11,015 research outputs found
Experimental investigation of a variable speed constant frequency electric generating system from a utility perspective
As efforts are accelerated to improve the overall capability and performance of wind electric systems, increased attention to variable speed configurations has developed. A number of potentially viable configurations have emerged. Various attributes of variable speed systems need to be carefully tested to evaluate their performance from the utility points of view. With this purpose, the NASA experimental variable speed constant frequency (VSCF) system has been tested. In order to determine the usefulness of these systems in utility applications, tests are required to resolve issues fundamental to electric utility systems. Legitimate questions exist regarding how variable speed generators will influence the performance of electric utility systems; therefore, tests from a utility perspective, have been performed on the VSCF system and an induction generator at an operating power level of 30 kW on a system rated at 200 kVA and 0.8 power factor
Dynamics of Viscous Dissipative Plane Symmetric Gravitational Collapse
We present dynamical description of gravitational collapse in view of Misner
and Sharp's formalism. Matter under consideration is a complicated fluid
consistent with plane symmetry which we assume to undergo dissipation in the
form of heat flow, radiation, shear and bulk viscosity. Junction conditions are
studied for a general spacetime in the interior and Vaidya spacetime in the
exterior regions. Dynamical equations are obtained and coupled with causal
transport equations derived in context of Mller Israel Stewart
theory. The role of dissipative quantities over collapse is investigated.Comment: 17 pages, accepted for publication in Gen. Relativ. Gra
Local Swift-BAT active galactic nuclei prefer circumnuclear star formation
We use Herschel data to analyze the size of the far-infrared 70micron
emission for z<0.06 local samples of 277 hosts of Swift-BAT selected active
galactic nuclei (AGN), and 515 comparison galaxies that are not detected by
BAT. For modest far-infrared luminosities 8.5<log(LFIR)<10.5, we find large
scatter of half light radii Re70 for both populations, but a typical Re70 <~ 1
kpc for the BAT hosts that is only half that of comparison galaxies of same
far-infrared luminosity. The result mostly reflects a more compact distribution
of star formation (and hence gas) in the AGN hosts, but compact AGN heated dust
may contribute in some extremely AGN-dominated systems. Our findings are in
support of an AGN-host coevolution where accretion onto the central black hole
and star formation are fed from the same gas reservoir, with more efficient
black hole feeding if that reservoir is more concentrated. The significant
scatter in the far-infrared sizes emphasizes that we are mostly probing spatial
scales much larger than those of actual accretion, and that rapid accretion
variations can smear the distinction between the AGN and comparison categories.
Large samples are hence needed to detect structural differences that favour
feeding of the black hole. No size difference AGN host vs. comparison galaxies
is observed at higher far-infrared luminosities log(LFIR)>10.5 (star formation
rates >~ 6 Msun/yr), possibly because these are typically reached in more
compact regions in the first place.Comment: 7 pages, 3 figures, accepted for publication in Astronomy &
Astrophysic
Proximal, Microbiological and Color Evaluation and Comparison of the Meat of Llamas (Lama glama) and Alpacas (Vicugna pacos)
In this study, the meat of llama (Lama glama) and alpaca (Vicugna pacos) were examined. Data were analyzed through the analysis of variance (ANOVA) using the Centurion Statgraphics software. The bromatological characteristics of the meat were evaluated through proximal analysis. A high percentage of protein content was identified, with a higher value in the llama meat (24.025%). Regarding the ethereal extract, minimum values were obtained in the alpaca meat (2.707%), indicating lean meat. The humidity was variable depending on the conditions of the conservation, and the organic matter present in the meat defined the ash content, which was not higher than 5%. In terms of the microbiological analyses, the value of viable aereobic mesophiles in llama meat was 1330 cfu/g, and in alpaca meat it was 1490 cfu/g; and the values for E. coli were 0.500 cfu/g and 1,250 cfu/g, respectively.
Keywords: software, Lama glama, Vicugna pacos, proximal analysis, microbiological requirements.
RESUMEN
La carne de Llama (Lama glama) y Alpaca (Vicugna pacos) cumple con los requisitos para ser considerada como carne; Mediante el análisis de varianza (ANOVA) utilizando el Software Statgraphics Centurion se evalúa los requisitos bromatológicos por medio del análisis proximal de las carnes en estudio, donde se identifica un alto porcentaje en el contenido de proteína, lo que conlleva a un elevado valor biológico en ambas especies, siendo más destacada, en la carne de llama con 24,025%; En cuanto a extracto etéreo se obtiene valores mínimos en especial en la carne de alpaca con 2,707%, favoreciendo a la obtención de carne magra; En lo referente a humedad va a ser variable dependiendo de las condiciones de conservación de la misma, mientras tanto la materia orgánica presente en la carne define el contenido de cenizas, el cual no podrá ser mayor al 5%. En relación a los análisis microbiológicos los valores de Mesófilos Aereobios Viables en la carne de llama fueron 1330 ufc/g, en la carne de alpaca 1490 ufc/g, para E. Coli de 0,500 ufc/g, y 1,250 ufc/g respectivamente encontrándose dentro de lo establecido en la Norma, y valores no permisibles por la presencia de Coliformes Totales.
Palabras clave: software, Lama glama, Vicugna pacos, análisis proximal, requerimientos microbiológicos
The Inverse Scattering Method, Lie-Backlund Transformations and Solitons for Low-energy Effective Field Equations of 5D String Theory
In the framework of the 5D low-energy effective field theory of the heterotic
string with no vector fields excited, we combine two non-linear methods in
order to construct a solitonic field configuration. We first apply the inverse
scattering method on a trivial vacuum solution and obtain an stationary
axisymmetric two-soliton configuration consisting of a massless gravitational
field coupled to a non-trivial chargeless dilaton and to an axion field endowed
with charge. The implementation of this method was done following a scheme
previously proposed by Yurova. We also show that within this scheme, is not
possible to get massive gravitational solitons at all. We then apply a
non-linear Lie-Backlund matrix transformation of Ehlers type on this massless
solution and get a massive rotating axisymmetric gravitational soliton coupled
to axion and dilaton fields endowed with charges. We study as well some
physical properties of the constructed massless and massive solitons and
discuss on the effect of the generalized solution generating technique on the
seed solution and its further generalizations.Comment: 17 pages in latex, changed title, improved text, added reference
How are riparian plants distributed along the riverbank topographic gradient in Mediterranean rivers? Application to minimally altered river stretches in Southern Spain.
Species structure and composition in Mediterranean riparian forests are determined by hydrological features, longitudinal zonation, and riverbank topography. This study assesses the distribution of four native riparian plants along the riverbank topographic gradient in three river stretches in southern Spain, with special emphasis on the occupation of adult and young feet of each species. The studied stretches suffered minimal human disturbances, displayed semi-arid conditions, and had wide riparian areas to allow the development of the target species: black alder (Alnus glutinosa), salvia leaf willow (Salix salviifolia), narrow-leafed ash (Fraxinus angustifolia), and oleander (Nerium oleander). Thalweg height was used to define the riverbank topographic gradient. The results showed a preferential zone for black alder and salvia leaf willow in the range of 0-150 cm from the channel thalweg, with adult alders and willows being more common between 51 and 150 cm and young alders being more common under 50 cm. Conversely, narrow-leafed ash and oleander were much more frequent, and showed greater development, in the ranges of 151-200 cm and 201-250 cm, respectively, whereas the young feet of both species covered the entire topographic range. Adult feet of the four species were spatially segregated along the riverbank topographic gradient, indicating their differential ability to cope with water stress from the non-tolerant alders and willows to more tolerant narrow-leafed ash trees and oleanders. Young feet, however, showed a strategy more closely linked to the initial availability of colonisation sites within riparian areas to the dispersion strategy of each species and to the distribution of adult feet. In Mediterranean areas, where riparian management has traditionally faced great challenges, the incorporation of species preferences along riverbank gradients could improve the performance of restoration projects
First record of Trithemis kirbyi Sélys, 1891 in Catalonia (Odonata, Libellulidae)
Trithemis kirbyi Sélys, 1891 is a native species from Africa and southern Asia, typically found in arid areas
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