Three dimensional fluid-kinetic model of a magnetically guided plasma jet

A fluid-kinetic model of the collisionless plasma row in a convergent-divergent magnetic nozzle is presented. The model combines the leading-order Vlasov equation and the fluid continuity and perpendicular momentum equation for magnetized electrons, and the fluid equations for cold ions, which must be solved iteratively to determine the self-consistent plasma response in a three-dimensional magnetic field. The kinetic electron solution identifies three electron populations and provides the plasma density and pressure tensor. The far downstream asymptotic behavior shows the anisotropic cooling of the electron populations. The fluid equations determine the electric potential and the fluid velocities. In the small ion-sound gyroradius case the solution is constructed one magnetic line at a time. In the large ion-sound gyroradius case, ion detachment from magnetic lines makes the problem fully three-dimensional.This work was supported by National R&D Plan (Grant ESP2016-75887) from the Gobierno de España. Jesús Ramos thanks the financial sponsorship of the Chair of Excellence award granted by UC3M and Banco de Santander

Analysis of Indoor Radon Distribution Within a Room By Means of Computational Fluid Dynamics (CFD) Simulation

Radon gas is recognized by international organizations such as the United States Environmental Protection Agency (US-EPA) as the main contributor of radiation environmental to which human beings are exposed. Therefore, the evaluation of indoor radon concentration is a matter of public interest. The emanation and the income of the gas inside a room will generate a negative impact on the quality of the air when the place is not properly ventilated. Understanding how this gas will be distributed inside the room will allow to predict the spatial and temporal variations of radon levels and identify these parameters will provide important information that researchers can be used for calculate radiation dose exposure. Consequently, this studies can prevent a health risk for the people that live or work within the room. Currently, several researchers use the technique called Computational Fluid Dynamics (CFD) to simulate the distribution of gas radon, making use of the various commercial programs that exist in the market. In this work, three simulations were developed in rooms that have a similar geometry but different dimensions, in order to observe how the gas is distributed inside a closed space and to analyze how this distribution varies when the volume of the place is increased. The results show that as the volume of the site increases the radon is mitigated more rapidly and therefore has lower levels of concentration of this gas, as long as the level of radon emanation is kept constant

Compositionally graded YSZ–NiO composites by surface laser melting

El pdf del artículo es la versión post-print.Laser surface melting has been applied to near eutectic NiO–YSZ sintered ceramics. The objective is to generate a functional gradient composite material with graded microstructure and composition. At low solidification rates the resultant material has a graded composition, with a severe NiO segregation towards the surface. A thick NiO layer whose thickness depends on the travelling speed is formed. Below this layer the microstructure is eutectic like with composition varying with depth. In contact with the ceramic, excess YSZ coming from the hypereutectic composition forms an almost continuous YSZ layer. The thickness of both segregated layers, NiO and YSZ can be controlled by traverse speed. Thickness decreases as travelling speed increases until a limiting travelling rate of 110 mm/h, at which no more segregation is found. Possible causes to explain the relevant NiO segregation towards the surface are discussed.Financial support from the Ministerio de Educación y Ciencia of Spain and the CE program FEDER under grant MAT2006-13005-C03-01 is gratefully acknowledged.Peer Reviewe

Feynman scaling violation on baryon spectra in pp collisions at LHC and cosmic ray energies

A significant asymmetry in baryon/antibaryon yields in the central region of high energy collisions is observed when the initial state has non-zero baryon charge. This asymmetry is connected with the possibility of baryon charge diffusion in rapidity space. Such a diffusion should decrease the baryon charge in the fragmentation region and translate into the corresponding decrease of the multiplicity of leading baryons. As a result, a new mechanism for Feynman scaling violation in the fragmentation region is obtained. Another numerically more significant reason for the Feynman scaling violation comes from the fact that the average number of cutted Pomerons increases with initial energy. We present the quantitative predictions of the Quark-Gluon String Model (QGSM) for the Feynman scaling violation at LHC energies and at even higher energies that can be important for cosmic ray physics.Comment: 21 pages, 11 figures, and 1 table. arXiv admin note: substantial text overlap with arXiv:1107.1615, arXiv:1007.320

Evaluation of two commercially available rumen buffers derived from calcified seaweed for grazing dairy cows: Pilot trial in commercial farms

Los productos a base de algas marinas calcificadas (CS) se han propuesto como un tampón de pH ruminal alternativo al bicarbonato de sodio. Se ha reportado que el magnesio puede ayudar en el control del pH ruminal, especialmente las formas naturales marinas. Evaluamos la capacidad amortiguadora del pH del rumen y la producción y composición de la leche de dos CS: Acid Buf (AB) y M12 (un CS natural enriquecido con magnesio marino), en vacas lecheras en pastoreo en un diseño de cuadrado latino replicado que involucró 2 granjas con rebaños lecheros en buen estado sanitario y de salud, 2 suplementos y 4 periodos de evaluación de un mes cada uno. Vacas lecheras Holstein Friesian se alimentaron con una ración parcial mixta (PMR) y se suplementaron durante cuatro períodos de 30 días cada uno con AB o M12. Se midió la producción total y la composición de la leche en cada granja y cinco vacas en cada rebaño recibieron bolos ruminales para monitorear el pH ruminal, permitiéndonos identificar y monitorear eventos de acidosis ruminal subaguda total (SARA) (es decir = 2 h con pH < 5.8). El pH promedio durante el período experimental fue 2% mayor (p < 0,05) y el número de eventos SARA por vaca fue menor (p = 0,007) para vacas suplementadas con M12 en comparación con AB. Considerando solo las vacas que desarrollaron eventos SARA, M12 tendió (p = 0,068) a reducir el número de eventos de SARA y su duración en comparación con aquellas vacas suplementadas con AB. La producción y composición de la leche fueron similares entre ambos tampones ruminales en todos los períodos

Short-Term Effect of Daily Herbage Allowance Restriction on Pasture Condition and the Performance of Grazing Dairy Cows during Autumn

The aim of this study was to evaluate the short-term effects of daily herbage allowance (DHA, defined as the product of pre-grazing herbage mass and offered area per animal) on pasture conditions and milk production of Holstein-Friesian dairy cows. Forty-four early lactation dairy cows were randomly assigned to one of four treatments in a 2 × 2 factorial design that tested two levels of DHA (17 and 25 kg DM/cow.day) and two levels of maize silage supplementation (MSS, 4.5 and 9 kg DM/cow.day) over a 77-day period. Low DHA decreased the post-grazing herbage mass from 1546 to 1430 kg DM/ha and the compressed sward height from 5 to 4.4 cm, while the grazing efficiency remained unaffected. Low DHA induced a faster herbage mass reduction, while the sward-height and pasture characteristics did not differ from the high DHA regime. Low DHA decreased the tiller production rates and daily lamina growth, while the leaf-production rate was not affected by the DHA. Daily increases of herbage mass were greater in the high DHA than in the low DHA treatments. Individual milk production and milk protein concentration decreased at a low DHA compared to high DHA, while the milk fat concentration was greater and the milk output per hectare increased by 1510 kg. Neither the MSS level nor the interaction DHA by the MSS level had any effect on the sward characteristics or the productivity of the cows. From these results, it is suggested that,in a high-quality pasture, using 17 kg DM/cow.day was appropriate for improving both herbage utilization and milk production per hectare while maintaining the short-term conditions of a pasture grazed by dairy cows in the autumn

Directionally solidified Al2O3-Yb3Al5O12 eutectics for selective emitters

Al2O3-Yb3Al5O12 eutectic rods were directionally solidified using the laser floating zone method at rates between 25 and 750 mm/h. The microstructure consisted of an interpenetrated network of both eutectic phases for all the growth rates. The size of the phases was strongly dependent on the growth rate, the eutectic interspacing decreasing from 4.5 µm at the lowest growth rate to 600 nm at 750 mm/h. The optical transmission of the sample with coarser microstructure was measured and compared with that of an Yb3Al5O12 single crystal grown "ad hoc" using the same method. The apparent "oscillator strength" of the single 2F7/2¿2F5/2 Yb3+ absorption band was larger in the eutectic sample than in the single crystal, which was attributed to the increase in the light path caused by multiple refractions at the eutectic interphases. The thermal emission of the eutectic rod was studied between 1000 °C and 1500 °C. An intense and relatively narrow emission band at about 1 µm corresponding to the 2F5/2¿2F7/2 Yb3+ electronic transition was observed in the whole temperature range. The intensity of the band increased with the temperature up to about 1300 °C. At higher temperatures a saturation of the selective emission was observed which was attributed to the competition between the increase in the thermal population of the excited state and the enhancement of the non-radiative de-excitation channels with the temperature

Behavior Effect of Hint Selection Penalties and Availability in an Intelligent Tutoring System

Proceedings of: Tenth International Confererence on Intelligent Tutoring Systems: Bridges to Learning (ITS 2010). Pittsburg, USA, June 14-18, 2010.his paper presents empirical results about the behavior effect of two different hinting strategies applied on exercises within an ITS: having some penalty on the scoring for viewing hints or not having any effect on the scoring; and hints directly available or only available as a result to an incorrect attempt. We analyze the students' behavior differences when these hinting techniques changed, taking into account the type and difficulty of the presented exercises.Work partially funded by the Learn3 project TIN2008-05163/TSI within the Spanish “Plan Nacional de I+D+I”, and the Madrid regional community project eMadrid S2009/TIC-1650.Publicad

Alternative symplectic structures for SO(3,1) and SO(4) four-dimensional BF theories

The most general action, quadratic in the B fields as well as in the curvature F, having SO(3,1) or SO(4) as the internal gauge group for a four-dimensional BF theory is presented and its symplectic geometry is displayed. It is shown that the space of solutions to the equations of motion for the BF theory can be endowed with symplectic structures alternative to the usual one. The analysis also includes topological terms and cosmological constant. The implications of this fact for gravity are briefly discussed.Comment: 13 pages, LaTeX file, no figure