7,200 research outputs found
Dynamical chiral symmetry breaking in sliding nanotubes
We discovered in simulations of sliding coaxial nanotubes an unanticipated
example of dynamical symmetry breaking taking place at the nanoscale. While
both nanotubes are perfectly left-right symmetric and nonchiral, a nonzero
angular momentum of phonon origin appears spontaneously at a series of critical
sliding velocities, in correspondence with large peaks of the sliding friction.
The non-linear equations governing this phenomenon resemble the rotational
instability of a forced string. However, several new elements, exquisitely
"nano" appear here, with the crucial involvement of Umklapp and of sliding
nanofriction.Comment: To appear in PR
Adiabatic dynamics in open quantum critical many-body systems
The purpose of this work is to understand the effect of an external
environment on the adiabatic dynamics of a quantum critical system. By means of
scaling arguments we derive a general expression for the density of excitations
produced in the quench as a function of its velocity and of the temperature of
the bath. We corroborate the scaling analysis by explicitly solving the case of
a one-dimensional quantum Ising model coupled to an Ohmic bath.Comment: 4 pages, 4 figures; revised version to be published in Phys. Rev.
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Liquid-like behavior of supercritical fluids
The high frequency dynamics of fluid oxygen have been investigated by
Inelastic X-ray Scattering. In spite of the markedly supercritical conditions
(, ), the sound velocity exceeds the hydrodynamic
value of about 20%, a feature which is the fingerprint of liquid-like dynamics.
The comparison of the present results with literature data obtained in several
fluids allow us to identify the extrapolation of the liquid vapor-coexistence
line in the (, ) plane as the relevant edge between liquid- and
gas-like dynamics. More interestingly, this extrapolation is very close to the
non metal-metal transition in hot dense fluids, at pressure and temperature
values as obtained by shock wave experiments. This result points to the
existence of a connection between structural modifications and transport
properties in dense fluids.Comment: 4 pages, 3 figures, accepted by Phys. Rev. Let
Complexity-Entropy Causality Plane as a Complexity Measure for Two-dimensional Patterns
Complexity measures are essential to understand complex systems and there are
numerous definitions to analyze one-dimensional data. However, extensions of
these approaches to two or higher-dimensional data, such as images, are much
less common. Here, we reduce this gap by applying the ideas of the permutation
entropy combined with a relative entropic index. We build up a numerical
procedure that can be easily implemented to evaluate the complexity of two or
higher-dimensional patterns. We work out this method in different scenarios
where numerical experiments and empirical data were taken into account.
Specifically, we have applied the method to i) fractal landscapes generated
numerically where we compare our measures with the Hurst exponent; ii) liquid
crystal textures where nematic-isotropic-nematic phase transitions were
properly identified; iii) 12 characteristic textures of liquid crystals where
the different values show that the method can distinguish different phases; iv)
and Ising surfaces where our method identified the critical temperature and
also proved to be stable.Comment: Accepted for publication in PLoS On
A mutation in caspase-9 decreases the expression of BAFFR and ICOS in patients with immunodeficiency and lymphoproliferation
Lymphocyte apoptosis is mainly induced by either death receptor-dependent activation of caspase-8 or mitochondria-dependent activation of caspase-9. Mutations in caspase-8 lead to autoimmunity/lymphoproliferation and immunodeficiency. This work describes a heterozygous H237P mutation in caspase-9 that can lead to similar disorders. H237P mutation was detected in two patients: Pt1 with autoimmunity/lymphoproliferation, severe hypogammaglobulinemia and Pt2 with mild hypogammaglobulinemia and Burkitt lymphoma. Their lymphocytes displayed defective caspase-9 activity and decreased apoptotic and activation responses. Transfection experiments showed that mutant caspase-9 display defective enzyme and proapoptotic activities and a dominant-negative effect on wild-type caspase-9. Ex vivo analysis of the patients' lymphocytes and in vitro transfection experiments showed that the expression of mutant caspase-9 correlated with a downregulation of BAFFR (B-cell-activating factor belonging to the TNF family (BAFF) receptor) in B cells and ICOS (inducible T-cell costimulator) in T cells. Both patients carried a second inherited heterozygous mutation missing in the relatives carrying H237P: Pt1 in the transmembrane activator and CAML interactor (TACI) gene (S144X) and Pt2 in the perforin (PRF1) gene (N252S). Both mutations have been previously associated with immunodeficiencies in homozygosis or compound heterozygosis. Taken together, these data suggest that caspase-9 mutations may predispose to immunodeficiency by cooperating with other genetic factors, possibly by downregulating the expression of BAFFR and ICO
Adiabatic dynamics of a quantum critical system coupled to an environment: Scaling and kinetic equation approaches
We study the dynamics of open quantum many-body systems driven across a
critical point by quenching an Hamiltonian parameter at a certain velocity.
General scaling laws are derived for the density of excitations and energy
produced during the quench as a function of quench velocity and bath
temperature. The scaling laws and their regimes of validity are verified for
the XY spin chain locally coupled to bosonic baths. A detailed derivation and
analysis of the kinetic equation of the problem is presented.Comment: 15 pages, 13 figure
Iterative Approximate Consensus in the presence of Byzantine Link Failures
This paper explores the problem of reaching approximate consensus in
synchronous point-to-point networks, where each directed link of the underlying
communication graph represents a communication channel between a pair of nodes.
We adopt the transient Byzantine link failure model [15, 16], where an
omniscient adversary controls a subset of the directed communication links, but
the nodes are assumed to be fault-free.
Recent work has addressed the problem of reaching approximate consen- sus in
incomplete graphs with Byzantine nodes using a restricted class of iterative
algorithms that maintain only a small amount of memory across iterations [22,
21, 23, 12]. However, to the best of our knowledge, we are the first to
consider approximate consensus in the presence of Byzan- tine links. We extend
our past work that provided exact characterization of graphs in which the
iterative approximate consensus problem in the presence of Byzantine node
failures is solvable [22, 21]. In particular, we prove a tight necessary and
sufficient condition on the underlying com- munication graph for the existence
of iterative approximate consensus algorithms under transient Byzantine link
model. The condition answers (part of) the open problem stated in [16].Comment: arXiv admin note: text overlap with arXiv:1202.609
Silicon photomultiplier readout of a scintillating noble gas detector for homeland security
Detectors based on scintillation by high pressure 4He are a viable technology for instruments against the illicit trafficking of nuclear material. A design based on the use of solid state photodetectors is presented in this paper and the preliminary qualification discussed
Allelic variation in the TNF-beta gene does not explain the low TNF-beta response in patients with primary biliary cirrhosis
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