960 research outputs found

### Population migration: A meta-heuristics for stochastic approaches to constraint satisfaction problems

A meta-heuristics for escaping from local optima to solve constraint satisfaction problems is proposed, which enables self-adaptive dynamic control of the temperature to adjust the locality of stochastic search. In our method, several groups with different temperatures are prepared. To each group the same number of candidate solutions are initially allotted. Then, the main process is repeated until the procedure comes to a certain convergence. The main process is composed of two phases: stochastic searching and population tuning. As for the latter phase, after evaluating the adaptation value of every group, migration of some number of candidate solutions in groups with lower values to groups with higher values are induced. Population migration is a kind ofparallel version of simulated annealing, where several temperatures are spatially distributed. Some experiments are performed to verify the efficiency of the method applied to constraint satisfaction problems. It is also demonstrated that population migration is exceptionally effective in the critical region where phase transitions occur

### Produção de pimenteira-do-reino micorrizada e adicionada de casca de caranguejo em condições de campo.

bitstream/item/19008/1/Doc-271.pdfVersão eletrônica. 1ª impressão: 2009

### Quantum Phase Transition in the Frustrated Heisenberg Antiferromagnet

Using the J_1-J_2 model, we present a description of quantum phase transition
from Neel ordered to the spin-liquid state based on the modified spin wave
theory. The general expression for the gap in the spectrum in the spin-liquid
phase is presented.Comment: 8 pages of REVTeX 3.0, one PostScript file appended (Eq. 15
corrected, two recent references added, + some minor changes

### Molecular Genetics of T Cell Development

T cell development is guided by a complex set of transcription factors that act recursively, in different combinations, at each of the developmental choice points from T-lineage specification to peripheral T cell specialization. This review describes the modes of action of the major T-lineage-defining transcription factors and the signal pathways that activate them during intrathymic differentiation from pluripotent precursors. Roles of Notch and its effector RBPSuh (CSL), GATA-3, E2A/HEB and Id proteins, c-Myb, TCF-1, and members of the Runx, Ets, and Ikaros families are critical. Less known transcription factors that are newly recognized as being required for T cell development at particular checkpoints are also described. The transcriptional regulation of T cell development is contrasted with that of B cell development, in terms of their different degrees of overlap with the stem-cell program and the different roles of key transcription factors in gene regulatory networks leading to lineage commitment

### Electro-Mechanical Fredericks Effects in Nematic Gels

The solid nematic equivalent of the Fredericks transition is found to depend
on a critical field rather than a critical voltage as in the classical case.
This arises because director anchoring is principally to the solid rubbery
matrix of the nematic gel rather than to the sample surfaces. Moreover, above
the threshold field, we find a competition between quartic (soft) and
conventional harmonic elasticity which dictates the director response. By
including a small degree of initial director misorientation, the calculated
field variation of optical anisotropy agrees well with the conoscopy
measurements of Chang et al (Phys.Rev.E56, 595, 1997) of the electro-optical
response of nematic gels.Comment: Latex (revtex style), 5 EPS figures, submitted to PRE, corrections to
discussion of fig.3, cosmetic change

### Modified Spin Wave Thoery of the Bilayer Square Lattice Frustrated Quantum Heisenberg Antiferromagnet

The ground state of the square lattice bilayer quantum antiferromagnet with
nearest and next-nearest neighbour intralayer interaction is studied by means
of the modified spin wave method. For weak interlayer coupling, the ground
state is found to be always magnetically ordered while the quantum disordered
phase appear for large enough interlayer coupling. The properties of the
disordered phase vary according to the strength of the frustration. In the
regime of weak frustration, the disordered ground state is an almost
uncorrelated assembly of interlayer dimers, while in the strongly frustrated
regime the quantum spin liquid phase which has considerable N\'eel type short
range order appears. The behavior of the sublattice magnetization and spin-spin
correlation length in each phase is discussed.Comment: 15 pages, revtex, figures upon reques

### Measurement of Direct Photon Emission in K^+ -> pi^+ pi^0 gamma Decay

We have performed a measurement of the K^+ -> pi^+ pi^0 gamma decay and have
observed 2 X 10^4 events. The best fit to the decay spectrum gives a branching
ratio for direct photon emission of (4.7\pm0.8\pm0.3) X 10^{-6} in the pi^+
kinetic energy region of 55 to 90 MeV and requires no component due to
interference with inner bremsstrahlung.Comment: 9 pages, 3 figures. To be submitted to PR

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