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Transition Regions (transition + regions)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

A spatial model of population dynamics of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan

FISHERIES OCEANOGRAPHY, Issue 2 2003
Maki Suda
Abstract We constructed a numerical model reproducing the transport, survival and individual growth of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan during 1978,93. The causes of early life stage mortality, including the influence of the effects of the spatial relationship between the spawning grounds and the Kuroshio on the mortality rate, were investigated. Survival and transport from egg stage to 60 days after spawning were modelled daily in a 1 × 1 degree mesh cell and individual growth in the period was modelled in each region (Kuroshio, Inshore, Offshore and Transition regions). Individual growth and survival from 60 to 180 days after spawning were modelled daily in the Transition region. Environmental data were taken from outside the model system. Our simulation indicates that survival variability in the larval stage (5,25 mm in standard length) is the key factor in determining the year-class strength. The simulation revealed that strong year classes occurred with good survival in the spawning ground and whilst entrained in the Kuroshio current being transported to the main feeding grounds in the Transition region. The simulation also indicated that survival rates in 1988,93 were low in the Inshore, Kuroshio and Offshore regions, which depressed the year-class strength during that period. [source]

Molecular dynamics of phase transitions in clusters of alkali halides

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2001
Pedro C. R. Rodrigues
Abstract Molecular dynamics simulations of unconstrained alkali halide clusters with 8, 64, 216, 512, 1000, 1728, 2744, 4096, 5832, and 8000 ions have been carried out using the Born,Mayer,Huggins potential. All the clusters exhibit first-order melting and freezing transitions. The melting temperature increases with the number of ions and approaches the melting temperature of the bulk. Clusters with a number of ions less than approximately 1000 present hysteresis cycles and practically do not have phase coexistence. Clusters with a number of ions over 1000 present phase coexistence during a significant part of the transition region and hysteresis is progressively eliminated as the clusters size increases. It is suggested that hysteresis is an intrinsic characteristic of small clusters. In the transition regions the calculations have been performed by fixing the total energy of the clusters. It is shown that such a technique provides a better way of analyzing the transition mechanism than the usual procedure of fixing the temperature by ad hoc rescaling the velocities or by using canonical molecular dynamics or Monte Carlo. A detailed analysis of the melting transition is presented. The effects of interfaces and impurities are discussed. A method based on the velocity autocorrelation functions is proposed, in order to determine the molar fraction of the ions present in the solid and liquid phases as well as to produce colored snapshots of the phases in coexistence. The overall agreement of the estimated melting points and enthalpies of melting with the experiment is fairly good. The estimated melting point and enthalpy of melting for KCl in particular are in excellent agreement with the experimental values. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 169,180, 2001 [source]

Network density control in epoxy,silica hybrids by selective silane functionalization of precursors

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2005
Luca Prezzi
Abstract Following previous work on the compatibilization of organic,inorganic hybrids through coupling reactions with the precursor components, the present study evaluates the relative efficiency of different types of coupling agents on the morphology and properties of epoxy,silica hybrids. In particular, this investigation compares the effects of introducing trialkoxysilane functional groups at the chain end (using amine- and mercapto-silanes) with similar types grafted in the middle of the chain of the constituent resin (using an isocyanate silane). The use of coupling agents with a basic character (amine silane type) brings about the formation of denser networks in both constituent phases of the resulting epoxy,silica hybrid, which is manifest through a large increase in the Tg and a more extensive suppression of the molecular relaxations within the glass transition regions. Increasing the number of alkoxysilane functional groups at the chain end, with the use of a bis-aminosilane, has a relatively minor effect on the morphology and dynamic mechanical spectra of the resulting epoxy,silica hybrids. It was also found that while the incorporation of small amounts of a high molecular weight epoxy resin causes considerable plasticization of the organic phase, much larger amounts of organic (aliphatic) co-agent within the siloxane phase are required to deteriorate those properties that are related to the inorganic character of the hybrid material. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24:91,102, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20033 [source]

Long-time asymptotics of the nonlinear Schrödinger equation shock problem

COMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 9 2007
Robert Buckingham
The long-time asymptotics of two colliding plane waves governed by the focusing nonlinear Schrödinger equation are analyzed via the inverse scattering method. We find three asymptotic regions in space-time: a region with the original wave modified by a phase perturbation, a residual region with a one-phase wave, and an intermediate transition region with a modulated two-phase wave. The leading-order terms for the three regions are computed with error estimates using the steepest-descent method for Riemann-Hilbert problems. The nondecaying initial data requires a new adaptation of this method. A new breaking mechanism involving a complex conjugate pair of branch points emerging from the real axis is observed between the residual and transition regions. Also, the effect of the collision is felt in the plane-wave state well beyond the shock front at large times. © 2007 Wiley Periodicals, Inc. [source]