1,032 research outputs found
A Quasi-Classical Model of Intermediate Velocity Particle Production in Asymmetric Heavy Ion Reactions
The particle emission at intermediate velocities in mass asymmetric reactions
is studied within the framework of classical molecular dynamics. Two reactions
in the Fermi energy domain were modelized, Ni+C and Ni+Au at 34.5
MeV/nucleon. The availability of microscopic correlations at all times allowed
a detailed study of the fragment formation process. Special attention was paid
to the physical origin of fragments and emission timescales, which allowed us
to disentangle the different processes involved in the mid-rapidity particle
production. Consequently, a clear distinction between a prompt pre- equilibrium
emission and a delayed aligned asymmetric breakup of the heavier partner of the
reaction was achieved.Comment: 8 pages, 7 figures. Final version: figures were redesigned, and a new
section discussing the role of Coulomb in IMF production was include
Microscopic description of the surface dipole plasmon in large Na_N clusters (950 < N < 12050)
Fully microscopic RPA/LDA calculations of the dipole plasmon for very large
neutral and charged sodium clusters, Na_N^Z+, in the size range 950
< N < 12050 are presented for the first time. 60 different sizes are
considered altogether, which allows for an in-depth investigation of the
asymptotic behavior of both the width and the position of the plasmon.Comment: Latex/Revtex, 4 pages with 4 Postscript figures, accepted for
publication in Physical Review
Validation of a Lysis Buffer Containing 4 M Guanidinium Thiocyanate (GITC)/ Triton X-100 for Extraction of SARS-CoV-2 RNA for COVID-19 Testing: Comparison of Formulated Lysis Buffers Containing 4 to 6 M GITC, Roche External Lysis Buffer and Qiagen RTL Lysis Buffer
The COVID-19 pandemic has resulted in increased need for diagnostic testing using reverse transcriptase real-time PCR (RT-PCR). An exponential increase in demand has resulted in a shortage of numerous reagents in particular those associated with the lysis buffer required to extract the viral RNA. Herein, we describe a rapid collective effort by hospital laboratory scientists, academic researchers and the biopharma industry to generate a validated lysis buffer. We have formulated a 4M Guanidinium thiocyanate (GITC)/ Triton X-100 Lysis buffer which provides comparable results with the recommended reagents. This buffer will ease the burden on hospital labs in their heroic efforts diagnose a large population of patients
Memorization of short-range potential fluctuations in Landau levels
We calculate energy spectra of a two-dimensional electron system in a
perpendicular magnetic field and periodic potentials of short periods. The
Coulomb interaction is included within a screened Hartree-Fock approximation.
The electrostatic screening is poor and the exchange interaction amplifies the
energy dispersion. We obtain, by numerical iterations, self-consistent
solutions that have a hysteresis-like property. With increasing amplitude of
the external potential the energy dispersion and the electron density become
periodic, and they remain stable when the external potential is reduced to
zero. We explain this property in physical terms and speculate that a real
system could memorize short-range potential fluctuations after the potential
has been turned off.Comment: 11 pages with 4 included figures, Revte
Density-functional theory of quantum wires and dots in a strong magnetic field
We study the competition between the exchange and the direct Coulomb
interaction near the edge of a two-dimensional electron gas in a strong
magnetic field using density-functional theory in a local approximation for the
exchange-energy functional. Exchange is shown to play a significant role in
reducing the spatial extent of the compressible edge channel regions obtained
from an electrostatic description. The transition from the incompressible edge
channels of the Hartree-Fock picture to the broad, compressible strips
predicted by electrostatics occurs within a narrow and experimentally
accessible range of confinement strengths.Comment: 24 pages latex and 10 postscript figures in self extracting fil
Constraints on the circumstellar dust around KIC 8462852
© The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.We present millimetre (SMA) and sub-millimetre (SCUBA-2) continuum observations of the peculiar star KIC 8462852 which displayed several deep and aperiodic dips in brightness during the Kepler mission. Our observations are approximately confusion-limited at 850 m and are the deepest millimetre and sub-millimetre photometry of the star that has yet been carried out. No significant emission is detected towards KIC 8462852. We determine upper limits for dust between a few 10 M and 10 M for regions identified as the most likely to host occluding dust clumps and a total overall dust budget of 7.7 M within a radius of 200 AU. Such low limits for the inner system make the catastrophic planetary disruption hypothesis unlikely. Integrating over the Kepler lightcurve we determine that at least 10 M of dust is required to cause the observed Q16 dip. This is consistent with the currently most favoured cometary breakup hypothesis, but nevertheless implies the complete breakup of 30 Comet 1/P Halley type objects. Finally, in the wide SCUBA-2 field-of-view we identify another candidate debris disc system that is potentially the largest yet discovered.Peer reviewedFinal Published versio
Exactly Soluble Model for Umklapp Scattering at Quantum-Hall Edges
We consider the low-energy, long-wave-length excitations of a reconstructed
quantum-Hall edge where three branches of chiral one-dimensional edge
excitations exist. We find that, in addition to forward scattering between the
three edge-excitation branches, Coulomb interaction gives rise to a novel
Umklapp-type scattering process that cannot be accounted for within a
generalized Tomonaga-Luttinger model. We solve the theory including Umklapp
processes exactly in the long-wave-length limit and calculate electronic
correlation functions.Comment: 5 pages, 1 figure, final version, to appear in PRL (20Dec1999
Measurements of sideward flow around the balance energy
Sideward flow values have been determined with the INDRA multidetector for
Ar+Ni, Ni+Ni and Xe+Sn systems studied at GANIL in the 30 to 100 A.MeV incident
energy range. The balance energies found for Ar+Ni and Ni+Ni systems are in
agreement with previous experimental results and theoretical calculations.
Negative sideward flow values have been measured. The possible origins of such
negative values are discussed. They could result from a more important
contribution of evaporated particles with respect to the contribution of
promptly emitted particles at mid-rapidity. But effects induced by the methods
used to reconstruct the reaction plane cannot be totally excluded. Complete
tests of these methods are presented and the origins of the
``auto-correlation'' effect have been traced back. For heavy fragments, the
observed negative flow values seem to be mainly due to the reaction plane
reconstruction methods. For light charged particles, these negative values
could result from the dynamics of the collisions and from the reaction plane
reconstruction methods as well. These effects have to be taken into account
when comparisons with theoretical calculations are done.Comment: 27 pages, 15 figure
HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and H I overview
Aims. The first half of THOR data (l = 14.0°−37.9°, and l = 47.1°−51.2°, |b|≤ 1.25°) has been published in our data release 1 paper. With this data release 2 paper, we publish all the remaining spectral line data and Stokes I continuum data with high angular resolution (10′′–40′′), including a new H I dataset for the whole THOR survey region (l = 14.0−67.4° and |b|≤ 1.25°). As we published the results of OH lines and continuum emission elsewhere, we concentrate on the H I analysis in this paper.
Methods. With the Karl G. Jansky Very Large Array (VLA) in C-configuration, we observed a large portion of the first Galactic quadrant, achieving an angular resolution of ≤40′′. At L Band, the WIDAR correlator at the VLA was set to cover the 21 cm H I line, four OH transitions, a series of Hnα radio recombination lines (RRLs; n = 151 to 186), and eight 128 MHz-wide continuum spectral windows, simultaneously.
Results. We publish all OH and RRL data from the C-configuration observations, and a new H I dataset combining VLA C+D+GBT (VLA D-configuration and GBT data are from the VLA Galactic Plane Survey) for the whole survey. The H I emission shows clear filamentary substructures at negative velocities with low velocity crowding. The emission at positive velocities is more smeared-out, likely due to higher spatial and velocity crowding of structures at the positive velocities. Compared to the spiral arm model of the Milky Way, the atomic gas follows the Sagittarius and Perseus Arm well, but with significant material in the inter-arm regions. With the C-configuration-only H I+continuum data, we produce an H I optical depth map of the THOR areal coverage from 228 absorption spectra with the nearest-neighbor method. With this τ map, we corrected the H I emission for optical depth, and the derived column density is 38% higher than the column density with optically thin assumption. The total H I mass with optical depth correction in the survey region is 4.7 × 10⁸ M⊙, 31% more than the mass derived assuming the emission is optically thin. If we applied this 31% correction to the whole Milky Way, the total atomic gas mass would be 9.4–10.5 × 10⁹ M⊙. Comparing the H I with existing CO data, we find a significant increase in the atomic-to-molecular gas ratio from the spiral arms to the inter-arm regions.
Conclusions. The high-sensitivity and resolution THOR H I dataset provides an important new window on the physical and kinematic properties of gas in the inner Galaxy. Although the optical depth we derive is a lower limit, our study shows that the optical depth correction issignificant for H I column density and mass estimation. Together with the OH, RRL and continuum emission from the THOR survey, these new H I data provide the basis for high-angular-resolution studies of the interstellar medium in different phases
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