355 research outputs found
Properties of tug-of-war model for cargo transport by molecular motors
Molecular motors are essential components for the biophysical functions of
the cell. Our current quantitative understanding of how multiple motors move
along a single track is not complete; even though models and theories for
single motor chemomechanics abound. Recently, M.J.I. Mller {\em
et al.} have developed a tug-of-war model to describe the bidirectional
movement of the cargo (PNAS(2008) 105(12) P4609-4614). Through Monte Carlo
simulations, they discovered that the tug-of-war model exhibits several
qualitative different motility regimes, which depend on the precise value of
single motor parameters, and they suggested the sensitivity can be used by a
cell to regulate its cargo traffic. In the present paper, we carry out a
thorough analysis of the tug-of-war model. All the stable, i.e., biophysically
observable, steady states are obtained. Depending on several parameters, the
system exhibits either uni-, bi- or tristability. Based on the separating
boundary of the different stable states and the initial numbers of the
different motor species that are bound to the track, the steady state of the
cargo movement can be predicted, and consequently the steady state velocity can
be obtained. It is found that, the velocity, even the direction, of the cargo
movement change with the initial numbers of the motors which are bound to the
track and several other parameters
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
Traffic by multiple species of molecular motors
We study the traffic of two types of molecular motors using the two-species
symmetric simple exclusion process (ASEP) with periodic boundary conditions and
with attachment and detachment of particles. We determine characteristic
properties such as motor densities and currents by simulations and analytical
calculations. For motors with different unbinding probabilities, mean field
theory gives the correct bound density and total current of the motors, as
shown by numerical simulations. For motors differing in their stepping
probabilities, the particle-hole symmetry of the current-density relationship
is broken and mean field theory fails drastically. The total motor current
exhibits exponential finite-size scaling, which we use to extrapolate the total
current to the thermodynamic limit. Finally, we also study the motion of a
single motor in the background of many non-moving motors.Comment: 23 pages, 6 figures, late
Where to Go on Your Next Trip? Optimizing Travel Destinations Based on User Preferences
Recommendation based on user preferences is a common task for e-commerce
websites. New recommendation algorithms are often evaluated by offline
comparison to baseline algorithms such as recommending random or the most
popular items. Here, we investigate how these algorithms themselves perform and
compare to the operational production system in large scale online experiments
in a real-world application. Specifically, we focus on recommending travel
destinations at Booking.com, a major online travel site, to users searching for
their preferred vacation activities. To build ranking models we use
multi-criteria rating data provided by previous users after their stay at a
destination. We implement three methods and compare them to the current
baseline in Booking.com: random, most popular, and Naive Bayes. Our general
conclusion is that, in an online A/B test with live users, our Naive-Bayes
based ranker increased user engagement significantly over the current online
system.Comment: 6 pages, 2 figures in SIGIR 2015, SIRIP Symposium on IR in Practic
Molecular motor traffic in a half-open tube
The traffic of molecular motors which interact through mutual exclusion is
studied theoretically for half-open tube-like compartments. These half-open
tubes mimic the shapes of axons. The mutual exclusion leads to traffic jams or
density plateaus on the filaments. A phase transition is obtained when the
motor velocity changes sign. We identify the relevant length scales and
characterize the jamming behavior using both analytical approximations and
Monte Carlo simulations of lattice models.Comment: 14 pages, 5 postscript figure
Selective Sweeps in Growing Microbial Colonies
Evolutionary experiments with microbes are a powerful tool to study mutations and natural selection. These experiments, however, are often limited to the well-mixed environments of a test tube or a chemostat. Since spatial organization can significantly affect evolutionary dynamics, the need is growing for evolutionary experiments in spatially structured environments. The surface of a Petri dish provides such an environment, but a more detailed understanding of microbial growth on Petri dishes is necessary to interpret such experiments. We formulate a simple deterministic reaction-diffusion model, which successfully predicts the spatial patterns created by two competing species during colony expansion. We also derive the shape of these patterns analytically without relying on microscopic details of the model. In particular, we find that the relative fitness of two microbial strains can be estimated from the logarithmic spirals created by selective sweeps. The theory is tested with strains of the budding yeast Saccharomyces cerevisiae, for spatial competitions with different initial conditions and for a range of relative fitnesses. The reaction-diffusion model also connects the microscopic parameters like growth rates and diffusion constants with macroscopic spatial patterns and predicts the relationship between fitness in liquid cultures and on Petri dishes, which we confirmed experimentally. Spatial sector patterns therefore provide an alternative fitness assay to the commonly used liquid culture fitness assays.Molecular and Cellular Biolog
Quantum-Dense Metrology
Quantum metrology utilizes entanglement for improving the sensitivity of
measurements. Up to now the focus has been on the measurement of just one out
of two non-commuting observables. Here we demonstrate a laser interferometer
that provides information about two non-commuting observables, with
uncertainties below that of the meter's quantum ground state. Our experiment is
a proof-of-principle of quantum dense metrology, and uses the additional
information to distinguish between the actual phase signal and a parasitic
signal due to scattered and frequency shifted photons. Our approach can be
readily applied to improve squeezed-light enhanced gravitational-wave detectors
at non-quantum noise limited detection frequencies in terms of a sub shot-noise
veto-channel.Comment: 5 pages, 3 figures; includes supplementary material
Gestational Weight Gain and Body Mass Index in Children: Results from Three German Cohort Studies
Previous studies suggested potential priming effects of gestational weight gain (GWG) on offspring's body composition in later life. However, consistency of these effects in normal weight, overweight and obese mothers is less clear.
We combined the individual data of three German cohorts and assessed associations of total and excessive GWG (as defined by criteria of the Institute of Medicine) with offspring's mean body mass index (BMI) standard deviation scores (SDS) and overweight at the age of 5-6 years (total: n = 6,254). Quantile regression was used to examine potentially different effects on different parts of the BMI SDS distribution. All models were adjusted for birth weight, maternal age and maternal smoking during pregnancy and stratified by maternal pre-pregnancy weight status.
In adjusted models, positive associations of total and excessive GWG with mean BMI SDS and overweight were observed only in children of non- overweight mothers. For example, excessive GWG was associated with a mean increase of 0.08 (95% CI: 0.01, 0.15) units of BMI SDS (0.13 (0.02, 0.24) kg/m(2) of 'real' BMI) in children of normal-weight mothers. The effects of total and excessive GWG on BMI SDS increased for higher- BMI children of normal-weight mothers.
Increased GWG is likely to be associated with overweight in offspring of non-overweight mothers
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