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101.
We consider stimulated pair production employing strong-field QED in a high-intensity laser background. In an infinite plane wave, we show that light-cone quasi-momentum can only be transferred to the created pair as a multiple of the laser frequency, i.e. by a higher harmonic. This translates into discrete resonance conditions providing the support of the pair creation probability which becomes a delta-comb. These findings corroborate the usual interpretation of multi-photon production of pairs with an effective mass. In a pulse, the momentum transfer is continuous, leading to broadening of the resonances and sub-threshold behaviour. The peaks remain visible as long as the number of cycles per pulse exceeds unity. The resonance patterns in pulses are analogous to those of a diffraction process based on interference of the produced pairs. We finally comment on the dependence of the peak positions, and in turn the effective mass, on the pulse shape. 相似文献
102.
Vladislav M. Vlasov 《Journal of Physical Organic Chemistry》2010,23(5):468-476
Changes of the activation parameters in aliphatic SN2 reactions with anionic and neutral nucleophiles in various solvents, ΔH≠ and ΔS≠, were correlated with σ constants of the substituents. The resultant δΔH≠ and δΔS≠ reaction constants are linearly related for variations of substituents at the substrate, leaving group and nucleophile. Correlations of δΔH≠ versus δΔS≠ allow the estimation of the contribution of changes of the internal enthalpy, δΔH, to the enthalpy reaction constant, δΔH≠, which gives a single linear dependence on the Hammett ρ reaction constants. The deviations from the dependence of δΔH versus ρ can be interpreted in terms of changes in the transition state structure in SN2 reactions. The results obtained show that the substituent effects on the charge development in the transition state are governed by the magnitude of δΔH. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
103.
Dmitrii O. Kharchenko Olga M. Shchokotova Vasyl O. Kharchenko Viktor V. Kupriienko S.V. Kokhan Xiaoyong Wu 《辐射效应与固体损伤》2020,175(7-8):602-626
ABSTRACT We study microstructure transformation in Zr–Nb system under neutron irradiation and its mechanical properties change under mechanical loads in a form of shear deformation by using phase field methodology. The developed phase field approach takes into account defects dynamics based on reaction rate theory and elastic contribution to study mechanical properties change. A numerical modeling is provided in three stages: sample preparation, irradiation of the prepared sample and mechanical loading of the irradiated sample. A precipitation of β-Niobium particles of the size of several nanometers is discussed. Results of phase field modeling indicate that β-Niobium particles grow slowly during irradiation due to point defects rearrangement. Statistical analysis of dynamics of radiation-induced microstructure transformations is provided. Simulation results of shear deformation of pre-irradiated and post-irradiated alloys are discussed. Maps of local distribution of strain and stress and strain–stress curves are obtained. Results are verified with experimental data. 相似文献
104.
Comparison of radiation degradation induced by x-ray and 3-MeV protons in 65-nm CMOS transistors 下载免费PDF全文
丁李利 Simone Gerardin Marta Bagatin Dario Bisello Serena Mattiazzo Alessandro Paccagnella 《中国物理 B》2016,25(9):96110-096110
The total ionizing dose(TID) response of 65-nm CMOS transistors is studied by 10-ke V x-ray and 3-Me V protons up to 1 Grad(SiO_2) total dose.The degradation levels induced by the two radiation sources are different to some extent.The main reason is the interface dose enhancement due to the thin gate oxide and the low energy photons.The holes' recombination also contributes to the difference.Compared to these two mechanisms,the influence of the dose rate is negligible. 相似文献
105.
Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with system size L and localization length l in the strong disorder limit. However, classical systems can always have metallic states in which Ohm’s law shows a constant g in d=2. We study a two-dimensional quantum percolation model by controlling dephasing effects. The numerical investigation of g aims at simulating a quantum-to-classical percolation evolution. An unexpected metallic phase, where g increases with L, generates immense interest before the system becomes completely classical. Furthermore, the analysis of the scaling plot of g indicates a metal-insulator crossover. 相似文献
106.
蓝宝石的冲击消光现象是高压领域中的研究热点.低压段(86 GPa范围内)的实验研究表明蓝宝石的冲击消光与晶向相关,但在高压段(压力范围:131255 GPa)是否也具有晶向相关性目前尚不清楚.为此,利用第一性原理方法,分别计算了八个不同晶向的蓝宝石理想晶体和含氧离子空位缺陷晶体在高压段的光吸收性质,结果发现:1)蓝宝石在高压段的冲击消光表现出明显的晶向效应,且该效应还随压力增大而增强;一步的数据分析可以看出,在冲击实验采用的波段内,a晶向的消光最弱(透明性最好),c晶向的消光最强与c晶向的消光接近,g晶向的消光要弱于s晶向的消光.鉴于此,如果在高压段开展加窗冲击波实验,建议选择a晶向或m晶向的蓝宝石作为其光学窗口.本文结果不仅有助于深入地认识蓝宝石在极端条件下的光学性质,而且对未来的实验研究有重要的参考作用. 相似文献
107.
This study extends the investigation of quantum dissipative effects of a cosmological scalar field by taking into account cosmic expansion and contraction.Cheung,Drewes,Kang,and Kim calculated the effective action and quantum dissipative effects of a cosmological scalar field in a recent work,where analytical expressions for the effective potential and damping coefficient were presented using a simple scalar model with quartic interactions,and the work was conducted using Minkowski-space propagators in loop diagrams.In this work,we incorporate the Hubble expansion and contraction of the cosmic background and focus on the thermal dynamics of a scalar field in a regime where the effective potential changes slowly.Given that the Hubble parameter,H,attains a small but non-zero value,we carry out calculations to the first order in H.If we set H=0,all results match those in flat spacetime.Interestingly,we must integrate over the resonances,which in turn leads to an amplification of the effects of a non-zero H.This is an intriguing phenomenon,which cannot be uncovered in flat spacetime.The implications on particle creations in the early universe will be studied in a forthcoming study. 相似文献
108.
H. Pan T. H. Lin 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):299-303
The supercurrent through an Aharonov-Bohm interferometer containing
two parallel quantum dots connected with two superconductor leads is
investigated theoretically. The possibility of controlling the
supercurrent is explored by tuning the quantum dot energy levels and
the total magnetic flux. By tuning the energy levels, both quantum
dots can be in the on-resonance or off-resonance states, and thus
the optimal modulation of the supercurrent can be achieved. The
supercurrent sign does not change by simply varying the quantum dot
energy levels. However, by tuning the magnetic flux, the
supercurrent can oscillate from positive to negative, which results
in the π-junction transition. 相似文献
109.
A. Vukics H. Ritsch 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):585-599
We present a framework for efficiently performing Monte Carlo
wave-function simulations in cavity QED with moving particles. It
relies heavily on the object-oriented programming paradigm as realised
in C++, and is extensible and applicable for simulating open
interacting qua
ntum dynamics in general. The user is provided with a
number of “elements”, e.g. pumped moving particles, pumped lossy
cavity modes, and various interactions to compose complex interacting
systems, which contain several particles moving in electromagnetic
fields of various configurations, and perform wave-function
simulations on such systems. A number of tools are provided to
facilitate the implementation of new elements. 相似文献
110.
Sonjoy Majumder B. K. Sahoo R. K. Chaudhuri B. P. Das D. Mukherjee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):441-445
Ab initio calculations have been carried out to study the magnetic dipole and
electric quadrupole hyperfine structure constants of 205Pb+. Many-body
effects have been considered to all orders using the relativistic coupled-cluster theory in the singles, doubles and partial
triples approximation. The trends of these
effects are found to be different from atomic systems that have been studied
earlier. 相似文献