A FORTRAN IV program for interpolating irregularly spaced data using the difference equations for minimum curvature

The interpolation of potential field data is a common problem in geophysics. It is accomplished each time a contour map or profile is drawn. These operations can be difficult and subjective if the data points are irregularly spaced. The method described here produces a “numerical surface”, or grid of values, that approaches the smoothest surface passing through the control points. Such a grid can be contoured automatically by standard routines, producing acceptable results. Alternatively, sections can be drawn through the surface on any azimuth—a more satisfactory procedure for constructing profiles than projecting the data points onto straight lines.     

Crystal structure of Escherichia coli L-asparaginase, an enzyme used in cancer therapy

The crystal structure of Escherichia coli asparaginase II (EC 3.5.1.1), a drug (Elspar) used for the treatment of acute lymphoblastic leukemia, has been determined at 2.3 A resolution by using data from a single heavy atom derivative in combination with molecular replacement. The atomic model was refined to an R factor of 0.143. This enzyme, active as a homotetramer with 222 symmetry, belongs to the class of alpha/beta proteins. Each subunit has two domains with unique topological features. On the basis of present structural evidence consistent with previous biochemical studies, we propose locations for the active sites between the N- and C-terminal domains belonging to different subunits and postulate a catalytic role for Thr-89.     

A comparative study of the fracture of various silica modifications using the Hertzian test

A comprehensive Hertzian fracture study has been made of quartz, fused silica and soda-lime glass. The two main aspects are: (i) vacuum tests, which reflect the intrinsic bond strength of the -Si-O- network, and (ii) water-environment tests, which reflect the rate processes involved in hydrolytic bond weakening. Temperature, load rate and chemical concentration are the variables investigated. The incorporation of new features into the elementary Si-O bond-rupture picture of crack extension is necessary to account for the results. In vacuum, the Hertzian fracture strength of quartz decreases dramatically as the inversion temperature is approached; no such effect is evident in the non-crystalline modifications. This result is interpreted in terms of thermal oscillations of the stacking tetrahedra in the SiO₂ structure. In water environments, the Hertzian strength is universally depressed, the effect becoming more pronounced at low load rates, high chemical concentrations. The physical state of the environment is an important factor in the kinetics of the hydrolytic weakening process: with the liquid state, the (thermally-activated) reaction between water molecules and crack-tip bonds is ratecontrolling; whereas with the gaseous state, it is the (temperature-insensitive) molecular diffusion along the fracture interface which controls. The secondary role of composition effects, dissipative crack-tip processes, etc., is also discussed.     

Classical conditioning with electrical stimulation of cerebellum as both conditioned and unconditioned stimulus.

Stimulating electrodes were implanted in rabbit cerebellum, providing an electrical conditioned stimulus (CS) activating cortical parallel fibers and thence Purkinje and other cells, and an electrical unconditioned stimulus (US) activating underlying white matter and eliciting unconditioned responses. Paired CS-US presentations led to the development of conditioned responses, which showed extinction following CS-alone trials and reacquisition with significant savings on reinstatement of paired trials. Increased local excitability as a result of paired training (but not following unpaired stimulus presentations) was observed in cerebellar cortex, as manifested in substantial decreases in CS threshold for response elicitation in all subjects. This preparation offers a model for the study of plastic neuronal interactions within cerebellar networks critically involved in associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perspectives on U.S. Great Lakes Chemical Toxic Substances Research

Because of their magnitude, their geographic and demographic characteristics, and their unique limnological properties, the Great Lakes appear to be especially susceptible to chemical contamination. The scientific basis for dealing with this contamination is very limited compared with the magnitude of the problem. This is particularly evident when the vast array of toxic xenobiotic substances of anthropogenic origin are considered. Major knowledge gaps exist on the critical transport pathways, ultimate fate, and ecological effects of toxic substances (of urgent importance are health effects on humans residing in the basin), as well as on the economic and social aspects of toxics management.The economic climate of the 1980s, however, is likely to severely limit the resources available for the conduct of research which is so badly needed. Consequently, it appears that the Great Lakes research community will have imposed upon it a markedly increased demand for information and a concomitant reduction in the resources available to accomplish the task. Finally, despite a pessimistic outlook for research support, there is optimism that the Great Lakes will respond positively, and in a relatively short time span (years as opposed to centuries), to the abatement of toxic inputs. Nevertheless, additional information on the processes affecting the distribution and fate of toxic substances is still critical to the understanding required to ensure effective remedial actions.     

A means for utilizing ancillary information in multispectral classification

A method is presented that allows information from ancillary data sources to be incorporated into the results of an existing classification of remotely sensed data. Based upon probabilistic label relaxation procedures, which are used for imbedding spatial context data in image-labeling problems, the method utilizes the source of ancillary information in the form of a set of probabilities. These are injected into a modified relaxation method called supervised relaxation labeling which, on application, develops a labeling for remotely sensed data that strikes a balance in consistency between spectral, spatial, and ancillary data sources of information. Results are presented of a forestry classification in which accuracy is improved from 68% to 81% by incorporating topographic elevation in the manner outlined.     

Calculation of the Transient Response of Long Chains of Slightly Lossy Coupled Resonators

Methods of calculating and of illustrating the transient response of chains of coupled resonators are discussed. Such calculations are particularly useful in understanding the rf field behavior in linear accelerator structures, both of the drift tube and waveguide or coupled cavity types. Resonator chains are also employed in certain kinds of filters and delay lines; the methods to be discussed are applicable in these areas, as well. A frequency adjustment is presented which permits difference equations with a large time step to accurately represent the differential equations for slightly lossy coupled resonators.