The strong weak convergence of the quasi-EA

In this paper, we investigate the convergence of a novel simulation scheme to the target diffusion process. This scheme, the Quasi-EA, is closely related to the Exact Algorithm (EA) for diffusion processes, as it is obtained by neglecting the rejection step in EA. We prove the existence of a myopic coupling between the Quasi-EA and the diffusion. Moreover, an upper bound for the coupling probability is given. Consequently we establish the convergence of the Quasi-EA to the diffusion with respect to the total variation distance

Liquid-phase oxidation of glycerol over a Pt/C catalyst : Optimization of the reaction conditions

La oxidación en fase líquida de glicerol (Gly) se investigó sistemáticamente empleando un catalizador Pt/C. El catalizador se preparó por impregnación con una solución de (NH4)2[PtCl4], con el fin de obtener un 1% en peso de Pt. Se lo caracterizó por AAS, TEM y TPR. Las condiciones de reacción se optimizaron realizando experimentos en el intervalo de temperatura entre 40 y 60ºC, relación molar Gly/Pt entre 4000 y 10000, pH entre 5 y 13 y concentración de H2O2como para obtener entre 2.5 y 10 volúmenes de oxígeno activo en el reactor. Las condiciones óptimas de reacción se identificaron como 60°C, Gly/Pt = 4000, pH = 5, concentración de H2O2 suficiente para obtener 10vol de O2, 100 mg de catalizador y agitación constante. Bajo estas condiciones, se obtuvo una selectividad máxima de ácido glicérico (GlyA) del 57.1% con una conversión de Gly de 37%.Liquid-phase glycerol (Gly) oxidation was investigated systematically over a Pt/C catalyst. The catalyst was prepared by impregnation with a (NH4)2[PtCl4] solution, in order to obtain a 1 wt% Pt. The catalyst was characterized by AAS, TEM and TPR techniques. The reaction conditions were optimized by conducting experiments in the range of temperature from 40 to 60°C, Gly/Pt molar ratio between 4000 and 10000, pH between 5 and 13 and H2O2 concentration in order to get between 2.5 and 10 volumes of active oxygen in the reactor. The optimum reaction conditions were identified as 60°C, Gly/Pt = 4000, pH= 5, H2O2 concentration enough to obtain 10vol of O2, 100 mg catalyst and constant stirring. Under these conditions, a maximum glyceric acid (GlyA) selectivity of 57.1% was obtained at 37% Gly conversion.Centro de Investigación y Desarrollo en Ciencias AplicadasFacultad de Ingenierí

Liquid-phase oxidation of glycerol over a Pt/C catalyst : Optimization of the reaction conditions

La oxidación en fase líquida de glicerol (Gly) se investigó sistemáticamente empleando un catalizador Pt/C. El catalizador se preparó por impregnación con una solución de (NH4)2[PtCl4], con el fin de obtener un 1% en peso de Pt. Se lo caracterizó por AAS, TEM y TPR. Las condiciones de reacción se optimizaron realizando experimentos en el intervalo de temperatura entre 40 y 60ºC, relación molar Gly/Pt entre 4000 y 10000, pH entre 5 y 13 y concentración de H2O2como para obtener entre 2.5 y 10 volúmenes de oxígeno activo en el reactor. Las condiciones óptimas de reacción se identificaron como 60°C, Gly/Pt = 4000, pH = 5, concentración de H2O2 suficiente para obtener 10vol de O2, 100 mg de catalizador y agitación constante. Bajo estas condiciones, se obtuvo una selectividad máxima de ácido glicérico (GlyA) del 57.1% con una conversión de Gly de 37%.Liquid-phase glycerol (Gly) oxidation was investigated systematically over a Pt/C catalyst. The catalyst was prepared by impregnation with a (NH4)2[PtCl4] solution, in order to obtain a 1 wt% Pt. The catalyst was characterized by AAS, TEM and TPR techniques. The reaction conditions were optimized by conducting experiments in the range of temperature from 40 to 60°C, Gly/Pt molar ratio between 4000 and 10000, pH between 5 and 13 and H2O2 concentration in order to get between 2.5 and 10 volumes of active oxygen in the reactor. The optimum reaction conditions were identified as 60°C, Gly/Pt = 4000, pH= 5, H2O2 concentration enough to obtain 10vol of O2, 100 mg catalyst and constant stirring. Under these conditions, a maximum glyceric acid (GlyA) selectivity of 57.1% was obtained at 37% Gly conversion.Centro de Investigación y Desarrollo en Ciencias AplicadasFacultad de Ingenierí

Posterior-based proposals for speeding up Markov chain Monte Carlo

Markov chain Monte Carlo (MCMC) is widely used for Bayesian inference in models of complex systems. Performance, however, is often unsatisfactory in models with many latent variables due to so-called poor mixing, necessitating development of application specific implementations. This paper introduces "posterior-based proposals" (PBPs), a new type of MCMC update applicable to a huge class of statistical models (whose conditional dependence structures are represented by directed acyclic graphs). PBPs generates large joint updates in parameter and latent variable space, whilst retaining good acceptance rates (typically 33%). Evaluation against other approaches (from standard Gibbs / random walk updates to state-of-the-art Hamiltonian and particle MCMC methods) was carried out for widely varying model types: an individual-based model for disease diagnostic test data, a financial stochastic volatility model, a mixed model used in statistical genetics and a population model used in ecology. Whilst different methods worked better or worse in different scenarios, PBPs were found to be either near to the fastest or significantly faster than the next best approach (by up to a factor of 10). PBPs therefore represent an additional general purpose technique that can be usefully applied in a wide variety of contexts.Comment: 54 pages, 11 figures, 2 table

First measurement of the 14N(p,gamma)15O cross section down to 70 keV

In stars with temperatures above 20*10^6 K, hydrogen burning is dominated by the CNO cycle. Its rate is determined by the slowest process, the 14N(p,gamma)15O reaction. Deep underground in Italy's Gran Sasso laboratory, at the LUNA 400 kV accelerator, the cross section of this reaction has been measured at energies much lower than ever achieved before. Using a windowless gas target and a 4pi BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn. The Gamow peak has been covered by experimental data for several scenarios of stable and explosive hydrogen burning. In addition, the strength of the 259 keV resonance has been remeasured. The thermonuclear reaction rate has been calculated for temperatures 90 - 300 *10^6 K, for the first time with negligible impact from extrapolations

Feasibility of low energy radiative capture experiments at the LUNA underground accelerator facility

The LUNA (Laboratory Underground for Nuclear Astrophysics) facility has been designed to study nuclear reactions of astrophysical interest. It is located deep underground in the Gran Sasso National Laboratory, Italy. Two electrostatic accelerators, with 50 and 400 kV maximum voltage, in combination with solid and gas target setups allowed to measure the total cross sections of the radiative capture reactions $^2$H(p,$\gamma$)3He and $^{14}$N(p,$\gamma$)$^{15}$O within their relevant Gamow peaks. We report on the gamma background in the Gran Sasso laboratory measured by germanium and bismuth germanate detectors, with and without an incident proton beam. A method to localize the sources of beam induced background using the Doppler shift of emitted gamma rays is presented. The feasibility of radiative capture studies at energies of astrophysical interest is discussed for several experimental scenarios.Comment: Submitted to Eur. Phys. J.

The scaling of X-ray variability with luminosity in Ultra-luminous X-ray sources

We investigated the relationship between the X-ray variability amplitude and X-ray luminosity for a sample of 14 bright Ultra-luminous X-ray sources (ULXs) with XMM-Newton/EPIC data, and compare it with the well established similar relationship for Active Galactic Nuclei (AGN). We computed the normalised excess variance in the 2-10 keV light curves of these objects and their 2-10 keV band intrinsic luminosity. We also determined model "variability-luminosity" relationships for AGN, under several assumptions regarding their power-spectral shape. We compared these model predictions at low luminosities with the ULX data. The variability amplitude of the ULXs is significantly smaller than that expected from a simple extrapolation of the AGN "variability-luminosity" relationship at low luminosities. We also find evidence for an anti-correlation between the variability amplitude and L(2-10 keV) for ULXs. The shape of this relationship is consistent with the AGN data but only if the ULXs data are shifted by four orders of magnitudes in luminosity. Most (but not all) of the ULXs could be "scaled-down" version of AGN if we assume that: i) their black hole mass and accretion rate are of the order of ~(2.5-30)x 10E+03 Msolar and ~ 1-80 % of the Eddington limit, and ii) their Power Spectral Density has a doubly broken power-law shape. This PDS shape and accretion rate is consistent with Galactic black hole systems operating in their so-called "low-hard" and "very-high" states.Comment: 10 pages, 5 figures, 2 tables, accepted for publication in A&

Unique Structural Modifications Are Present in the Lipopolysaccharide from Colistin-Resistant Strains of \u3ci\u3eAcinetobacter baumannii\u3c/i\u3e

Acinetobacter baumannii is a nosocomial opportunistic pathogen that can cause severe infections, including hospital-acquired pneumonia, wound infections, and sepsis. Multidrug-resistant (MDR) strains are prevalent, further complicating patient treatment. Due to the increase in MDR strains, the cationic antimicrobial peptide colistin has been used to treat A. baumannii infections. Colistin-resistant strains of A. baumannii with alterations to the lipid A component of lipopolysaccharide (LPS) have been reported; specifically, the lipid A structure was shown to be hepta-acylated with a phosphoethanolamine (pEtN) modification present on one of the terminal phosphate residues. Using a tandem mass spectrometry platform, we provide definitive evidence that the lipid A isolated from colistin-resistant A. baumannii MAC204 LPS contains a novel structure corresponding to a diphosphoryl hepta-acylated lipid A structure with both pEtN and galactosamine (GalN) modifications. To correlate our structural studies with clinically relevant samples, we characterized colistin-susceptible and -resistant isolates obtained from patients. These results demonstrated that the clinical colistin-resistant isolate had the same pEtN and GalN modifications as those seen in the laboratory-adapted A. baumannii strain MAC204. In summary, this work has shown complete structure characterization including the accurate assignment of acylation, phosphorylation, and glycosylation of lipid A from A. baumannii, which are important for resistance to colistin

Variability of X-ray binaries from an oscillating hot corona

The spectral and timing properties of an oscillating hot thermal corona are investigated. This oscillation is assumed to be due to a magneto-acoustic wave propagating within the corona and triggered by an external, non specified, excitation. A cylindrical geometry is adopted and, neglecting the rotation, the wave equation is solved in for different boundary conditions. The resulting X-ray luminosity, through thermal comptonization of embedded soft photons, is then computed, first analytically, assuming linear dependence between the local pressure disturbance and the radiative modulation. These calculations are also compared to Monte-Carlo simulations. The main results of this study are: (1) the corona plays the role of a low band-pass medium, its response to a white noise excitation being a at top noise Power Spectral Density (PSD) at low frequencies and a red noise at high frequency, (2) resonant peaks are present in the PSD. Their powers depend on the boundary conditions chosen and, more specifically, on the impedance adaptation with the external medium at the corona inner boundary. (3) The flat top noise level and break as well as the resonant peak frequencies are inversely proportional to the external radius rj. (4) Computed rms and f-spectra exhibit an overall increase of the variability with energy. Comparison with observed variability features, especially in the hard intermediate states of X-ray binaries are discussed.Comment: 12 pages, 7 figures, accepted for publication in MNRA

Oxidación de glicerol sobre catalizadores de platino soportados en carbón y modificados por bismuto

En el presente trabajo se estudian catalizadores de Pt y PtBi soportados sobre carbón para la reacción de oxidación de glicerol (GLY) en fase líquida. El objetivo de este proceso es obtener selectivamente productos de alto valor agregado a partir del glicerol. Se optimizaron las condiciones de reacción las cuales resultaron ser: temperatura 60ºC,un pH de 5, una cantidad de H2O2 para obtener una concentración de 10v de O2, 100 mg de catalizador y relación molar GLY/Pt de 400. Luego de 4 h de reacción el catalizador Pt/C alcanzó una conversión de GLY de 37% con una selectividad de 57% a ácido glicérico. Se estudió el efecto de la concentración de Bi variando la relación Pt:Bi. Se observó que la relación óptima entre ambos metales fue Bi/Pt 0.5 (PtBi0.50/C). Dicho catalizador presentó una selectividad a dihidroxiacetona de un 84.5% para una conversión de 43%.In the present work carbon-supported Pt and PtBi catalysts were studied in the liquid-phase glicerol (GLY) oxidation reaction. The aim of this process is selectively obtain products of high added value from glycerol. The optimum reaction conditions were: temperature 60°C, pH = 5, H2O2 concentration so as to obtain 10vol % O2, 100 mg of catalyst and a GLY/Pt molar ratio of 400. After 4 h of reaction the Pt/C catalyst achieved a GLY conversion of 37% with a selectivity to glyceric acid of 57%. The effect of the Bi concentration was studied by varying the Pt:Bi atomic ratio. It was observed that the optimum ratio between both metals was Bi/Pt = 0.5 (PtBi0.50/C). This catalyst showed a selectivity to dihydroxyacetone of 84.5% for a GLY conversion of 43%.Trabajo publicado en Álvarez, María E., Sandra G. Casuscelli, Mónica E. Crivello y Griselda A. Eimer (eds.). Actas del XX Congreso Argentino de Catálisis. Universidad Tecnológica Nacional, Facultad Regional Córdoba, Buenos Aires, 2017.Facultad de Ciencias Exacta