Showing papers by "Tulane University published in 2000"

Insulin resistance differentially affects the PI 3-kinase- and MAP kinase-mediated signaling in human muscle.

Abstract: The broad nature of insulin resistant glucose metabolism in skeletal muscle of patients with type 2 diabetes suggests a defect in the proximal part of the insulin signaling network. We sought to identify the pathways compromised in insulin resistance and to test the effect of moderate exercise on whole-body and cellular insulin action. We conducted euglycemic clamps and muscle biopsies on type 2 diabetic patients, obese nondiabetics and lean controls, with and without a single bout of exercise. Insulin stimulation of the phosphatidylinositol 3-kinase (PI 3-kinase) pathway, as measured by phosphorylation of the insulin receptor and IRS-1 and by IRS protein association with p85 and with PI 3-kinase, was dramatically reduced in obese nondiabetics and virtually absent in type 2 diabetic patients. Insulin stimulation of the MAP kinase pathway was normal in obese and diabetic subjects. Insulin stimulation of glucose-disposal correlated with association of p85 with IRS-1. Exercise 24 hours before the euglycemic clamp increased phosphorylation of insulin receptor and IRS-1 in obese and diabetic subjects but did not increase glucose uptake or PI 3-kinase association with IRS-1 upon insulin stimulation. Thus, insulin resistance differentially affects the PI 3-kinase and MAP kinase signaling pathways, and insulin-stimulated IRS-1-association with PI 3-kinase defines a key step in insulin resistance.

A Comparison of Approaches to Forming Composite Measures in Structural Equation Models

Abstract: A common practice in applications of structural equation modeling techniques is to create composite measures from individual items. The purpose of this article was to provide an empirical comparison of several composite formation methods on model fit. Data from 1, 177 public school teachers were used to test a model of union commitment in which alternative composite formation methods were used to specify the measurement components of the model. Bootstrapping procedures were used to generate data for two additional sample sizes. Results indicated that the use of composites, in general, resulted in improved overall model fit as compared to treating all items as individual indicators. Lambda values and explained criterion variance indicated that this improved model fit was due to the creation of strong measurement models. Implications of these results for researchers using composites are discussed.

Centrifugal and Centripetal Forces in Radical New Product Development Under Time Pressure

Abstract: Organizations must be ambidextrous to successfully develop new products—they must act creatively as well as collectively. However, how to do this is not clear. The author analyzes this problem and reviews the literature in terms of two opposing forces: the first increases the quantity and quality of ideas, information, and knowledge available for creative action while the second integrates these things into collective action. The author then models these forces to explain how the coexistence of contradictory structural elements and processes increases the probability of successful development.

Effect of metformin and rosiglitazone combination therapy in patients with type 2 diabetes mellitus: a randomized controlled trial.

Abstract: Context Most antidiabetic agents target only 1 of several underlying causes of diabetes. The complementary actions of the antidiabetic agents metformin hydrochloride and rosiglitazone maleate may maintain optimal glycemic control in patients with type 2 diabetes; therefore, their combined use may be indicated for patients whose diabetes is poorly controlled by metformin alone. Objective To evaluate the efficacy of metformin-rosiglitazone therapy in patients whose type 2 diabetes is inadequately controlled with metformin alone.

Impacts of a Global Climate Cycle on Population Dynamics of a Migratory Songbird

Abstract: Progress toward understanding factors that limit abundances of migratory birds, including climate change, has been difficult because these species move between diverse locations, often on different continents. For black-throated blue warblers (Dendroica caerulescens), demographic rates in both tropical winter quarters and north temperate breeding grounds varied with fluctuations in the El Nino Southern Oscillation. Adult survival and fecundity were lower in El Nino years and higher in La Nina years. Fecundity, in turn, was positively correlated with subsequent recruitment of new individuals into winter and breeding populations. These findings demonstrate that migratory birds can be affected by shifts in global climate patterns and emphasize the need to know how events throughout the annual cycle interact to determine population size.

Truth in mutual fund advertising: Evidence on future performance and fund flows

Abstract: We examine a sample of 294 mutual funds that are advertised in Barron's or Money magazine. The preadvertisement performance of these funds is significantly higher than that of the benchmarks. We test whether the sponsors select funds to signal continued superior performance or they use the past superior performance to attract more money into the funds. Our analysis shows that there is no superior performance in the postadvertisement period. Thus, the results do not support the signaling hypothesis. On the other hand, we find that the advertised funds attract significantly more money in comparison with a group of control funds.

Toward a quantitative description of large-scale neocortical dynamic function and EEG.

Abstract: A general conceptual framework for large-scale neocortical dynamics based on data from many laboratories is applied to a va- riety of experimental designs, spatial scales, and brain states. Partly distinct, but interacting local processes (e.g., neural networks) arise from functional segregation. Global processes arise from functional integration and can facilitate (top down) synchronous activity in re- mote cell groups that function simultaneously at several different spatial scales. Simultaneous local processes may help drive (bottom up) macroscopic global dynamics observed with electroencephalography (EEG) or magnetoencephalography (MEG). A local/global dynamic theory that is consistent with EEG data and the proposed conceptual framework is outlined. This theory is neutral about properties of neural networks embedded in macroscopic fields, but its global component makes several qualitative and semiquantitative predictions about EEG measures of traveling and standing wave phenomena. A more general "metatheory" suggests what large-scale quantitative theories of neocortical dynamics may be like when more accurate treatment of local and nonlinear effects is achieved. The theory describes the dynamics of excitatory and inhibitory synaptic action fields. EEG and MEG provide large-scale estimates of modulation of these synaptic fields around background levels. Brain states are determined by neuromodulatory control parameters. Purely local states are dominated by local feedback gains and rise and decay times of postsynaptic potentials. Dominant local frequen- cies vary with brain region. Other states are purely global, with moderate to high coherence over large distances. Multiple global mode frequencies arise from a combination of delays in corticocortical axons and neocortical boundary conditions. Global frequencies are iden- tical in all cortical regions, but most states involve dynamic interactions between local networks and the global system. EEG frequencies may involve a "matching" of local resonant frequencies with one or more of the many, closely spaced global frequencies.

Financial Packaging of IPO Firms in China

Abstract: This paper examines the earnings patterns of initial public offering (IPO) firms in China to shed light on the role of earnings management in the "financial packaging" of Chinese state-owned enterprises (SOEs) for public listing. We base our analysis on the case of B-Shares and H-Shares in China, two types of securities that now allow foreign investors to buy shares in SOEs previously wholly owned by the state. These IPOs mark the beginning of the stock market in China and signify an important step of Chinese economic reform. We examine the pre- and post-IPO earnings patterns for the entire sample, and separately for firms in protected vs. unprotected industries and for B-Shares vs. H-Shares. We find a statistically significant post-issue earnings decline for unprotected industry firms. This earnings decline is most significant for unprotected B-Share firms, and marginally significant for protected B-Share and unprotected H-Share firms, but not significant for protected H-Share firms. In addition, we find some evidence that the accounting accruals of sample firms in unprotected industries decline whereas their cash flows from operations increase after the IPO. Taken together, earnings management in the process of financial packaging seems to depend on the firm's relationship with the central government and on where the securities are listed. The evidence also suggests that the SOEs in unprotected industries may manage accounting accruals to boost earnings and/or list those business units with temporarily high profits resulting from high accounting accruals during the process of financial packaging.

The Gaucher registry: demographics and disease characteristics of 1698 patients with Gaucher disease.

Abstract: Background The Gaucher Registry, the largest database of patients with Gaucher disease (GD) worldwide, was initiated to better delineate the progressive nature of the disorder and determine optimal therapy. This report describes the demographic and clinical characteristics of 1698 patients with GD before they received enzyme replacement therapy. Methods Physicians worldwide who treat patients with GD were invited to submit prospective and retrospective data for an ongoing registry, using standardized data collection forms, for central processing and review. Results Most patients were from the United States (45%) and Israel (17%), but patients are from 38 countries. Most (94%) had type 1 GD, fewer than 1% had type 2, and 5% had type 3. Mutant allele frequency data, available for 45% of patients, showed the most common alleles to be N370S (53%), L444P (18%), 84GG (7%), and IVS2+1 (2%). Twenty-five percent of L444P homozygotes (13 of 52 patients) had type 1 GD phenotype. Mean age at diagnosis in patients with the N370S/N370S genotype was 27.2 years (SD, 19.7 years); in L444P/L444P patients, 2.3 years (SD, 3.2 years). Histories of bone pain and radiological bone disease were reported by 63% and 94% of patients, respectively; both were more likely in asplenic patients than in patients with spleens. Mean spleen and liver volumes were 19.8 and 2.0 multiples of normal, respectively. Anemia and thrombocytopenia were present in 64% and 56%, respectively. Thrombocytopenia was present in 13% of asplenic patients. Conclusions The Gaucher Registry permits a comprehensive understanding of the clinical spectrum of GD because of the uniquely large sample size. The Registry will be useful in evaluating the effects of specific therapies in GD and the possible influences of environment, ethnicity, and genotype on the natural history of the disorder.

Long-Term Effects of Weight Loss and Dietary Sodium Reduction on Incidence of Hypertension

Abstract: To examine the long-term effects of weight loss and dietary sodium reduction on the incidence of hypertension, we studied 181 men and women who participated in the Trials of Hypertension Prevention, phase 1, in Baltimore, Md. At baseline (1987 to 1988), subjects were 30 to 54 years old and had a diastolic blood pressure (BP) of 80 to 89 mm Hg and systolic BP or =160 mm Hg and/or diastolic BP > or =90 mm Hg and/or treatment with antihypertensive medication during follow-up. Body weight and urinary sodium were not significantly different among the groups at the posttrial follow-up. After 7 years of follow-up, the incidence of hypertension was 18.9% in the weight loss group and 40.5% in its control group and 22.4% in the sodium reduction group and 32.9% in its control group. In logistic regression analysis adjusted for baseline age, gender, race, physical activity, alcohol consumption, education, body weight, systolic BP, and urinary sodium excretion, the odds of hypertension was reduced by 77% (odds ratio 0.23; 95% confidence interval 0.07 to 0.76; P=0.02) in the weight loss group and by 35% (odds ratio 0.65; 95% confidence interval 0.25 to 1.69; P=0.37) in the sodium reduction group compared with their control groups. These results indicate that lifestyle modification such as weight loss may be effective in long-term primary prevention of hypertension.

Modules over non-Noetherian domains

Abstract: Commutative domains and their modules Valuation domains Prufer domains More non-Noetherian domains Finitely generated modules Projectivity and projective dimension Divisible modules Topology and filtration Injective modules Uniserial modules Heights, invariants and basic submodules Polyserial modules RD- and pure-injectivity Torsion modules Torsion-free modules of finite rank Infinite rank torsion-free modules Appendix on set theory Bibliography Author index Subject index.

Perspective on “Density functional approach to the frontier-electron theory of chemical reactivity”

Abstract: The Fukui function, f(→), was proposed as a tool for deducing the relative reactivity of different positions in a molecule by Parr and Yang in 1984. Herein we sketch the theory of the Fukui function, with special emphasis on its logical motivation, interpretation, qualitative characteristics, and practical computation. We conclude with some words about the Fukui function's extensions, limitations, and importance.

Cyanobacterial blooms in the Baltic Sea: Natural or human-induced?

Abstract: Massive summer blooms of nitrogen-fixing cyanobacteria have been documented in the Baltic Sea since the 19th century, but are reported to have increased in frequency, biomass, and duration in recen

A perception--action perspective on tool use development.

Abstract: In this essay I argue for a new wave of research on tool use development. Advances in the literature on perception-action development hold important clues for how tool use unfolds in children. These advances suggest that tool use may be a more continuous developmental achievement than has been previously believed. On this view, tool use is rooted in the perception-action routines that infants employ to gain information about their environments. Although tools alter the properties of effector systems, children use tools to explore and change their environments, building on efforts that originate in infancy. Based on this approach, new research directions are suggested, including efforts designed to investigate the processes by which children detect and relate affordances between objects, coordinate spatial frames of reference, and incorporate early-appearing action patterns into instrumental behaviors.

An improved control algorithm of shunt active filter for voltage regulation, harmonic elimination, power-factor correction, and balancing of nonlinear loads

Abstract: This paper deals with an implementation of a new control algorithm for a three-phase shunt active filter to regulate load terminal voltage, eliminate harmonics, correct supply power-factor, and balance the nonlinear unbalanced loads. A three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source inverter (CC-VSI) with a DC bus capacitor is used as an active filter (AF). The control algorithm of the AF uses two closed loop PI controllers. The DC bus voltage of the AF and three-phase supply voltages are used as feedback signals in the PI controllers. The control algorithm of the AF provides three-phase reference supply currents. A carrier wave pulse width modulation (PWM) current controller is employed over the reference and sensed supply currents to generate gating pulses of IGBTs of the AF. Test results are presented and discussed to demonstrate the voltage regulation, harmonic elimination, power-factor correction and load balancing capabilities of the AF system.

Imaging Cluster Surfaces with Atomic Resolution: The Strong Metal-Support Interaction State of Pt Supported on TiO 2 ( 110 )

Abstract: Nanosized platinum clusters were grown on a TiO2(110) surface and annealed in ultrahigh vacuum at high temperatures. This leads to the so-called strong metal-support interaction (SMSI) state, characterized by a complete encapsulation of the clusters with a reduced titanium oxide layer. We present atomically resolved scanning tunneling microscopy measurements of the cluster surfaces and an atomic model of the SMSI state. The ability to resolve the cluster surface geometry with atomistic detail may help to identify the active sites responsible for the SMSI.

Unfair treatment, neighborhood effects, and mental health in the Detroit metropolitan area.

Abstract: Why do racial differences in many indicators of mental and emotional well-being show inconsistent patterns? We propose that mental and emotional well-being are influenced by aspects of the social context, including experiences of unfair treatment and the concentration of households with incomes below the poverty level, and that differential exposure to these factors influences racial differences in mental well-being. We analyze the reporting of psychological distress and life satisfaction in a multistage area probability sample of 1,139 African American and white residents of the Detroit metropolitan area aged 18 and older. Both psychological distress and life satisfaction are significantly associated with exposure to unfair treatment and with the proportion of households in the census block group that were below the poverty level. Racial differences in psychological distress and life satisfaction were eliminated or reversed once differentials in the percent of households living below the poverty line and exposure to unfair treatment were accounted for. These findings contribute to a growing body of evidence that "race" effects operate through multiple pathways that include race-based residential segregation and its attendant economic disinvestment at the community level, and interpersonal experiences of unfair treatment.

On the Relationship of Synaptic Activity to Macroscopic Measurements: Does Co-Registration of EEG with fMRI Make Sense?

Abstract: Summary: A two-scale theoretical description outlines relationships between brain current sources and the resulting extracranial electric field ,r ecorded as EEG. Finding unknown sources of EEG, the so-called "inverse problem", is discussed in general terms, with emphasis on the fundamental non-uniqueness of inverse solutions. Hemodynamic signatures, measured with fMRI, are expressed as voxel integrals to facilitate comparisons with EEG. Two generally distinct cell groups (1 and 2), generating EEG and fMRI signals respectively, are embedded within the much broader class of synaptic action fields. Cell groups 1 and 2 may or may not overlap in specific experiments. Implications of this incomplete overlap for co-registration studies are considered. Each experimental measure of brain function is generally sensitive to a different kind of source activity and to different spatial and temporal scales. Failure to appreciate such distinctions can exacerbate conflicting views of brain function that emphasize either global integration or functional localization.

Long-term absolute benefit of lowering blood pressure in hypertensive patients according to the JNC VI risk stratification.

Abstract: —Blood pressure (BP) levels alone have been traditionally used to make treatment decisions in patients with hypertension. The sixth report of the Joint National Committee on Prevention, Det...

GAG‐augmented polysaccharide hydrogel: A novel biocompatible and biodegradable material to support chondrogenesis

Abstract: The quality of articular cartilage engineered using a cell-polymer construct depends, in part, on the chemical composition of the biomaterial and whether that biomaterial can support the chondrocytic phenotype. Acknowledging the supportive influence of tissue-specific matrix molecules on the chondrocytic phenotype, we have combined chondroitin sulfate-A (CSA) and chitosan, a glycosaminoglycan (GAG) analog, to develop a novel biomaterial to support chondrogenesis. Chitosan is a polycationic repeating monosaccharide of beta-1,4-linked glucosamine monomers with randomly located N-acetyl glucosamine units. Chitosan may be combined with the polyanionic CSA such that ionic crosslinking results in hydrogel formation. Bovine primary articular chondrocytes, when seeded onto a thin layer of CSA-chitosan, form discrete, focal adhesions to the material and maintain many characteristics of the differentiated chondrocytic phenotype, including round morphology, limited mitosis, collagen type II, and proteoglycan production. Our findings suggest CSA-chitosan may be well suited as a carrier material for the transplant of autologous chondrocytes or as a scaffold for the tissue engineering of cartilage-like tissue.

New grid of Arctic bathymetry aids scientists and mapmakers

Abstract: For over two decades, Sheet 5.17 of the Fifth Edition of the General Bathymetric Chart of the Oceans (GEBCO) [Canadian Hydrographic Service, 1979] has been considered the authoritative portrayal of the sea floor north of 64 N.This sheet was constructed from publicly available bathymetric data sets, which in the late 1970s were rather sparse, consisting almost entirely of underway measurements collected from ice-breakers, drifting ice islands, and point measurements obtained along snow-mobile tracks or using air support. Data coverage tended to be fairly good at lower latitudes where ice cover was not a hindrance, but at higher latitudes, where ice was more prevalent, major features such as the Amerasian and Eurasian Basins were not well delineated. This situation posed problems not only for expedition planners but also for scientific investigators, who needed an accurate description of the sea floor to design field experiments and to link their research with processes affecting or affected by the shape of the seabed (for example, sea level change, ocean circulation, sediment transport,seafloor spreading, and Pleistocene glaciation).

An O(T/sup 2/) boundary layer in sliding mode for sampled-data systems

Abstract: The use of a discontinuous control law (typically, sign functions) in a sampled-data system will bring about chattering phenomenon in the vicinity of the sliding manifold, leading to a boundary layer with thickness O(T), where T is the sampling period. However, by proper consideration of the sampling phenomenon in the discrete-time sliding mode control design, the thickness of the boundary layer can be reduced to O(T/sup 2/). In contrast to discontinuous control for continuous-time VSS, the discrete-time sliding mode control need not be of switching type.

The optic nerve head as a biomechanical structure: initial finite element modeling.

Abstract: Purpose To study the relationship between intraocular pressure (IOP) and the IOP-related stress (force/cross-sectional area) it generates within the load-bearing connective tissues of the optic nerve head Methods Thirteen digital, three-dimensional geometries were created representing the posterior scleral shell of 13 idealized human eyes Each three-dimensional geometry was then discretized into a finite element model consisting of 900 constituent finite elements In five models, the scleral canal was circular (diameters of 050, 150, 175, 200, and 256 mm), with scleral wall thickness (08 mm) and inner radius (120 mm) held constant In three models, the canal was elliptical (vertical-to-horizontal ratios of 2:1 [250 x 125 mm], 15:1 [21 x 14 mm], and 115:1 [192 x 167 mm]), with the same constant scleral wall thickness and inner radius In five additional models, scleral canal size was held constant (192 x 167 mm), and either scleral wall thickness (three models, 05, 10, and 15 mm) or inner radius (two models, 130 and 140 mm) was varied In all models, each finite element was assigned a single isotropic material property, either scleral (modulus of elasticity, 5500 kPa) or axonal (modulus of elasticity, 55 kPa) Maximum stresses within specific regions were calculated at an IOP of 15 mm Hg (2000 Pa) Results Larger scleral canal diameter, elongation of the canal, and thinning of the sclera increased IOP-related stress for a given level of IOP For all models, maximum IOP-related stress ranged from 6 x IOP (posterior sclera) to 122 x IOP (laminar trabeculae) For each model, maximum IOP-related stress was highest within the laminar trabecular region and decreased progressively through the laminar insertion, peripapillary scleral, and posterior scleral regions Varying the inner radius had little effect on the maximum IOP-related stress within the scleral canal Conclusions Initial finite element models show that IOP-related stress within the load-bearing connective tissues of the optic nerve head is substantial even at low levels of IOP Although the data suggest that scleral canal size and shape and scleral thickness are principal determinants of the magnitude of IOP-related stress within the optic nerve head, models that incorporate physiologic scleral canal and laminar geometries, a more refined finite element model meshwork, and nonisotropic material properties will be required to confirm these results