1,290 research outputs found
Nonequilibrium Microscopic Distribution of Thermal Current in Particle Systems
A nonequilibrium distribution function of microscopic thermal current is
studied by a direct numerical simulation in a thermal conducting steady state
of particle systems. Two characteristic temperatures of the thermal current are
investigated on the basis of the distribution. It is confirmed that the
temperature depends on the current direction; Parallel temperature to the
heat-flux is higher than antiparallel one. The difference between the parallel
temperature and the antiparallel one is proportional to a macroscopic
temperature gradient.Comment: 4 page
Linear Response for Granular Fluids
The linear response of an isolated, homogeneous granular fluid to small
spatial perturbations is studied by methods of non-equilibrium statistical
mechanics. The long wavelength linear hydrodynamic equations are obtained, with
formally exact expressions for the susceptibilities and transport coefficients.
The latter are given in equivalent Einstein-Helfand and Green-Kubo forms. The
context of these results and their contrast with corresponding results for
normal fluids are discussed.Comment: Submitted to PR
Kinetic Theory of Response Functions for the Hard Sphere Granular Fluid
The response functions for small spatial perturbations of a homogeneous
granular fluid have been described recently. In appropriate dimensionless
variables, they have the form of stationary state time correlation functions.
Here, these functions are expressed in terms of reduced single particle
functions that are expected to obey a linear kinetic equation. The functional
assumption required for such a kinetic equation, and a Markov approximation for
its implementation are discussed. If, in addition, static velocity correlations
are neglected, a granular fluid version of the linearized Enskog kinetic theory
is obtained. The derivation makes no a priori limitation on the density, space
and time scale, nor degree of inelasticity. As an illustration, recently
derived Helfand and Green-Kubo expressions for the Navier-Stokes order
transport coefficients are evaluated with this kinetic theory. The results are
in agreement with those obtained from the Chapman-Enskog solution to the
nonlinear Enskog kinetic equation.Comment: Submitted to J. Stat. Mec
Project Energize: intervention development and 10 years of progress in preventing childhood obesity
Prevention of childhood obesity is a global priority. The school setting offers access to large numbers of children and the ability to provide supportive environments for quality physical activity and nutrition. This article describes Project Energize, a through-school physical activity and nutrition programme that celebrated its 10-year anniversary in 2015 so that it might serve as a model for similar practices, initiatives and policies elsewhere. The programme was envisaged and financed by the Waikato District Health Board of New Zealand in 2004 and delivered by Sport Waikato to 124 primary schools as a randomised controlled trial from 2005 to 2006. The programme has since expanded to include all 242 primary schools in the Waikato region and 70 schools in other regions, including 53,000 children. Ongoing evaluation and development of Project Energize has shown it to be sustainable (ongoing for >10 years), both effective (lower obesity, higher physical fitness) and cost effective (one health related cost quality adjusted life year between 30,000) and efficient ($45/child/year) as a childhood 'health' programme. The programme's unique community-based approach is inclusive of all children, serving a population that is 42 % Ma¯ori, the indigenous people of New Zealand. While the original nine healthy eating and seven quality physical activity goals have not changed, the delivery and assessment processes has been refined and the health service adapted over the 10 years of the programme existence, as well as adapted over time to other settings including early childhood education and schools in Cork in Ireland. Evaluation and research associated with the programme delivery and outcomes are ongoing. The dissemination of findings to politicians and collaboration with other service providers are both regarded as priorities
Segregation of an intruder in a heated granular dense gas
A recent segregation criterion [V. Garz\'o, Phys. Rev. E \textbf{78},
020301(R) (2008)] based on the thermal diffusion factor of an
intruder in a heated granular gas described by the inelastic Enskog equation is
revisited. The sign of provides a criterion for the transition
between the Brazil-nut effect (BNE) and the reverse Brazil-nut effect (RBNE).
The present theory incorporates two extra ingredients not accounted for by the
previous theoretical attempt. First, the theory is based upon the second Sonine
approximation to the transport coefficients of the mass flux of intruder.
Second, the dependence of the temperature ratio (intruder temperature over that
of the host granular gas) on the solid volume fraction is taken into account in
the first and second Sonine approximations. In order to check the accuracy of
the Sonine approximation considered, the Enskog equation is also numerically
solved by means of the direct simulation Monte Carlo (DSMC) method to get the
kinetic diffusion coefficient . The comparison between theory and
simulation shows that the second Sonine approximation to yields an
improvement over the first Sonine approximation when the intruder is lighter
than the gas particles in the range of large inelasticity. With respect to the
form of the phase diagrams for the BNE/RBNE transition, the kinetic theory
results for the factor indicate that while the form of these diagrams
depends sensitively on the order of the Sonine approximation considered when
gravity is absent, no significant differences between both Sonine solutions
appear in the opposite limit (gravity dominates the thermal gradient). In the
former case (no gravity), the first Sonine approximation overestimates both the
RBNE region and the influence of dissipation on thermal diffusion segregation.Comment: 9 figures; to be published in Phys. Rev.
Representation of nonequilibrium steady states in large mechanical systems
Recently a novel concise representation of the probability distribution of
heat conducting nonequilibrium steady states was derived. The representation is
valid to the second order in the ``degree of nonequilibrium'', and has a very
suggestive form where the effective Hamiltonian is determined by the excess
entropy production. Here we extend the representation to a wide class of
nonequilibrium steady states realized in classical mechanical systems where
baths (reservoirs) are also defined in terms of deterministic mechanics. The
present extension covers such nonequilibrium steady states with a heat
conduction, with particle flow (maintained either by external field or by
particle reservoirs), and under an oscillating external field. We also simplify
the derivation and discuss the corresponding representation to the full order.Comment: 27 pages, 3 figure
Hydrodynamic modes, Green-Kubo relations, and velocity correlations in dilute granular gases
It is shown that the hydrodynamic modes of a dilute granular gas of inelastic
hard spheres can be identified, and calculated in the long wavelength limit.
Assuming they dominate at long times, formal expressions for the Navier-Stokes
transport coefficients are derived. They can be expressed in a form that
generalizes the Green-Kubo relations for molecular systems, and it is shown
that they can also be evaluated by means of -particle simulation methods.
The form of the hydrodynamic modes to zeroth order in the gradients is used to
detect the presence of inherent velocity correlations in the homogeneous
cooling state, even in the low density limit. They manifest themselves in the
fluctuations of the total energy of the system. The theoretical predictions are
shown to be in agreement with molecular dynamics simulations. Relevant related
questions deserving further attention are pointed out
Scoping review and characteristics of publicly available checklists for assessing clinical trial feasibility
BACKGROUND: Whether there is sufficient capacity and capability for the successful conduct and delivery of a clinical trial should be assessed by several stakeholders according to transparent and evidence-based criteria during trial planning. For this openly shared, user-tested, and validated tools are necessary. Therefore, we systematically examined the public availability and content of checklists which assess the study-level feasibility in the planning phase of clinical trials. METHODS: In our scoping review we systematically searched Medline, EMBASE, and Google (last search, June 2021). We included all publicly available checklists or tools that assessed study level feasibility of clinical trials, examined their content, and checked whether they were user-tested or validated in any form. Data was analysed and synthesised using conventional content analysis. RESULTS: A total of 10 publicly available checklists from five countries were identified. The checklists included 48 distinct items that were classified according to the following seven different domains of clinical trial feasibility: regulation, review and oversight; participant recruitment; space, material and equipment; financial resources; trial team resources; trial management; and pilot or feasibility studies. None of the available checklists appeared to be user-tested or validated. CONCLUSIONS: Although a number of publicly available checklists to assess the feasibility of clinical trials exist, their reliability and usefulness remain unclear. Openly shared, user-tested, and validated feasibility assessment tools for a better planning of clinical trials are lacking
Gaussian Kinetic Model for Granular Gases
A kinetic model for the Boltzmann equation is proposed and explored as a
practical means to investigate the properties of a dilute granular gas. It is
shown that all spatially homogeneous initial distributions approach a universal
"homogeneous cooling solution" after a few collisions. The homogeneous cooling
solution (HCS) is studied in some detail and the exact solution is compared
with known results for the hard sphere Boltzmann equation. It is shown that all
qualitative features of the HCS, including the nature of over population at
large velocities, are reproduced semi-quantitatively by the kinetic model. It
is also shown that all the transport coefficients are in excellent agreement
with those from the Boltzmann equation. Also, the model is specialized to one
having a velocity independent collision frequency and the resulting HCS and
transport coefficients are compared to known results for the Maxwell Model. The
potential of the model for the study of more complex spatially inhomogeneous
states is discussed.Comment: to be submitted to Phys. Rev.
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