50 research outputs found
Aging and Non Linear Glassy Dynamics in a Mean-Field Model
The mean-field dynamics of a particle in a random, but short range correlated
potential, offers the opportunity of observing both aging and driven stationary
regimes. Using a geometrical approach previously introduced by the author, we
study here the relation between these two situations, in the pure relaxational
limit, i.e. the zero temperature case. In the stationary regime, the
velocity(v) -force(f) characteristics is a power law, while the characteristic
times scale like powers of v, in agreement with an early proposal by Horner.
The cross-over between the aging, linear-response regime and the non linear
stationary regime is smooth, and we propose a parametrisation of the
correlation functions valid in both cases, by means of an "effective time". We
conclude that aging and non linear response are dual manifestations of a single
out-of-equilibrium state, which might be a generic situation.Comment: 15 pages, 7 figures, submitted to European Journal of Physics
Geometrical Approach for the Mean-Field Dynamics of a Particle in a Short Range Correlated Random Potential
The zero temperature relaxational dynamics of a particle in a short range
correlated random potential is addressed. We derive a set of "two-times"
mean-field dynamical equations, accounting for a possible mean displacement of
the particle when subject to an external force. We show first detailed results
from the numerical integration of the above mentionned equations. We mainly pay
attention to the exponentially decreasing spatial correlations case, for which
simple analytical arguments provide valuable results about the hessian of the
energy landscape, and we propose a geometrical description of the "mean-field
aging". Our numerical results and further analytical arguments give access to
the waiting time dependence of the main characteristic time scales.Comment: 22 pages, 7 figures, submitted to European Journal of Physics
Trotter Derivation of Algorithms for Brownian and Dissipative Particle Dynamics
This paper focuses on the temporal discretization of the Langevin dynamics,
and on different resulting numerical integration schemes. Using a method based
on the exponentiation of time dependent operators, we carefully derive a
numerical scheme for the Langevin dynamics, that we found equivalent to the
proposal of Ermak, and not simply to the stochastic version of the
velocity-Verlet algorithm. However, we checked on numerical simulations that
both algorithms give similar results, and share the same ``weak order two''
accuracy. We then apply the same strategy to derive and test two numerical
schemes for the dissipative particle dynamics (DPD). The first one of them was
found to compare well, in terms of speed and accuracy, with the best currently
available algorithms.Comment: to be published in J.Chem.Phy
A machine learning assessment of the two states model for lipid bilayer phase transitions
We have adapted a set of classification algorithms, also known as Machine
Learning, to the identification of fluid and gel domains close to the main
transition of dipalmitoyl-phosphatidylcholine (DPPC) bilayers. Using atomistic
molecular dynamics conformations in the low and high temperature phases as
learning sets, the algorithm was trained to categorize individual lipid
configurations as fluid or gel, in relation with the usual two-states
phenomenological description of the lipid melting transition. We demonstrate
that our machine can learn and sort lipids according to their most likely state
without prior assumption regarding the nature of the order parameter of the
transition. Results from our machine learning approach provides strong support
in favor of a two-states model approach of membrane fluidity
Increased Use and Large Variation in Strong Opioids and Metamizole (Dipyrone) for Minor and Major Musculoskeletal Injuries Between 2008 and 2018: An Analysis of a Representative Sample of Swiss Workers.
PURPOSE
Musculoskeletal (MSK) injuries are a major contributing factor for chronic pain. To date, little is known how pain medication use in MSK injuries has changed over time. We assessed pain medication prescription for MSK injuries in a representative sample of Swiss workers between 2008 and 2018.
METHODS
Retrospective analysis of the Swiss Accident Insurance Fund (Suva) data. We calculated annual pain medication use, treatment days, and costs associated with pain medication use in minor and major MSK injuries.
RESULTS
In total, 1,921,382 cases with MSK injuries with ≥ 1 pain medication were analyzed. Whereas MSK injuries with ≥ 1 pain medication increased by 9.4%, we observed a larger increase in metamizole (+ 254%), strong opioids (+ 88.4%), coxibs (+ 85.8%), and paracetamol (+ 28.1%). Strong opioids were increasingly used in minor (+ 91.4%) and major (+ 88.3%) injuries. The increase in metamizole (+ 390.6%) and coxibs (+ 115.5%) was larger in minor injuries compared to major injuries (+ 238.7% and + 80.6%, respectively). Medical expenses decreased in all medications except for strong opioids where a substantial increase was observed (+ 192.4% in minor; + 34% in major injuries).
CONCLUSIONS
We observed a disproportionate increase in metamizole, strong opioids, coxibs, and paracetamol prescriptions even in minor MSK injuries between 2008 and 2018. Whereas treatment costs decreased for all pain medications, there was a substantial increase in strong opioids. A more liberal prescription practice of opioids conflict with current evidence-based practice recommendations and need to be addressed by physicians and policy makers
Collision induced spatial organization of microtubules
The dynamic behavior of microtubules in solution can be strongly modified by
interactions with walls or other structures. We examine here a microtubule
growth model where the increase in size of the plus-end is perturbed by
collisions with other microtubules. We show that such a simple mechanism of
constrained growth can induce ordered structures and patterns from an initially
isotropic and homogeneous suspension. First, microtubules self-organize locally
in randomly oriented domains that grow and compete with each other. By imposing
even a weak orientation bias, external forces like gravity or cellular
boundaries may bias the domain distribution eventually leading to a macroscopic
sample orientation.Comment: Submitted to Biophysical Journa
Permeability of DOPC bilayers under photoinduced oxidation: Sensitivity to photosensitizer.
The modification of lipid bilayer permeability is one of the most striking yet poorly understood physical transformations that follow photoinduced lipid oxidation. We have recently proposed that the increase of permeability of photooxidized 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers is controlled by the time required by the oxidized lipid species to diffuse and aggregate into pores. Here we further probe this mechanism by studying photosensitization of DOPC membranes by methylene blue (MB) and DO15, a more hydrophobic phenothiazinium photosensitizer, under different irradiation powers. Our results not only reveal the interplay between the production rate and the diffusion of the oxidized lipids, but highlight also the importance of photosensitizer localization in the kinetics of oxidized membrane permeability