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

Electro-osmotic Instability of Concentration Enrichment in Curved Geometries for an Aqueous Electrolyte

We report that an electro-osmotic instability of concentration enrichment in curved geometries for an aqueous electrolyte, as opposed to the well-known one, is initiated exclusively at the enriched interface (anode), rather than at the depleted one (cathode). For this instability, the limitation of unrealistically high material Peclet number in planar geometry is eliminated by the strong electric field arising from the line charge singularity. In a model setup of concentric circular electrodes, we show by stability analysis, numerical simulation, and experimental visualization that instability occurs at the inner anode, below a critical radius of curvature. The stability criterion is also formulated in terms of a critical electric field and extended to arbitrary (2d) geometries by conformal mapping. This discovery suggests that transport may be enhanced in processes limited by salt enrichment, such as reverse osmosis, by triggering this instability with needle-like electrodes.Comment: 5 pages, 4 figure

Integral Equations for Heat Kernel in Compound Media

By making use of the potentials of the heat conduction equation the integral equations are derived which determine the heat kernel for the Laplace operator $-a^2\Delta$ in the case of compound media. In each of the media the parameter $a^2$ acquires a certain constant value. At the interface of the media the conditions are imposed which demand the continuity of the `temperature' and the `heat flows'. The integration in the equations is spread out only over the interface of the media. As a result the dimension of the initial problem is reduced by 1. The perturbation series for the integral equations derived are nothing else as the multiple scattering expansions for the relevant heat kernels. Thus a rigorous derivation of these expansions is given. In the one dimensional case the integral equations at hand are solved explicitly (Abel equations) and the exact expressions for the regarding heat kernels are obtained for diverse matching conditions. Derivation of the asymptotic expansion of the integrated heat kernel for a compound media is considered by making use of the perturbation series for the integral equations obtained. The method proposed is also applicable to the configurations when the same medium is divided, by a smooth compact surface, into internal and external regions, or when only the region inside (or outside) this surface is considered with appropriate boundary conditions.Comment: 26 pages, no figures, no tables, REVTeX4; two items are added into the Reference List; a new section is added, a version that will be published in J. Math. Phy

On functions of van der Waerden type

Let $\omega(t)$ be an arbitrary modulus of continuity type function, such that $\omega(t)/t\to+\infty$, as $t\to+0$. We construct a continuous nowhere-differentiable function $V_\omega(x)$, $x\in[0;1]$, that satisfies the following conditions: 1)  its modulus of continuity satisfies the estimate $O(\omega(t))$ as $t\to+0$; 2) for some positive $c$ at each point $x_0$ holds \limsup{|V_\omega(x){-}V_\omega(x_0)|}\big/{\omega(|x{-}x_0|)}>c as $x\to x_0$; 3) at each point $x_0$ holds $\liminf{|V_\omega(x){-}V_\omega(x_0)|}\big/{\omega(|x{-}x_0|)}=0$ as $x\to x_0$

Exceptional del Pezzo hypersurfaces

We compute global log canonical thresholds of a large class of quasismooth well-formed del Pezzo weighted hypersurfaces in $\mathbb{P}(a_{1},a_{2},a_{3},a_{4})$. As a corollary we obtain the existence of orbifold K\"ahler--Einstein metrics on many of them, and classify exceptional and weakly exceptional quasismooth well-formed del Pezzo weighted hypersurfaces in $\mathbb{P}(a_{1},a_{2},a_{3},a_{4})$.Comment: 149 pages, one reference adde

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

Case report: BRCA in the Ashkenazi population: are current testing guidelines too exclusive?

The BRCA1/2 genes account for a significant portion of hereditary breast and ovarian cancers and they are especially prevalent in the Ashkenazi Jewish population. Women who have a mutation can prevent breast and ovarian cancer with surgical intervention. We describe an Ashkenazi Jewish patient who illustrates that current testing criteria are too restrictive, particularly for this population of patients. The patient's sister was diagnosed with breast cancer at age 33; however, she was not a mutation carrier. Based on practice guidelines, the patient was not recommended genetic testing. She subsequently underwent direct-to-consumer (DTC) testing and discovered that she was a mutation carrier. This case demonstrates the need for clinicians to be aware of the higher prevalence of BRCA mutations in the Ashkenazi population. It also exemplifies the need to involve medical professionals, including genetic counselors, in the dissemination of DNA test results

Del Pezzo surfaces with many symmetries

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

Relationships between drug activity in NCI preclinical in vitro and in vivo models and early clinical trials

An analysis of the activity of compounds tested in pre-clinical in vivo and in vitro assays by the National Cancer Institute's Developmental Therapeutics Program was performed. For 39 agents with both xenograft data and Phase II clinical trials results available, in vivo activity in a particular histology in a tumour model did not closely correlate with activity in the same human cancer histology, casting doubt on the correspondence of the pre-clinical models to clinical results. However, for compounds with in vivo activity in at least one-third of tested xenograft models, there was correlation with ultimate activity in at least some Phase II trials. Thus, an efficient means of predicting activity in vivo models remains desirable for compounds with anti-proliferative activity in vitro. For 564 compounds tested in the hollow fibre assay which were also tested against in vivo tumour models, the likelihood of finding xenograft activity in at least one-third of the in vivo models tested rose with increasing intraperitoneal hollow fibre activity, from 8% for all compounds tested to 20% in agents with evidence of response in more than 6 intraperitoneal fibres (P< 0.0001). Intraperitoneal hollow fibre activity was also found to be a better predictor of xenograft activity than either subcutaneous hollow fibre activity or intraperitoneal plus subcutaneous activity combined. Since hollow fibre activity was a useful indicator of potential in vivo response, correlates with hollow fibre activity were examined for 2304 compounds tested in both the NCI 60 cell line in vitro cancer drug screen and hollow fibre assay. A positive correlation was found for histologic selectivity between in vitro and hollow fibre responses. The most striking correlation was between potency in the 60 cell line screen and hollow fibre activity; 56% of compounds with mean 50% growth inhibition below 10–7.5 M were active in more than 6 intraperitoneal fibres whereas only 4% of compounds with a potency of 10–4 M achieved the same level of hollow fibre activity (P< 0.0001). Structural parameters of the drugs analysed included compound molecular weight and hydrogen-bonding factors, both of which were found to be predictive of hollow fibre activity. © 2001 Cancer Research Campaign www.bjcancer.co