Showing papers by "Cornell University published in 1976"

Exchange and correlation in atoms, molecules, and solids by the spin-density-functional formalism

Abstract: The aim of this paper is to advocate the usefulness of the spin-density-functional (SDF) formalism. The generalization of the Hohenberg-Kohn-Sham scheme to and SDF formalism is presented in its thermodynamic version. The ground-state formalism is extended to more general Hamiltonians and to the lowest excited state of each symmetry. A relation between the exchange-correlation functional and the pair correlation function is derived. It is used for the interpretation of approximate versions of the theory, in particular the local-spin-density (LSD) approximation, which is formally valid only in the limit of slow and weak spatial variation in the density. It is shown, however, to give good account for the exchange-correlation energy also in rather inhomogeneous situations, because only the spherical average of the exchange-correlation hole influences this energy, and because it fulfills the sum rule stating that this hole should contain only one charge unit. A further advantage of the LSD approximation is that it can be systematically improved. Calculations on the homogeneous spin-polarized electron liquid are reported on. These calculations provide data in the form of interpolation formulas for the exchange-correlation energy and potentials, to be used in the LSD approximation. The ground-state properties are obtained from the Galitskii-Migdal formula, which relates the total energy to the one-electron spectrum, obtained with a dynamical self-energy. The self-energy is calculated in an electron-plasmon model where the electron is assumed to couple to one single mode. The potential for excited states is obtained by identifying the quasiparticle peak in the spectrum. Correlation is found to significantly weaken the spin dependence of the potentials, compared with the result in the Hartree-Fock approximation. Charge and spin response functions are calculated in the long-wavelength limit. Correlation is found to be very important for properties which involve a change in the spinpolarization. For atoms, molecules, and solids the usefulness of the SDF formalism is discussed. In order to explore the range of applicability, a few applications of the LSD approximation are made on systems for which accurate solutions exist. The calculated ionization potentials, affinities, and excitation energies for atoms propose that the valence electrons are fairly well described, a typical error in the ionization energy being 1/2 eV. The exchange-correlation holes of two-electron ions are discussed. An application to the hydrogen molecule, using a minimum basis set, shows that the LSD approximation gives good results for the energy curve for all separations studied, in contrast to the spin-independent local approximation. In particular, the error in the binding energy is only 0.1 eV, and bond breaking is properly described. For solids, the SDF formalism provides a framework for band models of magnetism. An estimate of the splitting between spin-up and spin-down energy bands of a ferromagnetic transition metal shows that the LSD approximation gives a correction of the correct sign and order of magnitude to published $X\ensuremath{\alpha}$ results. To stimulate further use of the SDF formalism in the LSD approximation, the paper is self-contained and describes the necessary formulas and input data for the potentials.

Plant apparency and chemical defense

Abstract: A major objective of insect ecology is to explain observed patterns of interaction between plants and herbivorous insects. We would like to understand both how such patterns are maintained in ecological time and also how they have come about in evolutionary time. A test of how far such understanding has progressed will be our ability to predict how patterns vary from one kind of community to another and how they will change when subjected to natural or human disturbance.

Functional properties of proteins in foods: A survey

Abstract: Proteins for foods, in addition to providing nutrition, should also possess specific functional properties that facilitate processing and serve as the basis of product performance. Functional properties of proteins for foods connote the physicochemical properties which govern the behavior of protein in foods. This general article collates the published information concerning the major functional properties of food proteins, e.g., solubility, binding properties, surfactant properties, viscogenic texturizing characteristics, etc. The effects of extraction and processing on functional properties and possible correlations between structure and function are discussed, in relation to practical performance in food systems. Modification of proteins to improve functional characteristics is briefly mentioned.

An axiomatic proof technique for parallel programs I

Abstract: A language for parallel programming, with a primitive construct for synchronization and mutual exclusion, is presented. Hoare's deductive system for proving partial correctness of sequential programs is extended to include the parallelism described by the language. The proof method lends insight into how one should understand and present parallel programs. Examples are given using several of the standard problems in the literature. Methods for proving termination and the absence of deadlock are also given.

Spatial distribution of earthquakes and subduction of the Nazca plate beneath South America

Abstract: A detailed study of the spatial distribution of precisely located hypocenters of South American earthquakes that occurred between lat 0° and 45°S shows that the data can be explained by the simple model of a descending oceanic plate beneath a continental plate and that the following conditions obtain: (1) The hypocenters clearly define five segments of inclined seismic zones, in each of which the zones have relatively uniform dips. The segments beneath northern and central Peru (about lat 2° to 15° S) and beneath central Chile (about lat 27° to 33° S) have very small dips (about 10°), whereas the three segments beneath southern Ecuador (about lat 0° to 2°S), beneath southern Peru and northern Chile (about lat 15° to 27°S), and beneath southern Chile (about lat 33° to 45°S) have steeper dips (25° to 30°). No clear evidence exists for further segmentation of the descending Nazca plate beneath South America. If the two flat segments are in contact with the lower boundary of the continental plate, the thickness of that plate is less than approximately 130 km. This is in marked contrast to the reports of thicknesses exceeding 300 km for the South American continental plate. (2) There is considerable seismic activity within the upper 50 km of the overriding South American plate. This seismic activity is well separated from the inclined seismic zones and probably occurs in the crustal part of the South American plate. Thus, hypocenters in South America are not evenly distributed through about a 300-km-thick zone as previously described. (3) A remarkable correlation exists between the two flat segments of the subducted Nazca plate and the absence of Quaternary volcanism on the South American plate. (4) The transition from the flat Peru segment to the steeper Chile segment is abrupt and is interpreted as a tear in the descending Nazca plate. The tear is located approximately beneath the northern limit of the Altiplano (a high plateau in the Andes), and about 200 km south of the projection of the oceanic Nazca ridge down the subduction zone. (5) A gap in seismic activity exists between depths of 320 and 525 km.

A rational model for Langmuir circulations

Abstract: A realistic theoretical model of steady Langmuir circulations is constructed. Vorticity in the wind direction is generated by the Stokes drift of the gravity-wave field acting upon spanwise vorticity deriving from the wind-driven current. We believe that the steady Langmuir circulations represent a balance between this generating mechanism and turbulent dissipation.Nonlinear equations governing the motion are derived under fairly general conditions. Analytical and numerical solutions are sought for the case of a directional wave spectrum consisting of a single pair of gravity waves propagating at equal and opposite angles to the wind direction. Also, a statistical analysis, based on linearized equations, is developed for more general directional wave spectra. This yields an estimate of the average spacing of windrows associated with Langmuir circulations. The latter analysis is applied to a particular example with simple properties, and produces an expected windrow spacing of rather more than twice the length of the dominant gravity waves.The relevance of our model is assessed with reference to known observational features, and the evidence supporting its applicability is promising.

Dynamo model of double radio sources

Abstract: A model of radio sources is proposed in which the magnetised accretion disk of a massive black hole acts as an electric dynamo producing two oppositely-directed beams of ultra-relativistic particles.

An improved technique for selective silver staining of nucleolar organizer regions in human chromosomes

Abstract: A reliable technique for staining human chromosomal nucleolar organizers (NOR's) with silver solutions is described. The NOR's can be selectively stained dark brown by silver solutions leaving the chromosome arms unstained and available for counterstaining with orcein or Giemsa dyes. Unequivocal identification of chromosome pairs bearing NOR's can be achieved using fluorescent banding techniques followed by silver staining. The silver staining procedure for NOR's was simplified and standardized through control of the chemical and physical conditions during silver impregnation and developing.

The Experimental Ecology of Education

Abstract: Ishall begin by stating three basic requirements that, in my judgment, must be met if we are to make progress in the scientific study of educational systems and processes. 1. Our researches cannot be reistricted to the laboratory; for the most part, they must be carried out in real-life educational settings. As will be indicated below, this does not mean that laboratory experiments cannot serve a useful and, indeed, essential purpose, but they must be carried out with explicit recognition of the delimiting and distorting nature of the laboratory as a setting and deliberately designed to articulate closely with and complement companion researches carried out in real-life situations. 2. Whether and how people learn in educational settings is a function of sets of forces, or systems, at two levels:

Verifying properties of parallel programs: an axiomatic approach

Abstract: An axiomatic method for proving a number of properties of parallel programs is presented Hoare has given a set of axioms for partial correctness, but they are not strong enough in most cases This paper defines a more powerful deductive system which is in some sense complete for partial correctness A crucial axiom provides for the use of auxiliary variables, which are added to a parallel program as an aid to proving it correct The information in a partial correctness proof can be used to prove such properties as mutual exclusion, freedom from deadlock, and program termination Techniques for verifying these properties are presented and illustrated by application to the dining philosophers problem

Functional properties of novel proteins: alfalfa leaf protein

Abstract: Functional properties of protein concentrates from alfalfa leaves (ALP) prepared by several methods were determined. Minimum solubilities occurred around pH 3.5–4; sodium chloride 0.05–0.2M had little effect on minimum solubility. Extraction of the lipids from ALP with acetone decreased solubility slightly; increased the bulk density (2-3-fold); and reduced water and fat absorption capacities by 50% compared to the controls. Both emulsifying activities and emulsion stabilities of ALP samples were generally better than those of soy protein concentrate but poorer than those of soy sodium proteinate i.e., average of 57, 48 and 87 and 60, 50 and 90%, respectively. Emulsifying capacity of ALP samples were reduced following acetone extraction.

The optical constants of several atmospheric aerosol species: Ammonium sulfate, aluminum oxide, and sodium chloride

Abstract: An investigation is conducted of problems which are related to a use of measured optical constants in the simulation of the optical constants of real atmospheric aerosols. The techniques of measuring optical constants are discussed, taking into account transmission measurements through homogeneous and inhomogeneous materials, the immersion of a material in a liquid of a known refractive index, the consideration of the minimum deviation angle of prism measurement, the interference of multiply reflected light, reflectivity measurements, and aspects of mathematical analysis. Graphs show the real and the imaginary part of the refractive index as a function of wavelength for aluminum oxide, NaCl, and ammonium sulfate. Tables are provided for the dispersion parameters and the optical constants.

Hypothesis for origin of planktonic patchiness

Abstract: ALTHOUGH environmental heterogeneity can contribute to the observed patchiness in oceanic planktonic populations, biological interactions between phytoplankton and herbivorous copepods can lead to similar patterns. The phenomenon of spontaneous pattern generation even in a homogeneous environment through the interplay of reaction and movement is a very general property of the class of mathematical ‘reaction–diffusion’ equations used to model such systems, and there are several ways in which such patterns may occur. The result may be either spatiotemporal patterns1 or time-independent spatial patterns. Usually one thinks of diffusion as damping inhomogeneities, and a hypothesis put forward by Steele2 essentially relies on a balance reached between the dehomogenising aspects of local interaction and the homogenising influence of diffusion to produce pattern. On the other hand, it has also been suggested3–6 that in some conditions diffusion can destabilise an otherwise stable interaction (in the manner originally suggested by Turing7) to produce pattern. We have explored5 this further in a nonlinear analysis that describes the final stages of pattern formation, and the resultant calculations provide some insights into the spatial scale of patterns which might arise in this way.

Cinderella's Stepsisters: A Feminist Perspective on Anorexia Nervosa and Bulimia

Abstract: During my early months of internship in 1974 in the mental health section of a university clinic, I encountered Anne, a lively, attractive, and slim young woman of eighteen. For three years she had been on a cycle of gorging and starving which had continued without relief. She felt desperate and out of control. Anne was the first in a series of 138 binger-starvers that I was to treat. It became clear that the exaggerated gorging and purging reported by these patients was part of a self-perpetuating syndrome that was primarily a problem of women.2 The women I interviewed were

Lateral motion of fluorescently labeled acetylcholine receptors in membranes of developing muscle fibers.

Abstract: We have made direct, quantitative measurements of the lateral motion and age-dependent distribution of acetylcholine receptors (AChR) on the surface of rat myotubes in primary culture. AChR were fluorescently marked with tetramethylrhodamine-labeled alpha-bungarotoxin and AChR lateral motion was measured by the fluoresence photobleaching recovery technique. We found two coexisting distinct classes of AChR: (i) mobile, uniformly distributed AChR that appear on all myotubes shortly after fusion from myoblasts; and (ii) immobile, dense, highly granular AChR in patches of 10-60 mum size that appear shortly after fusion and disappear after myotubes have become extensively interconnected. In addition, evidence of turnover of AChR labeled with tetramethylrhodamine-alpha-bungarotoxin is seen in the gradual internalization of surface fluorescence within 36 hr after labeling. The relevance of these results to an understanding of the membrane dynamics and localization of muscle AChR is discussed.

Nitrate Accumulation in Vegetables

Abstract: Publisher Summary This chapter focuses on the accumulation of nitrate in vegetable crops, which is a natural phenomenon resulting from uptake of the nitrate ion in excess of its reduction and subsequent assimilation. Accumulation of nitrate is dependent on and related to the genetic makeup of the plant, the nitrate supplying-power of the soil, and the environmental conditions under which the plant is grown. The chapter focusses on the hazards of nitrate and nitrite to human health. Factors affecting nitrate accumulation are discussed. A straightforward relationship between the nitrate concentration of outer leaves of head lettuce and the amounts of fertilizer-nitrite applied within a given planting date and nitrite source is presented. The chapter concludes by examining nitrate concentrations in vegetables. Nitrate concentrations are lowest in floral parts and increasing concentrations are found in fruit or grain, leaves, roots, and petioles or stems.

Differential files: their application to the maintenance of large databases

Abstract: The representation of a collection of data in terms of its differences from some preestablished point of reference is a basic storage compaction technique which finds wide applicability. This paper describes a differential database representation which is shown to be an efficient method for storing large and volatile databases. The technique confines database modifications to a relatively small area of physical storage and as a result offers two significant operational advantages. First, because the “reference point” for the database is inherently static, it can be simply and efficiently stored. Second, since all modifications to the database are physically localized, the process of backup and the process of recovery are relatively fast and inexpensive.

Circulation and Angular Momentum in the A Phase of Superfluid Helium-3

Abstract: It is shown that the curl of the velocity field generally identified with v/sub s/ in the A phase of superfluid $sup 3$He is entirely determined in the absence of singularities by the spatial gradients of the order-parameter symmetry axis 1. As a simple application of this relation it is argued that, in a texture of cylindrical symmetry in a volume V, the liquid should have a nonvanishing thermal-equilibrium orbital angular momentum of order rho/sub s/Vh/M. (AIP)

Slender-body theory for slow viscous flow

Abstract: Slow flow of a viscous incompressible fluid past a slender body of circular crosssection is treated by the method of matched asymptotic expansions. The main result is an integral equation for the force per unit length exerted on the body by the fluid. The novelty is that the body is permitted to twist and dilate in addition to undergoing the translating, bending and stretching, which have been considered by others. The method of derivation is relatively simple, and the resulting integral equation does not involve the limiting processes which occur in the previous work.

Asymmetry of the perceptual span in reading

Abstract: An on-line computer technique was used to determine whether three skilled readers acquired visual information equally far to the left and right of central vision during fixations in reading. None of the subjects appeared to use visual information more than four character positions to the left of the fixation point (smaller distances were not tested), though all of them acquired visual information substantially further than that to the right. Thus, the region of useful visual information in reading is asymmetric around the fixation point.

Terminal labeling and addition of homopolymer tracts to duplex DNA fragments by terminal deoxynucleotidyl transferase

Abstract: Terminal deoxynucleotidyl transferase, which requires a single-stranded DNA primer under the usual assay conditions, can be made to accept double-stranded DNA as primer for the addition of either rNMP or dNMP, if Mg+2 ion is replaced by Co+2 ion. The priming efficiency in the presence of Co+2 ion with respect to initial rate tested with 2 single-stranded primer, is 5-6 fold higher than that observed with Mg+2 ion. In the presence of Co+2 ion, the primer specificity is altered so that all forms of duplex DNA molecules can be labeled at their unique 3'-ends regardless of whether such ends are staggered or even. Thus, using ribonucleotide incorporation, we have for the first time employed this reaction for sequence analysis of duplex DNA fragments generated by restriction endonuclease cleavages. Furthermore, by using Co+2 ion, it is possible to add a long homopolymer tract of deoxyribonucleotides to the 3'-terminus of double-stranded DNA. Therefore, without prior treatment with lambda exonuclease to expose the 3' terminus as single-stranded primer, this reaction now permits insertion of homopolymer tails at the 3'-ends of all types of DNA molecules for the purpose of in vitro construction of recombinant DNA.