Showing papers by "National University of La Plata published in 2012"

The Chemistry of the Sulfur–Gold Interface: In Search of a Unified Model

Abstract: Over the last three decades, self-assembled molecular films on solid surfaces have attracted widespread interest as an intellectual and technological challenge to chemists, physicists, materials scientists, and biologists. A variety of technological applications of nanotechnology rely on the possibility of controlling topological, chemical, and functional features at the molecular level. Self-assembled monolayers (SAMs) composed of chemisorbed species represent fundamental building blocks for creating complex structures by a bottom-up approach. These materials take advantage of the flexibility of organic and supramolecular chemistry to generate synthetic surfaces with well-defined chemical and physical properties. These films already serve as structural or functional parts of sensors, biosensors, drug-delivery systems, molecular electronic devices, protecting capping for nanostructures, and coatings for corrosion protection and tribological applications.Thiol SAMs on gold are the most popular molecular fi...

Measurement of the azimuthal anisotropy for charged particle production in √ sNN = 2.76 TeV lead-lead collisions with the ATLAS detector

Abstract: Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at root sNN = 2.76 TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 mu b(-1). This anisotropy is characterized via a Fourier expansion of the distribution of charged particles in azimuthal angle relative to the reaction plane, with the coefficients v(n) denoting the magnitude of the anisotropy. Significant v(2)-v(6) values are obtained as a function of transverse momentum (0.5 = 3 are found to vary weakly with both eta and centrality, and their p(T) dependencies are found to follow an approximate scaling relation, v(n)(1/n)(p(T)) proportional to v(2)(1/2)(p(T)), except in the top 5% most central collisions. A Fourier analysis of the charged particle pair distribution in relative azimuthal angle (Delta phi = phi(a)-phi(b)) is performed to extract the coefficients v(n,n) = . For pairs of charged particles with a large pseudorapidity gap (|Delta eta = eta(a) - eta(b)| > 2) and one particle with p(T) < 3 GeV, the v(2,2)-v(6,6) values are found to factorize as v(n,n)(p(T)(a), p(T)(b)) approximate to v(n) (p(T)(a))v(n)(p(T)(b)) in central and midcentral events. Such factorization suggests that these values of v(2,2)-v(6,6) are primarily attributable to the response of the created matter to the fluctuations in the geometry of the initial state. A detailed study shows that the v(1,1)(p(T)(a), p(T)(b)) data are consistent with the combined contributions from a rapidity-even v(1) and global momentum conservation. A two-component fit is used to extract the v(1) contribution. The extracted v(1) isobserved to cross zero at pT approximate to 1.0 GeV, reaches a maximum at 4-5 GeV with a value comparable to that for v(3), and decreases at higher p(T).

Vvv dr1: the first data release of the milky way bulge and southern plane from the near-infrared eso public survey vista variables in the via lactea

Abstract: Context The ESO public survey VISTA variables in the V�a L�ctea (VVV) started in 2010 VVV targets 562 sq deg in the Galactic bulge and an adjacent plane region and is expected to run for about five years Aims: We describe the progress of the survey observations in the first observing season, the observing strategy, and quality of the data obtained Methods: The observations are carried out on the 4-m VISTA telescope in the ZYJHK s filters In addition to the multi-band imaging the variability monitoring campaign in the K s filter has started Data reduction is carried out using the pipeline at the Cambridge Astronomical Survey Unit The photometric and astrometric calibration is performed via the numerous 2MASS sources observed in each pointing Results: The first data release contains the aperture photometry and astrometric catalogues for 348 individual pointings in the ZYJHK s filters taken in the 2010 observing season The typical image quality is 09 arcsec {-10 arcsec} The stringent photometric and image quality requirements of the survey are satisfied in 100% of the JHK s images in the disk area and 90% of the JHK s images in the bulge area The completeness in the Z and Y images is 84% in the disk, and 40% in the bulge The first season catalogues contain 128 � 10 8 stellar sources in the bulge and 168 � 10 8 in the disk area detected in at least one of the photometric bands The combined, multi-band catalogues contain more than 163 � 10 8 stellar sources About 10% of these are double detections because of overlapping adjacent pointings These overlapping multiple detections are used to characterise the quality of the data The images in the JHK s bands extend typically 4 mag deeper than 2MASS The magnitude limit and photometric quality depend strongly on crowding in the inner Galactic regions The astrometry for K s = 15-18 mag has rms 35-175 mas Conclusions: The VVV Survey data products offer a unique dataset to map the stellar populations in the Galactic bulge and the adjacent plane and provide an exciting new tool for the study of the structure, content, and star-formation history of our Galaxy, as well as for investigations of the newly discovered star clusters, star-forming regions in the disk, high proper motion stars, asteroids, planetary nebulae, and other interesting objects Based on observations taken within the ESO VISTA Public Survey VVV, Programme ID 179B-2002

Polymer brushes here, there, and everywhere: Recent advances in their practical applications and emerging opportunities in multiple research fields

Abstract: Bottom-up surface processing with well-defined polymeric structures becomes increasingly important in many current technologies. Polymer brushes, that is, assemblies of macromolecules tethered at one end to a substrate, provide an exemplary system of materials capable of achieving such a goal. While the focus in the past decades has been mostly on their synthetic aspects and the in-depth study of their interesting properties, from several years now the core area of research has already started to shift towards specific practical applications. Ample functional versatility and relative ease of preparation are special strengths of polymer brushes, lending them a strong interdisciplinary character. To this end, this work is entirely dedicated to bringing together the latest research on applications of polymer brushes in multiple research fields. The aim of this review are twofold: first, to give a critical discussion of the current status of development of application-oriented research on polymer brushes, and second, to inform the reader as to what can be done with polymer brushes in multiple research fields. It is therefore hoped that the juxtaposition of perspectives from different disciplines in one place will stimulate and contribute to the ongoing process of cross-fertilization that is driving this fascinating and emerging area of polymer science. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Uniform ripening encodes a Golden 2-like transcription factor regulating tomato fruit chloroplast development.

Abstract: Modern tomato (Solanum lycopersicum) varieties are bred for uniform ripening (u) light green fruit phenotypes to facilitate harvests of evenly ripened fruit. U encodes a Golden 2-like (GLK) transcription factor, SlGLK2, which determines chlorophyll accumulation and distribution in developing fruit. In tomato, two GLKs--SlGLK1 and SlGLK2--are expressed in leaves, but only SlGLK2 is expressed in fruit. Expressing GLKs increased the chlorophyll content of fruit, whereas SlGLK2 suppression recapitulated the u mutant phenotype. GLK overexpression enhanced fruit photosynthesis gene expression and chloroplast development, leading to elevated carbohydrates and carotenoids in ripe fruit. SlGLK2 influences photosynthesis in developing fruit, contributing to mature fruit characteristics and suggesting that selection of u inadvertently compromised ripe fruit quality in exchange for desirable production traits.

An exact formula for the radiation of a moving quark in {N} = 4 super Yang Mills

Abstract: We derive an exact formula for the cusp anomalous dimension at small angles. This is done by relating the latter to the computation of certain 1/8 BPS Wilson loops which was performed by supersymmetric localization. This function of the coupling also determines the power emitted by a moving quark in $\mathcal{N} = 4$ super Yang Mills, as well as the coefficient of the two point function of the displacement operator on the Wilson loop. By a similar method we compute the near BPS expansion of the generalized cusp anomalous dimension.

The quark anti-quark potential and the cusp anomalous dimension from a TBA equation

Abstract: We derive a set of integral equations of the TBA type for the generalized cusp anomalous dimension, or the quark antiquark potential on the three sphere, as a function of the angles. We do this by considering a family of local operators on a Wilson loop with charge L. In the large L limit the problem can be solved in terms of a certain boundary reflection matrix. We determine this reflection matrix by using the symmetries and the boundary crossing equation. The cusp is introduced through a relative rotation between the two boundaries. Then the TBA trick of exchanging space and time leads to an exact equation for all values of L. The L = 0 case corresponds to the cusped Wilson loop with no operators inserted. We then derive a slightly simplified integral equation which describes the small angle limit. We solve this equation up to three loops in perturbation theory and match the results that were obtained with more direct approaches.

Physicochemical and functional characterization of by-products from chia (Salvia hispanica L.) seeds of Argentina

Abstract: The objective of this study was to characterize the physicochemical and functional properties of meals (M) and fibrous fractions (FRF) of chia seeds (Salvia hispanica L.), and to compare the effect of oil extraction methods (pressing -p- and solvent extraction -s-) and sieving process on these properties. Both processes affect the physicochemical and functional properties of residual meals and their corresponding fibrous fractions. Mp and FRFp showed a significantly higher residual oil content than Ms and FRFs (11.39, 10.85, 0.21 and 0.21 g/100 dry base, respectively). The sieving process of both meals allowed to obtain fibrous fractions with a significant increase of crude fiber (27.57, 32.84, 23.81 and 28.35 g/100 g in Ms, FRFs, Mp and FRFp, respectively), and a marked decrease of protein content (41.36, 35.32, 35.00 and 33.74 g/100 g in Ms, FRFs, Mp and FRFp, respectively). Total dietary fiber and their respective components (soluble and insoluble dietary fiber) were significantly higher in FRF. All the samples exhibited a high antioxidant activity due to the presence of phenolic compounds and tocopherols in the case of Mp and FRFp. Ms and FRFs presented a better oil-holding capacity, organic molecule absorption capacity, emulsifying activity and emulsion stability than Mp and FRFp, and allowed to achieve more stable emulsions. FRFs showed the highest values of water absorption and adsorption capacity.

Measurement of the inclusive W± and Z/γ∗ cross sections in the e and μ decay channels in pp collisions at √s=7TeV with the ATLAS detector

Abstract: The production cross sections of the inclusive Drell-Yan processes W-+/- -> l nu and Z/gamma* -> ll (l = e, mu) are measured in proton-proton collisions at root s = 7 TeV with the ATLAS detector. The cross sections are reported integrated over a fiducial kinematic range, extrapolated to the full range, and also evaluated differentially as a function of the W decay lepton pseudorapidity and the Z boson rapidity, respectively. Based on an integrated luminosity of about 35 pb(-1) collected in 2010, the precision of these measurements reaches a few percent. The integrated and the differential W-+/- and Z/gamma* cross sections in the e and mu channels are combined, and compared with perturbative QCD calculations, based on a number of different parton distribution sets available at next-to-next-to-leading order.

Measurement of the proton-air cross section at √s=57 TeV with the Pierre Auger Observatory.

Abstract: We report a measurement of the proton-air cross section for particle production at the center-of-mass energy per nucleon of 57 TeV. This is derived from the distribution of the depths of shower maxima observed with the Pierre Auger Observatory: systematic uncertainties are studied in detail. Analyzing the tail of the distribution of the shower maxima, a proton-air cross section of [505 +/- 22(stat)(-36)(+28)(syst)] mb is found.

The type IIB supernova 2011DH from a supergiant progenitor

Abstract: A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star-with R {approx} 200 R{sub Sun }-is needed to reproduce the early light curve (LC) of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star. From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be Almost-Equal-To 2 M{sub Sun }, the explosion energy to be E = (6-10) Multiplication-Sign 10{sup 50} erg, and the {sup 56}Ni mass to be approximately 0.06 M{sub Sun }. The progenitor star was composed of a helium core of 3-4 M{sub Sun} and a thin hydrogen-rich envelope of Almost-Equal-To 0.1M{sub Sun} with a main-sequence mass estimated to be in the range of 12-15 M{sub Sun }. Our models rule out progenitors with helium-core masses larger than 8 M{sub Sun }, which correspond to M{sub ZAMS} {approx}> 25M{sub Sun }. This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

Distinguishing chaotic and stochastic dynamics from time series by using a multiscale symbolic approach

Abstract: In this paper we introduce a multiscale symbolic information-theory approach for discriminating nonlinear deterministic and stochastic dynamics from time series associated with complex systems. More precisely, we show that the multiscale complexity-entropy causality plane is a useful representation space to identify the range of scales at which deterministic or noisy behaviors dominate the system's dynamics. Numerical simulations obtained from the well-known and widely used Mackey-Glass oscillator operating in a high-dimensional chaotic regime were used as test beds. The effect of an increased amount of observational white noise was carefully examined. The results obtained were contrasted with those derived from correlated stochastic processes and continuous stochastic limit cycles. Finally, several experimental and natural time series were analyzed in order to show the applicability of this scale-dependent symbolic approach in practical situations.

Thermalization with a chemical potential from AdS spaces

Abstract: The time-scale of thermalization in holographic dual models with a chemical potential in diverse number of dimensions is systematically investigated using the gauge/gravity duality. We consider a model with a thin-shell of charged dust collapsing from the boundary toward the bulk interior of asymptotically anti-de Sitter (AdS) spaces. In the outer region there is a Reissner-Nordstrom-AdS black hole (RNAdS-BH), while in the inner region there is an anti-de Sitter space. We consider renormalized geodesic lengths and minimal area surfaces as probes of thermalization, which in the dual quantum field theory (QFT) correspond to two-point functions and expectation values of Wilson loops, respectively. We show how the behavior of these extensive probes changes for charged black holes in comparison with Schwarzschild-AdS black holes (AdS-BH), for different values of the black hole mass and charge. The full range of values of the chemical potential over temperature ratio in the dual QFT is investigated. In all cases, the structure of the thermalization curves shares similar features with those obtained from the AdS-BH. On the other hand, there is an important difference in comparison with the AdS-BH: the thermalization times obtained from the renormalized geodesic lengths and the minimal area surfaces are larger for the RNAdS-BH, and they increase as the black hole charge increases.

The Growth of Conditional Cash Transfers in Latin America and the Caribbean: Did They Go Too Far?

Abstract: Conditional Cash Transfers (CCTs) are an endogenous innovation from Latin America and the Caribbean (LAC) that aims to reduce current poverty while developing the human capital of the next generation, in the attempt to break the intergenerational transmission of poverty. Pioneered in Brazil and Mexico in the late 1990s, by 2011 CCTs had spread to 18 countries in the region and covered as many as 135 million beneficiaries. In this paper, we use administrative and household survey data to document (i) the evolution of CCTs and poverty in LAC, (ii) the relationship between expanded coverage and the quality of targeting and (iii) the change in beneficiary household characteristics. We show that in most countries the transfers represent over 20% of poor beneficiaries' incomes, and the poverty headcount index would be on average 13% higher, had CCTs not been implemented.

The cusp anomalous dimension at three loops and beyond

Abstract: Fil: Correa, Diego Hernan. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Fisica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Fisica La Plata; Argentina

Thermalization and quantum correlations in exactly solvable models.

Abstract: The generalized Gibbs ensemble introduced for describing few-body correlations in exactly solvable systems following a quantum quench is related to the nonergodic way in which operators sample, in the limit of infinite time after the quench, the quantum correlations present in the initial state. The nonergodicity of the correlations is thus shown analyticallyto imply the equivalence with the generalized Gibbs ensemble for quantum Ising and $XX$ spin chains as well as for the Luttinger model the thermodynamic limit, and for a broad class of initial states and correlation functions of both local and nonlocal operators.

Double degenerate mergers as progenitors of high-field magnetic white dwarfs

Abstract: High-field magnetic white dwarfs have been long suspected to be the result of stellar mergers. However, the nature of the coalescing stars and the precise mechanism that produces the magnetic field are still unknown. Here, we show that the hot, convective, differentially rotating corona present in the outer layers of the remnant of the merger of two degenerate cores can produce magnetic fields of the required strength that do not decay for long timescales. Using a state-of-the-art Monte Carlo simulator, we also show that the expected number of high-field magnetic white dwarfs produced in this way is consistent with that found in the solar neighborhood.

The quark anti-quark potential and the cusp anomalous dimension from a TBA equation

Abstract: We derive a set of integral equations of the TBA type for the generalized cusp anomalous dimension, or the quark antiquark potential on the three sphere, as a function of the angles. We do this by considering a family of local operators on a Wilson loop with charge L. In the large L limit the problem can be solved in terms of a certain boundary reflection matrix. We determine this reflection matrix by using the symmetries and the boundary crossing equation. The cusp is introduced through a relative rotation between the two boundaries. Then the TBA trick of exchanging space and time leads to an exact equation for all values of L. The L=0 case corresponds to the cusped Wilson loop with no operators inserted. We then derive a slightly simplified integral equation which describes the small angle limit. We solve this equation up to three loops in perturbation theory and match the results that were obtained with more direct approaches.

Antennas for the detection of radio emission pulses from cosmic-ray induced air showers at the Pierre Auger Observatory

Abstract: The Pierre Auger Observatory is exploring the potential of the radio detection technique to study extensive air showers induced by ultra-high energy cosmic rays. The Auger Engineering Radio Array (AERA) addresses both technological and scientific aspects of the radio technique. A first phase of AERA has been operating since September 2010 with detector stations observing radio signals at frequencies between 30 and 80 MHz. In this paper we present comparative studies to identify and optimize the antenna design for the final configuration of AERA consisting of 160 individual radio detector stations. The transient nature of the air shower signal requires a detailed description of the antenna sensor. As the ultra-wideband reception of pulses is not widely discussed in antenna literature, we review the relevant antenna characteristics and enhance theoretical considerations towards the impulse response of antennas including polarization effects and multiple signal reflections. On the basis of the vector effective length we study the transient response characteristics of three candidate antennas in the time domain. Observing the variation of the continuous galactic background intensity we rank the antennas with respect to the noise level added to the galactic signal.

Environmental toxicology and chemistry in Latin America

Abstract: Fil: Carriquiriborde, Pedro. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Quimica. Centro de Investigaciones del Medio Ambiente; Argentina

Measurement of t(t)over-bar production with a veto on additional central jet activity in pp collisions at root s=7 TeV using the ATLAS detector

Abstract: A measurement of the jet activity in t (t) over bar events produced in proton-proton collisions at a centre-of-mass energy of 7 TeV is presented, using 2.05 fb(-1) of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. The t (t) over bar events are selected in the dilepton decay channel with two identified b-jets from the top quark decays. Events are vetoed if they contain an additional jet with transverse momentum above a threshold in a central rapidity interval. The fraction of events surviving the jet veto is presented as a function of this threshold for four different central rapidity interval definitions. An alternate measurement is also performed, in which events are vetoed if the scalar transverse momentum sum of the additional jets in each rapidity interval is above a threshold. In both measurements, the data are corrected for detector effects and compared to the theoretical models implemented in MC@NLO, POWHEG, ALPGEN and SHERPA. The experimental uncertainties are often smaller than the spread of theoretical predictions, allowing deviations between data and theory to be observed in some regions of phase space.

Toward ensemble asteroseismology of ZZ Ceti stars with fully evolutionary models

Abstract: ZZ Ceti stars form the most numerous group of degenerate variable stars. They are otherwise normal DA (H-rich atmospheres) white dwarfs that exhibit pulsations. Here, we present an asteroseismological analysis for 44 bright ZZ Ceti stars based on a new set of fully evolutionary DA white dwarf models characterized by detailed chemical profiles from the centre to the surface. One of our targets is the archetypal ZZ Ceti star G117−B15A, for which we obtain an asteroseismological model with an effective temperature and a surface gravity in excellent agreement with the spectroscopy. The asteroseismological analysis of a set of 44 ZZ Ceti stars has the potential to characterize the global properties of the class, in particular the thicknesses of the hydrogen envelope and the stellar masses. Our results support the belief that white dwarfs in the solar neighbourhood harbour a broad range of hydrogen-layer thickness.

Chemiresistive sensing with chemically modified metal and alloy nanoparticles.

Abstract: This review describes the use of chemically modified pure and alloyed metal nanoparticles for chemiresistive sensing applications. Chemically modified metal nanoparticles consist of a pure or alloyed metallic core with some type of chemical coating. Researchers have studied the electronic properties of 1D, 2D, and 3D assemblies of chemically modified metal nanoparticles, and even single individual nanoparticles. The interaction with the analyte alters the conductivity of the sensitive material, providing a signal to measure the analyte concentration. This review focuses on chemiresistive sensing of a wide variety of gas- and liquid-phase analytes with metal nanoparticles coated with organothiols, ions, polymers, surfactants, and biomolecules. Different strategies used to incorporate chemically modified nanoparticles into chemiresistive sensing devices are reviewed, focusing on the different types of metal and alloy compositions, coatings, methods of assembly, and analytes (vapors, gases, liquids, biological materials), along with other important factors.

Search for heavy neutrinos and right-handed W bosons in events with two leptons and jets in pp collisions at √s =7 TeV with the ATLAS detector

Abstract: This letter reports on a search for hypothetical heavy neutrinos, N, and right-handed gauge bosons, W-R, in events with high transverse momentum objects which include two reconstructed leptons and ...