801 research outputs found
On the propagation of a normal shock wave through a layer of incompressible porous material
A novel numerical formulation of the two-phase macroscopic balance equations governing the flow field in incompressible porous media is presented. The numerical model makes use of the Weighted Average Flux (WAF) method and Total Variation Diminishing (TVD) flux limiting techniques, and results in a second-order accurate scheme. A shock tube study was carried out to examine the interaction of a normal shock wave with a thin layer of porous, incompressible cellular ceramic foam. Particular attention was paid to the transmitted and reflected flow fields. The numerical model was used to simulate the experimental test cases, and their results compared with a view to validating the numerical model. A phenomenological model is proposed to explain the behaviour of the transmitted flow field
LAGOVirtual: A Collaborative Environment for the Large Aperture GRB Observatory
We present the LAGOVirtual Project: an ongoing project to develop platform to
collaborate in the Large Aperture GRB Observatory (LAGO). This continental-wide
observatory is devised to detect high energy (around 100 GeV) component of
Gamma Ray Bursts, by using the single particle technique in arrays of Water
Cherenkov Detectors (WCD) at high mountain sites (Chacaltaya, Bolivia, 5300 m
a.s.l., Pico Espejo, Venezuela, 4750 m a.s.l., Sierra Negra, Mexico, 4650 m
a.s.l). This platform will allow LAGO collaboration to share data, and computer
resources through its different sites. This environment has the possibility to
generate synthetic data by simulating the showers through AIRES application and
to store/preserve distributed data files collected by the WCD at the LAGO
sites. The present article concerns the implementation of a prototype of
LAGO-DR adapting DSpace, with a hierarchical structure (i.e. country,
institution, followed by collections that contain the metadata and data files),
for the captured/simulated data. This structure was generated by using the
community, sub-community, collection, item model; available at the DSpace
software. Each member institution-country of the project has the appropriate
permissions on the system to publish information (descriptive metadata and
associated data files). The platform can also associate multiple files to each
item of data (data from the instruments, graphics, postprocessed-data, etc.).Comment: Second EELA-2 Conference Choroni, Venezuela, November 25th to 27th
200
" Could you open this jar for me please": a pilot study of the physical nature of jar opening.
The Department of Trade and Industry have recently published a report
highlighting the problems of opening foodstuff packaging. The aim of this
pilot study was to observe and document the different techniques used by a
range of male and female subjects as they tried to open one of the packaging
types highlighted in the report as difficult to open, a vacuum-sealed fruit jam
jar. Three types of fruit jam jars were assessed with four subjects, two males
and two females. Each subject was physically characterised. During the task
performance upper limb posture and the forces applied through the jam jar
were recorded using a video camera, a CODA motion capture system and a
universal grip dynamometer (UGD). The relationship between the physical
characteristics and task performance will be discussed in relation to vacuum
jar packaging design, and the appropriateness of the assessment methods
used
Dynamic Kerr Effect and Spectral Weight Transfer in the Manganites
We perform pump-probe Kerr spectroscopy in the colossally magnetoresistive
manganite Pr0.67Ca0.33MnO3. Kerr effects uncover surface magnetic dynamics
undetected by established methods based on reflectivity and optical spectral
weight transfer. Our findings indicate the connection between spin and charge
dynamics in the manganites may be weaker than previously thought. Additionally,
important differences between this system and conventional ferromagnetic metals
manifest as long-lived, magneto-optical coupling transients, which may be
generic to all manganites.Comment: 12 text pages, 4 figure
Comparative analysis of cold ironing rules
Postprint (published version
The tail of the Jurassic fish Leedsichthys problematicus (Osteichthyes: Actinopterygii) collected by Alfred Nicholson Leeds - an example of the importance of historical records in palaeontology
The specimen of the tail of <i>Leedsichthys problematicus</i>, now in The Natural History Museum, London, was one of the most spectacular fossil vertebrates from the Oxford Clay Formation of Peterborough, but as an isolated find it shares no bones in common with the holotype of the genus and species. However, a letter from Alfred Nicholson Leeds and related documents cast valuable new light on the excavation of the tail, indicating that it was discovered with cranial bones, gill-rakers, and two pectoral fins, thereby including elements that can potentially be compared with those of the holotype. The documents also clearly indicate that The Natural History Museum's specimen is not part of the same individual as any other numbered specimen of <i>Leedsichthys</i> as had been speculated on other occasions. The maximum size of the animal represented by The Natural History Museum's specimen was possibly around 9 metres, considerably less than previous estimates of up to 27.6 metres for <i>Leedsichthys</i>. Historical documentary evidence should therefore be rigorously checked both when studying historical specimens in science, and in preparing text for museum display labels
Milk production and lamb growth in Ojinegra sheep breed
El presente trabajo pretende caracterizar la capacidad productiva de las ovejas de la raza Ojinegra a dos niveles de condición corporal (CC; BAJA, ≤ 2.50 vs. ALTA, > 2.50) y evaluar el crecimiento de sus corderos para la producción de corderos del tipo lechal (10-12 kg de peso vivo a 45 días de edad máxima). Para el ensayo se utilizaron 58 ovejas Ojinegras de Teruel con parto en invierno. La ración provista fue de 1 kg de pienso al día y paja de cereal a voluntad. Se registró el peso vivo peso (PV) de ovejas y corderos semanalmente durante las seis semanas de lactación, y la CC de las ovejas en el parto, a mitad de lactación (3ª semana) y al destete (6ª semana). De estas ovejas se eligió al azar un grupo de 22 ovejas para llevar a cabo el estudio de la producción de leche y concentraciones de metabolitos en sangre relacionados con el balance energético (ácidos grasos no esterificados, AGNE, y β-hidroxibutirato, BHB). Los resultados mostraron que el PV de la oveja Ojinegra (49,0 ± 1,5 kg) se vio afectado por la semana de lactación (P 0,05). Los contenidos de AGNE y BHB en sangre durante la lactación no se vieron afectados por la CC al parto (p > 0,05), mostrando valores medios de AGNE y BHB de 0,30 ± 0,06 y 0,54 ± 0,02 mmol/l, respectivamente. Sin embargo, los AGNE sí decrecieron significativamente a medida que avanzaba la lactación (P 0,05), obteniéndose una producción media de leche de 813 g/día (producción estándar de 702 ml/día). La ganancia media diaria (GMD) de los corderos durante la lactación fue independiente de la CC de la oveja al parto (148 vs. 154 ± 9 g/día, en ALTA vs. BAJA, P > 0,05). El peso medio de los corderos en el momento del destete fue de 9,6 ± 0,3 kg. De este trabajo se puede concluir que la producción de leche de las ovejas de raza Ojinegra de Teruel es moderada, permitiendo un crecimiento limitado de los corderos que puede condicionar el cumplimiento de la edad máxima para alcanzar el peso de la categoría lechal (45 días hasta 10-12 kg). Estos resultados deberían ser contrastados con futuros estudios que evalúen la capacidad lechera y maternal de dicha oveja con distintos sistemas de manejo y alimentación.The aim of this study was to characterize the productive potential of the Ojinegra sheep breed at two
levels of body condition score (BAJA, ≤ 2.50 vs. ALTA, > 2.50), so that to prospect the production of suckling
lambs (10-12 kg live weight at a threshold of 45 days old). Fifty-eight winter-lambing Ojinegra ewes were used. Ewes were stalled indoors and fed 1 kg of concentrate per day and cereal straw ad libitum.
Live weight (PV) of ewes and lambs were registered weekly during lactation (6 weeks). Body condition
score (CC) of ewes was measured at lambing and at weeks 3 and 6 of lactation. Twenty-two ewes were
randomly selected to evaluate milk production and blood metabolites related with energy balance (nonesterified
fatty acids, AGNE, and β-hydroxybutyrate, BHB). Ewes’ PV after lambing was affected by the
week of lactation (P 0.05). Blood AGNE and BHB contents
were not affected by CC at lambing (P > 0.05), with mean values of 0.30 ± 0.06 and 0.54 ± 0.02 mmol/l
for AGNE and BHB respectively. However, AGNE concentration decreased during lactation (P < 0.001). Week
of lactation and CC at lambing had no effect on milk production (P > 0.05); with mean milk production
of 813 g/day (mean standardized production 702 ml/day). The average daily gain (ADG) of lambs was not
affected by ewes’ CC at lambing (148 vs. 154 ± 9 g/day, for ALTA vs. BAJA, respectively; P > 0.05). The average
PV of lambs at weaning was 9.6 ± 0.3 kg. In conclusion, milk production of Ojinegra sheep breed
is moderate and it might condition the attainment of target 10-12 kg live-weight for suckling lamb category
at a maximum age of 45 days old. These results should be confirmed in future studies, assessing the
maternal capacity of Ojinegra ewe under diverse management and feeding systems
Institutional Repository saber.ula.ve: A testimonial perspective
In this paper, we describe our decade-long experience of building and
operating one of the most active Institutional Repository in the world:
www.saber.ula.ve (University of the Andes,
Merida-Venezuela). In order to share our experience with other institutions, we
firstly explain the steps we followed to preserve and disseminate the
scientific production of the University of Los Andes' researchers. We then
present some recent quantitative results about our repository activities and we
outline some methodological guidelines that could be applied in order to
replicate similar experiences. These guidelines list the ingredients or
building blocks as well as the processes followed for developing and
maintaining the services of an Institutional Repository. These include
technological infrastructure; institutional policies on preservation,
publication and dissemination of knowledge; recommendations on incentives for
open access publication; the process of selection, testing and adaptation of
technological tools; the planning and organization of services, and the
dissemination and support within the scientific community that will eventually
lead to the adoption of the ideas that lie behind the open access movement. We
summarize the results obtained regarding the acceptance, adoption and use of
the technological tools used for the publication of our institution's
intellectual production, and we present the main obstacles encountered on the
way.Comment: 7th International Conference on Open Access in Accra Ghana from 2nd
to 3rd November 200
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