591 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
On the Existence of the Logarithmic Correction Term in Black Hole Entropy-Area Relation
In this paper we consider a model universe with large extra dimensions to
obtain a modified black hole entropy-area relation. We use the generalized
uncertainty principle to find a relation between the number of spacetime
dimensions and the presence or vanishing of logarithmic prefactor in the black
hole entropy-area relation. Our calculations are restricted to the
microcanonical ensembles and we show that in the modified entropy-area
relation, the microcanonical logarithmic prefactor appears only when spacetime
has an even number of dimensions.Comment: 9 Pages, No Figure
The Impact of Blue Light Irradiation on Keratinocytes in Vitro
ABSTRACT
Background: This study examined the effects of irradiation with blue
light on HaCaT keratinocytes. As irradiation with blue light is known to be
antimicrobial, it offers a promising alternative therapy for contaminated
wounds. There is evidence that red light promotes wound healing, but
the potential benefits of irradiation with blue light have not yet been ad-
equately investigated.
Methods: The rate of wound closure in sterile and contaminated cells
was measured using an in vitro scratch assay wound-healing model. Ad-
ditionally, cell viability after treatment was determined using a Sulforho-
damine B (SRB) assay.
Results: In both the sterile and contaminated groups, treated cells
showed delayed wound closure when compared with cells not irradiated
with blue light. Additionally, treatment with blue light resulted in poorer
viability in the treatment groups.
Conclusion: Although irradiation with blue light may offer a promising
alternative therapy for reducing bacterial colonization, our data indicate
that re-epithelization may be negatively influenced by blue light. Further
research is needed to clarify possible wound healing applications
Entropy Corrections for Schwarzschild and Reissner-Nordstr\"om Black Holes
Schwarzschild black hole being thermodynamically unstable, corrections to its
entropy due to small thermal fluctuations cannot be computed. However, a
thermodynamically stable Schwarzschild solution can be obtained within a cavity
of any finite radius by immersing it in an isothermal bath. For these boundary
conditions, classically there are either two black hole solutions or no
solution. In the former case, the larger mass solution has a positive specific
heat and hence is locally thermodynamically stable. We find that the entropy of
this black hole, including first order fluctuation corrections is given by:
{\cal S} = S_{BH} - \ln[\f{3}{R} (S_{BH}/4\p)^{1/2} -2]^{-1} + (1/2)
\ln(4\p), where is its Bekenstein-Hawking entropy and is the
radius of the cavity. We extend our results to four dimensional
Reissner-Nordstr\"om black holes, for which the corresponding expression is:
{\cal S} = S_{BH} - \f{1}{2} \ln [ {(S_{BH}/\p R^2) ({3S_{BH}}/{\p R^2} -
2\sqrt{{S_{BH}}/{\p R^2 -\a^2}}) \le(\sqrt{{S_{BH}}/{\p R^2}} - \a^2 \ri)}/
{\le({S_{BH}}/{\p R^2} -\a^2 \ri)^2} ]^{-1} +(1/2)\ln(4\p). Finally, we
generalise the stability analysis to Reissner-Nordstr\"om black holes in
arbitrary spacetime dimensions, and compute their leading order entropy
corrections. In contrast to previously studied examples, we find that the
entropy corrections in these cases have a different character.Comment: 6 pages, Revtex. References added, minor changes. Version to appear
in Class. Quant. Gra
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