8,594 research outputs found
maigesPack: A Computational Environment for Microarray Data Analysis
Microarray technology is still an important way to assess gene expression in
molecular biology, mainly because it measures expression profiles for thousands
of genes simultaneously, what makes this technology a good option for some
studies focused on systems biology. One of its main problem is complexity of
experimental procedure, presenting several sources of variability, hindering
statistical modeling. So far, there is no standard protocol for generation and
evaluation of microarray data. To mitigate the analysis process this paper
presents an R package, named maigesPack, that helps with data organization.
Besides that, it makes data analysis process more robust, reliable and
reproducible. Also, maigesPack aggregates several data analysis procedures
reported in literature, for instance: cluster analysis, differential
expression, supervised classifiers, relevance networks and functional
classification of gene groups or gene networks
Hydrogen Recombination with Multilevel atoms
Hydrogen recombination is one of the most important atomic processes
in many astrophysical objects such as Type II supernova (SN~II)
atmospheres, the high redshift universe during the cosmological recombination
era, and H II regions in the interstellar medium. Accurate predictions of
the ionization fraction can be quite different from those given by a
simple solution
if one takes into account many angular momentum sub-states,
non-resonant processes, and calculates the rates of all atomic
processes from the solution of the radiative transfer equation
instead of using a Planck function under the assumption of thermal
equilibrium. We use the general
purpose model atmosphere code PHOENIX 1D to
compare how the fundamental probabilities such as the photo-ionization
probability, the escape probability, and the collisional de-excitation
probability are affected by the presence of other metals in the
environment, multiple angular momentum sub-states, and
non-resonant processes. Our comparisons are based on a model of SN
1999em, a SNe Type II, 20 days after its explosion.Comment: 29 pages, 12 figures, MNRAS, in pres
Implications of a Minimal SO(10) Higgs Structure
A minimal SO(10) Higgs structure involving a single adjoint field along with
spinors, vectors and singlets has been shown to break the SO(10) gauge symmetry
to the standard model while stabilizing the F-flat directions and solving the
doublet-triplet splitting problem naturally. With this minimal set of Higgs
fields, we show how to construct quark and lepton mass matrices which explain
well the many features of the observed spectrum, including the Georgi-Jarlskog
mass relations. A large mixing of the muon- and tau-neutrinos results naturally
as observed in the atmospheric neutrino data. A particular model relying on a
family symmetry has been constructed which realizes the desired mass matrices.Comment: 10 pages, REVTEX, contribution submitted to NEUTRINO 98 Conferenc
Resonant recoil in extreme mass ratio binary black hole mergers
The inspiral and merger of a binary black hole system generally leads to an
asymmetric distribution of emitted radiation, and hence a recoil of the remnant
black hole directed opposite to the net linear momentum radiated. The recoil
velocity is generally largest for comparable mass black holes and particular
spin configurations, and approaches zero in the extreme mass ratio limit. It is
generally believed that for extreme mass ratios eta<<1, the scaling of the
recoil velocity is V {\propto} eta^2, where the proportionality coefficient
depends on the spin of the larger hole and the geometry of the system (e.g.
orbital inclination). Here we show that for low but nonzero inclination
prograde orbits and very rapidly spinning large holes (spin parameter
a*>0.9678) the inspiralling binary can pass through resonances where the
orbit-averaged radiation-reaction force is nonzero. These resonance crossings
lead to a new contribution to the kick, V {\propto} eta^{3/2}. For these
configurations and sufficiently extreme mass ratios, this resonant recoil is
dominant. While it seems doubtful that the resonant recoil will be
astrophysically significant, its existence suggests caution when extrapolating
the results of numerical kick results to extreme mass ratios and near-maximal
spins.Comment: fixed references; matches PRD accepted version (minor revision); 9
pages, 2 figure
Superconductivity in metal rich Li-Pd-B ternary Boride
8K superconductivity was observed in the metal rich Li-Pd-B ternary system.
Structural, microstructural, electrical and magnetic investigations for various
compositions proved that Li2Pd3B compound, which has a cubic structure composed
of distorted Pd6B octahedrons, is responsible for the superconductivity. This
is the first observation of superconductivity in metal rich ternary borides
containing alkaline metal and Pd as a late transition metal. The compound
prepared by arc melting has high density, is stable in the air and has an upper
critical field, Hc2(0), of 6T.Comment: 4 pages, 5 figur
Growth and mineral nutrition responses of mycorrhizal and non-mycorrhizal cowpea, pigeon pea and groundnut to phosphorus sources of different solubilities
The effects of a superphosphate (SP) and a rock phosphate (RP), with equal total P contents, on the growth and mineral nutrition responses of mycorrhizal and nonmycorrhizal cowpea, pigeon pea and groundnut were investigated in a pot experiment using an air-dry gamma ray-sterilized (1.5Mrad) Andisol subsoil. Adequate amounts of micronutrients were added to the pot soils as supplements. The plants were inoculated with surface-sterilized 100 spores/pot of Glomus etunicatum or none and with
Rhizobium strains. At their maturities, dry weights of plant parts and nodule number, root length, arbuscular mycorrhizal fungal (AMF) colonization of roots and AMF spore production were also measured. Shoot nitrogen and phosphorus concentrations were determined by the Micro-Kjeldahl distillation and ammonium-molybdenum blue methods, respectively. Shoot copper and iron concentrations were measured by the atomic absorption spectrophotometry. Mycorrhiza formation was greater with superphosphate than with rock phosphate treatments. Rock phosphate enhanced mycorrhization in cowpea and pigeon pea but it decreased it in groundnut. Superphosphate-treated cowpea and pigeon pea plants were larger than RP-treated plants whether mycorrhizal or not but in
groundnut growth increased only when the plant was treated with SP and inoculated with AMF. Mycorrhizal enhancement of shoot growth in superphosphate-fertilized groundnut could be a direct consequence of improved P nutrition resulting from increased hyphal uptake and/or enlarged absorptive root surface due to increased root fineness. There were similarities in shoot dry matter yields as well as shoot P uptakes of both mycorrhizal and non-mycorrhizal RP-treated plants suggesting that the legumes were so unresponsive to the RP that even mycorrhization could not trigger any response in them. The increased contents of N, Cu and Fe in the shoots of mycorrhizal SP-fertilized plants were observed to be the result of larger shoot sizes except with Fe in groundnut shoot whose enhancement could be related to a good mycorrhiza formation and a concomitant improvement in P nutrition which may further have been influenced by its fine root structure. There was a very close interdependency of fine root structure, AMF colonization, AMFspore production and improved P and Fe nutrition in groundnut as a result of soluble phosphate application.Journal of Science & Technology (Ghana) Vol. 27 (2) 2007: pp. 43-5
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