental or behavioural problems, and over 10 000 admissions recorded for drug poisoning. Clinicians in all specialities can expect to encounter harmful drug use, especially those working in primary care, A & E, and psychiatric services. Presenting problems are protean, ranging from mood disorders, delirium, and psychosis to sepsis, malnutrition, and hepatitis. Blood-borne infections such as hepatitis C and HIV are widespread, as contaminated needles and syringes are shared by up to a quarter of problem drug users. Even smoking drugs such as crack cocaine can lead to increased transmission of hepatitis C through oral ulceration and contact with hot contaminated smoking pipes. Amongst the UK population, over half of IV drug users have hepatitis C, a quarter have antibodies to hepatitis B, and, by 2006, 4662 had been diagnosed with HIV. Non-prescription drug abuse is a leading cause of death and morbidity amongst the young adult population (those aged 16–35). In 2006 there were 1573 deaths where the underlying cause was poisoning, drug abuse, or dependence on substances controlled under the Misuse of Drugs Act. The vast majority (79%) were male. Young men, in particular, are at greater risk of violent death through associated criminal activity such as drug supplying and from deliberate and accidental overdose. The male-to-female ratio for deaths associated with mental and behavioural disorder is 6:1.
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Mann, Peter. Autonomous Geometrical Mechanics. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198822370.003.0022.
Testo completoAbstract (sommario):
This chapter examines the structure of the phase space of an integrable system as being constructed from invariant tori using the Arnold–Liouville integrability theorem, and periodic flow and ergodic flow are investigated using action-angle theory. Time-dependent mechanics is formulated by extending the symplectic structure to a contact structure in an extended phase space before it is shown that mechanics has a natural setting on a jet bundle. The chapter then describes phase space of integrable systems and how tori behave when time-dependent dynamics occurs. Adiabatic invariance is discussed, as well as slow and fast Hamiltonian systems, the Hannay angle and counter adiabatic terms. In addition, the chapter discusses foliation, resonant tori, non-resonant tori, contact structures, Pfaffian forms, jet manifolds and Stokes’s theorem.
Capitoli di libri sul tema "Non regular contact dynamics"
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Shahini, I., M. R. Ashory, S. Shahbazmohamadi, A. A. Maddah e M. M. Khatibi. "Non contact eddy current dampers for control systems". In Structural Dynamics, Volume 3, 1595–603. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-9834-7_144.
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Samarsky, A. A., A. P. Favorsky, V. F. Tishkin, V. F. Vasilevsky e K. V. Vyaznikov. "Non-Regular Adaptive Grids for 2-D Gas Dynamics". In European Consortium for Mathematics in Industry, 263–66. Wiesbaden: Vieweg+Teubner Verlag, 1992. http://dx.doi.org/10.1007/978-3-663-09834-8_53.
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Weidauer, Tim, e Kai Willner. "Reduced Order Modelling for Non-linear Rotating Systems in ALE Formulation with Contact". In Nonlinear Dynamics, Volume 1, 287–302. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-74280-9_31.
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Cappellini, A., D. Leva, C. Rivolta e M. Vanali. "Use of Non Contact Radar Techniques to Dynamics Measurement Purposes". In Topics in Modal Analysis II, Volume 6, 247–54. New York, NY: Springer New York, 2012. http://dx.doi.org/10.1007/978-1-4614-2419-2_23.
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Rodriguez, F. B., P. Varona, R. Huerta, M. I. Rabinovich e Henry D. I. Abarbanel. "Richer Network Dynamics of Intrinsically Non-regular Neurons Measured through Mutual Information". In Connectionist Models of Neurons, Learning Processes, and Artificial Intelligence, 490–97. Berlin, Heidelberg: Springer Berlin Heidelberg, 2001. http://dx.doi.org/10.1007/3-540-45720-8_58.
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Bradley, D. I., e G. R. Pickett. "Regular Vortex Production by a Moving Wire in Superfluid 3He-B". In Topological Defects and the Non-Equilibrium Dynamics of Symmetry Breaking Phase Transitions, 345–51. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-011-4106-2_16.
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Schiavoni, Mattia, Gianluca Standoli, Francesca Bianconi, Ersilia Giordano e Francesco Clementi. "Discontinuous Dynamics of Santa Maria Annunziata Church Under Seismic Loading: A Non-smooth Contact Dynamics Approach". In RILEM Bookseries, 484–93. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-39450-8_40.
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Lefaucheux, Engel, Joël Ouaknine, David Purser e Mohammadamin Sharifi. "Model Checking Linear Dynamical Systems under Floating-point Rounding". In Tools and Algorithms for the Construction and Analysis of Systems, 47–65. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-30823-9_3.
Testo completoAbstract (sommario):
AbstractWe consider linear dynamical systems under floating-point rounding. In these systems, a matrix is repeatedly applied to a vector, but the numbers are rounded into floating-point representation after each step (i.e., stored as a fixed-precision mantissa and an exponent). The approach more faithfully models realistic implementations of linear loops, compared to the exact arbitrary-precision setting often employed in the study of linear dynamical systems.Our results are twofold: We show that for non-negative matrices there is a special structure to the sequence of vectors generated by the system: the mantissas are periodic and the exponents grow linearly. We leverage this to show decidability of $$\omega $$ ω -regular temporal model checking against semialgebraic predicates. This contrasts with the unrounded setting, where even the non-negative case encompasses the long-standing open Skolem and Positivity problems.On the other hand, when negative numbers are allowed in the matrix, we show that the reachability problem is undecidable by encoding a two-counter machine. Again, this is in contrast with the unrounded setting where point-to-point reachability is known to be decidable in polynomial time.
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Hendriks, Jennifer. "Chapter 4. The dynamics of lifelong acquisition in dialect contact and change". In Lifespan Acquisition and Language Change, 84–103. Amsterdam: John Benjamins Publishing Company, 2024. http://dx.doi.org/10.1075/ahs.14.04hen.
Testo completoAbstract (sommario):
Acquisition research involving speakers of mutually intelligible varieties (dialects) or mutually unintelligible varieties (languages) reveals a wide range of possible acquisition outcomes at different life stages and their potential to shape language change across the community. Since contexts of dialect contact often include language contact, attempts to understand the link between dialect acquisition and dialect change must also consider language contact as a potential factor. This chapter surveys the research on dialect contact and lifespan change in contexts of language maintenance in both non-mobile and mobile languages users as a window into the human capacity for lifelong acquisition and change. The chapter adopts a linguistic repertoire focus, recognizing that bidialectalism/bilingualism is a matter of degree, and that language dominance plays a key role in crosslinguistic transfer. This proposal is illustrated with a case study of dialect and language contact in Early Modern Dutch.
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Karagiozis, K. N., M. P. PaïDoussis, E. Grinevich, A. K. Misra e M. Amabili. "Stability and Non-Linear Dynamics of Clamped Circular Cylindrical Shells in Contact with Flowing Fluid". In IUTAM Symposium on Integrated Modeling of Fully Coupled Fluid Structure Interactions Using Analysis, Computations and Experiments, 375–90. Dordrecht: Springer Netherlands, 2003. http://dx.doi.org/10.1007/978-94-007-0995-9_27.
Testo completoAtti di convegni sul tema "Non regular contact dynamics"
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Keogh, Patrick S., Chris Lusty e Nicola Y. Bailey. "Nonlinear Dynamics and Control of Rotors Operating Within the Clearance Gaps of Magnetic Bearing Systems". In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71865.
Testo completoAbstract (sommario):
Under normal operation a rotor spinning within an active magnetic bearing system will be levitated and hence rotor-stator contact conditions do not exist. In such a case, external disturbances and inherent unbalance will cause rotor responses that are maintained by the magnetic bearing control system to be within the clearance gap. However, magnetic bearings have limited dynamic load capacity due to magnetic material field saturation. Hence large external disturbances may be sufficient to cause the clearance gap to become closed and result in rotorstator contact. A touchdown bearing is usually incorporated as a sacrificial stator component to protect the expensive rotor, magnetic bearing and sensor components. Once contact has been made, rotor dynamic conditions may ensue resulting in persistent rotor bouncing or rubbing limit cycle responses. Prolonged exposure to these severe dynamics will cause touchdown bearing degradation and require regular replacement. A clear aim is therefore to restore contact-free levitation through available control capability in an efficient manner. This paper provides an analysis to gain an understanding of the uncontrolled rotor/touchdown contact dynamics. These will then be used to guide the control options that are available to restore contact-free levitation. The use of magnetic bearing control is appropriate if the required control forces are within saturation limits. It is also possible to actuate touchdown bearings and destabilize persistent rotor dynamic contact conditions. For example, piezo-based actuation offers larger control forces than those from magnetic bearing systems.
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Pontonnier, Soufiane, Samuel Quaegebeur, Fabrice Thouverez e Patricio Almeida. "Methodology for Modeling Non Linear Thermomechanical Response With Wear at High-Speed Interactions: Application to a Pin-Disk Configuration". In ASME Turbo Expo 2024: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2024. http://dx.doi.org/10.1115/gt2024-126280.
Testo completoAbstract (sommario):
Abstract An aircraft engine is a complex structure for which some components can come into contact at high speed. Modelling this behaviour is very complex as multiple physics must be considered. State-of-the-art methodologies usually account for permanent contact and thermal modelling. In this paper, a new approach is proposed and embeds various phenomena such as non-regular and non linear contact mechanics, surface rubbing, wear and non linear heat transfer. A non linear version of Moreau-Jean algorithm is employed to compute the transient response of the system and to capture accurately the contact dynamics. Moreover, the full non linear coupling between the dynamics and the heating process is taken into account through both a semi-analytical formulation and the finite-element method. At the contact interface, heat flux is generated by dry rubbing and flows into both interacting bodies. The heat flux partition is evaluated thanks to a coefficient that depends on the material properties of the solids in contact. The proposed method also accounts for the adhesive wear between the solids through an energetic approach. This methodology is applied to an academic, yet realistic, disk connected to a rotor shaft that is free to move axially and to rotate around its revolution axis. Gyroscopic effects and variation of the rotation velocity are included leading to a full non linear mechanical behaviour. The disk undergoes aerodynamic load moving it to contact with a clamped free pin. The rotor shaft and the pin are both modelled as 1D elastic bodies while the rotor disk is assumed to be rigid. Through this example, the developed strategy shows its potential to compute the complete transient highly non linear response of the breaking phenomenon, in an acceptable time simulation.
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Zafar, Madiha, e Muhammad Owais Qarni. "UNCOVERING DIVERSIFICATION BENEFITS: RETURN SPILLOVERS IN USA ESG AND NON-ESG ORIENTED BANKS". In International Conference on Business, Economics, Law, Language & Psychology, 18-19 June 2024, London. Global Research & Development Services, 2024. http://dx.doi.org/10.20319/icssh.2024.328329.
Testo completoAbstract (sommario):
Financial products are interconnected through the balance sheet and affect the overall economic system by connectedness. Investors are interested in the connectedness of markets, so our study investigated spillover dynamics and their influence on ESG and non-ESG-oriented banks in the USA. Our dataset comprises 2319 observations from January 1, 2015, to November 22, 2023. We employed the spillover index of Diebold and Yilmaz (2012) to conduct an extensive analysis of ESG-oriented and non-ESG-oriented banks in the USA. The study uncovered significant differences in interconnectedness and spillover effects between ESG-oriented and non-ESG-oriented banks, particularly during regular periods and the COVID-19 pandemic. ESG-oriented banks, in particular, exhibit higher levels of interconnectedness, with notable spillovers among themselves, indicating a need for cross-market diversification to manage risk. In contrast, non-ESG-oriented banks demonstrate lower interconnectedness and spillover effects. The study highlights the potential benefits of portfolio diversification across ESG and non-ESG banks. The research concludes that such diversification can offer significant risk reduction benefits. Findings suggested that banks must incorporate ESG and non-ESG investments in their portfolio to mitigate overall risk. Banks’ adoption of ESG standards may lead to investing in fewer projects, leading to ESG constraints in portfolio optimization. In this way, ESG investment restricts and constrains the diversification of portfolios, which increases risk and contagion.
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Al-Ani, Dhafar, Hamed H. Afshari e Saeid Habibi. "A Robust Controller of Multi DOF-Cooperating Planar Robotic Manipulators Using a Tuned PID Approach". In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-36052.
Testo completoAbstract (sommario):
Usually, a dynamic system with impact conditions is an interesting problem with practical applications in the fields of dynamics, vibrations, and control. One difficulty in controlling robotics (i.e., a multi DOF two-cooperating or two-link planar) is the subject to impact between the end-effectors of manipulators is that the dynamics (i.e., equations of motion) are different when the system status changes suddenly from a non-contact state to a contact state. In this paper, a Tuned PID controller with different design scenarios is developed to regulate the states of two dynamic systems that collide. Further, in this work, three types of errors are used to compare among different cases that are; (1) the steady state error, (2) the root mean square error, and (3) the final value error. The results of the Tuned PID controller are compared to those obtained by a classical PID controller. The PID controller is tuned using the Ziegler–Nicholas approach. The simulation results of the robotic manipulators confirmed the theoretical effectiveness of the proposed controller, based on MATLAB/Simulink. Unlike the classical PID results (i.e., the impact-induced force is found to be 2.0 N), the Tuned PID controller successfully determined the impact-induced force as same as the desired force (i.e., 0.6 N). Moreover, the Tuned PID satisfied all other desired design values.
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Bouzar Essaidi, Ahmed, Bachir Menkouz, Moussa Haddad e Taha Chettibi. "NON-REGULAR VEHICLE DYNAMICS. APPLICATION TO COLLISION". In VII European Congress on Computational Methods in Applied Sciences and Engineering. Athens: Institute of Structural Analysis and Antiseismic Research School of Civil Engineering National Technical University of Athens (NTUA) Greece, 2016. http://dx.doi.org/10.7712/100016.2133.9025.
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Qu, Jie, Chaoran Dou, Jianzhi Li, Zhonghao Rao e Ben Xu. "Numerical and Experimental Study of Bioink Transfer Process in Laser Induced Forward Transfer (LIFT) 3D Bioprinting". In ASME 2020 Heat Transfer Summer Conference collocated with the ASME 2020 Fluids Engineering Division Summer Meeting and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ht2020-9147.
Testo completoAbstract (sommario):
Abstract As a promising 3D bioprinting process, laser induced forward transfer (LIFT) has attracted attention in the last decade due to its advantages of non-contact, nozzle-free, high dropping rate and high resolution. However, the mechanism of bubble/jet formation under laser inducement has not been well comprehended yet. To better understand the multiphase process, the bubble formation and jet process under single laser pulse was explored in this study, using both the Computational Fluid Dynamics (CFD) model and experimental study. The results showed that under a laser pulse with the Gaussian distribution, a vapor bubble was formed around 0.1μs, then the bubble was expanded over time. During the bubble expansion process, the maximum magnitude of velocity could reach as high as 22m/s. The pressure near the laser interaction area was around 4.72 × 107 Pa, which is 470 times of the ambient pressure. After increasing the pulse energy and focal spot area, the liquid bubble layer moved downward to complete the bioink transfer process after the collapse of glycerol vapor bubble, which showed similar flow characteristics as the experimental results under the same laser fluence (1.4J/cm2). When the laser fluence was decreased to 0.8 J/cm2, a regular jet flow could be observed. The proposed multiphase numerical model can be used to understand the mechanism of bubble/jet formation under laser inducement and provide some insights into the bioink transfer during LIFT process, in order to eventually optimize the LIFT 3D-printing process with greater cell viability.
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Sharf, Inna, e Yuning Zhang. "A Contact Force Solution for Non-Colliding Contact Dynamics Simulation". In ASME 2006 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/detc2006-99139.
Testo completoAbstract (sommario):
Rigid-body impact modeling remains an intensive area of research spurred on by new applications in robotics, biomechanics, and more generally multibody systems. By contrast, the modeling of non-colliding contact dynamics has attracted significantly less attention. The existing approaches to solve non-colliding contact problems include compliant approaches in which the contact force between objects is defined explicitly as a function of local deformation, and complementarity formulations in which unilateral constraints are employed to compute contact interactions (impulses or forces) to enforce the impenetrability of the contacting objects. In this article, the authors develop a novel approach to solve the non-colliding contact problem for objects of arbitrary geometry in contact at multiple points. Similarly to the complementarity formulation, the solution is based on rigid-body dynamics and enforces contact kinematics constraints at the acceleration level. Differently, it leads to an explicit closed-form solution for the normal forces at the contact points. Integral to the proposed formulation is the treatment of tangential contact forces, in particular the static friction. These friction forces must be calculated as a function of microslip velocity or displacement at the contact point. Numerical results are presented for three test cases: 1) a thin rod sliding down a stationary wedge; 2) a cube rotating off the stationary wedge under application of an external moment and 3) the cube and the wedge both moving under application of a moment. To ascertain validity and correctness, the solutions to frictionless and frictional scenarios obtained with the proposed formulation are compared to those generated by using a commercial simulation tool MSC ADAMS.
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Wang, Xiaowen. "Passive control of hypersonic non-equilibrium boundary layers using regular porous coating". In 47th AIAA Fluid Dynamics Conference. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2017. http://dx.doi.org/10.2514/6.2017-4519.
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Huang, J., K. Krabbenhoft, M. Vicente da Silva e A. V. Lyamin. "SIMULATING GRANULAR COLUMN COLLAPSE BY NON-SMOOTH CONTACT DYNAMICS". In 10th World Congress on Computational Mechanics. São Paulo: Editora Edgard Blücher, 2014. http://dx.doi.org/10.5151/meceng-wccm2012-18460.
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Pfeiffer, Friedrich. "Steps Towards Non-Smooth Multibody Dynamics". In ASME 2021 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/detc2021-74773.
Testo completoAbstract (sommario):
Abstract Before the background of many thoughts about contact and impact behavior with and without friction in the past centuries a comprehensive theory appeared not before the second half of the last century, mainly connected with the names of Moreau in Montpellier and Panagiotopoulos in Thessaloniki. My former Institute has been part of this evolution focusing on non-smooth multibody dynamics and on large systems. The local development from simple impact to complex contact systems including all possible contact details will be subject of the paper, considering also the necessary mathematical evolution from classical multibody system theory with bilateral constraints and single-valued forces to non-smooth multibody system theory with unilateral constraints and set-valued forces. Paper will be illustrated by practical examples.
Rapporti di organizzazioni sul tema "Non regular contact dynamics"
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Ge, Haitao, Juan Carlos Quezada, Vincent Le Houerou e Cyrille Chazallon. Investigation of Tire-pavement Interaction Based on Non-smooth Contact Dynamics Method. Peeref, settembre 2022. http://dx.doi.org/10.54985/peeref.2209p2134642.
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Claire, Wolstenholme, e Nathaniel Pickering. Evaluation of bursary and college projects: Producers of Enhancement, Evaluation and Research (PEER). Sheffield Hallam University, 2024. https://doi.org/10.7190/steer/peer.
Testo completoAbstract (sommario):
This evaluation examined the Producers of Enhancement, Evaluation and Research (PEER) programme at Sheffield Hallam University. The study aimed to assess the implementation and outcomes of PEER, focusing on the benefits and challenges of staff-student collaboration. The PEER programme, which has employed nearly 200 students and delivered over 100 projects in three years, aims to enhance student experiences and outcomes through staff-student collaborations. This evaluation involved semi-structured interviews with 10 student researchers and 9 staff project leads, to understand their motivations, experiences, and perceptions of the programme's impacts. Findings indicate that involvement in PEER has, for some students, led to skills development, with students gaining valuable research experience, as well as the ability to work with staff in open and collaborative ways that may not have been previously experienced. Staff reported benefiting from the insights of students and the opportunity to get to know them in a more personal way. Challenges identified included communication issues, time constraints, and delays from ethical approval process difficulties. Effective communication and relationship-building between staff and students were important enablers of success. The study highlights the importance of clear guidance and support from the Student Engagement Evaluation and Research (STEER) team, which facilitated training and regular contact. Recommendations include improving the matching process for staff and student researchers, providing additional ethical support, and ensuring staff and students are clear about roles and expectations for working together. Overall, the PEER programme has positively impacted student and staff experiences, contributing to the university's strategic objectives and offering insights into the dynamics of student-staff partnerships in higher education.
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Morphett, Jane, Alexandra Whittaker, Amy Reichelt e Mark Hutchinson. Perineuronal net structure as a non-cellular mechanism of affective state, a scoping review. INPLASY - International Platform of Registered Systematic Review and Meta-analysis Protocols, agosto 2021. http://dx.doi.org/10.37766/inplasy2021.8.0075.
Testo completoAbstract (sommario):
Is the perineuronal net structure within emotional processing brain regions associated with changes in affective state? The objective of this scoping review is to bring together the literature on human and animal studies which have measured perineuronal net structure in brain regions associated with emotional processing (such as but not limited to amygdala, hippocampus and prefrontal cortex). Perineuronal nets are a specialised form of condensed extracellular matrix that enwrap and protect neurons (Suttkus et al., 2016), regulate synaptic plasticity (Celio and Blumcke, 1994) and ion homeostasis (Morawski et al., 2015). Perineuronal nets are dynamic structures that are influenced by external and internal environmental shifts – for example, increasing in intensity and number in response to stressors (Blanco and Conant, 2021) and pharmacological agents (Riga et al., 2017). This review’s objective is to generate a compilation of existing knowledge regarding the structural changes of perineuronal nets in experimental studies that manipulate affective state, including those that alter environmental stressors. The outcomes will inform future research directions by elucidating non-cellular central nervous system mechanisms that underpin positive and negative emotional states. These methods may also be targets for manipulation to manage conditions of depression or promote wellbeing. Population: human and animal Condition: affective state as determined through validated behavioural assessment methods or established biomarkers. This includes both positive and negative affective states. Context: PNN structure, measuringPNNs.
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Calafat, Francisco Mir, Thomas Frederikse e Kevin Horsburgh. Mediterranean trend and acceleration sea-level estimates. EuroSea, 2023. http://dx.doi.org/10.3289/eurosea_d5.2_v2.
Testo completoAbstract (sommario):
Sea-level change is geographically non-uniform, with regional departures that can reach several times the global average rate of change. Characterizing this spatial variability and understanding its causes is crucial to the design of adaptation strategies for sea-level rise. This, as it turns out, is no easy feat, primarily due to the sparseness of the observational sea-level record in time and space. Long tide gauge records are restricted to a few locations along the coast. Satellite altimetry offers a better spatial coverage but only since 1992. In the Mediterranean Sea, the tide gauge network is heavily biased towards the European shorelines, with only one record with at least 35 years of data on the African coasts. Past studies have attempted to address the difficulties related to this data sparseness in the Mediterranean Sea by combining the available tide gauge records with satellite altimetry observations. The vast majority of such studies represent sea level through a combination of altimetry-derived empirical orthogonal functions whose temporal amplitudes are then inferred from the tide gauge data. Such methods, however, have tremendous difficulty in separating trends and variability, make no distinction between relative and geocentric sea level, and tell us nothing about the causes of sea level changes. Here, we combine observational data from tide gauges and altimetry with sea-level fingerprints of land-mass changes using a Bayesian hierarchical model (BHM) to quantify the sources of sea-level changes since 1960 in the Mediterranean Sea. The Bayesian estimates are provided on 1/4o x 1/4o regular grid. We find that Mediterranean Sea level rose at a relatively low rate from 1960 to 1990, at which point it started rising significantly faster with comparable contributions from sterodynamic sea level (ocean dynamics and thermal expansion) and land-mass changes. (EuroSea Deliverable, D5.2_v2)
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Rarasati, Niken, e Rezanti Putri Pramana. Giving Schools and Teachers Autonomy in Teacher Professional Development Under a Medium-Capability Education System. Research on Improving Systems of Education (RISE), gennaio 2023. http://dx.doi.org/10.35489/bsg-rise-ri_2023/050.
Testo completoAbstract (sommario):
A mature teacher who continuously seeks improvement should be recognised as a professional who has autonomy in conducting their job and has the autonomy to engage in a professional community of practice (Hyslop-Margison and Sears, 2010). In other words, teachers’ engagement in professional development activities should be driven by their own determination rather than extrinsic sources of motivation. In this context, teachers’ self-determination can be defined as a feeling of connectedness with their own aspirations or personal values, confidence in their ability to master new skills, and a sense of autonomy in planning their own professional development path (Stupnisky et al., 2018; Eyal and Roth, 2011; Ryan and Deci, 2000). Previous studies have shown the advantages of providing teachers with autonomy to determine personal and professional improvement. Bergmark (2020) found that giving teachers the opportunity to identify areas of improvement based on teaching experience expanded the ways they think and understand themselves as teachers and how they can improve their teaching. Teachers who plan their own improvement showed a higher level of curiosity in learning and trying out new things. Bergmark (2020) also shows that a continuous cycle of reflection and teaching improvement allows teachers to recognise that the perfect lesson does not exist. Hence, continuous reflection and improvement are needed to shape the lesson to meet various classroom contexts. Moreover, Cheon et al. (2018) found that increased teacher autonomy led to greater teaching efficacy and a greater tendency to adopt intrinsic (relative to extrinsic) instructional goals. In developed countries, teacher autonomy is present and has become part of teachers’ professional life and schools’ development plans. In Finland, for example, the government is responsible for providing resources and services that schools request, while school development and teachers’ professional learning are integrated into a day-to-day “experiment” performed collaboratively by teachers and principals (Niemi, 2015). This kind of experience gives teachers a sense of mastery and boosts their determination to continuously learn (Ryan and Deci, 2000). In low-performing countries, distributing autonomy of education quality improvement to schools and teachers negatively correlates with the countries’ education outcomes (Hanushek et al., 2011). This study also suggests that education outcome accountability and teacher capacity are necessary to ensure the provision of autonomy to improve education quality. However, to have teachers who can meet dynamic educational challenges through continuous learning, de Klerk & Barnett (2020) suggest that developing countries include programmes that could nurture teachers’ agency to learn in addition to the regular content and pedagogical-focused teacher training materials. Giving autonomy to teachers can be challenging in an environment where accountability or performance is measured by narrow considerations (teacher exam score, administrative completion, etc.). As is the case in Jakarta, the capital city of Indonesia, teachers tend to attend training to meet performance evaluation administrative criteria rather than to address specific professional development needs (Dymoke and Harrison, 2006). Generally, the focus of the training relies on what the government believes will benefit their teaching workforce. Teacher professional development (TPD) is merely an assignment for Jakarta teachers. Most teachers attend the training only to obtain attendance certificates that can be credited towards their additional performance allowance. Consequently, those teachers will only reproduce teaching practices that they have experienced or observed from their seniors. As in other similar professional development systems, improvement in teaching quality at schools is less likely to happen (Hargreaves, 2000). Most of the trainings were led by external experts or academics who did not interact with teachers on a day-to-day basis. This approach to professional development represents a top-down mechanism where teacher training was designed independently from teaching context and therefore appears to be overly abstract, unpractical, and not useful for teachers (Timperley, 2011). Moreover, the lack of relevancy between teacher training and teaching practice leads to teachers’ low ownership of the professional development process (Bergmark, 2020). More broadly, in the Jakarta education system, especially the public school system, autonomy was never given to schools and teachers prior to establishing the new TPD system in 2021. The system employed a top-down relationship between the local education agency, teacher training centres, principals, and teachers. Professional development plans were usually motivated by a low teacher competency score or budgeted teacher professional development programme. Guided by the scores, the training centres organised training that could address knowledge areas that most of Jakarta's teachers lack. In many cases, to fulfil the quota as planned in the budget, the local education agency and the training centres would instruct principals to assign two teachers to certain training without knowing their needs. Realizing that the system was not functioning, Jakarta’s local education agency decided to create a reform that gives more autonomy toward schools and teachers in determining teacher professional development plan. The new system has been piloted since November 2021. To maintain the balance between administrative evaluation and addressing professional development needs, the new initiative highlights the key role played by head teachers or principals. This is based on assumption that principals who have the opportunity to observe teaching practice closely could help teachers reflect and develop their professionalism. (Dymoke and Harrison, 2006). As explained by the professional development case in Finland, leadership and collegial collaboration are also critical to shaping a school culture that could support the development of professional autonomy. The collective energies among teachers and the principal will also direct the teacher toward improving teaching, learning, and caring for students and parents (Hyslop-Margison and Sears, 2010; Hargreaves, 2000). Thus, the new TPD system in Jakarta adopts the feature of collegial collaboration. This is considered as imperative in Jakarta where teachers used to be controlled and join a professional development activity due to external forces. Learning autonomy did not exist within themselves. Hence, teachers need a leader who can turn the "professional development regulation" into a culture at schools. The process will shape teachers to do professional development quite autonomously (Deci et al., 2001). In this case, a controlling leadership style will hinder teachers’ autonomous motivation. Instead, principals should articulate a clear vision, consider teachers' individual needs and aspirations, inspire, and support professional development activities (Eyal and Roth, 2011). This can also be called creating a professional culture at schools (Fullan, 1996). In this Note, we aim to understand how the schools and teachers respond to the new teacher professional development system. We compare experience and motivation of different characteristics of teachers.
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Wolfenson, David, William W. Thatcher e James E. Kinder. Regulation of LH Secretion in the Periovulatory Period as a Strategy to Enhance Ovarian Function and Fertility in Dairy and Beef Cows. United States Department of Agriculture, dicembre 2003. http://dx.doi.org/10.32747/2003.7586458.bard.
Testo completoAbstract (sommario):
The general research objective was to increase herd pregnancy rates by enhancing corpus luteum (CL) function and optimizing follicle development, in order to increase conception rate and embryo survival. The specific objectives were: to determine the effect of the duration of the preovulatory LH surge on CL function; to determine the function of LH during the postovulatory period on CL development; to optimize CL differentiation and follicle development by means of a biodegradable GnRH implant; to test whether optimization of CL development and follicle dynamics in timed- insemination protocols would improve fertility in high-yielding dairy cows. Low fertility in cattle results in losses of hundreds of millions of dollars in the USA and Israel. Two major causes of low fertility are formation of a functionally impaired CL, and subsequent enhanced ovarian follicle development. A functionally impaired CL may result from suboptimal LH secretion. The two major causes of low fertility in dairy cattle in US and Israel are negative energy status and summer heat stress; in both situations, low fertility is associated with reductions in LH secretion and impaired development of the ovulatory follicle and of the CL. In Florida, the use of 450-mg deslorelin (GnRH analogue) implants to induce ovulation, under the Ovsynch protocol resulted in a higher pregnancy rates than use of 750-mg implants, and pregnancy losses tended to decrease compared to controls, due probably to decrease in follicular development and estradiol secretion at the time of conceptus signaling to maintain the CL. An alternative strategy to enhance progesterone concentrations involved induction of an accessory CL by injection of hCG on day 5 after the cows were inseminated. Treatment with hCG resulted in 86% of the cows having two CLs, compared with 23% of the control cows. Conception rates were higher among the hCG-treated cows than among the controls. Another approach was to replace the second injection of GnRH analogue, in a timed-insemination protocol, with estradiol cypionate (ECP) injected 24 h after the injection of PGF₂ₐ Pregnancy rates were comparable with those obtained under the regular Ovsynch (timed- AI) program. Use of ECP induced estrus, and cows inseminated at detected estrus are indeed more fertile than those not in estrus at the time of insemination. Collectively, the BARD-supported programs at the University of Florida have improved timed insemination programs. In Ohio, the importance of the frequency of LH episodes during the early stages of the estrous cycle of cattle, when the corpus luteum is developing, was studied in an in vivo experiment in which cows were subjected to various episodic exposures to exogenous bovine LH. Results indicate that the frequent LH episodes immediately following the time of ovulation are important in development of the corpus luteum, from the points of view of both size and functionality. In another study, rates of cell proliferation and numbers of endothelial cells were examined in vitro in CLs collected from cows that received post-ovulation pulsatile LH treatment at various frequencies. The results indicate that the corpora lutea growth that results from luteal cell proliferation is enhanced by the episodes of LH release that occur immediately after the time of ovulation in cattle. The results also show that luteal endothelial cell numbers did not differ among cows treated with different LH doses. In Israel. a longer duration of the preovulatory LH surge stimulated the steroidogenic capacity of granulosa-derived luteal cells, and might, thereby, contribute to a higher progesterone output from the bovine corpus luteum. In an in vivo study, a subgroup of high-yielding dairy cows with extended estrus to ovulation interval was identified. Associated with this extended interval were: low plasma progesterone and estradiol concentrations and a low preovulatory LH surge prior to ovulation, as well as low post- ovulation progesterone concentration. In experiments based on the above results, we found that injection of GnRH at the onset of estrus increased the LHpeak, prevented late ovulation, decreased the variability between cows and elicited high and uniform progesterone levels after ovulation. GnRH at estrus onset increased conception rates, especially in the summer, and among primiparous cows and those with low body condition. Another study compared ovarian functions in multiparous lactating cows with those in nulliparous non-lactating heifers. The results revealed differences in ovarian follicular dynamics, and in plasma concentrations of steroids and gonadotropins that may account for the differences in fertility between heifers and cows.
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MGR Monthly Infographics Report: August 2024. Microgovernance Research Initiative (MGR), novembre 2024. http://dx.doi.org/10.57189/mgrinfaug24.
Testo completoAbstract (sommario):
The Microgovernance Research Initiative (MGR) has been publishing monthly infographics on a regular basis to understand the latest trends and dynamics of political conflict and violence in Bangladesh. This infographic report is produced from the violence monitoring database that identifies and codes events of unrest, conflict, and violence in Bangladesh. Coding is based on a detailed codebook, a list of different variables, and codes about specific places, types, actors, victims, lethal and non-lethal causalities. While MGR strives to record incidents as precisely and accurately as possible, the initiative makes no claim and guarantee about the accuracy or biases of ‘news contents’, as we collect all the data from different newspapers with different backgrounds publicly available. However, it follows several methods, caveats, and safeguards to maintain accuracy and adequacy throughout the process. The infographics include data from 4 national newspapers- online and offline.
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MGR Quarterly Infographics Report: July - September, 2024. Microgovernance Research Initiative (MGR), ottobre 2024. http://dx.doi.org/10.57189/mgrinfq7js4.
Testo completoAbstract (sommario):
The Microgovernance Research Initiative (MGR) has been publishing quarterly infographics on a regular basis to understand the latest trends and dynamics of political conflict and violence in Bangladesh. This infographic report is produced from the violence monitoring database that identifies and codes events of unrest, conflict, and violence in Bangladesh. Coding is based on a detailed codebook, a list of different variables, and codes about specific places, types, actors, victims, lethal and non-lethal causalities. While MGR strives to record incidents as precisely and accurately as possible, the initiative makes no claim and guarantee about the accuracy or biases of ‘news contents’, as we collect all the data from different newspapers with different backgrounds publicly available. However, it follows several methods, caveats, and safeguards to maintain accuracy and adequacy throughout the process. The infographics include data from 4 national newspapers- online and offline.
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MGR Monthly Infographics Report: October 2024. Microgovernance Research Initiative (MGR), novembre 2024. http://dx.doi.org/10.57189/mgrinfoct24.
Testo completoAbstract (sommario):
The Microgovernance Research Initiative (MGR) has been publishing monthly infographics on a regular basis to understand the latest trends and dynamics of political conflict and violence in Bangladesh. This infographic report is produced from the violence monitoring database that identifies and codes events of unrest, conflict, and violence in Bangladesh. Coding is based on a detailed codebook, a list of different variables, and codes about specific places, types, actors, victims, lethal and non-lethal causalities. While MGR strives to record incidents as precisely and accurately as possible, the initiative makes no claim and guarantee about the accuracy or biases of ‘news contents’, as we collect all the data from different newspapers with different backgrounds publicly available. However, it follows several methods, caveats, and safeguards to maintain accuracy and adequacy throughout the process. The infographics include data from 4 national newspapers- online and offline.
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Monthly Infographics Report: January 2023. Microgovernance Research Initiative (MGR), febbraio 2023. http://dx.doi.org/10.57189/mgrinfjan23.
Testo completoAbstract (sommario):
The Microgovernance Research Initiative (MGR) has been publishing monthly infographics on a regular basis to understand the latest trends and dynamics of conflict and violence in Bangladesh. This infographic report is produced from the violence monitoring database that identifies and codes events of unrest, conflict, and violence in Bangladesh. Coding is based on a detailed codebook, a list of different variables, and codes about specific places, types, actors, victims, lethal and non-lethal causalities, etc. While MGR strives to record incidents as precisely and accurately as possible, the initiative makes no claim and guarantee about the accuracy or biases of ‘news contents’, as we collect all the data from different newspapers with different backgrounds publicly available. However, it follows several methods, caveats, and safeguards to maintain accuracy and adequacy throughout the process. The infographics include data from around 127 local and national newspapers- online and offline.