406 research outputs found
Smooth Paths on Three Dimensional Lattice
A particular class of random walks with a spin factor on a three dimensional
cubic lattice is studied. This three dimensional random walk model is a simple
generalization of random walk for the two dimensional Ising model. All critical
diffusion constants and associated critical exponents are calculated. Continuum
field theories such as Klein-Gordon, Dirac and massive Chern-Simons theories
are constructed near several critical points.Comment: 7 pages,NUP-A-94-
Joint stage recognition and anatomical annotation of drosophila gene expression patterns
Motivation: Staining the mRNA of a gene via in situ hybridization (ISH) during the development of a Drosophila melanogaster embryo delivers the detailed spatio-temporal patterns of the gene expression. Many related biological problems such as the detection of co-expressed genes, co-regulated genes and transcription factor binding motifs rely heavily on the analysis of these image patterns. To provide the text-based pattern searching for facilitating related biological studies, the images in the Berkeley Drosophila Genome Project (BDGP) study are annotated with developmental stage term and anatomical ontology terms manually by domain experts. Due to the rapid increase in the number of such images and the inevitable bias annotations by human curators, it is necessary to develop an automatic method to recognize the developmental stage and annotate anatomical terms
Oribatid mites show how climate and latitudinal gradients in organic matter can drive large-scale biodiversity patterns of soil communities
Aim: The factors determining spatial distributions and diversity of terrestrial invertebrates are typically investigated at small scales. Largeâscale studies are lacking for soil animals, which control microbial communities and represent one of the most diverse yet poorly known animal assemblages. Here, we analyzed a major group (Oribatida) to test whether belowground macroecological patterns can be predicted by climatic variables, vegetation and largeâscale variation in key soil properties.
Location: We modelled the multivariate distribution of more than 100 species using biodiversity data collected across Great Britain in the framework of the Countryside Survey (http://www.countrysidesurvey.org.uk).
Methods: We analyzed speciesâlevel data from 582 samples collected across 162 hectads (10 Ă 10 km) covering the largest possible range of vegetation types, soil properties and climatic conditions within GB. We created the first largeâscale maps of soil animal diversity metrics at the GB scale, including novel estimates of metrics of phylogenetic diversity (PD). Using structural equation modelling, we quantified the direct and indirect effects of location (latitude, longitude), plant community structure and abiotic factors such as precipitation on species composition, richness and PD.
Results: We found that variation in species composition follows a latitudinal gradient with diversity generally increasing northward. The latitudinal variation in species composition drives PD via changes in both species richness and phylogenetic distance between species. This gradient is mostly determined by latitudinal variation in precipitation and organic matter, which were very good predictors of species composition. Precipitation and organic matter were, however, relatively weak while statistically significant predictors of diversity metrics.
Conclusions: Past studies have emphasized the unpredictability of species distributions and variation in species composition in hyper diverse soil animal communities. However, past studies were conducted at small scales, where stochastic factors may weaken the signal of deterministic factors. Oribatid mites in our study show for the first time that the large scale latitudinal gradients in climate and organic matter predict not only variation in species composition but also taxonomic and PD of soil animal communities
Quantum phase transitions and collapse of the Mott gap in the dimensional half-filled Hubbard model
We study the low-energy asymptotics of the half-filled Hubbard model with a
circular Fermi surface in continuous dimensions, based on the
one-loop renormalization-group (RG) method. Peculiarity of the
dimensions is incorporated through the mathematica structure of the elementary
particle-partcile (PP) and particle-hole (PH) loops: infrared logarithmic
singularity of the PH loop is smeared for . The RG flows indicate
that a quantum phase transition (QPT) from a metallic phase to the Mott
insulator phase occurs at a finite on-site Coulomb repulsion for
. We also discuss effects of randomness.Comment: 12 pages, 10 eps figure
Differential effects of fluvoxamine and other antidepressants on the biotransformation of melatonin
Melatonin, the predominant product of the pineal gland, is involved in the maintenance of diurnal rhythms. Nocturnal blood concentrations of melatonin have been shown to be enhanced by fluvoxamine, but not by other serotonin reuptake inhibitors. Because fluvoxamine is an inhibitor of several cytochrome P450 (CYP) enzymes, the authors studied the biotransformation of melatonin and the effects of fluvoxamine on the metabolism of melatonin in vitro using human liver microsomes and recombinant human CYP isoenzymes. Melatonin was found to be almost exclusively metabolized by CYP1A2 to 6-hydroxymelatonin and N-acetylserotonin with a minimal contribution of CYP2C19. Both reactions were potently inhibited by fluvoxamine, with a Ki of 0.02 microM for the formation of 6-hydroxymelatonin and 0.05 microM for the formation of N-acetylserotonin. Other than fluvoxamine, fluoxetine, paroxetine, citalopram, imipramine, and desipramine were also tested at 2 and 20 microM. Among the other antidepressants, only paroxetine was able to affect the metabolism of melatonin at supratherapeutic concentrations of 20 microM, which did not reach by far the magnitude of the inhibitory potency of fluvoxamine. The authors concluded that fluvoxamine is a potent inhibitor of melatonin degradation. Because this inhibitory action is also found in vivo, fluvoxamine might be used as an enhancer of melatonin, which might offer new therapeutic possibilities of fluvoxamine
The nucleosynthesis of heavy elements in Stars : The key isotope 25Mg
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedWe have measured the radiative neutron-capture cross section and the total neutron-induced cross section of one of the most important isotopes for the s process, the 25Mg. The measurements have been carried out at the neutron time-of-flight facilities n-TOF at CERN (Switzerland) and GELINA installed at the EC-JRC-IRMM (Belgium). The cross sections as a function of neutron energy have been measured up to approximately 300 keV, covering the energy region of interest to the s process. The data analysis is ongoing and preliminary results show the potential relevance for the s process.Peer reviewe
Composite quasiparticle formation and the low-energy effective Hamiltonians of the one- and two-dimensional Hubbard Model
We investigate the effect of hole doping on the strong-coupling Hubbard model
at half-filling in spatial dimensions . We start with an
antiferromagnetic mean-field description of the insulating state, and show that
doping creates solitons in the antiferromagnetic background. In one dimension,
the soliton is topological, spinless, and decoupled from the background
antiferromagnetic fluctuations at low energies. In two dimensions and above,
the soliton is non-topological, has spin quantum number 1/2, and is strongly
coupled to the antiferromagnetic fluctuations. We derive the effective action
governing the quasiparticle motion, study the properties of a single carrier,
and comment on a possible description at finite concentration.Comment: REVTEX 3.0, 22 pages with 14 figures in the PostScript format
compressed using uufile. Submitted to Phys. Rev. B. The complete PostScript
file including figures can be obtained via ftp at
ftp://serval.berkeley.edu/hubbard.ps . It is also available via www at
http://roemer.fys.ku.dk/recent.ht
Interlayer tunneling in a non-Fermi-liquid metal
We study the effect of interlayer tunneling in the gauge theory describing a
quasi-two-dimensional paramagnetic metal close to a second-order or weakly
first-order antiferromagnetic phase boundary. In that theory, two species of
fermions have opposite (rather than equal) charges with respect to the gauge
field. We find that single-particle interlayer tunneling is suppressed at low
energies. The effect of pair tunneling is analyzed within the
expansion. The resulting phase diagram has superconducting and non-Fermi-liquid
normal phases, and so is compatible with that of the copper-oxide
superconductors.Comment: 13 pages, latex, one uuencoded postscript figur
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