31,427 research outputs found
Laser ignition of elastomer-modified cast double-base (EMCDB) propellant using a diode laser
An experimental study was conducted to investigate laser ignition using a diode laser for elastomer-modified cast double-base (EMCDB) propellant in order to develop more liable and greener laser ignitors for direct initiation of the propellant. Samples of the propellant were ignited using a 974 nm near-infrared diode laser. Laser beam parameters including laser power, beam width and pulse width were investigated to determine their effects on the ignition performance in terms of delay time, rise time and burn time of the propellant which was arranged in several different configurations. The results have shown that the smaller beam widths, longer pulse widths and higher laser powers resulted in shorter ignition delay times and overall burn times, however, there came a point at which increasing the amount of laser energy transferred to the material resulted in no significant reduction in either delay time or overall burn time. The propellant tested responded well to laser ignition, a discovery which supports continued research into the development of laser-based propellant ignitors
Local electronic nematicity in the one-band Hubbard model
Nematicity is a well known property of liquid crystals and has been recently
discussed in the context of strongly interacting electrons. An electronic
nematic phase has been seen by many experiments in certain strongly correlated
materials, in particular, in the pseudogap phase generic to many hole-doped
cuprate superconductors. Recent measurements in high superconductors has
shown even if the lattice is perfectly rotationally symmetric, the ground state
can still have strongly nematic local properties. Our study of the
two-dimensional Hubbard model provides strong support of the recent
experimental results on local rotational symmetry breaking. The
variational cluster approach is used here to show the possibility of an
electronic nematic state and the proximity of the underlying symmetry-breaking
ground state within the Hubbard model. We identify this nematic phase in the
overdoped region and show that the local nematicity decreases with increasing
electron filling. Our results also indicate that strong Coulomb interaction may
drive the nematic phase into a phase similar to the stripe structure. The
calculated spin (magnetic) correlation function in momentum space shows the
effects resulting from real-space nematicity
Topology of the polarization field in ferroelectric nanowires from first principles
The behaviour of the cross-sectional polarization field is explored for thin
nanowires of barium titanate from first-principles calculations. Topological
defects of different winding numbers have been obtained, beyond the known
textures in ferroelectric nanostructures. They result from the inward
accommodation of the polarization patterns imposed at the surface of the wire
by surface and edge effects. Close to a topological defect the polarization
field orients out of the basal plane in some cases, maintaining a close to
constant magnitude, whereas it virtually vanishes in other cases.Comment: 4 pages, 3 figure
In vitro and in vivo effects of salbutamol on neutrophil function in acute lung injury
Background: Intravenous salbutamol (albuterol) reduces lung water in patients with the acute respiratory
distress syndrome (ARDS). Experimental data show that it also reduces pulmonary neutrophil accumulation or
activation and inflammation in ARDS.
Aim: To investigate the effects of salbutamol on neutrophil function.
Methods: The in vitro effects of salbutamol on neutrophil function were determined. Blood and
bronchoalveolar lavage (BAL) fluid were collected from 35 patients with acute lung injury (ALI)/ARDS, 14
patients at risk from ARDS and 7 ventilated controls at baseline and after 4 days’ treatment with placebo or
salbutamol (ALI/ARDS group). Alveolar–capillary permeability was measured in vivo by thermodilution
(PiCCO). Neutrophil activation, adhesion molecule expression and inflammatory cytokines were measured.
Results: In vitro, physiological concentrations of salbutamol had no effect on neutrophil chemotaxis, viability
or apoptosis. Patients with ALI/ARDS showed increased neutrophil activation and adhesion molecule
expression compared with at risk-patients and ventilated controls. There were associations between alveolar–
capillary permeability and BAL myeloperoxidase (r = 0.4, p = 0.038) and BAL interleukin 8 (r = 0.38,
p = 0.033). In patients with ALI/ARDS, salbutamol increased numbers of circulating neutrophils but had no
effect on alveolar neutrophils.
Conclusion: At the onset of ALI/ARDS, there is increased neutrophil recruitment and activation. Physiological
concentrations of salbutamol did not alter neutrophil chemotaxis, viability or apoptosis in vitro. In vivo,
salbutamol increased circulating neutrophils, but had no effect on alveolar neutrophils or on neutrophil
activation. These data suggest that the beneficial effects of salbutamol in reducing lung water are unrelated to
modulation of neutrophil-dependent inflammatory pathways
Inhomogeneity Induces Resonance Coherence Peaks in Superconducting BSCCO
In this paper we analyze, using scanning tunneling spectroscopy, the density
of electronic states in nearly optimally doped BSCCO in zero field. Focusing on
the superconducting gap, we find patches of what appear to be two different
phases in a background of some average gap, one with a relatively small gap and
sharp large coherence peaks and one characterized by a large gap with broad
weak coherence peaks. We compare these spectra with calculations of the local
density of states for a simple phenomenological model in which a 2 xi_0 * 2
xi_0 patch with an enhanced or supressed d-wave gap amplitude is embedded in a
region with a uniform average d-wave gap.Comment: 4 pages, 3 figure
Evidence for multiple impurity bands in sodium-doped silicon MOSFETs
We report measurements of the temperature-dependent conductivity in a silicon
metal-oxide-semiconductor field-effect transistor that contains sodium
impurities in the oxide layer. We explain the variation of conductivity in
terms of Coulomb interactions that are partially screened by the proximity of
the metal gate. The study of the conductivity exponential prefactor and the
localization length as a function of gate voltage have allowed us to determine
the electronic density of states and has provided arguments for the presence of
two distinct bands and a soft gap at low temperature.Comment: 4 pages; 5 figures; Published in PRB Rapid-Communication
Dynamics of opinion formation in a small-world network
The dynamical process of opinion formation within a model using a local
majority opinion updating rule is studied numerically in networks with the
small-world geometrical property. The network is one in which shortcuts are
added to randomly chosen pairs of nodes in an underlying regular lattice. The
presence of a small number of shortcuts is found to shorten the time to reach a
consensus significantly. The effects of having shortcuts in a lattice of fixed
spatial dimension are shown to be analogous to that of increasing the spatial
dimension in regular lattices. The shortening of the consensus time is shown to
be related to the shortening of the mean shortest path as shortcuts are added.
Results can also be translated into that of the dynamics of a spin system in a
small-world network.Comment: 10 pages, 5 figure
Membrane in M5-branes Background
In this paper, we investigate the properties of a membrane in the M5-brane
background. Through solving the classical equations of motion of the membrane,
we can understand the classical dynamics of the membrane in this background.Comment: 15 pages, typos correcte
Cross-correlating the Thermal Sunyaev-Zel'dovich Effect and the Distribution of Galaxy Clusters
We present the analytical formulas, derived based on the halo model, to
compute the cross-correlation between the thermal Sunyaev-Zel'dovich (SZ)
effect and the distribution of galaxy clusters. By binning the clusters
according to their redshifts and masses, this cross-correlation, the so-called
stacked SZ signal, reveals the average SZ profile around the clusters. The
stacked SZ signal is obtainable from a joint analysis of an
arcminute-resolution cosmic microwave background (CMB) experiment and an
overlapping optical survey, which allows for detection of the SZ signals for
clusters whose masses are below the individual cluster detection threshold. We
derive the error covariance matrix for measuring the stacked SZ signal, and
then forecast for its detection from ongoing and forthcoming combined
CMB-optical surveys. We find that, over a wide range of mass and redshift, the
stacked SZ signal can be detected with a significant signal to noise ratio
(total S/N \gsim 10), whose value peaks for the clusters with intermediate
masses and redshifts. Our calculation also shows that the stacking method
allows for probing the clusters' SZ profiles over a wide range of scales, even
out to projected radii as large as the virial radius, thereby providing a
promising way to study gas physics at the outskirts of galaxy clusters.Comment: 11 pages, 6 figures, 3 tables, minor revisions reflect PRD published
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