光受激发射的稳定性

本文推导出描述三能级Laser工作过程的准经典方程组,并分析了输出振动的稳定性。在阈值以上,当T₁?T₂,q^-1时,只在1/(qT₂)>1时,输出振幅是稳定的(其中T₁,T₂,q^-1分别是分子纵向、横向及谐振腔的弛豫时间)。在稳定区域,趋向平衡的时间与T₁成正比。当分子线宽小于谐振腔宽度时,输出是不稳定的,而在1/(qT₂)减小时,平衡点由稳定变到不稳定时产生一个稳定的极限环,即输出振幅逐渐开始振动。关于稳定性的结论在气体Laser中是可以检验的。本文指出,在红宝石Laser中看到的输出不稳定,可能就是谐振腔的q很大的结果。     

检验π介子散射过程是否存在p态共振的一个实验方法的建议

An Experiment designed the p-resonance in π-π scattering process is suggested.     

跳跃机构与低渗杂半导体杂质电导

在渗杂度很低时,由于少数杂质电离后引起场的起伏,电子在杂质上主要处于局域状态,电声子作用使电子能够在不同杂质上跳跃,但由于电子坐标算符与电声子作用交换,在电场中电子的运动实际上是一种击穿效应,而由声子束补偿能量。针对低补偿情况,略去复杂能带结构,我们由刘维方程出发,把密度矩阵对电场,然后对电声子作用展开,得到电流表达式及密度矩阵对角元所满足的玻茲曼型方程.只取到重迭积分二次项,我们得到了Miller等的网络方程,可以简单地求出平均阻抗,在低温极限下,得到σ～e^{(-βε_{(Be-1.54(rd/a)3/2))}}N_A^1/8,βε₃=βe²/(εr_d) -1.93(βE_A)^3/4。借助网络模型,我们分析了密度矩阵各部分的贡献,特别是与通常输运过程的差别。最后利用Anderson的结果,若K<10^-2,在对电导起主要作用的链上,在Ge,Si中浓度要在10¹⁴及10¹⁶cm^-3以下才能形成局域态,我们认为,考虑了电子间库仑作用后,载流子非局域并不与目前实验矛盾。 关键词：     

基于亚微米尺度干涉阵列的超小型高分辨光谱仪(英文)

We present an ultra compact and high resolution free space optical spectrometer and demonstrate it by using FDTD simulations. The miniature interferometer-based speetrometer is a series of submicron phase objects on a polymethyl methacrylate（PMMA） film with a CCD as the detector. The speetrum is obtained by solving a system of simultaneous linear equations. The Tikhonov regularization method is used to achieve a resolution at the picometer level. Compared with conventional speetrometers, the proposed device is low-cost and easy to fabricate due to its simple structure. Furthermore, its compact feature renders the device ideal for miniaturization and integration as the systems in microfluidics architectures and lab-on-chip designs.     

Beispiele von Pseudo-Differentialoperator-Algebrenfl

Discussion of methods in theory of Partial Differential Operators (and Pseudo-Differential Operators) which are based on Gel'fand theory of commutative Banach Algebras. These methods all are discussed for the (non-compact) manifold Rⁿ, for L^p/-SobolefF spaces W_p,k (including k = ∞) and for operators of "Laplace-type", which, crudely, amounts to "elliptic type". Generalizations to general non-compact manifolds and to hypo-elliptic operators have been worked out in detail in [6], for example. Two types of symbol are introduced for a (Pseudo)-differential operator: the Laplace-symbol-quotient ^s (of order s) and the symbol σ. Among the results we have (a) necessary and sufficient criteria for the existence of an W^:p,-Fredholm inverse, (b) essential self-adjointness and (c) characterization of the essential spectrum of elliptic (Pseudo-) Differential operators.     

Supramolecular packing of alkyl substituted Janus face all-cis 2,3,4,5,6-pentafluorocyclohexyl motifs

This study uses X-ray crystallography, theory and Langmuir isotherm analysis to explore the conformations and molecular packing of alkyl all-cis 2,3,4,5,6-pentafluorocyclohexyl motifs, which are prepared by direct aryl hydrogenations from alkyl- or vinyl-pentafluoroaryl benzenes. Favoured conformations retain the more polar triaxial C–F bond arrangement of the all-cis 2,3,4,5,6-pentafluorocyclohexyl ring systems with the alkyl substituent adopting an equatorial orientation, and accommodating strong supramolecular interactions between rings. Langmuir isotherm analysis on a water subphase of a long chain fatty acid and alcohol carrying terminal all-cis 2,3,4,5,6-pentafluorocyclohexyl rings do not show any indication of monolayer assembly relative to their cyclohexane analogues, instead the molecules appear to aggregate and form higher molecular assemblies prior to compression. The study indicates the power and potential of this ring system as a motif for ordering supramolecular assembly.

Theory and Langmuir isotherm analysis was used to explore the conformations and molecular packing of alkyl all-cis 2,3,4,5,6-pentafluorocyclohexyl motifs, which are prepared by direct aryl hydrogenations from alkyl- or vinyl-pentafluoroaryl benzenes.     

Janus Face All-cis 1,2,4,5-tetrakis(trifluoromethyl)- and All-cis 1,2,3,4,5,6-hexakis(trifluoromethyl)- Cyclohexanes

We report the synthesis of all-cis 1,2,4,5-tetrakis (trifluoromethyl)- and all-cis 1,2,3,4,5,6-hexakis (trifluoromethyl)- cyclohexanes by direct hydrogenation of precursor tetrakis- or hexakis- (trifluoromethyl)benzenes. The resultant cyclohexanes have a stereochemistry such that all the CF₃ groups are on the same face of the cyclohexyl ring. All-cis 1,2,3,4,5,6-hexakis(trifluoromethyl)cyclohexane is the most sterically demanding of the all-cis hexakis substituted cyclohexanes prepared to date, with a barrier (ΔG) to ring inversion calculated at 27 kcal mol⁻¹. The X-ray structure of all-cis 1,2,3,4,5,6-hexakis(trifluoromethyl)cyclohexane displays a flattened chair conformation and the electrostatic profile of this compound reveals a large diffuse negative density on the fluorine face and a focused positive density on the hydrogen face. The electropositive hydrogen face can co-ordinate chloride (K≈10³) and to a lesser extent fluoride and iodide ions. Dehydrofluorination promoted decomposition occurs with fluoride ion acting as a base.     

Crystal structures of thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane

Structures of both thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane, ?C₆H₄?CH₂SCH₂?C₆H₁₀?CH₂SCH₂?, have been determined, wherecis andtrans refer to the attachments to the cyclohexane ring. Thecis form crystallizes in the monoclinic space groupP2₁/c witha=8.4299(11)Å,b=21.772(2)Å,c=8.9724(13)Å, β=116.574(11)^o, andZ=4. Thetrans isomer packs into the monoclinic space groupP2₁ witha=8.159(16)Å,b=10.185(5)Å,c=9.558(2)Å, β=112.435(18)^o, andZ=2. The cyclohexane ring of thecis isomer is in the chair conformation, while the cyclohexane of thetrans isomer is found in a twisted boat conformation.