4,755 research outputs found
Thermodynamics of Spin-1/2 AF-AF-F and F-F-AF Trimerized Quantum Heisenberg Chains
The magnetization process, the susceptibility and the specific heat of the
spin-1/2 AF-AF-F and F-F-AF trimerized quantum Heisenberg chains have been
investigated by means of the transfer matrix renormalization group (TMRG)
technique as well as the modified spin-wave (MSW) theory. A magnetization
plateau at for both trimerized chains is observed at low temperature.
The susceptibility and the specific heat show various behaviors for different
ferromagnetic and antiferromagnetic interactions and in different magnetic
fields. The TMRG results of susceptibility and the specific heat can be nicely
fitted by a linear superposition of double two-level systems, where two fitting
equations are proposed. Three branch excitations, one gapless excitation and
two gapful excitations, for both systems are found within the MSW theory. It is
observed that the MSW theory captures the main characteristics of the
thermodynamic behaviors at low temperatures. The TMRG results are also compared
with the possible experimental data.Comment: 11 pages, 10 figure
DNA sequences classification and computation scheme based on the symmetry principle
The DNA sequences containing multifarious novel symmetrical structure frequently play crucial role in how genomes work. Here we present a new scheme for understanding the structural features and potential mathematical rules of symmetrical DNA sequences using a method containing stepwise classification and recursive computation. By defining the symmetry of DNA sequences, we classify all sequences and conclude a series of recursive equations for computing the quantity of all classes of sequences existing theoretically; moreover, the symmetries of the typical sequences at different levels are analyzed. The classification and quantitative relation demonstrate that DNA sequences have recursive and nested properties. The scheme may help us better discuss the formation and the growth mechanism of DNA sequences because it has a capability of educing the information about structure and quantity of longer sequences according to that of shorter sequences by some recursive rules. Our scheme may provide a new stepping stone to the theoretical characterization, as well as structural analysis, of DNA sequences
Texture Synthesis Through Convolutional Neural Networks and Spectrum Constraints
This paper presents a significant improvement for the synthesis of texture
images using convolutional neural networks (CNNs), making use of constraints on
the Fourier spectrum of the results. More precisely, the texture synthesis is
regarded as a constrained optimization problem, with constraints conditioning
both the Fourier spectrum and statistical features learned by CNNs. In contrast
with existing methods, the presented method inherits from previous CNN
approaches the ability to depict local structures and fine scale details, and
at the same time yields coherent large scale structures, even in the case of
quasi-periodic images. This is done at no extra computational cost. Synthesis
experiments on various images show a clear improvement compared to a recent
state-of-the art method relying on CNN constraints only
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