2,698 research outputs found
Force-dependent unbinding rate of molecular motors from stationary optical trap data
Molecular motors walk along filaments until they detach stochastically with a
force-dependent unbinding rate. Here, we show that this unbinding rate can be
obtained from the analysis of experimental data of molecular motors moving in
stationary optical traps. Two complementary methods are presented, based on the
analysis of the distribution for the unbinding forces and of the motor's force
traces. In the first method, analytically derived force distributions for slip
bonds, slip-ideal bonds, and catch bonds are used to fit the cumulative
distributions of the unbinding forces. The second method is based on the
statistical analysis of the observed force traces. We validate both methods
with stochastic simulations and apply them to experimental data for kinesin-1
All-orders resummation for diphoton production at hadron colliders
We present a QCD calculation of the transverse momentum distribution of
photon pairs produced at hadron colliders, including all-orders soft-gluon
resummation valid at next-to-next-to-leading logarithmic accuracy. We specify
the region of phase space in which the calculation is most reliable, compare
our results with data from the Fermilab Tevatron, and make predictions for the
Large Hadron Collider. The uncertainty of predictions for production of
diphotons from fragmentation of final-state quarks is examined.Comment: 16 pages, 6 figures; minor change
Volterra-series approach to stochastic nonlinear dynamics: linear response of the Van der Pol oscillator driven by white noise
The Van der Pol equation is a paradigmatic model of relaxation oscillations.
This remarkable nonlinear phenomenon of self-sustained oscillatory motion
underlies important rhythmic processes in nature and electrical engineering.
Relaxation oscillations in a real system are usually coupled to environmental
noise, which further enriches their dynamics, but makes theoretical analysis of
such systems and determination of the equation's parameter values a difficult
task. In a companion paper we have proposed an analytic approach to a similar
problem for another classical nonlinear model, the bistable Duffing oscillator.
Here we extend our techniques to the case of the Van der Pol equation driven by
white noise. We analyze the statistics of solutions and propose a method to
estimate parameter values from the oscillator's time series. We use
experimental data of active oscillations in a biological system to demonstrate
how our method applies to real observations and how it can be generalized for
more complex models.Comment: 12 pages, 6 figures, 1 tabl
Somatodendritic integration under increased network activity in layer 5 pyramidal cells of the somatosensory cortex
Integrative properties of single neurons have been extensively studied in acute brain slices. However, these preparations are characterized by extremely low levels of synaptic and action potential activity. In comparison to in vivo, reduced intracortical input and lack of subcortical modulation increase the effective difference between mean membrane potential and spiking threshold, preventing self-sustained network activity in vitro. To elicit an increased and stable network activity (INA) in vitro comparable to that found in awake animals, we mimicked subcortical cholinergic and serotoninergic inputs using carbachol or barium alone or in combination with serotonin in layer 5 pyramidal cells in slices of mouse somatosensory cortex. INA is primarily induced by a modulation of intrinsic conductances resulting in a depolarization of the membrane potential. We studied the impact of INA on synaptic and somatodendritic integration using extracellular stimulation and dendritic calcium imaging. Synaptic inhibition is strengthened due to an increased driving force for chloride. The critical frequency at which somatic action potentials induce a dendritic calcium action potential is lowered. Simultaneous inhibitory synaptic input is powerful enough to suppress dendritic calcium action potential generation. Pharmacologically induced INA enables the study of neuronal integration in well-accessible cortical slices within an active networ
Erkundungen im Spannungsfeld von Pädagogik, Spielspass und technischer Machbarkeit. Gedanken zur Konzeption und Entwicklung spielbasierter digitaler Lernumgebung
Computerspiele sind heute aus der digitalen Medienwelt nicht mehr wegzudenken. Ihre rasante technische Entwicklung sowie ihre hohe Akzeptanz in der Jugendkultur werfen Fragen nach pädagogischer Verwertbarkeit dieses Mediums auf. Auf diesem Gebiet besteht Forschungsbedarf: Für den Einsatz aktueller Spielkonzepte als Lehrmittel existieren keine fundierten Theorien oder Konzepte. Der schöpferische Umgang mit Spielen durch Anwender («Emergent Gameplay») bietet hier durch sein hohes Motivationspotential einen vielversprechenden Ansatz. Die oft wenig beachtete Rolle der digitalen Spielen zugrunde liegenden Softwaretechnik sollte stärkere Berücksichtigung finden: Es existiert einerseits ein für die Akzeptanz beim Anwender notwendiges Minimum, andererseits ist der Einsatz des aktuellen technischen «state of the art» für die Umsetzung pädagogischer und didaktischer Ambitionen durch seine enormen Anforderungen wenig zielführend. Im Ergebnis sind Idee und Spielspass das Mass auch für Anwendungen des Game Based Learning
Becoming an Entrepreneur - The Role of Profit Taxes
In this paper we study the effects of profit taxation on the creation of new firms using a unique data set covering all firms created in Germany since 2000 irrespective of whether they are German or foreign owned. We exploit the fact that each municipality in Germany is able to independently set the rate of local profit taxation, whereas all tax-base related regulation is identical across municipalities. Our analyzes show that firms react to some incentives induced by profit taxes, but to a small extent and depending on the legal status of the firm
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