460 research outputs found
Bacterial contamination of anesthesia machines’ internal breathing-circuit-systems
Background: Bacterial contamination of anesthesia breathing machines and their potential hazard for pulmonary infection and cross-infection among anesthetized patients has been an infection control issue since the 1950s. Disposable equipment and bacterial filters have been introduced to minimize this risk. However, the machines’ internal breathing-circuit-system has been considered to be free of micro-organisms without providing adequate data supporting this view. The aim of the study was to investigate if any micro-organisms can be yielded from used internal machines’ breathing-circuit-system. Based on such results objective reprocessing intervals could be defined
Origin of complex crystal structures of elements at pressure
We present a unifying theory for the observed complex structures of the
sp-bonded elements under pressure based on nearly free electron picture (NFE).
In the intermediate pressure regime the dominant contribution to crystal
structure arises from Fermi-surface Brillouin zone (FSBZ) interactions -
structures which allow this are favoured. This simple theory explains the
observed crystal structures, transport properties, the evolution of internal
and unit cell parameters with pressure. We illustrate it with experimental data
for these elements and ab initio calculation for Li.Comment: 4 pages 5 figure
Evolving properties of two dimensional materials, from graphene to graphite
We have studied theoretically, using density functional theory, several
materials properties when going from one C layer in graphene to two and three g
raphene layers and on to graphite. The properties we have focused on are the
elastic constants, electronic structure (energy bands and density of state s),
and the dielectric properties. For any of the properties we have investigated
the modification due to an increase in the number of graphene layers is within
a few percent. Our results are in agreement with the analysis presented
recently by Kopelevich and Esquinazi (unpublished)
Non-equilibrium polaron hopping transport through DNA
We study the electronic transport through short DNA chains with various
sequences of base pairs between voltage-biased leads. The strong coupling of
the charge carriers to local vibrations of the base pairs leads to the
formation of polarons, and in the relevant temperature range the transport is
accomplished by sequential polaron hopping. We calculate the rates for these
processes, extending what is known as the -theory of single-electron
tunneling to the situation with site-specific local oscillators. The
non-equilibrium charge rearrangement along the DNA leads to sequence-dependent
current thresholds of the `semi-conducting' current-voltage characteristics
and, except for symmetric sequences, to rectifying behavior. The current is
thermally activated with activation energy approaching for voltages above the
threshold the bulk value (polaron shift or reorganization energy). Our results
are consistent with some recent experiments.Comment: 8 pages, 5 figures, submitted to PRB, References adde
Sodium atoms and clusters on graphite: a density functional study
Sodium atoms and clusters (N<5) on graphite (0001) are studied using density
functional theory, pseudopotentials and periodic boundary conditions. A single
Na atom is observed to bind at a hollow site 2.45 A above the surface with an
adsorption energy of 0.51 eV. The small diffusion barrier of 0.06 eV indicates
a flat potential energy surface. Increased Na coverage results in a weak
adsorbate-substrate interaction, which is evident in the larger separation from
the surface in the cases of Na_3, Na_4, Na_5, and the (2x2) Na overlayer. The
binding is weak for Na_2, which has a full valence electron shell. The presence
of substrate modifies the structures of Na_3, Na_4, and Na_5 significantly, and
both Na_4 and Na_5 are distorted from planarity. The calculated formation
energies suggest that clustering of atoms is energetically favorable, and that
the open shell clusters (e.g. Na_3 and Na_5) can be more abundant on graphite
than in the gas phase. Analysis of the lateral charge density distributions of
Na and Na_3 shows a charge transfer of about 0.5 electrons in both cases.Comment: 20 pages, 6 figure
The electronic properties of bilayer graphene
We review the electronic properties of bilayer graphene, beginning with a
description of the tight-binding model of bilayer graphene and the derivation
of the effective Hamiltonian describing massive chiral quasiparticles in two
parabolic bands at low energy. We take into account five tight-binding
parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra-
and interlayer asymmetry between atomic sites which induce band gaps in the
low-energy spectrum. The Hartree model of screening and band-gap opening due to
interlayer asymmetry in the presence of external gates is presented. The
tight-binding model is used to describe optical and transport properties
including the integer quantum Hall effect, and we also discuss orbital
magnetism, phonons and the influence of strain on electronic properties. We
conclude with an overview of electronic interaction effects.Comment: review, 31 pages, 15 figure
On the constitution of sodium at higher densities
Using density functional theory the atomic and electronic structure of sodium
are predicted to depart substantially from those expected of simple metals for
GPa). Newly-predicted phases include those with low
structural symmetry, semi-metallic electronic properties (including zero-gap
semiconducting limiting behavior), unconventional valence charge density
distributions, and even those that raise the possibility of superconductivity,
all at currently achievable pressures. Important differences emerge between
sodium and lithium at high densities, and these are attributable to
corresponding differences in their respective cores.Comment: 13 pages; 3 figure
The new generation CMB B-mode polarization experiment: POLARBEAR
We describe the Cosmic Microwave Background (CMB) polarization experiment
called Polarbear. This experiment will use the dedicated Huan Tran Telescope
equipped with a powerful 1,200-bolometer array receiver to map the CMB
polarization with unprecedented accuracy. We summarize the experiment, its
goals, and current status
Ultra High Energy Cosmology with POLARBEAR
Observations of the temperature anisotropy of the Cosmic Microwave Background
(CMB) lend support to an inflationary origin of the universe, yet no direct
evidence verifying inflation exists. Many current experiments are focussing on
the CMB's polarization anisotropy, specifically its curl component (called
"B-mode" polarization), which remains undetected. The inflationary paradigm
predicts the existence of a primordial gravitational wave background that
imprints a unique B-mode signature on the CMB's polarization at large angular
scales. The CMB B-mode signal also encodes gravitational lensing information at
smaller angular scales, bearing the imprint of cosmological large scale
structures (LSS) which in turn may elucidate the properties of cosmological
neutrinos. The quest for detection of these signals; each of which is orders of
magnitude smaller than the CMB temperature anisotropy signal, has motivated the
development of background-limited detectors with precise control of systematic
effects. The POLARBEAR experiment is designed to perform a deep search for the
signature of gravitational waves from inflation and to characterize lensing of
the CMB by LSS. POLARBEAR is a 3.5 meter ground-based telescope with 3.8
arcminute angular resolution at 150 GHz. At the heart of the POLARBEAR receiver
is an array featuring 1274 antenna-coupled superconducting transition edge
sensor (TES) bolometers cooled to 0.25 Kelvin. POLARBEAR is designed to reach a
tensor-to-scalar ratio of 0.025 after two years of observation -- more than an
order of magnitude improvement over the current best results, which would test
physics at energies near the GUT scale. POLARBEAR had an engineering run in the
Inyo Mountains of Eastern California in 2010 and will begin observations in the
Atacama Desert in Chile in 2011.Comment: 8 pages, 6 figures, DPF 2011 conference proceeding
The bolometric focal plane array of the Polarbear CMB experiment
The Polarbear Cosmic Microwave Background (CMB) polarization experiment is
currently observing from the Atacama Desert in Northern Chile. It will
characterize the expected B-mode polarization due to gravitational lensing of
the CMB, and search for the possible B-mode signature of inflationary
gravitational waves. Its 250 mK focal plane detector array consists of 1,274
polarization-sensitive antenna-coupled bolometers, each with an associated
lithographed band-defining filter. Each detector's planar antenna structure is
coupled to the telescope's optical system through a contacting dielectric
lenslet, an architecture unique in current CMB experiments. We present the
initial characterization of this focal plane
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