4,805 research outputs found
Performance of silicon solar cell assemblies
Solar cell assembly current-voltage characteristics, thermal-optical properties, and power performance were determined. Solar cell cover glass thermal radiation, optical properties, confidence limits, and temperature intensity effects on maximum power were discussed
The design and testing of an inflated sphere impact limiter
Structural and geometric requirements, design problems, and testing of optimum inflated sphere impact limiter landing vehicl
Quantum Pair Creation of Soliton Domain Walls
A large body of experimental evidence suggests that the decay of the false
vacuum, accompanied by quantum pair creation of soliton domain walls, can occur
in a variety of condensed matter systems. Examples include nucleation of charge
soliton pairs in density waves [eg. J. H. Miller, Jr. et al., Phys. Rev. Lett.
84, 1555 (2000)] and flux soliton pairs in long Josephon junctions. Recently,
Dias and Lemos [J. Math. Phys. 42, 3292 (2001)] have argued that the mass
of the soliton should be interpreted as a line density and a surface density,
respectively, for (2+1)-D and (3+1)-D systems in the expression for the pair
production rate. As the transverse dimensions are increased and the total mass
(energy) becomes large, thermal activation becomes suppressed, so quantum
processes can dominate even at relatively high temperatures. This paper will
discuss both experimental evidence and theoretical arguments for the existence
of high-temperature collective quantum phenomena
Superconducting p-branes and Extremal Black Holes
In Einstein-Maxwell theory, magnetic flux lines are `expelled' from a black
hole as extremality is approached, in the sense that the component of the field
strength normal to the horizon goes to zero. Thus, extremal black holes are
found to exhibit the sort of `Meissner effect' which is characteristic of
superconducting media. We review some of the evidence for this effect, and do
present new evidence for it using recently found black hole solutions in string
theory and Kaluza-Klein theory. We also present some new solutions, which arise
naturally in string theory, which are non-superconducting extremal black holes.
We present a nice geometrical interpretation of these effects derived by
looking carefully at the higher dimensional configurations from which the lower
dimensional black hole solutions are obtained. We show that other extremal
solitonic objects in string theory (such as p-branes) can also display
superconducting properties. In particular, we argue that the relativistic
London equation will hold on the worldvolume of `light' superconducting
p-branes (which are embedded in flat space), and that minimally coupled zero
modes will propagate in the adS factor of the near-horizon geometries of
`heavy', or gravitating, superconducting p-branes.Comment: 22 pages, 2 figure
Primary source of income is associated with differences in HIV risk behaviors in street-recruited samples
BACKGROUND: The relationship between primary source of income and HIV risk behaviors and the racial/ethnic differences in risk behavior profiles among disadvantaged populations have not been fully explored. This is unusual given that the phenomenon of higher risk in more disadvantaged populations is well-known but the mechanisms remain unclear. We examined the relationship between primary source of income and differences in HIV risk behaviors among four racial/ethnic groups in the southern United States. METHODS: Self-reported data on primary source of income and HIV risk behaviors were collected from 1494 African American, Hispanic, Asian, and White men and women in places of public congregation in Houston, Texas. Data were analyzed using calculation of percentages and by chi-square tests with Yates correction for discontinuity where appropriate. RESULTS: Data revealed that a higher proportion of whites were involved in sex for money exchanges compared to the other racial groups in this sample. The data suggest that similar street sampling approaches are likely to recruit different proportions of people by primary income source and by ethnicity. It may be that the study locations sampled are likely to preferentially attract those involved in illegal activities, specifically the white population involved in sex for drug or money exchanges. Research evidence has shown that people construct highly evolved sexual marketplaces that are localized and most unlikely to cross racial, ethnic, and socioeconomic or geographical boundaries. Thus, the areas that we sampled may have straddled a white sexual marketplace more than that of the other groups, leading to an over-representation of sex exchange in this group. Drug use was highest among those with illegal primary sources of income (sex exchange and drug dealing and theft), and they were also those most likely to have injected drugs rather than administered them by any other route (p < 0.001). In addition, bisexual or homosexual identification was reported by more respondents in the sex exchange as primary source of income category. The number of sexual partners in the last three months followed a similar pattern, with those whose primary source of income was drug dealing or theft reporting relatively high partner numbers. CONCLUSIONS: These data suggest that social disadvantage is associated with HIV risk in part by its association with drug and sex work for survival, and offers one variable that may be associated with the concentration of disease among those at greatest disadvantage by having an illegal and unstable primary income source
Topology, Entropy and Witten Index of Dilaton Black Holes
We have found that for extreme dilaton black holes an inner boundary must be
introduced in addition to the outer boundary to give an integer value to the
Euler number. The resulting manifolds have (if one identifies imaginary time)
topology and Euler number in contrast to
the non-extreme case with . The entropy of extreme dilaton black
holes is already known to be zero. We include a review of some recent ideas due
to Hawking on the Reissner-Nordstr\"om case. By regarding all extreme black
holes as having an inner boundary, we conclude that the entropy of {\sl all}
extreme black holes, including black holes, vanishes. We discuss the
relevance of this to the vanishing of quantum corrections and the idea that the
functional integral for extreme holes gives a Witten Index. We have studied
also the topology of ``moduli space'' of multi black holes. The quantum
mechanics on black hole moduli spaces is expected to be supersymmetric despite
the fact that they are not HyperK\"ahler since the corresponding geometry has
torsion unlike the BPS monopole case. Finally, we describe the possibility of
extreme black hole fission for states with an energy gap. The energy released,
as a proportion of the initial rest mass, during the decay of an
electro-magnetic black hole is 300 times greater than that released by the
fission of an nucleus.Comment: 51 pages, 4 figures, LaTeX. Considerably extended version. New
sections include discussion of the Witten index, topology of the moduli
space, black hole sigma model, and black hole fission with huge energy
releas
Dark matter scenarios in the minimal SUSY B-L model
We perform a study of the dark matter candidates of a constrained version of
the minimal R-parity-conserving supersymmetric model with a gauged
. It turns out that there are four additional candidates for dark
matter in comparison to the MSSM: two kinds of neutralino, which either
correspond to the gaugino of the or to a fermionic bilepton, as
well as "right-handed" CP-even and -odd sneutrinos. The correct dark matter
relic density of the neutralinos can be obtained due to different mechanisms
including new co-annihilation regions and resonances. The large additional
Yukawa couplings required to break the radiatively often lead to
large annihilation cross sections for the sneutrinos. The correct treatment of
gauge kinetic mixing is crucial to the success of some scenarios. All
candidates are consistent with the exclusion limits of Xenon100.Comment: 45 pages, 22 figures; v2: extended discussion of direct detection
cross section, matches published versio
The generalised NMSSM at one loop: fine tuning and phenomenology
We determine the degree of fine tuning needed in a generalised version of the
NMSSM that follows from an underlying Z4 or Z8 R symmetry. We find that it is
significantly less than is found in the MSSM or NMSSM and extends the range of
Higgs mass that have acceptable fine tuning up to Higgs masses of mh ~ 130 GeV.
For universal boundary conditions analogous to the CMSSM the phenomenology is
rather MSSM like with the singlet states typically rather heavy. For more
general boundary conditions the singlet states can be light, leading to
interesting signatures at the LHC and direct detection experiments.Comment: 20 pages, 9 figures, matches published versio
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