28,036 research outputs found
The conductance of a multi-mode ballistic ring: beyond Landauer and Kubo
The Landauer conductance of a two terminal device equals to the number of
open modes in the weak scattering limit. What is the corresponding result if we
close the system into a ring? Is it still bounded by the number of open modes?
Or is it unbounded as in the semi-classical (Drude) analysis? It turns out that
the calculation of the mesoscopic conductance is similar to solving a
percolation problem. The "percolation" is in energy space rather than in real
space. The non-universal structures and the sparsity of the perturbation matrix
cannot be ignored.Comment: 7 pages, 8 figures, with the correct version of Figs.6-
Total Quantum Zeno effect and Intelligent States for a two level system in a squeezed bath
In this work we show that by frequent measurements of adequately chosen
observables, a complete suppression of the decay in an exponentially decaying
two level system interacting with a squeezed bath is obtained. The observables
for which the effect is observed depend on the the squeezing parameters of the
bath. The initial states which display Total Zeno Effect are intelligent states
of two conjugate observables associated to the electromagnetic fluctuations of
the bath.Comment: 5 pages, 3 figure
Rate of energy absorption by a closed ballistic ring
We make a distinction between the spectroscopic and the mesoscopic
conductance of closed systems. We show that the latter is not simply related to
the Landauer conductance of the corresponding open system. A new ingredient in
the theory is related to the non-universal structure of the perturbation matrix
which is generic for quantum chaotic systems. These structures may created
bottlenecks that suppress the diffusion in energy space, and hence the rate of
energy absorption. The resulting effect is not merely quantitative: For a
ring-dot system we find that a smaller Landauer conductance implies a smaller
spectroscopic conductance, while the mesoscopic conductance increases. Our
considerations open the way towards a realistic theory of dissipation in closed
mesoscopic ballistic devices.Comment: 18 pages, 5 figures, published version with updated ref
Accurate Reaction-Diffusion Operator Splitting on Tetrahedral Meshes for Parallel Stochastic Molecular Simulations
Spatial stochastic molecular simulations in biology are limited by the
intense computation required to track molecules in space either in a discrete
time or discrete space framework, meaning that the serial limit has already
been reached in sub-cellular models. This calls for parallel simulations that
can take advantage of the power of modern supercomputers; however exact methods
are known to be inherently serial. We introduce an operator splitting
implementation for irregular grids with a novel method to improve accuracy, and
demonstrate potential for scalable parallel simulations in an initial MPI
version. We foresee that this groundwork will enable larger scale, whole-cell
stochastic simulations in the near future.Comment: 33 pages, 10 figure
Automatic annotation of bioinformatics workflows with biomedical ontologies
Legacy scientific workflows, and the services within them, often present
scarce and unstructured (i.e. textual) descriptions. This makes it difficult to
find, share and reuse them, thus dramatically reducing their value to the
community. This paper presents an approach to annotating workflows and their
subcomponents with ontology terms, in an attempt to describe these artifacts in
a structured way. Despite a dearth of even textual descriptions, we
automatically annotated 530 myExperiment bioinformatics-related workflows,
including more than 2600 workflow-associated services, with relevant
ontological terms. Quantitative evaluation of the Information Content of these
terms suggests that, in cases where annotation was possible at all, the
annotation quality was comparable to manually curated bioinformatics resources.Comment: 6th International Symposium on Leveraging Applications (ISoLA 2014
conference), 15 pages, 4 figure
Lattice Model of Sweeping Interface for Drying Process in Water-Granule Mixture
Based on the invasion percolation model, a lattice model for the sweeping
interface dynamics is constructed to describe the pattern forming process by a
sweeping interface upon drying the water-granule mixture. The model is shown to
produce labyrinthine patterns similar to those found in the experiment[Yamazaki
and Mizuguchi, J. Phys. Soc. Jpn. \textbf{69} (2000) 2387]. Upon changing the
initial granular density, resulting patterns undergo the percolation
transition, but estimated critical exponents are different from those of the
conventional percolation. Loopless structure of clusters in the patterns
produced by the sweeping dynamics seems to influence the nature of the
transition.Comment: 6 pages, 7 figure
- …