Deformation heterogeneity study of a 6061-T6 aluminum alloy processed by equal channel angular pressing

Among the severe plastic deformation techniques, the equal channel angular pressing (ECAP) has drastically improved the mechanical properties of the processed alloys. However, information regarding friction phenomenon, which modifies the deformation at the surface and the heterogeneity microstrain state produced by the process itself, is still scarce. In the present work, the deformation heterogeneity and the friction effect, at the surface in the bulk material of the 6061-T6 aluminum alloy processed by ECAP, is presented and discussed. The residual stress (RS) measurements were performed by means of X-Ray diffraction. By means of synchrotron diffraction, volumetric sections of the ECAPed samples were characterized. Finite element analysis showed a good agreement with the experimentally obtained residual stress and microhardness mapping results. The study also showed that the highest deformation zones were located at the outer parts of the deformed samples (top and bottom), while the inner zone showed strain oscillations of up to 49±2 MPa.Peer ReviewedPostprint (author's final draft

The spinorial geometry of supersymmetric heterotic string backgrounds

We determine the geometry of supersymmetric heterotic string backgrounds for which all parallel spinors with respect to the connection $\hat\nabla$ with torsion $H$, the NS$\otimes$NS three-form field strength, are Killing. We find that there are two classes of such backgrounds, the null and the timelike. The Killing spinors of the null backgrounds have stability subgroups K\ltimes\bR^8 in $Spin(9,1)$, for $K=Spin(7)$, SU(4), $Sp(2)$, $SU(2)\times SU(2)$ and $\{1\}$, and the Killing spinors of the timelike backgrounds have stability subgroups $G_2$, SU(3), SU(2) and $\{1\}$. The former admit a single null $\hat\nabla$-parallel vector field while the latter admit a timelike and two, three, five and nine spacelike $\hat\nabla$-parallel vector fields, respectively. The spacetime of the null backgrounds is a Lorentzian two-parameter family of Riemannian manifolds $B$ with skew-symmetric torsion. If the rotation of the null vector field vanishes, the holonomy of the connection with torsion of $B$ is contained in $K$. The spacetime of time-like backgrounds is a principal bundle $P$ with fibre a Lorentzian Lie group and base space a suitable Riemannian manifold with skew-symmetric torsion. The principal bundle is equipped with a connection $\lambda$ which determines the non-horizontal part of the spacetime metric and of $H$. The curvature of $\lambda$ takes values in an appropriate Lie algebra constructed from that of $K$. In addition $dH$ has only horizontal components and contains the Pontrjagin class of $P$. We have computed in all cases the Killing spinor bilinears, expressed the fluxes in terms of the geometry and determine the field equations that are implied by the Killing spinor equations.Comment: 73pp. v2: minor change

First Astronomical Application of a Cryogenic TES Spectrophotometer

We report on the first astronomical observations with a photon counting pixel detector that provides arrival time- (delta t = 100ns) and energy- (delta E_gamma < 0.15eV) resolved measurements from the near IR through the near UV. Our test observations were performed by coupling this Transition Edge Sensor (TES) device to a 0.6m telescope; we have obtained the first simultaneous optical near-IR phase-resolved spectra of the Crab pulsar. A varying infrared turnover gives evidence of self-absorption in the pulsar plasma. The potential of such detectors in imaging arrays from a space platform are briefly described.Comment: 4 pages, 5 figure

A review of current management of vitreomacular traction and macular hole

The paper presents a review of the sequence of events of posterior vitreous detachment (PVD), vitreomacular adhesion (VMA), vitreomacular traction (VMT), and macular hole (MH) from their pathophysiological aspects, clinical features, diagnostic implications, and current management strategies. A treatment algorithm to be used in clinical practice in patients with VMA, VMT, and MH based on the presence of symptoms, visual acuity, associated epiretinal membrane, and width of the vitreous attachment is presented. Observation, pharmacologic vitreolysis with ocriplasmin, and surgical treatment are positioned as treatment options in the different steps of the therapeutic algorithm, with clear indications of the paths to be followed according to the initial presenting manifestations and the patient's clinical course

The spinorial geometry of supersymmetric backgrounds

We propose a new method to solve the Killing spinor equations of eleven-dimensional supergravity based on a description of spinors in terms of forms and on the Spin(1,10) gauge symmetry of the supercovariant derivative. We give the canonical form of Killing spinors for N=2 backgrounds provided that one of the spinors represents the orbit of Spin(1,10) with stability subgroup SU(5). We directly solve the Killing spinor equations of N=1 and some N=2, N=3 and N=4 backgrounds. In the N=2 case, we investigate backgrounds with SU(5) and SU(4) invariant Killing spinors and compute the associated spacetime forms. We find that N=2 backgrounds with SU(5) invariant Killing spinors admit a timelike Killing vector and that the space transverse to the orbits of this vector field is a Hermitian manifold with an SU(5)-structure. Furthermore, N=2 backgrounds with SU(4) invariant Killing spinors admit two Killing vectors, one timelike and one spacelike. The space transverse to the orbits of the former is an almost Hermitian manifold with an SU(4)-structure and the latter leaves the almost complex structure invariant. We explore the canonical form of Killing spinors for backgrounds with extended, N>2, supersymmetry. We investigate a class of N=3 and N=4 backgrounds with SU(4) invariant spinors. We find that in both cases the space transverse to a timelike vector field is a Hermitian manifold equipped with an SU(4)-structure and admits two holomorphic Killing vector fields. We also present an application to M-theory Calabi-Yau compactifications with fluxes to one-dimension.Comment: Latex, 54 pages, v2: clarifications made and references added. v3: minor changes. v4: minor change

Comparison of CDMS [100] and [111] oriented germanium detectors

The Cryogenic Dark Matter Search (CDMS) utilizes large mass, 3" diameter $\times$ 1" thick target masses as particle detectors. The target is instrumented with both phonon and ionization sensors and comparison of energy in each channel provides event-by-event classification of electron and nuclear recoils. Fiducial volume is determined by the ability to obtain good phonon and ionization signal at a particular location. Due to electronic band structure in germanium, electron mass is described by an anisotropic tensor with heavy mass aligned along the symmetry axis defined by the [111] Miller index (L valley), resulting in large lateral component to the transport. The spatial distribution of electrons varies significantly for detectors which have their longitudinal axis orientations described by either the [100] or [111] Miller indices. Electric fields with large fringing component at high detector radius also affect the spatial distribution of electrons and holes. Both effects are studied in a 3 dimensional Monte Carlo and the impact on fiducial volume is discussed.Comment: Low Temperature Detector 14 conference proceedings to be published in the Journal of Low Temperature Physic

Guatemala's Pacific cetaceans: :Fifty years of history

Cetaceans have been studied in Guatemala since 1960s, but only a few scientific works based on the collected cetacean data were published. We reviewed literatures about cetaceans in Guatemala for the past fifty years to gain the biological knowledge for conservation and management plans. A total of 1,014 sighting records (1979- 2011), 62 tuna fishery by-catch events (1961-1985) and 16 stranding records (1975, 2007-2012) were obtained and analyzed with bathymetric maps and plot against maps with different anthropogenic pressures in the area. Nineteen species belonging to five different families of cetaceans, such as Balaenopteridae, Delphinidae, Ziphiidae, Kogiidae, and Physeteridae, were identified. Data sampling areas have been changed during 1961-2012. We identified several species-specific-spatial-distribution patterns. Species occurrence was higher in areas with complex topography. Although, all by-catch events were recorded offshore, species with coastal distribution occurred in areas with higher anthropogenic risk. Stranding events were reported for eight species, and occurred mainly in the department of Escuintla from 2007. Due to the great diversity in spatial-distribution patterns of cetacean in Guatemala, behavior and habitat use of cetaceans in the areas, combined with different anthropogenic risks, an integrative approach should be considered when conservation and management plans are implemented in Guatemala

Guatemala's Pacific cetaceans: :Fifty years of history

Cetaceans have been studied in Guatemala since 1960s, but only a few scientific works based on the collected cetacean data were published. We reviewed literatures about cetaceans in Guatemala for the past fifty years to gain the biological knowledge for conservation and management plans. A total of 1,014 sighting records (1979- 2011), 62 tuna fishery by-catch events (1961-1985) and 16 stranding records (1975, 2007-2012) were obtained and analyzed with bathymetric maps and plot against maps with different anthropogenic pressures in the area. Nineteen species belonging to five different families of cetaceans, such as Balaenopteridae, Delphinidae, Ziphiidae, Kogiidae, and Physeteridae, were identified. Data sampling areas have been changed during 1961-2012. We identified several species-specific-spatial-distribution patterns. Species occurrence was higher in areas with complex topography. Although, all by-catch events were recorded offshore, species with coastal distribution occurred in areas with higher anthropogenic risk. Stranding events were reported for eight species, and occurred mainly in the department of Escuintla from 2007. Due to the great diversity in spatial-distribution patterns of cetacean in Guatemala, behavior and habitat use of cetaceans in the areas, combined with different anthropogenic risks, an integrative approach should be considered when conservation and management plans are implemented in Guatemala