853 research outputs found
Levy ratchets with dichotomic random flashing
Additive symmetric L\'evy noise can induce directed transport of overdamped
particles in a static asymmetric potential. We study, numerically and
analytically, the effect of an additional dichotomous random flashing in such
L\'evy ratchet system. For this purpose we analyze and solve the corresponding
fractional Fokker-Planck equations and we check the results with Langevin
simulations. We study the behavior of the current as function of the stability
index of the L\'evy noise, the noise intensity and the flashing parameters. We
find that flashing allows both to enhance and diminish in a broad range the
static L\'evy ratchet current, depending on the frequencies and asymmetry of
the multiplicative dichotomous noise, and on the additive L\'evy noise
parameters. Our results thus extend those for dichotomous flashing ratchets
with Gaussian noise to the case of broadly distributed noises.Comment: 15 pages, 6 figure
Aspectos gerais da tectónica alpina no Algarve
The study of the tectonic strutures affecting the mesozoic and cenozoic deposits of Algarve's basin allows us to recognize the following phases of the Alpine orogeny:
Jurassic (Upper Triassic at least)-Lower Cretaceous N-S distension; N-S compression during the setting-up of the Monchique syenite dome at the uppermost Cretaceous;
Paleogene compression (?) (only locally? - at the Albufeira salt dome); Lower Miocene N-S distension; Upper Burdigalian to Lower Langhian N-S and E-W distension; N-S or NNW-SSE compression after the Middle Miocene;
E-W compression after the Upper Tortonian; N-S compression during the Quaternary.
NE-SW fractures affecting the Paleozoic basement are related with the first distension phases.
The mesozoic N-S distension are the main cause of the two E-W flexures so far recognized.
A tectonic inversion event did occur after the setting up of the Monchique syenite. If, the Lower Cretaceous Lower Miocene Albufeira's unconformity, is a local effect
of halokinesis then, the true tectonic inversion of the Algarve basin, did occur in the Middle Miocene.
These events correlate well with those knewn at Southern Spain and Morocco
Prospecção de endocarso através duma aplicação de SIG
Os parâmetros que condicionam o desenvolvimento dum carso em profundidade - endocarso - são complexos e difíceis de avaliar devido, por um lado, à diversidade e variabilidade dos factores envolvidos referentes ao meio e, por outro, à dificuldade de quantificar a sua interacção e influência no desenvolvimento da carsificação. É apresentada uma metodologia em ambiente SIG que visa a prospecção de estruturas cársicas de subsuperfície. Pretende-se efectuar, duma forma sistemática, a integração do conjunto de parâmetros que controlam o desenvolvimento deste tipo de carsificação, de forma a testar interacções e classificar áreas com maior aptidão para ocorrência de estruturas. O estudo incidiu sobre uma área piloto a Oeste de Sesimbra, região onde são conhecidas várias dessas estruturas, com particular relavância para as grutas do Zambujal2 e do Frade.publishersversionpublishe
A sol-gel method for growing superconducting MgB2 films
In this paper we report a new sol-gel method for the fabrication of MgB2
films. Polycrystalline MgB2 films were prepared by spin-coating a precursor
solution of Mg(BH_4)_2 diethyl ether on (001)Al2O3 substrates followed with
annealing in Mg vapor. In comparison with the MgB2 films grown by other
techniques, our films show medium qualities including a superconducting
transition temperature of Tc ~ 37 K, a critical current density of Jc(5 K, 0 T)
~ 5 {\times} 10^6 A cm^{-2}, and a critical field of H_{c2}(0) ~ 19 T. Such a
sol-gel technique shows potential in the commercial fabrication of practically
used MgB2 films as well as MgB2 wires and tapes.Comment: 8 pages, 5 figure
Immune sensing of Candida albicans requires cooperative recognition of mannans and glucans by lectin and Toll-like receptors
Peer reviewedPublisher PD
A review of Alpine tectonics in Portugal: Foreland detachment in basement and cover rocks
IL-23 plays a key role in Helicobacter hepaticus–induced T cell–dependent colitis
Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract that is caused in part by a dysregulated immune response to the intestinal flora. The common interleukin (IL)-12/IL-23p40 subunit is thought to be critical for the pathogenesis of IBD. We have analyzed the role of IL-12 versus IL-23 in two models of Helicobacter hepaticus–triggered T cell–dependent colitis, one involving anti–IL-10R monoclonal antibody treatment of infected T cell–sufficient hosts, and the other involving CD4+ T cell transfer into infected Rag−/− recipients. Our data demonstrate that IL-23 and not IL-12 is essential for the development of maximal intestinal disease. Although IL-23 has been implicated in the differentiation of IL-17–producing CD4+ T cells that alone are sufficient to induce autoimmune tissue reactivity, our results instead support a model in which IL-23 drives both interferon γ and IL-17 responses that together synergize to trigger severe intestinal inflammation
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