Remittances, Liquidity Constraints and Human Capital Investments in Ecuador

Over the last decade Ecuador has experienced a strong increase in financial transfers from migrated workers, amounting to 6.4 percent of GDP and 31.5 percent of total exports of goods and services in 2005. This paper investigates how remittances via trans-national networks affect human capital investments through relaxing resource constraints and facilitate households in consumption smoothing by reducing vulnerability to economic shocks. In particular, we explore the effects of remittances on school enrolment and child work in Ecuador. Identification relies on instrumental variables, exploiting information on source countries of remittances and regional variation in the availability of bank offices that function as formal channels for sending remittances. Our results show that remittances increase school enrolment and decrease incidence of child work, especially for girls and in rural areas. Furthermore, we find that aggregate shocks are associated with increased work activities, while remittances are used to finance education when households are faced with these shocks. This suggests that liquidity constraints and vulnerability to covariate risk are especially relevant in rural areas, as it affects household’s investments in human capital of school age children. In this context both child labour supply and transnational remittances serve as coping mechanisms.migration, remittances, trans-national networks, education, child labour, Ecuador

Molecular Dynamics simulations of concentrated aqueous electrolyte solutions

Transport properties of concentrated electrolytes have been analyzed using classical molecular dynamics simulations with the algorithms and parameters typical of simulations describing complex electrokinetic phenomena. The electrical conductivity and transport numbers of electrolytes containing monovalent (KCl), divalent (MgCl$_2$), a mixture of both (KCl + MgCl$_2$), and trivalent (LaCl$_3$) cations have been obtained from simulations of the electrolytes in electric fields of different magnitude. The results obtained for different simulation parameters have been discussed and compared with experimental measurements of our own and from the literature. The electroosmotic flow of water molecules induced by the ionic current in the different cases has been calculated and interpreted with the help of the hydration properties extracted from the simulations

The role of hydrogen bonding in the dehydration of bioalcohols in hydrophobic pervaporation membranes

The dehydration of bioalcohols is considered one of the major factors contributing to the cost of biofuel production. In this study, liquid phase separation of water from methanol and ethanol in a siliceous MFI pervaporation membrane was studied by performing concentration gradient driven molecular dynamic (CGD-MD) simulations. CGD-MD simulations work by imposing a higher concentration in the feed side and a lower concentration in the permeate side of the membrane. This creates a concentration gradient across the membrane that facilitates the diffusion of molecules from the feed to the permeate side, mimicking the experimental pervaporation membrane set up. Fluxes of methanol, ethanol and water were calculated in single component permeation simulations and in equimolar methanol–water and ethanol–water mixture separation simulations. It was found that water formed hydrogen bonds with the silanol (Si-OH) groups on the external surface of the MFI and did not enter the membrane in the single component permeation simulation. While this may suggest that MFI can be used to effectively dehydrate bioalcohols, our simulations showed that water permeated through the MFI membrane when it was in a mixture with either methanol or ethanol. Furthermore, in the alcohol-water mixture simulations, the fluxes of methanol and ethanol were significantly lower than that of expected based on their single component fluxes. A detailed analysis of hydrogen bonding in the alcohol-water mixture separation simulations revealed that water preferred making hydrogen bonds with methanol and ethanol rather than with the silanol groups. This resulted in drifting of water molecules along with permeating alcohol molecules in to the MFI membrane in mixture simulations, while slowing the permeation of methanol and ethanol fluxes. The hydrogen bonding between water and alcohol molecules indicates that it may not be possible to achieve complete alcohol selectivity even if defect-free membranes were manufactured; however, our findings also hint at the possibility of functionalizing membrane surfaces with chemical groups that will overcome water-alcohol hydrogen bonding and retain water molecules in order to approach complete selectivity

On-the-fly coarse-graining methodology for the simulation of chain formation of superparamagnetic colloids in strong magnetic fields

The aim of this work is the description of the chain formation phenomena observed in colloidal suspensions of superparamagnetic nanoparticles under high magnetic fields. We propose a new methodology based on an on-the-fly Coarse-Grain (CG) model. Within this approach, the coarse grain objects of the simulation are not fixed a priori at the beginning of the simulation but rather redefined on the fly. The motion of the CG objects (single particles or aggregates) is described by an anisotropic diffusion model and the magnetic dipole-dipole interaction is replaced by an effective short range interaction between CG objects. The new methodology correctly reproduces previous results from detailed Langevin Dynamics simulations of dispersions of superparamagnetic colloids under strong fields whilst requiring an amount of CPU time orders of magnitude smaller. This substantial improvement in the computational requirements allows the simulation of problems in which the relevant phenomena extends to time scales inaccessible with previous simulation techniques. A relevant example is the waiting time dependence of the relaxation time T_2 of water protons observed in Magnetic Resonance experiments containing dispersions of superparamagnetic colloids, which is correctly predicted by our simulations. Future applications may include other popular real-world applications of superparamagnetic colloids such as the magnetophoretic separation processes.Comment: 12 pages, 12 figure

La tendencia a restar en la resolución de problemas de m.c.d. en alumnos de primaria

En esta comunicación se presentan resultados de una investigación con alumnos de primaria sobre la resolución de problemas verbales ligados al concepto de máximo común divisor (m.c.d.) y mínimo común múltiplo (m.c.m.). Los principales objetivos de la investigación eran evaluar la competencia de los estudiantes en la resolución de este tipo de problemas y analizar los distintos patrones o procesos de resolución empleados. En particular, esta comunicación se centra en una dificultad que presentan los estudiantes en problemas cuya solución se correspondería con el m.c.d. de dos cantidades dadas en el enunciado. En este sentido, resultados, tanto cuantitativos como cualitativos, apuntan a que el origen de la dificultad podría deberse a que los estudiantes intentan relacionar las cantidades intervinientes en el enunciado mediante la sustracción atendiendo al tamaño de las cantidades conocidas y de la solución, sin involucrar en la resolución del problema las ideas de múltiplo y divisor

Modifying the hydrophobic nature of MAF-6

Using a combination of molecular simulations techniques, we evaluate the structural tunability of the metal azolate framework with zeolitic RHO topology, MAF-6. Two mechanisms are explored to induce hydrophilicity to this hydrophobic material. The study at a molecular level of water adsorption takes place under a variety of conditions. On a first step, we consider water mixtures containing benzene or alcohols, paying special attention to the effect of the size of the alcohol molecules. On a second approach, we analyse the effect of small weight percentages of salt into the MAF-6 on the water adsorption. We first validate the accuracy of the host–guest interactions by reproducing experimental data. A new set of Lennard-Jones parameters for the interaction water- MAF-6 is also provided. The water adsorption behaviour of MAF-6 is studied in terms of adsorption isotherms, heats of adsorption, radial distribution functions, hydrogen bonds formation, and water distribution inside the material. We found that the presence of long molecules of alcohols favours the water adsorption at low values of pressure by smoothing the phase transition of water withing the MAF-6. On the other hand the addition of salt to the structure creates additional adsorption sites for water enhancing its adsorption, while reducing the saturation capacity of the material since the presence of salt reduces the accessible pore volume