2,955 research outputs found
Summation and transformation formulas for elliptic hypergeometric series
Using matrix inversion and determinant evaluation techniques we prove several
summation and transformation formulas for terminating, balanced,
very-well-poised, elliptic hypergeometric series.Comment: 21 pages, AMS-LaTe
Transition from a phase-segregated state to single-phase incommensurate sodium ordering in Na_xCoO_2 with x \approx 0.53
Synchrotron X-ray diffraction investigations of two single crystals of
Na_xCoO_2 from different batches with composition x = 0.525-0.530 reveal
homogeneous incommensurate sodium ordering with propagation vector (0.53 0.53
0) at room-temperature. The incommensurate (qq0) superstructure exists between
220 K and 430 K. The value of q varies between q = 0.514 and 0.529, showing a
broad plateau at the latter value between 260 K and 360 K. On cooling, unusual
reversible phase segregation into two volume fractions is observed. Below 220
K, one volume fraction shows the well-known commensurate orthorhombic x = 0.50
superstructure, while a second volume fraction with x = 0.55 exhibits another
commensurate superstructure, presumably with a 6a x 6a x c hexagonal supercell.
We argue that the commensurate-to-incommensurate transition is an intrinsic
feature of samples with Na concentrations x = 0.5 + d with d ~ 0.03.Comment: Corrected/improved versio
Vector Theory of Gravity
We proposed a gravitation theory based on an analogy with electrodynamics on
the basis of a vector field. For the first time, to calculate the basic
gravitational effects in the framework of a vector theory of gravity, we use a
Lagrangian written with gravitational radiation neglected and generalized to
the case of ultra-relativistic speeds. This allows us to accurately calculate
the values of all three major gravity experiments: the values of the perihelion
shift of Mercury, the light deflection angle in the gravity field of the Sun
and the value of radar echo delay. The calculated values coincide with the
observed ones. It is shown that, in this theory, there exists a model of an
expanding Universe.Comment: 9 page
Multi-Wavelength Properties of the Type IIb SN 2008ax
We present the UV, optical, X-ray, and radio properties of the Type IIb SN
2008ax discovered in NGC 4490. The observations in the UV are one of the
earliest of a Type IIb supernova (SN). On approximately day four after the
explosion, a dramatic upturn in the u and uvw1 (lambda_c = 2600 Angstroms)
light curves occurred after an initial rapid decline which is attributed to
adiabatic cooling after the initial shock breakout. This rapid decline and
upturn is reminiscent of the Type IIb SN 1993J on day six after the explosion.
Optical/near-IR spectra taken around the peak reveal prominent H-alpha, HeI,
and CaII absorption lines. A fading X-ray source is also located at the
position of SN 2008ax, implying an interaction of the SN shock with the
surrounding circumstellar material and a mass-loss rate of the progenitor of
M_dot = (9+/-3)x10^-6 solar masses per year. The unusual time evolution (14
days) of the 6 cm peak radio luminosity provides further evidence that the
mass-loss rate is low. Combining the UV, optical, X-ray, and radio data with
models of helium exploding stars implies the progenitor of SN 2008ax was an
unmixed star in an interacting-binary. Modeling of the SN light curve suggests
a kinetic energy (E_k) of 0.5x10^51 ergs, an ejecta mass (M_ej) of 2.9 solar
masses, and a nickel mass (M_Ni) of 0.06 solar masses.Comment: Accepted to ApJ Letters, 14 pages, 3 figures, 2 table
Size of the Vela Pulsar's Radio Emission Region: 500 km
We use interstellar scattering of the Vela pulsar to determine the size of
its emission region. From interferometric phase variations on short baselines,
we find that radio-wave scattering broadens the source by 3.4+/-0.3
milliarcseconds along the major axis at position angle 81+/-3 degrees. The
ratio of minor axis to major axis is 0.51+/-0.03. Comparison of angular and
temporal broadening indicates that the scattering material lies in the Vela-X
supernova remnant surrounding the pulsar. From the modulation of the pulsar's
scintillation on very short baselines, we infer a size of 500 km for the
pulsar's emission region. We suggest that radio-wave refraction within the
pulsar's magnetosphere may plausibly explain this size.Comment: 14 pages, includes 2 figures. Also available at:
http://charm.physics.ucsb.edu:80/people/cgwinn/cgwinn_group/cgwinn_group.htm
Probing Kilonova Ejecta Properties Using a Catalog of Short Gamma-Ray Burst Observations
The discovery of GW170817 and GRB 170817A in tandem with AT 2017gfo cemented
the connection between neutron star mergers, short gamma-ray bursts (GRBs), and
kilonovae. To investigate short GRB observations in the context of diverse
kilonova behavior, we present a comprehensive optical and near-infrared (NIR)
catalog of 85 bursts discovered over 2005-2020 on timescales of
days. The sample includes previously unpublished observations of 23 bursts, and
encompasses both detections and deep upper limits. We identify 11.8% and 15.3%
of short GRBs in our catalog with upper limits that probe luminosities lower
than those of AT 2017gfo and a fiducial NSBH kilonovae model (for pole-on
orientations), respectively. We quantify the ejecta masses allowed by the
deepest limits in our catalog, constraining blue and `extremely blue' kilonova
components of 14.1% of bursts to . The
sample of short GRBs is not particularly constraining for red kilonova
components. Motivated by the large catalog as well as model predictions of
diverse kilonova behavior, we investigate altered search strategies for future
follow-up to short GRBs. We find that ground-based optical and NIR observations
on timescales of days can play a significant role in constraining
more diverse outcomes. We expect future short GRB follow up efforts, such as
from the {\it James Webb Space Telescope}, to expand the reach of kilonova
detectability to redshifts of .Comment: 33 pages, 7 figures, 3 tables. Submitted to Ap
Childhood Brain Tumours: Associations With Parental Occupational Exposure to Solvents
Background: Parental occupational exposures have been associated with childhood brain tumours (CBT), but results are inconsistent. Few studies have studied CBT risk and parental solvent exposure, suggesting a possible association. We examined the association between CBT and parental occupational exposure to solvents in a case–control study.Methods: Parents of 306 cases and 950 controls completed detailed occupational histories. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated for both maternal and paternal exposure to benzene, other aromatics, aliphatics and chlorinated solvents in key time periods relative to the birth of their child. Adjustments were made for matching variables (child’s age, sex and state of residence), best parental education and occupational exposure to diesel exhaust.Results: An increased risk of CBT was observed with maternal occupational exposures to chlorinated solvents (OR=8.59, 95% CI 0.94–78.9) any time before birth. Paternal exposure to solvents in the year before conception was associated with an increased CBT risk: OR=1.55 (95% CI 0.99–2.43). This increased risk appeared to be mainly attributable to exposure to aromatic solvents: OR=2.72 (95% CI 0.94–7.86) for benzene and OR=1.76 (95% CI 1.10–2.82) for other aromatics.Conclusions: Our results indicate that parental occupational exposures to solvents may be related to an increased risk of CBT
Media justice: Madeleine McCann, intermediatization and "trial by media" in the British press
Three-year-old Madeleine McCann disappeared on 3 May 2007 from a holiday apartment in Portugal. Over five years and multiple investigations that failed to solve this abducted child case, Madeleine and her parents were subject to a process of relentless ‘intermediatization’. Across 24–7 news coverage, websites, documentaries, films, YouTube videos, books, magazines, music and artworks, Madeleine was a mediagenic image of innocence and a lucrative story. In contrast to Madeleine’s media sacralization, the representation of her parents, Kate and Gerry McCann, fluctuated between periods of vociferous support and prolonged and libellous ‘trial by media’. This article analyses how the global intermediatization of the ‘Maddie Mystery’ fed into and fuelled the ‘trial by media’ of Kate and Gerry McCann in the UK press. Our theorization of ‘trial by media’ is developed and refined through considering its legal limitations in an era of ‘attack journalism’ and unprecedented official UK inquiries into press misconduct and criminality
Second order perturbations of a zero-pressure cosmological medium: Proofs of the relativistic-Newtonian correspondence
The dynamic world model and its linear perturbations were first studied in
Einstein's gravity. In the system without pressure the relativistic equations
coincide exactly with the later known ones in Newton's gravity. Here we prove
that, except for the gravitational wave contribution, even to the second-order
perturbations, equations for the relativistic irrotational zero-pressure fluid
in a flat Friedmann background coincide exactly with the previously known
Newtonian equations. Thus, to the second order, we correctly identify the
relativistic density and velocity perturbation variables, and we expand the
range of applicability of the Newtonian medium without pressure to all
cosmological scales including the super-horizon scale. In the relativistic
analyses, however, we do not have a relativistic variable which corresponds to
the Newtonian potential to the second order. Mixed usage of different gauge
conditions is useful to make such proofs and to examine the result with
perspective. We also present the gravitational wave equation to the second
order. Since our correspondence includes the cosmological constant, our results
are relevant to currently favoured cosmology. Our result has an important
practical implication that one can use the large-scale Newtonian numerical
simulation more reliably even as the simulation scale approaches near horizon.Comment: 10 pages, no figur
The Vela Pulsar and its Synchrotron Nebula
(Abridged) We present high-resolution Chandra X-ray observations of PSR
B0833-45, the 89 ms pulsar associated with the Vela supernova remnant. We have
acquired two observations separated by one month to search for changes in the
pulsar and its environment following an extreme glitch in its rotation
frequency. We find a well-resolved nebula with a toroidal morphology remarkably
similar to that observed in the Crab Nebula, along with an axial Crab-like jet.
Between the two observations the flux from the pulsar is found to be steady to
within 0.75%; the 3 sigma limit on the fractional increase in the pulsar's
X-ray flux is < ~10^-5 of the inferred glitch energy. We use this limit to
constrain parameters of glitch models and neutron star structure. We do find a
significant increase in the flux of the nebula's outer arc; if associated with
the glitch, the inferred propagation velocity is > 0.7c, similar to that seen
in the brightening of the Crab Nebula wisps. We propose an explanation for the
X-ray structure of the Vela synchrotron nebula based on a model originally
developed for the Crab Nebula. In a departure from the Crab model, the
magnetization parameter "sigma" of the Vela pulsar wind is allowed to be of
order unity; this is consistent with the simplest MHD transport of magnetic
field from the pulsar to the nebula, where B < 4 X 10^-4 G. We review effects
that may enhance the probability of alignment between the spin axis and space
velocity of a pulsar, and speculate that short-period, slowly moving pulsars
are just the ones best-suited to producing synchrotron nebulae with such
aligned structures.Comment: 16 pages with 8 figures, uses LaTex, emulateapj.sty. Refereed
version. To appear in The Astrophysical Journa
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