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61.
An active set subspace Barzilai-Borwein gradient algorithm for large-scale bound constrained optimization is proposed. The
active sets are estimated by an identification technique. The search direction consists of two parts: some of the components
are simply defined; the other components are determined by the Barzilai-Borwein gradient method. In this work, a nonmonotone
line search strategy that guarantees global convergence is used. Preliminary numerical results show that the proposed method
is promising, and competitive with the well-known method SPG on a subset of bound constrained problems from CUTEr collection.
This work was supported by the 973 project granted 2004CB719402 and the NSF project of China granted 10471036. 相似文献
62.
This paper presents techniques for solving the problem of minimizing investment costs on an existing gas transportation network. The goal of this program is to find, first, the optimal location of pipeline segments to be reinforced and, second, the optimal sizes (among a discrete commercial list of diameters) under the constraint of satisfaction of demands with high enough pressure for all users. 相似文献
63.
Yoshiki Kaneoke Masahiro Furuse Suguru Inao Katsuyoshi Saso Kazuo Yoshida Yoshimasa Motegi Motomu Mizuno Akira Izawa 《Magnetic resonance imaging》1987,5(6):415-420
Measurements were made of T1 of bound water (T1b) and bound water fraction () for gelatin solutions and human tissues (sera, brain tumor, cerebral white matter). Bound water fraction in each sample was measured by means of thermal analysis (differential scanning calorimetry: DSC). T1 values were measured by FONAR QED 80-. T1b values were calculated by an equation derived from the fast-exchange two-state model. In the study of gelatin solutions, the relationship between T1 and water content differed depending on the sort of solutions. This was considered to be due to differences in T1b values. In each biological tissue the values of T1b and had different distributions. These results indicate that values of T1b and for biological tissues may be altered in correspondence to the changes in pathophysiological states in those tissues. 相似文献
64.
M. Idrish Miah 《Physics letters. A》2009,374(1):75-77
We performed a three-photon excitation nonlinear photoluminescence (PL) spectroscopy in single crystals of wide-bandgap semiconductors (WBSs). The crystal temperature (TL)-dependent PL emission intensity (IPL) excited with different excitation power density (P) was measured. The PL emissions showed characteristics IPL with their maxima at around 520 nm. The IPL might be due to the presence of the photo-generated Frenkel defects (FDs) in WBSs. A detailed analysis of the PL spectra showed a third-order power law dependence of the maximum IPL on P for all the crystal temperature TL. The IPL was found to increase with decreasing TL. The results demonstrated the existence of the self-trapped excitons resulting from the presence of the FDs in the crystals. 相似文献
65.
We consider the superfluidity properties of a two-dimensional system of polaritons in an optical cavity. Deriving an expression
for the effective low-energy action for thermodynamic phase fluctuations, we simultaneously obtain the expression for an analogue
of superfluid density in the system in terms of the current-current correlation function and also find the expression for
the current operator. We describe the Bogoliubov approximation for a polariton system and calculate the superfluid density.
We discuss the Berezinskii-Kosterlitz-Thouless transition in the system under study.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 154, No. 2, pp. 372–384, February, 2008. 相似文献
66.
We consider two-stage pure integer programs with discretely distributed stochastic right-hand sides. We present an equivalent
superadditive dual formulation that uses the value functions in both stages. We give two algorithms for finding the value
functions. To solve the reformulation after obtaining the value functions, we develop a global branch-and-bound approach and
a level-set approach to find an optimal tender. We show that our method can solve randomly generated instances whose extensive
forms are several orders of magnitude larger than the extensive forms of those instances found in the literature.
This work is supported by National Science Foundation grants DMI-0217190 and DMI-0355433. 相似文献
67.
《中国物理 B》2021,30(5):53201-053201
The exciton Stark shift and polarization in hemispherical quantum dots(HQDs) each as a function of strength and orientation of applied electric field are theoretically investigated by an exact diagonalization method. A highly anisotropic Stark redshift of exciton energy is found. As the electric field is rotated from Voigt to Faraday geometry, the redshift of exciton energy monotonically decreases. This is because the asymmetric geometric shape of the hemispherical quantum dot restrains the displacement of the wave function to the higher orbital state in response to electric field along Faraday geometry. A redshift of hole energy is found all the time while a transition of electron energy from this redshift to a blueshift is found as the field is rotated from Voigt to Faraday geometry. Taking advantage of the diminishing of Stark effect along Faraday geometry, the hemispherical shapes can be used to improve significantly the radiative recombination efficiency of the polar optoelectronic devices if the strong internal polarized electric field is along Faraday geometry. 相似文献
68.
Polarized photoluminescence spectroscopy in WS2, WSe2 atomic layers and heterostructures by cylindrical vector beams
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Due to the large exciton binding energy, two-dimensional (2D) transition metal dichalcogenides (TMDCs) provide an ideal platform for studying excitonic states and related photonics and optoelectronics. Polarization states lead to distinct light-matter interactions which are of great importance for device applications. In this work, we study polarized photoluminescence spectra from intralayer exciton and indirect exciton in WS2 and WSe2 atomic layers, and interlayer exciton in WS2/WSe2 heterostructures by radially and azimuthally polarized cylindrical vector laser beams. We demonstrated the same in-plane and out-of-plane polarization behavior from the intralayer and indirect exciton. Moreover, with these two laser modes, we obtained interlayer exciton in WS2/WSe2 heterostructures with stronger out-of-plane polarization, due to the formation of vertical electric dipole moment. 相似文献
69.
70.