Correlations between interfacial oxides and resistance changes for W contacts on heavily doped Si-Ge

The effects of variations in processing on the thickness of an interfacial oxide and the resistance between W contact films and a doped Si-Ge alloy have been investigated. Auger electron spectroscopy in conjunction with sputter profiling indicated that the native interfacial oxide film could be reduced by 50% with an HF etch immediately prior to deposition of the W film. The interfacial oxide was found to thicken by approximately one monolayer upon being heated to 400 °C for 3 h in a sputtering vacuum chamber with a 3 × 10^-2 Torr argon atmosphere. This was correlated with a doubling in the contact resistance. The manner in which interface oxide could cause this increase in contact resistance is discussed.     

An Ad Hoc Method for Forecasting Series with Zero Values

When forecasting the demand for a product, it is sometimes necessary to model time series which are a mixture of zeros (i.e., no demand) and values much larger than zero. An ad hoc method is presented which consists of decomposing the original series into two series, one of which consists only of non-zero values, while the other is modeled as a Markov chain with states zero and one. The non-zero values are modeled as an ARIMA process. The Markov chain is classified using a statistical method due to Tong. These two series can then be used to generate an ensemble of forecasts for a given lead time, each with a specified probability of occurrence. Two illustrations of the method are made to series which represent market demand for steel.     

Computation of Mean Time to Failure for a System with Simple Redundancy

A system consisting of several independent components in series can be made more reliable by adding an "identical" component in parallel to some of the components. Two mathematical series are presented for computing the mean time to failure for the system when the failure times of the components are exponentially distributed. For large systems the evaluation of these series is not computationally feasible, but one of the series yields an accurate approximation if the series is truncated, and also yields an explicit solution if all components have identical failure rates. The explicit solution is then used to check the accuracy of solutions obtained using numerical integration. The method of numerical integration is highly accurate.     

Concentration of virus from water by osmotic ultrafiltration—II: Mass transport aspects

A membrane process is described which allows water samples to be concentrated by factors of 400 or more, without loss of viral infectivity. The requirements for effecting high ratios of initial to final volumes are examined in terms of two methods of solving the coupled transport equations. Initial volumes, membrane area, membrane transport coefficients, and osmotic coefficients are related to predict the rate and extent of concentration which can be achieved. The methods of characterizing membrane parameters to predict water transport rates are discussed. Experimental results are compared with computer predicted rates, using the two types of mathematical solutions.     

Forecasting the size of a collection in workflow models

A workflow management system (WFMS) is a system that completely defines, manages and executes workflow through the use of software whose order of execution is driven by a computer representation of the workflow logic. The correct sequence of tasks in the database can be automatically discovered by applying data mining technology to the data of the audit trail written by WFMS. During the data mining process, an attempt is made to find all of the objects of interest. In this paper, a model is presented which can be used to forecast the ultimate size of a complete collection. The model can also be used to estimate the expected time necessary to complete the collection, and the probability of finding more items in a fixed interval of time. The data necessary to compute these forecasts is the number of items which have already been found, and the time it took to collect them. A case study from the field of post card collecting is presented.     

Computation of the autocovariances of stationary arma processes

Autoregressive-moving average (ARMA) models are often used for the purpose of forecasting a time series. As an aide to chosing a model, use is made of the autocorrelation function which is estimated from the data. If the only interest in the model is for forecasting purposes, then it is not necessary to compute the autocorrelation function associated with the chosen model. For this reason, a method for computation of the autocorrelation function is not usually included in the software used for identifying ARMA models. However, there are applications of ARMA models where it is important to compute the autocovariance function.

This paper contains an algorithm and a listing of a FORTRAN program which computes the autocovariance directly from the solution to the difference equations which govern its behavior.     

An Investigation of the Measurements Systems Analysis “Analytic Method” for Attribute Gages

Three automotive corporations have developed and sanctioned the recently revised reference manual entitled Measurement Systems Analysis. This “standard” contains a procedure, called the “analytic method,” whose purpose is to estimate the gage bias and gage repeatability of an attribute gage. An improved estimation procedure for this standard is presented. The improved estimation procedure yields more accurate estimates than those obtained using the procedures currently presented in the standard. In addition, the improved procedure allows more flexibility in data collection than the current test protocol. A simulation study that evaluates the estimation procedure of the current standard and compares it with the improved estimation procedure is presented. Errors that are contained in the present standard are also noted.