Armed Conflict Exposure, Human Capital Investments and Child Labor: Evidence from Colombia

Using a unique combination of household and violence data sets and a duration analysis methodology, this paper estimates the effect that exposure to armed conflict has on school drop-out decisions of Colombian children between the ages of six and seventeen. After taking into account the possible endogeneity of municipal conflict related events through the use of instrumental variables, we find that armed conflict reduces the average years of schooling in 8.78% for all Colombian children. This estimate increases to 17.03% for children between sixteen and seventeen years old. We provide evidence that such effect may be induced mainly through higher mortality risks, and to lesser extent due to negative economic shocks and lower school quality; all of which induce a trade-off between schooling and child labor.Armed con.ict, School drop-out, Duration Analysis, Colombia

Induced magnetic moment for a spinless charged particle in the thin-layer approach

We determine the effective dynamics for a spinless charged particle, in the presence of electromagnetic fields, constrained to a space curve. We employ the thin-layer procedure and a perturbative expansion for the Schr\"odinger equation is derived. We find that the first-order term in the perturbative expansion couples the dynamics of the normal and tangent degrees of freedom. However, there is always a gauge transformation that allows decouple the dynamics. We find that the effective Schr\"odinger equation in the curve contains an induced Zeeman coupling, independent of the curvature and torsion, which has not been previously reported. This coupling is characteristic of reducing the dimension by two and allows to identify an induced magnetic moment.Comment: 7 pages. To be published in Europhysics Letter

First-principles study of the atomic and electronic structure of the Si(111)-(5x2-Au surface reconstruction

We present a systematic study of the atomic and electronic structure of the Si(111)-(5x2)-Au reconstruction using first-principles electronic structure calculations based on the density functional theory. We analyze the structural models proposed by Marks and Plass [Phys. Rev. Lett.75, 2172 (1995)], those proposed recently by Erwin [Phys. Rev. Lett.91, 206101 (2003)], and a completely new structure that was found during our structural optimizations. We study in detail the energetics and the structural and electronic properties of the different models. For the two most stable models, we also calculate the change in the surface energy as a function of the content of silicon adatoms for a realistic range of concentrations. Our new model is the energetically most favorable in the range of low adatom concentrations, while Erwin's "5x2" model becomes favorable for larger adatom concentrations. The crossing between the surface energies of both structures is found close to 1/2 adatoms per 5x2 unit cell, i.e. near the maximum adatom coverage observed in the experiments. Both models, the new structure and Erwin's "5x2" model, seem to provide a good description of many of the available experimental data, particularly of the angle-resolved photoemission measurements

The Airy fibre: an optical fibre that guides light diffracted by a circular aperture

We have designed and made an optical fibre that guides an approximate Airy pattern as one of its guided modes. The fibre's attenuation was 11.0 dB/km at 1550 nm wavelength, the match between the fibre's mode and the ideal infinite Airy pattern was 93.7%, and the far field resembled a top-hat beam. The guidance mechanism has strong similarities to photonic bandgap guidance.Comment: 11 page

Is justice blind? An examination of disparities in homicide sentencing in Colombia, 1980-2000

Evidence has repeatedly shown that disparities in crime sentences can be attributed to certain variables considered outside the legal dimensions of the case. The majority of research that investigates factors that contribute to such disparities has primarily focused on crimes of varying severities adjudicated in the U.S. court system. We expand research on this topic by focusing on disparities in homicide sentences using data from over 9000 homicide cases tried in Colombia from 1980 - 2000. We specifically explore whether judges use substantive rationality when deciding the length of the offender´s sentence and if the sentence should be above the legal minimum set for the severity of the crime according to the criminal code under which it is adjudicated. Results reveal that disparities in homicida sentences can be attributed to extra-legal variables such as: the city in which the homicide trial took place, where the body of the victim was retrieved, and whether the defendant was identified by an ID parade. However, we also find evidence that suggests that legal variables such as the defendant´s previous criminal record and the aggravating circumstances of the case engender greater differences in sentence outcomes than non-legal variables previously mentioned. Explanations and policy implications are discussed.Sentence Disparities, Homicide, Colombian Criminal Law

Role of the spin-orbit splitting and the dynamical fluctuations in the Si(557)-Au surface

Our it ab initio calculations show that spin-orbit coupling is crucial to understand the electronic structure of the Si(557)-Au surface. The spin-orbit splitting produces the two one-dimensional bands observed in photoemission, which were previously attributed to spin-charge separation in a Luttinger liquid. This spin splitting might have relevance for future device applications. We also show that the apparent Peierls-like transition observed in this surface by scanning tunneling microscopy is a result of the dynamical fluctuations of the step-edge structure, which are quenched as the temperature is decreased

Mirror matter admixtures in K_S to gamma gamma

The latest measurement of the K_S to gamma gamma branching ratio clearly shows an enhancement over the current theoretical prediction. As in other K and B meson decays, this invites to consider the possibility of the contribution of new physics. We study a particular form of the latter, which may be referred to as manifest mirror symmetry. The experimental data are described using previously determined values for the mixing angles of the admixtures of mirror matter in ordinary hadrons and by assuming that for pi^0, eta, eta', the mirror decay amplitudes have the same magnitudes as their ordinary counterparts

Upper Bound on the Hadronic Light-by-Light Contribution to the Muon g-2

There are indications that hadronic loops in some electroweak observables are almost saturated by parton level effects. Taking this as the hypothesis for this work, we propose a genuine parton level estimate of the hadronic light-by-light contribution to the anomalous magnetic moment of the muon, a_mu (LBL,had). Our quark mass definitions and values are motivated in detail, and the simplicity of our approach allows for a transparent error estimate. For infinitely heavy quarks our treatment is exact, while for asymptotically small quark masses a_mu (LBL,had) is overestimated. Interpolating, this suggests quoting an upper bound. We obtain a_mu (LBL,had) < 1.59 10^-9 (95% CL).Comment: 4 pages; 2 references added, some changes in text; final versio