9,403 research outputs found
Quality of social networks and educational investment decisions
All individuals belong to a social network with certain quality level. This paper analyzes the role of the quality of the social network in the educational decision making process. We propose a measure for quality of network based on the schooling level and the labor position of the members of the net. Our analysis compares individuals who are similar in at least two characteristics: socioeconomic level and intellectual ability. Although they belong to the same type of community (poor), they differ in the composition of their social network. The higher the quality of the network, the higher the probability of investing in education. Hence, socially disadvantaged and equally intelligent individuals may end up acquiring different schooling levels.
Sulfur doping effects on the electronic and geometric structures of graphitic carbon nitride photocatalyst: insights from first principles
We present here results of our first principles studies of the sulfur doping
effects on the electronic and geometric structures of graphitic carbon nitride
(g-C3N4). Using the Ab initio thermodynamics approach combined with some
kinetic analysis, we reveal the favorable S-doping configurations By analyzing
the valence charge densities of the doped and un-doped systems, we find that
sulfur partially donates its px- and py- electrons to the system with some back
donation to the S pz-states. To obtain accurate description of the excited
electronic states, we calculate the electronic structure of the systems using
the GW method. The band gap width calculated for g-C3N4 is found to be equal to
2.7 eV that is in agreement with experiment. We find the S doping to cause a
significant narrowing the gap. Furthermore, the electronic states just above
the gap become occupied upon doping that makes the material a conductor.
Analysis of the projected local densities of states provides insight into the
mechanism underlying such dramatic changes in the electronic structure of
g-C3N4 upon the S doping. Based on our results, we propose a possible
explanation for the S doping effect on the photo-catalytic properties of g-C3N4
observed in the experiments
First principles studies of the size and shape effects on reactivity of the Se modified Ru nanoparticles
We present here the results of our density-functional-theory-based
calculations of the electronic and geometric structures and energetics of Se
and O adsorption on Ru 93- and 105-atom nanoparticles. These studies have been
inspired by the fact that Se/Ru nanoparticles are considered promising
electrocatalysts for the oxygen reduction reaction (ORR) on the direct methanol
fuel cell cathodes and the oxygen binding energy is a descriptor for the
catalyst activity towards this reaction. We find the character of chemical
bonding of Se on a flat nanoparticle facet to be ionic, similar to that
obtained earlier for the Se/Ru(0001) surface, while in the case of a low
coordinated Ru configuration there is an indication of some covalent
contribution to the bonding leading to an increase in Se binding energy. Se and
O co-adsorbed on the flat facet, both accept electronic charge from Ru, whereas
the adsorption on low-coordinated sites causes more complicated valence charge
redistribution. The Se modification of the Ru particles leads to weakening of
the oxygen bonding to the particle. However, overall, O binding energies are
found to be higher for the particles than for Se/Ru(0001). High reactivity of
the Se/Ru nanoparticles found in this work is not favorable for ORR. We thus
expect that larger particles with well-developed flat facets are more efficient
ORR catalysts than small nanoparticles with a large fraction of
under-coordinated adsorption sites
Different channels of impact of education on poverty: an analysis for Colombia
This paper analyses pecuniary and non-pecuniary effects of education on poverty. Two are the main contributions: first, the pecuniary analysis employs the recently developed technique of instrumental variable quantile regression, very helpful method when one is interested in the lowest or highest extremes of the distribution function of the dependent variable. In fact, quantile regression offers coefficient estimations for any conditional quantile. The second contribution derives from our purpose to highlight the non-pecuniary returns to education: resources invested in education bring future returns to individuals, not only reflected in monetary earnings, but also in higher levels of satisfaction of basic needs.education, poverty, quantile regression, Colombia
Unbalanced groups in nonparametric survival tests
It is fairly common to find medical examples with survival data with unequal sample size
among the groups. There are several tests for those cases, but in practice, the use of one test
instead of another is done without justifying the election. Sometimes, the choice of one test or
another can lead to different conclusions, so it is important to have some guidelines to help to
choose the suitable test in unbalanced groups. The computation of the tests is done with the
statistical software (BMDP, SAS, SPSS, Stata, Statgraphics, and S-Plus). However the
commercial software only covers tests for the family of the weigthed tests, none of the score
tests, and the nomenclature is not unified, using different names for the same test. We perform
several simulations to give some pieces of advice for picking out the right test. Due to the fact
that there are situations where it is advisable to use a test from the family of the score tests
against a weighted one, we have developed a new software in JavaScript for Internet that
computes score and weighted tests versions (10 tests) that unifies the nomenclature (this
software is available from the authors upon request). We include real examples where we apply,
using the new JavaScript programs, the recommendations suggested by the simulations
Differentes canais de impacto da educação na pobreza
O artigo analisa os efeitos monetários e os não-monetários do nível de escolaridade do chefe de família na situação de pobreza. Propomos que o rendimento da escolaridade não seja pensado como um simples número– usualmente o coefi ciente de escolaridade em uma equação da renda–mas como um conjunto de elementos cuja extensão depende da quantidade de dimensões de pobreza identifi cadas. A análise monetária usa a técnica de Regressão Quantil, muito útil especialmente quando estamos interessados nos extremos da função de distribuição das rendas. Nossos resultados mostram diferenças entre os quantis dos retornos. Também encontrámos interessantes desigualdades conforme o sexo e a localização urbana-rural. Explorando os retornos não pecuniários, descobrimos que a educação do chefe de família infl uencia positivamente a saúde familiar e as condições de habitação.
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