Dissertations / Theses: 'Perturbation effect'

1

Lohmann, Ulrike, Leon Rotstayn, Trude Storelvmo, Andrew Jones, Surabi Menon, Johannes Quaas, Annica M. L. Ekman, Dorothy Koch, and Reto A. Ruedy. "Total aerosol effect: radiative forcing or radiative flux perturbation?" Copernicus Publications, 2010. https://ul.qucosa.de/id/qucosa%3A13832.

Full text

Abstract:

Uncertainties in aerosol radiative forcings, especially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation introduces feedbacks which can affect the rate of precipitation formation. In former assessments of aerosol radiative forcings, these effects have not been quantified. Also, with global aerosol-climate models simulating interactively aerosols and cloud microphysical properties, a quantification of the aerosol forcings in the traditional way is difficult to define properly. Here we argue that fast feedbacks should be included because they act quickly compared with the time scale of global warming. We show that for different forcing agents (aerosols and greenhouse gases) the radiative forcings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturbations (RFP), that takes these fast feedbacks and interactions into account. Based on our results, we recommend RFP as a valid option to compare different forcing agents, and to compare the effects of particular forcing agents in different models.

APA, Harvard, Vancouver, ISO, and other styles

2

Prentice, Jamie C. "The perturbation effect in wildlife systems : an emergent property of simple models." Thesis, University of York, 2012. http://etheses.whiterose.ac.uk/3233/.

Full text

Abstract:

Population reduction is often used as a control strategy when managing infectious diseases in wildlife populations, however it disrupts existing social structures and increases movement of infectives due to the vacuum effect, which may lead to enhanced disease transmission. Using a generic non-spatial model, key characteristics of disease systems are identified for which such effects reduce or even reverse the disease control benefits of population reduction. If population reduction is not sufficiently severe, then enhanced transmission can lead to the perturbation effect, whereby disease levels increase or disease can be stabilised where it would otherwise be unstable. Perturbation effects are enhanced for systems with low levels of disease, e.g. low levels of endemicity or emerging disease. Mechanisms observed in real systems are examined for their role in the perturbation effect. If population reduction is non-random and fails to target infected individuals, then vertical transmission (an important mechanism in many diseases including tuberculosis and paratuberculosis) can lead to the perturbation effect if horizontal transmission is low. The perturbation effect can also arise when population reduction preferentially targets resistant individuals, or mature individuals with low susceptibility, a factor implicated in wild boar and classical swine fever. In a stochastic spatial model of demography and disease dynamics with density dependent dispersal (implicated in the spread of rabies in foxes, and tuberculosis in badgers and wild boar due to the vacuum effect), enhanced transmission is found to arise implicitly as an emergent property of the disease-system, even when population reduction is entirely random. Culling strategies are examined, and the spatial heterogeneity of distribution of culling resources and timing of culling intervals are shown to influence the perturbation effect. Whilst the perturbation effect may not always be apparent, the various effects modelled are likely present in many disease systems, mitigating the results of population reduction.

APA, Harvard, Vancouver, ISO, and other styles

3

Lilli, Markus. "The effect of a singular perturbation to a 1-d non convex variational problem." Berlin Logos-Verl, 2004. http://deposit.ddb.de/cgi-bin/dokserv?id=2752886&prov=M&dok_var=1&dok_ext=htm.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Lilli, Markus. "The effect of a singular perturbation to a 1-d non convex variational problem /." Berlin : Logos-Verl, 2005. http://deposit.ddb.de/cgi-bin/dokserv?id=2752886&prov=M&dok_var=1&dok_ext=htm.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Harmidy, Kevin. "Perturbation of host cell cytoskeleton by cranberry proanthocyanidin and its effect on enteric infections." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104671.

Full text

Abstract:

Cranberry-derived compounds, including a fraction known as proanthocyanidins (PACs) exhibit anti-microbial, anti-infective, and anti-adhesive properties against a number of disease-causing organisms. This thesis illustrates the effect of cranberry proanthocyanidins (CPACs) on the infection of epithelial cells by two enteric bacterial pathogens, enteropathogenic Escherichia coli (EPEC) and Salmonella Typhimurium. Immunofluorescence data showed that actin pedestal formation, required for infection by enteropathogenic Escherichia coli (EPEC), was disrupted in the presence of CPACs. In addition, invasion of HeLa cells by Salmonella Typhimurium was significantly reduced. CPACs had no effect on bacterial growth, on the production of bacterial virulence proteins or the viability of host cells. Interestingly, we found that CPACs had a potent and dose-dependent effect on the host cell cytoskeleton that was evident even in uninfected cells. CPACs inhibited the phagocytosis of inert particles by a macrophage cell line, providing further evidence that actin-mediated host cell functions are disrupted in the presence of cranberry CPACs. Thus, although CPAC treatment inhibited Salmonella invasion and EPEC pedestal formation, our results suggest that this is likely primarily because of the perturbation of the host cell cytoskeleton by CPACs rather than an effect on bacterial virulence itself. Additional work suggests that while CPACs disrupt epithelial tight junctions in vitro, they are well tolerated in vivo. The use of CPACs for the treatment or prevention of enteric infection in vivo by Citrobacter rodentium was also evaluated, though no conclusions, positive or negative can be drawn thus far. These findings underline the difficulties of translating experimental results to living systems but have significant implications for the interpretation of experiments on the effects of CPACs on bacteria-host cell interactions.
Le fruit de la canneberge est depuis longtemps utilisé par la médecine traditionnelle dans le cadre d'infection urinaire, mais son mécanisme d'action reste mal connu. Récemment plusieurs études ont montré l'implication d'un composé majeur du fruit, le proanthocyanidine (CPAC), dans les propriétés antibactériennes et anti-infectieuses de la canneberge. Le travail présenté ici vise à évaluer l'effet du PAC sur les cellules épithéliales au cours de l'infection par deux bactéries intestinales : Salmonella Typhimurium et la souche d'Escherichia coli entéropathogène (ECEP). Nous avons montré par des techniques d'imagerie que le remodelage du cytosquelette d'actine des cellules hôtes, étape nécessaire à l'infection par les ECEP, était abolit en présence de CPAC, de même, une inhibition significative de l'infection de cellules HeLa par Salmonella Typhimurium est observée en présence du composé. L'absence d'effet du CPAC sur la prolifération bactérienne et sur la sécrétion de facteurs de virulence dans les deux systèmes expérimentaux suggère un impact du composé sur la permissivité des cellules hôtes. De façon concordante, nous avons montré un rôle critique du CPAC dans la polymérisation des filaments d'actine des cellules non-infectées. La phagocytose de particules inertes par une lignée macrophagique qui dépend d'un remodelage actif du cytosquelette est également inhibée par le CPAC, confirmant l'impact majeur du composé sur le fonctionnement cellulaire. Des expériences in vivo d'infection par Citrobater Rodentium (un modèle murin d'ECEP) n'ont pas permis de mettre en évidence d'effet significatif du CPAC sur l'incidence et la sévérité de la maladie malgré l'effet majeur observé in vitro sur les cellules épithéliales. L'ensemble de ces travaux apporte un nouvel éclairage sur l'effet du CPAC dans les interactions entre les pathogènes et les cellules hôtes, il souligne également les différences entre des systèmes expérimentaux in vitro et les mécanismes prenant place dans des organismes complexes in vivo. Des expériences supplémentaires prenant en compte différents paramètres comme le PH intestinal semblent nécessaires pour évaluer définitivement l'impact du CPAC sur les infections entériques.

APA, Harvard, Vancouver, ISO, and other styles

6

Thompson, Hershell William. "The effect of visual perturbation in planning landing from a jump in adult humans /." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61195.

Full text

Abstract:

Prelanding EMG responses in uniarticular and biarticular flexors and extensors of the leg were assessed during landing from jump-downs at a constant height (0.45 m) or randomly varying heights (0.35, 0.45 and 0.55 meters) in normal humans under four visual conditions: normal, occluded, stabilized by a visual conflict dome, and disrupted by stroboscopic flash at 8 Hz. Pressure sensitive foot-switches and video recordings of each jump-down from a sagittal view allowed the expression of EMG in temporal relation to limb trajectories and foot-ground contact.
Results from EMG analysis demonstrated a stable, global pattern of activation regardless of visual condition and independent of knowledge of the jump height. A generalized strategy of EMG activation was adequate for successful landing on stable height trials, but subjects developed a different default strategy for jumping at random height when inadequate visual update was provided. The prelanding EMG responses from the muscles recorded suggest that there are different roles for the muscles in preparing the body for ground impact. (Abstract shortened by UMI.)

APA, Harvard, Vancouver, ISO, and other styles

7

Martinez, Katherine M. "Effect of Stance Symmetry on Perturbation-Induced Protective Stepping in Persons Poststroke and Controls." Diss., NSUWorks, 2016. https://nsuworks.nova.edu/hpd_pt_stuetd/57.

Full text

Abstract:

Problem Statement: Stepping is a common strategy after a perturbation. Stroke survivors display a predilection for stepping with non-paretic leg. Insight into induced stepping between stroke survivors and age-matched control may guide our understanding for reactive postural control training post stroke. Purpose: To investigate the difference in perturbation-induced stepping between chronic stroke survivors and age-matched controls at three phases of the stepping response: preparation, execution, and landing and association with clinical outcome measures. Procedure: Twenty-one community-dwelling chronic stroke survivors (mean age 59y/o ±13yrs) and 17 age- and gender-matched controls (mean age 54.4y/o ±17yrs) completed this study. Clinical measures of gait, balance, range, sensation, and motor control were assessed. A mechanical weight drop of 10% body weight (BW) was used to create the anterior waist pull perturbation during three stance symmetry positions: equal stance (EQ) and two asymmetrical stance (70% BW on dominant leg and 70% BW on nondominant leg). Ten perturbation trials plus two catch trials at 2% BW were given in a standard randomly order at the three stance positions. Kinematic and kinetic data was collected for perturbation steps. Results: The asymmetrical trials resulted in two types of stepping response, steps with the leg bearing 70% BW (loaded steps – LS) and steps with the leg that had 30% BW (unloaded steps – ULS). All subjects initiated steps more often with their unloaded leg (ULS) in the asymmetrical stance trials. In the stroke group the ULS increased paretic leg stepping compared to EQ (p=0.001) and LS (p=0.001). The stroke group had significantly earlier APA onset with both non-paretic leg (p=0.003) and paretic leg (p=0.028), took significantly more steps with paretic (p=0.01) and non-paretic (p=0.07), shorter step length (paretic, p=0.025 and non-paretic p=0.003), and less change in momentum at landing with paretic leg (p=0.01) compared to controls. Conclusion: Reacting to a perturbation is more challenging for chronic stroke survivors than age- and gender-matched control subjects in the preparation, execution, and landing phase of the stepping response regardless of the leg used. Perturbation training should include stepping with both non-paretic and paretic leg.

APA, Harvard, Vancouver, ISO, and other styles

8

Herman, Mark Steven. "Born-Oppenheimer Corrections Near a Renner-Teller Crossing." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28200.

Full text

Abstract:

We perform a rigorous mathematical analysis of the bending modes of a linear triatomic molecule that exhibits the Renner-Teller effect. Assuming the potentials are smooth, we prove that the wave functions and energy levels have asymptotic expansions in powers of Îµ, where Îµ4 is the ratio of an electron mass to the mass of a nucleus. To prove the validity of the expansion, we must prove various properties of the leading order equations and their solutions. The leading order eigenvalue problem is analyzed in terms of a parameter bË , which is equivalent to the parameter originally used by Renner. For 0 < bË < 1, we prove self-adjointness of the leading order Hamiltonian, that it has purely discrete spectrum, and that its eigenfunctions and their derivatives decay exponentially. Perturbation theory and finite difference calculations suggest that the ground bending vibrational state is involved in a level crossing near bË = 0.925. We also discuss the degeneracy of the eigenvalues. Because of the crossing, the ground state is degenerate for 0 < bË < 0.925 and non-degenerate for 0.925 < bË < 1.
Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

9

Wilks, Theresa M. "Toroidal phasing of resonant magnetic perturbation effect on edge pedestal transport in the DIII-D tokamak." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47558.

Full text

Abstract:

Resonant Magnetic Perturbation (RMP) fields produced by external control coils are considered a viable option for the suppression of Edge Localized Modes (ELMs) in present and future tokamaks. Repeated reversals of the toroidal phase of the I-coil magnetic field in RMP shot 147170 on DIII-D has generated uniquely different edge pedestal profiles, implying different edge transport phenomena. The causes, trends, and implications of RMP toroidal phase reversal on edge transport is analyzed by comparing various parameters at 0 and 60 degree toroidal phases, with an I-coil mode number of n=3. An analysis of diffusive and non-diffusive transport effects of these magnetic perturbations it the plasma edge pedestal for this RMP shot is characterized by interpreting the ion and electron heat diffusivities, angular momentum transport frequencies, ion diffusion coefficients, and pinch velocities for both phases.

APA, Harvard, Vancouver, ISO, and other styles

10

Johnston, Hannah Elizabeth. "Systems redox biology analysis of cancer." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31348.

Full text

Abstract:

The Warburg effect describes the survival advantage of cancer cells in that they can proliferate under low oxygen/hypoxic conditions via a less efficient pathway known as glycolysis. It has not yet been documented at which point, in an oxygen gradient, phenotypic changes occur. Measuring the intracellular redox potential (IRP) and its impact on cellular dynamics would provide greater insight into how disruption of redox homeostasis caused by changes in oxygen concentration leads to aberrant cell signalling and diseases such as cancer. Current techniques in measuring IRP include redox-sensitive fluorescent proteins such as roGFP which is glutathione-specific. Measuring the concentration of one redox couple is, however, not an accurate representation of IRP as it does not necessarily inform about the state of other redox couples. Furthermore, fluorescent biosensors can suffer from photobleaching and may interact with other oxidants. The IRP was measured, in this work, using our newly developed novel-class of surface enhanced Raman scattering nanoparticles which can quantitatively measure the redox potential of cells in vitro. A 'homemade' device was created to keep the cells under fixed pO2 whilst obtaining measurements. The IRP was correlated with the transcriptomic and downstream metabolic profiles of MCF7 breast cancer cells, under perturbed pO2, using 1H NMR spectroscopy (NMR), mass spectrometry (MS) and RNA-sequencing. Discriminatory metabolites were all associated with energy and glucose metabolism. Discriminatory microRNAs were all affiliated with the hallmarks of cancer; the regulation of some is controlled by transcription factors containing redox-sensitive motifs in their DNA binding domains. Multivariate analysis techniques were used to analyse the different data streams in a holistic way that allows the correlation of redox potential, metabolism and transcription.

APA, Harvard, Vancouver, ISO, and other styles

11

Whatham, Andrew. "The effect of optical or pharmacological perturbation of focus on refractive development and ocular growth in the common marmoset." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312637.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Ansari, Mohammed Toseef. "Changes in coagulation, fibrinolysis, and endothelial perturbation markers in the lower limb venous blood associated with prolongedcramped sitting in healthy adult male volunteers in a simulation ofprolonged travel." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B31556991.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Walker, Nathan Thomas. "A Density Functional Theory and Many Body Perturbation Theory Based Study of Photo-Excited Charge Separation in Doped Silicon Nanowires with Gold Leads: Toy Models for the Photovoltaic Effect." Thesis, North Dakota State University, 2020. https://hdl.handle.net/10365/31785.

Full text

Abstract:

We analyze a toy model for p-n junction photovoltaic devices by simulating photoexcited state dynamics in silicon nanowires. One nanowire is approximately circular in cross section with a diameter of d = 1.17 nm. The other has an approximately rhombic cross-section with d1 = 1.16 nm and d2 = 1.71 nm. Both nanowires have been doped with aluminum and phosphorus atoms and capped with gold leads. We use Boltzmann transport equation (BE) that includes phonon emission, carrier multiplication (CM), and exciton transfer. BE rates are computed using non-equilibrium finite-temperature many-body perturbation theory (MBPT) based on Density Functional Theory (DFT) simulations, including excitonic effects from Bethe-Salpeter Equation. We compute total charge transfer amount generated from the initial photoexcitation and find an enhancement when CM is included. In particular, we see between 78% and 79% enhancement in the smaller wire, while we see 116% enhancement in the larger nanowire

APA, Harvard, Vancouver, ISO, and other styles

14

Susbielle, Guillaume. "Perturbation de la dynamique de l’hétérochromatine par des ligands synthétiques du petit sillon de l’ADN." Toulouse 3, 2006. http://www.theses.fr/2006TOU30109.

Full text

Abstract:

Les séquences satellites III (SATIII) présentes dans les régions péricentriques du chromosome X sont les seules séquences satellites alphoïdes chez la drosophile, similaires à celles retrouvées autour du centromère chez les mammifères. Leurs caractéristiques structurales liées à leur composition nucléotidique A•T riche en font des cibles pour différentes classes de molécules artificielles. Nous proposons d’utiliser le modèle des SATIII de la drosophile pour améliorer notre compréhension du code des histones, de la fonction des régions péricentriques ainsi que pour l’évaluation du potentiel pharmacologique des diamidines. Nos travaux à l’aide de ligands du petit sillon nous ont permis de mettre en évidence un rôle de la topoïsomérase II, une cible thérapeutique majeure, dans l’assemblage de l’hétérochromatine et dans le mode d’action antiprolifératif des diamidines
The satellite III sequences (SATIII) composing the pericentric regions of the X chromosome are the only alphoïd sequences found in Drosophila melanogaster. They are similar to those found near the centromeres of mammalian cells. Their structural characteristics, based on their biased, A•T rich, nucleotidic composition, make them good targets for different types of artificial and natural molecules. We propose to use the SAT III sequences as a model to study the histone code, the function of pericentric regions and as a tool to evaluate the pharmacological potential of diamidines. Our work with minor groove binding agents, allowed us to shed light on the functional role of topoisomerase II, a major target in anticancer and antiparasitic therapies, in the heterochromatin assembly process and in the antiproliferative mode of action of diamidines

APA, Harvard, Vancouver, ISO, and other styles

15

Raum, Peter Thomas. "Exact Diagonalization Studies of Strongly Correlated Systems." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/96440.

Full text

Abstract:

In this dissertation, we use exact diagonalization to study a few strongly correlated systems, ranging from the Fermi-Hubbard model to the fractional quantum Hall effect (FQHE). The discussion starts with an overview of strongly correlated systems and what is meant by strongly correlated. Then, we extend cluster perturbation theory (CPT), an economic method for computing the momentum and energy resolved Green's function for Hubbard models to higher order correlation functions, specifically the spin susceptibility. We benchmark our results for the one-dimensional Fermi-Hubbard model at half-filling. In addition we study the FQHE at fillings $nu = 5/2$ for fermions and $nu = 1/2$ for bosons. For the $nu = 5/2$ system we investigate a two-body model that effectively captures the three-body model that generates the Moore-Read Pfaffian state. The Moore-Read Pfaffian wave function pairs composite fermions and is believed to cause the FQHE at $nu = 5/2$. For the $nu = 1/2$ system we estimate the entropy needed to observe Laughlin correlations with cold atoms via an ansatz partition function. We find entropies achieved with conventional cooling techniques are adequate.
Doctor of Philosophy
Strongly correlated quantum many-body physics is a rich field that hosts a variety of exotic phenomena. By quantum many-body we mean physics that is concerned with the behavior of interacting particles, such as electrons, where the quantum behavior cannot be ignored. By strongly correlated, we mean when the interactions between particles are sufficiently strong such that they cannot be treated as a small perturbation. In contrast to weakly correlated systems, strongly correlated systems are much more difficult to solve. That is because methods that reduce the many-body problem to a single independent body problem do not work well. In this dissertation we use exact diagonalization, a method to computationally solve quantum many-body systems, to study two strongly correlated systems: the Hubbard model and the fractional quantum Hall effect.The Hubbard model captures the physics of many interesting materials and is the standard toy model. Originally developed with magnetic properties in mind, it has been extended to study superconductivity, topological phases, cold atoms, and much more. The fractional quantum Hall effect is a novel phase of matter that hosts exotic excitations, some of which may have applications to quantum computing.

APA, Harvard, Vancouver, ISO, and other styles

16

Fridström, Richard. "Resonant magnetic perturbation effect on the tearing mode dynamics : Novel measurements and modeling of magnetic fluctuation induced momentum transport in the reversed-field pinch." Doctoral thesis, KTH, Fusionsplasmafysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-218052.

Full text

Abstract:

The tearing mode (TM) is a resistive instability that can arise in magnetically confined plasmas. The TM can be driven unstable by the gradient of the plasma current. When the mode grows it destroys the magnetic field symmetry and reconnects the magnetic field in the form of a so-called magnetic island. The TMs are inherent to a type of device called the reversed-field pinch (RFP), which is a device for toroidal magnetic confinement of fusion plasmas. In the RFP, TMs arise at several resonant surfaces, i.e. where the field lines and the perturbation have the same pitch angle. These surfaces are closely spaced in the RFP and the neighboring TM islands can overlap. Due to the island overlap, the magnetic field lines become tangled resulting in a stochastic magnetic field, i.e. the field lines fill a volume instead of lying on toroidal surfaces. Consequently, a stochastic field results in an anomalously fast transport in the radial direction. Stochastic fields can also arise in other plasmas, for example, the tokamak edge when a resonant magnetic perturbation (RMP) is applied by external coils. This stochastization is intentional to mitigate the edge-localized modes. The RMPs are also used for control of other instabilities. Due to the finite number of RMP coils, however, the RMP fields can contain sidebands that decelerate and lock the TMs via electromagnetic torques. The locking causes an increased plasma-wall interaction. And in the tokamak, the TM locking can cause a plasma disruption which is disastrous for future high-energy devices like the ITER. In this thesis, the TM locking was studied in two RFPs (EXTRAP T2R and Madison Symmetric Torus) by applying RMPs. The experiments were compared with modern mode-locking theory. To determine the viscosity in different magnetic configurations where the field is stochastic, we perturbed the momentum via an RMP and an insertable biased electrode. In the TM locking experiments, we found qualitative agreement with the mode-locking theory. In the model, the kinematic viscosity was chosen to match the experimental locking instant. The model then predicts the braking curve, the short timescale dynamics, and the mode unlocking. To unlock a mode, the RMP amplitude had to decrease by a factor ten from the locking amplitude. These results show that mode-locking theory, including the relevant electromagnetic torques and the viscous plasma response, can explain the experimental features. The model required viscosity agreed with another independent estimation of the viscosity. This showed that the RMP technique can be utilized for estimations of the viscosity. In the momentum perturbation experiments, it was found that the viscosity increased 100-fold when the magnetic fluctuation amplitude increased 10-fold. Thus, the experimental viscosity exhibits the same scaling as predicted by transport in a stochastic magnetic field. The magnitude of the viscosity agreed with a model that assumes that transport occurs at the sound speed -- the first detailed test of this model. The result can, for example, lead to a clearer comparison between experiment and visco-resistive magnetohydrodynamics (MHD) modeling of plasmas with a stochastic magnetic field. These comparisons had been complicated due to the large uncertainty in the experimental viscosity. Now, the viscosity can be better constrained, improving the predictive capability of fusion science.

QC 20171122

APA, Harvard, Vancouver, ISO, and other styles

17

Iwata, Natsumi. "Nonlocal theory of relativistic ponderomotive force in high intensity lasers based on the phase space Lagrangian and the role in the interaction with various mediums." Kyoto University, 2014. http://hdl.handle.net/2433/188822.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Baidolda, Farida. "Search for planetary influences on solar activity." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEO001/document.

Full text

Abstract:

L'étude des variations de l'activité solaire et de ses effets sur les environnements climatiques reste une question ouverte, en dépit des nombreux efforts des chercheurs dans les différents domaines de la science. Par ailleurs, l'activité solaire est notamment un aspect important pour comprendre les relations Soleil-Terre et l'espace interplanétaire. Son étude nécessite différents types d'approches basées sur de nombreux modèles physiques. Le sujet de cette thèse est l'étude des influences possibles des perturbations planétaires sur l'activité solaire.Dans cette thèse, on a d'abord rappelé quelques connaissances générales sur les observations solaires, qui consistent à compter le nombre de taches solaires observées à la surface du Soleil. Les observations ont commencé au début du XVIIème siècle et se poursuivent actuellement. L'activité solaire est ainsi mesurée par le nombre de taches solaires. La physique solaire et les différentes approches pour expliquer les relations entre les planètes et le Soleil sont aussi brièvement évoquées.On a ensuite tenté d'étudier le comportement de l'activité solaire à court, moyen et long terme en utilisant l'analyse en fréquences pour déterminer les principales périodes solaires connues. L'analyse en fréquences permet ainsi de reconstruire une solution pour l'activité solaire, qui reproduit son évolution à long terme. On a vérifié la correspondance de cette solution avec les données d'activité solaire ainsi qu'avec les relevés géologiques de radioisotopes. Les minima et maxima de l'activité solaire reconstruite par l'analyse en fréquences sont aussi en bon accord avec les évènements géologiques connus. De nombreux travaux ont cherché à expliquer les influences directes ou partielles, extérieures (planètes,...) ou intérieures (dynamo,...) sur les variations de l'activité solaire. Dans ce travail, on a cherché à voir si une partie des variations observées de l'activité solaire pouvait être expliqué par la théorie des perturbations planétaires. Les possibles marées planétaires, qui influencent les variations du cycle solaire, sont également étudiées. On a ainsi mis au point un modèle dynamique plus réaliste pour décrire l'effet de marée exercé par les perturbations planétaires sur la déformation de la surface non sphérique du Soleil et qui peut moduler partiellement son activité. On s'intéresse uniquement aux effets dynamiques des planètes sur le Soleil et le modèle ne prend ainsi pas en compte leurs processus physiques internes. Le Soleil a été considéré comme un corps triaxial homogène et les planètes comme des points matériels.La variation des coefficients du potentiel induit par l'effet des marées solides a été calculée en utilisant les dernières éphémérides planétaires INPOP, qui sont transformées pour correspondre au repère de référence ici considéré. Le calcul des expressions semi-analytiques des coefficients de déformation du potentiel a été effectué. Ainsi, les estimations des effets des marées planétaires de chacune des planètes ainsi que l'effet total résultant ont été comparées aux observations de l'activité solaire et à l'évolution de l'activité solaire obtenue par l'analyse en fréquences. Enfin, la corrélation entre les déformations de la surface du Soleil et les variations de l'activité solaire est discutée
The causes of solar variations and their impact on climatic environments have been andstill are the subject of large debate. The possible influence of planetary perturbations on thesolar cycles have also been recently the subject of multiples controverses. The goal of thepresent thesis is to provide some insight on this problem by a new computation of the planetaryperturbations on the Sun, at short, middle and and long time scales.At first, we describe our current understanding of the physical causes of the solar activityand their major observable manifestations, such as the sun spots records. We provide somehistorical background for the numerous records of solar activity proxies. We also review thedifferent approaches to explain the solar planetary relationships through an analysis of thepublished literature.The main purpose of the present work is to study the possible influence of the planetarygravitational perturbations on the solar cycles. In a first part, we analyse the short, middle andlong term solar activity behavior by using the quasiperiodic approximations provided by thefrequency map analysis method to determine the main periodicities of the solar cycles. Thisallows us to provide some reconstruction of the long timescale changes of solar activity variation.The reconstructed activity series are compared with the observed solar activity data and thelong term natural archives such as radioisotopes proxies. The reconstructed series still preservethe well recorded historical grand minima and maxima events and provide us some extendeddata for the study of the long timescale evolution of solar cycles.There has already been some attempts to explain the direct or partial influences of anexternal (e.g., the planets ) or an internal (e.g., its dynamo) effects on the solar changes. In thepresent work, we investigate the planetary tidal influence on solar cycle variations. We havedeveloped a realistic dynamical model for describing the tidal effect exerted by the perturbationof the planets of the Solar system on the deformation of the non-spherical Sun’s surface whichmay partially modulate its activity variations. The model is limited to the dynamical effects ofthe planets on the Sun and do not take account any physical interior process of the Sun. TheSun is considered as an homogeneous three axial non spherical body.The variations of the potential coefficients induced by the effects of body tides are com-puted, using the last INPOP planetary ephemerides and the long term solutions La2004. Thesemi-analytical expressions of the deformation coefficients of potential are derived. Thus, theestimations of the planetary tides effects of each planets and their combinations are comparedto the solar activity records and their reconstructed series. Hence, the correlations between thevariations of the deformation of Sun’s surface and its activity records are discussed

APA, Harvard, Vancouver, ISO, and other styles

19

Vanderstraeten, Jacques. "Analyse de l'hypothèse de la perturbation des biorythmes par les champs magnétiques d'extrêmement basse fréquence: mécanismes possibles, impact en santé publique, protocoles de mise a l'épreuve." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209445.

Full text

Abstract:

RESUME GENERAL

Contexte :une association entre exposition prolongée aux champs magnétiques (CM) d’extrêmement basses fréquences (ELF) et risque sanitaire a été établie pour la leucémie infantile (CM 50/60 Hz de l’électricité, RR = 2,0 pour ≥ 0,4 µT d‘intensité moyennée dans le temps) et est suggérée pour le décès par maladie d’Alzheimer (CM 50/60 Hz, CM 16,7 Hz des voies ferrées pour 21 µT d’intensité moyennée dans le temps) et pour certaines hémopathies chez l’adulte (CM 16,7 Hz). Ces associations restent inexpliquées à ce jour. Sur base d’observations animales (effets des CM ELF sur la sécrétion de mélatonine) d’une part, et de la sensibilité magnétique confirmée des cryptochromes (régulateurs des biorythmes) d’autre part, il a été suggéré que ces associations puissent être dues à une perturbation des biorythmes par les CM ELF. Selon les instances internationales, une intensité > 1 mT est requise pour l’existence d’effets biologiques.

Objectifs et méthode :sur base d’une revue exhaustive de la littérature et de modèles théoriques reconnus, le présent travail développe certains mécanismes possibles pour un effet perturbateur des biorythmes par les CM ELF. L’impact en santé publique de cette hypothèse est ensuite évalué. Enfin, des protocoles sont proposés pour sa mise à l’épreuve, tenant compte des mécanismes envisagés.

Résultats :la possibilité existe d’une interaction des oscillations ELF de l’intensité et/ou de l’orientation du CM (somme vectorielle du CM ELF et du CM terrestre ou CMT) avec les cryptochromes rétiniens. Chez l’animal magnétosensible (dont le rongeur), une perturbation des biorythmes pourrait être consécutive à un mécanisme non spécifique de perturbation sensorielle. Toute observation animale pourrait donc ne pas être extrapolable à l’Homme. Chez ce dernier, une perturbation des biorythmes pourrait être causée par les oscillations de l’intensité du CM (peut- être dès < 100 µT d’intensité de CM ELF). Une telle perturbation pourrait aussi être causée par les variations spatiales de l’intensité du CMT qui existent dans l’environnement résidentiel (proximité de structures métalliques). Par ailleurs, dans l’éventualité de l’existence, chez l’Homme également, d’une sensibilité directionnelle basée sur les cryptochromes rétiniens, les oscillations de l’orientation du CM pourraient alors aussi interférer avec ces cryptochromes (peut-être dès ≤ 10 µT). Dans l’hypothèse où une telle interférence affecte les biorythmes, seules pourraient alors être concernées les oscillations dont l’amplitude atteint plusieurs degrés d’angle. Un tel mécanisme ne pourrait donc s’appliquer à la relation entre CM ELF et leucémie infantile que dans l’éventualité où les intensités les plus élevées (+ 1 à 2 SD) de CM ELF y jouent un rôle. Au cas où l’hypothèse de la perturbation des biorythmes par les CM ELF se voyait confirmée, d’autres troubles de santé seraient alors concernés et d’autres sources de CM seraient en cause, tels les CM statiques d’intensité variable émis par les lignes de transport électrifié. Les paramètres d’exposition considérés devraient inclure l’orientation relative CM ELF/CMT, mais aussi l’intensité locale du CMT (facteur à la fois déterminant et confondant dans la présente hypothèse). L’expérimentation animale devrait investiguer l’expression des clock genes. L’expérimentation humaine devrait investiguer les biorythmes chez l’enfant. Et l’épidémiologie devrait investiguer l’incidence de troubles liés à une perturbation des biorythmes en relation avec l’exposition aux CM ELF ainsi qu’aux variations locales de l’intensité du CMT.

Conclusions :malgré les incertitudes persistantes quant aux fonctions précises des cryptochromes de la rétine humaine et quant à l’exactitude des modèles théoriques qui décrivent les interactions entre CM et cryptochromes, certains mécanismes paraissent possibles pour une interaction entre CM ELF et biorythmes. En l’absence persistante d’alternative valide pour l’explication de l’association entre CM ELF et leucémie infantile, l’hypothèse de la perturbation des biorythmes par ces CM paraît devoir être investiguée plus avant, mais en tenant compte des variations locales d’intensité du CMT.

Background: An association between prolonged exposure to extremely low frequency (ELF) magnetic fields (MF) and health risk has been established for childhood leukemia (50/60 Hz MF of electricity, RR = 2.0 for ≥ 0.4 µT of time-averaged intensity) and is suggested for death by Alzheimer's disease (50/60 Hz MF, 16.7 Hz MF of railways at 21 µT of time-averaged intensity) and for some hematologic malignancies in adults (16.7 Hz MF). These associations remain unexplained so far. Based on animal studies (effects of ELF MF on melatonin secretion) on the one hand, and on the confirmed magnetic sensitivity of cryptochromes (regulators of biorhythms) on the other hand, it has been suggested that these associations may be due to a disruption of biorhythms by ELF MF. From current data, however, biological effects seem only possible at > 1 mT of intensity.

Objectives and methods: on the basis of an exhaustive literature review and with use of recognized theoretical models, this paper develops some possible mechanisms for disruption of biorhythms by ELF MF. The public health impact of this hypothesis is then evaluated. Finally, protocols are proposed for the testing of it, with taking into account the proposed mechanisms.

Results: an interaction seems possible between ELF oscillations of the intensity and/or the orientation of the ambient MF (the vector sum of both the ELF MF and the geomagnetic field or GMF) with retinal cryptochromes. In magnetosensitive animals (including rodents), disruption of biorhythms may then be secondary to a non-specific mechanism of sensory disturbance. All animal observation could therefore not be extrapolated to humans. In the latter, on his turn, a disruption of biorhythms may be caused by the oscillations of the MF intensity (perhaps from <100 µT of ELF MF intensity). Such disruption could also be caused by spatial variations of the intensity of the GMF that exist in residential environment (near steel structures). Moreover, in case of the existence in humans (like in animals) of a directional sensitivity based on retinal cryptochromes, then the oscillations of the MF orientation also could interfere with these cryptochromes (perhaps from ≤ 10 µT). In the event that such interference affects biorhythms, only oscillations of several degrees of amplitude would then be concerned. As a consequence, such a mechanism could apply to the relation between ELF MF and childhood leukemia only in the event that the highest MF intensities (Mean + 1-2 SD) also play a role in that relation. In the event the hypothesis of disruption of biorhythms by ELF MF is confirmed, other health problems would be concerned and other kind of MF would be involved, such as the static MF of variable intensity that are emitted by the lines of electrified transport. The considered exposure parameters should include the relative orientation of ELF MF and GMF, but also the local intensity of GMF (both determining factor and confounder in this case). Animal experiments should investigate the expression of clock genes. Human experimentation should investigate biorhythms in children. And epidemiology should investigate the incidence of disorders related to disruption of biorhythms in relation to exposure to ELF MF as well as to local variations in the intensity of the GMF.

Conclusions: Despite the persisting uncertainties about the precise functions of retinal cryptochrome as well as about the accuracy of the theoretical models that describe the interactions between MF and cryptochromes, some mechanisms seem possible for an interaction between ELF MF and biorhythms. In the persisting absence of valid alternative explanation for the association between childhood leukemia and ELF MF, the hypothesis of biorhythm disturbance by ELF MF deserves further investigation, however with taking into account local intensity variations of the GMF.

Doctorat en Sciences de la santé publique
info:eu-repo/semantics/nonPublished

APA, Harvard, Vancouver, ISO, and other styles

20

Ennaji, Hasna Sara. "The effect of external perturbations on the reactive balance response of young and older women in a simulated real-world context: public transportation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.

Find full text

Abstract:

Il progressivo invecchiamento della popolazione sta sempre più sottolineando la necessità di un’accurata comprensione del tema delle cadute. Ancora oggi per gli anziani esse rappresentano una delle maggior cause di comorbidità e morte. Il traporto pubblico è un’importante risorsa di inclusione sociale e autonomia personale per la popolazione anziana, tuttavia esso comporta anche una maggiore esposizione al rischio di caduta. Le donne, notoriamente più esposte al rischio di caduta rispetto la controparte maschile, risultano maggiormente colpite da questi incidenti. Il contributo delle nuove tipologie di allenamento “pertubation-based” potrebbero essere una valida soluzione per il miglioramento dei tempi e modalità di risposta del soggetto a perturbazioni esterne che possono comportare una perdita di equilibrio. Il presente studio ha incluso 36 donne suddivise in giovani e anziane con lo scopo di descriverne differenze e caratteristiche nella risposta reattiva quando esposte a perturbazioni esterne, come quelle che possono riscontrarsi sui mezzi pubblici. I risultati hanno evidenziato le potenzialità e i limiti dei protocolli di allenamento che fanno uso di “treadmill perturbativi”, e costituiscono un vero e proprio studio di fattibilità di questi nuovi metodi per la prevenzione delle cadute.

APA, Harvard, Vancouver, ISO, and other styles

21

Godongwana, Buntu. "Effect of nutrient momentum and mass transport on membrane gradostat reactor efficiency." Thesis, Cape Peninsula University of Technology, 2016. http://hdl.handle.net/20.500.11838/2149.

Full text

Abstract:

Thesis submitted in fulfilment of the requirements for the degree Doctor technologiae (engineering: chemical) In the faculty of engineering at the cape peninsula university of technology
Since the first uses of hollow-fiber membrane bioreactors (MBR’s) to immobilize whole cells were reported in the early 1970’s, this technology has been used in as wide ranging applications as enzyme production to bone tissue engineering. The potential of these devices in industrial applications is often diminished by the large diffusional resistances of the membranes. Currently, there are no analytical studies on the performance of the MBR which account for both convective and diffusive transport. The purpose of this study was to quantify the efficiency of a biocatalytic membrane reactor used for the production of enzymes. This was done by developing exact solutions of the concentration and velocity profiles in the different regions of the membrane bioreactor (MBR). The emphasis of this study was on the influence of radial convective flows, which have generally been neglected in previous analytical studies. The efficiency of the MBR was measured by means of the effectiveness factor. An analytical model for substrate concentration profiles in the lumen of the MBR was developed. The model was based on the solution of the Navier-Stokes equations and Darcy’s law for velocity profiles, and the convective-diffusion equation for the solute concentration profiles. The model allowed for the evaluation of the influence of both hydrodynamic and mass transfer operating parameters on the performance of the MBR. These parameters include the fraction retentate, the transmembrane pressure, the membrane hydraulic permeability, the Reynolds number, the axial and radial Peclet numbers, and the dimensions of the MBR. The significant findings on the hydrodynamic studies were on the influence of the fraction retentate. In the dead-end mode it was found that there was increased radial convective flow, and hence more solute contact with the enzymes/biofilm immobilised on the surface of the membrane. The improved solute-biofilm contact however was only limited to the entrance half of the MBR. In the closed shell mode there was uniform distribution of solute, however, radial convective flows were significantly reduced. The developed model therefore allowed for the evaluation of an optimum fraction retentate value, where both the distribution of solutes and radial convective flows could be maximised.

APA, Harvard, Vancouver, ISO, and other styles

22

Chaput, Ludovic. "Compréhension de l'énantiosélectivité de la lipase B de Candida antarctica : étude par modélisation moléculaire et expérimentation." Phd thesis, Université de La Rochelle, 2012. http://tel.archives-ouvertes.fr/tel-00825876.

Full text

Abstract:

La lipase B de Candida antarctica (CALB) est un enzyme présentant des propriétés énantiosélectives très intéressantes pour l'obtention de molécules énantio pures par dédoublement cinétique de mélanges racémiques,molécules utilisées comme synthons dans l'industrie pharmaceutique. En effet, le principe actif de nombreux médicaments est efficace sous une forme énantio pure, l'autre forme chirale pouvant se révéler délétère pour l'organisme.Les travaux de la thèse s'intéressent à mieux comprendre l'origine de l'énantiosélectivité de la lipase B de Candida antarctica, en particulier pour la résolution d'alcools secondaires par des réactions de transestérification.Nous utilisons pour la première fois la méthode de la perturbation de l'énergie libre pour estimer la différence d'énergie libre entre les intermédiaires tétraédriques obtenus avec les formes R et S d'alcools énantiomères pour une série d'alcools secondaires, dans le but de prédire in silico l'énantiosélectivité de la CALB. Les paramètres cinétiques apparents d'une réaction avec deux alcools substrats énantiopurs sont expérimentalement déterminés et permettent de définir la contribution respective du Km et du kcat de chaque énantiomère pour la définition de l'énantiosélectivité. L'étude expérimentale de l'effet d'empreinte par des molécules co-substrats est réalisée,ainsi qu'une étude par modélisation moléculaire de l'effet d'empreinte par le premier ester substrat de la réaction qui pourrait modifier la conformation du site actif de la CALB. La troisième partie porte sur l'étude de la CALB et de trois variants (T42V, S47A et T42V/S47A) chez lesquels les acides aminés dans la poche stéréospécifiques ont mutés. T42V et S47A permettent d'obtenir une augmentation de l'énantiosélectivité. L'étude propose une étude détaillée de la conformation du site actif à partir de simulations de trajectoires de dynamique moléculaire

APA, Harvard, Vancouver, ISO, and other styles

23

Lima, Neemias Alves de. "Expansão perturbativa regularizada para o efeito Kondo." Universidade de São Paulo, 1998. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-03062014-104535/.

Full text

Abstract:

Nas últimas duas décadas a teoria dos sistemas eletrônicos correlacionados teve enorme progresso, que sustentou o paralelo desenvolvimento da pesquisa experimental dos sistemas de férmions pesados. Dada a complexidade do problema proposto pelas correlações fortes, diversas técnicas complementares de cálculo foram desenvolvidas no período. O presente plano se propõe a explorar uma extensão de uma das mais antigas, a técnica do grupo de renormalização numérico (GRN), tratando perturbativamente o modelo de Kondo para uma impureza magnética em um hospedeiro metálico. É bem conhecido que a expansão perturbativa de propriedades físicas, como a susceptibilidade, em termos do acoplamento de troca diverge logaritmicamente próxima da temperatura de Kondo. A abordagem do GRN para isto considera a transformação discreta, T[HN] = HN+1, onde {HN} é uma seqüência de Hamiltonianos. Neste trabalho, para regularizar a expansão da susceptibilidade, usamos um procedimento alternativo considerando a transformação contínua análoga, Tδz[HN(z)] = HN(z+δz), onde z é um parâmetro arbitrário que generaliza a discretização logarítmica do GRN. Ao contrário do procedimento de Wilson, nós esperamos que este novo procedimento possa ser mais facilmente aplicável a Hamiltonianos mais complexos, complementando a diagonalização numérica.
In the last two decades the theory of electronic correlated systems has had an enormous progress, which has sustained the parallel development of the experimental research in heavy fermion systems. Given the complexity imposed by the strong correlations, several techniques appeared. The present work explores an extension of one of the oldest, the Numerical Renormalization Group (NRG), treating perturbatively the Kondo model for a magnetic impurity in a metallic host. It is well known that perturbative expansion of physical properties, like susceptibility, in terms of the exchange coupling diverges logarithmically near the Kondo temperature. The NRG approach for this consider the discrete transformation, T[HN] = HN+1, where {HN}, is a sequence of Hamiltonians. In this work we use an alternative procedure to regularize the expansion, using an analogous continuum transformation Tδz[HN(z)] = HN(z+δz), where z is an arbitrary parameter which generalizes the NRG logarithmic discretization. Unlike Wilson\'s procedure, we hope this new one can be easily applicable to more complex Hamiltonians, complementing the numerical diagonalization.

APA, Harvard, Vancouver, ISO, and other styles

24

Zaballa, Ignacio. "Cosmological effects of the primordial curvature perturbation." Thesis, Lancaster University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485250.

Full text

Abstract:

In this thesis we study the cosmological effects of the primordial curvature perturbation in two different research areas, which provide useful information about the origin and nature of the curvature perturbation on completely different range of scales. The first one investigates the' generation ofNon-Gaussianity on cosmological models in specific models for the origin of the curvature perturbation. In this case, we are interested in estimating the relative contribution of the NonGaussianity of the field perturbations arising during the inflationary epoch to the Non-Gaussianity of the primordial curvature perturbation. The second one concerns the formation of Primordial Black Holes inside the horizon at the end of inflation, and therefore explores a much smaller range of scales corresponding to horizon scales at the end of inflation.

APA, Harvard, Vancouver, ISO, and other styles

25

McBride, Patrick M. "The Effect of Polarization and InGaN Quantum Well Shape in Multiple Quantum Well Light Emitting Diode Heterostructures." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/822.

Full text

Abstract:

Previous research in InGaN/GaN light emitting diodes (LEDs) employing semi-classical drift-diffusion models has used reduced polarization constants without much physical explanantion. This paper investigates possible physical explanations for this effective polarization reduction in InGaN LEDs through the use of the simulation software SiLENSe. One major problem of current LED simulations is the assumption of perfectly discrete transitions between the quantum well (QW) and blocking layers when experiments have shown this to not be the case. The In concentration profile within InGaN multiple quantum well (MQW) devices shows much smoother and delayed transitions indicative of indium diffusion and drift during common atomic deposition techniques (e.g. molecular beam epitaxy, chemical vapor deposition). In this case the InGaN square QW approximation may not be valid in modeling the devices' true electronic behavior. A simulation of a 3QW InGaN/GaN LED heterostructure with an AlGaN electron blocking layer is discussed in this paper. Polarization coefficients were reduced to 70% and 40% empirical values to simulate polarization shielding effects. QW shapes of square (3 nm), trapezoidal, and triangular profiles were used to simulate realistic QW shapes. The J-V characteristic and electron-hole wavefunctions of each device were monitored. Polarization reduction decreased the onset voltage from 4.0 V to 3.0 V while QW size reduction decreased the onset voltage from 4.0 V to 3.5 V. The increased current density in both cases can be attributed to increased wavefunction overlap in the QWs.

APA, Harvard, Vancouver, ISO, and other styles

26

Von, Laue Lukas. "Transferts de protons par effet tunnel dans l'acide benzoique : le rôle des vibrations moléculaires." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10060.

Full text

Abstract:

Une description quantitative des transferts de protons inter- et intramoleculaires, qui sont parmi les reactions chimiques les plus fondamentales, demande une connaissance de la surface d'energie potentielle. Le present travail contribue a la caracterisation de cette surface pour un systeme modele, le monocristal d'acide benzoique. Proche des positions d'equilibre, la spectroscopie vibrationnelle apporte des informations, tandis que la barriere de potentiel est caracterisee par des mesures d'effet tunnel. Ces mesures, par spectroscopie optique (raman, absorption, emission) et diffusion quasi-elastique de neutrons, sont faites en combinaison avec des substitutions isotopiques (#1#8o) et sous pression hydrostatique. Une nouvelle methode permettant de calculer la dynamique sur la surface d'energie potentielle multidimensionnelle est presentee. Elle repose sur une approche perturbative qui utilise la technique des instantons et evite la reduction habituelle a 2 ou 3 dimensions. Cette theorie peut etre appliquee dans le but d'evaluer l'effet tunnel de facon generale : inversion de l'ammoniac, rotation des groupements methyles, etc. . Pour les transferts de protons dans des dimeres d'acides carboxyliques, on fait une comparaison avec les resultats experimentaux.

APA, Harvard, Vancouver, ISO, and other styles

27

Barbet, Bruno. "Stimulations électrohydrodynamique et thermique de jets de liquide conducteur." Grenoble 1, 1997. http://www.theses.fr/1997GRE10062.

Full text

Abstract:

Le travail presente une etude experimentale et theorique des stimulations electrohydrodynamique (ehd) et thermique. Ces stimulations produisent des perturbations qui sont amplifiees (instabilite capillaire) et menent a la brisure du jet a une distance bien definie de l'orifice et a la formation de gouttes calibrees. La stimulation ehd tire parti de la pression electrostatique sur le jet de liquide conducteur induite par un potentiel variable applique sur une electrode proche du jet. Avec plusieurs electrodes, l'efficacite de la stimulation est renforcee lorsqu'il y a synchronisation des effets exerces par chaque electrode mais est diminuee en regime de desynchronisation. Avec un signal sinusoidal simple, la brisure genere une goutte et un satellite. La forme du jet est modifiee en imposant un signal d'excitation plus complexe compose de deux modes (le fondamental et un harmonique 2). Les divers profils de brisure ont ete identifies et repertories en fonction du rapport de l'amplitude et du dephasage relatifs des deux modes. En particulier, les conditions de brisure sans satellite sont bien delimitees. Un autre type de stimulation ehd, intermittent, qui consiste a former une goutte isolee dans un jet continu en appliquant un creneau de tension asynchrone est aussi examine en detail. L'excitation thermique consiste a moduler la temperature et donc les proprietes du liquide. Une etude experimentale approfondie est presentee pour la stimulation thermique externe ou un faisceau laser d'intensite variable parfaitement controlee est focalise a la surface du jet. L'energie lumineuse absorbee induit une modulation de la tension superficielle. Il ressort que cette stimulation est equivalente a la stimulation ehd et permet de controler de facon analogue la forme du jet. De plus, il est montre que l'origine de la stimulation est l'effet marangoni (forces de surface tangentielles a l'interface). Enfin, une etude preliminaire de la stimulation thermique interne (chauffage du liquide a l'interieur du canal de buse par une resistance electrique) indique que l'on peut aussi stimuler le jet, ce qui ouvre des perspectives scientifiques et techniques.

APA, Harvard, Vancouver, ISO, and other styles

28

Gabriel, Christopher. "Effect of localized structural perturbations on dendrimer structure." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1155662110.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Gabriel, Christopher J. "Effect of localized structural perturbations on dendrimer structure." The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1155662110.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Vaske, Charles J. "Prediction and expansion of biological pathways from perturbation effects /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2009. http://uclibs.org/PID/11984.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Condeescu, Cezar. "Non-perturbative effects in string theory." Palaiseau, Ecole polytechnique, 2010. http://pastel.archives-ouvertes.fr/docs/00/56/57/62/PDF/Phd-thesis.pdf.

Full text

Abstract:

On étudie les effets non-perturbatifs généré par des branes instantoniques Euclidiens en compactifications de la théorie des cordes de type I/II avec orientifolds et D-branes magnétisées. Le focus est sur les instantons qui peuvent générer des corrections au superpotentiel. Une condition nécessaire est que les instantons doivent enrouler des cycles rigides. On considère la compactification de la théorie de Type I (IIB) sur l'orientifold T^6/Z_2xZ_2 avec torsion discrète et D-branes magnétisées. Les instantons enroulant le même cycle que l'O-plane exotique (requis par la torsion discrète) ont la structure désiré de modes zéro pour générer des corrections au superpotentiel. On construit des modèles globales basée sur cet orientifold ou les instantons génère des termes linaires et de termes de masse dans le superpotentiel. En théorie des cordes on calcule un couplage physique duquel on doit extraire la partie olomorphique pour obtenir le superpotentiel non-perturbatif. Les facteurs non-olomorphiques sont absorbés dans le potentiel de Kähler et dans redéfinitions des champs chiraux et modules des cordes fermées. On a dérivé ces redéfinitions pour les compactifications toroïdales (avec orientifolds) de la théorie de Type I avec branes magnétisées et lignes Wilson. Finalement, on a considéré des modèles globales avec des termes linéaires. On a calculé explicitement le superpotentiel non-perturbatif pour les orientifolds toroïdales. On a montré comment faire la somme sur les contributions a un instanton. Les modèles analysées possédaient des vides non-perturbatifs supersymétriques ou le group de jauge était brisé et certains modules des cordes ouvertes étaient stabilisés
We study non-perturbative effects generated by Euclidean brane instantons in compactifications of Type I/II string theory with orientifolds and magnetized D-branes. The focus is on instantons which can generate corrections to the superpotential. A necessary condition is that the instantons have to wrap rigid cycles. We consider the compactification of Type I (IIB) on the T^6/Z_2xZ_2 orientifold with discrete torsion and magnetized branes. The instantons wrapping the same cycle as the exotic O-planes (required by the presence of discrete torsion) have the desired uncharged zero-mode structure in order to generate corrections to the superpotential. We build global models based on this orientifold where stringy instantons generate linear terms and mass terms in the superpotential. Typically, in string theory one computes a physical coupling from which one has to extract a holomorphic part in order to obtain the non-perturbative superpotential. Various non-holomorphic factors are absorbed into the Kähler potential and redefinitions of chiral fields and closed string moduli. We have derived these redefinitions in the context of toroidal (orientifold) compactifications of Type I with magnetized branes and continuous Wilson lines. Finally, we have considered global models with linear terms in the superpotential generated non-perturbatively. We have computed explicitly the non-perturbative superpotential for toroidal orientifolds. We show how to sum coherently over the various one-instanton contributions. The explicit models analyzed possessed a non-perturbative supersymmetric vacuum where the gauge group was broken and certain open-string moduli were stabilized

APA, Harvard, Vancouver, ISO, and other styles

32

DEY, Ashis Kumar, Tadanori KITAMURA, and Tetsuro TSUJIMOTO. "PERTURBATIONS ALONG HEADCUT AND THEIR EFFECTS ON GULLY FORMATION." 土木学会, 2001. http://hdl.handle.net/2237/8640.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Godavarty, Dinesh. "Effects of Perturbations on the Onset of Vortex Asymmetry." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin995905161.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

Pomeroy, Neil B. "Multi-instantons and supersymmetric SU(N) gauge theories." Thesis, Durham University, 2002. http://etheses.dur.ac.uk/3757/.

Full text

Abstract:

In this thesis the proposed exact results for low energy effective N = 2 supersymmetric SU(N) Yang-Mills gauge theory coupled to Nf fundamental matter multiplets in four dimensions are considered. The proposed exact results are based upon the work of Seiberg and Witten for low energy effective four dimensional M = 2 supersymmetric SU[2) Yang-Mills gauge theory coupled to Nf fundamental matter multiplets. The testing and matching of the proposed exact results via supersymmetric instanton calculus are the motivation for two studies. Firstly, we study the ADHM construction of instantons for gauge groups U(N) and SU(2) and for topological charge two and three. The ADHM constraints which implicitly specify instanton gauge field configurations are solved for the explicit exact general form of instantons with topological charge two and gauge group U[N). This is the first explicit and general multi-instanton configuration for the unitary gauge groups. The U[N) ADHM two-instanton configuration may be used in further tests and matching of the proposed exact results in low energy effective M =2 supersymmetric SU(iV) Yang-Mills gauge theories by comparison with direct instanton calculations. Secondly, a one-instanton level test is performed for the reparameterization scheme proposed by Argyres and Pelland matching the conjectured exact low energy results and instanton predictions for the instanton contributions to the prepotential of low energy effective M = 2 supersymmetric SU [N) Yang-Mills gauge theory with Nf = 2N mass-less fundamental matter multiplets. The constants within the reparameterization scheme which ensure agreement between the exact results and the instanton predictions for general N > 1 are derived for the entire quantum moduli space. This constitutes a non-trivial test of the proposed reparameterization scheme, which eliminates the discrepancies arising when the two sets of results are compared.

APA, Harvard, Vancouver, ISO, and other styles

35

Byrne, David Kevin. "Genetic and environmental perturbation effects on metabolic networks and engineering objectives." Thesis, Boston University, 2012. https://hdl.handle.net/2144/12304.

Full text

Abstract:

Thesis (Ph.D.)--Boston University PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
Phenotypic variation is produced through a complex web of interactions between genes and the environment and determines whether a trait has the ability to respond to natural or artificial selection. In metabolism, these concerted interactions define how energy is supplied and distributed throughout the cell. Since metabolic engineers seek to use cellular processes to improve the synthesis of valuable biochemical substances, there is great interest among scientists and engineers alike in determining the relative importance of genetic and environmental factors. To study the environmental and genetic effects on metabolic engineering applications, I use constraint-based metabolic modeling to develop a computational framework that systematically simulates and analyzes extracellular and intracellular perturbations on the metabolism of three microorganisms: Escherichia coli, Saccharomyces cerevisiae, and Shewanella oneidensis. Media compositions and gene- deletion strains are designed to optimize single or multiple engineering objectives, such as the maximization of production rate, yield and purity, or the minimization of the economic cost of raw materials. I use the framework to evaluate the production of several industrially important chemical commodities such as acetate, D-lactate, hydrogen, ethanol, formate, and succinate. By evaluating over 435 million simulated conditions and using 36 engineering metabolic traits, I classify the resultant phenotypes into 10-30 dominant meta-phenotypes for each organism. The meta-phenotypes illustrate global phenotypic variation and highlight organism-specific differences in biological and engineering capabilities. I show biological causality of high-performance engineering phenotypes and make available a web-based tool that was developed to permit public queries and visualization of optimal engineering designs and resultant metabolic pathway activities. Finally, I discuss relationships between engineering traits and phenotypes, trade-offs among multiple engineering objectives, and differences in phenotypic sensitivities that depend on perturbation type. Given the increasing number of sequenced genomes, model accuracy and available computing power, it is foreseeable that the developed framework can be extended to query a growing range of organisms, phenotypic variability, engineering applications and biological insights.

APA, Harvard, Vancouver, ISO, and other styles

36

Iafelice, Pasquale Luca <1980&gt. "Perturbative and non perturbative effects in the Standard Model and orbifolded ADS/CFT based theories." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/844/.

Full text

Abstract:

We study some perturbative and nonperturbative effects in the framework of the Standard Model of particle physics. In particular we consider the time dependence of the Higgs vacuum expectation value given by the dynamics of the StandardModel and study the non-adiabatic production of both bosons and fermions, which is intrinsically non-perturbative. In theHartree approximation, we analyze the general expressions that describe the dissipative dynamics due to the backreaction of the produced particles. Then, we solve numerically some relevant cases for the Standard Model phenomenology in the regime of relatively small oscillations of the Higgs vacuum expectation value (vev). As perturbative effects, we consider the leading logarithmic resummation in small Bjorken x QCD, concentrating ourselves on the Nc dependence of the Green functions associated to reggeized gluons. Here the eigenvalues of the BKP kernel for states of more than three reggeized gluons are unknown in general, contrary to the large Nc limit (planar limit) case where the problem becomes integrable. In this contest we consider a 4-gluon kernel for a finite number of colors and define some simple toy models for the configuration space dynamics, which are directly solvable with group theoretical methods. In particular we study the depencence of the spectrum of thesemodelswith respect to the number of colors andmake comparisons with the planar limit case. In the final part we move on the study of theories beyond the Standard Model, considering models built on AdS5 S5/Γ orbifold compactifications of the type IIB superstring, where Γ is the abelian group Zn. We present an appealing three family N = 0 SUSY model with n = 7 for the order of the orbifolding group. This result in a modified Pati–Salam Model which reduced to the StandardModel after symmetry breaking and has interesting phenomenological consequences for LHC.

APA, Harvard, Vancouver, ISO, and other styles

37

Pritzel, Alexander. "Non-perturbative effects in field theory and gravity." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-177157.

Full text

Abstract:

Nonperturbative effects are crucial to fully understand the dynamics of quantum field theories including important topics such as confinement or black hole evaporation. In this thesis we investigate two systems where nonperturbative effects are of paramount importance. In the first part we study the dynamics of non-abelian gauge theories, while in the second part we try to shed light on mysterious properties of black holes using a model proposed earlier by Dvali and Gomez.\\ Non-abelian gauge theories are the central element in the standard model of particle physics and many dynamical aspects remain elusive. $\mathcal{N}=1$ supersymmetric Yang-Mills theories with $SU(N_C)$ allows for domain walls with several curious properties. They are expected to have gauge fields with a Chern-Simons (CS) term living on their worldvolume, while in the 't Hooft limit of a large number of colors many of their properties seem reminiscent of string theoretic D-Branes. Similar domain walls were also conjectured to be present in non supersymmetric Yang Mills theories. In our work, we investigate this problem from several points of view. We construct a toy model of how to localize a gauge field with a CS term on a domain wall extending earlier work by Dvali and Shifman. We then derive the peculiar properties of CS terms in terms of effects of the underlying microscopic dynamics. Then we look at the actual theory of interest. Here the main novelty is the focus on the topological part of the Yang-Mills theory allowing us to make robust statements despite working in a strongly coupled theory. We construct the low energy effective action of both the non-supersymmetric as well as the supersymmetric Yang Mills theory, which due to the presence of a mass gap is a topological field theory. This topological field theory encodes the Aharanov-Bohm phases in the theory as well as phases due to intersection of flux tubes. In this topological field theory we see that the worldvolume theory of domain walls contains a level $N_C$ CS term. The presence of this term was already conjectured in ealier works based on string theoretic constructions. Here we give its first purely field theoretical construction. Within this construction we also illuminate differences between domain walls in the supersymmetric and non-supersymmetric case.\\ Lastly we try to relate the effects observed to similar effects in critical string theories and we also speculate on whether the behaviour of these domain walls is due to an analog of the fractional quantum hall effect.\\ In the second part of this thesis we investigate non-perturbative aspects of black hole physics. Here we consider a model for a low energy description of black holes due to Dvali and Gomez, where black holes are described in terms of a Bose-Einstein condensate (BEC) of weakly interacting gravitons near a quantum critical point. We focus on nonperturbative properties of a system of attractively self-interacting non-relativistic bosons, which was proposed as a toy model for graviton BECs by Dvali and Gomez. In this thesis we investigate this system mostly relying on a fully non-perturbative approach called exact diagonalization. We first investigate entanglement properties of the ground state of the system, showing that the ground state becomes strongly entangled as one approaches the quantum critical point. In order to make this notion precise we introduce the notion of fluctuation entanglement. We then compute it in a Bogoliubov analysis and extract it from the exact diagonlization procedure as well. We also consider the real time evolution of the system. Here we are interested in finding an analog of the conjectured fast scrambling property of black holes originally introduced by Hayden and Preskill. We only consider the weaker notion of quantum breaking and show that the toy model has a quantum break time consistent with the fast scrambling time scale conjectured in the black hole context. We then conclude by pointing out several possible extensions of these results.

APA, Harvard, Vancouver, ISO, and other styles

38

Foreman, Alan Dean. "Determining the effects of ocean perturbations on marine phytoplankton assemblages." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/114369.

Full text

Abstract:

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 34-35).
The ocean provides a dynamic, constantly changing environment for marine phytoplankton. Understanding the effects of these changes on phytoplankton assemblages is fundamental when trying to anticipate future responses of primary producer's community to long-term environmental changes. In this study, artificial perturbation experiments were successfully performed on natural assemblages of phytoplankton to simulate conditions consistent with ocean acidification and North Pacific Subtropical Gyre (NPSG) upwelling patterns. These experiments demonstrated the feasibility and value of such perturbations in studying phytoplankton responses to environmental forcing.
by Alan D. Foreman.
S.B.

APA, Harvard, Vancouver, ISO, and other styles

39

Schneider, Steven Philip Liepmann H. W. Liepmann H. W. "Effects of controlled three-dimensional perturbations on boundary layer transition /." Diss., Pasadena, Calif. : California Institute of Technology, 1989. http://resolver.caltech.edu/CaltechETD:etd-02142007-094214.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Curtsdotter, Alva. "Extinctions in Ecological Communities : direct and indirect effects of perturbation on biodiversity." Doctoral thesis, Linköpings universitet, Teoretisk Biologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-108906.

Full text

Abstract:

In the dawning of what may become Earth’s 6th mass extinction the topic of this thesis, understanding extinction processes and what determines the magnitude of species loss, has become only too relevant. The number of known extinctions (~850) during the last centuries translates to extinction rates elevated above the background rate, matching those of previous mass extinction events. The main drivers of these extinctions have been human land use, introduction of exotic species and overexploitation. Under continued anthropogenic pressure and climate change, the current extinction rates are predicted to increase tenfold. Large perturbations, such as the extinction drivers mentioned above, affects species directly, causing a change in their abundance. As species are not isolated, but connected to each other through a multitude of interactions, the change in abundance of one species can in turn affect others. Thus, in addition to the direct effect, a perturbation can affect a species indirectly through the ecological network in which the species is embedded. With this thesis, I wish to contribute to our basic understanding of these indirect effects and the role they play in determining the magnitude of species loss. All the studies included here are so called in silico experiments, using mathematical models to describe ecological communities and computer simulations to observe the response of these communities to perturbation. When a perturbation is severe enough, a species will be driven to extinction. The loss of a species from a system is in itself a large perturbation, and may result in further extinctions, so called secondary extinctions. The traits of the species initially lost, can be a potential predictor of the magnitude of secondary species loss. In Paper I of this thesis, I show that when making such predictions, it is important to incorporate temporally dynamic species interactions and abundances, in order not to underestimate the importance of certain species, such as top predators. I further show that species traits alone are not particularly good predictors of secondary extinction risk (Paper I), but that in combination with community level properties they are (Paper II). Indeed, there seems to be an interaction such that the specific property making a community prone to secondary species loss, depends on what kind of species was lost in the primary extinction. As different types of perturbation put different types of species at risk of (primary) extinction, this means that the specific property making a community prone to secondary species loss, will depend on the type of perturbation the community is subjected to. One of the predicted main drivers of future species extinction is climate change. If the local climate becomes adverse, a species can either migrate to new and better areas or stay and evolve. Both these processes will be important in determining the magnitude of species loss under climate change. However, migration and evolution do not occur in vacuum – the biotic community in which these processes play out may modulate their effect on biodiversity. In paper III, I show that the strength of competition between species modulates the effect of both dispersal and evolution on the magnitude of species loss under climate change. The three-way interaction between interspecific competition, evolution and dispersal, creates a complex pattern of biodiversity responses, in which both evolution and dispersal can either increase or decrease the magnitude of species loss. Thus, when species interactions are incorporated, it is clear that even though migration and evolution may alleviate the impact of climate change for some species, they may indirectly aggravate the situation for others. In Paper III, the aspect of climate change incorporated in the model is an increase in mean annual temperature. But climate change is also predicted to increase environmental variability. Paper IV shows that species-rich communities are more sensitive to high environmental variability than species-poor ones. The smaller population sizes in the species-rich communities increased the extinction risk connected to population fluctuations driven by the variable environment. Hence, systems such as tropical forests and coral reefs are predicted to be particularly sensitive to the increased variability that may follow with climate change. In Paper IV, primary extinctions of primary producers result in extinction cascades of consumer species, when they lose their prey. However, in reality a consumer species might be able to switch to another prey, and such flexibility has both been observed and suggested as a potential rescue mechanism. But what is beneficial for an individual predator in the short-term can become detrimental to the ecological community in the long-term. Paper V shows that consumer flexibility often led to consumers continuously overexploiting their new prey, in the worst case to the point of system collapse. Thus, the suggested rescue mechanism aggravated the effect of initial species loss, rather than ameliorating it. Overall, the research presented here, underscores the importance of including population dynamics and biotic interactions when studying the effects of perturbation on biodiversity. Many of the results are complex, hard to foresee or even counter-intuitive, arising from the indirect effects of the perturbation being translated through the living web of species interactions.

APA, Harvard, Vancouver, ISO, and other styles

41

Morais, Maria Helena Moreira. "The effect of secular perturbations and mean motion resonances on Trojan dynamics." Thesis, Queen Mary, University of London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392148.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Miller, Emily Michele. "Effects of Obesity on Balance Recovery in Response to Small Postural Perturbations." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/35465.

Full text

Abstract:

Obesity is a major and growing health concern associated with an increased risk of falls. The majority of falls are thought to result from some kind of postural perturbation, yet the biomechanical mechanisms as to why obese individuals fall more often is unclear. Therefore, the goal of this study was to investigate the effects of obesity on balance recovery in response to small forward postural perturbations. Twenty male participants, including 10 lean (mean BMI Â± SD: 21.9 Â± 1.4) and 10 obese (BMI: 33.2 Â± 2.3), were exposed to two types of postural perturbations (force impulses applied with a pendulum and angular displacements administered with a release mechanism). Participants attempted to recover balance with only an ankle strategy such that neither a step nor hip flexion was utilized. Quiet standing trials were also conducted for comparison with the literature. Obese individuals exhibited less center of mass (COM) displacement and a slower COM velocity compared to lean individuals when exposed to identical force perturbations. When exposed to the force perturbations relative to body weight, and when released from identical lean angles, no differences in COM performance were found. During quiet standing, no differences in center of pressure (COP) velocity were observed between obese and lean groups. In all tasks, the obese generated higher ankle torque than the lean. Overall, the obese participants exhibited no differences in movement or less/slower movement than the lean participants when recovering from small forward postural perturbations as well as during quiet standing. These results imply that obesity in young adult males did not impair balance recovery for the tasks investigated.
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

43

Foles, Ana Catarina das Neves. "MPPT study from a solar photovoltaic panel according to perturbations induced by shadows." Master's thesis, Universidade de Évora, 2017. http://hdl.handle.net/10174/22071.

Full text

Abstract:

This work addresses the mathematical and physical modelling of photovoltaic cells and modules, in order to obtain the maximum power output under different environmental operation conditions, including the effect of shadow. Firstly, the Bisection, Newton-Raphson and Secant methods were evaluated for obtaining the characteristic curve of photovoltaic cells, based on the single diode five parameters model and using the values of ideal parameters. Subsequently, the Nelder and Mead algorithm was used to determine the five parameters of the model by fitting the characteristic curve to current and voltage measurements, and accounting to the dependence of cell temperature on environmental conditions by coupling this method to a thermal model of the module. Finally, partial shadowing of photovoltaic modules was studied through a laboratorial experiment, to which conditions the MPPT is calculated through the polynomial fitting of power-voltage curve; Resumo: Estudo do MPPT de um painel fotovoltaico em função de perturbações induzidas por sombras Este trabalho consiste na modelação física e matemática de células e módulos fotovoltaicos, com o intuito de obter a sua máxima potência sob diferentes condições de operação, incluído o efeito de sombreamento. Primeiramente, os métodos da Bisecção, Newton-Raphson e Secante foram avaliados recorrendo ao modelo de um díodo e cinco parâmetros de forma a obter a curva característica das células fotovoltaicas, com valores de parâmetros ideais. Seguidamente, o algoritmo de Nelder e Mead foi utilizado para determinar os cinco parâmetros do modelo, recorrendo ao ajuste da curva característica com medidas experimentais de corrente e tensão, e a dependência que os parâmetros ambientais têm na obtenção da temperatura da célula, através do acoplamento do algoritmo com um modelo térmico do módulo. Finalmente, foi estudado o sombreamento parcial de módulos fotovoltaicos através de uma experiência laboratorial, na qual o MPPT é calculado por um ajuste de um polinómio à curva potência-tensão.

APA, Harvard, Vancouver, ISO, and other styles

44

Chu, Chengjin, Andrew R. Kleinhesselink, Kris M. Havstad, Mitchel P. McClaran, Debra P. Peters, Lance T. Vermeire, Haiyan Wei, and Peter B. Adler. "Direct effects dominate responses to climate perturbations in grassland plant communities." NATURE PUBLISHING GROUP, 2016. http://hdl.handle.net/10150/617187.

Full text

Abstract:

Theory predicts that strong indirect effects of environmental change will impact communities when niche differences between competitors are small and variation in the direct effects experienced by competitors is large, but empirical tests are lacking. Here we estimate negative frequency dependence, a proxy for niche differences, and quantify the direct and indirect effects of climate change on each species. Consistent with theory, in four of five communities indirect effects are strongest for species showing weak negative frequency dependence. Indirect effects are also stronger in communities where there is greater variation in direct effects. Overall responses to climate perturbations are driven primarily by direct effects, suggesting that single species models may be adequate for forecasting the impacts of climate change in these communities.

APA, Harvard, Vancouver, ISO, and other styles

45

Ekwudo, Millicent Nkiruka. "Effects of Respiratory Perturbations on Aging and Healthspan in Daphnia magna." Digital Commons @ East Tennessee State University, 2021. https://dc.etsu.edu/etd/3903.

Full text

Abstract:

Aging is a degenerative process characterized by a decline in physiological functions and cellular activities. Environmental and pharmacological interventions affecting longevity pathways have been extensively studied in model organisms. This study investigated the effect of chronic mild intermittent hypoxia (4 mg O2/L) or mild mitochondrial uncoupling with three doses of 0 (control), 0.1, 1, and 5 μM of 2,4-Dinitrophenol (DNP), on life history and gene expression in four clones of Daphnia magna. Interestingly, clones from intermittent ponds displayed better tolerance to hypoxia and DNP. Although neither treatments extended longevity, hypoxia increased fecundity and body size, and decreased food consumption and respiration rate. We uncovered 12 candidate genes that were differentially expressed in hypoxia-tolerant and sensitive clones in response to hypoxia. Unexpectedly, DNP increased fecundity and mitochondrial membrane potential without affecting food intake. This work opens up an opportunity for genomic determination of the potentially important phenotypes in a model organism.

APA, Harvard, Vancouver, ISO, and other styles

46

Vardanyan, Alla. "Perturbation of heavy metal homeostasis and its effects on fertility in Drosophila melanogaster /." Zürich, 2008. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000278358.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Birman, Michael, Tatyana Suslina, and tanya@petrov stoic spb su. "Threshold Effects near the Lower Edge of the Spectrum for Periodic." ESI preprints, 2001. ftp://ftp.esi.ac.at/pub/Preprints/esi992.ps.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Szewc, Wojciech. "Theory and simulation of scanning gate microscopy : applied to the investigation of transport in quantum point contacts." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-00876522.

Full text

Abstract:

This work is concerned with the theoretical description of the Scanning Gate Microscopy (SGM) in general and with solving particular models of the quantum point contact (QPC) nanostructure, analytically and numerically. SGM is an experimental technique, which measures the conductance of a nanostructure, while a charged AFM tip is scanned above its surface. It gives many interesting results, such as lobed and branched images, interference fringes and a chequerboard pattern. A generally applicable theory, allowing for unambiguous interpretation of the results, is still missing. Using the Lippman-Schwinger scattering theory, we have developed a perturbative description of non-invasive SGM signal. First and second order expressions are given, pertaining to the ramp- and plateau-regions of the conductance curve. The maps of time-reversal invariant (TRI) systems, tuned to the lowest conductance plateau, are related to the Fermi-energy charge density. In a TRI system with a four-fold spatial symmetry and very wide leads, the map is also related to the current density, on any plateau. We present and discuss the maps calculated for two analytically solvable models of the QPC and maps obtained numerically, with Recursive Green Function method, pointing to the experimental features they reproduce and to the fundamental difficulties in obtaining good plateau tuning which they reveal.

APA, Harvard, Vancouver, ISO, and other styles

49

Bhattacharya, Atri, Rikard Enberg, Yu Seon Jeong, C. S. Kim, Mary Hall Reno, Ina Sarcevic, and Anna Stasto. "Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects." SPRINGER, 2016. http://hdl.handle.net/10150/622473.

Full text

Abstract:

We evaluate the prompt atmospheric neutrino flux at high energies using three different frameworks for calculating the heavy quark production cross section in QCD: NLO perturbative QCD, k(T) factorization including low-x resummation, and the dipole model including parton saturation. We use QCD parameters, the value for the charm quark mass and the range for the factorization and renormalization scales that provide the best description of the total charm cross section measured at fixed target experiments, at RHIC and at LHC. Using these parameters we calculate differential cross sections for charm and bottom production and compare with the latest data on forward charm meson production from LHCb at 7TeV and at 13TeV, finding good agreement with the data. In addition, we investigate the role of nuclear shadowing by including nuclear parton distribution functions (PDF) for the target air nucleus using two different nuclear PDF schemes. Depending on the scheme used, we find the reduction of the flux due to nuclear effects varies from 10% to 50% at the highest energies. Finally, we compare our results with the IceCube limit on the prompt neutrino flux, which is already providing valuable information about some of the QCD models.

APA, Harvard, Vancouver, ISO, and other styles

50

Siegel, Ethan R. "Cosmological perturbations and their effects on the universe from inflation to acceleration /." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013795.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Perturbation effect'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles