共查询到20条相似文献,搜索用时 31 毫秒
1.
被动调Q激光器以其结构简单、紧凑而获得了广泛的应用。为优化其性能参数,在总结近些年被动调Q基本理论基础上,对于具有能量上转换(Energy-transfer upconversion)的激光工作物质构成的被动调Q激光器,提出了可以将能量上转换引起的损耗归到线性损耗中进行优化设计的方法,并给出了输出镜的反射率和饱和吸收体的小信号透过率两者优化选择的直接关系图。根据被动调Q激光器的特有参数α,在总结提高调Q峰值功率的方法基础上,得出当α接近无穷大时,从被动调Q过渡到主动调Q,实现了被动调Q和主动调Q理论的统一。 相似文献
2.
Kh. Lotfy 《Waves in Random and Complex Media》2017,27(3):482-501
The dual-phase-lag (DPL) model with two different time translations and Lord–Shulman (LS) theory with one relaxation time are applied to study the effect of hydrostatic initial stress on medium under the influence of two temperature parameter(a new model will be introduced using two temperature theory) and photothermal theory. We solved the thermal loading at the free surface in the semi-infinite semiconducting medium-coupled plasma waves with the effect of mechanical force during a photothermal process. The exact expressions of the considered variables are obtained using normal mode analysis also the two temperature coefficient ratios were obtained analytically. Numerical results for the field quantities are given in the physical domain and illustrated graphically under the effects of several parameters. Comparisons are made between the results of the two different models with and without two temperature parameter, and for two different values of the hydrostatic initial stress. A comparison is carried out between the considered variables as calculated from the generalized thermoelasticity based on the DPL model and the LS theory in the absence and presence of the thermoelastic and thermoelectric coupling parameters. 相似文献
3.
The problem of deducing one-dimensional theory from two-dimensional theory for a homogeneous isotropic beam is investigated.
Based on elasticity theory, the refined theory of rectangular beams is derived by using Papkovich-Neuber solution and Lur’e
method without ad hoc assumptions. It is shown that the displacements and stresses of the beam can be represented by the angle of rotation and
the deflection of the neutral surface. Based on the refined beam theory, the exact equations for the beam without transverse
surface loadings are derived and consist of two governing differential equations: the fourth-order equation and the transcendental
equation. The approximate equations for the beam under transverse loadings are derived directly from the refined beam theory
and are almost the same as the governing equations of Timoshenko beam theory. In two examples, it is shown that the new theory
provides better results than Levinson’s beam theory when compared with those obtained from the linear theory of elasticity. 相似文献
4.
The algebraic foundation of cohomological field theory is presented. It is shown that these theories are based upon realizations of an algebra which contains operators for both BRST and vector supersymmetry. Through a localization of this algebra, we construct a theory of cohomological gravity in arbitrary dimensions. The observables in the theory are polynomial, but generally non-local operators, and have a natural interpretation in terms of a universal bundle for gravity. As such, their correlation functions correspond to cohomology classes on moduli spaces of Riemannian connections. In this uniformization approach, different moduli spaces are obtained by introducing curvature singularities on codimension two submanifolds via a puncture operator. This puncture operator is constructed from a naturally occuring differential form of co-degree two in the theory, and we are led to speculate on connections between this continuum quantum field theory, and the discrete Regge calculus. 相似文献
5.
The theory for the Doppler shifted light is developed by diffraction theory combined with galilean transformation. The theory developed is applied to a differential Doppler heterodyning technique in which two beams are brought simultaneously, but at different angles, into the same area, and the cross region made by the two beams becomes a probing volume. When the concentration of scattering particles is so low that only one particle is found in the probing volume, the theory can be classified into two cases of a single particle and many particles depending on the analysing time for the Fourier transform, i.e. whether the time, during which one particle passes through the probing volume, is longer than the observing time or not. When the concentration of particles in the probing volume becomes dense, the light scattered by the different particles interferes and the theory shows great complexity. The cases of two particles and many particles showing a very high density are studied. Comparisons are made for the difference between differential Doppler heterodyning and normal heterodyning techniques. 相似文献
6.
Steven M. Moore 《Foundations of Physics》1979,9(3-4):237-259
The prospects for a complete stochastic theory of microscopic phenomena are considered. The two traditional schools of stochastic physics, the diffusion process school and the zero-point electromagnetic field school, are reviewed. A completely relativistic theory, stochastic field theory, is proposed as an extension of the ideas of these two schools. Within the context of stochastic field theory we present the following new results: an elementary stochastization scheme which produces the zero-point electromagnetic field; a physical interpretation of the mathematical methods developed by Lukosz for calculating zero-point energies; a calculation of the first-order Lamb shift which generalizes that of Welton; a new setting for a finite-temperature theory; and comments on the bag model for quark confinement.Research financed in part by Colciencias. 相似文献
7.
We construct a theory of cohomological gravity in arbitrary dimensions based upon a local vector supersyrnmetry algebra. The observables in this theory are polynomial, but generally non-local operators, and have a natural interpretation in terms of a universal bundle for gravity. As such, their correlation functions correspond to cohomology classes on moduli spaces of Riemannian connections. In this uniformization approach different moduli spaces are obtained by introducing curvature singularities on codimension two submanifolds via a puncture operator. This puncture operator is constructed from a naturally occurring differential form of co-degree two in the theory, and we are led to speculate on connections between this continuum quantum field theory, and the discrete Regge calculus.This essay received an honorable mention from the Gravity Research Foundation, 1992-Ed. 相似文献
8.
Ellipsometric measurements on the adsorption system xenon on graphite [5] have been confronted with partly Drude's macroscopic theory, partly Sivukhin's microscopic theory. The optical constants necessary for the theory have been calculated for each monolayer, using two experimentally known quantities, the polarizability of a free xenon atom, and the nearest-neighbour distance Xe-Xe. The ellipsometric signals calculated for each of the five monolayers are in excellent agreement with experiment, the macroscopic theory giving the best quantitative agreement. For the first incomplete monolayer the results do not grant a statement in favour of one theory or the other. 相似文献
9.
L.S. Schulman 《Physica A》1977,89(3):597-604
The predictions of catastrophe theory for phase transitions involving more than one order parameter are given. These predictions are compared with those of other theories. For the simplest transition involving two order parameters it is found that there is a parameter which does not affect the topology of the phase diagram, which does affect certain angles in the diagram, and whose measured value will not depend on the scale of external physical variables. Comparison with renormalization theory predictions for this parameter leads to general observations on the relation of catastrophe theory and renormalization theory. 相似文献
10.
简单介绍了以经典Mie理论为基础的光散射测量技术在颗粒直径和颗粒浓度测量中广泛的应用。分别以Mie理论和离散偶极子近似理论(DDA)为基础, 用数值计算方法分析了球型颗粒的光散射特性,给出了微小颗粒对平行入射光散射的强度函数和散射偏振度的数值计算方法。得到了强度函数和偏振度随相关物理参量变化的三维图,为微小颗粒散射研究提供了一种三维视图。计算结果表明:当尺度参量x<4时,2种方法所得结果差异不大;随尺度参量增大,2种方法所得结果出现较大差异。与经典Mie理论相比,由于离散偶极子近似理论可以解决各种形状的颗粒散射问题,其应用前景更广泛。 相似文献
11.
We present a new model for Yang-Mills theory on the fuzzy sphere in which the configuration space of gauge fields is given
by a coadjoint orbit. In the classical limit it reduces to ordinary Yang-Mills theory on the sphere. We find all classical
solutions of the gauge theory and use nonabelian localization techniques to write the partition function entirely as a sum
over local contributions from critical points of the action, which are evaluated explicitly. The partition function of ordinary
Yang-Mills theory on the sphere is recovered in the classical limit as a sum over instantons. We also apply abelian localization
techniques and the geometry of symmetric spaces to derive an explicit combinatorial expression for the partition function,
and compare the two approaches. These extend the standard techniques for solving gauge theory on the sphere to the fuzzy case
in a rigorous framework. 相似文献
12.
Solutions for a cylindrically symmetric static gravitational field in Brans-Dicke theory are obtained. It is found that the condition for escape of photons emitted from the surface of the source depends on two parameters, instead of only the mass parameter as in the case of Mardar's solution in Einstein's theory. 相似文献
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The duality solution for elasticity and the biorthogonality relationship have been well researched. Now the couple stress
theory becomes a new research spot but there is few research for the biorthogonality relationship for couple stress theory
comparing to classical elasticity. A new state vector is presented for three dimensional couple stress problems of prismatic
structures. A new biorthogonality relationship of couple stress is discovered. The dual partial differential equations of
couple stress problem are derived by the new state vector. By two important identical equations the new biorthogonality relationship
is proved based on the method of separation of variables. The symplectic orthogonality relationship to three dimensional couple
stress theory may be decomposed into two independently and symmetrically orthogonality relationships. The new biorthogonality
relationship includes the symplectic orthogonality relationship. The biorthogonality relationship of couple stress may also
be degenerated into the theory of elasticity. The new state vector and biorthogonality relationship provide theoretic foundation
for the research on the schemes of separation of variables and eigenfunction expansion of couple stress theory. 相似文献
16.
P. Weinberger 《哲学杂志》2015,95(27):3039-3051
The original contributions of Arthur Cayley to the Philosophical Magazine on group theory and his ‘trees’ are revisited and to some extend reinterpreted. Both topics were and are of enormous importance not only in physics (group theory, graph theory), but also in quite a few other disciplines as diverse as information technology or, for example, linguistics (trees, graph theory). In order to show that these two topics originally arose from interests in the theory of permutations also Cayley’s ‘Mousetrap’ game is briefly mentioned. 相似文献
17.
In a previous paper second-order calculations were carried out on the two-level pairing force model using perturbation theory for projected states and the results were compared with those of BCS or ordinary perturbation theory. In the present paper criteria for convergence are applied to two different forms of the perturbation series for both the projected and ordinary perturbation theories. It is found that the superior results obtained for the convergence rates in the projected theory tally neatly with the results of the second-order calculations, and give further support to the use of the projected perturbation theory. 相似文献
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19.
We develop a theory for the nonequilibrium coherent transport through a mesoscopic region, based on thenonequilibrium Green function technique. The theory requires the weak coupling bet. ween the central mesoscopic regionand the multiple electrodes, but allows arbitrary hopping and interaction in the central region. An equation determiningthe nonequilibrium distribution in the central interacting region is derived and plays an important role in the theory.The theory is applied to two special cases for demonstrations, revealing the novel effects associated with the combinationof phase coherence, Coulomb interaction, and nonequilibrium distribution. 相似文献
20.
Gábor Zsolt Tóth 《Central European Journal of Physics》2012,10(2):349-360
The problem of extending quantum-mechanical formal scattering theory to a more general class of models that also includes
quantum field theories is discussed, with the aim of clarifying certain aspects of the definition of scattering states. As
the strong limit is not suitable for the definition of scattering states in quantum field theory, some other limiting procedure
is needed. Two possibilities are considered, the abelian limit and adiabatic switching. Formulas for the scattering states
based on both methods are discussed, and it is found that generally there are significant differences between the two approaches.
As an illustration of the applications and the features of these formulas, S-matrix elements and energy corrections in two
quantum field theoretical models are calculated using (generalized) old-fashioned perturbation theory. The two methods are
found to give equivalent results. 相似文献