462 research outputs found
Microtextures of Laterites and Bauxites Capping Deccan Trap Basalts in Western India
Thirty-five samples of laterites and bauxites representing both the high-level (elevation \u3e 1000 m) and low-level (elevation \u3c 100 m) deposits in western India have been examined by scanning electron microscopy. Megascopically, laterites exhibit vesicular, spongy and pisolitic textures, whereas bauxites display pisolitic, massive and nodular textures. Laterites, as well as bauxites are commonly characterized by framework microtexture produced by a three dimensional arrangement of crystallites. Locally, the luterites and bauxites exhibit crystalline-webby microtexture formed by a web-like arrangement of stacks of lamellar crystals. The individual crystals in the matrix of laterites and bauxites display anhedral forms and they range in size from about 0.5 μm to 20 μm. Crystals larger than 20 μm in size generally occur as linings of the vugs, in channels and veins, and they are usually euhedral. Pisolites and nodules in laterites and bauxites are composed of material generally finer than the material in the matrix around them. Platy morphology is most common for the minerals in laterites and bauxites. Gibbsite occurs in various forms ranging from prismatic, stubby slab-like to lath-shaped crystals.
Both high-level and low-level deposits of laterites are characterized by similar textures. The variations in textures of bauxites are also found to be independent of the elevation of the deposits
TransCanada Lawsuit Highlights Need to Scuttle TPP
The Obama administration is still trying, against the odds, to push the Trans-Pacific Partnership trade and investment agreement (TPP) through the lame-duck session of Congress after the November presidential vote. The administration knows that TPP can’t pass before the election because both Hillary Clinton and Donald Trump oppose it; therefore, they are hoping for a stealth Senate vote between the election and inauguration of the new president in 2017.We can therefore “thank” TransCanada for reminding us why the TPP needs to be scuttled
Stringy Robinson-Trautman Solutions
A class of solutions of the low energy string theory in four dimensions is
studied. This class admits a geodesic, shear-free null congruence which is
non-twisting but in general diverging and the corresponding solutions in
Einstein's theory form the Robinson-Trautman family together with a subset of
the Kundt's class. The Robinson-Trautman conditions are found to be frame
invariant in string theory. The Lorentz Chern-Simons three form of the stringy
Robinson-Trautman solutions is shown to be always closed. The stringy
generalizations of the vacuum Robinson-Trautman equation are obtained and three
subclasses of solutions are identified. One of these subclasses exists, among
all the dilatonic theories, only in Einstein's theory and in string theory.
Several known solutions including the dilatonic black holes, the pp- waves, the
stringy C-metric and certain solutions which correspond to exact conformal
field theories are shown to be particular members of the stringy
Robinson-Trautman family. Some new solutions which are static or asymptotically
flat and radiating are also presented. The radiating solutions have a positive
Bondi mass. One of these radiating solutions has the property that it settles
down smoothly to a black hole state at late retarded times.Comment: Latex, 30 Pages, 1 Figure; to appear in Phys. Rev.
The general form of supersymmetric solutions of N=(1,0) U(1) and SU(2) gauged supergravities in six dimensions
We obtain necessary and sufficient conditions for a supersymmetric field
configuration in the N=(1,0) U(1) or SU(2) gauged supergravities in six
dimensions, and impose the field equations on this general ansatz. It is found
that any supersymmetric solution is associated to an structure. The structure is characterized by a null Killing
vector which induces a natural 2+4 split of the six dimensional spacetime. A
suitable combination of the field equations implies that the scalar curvature
of the four dimensional Riemannian part, referred to as the base, obeys a
second order differential equation. Bosonic fluxes introduce torsion terms that
deform the structure away from a covariantly
constant one. The most general structure can be classified in terms of its
intrinsic torsion. For a large class of solutions the gauge field strengths
admit a simple geometrical interpretation: in the U(1) theory the base is
K\"{a}hler, and the gauge field strength is the Ricci form; in the SU(2)
theory, the gauge field strengths are identified with the curvatures of the
left hand spin bundle of the base. We employ our general ansatz to construct
new supersymmetric solutions; we show that the U(1) theory admits a symmetric
Cahen-Wallach solution together with a compactifying pp-wave. The
SU(2) theory admits a black string, whose near horizon limit is . We also obtain the Yang-Mills analogue of the Salam-Sezgin solution of
the U(1) theory, namely , where the is supported by a
sphaleron. Finally we obtain the additional constraints implied by enhanced
supersymmetry, and discuss Penrose limits in the theories.Comment: 1+29 pages, late
Cu/cuo composite track-etched membranes for catalytic decomposition of nitrophenols and removal of as(III)
One of the promising applications of nanomaterials is to use them as catalysts and sorbents to remove toxic pollutants such as nitroaromatic compounds and heavy metal ions for environmental protection. This work reports the synthesis of Cu/CuO-deposited composite track-etched membranes through low-temperature annealing and their application in catalysis and sorption. The synthesized Cu/CuO/poly(ethylene terephthalate) (PET) composites presented efficient catalytic activity with high conversion yield in the reduction of nitro aryl compounds to their corresponding amino derivatives. It has been found that increasing the time of annealing raises the ratio of the copper(II) oxide (CuO) tenorite phase in the structure, which leads to a significant increase in the catalytic activity of the composites. The samples presented maximum catalytic activity after 5 h of annealing, where the ratio of CuO phase and the degree of crystallinity were 64.3% and 62.7%, respectively. The catalytic activity of pristine and annealed composites was tested in the reduction of 4-nitroaniline and was shown to remain practically unchanged for five consecutive test cycles. Composites annealed at 140 °C were also tested for their capacity to absorb arsenic(III) ions in cross-flow mode. It was observed that the sorption capacity of composite membranes increased by 48.7% compared to the pristine sample and reached its maximum after 10 h of annealing, then gradually decreased by 24% with further annealing. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.Ministry of Education and Science of the Republic of Kazakhstan: AP05130797Funding: A.M. gratefully acknowledges the funding of the Ministry of Education and Science of the Republic of Kazakhstan (Project AP05130797)
Self-consistent local-equilibrium model for density profile and distribution of dissipative currents in a Hall bar under strong magnetic fields
Recent spatially resolved measurements of the electrostatic-potential
variation across a Hall bar in strong magnetic fields, which revealed a clear
correlation between current-carrying strips and incompressible strips expected
near the edges of the Hall bar, cannot be understood on the basis of existing
equilibrium theories. To explain these experiments, we generalize the
Thomas-Fermi--Poisson approach for the self-consistent calculation of
electrostatic potential and electron density in {\em total} thermal equilibrium
to a {\em local equilibrium} theory that allows to treat finite gradients of
the electrochemical potential as driving forces of currents in the presence of
dissipation. A conventional conductivity model with small values of the
longitudinal conductivity for integer values of the (local) Landau-level
filling factor shows that, in apparent agreement with experiment, the current
density is localized near incompressible strips, whose location and width in
turn depend on the applied current.Comment: 9 pages, 7 figure
The Conformal Penrose Limit and the Resolution of the pp-curvature Singularities
We consider the exact solutions of the supergravity theories in various
dimensions in which the space-time has the form M_{d} x S^{D-d} where M_{d} is
an Einstein space admitting a conformal Killing vector and S^{D-d} is a sphere
of an appropriate dimension. We show that, if the cosmological constant of
M_{d} is negative and the conformal Killing vector is space-like, then such
solutions will have a conformal Penrose limit: M^{(0)}_{d} x S^{D-d} where
M^{(0)}_{d} is a generalized d-dimensional AdS plane wave. We study the
properties of the limiting solutions and find that M^{(0)}_{d} has 1/4
supersymmetry as well as a Virasoro symmetry. We also describe how the
pp-curvature singularity of M^{(0)}_{d} is resolved in the particular case of
the D6-branes of D=10 type IIA supergravity theory. This distinguished case
provides an interesting generalization of the plane waves in D=11 supergravity
theory and suggests a duality between the SU(2) gauged d=8 supergravity of
Salam and Sezgin on M^{(0)}_{8} and the d=7 ungauged supergravity theory on its
pp-wave boundary.Comment: 20 pages, LaTeX; typos corrected, journal versio
Black-Hole-Wave Duality in String Theory
Extreme 4-dimensional dilaton black holes embedded into 10-dimensional
geometry are shown to be dual to the gravitational waves in string theory. The
corresponding gravitational waves are the generalization of pp-fronted waves,
called supersymmetric string waves. They are given by Brinkmann metric and the
two-form field, without a dilaton. The non-diagonal part of the metric of the
dual partner of the wave together with the two-form field correspond to the
vector field in 4-dimensional geometry of the charged extreme black holes.Comment: 12 pages, LaTeX, preprint UG-3/94, SU-ITP-94-11, QMW-PH-94-1
Correlation induced phonon softening in low density coupled bilayer systems
We predict a possible phonon softening instability in strongly correlated
coupled semiconductor bilayer systems. By studying the plasmon-phonon coupling
in coupled bilayer structures, we find that the renormalized acoustic phonon
frequency may be softened at a finite wave vector due to many-body local field
corrections, particularly in low density systems where correlation effects are
strong. We discuss experimental possibilities to search for this predicted
phonon softening phenomenon.Comment: 4 pages with 2 figure
Colliding Plane Waves in Einstein-Maxwell-Dilaton Fields
Within the metric structure endowed with two orthogonal space-like Killing
vectors a class of solutions of the Einstein-Maxwell-Dilaton field equations is
presented. Two explicitly given sub-classes of solutions bear an interpretation
as colliding plane waves in the low-energy limit of the heterotic string
theory.Comment: 14 pages, LaTex; To appear in Phys. Rev.
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