95,906 research outputs found
Sticky Particles and Stochastic Flows
Gaw\c{e}dzki and Horvai have studied a model for the motion of particles
carried in a turbulent fluid and shown that in a limiting regime with low
levels of viscosity and molecular diffusivity, pairs of particles exhibit the
phenomena of stickiness when they meet. In this paper we characterise the
motion of an arbitrary number of particles in a simplified version of their
model
Electrode geometry and preferential stimulation of spinal nerve fibers having different orientations: a modeling study
In a computer modeling study of epidural spinal cord stimulation using a longitudinal array of electrode contacts, the effect of contact geometry and contact combination on the threshold voltages for stimulation of dorsal column (DC) fibers and dorsal root (DR) fibers was investigated. It was concluded that DC-fiber stimulation will be favoured when a tripolar combination and small contact length and spacing are used, while DR-fiber stimulation will be favoured when unipolar stimulation and large contact length are used
Polyatomic trilobite Rydberg molecules in a dense random gas
Trilobites are exotic giant dimers with enormous dipole moments. They consist
of a Rydberg atom and a distant ground-state atom bound together by short-range
electron-neutral attraction. We show that highly polar, polyatomic trilobite
states unexpectedly persist and thrive in a dense ultracold gas of randomly
positioned atoms. This is caused by perturbation-induced quantum scarring and
the localization of electron density on randomly occurring atom clusters. At
certain densities these states also mix with a s-state, overcoming selection
rules that hinder the photoassociation of ordinary trilobites
Numerical homotopies to compute generic points on positive dimensional algebraic sets
Many applications modeled by polynomial systems have positive dimensional
solution components (e.g., the path synthesis problems for four-bar mechanisms)
that are challenging to compute numerically by homotopy continuation methods. A
procedure of A. Sommese and C. Wampler consists in slicing the components with
linear subspaces in general position to obtain generic points of the components
as the isolated solutions of an auxiliary system. Since this requires the
solution of a number of larger overdetermined systems, the procedure is
computationally expensive and also wasteful because many solution paths
diverge. In this article an embedding of the original polynomial system is
presented, which leads to a sequence of homotopies, with solution paths leading
to generic points of all components as the isolated solutions of an auxiliary
system. The new procedure significantly reduces the number of paths to
solutions that need to be followed. This approach has been implemented and
applied to various polynomial systems, such as the cyclic n-roots problem
Polyatomic trilobite Rydberg molecules in a dense random gas
Trilobites are exotic giant dimers with enormous dipole moments. They consist
of a Rydberg atom and a distant ground-state atom bound together by short-range
electron-neutral attraction. We show that highly polar, polyatomic trilobite
states unexpectedly persist and thrive in a dense ultracold gas of randomly
positioned atoms. This is caused by perturbation-induced quantum scarring and
the localization of electron density on randomly occurring atom clusters. At
certain densities these states also mix with a s-state, overcoming selection
rules that hinder the photoassociation of ordinary trilobites
A probability current analysis of energy transport in open quantum systems
We introduce a probability current analysis of excitation energy transfer
between states of an open quantum system. Expressing the energy transfer
through currents of excitation probability between the states in a site
representation enables us to gain key insights into the energy transfer
dynamics. It allows to, i) identify the pathways of energy transport in large
networks of sites and to quantify their relative weights, ii) quantify the
respective contributions of unitary dynamics, dephasing, and
relaxation/dissipation processes to the energy transfer, and iii) quantify the
contribution of coherence to the energy transfer. Our analysis is general and
can be applied to a broad range of open quantum system descriptions (with
coupling to non-Markovian environments) in a straightforward manner
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