4,055 research outputs found
The Stationary Phase Method for a Wave Packet in a Semiconductor Layered System. The applicability of the method
Using the formal analysis made by Bohm in his book, {\em "Quantum theory"},
Dover Publications Inc. New York (1979), to calculate approximately the phase
time for a transmitted and the reflected wave packets through a potential
barrier, we calculate the phase time for a semiconductor system formed by
different mesoscopic layers. The transmitted and the reflected wave packets are
analyzed and the applicability of this procedure, based on the stationary phase
of a wave packet, is considered in different conditions. For the applicability
of the stationary phase method an expression is obtained in the case of the
transmitted wave depending only on the derivatives of the phase, up to third
order. This condition indicates whether the parameters of the system allow to
define the wave packet by its leading term. The case of a multiple barrier
systems is shown as an illustration of the results. This formalism includes the
use of the Transfer Matrix to describe the central stratum, whether it is
formed by one layer (the single barrier case), or two barriers and an inner
well (the DBRT system), but one can assume that this stratum can be comprise of
any number or any kind of semiconductor layers.Comment: 15 pages, 4 figures although figure 4 has 5 graph
Local Anomalies, Local Equivariant Cohomology and the Variational Bicomplex
The locality conditions for the vanishing of local anomalies in field theory
are shown to admit a geometrical interpretation in terms of local equivariant
cohomology, thus providing a method to deal with the problem of locality in the
geometrical approaches to the study of local anomalies based on the
Atiyah-Singer index theorem. The local cohomology is shown to be related to the
cohomology of jet bundles by means of the variational bicomplex theory. Using
these results and the techniques for the computation of the cohomology of
invariant variational bicomplexes in terms of relative Gel'fand-Fuks cohomology
introduced in [6], we obtain necessary and sufficient conditions for the
cancellation of local gravitational and mixed anomalies.Comment: 36 pages. The paper is divided in two part
Detection of an ionized gas outflow in the extreme UV-luminous star-forming galaxy BOSS-EUVLG1 at z=2.47
BOSS-EUVLG1 is the most ultraviolet (UV) and Ly luminous galaxy
detected so far in the Universe, going through a very active starburst phase,
and forming stars at a rate (SFR) of 955 118 M yr. We
report the detection of a broad H component carrying 25% of the total
H flux. The broad H line traces a fast and massive ionized gas
outflow characterized by a total mass, of 7.94
0.15, an outflowing velocity (V) of 573 151 km s,
and an outflowing mass rate () of 44 20 M
yr. The presence of the outflow in BOSS-EUVLG1 is also supported by the
identification of blueshifted UV absorption lines in low and high ionization
states. The energy involved in the H outflow can be explained by the
ongoing star formation without the need for an Active Galactic Nucleus. The
derived low mass loading factor (= 0.05 0.03) indicates that
although massive, this phase of the outflow can not be relevant for the
quenching of the star formation. In addition, only a small fraction (
15%) of the ionized outflowing material with velocities above 372 km s
could escape the gravitational potential, and enrich the surrounding
circum-galactic medium at distances above tens of kpc. The ionized phase of the
outflow does not carry the mass and energy to play a relevant role neither in
the evolution of the host galaxy nor in the enrichment of the intergalactic
medium. Other phases of the outflow could be carrying most of the outflow
energy and mass in the form of hot X-ray emitting gas as predicted by some
recent simulations. The expected emission of the extended X-ray emitting halo
associated with the outflow in BOSS-EUVLG1 and similar galaxies could be
detected with the future X-ray observatory, {\it ATHENA} but could not be
resolved spatially.Comment: 8 pages, 3 figures, accepted in A&
Magneto-caloric effect in the pseudo-binary intermetallic YPrFe17 compound
We have synthesized the intermetallic YPrFe17 compound by arc-melting. X-ray
and neutron powder diffraction show that the crystal structure is rhombohedral
with View the MathML source space group (Th2Zn17-type). The investigated
compound exhibits a broad isothermal magnetic entropy change {\Delta}SM(T)
associated with the ferro-to-paramagnetic phase transition (TC \approx 290 K).
The |{\Delta}SM| (\approx 2.3 J kg-1 K-1) and the relative cooling power
(\approx 100 J kg-1) have been calculated for applied magnetic field changes up
to 1.5 T. A single master curve for {\Delta}SM under different values of the
magnetic field change can be obtained by a rescaling of the temperature axis.
The results are compared and discussed in terms of the magneto-caloric effect
in the isostructural R2Fe17 (R = Y, Pr and Nd) binary intermetallic alloys.Comment: Preprint, 5 pages (postprint), 4 figures, regular pape
Rotura traumática del colédoco
En el presente trabajo se describe un caso de rotura traumática del conducto colédoco, su diagnóstico, así como su tratamiento y evolución.The authours present in this article a case about a traumatic fracture of choledoco; diagnosis, treatment and evolution
Genetic differentiation between two geographic subpopulations of Bermeya goat
Ponencia publicada en ITEA, vol.104Este trabajo es un análisis preliminar de la diversidad y grado de diferenciación genética entre las subpoblaciones
Oriental y Occidental de la cabra de raza Bermeya de Asturias. Se han genotipado 27
microsatélites en 122 individuos pertenecientes a las poblaciones de cabra Bermeya Oriental, Bermeya
Occidental, del Guadarrama, Alpine y Saanen. Las poblaciones de raza Bermeya presentaron heterocigosis
esperadas menores de 0,6 y coascendencias moleculares dentro de población de 0,419, reflejando
una alta identidad genética entre individuos. Asimismo, el número medio de alelos por locus, ajustado
por el tamaño muestral, de las poblaciones Bermeya Oriental y Occidental fueron los menores
encontrados (3,8 y 3,9, respectivamente). La mayor coascendencia molecular se encontró entre las
poblaciones Bermeya Oriental-Guadarrama (0,388 ± 0,006), como consecuencia de la introgresión, en
el Oriente asturiano de individuos de tipo Pirenáico. Este parámetro entre las poblaciones de Bermeya
Oriental y Occidental fue de 0,371 ± 0,007. Puede ser necesario establecer estrategias de conservación
diferenciadas para las dos poblaciones geográficas de cabra Bermeya.Two geographic subpopulations (Eastern and Western) of the Asturian Bermeya goat were analysed
using 27 microsatellites. A total of 122 individuals of Bermeya, Guadarrama, Alpine and Saanen goat
breeds were genotyped. The Eastern and Western Bermeya subpopulations had expected
heterozygosity values lower than 0.6 and within-subpopulations molecular coancestry values of 0.419,
thus illustrating a high between individuals genetic identity. The rarefacted average number of alleles
per locus found in both the Eastern and the Western Bermeya subpopulations were the lowest in the
dataset (3.8 and 3.9, respectively). The higher between-populations molecular coancestry values was
found for the pair Eastern Bermeya-Guadarrama (0.388 ± 0.006), thus reflecting the introgression of
the Pyrenean-type goat into Eastern Asturias. This parameter between the two Bermeya
subpopulations was of 0.371 ± 0.007. It could be recommended the implementation of different
conservation strategies for each of the geographic subpopulations of Bermeya goat
Mapeo de Actores y Necesidades de Información Agroclimática en los Cultivos de Maíz y Frijol en sitios piloto - Colombia
Este trabajo presenta los resultados del mapeo de actores y necesidades de información agroclimática en los cultivos transitorios de seguridad alimentaria: maíz y frijol arbustivo en sitios piloto en Colombia. A través del mapeo de los actores que transmiten información a los agricultores, la confianza en la información proporcionada, y las necesidades de información para la toma de decisiones, logramos entender el ancho espectro de problemas y prioridades a tomar en cuenta en la producción de estos cultivos, y proponer soluciones útiles, relevantes, confiables, sostenibles y aplicables. Con este enfoque, se llevaron a cabo 27 entrevistas semi-estructuradas con informantes clave y 12 grupos focales con un total de 151 agricultores en los departamentos de Córdoba y Santander.
Los resultados evidencian que una de las prioridades de los agricultores es recibir información agroclimática confiable a escala local, que permita tomar mejores decisiones de siembra, variedades, insumos y manejo de suelos y cultivos ante eventos de variabilidad climática. Se evidencia una desconfianza en las instituciones oficiales que transmiten información climática y un sentimiento difuso de falta de interés de las instituciones hacia los pequeños agricultores. Los agricultores se endeudan para lograr producir fríjol arbustivo y maíz o subsidian la producción por otros cultivos, mientras el acceso a un seguro agrícola es limitado. El formato preferido para recibir información climática es a través de mensajes de texto (celular) y mensajes en la radio local. Grupos de interacción presencial o virtual entre agricultores y expertos parecen una alternativa útil y confiable para recibir y compartir información en tiempo real. Sin embargo, los agricultores están interesados en adoptar el manejo agrícola tras un pronóstico si: a) la información es local, b) proviene de una fuente considerada confiable como expertos u otros agricultores, c) se transmite en el momento adecuado para la toma de decisiones y d) si sus efectos son medibles, verificables y validados, por ejemplo, a través de resultados de pilotos o parcelas experimentales en dos años consecutivos.
ENGLISH
This working paper presents the results of the mapping of actors and of agroclimatic information needs in pilot sites in Colombia for two annual crops, fundamental for food security: maize and bush beans. The mapping of the actors that transmit information to farmers, the confidence the latter have in the information provided, and their information needs for decision-making, allows us to understand the broad spectrum of issues and priorities to be taken into account in the production of these crops, and suggest solutions that are useful, relevant, reliable, sustainable and applicable. Under this assumption, we conducted 27 semi-structured interviews with key informants and 12 focus groups with a total of 151 farmers in the departments of Córdoba and Santander.
Results show that one of the priorities of farmers is to receive reliable local agroclimatic information that enables them to take decisions on planting, varieties, inputs, soil and crop management, that address climate variability. We find a generalized distrust of official institutions that transmit weather information, and a feeling that institutions are not interested in smallholders. Farmers resort to indebtedness to produce beans and maize, or subsidize production with cash crops, while access to agricultural insurance is limited.
The format preferred to receive weather information is text messages (phone) and information through the local radio. The creation of groups of farmers and experts who interact in person or virtually seem a useful and reliable alternative to receive and share information in real time. However, farmers are only interested in adopting farm management changes after a forecast if: a) the information is local, b) the information is given by a trusted source such as experts or other farmers, c) the information is transmitted at the right time for decision-making d) the effects of taking these decisions are measurable, verifiable and validated, for example, through pilots or results from experimental plots in two consecutive years
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