142 research outputs found
A generalized drift-diffusion model for rectifying Schottky contact simulation
We present a discussion on the modeling of Schottky barrier rectifying contacts (diodes) within the framework of partial-differential-equation-based physical simulations. We propose a physically consistent generalization of the drift-diffusion model to describe the boundary layer close to the Schottky barrier where thermionic emission leads to a non-Maxwellian carrier distribution, including a novel boundary condition at the contact. The modified drift-diffusion model is validated against Monte Carlo simulations of a GaAs device. The proposed model is in agreement with the Monte Carlo simulations not only in the current value but also in the spatial distributions of microscopic quantities like the electron velocity and concentratio
dynamic simulation of the temperature inlet turbine control system for an unfired micro gas turbine in a concentrating solar tower
Abstract In this work, the dynamic performance of a mass flow regulation system, in a concentrating solar tower plant, with unfired closed micro gas turbine, during clouds transient will be presented. The adjustment system operates with the heliostats field control system, in order to control the temperature inlet turbine. To choose the best configuration, the performance of three heliostats sizes, for four Solar Multiple, has been evaluated. The design of the solar field was carried out by means of Solar Pilot, while the numerical models have been developed in Matlab/Simulink. The results show that a particular configuration is suitable for this purpose
Anomalous Aharonov--Bohm gap oscillations in carbon nanotubes
The gap oscillations caused by a magnetic flux penetrating a carbon nanotube
represent one of the most spectacular observation of the Aharonov-Bohm effect
at the nano--scale. Our understanding of this effect is, however, based on the
assumption that the electrons are strictly confined on the tube surface, on
trajectories that are not modified by curvature effects. Using an ab-initio
approach based on Density Functional Theory we show that this assumption fails
at the nano-scale inducing important corrections to the physics of the
Aharonov-Bohm effect. Curvature effects and electronic density spilled out of
the nanotube surface are shown to break the periodicity of the gap
oscillations. We predict the key phenomenological features of this anomalous
Aharonov-Bohm effect in semi-conductive and metallic tubes and the existence of
a large metallic phase in the low flux regime of Multi-walled nanotubes, also
suggesting possible experiments to validate our results.Comment: 7 figure
Painlev\'{e} test of coupled Gross-Pitaevskii equations
Painlev\'{e} test of the coupled Gross-Pitaevskii equations has been carried
out with the result that the coupled equations pass the P-test only if a
special relation containing system parameters (masses, scattering lengths) is
satisfied. Computer algebra is applied to evaluate j=4 compatibility condition
for admissible external potentials. Appearance of an arbitrary real potential
embedded in the external potentials is shown to be the consequence of the
coupling. Connection with recent experiments related to stability of
two-component Bose-Einstein condensates of Rb atoms is discussed.Comment: 13 pages, no figure
A Central Excess of Stripped-Envelope Supernovae within Disturbed Galaxies
This paper presents an analysis of core-collapse supernova distributions in
isolated and interacting host galaxies, paying close attention to the selection
effects involved in conducting host galaxy supernova studies. When taking into
account all of the selection effects within our host galaxy sample, we draw the
following conclusions: i) Within interacting, or 'disturbed', systems there is
a real, and statistically significant, increase in the fraction of
stripped-envelope supernovae in the central regions. A discussion into what may
cause this increased fraction, compared to the more common type IIP supernovae,
and type II supernovae without sub-classifications, is presented. Selection
effects are shown not to drive this result, and so we propose that this study
provides direct evidence for a high-mass weighted initial mass function within
the central regions of disturbed galaxies. ii) Within 'undisturbed' spiral
galaxies the radial distribution of type Ib and type Ic supernovae is
statistically very different, with the latter showing a more centrally
concentrated distribution. This could be driven by metallicity gradients in
these undisturbed galaxies, or radial variations in other properties (binarity
or stellar rotation) driving envelope loss in progenitor stars. This result is
not found in 'disturbed' systems, where the distributions of type Ib and Ic
supernovae are consistent.Comment: Accepted for publication in MNRA
The WISSH QSOs project IX. Cold gas content and environment of luminous QSOs at z~2.4-4.7
Sources at the brightest end of QSO luminosity function during the peak epoch
of star formation and black hole accretion (z~2-4, i.e. Cosmic noon) are
privileged sites to study the feeding & feedback cycle of massive galaxies. We
perform the first systematic study of cold gas properties in the most luminous
QSOs, by characterising their host-galaxies and environment. We analyse ALMA,
NOEMA and JVLA observations of FIR continuum, CO and [CII] emission lines in
eight QSOs ( erg/s) from the WISSH sample at
z~2.4-4.7. We report a 100% emission line detection rate and a 80% detection
rate in continuum emission, and we find CO emission to be consistent with the
steepest CO ladders observed so far. Sub-mm data reveal presence of (one or
more) bright companion galaxies around 80% of WISSH QSOs, at projected
distances of 6-130 kpc. We observe a variety of sizes for the molecular gas
reservoirs (1.7-10 kpc), associated with rotating disks with disturbed
kinematics. WISSH QSOs typically show lower CO luminosity and higher star
formation efficiency than FIR matched, z~0-3 main-sequence galaxies, implying
that, given the observed SFR ~170-1100 /yr, molecular gas is converted
into stars on <50 Myr. Most targets show extreme dynamical to black-hole mass
ratios , two orders of magnitude smaller than
local relations. The molecular gas fraction in WISSH hosts is lower by a factor
of ~10-100 than in star forming galaxies with similar . WISSH QSOs undergo
an intense growth phase of both the central SMBH and host-galaxy. They pinpoint
high-density sites where giant galaxies assemble and mergers play a major role
in the build-up of the final host-galaxy mass. The observed low molecular gas
fraction and short depletion timescale are likely due to AGN feedback, as
traced by fast AGN-driven ionised outflows in all our targets.Comment: Accepted for publication in A&
Immune Response to Mycobacterium tuberculosis Infection in the Parietal Pleura of Patients with Tuberculous Pleurisy
The T lymphocyte-mediated immune response to Mycobacterium tuberculosis infection in the parietal pleura of patients with tuberculous pleurisy is unknown. The aim of this study was to investigate the immune response in the parietal pleura of tuberculous pleurisy compared with nonspecific pleuritis. We have measured the numbers of inflammatory cells particularly T-cell subsets (Th1/Th2/Th17/Treg cells) in biopsies of parietal pleura obtained from 14 subjects with proven tuberculous pleurisy compared with a control group of 12 subjects with nonspecific pleuritis. The number of CD3+, CD4+ and CCR4+ cells and the expression of RORC2 mRNA were significantly increased in the tuberculous pleurisy patients compared with the nonspecific pleuritis subjects. The number of toluidine blue+ cells, tryptase+ cells and GATA-3+ cells was significantly decreased in the parietal pleura of patients with tuberculous pleurisy compared with the control group of nonspecific pleuritis subjects. Logistic regression with receiver operator characteristic (ROC) analysis for the three single markers was performed and showed a better performance for GATA-3 with a sensitivity of 75%, a specificity of 100% and an AUC of 0.88. There was no significant difference between the two groups of subjects in the number of CD8, CD68, neutrophil elastase, interferon (IFN)-Îł, STAT4, T-bet, CCR5, CXCR3, CRTH2, STAT6 and FOXP3 positive cells. Elevated CD3, CD4, CCR4 and Th17 cells and decreased mast cells and GATA-3+ cells in the parietal pleura distinguish patients with untreated tuberculous pleurisy from those with nonspecific pleuritis
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