11,812 research outputs found
Exponential Distributions in a Mechanical Model for Earthquakes
We study statistical distributions in a mechanical model for an earthquake
fault introduced by Burridge and Knopoff [R. Burridge and L. Knopoff, {\sl
Bull. Seismol. Soc. Am.} {\bf 57}, 341 (1967)]. Our investigations on the size
(moment), time duration and number of blocks involved in an event show that
exponential distributions are found in a given range of the paramenter space.
This occurs when the two kinds of springs present in the model have the same,
or approximately the same, value for the elastic constants. Exponential
distributions have also been seen recently in an experimental system to model
earthquake-like dynamics [M. A. Rubio and J. Galeano, {\sl Phys. Rev. E} {\bf
50}, 1000 (1994)].Comment: 11 pages, uuencoded (submitted to Phys. Rev. E
Energy-Aware Cloud Management through Progressive SLA Specification
Novel energy-aware cloud management methods dynamically reallocate
computation across geographically distributed data centers to leverage regional
electricity price and temperature differences. As a result, a managed VM may
suffer occasional downtimes. Current cloud providers only offer high
availability VMs, without enough flexibility to apply such energy-aware
management. In this paper we show how to analyse past traces of dynamic cloud
management actions based on electricity prices and temperatures to estimate VM
availability and price values. We propose a novel SLA specification approach
for offering VMs with different availability and price values guaranteed over
multiple SLAs to enable flexible energy-aware cloud management. We determine
the optimal number of such SLAs as well as their availability and price
guaranteed values. We evaluate our approach in a user SLA selection simulation
using Wikipedia and Grid'5000 workloads. The results show higher customer
conversion and 39% average energy savings per VM.Comment: 14 pages, conferenc
Transverse self-modulation of ultra-relativistic lepton beams in the plasma wakefield accelerator
The transverse self-modulation of ultra-relativistic, long lepton bunches in
high-density plasmas is explored through full-scale particle-in-cell
simulations. We demonstrate that long SLAC-type electron and positron bunches
can become strongly self-modulated over centimeter distances, leading to wake
excitation in the blowout regime with accelerating fields in excess of 20 GV/m.
We show that particles energy variations exceeding 10 GeV can occur in
meter-long plasmas. We find that the self-modulation of positively and
negatively charged bunches differ when the blowout is reached. Seeding the
self-modulation instability suppresses the competing hosing instability. This
work reveals that a proof-of-principle experiment to test the physics of bunch
self-modulation can be performed with available lepton bunches and with
existing experimental apparatus and diagnostics.Comment: 8 pages, 8 figures, accepted for publication in Physics of Plasma
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Electronic state spectroscopy of C<sub>2</sub>Cl<sub>4</sub>
The VUV spectrum of C2Cl4 is reported in the energy range 3.8-10.8 eV (325-115 nm). Several photoabsorption features are observed for the first time, including a very weak low-lying band which is provisionally attributed to a π → π* triplet transition. Recent ab initio calculations of the molecule’s electronic transitions [Arulmozhiraja et al. J. Chem. Phys. 129 (2008) 174506] provide the basis for the present assignments below 8.5 eV. An extended ndπ series is proposed to account for several higher-energy Rydberg bands. The identification of vibrational structure, dominated by symmetric C=C and CCl2 stretching in excitations from the HOMO, largely agrees with previous spectroscopic studies. The present absolute photoabsorption cross sections cover a wider energy range than the previous measurements and are used to calculate UV photolysis lifetimes of this aeronomic molecule at altitudes between 20 and 50 km
Critical steps to ensure the successful reintroduction of the Eurasian red squirrel
Pasos fundamentales para garantizar la eficacia de la reintroducción de la ardilla roja
El objetivo de las estrategias de reintroducción de fauna silvestre es establecer poblaciones viables a largo plazo, fomentar la concienciación con respecto a la conservación y aportar beneficios económicos para las comunidades locales. La ardilla roja (Sciurus vulgaris), que estaba extinta en Portugal desde el s. XVI, fue reintroducida en varios parques urbanos en la década de los años 90, principalmente con fines estéticos y recreativos. Evaluamos la eficacia de esta reintroducción en dos parques urbanos y describimos los pasos fundamentales de la misma. Se evaluaron la utilización del hábitat, la densidad y abundancia de la población y las medidas de gestión adoptadas durante los proyectos de reintroducción. Las reintroducciones fueron relativamente eficaces dado a que las ardillas seguÃan presentes 20 años después de la liberación. No obstante, las poblaciones en ambos parques están disminuyendo debido a la falta de una gestión activa y a la mala calidad del hábitat. La reintroducción eficaz de la ardilla roja en zonas donde no hay ardillas arborÃcolas exóticas conlleva tres etapas fundamentales. La etapa previa al proyecto comprende estudios sobre la calidad del hábitat; la proximidad genética entre los donantes y la población silvestre más cercana, y la salud de las poblaciones donantes. En la etapa de liberación, el número de individuos liberados dependerá de la variabilidad de los recursos disponibles; asimismo, se ha observado que la técnica de liberación dura es un método eficaz y viable desde el punto de vista económico. Las actividades posteriores a la liberación deberÃan analizar la adaptación, mitigar la mortalidad, hacer un seguimiento de la necesidad de aportar alimentación complementaria, prestar apoyo veterinario y fomentar la sensibilización pública y la educación.Wildlife reintroduction strategies aim to establish viable long–term populations, promote conservation awareness and provide economic benefits for local communities. In Portugal, the Eurasian red squirrel (Sciurus vulgaris) became extinct in the 16th century and was reintroduced in urban parks in the 1990s, mainly for aesthetic and leisure purposes. We evaluated the success of this reintroduction in two urban parks and here described the critical steps. We assessed habitat use, population density and abundance, and management steps carried out during reintroduction projects. Reintroductions have been successful to some extent given squirrels are present 20 years after release. However, populations in both parks are declining due to the lack of active management and poor quality habitat. Successful reintroduction of Eurasian red squirrel in areas without competition of alien tree squirrels involves three critical main stages. The pre–project stage includes studies on habitat quality, genetic proximity between donors and closest wild population, and health of donor stocks. In the release stage, the number of individuals released will depend on resource variability, and the hard release technique is an effective and economically viable method. Post–release activities should evaluate adaptation, mitigate mortality, monitor the need for supplementary feeding, provide veterinary support, and promote public awareness and education.Pasos fundamentales para garantizar la eficacia de la reintroducción de la ardilla roja
El objetivo de las estrategias de reintroducción de fauna silvestre es establecer poblaciones viables a largo plazo, fomentar la concienciación con respecto a la conservación y aportar beneficios económicos para las comunidades locales. La ardilla roja (Sciurus vulgaris), que estaba extinta en Portugal desde el s. XVI, fue reintroducida en varios parques urbanos en la década de los años 90, principalmente con fines estéticos y recreativos. Evaluamos la eficacia de esta reintroducción en dos parques urbanos y describimos los pasos fundamentales de la misma. Se evaluaron la utilización del hábitat, la densidad y abundancia de la población y las medidas de gestión adoptadas durante los proyectos de reintroducción. Las reintroducciones fueron relativamente eficaces dado a que las ardillas seguÃan presentes 20 años después de la liberación. No obstante, las poblaciones en ambos parques están disminuyendo debido a la falta de una gestión activa y a la mala calidad del hábitat. La reintroducción eficaz de la ardilla roja en zonas donde no hay ardillas arborÃcolas exóticas conlleva tres etapas fundamentales. La etapa previa al proyecto comprende estudios sobre la calidad del hábitat; la proximidad genética entre los donantes y la población silvestre más cercana, y la salud de las poblaciones donantes. En la etapa de liberación, el número de individuos liberados dependerá de la variabilidad de los recursos disponibles; asimismo, se ha observado que la técnica de liberación dura es un método eficaz y viable desde el punto de vista económico. Las actividades posteriores a la liberación deberÃan analizar la adaptación, mitigar la mortalidad, hacer un seguimiento de la necesidad de aportar alimentación complementaria, prestar apoyo veterinario y fomentar la sensibilización pública y la educación
Comparison of the Spherical Averaged Pseudopotential Model with the Stabilized Jellium Model
We compare Kohn-Sham results (density, cohesive energy, size and effect of
charging) of the Spherical Averaged Pseudopotential Model with the Stabilized
Jellium Model for clusters of sodium and aluminum with less than 20 atoms. We
find that the Stabilized Jellium Model, although conceptually and practically
more simple, gives better results for the cohesive energy and the elastic
stiffness. We use the Local Density Approximation as well as the Generalized
Gradient Approximation to the exchange and correlation energies.Comment: 13 pages, latex, 8 figures, compressed postscript version available
at http://www.fis.uc.pt/~vieir
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