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251.
We introduce a new technique for imaging oxygen concentrations in fuel/air mixtures that takes advantage of the different
responses of toluene and 3-pentanone to collisional quenching by molecular oxygen. Since laser-induced fluorescence signals
from both tracers upon excitation at 248 nm are spectrally well separated, simultaneous detection is possible. The technique
is first applied to instantaneous imaging in turbulent mixing processes of interacting seeded air and nitrogen flows.
Received: 1 August 2001 / Revised version: 29 October 2001 / Published online: 29 November 2001 相似文献
252.
Si衬底上ZnSe外延膜的低压MOCVD生长 总被引:2,自引:2,他引:0
以硒化氢(H2Se)和二甲基锌为源材料,生长温度是300℃时,用低压金属有机化学气相沉积(LP-MOCVD)系统在Si(111)衬底上外延生长了ZnSe薄膜。通过X射线衍射(XRD)、扫描电子显微镜的能量色散(EDS)以及光致发光(PL)实验验证ZnSe外延膜的质量,在X射线衍射谱中只有一个强的ZnSe(111)面衍射峰,这说明外延膜是(111)取向的单晶薄膜,在能量色散谱中除了Si,Zn和Se原子外,没有观测到其他原子,说明ZnSe外延膜中杂质含量较少。ZnSe外延膜中Zn/Se原子比接近1,有较好的化学配比。在ZnSe外延膜的77K光致发光谱中没有观测到与深中心发射相关的发光峰,表明ZnSe外延膜的晶格缺陷密度较小。77K时的近带边发射峰447nm在室温时移至465nm附近。 相似文献
253.
Alp E. E. Sturhahn W. Toellner T. S. Zhao J. Hu M. Brown D. E. 《Hyperfine Interactions》2002,144(1-4):3-20
Nuclear resonant inelastic X-ray scattering of synchrotron radiation is being applied to ever widening areas ranging from
geophysics to biophysics and materials science. Since its first demonstration in 1995 using the 57Fe resonance, the technique has now been applied to materials containing 83Kr, 151Eu, 119Sn, and 161Dy isotopes. The energy resolution has been reduced to under a millielectronvolt. This, in turn, has enabled new types of
measurements like Debye velocity of sound, as well as the study of origins of non-Debye behavior in presence of other low-energy
excitations. The effect of atomic disorder on phonon density of states has been studied in detail. The flux increase due to
the improved X-ray sources, crystal monochromators, and time-resolved detectors has been exploited for reducing sample sizes
to nano-gram levels, or using samples with dilute resonant nuclei like myoglobin, or even monolayers. Incorporation of micro-focusing
optics to the existing experimental setup enables experiments under high pressure using diamond-anvil cells. In this article,
we will review these developments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
254.
宽带Ⅱ-Ⅵ族半导体及其低维结构的生长和光学性质研究进展 总被引:9,自引:4,他引:5
本文系自1979年以来,宽带Ⅱ-Ⅵ族半导体研究组取得的主要研究成果的简要介绍。取得的主要研究成果可分为如下六个方面:第一,系统地研究了宽带Ⅱ-Ⅵ族半导体在电场激发下的自由激子发射;第二,创造性地提出并实 利用宽带Ⅱ-Ⅵ族超晶格的室温激子效应来实现在蓝绿区快响应的光学双稳的物理思想;第三,深入研究了宽带Ⅱ-Ⅵ族超晶格中的激子行为以及激子与元激发态的相互作用,为利用激子获得有效蓝色自发和受激发射提供物理基础和实验途径;第四,研究了ZnSe基非对称双量子阱和组合超晶格中激子的隧穿以及激子的自发和受激发射;第五,CdSe和ZnSeS自组装量子点的生长及其形成机理;第六,ZnO薄膜的生长及其紫外发射特性。 相似文献
255.
A. Cavallini B. Fraboni W. Dusi N. Auricchio M. Zanarini P. Chirco 《Applied Physics A: Materials Science & Processing》2002,75(3):427-429
The time recovery of the spectroscopic capabilities of CdZnTe and CdTe detectors, irradiated with increasing doses of high-
and low-energy neutrons, as well as electrons, has been investigated by studying their spectroscopic behavior at different
photon energies using leakage current measurements and PICTS (photo-induced current transient spectroscopy) analysis. The
detectors were stored at room temperature for up to one year to study the time evolution of their spectroscopic performance
and to correlate it with the presence of defective states in the material. We have observed a clear improvement in the material’s
detection properties with time, though only in those detectors which have not been severely degraded by the irradiation. The
recovery can be associated with a decrease in the concentration of some defective states, thus allowing the assessment of
the crucial role these play in determining the charge collection processes in the material and its spectroscopic capabilities.
Received: 1 August 2001 / Accepted: 3 August 2001 / Published online: 20 December 2001 相似文献
256.
257.
This note discusses the need to use various data-compaction schemes in the implementation of sophisticated large-scale linear programming codes on modest personal computers. It demonstrates a method whereby the overhead of using these schemes is significantly reduced on Intel 80 x 86 processors. 相似文献
258.
The optimal return function for a Borel measurable gambling problem with a bounded utility function was shown by Strauch (1967)
to be universally measurable when the problem is leavable in the sense that the gambler may terminate play at any time. The
same is shown here for the more general class of nonleavable problems.
Research supported by National Science Foundation Grant DMS-8801085. 相似文献
259.
Yu You George W. Kattawar Ping Yang Yong X. Hu Bryan A. Baum 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,100(1-3):470-482
Measurements from depolarized lidars provide a promising method to retrieve both cloud and aerosol properties and a versatile complement to passive satellite-based sensors. For lidar observations of clouds and aerosols, multiple scattering plays an important role in the scattering process. Monte Carlo simulations are carried out to investigate the sensitivity of lidar backscattering depolarization to cloud and aerosol properties. Lidar parameters are chosen to be similar to those of the upcoming space-based CALIPSO lidar. Cases are considered that consist of a single cloud or aerosol layer, as well as a case in which cirrus clouds overlay different types of aerosols. It is demonstrated that besides thermodynamic cloud phase, the depolarized lidar signal may provide additional information on ice or aerosol particle shapes. However, our results show little sensitivity to ice or aerosol particle sizes. Additionally, for the case of multiple but overlapping layers involving both clouds and aerosols, the depolarized lidar contains information that can help identify the particle properties of each layer. 相似文献
260.
W. Hufenbach R. Böhm A. Langkamp L. Kroll T. Ritschel 《Mechanics of Composite Materials》2006,42(2):151-162
The basic damage and failure models of multiaxially reinforced composites with a thermoplastic matrix are presented and verified.
Within the framework of continuum damage mechanics, a phenomenological model is introduced, where the damage is defined as
a change in the elasticity tensor. For damage identification, a specific ultrasonic device was developed. A combination of
an immersion set-up and a contact coupling device formed a system for an efficient determination of stiffness-tensor components
from convenient sets of velocity measurements. Linked to a tensile machine, it allowed us to measure the anisotropic damage
of the new materials group caused by tensile loading.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 221–234, March–April, 2006. 相似文献