Allan variances and spectral densities for DC voltage measurements with polarity reversals

Using a polarity reversal technique, precise dc voltage measurements were made with both digital and analog voltmeters. The results were analyzed by calculating Allan variances and spectral densities for polarity-reversed measurements and comparing them with similar analyses of unreversed or unipolar measurements of the same processes. The Allan variances and spectra for the two measurement methods were found to agree quite well, particularly for sampling times corresponding to the 1/f noise regime for the measurement of Zener-diode voltages. The results show that polarity reversals do not affect 1/f noise of the Zeners. In polarity-reversed measurements, a rectangular voltage waveform is presented to the detector. Since this waveform can be synthesized by ac waveforms, the results also demonstrate that ac detection does not remove 1/f noise in the voltage source being measured. We also estimated the spectral density and Allan variance of some thermal (Johnson) noise processes and found that the results agree with the Nyquist expression to within 4%. This provides direct validation of our measurement and analysis methods.     

数字钟集成电路应用及其功能扩展

本文介绍了由大规模时钟集成电路 LM85 60芯片组成的数字钟电路及其多种扩展电路 ;叙述了其在高校电子电路课程设计中应用的意义     

汞离子微波钟及其研究进展

汞离子微波钟是下一代星载原子钟、地面守时原子钟的有力候选者。文章介绍了本团队在汞离子微波钟的离子囚禁、缓冲气体冷却、微波综合器、汞光谱灯等关键技术取得的突破和进展，在此基础上，研制出了小型化汞离子钟整机，其频率稳定度达到了2.3 × 10^-15/10⁵ s，同时开展了分区式线形阱汞离子微波钟的技术研究，实现了离子的高效梭动及系统的闭环锁定，测得频率稳定度3.45 × 10^-13/τ^1/2（τ = 10 ～ 10 000 s），为汞离子微波钟技术的应用奠定了重要基础。     

吸附-扩散模型与溶解-扩散模型及其修正模型的相互关系

研究了吸附-扩散模型(ADM)与溶解扩散模型(SDM)及其修正模型的相互关系,对溶解-扩散模型(SDM)、扩展-溶解扩散模型(ESDM)、不完全的溶解扩散模型(SDIM)中参数作了进一步解释.吸附-扩散模型(ADM)的一级近似表达式与溶解-扩散模型(SDM)及其修正模型的数学形式和物理意义相似,验证了吸附-扩散模型(ADM)的正确性.     

Inversions related to the stress-strain-fabric relationship

The stress-strain-fabric relationship is an extension of the anisotropic form of Hooke's law to include a dependence of the elastic coefficients upon a second-rank tensor called the fabric tensor. The fabric tensor represents features of the material microstructure associated with the type and the degree of the anisotropy. The inversion considered first in this work is that in which the stress-strain-fabric relation is constructed from the strain-stress-fabric relation and vice versa. Next, a semi-inversion of the relationship between the fourth-rank tensor of elastic coefficients and the fabric tensor is developed. This latter inversion permits the determination of the fabric tensor from a fourth-rank tensor of elastic constants. Explicit, approximate forms of these results, including a numerical example, are given for the case when the fabric tensor is normalized and terms of order three and higher in the fabric tensor are neglected.     

Mathematical model for the noise–lifetime relationship and its application to reliability screening

This paper puts forward a two‐dimensional probability distribution. The first ‘wing’ of this distribution is the device lifetime. The second ‘wing’ is the most promising reliability indicator, namely the 1/f noise factor. The model is intended to serve as a basis for reliability screening. It involves the noise–reliability correlation coefficient and has an attractive engineering interpretation. It ascribes a two‐element series reliability structure to the device. The first element of this structure is noise‐independent and ‘real’ in the sense that its hazard rate is always of positive value. The second element is noise‐dependent. The element is imaginary in the sense that its hazard rate can be changed from positive to negative value as the noise–reliability correlation coefficient changes in the same direction. Copyright © 2000 John Wiley & Sons, Ltd.     

The dynamic Allan variance III: confidence and detection surfaces

The dynamic Allan variance (DAVAR) is a surface which describes the stability of a high-precision clock with respect to time. When the DAVAR is evaluated from experimental data, its surface shows random fluctuations caused by the estimation process. It is fundamental to assign a statistical significance to these fluctuations, so that they can be differentiated from the variations of the surface caused by clock anomalies. First, we develop confidence surfaces to assign a statistical significance to the random fluctuations of the DAVAR estimator. Then, we introduce detection surfaces to reveal the variations of the surface caused by clock anomalies. We validate the obtained results through numerical simulations.     

Communion and Disunion in the Work of Allan Sekula

What effect does a mounting technique have on a photograph? Zwelethu Mthethwa’s Interiors, a series of large colour photographs that depict residents of an informal settlement in Cape Town, offers a case study. In face-mounting the front of the photographic print is irreversibly bonded to Plexiglas. This has the effect of drawing the image to the surface, amplifying colours, and transforming the photographic print into a durable photographic object. Although largely unacknowledged in the critical literature, this material aspect of the photographs animates their utopian dimensions, shaping their intervention in the fraught politics of photographic representation in South Africa.     

The use of the Allan transformation to analyze the maximum performance of voltage standards and comparators

The problems involved when using the Allan transformation to investigate precision comparators and standards of dc voltage are considered. An approach to determining the parameters is proposed, which enables the maximum performance of the measuring instruments used to be estimated. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 49–52, June, 2006.     

Synthesising gene clock with toggle switch and oscillator

The usefulness of a genetic clock lies in its role to stimulate a sequence of logic reactions for sequential biological circuits. A clock signal is a periodic square wave, its amplitude alternates at a steady frequency between fixed minimal and maximal levels. Transition between the minimum and the maximum is instantaneous for an ideal square wave; however, the function is unrealisable in physical bio‐systems. This research develops a new genetic clock generator based on a genetic oscillator, in which, a sine wave generator is adopted as a signal oscillator. It is shown that combination of a genetic oscillator with a toggle switch is able to generate clock signals forming an efficient way to generate a near square wave. In silico study confirms the proposed idea.Inspec keywords: genetics, oscillators, biological techniques, square‐wave generators, switchesOther keywords: toggle switch, genetic clock, logic reaction sequence, sequential biological circuits, clock signal, periodic square wave, physical biosystem, genetic clock generator, sine wave generator, signal oscillator, genetic oscillator     

The implementation of a constitutive model with weighted dynamic recovery and its application

An explicit updating algorithm has been developed, based on the backward Euler integration methods for the modified Armstrong–Frederick type of nonlinear kinematic hardening constitutive model with weighted dynamic recovery. This has been achieved by considering the consistency of the updated stresses, back stresses and the yield function, resulting in three sets of nonlinear equations which are then linearised using the Newton method. The developed algorithm and a linearised version have been implemented in ABAQUS as user material subroutines. Numerical simulations show that as long as the size of the incremental plastic strain is small so that k₂ⁱp0.1, both the linearised and the nonlinear algorithm converge to the same solution. Numerical analysese have been conducted to predict the strain response near the fuel ventilation hole on a wing pivot fitting of fighter aircraft, and good agreement has been observed between the experimental and numerical results.     

Shrinkage behaviour of superplasticised RCCP and its relationship with internal temperature

Shrinkage properties of roller-compacted concrete pavement (RCCP) and its relationship with internal temperature variations in superplasticised RCCP were studied. The control and superplasticised RCCPs containing different amounts of sodium naphthalene sulphonate superplasticiser between 1 and 4% by weight of cement were compacted at their optimum water content. The short- and long-term shrinkage and internal temperature variations were monitored in isolated and non-isolated conditions. Micro-structural analysis was implemented using the electron scanning microscope and X-ray diffraction methods. The initial internal temperature of superplasticised RCCP during the first hours of setting was higher than the control mix. A dormant period of low internal temperature was found for superplasticised mixes which started after about 7–13 and 6–10 h in non-isolated and isolated conditions, respectively. For non-isolated condition, the dormant period lasted about 3 days. Under isolated condition, similar trend was found after 4–8 days. During the first day of curing, the total and drying shrinkages of the control RCCP were considerably higher than the superplasticised mixes. On the contrary, the long-term monitoring indicated higher total and drying shrinkages in superplasticised mixes. Based on statistical analysis, the relationship between the autogenous shrinkage and area under the internal temperature diagram was significant.     

The synthetic control chart based on two sample variances for monitoring the covariance matrix

In this article, we propose a new statistic to control the covariance matrix of bivariate processes. This new statistic is based on the sample variances of the two quality characteristics, in short VMAX statistic. The points plotted on the chart correspond to the maximum of the values of these two variances. The reasons to consider the VMAX statistic instead of the generalized variance | S | are its faster detection of process changes and its better diagnostic feature, that is, with the VMAX statistic it is easier to identify the out‐of‐control variable. We study the synthetic chart based on the VMAX statistic. The proposed chart is always more efficient than the chart based on the generalized variance | S |. An example is presented to illustrate the application of the proposed chart. Copyright © 2008 John Wiley & Sons, Ltd.     

The relevance of Industry 4.0 and its relationship with moving manufacturing out,back and staying at home

In view of the fact that Industry 4.0 is becoming increasingly essential, the implementation of Industry 4.0 technologies is believed to be an essential strategic component in further increasing the efficiency of manufacturing processes and in determining decisions concerning globalisation strategies. Thus, this paper provides an empirical analysis of the essential constructs of Industry 4.0, and drivers and barriers for Industry 4.0. The paper is based on 270 valid answers to a questionnaire-survey distributed among Danish manufacturers. Regression analyses were used to test the proposed hypotheses. The results of the analyses reveal that the identified drivers and barriers for Industry 4.0 have a positive impact on the perceived relevance of Industry 4.0 among companies. Furthermore, the analyses show that the perceived relevance of Industry 4.0 among companies has a positive impact on companies that have moved manufacturing back and on companies that have moved manufacturing out and back. Conversely, the perceived relevance of Industry 4.0 among companies has a negative impact on companies that have remained domestic. The perceived relevance of Industry 4.0 has no impact on companies that have moved manufacturing out. This research, in general, offers to both researchers and practitioners an increased consciousness concerning the relevant drivers and barriers for Industry 4.0 in decision processes about where to locate manufacturing.     

基于各向同性本构关系薄层单元的螺栓连接参数识别

针对螺栓连接建模与参数识别问题开展研究。基于各向同性本构关系薄层单元理论,提出螺栓连接结构接触面力学性能识别方法。对单个螺栓搭接及多个螺栓搭接两种结构分别进行有限元建模,忽略螺栓质量、螺孔影响,搭接界面采用各向同性本构关系的薄层单元模拟。根据试验模态参数构造优化问题,识别搭接界面薄层单元材料参数。结果表明,两种螺栓连接结构前四阶弯曲模态频率计算精度较高,薄层单元能准确反映接触界面力学性能。该方法适用于单个螺栓及螺栓较密集工况动力学精确模拟。     

Detection of atomic clock frequency jumps with the Kalman filter

Frequency jumps are common anomalies in atomic clocks aboard navigation system satellites. These anomalous behaviors must be detected quickly and accurately to minimize the impact on user positioning. We develop a detector for frequency jumps based on the Kalman filter. Numerical simulations show that the detector is fast, with high probability of detection and low probability of false alarms. It also has a low computational cost because it takes advantage of the recursive nature of the Kalman filter. Therefore, it can be used in applications in which little computational power is available, such as aboard navigation system satellites.