An eight-channel system for neutron-nuclear investigations by the time-of-flight method

Equipment and software for recording time-of-flight spectra with a small channel width (10 ns) in precision experiments under conditions of low neutron beam intensities or recording rare events have been designed. An eight-input time encoder operates without losses when the signal intensity is up to 10⁵s⁻¹ at any of the eight inputs. The use of the USB interface ensures the system mobility. The developed system integration procedure from components in the executed format allows one to obtain a distributed system, ensures a higher succession of the software, and the possibility of assembling the system by the user.     

一种改进的联合点乘算法及其应用

在现代密码系统中使用椭圆曲线密码(ECC)最频繁的一种方法是多点乘算法.通过分析ECC各种点乘计算方法,研究了不同算法性能的影响,并针对计算ECC多点乘算法耗时大的问题,提出了一种改进的联合点乘算法.该算法采用了基于基底4的布斯算法和结合相互对立形式(MOF)的标量表示方法.与传统方法相比较,该算法可以有效地提高运算速度,减少运算时间,并在椭圆曲线数字签名算法(ECDSA)中得到了应用.     

一种改进的小波阈值去噪算法

针对传统小波阈值去噪算法中阈值选取困难,提出一种新的小波-EMD-SVD差分谱组合模式。对原始信号做小波分解得到一系列细节信号,不再通过小波阈值将强噪声小波系数简单地置零,而是对其进行EMD-SVD差分谱微弱信号提取,最后进行重构。实验结果表明,该算法对强噪声环境下信号的去噪效果明显且平稳。     

Data acquisition schemes for continuous two-particle time-of-flight coincidence experiments

Three data acquisition schemes for two-particle coincidence experiments with a continuous source are discussed. The single-start/single-stop technique, implemented with a time-to-pulse-height converter, results in a complicated spectrum and breaks down severely at high count rates. The single-start/multiple-stop setup, based on a time-to-digital converter and the first choice in today's similar coincidence experiments, performs significantly better at high count rates, but its performance is still hampered if the time-of-flight range is large, and the false coincidence background is variable if the event frequency and the collection efficiency of the starts are both high. A straightforward, multistart/multistop setup is proposed for coincidence experiments. By collecting all detector data, it ensures the highest signal-to-noise ratio, constant background, and fast data acquisition and can now be easily constructed with commercially available time-to-digital converters. Analytical and numerically evaluated formulas are derived to characterize the performance of each setup in a variety of environments. Computer simulated spectra are presented to illustrate the analytically predicted features of the various raw time-of-flight distributions obtained with each technique.     

数控车床加工仿真的一种改进方法

根据车削加工的特点,研究了数控车床加工过程的三维仿真问题.提出了一种新的基于刀具轨迹斜率变化量的工件离散化和特征点筛选方法,与传统三维仿真方法相比,大大减少了工件建模所需的特征点数,提高了计算速度.文末通过算例证明了所提出方法的有效性.     

An improved method for analysing surface topography information

Inherent in the design of most surface texture profilometers is the assumption that their operators have the necessary experience to choose the appropriate cut-off wavelength for a given surface. A computer program is described which selects automatically the cut-off wavelength for a range of different surfaces and carries out checks on the quality of the measured surface data. A fully documented listing of the program can be obtained from the authors at the University of Leeds.     

An improved counting method for motile protozoan cultures

A simple counting method is described for routine cultures of highly motile organisms. It is based on dyeing the organisms with a suitable stain, filtering them through a Millipore filter and counting single organisms directly under a microscope after rendering the filter transparent.     

An improved cryo-jet freezing method

A new cryo-jet freezing apparatus is described that is easy to use and gives good results using a propane-butene mixture (3: 1). Our use of the freezer in the study of mouse spinal cord explant cultures is discussed. At the tissue surface, the quality of tissue preservation from freezing, followed by freeze substitution, rivals that of conventional electron microscopic methods. Certain intracellular structures are better visualized using our methods. There is no evidence of the tissue being distorted by the cryogen jet when the freezer is operated correctly. A new freeze substitution device is also discussed.     

Fusion neutron detector for time-of-flight measurements in z-pinch and plasma focus experiments

We have developed and tested sensitive neutron detectors for neutron time-of-flight measurements in z-pinch and plasma focus experiments with neutron emission times in tens of nanoseconds and with neutron yields between 10(6) and 10(12) per one shot. The neutron detectors are composed of a BC-408 fast plastic scintillator and Hamamatsu H1949-51 photomultiplier tube (PMT). During the calibration procedure, a PMT delay was determined for various operating voltages. The temporal resolution of the neutron detector was measured for the most commonly used PMT voltage of 1.4 kV. At the PF-1000 plasma focus, a novel method of the acquisition of a pulse height distribution has been used. This pulse height analysis enabled to determine the single neutron sensitivity for various neutron energies and to calibrate the neutron detector for absolute neutron yields at about 2.45 MeV.     

一种改进的i_p-i_q谐波电流和无功电流检测方法

当三相电压不对称时,i_p-i_q检测方法不能准确地检测出基波无功电流。该文提出了一种新的电流检测方法,通过快速合成的基波正序电压作为锁相环的基准参考电压,并在低通滤波器后加入PI调节器,提高了谐波电流的检测精度。经仿真验证,该方法在三相电压不对称时能够准确检测出基波无功电流和谐波电流。     

An improved time domain polyreference method for modal identification

An improved time domain polyreference method for global model identification is presented in this paper. A time domain preprocessing technique is developed to reduce the effects of random noise contamination on measured data. Compared with the polyreference complex exponential technique, the size of the estimation problem is considerably reduced and the judgement of the required computational order is made easier and more reliable in the low signal-to-noise ratio cases. A total least squares algorithm with singular value decomposition for parameter estimation is adopted to minimise the bias error. An improved procedure for residue calculation is proposed, which takes residual terms into account in the time domain.     

An improved element removal method for evolutionary structural optimization

The purpose of this study was to develop a new element removal method for ESO (Evolutionary Structural Optimization), which is one of the topology optimization methods, ESO starts with the maximum allowable design space and the optimal topology emerges by a process of removal of lowly stressed elements. The element removal ratio of ESO is fixed throughout topology optimization at 1 or 2%. BESO (bidirectional ESO) starts with either the least number of elements connecting the loads to the supports, or an initial design domain that fits within the maximum allowable domain, and the optimal topology evolves by adding or subtracting elements. But the convergence rate of BESO is also very slow. In this paper, a new element removal method for ESO was developed for improvement of the convergence rate. Then it was applied to the same problems as those in papers published previously. From the results, it was verified that the convergence rate was significantly improved compared with ESO as well as BESO.     

An improved method for photographing fluorescent human chromosomes*

In the photography of sequentially QFQ and RFA banded chromosomes, the fading problem can be solved by reducing exposure time. This can be accomplished by choosing the right light source, filter combinations, type of film and developer. Three different systems were employed to record the exposure time during photography. A ‘Vertical Illuminator III RS’ with a 50 w/AC mercury burner equipped with 400–490, BG 12–BG 38 excitation filters and 510 barrier filter was found to be the most efficient and satisfactory. QFQ banded chromosomes can be photographed within 3–5 s and RFA banded chromosomes within 10–15 s with this system.     

An improved Senarmont retardation analysis method

The phase difference between two plane polarized light rays whose electric field vectors (planes of polarization) are at right angles is often determined by Senarmont analysis. In this analysis, a quarter-wave plate whose vibration axes lie at an azimuth of ±45° to the planes of polarization of the two rays is inserted. The rotation of the analyser that leads to extinction is then determined by manual adjustment. This classical method has been significantly improved by, instead, measuring light intensities at thirty-two evenly spaced analyser angles which span 180° of analyser rotation. An unbiased estimate of the phase difference may then be extracted with high accuracy by analysis as a designed experiment. Of the several numerical analysis methods investigated, harmonic analysis is particularly attractive for routine use—especially with small computers. Iterative non-linear least-squares analysis on a mainframe computer was taken as the standard of numerical accuracy, against which direct algebraic solutions on a personal computer were evaluated. An ‘accuracy’ statistic (which measures the goodness-of-fit to the theoretical cosine function) has proven invaluable in assessing the validity of actual data. Data of exceptional quality are produced by the Leitz Jamin–Lebedeff optical system using intensities measured with a photodiode detector placed in the camera tube of the microscope. These data will support analysis to better than 0.0001° of analyser position, or <6×10^?7 periods. Since alignment of the optics with comparable accuracy is impossible, a method for accurately quantitating the contribution to the observed retardation that originates from within the optics, by performing the analysis on an air sample, has been devised.     

An improved particle image velocimetry method for efficient flow analyses

This study proposes a spatiotemporally Adaptive Search Area (SA) size selecting algorithm for Particle image velocimetry (PIV), ASAPiv. The presented method releases the constraint of conventionally used static SAs, offering a significant computational performance increase through optimizing the dimensions of the SA according to the local flow conditions in a transient manner. The algorithm is implemented as a part of a new PIV framework, developed within the MATLAB environment. The most relevant steps of PIV and the related methods are reviewed, starting from image pre-processing up to the post-processing of raw PIV results. The performance of the proposed algorithm and the PIV tool in general is demonstrated through three examples of different nature, including a synthetic image sequence, a conventional, laser illuminated PIV case and a large-scale, field application. The dynamic alteration of the SAs is found to be consistent with the prevailing flow conditions, while the accuracy of PIV in general is maintained. Total calculation times with static and dynamic SAs are compared. The benchmark cases highlight the relevance of adaptive SAs in cases of spatiotemporally varied flow conditions, where significant (up to 900%) computational performance increase is achieved. In case of unidirectional, steady flow conditions the method offers moderate speed-up compared to the employment of static SA sizes.     

An improved method for the scanning electron microscopy of spermatozoa

The authors carried out this research on an SEM technique and obtained a good preservation of spermatozoa. Among the many fixatires tested, potassium di-chromate mixed with osmium tetroxide and NaCl gave the best results. Generally, a rapid freeze drying of the fixed material, after a treatment with dimethylsul-phoxide, isopentane and liquid nitrogen improves the general standard of preservation.     

An improved method for determining the wear of polymeric coatings

A modification on the Taber Abrader is described in which a $\text{1}\text{4}$ in steel ball is substituted for the conventional sandpaper wheel. As a result, the endpoint of the test becomes much clearer and the test data are suitable for quantitative interpretation. The modified test is applicable not only to high pressure laminates but also to a wide variety of plastics and coatings. Further modifications are proposed to convert the wear path to a straight line instead of the circle found on the Taber Abrader and to increase the load on the ball. These changes are expected to make the testing time comparable to the present sandpaper wheel method.     

A novel method for digital ultrasonic time-of-flight measurement

Most ultrasonic ranging measurements are based on the determination of the ultrasonic time-of-flight (TOF). This paper develops a novel method for the TOF measurement which combines both the improved self-interference driving technique and the optional optimization signal processing algorithms. By stimulating the transmitter with the amplitude modulation and the phase modulation envelope square waveforms (APESWs), the proposed system can effectively reduce the errors caused by inertia delay and amplitude attenuation. In addition, based on different signal-to-noise ratio test conditions, the resultant received zero-crossing samples, which are deteriorated by noise, can be precisely inspected and calculated with two optimized algorithms named zero-crossing tracking (ZCT) and time-shifted superposition (TSS) method. The architecture of the designed system is divided into two parts. The novel APESW driving module, the received envelope zero-crossings phase detection module, and the ZCT method processing module are designed in a complex programmable logic device. The TSS signal processing module and the optimization algorithm discrimination program module are integrated in a digital signal processor. The TOF measurements calibrated in ultrasonic ranging experiments indicate that the relative errors of the method are limited in ±0.8%. Therefore, a feasible method is provided with the advantages of high noise immunity, accuracy, low cost, and ease of implementation.