Showing papers by "University of Costa Rica published in 1999"

The midsummer drought over Mexico and Central America

Abstract: The annual cycle of precipitation over the southern part of Mexico and Central America exhibits a bimodal distribution with maxima during June and September–October and a relative minimum during July and August, known as the midsummer drought (MSD). The MSD is not associated with the meridional migration of the intertropical convergence zone (ITCZ) and its double crossing over Central America but rather with fluctuations in the intensity and location of the eastern Pacific ITCZ. During the transition from intense to weak (weak to intense) convective activity, the trade winds over the Caribbean strengthen (weaken). Such acceleration in the trade winds is part of the dynamic response of the low-level atmosphere to the magnitude of the convective forcing in the ITCZ. The intensification of the trade winds during July and August and the orographic forcing of the mountains over most of Central America result in maximum precipitation along the Caribbean coast and minimum precipitation along the Pacific...

Ecosystem fertility and fallow function in the humid and subhumid tropics

Abstract: The regeneration of natural vegetation (fallowing) is a traditional practice for restoring fertility of agricultural land in many parts in the tropics. As a result of increasing human population and insufficient fertilizer inputs, the ecosystem fertility functions of traditional fallows must now be improved upon via the use of managed fallows. Interactions between vegetation and soil determine nutrient losses and gains in crop—fallow systems and are influenced by fallow species, patterns and rates of biomass allocation, and crop and fallow management. Nutrient losses occur through offtake in crop harvests during the cropping phase and through leaching, runoff, and erosion in the cropping phase and the initial stage of fallows $#x2014; when nutrient availability exceeds nutrient demand by vegetation. Gains in nutrient stocks in later stages of fallow are generally more rapid on soils with high than low base status due to greater quantities of weatherable minerals and lack of constraints to N2 fixation, deep rooting, and retrieval of subsoil nutrients by fallow vegetation. On low base status soils (exchangeable Ca 5 yr) are needed for recovery of cation stocks and crop performance on low base status soils. On both soils, however, residual benefits of fallows on crop yields usually last less than three crops.

Further Study of the Linear Trinickel(II) Complex of Dipyridylamide

Abstract: The title compound, Ni3(dpa)4Cl2 (dpa = di(2-pyridyl)amido anion), first reported 30 years ago, structurally characterized in 1991, has been obtained in two new crystal forms, Ni3(dpa)4Cl2·2CH2Cl2 (tetragonal, space group I4, with a = 27.3046(7) A, c = 12.2452(2) A, Z = 8) and Ni3(dpa)4Cl2·THF (orthorhombic, space group Pccn, with a = 12.673(1) A, b = 14.138(3) A, c = 23.890(2) A, Z = 4). They have been examined structurally, and the magnetic properties of one of them determined from 2 to 300 K. Also the proton NMR spectrum has been recorded. These data allow the following conclusions to be drawn: (1) the molecular structure is invariant in the three crystalline forms and has a symmetrical chain of nickel atoms, (2) the terminal metal atoms each have two unpaired electrons, while the central one is typical of diamagnetic square-planar NiII complexes, (3) the magnetic moments of the two terminal nickel(II) ions display antiferromagnetic coupling, with 2J = −108 cm-1, and (4) the Ni3 chain remains symmetr...

Protected Areas and Conservation of Biodiversity in the Tropics

Abstract: We compared deforestation rates and the extent of fragmentation inside and outside protected ar- eas in the Sarapiqui region of Costa Rica. We determined deforestation rates using remotely sensed images with supervised classification. We georeferenced the processed images and then transformed them to vector format for final mapping and parameter quantification. The deforestation rate in protected areas was low and declined sharply from 0.56% annually between 1976 and 1986 to 0.16% from 1991 to 1995. Outside the protected areas, the rate decreased from 3.6% in 1976-1986 to 2.8% in 1986-1991, but it increased again to 3.2% in 1991-1995. Fragmentation outside the protected areas increased considerably: the number of patches increased from 537 in 1976 to 1231 in 1996, while during the same period the average size of patches de- creased from 0.95 to 0.25 km 2 . Forest landscapes in the Sarapiqui region are likely to lose considerable biodi- versity because of the past forest loss and fragmentation even without further increases in deforestation and fragmentation.

Degradation of Polylactic Acid (PLA) Plastic in Costa Rican Soil and Iowa State University Compost Rows

Abstract: In this study the degradation of polylactic acid (PLA) plastic films in Costa Rican soil and in a leaf composting environment was investigated. Three types of PLA films were used: Ch-I, (PLA monolayer plastic films from Chronopol, Golden, CO), GII (PLA trilayer plastic films from Cargill Dow Polymers LLC, Minnetonka, MN), and Ca-I (PLA monolayer plastic films from Cargill Dow Polymers LLC). The average soil temperature and moisture content in Costa Rica were 27°C and 80%, respectively. The average degradation rate of PLA plastic films in the soil of the banana field was 7675 M w/week. Two compost rows were set up at the Iowa State University (ISU) (Ames) compost site. Temperature and relative humidity of the compost rows were kept at 55 ± 5°C and 50 ± 10% RH, respectively. The degradation rates of GII and Ca-I in the compost rows were 113,290 and 71,283 M w/week, respectively. Therefore, it was estimated that in Costa Rican soil and in compost rows, PLA would be visibly degraded in 6 months and in 3 weeks, respectively.

Cyclotron Line Features from Near-critical Magnetic Fields: The Effect of Optical Depth and Plasma Geometry

Abstract: A detailed analytical study of the relativistic profile for magnetic Compton scattering is performed and use is made of Monte Carlo methods to construct a numerical scheme for the production of relativistic theoretical cyclotron spectra from internally irradiated scattering atmospheres in the low-density/high-field regime. The cross section includes natural line widths, and the Monte Carlo implementation allows for spatial diffusion of photons in arbitrary geometries while accounting for relativistic angular redistribution. Detailed consideration of "Raman-Landau" scattering permits photon spawning from up to fourth harmonic photons. This scheme is utilized to make specific predictions on the effect of geometry and optical depth on the formation of cyclotron lines in hard incident continua. Even if the injection is isotropic, a strongly anisotropic radiation field ensues at relatively low optical depths. The scattering profiles at large angles and low fields are highly asymmetric and peak at the relativistic energy cutoff, not necessarily at the resonant energy. Higher harmonic features in general bear little resemblance to the fundamental even at high fields (B~10 TG), and slabs yield the deepest features, while cylinders present the widest lines at small angles. Moreover, the fundamental line photons in slab scattering regions tend to redistribute to the line wings from all angles, producing fairly broad emission line wings at small angles. Higher optical depths at those angles hampers such redistribution in cylindrical geometries.

On the ultraviolet behavior of quantum fields over noncommutative manifolds

Abstract: By exploiting the relation between Fredholm modules and the Segal–Shale–Stinespring version of canonical quantization, and taking as starting point the first-quantized fields described by Connes' axioms for noncommutative spin geometries, a Hamiltonian framework for fermion quantum fields over noncommutative manifolds is introduced. We analyze the ultraviolet behavior of second-quantized fields over noncommutative three-tori, and discuss what behavior should be expected on other noncommutative spin manifolds.

Parameter Uncertainty in CGE Modeling of the Environmental Impacts of Economic Policies

Abstract: This study explores the role of parameter uncertainty in CGE modeling of the environmental impacts of macroeconomic and sectoral policies, using Costa Rica as a case for study. A CGE model is constructed which includes eight environmental indicators covering deforestation, pesticides, overfishing, hazardous wastes, inorganic wastes, organic wastes, greenhouse gases, and air pollution. The parameters are treated as random variables drawn from prespecified distributions. Evaluation of each policy option consists of a Monte Carlo experiment. The impacts of the policy options on the environmental indicators are relatively robust to different parameter values, in spite of the wide range of parameter values employed.

Assessing the feasibility of linkage disequilibrium methods for mapping complex traits: an initial screen for bipolar disorder loci on chromosome 18.

Abstract: Summary Linkage disequilibrium (LD) analysis has been promoted as a method of mapping disease genes, particularly in isolated populations, but has not yet been used for genome-screening studies of complex disorders. We present results of a study to investigate the feasibility of LD methods for genome screening using a sample of individuals affected with severe bipolar mood disorder (BP-I), from an isolated population of the Costa Rican central valley. Forty-eight patients with BP-I were genotyped for markers spaced at ∼6-cM intervals across chromosome 18. Chromosome 18 was chosen because a previous genome-screening linkage study of two Costa Rican families had suggested a BP-I locus on this chromosome. Results of the current study suggest that LD methods will be useful for mapping BP-I in a larger sample. The results also support previously reported possible localizations (obtained from a separate collection of patients) of BP-I–susceptibility genes at two distinct sites on this chromosome. Current limitations of LD screening for identifying loci for complex traits are discussed, and recommendations are made for future research with these methods.

Remarkable Effects of Axial π* Coordination on the Cr−Cr Quadruple Bond in Dichromium Paddlewheel Complexes

Abstract: It is well-known that donation of electron density into the σ* orbital of a Cr−Cr quadruple bond causes major lengthening of the Cr−Cr distance, and there is some prior evidence that a similar lengthening is caused by dative interaction with the π* orbitals. Some molecules have now been made that allow a definitive assessment of this axial π* effect. A molecule has been designed to ensure that there is axial donation into the π* orbitals but not onto the σ* orbital; ligands have been used in which the donor atoms are tethered to the bridging ligands in such a way that they can reach only the π* orbitals but not the σ* orbital. The ligands used for this purpose are the anions of 2,6-di(phenylimino)piperidine (DPhIP) and 2,2‘-dipyridylamine (dpa). In the compound Cr2(DPhIP)4 four imino nitrogen lone pairs are suitably positioned to donate to the π* orbitals and the Cr−Cr bond length is 2.265(1) A. For direct comparison, the compound Cr2(PhIP)4 (PhIP is the anion of 2-(phenylimino)piperidine) was made and fo...

Elapid venom toxins: multiple recruitments of ancient scaffolds

Abstract: Nigroxins A and B, two myotoxic phospholipases A2 (PLA2s) from the venom of the American elapid Micrurus nigrocinctus, belong to a new PLA2 subclass. Their primary structures were established and compared with those of PLA2s that have already been studied with respect to myotoxic activity. The combination of amino acid residues Arg15, Ala100, Asn108 and a hydrophobic residue at position 109 is present exclusively in class I PLA2s that display myotoxic activity. These residues cluster within a surface region rich in positive charges and are suggested to play a role in the interaction with the target membrane of the muscle fibers. It is concluded that the myotoxic PLA2s resulted from recruitment of an ancient scaffold. Dendrotoxins and α-neurotoxins are similarly derived from other old structures, which are, however, now also present in nontoxic proteins that are widely distributed throughout the animal kingdom. The evolutionary pathways by which elapid PLA2s acquired myotoxicity and dendrotoxins acquired K+-channel blocker activity are traced. They demonstrate how existing scaffolds were adapted stepwise to serve toxic functions by exchange of a few surface-exposed residues.

Linear Tricobalt Compounds with Di-(2-pyridyl)amide (dpa) Ligands: Studies of the Paramagnetic Compound Co3(dpa)4Cl2 in Solution

Abstract: Solutions of Co3(dpa)4Cl2, where dpa = di(2-pyridyl)amide ion, in CD2Cl2 were studied by NMR in the temperature range 183−303 K. The spectra show only four 1H and five 13C resonance signals, consistent with the D4 symmetry of the molecules found in the solid. The magnetic susceptibility in solution was determined by the Evans method from 193 to 308 K. These observations can be modeled as an S = 1/2 to S = 5/2 spin-transition process with ΔH = 7.7(2) kJ mol-1 and ΔS = 20.8(8) J K-1 mol-1.

Don't forget the biology: a reply to green.

Abstract: In our 1998 paper (Eberhard et al. 1998), we tested several hypotheses regarding the possible selective factors involved in the evolution of animal genitalia. We compared the slopes of log-log ordinary least squares (OLS) regressions of genitalia on indicators of body size with the slopes of other body parts on the same indicators in 20 species of insects and spiders. Our major conclusions regarding the rejection of male-female conflict, good viability genes, and lock and key arguments (see Abstract) are unaffected by the reanalysis proposed by Green (1999), even if it were more appropriate than ours, which we doubt (see below). In neither our OLS regressions nor Green’s reduced major axis (RMA) regressions are the slopes of genitalia greater than those of other body parts, as would be expected if genitalia were used as weapons in forceful intraspecific battles (the male-female conflict hypothesis) or as signals of male size (good viability genes hypothesis). Instead, the slopes show a statistically significant trend to be lower in both analyses. In addition, neither we nor Green found differences on comparing the slopes of the genitalia of the species in which lock and key considerations might be important (species in which male genitalia fit against rigid female genitalic structures) with the slopes in species in which lock and key can be ruled out because of the mechanical mesh of the male’s genitalia with those of the female. So, conservatively, we conclude that the major conclusions of our paper are not affected under Green’s reanalysis. It is important not to lose sight of the biological questions being tested in debates over statistical methods. There are a number of reasons, however, to doubt several of Green’s points. Green’s claim that reanalysis is needed, the analysis he performed, and the additional explanations that he proposed in preference to those we mentioned in our original paper all have serious problems. We will discuss first the statistical questions, and then the more directly biological questions. Is RMA Regression More Appropriate?

The outer membrane of Brucella ovis shows increased permeability to hydrophobic probes and is more susceptible to cationic peptides than are the outer membranes of mutant rough Brucella abortus strains

Abstract: The permeability of the outer membrane (OM) to hydrophobic probes and its susceptibility to bactericidal cationic peptides were investigated for natural rough Brucella ovis and for mutant rough Brucella abortus strains. The OM of B. ovis displayed an abrupt and faster kinetic profile than rough B. abortus during the uptake of the hydrophobic probe N-phenyl-naphthylamine. B. ovis was more sensitive than rough B. abortus to the action of cationic peptides. Bactenecins 5 and 7 induced morphological alterations on the OMs of both rough Brucella strains. B. ovis lipopolysaccharide (LPS) captured considerably more polymyxin B than LPSs from both rough and smooth B. abortus strains. Polymyxin B, poly-L-lysine, and poly-L-ornithine produced a thick coating on the surfaces of both strains, which was more evident in B. ovis than in rough B. abortus. The distinct functional properties of the OMs of these two rough strains correlate with some structural differences of their OMs and with their different biological behaviors in animals and culture cells.

Political Competition and Electoral Fraud: A Latin American Case Study

Abstract: This study aims to begin filling this void by drawing upon a rich documentary source--the petitions to nullify electoral results (demandas de nulidad)--from Costa Rica, a country noted for its long history of democratic government. The petitions contain a wealth of material about the frequency, nature, and geographical basis of accusations of electoral fraud. They were generally lodged by those with legal training and typically published by the daily government gazette (La Gaceta). They were one of the weapons most frequently used by the opposition to combat the prerogatives largely held by presidents until the mid-twentieth century, namely, the production of the electoral registry, the holding of elections, and the tally of the vote. They are valuable precisely because of their partisan origins: By virtue of what they say and do not say, they trace the frontier delimiting acceptable from unacceptable behavior.

Genetic variation at twentythree microsatellite loci in sixteen human populations

Abstract: We have analysed genetic variation at 23 microsatellite loci in a global sample of 16 ethnically and geographically diverse human populations. On the basis of their ancestral heritage and geographic locations, the studied populations can be divided into five major groups, viz. African, Caucasian, Asian Mongoloid, American Indian and Pacific Islander. With respect to the distribution of alleles at the 23 loci, large variability exists among the examined populations. However, with the exception of the American Indians and the Pacific Islanders, populations within a continental group show a greater degree of similarity. Phylogenetic analyses based on allele frequencies at the examined loci show that the first split of the present-day human populations had occurred between the Africans and all of the non-African populations, lending support to an African origin of modern human populations. Gene diversity analyses show that the coefficient of gene diversity estimated from the 23 loci is, in general, larger for populations that have remained isolated and probably of smaller effective sizes, such as the American Indians and the Pacific Islanders. These analyses also demonstrate that the component of total gene diversity, which is attributed to variation between groups of populations, is significantly larger than that among populations within each group. The empirical data presented in this work and their analyses reaffirm that evolutionary histories and the extent of genetic variation among human populations can be studied using microsatellite loci.

Comparative study on the ability of IgG and F(ab')2 antivenoms to neutralize lethal and myotoxic effects induced by Micrurus nigrocinctus (coral snake) venom

Abstract: A comparative study was performed on the ability of IgG and F(ab')2 antivenoms to neutralize lethal and myotoxic activities of Micrurus nigrocinctus venom. Both antivenoms were adjusted to a similar neutralizing potency in experiments where venom and antivenoms were preincubated prior to injection. No significant differences were observed between IgG and F(ab')2 antivenoms concerning neutralization of lethal effect in rescue experiments, i.e., when antivenom was administered intravenously after envenomation. However, F(ab')2 antivenom was more effective in prolonging the time of death when subneutralizing doses were administered immediately after venom injection. Both products partially reversed the binding of M. nigrocinctus alpha-neurotoxins to acetylcholine receptor in vitro. The IgG and F(ab')2 antivenoms effectively neutralized venom-induced myotoxicity when administered intravenously immediately after envenomation, although neutralization was poor if antivenom injections were delayed. Intramuscular injection of venom promoted diffusion of antivenom antibodies throughout muscle tissue, and F(ab')2 diffused to a higher extent than IgG molecules. Thus, despite the observation that F(ab')2 antivenom was more effective than IgG antivenom in prolonging the time of death when subneutralizing doses were administered immediately after envenomation, no major differences were observed in antivenom neutralization of lethal and myotoxic effects or in their capacity to reverse neurotoxin binding to the acetylcholine receptor.

Trade liberalization and the environment in Costa Rica

Abstract: This study examines the environmental impacts of trade liberalization in Costa Rica. A CGE model is constructed which includes eight environmental indicators covering deforestation, pesticides, overfishing, hazardous wastes, inorganic wastes, organic wastes, greenhouse gases, and air pollution. Three trade liberalization scenarios are examined. Two sets of analyses are conducted for each scenario, one in which technologies do not change in response to trade liberalization and the other in which total factor productivity in each sector changes in response to changes in imports of machinery and equipment. To account for uncertainty regarding values of the model's parameters, a Monte Carlo experiment is conducted for each policy option. The impacts of trade liberalization on the environmental indicators are generally negative in sign but small or moderate in magnitude, both when technology is constant and when technology is allowed to vary.