2,263 research outputs found
Quantum Stability of Accelerated Black Holes
We study quantum aspects of the accelerated black holes in some detail.
Explicitly shown is the fact that a uniform acceleration stabilizes certain
charged black holes against the well-known thermal evaporation. Furthermore, a
close inspection of the geometry reveals that this is possible only for
near-extremal black holes and that most nonextremal varieties continue to
evaporate with a modified spectrum under the acceleration. We also introduce a
two-dimensional toy model where the energy-momentum flow is easily obtained for
general accelerations, and find the behavior to be in accordance with the
four-dimensional results. After a brief comparison to the classical system of a
uniformly accelerated charge, we close by pointing out the importance of this
result in the WKB expansion of the black hole pair-creation rate.Comment: LaTeX, 22 pages, 5 uuencoded figures (minor errors corrected, more
discussions on the case with black holes formed by gravitational collapse.
Geophysical Exploration of Vesta
Dawn’s year-long stay at Vesta allows
comprehensive mapping of the shape, topography,
geology, mineralogy, elemental abundances, and
gravity field using it’s three instruments and highprecision
spacecraft navigation. In the current Low
Altitude Mapping Orbit (LAMO), tracking data is being
acquired to develop a gravity field expected to be
accurate to degree and order ~20 [1, 2]. Multi-angle
imaging in the Survey and High Altitude Mapping
Orbit (HAMO) has provided adequate stereo coverage
to develop a shape model accurate to ~10 m at 100 m
horizontal spatial resolution. Accurate mass determination
combined with the shape yields a more precise
value of bulk density, albeit with some uncertainty
resulting from the unmeasured seasonally-dark north
polar region. The shape and gravity of Vesta can be
used to infer the interior density structure and investigate
the nature of the crust, informing models for Vesta’s
formation and evolution
Southern Ocean Control of 2°C Global Warming in Climate Models
Global warming will soon reach the Paris Agreement targets of 1.5°C/2°C temperature increase above pre-industrial levels. Under a business-as-usual scenario, the time to reach these targets varies widely among climate models. Using Coupled Model Intercomparison Project Phase 5 and 6, we show that a 2°C global warming is determined by Southern Ocean (SO) state closely tied with a low-level cloud (LLC) amount feedback strength during reference (1861–1900) period; climate models with cold SO tend to accompany more low-level cloudiness and Antarctic sea ice concentration due to a strong LLC amount feedback. Consequently, initially cold SO models tend to simulate a fast global warming by absorbing more downward shortwave radiation compared to initially warm SO models because more LLC disappears due to a strong LLC amount feedback during the 2°C rise. Our results demonstrate that climate models that correctly simulate initial SO state can improve 2°C warming projections with reduced uncertainties.publishedVersio
Design and fabrication of double pancake coil using 2G wire for conduction cooled superconducting magnet
AbstractA large bore double pancake coil(DPC) was designed and tested with 2G HTS wire to develop the conduction cooled superconducting magnet with central field intensity of 3 T at 20K operating temperature and clear bore of 100mm at room temperature. The effect of insulation between turns of double pancake coils was tested. Two double pancake coils with and without turn to turn insulation were wound using 4mm wide 2G conductor. A temporary result suggests that the coil wound without electrical insulation can be protected from higher over current and shows improved stability
Poisson Algebra of Diffeomorphism Generators in a Spacetime Containing a Bifurcation
In this article we will analyze the possibility of a nontrivial central
extension of the Poisson algebra of the diffeomorphism generators, which
respect certain boundary conditions on the black hole bifurcation. The origin
of a possible central extension in the algebra is due to the existence of
boundary terms in the in the canonical generators. The existence of such
boundary terms depend on the exact boundary conditions one takes. We will check
two possible boundary conditions i.e. fixed bolt metric and fixed surface
gravity. In the case of fixed metric the the action acquires a boundary term
associated to the bifurcation but this is canceled in the Legendre
transformation and so absent in the canonical generator and so in this case the
possibility of a nontrivial central extension is ruled out. In the case of
fixed surface gravity the boundary term in the action is absent but present in
the Hamiltonian. Also in this case we will see that there is no nontrivial
central extension, also if there exist a boundary term in the generator.Comment: LaTex 20 pages, some misprints corrected, 2 references added.
Accepted for publication on Phys. Rev.
Magnetic moment of hyperons in nuclear matter by using quark-meson coupling models
We calculate the magnetic moments of hyperons in dense nuclear matter by
using relativistic quark models. Hyperons are treated as MIT bags, and the
interactions are considered to be mediated by the exchange of scalar and vector
mesons which are approximated as mean fields. Model dependence is investigated
by using the quark-meson coupling model and the modified quark-meson coupling
model; in the former the bag constant is independent of density and in the
latter it depends on density. Both models give us the magnitudes of the
magnetic moments increasing with density for most octet baryons. But there is a
considerable model dependence in the values of the magnetic moments in dense
medium. The magnetic moments at the nuclear saturation density calculated by
the quark meson coupling model are only a few percents larger than those in
free space, but the magnetic moments from the modified quark meson coupling
model increase more than 10% for most hyperons. The correlations between the
bag radius of hyperons and the magnetic moments of hyperons in dense matter are
discussed.Comment: substantial changes in the text, submitted to PL
Ni/HZSM-5 catalyst preparation by deposition-precipitation. Part 2. Catalytic hydrodeoxygenation reactions of lignin model compounds in organic and aqueous systems
Nickel metal supported on HZSM-5 (zeolite) is a promising catalyst for lignin depolymerization. In this work, the ability of catalysts prepared via deposition-precipitation (DP) to perform hydrodeoxygenation (HDO) on two lignin model compounds in organic and aqueous solvents was evaluated; guaiacol in dodecane and 2-phenoxy-1-phenylethanol (PPE) in aqueous solutions. All Ni/HZSM-5 catalysts were capable of guaiacol HDO into cyclohexane at 523 K. The role of the HZSM-5 acid sites was confirmed by comparison with Ni/SiO2 (inert support) which exhibited incomplete deoxygenation of guaiacol due to the inability to perform the cyclohexanol dehydration step. The catalyst prepared with 15 wt% Ni, a DP time of 16 h, and a calcination temperature of 673 K (Ni(15)/HZSM-5 DP16_Cal673), performed the guaiacol conversion with the greatest selectivity towards HDO products, with an intrinsic rate ratio (HDO rate to conversion rate) of 0.31, and 90% selectivity to cyclohexane. Catalytic activity and selectivity of Ni/HZSM-5 (15 wt%) in aqueous environments (water and 0.1 M NaOH solution) was confirmed using PPE reactions at 523 K. After 30 min reaction time in water, Ni/HZSM-5 exhibited ~100% conversion of PPE, and good yield of the desired products; ethylbenzene and phenol (~35% and 23% of initial carbon, respectively). Ni/HZSM-5 in NaOH solution resulted in significantly higher ring saturation compared to the Ni/HZSM-5 in water or the NaOH solution control
Study on the fishing performance of an alternative tubular-type pot for the common octopus, Octopus minor, in Korean coastal waters
We aimed to develop alternative fishing gear for catching the common octopus, to decrease the use of bait and operating costs in comparison to commercial net pots. A tubular-type pot was designed, and behavioral responses of the common octopus were experimentally monitored in tank and replicated 10 times to compare fishing performances between 300 experimental and 300 commercial net pots in the coastal sea of Gangjin, Korea. The behavioral responses under experimental conditions included emergence from the mud den, detection of the bait on the pot surface, and entry into the pot (toward the bait). The field experiment results indicate that numbers and weights of the catch during offshore fishing were 703 (56.0 kg) and 795 (86.3 kg) via tubular-type and net pots, respectively. The catch per unit effort (CPUE) for the number and weight of the tubular-type pot from 10 trials were 0.23 individuals/pot and 18.87 g/pot, respectively and weight for the net pot were 0.27 individuals/pot and 28.77 g/pot, respectively. No significant difference was noted between the CPUE in catch number for tubular-type and net pots (Kruskal–Wallis test, p=0.305 > 0.05) however, the CPUE by weight was significantly higher using net pot than tubular-type pot (Kruskal–Wallis test, p= 0.01<0.05). The amount of bait used during the experimental period for the tubular-type pots were 1/3.4 less than that of the commercial net pot. Therefore, fishing operating cost for common octopus was reduced using tubular-type pot
Chemistry of Chern-Simons Supergravity: reduction to a BPS kink, oxidation to M-theory and thermodynamical aspects
We construct a supersymmetric extension of the two dimensional
Kaluza-Klein-reduced gravitational Chern-Simons term, and globally study its
solutions, labelled by mass and U(1) charge c. The kink solution is BPS, and in
an appropriate conformal frame all solutions asymptotically approach AdS. The
thermodynamics of the Hawking effect yields interesting behavior for the
specific heat and hints at a Hawking-Page-like transition at T_{critical} \sim
c^{3/2}. We address implications for higher dimensions ("oxidation"), in
particular D=3,4 and 11, and comment briefly on AdS/CFT aspects of the kink.Comment: 39 pages, 2 figures. v2: reference added, minor changes, typo
Dual stem cell therapy synergistically improves cardiac function and vascular regeneration following myocardial infarction
Since both myocardium and vasculature in the heart are excessively damaged following myocardial infarction (MI), therapeutic strategies for treating MI hearts should concurrently target both so as to achieve true cardiac repair. Here we demonstrate a concomitant method that exploits the advantages of cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) and human mesenchymal stem cell-loaded patch (hMSC-PA) to amplify cardiac repair in a rat MI model. Epicardially implanted hMSC-PA provide a complimentary microenvironment which enhances vascular regeneration through prolonged secretion of paracrine factors, but more importantly it significantly improves the retention and engraftment of intramyocardially injected hiPSC-CMs which ultimately restore the cardiac function. Notably, the majority of injected hiPSC-CMs display adult CMs like morphology suggesting that the secretomic milieu of hMSC-PA constitutes pleiotropic effects in vivo. We provide compelling evidence that this dual approach can be a promising means to enhance cardiac repair on MI hearts.11Ysciescopu
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