On the analytical determination of relaxation modulus of viscoelastic materials by Prony's interpolation method

A computer implementation to Prony's curve fitting by exponential functions is presented. The method, although more than one hundred years old, has not been utilized to its fullest capabilities due to the restriction that the time range must be given in equal increments in order to obtain the best curve fit for a given set of data. The procedure used in this paper utilizes the 3-dimensional capabilities of the Interactive Graphics Design System (I.G.D.S.) in order to obtain the equal time increments. The resultant information is then input into a computer program that solves directly for the exponential constants yielding the best curve fit. Once the exponential constants are known, a simple least squares solution can be applied to obtain the final form of the equation

Anomalous Nernst Effect in the Vortex-Liquid Phase of High-Temperature Superconductors by Layer Decoupling

Linear diamagnetism is predicted in the vortex-liquid phase of layered superconductors at temperatures just below the mean-field phase transition on the basis of a high-temperature analysis of the corresponding frustrated XY model. The diamagnetic susceptibility, and the Nernst signal by implication, is found to vanish with temperature as (T_c0 - T)^3 in the vicinity of the meanfield transition at T_c0. Quantitative agreement with recent experimental observations of a diamagnetic signal in the vortex-liquid phase of high-temperature superconductors is obtained.Comment: 8 pages, 3 figure

Evolutionary relationships among bifidobacteria and their hosts and environments.

BACKGROUND:The assembly of animal microbiomes is influenced by multiple environmental factors and host genetics, although the relative importance of these factors remains unclear. Bifidobacteria (genus Bifidobacterium, phylum Actinobacteria) are common first colonizers of gut microbiomes in humans and inhabit other mammals, social insects, food, and sewages. In humans, the presence of bifidobacteria in the gut has been correlated with health-promoting benefits. Here, we compared the genome sequences of a subset of the over 400 Bifidobacterium strains publicly available to investigate the adaptation of bifidobacteria diversity. We tested 1) whether bifidobacteria show a phylogenetic signal with their isolation sources (hosts and environments) and 2) whether key traits encoded by the bifidobacteria genomes depend on the host or environment from which they were isolated. We analyzed Bifidobacterium genomes available in the PATRIC and NCBI repositories and identified the hosts and/or environment from which they were isolated. A multilocus phylogenetic analysis was conducted to compare the genetic relatedness the strains harbored by different hosts and environments. Furthermore, we examined differences in genomic traits and genes related to amino acid biosynthesis and degradation of carbohydrates. RESULTS:We found that bifidobacteria diversity appears to have evolved with their hosts as strains isolated from the same host were non-randomly associated with their phylogenetic relatedness. Moreover, bifidobacteria isolated from different sources displayed differences in genomic traits such as genome size and accessory gene composition and on particular traits related to amino acid production and degradation of carbohydrates. In contrast, when analyzing diversity within human-derived bifidobacteria, we observed no phylogenetic signal or differences on specific traits (amino acid biosynthesis genes and CAZymes). CONCLUSIONS:Overall, our study shows that bifidobacteria diversity is strongly adapted to specific hosts and environments and that several genomic traits were associated with their isolation sources. However, this signal is not observed in human-derived strains alone. Looking into the genomic signatures of bifidobacteria strains in different environments can give insights into how this bacterial group adapts to their environment and what types of traits are important for these adaptations

Repeated Relativistic Ejections in GRS 1915+105

In 1994 February-August we observed with the VLA four ejection events of radio emitting clouds from the high energy source GRS 1915+105. These events are all consistent with anti-parallel ejections of twin pairs of clouds moving away from the compact source at $\sim$ 0.92 of the speed of light and angles of $\sim$ 70$^{\circ}$ with respect to the line of sight. The flux ratios and time evolution of the expelled clouds are consistent with actual motions of the radiating matter rather than with the simple propagation of pulses in a medium moving at slower velocities. The large kinetic power of the sudden, short, and rather discontinuous ejections exceeds by more than an order of magnitude the maximum steady photon luminosity of the source, suggesting that in GRS 1915+105 a radiation acceleration mechanism of the ejecta is unlikely. As in other galactic and extragalactic radio sources, the decrease in flux density as a function of angular separation from the central source shows a steepening with distance. Additional ejection events have been observed in 1995 and 1997 and we compare them with the 1994 events.Comment: 20 pages, 7 figures. To appear in The Astrophysical Journal, January 10, 1999 issu