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131.
A. V. Antonov V. I. Gavrilenko A. V. Ikonnikov K. V. Maremyanin A. A. Lastovkin S. V. Morozov D. V. Ushakov Yu. G. Sadofyev N. Samal 《Radiophysics and Quantum Electronics》2009,52(7):494-499
We calculated energy levels, wave functions, and energies of radiative transitions in terahertz quantum cascade lasers based
on GaAs/Al0.15Ga0.85As heterostructures. Current-voltage characteristics and current dependences of laser radiation intensity were measured, and
the maximum operating temperatures reaching 85 K were determined. Radiation spectra of quantum cascade lasers were measured
for different temperatures, and the effect of intensity “pumping” from low-frequency modes to high-frequency modes was found
to happen in the case of an increase in the current and time delay of the signal capture, which is explained by heating of
the sample during a pulse of the current. Application of the lasers for registration of impurity photoconductivity signals
in semiconductor heterostructures was demonstrated. 相似文献
132.
Strained epitaxial La0.5Sr0.5CoO3 films are grown on LaAlO3 substrate. Structural, electrical, and magnetic measurements were carried out. Out of plane lattice parameter of the film undergoes compressive strain and the coercivity is enhanced. The zero field cooled (ZFC) magnetization curve for a field applied parallel to the film plane shows a jump, which suggests a spin reorientation transition (SRT), while ZFC magnetization for a field applied perpendicular to the film plane is featureless. This jump in magnetization is shifted to higher temperatures when the magnetic field is reduced. The SRT is attributed to the strain in the film. 相似文献
133.
Dwell fatigue crack nucleation model based on crystal plasticity finite element simulations of polycrystalline titanium alloys 总被引:2,自引:0,他引:2
Masoud Anahid Mahendra K. Samal Somnath Ghosh 《Journal of the mechanics and physics of solids》2011,59(10):2157-2176
In this paper a crystal plasticity-based crack nucleation model is developed for polycrystalline microstructures undergoing cyclic dwell loading. The fatigue crack nucleation model is developed for dual-phase titanium alloys admitting room temperature creep phenomenon. It is a non-local model that accounts for the cumulative effect of slip on multiple slip systems, and involves evolving mixed-mode stresses in the grain along with dislocation pileups in contiguous grains. Rate dependent, highly anisotropic behavior causes significant localized stress concentration that increases with loading cycles. The crystal plasticity finite element (CPFE) model uses rate and size-dependent anisotropic elasto-crystal plasticity constitutive model to account for these effects. Stress rise in the hard grain is a consequence of time-dependent load shedding in adjacent soft grains, and is the main cause of crack nucleation in the polycrystalline titanium microstructure. CPFE simulation results are post-processed to provide inputs to the crack nucleation model. The nucleation model is calibrated and satisfactorily validated using data available from acoustic microscopy experiments for monitoring crack evolution in dwell fatigue experiments. 相似文献
134.
The no-hiding theorem says that if any physical process leads to bleaching of quantum information from the original system, then it must reside in the rest of the Universe with no information being hidden in the correlation between these two subsystems. Here, we report an experimental test of the no-hiding theorem with the technique of nuclear magnetic resonance. We use the quantum state randomization of a qubit as one example of the bleaching process and show that the missing information can be fully recovered up to local unitary transformations in the ancilla qubits. 相似文献
135.
The graft copolymerization of methyl methacrylate (MMA) onto native and reduced Indian Chokla wool fibers was studied in aqueous solution using an acetylacetonate complex of Fe(III). Perchloric acid was found to catalyze the reaction. The rate of grafting was investigated by varying the concentration of the monomer and the complex, the acidity of the medium, and the solvent composition of the reaction medium. The graft yield increases with increasing concentration of the initiator and with increasing temperature. An increase of monomer concentration up to 0.5634 mol/L and of the HClO4 concentration up to 0.01 mol/L increases the graft yield. Reduced and oxidized wools were found to be better substrates than untreated, esterified, cross-linked, and trinitrophenylated wools. Among the various monomers studied, MMA was found to be the most active. A suitable kinetic scheme is proposed. From the activation energy data, average molecular weight, and spectral studies, the reactivity of -SH groups, and the extent of chain transfer is ascertained. 相似文献
136.
Polymerization of Acrylonitrile: Kinetics of the Reaction Initiated by the Redox System Mn3/Mannitol
R. K. Samal G. V. Suryanarayan G. Panda N. K. Dash D. P. Das M. C. Nayak 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(5):791-800
Polymerization of acrylonitrile initiated by the redox system Mn3+/mannitol has been investigated in aqueous sulfuric acid in the temperature range 35–50°C. The rate of polymerization Rp and the rate of disappearance of Mn+3 (?RM) were measured. The effect of certain water-miscible organic solvents, inorganic salts and complexing agents on the rate of polymerization have been investigated. Based on the experimental results, a suitable reaction mechanism is suggested involving the formation of complex between Mn3+ and the hydroxyl group of the substrate molecule, whose decomposition yields the initiating free radical; the polymer chain is terminated by the mutual combination of growing chains. 相似文献
137.
Abstract Kinetics of vinyl polymerization of methyl methacrylate (MMA) initiated by an acidic peroxo salt, such as potassium monopersulfate coupled with silver nitrate, have been investigated in aqueous medium over the temperature range from 35 to 50°C. The rates of polymerization (Rp) have been computed for various concentrations of the monomer and initiator. The effectiveness of various metal salts in catalyzing the polymerization reaction has been determined from the observed Rp values. The effects of the catalyst (AgNO3), initiator, monomer, and various secondary aliphatic and aromatic amines on Rp and percentage conversion have been studied. The endgroups of the resultant polymers have been studied using standard methods. From the observed endgroups and kinetic results, a reaction scheme has been proposed involving initiation by ′OH or SO4 ? radicals, generated by the interaction of the initiator with silver nitrate and termination by mutual combination. 相似文献