1,691 research outputs found
Alaska’s Judicial Retention Elections: A Comparative Analysis
The results of recent judicial retention elections in Alaska, and the recent increase in political activities related to judicial selection in Alaska and many other states, have given rise to concerns about the fates of future Alaska retention candidates. This Article analyzes the results of retention elections nationwide and suggests that there may be good reason for Alaska judges to be worried. Baseline levels of voter support for retention candidates in most of Alaska are among the lowest in the country, and have gradually been declining over time. In addition, Alaskan voters have targeted individual judges for removal more frequently than voters in most other states. This Article’s analysis indicates that ensuring the retention of competent Alaska judges in the future requires more than simply improving the effectiveness of pro-retention campaigns for individual candidates, and that understanding and addressing deeply held voter attitudes must be part of a more comprehensive effort
Phase transitions in systems with two species of molecular motors
Systems with two species of active molecular motors moving on (cytoskeletal)
filaments into opposite directions are studied theoretically using driven
lattice gas models. The motors can unbind from and rebind to the filaments. Two
motors are more likely to bind on adjacent filament sites if they belong to the
same species. These systems exhibit (i) Continuous phase transitions towards
states with spontaneously broken symmetry, where one motor species is largely
excluded from the filament, (ii) Hysteresis of the total current upon varying
the relative concentrations of the two motor species, and (iii) Coexistence of
traffic lanes with opposite directionality in multi-filament systems. These
theoretical predictions should be experimentally accessible.Comment: 7 pages, 4 figures, epl style (.cls-file included), to appear in
Europhys. Lett. (http://www.edpsciences.org/epl
Quantum transport and localization in biased periodic structures under bi- and polychromatic driving
We consider the dynamics of a quantum particle in a one-dimensional periodic
potential (lattice) under the action of a static and time-periodic field. The
analysis is based on a nearest-neighbor tight-binding model which allows a
convenient closed form description of the transport properties in terms of
generalized Bessel functions. The case of bichromatic driving is analyzed in
detail and the intricate transport and localization phenomena depending on the
communicability of the two excitation frequencies and the Bloch frequency are
discussed. The case of polychromatic driving is also discussed, in particular
for flipped static fields, i.e. rectangular pulses, which can support an almost
dispersionless transport with a velocity independent of the field amplitude.Comment: 18 pages, 11 figur
Cooperative transport by small teams of molecular motors
Molecular motors power directed transport of cargoes within cells. Even if a
single motor is sufficient to transport a cargo, motors often cooperate in
small teams. We discuss the cooperative cargo transport by several motors
theoretically and explore some of its properties. In particular we emphasize
how motor teams can drag cargoes through a viscous environment.Comment: 9 pages, 1 figure, uses ws-brl.cls, presented at Bio-Systems
conference, Berlin, June 200
Tug-of-war as a cooperative mechanism for bidirectional cargo transport by molecular motors
Intracellular transport is based on molecular motors that pull cargos along
cytoskeletal filaments. One motor species always moves in one direction, e.g.
conventional kinesin moves to the microtubule plus end, while cytoplasmic
dynein moves to the microtubule minus end. However, many cellular cargos are
observed to move bidirectionally, involving both plus-end and minus-end
directed motors. The presumably simplest mechanism for such bidirectional
transport is provided by a tug-of-war between the two motor species. This
mechanism is studied theoretically using the load-dependent transport
properties of individual motors as measured in single-molecule experiments. In
contrast to previous expectations, such a tug-of-war is found to be highly
cooperative and to exhibit seven different motility regimes depending on the
precise values of the single motor parameters. The sensitivity of the transport
process to small parameter changes can be used by the cell to regulate its
cargo traffic.Comment: 17 pages, latex, 11 figures, 4 tables, includes Supporting
Informatio
Concept of Personal Freedom in Berdyaev
This paper will attempt to describe Berdyaev’s thinking on the subject of personal freedom. No attempt will be made to criticize or evaluate his thinking by either the criteria of philosophy or theology although instances in which he takes issue or attacks Orthodox Christianity will be noted. In presenting Berdyavev’s concept of personal freedom an attempt will be made to remain within the framework of his thought as it is available in his English writings
Transport by molecular motors in the presence of static defects
The transport by molecular motors along cytoskeletal filaments is studied
theoretically in the presence of static defects. The movements of single motors
are described as biased random walks along the filament as well as binding to
and unbinding from the filament. Three basic types of defects are
distinguished, which differ from normal filament sites only in one of the
motors' transition probabilities. Both stepping defects with a reduced
probability for forward steps and unbinding defects with an increased
probability for motor unbinding strongly reduce the velocities and the run
lengths of the motors with increasing defect density. For transport by single
motors, binding defects with a reduced probability for motor binding have a
relatively small effect on the transport properties. For cargo transport by
motors teams, binding defects also change the effective unbinding rate of the
cargo particles and are expected to have a stronger effect.Comment: 20 pages, latex, 7 figures, 1 tabl
Deterministic and stochastic descriptions of gene expression dynamics
A key goal of systems biology is the predictive mathematical description of
gene regulatory circuits. Different approaches are used such as deterministic
and stochastic models, models that describe cell growth and division explicitly
or implicitly etc. Here we consider simple systems of unregulated
(constitutive) gene expression and compare different mathematical descriptions
systematically to obtain insight into the errors that are introduced by various
common approximations such as describing cell growth and division by an
effective protein degradation term. In particular, we show that the population
average of protein content of a cell exhibits a subtle dependence on the
dynamics of growth and division, the specific model for volume growth and the
age structure of the population. Nevertheless, the error made by models with
implicit cell growth and division is quite small. Furthermore, we compare
various models that are partially stochastic to investigate the impact of
different sources of (intrinsic) noise. This comparison indicates that
different sources of noise (protein synthesis, partitioning in cell division)
contribute comparable amounts of noise if protein synthesis is not or only
weakly bursty. If protein synthesis is very bursty, the burstiness is the
dominant noise source, independent of other details of the model. Finally, we
discuss two sources of extrinsic noise: cell-to-cell variations in protein
content due to cells being at different stages in the division cycles, which we
show to be small (for the protein concentration and, surprisingly, also for the
protein copy number per cell) and fluctuations in the growth rate, which can
have a significant impact.Comment: 23 pages, 5 figures; Journal of Statistical physics (2012
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