Showing papers by "University of Los Andes published in 2002"

A Human Genome Diversity Cell Line Panel

Abstract: A resource of 1064 cultured lymphoblastoid cell lines (LCLs) ([1][1]) from individuals in different world populations and corresponding milligram quantities of DNA is deposited at the Foundation Jean Dausset (CEPH) ([2][2]) in Paris. LCLs were collected from various laboratories by the Human Genome

CDMA uplink power control as a noncooperative game

Abstract: We present a game-theoretic treatment of distributed power control in CDMA wireless systems. We make use of the conceptual framework of noncooperative game theory to obtain a distributed and market-based control mechanism. Thus, we address not only the power control problem, but also pricing and allocation of a single resource among several users. A cost function is introduced as the difference between the pricing and utility functions, and the existence of a unique Nash equilibrium is established. In addition, two update algorithms, namely, parallel update and random update, are shown to be globally stable under specific conditions. Convergence properties and robustness of each algorithm are also studied through extensive simulations.

Evidence That Intermittent, Excessive Sugar Intake Causes Endogenous Opioid Dependence

Abstract: COLANTUONI, CARLO, PEDRO RADA, JOSEPH Mc-CARTHY, CAROLINE PATTEN, NICOLE M. AVENA,ANDREW CHADEAYNE, AND BARTLEY G. HOEBEL.Evidence that intermittent, excessive sugar intake causesendogenous opiod dependence. Obes Res. 2002;10:478–488.Objective: The goal was to determine whether withdrawalfrom sugar can cause signs of opioid dependence. Becausepalatable food stimulates neural systems that are implicatedin drug addiction, it was hypothesized that intermittent,excessive sugar intake might create dependency, as indi-cated by withdrawal signs.Research Methods and Procedures: Male rats were food-deprived for 12 hours daily, including 4 hours in the earlydark, and then offered highly palatable 25% glucose inaddition to chow for the next 12 hours. Withdrawal wasinduced by naloxone or food deprivation. Withdrawal signswere measured by observation, ultrasonic recordings, ele-vated plus maze tests, and in vivo microdialysis.Results: Naloxone (20 mg/kg intraperitoneally) causedsomatic signs, such as teeth chattering, forepaw tremor,and head shakes. Food deprivation for 24 hours causedspontaneous withdrawal signs, such as teeth chattering.Naloxone (3 mg/kg subcutaneously) caused reduced timeon the exposed arm of an elevated plus maze, whereagain significant teeth chattering was recorded. The plusmaze anxiety effect was replicated with four controlgroups for comparison. Accumbens microdialysis re-vealed that naloxone (10 and 20 mg/kg intraperitoneally)decreased extracellular dopamine (DA), while dose-depen-dently increasing acetylcholine (ACh). The naloxone-inducedDA/ACh imbalance was replicated with 10% sucrose and 3mg/kg naloxone subcutaneously.Discussion: Repeated, excessive intake of sugar created astate in which an opioid antagonist caused behavioral andneurochemical signs of opioid withdrawal. The indices ofanxiety and DA/ACh imbalance were qualitatively similarto withdrawal from morphine or nicotine, suggesting thatthe rats had become sugar-dependent.Key words: glucose, addiction, dopamine, plus maze,acetylcholine

A model for evaluating the degree of leanness of manufacturing firms

Abstract: Clarifies the concept of lean manufacturing and what it comprises. Commences with a review of the lean production literature and, specifically, existing models that identify the variables and component elements of lean production firms. Presents a research instrument for measuring the degree of leanness possessed by manufacturing firms. Research questions were developed and incorporated into structured survey questionnaires for both manufacturing directors and managing directors that enabled a quantitative assessment to be made for the various components of leanness. The survey was completed by over 30 firms in the UK ceramics tableware industry and so represents a comprehensive overview of the state of play in that sector. The figures derived allowed for hypotheses testing and a quantitative analysis. Presents selected results and conclusions from the current survey to illustrate the application and usefulness of the instrument. Argues that, though developed specifically for the tableware industry, the research instrument can be adapted for use in other industries.

Competitive routing in networks with polynomial costs

Abstract: We study a class of noncooperative general topology networks shared by N users. Each user has a given flow which it has to ship from a source to a destination. We consider a class of polynomial link cost functions adopted originally in the context of road traffic modeling, and show that these costs have appealing properties that lead to predictable and efficient network flows. In particular, we show that the Nash equilibrium is unique, and is moreover efficient. These properties make the polynomial cost structure attractive for traffic regulation and link pricing in telecommunication networks. We finally discuss the computation of the equilibrium in the special case of the affine cost structure for a topology of parallel links.

Decoherence of quantum registers

Abstract: The dynamical evolution of a quantum register of arbitrary length coupled to an environment of arbitrary coherence length is predicted within a relevant model of decoherence. The results are reported for quantum bits (qubits) coupling individually to different environments (``independent decoherence'') and qubits interacting collectively with the same reservoir (``collective decoherence''). In both cases, explicit decoherence functions are derived for any number of qubits. The decay of the coherences of the register is shown to strongly depend on the input states: We show that this sensitivity is a characteristic of both types of coupling (collective and independent) and not only of the collective coupling, as has been reported previously. A nontrivial behavior (``recoherence'') is found in the decay of the off-diagonal elements of the reduced density matrix in the specific situation of independent decoherence. Our results lead to the identification of decoherence-free states in the collective decoherence limit. These states belong to subspaces of the system's Hilbert space that do not get entangled with the environment, making them ideal elements for the engineering of ``noiseless'' quantum codes. We also discuss the relations between decoherence of the quantum register and computational complexity based on the dynamical results obtained for the register density matrix.

Photo-Fenton treatment of a biorecalcitrant wastewater generated in textile activities: biodegradability of the photo-treated solution

Abstract: Photo-Fenton process was explored as photochemical pre-treatment to improve the biodegradability of a wastewater coming from a textile industry located in the south of France, which was characterized as very biorecalcitrant by means of Zahn–Wellens biodegradability test. The effect of H2O2, Fe(III) and temperature on the photo-mineralization processes have been studied and the optimal conditions were found. Experiments were made to obtain information concerning the evolution of the biodegradability of the treated effluent after 40 and 70% of photo-mineralization. The photo-treated effluent is not biocompatible and its complete mineralization cannot be performed by biological means. UV–VIS and high-performance liquid chromatography (HPLC) analyses show that aromatic intermediates remain in the effluent after the photo-treatment, which have been identified as the principal reason of the biorecalcitrance.

Large surface magnetic contribution in amorphous ferromagnetic nanoparticles

Abstract: We present magnetization measurements on \ensuremath{\sim}3-nm $({\mathrm{Fe}}_{0.26}{\mathrm{Ni}}_{0.74}{)}_{50}{\mathrm{B}}_{50}$ ferromagnetic amorphous nanoparticles. Our results show evidence of the surface contribution to the magnetic properties in the $M(H),$ $M(T)$ and relaxation measurements. We observe a large increase in the magnetization with decreasing temperature, a nonsaturated component in the $M(H)$ curves, the presence of two maxima in the zero-field-cooling $M(T)$ data, and two viscosity regimes in magnetization relaxation data. The results have been interpreted by a simple model where we consider each single-domain particle as a core plus shell system with a uniaxial anisotropy acting on the core and a surface anisotropy acting on the shell. Monte Carlo simulations based in this core-shell model qualitatively reproduce all the observed phenomena.

Magnetic properties of maghemite nanoparticle systems: surface anisotropy and interparticle interaction effects

Abstract: The static and dynamic magnetic properties of powders of maghemite nanoparticles with average diameter D =2.7, 4.6 and 8.7 nm have been investigated by magnetisation, AC susceptibility at variable frequency (5 ν 4 Hz) and Mossbauer spectroscopy measurements. The results provide an insight into the correlation between intra-particle and inter-particle effects.

Hybrid sterility, Haldane's rule and speciation in Heliconius cydno and H. melpomene.

Abstract: Most genetic studies of Haldane9s rule, in which hybrid sterility or inviability affects the heterogametic sex preferentially, have focused on Drosophila. It therefore remains unclear to what extent the conclusions of that work apply more generally, particularly in female-heterogametic taxa such as birds and Lepidoptera. Here we present a genetic analysis of Haldane9s rule in Heliconius butterflies. Female F 1 hybrids between Heliconius melpomene and H. cydno are completely sterile, while males have normal to mildly reduced fertility. In backcrosses of male F 1 hybrids, female offspring range from completely sterile to fully fertile. Linkage analysis using the Z-linked triose-phosphate isomerase locus demonstrates a “large X” (Z) effect on sterility. Expression of female sterility varies among crosses in this and a previous study of Heliconius. Sterility may result from the production of normal but infertile eggs, production of small infertile eggs, or from a complete failure to develop ovarioles, which suggests multiple routes to the evolution of hybrid sterility in these Heliconius species. These results conform to the expectations of the “dominance” rather than “faster male” theories of Haldane9s rule and suggest that relatively few loci are responsible. The two species are broadly sympatric and hybridize in the wild, so that female hybrid sterility forms one of several strong but incomplete barriers to gene flow in nature. The effect of female sterility is comparable to that of selection against non-mimetic hybrids, while mate choice forms a much stronger barrier to gene transfer.

Human Carcinogenesis and Bracken Fern: A Review of the Evidence

Abstract: The complex taxon embraced in the Pteridium genus, popularly known as bracken fern and notorious weeds in many parts of the world, is one of the few vascular plants known to induce cancer naturally in animals. It has been known for long to be acutely toxic to livestock and sublethal chronic oral feeding of bracken fronds leads to cancerous lesions in the urinary bladder, or bovine enzootic haematuria (BEH) and ileum of cattle. Bracken poisoning has been attributed chiefly to ptaquiloside, a norsesqui-terpene which is also a potent carcinogen inducing various malignancies in laboratory animals. It is capable of alkylating uncoiled DNAbases at key proto-oncogenes of selected organs. Some human populations also eat young bracken shoots and epidemiological studies in Japan and Brazil have shown a close association between bracken consumption and cancers of the upper alimentary tract. In addition, other studies reveal that the mere presence of bracken swards represents a greater risk to die of gastric adenocarcinoma for people who live more than 20 years in such areas or are exposed in childhood. This work reviews the bracken-cancer connections established by in vitro and in vivo experiments and epidemiological studies in various parts of the world, and provides insights into the possible bridges for bracken carcinogens to reach the human diet. Also, specific points where more research is needed are highlighted.

Effects of seed dispersal by three ateline monkey species on seed germination at Tinigua National Park, Colombia

Abstract: We examined the effect of seed ingestion by three ateline primates: woolly monkeys, Lagothrix lagothricha; spider monkeys, Ateles belzebuth; and, red howler, Alouatta seniculus on germination rates and latency periods of seeds of several plant species in Tinigua National Park, Colombia. We collected dispersed seeds from feces and control seeds from the parental trees and washed them for germination trials. For the majority of plants, dispersed seeds germinated as well or better than control seeds did. Although spider monkeys depend more heavily on fruits than the other monkey species do, they were not more efficient than howlers or woolly monkeys at improving germination rates. A considerable proportion of the seeds dispersed by howlers and woolly monkeys showed reduced latency periods to germination, but spider monkeys showed less effect on reducing germination time. This result may be related to longer gut retention times, but such a trend has not been observed in other primate species. We conclude that, like many other primates, ateline monkeys are effective seed dispersers in terms of their effects on the seeds they swallow because they rarely decrease their germination rates. We discuss problems that make interspecific comparisons difficult, such as inappropriate control seeds and differences associated with germination substrates, and we stress the importance of studying other components of seed dispersal effectiveness.

Decomposition of standard plant material along an altitudinal transect (65–3968m) in the tropical Andes

Abstract: The dynamics of plant decomposition in the soil were analysed in an altitudinal transect from 65 to 3968 m under tropical conditions. Six sites were studied, with a mean annual temperature ranging from 5.5 to 27.4°C, and an annual precipitation from 790 to 1992 mm. A 14 C-labelled standard plant material was incubated in situ, at 5 cm depth, over a period of 1.5–3 years, depending on the altitude. The aim was to determine the contribution of climate (temperature and moisture) and of other factors, such as soil properties, to explaining the differences in mineralisation between the sites. Data analysis was performed using two-compartment models with first-order kinetics. To evaluate the effect of climate on decomposition, a response function to temperature ( τ ) and a response function to moisture ( μ ) were calculated. The kinetics of the remaining 14 C were adjusted to the two-compartment first-order model considering successively time, τ cum (cumulated τ ), and τμ cum (cumulated τμ ) as independent variables. The assumption was that if the introduction of a climatic component into the explanatory variable reduces the distances between the decomposition curves of the sites, the differences are related to this factor. If the distance is not reduced, other factors in addition to climate must influence decomposition and/or the climatic response to altitude is not linear. The results show a clear decrease in decomposition with increasing altitude. Nevertheless, the altitudinal effect is not equal for the two fractions estimated using the two-compartment model. The size of the labile fraction decreased with altitude, whereas the recalcitrant fraction increased. The labile fraction decomposed very quickly, independently of the altitude, whereas the rate of decomposition of the recalcitrant fraction decreased with altitude. When τ cum is used as the independent variable, the distance between the curves diminishes, indicating the great effect of temperature on decomposition, but in the high mountain sites, additional factors act. Using τμ cum the difference between sites was not reduced, showing that the moisture effect is low or that the moisture response function is not appropriate.

Global Optimization of Gas Allocation to a Group of Wells in Artificial Lift Using Nonlinear Constrained Programming

Abstract: Continuous flow gas lift is one of the most common artificial lift methods widely used in the oil industry. A continuous volume of high-pressure gas is injected as deep as possible into the tubing, to gasify the oil column, and thus facilitate the production. If there is no restriction in the amount of injection gas available, sufficient gas can be injected into each oil well to reach maximum production. However, the injection gas available is generally insufficient. An inefficient gas allocation in a field with limited gas supply reduces the revenues, since excessive gas injection is expensive due to the high gas prices and compressing costs. Therefore, it is necessary to assign the injection gas into each well in optimal form to obtain the field maximum oil production rate. The gas allocation optimization can be considered as a maximization of a nonlinear function, which models the total oil production rate for a group of wells. The variables or unknowns for this function are the gas injection rates for each well, which are subject to physical restrictions. In this work a nonlinear optimization technique, based on an objective function with constraints, was implemented to find the optimal gas injection rates. A new mathematical fit to the gas-lift performance curve (GLPC) is presented and the numeric results of the optimization are given and compared with those of other methods published in the specialized literature. The GLPC can be either measured in the field, or alternatively generated by computer simulations, by mean of nodal analysis. The optimization technique proved fast convergence and broad application.

Increase in the woody component of seasonal savannas under different fire regimes in Calabozo, Venezuela

Abstract: Aim We tested the hypothesis that exclusion from fire and cattle is responsible for the increase in tree cover in open savanna vegetation. Location Four plots in open savanna vegetation from the Calabozo region in central Venezuela were studied. Plot A was located in a Biological Station (EBL) that was excluded from fire and cattle between 1961 and 1991, with only two burning events in 1964 and 1968. The other plots (B, C, D) were located within 2 km distance from A, in neighbouring farms with soils similar to those in A but under various regimes of land use and fire frequency. Methods We measured the cover of isolated trees, small tree groups and groves of each plot in 1960 and 1977 using geographic information system (GIS) and digitalized aerial photographs. Additionally, the plots were located in the field and the open grassland was sampled in 1995 for species composition and density of stems above 20 cm height. Information on land use was obtained surveying people at the farms. Results There was an increase in the woody component of all plots during the 17-year interval (1960‐1977). Total woody cover in the four plots as a whole increased from 4.5% to 17.9%. All three components measured, groves, tree groups and isolated trees, increased despite differences in land use and fire frequency between plots. Contrary to our expectations, the field survey performed in 1995 showed that fire-sensitive species were abundant in the open savanna in plots B, C and D, which were not excluded. Plot B, with the most intense agricultural use showed the highest rate of woody increase, and plot C, under extensive cattle ranching, was second. The results also showed that woody cover increased by aggregation from single trees and small tree groups into groves. As a consequence of these changes, savanna physiognomy changed from open to dense savanna parkland with a woody cover reaching over 25% in one of the four plots. Conclusions The results agree with other reported increases in woody cover in savannas under exclusion or with annual fires during the same time period in Africa (Dauget & Menaut, 1992). Our results support evidence from previous studies showing that fire and grazing are only part of a complex system of interacting factors affecting the structure of savanna communities.

Iron(III) photoxidation of organic compounds in aqueous solutions

Abstract: The treatment of aqueous phenol (100 mg l −1 ) and nitrobenzene (50 mg l −1 ) solutions using iron(III) and UV radiation has been carried out. The quantum yield of photodegradation of both compounds has been determined ( φ phenol =11.2±2.0 mmol einstein −1 , φ NB =6.0±0.5 mmol einstein −1 ). The effect of the amount of ferric ion in the degradation rate has been studied in the range of molar iron(III) to organic compound ratios from 0 to 6. The reaction rate showed to follow a first-order kinetic with respect to the substrate and the kinetic constant depends on the Fe(III)/organic ratio. Optimal values of these kinetic constants have been found.

Operators which have a closed quasi-nilpotent part

Abstract: We find several conditions for the quasi-nilpotent part of a bounded operator acting on a Banach space to be closed. Most of these conditions are established for semi-Fredholm operators or, more generally, for operators which admit a generalized Kato decomposition. For these operators the property of having a closed quasi-nilpotent part is related to the so-called single valued extension property.

A novel uninterruptible power supply system with active power factor correction

Abstract: This paper presents a simplified sinusoidal uninterruptible power supply (UPS) system. The proposed scheme includes features such as high power factor, low total harmonic distortion and good dynamic response at the AC output voltage. In addition, the scheme has the desirable characteristics, of high efficiency, simple circuit and low cost compared with a traditional standalone multiple stages UPS with power factor correction. The paper also presents the circuit operation, the analysis and, experimental results of the proposed UPS scheme. The proposed UPS approach is a good solution in low. power applications (/spl les/500 W).

Inequalities in health in Latin America and the Caribbean: descriptive and exploratory results for self-reported health problems and health care in twelve countries

Abstract: Objective. To explore and describe inequalities in health and use of health care as revealed by self-report in 12 countries of Latin America and the Caribbean. Methods. A descriptive and exploratory study was performed based on the responses to questions on health and health care utilization that were included in general purpose household surveys. Inequalities are described by quintile of household expenditures (or income) per capita, sex, age group (children, adults, and older adults), and place of residence (urban vs. rural area). For those who sought health care, median polishing was performed by economic status and sex, for the three age groups. Results. Although the study is exploratory and descriptive, its findings show large economic gradients in health care utilization in these countries, with generally small differences between males and females and higher percentages of women seeking health care than men, although there were some exceptions among the lower economic strata in urban areas. Conclusions. Inequalities in self-reported health problems among the different economic strata were small, and such problems were usually more common among women than men. The presence of small inequalities may be due to cultural and social differences in the perception of health. However, in most countries included in the study, large inequalities were found in the use of health care for the self-reported health problems. It is important to develop regional projects aimed at improving the questions on self-reported health in household interview surveys so that the determinants of the inequalities in health can be studied in depth. The authors conclude that due to the different patterns of economic gradients among different age groups and among males and females, the practice of standardization used in constructing concentration curves and in computing concentration indices should be avoided. At the end is a set of recommendations on how to improve these sources of data. Despite their shortcomings, household interview surveys are very useful in understanding the dimensions of health inequalities in these countries.

Model theory of stochastic processes

Abstract: This book presents new research in probability theory using ideas from mathematical logic. It is a general study of stochastic processes on adapted probability spaces, employing the concept of similarity of stochastic processes based on the notion of adapted distribution. The authors use ideas from model theory and methods from nonstandard analysis. The construction of spaces with certain richness properties, defined by insights from model theory, becomes easy using nonstandard methods, but remains difficult or impossible without them.

Physiological Responses to Ambient Temperature Manipulation by three Species of Bats from Andean Cloud Forests

Abstract: ´ridas, Universidad Nacional Experimental Francisco de Miranda, Apartado 7506 Coro, Venezuela (AA) In this paper we test the hypothesis that bats of the Andean highlands show distinctive metabolic responses compared with bats from lowland forests. We compared existing literature with new information on 3 bat species having the following food habits: a nectarivore (Anoura latidens), a frugivore (Sturnira erythromos), and an insectivore (Tadarida brasiliensis). Basal metabolic rate, as determined by oxygen consumption, thermal conductance, and body temperature were measured at ambient temperatures of 10‐38 8C. Some distinctive metabolic responses of these bat species, although varying with respect to food guild, allow us to separate them from counterpart species that are typically found in lowland forests. A. latidens is characterized by higher basal metabolic rate; however, thermal conductance and lower critical temperature values do not show an adaptation to cool environments, as expected. S. erythromos also increases its basal metabolic rate, but it maintains thermal conductance as expected, which implies a very important displacement of thermoneutral zone to lower temperatures. At temperatures below lower critical temperature, in addition to an endothermic response, S. erythromos sometimes expresses a hypothermic response or facultative torpor, independent of sex and body mass. T. brasiliensis has a lower basal metabolic rate and thermal conductance and also has its thermoneutral zone range displaced toward lower temperatures. Likewise, this species enters obligate torpor when ambient temperatures are below 22 8C.