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531.
调制对磁共振谱的线宽,线形及幅值的影响 总被引:2,自引:2,他引:0
用付里叶分析方法从理论上分析计算了磁场调制对谱线(单一或重迭的)的线宽、线形及幅值的影响,并将理论计算结果与激光磁共振谱的调制效应的实验结果作了比较,两者符合得很好。据此作者提出了对于采用调制相检技术的磁共振谱技术普遍适用的选择调制参数的方法、步骤和原则。 相似文献
532.
R.J. Baken 《Journal of voice》1990,4(3)
Fractal geometry, a relatively young branch of mathematics, offers new ways of evaluating the irregularity of the physiologic and acoustic aspects of speech. The validity and reliability of a box-counting method for estimating the fractal dimension (DF) of the period and amplitude of vocal signals were demonstrated, and the method was applied to sustained vowels produced by four men and four women. Mean DF of the fundamental period was 1.46; DF of the amplitude records averaged a slightly, but significantly, higher 1.54. The potential of DF as a research and clinical tool is considered. 相似文献
533.
Summary A numerical procedure, partly based on the Monte Carlo method, is employed to examine the effect of inhomogeneity of a turbid
medium on the Modulation Transfer Function of an optical system. The results, both for a particulate of small size and of
size comparable with wavelength, show a general effect of the ?shower curtain? type. 相似文献
534.
微波辐照频率为1.2~2.0 GHz时,利用宽带天线对微型计算机主板进行微波辐照,考察了微波辐照载波频率、调制方式和调制深度对微波辐照效应的影响,得到了计算机分别处于满负荷工作、内存读写操作、磁盘读写操作和系统空闲4种工作状态下的微波辐照干扰功率阈值。实验结果表明:微波辐照的载波频率为1.47 GHz时,辐照干扰功率阈值最低,为32.7 dBm,计算机最易被干扰;瞬时功率是干扰微型计算机的关键参数,调制方式、调制频率和深度对微波辐照干扰功率阈值影响不大;处于高负荷工作状态的微型计算机更易于被微波辐射干扰;计算机启动的干扰功率阈值为32.0 dBm,小于正常工作状态时的阈值。 相似文献
535.
为分析振幅和相位发生畸变情况下光束焦斑质心位置所受的影响,以光波标量衍射理论中的夫琅和费衍射公式为基础,根据光斑强度分布一阶矩质心位置的定义,推导了直接依赖于光束近场复振幅分布的焦斑质心位置的一般表达式。进一步推导了焦斑质心位置对光束近场强度分布和相位斜率分布的依赖关系式,并对该式清晰的物理意义进行了阐述。利用焦斑质心位置表达式,可分析和确定由于振幅调制和相位畸变导致的质心位置偏移。最后,对无相位畸变和存在低阶泽尼克相位畸变情况下的简单畸变光束进行了相应的分析讨论。 相似文献
536.
《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,103(1):83-101
Electromagnetic scattering provides useful signatures for nonintrusive particle characterization. Scattered wave which carries characteristic information about particles is identified completely by its intensity, polarization state and phase. Recent developments in measurement techniques have enabled measurement of phase of the scattered wave which is a source of additional information about particles. In the present study, accuracy of discrete dipole approximation (DDA) in predicting amplitude and phase of scattered wave is investigated via publicly available DDSCAT code by Draine and Flatau, which is a well-established tool for DDA and has found wide range of applications in the literature due to its flexibility. DDSCAT routine is modified to enable accurate computation of phase of complex amplitude scattering matrix (ASM) elements as well as their magnitude. DDA method was implemented by using lattice dispersion relation for dipole polarizabilities, generalized prime factor algorithm for fast-Fourier transformation and pre-conditioned bi-conjugate gradient method with stabilization for the solution of the complex linear system of equations. Accuracy of ASM elements predicted by DDA is assessed on single sphere problems with various size parameters and refractive indices by validation against Mie theory solutions. Excellent agreement between predictions and exact solutions proves the reliability of the modified DDSCAT code for prediction of amplitude and phase of scattered electromagnetic wave. Applicability conditions and requirements of the present DDA application to ensure accurate prediction of complete set of scattering parameters are mapped for single spheres, on an extensive domain of size parameters and refractive indices. A correlation is presented to estimate the magnitude and phase errors associated with given size parameter, refractive index and cubic lattice subdivision. Assessment of computational time requirements for different optical constants shows that implementation of DDA with the present specifications is unfeasible for size parameters larger than 4 when Re(m)>2 and Im(m)<0.1 at the same time, due to slow convergence rate. 相似文献
537.
In electronic speckle pattern interferometry (ESPI), for a fast and objective analysis of measurement data which occur with a high repetition rate, an automated data processing is of particular advantage. For this reason, investigations were carried out to determine if the modulation of speckle interferograms can be applied as a quality parameter for the selection of suitable interferogram data for further evaluation e.g. phase unwrapping when spatial phase shifting (SPS) is performed. Six methods for determining the modulation of speckle interferograms are characterised and compared. The applicability of the speckle interferogram modulation as a parameter for mask generation in the unwrapping process of the phase difference is demonstrated by the evaluation of measurement data obtained from experiments with a spatial phase shifting endoscopic ESPI system on a technical surface and on a human gastrectomy specimen. 相似文献
538.
In terms of the coupled mode theory and the transfer matrix technique, novel formulas of the transfer functions are presented for a 2-D microring resonator array. By using these formulas, transmission characteristics are analyzed for this kind of Si based polymer device. Simulation shows that by means of parallel-cascading multiple microrings in every filter element, the passband can be flattened, and the box-like spectral response can be formed; in terms of series-cascading such several filter elements, the passband becomes precipitous, and the non-resonant light and the crosstalk become weak. 相似文献
539.
Inhaled corticosteroids (ICS) have become the prevalent treatment in asthmatics. Hazards to voice are under-recognized. A total of 38 patients with voice complaints associated with the use of ICS were assessed by 79 strobovideolaryngoscopy (SVL) examinations, 24 single and 14 multiple SVL. Hoarseness and dysphonia were the primary reasons for referral. The ICS initially used most frequently was Advair Diskus (fluticasone propionate and salmeterol-inhalation powder-[IP]) in 22 patients, followed by Flovent (fluticasone propionate inhalation aerosol-pressurized metered-dose inhaler-[PMDI]) in 11. Duration of ICS usage varied from 2 weeks to 4-5 years. Higher dosage and frequency of use exacerbated problems. Hazards to voice previously unrecognized by real-time indirect mirror or fiberoptic laryngoscopy were identified by meticulous attention to SVL abnormalities. There was essentially no difference in occurrence of abnormalities whether analyzed from the perspective of the initial 38 or all 79 examinations. These included abnormal mucosal wave symmetry/periodicity (76-63%), phase closure (74-63%), glottic closure (63-59%), mucosal wave amplitude/magnitude (50-35%), supraglottic hyperactivity (39-25%), mucosal quality (34-34%), and glottic plane (10-5%).Candidiasis of the larynx was infrequently observed. Fluticasone ICS were a cause of steroid inhaler laryngitis, and the best treatment was their avoidance or cessation. Further prospective studies ideally might include SVL documented as a pretherapy baseline and then repeated in each ICS patient who developed hoarseness/dysphonia. 相似文献
540.