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排序方式: 共有498条查询结果,搜索用时 15 毫秒
491.
Light beams with minimum phase space product 总被引:1,自引:0,他引:1
We derive a reciprocity inequality involving the product of the effective size of a statistically stationary, planar, secondary source of any state of coherence and of the angular spread of the far-zone intensity generated by the source. We show that of all possible such sources, the fully spatially coherent lowest-order Hermite-Gaussian laser mode has the smallest possible reciprocity product. 相似文献
492.
Lorin Crawford Vadim Ponomarenko Jason Steinberg Marla Williams 《Results in Mathematics》2014,66(1-2):227-245
For certain \({a,b \in \mathbb{N}}\) , an Arithmetic Congruence Monoid M(a, b) is a multiplicatively closed subset of \({\mathbb{N}}\) given by \({\{x\in\mathbb{N}:x \equiv a \pmod{b}\} \cup\{1\}}\) . An irreducible in this monoid is any element that cannot be factored into two elements, each greater than 1. Each monoid element (apart from 1) may be factored into irreducibles in at least one way. The elasticity of a monoid element (apart from 1) is the longest length of a factorization into irreducibles, divided by the shortest length of a factorization into irreducibles. The elasticity of the monoid is the supremum of the elasticities of the monoid elements. A monoid has accepted elasticity if there is some monoid element that has the same elasticity as the monoid. An Arithmetic Congruence Monoid is local if gcd(a, b) is a prime power (apart from 1). It has already been determined whether Arithmetic Congruence Monoids have accepted elasticity in the non-local case; we make make significant progress in the local case, i.e. for many values of a, b. 相似文献
493.
Multiphoton and electron-impact ionization of a gas-dynamic beam of xenon atoms are compared in order to determine the effective multiphoton ionization cross sections. The three-photon ionization cross section of the xenon atom is determined. 相似文献
494.
N. P. Yevlampieva A. P. Khurchak Yu. N. Luponosov E. A. Kleimyuk S. A. Ponomarenko E. I. Ryumtsev 《Russian Journal of Applied Chemistry》2013,86(5):747-755
Star-thiophene derivatives with a silicon atom as the branching center were investigated by absorption spectroscopy and electro-optical Kerr effect in solutions at variations in a number and chemical structure of branches. The star-shaped oligomers were compared with dendritic analogues containing silicon atoms at the points of branching. It is shown that thiophene-containing moieties determine both spectral and electrooptical properties of the molecules. Molecular parameters of the star-shaped oligomers of various structure vary identically with increasing the number of branches. The absorption of star-shaped oligomers is additive due to the autonomy of the absorption of radiation by the separate branches. For dendritic molecules the additive nature of the absorption is kept, but their electro-optical properties are independent of a generation number. It was shown that the latter is a consequence of the manifestation by dendrimers of deformation flexibility, which is not peculiar to the starshaped derivatives. 相似文献
495.
Yurii A. Serguchev Lyudmila F. LourieMaxim V. Ponomarenko Eduard B. RusanovNikolai V. Ignat’ev 《Tetrahedron letters》2011,52(40):5166-5169
Fluorolactonization of unsaturated carboxylic acids under action of the electrophilic reagent F-TEDA-BF4 in ionic liquids (ILs) has been studied. This reaction proceeds in ILs faster and provides a better stereoselectivity in comparison to acetonitrile as reaction media. Gem-difluorinated γ-lactones have been synthesized by interaction of unsaturated carboxylic acids with F-TEDA-BF4 in ILs. 相似文献
496.
Yu. V. Kabirov M. F. Kupriyanov E. V. Petrovich Sh. I. Duimakaev V. O. Ponomarenko 《Physics of the Solid State》2011,53(1):114-118
Solid solutions of two antiferroelectrics, namely, lead zirconate and lead hafnate, i.e., PbZr1 − x
Hf
x
O3 (x = 0, 0.3, 0.5, 0.7, 1.0), have been prepared by solid-phase synthesis from simple oxides. The elemental composition of the
samples and their structure have been studied using X-ray fluorescence and X-ray diffraction analyses. The phase transformations
of the solid solutions have been determined in the temperature range 20°C < T < 300°C. 相似文献
497.
We derive an expression for the lower bound of the phase-space beam quality factor M(2) of an ultrashort pulse. We show that the condition M(2)>or=1 does not, in general, hold for such pulsed beams. Rather, the minimum value of M(2) depends on the pulse spectrum. We also show that M(2) attains minimum only for pulsed beams whose spot size varies with frequency as omega(-1/2), and that the radial intensity profile of the best-quality pulsed beam can be non-Gaussian. 相似文献
498.
In order to verify notions about the nature of the stage behaviour in KCl crystals the influence of purity and dimensions of KCl crystals on the stage behaviour of the workhardening curve τ(ϵ) has been studied. It is shown that in soft KCl crystals up to six stages of work hardening are observed. With increasing rigidity and decreasing sample dimensions (less than 2 mm2 cross section) the number of observable stages is reduced to three. As work hardening builds up the extent of odd stages (I, III, V) grows and that of even stages (II, IV) falls. The dependence of 1/γ on strain ϵ (γ-activation “volume” of dislocation motion) for all the crystals studied is shown to replicate the τ(ϵ) curve. The rule of increasing the linear density of thermally surmountable obstacles on dislocations is the same for every pair of stages. This indicates that the nature of stages III and V is the same and caused by the activity of new slip systems oblique to the primarily active in stages II and IV, respectively. 相似文献