8,906 research outputs found
Ultraspinning instability: the missing link
We study linearized perturbations of Myers-Perry black holes in d=7, with two
of the three angular momenta set to be equal, and show that instabilities
always appear before extremality. Analogous results are expected for all higher
odd d. We determine numerically the stationary perturbations that mark the
onset of instability for the modes that preserve the isometries of the
background. The onset is continuously connected between the previously studied
sectors of solutions with a single angular momentum and solutions with all
angular momenta equal. This shows that the near-extremality instabilities are
of the same nature as the ultraspinning instability of d>5 singly-spinning
solutions, for which the angular momentum is unbounded. Our results raise the
question of whether there are any extremal Myers-Perry black holes which are
stable in d>5.Comment: 19 pages. 1 figur
Effect of surface roughness and sterilization on bacterial adherence to ultra-high molecular weight polyethylene
AbstractSterilization with ethylene oxide (EO) and gas plasma (GP) are well-known methods applied to ultra-high molecular weight polyethylene (UHMWPE) surfaces in the belief that they prevent major material changes caused by gamma irradiation. However, the influence of these surface sterilization methods on bacterial adherence to UHMWPE is unknown. UHMWPE samples with various degrees of roughness (0.3, 0.8 and 2.0 µm) were sterilized with either GP or EO. The variations in hydrophobicity, surface free energy and surface functional groups were investigated before and after sterilization. Sterilized samples were incubated with either Staphylococcus aureus or Staphylococcus epidermidis in order to study bacterial adherence to these materials. Fewer bacteria adhered to UHMWPE after sterilization with EO than after sterilization with GP, especially to the smoothest surfaces. No changes in chemical composition of the UHMWPE surface due to sterilization were observed using X-ray photoemission spectroscopy analysis. The decreased bacterial adherence to UHMWPE found at the smoothest surfaces after sterilization with EO was not directly related to changes in chemical composition. Increased bacterial adherence to rougher surfaces was associated with increased polar surface energy of EO-sterilized surfaces
A mid-term astrometric and photometric study of Trans-Neptunian Object (90482) Orcus
From CCD observations of a fixed and large star field that contained the
binary TNO Orcus, we have been able to derive high-precision relative
astrometry and photometry of the Orcus system with respect to background stars.
The RA residuals of an orbital fit to the astrometric data revealed a
periodicity of 9.7+-0.3 days, which is what one would expect to be induced by
the known Orcus companion. The residuals are also correlated with the
theoretical positions of the satellite with regard to the primary. We therefore
have revealed the presence of Orcus' satellite in our astrometric measurements.
The photocenter motion is much larger than the motion of Orcus around the
barycenter, and we show here that detecting some binaries through a carefully
devised astrometric technique might be feasible with telescopes of moderate
size. We also analyzed the system's mid-term photometry to determine whether
the rotation could be tidally locked to the satellite's orbital period. We
found that a photometric variability of 9.7+-0.3 days is clear in our data, and
is nearly coincident with the orbital period of the satellite. We believe this
variability might be induced by the satellite's rotation. There is also a
slight hint for an additional small variability in the 10 hr range that was
already reported in the literature. This short-term variability would indicate
that the primary is not tidally locked and therefore the system would not have
reached a double synchronous state. Implications for the basic physical
properties of the primary and its satellite are discussed. From angular
momentum considerations we suspect that the Orcus satellite might have formed
from a rotational fission. This requires that the mass of the satellite would
be around 0.09 times that of the primary, close to the value that one derives
by using an albedo of 0.12 for the satellite and assuming equal densities for
both objects.Comment: in Press at A&
Global Equation of State of two-dimensional hard sphere systems
Hard sphere systems in two dimensions are examined for arbitrary density.
Simulation results are compared to the theoretical predictions for both the low
and the high density limit, where the system is either disordered or ordered,
respectively. The pressure in the system increases with the density, except for
an intermediate range of volume fractions , where a
disorder-order phase transition occurs. The proposed {\em global equation of
state} (which describes the pressure {\em for all densities}) is applied to the
situation of an extremely dense hard sphere gas in a gravitational field and
shows reasonable agreement with both experimental and numerical data.Comment: 4 pages, 2 figure
Molecular studies of the brazilian infectious bronchitis virus isolates.
Avian infectious bronchitis virus (IBV) isolates have been widely characterized by reverse transcription followed by polymerase chain reaction and DNA sequencing. In present study, these techniques were applied to three viral genomic regions comprising the complete and/or a partial S1 segment, S2 and nucleocapsid genes. DNA sequences from viral isolates obtained from 1972 to 1989 and from 2006 to 2008 were compared. High similarity (>90%) was observed among some of the genomic segments, including S1 hypervariable region, which could suggest a common origin or ancestry. DNA sequences from S2 and N protein genes obtained from different infected tissues of the same flock were analyzed, and a clear segregation between respiratory and intestinal tract was observed. Therefore, these data suggest cocirculation of more than one viral strain in the same flock. 57.1% of DNA sequences from the S1 complete segment samples, 53.3% from the S2 fragment and 62.5% from the partial N gene were found to be different from analyzed sequences from reference strains leading to the conclusion that parte of viral isolates included in this study may be considered region specific. Considering the simultaneous analysis of the three genes, a large IBV genetic profile was observed in both old and recent isolates groups. However, most prominent diversity between viral isolates was obtained in the period from 1972 and 1989, showing the presence of a large number of variants in the state of Minas Gerais before the official approval of vaccination (1980)
Physicochemical properties of the oil from murumuruí fruit (Astrocaryum acaule): reason w-6/w-3 and w-9 potencial.
First Dark Matter Results from the XENON100 Experiment
The XENON100 experiment, in operation at the Laboratori Nazionali del Gran
Sasso in Italy, is designed to search for dark matter WIMPs scattering off 62
kg of liquid xenon in an ultra-low background dual-phase time projection
chamber. In this letter, we present first dark matter results from the analysis
of 11.17 live days of non-blind data, acquired in October and November 2009. In
the selected fiducial target of 40 kg, and within the pre-defined signal
region, we observe no events and hence exclude spin-independent WIMP-nucleon
elastic scattering cross-sections above 3.4 x 10^-44 cm^2 for 55 GeV/c^2 WIMPs
at 90% confidence level. Below 20 GeV/c^2, this result constrains the
interpretation of the CoGeNT and DAMA signals as being due to spin-independent,
elastic, light mass WIMP interactions.Comment: 5 pages, 5 figures. Matches published versio
A scalar field condensation instability of rotating anti-de Sitter black holes
Near-extreme Reissner-Nordstrom-anti-de Sitter black holes are unstable
against the condensation of an uncharged scalar field with mass close to the
Breitenlohner-Freedman bound. It is shown that a similar instability afflicts
near-extreme large rotating AdS black holes, and near-extreme hyperbolic
Schwarzschild-AdS black holes. The resulting nonlinear hairy black hole
solutions are determined numerically. Some stability results for (possibly
charged) scalar fields in black hole backgrounds are proved. For most of the
extreme black holes we consider, these demonstrate stability if the ``effective
mass" respects the near-horizon BF bound. Small spherical
Reissner-Nordstrom-AdS black holes are an interesting exception to this result.Comment: 34 pages; 13 figure
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