The Business Cycles of Balance-of-Payment Crises: A Revision of Mundellan Framework

In his seminal 1960 article Robert Mundell proposed a model of balance-of-payments crises in which confidence in the continuation of a currency peg depended on the observed holdings of central bank foreign reserves. We examine the implications of a reformulation of this view from the perspective of an equilibrium business cycle model in which the probability of devaluation is an endogenous variable conditioned on foreign reserves. The model explains some business cycle regularities of exchange-rate-based stabilizations while also producing devaluation probabilities that capture some features of devaluation probabilities estimated in the data. The analysis aims to explain both the real effects and the collapse of temporary fixed-exchange-rate regimes in an unified framework, and provides an economic interpretation for the evidence that foreign reserves are a robust leading indicator of currency crises.

Devaluation Risk and the Syndrome of Exchange-Rate-Based Stabilizations

This paper shows that the risk of devaluation can be an important factor accounting for the stylized facts of exchange-rate-based stabilizations. This conclusion follows from studying the quantitative implications of a two-sector equilibrium business cycle model of a small open economy calibrated to Mexico's 1987-1994 stabilization plan. In the model a time-variant interest rate differential that acts as a stochastic tax on money demand, labor supply, investment, and saving. Under incomplete markets, this tax induces endogenous state-contingent wealth effects via fiscal adjustment and suboptimal investment. Devaluation risk entails large welfare costs in this environment.

Biodiversity of phytoparasitic nematodes associated with Musaceae and fruit crops in Colombia

Wide distributions of economically important plant-parasitic nematodes belonging to the genera Meloidogyne, Pratylenchus and Radopholus have been recorded in plantain and fruit crops in Colombia. Despite of significant economic losses, taxonomic research on these taxa in Colombia is limited. This thesis focuses mainly on two composition components of biodiversity (species and genes) as a contribution to the analyses of biodiversity of economically important plant-parasitic nematodes in Colombia. Samples were taken from 16 different regions of the country. Identification, characterization, and description of known and new nematode species should be based on a combination of as many data as possible, using different approaches. Morphometrical and morphological studies were based on LM and SEM observations, combined with other taxonomical methods such as analyses of proteins and use of species-specific primers (only for Meloidogyne populations), molecular analyses of sequences and phylogenetic analyses. In the current study, morphometric and/or morphological features allowed to separate populations into small species groups as a first step towards identification. Hereby, features of perineal pattern of females or head shape of males in Meloidogyne; head annulation number in Pratylenchus and tail length of Radopholus were the most helpful features at species level and reduced the number of species to be taken into account. From the combination of these analyses it turned out that several species ocurred together in the field. Thus, purification of populations is recommended as a second step in the identification process. In this study, only three Meloidogyne “populations” could be successfully purified. However, to overcome the mixed species problem for all other species, Meloidogyne identification was based on a single young egg-laying female (protein analysis) and DNA (for species-specific PCR and sequence analyses) was always extracted from a single juvenile. The highest diversity was analyzed in the genus Meloidogyne since a large number of populations (24) were available for this study. Six Meloidogyne species: M. incognita, M. javanica, M. arenaria, M. hapla, M. paranaensis and M. konaensis were found associated with four fruit crops and plantain in Colombia. The last two species had never been recorded previously in Colombia but since they show morphological features of M. incognita, they were probably misidentified in the past. Only the use of combined methods allows accurate identification to species level. Analyses of esterase and malate dehydrogenase resulted in a profile that is typical of both species, P1 fitted both M. paranaensis and M. konaensis. Though, the morphological feature, number of projections protruding from the stylet shaft of males allowed their separation. Isozyme analysis also recovered phenotypes that could not be connected to known Meloidogyne species. E3N1, E3N2 phenotypes were found in populations P5a, P19a and P19b. These phenotypes represent a new species that is currently under investigation based on populations from Iran, Africa, Chile and Brazil by Karssen, Carneiro and collaborators (personal communication; December 10, 2007). Furthermore, the phenotype E1bN1b (population P14a) matched with M. hapla but the Mdh band was very slow and morphological features of this population agreed with M. javanica. Populations P3a, P10 and P11 yielded two esterase bands (E2N2): one slow band, and one fast band with a migration rate largely similar to the I1 band of the M. incognita phenotype. E1bN1b and phenotypes probably represent a new species. However additional specimens are needed for accurate morphological and morphometrical studies. Analyses of Colombian Meloidogyne populations (based on 65 nematode specimens) in combination with Meloidogyne populations from GenBank at different rDNA regions (D2D3, 18S and ITS1-5.8-ITS2) yielded phylogenetic trees with similar topologies. All of the generated trees contained three identical clades, strongly supported by high PP values. Meloidogyne populations containing mainly temperate species (as obtained from GenBank) were consistently placed as a separate clade (clade 0). Clade 1 contained M. hapla populations; clade 2 grouped six populations (P1, P2, P5a, P15, P22 and P23) not identified at species level and therefore with unknown reproductive strategies, and clade 3 contained M. incognita, M. javanica and M. arenaria. These topologies agreed with morphological and morphometric data, protein analyses and species-specific PCR. However, populations P1 and P15 formed exceptions. The tree topology and analyses of individual sequences showed that species-specific PCR results of populations P1 and P15 were wrong. For the latter populations the absence of autapomorphic characters typical of M. hapla species allowed to recognize the error. Only one Pratylenchus population was obtained, but morphological analyses were completed with comprehensive molecular divergence and phylogenetic analyses (based on eight nematode specimens from Colombia and additional Genbank material). Their outcome resulted in the description of a new species, indicated here as Pratylenchus sp. n. The new species is closely related to three Pratylenchus species but clearly differs from the other species within genus. It shares with P. coffeae, P. loosi and P. jaehni morphology features: amphimictic lesion nematodes with two lip annuli, and lip sectors fused together and also fused with the oral disc to a smooth face. Molecular distinctions between Pratylenchus n. sp., P. coffeae, P. jaehni and P. loosi are more clear-cut than are morphological differences. The sequence comparison of the D2D3 rDNA expansion region clearly separates the new species from P. jaehni, P. loosi and P. coffeae. Pratylenchus n. sp. had a sister relation with P. jaehni. P. loosi and P. coffeae were more distinctly related. Clear autapomorphic characters of the new species were present in all specimens studied, differentiating its D2D3 expansion region of 28S rDNA from the observations of its sister species P. jaehni. Our results fulfill the requirements of the evolutionary species concept and phylogenetic species concept sensu Adams (1998). Additionally, our new species is a typological morphospecies compared with most species included in the genus; morphometric characters overlap only with P. jaehni and P. loosi. In general, Pratylenchus species are polyphagous, but differences in host preference occur among the species. Type host for Pratylenchus n. sp. is Musa ABB (plantain, hartón cultivar), a host also reported for P. coffeae. So far, P. jaehni and P. loosi have not yet been recorded on Musa plants. Morphological data of two obtained Radopholus populations were supplemented with sequence divergence and phylogenetic analyses (D2D3, 18S and ITS1-5.8-ITS2) based on 23 specimens of nematodes of Colombia and additional Genbank material. All specimens were identified as R. similis. With respect to morphological characters and morphometric data, Colombian populations of R. similis females only slightly extend the inferior limits of the other R. similis populations described from different localities around the world, particularly with respect to body length, diameter at mid body and anus, length of the neck region, hyaline part of tail and length of the ovaries. The topology of ITS1-5.8-ITS tree positioned Colombian populations of R. similis together with populations from different countries and hosts in the same clade. Percentage of divergence yielded similar results except for the Costa Rican population which showed 11.7% divergence with respect to Colombian populations from the same clade. The populations of R. similis did not cluster together according to geographical distribution, nor did they for host. For example, accessions from the same host (banana plants) and from the same country (Sudan) were positioned in different clades and showed the largest differences in percentage of divergence. The populations analyzed by Elbadri (2000) from Sudan, Uganda, Cuba and Germany and sharing clade with Colombian populations in phylogenetic tree, were found to be the most pathogenic populations for banana among all the tested populations by this author. The phylogenetic position of Radopholus species in the ITS1-5.8-ITS tree, more particularly of R. arabocoffee, P. duriophilus, R. similis from Sudan and Belgium suggests that “R. similis” could represent a species complex; more research is needed to unravel these relationships. In conclusion, all retrieved Meloidogyne species were widely distributed and present in most of the fruit crops. R. similis and Pratylenchus n. sp. were restricted to Musa plants, but an incomplete distribution picture related to flawed sampling/transported processing can not be excluded for the Pratylenchidae. Correct species identification is crucial for reliable crop management because of differences in host range and virulence between species. Our results suggest that if more hosts and localities would be included in future studies, the number of new species, not only of Meloidogyne but also of other plant parasitic nematodes, will increase in correspondence with the high biodiversity of fauna and flora in Colombia. Additionally, studies on biodiversity represent a long-term multidisciplinary task, including descriptions of the new species, data on distribution, host associations, potential damage and relationships with other ecosystem components

Polinomios y Ecuaciones Relacionadas

Con este cursillo se pretende dar a conocer algunas propiedades de los polinomios como lo son las fórmulas de Vieta, algunas herramientas simples para encontrar raíces, las transformaciones de los polinomios y las identidades de Newton. Estas propiedades dan alternativas que generan problemas con un alto contenido de buenos hechos, los cuales ayudarán a enriquecer los conocimientos sobre polinomios y dar alternativas de solución a problemas de ecuaciones que a simple vista pueden parecer complicados

Measuring Solution Viscosity and its Effect on Enzyme Activity

In proteins, some processes require conformational changes involving structural domain diffusion. Among these processes are protein folding, unfolding and enzyme catalysis. During catalysis some enzymes undergo large conformational changes as they progress through the catalytic cycle. According to Kramers theory, solvent viscosity results in friction against proteins in solution, and this should result in decreased motion, inhibiting catalysis in motile enzymes. Solution viscosity was increased by adding increasing concentrations of glycerol, sucrose and trehalose, resulting in a decrease in the reaction rate of the H(+)-ATPase from the plasma membrane of Kluyveromyces lactis. A direct correlation was found between viscosity (η) and the inhibition of the maximum rate of catalysis (V (max)). The protocol used to measure viscosity by means of a falling ball type viscometer is described, together with the determination of enzyme kinetics and the application of Kramers’ equation to evaluate the effect of viscosity on the rate of ATP hydrolysis by the H(+)-ATPase

Mass fluctuation kinetics: analysis and computation of equilibria and local dynamics

The mass fluctuation kinetics (MFK) model is a set of coupled ordinary differential equations approximating the time evolution of means and covariances of species concentrations in chemical reaction networks. It generalises classical mass action kinetics (MAK), in which fluctuations around the mean are ignored. MFK may be used to approximate stochasticity in system trajectories when stochastic simulation methods are prohibitively expensive computationally. This study presents a set of tools to aid in the analysis of systems within the MFK framework. A closed-form expression for the MFK Jacobian matrix is derived. This expression facilitates the computation of MFK equilibria and the characterisation of the dynamics of small deviations from the equilibria (i.e. local dynamics). Software developed in MATLAB to analyse systems within the MFK framework is also presented. The authors outline a homotopy continuation method that employs the Jacobian for bifurcation analysis, that is, to generate a locus of steady-state Jacobian eigenvalues corresponding to changing a chosen MFK parameter such as system volume or a rate constant. This method is applied to study the effect of small-volume stochasticity on local dynamics at equilibria in a pair of example systems, namely the formation and dissociation of an enzyme-substrate complex and a genetic oscillator. For both systems, this study reveals volume regimes where MFK provides a quantitatively and/or qualitatively correct description of system behaviour, and regimes where the MFK approximation is inaccurate. Moreover, our analysis provides evidence that decreasing volume from the MAK regime (infinite volume) has a destabilising effect on system dynamics

Mercury removal in wastewater by iron oxide nanoparticles

Mercury is one of the persistent pollutants in wastewater; it is becoming a severe environmental and public health problem, this is why nowadays its removal is an obligation. Iron oxide nanoparticles are receiving much attention due to their properties, such as: great biocompatibility, ease of separation, high relation of surface-area to volume, surface modifiability, reusability, excellent magnetic properties and relative low cost. In this experiment, Fe3O4 and γ-Fe2O3 nanoparticles were synthesized using iron salts and NaOH as precipitation agents, and Aloe Vera as stabilizing agent; then these nanoparticles were characterized by three different measurements: first, using a Zetasizer Nano ZS for their size estimation, secondly UV-visible spectroscopy which showed the existence of resonance of plasmon at λmax∼360 nm, and lastly by Scanning Electron Microscopy (SEM) to determine nanoparticles form. The results of this characterization showed that the obtained Iron oxides nanoparticles have a narrow size distribution (∼100nm). Mercury removal of 70% approximately was confirmed by atomic absorption spectroscopy measurements