2,433 research outputs found
Ion beam effect on Ge-Se chalcogenide glass films: Non-volatile memory array formation, structural changes and device performance
The conductive bridge non-volatile memory technology is an emerging way to
replace traditional charge based memory devices for future neural networks and
configurable logic applications. An array of the memory devices that fulfills
logic operations must be developed for implementing such architectures. A
scheme to fabricate these arrays, using ion bombardment through a mask, has
been suggested and advanced by us. Performance of the memory devices is
studied, based on the formation of vias and damage accumulation due to the
interactions of Ar+ ions with GexSe1-x (x=0.2, 0.3 and 0.4) chalcogenide
glasses as a function of the ion energy and dose dependence. Blanket films and
devices were created to study the structural changes, surface roughness, and
device performance. Raman Spectroscopy, Atomic Force Microscopy (AFM), Energy
Dispersive X-Ray Spectroscopy (EDS) and electrical measurements expound the Ar+
ions behavior on thin films of GexSe1-x system. Raman studies show that there
is a decrease in area ratio between edge-shared to corner-shared structural
units, revealing occurrence of structural reorganization within the system as a
result of ion/film interaction. AFM results demonstrate a tendency in surface
roughness improvement with increased Ge concentration, after ion bombardment.
EDS results reveal a compositional change in the vias, with a clear tendency of
greater interaction between ions and the Ge atoms, as evidenced by greater
compositional changes in the Ge rich films
CFHT AO Imaging of the CLASS Gravitational Lens System B1359+154
We present adaptive optics imaging of the CLASS gravitational lens system
B1359+154 obtained with the Canada-France-Hawaii Telescope (CFHT) in the
infrared K band. The observations show at least three brightness peaks within
the ring of lensed images, which we identify as emission from multiple lensing
galaxies. The results confirm the suspected compound nature of the lens, as
deduced from preliminary mass modeling. The detection of several additional
nearby galaxies suggests that B1359+154 is lensed by the compact core of a
small galaxy group. We attempted to produce an updated lens model based on the
CFHT observations and new 5-GHz radio data obtained with the MERLIN array, but
there are too few constraints to construct a realistic model at this time. The
uncertainties inherent with modeling compound lenses make B1359+154 a
challenging target for Hubble constant determination through the measurement of
differential time delays. However, time delays will offer additional
constraints to help pin down the mass model. This lens system therefore
presents a unique opportunity to directly measure the mass distribution of a
galaxy group at intermediate redshift.Comment: 12 pages including 3 figures; ApJL accepte
Galaxy bimodality versus stellar mass and environment
We analyse a z<0.1 galaxy sample from the Sloan Digital Sky Survey focusing
on the variation of the galaxy colour bimodality with stellar mass and
projected neighbour density Sigma, and on measurements of the galaxy stellar
mass functions. The characteristic mass increases with environmental density
from about 10^10.6 Msun to 10^10.9 Msun (Kroupa IMF, H_0=70) for Sigma in the
range 0.1--10 per Mpc^2. The galaxy population naturally divides into a red and
blue sequence with the locus of the sequences in colour-mass and
colour-concentration index not varying strongly with environment. The fraction
of galaxies on the red sequence is determined in bins of 0.2 in log Sigma and
log mass (12 x 13 bins). The red fraction f_r generally increases continuously
in both Sigma and mass such that there is a unified relation: f_r =
F(Sigma,mass). Two simple functions are proposed which provide good fits to the
data. These data are compared with analogous quantities in semi-analytical
models based on the Millennium N-body simulation: the Bower et al. (2006) and
Croton et al. (2006) models that incorporate AGN feedback. Both models predict
a strong dependence of the red fraction on stellar mass and environment that is
qualitatively similar to the observations. However, a quantitative comparison
shows that the Bower et al. model is a significantly better match; this appears
to be due to the different treatment of feedback in central galaxies.Comment: 19 pages, 17 figures; accepted by MNRAS, minor change
High-rate, high-fidelity entanglement of qubits across an elementary quantum network
We demonstrate remote entanglement of trapped-ion qubits via a
quantum-optical fiber link with fidelity and rate approaching those of local
operations. Two Sr qubits are entangled via the polarization
degree of freedom of two photons which are coupled by high-numerical-aperture
lenses into single-mode optical fibers and interfere on a beamsplitter. A novel
geometry allows high-efficiency photon collection while maintaining unit
fidelity for ion-photon entanglement. We generate remote Bell pairs with
fidelity at an average rate (success
probability ).Comment: v2 updated to include responses to reviewers, as published in PR
Analysis of the role of predicted RNA secondary structures in Ebola virus replication
AbstractThermodynamic modeling of Ebola viral RNA predicts the formation of RNA stem-loop structures at the 3âČ and 5âČ termini and panhandle structures between the termini of the genomic (or antigenomic) RNAs. Sequence analysis showed a high degree of identity among Ebola Zaire, Sudan, Reston, and Cote dâIvoire subtype viruses in their 3âČ and 5âČ termini (18 nucleotides in length) and within a second region (internal by approximately 20 nucleotides). While base pairing of the two conserved regions could lead to the formation of the base of the putative stem-loop or panhandle structures, the intervening sequence variation altered the predictions for the rest of the structures. Using an in vivo minigenome replication system, we engineered mutations designed to disrupt potential base pairing in the viral RNA termini. Analysis of these variants by screening for enhanced green fluorescent protein reporter expression and by quantitation of minigenomic RNA levels demonstrated that the upper portions of the putative panhandle and 3âČ genomic structures can be destabilized without affecting virus replication
Clustering of loose groups and galaxies from the Perseus--Pisces Survey
We investigate the clustering properties of loose groups in the
Perseus--Pisces redshift Survey (PPS). Previous analyses based on CfA and SSRS
surveys led to apparently contradictory results. We investigate the source of
such discrepancies, finding satisfactory explanations for them. Furthermore, we
find a definite signal of group clustering, whose amplitude exceeds the
amplitude of galaxy clustering (,
for the most significant case; distances are
measured in \hMpc). Groups are identified with the adaptive
Friends--Of--Friends (FOF) algorithms HG (Huchra \& Geller 1982) and NW
(Nolthenius \& White 1987), systematically varying all search parameters.
Correlation strenght is especially sensitive to the sky--link (increasing
for stricter normalization ), and to the (depth \mlim of the) galaxy
data. It is only moderately dependent on the galaxy luminosity function
, while it is almost insensitive to the redshift--link (both to
the normalization and to the scaling recipes HG or NW).Comment: 28 pages (LaTeX aasms4 style) + 5 Postscript figures ; ApJ submitted
on May 4th, 1996; group catalogs available upon request
([email protected]
The XMM Cluster Survey: The Dynamical State of XMMXCS J2215.9-1738 at z=1.457
We present new spectroscopic observations of the most distant X-ray selected
galaxy cluster currently known, XMMXCS J2215.9-1738 at z=1.457, obtained with
the DEIMOS instrument at the W. M. Keck Observatory, and the FORS2 instrument
on the ESO Very Large Telescope. Within the cluster virial radius, as estimated
from the cluster X-ray properties, we increase the number of known
spectroscopic cluster members to 17 objects, and calculate the line of sight
velocity dispersion of the cluster to be 580+/-140 km/s. We find mild evidence
that the velocity distribution of galaxies within the virial radius deviates
from a single Gaussian. We show that the properties of J2215.9-1738 are
inconsistent with self-similar evolution of local X-ray scaling relations,
finding that the cluster is underluminous given its X-ray temperature, and that
the intracluster medium contains ~2-3 times the kinetic energy per unit mass of
the cluster galaxies. These results can perhaps be explained if the cluster is
observed in the aftermath of an off-axis merger. Alternatively, heating of the
intracluster medium through supernovae and/or Active Galactic Nuclei activity,
as is required to explain the observed slope of the local X-ray
luminosity-temperature relation, may be responsible.Comment: 13 pages, 6 figures, accepted for publication in Ap
Global analysis of neutrino masses, mixings and phases: entering the era of leptonic CP violation searches
We perform a global analysis of neutrino oscillation data, including
high-precision measurements of the neutrino mixing angle theta_13 at reactor
experiments, which have confirmed previous indications in favor of theta_13>0.
Recent data presented at the Neutrino 2012 Conference are also included. We
focus on the correlations between theta_13 and the mixing angle theta_23, as
well as between theta_13 and the neutrino CP-violation phase delta. We find
interesting indications for theta_23< pi/4 and possible hints for delta ~ pi,
with no significant difference between normal and inverted mass hierarchy.Comment: Updated version, including recent data released at the Neutrino 2012
Conference. Some references adde
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