Methods of Extending the Range of Frequency Counters

The various methods of extending the range of frequency counters are discussed and some of the shortcomings of each are pointed out. A new method that minimizes these short-comings is in the range of frequencies that can be counted entirely by the frequency limitations of AND gates; also it requires no tuning and its counting precision is the same as that of the basic counter.     

Digital Frequency Multiplier for Spectrum Measurement of Periodic Signals

Frequency multipliers find applications in the Fourier and Walsh spectrum measurements of periodic signals. Earlier digital frequency multipliers use two counters: 1) An upcounter which is partitioned into a fractional counter of kbits in cascade with an integral counter. This determines the period of the input signal by the number of clock pulses that are accumulated in a period of the signal. 2) A downcounter which is next fed from the same clock, and which is periodically preset to the contents of the integral counter whenever the downcounter reaches zero. In this process an error is introduced in the output frequency because the fractional counter contents are ignored in the frequency multiplication phase. To minimize this error, a high clock frequency is required so that the fractional count is small compared with the integral count. The maximum output pulse frequency is limited by the speed of the counters used. A new method is described which also uses the contents of the fractional counter. The clock frequency is reduced substantially and the maximum output pulse frequency is limited by the settling time of a D/A converter: If the settling time is 200 ns, the maximum output frequency is ten times that of earlier methods.     

Considerations on the measurement of the stability of oscillators with frequency counters

The most common time-domain measure frequency stability, the Allan variance, is typically estimated using a frequency counter. Close examination the operation of modern high-resolution frequency counters shows that they do not make measurements in the commonly assumed. The consequence is that the results typically reported by many laboratories using these counters are not, in fact, the Allan variance, but a distorted representation. We elucidate the action of these counters by consideration of their operation in the Fourier domain, and demonstrate that the difference between the actual Allan variance and that delivered by these counters can very significant for some types of oscillators. We also discuss ways to avoid, or account for, a distorted estimation of Allan variance.     

Measurement of high momentum transfer reactions by recoil detection

A method is described for studying reactions at medium energies by measuring the magnetic rigidity, time of flight, and energy loss of the resulting recoil products. The method works best for reactions with two-body final states where one of the outgoing particles is relatively light. A magnetic spectrometer with a special focal plane detector has been used. The detector consists of two position sensitive parallel plate avalanche counters and two proportional counters. Differential cross sections for the ¹²C(p, π⁺¹³C reaction at recoil angles which correspond to the pion being emitted at a backward angle in the center of mass have been measured at bombarding energies of 166 and 186 MeV. Data were also obtained for previously unobserved ¹²C(p, π⁰)¹³N reaction. Several advantages of the method are discussed.     

基于局部密集应变响应的海洋平台冰载荷反演方法

冰载荷的现场测量工作对于描述冰载荷与海洋平台的相互作用规律十分重要。回顾了自六十年代以来的各地冰载荷的测量情况,针对在采用压力盒进行直接测量和利用结构整体响应进行间接反算的过程中存在的困难,提出了一种利用局部应变响应信息来有效反演海洋平台冰载荷的新方法,并设计了用于反演的附加套筒结构模型。阐述了反演的基本原理,从理论上分析了反演的误差来源以及误差的稳定性,并讨论了反演时载荷作用区域的判断方法和测点的布置原则。最后,通过计算机仿真的反演算例和一缩尺模型的反演实验(包括模型应变响应的动态标定)验证了这种方法的可靠性。     

Distance and velocity measurements by the use of an orthogonal Michelson interferometer

A novel signal processing scheme for detecting distance and velocity signals simultaneously is demonstrated. In this method, a frequency-modulated diode laser is used to illuminate a dual-channel Michelson interferometer with two orthogonal output signals. The distance and the velocity signals then exist on the beat frequencies of the output interferometric signal. Two interferometric output signals with a quadrature phase shift are used to adjust the gating time period of frequency counters for beat-frequency measurement. The distance and velocity signals can thus be obtained from the counting number within the gated-in time period.     

Development of a fast neutron spectrometer composed of silicon-SSD and position-sensitive proportional counters

A new fast neutron spectrometer has been developed. The spectrometer is composed of a silicon surface barrier detector and three position-sensitive proportional counters with methane gas working as counting gas and a radiator. A collimated incident neutron interacts with a hydrogen atom in the methane gas to generate a recoil proton. The position information on the path of the recoil proton obtained from the three position-sensitive proportional counters gives the recoil angle. In the meanwhile, the energy of the recoil protons is measured with the three proportional counters and the silicon surface barrier detector. The characteristics of the spectrometer were evaluated with a monoenergetic neutron beam. The best energy resolution was 1.8% for 5.0 MeV neutrons.     

A Frequency Synthesizer for 10/2? kHz

A sinusoidal voltage source of frequency nominally 10/2? kHz (? = 104 rad/s) is derived from a 5-MHz standard. Digital counters are used to generate the required frequency, which differs from 10/2? kHz by less than 2 parts in 108, and is as stable as the standard. Using a crystal filter and low-distortion amplifiers, an output of 10 V rms with total harmonic distortion less than 1 part in 103 is obtained.     

Long-wavelength infrared cascade laser with coherent transport of electrons

Possible ways to overcome difficulties encountered in the creation of cascade lasers with collisionless tunneling of electrons are discussed. A structure of an IR laser using a single three-barrier structure and capable of working at a frequency of 4.5 THz is proposed.     

PARTICLE COUNTING OIL AND WATER EMULSIONS

Because of their speed and convenience, optical particle counters are widely used for particle size analysis of liquid samples. In some cases, both solid particles and emulsified water or oil may be present in a sample. Since emulsion droplets are counted as if they are solid particles, analysis and data interpretation for these samples are difficult. Until recently, no suitable method existed for distinguishing solid contaminants from emulsion droplets. This paper discusses a method which overcomes this limitation. Through the use of a surfactant-laden nonpolar dilution fluid, water is incorporated into reverse micelles too small to be seen by most optical particle counters. As a result, only solid contaminants are counted, and many problems associated with the analysis of emulsions are overcome. Results obtained from a wide range of oil and water emulsions are used to evaluate the merits and possible applications of the new technique.     

一种颗粒系超声衰减谱的改进计算方法

Epstein和Carhart,Allegra和Hawley先后研究建立起的超声谱颗粒粒径测量的经典理论模型——ECAH,针对直接求解ECAH理论模型预测颗粒两相系中物理量声衰减系数时出现的困难,通过构造与Bessel（Hankel）函数有关的新变量,改造原有系数矩阵,降低矩阵的条件数,避免了数值溢出问题,拓展该模型的计算范围至频率100MHz和毫米级颗粒,通过与BLBL（Bouguer-Lambert-Beer-Law）散射方法的比较验证了文中提出的改进方法的有效性。     

Curvature controlled arc-length method

A path-following technique that monitors and uses the curvature of the equilibrium path to predict both the step size and forward direction is proposed. The technique is based on somewhat new geometrical interpretations of the arc-length method in a multi-dimensional load-displacement space. These interpretations should help to understand certain difficulties that the path-following methods may experience. In particular, the pros and cons of the equilibrium iterations utilizing Crisfield's method and the method of explicit spherical iterations are briefly discussed. A simple example is used to illustrate the proposed approach. Received 2 February 1999     

A new method for estimating the aperture uncertainty of A/Dconverters

Aperture uncertainty measurements are strongly influenced by quantization, converter nonlinearity and test setup noise. The proposed method solves the difficulties arising from quantization, and nonlinearity. The method estimates the noise distribution function by fine adjustment of the input signal offset. The contribution of jitter-induced voltage noise is separated from additive noise in two different ways. Finally, the aperture uncertainty, assumed independent of the frequency, is estimated by varying the signal frequency. Experimental results obtained on 8 and 10 bit converters are discussed     

PARTICLE COUNTING OIL AND WATER EMULSIONS

ABSTRACT

Because of their speed and convenience, optical particle counters are widely used for particle size analysis of liquid samples. In some cases, both solid particles and emulsified water or oil may be present in a sample. Since emulsion droplets are counted as if they are solid particles, analysis and data interpretation for these samples are difficult. Until recently, no suitable method existed for distinguishing solid contaminants from emulsion droplets. This paper discusses a method which overcomes this limitation. Through the use of a surfactant-laden nonpolar dilution fluid, water is incorporated into reverse micelles too small to be seen by most optical particle counters. As a result, only solid contaminants are counted, and many problems associated with the analysis of emulsions are overcome. Results obtained from a wide range of oil and water emulsions are used to evaluate the merits and possible applications of the new technique.     

抛光用磁流变液的研究

磁流变抛光是一种新兴的先进光学加工技术,已引起人们广泛关注.本文综述了磁流变抛光技术的应用状况及抛光机理,介绍了抛光用磁流变液的制备原理、制备方法及流变特性.并对影响抛光用磁流变液稳定性的因素及改进方法进行了详细分析,最后展望了今后的研究方向.     

On the aging of the scintillation counters for RUN II Muon System at CDF

The CDF II Muon System has an important role in the CDF detector, particularly in investigations of processes, as with heavy quarks. JINR and INFN physicists at FNAL are responsible for maintenance to perform the highly efficient functioning of the scintillation counters involved into the CDF Muon system.In the course of several years, we carried out the light yield measurements, at ends farthest from photomultiplier, of the various types of scintillation counters installed at CDF. On the basis of the results obtained, conclusions about the aging rate of the counters and long-range forecast of their efficiency during physics data taking at CDF RUN II could be made.One can see that the new generation counters with wavelength-shifter fibers technology for light collection have higher long-range efficiency compared to counters using a classic plexiglas light-guide for light propagation.     

多元金属硫族化合物的合成和结构表征

介绍新的发展起来的反应性熔盐法及其在多元金属硫族化合物中温固相合成中的应用，并讨论了这类化合物的结构特征，低维性和热力学介稳性。     

Common-use check-in counter reassignments with a variable number of service lines and variable length of time window

In the real world, there are a number of common factors that can cause perturbations at check-in counters, such as an airport closure, a temporary power failure, crashing of the counter computer, baggage conveyor belt malfunctions, and so on, forcing the airport authority to reassign flights to new check-in counters. In this study, we develop a model and a solution method to solve common-use check-in counter reassignment problems with a variable number of service lines and a variable length of time window. To test how well the proposed model and the solution method can be applied to the real world, we perform numerical tests based on a hypothetical incident in relation to a Taiwan airport’s operations. The test results show that the model and solution would be useful for the airport authority in actual operations.     

Constrained boundary recovery for three dimensional Delaunay triangulations

A new constrained boundary recovery method for three dimensional Delaunay triangulations is presented. It successfully resolves the difficulties related to the minimal addition of Steiner points and their good placement. Applications to full mesh generation are discussed and numerical examples are provided to illustrate the effectiveness of guaranteed recovery procedure. Copyright © 2004 John Wiley & Sons, Ltd.     

桁架结构材料非线性弹性问题的广义逆力法

通过回顾传统位移法和传统力法的思路,比较了两种传统方法,分别指出了它们在计算机求解材料非线性问题中的优缺点。从经典力法的求解思路出发介绍了用于桁架结构材料非线性弹性问题的广义逆力法(AforcemethodbasedonGeneralizedInverseMatrix,GIM),给出了该算法的推导思路及求解过程。特别指出了传统力法用计算机求解材料非线性问题所遇到的困难,对如何解决这些困难作了探讨,从而给出了结构力学计算的一个全新视角,也使得力法在计算机计算领域重新得到发展空间。广义逆力法是一种基于力法和广义逆矩阵理论的新的迭代解法,对于材料非线性问题,由于无需像传统的基于位移法的逐步增量法那样逐步递进计算,所以也称特大增量步算法(LargeIncrementMethod,LIM)。同时也指出了该算法在结构并行计算方面不同于传统的子结构并行计算的新的特点。做为一种新的迭代算法,也给出了该算法求解的唯一性和收敛性证明。