The effect of model uncertainty on maintenance optimization

Much operational reliability data available, e.g., in the nuclear industry, is heavily right-censored by preventive maintenance. The common methods for dealing with right-censored data (total time on test statistic, Kaplan-Meier estimator, adjusted rank methods) assume the s-independent competing-risk model for the underlying failure process and the censoring process, even though there are, many s-dependent competing-risk models that can also interpret the data. It is not possible to identify the "correct" competing risk model from censored data. A reasonable question is whether this model uncertainty is of practical importance. This paper considers the impact of this model-uncertainty on maintenance optimization, and shows that it can be substantial. Three competing-risk model classes are presented which can be used to model the data, and determine an optimal maintenance policy. Given these models, then consider the error that is made when optimizing costs using the wrong model. Model uncertainty can be expressed in terms of the "dependence between competing risks" which can be quantified by expert judgment. This enables reformulating the maintenance optimization problem to account for model uncertainty.     

New experiments on the electrodeposition of iron in porous silicon

We report here the study about the electrodeposition of iron into porous silicon made in p-type (15–25 Ω cm) silicon wafers. Chronoamperometry measurements were performed to show that the iron nucleation does not start only at the bottom of the pores, which is confirmed by the high quality SEM images. The energy band of the heterostructure Si/PS is used to explain the mechanisms involved in the electrodeposition of iron and the porous silicon formation. This new structure (iron and porous silicon), once well controlled might have an influence on the new device developments.     

The low frequency noise in HFETs estimates the effect of electrical stress

The effect of electrical stress on the low frequency noise in heterostructure field effect transistors is investigated in detail and is compared to the DC characteristics. Additionally, a model has been developed to describe the increase of the low frequency noise, depending on the change of other transistor parameters during the stress. Finally, a discussion about the model ability to be used for other devices is given.     

The effect of propagation delay uncertainty on the speed oftime-of-flight digital optoelectronic circuits

Time-of-flight synchronization is a new digital design methodology for optoelectronics that eliminates latches, allowing higher clock rates than alternative timing schemes. Synchronization is accomplished by precisely balancing connection delays. Circuits use pulse-mode signaling and clock gates to restore pulse timing. Many effective pipeline stages are created within combinational logic without extra hardware bounding the stages. Time-of-flight design principles are applicable to packet routing and sorting processors for optical interconnection networks. Circuits are unique because the clock rate is limited primarily by imprecision in propagation delay rather than absolute delay, as in circuits with latches. We develop a general model of delay uncertainty and focus on the effect that static and dynamic uncertainty accumulated over circuit paths has on the minimum feasible clock period. We present a method for traversing the circuit graph representation of a time-of-flight circuit to compute arrival time uncertainty at each pulse interaction point. Arrival time uncertainties give rise to pulse width and overlap constraints. From these constraints we formulate a constrained minimization to find the minimum clock period. We demonstrate our method on circuits implemented with 2×2 electro-optic switches and optical waveguides and find the electronic component of path uncertainty frequently limits speed     

Histogenesis of endocardial tumors in rats

10 endocardial tumours (two tumours induced by N-nitrosoethylurea and eight spontaneous) of BD VI rats were examined for protein S-100 using specific antiserum in an immunoperoxidase reaction. The presence of protein S-100 in tumour cells is demonstrated in all cases and is considered as a proof of Schwann cell origin of these tumours.     

The effect of potential obstacles on charge transfer in imagesensors

Numerical methods are presented to investigate charge transfer in charge-coupled devices (CCDs) when potential barriers or wells occur. A Monte Carlo simulation of electron thermal diffusion and field-aided drift is used to determine the time scale for charge transfer. The Monte Carlo approach is useful for exploring new problems, but it requires considerable amounts of computer time. A quicker technique, that of the mean first passage time, is introduced. This method reduces the solution of the carrier continuity equation for charge transfer to the evaluation of a double integral that yields the characteristic time τ for e^-tτ/. This provides the leading or dominant time dependence of the carrier continuity equation's solution. Numerical examples are presented to show how τ varies with the size and location of the potential obstacle. The mean first passage time approach permits rapid estimates of the effects of potential obstacles on charge transfer in CCD's. These estimates are in excellent agreement with the results of the Monte Carlo simulations     

A Monte-Carlo simulation of the electrodeposition process

Nucleation, grain growth, texture formation, and porosity formation in the electro-deposition process has been simulated with a Monte-Carlo method. In the simulation, a two-dimensional hexagonal lattice containing 12000 lattice sites are used to map the microstructure at the cross section of deposit. The criterion for grain growth is based on the energy state of the lattice site which is set by counting the interactions between the site and its nearest neighbors. This model can be used to obtain information of how the deposition rate affects the microstructure and porosity. The texture formation during the deposition process is modeled by taking surface energy anisotropy and deposition rate into account.     

Improved surface laplacian estimates of cortical potential using realistic models of head geometry

Surface Laplacian of scalp EEG can be used to estimate the potential distribution on the cortical surface as an alternative to invasive approaches. However, the accuracy of surface Laplacian estimation depends critically on the geometric shape of the head model. This paper presents a new method for computing the surface Laplacian of scalp potential directly on realistic scalp surfaces in the form of a triangular mesh reconstructed from MRI scans. Unlike previous methods, this algorithm does not resort to any surface fitting proxy and can improve the surface Laplacian estimation of cortical potential patterns by as much as 34% on realistically shaped head models. Simulations and experimental data are presented to demonstrate the advantage of the proposed method over the conventional spherical approximation and the utility of a more accurate surface Laplacian method for estimating cortical potentials from scalp electrodes.     

The effect of potential on electrodeposited CdSe thin films

Cadmium selenide (CdSe) thin films have been successfully prepared by the electrodeposition technique on indium doped tin oxide (ITO) substrates with aqueous solutions of cadmium sulphate and selenium dioxide. The deposited films were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis by X-rays (EDAX), photoluminescence (PL), UV spectrometry and electrical resistivity measurements. XRD analysis shows that the films are polycrystalline in nature with hexagonal crystalline structure. The various parameters such as crystallite size, micro strain, dislocation density and texture coefficients were evaluated. SEM study shows that the total substrate surface is well covered with uniformly distributed spherical shaped grains. Photoluminescence spectra of films were recorded to understand the emission properties of the films. The presence of direct transition with band gap energy 1.75 eV is established from optical studies. The electrical resistivity of the thin films is found to be 10⁶ Ω cm and the results are discussed.     

盲孔镀铜过程中添加剂的作用研究

熟悉盲孔镀铜配方中各种添加剂的作用,对理论研究和实际生产都具有重要的意义。文章以一种常见的镀铜配方为例,借助金像显微镜和循环伏安溶出法(CVS)详细研究了配方中各种添加剂的作用。     

The effect of potential beam energy on the performance of linear beam devices

The potential energy stored in a bunched electron beam is calculated using analytical and numerical methods. The ratio of stored potential energy to the total beam energyW_{p}/W_{0}increases rapidly with the degree of bunching and with decreasing beam filling factorb/a.W_{p}/W_{0}is proportional to the beam perveance and independent of the beam voltage, as long as relativistic effects are neglected. In a velocity-modulated linear beam-type device, such as a klystron or a traveling-wave beam tube, stored potential beam energy affects both the bunching process and the process of dc to RE energy conversion adversely. For maximum conversion efficiencyW_{p}/W_{0}should be kept as low as possible. Several ways of reducingW_{p}/W_{0}are discussed.     

Prospects for the pulsed electrodeposition of zinc-oxide hierarchical nanostructures

Studies into the effect of the conditions of pulsed electrodeposition upon the structural and sub-structural parameters, morphology, and optical properties of ZnO-crystallite arrays make it possible to establish those parameters optimal for the formation of ZnO nanorods oriented normally to the substrate surface. These parameters are as follows: an electrolyte temperature of 70–85°C, duty cycle of 40%, and a pulse-repetition frequency of 2 Hz. The nanorod dimensions can be varied by heating or cooling the electrolyte within the above-indicated limits; as a result, small-sized nanorods can be electrically deposited on the surface of larger nanorods to form hierarchical nanostructures. By varying the duty cycle, it is possible to modify the surface morphology of the arrays up to the formation of mesoporous ZnO networks. In combination with ZnO nanorods, such networks are capable of forming hierarchical nanostructures with large specific areas.     

The effect of anisotropy on the potential distribution in biological tissue and its impact on nerve excitation simulations

We present a finite difference solution of the potential distribution associated with electrical current stimulation in an anisotropic in-homogeneous tissue environment and compare it to the isotropic case. The results demonstrate that there can be significant errors associated with the assumption of isotropic tissue properties in calculating the potential distribution along an axon in nerve excitation simulations. These errors can have a significant impact on predicted nerve fiber recruitment patterns when evaluating the efficacy of specific surface or intramuscular stimulus electrode configurations. The results of this study also suggest when a more comprehensive tissue model should be implemented in an electrode design study. Simulation results indicate that the isotropy assumption is worst under bipolar electrode stimulation as opposed to monopolar stimulation and that the bipolar error increases as the distance between electrodes decreases. In light of these results, it is concluded that in order to avoid large errors in the calculated potential distribution along an axon, the isotropy assumption should only be used when the transverse depth from the electrode to the nerve is relatively small.     

Matched filter identification of left-ventricular endocardial borders in transesophageal echocardiograms

The use of one-dimensional spatial matched filtering for identifying the left ventricular endocardial borders in human transesophageal echocardiograms recorded during surgery is investigated. A maximum-likelihood method was used to choose the endocardial intensity profiles centered within the ventricle. The computer-generated border points were compared to those identified by an experienced ultrasonographer. A 16-pixel step template located 63.2% of the border points within 2 mm of the manual border. Median prefiltering of the images reduced detection accuracy by 3% to 6%. No statistically significant difference in accuracy was found between longer and shorter templates or between data-derived and step templates. Compared to manual estimates, computer generated cross-sectional area determinations were correlated with a coefficient of 0.93. Matched filtering executes rapidly, does not require prefiltering, and performs as well as other reported methods in estimating ventricular area.     

The effect of a nonmonotonic potential profile on edge magnetic states

The dispersion law for electrons moving along a specularly reflecting boundary of a two-dimensional electron gas in the presence of a near-boundary potential well and a weak magnetic field is investigated theoretically. Numerical simulation is used to identify a number of features of the density of edge magnetic states that can be observed by magnetotransport and magnetooptics investigations. Ways to fabricate structures for studying these states are discussed. It is demonstrated that perfect-crystal interterrace boundaries can be created for a two-dimensional electron gas by introducing oblique slip planes into the heterostructure. Fiz. Tekh. Poluprovodn. 32, 1083–1088 (September 1998)     

Effects of Sb-doping on the grain growth of CIGS thin films fabricated by electrodeposition

Cu(In Ga)Se2(CIGS) solar cells become one of the most important thin film photovoltaic devices thus far. The doping of Sb has improved the grain size of CIGS thin film and therefore led to the enhancement of solar cell efficiency. Various approaches have been used for the Sb doping. Not many reports of electrodeposition of In, Ga and Sb alloy have been reported. In this work, the Sb thin film was coated over Cu film surface prior to the In and Ga deposition in order to form a Cu/Sb/In/Ga metal p...     

A note on the uncertainty product of bandlimited functions

In this paper it is shown that the lower bound $\text{1}\text{2}$ of the Heisenberg uncertainty principle is approached, as closely as desired, when the Fourier transform of a bandlimited function is a parabolic cylinder function. The behaviour of $\text{ΔTΔΩ}$ versus the bandwidth is presented.     

电阻值的测量不确定度研究

提出了一种基于JJF1059-1999测量不确定度评定与表示原则,应用HP4338微欧计于型号为RT14-1/4W的1Ω直流电阻测量的不确定度计算模型,并对不确定度结果进行了评定.