4,069 research outputs found
Statistical analysis of Ni nanowires breaking processes: a numerical simulation study
A statistical analysis of the breaking behavior of Ni nanowires is presented.
Using molecular dynamic simulations, we have determined the time evolution of
both the nanowire atomic structure and its minimum cross section (Sm(t)).
Accumulating thousands of independent breaking events, Sm histograms are built
and used to study the influence of the temperature, the crystalline stretching
direction and the initial nanowire size. The proportion of monomers, dimers and
more complex structures at the latest stages of the breaking process are
calculated, finding important differences among results obtained for different
nanowire orientations and sizes. Three main cases have been observed. (A) [111]
stretching direction and large nanowire sizes: the wire evolves from more
complex structures to monomers and dimers prior its rupture; well ordered
structures is presented during the breaking process. (B) Large nanowires
stretched along the [100] and [110] directions: the system mainly breaks from
complex structures (low probability of finding monomers and dimers), having
disordered regions during their breakage; at room temperature, a huge histogram
peak around Sm=5 appears, showing the presence of long staggered pentagonal Ni
wires with ...-5-1-5-... structure. (C) Initial wire size is small: strong size
effects independently on the temperature and stretching direction. Finally, the
local structure around monomers and dimmers do not depend on the stretching
direction. These configurations differ from those usually chosen in static
studies of conductance.Comment: 18 pages, 13 figure
The illegal wildlife trade is a likely source of alien species
The illegal wildlife trade is driving biodiversity declines worldwide, yet its role in transporting alien species with a high likelihood of establishment is seldom considered. We demonstrate the threat posed by the illegal reptile trade in Australia. We modeled the establishment success of alien reptiles in Australia, revealing the importance of both minimum number of release events and the body length of the species. Using our model, we screened 28 alien reptiles illegally traded in Victoria, Australia. Establishment risk varied widely across species, and a whole-pathway analysis revealed that 5 out of the 28 species (17.9%) are likely to become established if released. The global dimension of the illegal wildlife trade calls for a tight transnational collaboration, via multilateral cooperation agreements arranging the share of resources. Complementary to this, we encourage conducting campaigns to raise public awareness about the risk and legal consequences of participating in the wildlife black market.Pablo García-Díaz, Joshua V. Ross, Andrew P. Woolnough, and Phillip Casse
Gravitino Dark Matter and Neutrino Masses in Partial Split Supersymmetry
Partial Split Supersymmetry with bilinear R-parity violation allows to
reproduce all neutrino mass and mixing parameters. The viable dark matter
candidate in this model is the gravitino. We study the hypothesis that both
possibilities are true: Partial Split Supersymmetry explains neutrino physics
and that dark matter is actually composed of gravitinos. Since the gravitino
has a small but non-zero decay probability, its decay products could be
observed in astrophysical experiments. Combining bounds from astrophysical
photon spectra with the bounds coming from the mass matrix in the neutrino
sector we derive a stringent upper limit for the allowed gravitino mass. This
mass limit is in good agreement with the results of direct dark matter
searches.Comment: 22 pages, 3 figure
The structure of algebraic covariant derivative curvature tensors
We use the Nash embedding theorem to construct generators for the space of
algebraic covariant derivative curvature tensors
Enfermedades y fisiopatías que afectan a la calidad del ajo en postcosecha
Las
enfermedades
y
fisiopatías
que
afectan
al
ajo
pueden
llegar
a
ocasionar
importantes
pérdidas
en
postcosecha,
de
vital
importancia
cuando
el
producto
se
destina
a
la
exportación
a
mercados
que
cada
día
son
más
exigentes.
En
2008,
distintos
agricultores
de
varios
municipios
de
Castilla
y
León
detectaron
bulbos
de
ajo
que
presentaban
síntomas
de
podredumbre
húmeda
durante
el
almacenamiento.
Posteriormente,
en
el
año
2009,
esta
misma
podredumbre
se
observó
también
en
las
provincias
de
Albacete
y
Cuenca
y
en
muestras
procedentes
de
Córdoba.
Hasta
la
fecha
se
ha
identificado
a
Fusarium
proliferatum
como
el
agente
causal
de
la
podredumbre
del
diente
Efecto de la suplementación con concentrado de soja entera extrusionada en vacas Jersey en pastoreo sobre el contenido de ácido linoléico conjugado en la leche
Contradictory results has been found on the effects of soybean supplementation and conjugated linoleic acid (CLA)
content in milk on feeding systems based on fresh forage The objective of the study was to evaluate the effect of a
dietary supplement with different quantities of extruded whole soybean on the production and composition of milk,
and CLA concentration or their isomers in Jersey cows under pasture conditions. Twenty-one Jersey cows were randomly
assigned into 3 groups of 7 animals each. The cows were supplemented with a dietary concentrate (5 kg d–1),
and each group received one of the three next treatments: control without soybean (0-SB), with extruded whole soybean
at 0.5 kg d–1 (0.5-SB) or at 1 kg d–1 (1-SB). The basic diet was a pasture composed of Lolium perenne (70%), Trifolium
repens (25%) and other species. The duration of the study was 75 d. Milk production (p = 0.706) and protein production
(p = 0.926) were not affected by treatments. Fat (p = 0.015) and protein (p = 0.045) content as well as fat
production (p = 0.010) were lower in the 1-SB group. There was no effect of the inclusion of extruded soybean on
total CLA content (p = 0.290) or the content of cis-9, trans-11 (p = 0.582), trans-10, cis-12 (p = 0.136) and cis-10,
cis-12 (p = 0.288) isomers. However, concentrations of all isomers were affected by the nutritional quality of the pasture,
with low values observed at greater maturity stages of pastureleche es contradictorio. El objetivo de este estudio fue evaluar en vacas Jersey en pastoreo, el efecto de la suplementación
de un concentrado con diferentes cantidades de soja entera extrusionada sobre la producción de leche y su composición,
especialmente sobre el contenido en CLA y sus isómeros. 21 vacas Jersey fueron divididas al azar en 3 grupos de
7 animales cada uno. Los animales fueron suplementados con un concentrado (5 kg d–1) y a cada grupo se le asignó uno
de los tres siguientes tratamientos: control sin soja (0-SB), con 0.5 kg d–1 de soja (0.5-SB) y con 1 kg d–1 de soja (1-SB).
La base de la alimentación fue el pasto, compuesto mayoritariamente por Lolium perenne (70%) y Trifolium repens (25%).
La duración del estudio fue de 75 días. La producción de leche (p = 0.706) y la producción de proteína (p = 0.926) no se
vieron afectados. Los porcentajes de grasa (p = 0.015) y proteína (p = 0.045) y la producción de grasa (p = 0.010) fueron
más bajos en el grupo 1-SB. Las cantidades de soja no modificaron los contenidos de CLA total (p = 0.290) y de los
isómeros cis-9, trans-11 (p = 0.582), trans-10, cis-12 (p = 0.136) y cis-10, cis-12 (p = 0.288), pero si fueron afectados
por la calidad nutritiva del pasto, observándose menores valores al aumentar la madurez del pasto
Demographic limitation processes
20 páginas, 2 figuras, 1 tabla, 3 cuadros.-- Editor: Valladares, F.[ES]: Procesos de limitación demográfica. Este capítulo ofrece una revisión de los factores que afectan a la regeneración natural de la vegetación, considerando la serie de etapas demográficas que determinan la dinámica demográfica de una pobla- ción. Son muy escasos los estudios disponibles que analizan toda la serie de eventos concatenados entre la producción de flores y frutos y el establecimiento exitoso de una planta adulta reproductiva. También son escasos los trabajos que permiten establecer los efectos aplazados que tienen las interacciones con animales a lo largo del ciclo de regeneración. La aproximación que proponemos cuantifica las pérdidas de propágulos en cada etapa demográfica e identifica “cuellos de botella” del reclutamiento que pue- den colapsar la regeneración natural de una especie. Revisamos una serie de casos de estudio que ilustran diversos procesos de limitación demográfica. El uso de técnicas explícitamente demográficas es fundamental para comprender la evolución de las especies forestales Mediterráneas y para diseñar actuaciones de preservación de sus poblaciones y de su extraordinaria diversidad.[EN]: We review the main factors
influencing recruitment limitation in Mediterranean woody species by considering the
sequential stages that determine the demographic cycle. Very few studies examine the
whole set of demographic stages, from flower production to the successful establishment
of adult reproductive plants, and their influence on recruitment. There are also few studies
exploring the delayed effects of animal interactions throughout the regeneration
cycle, but the information on stage-specific effects is more detailed. We propose an
approach that quantifies the propagule losses at each sequential demographic stage and
identifies demographic bottlenecks that might collapse population growth. We review a
series of case studies illustrating different limitation processes. The use of explicit demographic
techniques is central to understand the evolution of Mediterranean woody species
and to design sound, ecologically-based, conservation plans to preserve their extraordinary
diversity.Juan Arroyo agradece la financiación otorgada a los proyectos 4474-91
(National Geographic Society), PB 91-0894, PB95-0551, 1FD97-0743-CO3-03, PB98-1144,
BOS200307924-CO2-01 (MECD, MCyT). Los trabajos de Pedro Jordano han sido financiados con proyectos MECD y MCyT (1FD97-0743-CO3-01, PB
96-0857, BOS2000-1366-C02-01 y REN2003-00273), así como la Junta de Andalucía (PAI).
Juan Luis García-Castaño estuvo financiado durante su período pre-doctoral con una beca
FPU, AP96-27318040. El trabajo de Fernando Pulido ha sido parcialmente financiado por una
beca FPI de la Junta de Extremadura y los proyectos regional IPR-0A050 y estatal BOS2002-
12222-E del Ministerio de Ciencia y Tecnología. Los trabajos de Patricio García-Fayos han
sido financiados con proyectos MCyT (1FD97-0551), de la Generalitat Valenciana (02-046)
y de la Institució Alfons el Magnánim (02-046)Peer reviewe
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