Unified description of the dynamics of quintessential scalar fields

Using the dynamical system approach, we describe the general dynamics of cosmological scalar fields in terms of critical points and heteroclinic lines. It is found that critical points describe the initial and final states of the scalar field dynamics, but that heteroclinic lines which give a more complete description of the evolution in between the critical points. In particular, the heteroclinic line that departs from the (saddle) critical point of perfect fluid-domination is the representative path in phase space of quintessence fields that may be viable dark energy candidates. We also discuss the attractor properties of the heteroclinic lines, and their importance for the description of thawing and freezing fields.Comment: Minor changes to the text and two new figures, main conclusions unchanged. 12 pages, 11 figures, uses RevTe

Clustering Algorithms: Their Application to Gene Expression Data

Gene expression data hide vital information required to understand the biological process that takes place in a particular organism in relation to its environment. Deciphering the hidden patterns in gene expression data proffers a prodigious preference to strengthen the understanding of functional genomics. The complexity of biological networks and the volume of genes present increase the challenges of comprehending and interpretation of the resulting mass of data, which consists of millions of measurements; these data also inhibit vagueness, imprecision, and noise. Therefore, the use of clustering techniques is a first step toward addressing these challenges, which is essential in the data mining process to reveal natural structures and iden-tify interesting patterns in the underlying data. The clustering of gene expression data has been proven to be useful in making known the natural structure inherent in gene expression data, understanding gene functions, cellular processes, and subtypes of cells, mining useful information from noisy data, and understanding gene regulation. The other benefit of clustering gene expression data is the identification of homology, which is very important in vaccine design. This review examines the various clustering algorithms applicable to the gene expression data in order to discover and provide useful knowledge of the appropriate clustering technique that will guarantee stability and high degree of accuracy in its analysis procedure

The Influence of Age and Sex on Genetic Associations with Adult Body Size and Shape : A Large-Scale Genome-Wide Interaction Study

Genome-wide association studies (GWAS) have identified more than 100 genetic variants contributing to BMI, a measure of body size, or waist-to-hip ratio (adjusted for BMI, WHRadjBMI), a measure of body shape. Body size and shape change as people grow older and these changes differ substantially between men and women. To systematically screen for age-and/or sex-specific effects of genetic variants on BMI and WHRadjBMI, we performed meta-analyses of 114 studies (up to 320,485 individuals of European descent) with genome-wide chip and/or Metabochip data by the Genetic Investigation of Anthropometric Traits (GIANT) Consortium. Each study tested the association of up to similar to 2.8M SNPs with BMI and WHRadjBMI in four strata (men 50y, women 50y) and summary statistics were combined in stratum-specific meta-analyses. We then screened for variants that showed age-specific effects (G x AGE), sex-specific effects (G x SEX) or age-specific effects that differed between men and women (G x AGE x SEX). For BMI, we identified 15 loci (11 previously established for main effects, four novel) that showed significant (FDR= 50y). No sex-dependent effects were identified for BMI. For WHRadjBMI, we identified 44 loci (27 previously established for main effects, 17 novel) with sex-specific effects, of which 28 showed larger effects in women than in men, five showed larger effects in men than in women, and 11 showed opposite effects between sexes. No age-dependent effects were identified for WHRadjBMI. This is the first genome-wide interaction meta-analysis to report convincing evidence of age-dependent genetic effects on BMI. In addition, we confirm the sex-specificity of genetic effects on WHRadjBMI. These results may providefurther insights into the biology that underlies weight change with age or the sexually dimorphism of body shape.Peer reviewe

Mechanical properties of Blair dolomite

Pressure-volume, uniaxial stress loading to failure, uniaxial strain, and acoustic velocity determinations were made on Blair dolomite at confining pressures ranging to 3.5 GPa (Pa = Paschals where 10/sup 5/ Pa = 1 bar or 0.1 GPa = 1 kbar). The bulk modulus K, rapidly rises from an initial 10.4 GPa (at atmospheric pressure) to 102.0 GPa at 1 GPa pressure. At higher pressures, K remains essentially constant (110 GPa). The maximum volume change on loading is 3.9% at 3.5 GPa; the unloading closely follows the loading path. Comparison of uninxial stress tests in compression to 0.7 GPa and extension to 2.1 GPa confining pressure demonstrates that the characteristic shear stress at failure as well as the transition from brittle fracture to ductile flow is strongly dependent upon both the value of the intermediate principal stress sigma /sub 2/ and the rate of strain. The onset of dilatancy as determined in uniaxial compression occurs at about two-thirds of the failure stress. The uniaxial strain loading path is well below the failure envelope in compression. In uniaxial stress loading (compression), Young' s modulus (E) and shear modulus ( mu ) are demonstrated to be very sensitive to both confining pressure and to the level of shear stress. For example, at pressures of 0.1 MPa to 0.5 GPa, both E and mu first increase up to shear stresses of 0.05 to 0.15 GPa and then decrease at all higher stress values. These moduli are shown to be very sensitive indicators of the onset of dilatancy. Elastic moduli as derived from acoustic velocity measurements also increase with confining pressure (to 1 GPa), with the major change occurring below 0.1 GPa. All of the observations made at nonhydrostatic conditions are consistent with the closure of preexisting cracks at low pressures and low shear stresses followed by an increasing rate of crack growth as stress is increased, even at the higher corfining pressures. However, some cracks, which would normally close with hydrostatic pre ssure, remain open under uniaxial stress loading at similar mean pressures. (auth

High-pressure mechanical properties of Kayenta sandstone

Pressure-volume, uniaxial strain loading, uniaxial stress loading to failure, and ultrasoric velocity detemninations have been performed on samples of Kayenta sandstone from the site of the Mixed Company event. Hydrostatic pressure of 3 GPa produces about 23% volume compression, with 9% permanent compaction remaining upon unloading. The pressure-volume data indicate that crush-up of porosity begins between 200 and 300 MPa. In uniaxial strain loading, the sandstone loads directly to the vicinity of the failure envelope, then parallels that envelope to the highest confining pressure (480 MPa). At strain rates of about 10/sup -4//s, the loading path in uniaxial strain up to 200 MPa is coincident in pressure-volume space with the shock-loading path (at a strain rate of about 10/sup 5//s) observed on samples from the same block. The permanent compaction, after unloading under conditions of uniaxial strain from 625 MPa mean pressure, is about 3.8%. Uniaxial stress loading indicates a brittle-ductile transition between 400 and 500 MPa mean pressure. Between 100 and 500 MPa mean pressure, the slope of the failure envelope is decreased consideably with respect to that below 100 MPa and between 500 and 900 MPa. This plateau, which is not present in the failure envelope for material subjected to a 700-MPa confining pressure before the uniaxial stress test, is interpreted as being due to pore crush-up during hydrostatic loading. As confining pressure is increased from 0.1 MPa to 1 GPa, the measured compressional velocity increases from 3.0 km/s to 5.0 km/s and the shear velocity increases from 1.5 km/s to 2.4 km/s. Small decreases in compressional velocity ( approximates 5%1 between 10 and 40 MPa are attributed to local brittle failure resulting from highly localized stress concentrations within the sample under hydrostatic loading. (auth

Mechanical properties of Nugget sandstone

The mechanical properties of Nugget sandstone have been determined from a number of independent measurements at pressures up to 30 kbar. Pressure- volume, strength, uniaxial stress, and uniaxial strain tests yield the failure surface and effective moduli as a function of stress state, i.e., mean pressure and shear stress. Acoustic velocity determinations provide the effective moduli for low-amplitude dynamic waves. At atmospheric pressure the initial effective bulk modulus in tests with applied differential stresses (~40 kbar) differs from that determined hydrostatically (23 kbar). This and a large pressure derivative of the shear modulus at low pressure are believed to be due to an abundance of cracks with low aspect ratios. The initial effective shear modulus of about 55 kbar increases rapidly with the closing of cracks. At 1 kbar confining pressure, a shear modulus of about l20 kbar is determined in both uniaxial stress and uniaxial strain experiments. The rock has an ultimate strength comparable to granite (1.2 kbar unconfined) and exhibits brittle behavior at failure to the highest mean pressure studied (14 kbar). Failure is preceded by dilatant behavior. (auth