4,372 research outputs found
Singular Lagrangian Systems on Jet Bundles
The jet bundle description of time-dependent mechanics is revisited. The
constraint algorithm for singular Lagrangians is discussed and an exhaustive
description of the constraint functions is given. By means of auxiliary
connections we give a basis of constraint functions in the Lagrangian and
Hamiltonian sides. An additional description of constraints is also given
considering at the same time compatibility, stability and second-order
condition problems. Finally, a classification of the constraints in first and
second class is obtained using a cosymplectic geometry setting. Using the
second class constraints, a Dirac bracket is introduced, extending the
well-known construction by Dirac.Comment: 65 pages. LaTeX fil
Knudsen Effect in a Nonequilibrium Gas
From the molecular dynamics simulation of a system of hard-core disks in
which an equilibrium cell is connected with a nonequilibrium cell, it is
confirmed that the pressure difference between two cells depends on the
direction of the heat flux. From the boundary layer analysis, the velocity
distribution function in the boundary layer is obtained. The agreement between
the theoretical result and the numerical result is fairly good.Comment: 4pages, 4figure
Free Thermal Convection Driven by Nonlocal Effects
We report and explain a convective phenomenon observed in molecular dynamics
simulations that cannot be classified either as a hydrodynamics instability nor
as a macroscopically forced convection. Two complementary arguments show that
the velocity field by a thermalizing wall is proportional to the ratio between
the heat flux and the pressure. This prediction is quantitatively corroborated
by our simulations.Comment: RevTex, figures is eps, submited for publicatio
The unit cell parameters and electrical conduction of some new solar cell materials
New materials are being investigated that could yield solar energy conversion efficiency comparable in device production cost to the standard electric power generators. Continuing with this effort, in recent years solar cells with efficiency close to 20 %, prepared with alloys of CuIn1-xGaxSe2 has been reported. It is shown that the normalized values of the unit cell parameters a and c of the ordered defect compounds with respect to their corresponding 1:1:2 phase, that are formed on the In(Ga)-rich side of the pseudo-binary phase diagram of [Cu2(Se,Te)]X–[(In2,Ga2)(Se3,Te3)]1-X, vary linearly with the effective cation radius reff for the tellurides and selenides of Cu-In and Cu-Ga systems. This universal relationship has important significance. The unit cell dimensions of other chalcopyriterelated ordered defect compounds of these systems that have not been synthesized so far can be estimated. Because of the presence of shallow donor and acceptor levels due to the presence of cation-cation disorders in Cu(In,Ga)Se2 and ordered defects in Cu(In,Ga)3(Se,Te)5, the impurity band in these compounds starts to form between liquid helium and nitrogen temperatures. This permits to study the variable range hopping (VRH) conduction in the impurity band over a much wider temperature range
Nuclear Activity and the Conditions of Star-formation at the Galactic Center
The Galactic Center is the closest galactic nucleus that can be studied with
unprecedented angular resolution and sensitivity. We summarize recent basic
observational results on Sagittarius A* and the conditions for star formation
in the central stellar cluster. We cover results from the radio, infrared, and
X-ray domain and include results from simulation as well. From (sub-)mm and
near-infrared variability and near-infrared polarization data we find that the
SgrA* system (supermassive black hole spin, a potential temporary accretion
disk and/or outflow) is well ordered in its geometrical orientation and in its
emission process that we assume to reflect the accretion process onto the
supermassive black hole (SMBH).Comment: 11 pages, 4 figures, 1 table; published in PoS-SISSA Proceedings of
the: Frontier Research in Astrophysics - II, 23-28 May 2016, Mondello
(Palermo), Ital
Clinical efficacy of β-lactam/β-lactamase inhibitor combinations for the treatment of bloodstream infection due to extended-spectrum β-lactamase- producing Enterobacteriaceae in haematological patients with neutropaenia: a study protocol for a retrospect observational study (BICAR).
Introduction: Bloodstream infection (BSI) due to
extended-spectrum β-lactamase-producing Gram-
negative bacilli (ESBL-GNB) is increasing at an
alarming pace worldwide. Although β-lactam/β-
lactamase inhibitor (BLBLI) combinations have been
suggested as an alternative to carbapenems for the
treatment of BSI due to these resistant organisms in
the general population, their usefulness for the
treatment of BSI due to ESBL-GNB in haematological
patients with neutropaenia is yet to be elucidated. The
aim of the BICAR study is to compare the efficacy of
BLBLI combinations with that of carbapenems for the
treatment of BSI due to an ESBL-GNB in this
population.
Methods and analysis: A multinational, multicentre,
observational retrospective study. Episodes of BSI due
to ESBL-GNB occurring in haematological patients and
haematopoietic stem cell transplant recipients with
neutropaenia from 1 January 2006 to 31 March 2015
will be analysed. The primary end point will be case-
fatality rate within 30 days of onset of BSI. The
secondary end points will be 7-day and 14-day case-
fatality rates, microbiological failure, colonisation/
infection by resistant bacteria, superinfection, intensive
care unit admission and development of adverse events.
Sample size: The number of expected episodes of BSI
due to ESBL-GNB in the participant centres will be 260
with a ratio of control to experimental participants of 2.
Ethics and dissemination: The protocol of the
study was approved at the first site by the Research
Ethics Committee (REC) of Hospital Universitari de
Bellvitge. Approval will be also sought from all relevant
RECs. Any formal presentation or publication of data
from this study will be considered as a joint
publication by the participating investigators and will
follow the recommendations of the International
Committee of Medical Journal Editors (ICMJE). The
study has been endorsed by the European Study Group
for Bloodstream Infection and Sepsis (ESGBIS) and the
European Study Group for Infections in Compromised
Hosts (ESGICH).Ministerio de Economía y Competitividad REIPI RD12/001
Evidence of topological superconductivity in planar Josephson junctions
Majorana zero modes are quasiparticle states localized at the boundaries of
topological superconductors that are expected to be ideal building blocks for
fault-tolerant quantum computing. Several observations of zero-bias conductance
peaks measured in tunneling spectroscopy above a critical magnetic field have
been reported as experimental indications of Majorana zero modes in
superconductor/semiconductor nanowires. On the other hand, two dimensional
systems offer the alternative approach to confine Ma jorana channels within
planar Josephson junctions, in which the phase difference {\phi} between the
superconducting leads represents an additional tuning knob predicted to drive
the system into the topological phase at lower magnetic fields. Here, we report
the observation of phase-dependent zero-bias conductance peaks measured by
tunneling spectroscopy at the end of Josephson junctions realized on a InAs/Al
heterostructure. Biasing the junction to {\phi} ~ {\pi} significantly reduces
the critical field at which the zero-bias peak appears, with respect to {\phi}
= 0. The phase and magnetic field dependence of the zero-energy states is
consistent with a model of Majorana zero modes in finite-size Josephson
junctions. Besides providing experimental evidence of phase-tuned topological
superconductivity, our devices are compatible with superconducting quantum
electrodynamics architectures and scalable to complex geometries needed for
topological quantum computing.Comment: main text and extended dat
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