Showing papers by "Cornell University published in 1975"

A vector space model for automatic indexing

Abstract: In a document retrieval, or other pattern matching environment where stored entities (documents) are compared with each other or with incoming patterns (search requests), it appears that the best indexing (property) space is one where each entity lies as far away from the others as possible; in these circumstances the value of an indexing system may be expressible as a function of the density of the object space; in particular, retrieval performance may correlate inversely with space density. An approach based on space density computations is used to choose an optimum indexing vocabulary for a collection of documents. Typical evaluation results are shown, demonstating the usefulness of the model.

The renormalization group: Critical phenomena and the Kondo problem

Abstract: This review covers several topics involving renormalization group ideas. The solution of the $s$-wave Kondo Hamiltonian, describing a single magnetic impurity in a nonmagnetic metal, is explained in detail. See Secs. VII-IX. "Block spin" methods, applied to the two dimensional Ising model, are explained in Sec. VI. The first three sections give a relatively short review of basic renormalization group ideas, mainly in the context of critical phenomena. The relationship of the modern renormalization group to the older problems of divergences in statistical mechanics and field theory and field theoretic renormalization is discussed in Sec. IV. In Sec. V the special case of "marginal variables" is discussed in detail, along with the relationship of the modern renormalization group to its original formulation by Gell-Mann and Low and others.

Hamiltonian Formulation of Wilson's Lattice Gauge Theories

Abstract: Wilson's lattice gauge model is presented as a canonical Hamiltonian theory. The structure of the model is reduced to the interactions of an infinite collection of coupled rigid rotators. The gauge-invariant configuration space consists of a collection of strings with quarks at their ends. The strings are lines of non-Abelian electric flux. In the strong-coupling limit the dynamics is best described in terms of these strings. Quark confinement is a result of the inability to break a string without producing a pair.

The span of the effective stimulus during a fixation in reading.

Abstract: A computer-based eye-movement controlled, display system was developed for the study of perceptual processes in reading. A study was conducted to identify the region from which skilled readers pick up various types of visual information during a fixation while reading. This study involved making display changes, based on eye position, in the text pattern as the subject was in the act of reading from it, and then examining the effects these changes produced on eye behavior. The results indicated that the subjects acquired word-length pattern information at least 12 to 15 character positions to the right of the fixation point, and that this information primarily influenced saccade lengths. Specific letter- and word-shape information were acquired no further than 10 character positions to the right of the fixation point.

A Globally Convergent Method for Nonlinear Programming

Abstract: Recently developd Newton and quasi-Newton methods for nonlinear programming possess only local convergence properties. Adopting the concept of the damped Newton method in unconstrained optimization, we propose a stepsize procedure to maintain monotone decrease of an exact penalty function. In so doing, the convergence of the method is globalized. Keywords: nonlinear programming, global convergence, exact penalty function.

Experimental and theoretical aspects of protein folding.

Abstract: Publisher Summary In the proper environment, a polypeptide chain can fold spontaneously to the three-dimensional structure of a native protein, and despite the possible presence of barriers in conformational space, the chain can find its way around these barriers to reach the structure of lowest free energy. This chapter describes the spontaneous folding of proteins; in vitro complementation of protein fragments; flexibility of proteins in solution: effect of cross-links and ligands, synthetic analogs of proteins; experimental approaches to the study of conformation; and energetic factors determining protein folding. The interatomic interactions within the chain and between the chain and the solvent dictate the folding and the range of the forces involved, is such that near-neighbor interactions are dominant. Folding is envisaged as taking place by the formation of nucleation sites in various parts of the chain, in response to near-neighbor interactions; the various nucleation sites become stabilized, when they are brought into proximity, so that long-range interactions can become operative. However, the development of conformational energy calculation procedures will enable the three-dimensional structure of a native protein to be predicted from the knowledge of its amino acid sequence and its interactions with the solvent in which it is dissolved.

Vertex Packings: Structural Properties and Algorithms.

Abstract: We consider a binary integer programming formulation (VP) for the weighted vertex packing problem in a simple graph. A sufficient “local” optimality condition for (VP) is given and this result is used to derive relations between (VP) and the linear program (VLP) obtained by deleting the integrality restrictions in (VP). Our most striking result is that those variables which assume binary values in an optimum (VLP) solution retain the same values in an optimum (VP) solution. This result is of interest because variables are (0, 1/2, 1). valued in basic feasible solutions to (VLP) and (VLP) can be solved by a “good” algorithm. This relationship and other optimality conditions are incorporated into an implicit enumeration algorithm for solving (VP). Some computational experience is reported.

Saddle points and instability of nonlinear hyperbolic equations

Abstract: A number of authors have investigated conditions under which weak solutions of the initial-boundary value problem for the nonlinear wave equation will blow up in a finite time. For certain classes of nonlinearities sharp results are derived in this paper. Extensions to parabolic and to abstract operator equations are also given.

Spectrum of Charmed Quark-Antiquark Bound States

Abstract: The discovery of narrow resonances at 3.1 and 3.7 GeV and their interpretation as charmed quark-antiquark bound states suggest additional narrow states between 3.0 and 4.3 GeV. A model which incorporates quark confinement is used to determine the quantum numbers and estimate masses and decay widths of these states. Their existence should be revealed by $\ensuremath{\gamma}$-ray transitions among them.

The Psychology of Reading

Abstract: In this book, two psychologists apply principles of cognitive psychology to understanding reading. Unlike most other books on the subject, this one presents a consistent theoretical point of view and applies it to the acquisition of reading and what the skilled reader does.The first part of The Psychology of Reading covers perceptual learning, the development of cognitive strategies, the development of language, the nature of writing systems, and an extensive review of the research on word recognition.In the second part of the book, the authors look closely at abilities that children bring to school before learning to read. They describe the acquisition of initial reading skills and transition to skilled reading, the nature of the reading process in adult readers, and the ways people learn from reading.The book's third part takes up questions people frequently ask about reading -- such as reading by deaf children, dyslexia, the influence of nonstandard dialects on learning to read, comparison of reading achievement across different nations and different languages, and the debatable virtues of "speed reading." The authors conclude that reading cannot be understood simply as associative learning -- that is, the learning of an arbitrary code connecting written symbols and their sounds. Reading involves higher-level mental processes such as the discovery of rules and order, and the extraction of structured, meaningful information.

Optical studies of the vibrational properties of disordered solids

Abstract: Since approximately 1950 an increasing portion of experimental solid state physics research has been concerned with studying defects in crystals. This trend might appear to be a rather belated recognition that most of the materials we come into contact with have a random structure. In fact the theoretical understanding and controlled preparation of compounds with defects or random structure has been very slow in developing. The present paper examines and reviews our knowledge of the lattice vibrations associated with defects. The coverage is extremely broad, as shown by the table of contents. It includes localized and resonant modes of isolated defects as well as the modes in highly disordered mixed crystals and glasses. It is primarily a review of experimental work but theoretical results are included where the latter explain or predict significant features. In order to be self-contained several sections of the paper deal entirely with theoretical matters. There is a chapter on explicit solutions of the linear chain vibration problem and a short chapter on Green's function methods. The review emphasizes the infrared absorption and Raman scattering of defects. This is simply because other techniques have not yielded nearly so much information. Neutron scattering and electron tunneling are referred to only where they have shed light on certain systems. Extensive tables of defects and mode frequencies are included for each type of solid. The major solids which are reviewed include semiconductors, ionic compounds, organic compounds, and amorphous insulators.

Subduction and Accretion in Trenches

Abstract: Although the reality of subduction has been greatly strengthened by recent investigations, there is little information dealing with the mechanisms by which material is subducted or accreted to the upper plate. An attempt to determine the gross evolution of subduction zones has been made, assuming that geographic variations in morphologic and geophysical characteristics of trenches can be transformed into temporal trends. Deformation associated with subduction extends across the lower trench slope, from the trench axis to the trench-slope break. This region is a rising tectonic element, but the upper slope is a subsiding region of sediment accumulation. An upper slope discontinuity separates this zone of subsidence from the rising frontal-arc block. Examination of very young trenches indicates that the upper-slope discontinuity marks the upper section of the continental or insular slope that existed before a subduction pulse began. As material is fed to the subduction zone, the distance between the upper slope discontinuity and the trench increases, and an accretionary prism develops, but its shape depends on the relative rates of sediment feed from the arc and from the offshore basin. The lower boundary of the accretionary prism is the upper section of the seismic zone, which apparently widens and flattens as one or more accretionary prisms accumulate. The sediment cover on the downgoing plate and some of the igneous crust appears to be stripped off the plate before it reaches a point beneath the volcanic chain. Turbiditic sediments deposited in the trench axis are preferentially sheared off the underlying pelagic sediments and are accreted to the lower trench wall. The pelagic sediments and crustal material are probably accreted at deeper structural levels. Where turbidites overlie pelagic sediments in the trench axis, the turbidites are stripped off in fold packets with axial surfaces having very low dips. These dewatered and rigidified structural units move up the lower slope, as subsequent packets are accreted. In trenches that subduct lithosphere carrying very thin pelagic sediment covers, accretion and uplift of crustal slabs seem to occur as topographic irregularities enter the trench.

Energy Flow and Nutrient Cycling in Salamander Populations in the Hubbard Brook Experimental Forest, New Hampshire

Abstract: Energy flow through salamander populations in the Hubbard Brook Ecosystem is about 11,000 kcal/ha yr (=46,000 kJ/ha yr). This is approx. = 0.02% of the net primary productivity, and is approx. = 20% of the energy flow through bird and mammal populations. Salamanders are efficient (60%) at converting ingested energy into new tissue and produce more new tissue annually than do bird populations. Salamanders are insignificant agents as sinks for nutrients or as agents for nutrient cycling in the ecosystem. Sodium is the possible exception, as an amount equivalent to >8% of the Na in annual litter fall passes through salamander populations; all other nutrients (Ca, Mg, K, P, N, S, and Zn) are that of most of their invertebrate prey. There is some evidence that invertebrates rich in Ca content, such as snails and mites, are necessary components of the diet of salamanders. Salamander tissue is higher in protein content than that of birds and mammals and represents a source of high-quality energy for potential predators. Salamanders have restricted home ranges and are not significant agents in the movement of nutrients into or out of the system.

Empathy and attribution: Turning observers into actors.

Abstract: A laboratory experiment was conducted to test Jones and Nisbett's information-processing explanation of the often-observed tendency for individuals (actors) to provide relatively more situational and less dispositional causal attributions for their behavior than those provided by observers of the same behavior. According to this explanation, aspects of the situation are phenomenologically more salient for actors, whereas characteristics of the actor and his behavior are more salient for observers. To test this explanation, the phenomenological perspective of observers are altered without making available any additional information. Subjects watched a videotape of a get-acquainted conversation after instructions either to observe a target conversant or to empathize with her. As predicted, taking the perspective of the target through empathy resulted in attributions that were relatively more situational and less dispositional than attributions provided by standard observers. The results support Jones and Nisbett's information-processing explanation of actor-observer attributional differences, and shed additional light on the process of empathy.

The expansion of a plasma into a vacuum

Abstract: This paper reports calculations of the collision-free expansion of a semi-infinite plasma It is shown that the ion front is accelerated to velocities comparable with the thermal velocity of the electrons

The assumptions and rationales of a computer model of phytoplankton population dynamics1

Abstract: Predictions of phytoplankton growth dynamics and nutrient assimilation by a computer simulation model are consistent with studies of field and laboratory populations. The model simulates population dynamics and gross physiology of phytoplankton species in the epilimnion of a lake where algal growth is subject to temperature, light, and nutrient constraints and includes luxury consumption, end-product inhibition of both carbon fixation and nutrient uptake, and species-specific differential efficiencies of nutrient assimilation. C : P, C : N, and N : P ratios of the algal cells respond to changes in external nutrient conditions, and nutrient storage by the cells permits biological effects of nutrient pulses to be evident long after assimilation of dissolved nutrients forces the pulses to decline. Species succession results when abundances of specific taxa decline due to such factors as sinking or grazing, which assume overriding importance when cell division rates arc slowed by chemical or physical limitations. The physiological tenets and limiting assumptions of the model have been used to formulate patterns of competition among

Carbohydrate and energy metabolism in perinatal rat brain: relation to survival in anoxia.

Abstract: — The ability of rats of different ages to survive exposure to anoxia was correlated with rates of high energy phosphate consumption (metabolic rates) of the fore-brain. Fetal rats at term, delivered by hysterotomy following maternal decapitation, survived in nitrogen at 37°C twice as long as 1-day-old neo-nates, 5 times longer than 7-day-old rats, and 45 times longer than adults. During ischemia induced by decapitation, the cerebral concentrations of the labile energy reserves (ATP, ADP, P-creatine, glucose and glycogen) and of lactate were determined in fetuses, 1- and 7-day post-natal animals. From the changes, the cerebral energy use rates were calculated to be 1·57 mmol/kg/min in fetuses, 1·33 mmol/kg/min in 1-day-olds and 2·58 mmol/kg/min in 7-day-olds. Maximal rates of lactate accumulation during ischemia, as a measure of glycolytic capacity, were comparable in fetuses and neonates, but were about twice as great in 7-day-old rats. It is concluded that in post-natal animals survival in anoxia and cerebral energy consumption are inversely, and nearly quantitatively, related. However, the reduced cerebral energy requirement cannot entirely account for the greater anoxic resistance of fetuses.

On the Uniqueness of the Shapley Value

Abstract: L.S. Shapley [1953] showed that there is a unique value defined on the classD of all superadditive cooperative games in characteristic function form (over a finite player setN) which satisfies certain intuitively plausible axioms. Moreover, he raised the question whether an axiomatic foundation could be obtained for a value (not necessarily theShapley value) in the context of the subclassC (respectivelyC′, C″) of simple (respectively simple monotonic, simple superadditive) gamesalone. This paper shows that it is possible to do this. Theorem I gives a new simple proof ofShapley's theorem for the classG ofall games (not necessarily superadditive) overN. The proof contains a procedure for showing that the axioms also uniquely specify theShapley value when they are restricted to certain subclasses ofG, e.g.,C. In addition it provides insight intoShapley's theorem forD itself. Restricted toC′ orC″, Shapley's axioms donot specify a unique value. However it is shown in theorem II that, with a reasonable variant of one of his axioms, a unique value is obtained and, fortunately, it is just theShapley value again.

The Ovarian Cycle of the Bitch: Plasma Estrogen, LH and Progesterone

Abstract: Plasma levels of luteinizing hormone (LH) progesterone and estrogen were determined in pregnant and nonpregnant cycles of female beagle dogs. Mean basal LH levels during estrus and proestrus were 1.4 + or -.1 ng/ml and peaked at 7.5 + or -.8 ng/ml on the 1st day of estru s. Preovulatory increases in progesterone and LH appeared to be temporally correlated and were significantly elevated by the 2nd day of estrus (p less than .001). Progesterone levels reached their maximum on the 25th day of estrus (22.9 + or -2.7). Estrogen levles increased from 26 + or -4 on Day 10 prior to the LH peak to 62 + or -4 pg/ml 1 day before the LH peak. Once the LH peak was established estrogen levels fell rapidly. In the luteal phases of 12 pregnant and 10 nonpregnant cycles there were no marked differences in mean maximum progesterone levels the ranges of individual maximum levels or the time of their occurrence. After Day 30 progesterone levels declined gradually and were significantly (p less than .001) variable in nonpregnant cycles compared with pregnant cycles once progesterone levels dropped below 1 ng/ml. Progesterone levels showed significant (p less than .05) daily changes during the 2 days prior to parturition. Plasma Estrogen levels were constant in nonpregnant cycles but significantly (p less than .01) increased during the 3 weeks prior to parturition. The results suggest that plasma estrogen initiates or potentiates the preovulatory release of LH that the early preovulatory release of progesterone may encourage the LH peak surge and the onset of behavioral estrus and that mechanisms exist that maintain elevated levels of plasma progesterone throughout pregnancy.

Differential staining of the satellite regions of human acrocentric chromosomes

Abstract: Es wird eine neue Ammoniak-Silber-Methode fur das Farben menschlicher Chromosomen in der Metaphase beschrieben, wodurch die Satelliten aller 10 akrozentrischen Chromosomen zu unterscheiden sind

Sites of Organic Acid Production and Patterns of Digesta Movement in the Gastrointestinal Tract of Dogs

Abstract: Twelve swine were used to assess the movement of fluid and particulate digesta through their gastrointestinal tracts and to determine the diurnal variations in organic acid levels for various segments of the tract. Animals were fed twice daily at 12-hour intervals. Fluid (polyethylene glycol and chromium-labeled ethylenediamine-tetraacetic acid) and particulate markers (2 mm OD, and 2 mm and 1 and 2 cm long) were administration of markers. The gastrointestinal tract was divided into 12 segments for measurements of markers, pH, volatile fatty acids (VFA), and lactic acid (LA) contents. The data indicated a rapid evacuation of the fluid and the smaller particles from the stomach and their relatively rapid passage through the small intestine and cecum. There was, however, prolonged retention of both fluid and particulate markers first in the ascending and then in the descending colon. Larger particles (2 cm) were retained in the stomach throughout much of the 60-hour experimental period. LA levels were observed 8 hours postfeeding. The highest levels of VFA in gastric contents averaged 20 mmoles/liter. Gastrointestinal pH values showed significant changes with time postfeeding only within the stomach, where they did not reflect the changes in LA of VFA concentrations. VFA constituted 92% of the organic acids present in the large intestine. Their concentrations varied markedly with time (150-230 mmoles/liter), but the VFA at all times constituted the major anions in the large intestinal contents. The results demonstrated that digesta can be retained for prolonged periods of time in that swine stomach and colon. The high concentrations of organic acids also indicated that substantial degrees of microbial digestion of carbohydrates occurred at both sites.