Ore paragenesis of the Tajo Vein, Paramillos de Uspallata ore deposit, Mendoza Province, Argentina

La Veta Tajo forma par te del yacimiento Paramillos de Uspallata (32°28’29.6”S; 69°08’46”O), ubicado en la Precordillera Occidental de la provincia de Mendoza. Este yacimiento está formado por un conjunto de vetas con mineralización de Pb-Zn-Ag hospedadas en basaltos triásico-jurásicos y en sedimentitas triásicas. Los estudios mineraló- gicos (microscopía óptica convencional y SEM-EDX) realizados sobre muestras provenientes de la veta Tajo permitieron determinar que la paragénesis de mena está compuesta por galena argentífera, esfalerita, calcopirita, tetraedrita, freibergita, boulangerita, owyheeita, pirita, arsenopirita y marcasita así como la existencia de dos pulsos de mineralización, un primer pulso principalmente de Pb-Zn-Ag-(Cu) en ganga carbonática y un segundo pulso estéril en ganga de cuarzo. Por otra parte los análisis de química mineral permitieron determinar la composición de los minerales de mena y de esta forma establecer cuáles son aquellos portadores de Ag.The Tajo Vein is par t of the Paramillos de Uspallata ore deposit (32°28’29.6”S; 69°08’46”W) that is located in the Western Precordillera of Mendoza Province. This ore deposit consists of Pb-Zn-Ag veins hosted by Triassic-Jurassic basalts and Triassic sedimentary rocks. Mineralogical studies (optical microscopy and SEM-EDX analyses) carried out on samples from the Tajo Vein allowed the identification of an ore paragenesis consisting of Ag-galena, sphalerite, chalcopyrite, tetrahedrite, freibergite, boulangerite, owyheeite, pyrite, arsenopyrite and marcasite, occurring in two mineralization stages, the first consisting of Pb-Zn-Ag-(Cu) mineralization with a carbonate gangue and the barren second one with a quartz gangue. Chemical analyses allowed to determine the composition of the ore minerals and the Ag-bearing phases.Fil: Carrasquero, S. I.. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Instituto de Recursos Minerales. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Recursos Minerales; ArgentinaFil: Rubinstein, Nora Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Bevins, R. E.. National Museum of Wales; Reino Unid

Random walk approach to the d-dimensional disordered Lorentz gas

A correlated random walk approach to diffusion is applied to the disordered nonoverlapping Lorentz gas. By invoking the Lu-Torquato theory for chord-length distributions in random media [J. Chem. Phys. 98, 6472 (1993)], an analytic expression for the diffusion constant in arbitrary number of dimensions d is obtained. The result corresponds to an Enskog-like correction to the Boltzmann prediction, being exact in the dilute limit, and better or nearly exact in comparison to renormalized kinetic theory predictions for all allowed densities in d=2,3. Extensive numerical simulations were also performed to elucidate the role of the approximations involved.Comment: 5 pages, 5 figure

Reduction of mean-square advection in turbulent passive scalar mixing

Direct numerical simulation data show that the variance of the coupling term in passive scalar advection by a random velocity field is smaller than it would be if the velocity and scalar fields were statistically independent. This effect is analogous to the "depression of nonlinearity" in hydrodynamic turbulence. We show that the trends observed in the numerical data are qualitatively consistent with the predictions of closure theories related to Kraichnan's direct interaction approximation. The phenomenon is demonstrated over a range of Prandtl numbers. In the inertial-convective range the depletion is approximately constant with respect to wavenumber. The effect is weaker in the Batchelor range

Spatial and spectral properties of the pulsed second-harmonic generation in a PP-KTP waveguide

Spatial and spectral properties of the pulsed second harmonic generation in a periodically-poled KTP waveguide exploiting simultaneously the first, second, and third harmonics of periodic nonlinear modulation are analyzed. Experimental results are interpreted using a model based on finite elements method. Correlations between spatial and spectral properties of the fundamental and second-harmonic fields are revealed. Individual nonlinear processes can be exploited combining spatial and spectral filtering. Also the influence of waveguide parameters to the second-harmonic spectra is addressed.Comment: 13 pages, 8 figure

Del Pezzo surfaces with many symmetries

We classify smooth del Pezzo surfaces whose alpha-invariant of Tian is bigger than one.Comment: 23 page

On the Decoupling of Layered Superconducting Films in Parallel Magnetic Field

The issue of the decoupling of extreme type-II superconducting thin films ($\lambda_L\rightarrow\infty$) with weakly Josephson-coupled layers in magnetic field parallel to the layers is considered via the corresponding frustrated $XY$ model used to describe the mixed phase in the critical regime. For the general case of arbitrary field orientations such that the perpendicular magnetic field component is larger than the decoupling cross-over scale characteristic of layered superconductors, we obtain independent parallel and perpendicular vortex lattices. Specializing to the double-layer case, we compute the parallel lower-critical field with entropic effects included, and find that it vanishes exponentially as temperature approaches the layer decoupling transition in zero-field. The parallel reversible magnetization is also calculated in this case, where we find that it shows a cross-over phenomenon as a function of parallel field in the intermediate regime of the mixed phase in lieu of a true layer-decoupling transition. It is argued that such is the case for any finite number of layers, since the isolated double layer represents the weakest link.Comment: 29 pages of plain TeX, 2 postscript figures, improved discussio

Stabilization of Ion Concentration Polarization Using a Heterogeneous Nanoporous Junction

We demonstrate a recycled ion-flux through heterogeneous nanoporous junctions, which induce stable ion concentration polarization with an electric field. The nanoporous junctions are based on integration of ionic hydrogels whose surfaces are negatively or positively charged for cationic or anionic selectivity, respectively. Such heterogeneous junctions can be matched up in a way to achieve continuous ion-flux operation for stable concentration gradient or ionic conductance. Furthermore, the combined junctions can be used to accumulate ions on a specific region of the device.Korea Research Foundation (Grant MOEHRD: KRF-2007-331-D00040)Korean Science and Engineering Foundation (Grant MOST: R01-2007-000-20675-0)Korea Research Foundation (Grant MOEHRD: KRF-J03000)National Research Foundation of Korea (Grant NRF-2009- 352-D00034)National Institutes of Health (U.S.) (EB005743)National Science Foundation (U.S.). (CBET-0347348

Anomalous scaling of passively advected magnetic field in the presence of strong anisotropy

Inertial-range scaling behavior of high-order (up to order N=51) structure functions of a passively advected vector field has been analyzed in the framework of the rapid-change model with strong small-scale anisotropy with the aid of the renormalization group and the operator-product expansion. It has been shown that in inertial range the leading terms of the structure functions are coordinate independent, but powerlike corrections appear with the same anomalous scaling exponents as for the passively advected scalar field. These exponents depend on anisotropy parameters in such a way that a specific hierarchy related to the degree of anisotropy is observed. Deviations from power-law behavior like oscillations or logarithmic behavior in the corrections to structure functions have not been found.Comment: 15 pages, 18 figure

Chaotic motion of space charge wavefronts in semiconductors under time-independent voltage bias

A standard drift-diffusion model of space charge wave propagation in semiconductors has been studied numerically and analytically under dc voltage bias. For sufficiently long samples, appropriate contact resistivity and applied voltage - such that the sample is biased in a regime of negative differential resistance - we find chaos in the propagation of nonlinear fronts (charge monopoles of alternating sign) of electric field. The chaos is always low-dimensional, but has a complex spatial structure; this behavior can be interpreted using a finite dimensional asymptotic model in which the front (charge monopole) positions and the electrical current are the only dynamical variables.Comment: 12 pages, 8 figure