Results 1 - 10 of 445
Results 1 - 10 of 445. Search took: 0.039 seconds
|Sort by: date | relevance|
[en] Results of theoretical studies of photoelectron spectra resulting from VUV single-photon ionization of H2O (1b1-1), H2S (2b1-1), H2CO (2b2-1), and CH3 (1a2 double-prime -1) are reported. The agreement between these calculated and available measured photoelectron spectra is generally very encouraging. In addition to the expected type c (triangle Ka = odd, triangle Kc = even) transitions, type a (triangle Ka = even, triangle Kc = odd) transitions, which arise from odd partial wave components of the photoelectron matrix elements, are also observed for photoionization of H2O and H2S. Whereas type c and type b (triangle Ka = odd, triangle Kc = odd) transitions are predicted for photoionization of H2CO, a triangle K = even selection rule is predicted for CH3. These studies serve to highlight the rich dynamics of rotationally resolved photoelectron spectra of nonlinear molecules and provide interpretations of key spectral features of interest in related experiments
[en] The space--time development of the hadronic system formed immediately after the high energy hadron collision is described with the following picture. Initially the system is highly compressed along the longitudinal direction. The sudden relaxation of this compression leads to a violent acceleration along this direction and perhaps a weak acceleration along the transverse direction. When these accelerations cease, it is proposed that the system acquires a frame independence symmetry with its further expansion governed by the hydrodynamic equation of motion. Within the scheme, this symmetry provides a natural mechanism which eventually leads to a flat inclusive longitudinal rapidity distribution and it also admits a sharp cutoff in the inclusive transverse momentum distribution. The latter is to be contrasted with the prediction of Landau's model, where the average transverse momentum increases with c.m. energy W, [p/sub T/] -W/sup 1/6./. Finally effects of clustering can also be easily incorporated within the framework. (U.S.)
[en] Temperature-dependent conductance-frequency, capacitance-frequency and current-voltage measurements have been carried out on hydrogenated nanocrystalline silicon (nc-Si:H) films grown by plasma-enhanced chemical vapor deposition. The nanocrystalline size of the films, obtained from Raman scattering and X-ray diffraction measurements, is found to be consistent with the observed Coulomb-blockade effect at temperature below 150 K, which demonstrates the good order of the nanostructure thin films. An improved series resistance equivalent circuit model has been proposed to extract valuable electrical information of the nanocrystalline Si samples. The frequency dependence of AC conductance at low temperature is similar to that of the amorphous materials, indicating that the hopping conduction plays an important role in nc-Si:H at low temperature. The temperature dependence of AC conductance reveals an overlapping large polaron tunneling mechanism in nc-Si:H. The temperature-dependent capacitance is found to be determined by the competition of carrier charging/discharging processes between the energy levels of the natural quantum dots and the localized states of the amorphous interface regions, and therefore shows frequency dependence
[en] We report bias- and frequency-dependent capacitance characteristics in Pb1-xSrxSe thin films with Sr composition from 0.066 to 0.276 grown by molecular beam epitaxy on BaF2 substrates. A grain boundary barrier model has been presented, which can well explain the experimental observation of the capacitance in relation with the bias, frequency, as well as the Sr composition. Negative capacitance phenomenon has been observed for samples with different Sr compositions under different bias and frequency conditions. The origin of this negative capacitance effect is believed to be due to the accumulation of minority carriers at the grain boundaries, which produces an additional dynamic capacitance with an opposite sign. In addition, the success in explaining the Sr composition dependent dark current characteristics gives further evidence for the model
[en] We report the evolution of thermal transport properties of KxFe2-ySe2 with sulfur substitution at Se sites. Sulfur doping suppresses the superconducting Tc. The Seebeck coefficient of all crystals in the low-temperature range can be described very well by a diffusive thermoelectric response model. The zero-temperature extrapolated value of the Seebeck coefficient divided by temperature, S/T, gradually decreases from -0.48 μV/K2 to a very small value, ∼0.03 μV/K2, where Tc is completely suppressed. The normal-state electron Sommerfeld term (γn) of specific heat also decreases with the increase in sulfur content. The decrease of S/T and γn reflects a suppression of the density of states at the Fermi energy, or a change in the Fermi surface that would induce the suppression of correlation strength. Our results imply little relevance of strong electron correlations to superconductivity.
[en] We have investigated the modification of the three-phonon Umklapp process in a quantum wire caused by the effect of phonon confinement. Our formalism rigorously takes into account variations in phonon group velocity as well as the presence of an energy gap between the phonon modes due to the quantization of the radial phonon wave vector. Numerical calculations of the Umklapp relaxation rate were carried out for Si wires. Based on the obtained results we predict the suppression of the acoustic phonon modes decay at low temperatures that can lead to the unusual thermal conductivity increase. We also present a simplified empiric formula for the Umklapp relaxation rate calculation in a quantum wire. copyright 2001 American Institute of Physics
[en] To investigate the effect of heat treatment and hot deformation on the secondary α phase evolution, the heat treatment and isothermal compression were carried out for the as-received TC8 titanium alloy respectively. An optical microscope (OM) and a scanning electron microscope (SEM) were used to examine the microstructure. In the heat treatment, the secondary α phase can precipitate only as the TC8 titanium alloy is heat treated at a heating temperature of 980 °C followed by air cooling. In the isothermal compression, the secondary α phase precipitates as an irregular morphology due to the high dislocation content in the deformed β phase at a low deformation temperature of 860 °C, while as a regular lamellar colony due to the high supersaturation in the deformed β phase at a high deformation temperature of 940 °C. Meanwhile, the height reduction has a significant effect on the content and morphology of secondary α phase in the isothermally compressed TC8 titanium alloy. Comparing the secondary α phase evolution in the isothermal compression with that in the heat treatment of TC8 titanium alloy, it can be concluded that the hot deformation has a promoting effect on the precipitation of secondary α phase due to the deformation heat, crystal defect and dynamic recrystallization of β phase generated in the isothermal compression of TC8 titanium alloy
[en] We have synthesized single crystals of K1.00(3)Fe0.85(2)Ag1.15(2)Te2.0(1). The material crystallizes in the ThCr2Si2 structure with I4/mmm symmetry and without K and Fe/Ag deficiencies, unlike in KxFe2-ySe2 and KxFe2-yS2. Transport, magnetic, and heat-capacity measurements indicate that KFe0.85Ag1.15Te2 is a semiconductor with long-range antiferromagnetic transition at TN = 35 K.
[en] The TC8 titanium alloy was isothermally compressed at the deformation temperatures ranging from 820 °C to 980 °C, strain rates of 10 s−1, 30 s−1 and 50 s−1, and a height reduction of 60%. An optical microscope (OM) and a transmission electron microscope (TEM) were used to examine the microstructure. The flow stress decreases with the increasing of deformation temperature and decreasing of strain rate. The strain rate sensitivity exponent m increases gradually to a maximum value as the deformation temperature increases from 820 °C to 940 °C, and then decreases at the deformation temperature of 980 °C. The strain hardening exponent n decreases with the decreasing of deformation temperature, and gets a maximum value at the strain rate of 30 s−1 and a given deformation temperature. According to the microstructure examination, the variation of flow stress, m and n values are found to depend on the phase transformation, grain morphology, dislocation content, dynamic recovery (DRV) and dynamic recrystallization (DRX) of primary α and β phases. The apparent activation energy for deformation is 429.766±80.394–383.478±78.734 kJ mol−1, and indicates that the dislocation climbing is not the main deformation mechanism. This deduction agrees well with the microstructure examination which shows that the DRX of primary α phase and β phase play an important role in the isothermal compression of TC8 titanium alloy