345 research outputs found
Origin of G Magnetic Fields in the Central Engine of Gamma Ray Bursts
Various authors have suggested that the gamma-ray burst (GRB) central engine
is a rapidly rotating, strongly magnetized, G) compact
object. The strong magnetic field can accelerate and collimate the relativistic
flow and the rotation of the compact object can be the energy source of the
GRB. The major problem in this scenario is the difficulty of finding an
astrophysical mechanism for obtaining such intense fields. Whereas, in
principle, a neutron star could maintain such strong fields, it is difficult to
justify a scenario for their creation. If the compact object is a black hole,
the problem is more difficult since, according to general relativity it has "no
hair" (i.e., no magnetic field). Schuster, Blackett, Pauli, and others have
suggested that a rotating neutral body can create a magnetic field by
non-minimal gravitational-electromagnetic coupling (NMGEC). The
Schuster-Blackett form of NMGEC was obtained from the Mikhail and Wanas's
tetrad theory of gravitation (MW). We call the general theory NMGEC-MW.
We investigate here the possible origin of the intense magnetic fields G in GRBs by NMGEC-MW. Whereas these fields are difficult to
explain astrophysically, we find that they are easily explained by NMGEC-MW. It
not only explains the origin of the G fields when the
compact object is a neutron star, but also when it is a black hole.Comment: 9 pages, accepted for publication in JCA
Evolving Lorentzian Wormholes
Evolving Lorentzian wormholes with the required matter satisfying the Energy
conditions are discussed. Several different scale factors are used and the
corresponding consequences derived. The effect of extra, decaying (in time)
compact dimensions present in the wormhole metric is also explored and certain
interesting conclusions are derived for the cases of exponential and
Kaluza--Klein inflation.Comment: 10 pages( RevTex, Twocolumn format), Two figures available on request
from the first author. transmission errors corrected
Fate of the first traversible wormhole: black-hole collapse or inflationary expansion
We study numerically the stability of Morris & Thorne's first traversible
wormhole, shown previously by Ellis to be a solution for a massless ghost
Klein-Gordon field. Our code uses a dual-null formulation for spherically
symmetric space-time integration, and the numerical range covers both universes
connected by the wormhole. We observe that the wormhole is unstable against
Gaussian pulses in either exotic or normal massless Klein-Gordon fields. The
wormhole throat suffers a bifurcation of horizons and either explodes to form
an inflationary universe or collapses to a black hole, if the total input
energy is respectively negative or positive. As the perturbations become small
in total energy, there is evidence for critical solutions with a certain
black-hole mass or Hubble constant. The collapse time is related to the initial
energy with an apparently universal critical exponent. For normal matter, such
as a traveller traversing the wormhole, collapse to a black hole always
results. However, carefully balanced additional ghost radiation can maintain
the wormhole for a limited time. The black-hole formation from a traversible
wormhole confirms the recently proposed duality between them. The inflationary
case provides a mechanism for inflating, to macroscopic size, a Planck-sized
wormhole formed in space-time foam.Comment: 10 pages, RevTeX4, 11 figures, epsf.st
Static and dynamic traversable wormhole geometries satisfying the Ford-Roman constraints
It was shown by Ford and Roman in 1996 that quantum field theory severely
constrains wormhole geometries on a macroscopic scale. The first part of this
paper discusses a wide class of wormhole solutions that meet these constraints.
The type of shape function used is essentially generic. The constraints are
then discussed in conjunction with various redshift functions. Violations of
the weak energy condition and traversability criteria are also considered. The
second part of the paper analyzes analogous time-dependent (dynamic) wormholes
with the aid of differential forms. It is shown that a violation of the weak
energy condition is not likely to be avoidable even temporarily.Comment: 16 pages AMSTe
Recommended from our members
Evaluation of the capabilities of the Hanford Reservation and Envirocare of Utah for disposal of potentially problematic mixed low-level waste streams
The US Department of Energy`s (DOE) Mixed Waste Focus Area is developing a program to address and resolve issues associated with final waste form performance in treating and disposing of DOE`s mixed low-level waste (MLLW) inventory. A key issue for the program is identifying MLLW streams that may be problematic for disposal. Previous reports have quantified and qualified the capabilities of fifteen DOE sites for MLLW disposal and provided volume and radionuclide concentration estimates for treated MLLW based on the DOE inventory. Scoping-level analyses indicated that 101 waste streams identified in this report (approximately 6,250 m{sup 3} of the estimated total treated MLLW) had radionuclide concentrations that may make their disposal problematic. The radionuclide concentrations of these waste streams were compared with the waste acceptance criteria (WAC) for a DOE disposal facility at Hanford and for Envirocare`s commercial disposal facility for MLLW in Utah. Of the treated MLLW volume identified as potentially problematic, about 100 m{sup 3} exceeds the WAC for disposal at Hanford, and about 4,500 m{sup 3} exceeds the WAC for disposal at Envirocare. Approximately 7% of DOE`s total MLLW inventory has not been sufficiently characterized to identify a treatment process for the waste and was not included in the analysis. In addition, of the total treated MLLW volume, about 30% was associated with waste streams that did not have radionuclide concentration data and could not be included in the determination of potentially problematic waste streams
Linking the trans-Planckian and the information loss problems in black hole physics
The trans-Planckian and information loss problems are usually discussed in
the literature as separate issues concerning the nature of Hawking radiation.
Here we instead argue that they are intimately linked, and can be understood as
"two sides of the same coin" once it is accepted that general relativity is an
effective field theory.Comment: 10 pages, 2 figures. Replaced with the version to be published in
General Relativity and Gravitatio
-Dimensional Lorentzian Wormholes in an Expanding Cosmological Background
We discuss -dimensional dynamical wormholes in an evolving
cosmological background with a throat expanding with time. These solutions are
examined in the general relativity framework. A linear relation between
diagonal elements of an anisotropic energy-momentum tensor is used to obtain
the solutions. The energy-momentum tensor elements approach the vacuum case
when we are far from the central object for one class of solutions. Finally, we
discuss the energy-momentum tensor which supports this geometry, taking into
account the energy conditions .Comment: 12 pages, 14 figures, references added, to appear in Astophysics and
Space Scienc
Gravitational radiation from gamma-ray bursts as observational opportunities for LIGO and VIRGO
Gamma-ray bursts are believed to originate in core-collapse of massive stars.
This produces an active nucleus containing a rapidly rotating Kerr black hole
surrounded by a uniformly magnetized torus represented by two counter-oriented
current rings. We quantify black hole spin-interactions with the torus and
charged particles along open magnetic flux-tubes subtended by the event
horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of
frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with
GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii)
aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich
et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al.
2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating
LIGO/Virgo detectors enables searches for nearby events and their spectral
closure density 6e-9 around 250Hz in the stochastic background radiation in
gravitational waves. At current sensitivity, LIGO-Hanford may place an upper
bound around 150MSolar in GRB030329. Detection of Egw thus provides a method
for identifying Kerr black holes by calorimetry.Comment: to appear in PRD, 49
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
Patient-reported treatment toxicity and adverse events in Black and White women receiving chemotherapy for early breast cancer
Purpose: It is not known whether chemotherapy-related symptom experiences differ between Black and White women with early breast cancer (Stage I–III) receiving current chemotherapy regimens and, in turn, influences dose delay, dose reduction, early treatment discontinuation, or hospitalization. Methods: Patients self-reported their race and provided symptom reports for 17 major side effects throughout chemotherapy. Toxicity and adverse events were analyzed separately for anthracycline and non-anthracycline regimens. Fisher’s exact tests and two-sample t-tests compared baseline patient characteristics. Modified Poisson regression estimated relative risks of moderate, severe, or very severe (MSVS) symptom severity, and chemotherapy-related adverse events.Please check and confirm that the authors and their respective affiliations have been correctly identified and amend if necessary.no changes Results: In 294 patients accrued between 2014 and 2020, mean age was 58 (SD13) and 23% were Black. For anthracycline-based regimens, the only significant difference in MSVS symptoms was in lymphedema (41% Black vs 20% White, p =.04) after controlling for axillary surgery. For non-anthracycline regimens, the only significant difference was MSVS peripheral neuropathy (41% Blacks vs. 23% White) after controlling for taxane type (p =.05) and diabetes (p =.05). For all other symptoms, severity scores were similar. Dose reduction differed significantly for non-anthracycline regimens (49% Black vs. 25% White, p =.01), but not for anthracycline regimens or in dose delay, early treatment discontinuation, or hospitalization for either regimen. Conclusion: Except for lymphedema and peripheral neuropathy, Black and White patients reported similar symptom severity during adjuvant chemotherapy. Dose reductions in Black patients were more common for non-anthracycline regimens. In this sample, there were minimal differences in patient-reported symptoms and other adverse outcomes in Black versus White patients
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