669 research outputs found
Instability of generalised AdS black holes and thermal field theory
We study black holes in AdS-like spacetimes, with the horizon given by an
arbitrary positive curvature Einstein metric. A criterion for classical
instability of such black holes is found in the large and small black hole
limits. Examples of large unstable black holes have a B\"ohm metric as the
horizon. These, classically unstable, large black holes are locally
thermodynamically stable. The gravitational instability has a dual description,
for example by using the version of the AdS/CFT
correspondence. The instability corresponds to a critical temperature of the
dual thermal field theory defined on a curved background.Comment: 1+16 pages. 1 figure. LaTeX. Minor clarification
Callous-Unemotional Traits among Children and Adolescents in Asian Cultures: A Systematic Review
Callous-Unemotional Traits among Children and Adolescents in Asian Cultures: A Systematic Review
Considerable evidence now exists for callous and unemotional (CU) traits as markers for a high-risk pathway to child and adolescent conduct problems implicating unique risk processes and treatment needs, but research has been limited largely to Western countries. We review the evidence base related to CU traits in Asian countries that has emerged in recent years, with respect to four key questions. Specifically, are higher CU traits among Asian children and adolescents associated with (1) increased severity of conduct problems; (2) similar neurodevelopmental and neurocognitive correlates as reported in Western countries; (3) similar environmental risk factors as reported in Western countries; and (4) poorer treatment outcomes? A systematic search identified 28 studies that have reported on child and adolescent CU traits in Asian countries. Consistent with Western samples, CU traits were associated with individual risk factors including atypical neural activation during cognitive tasks and poor empathy, as well as parenting risk factors. CU traits were also positively associated with most measures of conduct problems. Differences from findings in Western samples, however, emerged for areas such as correlates of reactive aggression and delinquent peer influence. Treatment has been investigated in only one study to date and is therefore a high priority for future research. The limitations of existing evidence are addressed along with key directions for future cross-cultural research, including measurement research with children and adolescents.</p
Temperature dependent resistivity of spin-split subbands in GaAs 2D hole system
We calculate the temperature dependent resistivity in spin-split subbands
induced by the inversion asymmetry of the confining potential in GaAs 2D hole
systems. By considering both temperature dependent multisubband screening of
impurity disorder and hole-hole scattering we find that the strength of the
metallic behavior depends on the symmetry of the confining potential (i.e.,
spin-splitting) over a large range of hole density. At low density above the
metal-insulator transition we find that effective disorder reduces the
enhancement of the metallic behavior induced by spin-splitting. Our theory is
in good qualitative agreement with existing experiments
Obstructions to the Existence of Sasaki-Einstein Metrics
We describe two simple obstructions to the existence of Ricci-flat Kahler
cone metrics on isolated Gorenstein singularities or, equivalently, to the
existence of Sasaki-Einstein metrics on the links of these singularities. In
particular, this also leads to new obstructions for Kahler-Einstein metrics on
Fano orbifolds. We present several families of hypersurface singularities that
are obstructed, including 3-fold and 4-fold singularities of ADE type that have
been studied previously in the physics literature. We show that the AdS/CFT
dual of one obstruction is that the R-charge of a gauge invariant chiral
primary operator violates the unitarity bound.Comment: 35 pages, 1 figure; references and a footnote adde
Time and Amplitude of Afterpulse Measured with a Large Size Photomultiplier Tube
We have studied the afterpulse of a hemispherical photomultiplier tube for an
upcoming reactor neutrino experiment. The timing, the amplitude, and the rate
of the afterpulse for a 10 inch photomultiplier tube were measured with a 400
MHz FADC up to 16 \ms time window after the initial signal generated by an LED
light pulse. The time and amplitude correlation of the afterpulse shows several
distinctive groups. We describe the dependencies of the afterpulse on the
applied high voltage and the amplitude of the main light pulse. The present
data could shed light upon the general mechanism of the afterpulse.Comment: 11 figure
Spatial infinity in higher dimensional spacetimes
Motivated by recent studies on the uniqueness or non-uniqueness of higher
dimensional black hole spacetime, we investigate the asymptotic structure of
spatial infinity in n-dimensional spacetimes(). It turns out that the
geometry of spatial infinity does not have maximal symmetry due to the
non-trivial Weyl tensor {}^{(n-1)}C_{abcd} in general. We also address static
spacetime and its multipole moments P_{a_1 a_2 ... a_s}. Contrasting with four
dimensions, we stress that the local structure of spacetimes cannot be unique
under fixed a multipole moments in static vacuum spacetimes. For example, we
will consider the generalized Schwarzschild spacetimes which are deformed black
hole spacetimes with the same multipole moments as spherical Schwarzschild
black holes. To specify the local structure of static vacuum solution we need
some additional information, at least, the Weyl tensor {}^{(n-2)}C_{abcd} at
spatial infinity.Comment: 6 pages, accepted for publication in Physical Review D, published
versio
Crystal structure and two-stage hydrolysis of dimethoxo(meso-tetra(4-methoxyphenylporphyrinato))tin(IV), Sn(tmpp)(OMe)(2)
In this work, we determine the crystal structure of dimethoxo(meso-tetra(4-methoxyphenylporphyrinato))tin(IV), Sn(tmpp)(OMe)(2) (1). Experimental results indicate that the tin atom has an octahedral geometry. The geometry around the tin center has Sn(1)-O(5) = 2.020(6), Sn(1)-O(6) = 2.003(7) Angstrom and an average Sn(1)-N = 2.10(1) Angstrom. The two methoxo groups are unidentately coordinated to the tin(IV) atom. Two-stage hydrolysis of Sn(tmpp)(OMe)(2) in CDCl3 was observed by H-1 and C-13 NMR spectroscopy. Compound (1) crystallizes in the space group P2(1)/n with a = 14.7492(1), b = 19.2022(3), c = 16.0806(2) Angstrom, beta = 94.104(1)degrees and Z = 4
Analysis of the vector and axialvector mesons with QCD sum rules
In this article, we study the vector and axialvector mesons with the
QCD sum rules, and make reasonable predictions for the masses and decay
constants, then calculate the leptonic decay widths. The present predictions
for the masses and decay constants can be confronted with the experimental data
in the future. We can also take the masses and decay constants as basic input
parameters and study other phenomenological quantities with the three-point
vacuum correlation functions via the QCD sum rules.Comment: 14 pages, 16 figure
Topology change in General Relativity and the black-hole black-string transition
In the presence of compact dimensions massive solutions of General Relativity
may take one of several forms including the black-hole and the black-string,
the simplest relevant background being R^{3+1} * S^1. It is shown how Morse
theory places constraints on the qualitative features of the phase diagram, and
a minimalistic diagram is suggested which describes a first order transition
whose only stable phases are the uniform string and the black-hole. The diagram
calls for a topology changing ``merger'' transition in which the black-hole
evolves continuously into an unstable black-string phase. As evidence a local
model for the transition is presented in which the cone over S^2 * S^2 plays a
central role. Horizon cusps do not appear as precursors to black hole merger. A
generalization to higher dimensions finds that whereas the cone has a tachyon
function for d=5, its stability depends interestingly on the dimension - it is
unstable for d10.Comment: 28 pages, 13 figures, v2: minor changes, v3: published version. See
"Note added" at end of introductio
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