9,713 research outputs found

    Domain Coarsening in Systems Far from Equilibrium

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    The growth of domains of stripes evolving from random initial conditions is studied in numerical simulations of models of systems far from equilibrium such as Rayleigh-Benard convection. The scaling of the size of the domains deduced from the inverse width of the Fourier spectrum is studied for both potential and nonpotential models. The morphology of the domains and the defect structures are however quite different in the two cases, and evidence is presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende

    The Ties That Bind: Preemptive Rights and Restraints on Alienation That Commonly Burden Oil and Gas Properties

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    This paper will address four contractual provisions that often come into play in the acquisition and disposition of oil and gas properties: preferential rights to purchase, maintenance of uniform interest, areas of mutual interest, and consents required for assignment. These provisions each address valid commercial purposes and when consciously and deliberately implemented, can reflect a negotiated allocation of value and risk among the parties to the various agreements where they are found. However, they are all long-lived, if not perpetual, and at some point when performance of, or compliance with, them is at issue, it will be in the interest of one party or a successor in interest that the provisions either not apply or not be enforced. Thus, there is a constant testing of the boundaries in the commercial arena and frequent legal challenges in the courts. Each of these four provisions share certain elements with others, so that common legal principles and bodies of law are relevant in establishing the boundaries and evaluating the inevitable challenges. Preferential rights to purchase and areas of mutual interest contemplate future vesting which implicates the Rule Against Perpetuities. Preferential rights, the maintenance of uniform interest provision, and consents as conditions to assignment are restraints on alienation which involve the common law Rule Against Unreasonable Restraints on Alienation. All of these provisions purport to burden real property, so that the Statute of Frauds and the law regarding covenants running with the land are relevant. This paper will not cover all of these issues in depth, but will attempt to identify relevant Texas cases that directly bear on the current status of these provisions

    Extensive chaos in Rayleigh-Bénard convection

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    Using large-scale numerical calculations we explore spatiotemporal chaos in Rayleigh-Bénard convection for experimentally relevant conditions. We calculate the spectrum of Lyapunov exponents and the Lyapunov dimension describing the chaotic dynamics of the convective fluid layer at constant thermal driving over a range of finite system sizes. Our results reveal that the dynamics of fluid convection is truly chaotic for experimental conditions as illustrated by a positive leading-order Lyapunov exponent. We also find the chaos to be extensive over the range of finite-sized systems investigated as indicated by a linear scaling between the Lyapunov dimension of the chaotic attractor and the system size

    Direct Separation of Short Range Order in Intermixed Nanocrystalline and Amorphous Phases

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    Diffraction anomalous fine-structure (DAFS) and extended x-ray absorption fine-structure (EXAFS) measurements were combined to determine short range order (SRO) about a single atomic type in a sample of mixed amorphous and nanocrystalline phases of germanium. EXAFS yields information about the SRO of all Ge atoms in the sample, while DAFS determines the SRO of only the ordered fraction. We determine that the first-shell distance distribution is bimodal; the nanocrystalline distance is the same as the bulk crystal, to within 0.01(2)   Å, but the mean amorphous Ge-Ge bond length is expanded by 0.076(19)   Å. This approach can be applied to many systems of mixed amorphous and nanocrystalline phases

    Studies of surface two-dimensional photonic band-gap structures

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    Two-dimensional (2D) surface photonic band-gap (SPBG) structures can be obtained by providing a shallow corrugation of the inner surface of a waveguide wall. It can be used as a distributed mirror, a cavity, or a filter in integrated optics or microwave electronics. These structures can also be an alternative to conventional 2D PBG or 1D Bragg structures. In this article, we present the results of theoretical and experimental studies of 2D SPBG structures. Data obtained from experiments are compared with theoretical results and good agreement between theory and experiment is demonstrated. Comparison of a coaxial 2D SPBG structure with a conventional 1D Bragg structure is also presented

    The use of genetic markers in the study of marine natural populations

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    Crassostrea angulata (Lamarck, 1819), known as the Portuguese oyster, is a species naturally located in the southwest Iberian Peninsula, mainly at river mouths and the heads of estuaries with suitable hard substrates. Genetic data on C. angulata are scarce, and Spanish natural populations (the main beds of the species) have not been studied previously. Electrophoresis is a good detector of variability, and isozyme polymorphisms have been widely used in genetic studies. The present paper reports on the electrophoretic examination of seven allozyme loci at 14 sites located between the mouth of the Guadiana River and the Straits of Gibraltar, which found a high level of genetic variability in terms of average number of alleles (min. of 2.71 and max. of 3.71), polymorphism (P₉₅ ≥ 71.43 %) and mean heterozygosities (H = 0.264). All populations showed a deficit of heterozygotes as well as the genes Lap, Mdh-1, Mdh-2, Me-2, Pgi and Xdh across populations. However, Pgm showed heterozygous excess. Null alleles appeared in Lap and Mdh loci, which could be responsible for this disequilibrium, at least in Mdh, because the increase in frequencies of null alleles was also related to the increase in heterozygote deficit. Values of genetic distance between populations have been used to cluster the populations, and the F-statistics showed a mean FST value across loci of 0.023 and Mdh-1 surveyed the highest value (0.046). At the same time, heterogeneity in allelic frequencies found in all genes indicated genetic differentiation between populations, in spite of the high dispersal of the species, probably due to local selective conditions.Crassostrea angulata (Lamarck, 1819), conocida como ostra portuguesa, es una especie que se encuentra localizada en el suroeste de la península Ibérica, principalmente en la desembocadura de los ríos y en la cabecera de estuarios con sustrato duro disponible. Los datos sobre la genética de C. angulata son escasos y las poblaciones naturales de España (la principal fuente de esta especie) no habían sido estudiadas. La electroforesis es un buen detector de la variabilidad, y los polimorfismos isoenzimáticos han sido ampliamente usados en estudios genéticos. Este trabajo está basado en el análisis electroforético de siete loci y catorce puntos de muestreo entre la desembocadura del río Guadiana y el estrecho de Gibraltar y se ha encontrado un alto nivel de variabilidad genética en términos de número medio de alelos (mínimo de 2,71 y máximo de 3,71), polimorfismos (P₉₅ ≥ 71,43 %) y heterocigosis media (H = 0,264). Todas las poblaciones mostraron un déficit de heterocigotos en los genes Lap, Mdh-1, Mdh-2, Me-2, Pgi y Xdh. En cambio, el sistema Pgm mostró un exceso de heterocigotos. Aparecieron alelos nulos en los loci Lap y Mdh que podrían ser los responsables del desequilibrio, al menos, en Mdh debido a que el incremento en la frecuencia de los alelos nulos estaba relacionado con un incremento en el déficit de heterocigotos. Las poblaciones se han agrupado según los valores de distancia genética obtenidos y también se han calculado los estadísticos F, obteniéndose un valor medio de FST en los loci de 0,023; Mdh mostró el valor mayor (0,046). Simultáneamente, la heterogeneidad en las frecuencias alélicas encontradas en todos los genes indicaban diferenciación genética entre las poblaciones, a pesar de la gran dispersión de la especie, probablemente debido a condiciones selectivas locales.Instituto Español de Oceanografí
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