This work utilizes pulsed, melt-mediated laser crystallization techniques to control the spatial distribution of crystalline zones within an as sputter-deposited amorphous matrix. Since shape memory responses stem fro...
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(纸本)9780912035888
This work utilizes pulsed, melt-mediated laser crystallization techniques to control the spatial distribution of crystalline zones within an as sputter-deposited amorphous matrix. Since shape memory responses stem from crystallographic shifts, only the selectively crystallized regions exhibit these properties. This process provides not only spatial control over the shape memory response, but potentially, through proper use of operational parameters, the shape memory response itself, i.e. phase transformation temperature, transformation strain, recovery stress etc. The solidification process is monitored in situ via transient reflectance. Furthermore, the effects of varying energy density within the irradiated region are examined with respect to the resulting micro-structure via atomic force microscopy (AFM), electron backscatter diffraction (EBSD) and x-ray diffraction (XRD).
Using inverse statistical-mechanical optimization techniques, we have discovered isotropic pair interaction potentials with strongly repulsive cores that cause the tetrahedrally coordinated diamond and wurtzite lattic...
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Using inverse statistical-mechanical optimization techniques, we have discovered isotropic pair interaction potentials with strongly repulsive cores that cause the tetrahedrally coordinated diamond and wurtzite lattices to stabilize, as evidenced by lattice sums, phonon spectra, positive-energy defects, and self-assembly in classical molecular dynamics simulations. These results challenge conventional thinking that such open lattices can only be created via directional covalent interactions observed in nature. Thus, our discovery adds to fundamental understanding of the nature of the solid state by showing that isotropic interactions enable the self-assembly of open crystal structures with a broader range of coordination number than previously thought. Our work is important technologically because of its direct relevance generally to the science of self-assembly and specifically to photonic crystal fabrication.
This paper describes the dynamic load-balancing and high performance communication provided in Jcluster, an efficient Java parallel environment. For the efficient load-balancing, we implement a task scheduler based on...
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This paper describes the dynamic load-balancing and high performance communication provided in Jcluster, an efficient Java parallel environment. For the efficient load-balancing, we implement a task scheduler based on a transitive random stealing algorithm, which improves the random stealing, a well-known load-balancing algorithm. The experiment results show that the scheduler performs efficiently, especially for a large-scale cluster. With the method of asynchronously multithreaded transmission, a high performance PVM-like and MPI-like message passing interface is implemented in pure Java. The evaluation of the communication performance is conducted among Jcluster, LAM-MPI and mpiJava on LAM-MPI based on the Java Grande Forum's pingpong benchmark.
Using a semiclassical rescattering model, we investigate the nonsequential double ionization (NSDI) process of diatomic molecules aligned parallel and perpendicular to the intense linearly polarized field. It is shown...
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Using a semiclassical rescattering model, we investigate the nonsequential double ionization (NSDI) process of diatomic molecules aligned parallel and perpendicular to the intense linearly polarized field. It is shown that a simple hydrogen-molecule-like model can simulate a nitrogen molecule effectively by giving the alignment dependence of the ratio of double to single ionization and the momentum distribution qualitatively consistent with the experimental result of N2. However, the alignment dependence of the momentum correlation of two ejected electrons does not agree with the experimental result, which indicates that the quantum effect needs to be included in the rescattering and the field-ionization process to explain the experimental observation.
Manipulating the Kondo effect by quantum confinement has been achieved by placing magnetic molecules on silicon-supported nanostructures. The Kondo resonance of individual manganese phthalocyanine (MnPc) molecules ads...
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Manipulating the Kondo effect by quantum confinement has been achieved by placing magnetic molecules on silicon-supported nanostructures. The Kondo resonance of individual manganese phthalocyanine (MnPc) molecules adsorbed on the top of Pb islands was studied by scanning tunneling spectroscopy. Oscillating Kondo temperatures as a function of film thickness were observed and attributed to the formation of the thickness-dependent quantum-well states in the host Pb islands. The present approach provides a technologically feasible way for single spin manipulation by precise thickness control of thin films.
We show that a double quantum-dot system made of diluted magnetic semiconductor behaves unlike the usual molecules. In a semiconductor double quantum dot or in a diatomic molecule, the ground state of a single carrier...
We show that a double quantum-dot system made of diluted magnetic semiconductor behaves unlike the usual molecules. In a semiconductor double quantum dot or in a diatomic molecule, the ground state of a single carrier is described by a symmetric orbital. In a magnetic material molecule, new ground states with broken symmetry can appear due the competition between the tunneling and magnetic polaron energy. With decreasing temperature, the ground state changes from the normal symmetric state to a state with spontaneously broken symmetry. Interestingly, the symmetry of a magnetic molecule is recovered at very low temperatures. A magnetic double quantum dot with broken-symmetry phases can be used as a voltage-controlled nanoscale memory cell.
Chiral magnetic ordering due to Dzyaloshinsky-Moriya interaction on two-dimensional lattices is studied theoretically. Several competing Dzyaloshinsky-Moriya vectors are introduced on the basis of symmetry arguments. ...
Chiral magnetic ordering due to Dzyaloshinsky-Moriya interaction on two-dimensional lattices is studied theoretically. Several competing Dzyaloshinsky-Moriya vectors are introduced on the basis of symmetry arguments. The role of the exchange interaction, magnetic anisotropy, and dipolar coupling for the ordering in chiral nanomagnets is investigated. It is demonstrated that the periodicity of the modulated structure, which is determined by all interactions involved, is lattice dependent; the direction of spiral propagation and orientation of magnetization is determined by the competition between different Dzyaloshinsky-Moriya vectors and anisotropy; the anisotropy can induce a domain formation or destroy the chiral ordering depending on its orientation. We show that the Dzyaloshinsky-Moriya coupling is responsible for the chiral magnetic ordering in Fe∕W(110).
Continuing on recent computational and experimental work on jammed packings of hard ellipsoids [Donev et al., Science 303, 990 (2004)] we consider jamming in packings of smooth strictly convex nonspherical hard parti...
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Continuing on recent computational and experimental work on jammed packings of hard ellipsoids [Donev et al., Science 303, 990 (2004)] we consider jamming in packings of smooth strictly convex nonspherical hard particles. We explain why an isocounting conjecture, which states that for large disordered jammed packings the average contact number per particle is twice the number of degrees of freedom per particle (Z¯=2df), does not apply to nonspherical particles. We develop first- and second-order conditions for jamming and demonstrate that packings of nonspherical particles can be jammed even though they are underconstrained (hypoconstrained, Z¯<2df). We apply an algorithm using these conditions to computer-generated hypoconstrained ellipsoid and ellipse packings and demonstrate that our algorithm does produce jammed packings, even close to the sphere point. We also consider packings that are nearly jammed and draw connections to packings of deformable (but stiff) particles. Finally, we consider the jamming conditions for nearly spherical particles and explain quantitatively the behavior we observe in the vicinity of the sphere point.
We present the point symmetry classification and invariant characterization of a system of two geodesic equations. Previously, Aminova and Aminovl attempted the point symmetry classification. However, they did not ide...
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Heterogeneous materials abound in nature and man-made situations. Examples include porous media, biological materials, and composite materials. Diverse and interesting properties exhibited by these materials result fr...
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Heterogeneous materials abound in nature and man-made situations. Examples include porous media, biological materials, and composite materials. Diverse and interesting properties exhibited by these materials result from their complex microstructures, which also make it difficult to model the materials. Yeong and Torquato [Phys. Rev. E 57, 495 (1998)] introduced a stochastic optimization technique that enables one to generate realizations of heterogeneous materials from a prescribed set of correlation functions. In this first part of a series of two papers, we collect the known necessary conditions on the standard two-point correlation function S2(r) and formulate a conjecture. In particular, we argue that given a complete two-point correlation function space, S2(r) of any statistically homogeneous material can be expressed through a map on a selected set of bases of the function space. We provide examples of realizable two-point correlation functions and suggest a set of analytical basis functions. We also discuss an exact mathematical formulation of the (re)construction problem and prove that S2(r) cannot completely specify a two-phase heterogeneous material alone. Moreover, we devise an efficient and isotropy-preserving construction algorithm, namely, the lattice-point algorithm to generate realizations of materials from their two-point correlation functions based on the Yeong-Torquato technique. Subsequent analysis can be performed on the generated images to obtain desired macroscopic properties. These developments are integrated here into a general scheme that enables one to model and categorize heterogeneous materials via two-point correlation functions. We will mainly focus on basic principles in this paper. The algorithmic details and applications of the general scheme are given in the second part of this series of two papers.
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