17,299 research outputs found
Loop quantum effect and the fate of tachyon field collapse
We study the fate of gravitational collapse of a tachyon field matter. In
presence of an inverse square potential a black hole forms. Loop quantum
corrections lead to the avoidance of classical singularities, which is followed
by an outward flux of energy.Comment: Contribution to the conference of Loops'11, Madri
UVOT Measurements of Dust and Star Formation in the SMC and M33
When measuring star formation rates using ultraviolet light, correcting for
dust extinction is a critical step. However, with the variety of dust
extinction curves to choose from, the extinction correction is quite uncertain.
Here, we use Swift/UVOT to measure the extinction curve for star-forming
regions in the SMC and M33. We find that both the slope of the curve and the
strength of the 2175 Angstrom bump vary across both galaxies. In addition, as
part of our modeling, we derive a detailed recent star formation history for
each galaxy.Comment: 6 pages, 5 figures, conference proceedings from Swift: 10 years of
Discovery, held in Rome (2-5 Dec. 2014
High-resolution and functional magnetic resonance imaging of the brachial plexus using an isotropic 3D T2 STIR (Short Term Inversion Recovery) SPACE sequence and diffusion tensor imaging
This technical note demonstrates the relevance of the isotropic 3D T2 turbo-spin-echo (TSE) sequence with short-term inversion recovery (STIR) and variable flip angle RF excitations (SPACE: Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions) for high-resolution brachial plexus imaging. The sequence was used in 11 patients in the diagnosis of brachial plexus pathologies involving primary and secondary tumors, and in six volunteers. We show that 3D STIR imaging is not only a reliable alternative to 2D STIR imaging, but it also better evaluates the anatomy, nerve site compression and pathology of the plexus, especially to depict space-occupying tumors along its course. Finally, due to its appropriate contrast we describe how 3D-STIR can be used as a high-resolution mask to be fused with fraction of anisotropy (FA) maps calculated from diffusion tensor imaging (DTI) data of the plexu
Stretched Polymers in Random Environment
We survey recent results and open questions on the ballistic phase of
stretched polymers in both annealed and quenched random environments.Comment: Dedicated to Erwin Bolthausen on the occasion of his 65th birthda
Inter-band B(E2) transition strengths in odd-mass heavy deformed nuclei
Inter-band B(E2) transition strengths between different normal parity bands
in 163Dy and 165Er are described using the pseudo-SU(3) model. The Hamiltonian
includes Nilsson single-particle energies, quadrupole-quadrupole and pairing
interactions with fixed, parametrized strengths, and three extra rotor terms
used to fine tune the energy spectra. In addition to inter-band transitions,
the energy spectra and the ground state intra-band B(E2) strengths are
reported. The results show the pseudo-SU(3) shell model to be a powerful
microscopic theory for a description of the normal parity sector in heavy
deformed odd-A nuclei.Comment: 4 figures, 2 table
Measuring fast gene dynamics in single cells with time-lapse luminescence microscopy.
Time-lapse fluorescence microscopy is an important tool for measuring in vivo gene dynamics in single cells. However, fluorescent proteins are limited by slow chromophore maturation times and the cellular autofluorescence or phototoxicity that arises from light excitation. An alternative is luciferase, an enzyme that emits photons and is active upon folding. The photon flux per luciferase is significantly lower than that for fluorescent proteins. Thus time-lapse luminescence microscopy has been successfully used to track gene dynamics only in larger organisms and for slower processes, for which more total photons can be collected in one exposure. Here we tested green, yellow, and red beetle luciferases and optimized substrate conditions for in vivo luminescence. By combining time-lapse luminescence microscopy with a microfluidic device, we tracked the dynamics of cell cycle genes in single yeast with subminute exposure times over many generations. Our method was faster and in cells with much smaller volumes than previous work. Fluorescence of an optimized reporter (Venus) lagged luminescence by 15-20 min, which is consistent with its known rate of chromophore maturation in yeast. Our work demonstrates that luciferases are better than fluorescent proteins at faithfully tracking the underlying gene expression
Parallel Evolution of Quasi-separatrix Layers and Active Region Upflows
Persistent plasma upflows were observed with Hinode's EUV Imaging
Spectrometer (EIS) at the edges of active region (AR) 10978 as it crossed the
solar disk. We analyze the evolution of the photospheric magnetic and velocity
fields of the AR, model its coronal magnetic field, and compute the location of
magnetic null-points and quasi-sepratrix layers (QSLs) searching for the origin
of EIS upflows. Magnetic reconnection at the computed null points cannot
explain all of the observed EIS upflow regions. However, EIS upflows and QSLs
are found to evolve in parallel, both temporarily and spatially. Sections of
two sets of QSLs, called outer and inner, are found associated to EIS upflow
streams having different characteristics. The reconnection process in the outer
QSLs is forced by a large-scale photospheric flow pattern which is present in
the AR for several days. We propose a scenario in which upflows are observed
provided a large enough asymmetry in plasma pressure exists between the
pre-reconnection loops and for as long as a photospheric forcing is at work. A
similar mechanism operates in the inner QSLs, in this case, it is forced by the
emergence and evolution of the bipoles between the two main AR polarities. Our
findings provide strong support to the results from previous individual case
studies investigating the role of magnetic reconnection at QSLs as the origin
of the upflowing plasma. Furthermore, we propose that persistent reconnection
along QSLs does not only drive the EIS upflows, but it is also responsible for
a continuous metric radio noise-storm observed in AR 10978 along its disk
transit by the Nan\c{c}ay Radio Heliograph.Comment: 29 pages, 10 figure
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