933 research outputs found
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Thermal conductivity of thermal-battery insulations
The thermal conductivities of a variety of insulating materials used in thermal batteries were measured in atmospheres of argon and helium using several techniques. (Helium was used to simulate the hydrogen atmosphere that results when a Li(Si)/FeS{sub 2} thermal battery ages.) The guarded-hot-plate method was used with the Min-K insulation because of its extremely low thermal conductivity. For comparison purposes, the thermal conductivity of the Min-K insulating board was also measured using the hot-probe method. The thermal-comparator method was used for the rigid Fiberfrax board and Fiberfrax paper. The thermal conductivity of the paper was measured under several levels of compression to simulate the conditions of the insulating wrap used on the stack in a thermal battery. The results of preliminary thermal-characterization tests with several silica aerogel materials are also presented
Gravitational quasinormal radiation of higher-dimensional black holes
We find the gravitational resonance (quasinormal) modes of the higher
dimensional Schwarzschild and Reissner-Nordstrem black holes. The effect on the
quasinormal behavior due to the presence of the term is investigated.
The QN spectrum is totally different for different signs of . In more
than four dimensions there excited three types of gravitational modes: scalar,
vector, and tensor. They produce three different quasinormal spectra, thus the
isospectrality between scalar and vector perturbations, which takes place for
D=4 Schwarzschild and Schwarzschild-de-Sitter black holes, is broken in higher
dimensions. That is the scalar-type gravitational perturbations, connected with
deformations of the black hole horizon, which damp most slowly and therefore
dominate during late time of the black hole ringing.Comment: 13 pages, 2 figures, several references are adde
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Mental health and wellbeing of postgraduate researchers: exploring the relationship between mental health literacy, help-seeking behaviour, psychological distress, and wellbeing.
Studies of Postgraduate Researchers (PGRs) have highlighted that the population may be at risk of developing symptoms of common mental health problems. Early intervention and preventative measures may reduce this risk, such as improving mental health literacy (MHL). However, it is unclear what the relationship is between MHL and outcomes such as help-seeking behaviour, psychological distress and wellbeing, in PGRs. Therefore, the current study aimed to explore this relationship. A secondary aim of this study was to compare data collected from PGRs with undergraduate students. Two hundred and forty-one PGRs from two universities in England completed an anonymous online quantitative survey, with PGRs reporting on their MHL, help-seeking behaviour, psychological distress, and wellbeing, in addition to demographic and academic characteristics. Results indicated that 70% of PGRs were experiencing symptoms categorised as mild to severe psychological distress. Stepwise multiple regressions revealed that lower levels of wellbeing predicted higher levels of distress and lower levels of help-seeking behaviour. Compared with undergraduate students, PGRs in this study reported higher levels of psychological distress compared to undergraduate students, after adjusting for age, sex, and previous diagnosis of a mental health problem, as well as MHL, after adjusting for sex and previous diagnosis (p 0.05). Study findings suggest that PGRs, at the start of the academic year, are distressed and may not be seeking appropriate help for their concerns. Further studies should explore the environmental factors that may exacerbate mental health concerns beyond that associated with a challenging degree, within the PGR population
Quantum lump dynamics on the two-sphere
It is well known that the low-energy classical dynamics of solitons of
Bogomol'nyi type is well approximated by geodesic motion in M_n, the moduli
space of static n-solitons. There is an obvious quantization of this dynamics
wherein the wavefunction evolves according to the Hamiltonian H_0 equal to
(half) the Laplacian on M_n. Born-Oppenheimer reduction of analogous mechanical
systems suggests, however, that this simple Hamiltonian should receive
corrections including k, the scalar curvature of M_n, and C, the n-soliton
Casimir energy, which are usually difficult to compute, and whose effect on the
energy spectrum is unknown. This paper analyzes the spectra of H_0 and two
corrections to it suggested by work of Moss and Shiiki, namely H_1=H_0+k/4 and
H_2=H_1+C, in the simple but nontrivial case of a single CP^1 lump moving on
the two-sphere. Here M_1=TSO(3), a noncompact kaehler 6-manifold invariant
under an SO(3)xSO(3) action, whose geometry is well understood. The symmetry
gives rise to two conserved angular momenta, spin and isospin. A hidden
isometry of M_1 is found which implies that all three energy spectra are
symmetric under spin-isospin interchange. The Casimir energy is found exactly
on the zero section of TSO(3), and approximated numerically on the rest of M_1.
The lowest 19 eigenvalues of H_i are found for i=0,1,2, and their spin-isospin
and parity compared. The curvature corrections in H_1 lead to a qualitatively
unchanged low-level spectrum while the Casimir energy in H_2 leads to
significant changes. The scaling behaviour of the spectra under changes in the
radii of the domain and target spheres is analyzed, and it is found that the
disparity between the spectra of H_1 and H_2 is reduced when the target sphere
is made smaller.Comment: 35 pages, 3 figure
Area Spectrum of Extremal Reissner-Nordstr\"om Black Holes from Quasi-normal Modes
Using the quasi-normal modes frequency of extremal Reissner-Nordstr\"om black
holes, we obtain area spectrum for these type of black holes. We show that the
area and entropy black hole horizon are equally spaced. Our results for the
spacing of the area spectrum differ from that of schwarzschild black holes.Comment: 6 pages, no figure, accepted for publication in Phys. Rev.
Quasinormal behavior of the D-dimensional Schwarzshild black hole and higher order WKB approach
We study characteristic (quasinormal) modes of a -dimensional Schwarzshild
black hole. It proves out that the real parts of the complex quasinormal modes,
representing the real oscillation frequencies, are proportional to the product
of the number of dimensions and inverse horizon radius . The
asymptotic formula for large multipole number and arbitrary is derived.
In addition the WKB formula for computing QN modes, developed to the 3rd order
beyond the eikonal approximation, is extended to the 6th order here. This gives
us an accurate and economic way to compute quasinormal frequencies.Comment: 15 pages, 6 figures, the 6th order WKB formula for computing QNMs in
Mathematica is available from https://goo.gl/nykYG
Decay of charged scalar field around a black hole: quasinormal modes of R-N, R-N-AdS and dilaton black holes
It is well known that the charged scalar perturbations of the
Reissner-Nordstrom metric will decay slower at very late times than the neutral
ones, thereby dominating in the late time signal. We show that at the stage of
quasinormal ringing, on the contrary, the neutral perturbations will decay
slower for RN, RNAdS and dilaton black holes. The QN frequencies of the nearly
extreme RN black hole have the same imaginary parts (damping times) for charged
and neutral perturbations. An explanation of this fact is not clear but,
possibly, is connected with the Choptuik scaling.Comment: 10 pages, LaTeX, 4 figures, considerable changes made and wrong
interpretation of computations correcte
Quasinormal modes from potentials surrounding the charged dilaton black hole
We clarify the purely imaginary quasinormal frequencies of a massless scalar
perturbation on the 3D charged-dilaton black holes. This case is quite
interesting because the potential-step appears outside the event horizon
similar to the case of the electromagnetic perturbations on the large
Schwarzschild-AdS black holes. It turns out that the potential-step type
provides the purely imaginary quasinormal frequencies, while the
potential-barrier type gives the complex quasinormal modes.Comment: 19 pages, 8 figure
Quasinormal modes for massless topological black holes
An exact expression for the quasinormal modes of scalar perturbations on a
massless topological black hole in four and higher dimensions is presented. The
massive scalar field is nonminimally coupled to the curvature, and the horizon
geometry is assumed to have a negative constant curvature.Comment: CECS style, 11 pages, no figures. References adde
A note on quasinormal modes: A tale of two treatments
There is an apparent discrepancy in the literature with regard to the
quasinormal mode frequencies of Schwarzschild-de Sitter black holes in the
degenerate-horizon limit. On the one hand, a Poschl-Teller-inspired method
predicts that the real part of the frequencies will depend strongly on the
orbital angular momentum of the perturbation field whereas, on the other hand,
the degenerate limit of a monodromy-based calculation suggests there should be
no such dependence (at least, for the highly damped modes). In the current
paper, we provide a possible resolution by critically re-assessing the limiting
procedure used in the monodromy analysis.Comment: 11 pages, Revtex format; (v2) new addendum in response to reader
comments, also references, footnote and acknowledgments adde
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