1,070 research outputs found
Systematic coarse-graining of the dynamics of entangled polymer melts: the road from chemistry to rheology
For optimal processing and design of entangled polymeric materials it is
important to establish a rigorous link between the detailed molecular
composition of the polymer and the viscoelastic properties of the macroscopic
melt. We review current and past computer simulation techniques and critically
assess their ability to provide such a link between chemistry and rheology. We
distinguish between two classes of coarse-graining levels, which we term
coarse-grained molecular dynamics (CGMD) and coarse-grained stochastic dynamics
(CGSD). In CGMD the coarse-grained beads are still relatively hard, thus
automatically preventing bond crossing. This also implies an upper limit on the
number of atoms that can be lumped together and therefore on the longest chain
lengths that can be studied. To reach a higher degree of coarse-graining, in
CGSD many more atoms are lumped together, leading to relatively soft beads. In
that case friction and stochastic forces dominate the interactions, and actions
must be undertaken to prevent bond crossing. We also review alternative methods
that make use of the tube model of polymer dynamics, by obtaining the
entanglement characteristics through a primitive path analysis and by
simulation of a primitive chain network. We finally review super-coarse-grained
methods in which an entire polymer is represented by a single particle, and
comment on ways to include memory effects and transient forces.Comment: Topical review, 31 pages, 10 figure
Variational Perturbation Theory for Markov Processes
We develop a convergent variational perturbation theory for conditional
probability densities of Markov processes. The power of the theory is
illustrated by applying it to the diffusion of a particle in an anharmonic
potential.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html Latest update of
paper also at http://www.physik.fu-berlin.de/~kleinert/33
Implementing measurement-based care (iMBC) for depression in community mental health: a dynamic cluster randomized trial study protocol
BACKGROUND: Measurement-based care is an evidence-based practice for depression that efficiently identifies treatment non-responders and those who might otherwise deteriorate [1]. However, measurement-based care is underutilized in community mental health with data suggesting fewer than 20 % of behavioral health providers using this practice to inform treatment. It remains unclear whether standardized or tailored approaches to implementation are needed to optimize measurement-based care fidelity and penetration. Moreover, there is some suggestion that prospectively tailored interventions that are designed to fit the dynamic context may optimize public health impact, though no randomized trials have yet tested this notion [2]. This study will address the following three aims: (1) To compare the effect of standardized versus tailored MBC implementation on clinician-level and client-level outcomes; (2) To identify contextual mediators of MBC fidelity; and (3) To explore the impact of MBC fidelity on client outcomes.
METHODS/DESIGN: This study is a dynamic cluster randomized trial of standardized versus tailored measurement-based care implementation in Centerstone, the largest provider of community-based mental health services in the USA. This prospective, mixed methods implementation-effectiveness hybrid design allows for evaluation of the two conditions on both clinician-level (e.g., MBC fidelity) and client-level (depression symptom change) outcomes. Central to this investigation is the focus on identifying contextual factors (e.g., attitudes, resources, process, etc.) that mediate MBC fidelity and optimize client outcomes.
DISCUSSION: This study will contribute generalizable and practical strategies for implementing systematic symptom monitoring to inform and enhance behavioral healthcare.
TRIAL REGISTRATION: Clinicaltrials.gov NCT02266134
Low Reynolds number hydrodynamics of asymmetric, oscillating dumbbell pairs
Active dumbbell suspensions constitute one of the simplest model system for
collective swimming at low Reynolds number. Generalizing recent work, we derive
and analyze stroke-averaged equations of motion that capture the effective
hydrodynamic far-field interaction between two oscillating, asymmetric
dumbbells in three space dimensions. Time-averaged equations of motion, as
those presented in this paper, not only yield a considerable speed-up in
numerical simulations, they may also serve as a starting point when deriving
continuum equations for the macroscopic dynamics of multi-swimmer suspensions.
The specific model discussed here appears to be particularly useful in this
context, since it allows one to investigate how the collective macroscopic
behavior is affected by changes in the microscopic symmetry of individual
swimmers.Comment: 10 pages, to appear in EPJ Special Topic
OpenPNM: A Pore Network Modeling Package
Pore network modeling is a widely used technique for simulating multiphase transport in porous materials, but there are very few software options available. This work outlines the OpenPNM package that was jointly developed by several porous media research groups to help address this gap. OpenPNM is written in Python using NumPy and SciPy for most mathematical operations, thus combining Python's ease of use with the performance necessary to perform large simulations. The package assists the user with managing and interacting with all the topological, geometrical, and thermophysical data. It also includes a suite of commonly used algorithms for simulating percolation and performing transport calculations on pore networks. Most importantly, it was designed to be highly flexible to suit any application and be easily customized to include user-specified pore-scale physics models. The framework is fast, powerful, and concise. An illustrative example is included that determines the effective diffusivity through a partially water-saturated porous material with just 29 lines of code
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