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121.
Giuseppe Annino Mario Cassettari Massimo Martinelli 《International Journal of Infrared and Millimeter Waves》2002,23(4):597-615
Several basic properties of homogeneous planar Whispering Gallery dielectric resonators are investigated through a general approach. In particular the values for the minimum and maximum allowed radius, defined by irradiation and dielectric losses, respectively, are obtained in terms of the complex dielectric constant of the involved media. The same approach is employed in the analysis of the limit allowed frequencies of a fixed family of mode, leading to the definition of the ideal frequency band. The role of the transverse mode is then discussed, and the effective frequency band is introduced and determined both in simple disc and circular ring resonators. The extension of the effective band is limited at least by a factor 3, in terms of decades, in comparison to the extension of the ideal one; this limitation, due to the presence of transverse modes, can be overcome using suitable designed nonhomogeneous resonators, as discussed in a following companion paper. 相似文献
122.
Ch. Lisdat N. Vanhaecke D. Comparat P. Pillet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(3):299-309
Two-photon photoassociation spectra in a Λ-type excitation scheme are analysed under the systematically varied experimental conditions of frequency detunings and laser
intensities. Line shape fits are presented as well as the investigation of intensity and detuning dependent line shifts. From
both we determine the attained spectroscopic precision, that is corrected for a systematic line shift due to the thermal distribution
of atoms in the trap. An energy correction for this effect is given. Information about the feasibility of generating translationally
cold molecules in a well defined rotational and vibrational level by the photoassociation process is derived from the analysis.
Received 21 May 2002 Published online 15 October 2002
RID="a"
ID="a"Current address e-mail: christian.lisdat@ptb.de
RID="b"
ID="b"e-mail: pierre.pillet@lac.u-psud.fr 相似文献
123.
研究墙体对微波脉冲的衰减特性,测量了微波脉冲垂直入射墙体后的脉冲信号,经过计算得到普通砖混墙、普通钢筋混凝土墙、钢筋网混凝土墙对窄带微波和超宽带微波的衰减值;分析了微波脉冲穿越不同墙体的频谱变化。研究结果表明,普通钢筋混凝土墙和普通砖混墙对窄带微波脉冲的衰减为0.342~0.699 dB/cm,对超宽带信号的衰减为0.134~0.183 dB/cm。钢筋网混凝土墙(厚65 cm)对超宽带信号的衰减较大(29.07~45.79 dB),同时使穿透墙体的超宽带信号频率分布向高频位移。 相似文献
124.
系统地研究了波长为2.7μm的InGaAsSb/AlGaAsSb多量子阱激光器中有源区的优化设计.分别用含应变势的6带KP模型和抛物带模型计算价带和导带的能带结构,并得到薛定谔方程和泊松方程的自洽解,由此计算量子阱在载流子注入时的增益谱.研究表明制约量子阱增益的主要因素不是跃迁矩阵元,而是粒子数反转程度,尤其是空穴填充HH1子带的概率.增加压应变或减小阱宽都会提高量子阱增益.前者降低了价带HH1子带空穴的平面内有效质量;后者拉大了价带子带间距,尽管它同时略微增加了空穴有效质量.这两种因素都导致价带顶空穴态 相似文献
125.
This paper is mainly concerned with elastic and acoustic properties of vitrous silica besides the computation of phonon frequencies.
Thus the phonon frequencies of vitrous silica have been calculated assuming the electronic bulk modulus,K
e, as equal to zero. New equations have been derived to relate the pressure derivatives of second order elastic constants to
the acoustic Gruneisen’s parameters using both Bhatia-Singh’s parameters and Schofield’s equations. The calculated longitudinal
and transverse Gruneisen’s parameters and the predicted absorption band spectra from Nagendranath’s equation and Bhatia Singh’s
parameters are in good agreement with experiment. The calculated mean acoustic mode Gruneisen’s parameter evaluated from the
pressure derivative of Nagendranath’s equation is also in good agreement with experiment.
An erratum to this article is available at . 相似文献
126.
127.
V. M. Naumenko 《International Journal of Infrared and Millimeter Waves》1981,2(1):149-158
Interaction of host magnons with impurity magnetic excitations in antiferromagnetic crystals CoCO3 and CoF2 containing substitutional impurity amounting to 10–4 and (4±2)×10–3 (by weight) Mn2+ respectively, has been investigated in the wavelength range 0.35–0.8 mm in a magnetic field of up to 20 T. In the CoCO3+10–4 Mn2+ crystal the impurity line was observed to merge with the AFMR line, which is peculiar to incoherent spectrum rearrangement. In the CoF2+4×10–3 Mn2+ crystal the cross splitting of spectrum was revealed as the impurity lower lying Zeeman level approached the AFMR low frequency mode, peculiar to coherent spectrum rearrangement. In both cases the impurity line intensity increases very much as it approaches the spin-wave band of the crystal. The constant of resonance interaction of the impurity excitation with magnons is determined for CoF2+Mn2+ to be m=18 cm–1. 相似文献
128.
129.
D.T. Petkie B.P. Winnewisser R.A.H. Butler F.C. De Lucia 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,92(2):129-141
The results of millimeter and submillimeter wave rotational spectroscopy are used to simulate the complex structure of the 2ν9-ν9 and ν5-ν9 hot bands. The comparison data were obtained with a high-resolution Bruker FTIR. The combination of the quality of these data and the complexity of the spectra of these interacting states represents a stringent test for the simulation. It is shown that the agreement is very good and that this approach is generally advantageous. From this simulation, the ratios of the transition dipole moments for the 2ν9-ν9 and ν5-ν9 hot bands with respect to the ν9 fundamental band were found to be 1.38(11) and 0.67(20), respectively. Using these results, the calculated integrated band intensities for the hot bands at were determined to be and . These results were used to successfully simulate high-resolution stratospheric spectra obtained from a balloon flight of the FIRS-2 spectrometer. The more general problem of the rotation-vibration database and the optimal use of both microwave and infrared data to define it is discussed. It is concluded that it is best if the combination of data takes place at the level of the original spectra. 相似文献
130.
Bridging the Length Scales: Micromechanics of Granular Media 总被引:1,自引:0,他引:1
Aristotle's statement that the whole is more than the sum of its parts aptly describes the essence of a granular material's rich and complex behaviour, which ultimately arises from internal mechanisms developed on many length scales. Recently, non-invasive experimental studies have given remarkable insight into the evolution of these mechanisms, thereby providing benchmarks and a unique opportunity for the theoretical modelling of these systems. This paper focuses on the challenges of capturing these multiscale mechanisms within the framework of continuum theory. In particular, a new approach toward developing a non-local micropolar constitutive model of granular media using micromechanics and internal variable theory is discussed. To demonstrate the predictive potential of these models, we present their application in the analysis of two fundamental problems to the mechanics of granular media: (i) formation and evolution of shear bands (the precursors of material failure), (ii) the classical Flamant problem. Finally, we briefly discuss the computational challenges in bridging the gap between micromechanical studies of granular media and the applications of continuum theory on the macro-scale via a finite element analysis of the flat punch problem. In practice, this problem is used to assess the load bearing capacity of a material and is fundamental to civil and structural engineering. 相似文献