磁场对光轴运信号的影响

摘 要;在做光泵磁共振实验时,分别研究了竖直线圈和水平线圈产生的磁场对光抽运信号的影响．并做出了它们之间的关系曲线．由此曲线计算了北京地磁场的垂直分量为（0. 0881±0·0015）×10-4T ,估算出北京地磁场的水平分量约为 0．425 ×10-4T．同时,这项工作对于区分光抽运信号和磁共振吸收信号也有一定的帮助．     

Influence of Signal and Noise on Statistical Fluctuation of Single-Mode Laser System

On the basis of calculating the steady-state mean normalized intensity fluctuation of a signal-mode laser system driven by both colored pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts, we analyze the influence of modulation signal, noise, and its correlation form on the statistical fluctuation of the laser system. We have found that when the amplitude of modulation signal weakens and its frequency quickens, the statistical fluctuation will reduce rapidly. The by reducing the intensity of pump noise and quantum noise. statistical fluctuation of the laser system can be restrained Moreover, with prolonging of colored cross-correlation time, the statistical fluctuation of laser system experiences a repeated changing process, that is, from decreasing to augmenting, then to decreasing, and finally to augmenting again. With the decreasing of the value of cross-correlation coe~cient, the statistical fluctuation will decrease too. When the cross-correlation form between the real part and imaginary part of quantum noise is zero correlation, the statistical fluctuation of laser system has a minimum. Compared with the influence of intensity of pump noise, the influence of intensity of quantum noise on the statistical fluctuation is smaller.     

The statistical fluctuation of a single-mode laser system driven by coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts

Using the linear approximation method, this paper studies the statistical property of a single-mode laser driven by both coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts, and calculates the steady-state mean normalized intensity fluctuation and intensity correlation time. It analyses the influences of the modulation signal, the net gain coefficient, the noise and its correlation form on the statistical fluctuation of the laser system respectively. It is found that the coloured pump noise modulated by the signal has a great suppressing action on the statistical fluctuation of the laser system; the pump noise self-correlation time and the specific frequency of modulation signal have the result that the statistical fluctuation tends to zero. Furthermore, the `colour' correlation of pump noise has much influences on the statistical fluctuation of the laser system. Increasing the intensity of pump noise will augment the statistical fluctuation of the laser system, but the intensity of quantum noise and the coefficient of cross-correlation between its real and imaginary parts have less influence on the statistical fluctuation of the laser system. Therefore, from the conclusions of this paper the statistical property can be known and a theoretical basis for steady operation and output of the laser system can be provided.     

基于DSP的全数字低场MRI信号接收算法研究

针对低场磁共振成像（MRI）系统,提出一种实用的基于通用浮点DSP的全数字高精度、高效率信号接收算法. 对经前端调理的回波信号直接采样数字化,在通用浮点DSP上进行数字正交解调, 采用高效的积分梳状滤波器(CIC)、半带滤波器(HB)、FIR滤波器等进行多级滤波抽取,极大的减少了运算量,提高了运算效率,最后得到用于成像的原始数据. 整个数字信号处理过程全部采用单精度浮点数据格式,用软件实现,提高了运算精度,增加了信号检测系统的灵活性. 最后通过CCS2.2软件仿真,验证了本算法的实时性和实用性.     

Phasing of lysozyme using one－wavelength anomalous scattering of sulphur atoms through the combination of direct methods and density modification

A new method of combining one-wavelength anomalous scattering (OAS) phasing and density modification has been described, in which the improved phases from density modification axe re-introduced into OAS phasing. In this way, the phases could be improved iteratively until convergence. The OAS phasing method is based on the previously established sign-probability formula, which breaks the phase ambiguity in the OAS phasing. The implementation of this method has been available in CCP4 as OASIS. This method, although based on direct-methods, could also incorporate known phases and figures of merit into its sign-probability formula. In the implementation of OASIS, the known phases axe from the positions of the anomalous scatters. In the current method, the known phases are from the density modification. The current method was tested on phasing a lysozyme crystal using anomalous scattering of sulphur atoms with diffraction data collected on an in-house x-ray source. The resulting map was well connected for the backbone atoms and clearly traceable, with an average map correlation coefficient of 0.6622 for the backbone atoms.     

一种基于三苯胺类共轭聚合物荧光信号开启的汞离子检测方法

通过Suzuki反应合成出主链中含9,9-二(4-二苯胺基苯基)-3,6-芴的蓝光共轭聚合物—聚[2,7-(9,9-二辛基芴)-co-3,6-(9,9-二三苯胺基芴)] (36PFT).36PFT可特异地与I-相互作用,并淬灭36PFT的荧光.当I-的浓度为0.24 mmol/L时,36PFT的荧光淬灭程度可达95％,...     

铂电极响应非电对离子的机理研究(Ⅱ)

预处理的铂电极对一系列金属离子Ｍ＾２＋活度阶梯变化的响应都是非单一突跃型瞬时信号。提出了离子交换反应历程,认为离子水合吉氏自由能－ΔＧ＾０ｈ（Ｍ＾２＋）相当于离子交换反应的活化能。用离子交换过程ΔＧ＾－ｈ（Ｐ＾２＋ｔ）与ΔＧ＾０ｈ（Ｍ＾２＋）之差合理地解释了不同离子瞬时信号峰高的次序。证明电极瞬时电位不是决定于离子扩散速度而是决定于离子交换速度。     

新型自适应光学双光子荧光显微镜研制成功

像差问题一直困扰着光学领域的工作者。像差会使光波前发生形变，不仅降低成像的信噪比和分辨率，使得很多时候我们只能“雾里看花”，更甚者，产生赝像，或无法获得有意义的图像。像差问题对双光子成像的影响尤为严重，因为在那里，荧光信号对人射光强度的依赖是平方关系.     

Theory study on a photonic-assisted radio frequency phase shifter with direct current voltage control

A photonic-assisted radio frequency phase shifter with direct current voltage control is proposed using a polymer- based integrated Mach-Zehnder modulator. A closed-form expression of radio frequency （RF） signal power and phase is given. Theoretical calculation reveals that by carefully setting the bias voltages, RF signal power variation lower than 1-dB and phase accuracy less than 3° can be achieved and are not degraded by perturbation of modulation index once the bias voltage drift is kept within -3% -- 3%.     

A subspace fitting algorithm of acoustic vector sensor array and corresponding matrix pre-filter design

In order to ease the pass-band response distortion of the matrix pre-filter,a simple approach for designing matrix spatial filter is proposed,which minimizes the sum of the k maximal distortion norm（k is the number of the constraint points）within the pass-band,while constraining the filter response within the stop-band.Considering the costly amount of calculation of the high-resolution methods,an algorithm with small amount of calculation based on matrix pre-filtering and subspace fitting using acoustic vector array（MF-VSSF）is proposed.Through joint processing of signal subspace of both pressure and particle velocity,the pre-filtering matrix and the signal subspace is decreased to M-dimensional（M is the number of array-element）,hence reduces the time-consumption of the matrix pre-filter design and DOA searching.Simulation results show that,the method offers the same performance as MUSIC with pre-filtering,but has much lesser amount of calculation.Moreover,the designed prefilter can efficiently suppress the interference in the stop-band and improve the estimation and resolution performance of successive DOA estimators.