Showing papers by "University of Los Andes published in 1994"

The DØ detector

Abstract: The DO detector is a large general purpose detector for the study of short-distance phenomena in high energy antiproton-proton collisions, now in operation at the Fermilab Tevatron collider. The detector focusses upon the detection of electrons, muons, jets and missing transverse momentum. We describe the design and performance of the major elements of the detector, including the tracking chambers, transition radiation detector, liquid argon calorimetry and muon detection. The associated electronics, triggering systems and data acquisition systems are presented. The global mechanical, high voltage, and experiment monitoring and control systems which support the detector are described. We also discuss the design and implementation of software and software support systems that are specific to DO.

Time-frequency digital filtering based on an invertible wavelet transform: an application to evoked potentials

Abstract: Presents a method to analyze and filter digital signals of finite duration by means of a time-frequency representation. This is done by defining a purely invertible discrete transform, representing a signal either in the time or in the time-frequency domain, as simply as possible with the conventional discrete Fourier transform between the time and the frequency domains. The wavelet concept has been used to build this transform. To get a correct invertibility of this procedure, the authors have proposed orthogonal and periodic basic discrete wavelets. The properties of such a transform are described, and examples on brain-evoked potential signals are given to illustrate the time-frequency filtering possibilities. >

Ecological strategies of woolly monkeys (Lagothrix lagotricha) at Tinigua National Park, Colombia.

Abstract: Information on the use of space, activity patterns, diet, and social interactions were recorded for a group of woolly monkeys (Lagothrix lagotricha) during 13 months at Tinigua National Park, Macarena, Colombia. In this region, fruit abundance changes throughout the year with a peak during March-April (beginning of the rainy season) and less fruit during September-November (end of rainy season). Woolly monkeys spent most of their time in mature forest where fruit abundance is higher than in opendegraded or flooded forests. Changes in habitat used by monkeys were coupled with changes in fruit supply across vegetation types. On an annual basis, woolly monkeys spent 24% of point samples locomoting, 36% resting, 36% feeding, and 4% on other activities. However, these proportions varied across the year depending on fruit availability. Based on instantaneous samples, the diet consisted mostly of fruits (60%), arthropods (23%), vegetative parts and flowers (17%), and other items (1%). Non-lactating females and juveniles spent more time eating insects than adult males and lactating females; however, significant differences between classes were detected only during the period of fruit scarcity. These differences are probably due to the high extent to which non-lactating females and juveniles were excluded from fruiting trees by males. The high proportion of arthropods in their diet is unusual for primates with large body size and is a possible factor influencing group cohesiveness in woolly monkeys. © 1994 Wiley-Liss, Inc.

Gender-related differences in the impact of tropical diseases on women: what do we know?

Abstract: This paper explores the importance of gender differences in the impact of tropical diseases on women. Malaria and schistosomiasis are used as examples but most of the observations also apply to other diseases endemic to developing countries. The distinction between sex and gender is discussed and evidence of sex and gender differences in the determinants and consequences of malaria and schistosomiasis, particularly their economic, social and personal dimensions, is reviewed. Issues on which research and intervention studies are needed are identified.

Composition of Venezuelan honeys from stingless bees (Apidae: Meliponinae) and Apis mellifera L

Abstract: Summary — Forty stingless-bee and 21 Apis mellifera honeys from Venezuela were analysed for their essential composition. The stingless bees comprised 3 Melipona and 5 Trigona species. The moisture content of the honeys from the different stingless-bee species was significantly higher than that of the A mellifera honeys. Generally, the stingless-bee honeys had a higher acidity than the A mellifera honeys. The honeys from the Melipona species had lower diastase activity than the Trigona species. There were also differences in the acidity and the ash and nitrogen content of the honeys of the different stingless-bee species, but these differences might also be due to a different floral origin. While the A mellifera honeys fulfilled the quality requirements set by the Codex Alimentarius, the honeys from the stingless bees failed to do so for several parameters, especially the quality factors such as water content, reducing sugars, acidity, and ash content.

Optimization of HPLC Conditions to Analyze Widely Distributed Ethoxylated Alkylphenol Surfactants

Abstract: Commercial ethoxylated alkylphenol surfactants are always a mixture of oligomers with different ethylene oxide number (EON). The different oligomers can be separated by various HPLC techniques. Isocratic mode with mixed solvent on silica column allows to separate oligomers up to EON = 10; gradient programming moves the limit up to EON = 15. For higher EON values (up to 25) a NH2 column has to be used, either with isocratic or gradient mode. Applications to the analysis of microemulsion systems and to the separation of tributyl phenol ethoxylates are discussed. Extreme separation of wide range EON distribution is attained with two columns (Si and NH2) in series, and a solvent programming.

Dynamical discontinuous feedback strategies in the regulation of nonlinear chemical processes

Abstract: In this article, a unified approach is proposed for the design of dynamical discontinuous feedback controllers leading to the chattering-free stabilization of nonlinear single-input single-output systems describing chemical processes. The adopted framework is that of a generalized state representation form of the given nonlinear plant. Use is made of the associated generalized observability canonical form of such representation. Unification of discontinuous feedback policies is achieved by zeroing of an input-dependent auxiliary output function using simple discontinuous feedback control paradigms of various kinds. The zeroing of such scaler stabilizing function induces asymptotically stable controlled dynamics on the given nonlinear minimum-phase plant. Pulse-frequency-modulation, pulse-width-modulation and sampled sliding mode control strategies are considered from this unified viewpoint. Examples are provided including simulations. >

A regional analysis of Barí land use intensification and its impact on landscape heterogeneity

Abstract: Since pacification 30 years ago, the Bari of northwest Venezuela have aggregated in villages and have begun to produce cattle and some crops for sale in regional markets. This research analyzes satellite imagery to compare patterns of land use among Bari settlements that differ in their population size, cattle holdings, and distance to nearest marketplace. These comparisons indicate that settlement history mediates the effect of population pressure and herd sizes on land use. Moreover, intensification of land use is associated with greater deforestation and a more heterogeneous landscape, but less biodiversity in woody species.

Epidemiology of cutaneous leishmaniasis in Merida, Venezuela. III. Altitudinal distribution, age structure, natural infection and feeding behaviour of sandflies and their relation to the risk of transmission.

Abstract: An entomological survey revealed that the distribution of the Lutzomyia species in Merida, Venezuela, varies with altitude. Of the 21 species encountered, 12 (57%) are known to be anthropophilic. The significance of the predominant man-biting species at any altitude is discussed in terms of the risk of transmission of cutaneous leishmaniasis. The general parous rate (and perhaps the ability of a female sandfly to survive oviposition and transmit Leishmania parasites during a second or subsequent bloodmeal) was found to be related to rainfall and altitude. The finding of Leishmania infections in wild-caught parous females of anthropophilic species indicates the high risk of acquiring leishmaniasis in the study area. Observations on the feeding habits of the sandflies indicate that some species are opportunistic feeders, attracted to a variety of hosts, including man.

Evidence of mitochondrial DNA diversity in South American aboriginals

Abstract: The absence in South American aboriginals of an Asian-specific marker, a 9-bp deletion between the genes for the second subunit of cytochrome oxidase II and lysine transfer RNA in region V, has been interpreted as a bottlenecking effect at the Isthmus of Panama during the peopling of the Americas. We screened mitochondrial DNA (mtDNA) for this 9-bp tandem repeat and for polymorphisms in specific regions of the mtDNA in 2 ancient and 31 contemporary samples from South American aboriginals. We found additional (mtDNA) diversity in South American aboriginals in three ways. First, an Asian-specific marker not previously reported in South American aboriginals was identified by a sequencing analysis in both the contemporary Andean and Amazonian aboriginal peoples. Second, two new haplotypes so far unique to South American aboriginals were found. Additionally, we show that South American aboriginals fall into discrete populations. These results suggest that the prehistoric colonization of South America is the outcome of multiple migrations; the data do not support a bottlenecking effect at the Isthmus of Panama.

Identification and detection of Trypanosoma cruzi by using a DNA amplification fingerprint obtained from the ribosomal intergenic spacer.

Abstract: We designed a PCR assay targeted on repeated elements of the ribosomal intergenic spacer which produces highly polymorphic DNA band patterns for different strains of Trypanosoma cruzi. By labeling the PCR products with digoxigenin and by chemiluminescence detection, we improved the assay sensitivity by three orders of magnitude to get T. cruzi strain fingerprints in feces of the trypanosome-infected triatomine bug vector. We also developed a capture assay for the digoxigenin-labeled PCR products that allowed us to detect T. cruzi in triatomine bug vector feces and in human serum samples with a solid support.

Bulk and surface phonon polaritons in three-layer superlattices

Abstract: Three-layered superlattices are formed from a periodic repetition of three different slabs. Closed-form expressions for the study of bulk and surface polaritons in such materials are given in this paper with a few illustrative applications.

Antimony determination in tissues and serum of hamsters infected with Leishmania garnhami and treated with meglumine antimoniate.

Abstract: Hamsters were experimentally infected with Leishmania garnhami and then treated for 10 days with N-methyl-glucamine antimoniate (Glucantime); 60 mg/kg/day by intramuscular (im) or intralesional (il) routes. Hydride generation-atomic absorption spectroscopy was used to determine the concentrations of SbIII and SbV in the blood serum and total Sb in the tissues of the hamsters from 1 to 30 days after initiation of the treatment. Serum concentrations of SbIII and SbV were always similar. Total Sb concentrations were significantly higher in the relatively parasite-rich spleen and lesion than in any other tissue, whether treatment had been given im or il. Reduction of SbV to SbIII is probably associated with decreasing size and healing of the leishmanial ulcers. Tissue Sb kinetics is related to Leishmania behaviour and attention is drawn to the use of antimonial pentavalent compounds for diseases, other than leishmaniasis, that can affect the heart, liver and/or spleen, such as Chagas disease.

Melissopalynology for stingless bees (Apidae: Meliponinae) from Venezuela

Abstract: SUMMARYPollen spectra were obtained for honey samples taken from the nests of 48 Melipona spp. and 20 other stingless bee species at 23 locations in Venezuela from 1987 to 1989. The order of abundance for dominant pollens in Melipona spp. honeys was: Mimosa pudica gr, Scrophulariaceae, Machaerium gr., Avicennia, Myrtaceae, Mimosa scabrella gr., Cassia, Myrcia, Piper, Philoxerus, Xanthoxylum, Alter-nanthera and Astragalus. Pollens of Trema, Triumfetta, Avicennia, Palmae, Fagara, Hyptis gr., Rhamnaceae, Xanthoxylum and Acalypha were dominant in the non-Melipona samples. The abundance of dominant pollens from nectarless plants, such as Mimosa pudica gr., Mimosa scabrella gr., Alternanthera, Piper and Trema, considerably reduces the list of major nectar sources found for the stingless bees studied; their presence could be due to mixing of the honey with pollen pots inside the nest.

A new species of Anoura (Mammalia Chiroptera Phyllostomidae) from the Andes of northern South America

Abstract: A new species of Anoura Gray 1838 is described. The taxon is known from 48 specimens collected at eight localities in the Venezuelan Andes, and its distribution is likely to include at least the Colombian Andes. The new species is smaller than any of the four species of Anoura recognized to date, and possesses a distinctive combination of external, cranial, and dental characters. The new species inhabits forests at medium and high elevations, roosts in caves, and feeds at least partly on nectar and pollen.

Low-temperature electron mobility in a δ-doped semiconductor

Abstract: The low-temperature electron mobility in \ensuremath{\delta}-doped GaAs is calculated by using the Boltzmann equation and the relaxation-time approximation. It is assumed that the electrons are scattered from ionized impurities. Screening of charged impurities by electrons occupying several subbands is described with the help of (i) the random-phase approximation, (ii) the Thomas-Fermi method, and (iii) the bulk dielectric constant only. Among those methods mentioned above, the random-phase approximation has proved quite successful in studying the screening while the other two methods are inadequate. The mobility exhibits a drop when the excited subbands become occupied. It is shown, however, that as a consequence of the parity of the subband wave functions, the drop in the mobility when the Fermi level coincides with the bottom of the first excited subband is negligible.

A new bioassay for testing plant extracts and pure compounds using red flour beetleTribolium castaneum Herbst.

Abstract: We designed a new bioassay to test plant extract activity against stored product pests. Plant compounds were added to feed disks composed of wheat flour and yeast and fed to the red flour bettle (Tribolium castaneum). By measuring insect mass, disk mass, and insect mortality over time it was possible to calculate a phagodepression index, an antifeedant index, the amount of treatment chemical ingested by the beetles, the mortality rate, and the efficiency of conversion of ingested food. The assay was performed for 60 hr to allow for possible habituation effects and to discriminate between phagodeterrency and physiological stress caused by treatments. α- and β-Pinene, eugenol, kaurenic acid, sparteine, essential oils ofMinthostachis mollis andMelaleuca quinquenervia, and extracts ofSapindus saponaria were tested. Using this assay we detected the presence of both phagodepressant and phagostimulant compounds inS. saponaria extracts, and we quantified the pronounced effects of sparteine onT. castaneum.