Showing papers by "Cornell University published in 1989"

Preliminary report: Effect of encainide and flecainide on mortality in a randomized trial of arrhythmia suppression after myocardial infarction

Abstract: The occurrence of ventricular premature depolarizations in survivors of myocardial infarction is a risk factor for subsequent sudden death, but whether antiarrhythmic therapy reduces the risk is not known. The Cardiac Arrhythmia Suppression Trial (CAST) is evaluating the effect of antiarrhythmic therapy (encainide, flecainide, or moricizine) in patients with asymptomatic or mildly symptomatic ventricular arrhythmia (six or more ventricular premature beats per hour) after myocardial infarction. As of March 30, 1989, 2309 patients had been recruited for the initial drug-titration phase of the study: 1727 (75 percent) had initial suppression of their arrhythmia (as assessed by Holter recording) through the use of one of the three study drugs and had been randomly assigned to receive active drug or placebo. During an average of 10 months of follow-up, the patients treated with active drug had a higher rate of death from arrhythmia than the patients assigned to placebo. Encainide and flecainide accounted for the excess of deaths from arrhythmia and nonfatal cardiac arrests (33 of 730 patients taking encainide or flecainide [4.5 percent]; 9 of 725 taking placebo [1.2 percent]; relative risk, 3.6; 95 percent confidence interval, 1.7 to 8.5). They also accounted for the higher total mortality (56 of 730 [7.7 percent] and 22 of 725 [3.0 percent], respectively; relative risk, 2.5; 95 percent confidence interval, 1.6 to 4.5). Because of these results, the part of the trial involving encainide and flecainide has been discontinued. We conclude that neither encainide nor flecainide should be used in the treatment of patients with asymptomatic or minimally symptomatic ventricular arrhythmia after myocardial infarction, even though these drugs may be effective initially in suppressing ventricular arrhythmia. Whether these results apply to other patients who might be candidates for antiarrhythmic therapy is unknown.

Thermal boundary resistance

Abstract: The thermal boundary resistance present at interfaces between helium and solids (Kapitza resistance) and the thermal boundary resistance at interfaces between two solids are discussed for temperatures above 0.1 K. The apparent qualitative differences in the behavior of the boundary resistance at these two types of interfaces can be understood within the context of two limiting models of the boundary resistance, the acoustic mismatch model, which assumes no scattering, and the diffuse mismatch model, which assumes that all phonons incident on the interface will scatter. If the acoustic impedances of the two media in contact are very different, as is the case for helium (liquid or solid) in contact with a solid, then phonon scattering at the interface will reduce the boundary resistance. In the limiting case of diffuse mismatch, this reduction is typically over 2 orders of magnitude. Phonons are very sensitive to surface defects, and therefore the Kapitza resistance is very sensitive to the condition of the interface. For typical solid-solid interfaces, at which the acoustic impedances are less different, the influence of diffuse scattering is relatively small; even for the two limiting cases of acoustic mismatch and diffuse mismatch the predicted boundary resistances differ by very little (\ensuremath{\lesssim} 30%). Consequently, the experimentally determined values are expected to be rather insensitive to the condition of the interface, in agreement with recent observations. Subsurface (bulk) disorder and imperfect physical contact between the solids play far more important roles and led to the irreproducibilities observed in the early measurements of the solid-solid thermal boundary resistance.

Organizational Theories: Some Criteria for Evaluation

Abstract: A set of ground rules and vocabulary to facilitate focused discussion about the structure of organization and management theories are proposed. The many previous efforts at defining and evaluating theory help establish criteria for theory construction and evaluation. In the establishment of these criteria, description is distinguished from theory, and a matrix of criteria for evaluating the variables, constructs, and relationships that together compose a theory is developed. The proposed matrix may be useful both for defining the necessary components of good theory and for evaluating and/or comparing the quality of alternative theories. Finally, a discussion of the way theories fit together to give a somewhat broader picture of empirical reality reveals the lines of tension between the two main criteria for evaluating theory.

Concepts, Kinds, and Cognitive Development

Abstract: In "Concepts, Kinds, and Cognitive Development, "Frank Keil provides a coherent account of how concepts and word meanings develop in children, adding to our understanding of the representational nature of concepts and word meanings at all ages.Keil argues that it is impossible to adequately understand the nature of conceptual representation without also considering the issue of learning. Weaving together issues in cognitive development, philosophy, and cognitive psychology, he reconciles numerous theories, backed by empirical evidence from nominal kinds studies, natural-kinds studies, and studies of fundamental categorical distinctions. He shows that all this evidence, when put together, leads to a better understanding of semantic and conceptual development.The book opens with an analysis of the problems of modeling qualitative changes in conceptual development, investigating how concepts of natural kinds, nominal kinds, and artifacts evolve.The studies on nominal kinds document a powerful and unambiguous developmental pattern indicating a shift from a reliance on global tabulations of characteristic features to what appears to be a small set of defining ones. The studies on natural kinds document an analogous shift toward a core theory instead of simple definition. Both sets of studies are strongly supported by cross cultural data.While these patterns seem to suggest that the young child organizes concepts according to characteristic features, Kell argues that there is a framework of conceptual categories and causal beliefs that enables even very young children to understand kinds at a deeper, theoretically guided, level. This account suggests a new way of understanding qualitative change and carries strong implications for how concepts are represented at any point in development.Frank Keil is Professor of Psychology at Cornell University and Co Director of the Cognitive Studies Program at Cornell. "Concepts, Kinds, and Cognitive Development" is included in the series Learning, Development, and Conceptual Change. A Bradford Book.

Nitric oxide. A macrophage product responsible for cytostasis and respiratory inhibition in tumor target cells

Abstract: A metabolic pathway of activated macrophages (M phi) involving oxidation of the guanido nitrogens of L-arginine is required for inhibition of growth and respiration of some target cells. The goal of this study was to identify the M phi metabolite(s) that induce these injuries. The stable products of the L-arginine pathway, NO2- and NO3-, were incapable of causing cytostasis under coculture conditions. However, NO2- became cytostatic upon mild acidification, which favors its transformation into nitrogen oxides of greater reactivity. This suggested that NO. (and/or NO2), recently identified as an M phi metabolite of L-arginine, could be a mediator. Authentic NO. caused cytostasis and respiratory inhibition in L1210 cells in a dose-dependent manner. The mitochondrial lesions caused by NO. were confined to complex 1 and 2, a pattern of injury identical to that seen after coculture with activated M phi. Inclusion of NO. scavenger systems prevented cytostasis from developing in M phi-L1210 cocultures. Thus, M phi-generated NO. can account for L-arginine-dependent cytostasis and respiratory inhibition.

Visualization and Interpretation of Plant Isozymes

Abstract: Gel electrophoresis of proteins has become a standard and powerful research tool for application in a multitude of biological disciplines One form of protein electrophoresis, isozyme analysis, has become particularly prominent in systematic and evolutionary biology as well as agronomy (Tanksley and Orton, 1983) Isozymes, or multiple molecular forms of enzymes, are enzymes that share a common substrate but differ in electrophoretic mobility (Markert and Moller, 1959) They are revealed when tissue extracts are subjected to electrophoresis in various types of gels and subsequently submersed in solutions containing enzyme-specific stains Genetic analysis may indicate that some of the variant electromorphs are encoded by alternate alleles at a single locus, in which case the allelic products are termed allozymes (Prakash et al, 1969) Data retrieved from electrophoretic gels consist of the number and relative mobilities of various enzyme products, which with appropriate genetic analyses become transformed into single or multilocus genotypes for each individual analyzed Reasons are many for the popularity of electrophoretic data (Avise, 1975; Gottlieb, 1977; Crawford, 1983), but foremost among these is that isozymes provide a series of readily scored, single-gene markers

RFLP Mapping in Plant Breeding: New Tools for an Old Science

Abstract: Breeders have traditionally improved plant varieties by selecting on the basis of phenotype. Now restriction fragment length polymorphism (RFLP) linkage maps are being constructed for most major crop plants and these maps provide a more direct method for selecting desirable genes via their linkage to easily detectable RFLP markers. The integration of RFLP techniques into plant breeding promises to: (1) Expedite the movement of desirable genes among varieties, (2) Allow the transfer of novel genes from related wild species, (3) Make possible the analysis of complex polygenic characters as ensembles of single Mendelian factors, and (4) Establish genetic relationships between sexually incompatible crop plants. In the future, high density RFLP maps may also make it possible to clone genes whose products are unknown, such as genes for disease resistance or stress tolerance.

Morphogenesis of the polarized epithelial cell phenotype

Abstract: Polarized epithelial cells play fundamental roles in the ontogeny and function of a variety of tissues and organs in mammals. The morphogenesis of a sheet of polarized epithelial cells (the trophectoderm) is the first overt sign of cellular differentiation in early embryonic development. In the adult, polarized epithelial cells line all body cavities and occur in tissues that carry out specialized vectorial transport functions of absorption and secretion. The generation of this phenotype is a multistage process requiring extracellular cues and the reorganization of proteins in the cytoplasm and on the plasma membrane; once established, the phenotype is maintained by the segregation and retention of specific proteins and lipids in distinct apical and basal-lateral plasma membrane domains.

AGRICULTURE AND THE STATE SYSTEM: The rise and decline of national agricultures, 1870 to the present

Abstract: This paper explores the role of agriculture in the development of the capitalist world economy, and in the trajectory of the state system. At present, when food security and foreign debt command policy attention, it is useful to examine the assumptions behind attempts to build up national agricultures in Third World countries. We maintain that these assumptions, when considered from a world-historical perspective, have certain shortcomings in theory and real obstacles in practice. Our argument is that contrary to the prevailing development model of the ideal national economy in which agriculture and industry complement one another dynamically (Rostow 1960; Johnston & Kilby 1975; Senghaas 1988), the historical relations between 'agriculture' and 'industry' have been rather more fluid and global in scope. The very distinction between advanced capitalist and underdeveloped or peripheral economies assumes that the former, in contrast to the latter, are articulated, that is, the main growth dynamic derives from intersectoral exchanges within the national economy (Amin 1974; de Janvry 1981). We argue, however, that this unexamined assumption applies possibly to one nation-state only, and then only for a brief historical period in a context of growing transnational capital movement that has increasingly precluded the model's extension to other countries. This case is the United States, in which agriculture was a source of demand for domestic industry during the period of protectionism accompanying late nineteenth century British hegemony and its decline through to the end of the Second World War. Yet even then US agriculture was principally export-oriented. The ideal of national inter-sectoral balance nevertheless stems from this historical conjuncture, and gained currency with the rise of American hegemony and the proliferation of modernization and dependency theories that generalized the American model. Our goal, then, is to reconstruct a preliminary history of agriculture to shed light on its impact on the state system, and thereby to offer a critique

Ambiguity and self-evaluation: the role of idiosyncratic trait definitions in self-serving assessments of ability

Abstract: When people are asked to evaluate their own abilities, the assessments they provide tend to be self-serving. Indeed, often the appraisals that people endorse appear to be favorable to a logically impossible degree. Perhaps the most direct demonstration of self-serving appraisal is the above average effect . When asked to judge their own capacities and performances in a specific domain against those of their peers, people predominantly respond, “I'm above average.” The above average effect has been demonstrated in the realm of driving ability (Svenson, 1981), ethics (Baumhart, 1968), health (Larwood, 1978: Weinstein, 1980), and managerial skills (Larwood & Whittaker, 1977). The most extreme documentation of this phenomenon comes from a survey conducted by the College Board in 1976–1977 of 1 million high school students. When rating themselves vis-a-vis their peers, 70% rated themselves as above average in leadership ability, whereas only 2% judged themselves as below average. When considering athletic ability, 60% considered themselves above the median and only 6%, below. When asked to judge their ability to get along with others, all students rated themselves as at least average, 60% placed themselves in the top 10%, and 25% placed themselves in the top 1%. The extremity of the phenomenon in this particular survey might be chalked up to youthful exuberance, although the above average effect occurs even among older and more educated people.

Delayed decision-feedback sequence estimation

Abstract: The authors delayed-decision-feedback sequence estimation (DDFSE) for uncoded PAM signals is considered. Estimates on the performance of the algorithm are given, and simulation results are provided for several examples. A more general form of DDFSE applicable to coded modulation systems is also presented. As an example, detection of trellis-coded QPSK (quadrature phase-shift keyed) signals over intersymbol interference channels is discussed. >

Increasing rates of depression.

Abstract: Several recent, large epidemiologic and family studies suggest important temporal changes in the rates of major depression: an increase in the rates in the cohorts born after World War II; a decrease in the age of onset with an increase in the late teenaged and early adult years; an increase between 1960 and 1975 in the rates of depression for all ages; a persistent gender effect, with the risk of depression consistently two to three times higher among women than men across all adult ages; a persistent family effect, with the risk about two to three times higher in first-degree relatives as compared with controls; and the suggestion of a narrowing of the differential risk to men and women due to a greater increase in risk of depression among young men These trends, drawn from studies using comparable methods and modern diagnostic criteria, are evident in the United States, Sweden, Germany, Canada, and New Zealand, but not in comparable studies conducted in Korea and Puerto Rico and of MexicanAmericans living in the United States These cohort changes cannot be fully attributed to artifacts of reporting, recall, mortality, or labeling and have implications for understanding the etiology of depression and for clinical practice (JAMA 1989;261:2229-2235)

Solution of Schrödinger's equation for large systems.

Abstract: Iterative diagonalization of the Hamiltonian matrix is required to solve very large electronic-structure problems. Present algorithms are limited in their convergence rates at low wave numbers by stability problems associated with large changes in the Hartree potential, and at high wave numbers with large changes in the kinetic energy. A new method is described which includes the effect of density changes on the potentials and properly scales the changes in kinetic energy. The use of this method has increased the rate of convergence by over an order of magnitude for large problems.

Biological reductive dechlorination of tetrachloroethylene and trichloroethylene to ethylene under methanogenic conditions.

Abstract: A biological process for remediation of groundwater contaminated with tetrachloroethylene (PCE) and trichloroethylene (TCE) can only be applied if the transformation products are environmentally acceptable. Studies with enrichment cultures of PCE- and TCE-degrading microorganisms provide evidence that, under methanogenic conditions, mixed cultures are able to completely dechlorinate PCE and TCE to ethylene, a product which is environmentally acceptable. Radiotracer studies with [14C]PCE indicated that [14C]ethylene was the terminal product; significant conversion to 14CO2 or 14CH4 was not observed. The rate-limiting step in the pathway appeared to be conversion of vinyl chloride to ethylene. To sustain reductive dechlorination of PCE and TCE, it was necessary to supply an electron donor; methanol was the most effective, although hydrogen, formate, acetate, and glucose also served. Studies with the inhibitor 2-bromoethanesulfonate suggested that methanogens played a key role in the observed biotransformations of PCE and TCE.

Lipoprotein(a) modulation of endothelial cell surface fibrinolysis and its potential role in atherosclerosis.

Abstract: Endothelial cells play a critical role in thromboregulation by virtue of a surface-connected fibrinolytic system. Cultured endothelial cells synthesize and secrete tissue-type plasminogen activator (t-PA) which can bind to at least two discrete sites on the cell surface. These binding sites preserve the catalytic activity of t-PA and protect it from its physiological inhibitor (PAI-1). N-terminal glutamic acid plasminogen (Glu-PLG), the main circulating fibrinolytic zymogen, also interacts specifically with the endothelial cell surface. Binding is associated with a 12-fold increase in catalytic efficiency of plasmin generation by t-PA which may reflect conversion of Glu-PLG to its plasmin-modified form, N-terminal lysine plasminogen (Lys-PLG). Lipoprotein(a) is an atherogenic lipoprotein particle which contains the plasminogen-like apolipoprotein(a) bound to low density lipoprotein. We report here that lipoprotein(a) interferes with endothelial cell fibrinolysis by inhibiting plasminogen binding and hence plasmin generation. In addition, we demonstrate lipoprotein(a) accumulation in atherosclerotic lesions. These findings may provide a link between impaired cell surface fibrinolysis and progressive atherosclerosis.

Reactions controlling heavy metal solubility in soils

Abstract: Soil chemists have long-recognized that knowledge of the elemental composition of soils is generally of little use in assessing the availability of these elements to plants. An obvious illustration of this principle is the common occurrence of Fe and Mn deficiency in plants despite the relatively high levels of Fe and Mn in many soils. For this reason, chemical soil tests have relied on measurement of extractable or “labile” fractions of elements. Such tests are empirical and provide little basis to relate metal extractability to the chemical forms of the metal in the soil. As soils are increasingly used in our society for purposes other than agriculture, the frequency and extent of soil contamination by toxic metals will increase. Empirical relationships may have to be replaced by a more fundamental understanding of the soil processes controlling metal solubility to prevent practices that could have deleterious effects on soil productivity and environmental quality.

Proteins in whey: chemical, physical, and functional properties

Abstract: There is abundant information concerning the functional behavior of whey proteins in model systems. The data on functional properties reported by different researchers, however, reveal wide discrepancies in values. For example, in the case of comparable whey preparations, apparent solubilities may range from 10 to 100%; strength of gels from 0.3 to greater than 10 N, foam overruns from 250 to 1500%, and foam stabilities from 0.5 to 30 min. Many of the data are of limited value in assessing the true functional characteristics of different preparations, treatments, or processing effects. Reports to date are useful in indicating the relative behavior of different proteins; however, the data do not always predict the performance of such proteins in actual food systems. This reflects the fact that in foods, extensive interactions with other components may occur, resulting in modified behavior of the proteins. Harper, (1984) has advocated the testing of these various preparations in simulated food systems which should validly relate the behavior to performance in commercial systems. Emphasis on standardization of specific protocols, with regard to order of addition in ingredients, temperature, pH control, and amount of energy input during mixing, homogenization, emulsification, etc. deserves serious consideration. While this approach is justifiable in terms of providing valuable data to commercial users, it does not minimize the importance of examining these proteins in model systems where the physicochemical basis of each functional attribute can be described in molecular terms (Kinsella, 1987). Such information is necessary to expedite appropriate methods of processing in order to control compositional variability, extent of denatauration, and possible protein modification. In addition, rapid, reliable tests for routine quality assurance that can provide practical information concerning functional applications would be of great value. Whey protein preparations vary immensely in functional behavior and are presently relegated to limited use as functional ingredients in the food industry. This need not be the case since conventional and new technologies permit rigorous control of production protocols, e.g., careful control of heat treatments can result in the production of whey protein preparations with consistent, reliable functional properties (deWit, 1981, 1984; Harper, 1984; Morr, 1985). As the market for functional proteins continues to expand, the whey industry must seek the means to refine whey protein products; determine useful functional properties; develop standardized manufacturing protocols; demonstrate the effectiveness of whey as a functional ingredient; promote, and then market, whey on the basis of performance at competitive cost.

Animal mitochondrial DNA as a genetic marker in population and evolutionary biology

Abstract: Animal mitochondrial DNA (mtDNA) is playing an increasingly important role as a genetic marker in population and evolutionary biology. The popularity of this molecule derives, in part, from the relative ease with which clearly homologous sequences can be isolated and compared. Simple sequence organization, maternal inheritance and absence of recombination make mtDNA an ideal marker for tracing maternal genealogies. Rapid rate of sequence divergence (at least in vertebrates) allows discrimination of recently diverged lineages. Studies of mtDNAs from a diversity of animal groups have revealed significant variation among taxa in mtDNA sequence dynamics, gene order and genome size. They have also provided important insights into population structure, geographic variation, zoogeography and phylogeny.

Genetics of Plant Isozymes

Abstract: The ability to observe allelic variation at isozyme loci has revolutionized research in the fields of biochemical genetics, population genetics, and evolution. This variation, called allozymic polymorphism, has been used in plants to examine genetic processes at every stage of the life cycle and to ascertain genetic diversity in all major crops as well as many other species. Yet the potential for using allozymes as genetic markers was not immediately predicted when isozyme variability was initially described (Hunter and Marker, 1957; Markert and Moller, 1959). In fact, the extent and prevalence of allozyme polymorphism was a rather disconcerting surprise to evolutionary biologists. Classical evolutionary theory had predicted that the most “efficient” form of an enzyme should, over time, become predominant in isolated populations, with an occasional rare allele produced through mutation. The discovery in many populations of relatively high levels of polymorphism at isozyme loci has forced a major reconsideration of evolutionary theory (Kimura and Crow, 1964; Koehn et al., 1983; Kimura, 1983).

Voyager 2 at neptune: imaging science results.

Abstract: Voyager 2 images of Neptune reveal a windy planet characterized by bright clouds of methane ice suspended in an exceptionally clear atmosphere above a lower deck of hydrogen sulfide or ammonia ices. Neptune's atmosphere is dominated by a large anticyclonic storm system that has been named the Great Dark Spot (GDS). About the same size as Earth in extent, the GDS bears both many similarities and some differences to the Great Red Spot of Jupiter. Neptune's zonal wind profile is remarkably similar to that of Uranus. Neptune has three major rings at radii of 42,000, 53,000, and 63,000 kilometers. The outer ring contains three higher density arc-like segments that were apparently responsible for most of the ground-based occultation events observed during the current decade. Like the rings of Uranus, the Neptune rings are composed of very dark material; unlike that of Uranus, the Neptune system is very dusty. Six new regular satellites were found, with dark surfaces and radii ranging from 200 to 25 kilometers. All lie inside the orbit of Triton and the inner four are located within the ring system. Triton is seen to be a differentiated body, with a radius of 1350 kilometers and a density of 2.1 grams per cubic centimeter; it exhibits clear evidence of early episodes of surface melting. A now rigid crust of what is probably water ice is overlain with a brilliant coating of nitrogen frost, slightly darkened and reddened with organic polymer material. Streaks of organic polymer suggest seasonal winds strong enough to move particles of micrometer size or larger, once they become airborne. At least two active plumes were seen, carrying dark material 8 kilometers above the surface before being transported downstream by high level winds. The plumes may be driven by solar heating and the subsequent violent vaporization of subsurface nitrogen.