This paper is concerned with the geometrical similarity of heat conduction-elastioplastic structural problems. When the dimensions of a structure are geometrically scaled down/up, the similarity relations for both iso...
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This paper is concerned with the geometrical similarity of heat conduction-elastioplastic structural problems. When the dimensions of a structure are geometrically scaled down/up, the similarity relations for both isolated heat conduction and elastoplastic structural problems are derived. For cases of thermo-structural coupled, it is concluded that heat conduction-static elastoplastic problems can be geometrically similarly scaled down/up and a set of similarity relations are drawn accordingly. As examples, a full-, half- and quarter-scale unilaterally-tensioned plate and internally-pressured cylindrical shell irradiated by a laser pulse are numerically analysed and the numerical results have confirmed this conclusion. However, heat conduction-dynamic elastoplastic problems are found not to comply compatibly with the geometrically similar scaling.
Conventional density functional theory (DFT) fails for materials with strongly correlated electrons, such as late transition metal oxides. Large errors in the intra-atomic Coulomb and exchange interactions are the sou...
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Conventional density functional theory (DFT) fails for materials with strongly correlated electrons, such as late transition metal oxides. Large errors in the intra-atomic Coulomb and exchange interactions are the source of this failure. The DFT+U method has provided a means, through empirical parameters, to correct these errors. Here, we present a systematic ab initio approach in evaluating the intra-atomic Coulomb and exchange terms, U and J, respectively, in order to make the DFT+U method a fully first-principles technique. The method is based on a relationship between these terms and the Coulomb and exchange integrals evaluated in the basis of unrestricted Hartree-Fock molecular orbitals that represent localized states of the extended system. We used this ab initio scheme to evaluate U and J for chromia (Cr2O3). The resulting values are somewhat higher than those determined earlier either empirically or in constrained DFT calculations but have the advantage of originating from an ab initio theory containing exact exchange. Subsequent DFT+U calculations on chromia using the ab initio derived U and J yield properties consistent with experiment, unlike conventional DFT. Overall, the technique developed and tested in this work holds promise in enabling accurate and fully predictive DFT+U calculations of strongly correlated electron materials.
Functional Magnetic Resonance Imaging (fMRI) provides dynamical access into the complex functioning of the human brain, detailing the hemodynamic activity of thousands of voxels during hundreds of sequential time poin...
ISBN:
(纸本)9781605603520
Functional Magnetic Resonance Imaging (fMRI) provides dynamical access into the complex functioning of the human brain, detailing the hemodynamic activity of thousands of voxels during hundreds of sequential time points. One approach towards illuminating the connection between fMRI and cognitive function is through decoding; how do the time series of voxel activities combine to provide information about internal and external experience? Here we seek models of fMRI decoding which are balanced between the simplicity of their interpretation and the effectiveness of their prediction. We use signals from a subject immersed in virtual reality to compare global and local methods of prediction applying both linear and nonlinear techniques of dimensionality reduction. We find that the prediction of complex stimuli is remarkably low-dimensional, saturating with less than 100 features. In particular, we build effective models based on the decorrelated components of cognitive activity in the classically-defined Brodmann areas. For some of the stimuli, the top predictive areas were surprisingly transparent, including Wernicke's area for verbal instructions, visual cortex for facial and body features, and visual-temporal regions for velocity. Direct sensory experience resulted in the most robust predictions, with the highest correlation (c ~ 0.8) between the predicted and experienced time series of verbal instructions. Techniques based on non-linear dimensionality reduction (Laplacian eigenmaps) performed similarly. The interpretability and relative simplicity of our approach provides a conceptual basis upon which to build more sophisticated techniques for fMRI decoding and offers a window into cognitive function during dynamic, natural experience.
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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ISBN:
(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).
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 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.
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).
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