Showing papers by "Cornell University published in 1985"

Algorithms for the rapid simulation of Rutherford backscattering spectra

Abstract: A computer program which simulates Rutherford backscattering spectra is currently in use at Cornell University and other institutions. Straggling and detector resolution are among the effects included. Samples are considered to be made up of a finite number of layers, each with uniform composition. The emphasis in the mathematics is on accuracy beyond that of iterated surface approximation methods. Thicker layers can thus be analyzed without a net loss in accuracy. The mathematical description of the sample can then have fewer layers and fewer calculations are required. This paper provides estimates of the number of arithmetic operations used by the program for any simulation to demonstrate the tradeoffs between accuracy, computation time, and algorithm sophistication.

Isolation and characterization of rat and human glyceraldehyde-3-phosphate dehydrogenase cDNAs: genomic complexity and molecular evolution of the gene

Abstract: Full length cDNAs encoding the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from rat and man have been isolated and sequenced. Many GAPDH gene-related sequences have been found in both genomes based on genomic blot hybridization analysis. Only one functional gene product is known. Results from genomic library screenings suggest that there are 300-400 copies of these sequences in the rat genome and approximately 100 in the human genome. Some of these related sequences have been shown to be processed pseudogenes. We have isolated several rat cDNA clones corresponding to these pseudogenes indicating that some pseudogenes are transcribed. Rat and human cDNAs are 89% homologous in the coding region, and 76% homologous in the first 100 base pairs of the 3'-noncoding region. Comparison of these two cDNA sequences with those of the chicken, Drosophila and yeast genes allows the analysis of the evolution of the GAPDH genes in detail.

Interfacial charge-spin coupling: Injection and detection of spin magnetization in metals.

Abstract: The strong inequivalence of spin-up and spin-down subbands in a ferromagnet causes a coupling between the charge and spin transport across the interface of a ferromagnetic and a contiguous paramagnetic metal. This allows the use of sensitive electronic measurements to probe spin transport. Application of small static magnetic fields results in a Hanle effect which permits determination of the spin-relaxation time ${\mathrm{T}}_{2}$. The unique features of the method should make it applicable to a wide range of studies.

Choosing the Right Pond: Human Behavior and the Quest for Status

Abstract: Is it better to be a big frog in a small pond or a small frog in a big pond? In this lively and original book, the author argues persuasively that people's concerns about status permeate and profoundly alter a broad range of human behaviour. He takes issue with his fellow economists for too often neglecting fundamental elements in human nature in their study of how people make basic economic choices.

The geometry of phonological features

Abstract: On the notion ‘feature bundle’ The study of the phonological aspect of human speech has advanced greatly over the past decades as a result of one of the fundamental discoveries of modern linguistics – the fact that phonological segments, or phonemes, are not the ultimate constituents of phonological analysis, but factor into smaller, simultaneous properties or features. The apparently vast number of speech sounds found in the languages of the world turn out to be surface-level realisations of a limited number of combinations of a very small set of such features – some twenty or so, in current analyses. This conclusion is strongly supported by the similar patterning of speech sounds in language after language, and by many extragrammatical features of language use, such as patterns of acquisition, language disablement and language change.

HTLV-III infection in brains of children and adults with AIDS encephalopathy

Abstract: Unexplained debilitating dementia or encephalopathy occurs frequently in adults and children with the acquired immune deficiency syndrome (AIDS). Brains from 15 individuals with AIDS and encephalopathy were examined by Southern analysis and in situ hybridization for the presence of human T-cell leukemia (lymphotropic) virus type III (HTLV-III), the virus believed to be the causative agent of AIDS. HTLV-III DNA was detected in the brains of five patients, and viral-specific RNA was detected in four of these. In view of these findings and the recent demonstration of morphologic and genetic relatedness between HTLV-III and visna virus, a lentivirus that causes a chronic degenerative neurologic disease in sheep, HTLV-III should be evaluated further as a possible cause of AIDS encephalopathy.

Glucocorticoids potentiate ischemic injury to neurons: therapeutic implications.

Abstract: Sustained exposure to glucocorticoids, the adrenocortical stress hormones, is toxic to neurons, and such toxicity appears to play a role in neuron loss during aging. Previous work has shown that glucocorticoids compromise the capacity of neurons to survive a variety of metabolic insults. This report extends those observations by showing that ischemic injury to neurons in rat brain is also potentiated by exposure to high physiological titers of glucocorticoids and is attenuated by adrenalectomy. The synergy between ischemic and glucocorticoid brain injury was seen even when glucocorticoid levels were manipulated after the ischemic insult. Pharmacological interventions that diminish the adrenocortical stress response may improve neurological outcome from stroke or cardiac arrest.

Effect of friction on electron transfer in biomolecules

Abstract: In biological and chemical electron transfer, a nuclear reaction coordinate is coupled to other nuclear and/or ‘‘solvent’’ coordinates. This coupling, or friction, if strong enough, may substantially slow down motion along the reaction coordinate, and thus vitiate the assumption of electron transfer being nonadiabatic with respect to the nuclei. Here, a simple, fully quantum mechanical model for electron transfer using a one mode treatment which incorporates this coupling is studied. Path integral methods are used to study the dependence of the reaction rate on friction, and the limits of the moderate and the high friction are analyzed in detail. The first limit will prevail if the reaction coordinate is, e.g., an underdamped nuclear vibration, whereas the second limit will prevail if it corresponds to a slow or diffusive degree of freedom. In the high‐friction limit, the reaction rate is explicitly shown to vary between the nonadiabatic and adiabatic expressions as the tunneling matrix element and/or the friction are varied. Starting from a path integral expression for the time evolution of the reduced density matrix for the electron and reaction coordinate, a Fokker–Planck equation is obtained which reduces in the high‐friction limit to a Smoluchowski equation similar to one solved by Zusman.

Diffusion of autoinducer is involved in regulation of the Vibrio fischeri luminescence system.

Abstract: The enzymes for luminescence in Vibrio fischeri are induced by the accumulation of a species-specific metabolite (autoinducer) in the culture medium Tritium-labeled autoinducer was used to study the mechanism of autoinduction When 3H-autoinducer was added to suspensions of V fischeri or Escherichia coli, cellular concentrations equaled external concentrations For V fischeri, equilibration of 3H-autoinducer was rapid (within 20 s), and greater than 90% of the cellular tritium remained in unmodified autoinducer When V fischeri or E coli cells containing 3H-autoinducer were transferred to autoinducer-free buffer, 85 to 995% of the radiotracer escaped from the cells, depending on the strain Concentrations of autoinducer as low as 10 nM, which is equivalent to 1 or 2 molecules per cell, were sufficient for induction, and the maximal response to autoinducer occurred at about 200 nM If external autoinducer concentrations were decreased to below 10 nM after induction had commenced, the induction response did not continue Based on this study, a model for autoinduction is described wherein autoinducer association with cells is by simple diffusion and binding of autoinducer to its active site is reversible

NP is as easy as detecting unique solutions

Abstract: For all known NP-complete problems the number of solutions in instances having solutions may vary over an exponentially large range. Furthermore, most of the well-known ones, such as satisfiability, are parsimoniously interreducible, and these can have any number of solutions between zero and an exponentially large number. It is natural to ask whether the inherent intractability of NP-complete problems is caused by this wide variation. In this paper we give a negative answer to this using randomized reductions. We show that the problems of distinguishing between instances of SAT having zero or one solution, or finding solutions to instances of SAT having unique solutions, are as hard as SAT itself. Several corollaries about the difficulty of specific problems follow. For example if the parity of the number of solutions of SAT can be computed in RP then NP = RP. Some further problems can be shown to be hard for NP or DP via randomized reductions.

Asynchronous consensus and broadcast protocols

Abstract: A consensus protocol enables a system of n asynchronous processes, some of which are faulty, to reach agreement. There are two kinds of faulty processes: fail-stop processes that can only die and malicious processes that can also send false messages. The class of asynchronous systems with fair schedulers is defined, and consensus protocols that terminate with probability 1 for these systems are investigated. With fail-stop processes, it is shown that ⌈(n + 1)/2⌉ correct processes are necessary and sufficient to reach agreement. In the malicious case, it is shown that ⌈(2n + 1)/3⌉ correct processes are necessary and sufficient to reach agreement. This is contrasted with an earlier result, stating that there is no consensus protocol for the fail-stop case that always terminates within a bounded number of steps, even if only one process can fail. The possibility of reliable broadcast (Byzantine Agreement) in asynchronous systems is also investigated. Asynchronous Byzantine Agreement is defined, and it is shown that ⌈(2n + 1)/3⌉ correct processes are necessary and sufficient to achieve it.

Projections from the nucleus tractus solitarii to the rostral ventrolateral medulla

Abstract: Projections from the nucleus tractus solitarii (NTS) to autonomic control regions of the ventrolateral medulla, particularly the nucleus reticularis rostroventrolateralis (RVL), which serves as a tonic vasomotor center, were analyzed in rat by anterograde, retrograde, and combined axonal transport techniques. Autonomic portions of the NTS, including its commissural, dorsal, intermediate, interstitial, ventral, and ventrolateral subnuclei directly project to RVL as well as to other regions of the ventrolateral medulla. The projections are organized topographically. Rostrally, a small cluster of neurons in the intermediate third of NTS, the subnucleus centralis, and neurons in proximity to the solitary tract selectively innervate neurons in the retrofacial nucleus and nucleus ambiguus. Neurons generally located in more caudal and lateral sites in the NTS innervate the caudal ventrolateral medulla (CVL). The RVL, CVL, and nucleus retroambiguus are interconnected. A combined retrograde and anterograde transport technique was developed so as to prove that projections from the NTS to the ventrolateral medulla specifically innervate the region of RVL containing neurons projecting to the thoracic spinal cord or the region of the nucleus containing vagal preganglionic neurons. When the retrograde tracer, fast blue, was injected into the thoracic spinal cord, and wheat germ agglutinin-conjugate horseradish peroxidase (HRP) was injected into the NTS, anterogradely labeled terminals from the NTS surrounded the retrogradely labeled neurons in the RVL and in the nucleus retroambiguus in the caudal medulla. Among the bulbospinal neurons in the RVL innervated by the NTS were adrenaline-synthesizing neurons of the C1 group. When fast blue was applied to the cervical vagus, and HRP was injected into the NTS, anterogradely labeled terminals from the NTS surrounded retrogradely labeled neurons in the rostral dorsal motor nucleus of the vagus, the region of the nucleus ambiguus, the retrofacial nucleus, and the dorsal portion of the RVL, a region previously shown to contain cardiac vagal preganglionic neurons. This combined anterograde and retrograde transport technique provides a useful method for tracing disynaptic connections in the brain. These data suggest that the RVL is part of a complex of visceral output regions in the ventrolateral medulla, all of which receive afferent projections from autonomic portions of the NTS. Bulbospinal neurons in the RVL, in particular the C1 adrenaline neurons, may provide a portion of the anatomic substrate of the baroreceptor and other visceral reflexes.

Projections to the subcortical forebrain from anatomically defined regions of the medial geniculate body in the rat.

Abstract: Although the auditory cortex is believed to be the principal efferent target of the medial geniculate body (MG), our recent behavioral studies indicate that in rats the conditioned coupling of emotional responses to an acoustic stimulus is mediated by subcortical projections of the MG. In the present study we have therefore used WGA-HRP as an anterograde and retrograde axonal marker to (1) define the full range of subcortical efferent projections of the MG; (2) identify the cells of origin within the MG of each projection; and (3) determine whether the subregions of the MG that project to subcortical areas receive inputs from acoustic relay nuclei of the mid-brain, particularly the inferior colliculus. The rat MG was first parcelled into three major cytoarchitectural areas: the ventral, medial, and dorsal divisions. The suprageniculate nucleus, located within the body of the MG just dorsal to the medial division, was also identified. Efferent projections of the MG were determined by combined anterograde and retrograde tracing methods. Injections of WGA-HRP in the MG produced anterograde transport to cortex and several subcortical areas, including the posterior caudate-putamen and amygdala, the ventromedial nucleus of the hypothalamus, and the subparafascicular thalamic nucleus. The cells of origin of the subcortical projections were then mapped retrogradely after injections in the anterogradely labeled areas. Injections in the caudate-putamen or amygdala retrogradely labeled the medial division of the MG and the suprageniculate nucleus, as well as several adjacent areas of the posterior thalamus surrounding the MG. In contrast, injections in the ventromedial nucleus of the hypothalamus or the subparafascicular thalamic nucleus only produced labeling in the areas surrounding MG. Afferents to MG from the inferior colliculus were then identified. The central nucleus of the inferior colliculus, the main lemniscal acoustic relay nucleus in the midbrain, was found to project to the ventral and medial divisions of the MG. In contrast, the dorsal cortex and external nucleus of the inferior colliculus project to each division of the MG and to several additional nuclei in adjacent areas of the posterior thalamus. These data demonstrate that the medial division of MG, the suprageniculate nucleus, and immediately adjacent areas of the posterior thalamus provide a direct linkage between auditory neurons in the inferior colliculus and subcortical areas of the forebrain and thereby support the view that thalamic sensory nuclei relay afferent signals to subcortical as well as cortical areas.

The hemi-cube: a radiosity solution for complex environments

Abstract: This paper presents a comprehensive method to calculate object to object diffuse reflections within complex environments containing hidden surfaces and shadows. In essence, each object in the environment is treated as a secondary light source. The method provides an accurate representation of the "diffuse" and "ambient" terms found in typical image synthesis algorithms. The phenomena of "color bleeding" from one surface to another, shading within shadow envelopes, and penumbras along shadow boundaries are accurately reproduced. Additional advantages result because computations are indepedent of viewer position. This allows the efficient rendering of multiple views of the same scene for dynamic sequences. Light sources can be modulated and object reflectivities can be changed, with minimal extra computation. The procedures extend the radiosity method beyond the bounds previously imposed.

Selective Neuronal Vulnerability: Morphological and Molecular Characteristics*

Abstract: Publisher Summary This chapter discusses the distinct morphological patterns of ischemic brain injury and discusses the possible pathogenesis of ischemic damage to selectively vulnerable brain neurons. The neuropathologists have defined at least three morphologically distinct varieties of ischemic brain damage, including autolysis, infarction, and selective neuronal necrosis (SNN). A fourth pattern may be added as generalized neuronal necrosis (GNN). Autolytic brain damage is characterized by chromatin clumping, mitochondrial swelling, and dispersion of ribosomes uniformly throughout all the brain cells. Such changes are the consequence of terminal ischemia of the brain without reperfusion and are seen in post-mortem brain tissue. Infarction has been defined by the neuropathologists as an area of pannecrosis—that is, irreversible damage to all cell types, including astroglia and endothelial cells within a specific vascular territory of the brain. The transition zone between an area of cerebral infarction and the entirely normal brain tissue frequently contains necrotic neurons but normal astroglia. Such border zone necrosis of neurons develops irrespective of the brain region, and therefore, differs from selective neuronal necrosis that occurs only in those populations of vulnerable neurons.

An Introduction to Empirical Bayes Data Analysis

Abstract: Empirical Bayes methods have been shown to be powerful data-analysis tools in recent years. The empirical Bayes model is much richer than either the classical or the ordinary Bayes model and often provides superior estimates of parameters. An introduction to some empirical Bayes methods is given, and these methods are illustrated with two examples.

98%-Effective Integer-Ratio Lot-Sizing for One-Warehouse Multi-Retailer Systems

Abstract: A warehouse supplies N retailers. Constant external demand occurs at each retailer, and shortages are not allowed. There are linear holding costs and fixed costs for ordering at the warehouse and at each retailer. The goal is to minimize the long-run average cost over an infinite time horizon. We define a new class of policies for this problem whose simple structure facilitates both computation and implementation. The cost of a policy that is optimal within this class is shown to be within 2% of the cost of an optimal policy for the original problem, in the worst case. Such a policy can be computed in ON log N time.