Showing papers by "University of Los Andes published in 1999"

Culture specific and cross-culturally generalizable implicit leadership theories: Are attributes of charismatic/transformational leadership universally endorsed?

Abstract: This study focuses on culturally endorsed implicit theories of leadership (CLTs). Although cross-cultural research emphasizes that different cultural groups likely have different conceptions of what leadership should entail, a controversial position is argued here: namely that attributes associated with charismatic/transformational leadership will be universally endorsed as contributing to outstanding leadership. This hypothesis was tested in 62 cultures as part of the Global Leadership and Organizational Behavior Effectiveness (GLOBE) Research Program. Universally endorsed leader attributes, as well as attributes that are universally seen as impediments to outstanding leadership and culturally contingent attributes are presented here. The results support the hypothesis that specific aspects of charismatic/transformational leadership are strongly and universally endorsed across cultures.

Body weight gain induced by antipsychotic drugs: mechanisms and management.

Abstract: Long-term administration of typical and atypical antipsychotic drugs (AP) induces excessive weight gain which afflicts up to 50% of patients, impairs health and interferes with treatment compliance. Basic and clinical research has shown that AP may affect body weight through diverse mechanisms. Increased appetite is probably related to the interaction of AP with neuronal receptors to dopamine, serotonin and histamine. Additional metabolic-endocrine disruption of weight regulation may be related to the effects of AP-induced hyperprolactinaemia on gonadal-adrenal steroids and insulin sensitivity. In humans, programmed physical activity, dietary restriction, anorectic agents, and drugs that counteract hyperprolactinaemia have been shown to be successful in a limited number of studies. Two novel strategies could expand the available therapeutic options. First, in preclinical experiments in female rats the estradiol antagonist/agonist drug tamoxifen or estradiol itself have been shown to completely prevent the obesity provoked by the AP sulpiride, and to induce an endocrine-metabolic milieu that seems to counteract AP-induced obesity. Secondly, it has also been shown that oral antihyperglycaemic agents such as metformin may decrease body weight and counteract insulin resistance and hyperinsulinaemia which is correlated with several metabolic abnormalities in obese subjects. Lastly, estradiol replacement, tamoxifen and/or antihyperglycaemic agents are not devoid of significant side-effects, and these drugs have not been tested in obese psychiatric patients. Therefore, further research is needed before their clinical use may be recommended.

Partitioning of soil water among canopy trees in a seasonally dry tropical forest

Abstract: Little is known about partitioning of soil water resources in species-rich, seasonally dry tropical forests. We assessed spatial and temporal patterns of soil water utilization in several canopy tree species on Barro Colorado Island, Panama, during the 1997 dry season. Stable hydrogen isotope composition (δD) of xylem and soil water, soil volumetric water content (θv), and sap flow were measured concurrently. Evaporative fractionation near the soil surface caused soil water δD to decrease from about –15‰ at 0.1 m to –50 to –55‰ at 1.2 m depth. Groundwater sampled at the sources of nearby springs during this period yielded an average δD value of –60‰. θv increased sharply and nearly linearly with depth to 0.7 m, then increased more slowly between 0.7 and 1.05 m. Based on xylem δD values, water uptake in some individual plants appeared to be restricted largely to the upper 20 cm of the soil profile where θv dropped below 20% during the dry season. In contrast, other individuals appeared to have access to water at depths greater than 1 m where θv remained above 45% throughout the dry season. The depths of water sources for trees with intermediate xylem δD values were less certain because variation in soil water δD between 20 and 70 cm was relatively small. Xylem water δD was also strongly dependent on tree size (diameter at breast height), with smaller trees appearing to preferentially tap deeper sources of soil water than larger trees. This relationship appeared to be species independent. Trees able to exploit progressively deeper sources of soil water during the dry season, as indicated by increasingly negative xylem δD values, were also able to maintain constant or even increase rates of water use. Seasonal courses of water use and soil water partitioning were associated with leaf phenology. Species with the smallest seasonal variability in leaf fall were also able to tap increasingly deep sources of soil water as the dry season progressed. Comparison of xylem, soil, and groundwater δD values thus pointed to spatial and temporal partitioning of water resources among several tropical forest canopy tree species during the dry season.

Myocardial parasite persistence in chronic chagasic patients.

Abstract: The persistence of Trypanosoma cruzi tissue forms was detected in the myocardium of seropositive individuals clinically diagnosed as chronic chagasic patients following endomyocardial biopsies (EMBs) processed by immunohistochemical (peroxidase-anti-peroxidase [PAP] staining) and molecular (polymerase chain reaction [PCR]) techniques. An indirect immunofluorescent technique revealed antigenic deposits in the cardiac tissue in 24 (88.9%) of 27 patients. Persistent T. cruzi amastigotes were detected by PAP staining in the myocardium of 22 (84.6%) of 26 patients. This finding was confirmed with a PCR assay specific for T. cruzi in 21 (91.3%) of 23 biopsy specimens from the same patients. Statistical analysis revealed substantial agreement between PCR and PAP techniques (k = 0.68) and the PCR and any serologic test (k = 0.77). The histopathologic study of EMB specimens from these patients revealed necrosis, inflammatory infiltrates, and fibrosis, and made it possible to detect heart abnormalities not detected by electrocardiogram and/or cineventriculogram. These indications of myocarditis were supported by the detection of T. cruzi amastigotes by the PAP technique or its genome by PCR. They suggest that although the number of parasites is low in patients with chronic Chagas' disease, their potential for heart damage may be comparable with those present during the acute phase. The urgent necessity for testing new drugs with long-term effects on T. cruzi is discussed in the context of the present results.

Entangled bell and greenberger-horne-zeilinger states of excitons in coupled quantum dots

Abstract: We show that excitons in coupled quantum dots are ideal candidates for reliable preparation of entangled states in solid-state systems. An optically controlled exciton transfer process is shown to lead to the generation of Bell and Greenberger-Horne-Zeilinger states in systems comprising two and three coupled dots, respectively. The strength and duration of selective light pulses for producing maximally entangled states are identified by both analytic and full numerical solution of the quantum dynamical equations. Experimental requirements to build such entangled states are discussed.

Isolation of Trypanosoma cruzi DNA in 4,000-year-old mummified human tissue from northern Chile.

Abstract: A segment of DNA unique to the kinetoplast of Trypanosoma cruzi was isolated from spontaneously mummified human remains from the coastal area of northern Chile at sites dated from 2000 BC to about AD 1400. Following rehydration of the desiccated human tissue samples of heart, esophagus, or colon, the samples were extracted and primers employed to bind to a 330 bp kinetoplast minicircle DNA sequence present in T. cruzi. This segment was then amplified using the polymerase chain reaction (PCR), and the target segment was visualized by gel electrophoresis. This method enables the identification of Chagas' disease in an ancient body in the absence of recognizable anatomic pathological changes.

Properties of Resins Extracted from Boscan Crude Oil and Their Effect on the Stability of Asphaltenes in Boscan and Hamaca Crude Oils

Abstract: Experimental results confirm that resins isolated from Boscan crude oil have a stabilizing effect on asphaltenes in Hamaca crude oil and in Boscan crude oil. A simple experimental technique, referred to as the filter drop spreading method, was used to detect the onset of flocculation quite accurately for crude oil mixtures and for mixtures of crude oils plus additives.

Acute Chagas' disease in western Venezuela: a clinical, seroparasitologic, and epidemiologic study.

Abstract: A clinical, parasitologic, and serologic study carried out between 1988 and 1996 on 59 acute-phase patients in areas of western Venezuela where Chagas' disease is endemic showed 19 symptomatic patterns or groups of symptoms appearing in combination with different frequencies The symptomatic pattern with the highest frequency was that showing simultaneously fever, myalgia, headache, and Romana's sign, which was detected in 20% of the acute-phase patients Asymptomatic individuals and patients with fever as the only sign of the disease made up 15% and 119% of the total acute cases, respectively Statistical correlation analysis revealed that xenodiagnosis and hemoculture were the most reliable and concordant of the five parasitologic methods used; these two methods also showed the highest proportions in detecting any clinical symptomatic pattern in acute-phase patients A similar high reliability and concordance was obtained with a direct agglutination test, an indirect immunofluorescent antibody test, and an ELISA as serologic tests, which also showed a higher proportion of positive detection of clinical patterns than parasitologic methods (P < 0001) It is recommended that individuals coming from endemic areas showing mild and/or severe clinical manifestations should be suspected of being in contact or having been in contact with Trypanosoma cruzi, be referred for parasitologic and serologic evaluations to confirm the presumptive clinical diagnosis of acute Chagas' disease, and start specific treatment The epidemiologic implications of the present findings are discussed and the use of similar methodology to evaluate other areas where Chagas' disease is endemic is suggested

Search for charged Higgs bosons in decays of top quark pairs

Abstract: We present a search for charged Higgs bosons in decays of pair-produced top quarks using 109.2{plus_minus}5.8 pb{sup {minus}1} of data recorded from p{ovr p} collisions at {radical}(s)=1.8 TeV by the D0 detector during 1992{endash}1996 at the Fermilab Tevatron. No evidence is found for charged Higgs production, and most parts of the [M{sub H{sup +}} {beta}] parameter space where the decay t{r_arrow}H{sup +}b has a branching fraction close to or larger than that for t{r_arrow}W{sup +}b are excluded at 95{percent} confidence level. Assuming m{sub t}=175 GeV and {sigma}(p{ovr p}{r_arrow} t{ovr t})=5.5 pb , for M{sub H{sup +}}=60 GeV , we exclude tan{number_sign}{beta}{lt}0.97 and tan{number_sign}{beta}{gt}40.9 . {copyright} {ital 1999} {ital The American Physical Society}

Variable structure control applied to chemical processes with inverse response

Abstract: This article proposes the use of a sliding mode controller based on a first-order-plus-deadtime model of the system for controlling higher-order chemical processes with inverse response. The controller has a simple and fixed structure with a set of tuning equations as a function of the characteristic parameters of the first order-plus-deadtime model. The controller performance was judged via computer simulations using linear and nonlinear models of chemical processes with inverse response.

Output-feedback global stabilization of a nonlinear benchmark system using a saturated passivity-based controller

Abstract: We address the problem of regulation of the benchmark rotational/translational proof mass actuator using a passivity-based controller, We show that a (relatively straightforward) modification of the output feedback saturated input controller proposed by the authors in a previous paper provides a simple and robust solution to the global asymptotic stabilization problem. The design technique is based on the practically appealing principles of energy shaping and damping injection. Computer simulations show that the performance is comparable, and in some respects better, than the one obtained with a far more complicated full-state unsaturated feedback controller.

Mannose receptor is present in a functional state in rat microglial cells.

Abstract: We studied the expression of the mannose receptor (ManR) in rat microglial cells. Microglial cells are the central nervous system resident macrophages, key participants of the innate immune response. ManR is a differentiation marker and a relevant glycoprotein for the phagocytic and endocytic function of macrophages. Because there is evidence suggesting that ManR could mediate some of the nonenzymatic effects of acetilcholinesterase (AchE) and the enzyme seems to be involved in Alzheimer's disease (AD), we looked for ManR in microglia, evaluating the functionality of the receptor. We isolated microglial cells from the brain of 2-day-old neonatal rats. Microglial cells, identified by their specific staining with the lectin Griffonia simplicifolia, expressed ManR, being detected by immunocytochemistry, Western blot, and immunoprecipitation. Microglial ManR was downregulated by lipopolysaccharide (LPS) and upregulated by dexamethasone, as described for peripheral macrophages. Microglial ManR was functional and able to internalize horseradish peroxidase (HRP), a known ManR ligand, in a mannan-inhibitable manner. The presence of a functional ManR in microglia opens the possibility that ManR could participate in multiple physiologic and pathologic conditions in the central nervous system (CNS), including inflammation, ischaemia, and neurodegenerative diseases such as AD.

Determination of the absolute jet energy scale in the DØ calorimeters

Abstract: The DO detector is used to study p p collisions at the 1800 and 630 GeV center-of-mass energies available at the Fermilab Tevatron. To measure jets, the detector uses a sampling calorimeter composed of uranium and liquid argon as the passive and active media, respectively. Understanding the jet energy calibration is not only crucial for precision tests of QCD, but also for the measurement of particle masses and the determination of physics backgrounds associated with new phenomena. This paper describes the energy calibration of jets observed with the DO detector at the two p p center-of-mass energies in the transverse energy and pseudorapidity range ET>8 GeV and |η|

Measurement of the high-mass Drell-Yan cross section and limits on quark-electron compositeness scales

Abstract: We present a measurement of the Drell-Yan cross section at high dielectron invariant mass using $120\mathrm{pb}{}^{\ensuremath{-}1}$ of data collected in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ by the D0 Collaboration during 1992--1996. No deviation from standard model expectations is observed. We use the data to set limits on the quark-electron compositeness scale. The $95%$ confidence level lower limits on the compositeness scale vary between 3.3 and 6.1 TeV depending on the assumed form of the effective contact interaction.

Levels of amino acid neurotransmitters during mouse cerebellar neurogenesis and in histotypic cerebellar cultures.

Abstract: The variation in the levels of excitatory (glutamate and aspartate) and inhibitory (GABA, glycine and taurine) neurotransmitters during neurogenesis in mouse cerebellum, from embryonic day (E) 15 until the young adult stage, was analyzed by high-pressure liquid chromatography. Between E15 and E21, high contents of GABA, glutamate and aspartate were detected, with the GABA levels approximately 2- to 3-fold higher than those of glutamate and aspartate. After birth, the levels of GABA remained high during the first 2 postnatal weeks and then reached a plateau comparable to adult values by the third week. The levels of glutamate and aspartate increased gradually from birth to the young adult stage, showing peak values at postnatal days (P) 3 and P11. Glycine and taurine were present at relatively low concentrations during the prenatal period, then rose significantly by about 4-fold after birth; their levels decreased by the end of the first postnatal week but increased gradually thereafter until reaching adult values by the third week. To determine the endogenous neurotransmitter production in the cerebellar cortex, primary histotypic cerebellar cultures prepared at P10 were analyzed and the in vitro transmitter contents were compared with the adult in situ values. The cultures showed about the same levels of glutamate and aspartate; however, their concentrations were lower by half than in vivo, suggesting that both play an equally important role in the excitatory neurotransmission of the cerebellar cortex internal circuitry pathways and that in mature cerebellum, about 50% of the excitatory synaptic inputs derive from the afferent climbing and mossy fibers. The in vitro GABA and glycine contents were comparable with the in vivo levels, whereas the taurine concentrations were about 5-fold lower in vitro than in vivo. These findings indicate that most of the GABA and glycine transmitters are produced intrinsically while a high proportion of taurine in the cerebellum comes from extracerebellar afferents. This study provides data on the changing levels of the amino acid neurotransmitters in developing mouse cerebellum and the relative proportions of neurotransmitter contents that are produced by intrinsic neurons in contrast to those derived from extrinsic afferent fibers.

Search for squarks and gluinos in events containing jets and a large imbalance in transverse energy

Abstract: Using data corresponding to an integrated luminosity of $79{\mathrm{pb}}^{\ensuremath{-}1}$, D0 has searched for events containing multiple jets and large missing transverse energy in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}18\phantom{\rule{0ex}{0ex}}\mathrm{TeV}$ at the Fermilab Tevatron collider Observing no significant excess beyond what is expected from the standard model, we set limits on the masses of squarks and gluinos and on the model parameters ${m}_{0}$ and ${m}_{1/2}$, in the framework of the minimal low-energy supergravity models of supersymmetry For $\mathrm{tan}\ensuremath{\beta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$ and ${A}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$, with $\ensuremath{\mu}l0$, we exclude all models with ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{q}}l250\phantom{\rule{0ex}{0ex}}\mathrm{GeV}{/c}^{2}$ For models with equal squark and gluino masses, we exclude $ml260\phantom{\rule{0ex}{0ex}}\mathrm{GeV}{/c}^{2}$

Effects of irrigation on litterfall, fine root biomass and production in a semideciduous lowland forest in Panama

Abstract: The effects of irrigation on fine root biomass, root production and litterfall were measured at the community level, in a semideciduous lowland forest in Panama. Biomass of roots less than 2 mm in dia. in the first 10 cm of the soil (measured with soil cores), was higher in irrigated (1.80 Mg ha-1) than in non-irrigated plots (1.24 Mg ha-1). During the dry season, productivity of roots (measured with ingrowth cylinders filled with root-free soil), was higher in irrigated (1.6 g m-2 day-1) than in control plots (0.3 g m-2 day-1). In control plots, root productivity was highly seasonal. Maximum root growth into the root-free soil, occurred during the transitions from dry to wet, and from wet to dry season, possibly as a response to water and/or nutrient pulses. Litterfall was not significantly different between irrigated (3.8 g m-2 day-1) and control plots (3.7 g m-2 day-1). The results of this study show that root-productivity is limited by the water supply during the dry season, and that water by itself, is not a limiting factor for community-level litter production.

Visions of community for community OR

Abstract: Operational researchers in the United States have been working with community groups since the late 1960s (Ackoff, 1970), and in the UK since the mid-1970s (Noad and King, 1977; Trist and Burgess, 1978)—some ten years before the term ‘community OR’ was first coined. However, the labelling of community OR as a specific sub-discipline of operational research facilitated a significant expansion of this kind of activity. In 1986, funding from the Operational Research Society was secured to base a Community OR Unit at Northern College in the UK, and this opened in 1988. In 1987, the Community OR Network (a study group of the Operational Research Society) was formed (with over 300 members), and the Centre for Community OR was opened at the University of Hull (later to be merged into the Centre for Systems Studies, resulting in a massive expansion of community OR activity at Hull). Since 1987, there have been community OR streams at many national and international conferences, and two conferences have been dedicated solely to community OR. More detailed histories of the institutional development of the community OR movement can be found elsewhere (Parry and Mingers, 1991; Ritchie, 1994).

Antipsychotic drugs and reproductive hormones: relationship to body weight regulation.

Abstract: Excessive body weight gain is an undesirable side effect of prolonged administration of antipsychotic drugs (AP), which affects health and interferes with treatment compliance. It has been suggested that hyperprolactinemia-induced endocrine and metabolic abnormalities, particularly in the gonadal steroids, might be involved in the development of this type of weight gain. To test this hypothesis, reproductive hormones, cortisol, dehydro-epiandrosterone-sulfate (DHEA-S), thyroid hormones, and body weight gain were assessed in 18 patients (9 men, 9 women) with mental disorders receiving AP who had been medication-free for at least 3 months before the study, and in 27 placebo-treated subjects (10 men, 17 women). In women, hormones were evaluated during several phases of the menstrual cycle. A significant weight gain was observed in men but not in women. Under AP administration, women displayed significantly lower serum levels of estradiol and progesterone, whereas in men the levels of free testosterone and DHEA-S were significantly lower than in controls. Hyperprolactinemia was observed in both sexes. The levels of follicle-stimulating hormone in women and luteinizing hormone in men were significantly elevated by treatment, thus suggesting that the functioning of the hypothalamus-pituitary gonads was preserved. In men, such an endocrine profile resembles that observed in subjects with primary obesity. Women under AP administration were found to be relatively hyperandrogenic because of decreased serum estradiol levels, whereas women with primary obesity are known to display actual increased levels of androgens. These endocrine abnormalities may contribute to the excessive weight gain observed after AP treatment, and these could be the target of novel pharmacological treatments.

Non-local equation of state in general relativistic radiating spheres

Abstract: We show that under particular circumstances a general relativistic spherically symmetric bounded distribution of matter could satisfy a non-local equation of state. This equation describes, at a given point, the components of the corresponding energy-momentum tensor not only as a function at that point, but as a functional throughout the enclosed configuration. We have found that these types of dynamic bounded matter configurations, with constant compactness or gravitational potentials at the surface, admit a conformal Killing vector field and fulfil the energy conditions for anisotropic imperfect fluids. We present several analytical and numerical models satisfying these equations of state which collapse as reasonable radiating anisotropic spheres in general relativity.