4,643 research outputs found
Physical parameters of the Cen X-3 system
Photographic spectra of Cen X-3 show that the primary star has a spectral type near 06.5 with weak, variable emission at wavelength 4640 and 4686. No orbital motion of the emission or absorption lines is detected; for the latter the upper limit is approximately + or - 50 km/s. Analysis of the available data indicates that the primary is a factor of 2-3 less massive than expected from normal evolutionary models while the X-ray source has a solar mass near 1.5
A fast stroboscopic spectral method for rotating systems in numerical relativity
We present a numerical technique for solving evolution equations, as the wave
equation, in the description of rotating astrophysical compact objects in
comoving coordinates, which avoids the problems associated with the light
cylinder. The technique implements a fast spectral matching between two domains
in relative rotation: an inner spherical domain, comoving with the sources and
lying strictly inside the light cylinder, and an outer inertial spherical
shell. Even though the emphasis is placed on spectral techniques, the matching
is independent of the specific manner in which equations are solved inside each
domain, and can be adapted to different schemes. We illustrate the strategy
with some simple but representative examples.Comment: 16 pages, 15 figure
Retrieval of Infotainment System Artifacts from Vehicles Using iVe
The analysis of mobile devices and hard drives has been the focus of the digital forensics world for years, but there is another source of potential evidence not often considered: vehicles. Many of today’s “connected cars” have systems that function like computers, storing information they process including user data from devices synced to the system. There has been little to no research done regarding what types of user artifacts can be found on the system, how long these artifacts remain, whether or not the user can remove those artifacts, and whether certain systems provide more information than others. For this study, two different makes and models of vehicle infotainment systems were used for data acquisition: a Uconnect® system and a Toyota™ Extension Box. It was found that the Toyota™ system provided a significant amount of user information (contacts, call logs, media file information, and locations), while the Uconnect® system provided only locations. This indicates valuable user data can be obtained in this manner
Time-Series Photometry of M67: W UMa Systems, Blue Stragglers, and Related Systems
We present an analysis of over 2200 V images taken on 14 nights at the Mt.
Laguna 1 m telescope of the open cluster M67. Our observations overlap but
extend beyond the field analyzed by Gilliland et al. (1991), and complement
data recently published by van den Berg et al. (2002) and Stassun et al.
(2002). We show variability in the light curves of all 4 of the known W UMa
variables on timescales ranging from a day to decades (for AH Cnc). We have
modeled the light curve of AH Cnc, and the total eclipses allow us to determine
q = 0.16 +0.03/-0.02 and i = 86 +4/-8 degrees. The position of this system near
the turnoff of M67 makes it useful for constraining the turnoff mass for the
cluster. We have also detected two unusual features in the light curve of AH
Cnc that may be caused by prominences. We have also monitored cluster blue
stragglers for variability, and we present evidence hinting at low level
variations in the stragglers S752, S968, and S1263, and we place limits on the
variability of a number of other cluster blue stragglers. Finally, we provide
photometry of the sub-subgiant branch star S1063 showing variability on
timescales similar to the orbital period, while the ``red straggler'' S1040
shows evidence of an unexplained drop in brightness at phases corresponding to
the passage of the white dwarf in front of the giant.Comment: 44 pages, 16 figures, AASTeX, accepted for A
The density and pressure of helium nano-bubbles encapsulated in silicon
The excitation in confined and compressed helium atoms in
either the bulk material or encapsulated in a bubble is shifted to energies
higher than that in the free atom. For bulk helium, the energy shifts predicted
from non-empirical electronic structure computations are in excellent agreement
with the experimentally determined values. However, there are significant
discrepancies both between the results of experiments on different bubbles and
between these and the well established descriptions of the bulk. A critique is
presented of previous attempts to determine the densities in bubbles by
measuring the intensities of the electrons inelastically scattered in STEM
experiments. The reported densities are untrustworthy because it was assumed
that the cross section for inelastic electron scattering was the same as that
of a free atom whilst it is now known that this property is greatly enhanced
for atoms confined at significant pressures.
It is shown how experimental measurements of bubbles can be combined with
data on the bulk using a graphical method to determine whether the behavior of
an encapsulated guest differs from that in the bulk material. Experimental
electron energy loss data from an earlier study of helium encapsulated in
silicon is reanalyzed using this new method to show that the properties of the
helium in these bubbles do not differ significantly from those in the bulk
thereby enabling the densities in the bubbles to be determined. These enable
the bubble pressures to be deduced from a well established experimentally
derived equation of state. It is shown that the errors of up to 80% in the
incorrectly determined densities are greatly magnified in the predicted
pressures which can be too large by factors of over seven. This has major
practical implications for the study of radiation damage of materials exposed
to particle bombardment
Recovery of the X-Ray Transient QX Nor (=X1608-52) in Outburst and Quiescence
We present optical and near-IR observations of QX Nor, the counterpart to the
recurrent soft X-ray transient X1608-52, after its reappearance following the
X-ray outburst in February 1996. The object has been seen only once before,
during an X-ray outburst in 1977. Data from 3-5 months after the outburst show
the counterpart at a mean magnitude of R=20.2 and variable on timescales of
days. A comparison with identical observations in 1995 implies that the object
has brightened by at least 1.8 mag in R following the X-ray outburst. We also
detected QX Nor in the IR in both quiescence and outburst. A faint source is
visible in the J but not the R band in May 1995. These first observations in
the quiescent state yield magnitudes and colors consistent with optical
emission from a low mass companion in the binary system, as is true in other
soft X-ray transients.Comment: 10 pages including 4 figures and 2 tables; Uses AASTeX 4.0; Accepted
for publication in The Astrophysical Journal, Volume 485, August 20, 199
Complete mapping of mutations to the SARS-CoV-2 spike receptor-binding domain that escape antibody recognition
Antibodies targeting the SARS-CoV-2 spike receptor-binding domain (RBD) are being developed as therapeutics and are a major contributor to neutralizing antibody responses elicited by infection. Here, we describe a deep mutational scanning method to map how all amino-acid mutations in the RBD affect antibody binding and apply this method to 10 human monoclonal antibodies. The escape mutations cluster on several surfaces of the RBD that broadly correspond to structurally defined antibody epitopes. However, even antibodies targeting the same surface often have distinct escape mutations. The complete escape maps predict which mutations are selected during viral growth in the presence of single antibodies. They further enable the design of escape-resistant antibody cocktails-including cocktails of antibodies that compete for binding to the same RBD surface but have different escape mutations. Therefore, complete escape-mutation maps enable rational design of antibody therapeutics and assessment of the antigenic consequences of viral evolution
Quasistationary binary inspiral. I. Einstein equations for the two Killing vector spacetime
The geometry of two infinitely long lines of mass moving in a fixed circular
orbit is considered as a toy model for the inspiral of a binary system of
compact objects due to gravitational radiation. The two Killing fields in the
toy model are used, according to a formalism introduced by Geroch, to describe
the geometry entirely in terms of a set of tensor fields on the two-manifold of
Killing vector orbits. Geroch's derivation of the Einstein equations in this
formalism is streamlined and generalized. The explicit Einstein equations for
the toy model spacetime are derived in terms of the degrees of freedom which
remain after a particular choice of gauge.Comment: 37 pages, REVTeX, one PostScript Figure included with epsfig; minor
formatting changes and copyright notice added for journal publicatio
Modeling the decoherence of spacetime
The question of whether unobserved short-wavelength modes of the
gravitational field can induce decoherence in the long-wavelength modes (``the
decoherence of spacetime'') is addressed using a simplified model of
perturbative general relativity, related to the Nordstrom-Einstein-Fokker
theory, where the metric is assumed to be conformally flat. For some
long-wavelength coarse grainings, the Feynman-Vernon influence phase is found
to be effective at suppressing the off-diagonal elements of the decoherence
functional. The requirement that the short-wavelength modes be in a
sufficiently high-temperature state places limits on the applicability of this
perturbative approach.Comment: 38 pages, REVTeX; 7 diagrams and 6 PostScript figures included via
epsfig. Final cosmetic changes made at publicatio
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