53,448 research outputs found
Lasercooled RaF as a promising candidate to measure molecular parity violation
The parameter , which characterizes nuclear spin-dependent
parity violation effects within the effective molecular spin-rotational
Hamiltonian, was computed for the electronic ground state of radium fluoride
(RaF) and found to be one of the largest absolute values predicted so far.
These calculations were performed with the complex generalised Hartree-Fock
method within a two-component (quasi-relativistic) zeroth-order regular
approximation framework. Peculiarities of the molecular electronic structure of
RaF lead to highly diagonal Franck-Condon matrices between vibrational states
of the electronic ground and first excited states, which renders the molecule
in principle suitable for direct laser cooling. As a trapped gas of cold
molecules offers a superior coherence time, RaF can be considered a promising
candidate for high-precision spectroscopic experiments aimed at the search of
molecular parity-violation effects.Comment: 4.5 pages, 1 figure, 2 tables. Supplementary material can be
requested from the authors. Minor changes to version
Spatio-Temporal Scaling of Solar Surface Flows
The Sun provides an excellent natural laboratory for nonlinear phenomena. We
use motions of magnetic bright points on the solar surface, at the smallest
scales yet observed, to study the small scale dynamics of the photospheric
plasma. The paths of the bright points are analyzed within a continuous time
random walk framework. Their spatial and temporal scaling suggest that the
observed motions are the walks of imperfectly correlated tracers on a turbulent
fluid flow in the lanes between granular convection cells.Comment: Now Accepted by Physical Review Letter
325 MHz VLA Observations of Ultracool Dwarfs TVLM 513-46546 and 2MASS J0036+1821104
We present 325 MHz (90 cm wavelength) radio observations of ultracool dwarfs
TVLM 513-46546 and 2MASS J0036+1821104 using the Very Large Array (VLA) in June
2007. Ultracool dwarfs are expected to be undetectable at radio frequencies,
yet observations at 8.5 GHz (3.5 cm) and 4.9 GHz (6 cm) of have revealed
sources with > 100 {\mu}Jy quiescent radio flux and > 1 mJy pulses coincident
with stellar rotation. The anomalous emission is likely a combination of
gyrosynchrotron and cyclotron maser processes in a long-duration, large-scale
magnetic field. Since the characteristic frequency for each process scales
directly with the magnetic field magnitude, emission at lower frequencies may
be detectable from regions with weaker field strength. We detect no significant
radio emission at 325 MHz from TVLM 513-46546 or 2MASS J0036+1821104 over
multiple stellar rotations, establishing 2.5{\sigma} total flux limits of 795
{\mu}Jy and 942 {\mu}Jy respectively. Analysis of an archival VLA 1.4 GHz
observation of 2MASS J0036+1821104 from January 2005 also yields a
non-detection at the level of < 130 {\mu}Jy . The combined radio observation
history (0.3 GHz to 8.5 GHz) for these sources suggests a continuum emission
spectrum for ultracool dwarfs which is either flat or inverted below 2-3 GHz.
Further, if the cyclotron maser instability is responsible for the pulsed radio
emission observed on some ultracool dwarfs, our low-frequency non-detections
suggest that the active region responsible for the high-frequency bursts is
confined within 2 stellar radii and driven by electron beams with energies less
than 5 keV.Comment: 11 pages, 5 figures, submitted to A
Advanced solid electrolyte cell for CO2 and H2O electrolysis
A solid electrolyte cell with improved sealing characteristics was examined. A tube cell was designed, developed, fabricated, and tested. Design concepts incorporated in the tube cell to improve its sealing capability included minimizing the number of seals per cell and moving seals to lower temperature regions. The advanced tube cell design consists of one high temperature ceramic cement seal, one high temperature gasket seal, and three low temperature silicone elastomer seals. The two high temperature seals in the tube cell design represent a significant improvement over the ten high temperature precious metal seals required by the electrolyzer drum design. For the tube cell design the solid electrolyte was 8 mole percent yttria stabilized zirconium oxide slip cast into the shape of a tube with electrodes applied on the inside and outside surfaces
Harmonic coordinate method for simulating generic singularities
This paper presents both a numerical method for general relativity and an
application of that method. The method involves the use of harmonic coordinates
in a 3+1 code to evolve the Einstein equations with scalar field matter. In
such coordinates, the terms in Einstein's equations with the highest number of
derivatives take a form similar to that of the wave equation. The application
is an exploration of the generic approach to the singularity for this type of
matter. The preliminary results indicate that the dynamics as one approaches
the singularity is locally the dynamics of the Kasner spacetimes.Comment: 5 pages, 4 figures, Revtex, discussion expanded, references adde
On the Spread of Viruses on the Internet
We analyze the contact process on random graphs generated according to the preferential attachment scheme as a model for the spread of viruses in the Internet. We show that any virus with a positive rate of spread from a node to its neighbors has a non-vanishing chance of becoming epidemic. Quantitatively, we discover an interesting dichotomy: for it virus with effective spread rate λ, if the infection starts at a typical vertex, then it develops into an epidemic with probability λ^Θ ((log (1/ λ)/log log (1/ λ))), but on average the epidemic probability is λ^(Θ (1))
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