Effect of palladium on gold in core-shell catalyst for electrooxidation of ethanol in alkaline medium

In this paper the effect of small amounts of palladium deposited on gold nanoparticles supported on Vulcan XC-72 carbon (core-shell structure denoted Au@Pd/C) is studied. Different nominal atomic compositional ratios of Au@Pdx maintaining fixed gold nuclei and varying the amount of palladium (x = 0.10; 0.80 and 1.60) were synthesized via seed growth method for the ethanol oxidation reaction in alkaline medium. UV–Vis spectrometric, X-ray powder diffraction, X-ray energy dispersive spectroscopy, transmission electron microscopy and electrochemical measurements were performed for the characterization of these catalysts. Electrocatalytic activity toward ethanol oxidation on Au@Pd/C catalysts were investigated by cyclic voltammetry and chronoamperometry showed that [email protected]/C electrocatalyst has the highest current density and low onset potential for ethanol oxidation reaction in alkaline medium. In-situ Fourier transform infrared spectroscopy measurements demonstrated that acetate is the main product of ethanol oxidation and CO2 can be slightest observed, the latter could be visualized in greater quantity on catalyst [email protected]/C catalyst

Cultivo de ñame.

Se indica la importancia del cultivo del ñame en la Costa Atlántica de Colombia, el área cultivada, la producción y el rendimiento. Se señala su origen y la clasificación botánica del cultivo. Se indican los requerimientos ambientales, en términos de suelos, topografa, régimen pluviométrico y temperatura. Se mencionan las principales labores de cultivo como preparación del suelo, siembra, selección de semilla, aporque, tutorado, capado, desyerbas, control de plagas y enfermedades, cosecha y almacenamientoÑame-Dioscorea spp

Deterministically Driven Avalanche Models of Solar Flares

We develop and discuss the properties of a new class of lattice-based avalanche models of solar flares. These models are readily amenable to a relatively unambiguous physical interpretation in terms of slow twisting of a coronal loop. They share similarities with other avalanche models, such as the classical stick--slip self-organized critical model of earthquakes, in that they are driven globally by a fully deterministic energy loading process. The model design leads to a systematic deficit of small scale avalanches. In some portions of model space, mid-size and large avalanching behavior is scale-free, being characterized by event size distributions that have the form of power-laws with index values, which, in some parameter regimes, compare favorably to those inferred from solar EUV and X-ray flare data. For models using conservative or near-conservative redistribution rules, a population of large, quasiperiodic avalanches can also appear. Although without direct counterparts in the observational global statistics of flare energy release, this latter behavior may be relevant to recurrent flaring in individual coronal loops. This class of models could provide a basis for the prediction of large solar flares.Comment: 24 pages, 11 figures, 2 tables, accepted for publication in Solar Physic

The cosmic ray positron excess and neutralino dark matter

Using a new instrument, the HEAT collaboration has confirmed the excess of cosmic ray positrons that they first detected in 1994. We explore the possibility that this excess is due to the annihilation of neutralino dark matter in the galactic halo. We confirm that neutralino annihilation can produce enough positrons to make up the measured excess only if there is an additional enhancement to the signal. We quantify the `boost factor' that is required in the signal for various models in the Minimal Supersymmetric Standard Model parameter space, and study the dependence on various parameters. We find models with a boost factor greater than 30. Such an enhancement in the signal could arise if we live in a clumpy halo. We discuss what part of supersymmetric parameter space is favored (in that it gives the largest positron signal), and the consequences for other direct and indirect searches of supersymmetric dark matter.Comment: 11 pages, 6 figures, matches published version (PRD

Analysis of the origin and training of the labor dedicated to the post-harvest process of banana in Tecomán, Cerro de Ortega, Colima, Mexico

Objective: Analyze and identify the place of origin, skills and working conditions of the workforce dedicated to working in the banana cutting and packaging process in the town of Cerro de Ortega, Tecomán Colima. Design / Methodology / Approach: A field checklist was designed and applied to 32% of the local crews and a survey directed to the members of the crews, surveying 21.3% of the total population. Results: Information was obtained to carry out the analysis of origin and the current situation of workforce dedicated to the post-harvest process of plantain in the study area. Limitations of the study: An important limitation for the investigation was the insecurity during the field work, which was present derived from the organized crime settled in the area. Findings / Conclusions: The most specialized workers in the area who are dedicated to the activities of cutting and packing bananas are not native to the municipality of Tecomán, much less the state of Colima, they belong to the states of Chiapas and Michoacán.Objective: To analyze and identify the place of origin, skills and working conditions of the laborers dedicated to the banana cutting and packaging process in the town of Cerro de Ortega, Tecomán, Colima. Design / Methodology / Approach: A field checklist was designed and applied to 32% of the local crews and a survey directed to the members of the crews, surveying 21.3% of the total population. Results: Information was obtained to carry out the analysis of origin and the current situation of laborers dedicated to the post-harvest process of banana in the study area. Limitations of the study: An important limitation for the research was insecurity during the field surveys, which was present derived from the organized crime settled in the area. Findings / Conclusions: The most specialized workers in the area who are dedicated to the activities of cutting and packing bananas are not native people from the municipality of Tecomán, nor from the state of Colima. They belong to the states of Chiapas and Michoacan

Astrophysical Axion Bounds

Axion emission by hot and dense plasmas is a new energy-loss channel for stars. Observational consequences include a modification of the solar sound-speed profile, an increase of the solar neutrino flux, a reduction of the helium-burning lifetime of globular-cluster stars, accelerated white-dwarf cooling, and a reduction of the supernova SN 1987A neutrino burst duration. We review and update these arguments and summarize the resulting axion constraints.Comment: Contribution to Axion volume of Lecture Notes in Physics, 20 pages, 3 figure

Progressive transformation of a flux rope to an ICME

The solar wind conditions at one astronomical unit (AU) can be strongly disturbed by the interplanetary coronal mass ejections (ICMEs). A subset, called magnetic clouds (MCs), is formed by twisted flux ropes that transport an important amount of magnetic flux and helicity which is released in CMEs. At 1 AU from the Sun, the magnetic structure of MCs is generally modeled neglecting their expansion during the spacecraft crossing. However, in some cases, MCs present a significant expansion. We present here an analysis of the huge and significantly expanding MC observed by the Wind spacecraft during 9 and 10 November, 2004. After determining an approximated orientation for the flux rope using the minimum variance method, we precise the orientation of the cloud axis relating its front and rear magnetic discontinuities using a direct method. This method takes into account the conservation of the azimuthal magnetic flux between the in- and out-bound branches, and is valid for a finite impact parameter (i.e., not necessarily a small distance between the spacecraft trajectory and the cloud axis). Moreover, using the direct method, we find that the ICME is formed by a flux rope (MC) followed by an extended coherent magnetic region. These observations are interpreted considering the existence of a previous larger flux rope, which partially reconnected with its environment in the front. These findings imply that the ejected flux rope is progressively peeled by reconnection and transformed to the observed ICME (with a remnant flux rope in the front part).Comment: Solar Physics (in press

LHC sensitivity to the resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector

We present a unified analysis of the two main production processes of vector boson pairs at the LHC, VV-fusion and qqbar annihilation, in a minimal strongly interacting electroweak symmetry breaking sector. Using a unitarized electroweak chiral Lagrangian formalism and modeling the final V_L V_L strong rescattering effects by a form factor, we describe qqbar annihilation processes in terms of the two chiral parameters that govern elastic V_L V_L scattering. Depending on the values of these two chiral parameters, the unitarized amplitudes may present resonant enhancements in different angular momentum-isospin channels. Scanning this two parameter space, we generate the general resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector and determine the regions that can be probed at the LHC.Comment: Final version to appear in Phys. Rev. D, including a more detailed exposition and a few more references. Conclusions and results unchanged. 14 pages, 5 figure