11,082 research outputs found
Nano-crystalline inclusions as a low-pass filter for thermal transport in a-Si
We use atomistic simulations to study the resonant acoustic modes and compare
different calculations of the acoustic mean-free path in amorphous systems with
nanometric crystalline spherical inclusions. We show that the resonant acoustic
properties are not a simple combination of the vibrations in the inclusions and
in the amorphous matrix. The presence of the inclusion affects the transport
properties mainly in the frequency range separating simple scattering from
multiple scattering processes. However, propagation of acoustic wavepackets is
spatially heterogeneous and shows that the amorphous/crystalline interface acts
as a low energy pass filter slowing down the high kinetic energy motion
whatever the vibration frequency. These heterogeneities cannot be catched by
the mean free path, but still they must play an important role in thermal
transport, thus raising the question of the correct modeling of thermal
transport in composite systems
Plasmon Decay: From QED to QCD
Upon using the same theoretical framework, I describe two interesting decay
processes: the electromagnetic plasmon decay into neutrinos, which can be the
dominant cooling mechanism for red giants and white dwarfs, and the gluonic
plasmon decay into quarks, which can be measured in ultra-relativistic
heavy-ion collisions.Comment: 6 pages, 2 PostScript figures included (Talk given at the 3rd
Workshop on Thermal Field Theories and their Applications, Banff, Canada,
August 1993
Exact two-terminal reliability of some directed networks
The calculation of network reliability in a probabilistic context has long
been an issue of practical and academic importance. Conventional approaches
(determination of bounds, sums of disjoint products algorithms, Monte Carlo
evaluations, studies of the reliability polynomials, etc.) only provide
approximations when the network's size increases, even when nodes do not fail
and all edges have the same reliability p. We consider here a directed, generic
graph of arbitrary size mimicking real-life long-haul communication networks,
and give the exact, analytical solution for the two-terminal reliability. This
solution involves a product of transfer matrices, in which individual
reliabilities of edges and nodes are taken into account. The special case of
identical edge and node reliabilities (p and rho, respectively) is addressed.
We consider a case study based on a commonly-used configuration, and assess the
influence of the edges being directed (or not) on various measures of network
performance. While the two-terminal reliability, the failure frequency and the
failure rate of the connection are quite similar, the locations of complex
zeros of the two-terminal reliability polynomials exhibit strong differences,
and various structure transitions at specific values of rho. The present work
could be extended to provide a catalog of exactly solvable networks in terms of
reliability, which could be useful as building blocks for new and improved
bounds, as well as benchmarks, in the general case
Improved one-sided deviation inequalities under regularity assumptions for product measures
This note is concerned with lower tail estimates for product measures. Some
improved deviation inequalities are obtained for functions satisfying some
regularity and monotonicity assumptions. The arguments are based on semigroup
interpolation together with Harris's negative association inequality and
hypercontractive estimates.Comment: 14 page
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