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Showing 41 to 50 of 62 (0.027 seconds)Spelling suggestions: "subject:"anomalia"" "subject:"anomalias""
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Critical fluctuations and anomalous diffusion in two-component lipid membranes: Monte Carlo simulations on experimentally relevant scalesEhrig, Jens 18 February 2013 (has links) (PDF)
This work addresses properties of two-component lipid membranes on the experimentally relevant spatial scales of order of a micrometer and time intervals of order of a second by means of lattice-based Monte Carlo (MC) simulations. To be able to do that with reasonable computational efforts the lipid membrane is modeled as a square lattice of lipid molecules with next-neighbor interaction. This allows for efficient computation and thus provides a large-scale simulation with which it was possible to obtain important results previously not reported in simulation studies of lipid membranes. After properly tuning the next-neighbor interaction energies the simulation reproduces the experimental phase diagram of the DMPC/DSPC lipid system which is used as a model system in this work. Beyond that, the MC simulation provides a more detailed description of the phase behavior of the lipid mixture than the experimental data. It is found that, within a certain range of lipid compositions, the phase transition from the fluid phase to the fluid–gel phase coexistence proceeds via near-critical fluctuations, while for other lipid compositions this phase transition has a quasi-abrupt character. The complete combined state and component phase diagram is constructed by structure function analysis which confirms the existence of a critical point in the system.
The dynamics of membrane coarsening after an abrupt temperature quench to the fluid–gel coexistence region of the phase diagram are studied. In this context, it is found that lateral diffusion of lipids plays an important role in the fluid–gel phase separation process. Dynamic scaling is observed only if the ratio of gel and fluid phase in the membrane stays constant in time.
The line tension characterizing lipid domains in the fluid–gel coexistence region is found to be in the pN range thus matching values both predicted theoretically and measured experimentally. When approaching the critical point, the line tension, the inverse correlation length of fluid–gel spatial fluctuations, and the corresponding inverse order parameter susceptibility of the membrane vanish in agreement with recent experimental findings for model lipid membranes.
By simulating single particle tracking and fluorescence correlation spectroscopy experiments it is found that in the presence of near-critical fluctuations lipid molecules show transient subdiffusive behavior, which is a new result important for understanding the origins of subdiffusion in cell membranes which are believed to be close to a critical point.
The membrane–cytoskeleton interaction strongly affects phase separation, enhances subdiffusion, and eventually leads to hop diffusion of lipids. Thus, a minimum realistic model for membrane rafts showing the features of both microscopic phase separation and subdiffusion is established.
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| 42 |
Effect of crowdedness in the life cycle of lysenin studied by high-speed atomic force microscopyLopez de Blas, Ignacio 13 June 2017 (has links)
De nombreuses fonctions de la membrane plasma dépendent de manière vitale de sa structure et de sa dynamique. L’observation d’une diffusion anomale in vivo et in vitro par l’utilisation de la microscopie en fluorescence et par le pistage de particules Isolées ont permis de développer notre conception de la membrane, en la faisant passer d’un fluide homogène à deux couches avec des protéines se diffusant librement, à une mosaïque extrêmement organisée, surpeuplée et agglomérée de lipides et de protéines. Malheureusement, il n’a pas été possible d’apparenter les diffusions anomales à des détails moléculaires en raison du manque de capacité d’observation moléculaire directe et unmarqués Dans cotre cas, nous utilisons la microscopie à force atomique à grande vitesse, et une méthodologie d’analyse innovante pour analyser le pore en formant la protéine Lysine dans un environnement surpeuplé et nous documentons l’existence de différents régimes de diffusion au sein de la même membrane. Nous montrons la formation de phases locales de verre, où les protéines sont attrapées dans des cages formées par proximité cages sur des échelles de temps allant jusqu’à 10 s, ce qui n’avait pas été antérieurement observé de manière expérimentale pour les membranes biologiques. De plus, autour de patchs d’apparence solide et de molécules immobiles nous avons pu détecter une phase du verre plus lente qui mène à l’emprisonnement de la protéine et à la création d’un périmètre de diffusion de la membrane diminué . / Many functions of the plasma membrane depend critically on itsstructure and dynamics. Observation of anomalous diffusion in vivo and in vitro usingfluorescence microscopy and single particle tracking has advanced our concept of themembrane from a homogeneous fluid bilayer with freely diffusing proteins to a highlyorganized crowded and clustered mosaic of lipids and proteins. Unfortunately,anomalous diffusion could not be related to local molecular details given the lack ofdirect and unlabeled molecular observation capabilities. Here, we use high-speedatomic force microscopy and a novel analysis methodology to analyze the poreforming protein lysenin in a highly crowded environment and document coexistenceof several diffusion regimes within one membrane. We show the formation of localglassy phases, where proteins are trapped in neighbor-formed cages for time scales upto 10 s, which had not been previously experimentally reported for biologicalmembranes. Furthermore, around solid-like patches and immobile molecules aslower glass phase is detected leading to protein trapping and creating a perimeter ofdecreased membrane diffusion.
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| 43 |
Random Walks in Complex Systems - Anomalous RelaxationSchubert, Sven 04 March 1999 (has links)
Ziel dieser Arbeit ist die Untersuchung der Dynamik
in komplexen Systemen. Eine zentrale Rolle spielen
dabei Random Walks, mit deren Hilfe die anomale Relaxation
in solchen Systemen simuliert wird. Die Komplexität der
in dieser Arbeit untersuchten Systeme spiegelt sich
in hohem Maße in deren Zustandsraumstruktur wider.
Nach einer Einführung verschiedener komplexer Systeme wird
kurz auf Algorithmen eingegangen, die bei der Erfassung der
zum Teil sehr großen Zustandsräume eine wichtige Rolle
spielen. Ein sogenannter Branch-and-Bound Algorithmus
wird für die Untersuchung des niedrigenergetischen Anteils
komplexer Zustandsräume eingesetzt.
Die Simulation der Dynamik wird durch Random Walk Prozesse
simuliert und im Wahrscheinlichkeitsbild durch eine Mastergleichung
beschrieben. Auf verschiedene Formen der Mastergleichung und
deren Lösung wird detailliert eingegangen.
Wichtige Anwendungen sind Simulationen von Random Walks auf
Fraktalen bzw. auf hierarchischen Baumstrukturen. Solche
Simulationen lassen den Vergleich mit experimentellen Befunden
zu, wie z.B. der anomalen Diffusion bzw. den Nichtgleichgewichts-
phänomenen in Spingläsern. Anhand einer solchen Modellbildung
können experimentelle Ergebnisse reproduziert und besser verstanden
werden. Ein weiterer wichtiger Beitrag zum Verständnis solcher
Prozesse wird durch einen neu entwickelten Algorithmus zur
Vergröberung des Zustandsraumes geleistet.
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| 44 |
Anomalous Diffusion and Random Walks on FractalsSchulzky, Christian Berthold 14 July 2000 (has links)
In dieser Arbeit werden verschieden Ansätze diskutiert, die zum Verständnis und zur Beschreibung anomalen Diffusionsverhaltens beitragen, wobei insbesondere zwei unterschiedliche Aspekte hervorgehoben werden. Zum einen wird das Entropieproduktions-Paradoxon beschrieben, welches bei der Analyse der Entropieproduktion bei der anomalen Diffusion, beschrieben durch fraktionale Diffusionsgleichungen auftritt. Andererseits wird ein detaillierter Vergleich zwischen Lösungen verallgemeinerter Diffusionsgleichungen mit numerischen Daten präsentiert, die durch Iteration der Mastergleichung auf verschiedenen Fraktalen produziert worden sind.
Die Entropieproduktionsrate für superdiffusive Prozesse wird berechnet und zeigt einen unerwarteten Anstieg beim Übergang von dissipativer Diffusion zur reversiblen Wellenausbreitung. Dieses Entropieproduktions-Paradoxon ist die direkte Konsequenz einer anwachsenden intrinsischen Rate bei Prozessen mit zunehmendem Wellencharakter. Nach Berücksichtigung dieser Rate zeigt die Entropie den erwarteten monotonen Abfall. Diese Überlegungen werden für generalisierte Entropiedefinitionen, wie die Tsallis- und Renyi-Entropien, fortgeführt.
Der zweite Aspekt bezieht sich auf die anomale Diffusion auf Fraktalen, im Besonderen auf Sierpinski-Dreiecke und -Teppiche. Die entsprechenden Mastergleichungen werden iteriert und die auf diese Weise numerisch gewonnenen Wahrscheinlichkeitsverteilungen werden mit den Lösungen vier verschiedener verallgemeinerter Diffusionsgleichungen verglichen.
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| 45 |
Diffusion on FractalsPrehl, geb. Balg, Janett 21 March 2006 (has links)
We study anomalous diffusion on fractals with a static external field applied.
We utilise the master equation to calculate particle distributions and from
that important quantities as for example the mean square displacement
<r^2(t)>.
Applying different bias amplitudes on several regular Sierpinski
carpets we obtain maximal drift velocities for weak field strengths.
According to <r^2(t)>~t^(2/d_w), we
determine random walk dimensions of d_w<2 for applied external
fields.
These d_w corresponds to superdiffusion, although diffusion is hindered
by the structure of the carpet, containing dangling ends.
This seems to result from two competing effects arising within an external
field.
Though the particles prefer to move along the biased direction,
some particles get trapped by dangling ends.
To escape from there they have to move against the field direction.
Due to the by the bias accelerated particles and the trapped ones the
probability distribution gets wider and thus d_w<2. / In dieser Arbeit untersuchen wir anomale Diffusion auf Fraktalen unter
Einwirkung eines statisches äußeres Feldes.
Wir benutzen die Mastergleichung, um die Wahrscheinlichkeitsverteilung der
Teilchen zu berechnen, um
daraus wichtige Größen wie das mittlere Abstandsquadrat <r^2(t)> zu bestimmen.
Wir wenden unterschiedliche Feldstärken bei verschiedenen regelmäßigen
Sierpinski-Teppichen an und erhalten maximale Driftgeschwindigkeiten
für schwache Feldstärken.
Über <r^2(t)>~t^{2/d_w} bestimmen wir die Random-Walk-Dimension d_w als d_w<2.
Dieser Wert für d_w entspricht der Superdiffusion, obwohl der
Diffusionsprozess durch Strukturen des Teppichs, wie Sackgassen, behindert wird.
Es schient, dass dies das Ergebnis zweier konkurrierender Effekte ist, die durch
das Anlegen eines äußeren Feldes entstehen.
Einerseits bewegen sich die Teilchen bevorzugt entlang der Feldrichtung.
Andererseits gelangen einige Teilchen in Sackgassen.
Um die Sackgassen, die in Feldrichtung liegen, zu verlassen, müssen sich die
Teilchen entgegen der Feldrichtung bewegen. Somit sind die Teilchen eine
gewisse Zeit in der Sackgasse gefangen.
Infolge der durch das äußere Feld beschleunigten und der gefangenen Teilchen,
verbreitert sich die Wahrscheinlichkeitsverteilung der Teilchen und somit ist
d_w<2.
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| 46 |
Measurement of Electroweak Gauge Boson Scattering in the Channel pp → W ± W ± jj with the ATLAS Detector at the Large Hadron ColliderGumpert, Christian 27 February 2015 (has links)
Particle physics deals with the elementary constituents of our universe and their interactions. The electroweak symmetry breaking mechanism in the Standard Model of Particle Physics is of paramount importance and it plays a central role in the physics programmes of current high-energy physics experiments at the Large Hadron Collider. The study of scattering processes of massive electroweak gauge bosons provides an approach complementary to the precise measurement of the properties of the recently discovered Higgs boson. Owing to the unprecedented energies achieved in proton-proton collisions at the Large Hadron Collider and the large amount of data collected, experimental studies of these processes become feasible for the first time. Especially the scattering of two W± bosons of identical electric charge is considered a promising process for an initial study due to its distinct experimental signature. In the course of this work, 20.3 fb−1 of proton-proton collision data recorded by the ATLAS detector at a centre-of-mass energy of √s = 8 TeV are analysed. An analysis of the production of two W± bosons of identical electric charge in association with two jets, pp → W ± W ± jj, is conducted in the leptonic decay channel of the W± bosons.
Thereby, emphasis is put on the development of methods for the estimation of experimental backgrounds as well as on the optimisation of the event selection. As a result of this work, first experimental evidence for the existence of the aforementioned process is established with an observed significance of 4.9. Based on the number of observed events in the selected phase space the extracted fiducial cross section is σ(fid) = (2.3 ± 0.5(stat.) +0.4/−0.3 (sys.)) fb which is in agreement with the prediction of the Standard Model of σ(fid,SM) = (1.6 ± 0.2) fb. Of particular theoretical interest are electroweak contributions to the pp → W ± W ± jj process due to their sensitivity to the nature of the electroweak symmetry breaking mechanism. Criteria for a dedicated event selection are investigated and implemented in the analysis with the goal of enhancing the sensitivity to these contributions. First experimental evidence for the presence of electroweak contributions to the pp → W ± W ± jj process can be claimed with an observed significance of 4.1. The cross section extracted in the selected phase space region is found to be σ(fid) = (1.7 +0.5/−0.4 (stat.) ± 0.3(sys.)) fb which is 1.3 standard deviations above the theoretical prediction of the Standard Model of σ(fid,SM) = (1.0 ± 0.1) fb.
A variety of extensions to the Standard Model predict modifications to the electroweak gauge sector. In the context of the electroweak chiral Lagrangian, which serves as an effective approximation of these theories in the energy regime E = 1 − 3 TeV, anomalous contributions to the quartic WWWW gauge coupling can be described by the parameters α4 and α5 . The selection of events is optimised again to enhance the sensitivity to these two parameters. On the basis of the number of events observed in this phase space region, the following one-dimensional confidence intervals at the 95% confidence level are derived: −0.09 ≤ α4 ≤ 0.10 and −0.15 ≤ α5 ≤ 0.15. At present, these limits represent the most stringent constraints on contributions from new physics processes to the quartic WWWW gauge coupling.
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| 47 |
Deterministic transport: from normal to anomalous diffusionKorabel, Nickolay 05 November 2004 (has links)
The way in which macroscopic transport results from microscopic dynamics is one of the important questions in statistical physics. Dynamical systems theory play a key role in a resent advance in this direction. Offering relatively simple models which are easy to study, dynamical systems theory became a standard branch of modern nonequilibrium statistical physics. In the present work the deterministic diffusion generated by simple dynamical systems is considered. The deterministic nature of these systems is more clearly expressed through the dependencies of the transport quantities as functions of systems parameters. For fully hyperbolic dynamical systems these dependencies were found to be highly irregular and, in fact, fractal. The main focus in this work is on nonhyperbolic and on intermittent dynamical systems. First, the climbing sine map is considered which is a nonhyperbolic system with many physical applications. Then we treat anomalous dynamics generated by a paradigmatic subdiffusive map. In both cases these systems display deterministic transport which, under variation of control parameters, is fractal. For both systems we give an explanation of the observed phenomena. The third part of the thesis is devoted to the relation between chaotic and transport properties of dynamical systems. This question lies at the heart of dynamical systems theory. For closed hyperbolic dynamical systems the Pesin theorem links the sum of positive Lyapunov exponents to the Kolmogorov-Sinai entropy. For open hyperbolic systems the escape rate formula is valid. In this work we have formulated generalizations of these formulas for a class of intermittent dynamical systems where the chaotic properties are weaker.
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| 48 |
Critical fluctuations and anomalous diffusion in two-component lipid membranes: Monte Carlo simulations on experimentally relevant scalesEhrig, Jens 23 November 2012 (has links)
This work addresses properties of two-component lipid membranes on the experimentally relevant spatial scales of order of a micrometer and time intervals of order of a second by means of lattice-based Monte Carlo (MC) simulations. To be able to do that with reasonable computational efforts the lipid membrane is modeled as a square lattice of lipid molecules with next-neighbor interaction. This allows for efficient computation and thus provides a large-scale simulation with which it was possible to obtain important results previously not reported in simulation studies of lipid membranes. After properly tuning the next-neighbor interaction energies the simulation reproduces the experimental phase diagram of the DMPC/DSPC lipid system which is used as a model system in this work. Beyond that, the MC simulation provides a more detailed description of the phase behavior of the lipid mixture than the experimental data. It is found that, within a certain range of lipid compositions, the phase transition from the fluid phase to the fluid–gel phase coexistence proceeds via near-critical fluctuations, while for other lipid compositions this phase transition has a quasi-abrupt character. The complete combined state and component phase diagram is constructed by structure function analysis which confirms the existence of a critical point in the system.
The dynamics of membrane coarsening after an abrupt temperature quench to the fluid–gel coexistence region of the phase diagram are studied. In this context, it is found that lateral diffusion of lipids plays an important role in the fluid–gel phase separation process. Dynamic scaling is observed only if the ratio of gel and fluid phase in the membrane stays constant in time.
The line tension characterizing lipid domains in the fluid–gel coexistence region is found to be in the pN range thus matching values both predicted theoretically and measured experimentally. When approaching the critical point, the line tension, the inverse correlation length of fluid–gel spatial fluctuations, and the corresponding inverse order parameter susceptibility of the membrane vanish in agreement with recent experimental findings for model lipid membranes.
By simulating single particle tracking and fluorescence correlation spectroscopy experiments it is found that in the presence of near-critical fluctuations lipid molecules show transient subdiffusive behavior, which is a new result important for understanding the origins of subdiffusion in cell membranes which are believed to be close to a critical point.
The membrane–cytoskeleton interaction strongly affects phase separation, enhances subdiffusion, and eventually leads to hop diffusion of lipids. Thus, a minimum realistic model for membrane rafts showing the features of both microscopic phase separation and subdiffusion is established.
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Data-based scientific reasoning: Uncovering perceptual and interpretational processes involved in responses to anomalous data in science educationMeister, Sabine 23 January 2024 (has links)
In der Dissertation wird der Frage nachgegangen, welche kognitiven Prozesse der Informationsverarbeitung von wissenschaftlichen Daten beim konzeptuellen Lernen von biologischen Inhalten eine Rolle spielen. Dafür wird ein theoriebasiertes Modell des data-based scientific reasoning beschrieben, welches ebenfalls Aspekte der visuellen Wahrnehmung einbezieht. Dabei kann eine Synthese sogenannter bottom-up- und top-down-Effekte die visuelle Wahrnehmung der dargestellten Daten beeinflussen. Von Interesse sind hierbei Charakteristika der Repräsentation der Daten, sowie die individuellen Vorstellungen zum Kontext und ob, die Daten diese stützen oder widerlegen (anomale Daten). Weiterhin wird in der Arbeit die Rolle von data-based scientific reasoning auf wissenschaftliche Modellierungsprozesse untersucht, da Modellieren als übergreifende wissenschaftliche Praxis gesehen werden kann. In vier empirischen Studien wurden kognitive Prozesse beim Umgang mit Daten bei angehenden Biologielehrkräften, mit Fragebögen, Eye Tracking und lautem Denken untersucht. Die Ergebnisse der durchgeführten Studien heben die Rolle der visuellen Wahrnehmung als entscheidenden Schritt beim data-based scientific reasoning hervor. In Bezug auf Charakteristika der Repräsentation erscheint es notwendig, die visuelle Aufmerksamkeit der Lernenden auf spezifische Merkmale zu lenken und mit entsprechendem konzeptuellem Wissen zu verknüpfen. Die Ergebnisse legen nahe, dass anomale Daten zwar mit wissenschaftlich adäquatem Wissen erklärt werden, dies aber nicht automatisch zur Änderung ursprünglicher Vorstellungen bezüglich des Kontexts führt. Diese Tendenz scheint mit Unsicherheit gegenüber den Daten verbunden zu sein. Darüber hinaus spielen anomale Daten eine zentrale Rolle in wissenschaftlichen Modellierungsprozessen. Die Ergebnisse der entsprechenden Studie deuten darauf hin, dass hoch ausgeprägte Kompetenzen des data-based scientific reasoning mit elaborierten Modellierungsprozessen zusammenhängen. / The thesis focusses on the relevance of reasoning with scientific data for conceptual learning in biology. It aims to contribute to the question which cognitive processes are involved when learners encounter data sets that support or contradict their individual expectations. Therefore, a theoretical model of data-based scientific reasoning is described that is grounded on a general model of information processing. In this model, aspects of visual perception are emphasized. However, visual perception is influenced by a synthesis of so-called bottom-up and top-down effects. Furthermore, the theoretical perspective on the role of responses to anomalous data for scientific practices was extended by investigating how learners react and integrate anomalous data during modeling processes. In four empirical studies cognitive processes leading to responses to anomalous data in science education were investigated by applying a mixture of questionnaires, eye tracking techniques, and think aloud. The findings of the conducted studies highlight the role of perceptual processes as a key step during data-based scientific reasoning. Regarding representational characteristics it seems necessary to guide learners´ visual attention and connect specific features with corresponding conceptual knowledge. However, the findings suggest that a use of adequate scientific knowledge for explaining anomalous data does not lead to a change in initial conceptions regarding the context, since participants of the studies still tended to maintain their initial expectations. This tendency seems to be linked to a high need for encompassing information and a connected uncertainty towards the perceived data. Furthermore, anomalous data play a central role during modelling processes. The results of the corresponding study, indicate that sophisticated competencies of data-based reasoning with anomalous data relate to elaborate modeling processes.
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Probing Electroweak Gauge Boson Scattering with the ATLAS Detector at the Large Hadron ColliderAnger, Philipp 07 October 2014 (has links) (PDF)
Electroweak gauge bosons as central components of the Standard Model of particle physics are well understood theoretically and have been studied with high precision at past and present collider experiments. The electroweak theory predicts the existence of a scattering process of these particles consisting of contributions from triple and quartic bosonic couplings as well as Higgs boson mediated interactions. These contributions are not separable in a gauge invariant way and are only unitarized in the case of a Higgs boson as it is described by the Standard Model. The process is tied to the electroweak symmetry breaking which introduces the longitudinal modes for the massive electroweak gauge bosons. A study of this interaction is also a direct verification of the local gauge symmetry as one of the fundamental axioms of the Standard Model. With the start of the Large Hadron Collider and after collecting proton-proton collision data with an integrated luminosity of 20.3/fb at a center-of-mass energy of 8 TeV with the ATLAS detector, first-ever evidence for this process could be achieved in the context of this work.
A study of leptonically decaying WWjj, same-electric-charge diboson production in association with two jets resulted in an observation of the electroweak WWjj production with same electric charge of the W bosons, inseparably comprising WW->WW electroweak gauge boson scattering contributions, with a significance of 3.6 standard deviations. The measured production cross section is in agreement with the Standard Model prediction.
In the course of a study for leptonically decaying WZ productions, methods for background estimation, the extraction of systematic uncertainties and cross section measurements were developed. They were extended and applied to the WZjj final state whereof the purely electroweakly mediated contribution is intrinsically tied to the scattering of all Standard Model electroweak gauge bosons: Wγ->WZ and WZ->WZ. Three charged leptons and a neutrino from the decay of the final state bosons allow inferences about the scattering process. A distinct signature is provided by the two accompanying tagging jets as remnants of the incoming quarks radiating the initial electroweak gauge bosons. The cross section of the electroweak WZjj production was measured to σ(fiducial, observed) = (0.63 +0.32 -0.28 (stat.) +0.41 -0.24 (syst.)) fb and was found to be consistent with the Standard Model prediction at next-to-leading order in perturbative quantum chromodynamics, σ(fiducial, theory) = (0.31 +0.03 -0.05) fb. Unfolded differential cross sections of kinematic variables sensitive to models of new physics were derived. Anomalous quartic electroweak gauge couplings are introduced as dimensionless coupling parameters of additional operators within an effective field theory approach. Constraints on the parameters of operators with dimension eight were set employing a unitarization prescription based on form factors.
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