531 research outputs found
A Minimal Model of Burst-Noise Induced Bistability
We investigate the influence of intrinsic noise on stable states of a
one-dimensional dynamical system that shows in its deterministic version a
saddle-node bifurcation between monostable and bistable behaviour. The system
is a modified version of the Schl\"ogl model, which is a chemical reaction
system with only one type of molecule. The strength of the intrinsic noise is
varied without changing the deterministic description by introducing bursts in
the autocatalytic production step. We study the transitions between monostable
and bistable behavior in this system by evaluating the number of maxima of the
stationary probability distribution. We find that changing the size of bursts
can destroy and even induce saddle-node bifurcations. This means that a bursty
production of molecules can qualitatively change the dynamics of a chemical
reaction system even when the deterministic description remains unchanged.Comment: 7 pages, 9 figure
Reference Points and Effort Provision
A key open question for theories of reference-dependent preferences is what determines the reference point. One candidate is expectations: what people expect could affect how they feel about what actually occurs. In a real-effort experiment, we manipulate the rational expectations of subjects and check whether this manipulation influences their effort provision. We find that effort provision is significantly different between treatments in the way predicted by models of expectation-based reference-dependent preferences: if expectations are high, subjects work longer and earn more money than if expectations are low.Reference Points; Expectations; Loss Aversion; Disappointment; Experiment
Reference Points and Effort Provision
A key open question for theories of reference-dependent preferences is what determines the reference point. One candidate is expectations: what people expect could affect how they feel about what actually occurs. In a real-effort experiment, we manipulate the rational expectations of subjects and check whether this manipulation influences their effort provision. We find that effort provision is significantly different between treatments in the way predicted by models of expectation-based reference-dependent preferences: if expectations are high, subjects work longer and earn more money than if expectations are low.reference points, expectations, loss aversion, risk aversion, disappointment, experiment
Context in Synthetic Biology: Memory Effects of Environments with Mono-molecular Reactions
Synthetic biology aims at designing modular genetic circuits that can be
assembled according to the desired function. When embedded in a cell, a circuit
module becomes a small subnetwork within a larger environmental network, and
its dynamics is therefore affected by potentially unknown interactions with the
environment. It is well-known that the presence of the environment not only
causes extrinsic noise but also memory effects, which means that the dynamics
of the subnetwork is affected by its past states via a memory function that is
characteristic of the environment. We study several generic scenarios for the
coupling between a small module and a larger environment, with the environment
consisting of a chain of mono-molecular reactions. By mapping the dynamics of
this coupled system onto random walks, we are able to give exact analytical
expressions for the arising memory functions. Hence, our results give insights
into the possible types of memory functions and thereby help to better predict
subnetwork dynamics.Comment: 14 pages, 6 figures Accepted Versio
Cardiovascular Consequences of Unfair Pay
This paper investigates physiological responses to perceptions of unfair pay. In a simple principal agent experiment agents produce revenue by working on a tedious task. Principals decide how this revenue is allocated between themselves and their agents. In this environment unfairness can arise if an agent's reward expectation is not met. Throughout the experiment we record agents' heart rate variability. Our findings provide evidence of a link between perceived unfairness and heart rate variability. The latter is an indicator of stress-related impaired cardiac autonomic control, which has been shown to predict coronary heart diseases in the long run. Establishing a causal link between unfair pay and heart rate variability therefore uncovers a mechanism of how perceptions of unfairness can adversely affect cardiovascular health. We further test potential adverse health effects of unfair pay using data from a large representative data set. Complementary to our experimental findings we find a strong and highly significant association between health outcomes, in particular cardiovascular health, and fairness of pay.fairness, social preferences, inequality, heart rate variability, health, experiments, SOEP
Cardiovascular Consequences of Unfair Pay
This paper investigates physiological responses to perceptions of unfair pay. In a simple principal agent experiment agents produce revenue by working on a tedious task. Principals decide how this revenue is allocated between themselves and their agents. In this environment unfairness can arise if an agent's reward expectation is not met. Throughout the experiment we record agents' heart rate variability. Our findings provide evidence of a link between perceived unfairness and heart rate variability.The latter is an indicator of stressrelated impaired cardiac autonomic control, which has been shown to predict coronary heart diseases in the long run. Establishing a causal link between unfair pay and heart rate variability therefore uncovers a mechanism of how perceptions of unfairness can adversely affect cardiovascular health. Wefurther test potential adverse health effects of unfair pay using data from a large representative data set. Complementary to our experimental findings we find a strong and highly significant association between health outcomes, in particular cardiovascular health, and fairness of pay.Fairness, social preferences, inequality, heart rate variability, health, experiments, SOEP
Reference Points and Effort Provision
A key open question for theories of reference-dependent preferences is what determines the reference point. One candidate is expectations: what people expect could affect how they feel about what actually occurs. In a real-effort experiment, we manipulate the rational expectations of subjects and check whether this manipulation influences their effort provision. We find that effort provision is significantly different between treatments in the way predicted by models of expectation-based reference-dependent preferences: if expectations are high, subjects work longer and earn more money than if expectations are low
Stochastische Modelle und Umgebungseffekte im Kontext der Synthetischen Biologie
Die Synthetische Biologie versteht sich als ein interdisziplinÀres Forschungsgebiet, das die
Entwicklung komplexer kĂŒnstlicher biologischer Systeme zum Ziel hat. Neben der erfolgreichen
Integration von synthetischen Schaltungen in lebende Organismen, bedarf es hierzu passender
Analyse- und Messtechnik sowie eines theoretischen VerstÀndnisses der zugrunde liegenden
komplexen biochemischen Wechselwirkungen. In der Synthetischen Biologie arbeiten folglich
Biologie und Chemie eng mit Ingenieurwissenschaften, Physik und Informatik zusammen. Im
Kontext dieser InterdisziplinaritÀt werden in der vorliegenden Arbeit Methoden und Modelle der
theoretischen Physik beschrieben, welche in der Synthetischen Biologie Anwendung finden.
Im ersten Teil der Arbeit wird ein konkretes biologisches System, ein auf dem CRISPR/dCas9-
System beruhender logischer Schalter, analysiert und modelliert. Experimentelle Daten von
Messungen an Hefezellen zeigen hier, dass das System ein bimodales Schaltverhalten zeigt. Zur
ErklÀrung dieser Beobachtung werden ein deterministisches sowie ein stochastisches Modell ent-
wickelt. Mithilfe dieser Modelle lÀsst sich das Verhalten des CRISPR/dCas9-Systems nachbilden,
womit ein ErklĂ€rungsansatz fĂŒr die zugrunde liegenden biologischen ZusammenhĂ€nge gegeben
wird.
Der zweite Teil dieser Arbeit geht auf ein generelles Problem der Synthetischen Biologie ein,
nÀmlich die sogenannten Kontexteffekte. Hiermit werden allgemein alle Effekte bezeichnet,
die durch die Umgebung, in welche ein synthetischer Schaltkreis eingebettet wird, verursacht
werden. Zur besseren Analyse dieser oft nicht vernachlÀssigbaren Einwirkungen werden die durch
verschiedene mögliche Umgebungstopologien erzeugten Memory-Effekte analytisch berechnet.
Anhand von verschiedenen biologischen Beispielen zeigen wir dann, wie stark sich die Umgebung
auf das Verhalten des Schaltkreises auswirken kann.
Das PhÀnomen, dass deterministische und probabilistische Beschreibung grundlegend verschie-
dene Ergebnisse liefern, betrachtet der dritte Teil der Arbeit. Die theoretische Physik ist bestrebt,
beobachtbare PhÀnomene durch möglichst einfache und zugÀngliche Modelle darzustellen und
damit auch zu erklÀren. Zu diesem Zweck wird im dritten Teil ein minimales Modell vorgestellt,
welches ausreichend ist, um durch sogenanntes Burstrauschen verursachte stabile ZustÀnde
darzustellen. Mittels deterministischer Methoden kann das beobachtete Systemverhalten nicht
korrekt vorhergesagt werden. Zur Analyse des Effektes nutzen wir daher eine Gleichung, welche
die Extrema der Wahrscheinlichkeitsverteilung beschreibt.
Aufbauend auf den Ergebnissen des vorigen Kapitels wird im letzten Teil dieser Arbeit kurz die
Rolle von minimalen Modellen in der Synthetischen Biologie diskutiert. Insbesondere vor dem
Hintergrund der verschiedenen erkenntnistheoretischen Ziele von Ingenieur- und Naturwissen-
schaften beleuchten wir dabei, ob und wie theoretische Modelle Nutzen in der Synthetischen
Biologie entfalten können.
Zusammenfassend wird in dieser Arbeit aufgezeigt, wie stochastische Modellierung und die
analytische Behandlung von Umgebungseffekten in der Synthetischen Biologie eingesetzt werden
können. Die verschiedenen vorgestellten Herangehensweisen lassen sich dabei als grundlegende
Methoden verstehen, auf die Modellierer in Zukunft zurĂŒckgreifen können
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