Upper Limits on the Extragalactic Background Light from the Gamma-Ray Spectra of Blazars

The direct measurement of the extragalactic background light (EBL) is difficult at optical to infrared wavelengths because of the strong foreground radiation originating in the Solar System. Very high energy (VHE, E$>$100 GeV) gamma rays interact with EBL photons of these wavelengths through pair production. In this work, the available VHE spectra from six blazars are used to place upper limits on the EBL. These blazars have been detected over a range of redshifts and a steepening of the spectral index is observed with increasing source distance. This can be interpreted as absorption by the EBL. In general, knowledge of the intrinsic source spectrum is necessary to determine the density of the intervening EBL. Motivated by the observed spectral steepening with redshift, upper limits on the EBL are derived by assuming that the intrinsic spectra of the six blazars are $\propto E^{-1.8}$. Upper limits are then placed on the EBL flux at discrete energies without assuming a specific spectral shape for the EBL. This is an advantage over other methods since the EBL spectrum is uncertain.Comment: 33 pages, 14 figures, accepted by Ap

The Consequences of Child Market Work on the Growth of Human Capital

Child labor is a phenomenon that has attracted a great amount of attention and research. theoretical propositions suggest that child labor is inefficient if it adversely affects future potential earning ability. this paper contributes to the literature on the effects of child market work on human capital by focusing on the long-term growth in human capital, which is widely known to significantly affect earning ability. the paper also uses better measures of human capital by focusing on the output of the human capital production function: numeracy skills, cognitive skills, and pulmonary function. using a rich longitudinal dataset on Indonesia, we find strong negative effects of child labor on the growth of both numeracy and cognitive skills in the next seven years. in addition, we find a strong and negative effect on pulmonary function as measured through lung capacity. comparing the effects by gender and type of work, we find that female child workers suffer from more adverse effects on their mathematical skills growth, while male child workers experience a much smaller growth in their pulmonary function. we also find that child workers who work for a wage outside the family bear worse effects compared to child workers who work in the family business. keywords: child labor, human capital, skills, health, Indonesia jel classifications: i12, i21, j13, j22, o1

Micro-evaporators for kinetic exploration of phase diagrams

We use pervaporation-based microfluidic devices to concentrate species in aqueous solutions with spatial and temporal control of the process. Using experiments and modelling, we quantitatively describe the advection-diffusion behavior of the concentration field of various solutions (electrolytes, colloids, etc) and demonstrate the potential of these devices as universal tools for the kinetic exploration of the phases and textures that form upon concentration

The ground state of binary systems with a periodic modulation of the linear coupling

We consider a quasi-one-dimensional two-component systm, described by a pair of Nonlinear Schr\"{o}dinger/Gross-Pitaevskii Equations (NLSEs/GPEs), which are coupled by the linear mixing, with local strength $\Omega$, and by the nonlinear incoherent interaction. We assume the self-repulsive nonlinearity in both components, and include effects of a harmonic trapping potential. The model may be realized in terms of periodically modulated slab waveguides in nonlinear optics, and in Bose-Einstein condensates too. Depending on the strengths of the linear and nonlinear couplings between the components, the ground states (GSs) in such binary systems may be symmetric or asymmetric. In this work, we introduce a periodic spatial modulation of the linear coupling, making $\Omega$ an odd, or even function of the coordinate. The sign flips of $\Omega (x)$ strongly modify the structure of the GS in the binary system, as the relative sign of its components tends to lock to the local sign of $\Omega$. Using a systematic numerical analysis, and an analytical approximation, we demonstrate that the GS of the trapped system contains one or several kinks (dark solitons) in one component, while the other component does not change its sign. Final results are presented in the form of maps showing the number of kinks in the GS as a function of the system's parameters, with the odd/even modulation function giving rise to the odd/even number of the kinks. The modulation of $\Omega (x)$ also produces a strong effect on the transition between states with nearly equal and strongly unequal amplitudes of the two components.Comment: 8 pages, 3 figure

Classical Loop Actions of Gauge Theories

Since the first attempts to quantize Gauge Theories and Gravity in the loop representation, the problem of the determination of the corresponding classical actions has been raised. Here we propose a general procedure to determine these actions and we explicitly apply it in the case of electromagnetism. Going to the lattice we show that the electromagnetic action in terms of loops is equivalent to the Wilson action, allowing to do Montecarlo calculations in a gauge invariant way. In the continuum these actions need to be regularized and they are the natural candidates to describe the theory in a ``confining phase''.Comment: LaTeX 14 page

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4: II. 2H and 7Li NMR stimulated-echo experiment

We use 2H NMR stimulated-echo spectroscopy to measure two-time correlation functions characterizing the polymer segmental motion in polymer electrolytes PPO-LiClO4 near the glass transition temperature Tg. To investigate effects of the salt on the polymer dynamics, we compare results for different ether oxygen to lithium ratios, namely, 6:1, 15:1, 30:1 and infinity. For all compositions, we find nonexponential correlation functions, which can be described by a Kohlrausch function. The mean correlation times show quantitatively that an increase of the salt concentration results in a strong slowing down of the segmental motion. Consistently, for the high 6:1 salt concentration, a high apparent activation energy E_a=4.1eV characterizes the temperature dependence of the mean correlation times at Tg < T< 1.1T_g, while smaller values E_a=2.5eV are observed for moderate salt contents. The correlation functions are most nonexponential for 15:1 PPO-LiClO4, whereas the stretching is reduced for higher and lower salt concentrations. A similar dependence of the correlation functions on the evolution time in the presence and in the absence of ions indicates that addition of salt hardly affects the reorientational mechanism. For all compositions, mean jump angles of about 15 degree characterize the segmental reorientation. In addition, comparison of results from 2H and 7Li NMR stimulated-echo experiments suggests a coupling of ion and polymer dynamics in 15:1 PPO-LiClO4.Comment: 14 pages, 12 figure

A Survey of Satisfiability Modulo Theory

Satisfiability modulo theory (SMT) consists in testing the satisfiability of first-order formulas over linear integer or real arithmetic, or other theories. In this survey, we explain the combination of propositional satisfiability and decision procedures for conjunctions known as DPLL(T), and the alternative "natural domain" approaches. We also cover quantifiers, Craig interpolants, polynomial arithmetic, and how SMT solvers are used in automated software analysis.Comment: Computer Algebra in Scientific Computing, Sep 2016, Bucharest, Romania. 201

The First Detections of the Extragalactic Background Light at 3000, 5500, and 8000A (III): Cosmological Implications

(Abridged) We have used HST WFPC2 and ground-based spectroscopy to measure the integrated extragalactic background light (EBL) at optical wavelengths. We have also computed the integrated light from individual galaxy counts in the images used to measure the EBL and in the Hubble Deep Field. We find that the flux in galaxies as measured by standard galaxy photometry methods has generally been underestimated by about 50%. Further, we find that the total flux in individually detected galaxies is a factor of 2 to 3 less than the EBL at 3000--8000A. We show that a significant fraction of the EBL may come from normal galaxies at z<4, which are simply undetectable as a result of K-corrections and cosmological surface brightness dimming. This is consistent with recent redshift surveys at z<4. In the context of some simple models, we discuss the constraints placed by the EBL on the evolution of the luminosity density at z>1. Based on our optical EBL and published UV and IR EBL measurements, we estimate that the total EBL from 0.1--1000 microns is 100+/-20 nW/m^2/sr. If the total EBL were produced entirely by stellar nucleosynthesis, then we estimate that the total baryonic mass processed through stars is Omega_* = 0.0062 (+/- 0.0022) h^{-2}, which corresponds to 0.33+/-0.12 Omega_B for currently favored values of the baryon density. This estimate is smaller by roughly 7% if 7 h_{0.7} nW/m^2/sr of the total EBL comes from accretion onto central black holes. This estimate of Omega_* suggests that the universe has been enriched to a total metal mass of 0.21(+/-0.13) Z_sun Omega_B. Our estimate is consistent with other measurements of the cumulative metal mass fraction of stars, stellar remnants, and the intracluster medium of galaxy clusters in the local universe.Comment: Accepted for publication in ApJ, 20 pages using emulateapj.sty, version with higher resolution figures available at http://www.astro.lsa.umich.edu/~rab/publications.html or at http://nedwww.ipac.caltech.edu/level5/Sept01/Bernstein3/frames.htm