6,411 research outputs found
Fermionic entanglement ambiguity in non-inertial frames
We analyse an ambiguity in previous works on entanglement of fermionic fields
in non-inertial frames. This ambiguity, related to the anticommutation
properties of field operators, leads to non-unique results when computing
entanglement measures for the same state. We show that the ambiguity disappears
when we introduce detectors, which are in any case necessary as a means to
probe the field entanglement.Comment: 9 pages, 4 figures. Revtex 4.1, added Journal referenc
Broadening of HO rotational lines by collision with He atoms at low temperature
We report pressure broadening coefficients for the 21 electric-dipole
transitions between the eight lowest rotational levels of ortho-HO and
para-HO molecules by collisions with He at temperatures from 20 to 120 K.
These coefficients are derived from recently published experimental
state-to-state rate coefficients for HO:He inelastic collisions, plus an
elastic contribution from close coupling calculations. The resulting
coefficients are compared to the available experimental data. Mostly due to the
elastic contribution, the pressure broadening coefficients differ much from
line to line, and increase markedly at low temperature. The present results are
meant as a guide for future experiments and astrophysical observations.Comment: 2 figures, 2 table
Mixing Effects in the Crystallization of Supercooled Quantum Binary Liquids
By means of Raman spectroscopy of liquid microjets we have investigated the
crystallization process of supercooled quantum liquid mixtures composed of
parahydrogen (pH) diluted with small amounts of up to 5\% of either neon or
orthodeuterium (oD), and of oD diluted with either Ne or pH. We
show that the introduction of Ne impurities affects the crystallization
kinetics in both the pH-Ne and oD-Ne mixtures in terms of a significant
reduction of the crystal growth rate, similarly to what found in our previous
work on supercooled pH-oD liquid mixtures [M. K\"uhnel et {\it al.},
Phys. Rev. B \textbf{89}, 180506(R) (2014)]. Our experimental results, in
combination with path-integral simulations of the supercooled liquid mixtures,
suggest in particular a correlation between the measured growth rates and the
ratio of the effective particle sizes originating from quantum delocalization
effects. We further show that the crystalline structure of the mixture is also
affected to a large extent by the presence of the Ne impurities, which likely
initiate the freezing process through the formation of Ne crystallites.Comment: 19 pages, 7 figures, submitted to J. Chem. Phy
Sulphur abundance determinations in star-forming regions-I: Ionization Correction Factor
In the present work we used a grid of photoionization models combined with
stellar population synthesis models to derive reliable Ionization Correction
Factors (ICFs) for the sulphur in star-forming regions. These models cover a
large range of nebular parameters and yielding ionic abundances in consonance
with those derived through optical and infrared observational data of
star-forming regions. From our theoretical ICFs, we suggested an {\alpha} value
of 3.27 in the classical Stasinska formulae. We compared the total sulphur
abundance in the gas phase of a large sample of objects by using our
Theoretical ICF and other approaches. In average, the differences between the
determinations via the use of the different ICFs considered are similar to the
uncertainties in the S/H estimations. Nevertheless, we noted that for some
objects it could reach up to about 0.3 dex for the low metallicity regime.
Despite of the large scatter of the points, we found a trend of S/O ratio to
decrease with the metallicity, independently of the ICF used to compute the
sulphur total abundance.Comment: Accepted for publication in MNRAS, 21 pages, 8 figures, 5 table
Management of Virtual Machines on Globus Grids Using GridWay
Virtual machines are a promising technology to over-come some of the problems found in current Grid infras-tructures, like heterogeneity, performance partitioning or application isolation. In this work, we present an straight-forward deployment of virtual machines in Globus Grids. This solution is based on standard services and does not re-quire additional middleware to be installed. Also, we assess the suitability of this deployment in the execution of a high throughput scientific application, the XMM-Newton Scien-tific Analysis System
Fermionic entanglement extinction in non-inertial frames
We study families of fermionic field states in non-inertial frames which show
no entanglement survival in the infinite acceleration limit. We generalise some
recent results where some particular examples of such states where found. We
analyse the abundance and characteristics of the states showing this behaviour
and discuss its relation with the statistics of the field. We also consider the
phenomenon beyond the single mode approximation.Comment: 6 pages, 4 figures, revtex4-
The extended HeII4686-emitting region in IZw18 unveiled: clues for peculiar ionizing sources
New integral field spectroscopy has been obtained for IZw18, the nearby
lowest-metallicity galaxy considered our best local analog of systems forming
at high-z. Here we report the spatially resolved spectral map of the nebular
HeII4686 emission in IZw18, from which we derived for the first time its total
HeII-ionizing flux. Nebular HeII emission implies the existence of a hard
radiation field. HeII-emitters are observed to be more frequent among high-z
galaxies than for local objects. So investigating the HeII-ionizing source(s)
in IZw18 may reveal the ionization processes at high-z. HeII emission in
star-forming galaxies, has been suggested to be mainly associated with
Wolf-Rayet stars (WRs), but WRs cannot satisfactorily explain the
HeII-ionization at all times, in particular at lowest metallicities. Shocks
from supernova remnants, or X-ray binaries, have been proposed as additional
potential sources of HeII-ionizing photons. Our data indicate that conventional
HeII-ionizing sources (WRs, shocks, X-ray binaries) are not sufficient to
explain the observed nebular HeII4686 emission in IZw18. We find that the
HeII-ionizing radiation expected from models for either low-metallicity
super-massive O stars or rotating metal-free stars could account for the
HeII-ionization budget measured, while only the latter models could explain the
highest values of HeII4686/Hbeta observed. The presence of such peculiar stars
in IZw18 is suggestive and further investigation in this regard is needed. This
letter highlights that some of the clues of the early Universe can be found
here in our cosmic backyard.Comment: 6 pages, 3 figures. Accepted for publication in ApJ Letter
Localized starbursts in dwarf galaxies produced by impact of low metallicity cosmic gas clouds
Models of galaxy formation predict that gas accretion from the cosmic web is
a primary driver of star formation over cosmic history. Except in very dense
environments where galaxy mergers are also important, model galaxies feed from
cold streams of gas from the web that penetrate their dark matter haloes.
Although these predictions are unambiguous, the observational support has been
indirect so far. Here we report spectroscopic evidence for this process in
extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of
localized starbursts associated with gas having low metallicity. Detailed
abundance analyses based on Gran Telescopio Canarias (GTC) optical spectra of
ten XMPs show that the galaxy hosts have metallicities around 60 % solar on
average, while the large star-forming regions that dominate their integrated
light have low metallicities of some 6 % solar. Because gas mixes azimuthally
in a rotation timescale (a few hundred Myr), the observed metallicity
inhomogeneities are only possible if the metal-poor gas fell onto the disk
recently. We analyze several possibilities for the origin of the metal-poor
gas, favoring the metal-poor gas infall predicted by numerical models. If this
interpretation is correct, XMPs trace the cosmic web gas in their surroundings,
making them probes to examine its properties.Comment: Accepted for publication in ApJ
1.5V fully programmable CMOS Membership Function Generator Circuit with proportional DC-voltage control
A Membership Function Generator Circuit (MFGC) with bias supply of 1.5 Volts and independent DC-voltage programmable functionalities is presented. The realization is based on a programmable differential current mirror and three compact voltage-to-current converters, allowing continuous and quasi-linear adjustment of the center position, height, width and slopes of the triangular/trapezoidal output waveforms. HSPICE simulation results of the proposed circuit using the parameters of a double-poly, three metal layers, 0.5 μm CMOS technology validate the functionality of the proposed architecture, which exhibits a maximum deviation of the linearity in the programmability of 7 %
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