Electronic system for high power load control

Parallel current paths are divided into two groups, with control devices in the current paths of one group each having a current limiting resistor, and the control devices in the other group each having no limiting resistor, so that when the control devices of the second group are turned fully on, a short circuit is achieved by the arrangement of parallel current paths. Separate but coordinated control signals are provided to turn on the control devices of the first group and increase their conduction toward saturation as a function of control input, and when fully on, or shortly before, to turn on the control devices of the second group and increase their conduction toward saturation as a function of the control input as that input continues to increase. Electronic means may be used to generate signals. The system may be used for 1-V characteristic measurements of solar arrays as well as for other load control purposes

Technique for pinpointing submicron particles in the electron microprobe

Series of electron micrographs at successively lower magnifications can localize the substrate area sufficiently for a particle to be picked up by the beam of the electron microprobe. This approach could be modified to apply to fractographic studies, particularly of oxidation products stripped from fractures

Reynolds number dependence of scalar fluctuations in a high Schmidt number turbulent jet

The scalar rms fluctuations in a turbulent jet were investigated experimentally, using high-resolution, laser-induced fluorescence techniques. The experiments were conducted in a high Schmidt number fluid (water), on the jet centerline, over a jet Reynolds number range of 30003000 or 6500

Microprobe investigation of brittle segregates in aluminum MIG and TIG welds

Quantitative microprobe analysis of segregated particles in aluminum MIG /Metal Inert Gas/ and TIG /Tungsten Inert Gas/ welds indicated that there were about ten different kinds of particles, corresponding to ten different intermetallic compounds. Differences between MIG and TIG welds related to the individual cooling rates of these welds

Stochastic geometric properties of scalar interfaces in turbulent jets

Experiments were conducted in which the behavior of scalar interfaces in turbulent jets was examined, using laser-induced fluorescence (LIF) techniques. The experiments were carried out in a high Schmidt number fluid (water), on the jet centerline, over a jet Reynolds number range of 1000<=Re<=24 000. Both two-dimensional scalar data, c(r,t) at fixed x/d, and one-dimensional scalar data, c(t) at fixed x/d and r/x, were analyzed using standard one- and two-dimensional fractal box-counting algorithms. Careful treatment was given to the handling of noise. Both long and short records as well as off-centerline measurements were also investigated. The important effect of threshold upon the results is discussed. No evidence was found of a constant (power-law) fractal dimension over the range of Reynolds numbers studied. On the other hand, the results are consistent with the computed behavior of a simple stochastic model of interface geometry

Measurements of scalar power spectra in high Schmidt number turbulent jets

We report on an experimental investigation of temporal, scalar power spectra of round, high Schmidt number (Sc ≃ 1.9 × 10^3), momentum-dominated turbulent jets, for jet Reynolds numbers in the range of 1.25 × 10^4 ≤ Re ≤ 7.2 × 10^4. At intermediate scales, we find a spectrum with a slope (logarithmic derivative) that increases in absolute value with Reynolds number, but remains less than 5/3 at the highest Reynolds number in our experiments. At the smallest scales, our spectra exhibit no k^(−1) power-law behaviour, but, rather, seem to be approximated by a log-normal function, over a range of scales exceeding a factor of 40, in some cases

Some consequences of the boundedness of scalar fluctuations

Values of the scalar field c(x,t), if initially bounded, will always be bounded by the limits set by the initial conditions. This observation permits the maximum variance ∼(c′^2) to be computed as a function of the mean value c. It is argued that this maximum should be expected in the limit of infinite Schmidt numbers (zero scalar species diffusivity). This suggests that c′/c on the axis of turbulent jets, for example, may not tend to a constant, i.e., independent of x/d, in the limit of very large Schmidt numbers. It also underscores a difficulty with the k^(−1) scalar spectrum proposed by Batchelor [J. Fluid Mech. 5, 113 (1959)]

AN ANALYSIS OF ALTERNATIVE NET PRESENT VALUE CAPITAL INVESTMENT DECISION MODELS

We have found that the disagreement between Returns-to-Assets (RTA) and Returns-to-Equity (RTE) proponents is not confined to agricultural economics. Depending on the course they are taking and the accompanying text, students are likely to learn that there is a "right" way to calculate Net Present Values (NPVs), either by the RTA method or the RTE method. In most cases, only one of the two methods is discussed and illustrated with numerical examples. Less common are texts that compare the two methods, discuss their underlying assumptions, or show how the NPVs from the two methods can be reconciled. The paper is organized as follows. The first section of the main body of the paper provides a comparative overview of the RTA and RTE methods; the second section discusses our textbook survey; the final section offers our conclusions. Appendix A contains a brief history of the theoretical development of discounted cash flow (DCF) concepts. Appendix B contains additional details on defining components of NPV models. Finally, Appendix C is a listing of some additional references.Research Methods/ Statistical Methods,

Introductory comments

Vibroacoustic and thermal environment data gathered from the first three flights of the space shuttle are presented. The characterization of the particulate, gaseous, and electromagnetic emissions associated with the shuttle flight is emphasized. Measurements of vehicle glow light emissions and material effects (mass loss) due to the low Earth environment interactions with the shuttle vehicle are presented

On the dynamic response of pressure transmission lines in the research of helium-charged free piston Stirling engines

In free piston Stirling engine research the integrity of both amplitude and phase of the dynamic pressure measurements is critical to the characterization of cycle dynamics and thermodynamics. It is therefore necessary to appreciate all possible sources of signal distortion when designing pressure measurement systems for this type of research. The signal distortion inherent to pressure transmission lines is discussed. Based on results from classical analysis, guidelines are formulated to describe the dynamic response properties of a volume-terminated transmission tube for applications involving helium-charged free piston Stirling engines. The scope and limitations of the dynamic response analysis are considered