930 research outputs found
Recalculation of QCD Corrections to Decay
We give a more complete calculation of decay, including
leading log QCD corrections from to in addition to corrections
from to . We have included the full set of dimension-6 operators
and corrected numerical mistakes of anomalous dimensions in a previous
paper\cite{Cho}. Comparing with the calculations without QCD running from
to \cite{Mis}, the inclusive decay rate is found to be enhanced.
At GeV, it results in 12\% enhancement, and for GeV, 15\% is
found. The total QCD effect makes an enhanced factor of 4.2 at GeV,
and 3.2 for GeV.Comment: 16 pages, 7 figures (uuencoded ps files), Changes of description. To
appear in Phys. Rev.
Counting and computing regions of -decomposition: algebro-geometric approach
New methods for -decomposition analysis are presented. They are based on
topology of real algebraic varieties and computational real algebraic geometry.
The estimate of number of root invariant regions for polynomial parametric
families of polynomial and matrices is given. For the case of two parametric
family more sharp estimate is proven. Theoretic results are supported by
various numerical simulations that show higher precision of presented methods
with respect to traditional ones. The presented methods are inherently global
and could be applied for studying -decomposition for the space of parameters
as a whole instead of some prescribed regions. For symbolic computations the
Maple v.14 software and its package RegularChains are used.Comment: 16 pages, 8 figure
Spin-phonon interaction and band effects in the high-T_C superconductor HgBa_2CuO_4
Band calculations show that a stripe-like anti-ferromagnetic spin wave is
enforced by a 'half-breathing' phonon distortion within the CuO plane of
HgBa_2CuO_4. This spin-phonon coupling is increased further by shear distortion
and by increased distance between Cu and apical oxygens. The effects from
spin-phonon coupling are consistent with many observations in high-T_C
materials. Spin-phonon coupling can be important for the mechanism of spin
fluctuations and superconductivity, although the effects are quantitatively
weak when using the local density potential.Comment: 4 pages, 1 figur
Study of temperature dependent atomic correlations in MgB
We have studied the evolution with temperature of the local as well as the
average crystal structure of MgB using the real-space atomic pair
distribution function (PDF) measured by high resolution neutron powder
diffraction. We have investigated the correlations of the B-B and B-Mg nearest
neighbor pair motion by comparing, in the wide temperature range from T=10 K up
to T=600 K, the mean-square displacements (MSD) of single atoms with the
mean-square relative displacements (MSRD) obtained from the PDF peak
linewidths. The results show that the single atom B and Mg vibrations are
mostly decoupled from each other, with a small predominance of positive (in
phase) correlation factor for both the B-B and B-Mg pairs. The small positive
correlation is almost temperature independent, in contrast with our theoretical
calculations; this can be a direct consequence of the strong decay processes of
the anharmonic phonons
Formation of Subtropical Mode Water in a high-resolution ocean simulation of the Kuroshio Extension region
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Ocean Modelling 17 (2007): 338-356, doi:10.1016/j.ocemod.2007.03.002.A high-resolution numerical model is used to examine the formation and variability of the North Pacific Subtropical
ModeWater (STMW) over a 3-year period. The STMW distribution is found to be highly variable in both
space and time, a characteristic often unexplored because of sparse observations or the use of coarse resolution
simulations. Its distribution is highly dependent on eddies, and where it was renewed during the previous winter.
Although the potential vorticity fluxes associated with down-front winds can be of the same order of magnitude
or even greater than the diabatic ones due to air-sea temperature differences, the latter dominate the potential
vorticity budget on regional and larger scales. Air-sea fluxes, however, are dominated by a few strong wind events,
emphasizing the importance of short time scales in the formation of mode waters. In the Kuroshio Extension
region, both advection and mixing play important roles to remove the STMW from the formation region.This work was sponsored by the National Science Foundation OCE-0220161 (S.J.) and OCE-0221781/0549225 (J.M.), the Office of Naval Research (J.M., M.M.), Department of Energy/CCPP (M.M.), and the Office of Science (BER), US Department of Energy, Grant No. DE-FG02-05ER64119 (J.M.)
Accessing Transversity in Double-Spin Asymmetries at the BNL-RHIC
We give upper bounds for transverse double-spin asymmetries in polarized
proton-proton collisions by saturating the positivity constraint for the
transversity densities at a low hadronic resolution scale. We consider prompt
photon, jet, pion, and heavy flavor production at the BNL Relativistic Heavy
Ion Collider (RHIC). Estimates of the expected statistical accuracy for such
measurements are presented, taking into account the acceptance of the RHIC
detectors.Comment: 15 pages, LaTeX, 2 figures as eps file
Fluctuating diamagnetism in underdoped high temperature superconductors
The fluctuation induced diamagnetism of underdoped high temperature
superconductors is studied in the framework of the Lawrence-Doniach model. By
taking into account the fluctuations of the phase of the order parameter only,
the latter reduces to a layered XY-model describing a liquid of vortices which
can be either thermally excited or induced by the external magnetic field. The
diamagnetic response is given by a current-current correlation function which
is evaluated using the Coulomb gas analogy. Our results are then applied to
recent measurements of fluctuation diamagnetism in underdoped YBCO. They allow
to understand both the observed anomalous temperature dependence of the
zero-field susceptibility and the two distinct regimes appearing in the
magnetic field dependence of the magnetization.Comment: 12 pages, 4 figures included, accepted for publication in PR
Relaxation Effects in the Transition Temperature of Superconducting HgBa2CuO4+delta
In previous studies on a number of under- and overdoped high temperature
superconductors, including YBa_{2}Cu_{3}O_{7-y} and Tl_{2}Ba_{2}CuO_{6+\delta},
the transition temperature T_c has been found to change with time in a manner
which depends on the sample's detailed temperature and pressure history. This
relaxation behavior in T_c is believed to originate from rearrangements within
the oxygen sublattice. In the present high-pressure studies on
HgBa_{2}CuO_{4+\delta} to 0.8 GPa we find clear evidence for weak relaxation
effects in strongly under- and overdoped samples () with
an activation energy . For overdoped
HgBa_{2}CuO_{4+\delta} E_{A} increases under pressure more rapidly than
previously observed for YBa_{2}Cu_{3}O_{6.41}, yielding an activation volume of
+11 \pm 5 cm^{3}; the dependence of T_c on pressure is markedly nonlinear, an
anomalous result for high-T_c superconductors in the present pressure range,
giving evidence for a change in the electronic and/or structural properties
near 0.4 GPa
Museum Genomics Confirms that the Lord Howe Island Stick Insect Survived Extinction
The Lord Howe Island stick insect, Dryococelus australis, was once common on the island but was driven to extinction after the arrival of ship rats in the early 20th century [1, 2]. It was thought to be extinct for decades, until a tiny population of similar-looking stick insects was discovered 20 km away, on the islet of Ball’s Pyramid, in 2001 [2]. Individuals from this population are currently being reared in Australia and elsewhere in the world, with the eventual goal of recolonizing Lord Howe Island [3]. Recent surveys of the wild population on Ball’s Pyramid suggest that it is among the world’s rarest species. However, there are significant morphological differences between Ball’s Pyramid and museum specimens, and there has never been a genetic confirmation of the rediscovered population’s species identity. Because Dryococelus is monotypic, there are also no known extant relatives for comparison. Using shotgun genomic data from the Ball’s Pyramid population, we assembled a draft genome and the complete mitochondrial genome. We found that the genome is massive, over 4 Gb in size, and is most likely hexaploid. We re-sequenced mitochondrial genomes from historic museum specimens collected on Lord Howe Island before the extinction event. Sequence divergence between the two populations is less than 1% and is within the range of intraspecific differences between the museum specimens, suggesting that they are conspecific and that D. australis has successfully evaded extinction so far. This work highlights the importance of museum collections for taxonomic validation in the context of ongoing conservation efforts
Bulk Electronic structure of NaCoO.1.3HO
High-energy (h = 5.95 keV) synchrotron Photoemission spectroscopy (PES)
is used to study bulk electronic structure of NaCoO.1.3HO,
the layered superconductor. In contrast to 3-dimensional doped Co oxides, Co
core level spectra show well-separated Co and Co ions.
Cluster calculations suggest low spin Co and Co character, and a
moderate on-site Coulomb correlation energy U3-5.5 eV. Photon
dependent valence band PES identifies Co and O derived
states, in near agreement with band structure calculations.Comment: 4 pages 4 figures Revised text added referenc
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