2,178 research outputs found
Granular Brownian motion
We study the stochastic motion of an intruder in a dilute driven granular
gas. All particles are coupled to a thermostat, representing the external
energy source, which is the sum of random forces and a viscous drag. The
dynamics of the intruder, in the large mass limit, is well described by a
linear Langevin equation, combining the effects of the external bath and of the
"granular bath". The drag and diffusion coefficients are calculated under few
assumptions, whose validity is well verified in numerical simulations. We also
discuss the non-equilibrium properties of the intruder dynamics, as well as the
corrections due to finite packing fraction or finite intruder mass.Comment: 19 pages, 4 figures, in press on Journal of Statistical Mechanics:
Theory and Experiment
Dynamics of a massive intruder in a homogeneously driven granular fluid
A massive intruder in a homogeneously driven granular fluid, in dilute
configurations, performs a memory-less Brownian motion with drag and
temperature simply related to the average density and temperature of the fluid.
At volume fraction the intruder's velocity correlates with the
local fluid velocity field: such situation is approximately described by a
system of coupled linear Langevin equations equivalent to a generalized
Brownian motion with memory. Here one may verify the breakdown of the
Fluctuation-Dissipation relation and the presence of a net entropy flux - from
the fluid to the intruder - whose fluctuations satisfy the Fluctuation
Relation.Comment: 6 pages, 2 figures, to be published on "Granular Matter" in a special
issue in honor of the memory of Prof. Isaac Goldhirsc
Nickel hydrogen bipolar battery electrode design
The preferred approach of the NASA development effort in nickel hydrogen battery design utilizes a bipolar plate stacking arrangement to obtain the required voltage-capacity configuration. In a bipolar stack, component designs must take into account not only the typical design considerations such as voltage, capacity and gas management, but also conductivity to the bipolar (i.e., intercell) plate. The nickel and hydrogen electrode development specifically relevant to bipolar cell operation is discussed. Nickel oxide electrodes, having variable type grids and in thicknesses up to .085 inch are being fabricated and characterized to provide a data base. A selection will be made based upon a system level tradeoff. Negative (hydrpogen) electrodes are being screened to select a high performance electrode which can function as a bipolar electrode. Present nickel hydrogen negative electrodes are not capable of conducting current through their cross-section. An electrode was tested which exhibits low charge and discharge polarization voltages and at the same time is conductive. Test data is presented
On anomalous diffusion and the out of equilibrium response function in one-dimensional models
We study how the Einstein relation between spontaneous fluctuations and the
response to an external perturbation holds in the absence of currents, for the
comb model and the elastic single-file, which are examples of systems with
subdiffusive transport properties. The relevance of non-equilibrium conditions
is investigated: when a stationary current (in the form of a drift or an energy
flux) is present, the Einstein relation breaks down, as is known to happen in
systems with standard diffusion. In the case of the comb model, a general
relation, which has appeared in the recent literature, between the response
function and an unperturbed suitable correlation function, allows us to explain
the observed results. This suggests that a relevant ingredient in breaking the
Einstein formula, for stationary regimes, is not the anomalous diffusion but
the presence of currents driving the system out of equilibrium.Comment: 10 pages, 4 figure
Irreversible effects of memory
The steady state of a Langevin equation with short ranged memory and coloured
noise is analyzed. When the fluctuation-dissipation theorem of second kind is
not satisfied, the dynamics is irreversible, i.e. detailed balance is violated.
We show that the entropy production rate for this system should include the
power injected by ``memory forces''. With this additional contribution, the
Fluctuation Relation is fairly verified in simulations. Both dynamics with
inertia and overdamped dynamics yield the same expression for this additional
power. The role of ``memory forces'' within the fluctuation-dissipation
relation of first kind is also discussed.Comment: 6 pages, 1 figure, publishe
Wave Energy: a Pacific Perspective
This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by The Royal Society and can be found at: http://rsta.royalsocietypublishing.org/.This paper illustrates the status of wave energy development in Pacific Rim countries by characterizing the available resource and introducing the region‟s current and potential future leaders in wave energy converter development. It also describes the existing licensing and permitting process as well as potential environmental concerns. Capabilities of Pacific Ocean testing facilities are described in addition to the region‟s vision of the future of wave energy
Fluctuation-Dissipation relation in sub-diffusive systems: the case of granular single-file
We study a gas of hard rods on a ring, driven by an external thermostat, with
either elastic or inelastic collisions, which exhibits sub-diffusive behavior
. We show the validity of the usual
Fluctuation-Dissipation (FD) relation, i.e. the proportionality between the
response function and the correlation function, when the gas is elastic or
diluted. On the contrary, in strongly inelastic or dense cases, when the tracer
velocity is no more independent of the other degrees of freedom, the Einstein
formula fails and must be replaced by a more general FD relation.Comment: 9 pages, 3 figure
Optimality Conditions for Nondifferentiable Multiobjective Semi-Infinite Programming Problems
We have considered a multiobjective semi-infinite programming problem with a feasible set defined by inequality constraints. First we studied a Fritz-John type necessary condition. Then, we introduced two constraint qualifications and derive the weak and strong Karush-Kuhn-Tucker (KKT in brief) types necessary conditions for an efficient solution of the considered problem. Finally an extension of a Caristi-Ferrara-Stefanescu result for the (Φ,ρ)-invexity is proved, and some sufficient conditions are presented under this weak assumption. All results are given in terms of Clark subdifferential
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