9,667 research outputs found
Evidence for a rapid decrease in Pluto's atmospheric pressure revealed by a stellar occultation in 2019
We report observations of a stellar occultation by Pluto on 2019 July 17. A
single-chord high-speed (time resolution s) photometry dataset was
obtained with a CMOS camera mounted on the Tohoku University 60 cm telescope
(Haleakala, Hawaii). The occultation light curve is satisfactorily fitted to an
existing Pluto's atmospheric model. We find the lowest pressure value at a
reference radius of among those reported after 2012,
indicating a possible rapid (approximately of the previous
value) pressure drop between 2016 (the latest reported estimate) and 2019.
However, this drop is detected at a level only and still requires
confirmation from future observations. If real, this trend is opposite to the
monotonic increase of Pluto's atmospheric pressure reported by previous
studies. The observed decrease trend is possibly caused by ongoing
condensation processes in the Sputnik Planitia glacier associated with an
orbitally driven decline of solar insolation, as predicted by previous
theoretical models. However, the observed amplitude of the pressure decrease is
larger than the model predictions.Comment: 7 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
Monopoles, noncommutative gauge theories in the BPS limit and some simple gauge groups
For three conspicuous gauge groups, namely, SU(2), SU(3) and SO(5), and at
first order in the noncommutative parameter matrix h\theta^{\mu\nu}, we
construct smooth monopole --and, some two-monopole-- fields that solve the
noncommutative Yang-Mills-Higgs equations in the BPS limit and that are formal
power series in h\theta^{\mu\nu}. We show that there exist noncommutative BPS
(multi-)monopole field configurations that are formal power series in
h\theta^{\mu\nu} if, and only if, two a priori free parameters of the
Seiberg-Witten map take very specific values. These parameters, that are not
associated to field redefinitions nor to gauge transformations, have thus
values that give rise to sharp physical effects.Comment: 30 pages, no figure
Low Frequency of Loss and Heterozygosity At the Nevoid Basal Cell Carcinoma Locus and Other Selected Loci in Appendageal Tumors
Previous studies of loss of heterozygosity (LOH) have revealed distinct patterns of allelic loss in some skin tumors. In basal cell carcinomas (BCCs) loss of heterozygosity is virtually restricted to chromosome 9, whereas in squamous cell carcinomas (SCCs) and actinic keratoses loss is more widespread involving chromosomes 3, 9, 13, and 17. Because there are histological similarities between BCCs and some appendageal tumors, and because some lines of evidence suggest that BCCs are appendageal in origin, we carried out a limited allelotype in 41 appendageal tumors. The overall frequency of allelic loss was low (4 out of 247 informative loci; 1.6%). LOH was seen in a proliferating trichilemmal cyst (l7p), a sebaceous epithelioma (l7q), an eccrine porocarcinoma (17q), a trichoepithelioma (9q), and in two basal cell carcinomas showing eccrine or granular cell differentiation that were originally misdiagnosed (9q). The pattern of loss in this mixed group of appendageal tumors shows differences from both BCCs and SCCs, and further emphasizes the unique genetic profile and behavior of BCCs. The finding of 9q loss in BCCs with eccrine or granular cell differentiation shows that 9q loss occurs in different histological subtypes of BCCs
Dynamical response of the nuclear pasta in neutron star crusts
The nuclear pasta -- a novel state of matter having nucleons arranged in a
variety of complex shapes -- is expected to be found in the crust of neutron
stars and in core-collapse supernovae at subnuclear densities of about
g/cm. Due to frustration, a phenomenon that emerges from the
competition between short-range nuclear attraction and long-range Coulomb
repulsion, the nuclear pasta displays a preponderance of unique low-energy
excitations. These excitations could have a strong impact on many transport
properties, such as neutrino propagation through stellar environments. The
excitation spectrum of the nuclear pasta is computed via a molecular-dynamics
simulation involving up to 100,000 nucleons. The dynamic response of the pasta
displays a classical plasma oscillation in the 1-2 MeV region. In addition,
substantial strength is found at low energies. Yet this low-energy strength is
missing from a simple ion model containing a single-representative heavy
nucleus. The low-energy strength observed in the dynamic response of the pasta
is likely to be a density wave involving the internal degrees of freedom of the
clusters.Comment: 4 pages, 3 figures, Phys Rev C in pres
TeV Strings and the Neutrino-Nucleon Cross Section at Ultra-high Energies
In scenarios with the fundamental unification scale at the TeV one expects
string excitations of the standard model fields at accessible energies. We
study the neutrino-nucleon cross section in these models. We show that duality
of the scattering amplitude forces the existence of a tower of massive
leptoquarks that mediate the process in the s-channel. Using the narrow-width
approximation we find a sum rule for the production rate of resonances with
different spin at each mass level. We show that these contributions can
increase substantially the standard model neutrino-nucleon cross section,
although seem insufficient in order to explain the cosmic ray events above the
GZK cutoff energy.Comment: 10 pages, 1 figure, version to appear in PR
Critical Behavior of J/psi across the Phase Transition from QCD sum rules
We study behavior of J/psi in hot gluonic matter using
QCD sum rules. Taking into account temperature dependences of the gluon
condensates extracted from lattice thermodynamics for the pure SU(3) system, we
find that the mass and width of J/psi exhibit rapid change across the critical
temperature.Comment: 5 pages, 3 figures. Poster contribution for Quark Matter 2008. To be
published in the proceeding
BPS Solitons in M5-Brane Worldvolume Theory with Constant Three-Form Field
We study BPS solutions for a self-dual string and a neutral string in
M5-brane worldvolume theory with constant three-form field. We further
generalize such solitons to superpose with a calibrated surface. We also study
a traveling wave on a calibrated surface in the constant three-form field
background.Comment: 12 pages, LaTeX, minor correction, added referenc
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