156,904 research outputs found
Low-Latitude Coronal Holes at the Minimum of the 23rd Solar Cycle
Low and mid-latitude coronal holes (CHs) observed on the Sun during the
current solar activity minimum (from September 21, 2006, Carrington rotation
(CR) 2048, until June 26, 2009 (CR 2084)) were analyzed using {\it SOHO}/EIT
and STEREO-A SECCHI EUVI data. From both the observations and Potential Field
Source Surface (PFSS) modeling, we find that the area occupied by CHs inside a
belt of around the solar equator is larger in the current 2007
solar minimum relative to the similar phase of the previous 1996 solar minimum.
The enhanced CH area is related to a recurrent appearance of five persistent
CHs, which survived during 7-27 solar rotations. Three of the CHs are of
positive magnetic polarity and two are negative. The most long-lived CH was
being formed during 2 days and existed for 27 rotations. This CH was associated
with fast solar wind at 1 AU of approximately 620 km s. The 3D
MHD modeling for this time period shows an open field structure above this CH.
We conclude that the global magnetic field of the Sun possessed a multi-pole
structure during this time period. Calculation of the harmonic power spectrum
of the solar magnetic field demonstrates a greater prevalence of multi-pole
components over the dipole component in the 2007 solar minimum compared to the
1996 solar minimum. The unusual large separation between the dipole and
multi-pole components is due to the very low magnitude of the dipole component,
which is three times lower than that in the previous 1996 solar minimum.Comment: 14 pages, 7 figure
Fluorine in a Carbon-Enhanced Metal-Poor Star
The fluorine abundance of the Carbon-Enhanced Metal-Poor (CEMP) star HE
1305+0132 has been derived by analysis of the molecular HF (1-0) R9 line at
2.3357 microns in a high-resolution (R = 50,000) spectrum obtained with the
Phoenix spectrometer and Gemini-South telescope. Our abundance analysis makes
use of a CNO-enhanced ATLAS12 model atmosphere characterized by a metallicity
and CNO enhancements determined utilizing medium-resolution (R = 3,000) optical
and near-IR spectra. The effective iron abundance is found to be [Fe/H] = -2.5,
making HE 1305+0132 the most Fe-deficient star, by more than an order of
magnitude, for which the abundance of fluorine has been measured. Using
spectral synthesis, we derive a super-solar fluorine abundance of A(19F) = 4.96
+/- 0.21, corresponding to a relative abundance of [F/Fe] = 2.90. A single line
of the Phillips C_2 system is identified in our Phoenix spectrum, and along
with multiple lines of the first-overtone vibration-rotation CO (3-1) band
head, C and O abundances of A(12C) = 8.57 +/- 0.11 and A(16O) = 7.04 +/- 0.14
are derived. We consider the striking fluorine overabundance in the framework
of the nucleosynthetic processes thought to be responsible for the
C-enhancement of CEMP stars and conclude that the atmosphere of HE 1305+0132
was polluted via mass transfer by a primary companion during its asymptotic
giant branch phase. This is the first study of fluorine in a CEMP star, and it
demonstrates that this rare nuclide can be a key diagnostic of nucleosynthetic
processes in the early Galaxy.Comment: 13 pages, 3 figures; Accepted for publication in ApJ Letter
Temperature-dependent errors in nuclear lattice simulations
We study the temperature dependence of discretization errors in nuclear
lattice simulations. We find that for systems with strong attractive
interactions the predominant error arises from the breaking of Galilean
invariance. We propose a local "well-tempered" lattice action which eliminates
much of this error. The well-tempered action can be readily implemented in
lattice simulations for nuclear systems as well as cold atomic Fermi systems.Comment: 33 pages, 17 figure
Reliable and robust molecular sexing of the hen harrier (Circus cyaneus) using PCR-RFLP of the CHD1 gene
The hen harrier (Circus cyaneus) is a bird of prey that is persecuted in the United Kingdom, and there is a need for a DNA-based individual identification and sexing system for the use in forensic investigations. This study reports a new set of PCR primers for the chromo-helicase-DNA-binding protein 1 gene, which allows sexing using PCR-RFLP. Instead of exonic primers that amplify across a large intron, this set consists of a primer within the intron, enabling reduction in amplicon sizes from 356 to 212 bp and 565 to 219 bp in W and Z chromosomes. DNA degradation and dilution experiments demonstrate that this set is significantly more robust than one that amplifies across the intron, and sequencing of the intronic primer-binding region across several individuals shows that it is highly conserved. While our objective is to incorporate this primer set into an STR-based individualization kit, it may in the meantime prove useful in forensic or conservation studies
Generalized Hamilton-Jacobi equations for nonholonomic dynamics
Employing a suitable nonlinear Lagrange functional, we derive generalized
Hamilton-Jacobi equations for dynamical systems subject to linear velocity
constraints. As long as a solution of the generalized Hamilton-Jacobi equation
exists, the action is actually minimized (not just extremized)
Modulation Doping near Mott-Insulator Heterojunctions
We argue that interesting strongly correlated two-dimensional electron
systems can be created by modulation doping near a heterojunction between Mott
insulators. Because the dopant atoms are remote from the carrier system, the
electronic system will be weakly disordered. We argue that the competition
between different ordered states can be engineered by choosing appropriate
values for the dopant density and the setback distance of the doping layer. In
particular larger setback distances favor two-dimensional antiferromagnetism
over ferromagnetism. We estimate some key properties of modulation-doped Mott
insulator heterojunctions by combining insights from Hartree-Fock-Theory and
Dynamical-Mean-Field-Theory descriptions and discuss potentially attractive
material combinations.Comment: 9 pages, 9 figures, submitte
Inhibition of DNA ejection from bacteriophage by Mg+2 counterions
The problem of inhibiting viral DNA ejection from bacteriophages by
multivalent counterions, specifically Mg counterions, is studied.
Experimentally, it is known that MgSO salt has a strong and non-monotonic
effect on the amount of DNA ejected. There exists an optimal concentration at
which the minimum amount of DNA is ejected from the virus. At lower or higher
concentrations, more DNA is ejected from the capsid. We propose that this
phenomenon is the result of DNA overcharging by Mg multivalent
counterions. As Mg concentration increases from zero, the net charge of
DNA changes from negative to positive. The optimal inhibition corresponds to
the Mg concentration where DNA is neutral. At lower/higher
concentrations, DNA genome is charged. It prefers to be in solution to lower
its electrostatic self-energy, which consequently leads to an increase in DNA
ejection. By fitting our theory to available experimental data, the strength of
DNADNA short range attraction energies, mediated by Mg, is found to
be 0.004 per nucleotide base. This and other fitted parameters agree
well with known values from other experiments and computer simulations. The
parameters are also in aggreement qualitatively with values for tri- and
tetra-valent counterions.Comment: 17 pages, 4 figures, improved manuscript. Submitted to J. Chem. Phys
(2010
Chiral symmetry breaking in a uniform external magnetic field II. Symmetry restoration at high temperatures and chemical potentials
Chiral symmetry is dynamically broken in quenched, ladder QED at weak gauge
couplings when an external magnetic field is present. In this paper, we show
that chiral symmetry is restored above a critical chemical potential and the
corresponding phase transition is of first order. In contrast, the chiral
symmetry restoration at high temperatures (and at zero chemical potential) is a
second order phase transition.Comment: Latex; 12 pages; 8 postscript figures include
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