86,369 research outputs found
HI emission from the red giant Y CVn with the VLA and FAST
Imaging studies with the VLA have revealed HI emission associated with the
extended circumstellar shells of red giants. We analyse the spectral map
obtained on Y CVn, a J-type carbon star on the AGB. The HI line profiles can be
interpreted with a model of a detached shell resulting from the interaction of
a stellar outflow with the local interstellar medium. We reproduce the spectral
map by introducing a distortion along a direction corresponding to the star's
motion in space. We then use this fitting to simulate observations expected
from the FAST radiotelescope, and discuss its potential for improving
ourdescription of the outer regions of circumstellar shells.Comment: accepted for publication in RA
Discovery of a Shell of Neutral Atomic Hydrogen Surrounding the Carbon Star IRC+10216
We have used the Robert C. Byrd Green Bank Telescope to perform the most
sensitive search to date for neutral atomic hydrogen (HI) in the circumstellar
envelope (CSE) of the carbon star IRC+10216. Our observations have uncovered a
low surface brightness HI shell of diameter ~1300" (~0.8 pc), centered on
IRC+10216. The HI shell has an angular extent comparable to the far
ultraviolet-emitting astrosphere of IRC+10216 previously detected with the
GALEX satellite, and its kinematics are consistent with circumstellar matter
that has been decelerated by the local interstellar medium. The shell appears
to completely surround the star, but the highest HI column densities are
measured along the leading edge of the shell, near the location of a previously
identified bow shock. We estimate a total mass of atomic hydrogen associated
with IRC+10216 CSE of M_HI~3x10e-3 M_sun. This is only a small fraction of the
expected total mass of the CSE (<1%) and is consistent with the bulk of the
stellar wind originating in molecular rather than atomic form, as expected for
a cool star with an effective temperature T_eff<~2200 K. HI mapping of a 2 deg
x 2 deg region surrounding IRC+10216 has also allowed us to characterize the
line-of-sight interstellar emission in the region and has uncovered a link
between diffuse FUV emission southwest of IRC+10216 and the Local Leo Cold
Cloud.Comment: Accepted to MNRAS. 16 pages. A version with full resolution figures
may be found at
http://www.haystack.mit.edu/hay/staff/lmatthew/Matthews_etal_IRC+10216.pd
and mesons at finite temperature and density in the NJL model with dimensional regularization
Dynamical Symmetry breaking and meson masses are studied in the
Nambu-Jona-Lasinio (NJL) model at finite temperature and chemical potential
using the dimensional regularization. Since the model is not renormalizable in
four space-time dimensions, physical results and parameters depend on the
regularization method. Following the imaginary time formalism, we introduce the
temperature, and the chemical potential, . The parameters in the model
are fixed by calculating the pion mass and decay constant in the dimensional
regularization at .Comment: 28 pages, 9 figures, v2: a few points corrected and references adde
A mathematical formalization of the parallel replica dynamics
The purpose of this article is to lay the mathematical foundations of a well
known numerical approach in computational statistical physics and molecular
dynamics, namely the parallel replica dynamics introduced by A.F. Voter. The
aim of the approach is to efficiently generate a coarse-grained evolution (in
terms of state-to-state dynamics) of a given stochastic process. The approach
formally consists in concurrently considering several realizations of the
stochastic process, and tracking among the realizations that which, the
soonest, undergoes an important transition. Using specific properties of the
dynamics generated, a computational speed-up is obtained. In the best cases,
this speed-up approaches the number of realizations considered. By drawing
connections with the theory of Markov processes and, in particular, exploiting
the notion of quasi-stationary distribution, we provide a mathematical setting
appropriate for assessing theoretically the performance of the approach, and
possibly improving it
Answering Mermin's Challenge with Conservation per No Preferred Reference Frame
In 1981, Mermin published a now famous paper titled, "Bringing home the
atomic world: Quantum mysteries for anybody" that Feynman called, "One of the
most beautiful papers in physics that I know." Therein, he presented the
"Mermin device" that illustrates the conundrum of quantum entanglement per the
Bell spin states for the "general reader." He then challenged the "physicist
reader" to explain the way the device works "in terms meaningful to a general
reader struggling with the dilemma raised by the device." Herein, we show how
"conservation per no preferred reference frame (NPRF)" answers that challenge.
In short, the explicit conservation that obtains for Alice and Bob's
Stern-Gerlach spin measurement outcomes in the same reference frame holds only
on average in different reference frames, not on a trial-by-trial basis. This
conservation is SO(3) invariant in the relevant symmetry plane in real space
per the SU(2) invariance of its corresponding Bell spin state in Hilbert space.
Since NPRF is also responsible for the postulates of special relativity, and
therefore its counterintuitive aspects of time dilation and length contraction,
we see that the symmetry group relating non-relativistic quantum mechanics and
special relativity via their "mysteries" is the restricted Lorentz group.Comment: 18 pages, 9 figures. This version as revised and resubmitted to
Scientific Report
A new root-knot nematode, Meloidogyne moensi n. sp. (Nematoda : Meloidogynidae), parasitizing Robusta coffee from Western Highlands, Vietnam
A new root-knot nematode, parasitizing Robusta coffee in Dak Lak Province, Western Highlands of Vietnam, is described as Meloidogyne moensi n. sp. Morphological and molecular analyses demonstrated that this species differs clearly from other previously described root-knot nematodes. Morphologically, the new species is characterized by a swollen body of females with a small posterior protuberance that elongated from ovoid to saccate; perineal patterns with smooth striae, continuous and low dorsal arch; lateral lines marked as a faint space or linear depression at junction of the dorsal and ventral striate; distinct phasmids; perivulval region free of striae; visible and wide tail terminus surrounding by concentric circles of striae; medial lips of females in dumbbell-shaped and slightly raised above lateral lips; female stylet is normally straight with posteriorly sloping stylet knobs; lip region of second stage juvenile (J2) is not annulated; medial lips and labial disc of J2 formed dumbbell shape; lateral lips are large and triangular; tail of J2 is conoid with rounded unstriated tail tip; distinct phasmids and hyaline; dilated rectum. Meloidogyne moensi n. sp. is most similar to M. africana, M. ottersoni by prominent posterior protuberance. Results of molecular analysis of rDNA sequences including the D2-D3 expansion regions of 28S rDNA, COI, and partial COII/16S rRNA of mitochondrial DNA support for the new species status
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