Influence of the miniband on emission mechanism in Zn1−xCdxSe/ZnSe quantum wells

[[abstract]]The stimulated emission has been investigated in Zn1-xCdxSe/ZnSe quantum wells with a constant sample width of 60 Å and barrier widths from 47 Å to 500 Å. A redshift of the stimulated emission peak with increasing excitation intensity was observed in samples with barrier widths narrower than 350 Å, and the stimulated emission mechanism in these samples is found to be dominated by exciton-exciton scattering. In contrast, no redshifts were observed for the sample with a barrier width of 500 Å, and the stimulated emission in this sample appears to be dominated by biexcitons. Time-resolved spectroscopy measurements were also performed on samples with barrier width of 47 and 500 Å below the threshold of stimulated emission, and it was found that the exciton lifetime decreases with increasing exciton energy for both of the samples. With a ten times smaller barrier width in the 47 Å sample, the lifetime of high energy exciton is significantly shorter than that of the other sample, while the low energy lifetime becomes longer. This implies that with a narrower barrier width of the quantum wells the excitons move faster to lower energy regions. The narrower the barrier, the easier it is for excitons to move through the miniband. This freedom of movement increases the exciton concentration at low energies in localized areas in the wells. High exciton concentration made exciton-exciton scattering more probable and reduce the stimulated emission threshold value.[[notice]]補正完畢[[booktype]]紙

Relationship Between Radial Compressive Modulus of Elasticity and Shear Modulus of Wood

Wood properties in transverse compression are difficult to determine because of such factors as anatomical complexity, specimen geometry, and loading conditions. The mechanical properties of wood, considered as an anisotropic or orthotropic material, are related by certain tensor transformation rules when the reference coordinate system changes its orientation. In this paper, we used our verified shear modulus model to estimate compressive modulus of elasticity in the radial direction by means of certain established tensor transformation rules. The obtained basic engineering constants form a viable set that agrees with reliable test data and the anisotropic elasticity theory

Concentration dependence of the exchange interaction in Pb1-xEuxTe

[[abstract]]From low-field measurements of the susceptibility at temperatures up to 385 K, fitted to the Curie-Weiss expression, the exchange constant J/kB of Pb1-xEuxTe has been obtained for different values of x. It has been observed that J/kB decreases with increasing x. Reasons for this decrease are proposed. Measurements of the low-temperature magnetization at fields up to 23 T yield a value of the pair exchange constant Jp/kB, which is somewhat larger than the values from the susceptibility measurements and is nearly independent of x. This result seems to be due to the clustering of Eu atoms.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子

Rational Approximate Symmetries of KdV Equation

We construct one-parameter deformation of the Dorfman Hamiltonian operator for the Riemann hierarchy using the quasi-Miura transformation from topological field theory. In this way, one can get the approximately rational symmetries of KdV equation and then investigate its bi-Hamiltonian structure.Comment: 14 pages, no figure

On the water-bag model of dispersionless KP hierarchy

We investigate the bi-Hamiltonian structure of the waterbag model of dKP for two component case. One can establish the third-order and first-order Hamiltonian operator associated with the waterbag model. Also, the dispersive corrections are discussed.Comment: 19 page

On the Miura map between the dispersionless KP and dispersionless modified KP hierarchies

We investigate the Miura map between the dispersionless KP and dispersionless modified KP hierarchies. We show that the Miura map is canonical with respect to their bi-Hamiltonian structures. Moreover, inspired by the works of Takasaki and Takebe, the twistor construction of solution structure for the dispersionless modified KP hierarchy is given.Comment: 19 pages, Latex, no figure

Foraging behavior and Doppler shift compensation in echolocating hipposiderid bats, I-Iipposideros bicolor and I-Iipposideros speoris

1. Two hipposiderid bats,H. bicolor andH. speoris, were observed in their natural foraging areas in Madurai (South India). Both species hunt close together near the foliage of trees and bushes but they differ in fine structure of preferred hunting space:H. bicolor hunts within the foliage, especially whenH. speoris is active at the same time, whereasH. speoris never flies in dense vegetation but rather in the more open area (Fig. 1, Table 1). 2. Both species emit CF/FM-sounds containing only one harmonic component in almost all echolocation situations. The CF-parts of CF/FM-sounds are species specific within a band of 127–138 kHz forH. speoris and 147–159 kHz forH. bicolor (Tables 2 and 3). 3. H. speoris additionally uses a complex harmonic sound during obstacle avoidance and during laboratory tests for Doppler shift compensation.H. bicolor consistently emits CF/FM-sounds in these same situations (Fig. 2). 4. Both hipposiderid bats respond to Doppler shifts in the returning echoes by lowering the frequency of the emitted sounds (Fig. 3). However, Doppler compensations are incomplete as the emitted frequencies are decreased by only 55% and 56% (mean values) of the full frequency shifts byH. speoris andH, bicolor, respectively. 5. The differences in Doppler shift compensation, echolocating and hunting behavior suggest thatH. speoris is less specialized on echolocation with CF/FM-sounds thanH. bicolor

PHOTOCHEMICAL RING-OPENING IN meso-CHLORINATED CHLOROPHYLLS

Irradiation of 20-chloro-chlorophylls of the a-type with visible light produces long-wavelength shifted photoproducts, which transform in the dark to linear tetrapyrroles (bile pigments). The possible significance for chlorophyll degradation is discussed