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排序方式: 共有48条查询结果,搜索用时 15 毫秒
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Schreiner PR Chernish LV Gunchenko PA Tikhonchuk EY Hausmann H Serafin M Schlecht S Dahl JE Carlson RM Fokin AA 《Nature》2011,477(7364):308-311
Steric effects in chemistry are a consequence of the space required to accommodate the atoms and groups within a molecule, and are often thought to be dominated by repulsive forces arising from overlapping electron densities (Pauli repulsion). An appreciation of attractive interactions such as van der Waals forces (which include London dispersion forces) is necessary to understand chemical bonding and reactivity fully. This is evident from, for example, the strongly debated origin of the higher stability of branched alkanes relative to linear alkanes and the possibility of constructing hydrocarbons with extraordinarily long C-C single bonds through steric crowding. Although empirical bond distance/bond strength relationships have been established for C-C bonds (longer C-C bonds have smaller bond dissociation energies), these have no present theoretical basis. Nevertheless, these empirical considerations are fundamental to structural and energetic evaluations in chemistry, as summarized by Pauling as early as 1960 and confirmed more recently. Here we report the preparation of hydrocarbons with extremely long C-C bonds (up to 1.704??), the longest such bonds observed so far in alkanes. The prepared compounds are unexpectedly stable--noticeable decomposition occurs only above 200?°C. We prepared the alkanes by coupling nanometre-sized, diamond-like, highly rigid structures known as diamondoids. The extraordinary stability of the coupling products is due to overall attractive dispersion interactions between the intramolecular H???H contact surfaces, as is evident from density functional theory computations with and without inclusion of dispersion corrections. 相似文献
4.
The influence of laser beam smoothing on stimulated Brillouin backscattering (SBBS) is studied analytically in the limit of the independent hot spot model. It is shown that the temporal beam smoothing can reduce the SBBS reflectivity significantly even though the laser bandwidth is smaller than the growth rate for the average intensity. The explanation of this reduction effect is given in terms of SBBS growth in the statistically significant hot spots. The minimum laser bandwidth corresponding to an important reduction of the reflectivity is thus determined properly. The dependence of this reduction effect on the acoustic damping for a given laser bandwidth is discussed. 相似文献
5.
Collective properties of a relativistic electron beam injected into a high intensity optical lattice
I. A. Andriyash Ph. Balcou V. T. Tikhonchuk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(3):533-540
Behaviour of a relativistic electron bunch, injected and trapped in a high intensity
optical lattice resulting from the interference of two laser beams is studied. The optical
lattice modifies the phase space distribution of the electron bunch due to the trapping
and compression of the electrons by a ponderomotive force. High-frequency longitudinal
beam eigenmodes of the trapped electron bunch are described in the framework of fluid and
kinetic models. Such beam oscillations are expected to play a pivotal role in a stimulated
Raman scattering of laser beams on the electrons. 相似文献
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A theory for the nonlinear saturation of convective parametric instabilities in inhomogeneous plasmas is proposed. The role of parametric processes in laser light absorption in a dense plasma corona is discussed on the basis of this theory. 相似文献
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N. Naumova T. Schlegel V. T. Tikhonchuk C. Labaune I. V. Sokolov G. Mourou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(2):393-398
Short laser pulses at super-high intensities such as those proposed in the Extreme Light Infrastructure (ELI) project
open new prospects for efficient acceleration of ions in overdense plasmas. A simple analytical model and numerical simulations
demonstrate that pulses with intensities exceeding 1022 W/cm2 may efficiently accelerate ions to high energies up to a few GeV.
Maximum ion energy and the energy spectrum of the accelerated ions can be tuned by an appropriate choice of laser pulse intensity
and duration at a given plasma density distribution. 相似文献
9.
S.P. Davis R. Capdessus E. d'Humières S. Jequier I. Andriyash V. Tikhonchuk 《High Energy Density Physics》2013,9(1):231-238
Collisionless shock formation is investigated with large scale fully electromagnetic two-dimensional Particle-in-Cell numerical simulations. Two plasmas are colliding in the center of mass reference frame at sub-relativistic velocities. Their interaction leads to collisionless stochastic electron heating, ion slowing down and formation of a shock front. We focus here on the initial stage of evolution where electron heating is due to the Weibel-like micro-instability driven by the high-speed ion flow. A two stage process is described in the detailed analysis of our simulation results. Filament generation, followed by turbulent mixing, constitute the dominant mechanism for energy repartition. The global properties are illustrated by examination of single filament evolution in terms of energy/particle density and fields. 相似文献
10.
G. S. Sarkisov V. Yu. Bychenkov V. T. Tikhonchuk A. Maksimchuk S. Y. Chen R. Wagner G. Mourou D. Umstadter 《JETP Letters》1997,66(12):828-834
We report the first interferometric observations of the dynamics of electron-ion cavitation of relativistically self-focused
intense 4 TW, 400 fs laser pulse in a He gas jet. The electron density in a channel 1 mm long and 30 μm in diameter drops
by a factor of approximately 10 from the maximum value of ∼8×1019 cm−3. A high radial velocity of the plasma expansion, ∼3.8×108 cm/s, corresponding to an ion energy of about 300 keV, is observed. The total energy of fast ions is estimated to be 6% of
the laser pulse energy. The high-velocity radial plasma expulsion is explained by a charge separation due to the strong ponderomotive
force. This experiment demonstrates a new possibility for direct transmission of a significant portion of the energy of a
laser pulse to ions.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 787–792 (25 December 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献