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941.
利用微机械加工技术制造出一种新型微扫描镜,结合半导体激光器,可用于投影显示.激光器发出的光束被两个分别沿着X轴、Y轴扭转的镜面相继反射,扫描出二维图形.实验测得扫描镜在15 V电压,频率为扫描镜谐振频率2倍的方波信号驱动下,镜子的光学扫描角度达±12°.由于每个镜子都沿各自轴以简谐规律扭转,扫描所得投影为李萨如图形.通过分析图形的形成原理并用Matlab仿真,选出了适用用于任意图案显示的扫描镜谐振频率组合(X轴2 400 Hz, Y轴2 425 Hz).该组合可以形成194×192个像素点,刷新频率为25 Hz.在此基础上提出了一种通过调制激光开关来进行投影显示的方法. 相似文献
942.
943.
瑞利布里渊光时域分析系统能够以非破坏性方式实现单光源、单端工作,利用强度型电光调制器同时调制脉冲基底和脉冲信号是获得该系统所需连续光和脉冲光的关键技术.本文理论分析、仿真和实验研究了一种将脉冲信号输入到电光调制器偏置端、微波信号输入到电光调制器射频端同时调制脉冲基底和脉冲信号的新调制方法,探讨了电光调制器用于瑞利布里渊光时域分析系统时的最佳工作点问题.结果表明,当调制脉冲基底和脉冲时分别将电光调制器偏置在传输曲线的谷点和峰点,并根据实际系统的组成和性能指标要求选择合适的微波调制信号幅度,可获得满足瑞利布里渊光时域分析系统要求的连续光和脉冲光.本文的研究结果为瑞利布里渊光时域分析系统的最佳化设计提供了理论依据. 相似文献
944.
Harmonics-to-Noise Ratio: An Index of Vocal Aging 总被引:3,自引:0,他引:3
Distinguishing between vocal changes that occur with normal aging and those that are associated with disease is an important goal of research in voice. Several acoustic measures have been used in an attempt to illuminate the integrity of the vocal mechanism, including harmonics-to-noise ratio (HNR), jitter, and fundamental frequency (F0). HNR is a measure that quantifies the amount of additive noise in the voice signal; jitter reflects the periodicity of vocal fold vibration. In this study, measures of HNR, jitter and F0 were used to compare vocal function in three groups of normally speaking women: young adults, middle-aged adults, and elderly adults. Significant differences in HNR emerged between the elderly women and the other two groups. F0 differences were also apparent between the elderly group and the two younger groups; there were no significant differences in jitter between the three groups. HNR was found to be a more sensitive index of vocal function than jitter. The significant lowering of HNR evident in the elderly speakers may be attributable in part to medications taken by the majority of these elderly subjects. 相似文献
945.
Professional vocalists encounter demands requiring voluntary control of phonation, while utilizing a considerable range of frequency and intensity. These quantifiable acoustic events can be measured and represented in a phonetogram. Previous research has compared the phonetograms of trained and untrained voices and found significant differences between these groups. This study was designed to assess the effects of vocal training for singers over a period of nine months. Phonetogram contour changes were examined, with the primary focus on expansion of frequency range and/or intensity control. Twenty-one first-year, master's level, vocal music students, who were engaged in an intensive vocal performance curriculum, participated in this study. Following nine months of vocal training, significant differences were revealed in the subjects' mean frequency range and minimum vocal intensity across frequency levels. There was no significant difference for the mean maximum vocal intensity across frequency levels following vocal training. 相似文献
946.
Richard I. Zraick Justine L. Nelson James C. Montague Patricia K. Monoson 《Journal of voice》2000,14(2):154-160
The purpose of this study was to investigate if there was an effect of task on determination of maximum phonational frequency range (MPFR). Two tasks commonly used to elicit MPFR in clinical voice evaluations were compared. Normal adult females (N = 30) were examined. No statistically significant effect of task was found. Both tasks (glissando and discrete-step) were found to have a high positive correlation (0.84). Implications of the use of one task for determination of maximum phonational frequency range are discussed, as is the possibility of a task effect on determination of other voice parameters. 相似文献
947.
948.
The study presents the characterization of a novel variable frequency (11–50 kHz) Atmospheric Pressure Plasma Jet (APPJ) source and comparison of the results with 13.56 MHz source, in terms of species generation and species temperature. The behavior of variable frequency APPJ at different frequency regimes was investigated using optical emission spectroscopy to understand the interaction with the ambient environment. The quantitative dependence of the radical generation on driving frequency and time of treatment was also analyzed by direct synthesis of H2O2 by plasma-water interaction. The plasma formed with a kHz driving frequency had a low treatment temperature, which was suitable for biological species, but the plasma generated with a 13.56 MHz driving frequency had a substantially higher radical density than the kHz plasma. As a result, the APPJ device's ability to tune the radical density and treatment temperature with a change in kHz frequency has been demonstrated. 相似文献
949.
We report on an idler-resonant femtosecond optical parametrical oscillator(OPO)based on BiB3O6(BiBO)crystal,synchronously pumped by a frequency-doubled,mode-locked Yb:KGW laser at 515 nm.The idler wavelengths of OPO can be tuned from 1100 nm to 1540 nm.At a repetition rate of 75.5 MHz,the OPO generates as much as 400 mW of idler power with 3.1 W of pump power,the corresponding pulse duration is 80 fs,which is 1.04 times of Fourier transform-limited(FTL)pulse duration at 1305 nm.In addition,the OPO exhibits excellent beam quality with M2<1.8 at 1150 nm.To the best of our knowledge,this is the first idler-resonant femtosecond OPO pumped by 515 nm. 相似文献
950.
Based upon the new designed helical resonator, the resonant radio frequency (RF) for trapping ions can be consecutively adjusted in a large range (about 12 MHz to 29 MHz) with high Q-factors (above 300). We analyze the helical resonator with a lumped element circuit model and find that the theoretical results fit well with the experimental data. With our resonator system, the resonant frequency near magic RF frequency (where the scalar Stark shift and the second-order Doppler shift due to excess micromotion cancel each other) can be continuously changed at kHz level. For 88Sr+ ion, compared to earlier results, the measurement accuracy of magic RF frequency can be improved by an order of magnitude upon rough calculation, and therefore the net micromotion frequency shifts can be further reduced. Also, the differential static scalar polarizability Δα0 of clock transition can be experimentally measured more accurately. 相似文献