Showing papers by "Columbia University published in 1988"

A structured interview guide for the Hamilton Depression Rating Scale.

Abstract: • The Hamilton Depression Rating Scale (HDRS) is the most widely used scale for patient selection and follow-up in research studies of treatments of depression. Despite extensive study of the reliability and validity of the total scale score, the psychometric characteristics of the individual items have not been well studied. In the only reliability study to report agreement on individual items using a test-retest interview method, most of the items had only fair or poor agreement. Because this is due in part to variability in the way the Information is obtained to make the various rating distinctions, the Structured Interview Guide for the HDRS (SIGH-D) was developed to standardize the manner of administration of the scale. A test-retest reliability study conducted on a series of psychiatric inpatients demonstrated that the use of the SIGH-D results in a substantially improved level of agreement for most of the HDRS items.

Optimality in human motor performance: Ideal control of rapid aimed movements.

Abstract: A stochastic optimized-submovement model is proposed for Pitts' law, the classic logarithmic tradeoff between the duration and spatial precision of rapid aimed movements. According to the model, an aimed movement toward a specified target region involves a primary submovement and an optional secondary corrective submovement. The submovements are assumed to be programmed such that they minimize average total movement time while maintaining a high frequency of target hits. The programming process achieves this minimization by optimally adjusting the average magnitudes and durations of noisy neuromotor force pulses used to generate the submovements. Numerous results from the literature on human motor performance may be explained in these terms. Two new experiments on rapid wrist rotations yield additional support for the stochastic optimizedsubmovement model. Experiment 1 revealed that the mean durations of primary submovements and of secondary submovements, not just average total movement times, conform to a square-root approximation of Pitts' law derived from the model. Also, the spatial endpoints of primary submovements have standard deviations that increase linearly with average primary-submovement velocity, and the average primary-submovement velocity influences the relative frequencies of secondary submovements, as predicted by the model. During Experiment 2, these results were replicated and extended under conditions in which subjects made movements without concurrent visual feedback. This replication suggests that submovement optimization may be a pervasive property of movement production. The present conceptual framework provides insights into principles of motor performance, and it links the study of physical action to research on sensation, perception, and cognition, where psychologists have been concerned for some time about the degree to which mental processes incorporate rational and normative rules. An enduring issue in the study of the human mind concerns of mathematical probability theory and statistical decision thethe rationality and optimality of the mental processes that guide ory (e.g., see Edwards, 1961; Edwards, Lindman, & Savage,

A safe packaging line for gene transfer: separating viral genes on two different plasmids.

Abstract: A retrovirus packaging cell line was constructed by using portions of the Moloney murine leukemia virus in which the gag, pol, and env genes of the helper virus were separated onto two different plasmids and in which the psi packaging signal and 3' long terminal repeat were removed. The plasmid containing the gag and pol genes and the plasmid containing the env gene were cotransfected into NIH 3T3 cells. Clones that produced high levels of reverse transcriptase and env protein were tested for their ability to package the replication-defective retrovirus vectors delta neo and N2. One of the gag-pol and env clones (GP+E-86) was able to transfer G418 resistance to recipient cells at a titer of as high as 1.7 X 10(5) when it was used to package delta neo and as high as 4 X 10(6) when it was used to package N2. Supernatants of clones transfected with the intact parent gag-pol-env plasmid 3P0 had comparable titers (as high as 6.5 X 10(4) with delta neo; as high as 1.7 X 10(5) with N2). Tests for recombination events that might result in intact retrovirus showed no evidence for the generation of replication-competent virus. These results suggest that gag, pol, and env, when present on different plasmids, may provide an efficient and safe packaging line for use in retroviral gene transfer.

Amiloride and its analogs as tools in the study of ion transport.

Abstract: Amiloride inhibits most plasma membrane Na+ transport systems. We have reviewed the pharmacology of inhibition of these transporters by amiloride and its analogs. Thorough studies of the Na+ channel, the Na+/H+ exchanger, and the Na+/Ca2+ exchanger, clearly show that appropriate modification of the structure of amiloride will generate analogs with increased affinity and specificity for a particular transport system. Introduction of hydrophobic substituents on the terminal nitrogen of the guanidino moiety enhances activity against the Na+ channel; whereas addition of hydrophobic (or hydrophilic) groups on the 5-amino moiety enhances activity against the Na+/H+ exchanger. Activity against the Na+/Ca2+ exchanger and Ca2+ channel is increased with hydrophobic substituents at either of these sites. Appropriate modification of amiloride has produced analogs that are several hundred-fold more active than amiloride against specific transporters. The availability of radioactive and photoactive amiloride analogs, anti-amiloride antibodies, and analogs coupled to support matrices should prove useful in future studies of amiloride-sensitive transport systems. The use of amiloride and its analogs in the study of ion transport requires a knowledge of the pharmacology of inhibition of transport proteins, as well as effects on enzymes, receptors, and other cellular processes, such as DNA, RNA, and protein synthesis, and cellular metabolism. One must consider whether the effects seen on various cellular processes are direct or due to a cascade of events triggered by an effect on an ion transport system.

Calculating the electrostatic potential of molecules in solution: Method and error assessment

Abstract: We present a numerical method for calculating the electrostatic potential of molecules in solution, using the linearized Poisson-Boltzmann equation. The emphasis in this work is on applications to biological macromolecules. The accuracy of the method is assessed by comparisons with analytic solutions for the case of a single charge in a dielectric sphere (Tanford-Kirkwood theory), which serves as a model for a macromolecule. We find that the solutions are generally accurate to within 5%. Larger errors occur close to the charge and the dielectric boundary, but the maximum error found at ion-bonding distance (3 A) from a charge close to the boundary (1 A deep) is only ∼15%. Several algorithmic improvements, described here, contribute to the accuracy of the method. The programs involved compose a coherent software package, called Del Phi, which goes from a Brookhaven Protein Data Bank format file to calculated electrostatic fields.

Kinetic control of dissolved phosphate in natural rivers and estuaries: A primer on the phosphate buffer mechanism1

Abstract: The primary mode of interaction of dissolved phosphate with fluvial inorganic suspended particles is via a reversible two-step sorption process. The first step, adsorption/desorption on surfaces, has fast kinetics (minutes-hours). The second step, solid-state diffusion of adsorbed phosphate from the surface into the interior of particles, has slow kinetics (days-months) and is dependent on the time history of the previous surface sorption and the chemistry of the solid diffusional layer. Natural clay particles with a surficial armoring of reactive iron and aluminum hydroxyoxides resulting from chemical weathering of rocks and soils have a high capacity for absorbing phosphate in the second step and for maintaining low “equilibrium phosphate concentrations” in solution. Extrapolation of laboratory sorption and extraction experiments with natural soils and suspended sediments to the environment suggests that the phosphate concentrations of unperturbed turbid rivers (SPM > 50 mg liter I) are controlled near the dynamic equilibrium phosphate concentration of their particles (EPC, = 0.2-l .5 PM) and that fluvial suspended particles “at equilibrium” contain up to 10 pmol-P g-l that is desorbable. Release of this phosphate from particles entering the sea produces the characteristic shape and magnitude of input profiles of dissolved phosphate observed in unperturbed estuaries. On a global scale, fluvial particulates could transport from 1.4 to 14 x 1O’O mol yr-I of reactive phosphate to the sea, some 2-5 times more than that in the dissolved load alone.

Information-Based Complexity

Abstract: This book provides a comprehensive treatment of information-based complexity, the branch of computational complexity that deals with the intrinsic difficulty of the approximate solution of problems for which the information is partial, noisy, and priced. Such problems arise in many areas including economics, physics, human and robotic vision, scientific and engineering computation, geophysics, decision theory, signal processing and control theory.

Joint ventures and competitive strategy

Abstract: A framework for using joint ventures (and other forms of cooperative strategy) within varying competitive environments is constructed, and hypotheses are developed concerning the impact of particular industry traits upon firms' options in pursuing them. Industry examples illustrate the framework's hypotheses. In this framework, demand traits suggest what types of cooperative strategies are needed. Competitor traits suggest how firms will respond to these needs for cooperation. Since joint ventures can be inherently unstable organizational forms, it is important for managers to (1) select the right cooperative strategy option and (2) modify the autonomy from (and coordination with) sponsoring firms that ventures enjoy as their industry structures evolve. Familiarity with cooperative strategy options is important because (1) as growth slows, (2) as markets shrink or become crowded, (3) as industries become global, or (4) as technological change accelerates to speeds where individual firms cannot recover their initial investments, managers will have less margin for error. If managers do not learn how to use cooperative strategies advantageously their firms may encounter difficulties in delivering adequate value to their customers, replenishing their base of skills, andlor safeguarding their abilities to increase long-term shareholder value.

Structural and Functional Roles of Glycosyl-Phosphatidylinositol in Membranes

Abstract: Glycosylated forms of phosphatidylinositol, which have only recently been described in eukaryotic organisms, are now known to play important roles in biological membrane function. These molecules can serve as the sole means by which particular cell-surface proteins are anchored to the membrane. Lipids with similar structures may also be involved in signal transduction mechanisms for the hormone insulin. The utilization of this novel class of lipid molecules for these two distinct functions suggests new mechanisms for the regulation of proteins in biological membranes.

Racelessness as a factor in Black students' school success: Pragmatic strategy or pyrrhic victory?

Abstract: Signithia Fordham presents an analysis of the tensions high-achieving Black students feel when they strive for academic success. Students are pulled by their dual relationships to the indigenous Black fictive-kinship system and the individualistic, competitive ideology of American schools. By analyzing ethnographic data on six high-achieving Black high school students, the author finds that the characteristics required for success in society contradict an identification and solidarity with Black culture. Students who feel the conflict between "making it" and group identification develop the particular strategy of racelessness.

The development of scientific thinking skills

Abstract: D. Kuhn, Introduction. The Development of Scientific Thinking. Related Work. D. Kuhn and E. Amsel with the assistance of L. Schauble, The Evaluation of Evidence. The Interpretation of Covariation and Noncovariation Evidence. The Influence of Theory on Evaluation of Evidence. The Reconstruction of Theory and Evidence. D. Kuhn and M. O'Loughlin with the assistance of W. Yotive, The Coordination of Theory and Evidence. Replication: The Evaluation of Evidence. The Interpretation of Insufficient and Mixed Evidence. The Coordination of Evidence with Multiple Theories. The Generation of Evidence to Evaluate Theories. The Development of Skills in Coordinating Theory and Evidence. D. Kuhn and B. Leadbeater, The Connection of Theory and Evidence. The Interpretation of Divergent Evidence. D. Kuhn, Conclusion. Summary and Conclusions. References. Index.

Influence of late Cenozoic mountain building on ocean geochemical cycles

Abstract: In a steady-state ocean, input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes For the elements strontium, calcium, and carbon, rivers provide the primary input, whereas marine biogenic sedimentation dominates removal Dissolved fluxes in rivers are related to rates of continental weathering, which in turn are strongly dependent on rates of uplift The largest dissolved fluxes today arise in the Himalayan and Andean mountain ranges and the Tibetan Plateau During the past 5 my, uplift rates in these areas have increased significantly; this suggests that weathering rates and river fluxes may have increased also The oceanic records of carbonate sedimentation, level of the calcite compensation depth, and delta/sup 13/C and delta/sup 87/Sr in biogenic sediments are consistent with a global increase in river fluxes since the late Miocene The cooling of global climate over the past few million years may be linked to a decrease in atmospheric CO/sub 2/ driven by enhanced continental weathering in these tectonically active regions

The nature of adolescent competencies predicted by preschool delay of gratification.

Abstract: Delay of gratification, assessed in a series of experiments when the subjects were in preschool, was related to parental personality ratings obtained a decade later for 95 of these children in adolescence. Clear and consistent patterns of correlations between self-imposed delay time in preschool and later ratings were found for both sexes over this time span. Delay behavior predicted a set of cognitive and social competencies and stress tolerance consistent with experimental analyses of the process underlying effective delay in the preschool delay situation. Specifically, children who were able to wait longer at age 4 or 5 became adolescents whose parents rated them as more academically and socially competent, verbally fluent, rational, attentive, planful, and able to deal well with frustration and stress. Comparisons with related longitudinal research using other delay situations help to clarify the important features of the situations and person variables involved in different aspects of delay of gratification.

Calculation of the total electrostatic energy of a macromolecular system: Solvation energies, binding energies, and conformational analysis

Abstract: In this report we describe an accurate numerical method for calculating the total electrostatic energy of molecules of arbitrary shape and charge distribution, accounting for both Coulombic and solvent polarization terms. In addition to the solvation energies of individual molecules, the method can be used to calculate the electrostatic energy associated with conformational changes in proteins as well as changes in solvation energy that accompany the binding of charged substrates. The validity of the method is examined by calculating the hydration energies of acetate, methyl ammonium, ammonium, and methanol. The method is then used to study the relationship between the depth of a charge within a protein and its interaction with the solvent. Calculations of the relative electrostatic energies of crystal and misfolded conformations of Themiste dyscritum hemerythrin and the VL domain of an antibody are also presented. The results indicate that electrostatic charge-solvent interactions strongly favor the crystal structures. More generally, it is found that charge-solvent interactions, which are frequently neglected in protein structure analysis, can make large contributions to the total energy of a macromolecular system.

Financial Market Imperfections and Business Cycles

Abstract: This paper develops a simple model of macroeconomic behavior which incorporates the impact of financial market "imperfections," such as those generated by asymmetric information in financial markets. These information asymmetries may lead to breakdowns in markets, like that for equity, in which risks arm shared. In particular, we analyze firm behavior in the presence of equity rationing and imperfect futures markets, in which there are lags in production. Aft a consequence, firms act in a risk-averse manner. We trace out the macroeconomic consequences, and show that they are able to account for many of the widely observed aspects of actual business cycles.

Estimates of the prevalence of childhood maladjustment in a community survey in Puerto Rico. The use of combined measures.

Abstract: • A two-stage epidemiologic survey was carried out on a probability sample of the population aged 4 through 16 years in Puerto Rico. The survey used the Child Behavior Checklist as a screening instrument, and prevalence rates were estimated on the basis of clinical diagnoses and other measures provided by child psychiatrists during the second stage. Maladjustment was operationally defined through the use of combined measures, including DSM-III diagnosis and a scale of functional impairment. Data were provided on the demographic correlates of maladjustment and on the comorbidity of DSM-III diagnostic domains. The prevalence rates obtained vis-a-vis the availability of mental health services on the island reflected a major public health problem.

Pleistocene climates in China dated by magnetic susceptibility

Abstract: The magnetic susceptibility of loess and interbedded soils in central China varies with the degree of pedogenesis and serves as a proxy measure of climate. The concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the Brunhes epoch. Susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology. On this scale, the susceptibility record closely parallels the oxygen-isotope fluctuations in deep-sea sediments, suggesting a close interdependence of the Chinese dust falls, the volume of land-based ice, and global climate.

The Geometry of String Perturbation Theory

Abstract: This paper is devoted to recent progress made towards the understanding of closed bosonic and fermionic string perturbation theory, formulated in a Lorentz-covariant way on Euclidean space-time. Special emphasis is put on the fundamental role of Riemann surfaces and supersurfaces. The differential and complex geometry of their moduli space is developed as needed. New results for the superstring presented here include the supergeometric construction of amplitudes, their chiral and superholomorphic splitting and a global formulation of supermoduli space and amplitudes.

Molecular characterization of a functional cDNA encoding the serotonin 1c receptor.

Abstract: Neurons that release serotonin as a neurotransmitter project to most regions of the central and peripheral nervous system and mediate diverse neural functions. The physiological effects of serotonin are initiated by the activation of multiple, distinct receptor subtypes. Cloning in RNA expression vectors was combined with a sensitive electrophysiological assay in Xenopus oocytes in order to isolate a functional cDNA clone encoding the 5HTlc serotonin receptor. Injection of RNA transcribed in vitro from this clone into Xenopus oocytes elicits serotonin sensitivity. Mouse fibroblasts transformed with this clone bind serotonin agonists and antagonists and exhibit an increase in intracellular Ca2+ concentrations in response to serotonin. The sequence of the 5HTlc receptor reveals that it belongs to the family of G protein-coupled receptors, which are thought to traverse the cytoplasmic membrane seven times. Moreover, in situ hybridization and RNA blot analysis indicate that the 5HTlc receptor is expressed in neurons in many regions of the central nervous system and suggest that this subclass of receptor may mediate many of the central actions of serotonin.

Axon guidance and the patterning of neuronal projections in vertebrates

Abstract: Over the past decade, new insights have been obtained into the cellular strategies and molecular mechanisms that guide axons to their targets in the developing vertebrate nervous system. Axons select pathways by recognizing specific cues in their environment. These cues include cell surface and extracellular matrix molecules that mediate cell and substrate adhesion and axon fasciculation, molecules with contact-dependent inhibitory properties, and diffusible tropic factors. Several guidance cues may operate in a coordinated way to generate the distinct axonal trajectories of individual neurons.

Chemotropic guidance of developing axons in the mammalian central nervous system

Abstract: In the developing nervous system, axons project considerable distances along stereotyped pathways to reach their targets. Axon guidance depends partly on the recognition of cell-surface and extracellular matrix cues derived from cells along the pathways1. It has also been proposed that neuronal growth cones are guided by gradients of chemoattractant molecules emanating from their intermediate or final cellular targets2. Although there is evidence that the axons of some peripheral neurons in vertebrates are guided by chemotropism3,4 and the directed growth of some central axons to their targets is consistent with such a mechanism5–7, it remains to be determined whether chemotropism operates in the central nervous system. During development of the spinal cord, commissural axons are deflected towards a specialized set of midline neural epithelial cells, termed the floor plate8–10, which could reflect guidance by substrate cues or by diffusible chemoattractant molecules. Here we provide evidence in support of chemotropic guidance by demonstrating that the rat floor-plate cells secrete a diffusible factor(s) that influences the pattern and orientation of commissural axon growth in vitro without affecting other embryonic spinal cord axons. These findings support the hypothesis2 that chemotropic mechanisms guide developing axons to their intermediate targets in the vertebrate CNS.

On Jump Processes in the Foreign Exchange and Stock Markets

Abstract: exchange rates exhibit systematic discontinuities, even after allowingfor conditional heteroskedasticity in the diffusion process. The results are much more significant in theforeign exchange market than in the stock market, which suggests differences in the structure of these markets. Finally, this jump component is shown to explain some of the empirically observed mispricings in the currency options market. The objective of this article is to analyze and compare the empirical distribution of returns in the stock market and in the foreign exchange market. There are a number of reasons why a better understanding of the stochastic processes driving prices in these markets would be useful. Many financial models rely heavily on the assumption of a particular stochastic process, while relatively little attention is paid to the empirical fit of the postulated distribution. As a result, models like option pricing models are applied indiscriminately to various markets such as the stock market and the foreign exchange market when the underlying processes may be fundamentally different. The foreign exchange market, for instance, is characterized by active exchange rate man

Deletions of mitochondrial DNA in Kearns‐Sayre syndrome

Abstract: We have identified large-scale deletions in muscle mitochondrial DNA (mtDNA) in seven of seven patients with Kearns-Sayre syndrome (KSS). We found no detectable deletions in the mtDNA of ten non-KSS patients with other mitochondrial myopathies or encephalomyopathies, or three normal controls. The deletions ranged in size from 2.0 to 7.0 kb, and did not localize to any single region of the mitochondrial genome. The proportion of mutated genomes in each KSS patient ranged from 45% to 75% of total mtDNA. There was no correlation between the size or site of the deletion, biochemical abnormality of mitochondrial enzymes, or clinical severity. The data bolster arguments that KSS is a unique disorder and genetic in origin.

The barite-opal-organic carbon association in oceanic particulate matter

Abstract: Barite particles 0.5–5 μm in size are ubiquitous in the ocean and their formation, sinking and dissolution is a major part of the marine barium cycle1,2. Barite formation appears to be caused by biological activity in the upper water column, but the exact mechanism is unknown. Analysis of 1–53 μm and >53 μm sized particles obtained by large volume in situ filtration in the Atlantic suggests that barites are formed in the >53 fxm fraction in near-surface waters and released into the 1–53 μm fraction at depths below the euphotic zone. Scanning electron microscopy and energy dispersive X-ray fluorescence analysis of both size fractions shows first, that barites are formed almost exclusively in microenvironments containing decaying organic matter and the remains of siliceous plankton, and second that barites do not appear to be actively formed by the planktonic organism sampled. This explains the origin of suspended barite, and the similarity of dissolved Si and Ba distributions in the ocean. Suspended and sedimented barite may indicate the intensity of organic matter regeneration in the water column.