An efficient shrinkage bootstrap bias estimator for smooth functions of sample means

Summary  Since it is not always possible to calculate bootstrap estimators, they are usually approximated by simulation. In this article, we propose a bootstrap bias estimator for smooth functions of sample means that has less mean squared error, due to the simulation process, than the ordinary bootstrap. The estimator is based on shrinking the bootstrap mean towards the original sample mean. It can easily be implemented while demanding almost no additional computational effort.     

Constructing integer programming models by the predicate calculus

A modelling language for Integer Programming (IP) based on the Predicate Calculus is described. This is particularly suitable for building models with logical conditions. Using this language a model is specified in terms of predicates. This is then converted automatically by a series of transformation rules into a normal form from which an IP model can be created. There is also some discussion of alternative IP formulations which can be incorporated into the system as options. Further practical considerations are discussed briefly concerning implementation language and incorporation into practical Mathematical Programming Systems.     

Correction to `surface snow properties effects on millimeter-wavebackscatter' (May 1988 300-306)

In the above mentioned paper (ibid., vol.26, no.3, May 1988) the exponential coefficients of percent liquid water content V_W in Table II are too large in magnitude by a factor of 10 (i.e. -0.990 should be -0.0990, etc.)     

On Administering Questionnaires in Organizational Settings

The administration of a questionnaire is much more difficult than implied in the phrase noted earlier, "The questionnaire was administered to all members of the system on system time." Every person who has used the technique more than once or twice is, or should be aware of many of the things mentioned above. Somehow their hard won inspirations are not passed on to others and the uninitiated wander in and come away bloodied if not bowed.     

Homotopically nontrivial solutions for a spherically symmetric gravitational field

The structure of kink solutions to the Einstein field equations is discussed and the most general form of spherically symmetric kink metric is constructed. A number of fluid solutions are investigated and an imperfect fluid solution with nonzero heat conduction is presented.     

无铅钎料对波峰焊设备的影响

目前,无铅钎料应用的日益推广使得波峰焊设备问题更加突出.其中主要的问题是设备的腐蚀及材料的寿命.为此,许多设备制造商提出了不同的方案来解决此类问题.这些方案涉及范围从不对元件进行改进到使用昂贵的金替代整个钎料锅及喷嘴.本文对制造波峰焊设备"钎料元件"的所用材料进行评估.     

Picosecond pulse generation with ultralow jitter in 1.5-μmmulticontact MQW lasers using Q-switching

High-peak-power picosecond pulses with ultralow jitter of 65 fs (50-500 Hz) have been generated by Q-switching multi-quantum-well (MQW) distributed-feedback (DFB) and Fabry-Perot (FP) multicontact lasers. Peak pulse powers of 80 mW have been measured for pulses having durations of 26 ps and repetition rates of 1.25 GHz     

Effects of cooling rate on the microstructure and tensile behavior of a Sn-3.5wt.%Ag solder

The tensile behavior and microstructure of bulk, Sn-3.5Ag solders as a function of cooling rate were studied. Cooling rate is an important processing parameter that affects the microstructure of the solder and, therefore, significantly influences mechanical behavior. Controlled cooling rates were obtained by cooling specimens in different media: water, air, and furnace. Cooling rate significantly affected secondary dendrite-arm size and spacing of the Sn-rich phase, as well as the aspect ratio of Ag₃Sn. The Sn-rich dendrite-arm size and spacing were smaller for water-cooled specimens than for air-cooled specimens. Furnace cooling yielded a nearly eutectic microstructure because the cooling rate approached equilibrium cooling. The morphology of Ag₃Sn also changed from spherical, at a fast cooling rate, to a needlelike morphology for slower cooling. The changes in the microstructure induced by the cooling rate significantly affected the mechanical behavior of the solder. Yield strength was found to increase with increasing cooling rate, although ultimate tensile strength and strain-to-failure seemed unaffected by cooling rate. Cooling rate did not seem to affect Young’s modulus, although a clear coorelation between modulus and porosity was obtained. The mechanical behavior was correlated with the observed microstructure, and fractographic analysis was employed to elucidate the underlying damage mechanisms.     

An optimal vector-network-analyzer calibration algorithm

We present an iterative algorithm for calibrating vector network analyzers based on orthogonal distance regression. The algorithm features a robust, yet efficient, search algorithm, an error analysis that includes both random and systematic errors, a full covariance matrix relating calibration and measurement errors, 95% coverage factors, and an easy-to-use user interface that supports a wide variety of calibration standards. We also discuss evidence that the algorithm outperforms the MultiCal software package in the presence of measurement errors and accurately estimates the uncertainty of its results.