Improved strain-anneal crystal growth technique

A new method of growing iron single crystals* of predetermined orientation is described. *U.S. Patent No. 3694269. This technique differs from the conventional strain-anneal method in that pulse heating is used to suppress random nucleation of undesired grains ahead of the growth interface, rather than a traveling “sharp” temperature gradient which is often difficult to attain. The procedures used to grow large α-iron single crystals with the new technique are fully described. A significant advantage of this method is that large oriented single crystals, 25 cm (10 in.) or greater in length, can be grown from rods or strip in a few hours, with a much higher probability of success than can be obtained with the conventional technique, which typically requires several days to obtain crystals of this size.     

Mapping forest alliances and associations using fuzzy systems and nearest neighbor classifiers

The study and management of biological communities depends on systems of classification and mapping for the organization and communication of resource information. Recent advances in remote sensing technology may enable the mapping of forest plant associations using image classification techniques. But few areas outside Europe have alliances and associations described in detail sufficient to support remote sensing-based modeling. Northwestern Montana has one of the few completed plant association classifications in the United States compliant with the recently established National Vegetation Classification system. This project examined the feasibility of mapping forest plant associations using Landsat Enhanced Thematic Mapper Plus data and advanced remote sensing technology and image classification techniques.Suitable reference data were selected from an extensive regional database of plot records. Fifteen percent of the plot samples were reserved for validation of map products, the remainder of plots designated as training data for map modeling. Key differentiae for image classification were identified from a suite of spectral and biophysical variables. Fuzzy rules were formulated for partitioning physiognomic classes in the upper levels of our image classification hierarchy. Nearest neighbor classifiers were developed for classification of lower levels (alliances and associations), where spectral and biophysical contrasts are less distinct.Maps were produced to reflect nine forest alliances and 24 associations across the study area. Error matrices were constructed for each map based on stratified random selections of map validation samples. Accuracy for the alliance map was estimated at 60%. Association classifiers provide between 54 and 86% accuracy within their respective alliances. Alternative techniques are proposed for aggregating classes and enhancing decision tree classifiers to model alliances and associations for interior forest types.     

Heat conduction by liquid helium II in capillary tubes. IV. Mutual friction under pressure

We report measurements of supercritical heat conduction in liquid helium II at pressures above the vapor pressure. The measurements were made in glass capillary tubes of diameter 50.5 and 366.8 m in the temperature range from 1.2 to 2.1 K. As in our previous results at the vapor pressure, a clear distinction can be made between two regimes in which the average separation of vortex lines is either comparable with or larger than the size of the flow channel. In the wider tube, at high relative velocities v between the superfluid and normal component, where the vortex spacing is small, a modified form of Gorter-Mellink mutual friction F _sn is observed which varies as F_sn=A_snv(v–v₀)². The coefficient A increases with pressure, and its variation with T/T(p) is in fairly good agreement with Schwarz ' microscopic theory of superfluid turbulence. However, the absolute magnitude of A is in general larger than in Schwarz ' theory and also larger than most other experimental values. In the narrower tube the measurements are all in the regime where the vortex spacing is comparable with the tube size, and they do not agree with the predictions of the Gorter-Mellink law. At present, the data cannot be analyzed quantitatively in the terms of the vortex line density, because B, the vortex line scattering coefficient, is not known at high pressures.Preparation of this paper was supported by a U.S. National Science Foundation grant DMR 7901073 and by a UK Science Research Council Senior Fellowship (DFB).SRC Senior Fellow.     

Anomalies in adsorbed films of He4 above the lambda temperature

Previous measurements of adsorption isotherms of He⁴ on an argon-coated copper substrate have suggested that a phase transition may take place in adsorbed He⁴ films at temperatures above the normal bulk liquid lambda point. We have made high-precision adsorption measurements on a substrate of porous Vycor glass (mean pore diameter 62.4 Å, surface area 580 m²) and failed to find any evidence of anomalous adsorption. Reasons for the conflict in results are discussed.     

Ordering and precipitation effects in the specific heat and magnetization of copper-iron alloys

There is evidence in the specific heat of dilute copper-iron alloys of magnetic interaction phenomena whose behavior varies according to the range of solute concentration. At temperatures well below T_Kondo and at low concentrations two essentially independent contributions to the specific heat are found. One arises from the thermal excitations in the solid solution and the other from those in a rudimentary fine-scale coherent precipitate.The research was supported by the Science Research Council by provision of a Research Studentship, and by the Ministry of Technology, through the National Physical Laboratory, under Contract No. AD 34/8/04/26, by a Research Studentship (D.J.E.) and a Research Grant.     

On the design of feedback control for relative stability

A basic theorem on relative stability is generalized and carefully interpreted. Two new theorems are then presented which simplify the calculation of feedback gains to achieve a prescribed damping ratio.     

The case for technology in developing regions

Alongside good governance, technology is considered among the greatest enablers for improved quality of life. However, the majority of its benefits have been concentrated in industrialized nations and therefore limited to a fraction of the world's population. We believe that technology has a large role to play in developing regions, that "First World" technology to date has been a poor fit in these areas, and that there is thus a need for technology research for developing regions. Despite the relative infancy of technology studies in developing regions, anecdotal evidence suggests that access to technology has a beneficial economic impact. Cellular telephony is probably the most visible application, but there are many others, some of which we cover in this article. The World Bank's infoDev site catalogs hundreds of information and communications technologies (ICT) projects, albeit not all successful. Most of these projects use existing off-the-shelf technology designed for the industrialized world. Although it is clear that there are large differences in assumptions related to cost, power, and usage, there has been little work on how technology needs in developing regions differ from those of industrialized nations. We argue that Western market forces continue to meet the needs of developing regions accidentally at best.     

Using interval arithmetic for robust state feedback design

A problem of a modal P-regulator synthesis for a linear multivariable dynamical system with uncertain (interval) parameters in state space is considered. The designed regulator has to place all coefficients of the system characteristic polynomial within assigned intervals. We have developed the approach proposed earlier in Dugarova and Smagina (Avtomat. i Telemech. 11 (1990) 176) and proved a direct correlation between interval system controllability and existence of robust modal P-regulator.