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991.
The beam quality of a single-rod Nd: YAG laser with wavelength of 1.06 m was improved almost up to the diffraction limit by using a phase-conjugating mirror (PCM) based on stimulated Brillouin scattering (SBS) with acetone as the SBS medium. The new start cavity, which is the concave-convex cavity operating near the limit of stability in the g diagram, and the phase conjugation cavity of the SBS oscillator were designed. The thermal lens of the material with focal lengths of less than 140 m at pump powers of 60 J was compensated by the PCM. The laser is Q-switched by the nonlinear reflectivity of the PCM and the system works with an average repetition rate of about 5 kHz and single Q-switch pulse showed a width of 10 ns. It is demonstrated that if the start cavity is fit for SBS and the SBS phase conjugation mirror can be optimized, the beam quality of solid laser can be surely enhanced because of this technology of nonlinear optics. 相似文献
992.
U. K.?Sapaev J.?KutznerEmail author K.?Finsterbusch 《Optical and Quantum Electronics》2005,37(6):515-527
Type-II frequency doubling of short Gaussian laser pulses is studied theoretically. The situation is analysed when the group velocity mismatch and the walk-off angle of the interacting waves limit the frequency conversion efficiency. It is shown that with collinear ‘o’ and ‘e’ polarized fundamental waves a temporal and spatial separation of the fundamental beams is necessary to compensate for both effects. Results of the presented model are discussed for KDP crystals. 相似文献
993.
A. V. Latyshev V. N. Popov A. A. Yushkanov 《Journal of Applied Mechanics and Technical Physics》2004,45(1):17-22
The slip velocity of a rarefied gas with inhomogeneous temperature and mass velocity on a solid spherical surface is calculated with the use of a twomoment boundary condition in the linear approximation in terms of the Knudsen number. The dependence of the slip velocity on accommodation coefficients of the two first moments of the distribution function is studied. 相似文献
994.
Takashi Shioya 《Geometriae Dedicata》2004,103(1):1-32
We study the behavior of maximal geodesics in a finitely connected complete two-dimensional Riemannian manifold M admitting curvature at infinity. In the case where M is homeomorphic to 2 the Cohn–Vossen theorem states that the total curvature of M, say c(M), is 2. We already studied the case c(M)<2 in our previous paper. So we study the behavior of geodesics in M with total curvature 2 in this paper. Next we consider the case where M has nonempty boundary. In order to know the behavior of distant geodesics in M with boundary, it is useful to investigate the 'visual image' of the boundary of M. The latter half of this paper will be spent to study the asymptotic behavior of the visual image of a subset of M with located point tending to infinity. 相似文献
995.
996.
In the early 1960s of the 20th century de Broglie was able to explain the cosmological observable red shift, without ad hoc assumptions. Starting from basic quantum considerations he developed his tired light model for the photon. This model explains in a single and beautiful causal way the cosmological redshift without need of assuming the Big Bang and consequently a beginning for the universe. Evidence coming from Earth sciences seems also to confirm these ideas and furthermore concrete proposal of laboratorial scale experiments that can test the model are reviewed. 相似文献
997.
Ji-Suo Wang Tang-Kun Liu Jian Feng Jin-Zuo Sun 《International Journal of Theoretical Physics》2004,43(9):1891-1905
A class of k-quantum nonlinear coherent states, i.e., the k eigenstates of the powers B
k
(k 3) of the annihilation operator
of f-oscillators, is obtained and its completeness is investigated. An alternative method to construct them is proposed. We introduce a new kind of higher-order squeezing and sub-Poissonian distribution. The quantum statistical properties of the k states are studied. The result shows that all of the eigenstates can be generated by a linear superposition of k Roy-type nonlinear coherent states. These states may form a complete Hilbert space, and the M-th order [M = (n + 1/2)k; n = 0,1, ...] squeezing effects exist in all of the k states when k is even. There is the sub-Poissonian distribution in all of the states. 相似文献
998.
The evolution of 2-D disturbances in hypersonic boundary layer with Mach number 6,8, and 10 was investigated numerically by
three different numerical schemes. At the entrance, second mode T-S waves with different amplitudes were introduced, and the
relation between the Mach number and the amplitude of the disturbance when shocklets started to appear was investigated. By
comparing the disturbance velocity profiles with those provided by linear stability theory, the effects of shocklets on flow
structures were also investigated. 相似文献
999.
High-spatial energy dispersive X-ray (EDX) microanalysis has been applied in order to reveal changes of chemical composition accompanying the formation of the lamellar structure due to discontinuous precipitation reaction in Al-22at.% Zn alloy. The line-scans performed in the reaction zone have shown that the region left behind the grain boundary (GB) after its displacement from the original position is solute depleted, similar to the de-alloying case of diffusion induced grain boundary migration. This enables the allotriomorphs to be transformed into solute-rich lamellae and development of lamellar + structure, especially if the GB moves in the direction perpendicular to its original location. If the direction of movement is strongly inclined to the original location of the GB, the growth usually stops after a short period of time, mainly due to formation of the precipitation free zone (PFZ) ahead of the reaction front. The detailed EDX examination revealed that there is a sharp change in solute content at the lamella/PFZ and PFZ/matrix alloy interfaces. The solute content in the PFZ is lower than in the neighbouring lamella and it corresponds to the equilibrium state. Therefore, one can suppose that the PFZ is formed due to backward movement of the reaction front in order to consume the excess of solute atoms stored in the lamellae in comparison with the equilibrium state. As soon as the equilibrium state is attained within the PFZ, the growth of the colony is completed. 相似文献
1000.
We find existence of a nonnegative compactly supported solution of the problem Δu=uα in , ∂u/∂ν=u on . Moreover, we prove that every nonnegative solution with finite energy is compactly supported and radially symmetric in the tangential variables. 相似文献