High-Tc dc-SQUID magnetometer and its application in eddy current non-destructive evaluation

We have fabricated and tested a high-T_c dc-SQUID magnetometer patterned on a YBCO thin film deposited on a SrTiO₃ bicrystal substrate. The measurement of noise spectrum at 77 K showed that the magnetometer has a white noise of 333 fT/Hz^1/2 without superconducting shield, corresponding to a flux sensitivity of 14.5 μΦ₀/Hz^1/2. We constructed a test system for eddy current non-destructive evaluation of conducting aluminum plates by using the magnetometer. Flaws over 10 mm below the surface can be clearly identified. By mapping the magnetic field distribution, we can locate the flaw position. The signals caused by flaw were expanded due to the use of double-D type driving coil with a wider central slit. The experimental results confirmed that this test system could operate in a magnetic unshielded environment.     

Boiling: Size Distribution of Bubbles as Demanded by the Principle of Maximum Information

The principle of maximum informational entropy is used to find the probability density function for the departure radius of a bubble in boiling on a solid surface. A general relation is derived, which leads to particular expressions.     

The Effect of Structural Defects on the Thermal Conductivity of ZnS, ZnSe, and CdTe Polycrystals

ZnS, ZnSe, and CdTe polycrystals are experimentally investigated. Mechanisms are treated which restrict the thermal conductivity in samples prepared by recrystallization pressing and by deposition from the vapor phase and subjected to additional strain. Anomalies are observed on the temperature dependences of the thermal resistance of investigated samples, which are due to the special features of their phonon spectra and to the variation of the contribution made by longitudinal and transverse phonon branches to the heat transfer in the Debye temperature region and higher.     

The Difference in Turbulent Diffusion between the Active and Passive Scalars in a Thermally Stably Stratified Medium

The difference in the turbulent diffusion between the active (heat) and passive (mass) scalars in a thermally stably stratified medium is investigated. The axisymmetric problem is treated on the formation of a turbulent circulation flow above a heated disk and on the turbulent diffusion of a passive scalar (impurity) from a continuous surface source in a stably stratified medium. The results indicate that the thermal stratification causes appreciable differences in the coefficients of turbulent transfer between the active (heat) and passive (mass) scalars. This means that the assumption of the identity of the coefficient of turbulent diffusion of heat and mass, employed in conventional models of turbulence, produces significant errors in estimating the heat and mass transfer in a thermally stably stratified medium.     

Filtration of Non-Newtonian Hydrocarbon Fluid in a High-Frequency Electromagnetic Field

The paper gives the results of experimental investigations of the initial pressure gradient of bituminous oil and the time dependences of variation of the temperature in a formation model and of the well production rate in a microwave-frequency electromagnetic field. The effect of strong decay of the non-Newtonian properties of bituminous oil is revealed. The nonuniformity of temperature distribution over the formation thickness is demonstrated, which depends on the initial production rate of the well and on the duration of stimulation of the bottom-hole zone of formation.     

Application of autoregressive spectral analysis to missing data problems

Time series solutions for spectral analysis in missing data problems use reconstruction of the missing data, or a maximum likelihood approach that analyzes only the available measured data. Maximum likelihood estimation yields the most accurate spectra. An approximate maximum likelihood algorithm is presented that uses only previous observations falling in a finite interval to compute the likelihood, instead of all previous observations. The resulting nonlinear estimation algorithm requires no user-provided initial solution, is suited for order selection, and can give very accurate spectra even if less than 10% of the data remains.     

Finite sample properties of ARMA order selection

The cost of order selection is defined as the loss in model quality due to selection. It is the difference between the quality of the best of all available candidate models that have been estimated from a finite sample of N observations and the quality of the model that is actually selected. The order selection criterion itself has an influence on the cost because of the penalty factor for each additionally selected parameter. Also, the number of competitive candidate models for the selection is important. The number of candidates is, of itself, small for the nested and hierarchical autoregressive/moving average (ARMA) models. However, intentionally reducing the number of selection candidates can be beneficial in combined ARMA(p,q) models, where two separate model orders are involved: the AR order p and the MA order q. The selection cost can be diminished by creating a nested sequence of ARMA(r,r-1) models. Moreover, not evaluating every combination (p,q) of the orders considerably reduces the required computation time. The disadvantage may be that the true ARMA(p,q) model is no longer among the nested candidate models. However, in finite samples, this disadvantage is largely compensated for by the reduction in the cost of order selection by considering fewer candidates. Thus, the quality of the selected model remains acceptable with only hierarchically nested ARMA(r,r-1) models as candidates.     

CMOS circuit testing via time-resolved luminescence measurements and simulations

The continuous trend in modern CMOS technology toward smaller devices and faster clock frequency is challenging the picosecond imaging circuit analysis technique. In this paper we discuss the role of the single-photon avalanche diode with very sharp time resolution in testing CMOS circuits. Thanks to the 30 ps-time resolution, innovative measurements regarding delays and jitter are presented, along with a case study. A compact model of the luminescence is also proposed and used to compare on-chip electrical signals with optical waveforms.     

Implementation of a mechanics-based system for estimating the strength of timber

The most accurate way of determining the strength of lumber requires destructive testing. An intelligent mechanics-based lumber-grading system was developed to provide a better estimation of the strength of a board nondestructively. This system processed X-ray-extracted geometric features (of 1080 boards that eventually underwent destructive strength testing) by using finite element methods to generate associated stress fields. The stress fields were then fed to a feature-extracting-processor, which produced 26 strength predicting features. The best strength predicting features were determined from the coefficient of determination (correlation r/sup 2/) between the features and actual strengths of the boards. The coefficients of determination of each feature (or combination of features), with the actual strength of the board, were calculated and compared. A coefficient of determination of 0.4158 was achieved by using a longitudinal (along the local grain angle) maximum stress concentration (MSC) feature to predict the estimated strength of lumber.