Explaining the subpulse drift velocity of pulsar magnetosphere within the space-charge limited flow model

We try to explain the subpulse drift phenomena adopting the space-charge limited flow (SCLF) model and comparing the plasma drift velocity in the inner region of pulsar magnetospheres with the observed velocity of drifting subpulses. We apply the approach described in a recent paper of van Leeuwen & Timokhin (2012), where it was shown that the standard estimation of the subpulse drift velocity through the total value of the scalar potential drop in the inner gap gives inaccurate results, while the exact expression relating the drift velocity to the gradient of the scalar potential should be used instead. After considering a selected sample of sources taken from the catalog of Weltevrede, Edwards & Stappers (2006) with coherently drifting subpulses and reasonably known observing geometry, we show that their subpulse drift velocities would correspond to the drift of the plasma located very close or above the pair formation front. Moreover, a detailed analysis of PSR B0826-34 and PSR B0818-41 reveals that the variation of the subpulse separation with the pulse longitude can be successfully explained by the dependence of the plasma drift velocity on the angular coordinates.Comment: 14 pages, 6 figures, 2 table

ADER-WENO Finite Volume Schemes with Space-Time Adaptive Mesh Refinement

We present the first high order one-step ADER-WENO finite volume scheme with Adaptive Mesh Refinement (AMR) in multiple space dimensions. High order spatial accuracy is obtained through a WENO reconstruction, while a high order one-step time discretization is achieved using a local space-time discontinuous Galerkin predictor method. Due to the one-step nature of the underlying scheme, the resulting algorithm is particularly well suited for an AMR strategy on space-time adaptive meshes, i.e.with time-accurate local time stepping. The AMR property has been implemented 'cell-by-cell', with a standard tree-type algorithm, while the scheme has been parallelized via the Message Passing Interface (MPI) paradigm. The new scheme has been tested over a wide range of examples for nonlinear systems of hyperbolic conservation laws, including the classical Euler equations of compressible gas dynamics and the equations of magnetohydrodynamics (MHD). High order in space and time have been confirmed via a numerical convergence study and a detailed analysis of the computational speed-up with respect to highly refined uniform meshes is also presented. We also show test problems where the presented high order AMR scheme behaves clearly better than traditional second order AMR methods. The proposed scheme that combines for the first time high order ADER methods with space--time adaptive grids in two and three space dimensions is likely to become a useful tool in several fields of computational physics, applied mathematics and mechanics.Comment: With updated bibliography informatio

4D gravity on a brane from bulk higher-curvature terms

We study a gravity model where a tensionful codimension-one three-brane is embedded on a bulk with infinite transverse length. We find that 4D gravity is induced on the brane already at the classical level if we include higher-curvature (Gauss-Bonnet) terms in the bulk. Consistency conditions appear to require a negative brane tension as well as a negative coupling for the higher-curvature terms.Comment: 10 pages, no figures; a minor change in wording (to appear in MPLA

Hong-Ou-Mandel interferometer with cavities: theory

We study the number of coincidences in a Hong-Ou-Mandel interferometer exit whose arms have been supplemented with the addition of one or two optical cavities. The fourth-order correlation function at the beam-splitter exit is calculated. In the regime where the cavity length are larger than the one-photon coherence length, photon coalescence and anti-coalescence interference is observed. Feynman's path diagrams for the indistinguishable processes that lead to quantum interference are presented. As application for the Hong-Ou-Mandel interferometer with two cavities, it is discussed the construction of an optical XOR gate

New Relativistic Effects in the Dynamics of Nonlinear Hydrodynamical Waves

In Newtonian and relativistic hydrodynamics the Riemann problem consists of calculating the evolution of a fluid which is initially characterized by two states having different values of uniform rest-mass density, pressure and velocity. When the fluid is allowed to relax, one of three possible wave-patterns is produced, corresponding to the propagation in opposite directions of two nonlinear hydrodynamical waves. New effects emerge in a special relativistic Riemann problem when velocities tangential to the initial discontinuity surface are present. We show that a smooth transition from one wave-pattern to another can be produced by varying the initial tangential velocities while otherwise maintaining the initial states unmodified. These special relativistic effects are produced by the coupling through the relativistic Lorentz factors and do not have a Newtonian counterpart.Comment: 4 pages, 5 figure

Activation and Isomerization of n-Butane on Sulfated Zirconia Model Systems - An Integrated Study Across the Materials and Pressure Gaps

Butane activation has been studied using three types of sulfated zirconia materials, single-crystalline epitaxial films, nanocrystalline films, and powders. A surface phase diagram of zirconia in interaction with SO3 and water was established by DFT calculations which was verified by LEED investigations on single-crystalline films and by IR spectroscopy on powders. At high sulfate surface densities a pyrosulfate species is the prevailing structure in the dehydrated state; if such species are absent, the materials are inactive. Theory and experiment show that the pyrosulfate can react with butane to give butene, H2O and SO2, hence butane can be activated via oxidative dehydrogenation. This reaction occurred on all investigated materials; however, isomerization could only be proven for powders. Transient and equilibrium adsorption measurements in a wide pressure and temperature range (isobars measured via UPS on nanocrystalline films, microcalorimetry and temporal analysis of products measurements on powders) show weak and reversible interaction of butane with a majority of sites but reactive interaction with < 5 µmol/g sites. Consistently, the catalysts could be poisoned by adding sodium to the surface in a ratio S/Na=35. Future research will have to clarify what distinguishes these few sites

Acid-Base Catalyzed Activation of n-Alkanes: Isomerization of n-Butane

Due to its unique activity for skeletal isomerization of short alkanes at low temperature, sulfated zirconia (SZ) is generally recognized as the most promising alternative for the zeolite based hydroisomerization catalysts. However, despite the large amount of investigations, several important topics related to SZ are still discussed controversially. Here we report on our detailed investigation of the mechanism of butane skeletal isomerization on SZ. Typically, SZ had an induction period followed by a period of virtually constant activity. The selectivity to isobutene was higher than 96%, the byproducts being propane and pentanes. The induction period can be related to the formation and accumulation of reactive intermediates on the catalyst surface. We show that the alkane activation is initiated via stoichiometric oxidative dehydrogenation of butane by sulphate species to butane, water and SO2. For the first time, direct experimental evidence is given for all reaction products formed by oxidative dehydrogenation. In situ IR spectroscopy and density functional calculations indicate that pyrosulfate or re-adsorbed SO3 species are the active species for the oxidation. Butene formed interacts with Bronsted acid sites and forms sec-butoxy groups which isomerize mono-molecularly to tert-butoxy groups, as deduced from the 100% selectivity to isobutane at zero conversion. The tert-butoxy group undergoes hydride transfer from n-butane, forming a new sec-butoxy group and isobutane. The lower selectivity to isobutane with increasing conversion is explained by the higher isobutene concentration which triggers a bimolecular pathway. Note that isobutane is kinetically a primary product, while propane and pentanes are secondary products formed in sequential reactions. The larger amount of propane with respect to pentanes for conversion above 40% is attributed to multiple alkylation reactions followed by cracking. Transient experiments showed conclusively that the isomerization of the carbenium ion is the rate-determining step in the chain sequence and that hydride transfer is in quasi equilibrium. A kinetic model for butane isomerization under differential conditions is presented showing that the overall rate of butane conversion is proportional to the rate constant of the monomolecular isomerization of the carbenium ion, the concentration of Bronsted acid sites, the partial pressure of the alkane and the concentration of the labile sulfate-based redox sites. We show here that the key to successful catalysts for skeletal isomerization does not lie in high acid strength, but that a subtle balance between redox and acid sites is necessary

One-year timeline kinetics of cytokine-mediated cellular immunity in dogs vaccinated against visceral leishmaniasis

BACKGROUND: The main control strategy for visceral leishmaniasis in Brazil has been based on the elimination of seropositive dogs, although this is not widely accepted. In this context, the use of a long-lasting protective vaccine against canine visceral leishmaniasis (CVL) has been highly expected. The aim of this work was to determine the timeline kinetics of the cytokine microenvironment derived from circulating leukocytes as supportive immunological biomarkers triggered by Leishmune® vaccine. Cross-sectional kinetic analysis of cellular immunity cytokines was carried out at three times (1, 6 and 12 months) after primovaccination with Leishmune®. In vitro short-term whole blood cultures were stimulated with Leishmania infantum soluble antigen (SLAg). The secreted cytokine signatures and their major sources were determined. RESULTS: At six months after vaccination, Leishmune® induced an increase in IL-8, IFN-γ, IL-17a and TNF-α levels and a decrease in IL-10. Cytokine signature analysis revealed a shift in the microenvironment towards a pro-inflammatory profile mediated by IL-8 and IFN-γ. Both, CD4(+) (↑TNF-α(+) and ↑IFN-γ (+)) and CD8(+) (↑IL-17a and ↓IL-4) T-cells contributed to the acquired immune responses observed after stimulation with SLAg. CONCLUSIONS: The changes observed in the cytokine profile suggested that Leishmune® was able to induce an effective response at six months after primovaccination. After one year, it returned to baseline suggesting the need of additional boosting

Smooth tensionful higher-codimensional brane worlds with bulk and brane form fields

Completely regular tensionful codimension-n brane world solutions are discussed, where the core of the brane is chosen to be a thin codimension-(n-1) shell in an infinite volume flat bulk, and an Einstein-Hilbert term localized on the brane is included (Dvali-Gabadadze-Porrati models). In order to support such localized sources we enrich the vacuum structure of the brane by the inclusion of localized form fields. We find that phenomenological constraints on the size of the internal core seem to impose an upper bound to the brane tension. Finite transverse-volume smooth solutions are also discussed.Comment: 1+14 pages, 2 figures; section 2.3 improved, typos corrected and references added. Published versio