6,700 research outputs found
Lower limit on the entropy of black holes as inferred from gravitational wave observations
Black hole (BH) thermodynamics was established by Bekenstein and Hawking, who
made abstract theoretical arguments about the second law of thermodynamics and
quantum theory in curved spacetime respectively. Testing these ideas
experimentally has, so far, been impractical because the putative flux of
Hawking radiation from astrophysical BHs is too small to be distinguished from
the rest of the hot environment. Here, it is proposed that the spectrum of
emitted gravitational waves (GWs) after the merger of two BHs, in particular
the spectrum of GW150914, can be used to infer a lower limit on the magnitude
of the entropy of the post-merger BH. This lower bound is potentially
significant as it could be of the same order as the Bekenstein-Hawking entropy.
To infer this limit, we first assume that the result of the merger is an
ultracompact object with an external geometry which is Schwarzschild or Kerr,
but with an outer surface which is capable of reflecting in-falling GWs rather
than fully absorbing them. If the absence of deviations from the predictions of
general relativity in detected GW signals will be verified, we will then obtain
a bound on the minimal redshift factor of GWs that emerge from the vicinity of
the object's surface. This lack of deviations would also mean that the remnant
of the merger has to have a strongly absorbing surface and must then be a BH
for all practical purposes. We conclude that a relationship between the minimal
redshift factor and the BH entropy, which was first proposed by 't Hooft, could
then be used to set a lower bound on the entropy of the post-merger BH.Comment: Corrected error in estimation of current bounds on the entropy.
Improved discussion of energy stored in echoes, V3 replaced to match
published version, clarifications and explanations adde
Probing the size of extra dimension with gravitational wave astronomy
In Randall-Sundrum II (RS-II) braneworld model, it has been conjectured
according to the AdS/CFT correspondence that brane-localized black hole (BH)
larger than the bulk AdS curvature scale cannot be static, and it is
dual to a four dimensional BH emitting the Hawking radiation through some
quantum fields. In this scenario, the number of the quantum field species is so
large that this radiation changes the orbital evolution of a BH binary. We
derived the correction to the gravitational waveform phase due to this effect
and estimated the upper bounds on by performing Fisher analyses. We
found that DECIGO/BBO can put a stronger constraint than the current table-top
result by detecting gravitational waves from small mass BH/BH and BH/neutron
star (NS) binaries. Furthermore, DECIGO/BBO is expected to detect 10 BH/NS
binaries per year. Taking this advantage, we found that DECIGO/BBO can actually
measure down to m for 5 year observation if we know that
binaries are circular a priori. This is about 40 times smaller than the upper
bound obtained from the table-top experiment. On the other hand, when we take
eccentricities into binary parameters, the detection limit weakens to m due to strong degeneracies between and eccentricities. We also
derived the upper bound on from the expected detection number of extreme
mass ratio inspirals (EMRIs) with LISA and BH/NS binaries with DECIGO/BBO,
extending the discussion made recently by McWilliams. We found that these less
robust constraints are weaker than the ones from phase differences.Comment: 19 pages, 10 figures. Published in PRD, typos corrected, references
and footnotes adde
First principles investigation of transition-metal doped group-IV semiconductors: RY (R=Cr, Mn, Fe; Y=Si, Ge)
A number of transition-metal (TM) doped group-IV semiconductors,
RY (R=Cr, Mn and Fe; Y=Si, Ge), have been studied by the first
principles calculations. The obtained results show that antiferromagnetic (AFM)
order is energetically more favored than ferromagnetic (FM) order in Cr-doped
Ge and Si with =0.03125 and 0.0625. In 6.25% Fe-doped Ge, FM interaction
dominates in all range of the R-R distances while for Fe-doped Ge at 3.125% and
Fe-doped Si at both concentrations of 3.125% and 6.25%, only in a short R-R
range can the FM states exist. In the Mn-doped case, the RKKY-like mechanism
seems to be suitable for the Ge host matrix, while for the Mn-doped Si, the
short-range AFM interaction competes with the long-range FM interaction. The
different origin of the magnetic orders in these diluted magnetic
semiconductors (DMSs) makes the microscopic mechanism of the ferromagnetism in
the DMSs more complex and attractive.Comment: 14 pages, 2 figures, 6 table
Inhibition of I κ B-α phosphorylation at serine and tyrosine acts independently on sensitization to DNA damaging agents in human glioma cells
Molecular mechanisms and/or intrinsic factors controlling cellular radiosensitivity are not fully understood in mammalian cells. The recent studies have suggested that nuclear factor κB (NF-κB) is one of such factors. The activation and regulation of NF-κB are tightly controlled by IκB-α, a cellular inhibitory protein of NF-κB. Most importantly, phosphorylation regulates activity of the inhibitor IκB-α, which sequesters NF-κB in the cytosol. Two different pathways for the phosphorylation of IκB-α are demonstrated, such as serine (at residues 32 and 36) and tyrosine (at residue 42) phosphorylations. To assess a role of the transcription factor, NF-κB, on cellular sensitivity to DNA damaging agents, we constructed three different types of expression plasmids, i.e. S-IκB (mutations at residues 32 and 36), Y-IκB (mutation at residue 42) and SY-IκB (mutations at residues 32, 36 and 42). The cell clones expressing S-IκB and Y-IκB proteins became sensitive to X-rays as compared with the parental and vector-transfected cells. The cell clones expressing SY-IκB were further radiosensitive. By the treatment with herbimycin A, an inhibitor of phosphorylation, the X-ray sensitivity of cells expressing SY-IκB did not change, while that of the cells expressing S-IκB and Y-IκB and the parental cells was enhanced. Change in the sensitivity to adriamycin and UV in those clones was very similar to that in the X-ray sensitivity. The inhibition of IκB-α phosphorylation at serine and tyrosine acts independently on the sensitization to X-rays, adriamycin and UV. These findings suggest that the transcriptional activation induced by NF-κB may play a role in the DNA damage repair. The present study proposes a possibility that the inactivation of NF-κB by inhibition of both serine and tyrosine phosphorylations may be useful for the treatment of cancer in radio- and chemotherapies. © 2000 Cancer Research Campaig
Influence of Charge and Energy Imbalances on the Tunneling Current through a Superconductor-Normal Metal Junction
We consider quasiparticle charge and energy imbalances in a thin
superconductor weakly coupled with two normal-metal electrodes via tunnel
junctions at low temperatures. Charge and energy imbalances, which can be
created by injecting quasiparticles at one junction, induce excess tunneling
current at the other junction. We numerically obtain
as a function of the bias voltage across the detection junction.
We show that at the zero bias voltage is purely determined by the
charge imbalance, while the energy imbalance causes a nontrivial -dependence of . The obtained voltage-current characteristics
qualitatively agree with the experimental result by R. Yagi [Phys. Rev. B {\bf
73} (2006) 134507].Comment: 10 pages, 5 figure
Gravitational Waves from Quasi-Circular Black Hole Binaries in Dynamical Chern-Simons Gravity
Dynamical Chern-Simons gravity cannot be strongly constrained with current
experiments because it reduces to General Relativity in the weak-field limit.
This theory, however, introduces modifications in the non-linear, dynamical
regime, and thus, it could be greatly constrained with gravitational waves from
the late inspiral of black hole binaries. We complete the first self-consistent
calculation of such gravitational waves in this theory. For favorable
spin-orientations, advanced ground-based detectors may improve existing
solar-system constraints by 6 orders of magnitude.Comment: 6 pages, 1 figure; errors corrected in Eqs. (8) and (9
Newcomers Meet the Intracluster Medium in the Coma Cluster
A main topic at this meeting is how galaxies are affected when they enter for
the first time the cluster environment from the outskirts. Most of the times we
are forced to infer the environmental effects indirectly, relying on systematic
variations of galaxy properties with environment, but there aren't many
examples of direct observations able to unveil ongoing transformations taking
place, and the corresponding mechanism producing it. We present a case in which
it is possible to identify the cluster environment, and in particular the
intracluster medium and the recent infall history of galaxies onto the cluster,
as the cause for a recent, abrupt change in the evolutionary history of
galaxies.Comment: 5 pages, 1 postscript figure -- to appear in "Outskirts of Galaxy
Clusters: intense life in the suburbs", IAU Colloquium N. 195, 2004, ed. A
Diaferi
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