691 research outputs found
First-principle study of excitonic self-trapping in diamond
We present a first-principles study of excitonic self-trapping in diamond.
Our calculation provides evidence for self-trapping of the 1s core exciton and
gives a coherent interpretation of recent experimental X-ray absorption and
emission data. Self-trapping does not occur in the case of a single valence
exciton. We predict, however, that self-trapping should occur in the case of a
valence biexciton. This process is accompanied by a large local relaxation of
the lattice which could be observed experimentally.Comment: 12 pages, RevTex file, 3 Postscript figure
On the Canonical Formalism for a Higher-Curvature Gravity
Following the method of Buchbinder and Lyahovich, we carry out a canonical
formalism for a higher-curvature gravity in which the Lagrangian density is given in terms of a function of the salar curvature as . The local Hamiltonian is obtained by a
canonical transformation which interchanges a pair of the generalized
coordinate and its canonical momentum coming from the higher derivative of the
metric.Comment: 11 pages, no figures, Latex fil
UV-B radiation amplification factor determined based on the simultaneous observation of total ozone and global spectral irradiance
The Japan Meteorological Agency started the spectral observation of solar ultraviolet (UV) irradiance on 1 January 1990 at Tateno, Aerological Observatory in Tsukuba (35 deg N, 140 deg E). The observation has been carried out using the Brewer spectrophotometer for the wavelengths from 290 to 325 nm with a 0.5 nm interval every hour from 30 minutes before sunrise to 30 minutes after sunset throughout a year. Because of remarkable similarity within observed spectra, an observed spectrum can be expressed by a simple combination of a reference spectrum and two parameters expressing the deformation of the observed spectrum from the reference. By use of the relation between one of the deformation parameters and the total ozone simultaneously observed with the Dobson spectrophotometer, the possible increase of UV irradiance due to ozone depletion is estimated. For damaging UV, the irradiance possibly increases about 19 percent with the ozone depletion of 10 percent at noon throughout the year in the northern midlatitudes. DUV at noon on the summer solstice possibly increases about 5.6 percent with the ozone depletion of 10 m atm-cm for all latitudes in the Northern Hemisphere
Microstructure and mechanical effects of spark plasma sintering in alumina monolithic ceramics
The specific effects of spark plasma sintering (SPS) on the creep behavior, microstructure and mechanical properties of alumina monolithic ceramic were investigated. SPS introduces strains that concentrate at grain boundaries and inhibit crack growth, resulting in an improvement in the flexural strength and fracture toughness. However, creep blocks grain boundary movements and decreases the reliability of the material. These strains can be removed by a post-sintering thermal treatment, which plays an important role in the distribution of dislocations. Crown Copyright (c) 2012 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.The authors would like to acknowledge the help of the EU for the financial support received under the IP-NANOKER NMP3-CT-2005-515784. A.B. acknowledges the Spanish Ministry of Science and Innovation for her Juan de la Cierva Contract (JCI-2011-10498). The authors are grateful to the Central Support Service in Experimental Research (SCSIE), University of Valencia for providing the HR-TEM facility.Alvarez-Clemares, I.; Borrell Tomás, MA.; Agouram, S.; Torrecillas, R.; Fernandez, A. (2013). Microstructure and mechanical effects of spark plasma sintering in alumina monolithic ceramics. Scripta Materialia. 68(8):603-606. https://doi.org/10.1016/j.scriptamat.2012.12.016S60360668
Statistical Parsimony Networks and Species Assemblages in Cephalotrichid Nemerteans (Nemertea)
BACKGROUND: It has been suggested that statistical parsimony network analysis could be used to get an indication of species represented in a set of nucleotide data, and the approach has been used to discuss species boundaries in some taxa. METHODOLOGY/PRINCIPAL FINDINGS: Based on 635 base pairs of the mitochondrial protein-coding gene cytochrome c oxidase I (COI), we analyzed 152 nemertean specimens using statistical parsimony network analysis with the connection probability set to 95%. The analysis revealed 15 distinct networks together with seven singletons. Statistical parsimony yielded three networks supporting the species status of Cephalothrix rufifrons, C. major and C. spiralis as they currently have been delineated by morphological characters and geographical location. Many other networks contained haplotypes from nearby geographical locations. Cladistic structure by maximum likelihood analysis overall supported the network analysis, but indicated a false positive result where subnetworks should have been connected into one network/species. This probably is caused by undersampling of the intraspecific haplotype diversity. CONCLUSIONS/SIGNIFICANCE: Statistical parsimony network analysis provides a rapid and useful tool for detecting possible undescribed/cryptic species among cephalotrichid nemerteans based on COI gene. It should be combined with phylogenetic analysis to get indications of false positive results, i.e., subnetworks that would have been connected with more extensive haplotype sampling
Parton energy loss at strong coupling and the universal bound
The apparent universality of jet quenching observed in heavy ion collisions
at RHIC for light and heavy quarks, as well as for quarks and gluons, is very
puzzling and calls for a theoretical explanation. Recently it has been proposed
that the synchrotron--like radiation at strong coupling gives rise to a
universal bound on the energy of a parton escaping from the medium. Since this
bound appears quite low, almost all of the observed particles at high
transverse momentum have to originate from the surface of the hot fireball.
Here I make a first attempt of checking this scenario against the RHIC data and
formulate a "Universal Bound Model" of jet quenching that can be further tested
at RHIC and LHC.Comment: 8 pages, 2 figures, invited plenary talk given at "Hard Probes 2008"
Conference, 8-14 June 2008, Illa da Toxa, Galicia, Spai
Quadrupole Anisotropy in Dihadron Azimuthal Correlations in Central Au Collisions at =200 GeV
The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC)
reports measurements of azimuthal dihadron correlations near midrapidity in
Au collisions at =200 GeV. These measurements
complement recent analyses by experiments at the Large Hadron Collider (LHC)
involving central Pb collisions at =5.02 TeV, which
have indicated strong anisotropic long-range correlations in angular
distributions of hadron pairs. The origin of these anisotropies is currently
unknown. Various competing explanations include parton saturation and
hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies
in Au collisions compared to those seen in Pb collisions at the
LHC. The larger extracted values in Au collisions at RHIC are
consistent with expectations from hydrodynamic calculations owing to the larger
expected initial-state eccentricity compared with that from Pb
collisions. When both are divided by an estimate of the initial-state
eccentricity the scaled anisotropies follow a common trend with multiplicity
that may extend to heavy ion data at RHIC and the LHC, where the anisotropies
are widely thought to arise from hydrodynamic flow.Comment: 375 authors, 7 pages, 5 figures. Published in Phys. Rev. Lett. v2 has
minor changes to text and figures in response to PRL referee suggestions.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Neuroinflammation, Mast Cells, and Glia: Dangerous Liaisons
The perspective of neuroinflammation as an epiphenomenon following neuron damage is being replaced by the awareness of glia and their importance in neural functions and disorders. Systemic inflammation generates signals that communicate with the brain and leads to changes in metabolism and behavior, with microglia assuming a pro-inflammatory phenotype. Identification of potential peripheral-to-central cellular links is thus a critical step in designing effective therapeutics. Mast cells may fulfill such a role. These resident immune cells are found close to and within peripheral nerves and in brain parenchyma/meninges, where they exercise a key role in orchestrating the inflammatory process from initiation through chronic activation. Mast cells and glia engage in crosstalk that contributes to accelerate disease progression; such interactions become exaggerated with aging and increased cell sensitivity to stress. Emerging evidence for oligodendrocytes, independent of myelin and support of axonal integrity, points to their having strong immune functions, innate immune receptor expression, and production/response to chemokines and cytokines that modulate immune responses in the central nervous system while engaging in crosstalk with microglia and astrocytes. In this review, we summarize the findings related to our understanding of the biology and cellular signaling mechanisms of neuroinflammation, with emphasis on mast cell-glia interactions
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