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Ground-state phase diagrams of ultrathin epitaxial alloy films are studied within the framework of a discrete lattice-model Hamiltonian incorporating competing elastic and chemical interactions. For bulk-immiscible alloy systems an infinite number of commensurate, long-period stripe-superstructure ground states are obtained as a function of chemical potential. The average periodicity of these stripe superstructures is found to be a nonmonotonic function of alloy composition, in contrast to the predictions of continuum theories for two-dimensional systems with competing interactions.  相似文献   
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The extension of strongly anisotropic or dynamical scaling to local scale invariance is investigated. For the special case of an anisotropy or dynamical exponent =z=2, the group of local scale transformation considered is the Schrödinger group, which can be obtained as the nonrelativistic limit of the conformal group. The requirement of Schrödinger invariance determines the two-point function in the bulk and reduces the three-point function to a scaling form of a single variable. Scaling forms are also derived for the two-point function close to a free surface which can be either spacelike or timelike. These results are reproduced in several exactly solvable statistical systems, namely the kinetic Ising model with Glauber dynamics, lattice diffusion, Lifshitz points in the spherical model, and critical dynamics of the spherical model with a nonconserved order parameter. For generic values of , evidence from higher-order Lifshitz points in the spherical model and from directed percolation suggests a simple scaling form of the two-point function.  相似文献   
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Malte Kob 《Applied Acoustics》2004,65(12):1249-1259
Overtone singing, also called biphonic singing, xöömij or chant diphonique in french; is a special singing style that exhibits two or more separate sounds - one “drone” sound of relatively low pitch and one or more high pitch melody sounds. The perceived pitches of the upper tones are multiples of the drone sound, i.e. taken from its overtone scale. Compared to voiced sounds of western style singers, the relative amplitude of the melody pitches is quite high, and the formant bandwidth of overtone sounds is small. This paper tries to answer the question of how these formant properties are achieved. Experimental investigations and numerical calculations prove the existence of two closely neighboured formants for the production of the melody sound in the sygyt style.  相似文献   
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Zirconia microspheres synthesized by a wet‐chemical sol–gel process are promising building blocks for various photonic applications considered for heat management and energy systems, including highly efficient reflective thermal barrier coatings and absorbers/emitters used in thermophotovoltaic systems. As previously shown, pure zirconia microparticles deteriorate at working temperatures of ≥1000 °C. While the addition of yttrium as a dopant has been shown to improve their phase stability, pronounced grain growth at temperatures of ≥1000 °C compromises the photonic structure of the assembled microspheres. Here, a new approach for the fabrication of highly stable ceramic microparticles by doping with lanthanum, gadolinium, and a combination of those with yttrium is introduced. The morphological changes of the particles are monitored by scanning electron microscopy, ex situ X‐ray diffraction (XRD), and in situ high‐energy XRD as a function of dopant concentration up to 1500 °C. While the addition of lanthanum or gadolinium has a strong grain growth attenuating effect, it alone is insufficient to avoid a destructive tetragonal‐to‐monoclinic phase transformation occurring after heating to >850 °C. However, combining lanthanum or gadolinium with yttrium leads to particles with both efficient phase stabilization and attenuated grain growth. Thus, ceramic microspheres are yielded that remain extremely stable after heating to 1200 °C.  相似文献   
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Using an in situ combination of tensile tests and x-ray diffraction, we have determined the mechanical properties of both the crystalline and the disordered phase of the biological nanocomposite silk by adapting a model from linear viscoelastic theory to the semicrystalline morphology of silk. We observe a strong interplay between morphology and mechanical properties. Silk's high extensibility results principally from the disordered phase; however, the crystals are also elastically deformed.  相似文献   
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We describe in this Minireview the synthesis, properties, and applications of artificial genetic sets built from base pairs that are larger than the natural Watson–Crick architecture. Such designed systems are being explored by several research groups to investigate basic chemical questions regarding the functions of the genetic information storage systems and thus of the origin and evolution of life. For example, is the terrestrial DNA structure the only viable one, or can other architectures function as well? Working outside the constraints of purine–pyrimidine geometry provides more chemical flexibility in design, and the added size confers useful properties such as high binding affinity and helix stability as well as fluorescence. These features are useful for the investigation of fundamental biochemical questions as well as in the development of new biotechnological, biomedical, and nanostructural tools and methods.  相似文献   
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