405 research outputs found
Vibrational properties of amorphous silicon from tight-binding O(N) calculation
We present an O(N) algorithm to study the vibrational properties of amorphous
silicon within the framework of tight-binding approach. The dynamical matrix
elements have been evaluated numerically in the harmonic approximation
exploiting the short-range nature of the density matrix to calculate the
vibrational density of states which is then compared with the same obtained
from a standard O() algorithm. For the purpose of illustration, an
1000-atom model is studied to calculate the localization properties of the
vibrational eigenstates using the participation numbers calculation.Comment: 5 pages including 5 ps figures; added a figure and a few references;
accepted in Phys. Rev.
Bio-Intervention of Naturally Occurring Silicate Minerals for Alternative Source of Potassium: Challenges and Opportunities
Soil needs simultaneous replenishment of various nutrients to maintain its inherent fertility status under extensive cropping systems. Replenishing soil nutrients with commercial fertilizer is costly. Among various fertilizers, deposits of potassium (K) ore suitable for the production of commercial K fertilizer (KCl) are distributed in few northern hemisphere countries (Canada, Russia, Belarus, and Germany) which control more than 70% of the world's potash market. Naturally occurring minerals, particularly silicate minerals, could be used as a source of K, but not as satisfactorily as commercial K fertilizers. In this context, bio-intervention (in combination with microorganisms and/or composting) of silicate minerals has been found quite promising to improve plant K availability and assimilation. This is an energy efficient and environmentally friendly approach. Here we present a critical review of existing literature on direct application of silicate minerals as a source of K for plant nutrition as well as soil fertility enhancement by underpinning the bio-intervention strategies and related K solubilization mechanisms. An advancement of knowledge in this field will not only contribute to a better understanding of the complex natural processes of soil K fertility, but also help to develop a new approach to utilize natural mineral resources for sustainable and environmental friendly agricultural practices
Complete Break Up of Ortho Positronium (Ps)- Hydrogenic ion System
The dynamics of the complete breakup process in an Ortho Ps - He+ system
including electron loss to the continuum (ELC) is studied where both the
projectile and the target get ionized. The process is essentially a four body
problem and the present model takes account of the two centre effect on the
electron ejected from the Ps atom which is crucial for a proper description of
the ELC phenomena. The calculations are performed in the framework of Coulomb
Distorted Eikonal Approximation. The exchange effect between the target and the
projectile electron is taken into account in a consistent manner. The proper
asymptotic 3-body boundary condition for this ionization process is also
satisfied in the present model. A distinct broad ELC peak is noted in the fully
differential cross sections (5DCS) for the Ps electron corroborating
qualitatively the experiment for the Ps - He system. Both the dynamics of the
ELC from the Ps and the ejected electron from the target He+ in the FDCS are
studied using coplanar geometry. Interesting features are noted in the FDCS for
both the electrons belonging to the target and the projectile.Comment: 14 pages,7 figure
Toric AdS4/CFT3 duals and M-theory Crystals
We study the recently proposed crystal model for three dimensional
superconformal field theories arising from M2-branes probing toric Calabi-Yau
four-fold singularities. We explain the algorithms mapping a toric Calabi-Yau
to a crystal and vice versa, and show how the spectrum of BPS meson states fits
into the crystal model.Comment: 24 pages, 24 figure
Time-Varying Dark Energy Constraints From the Latest SN Ia, BAO and SGL
Based on the latest SNe Ia data provided by Hicken et al. (2009) with using
MLCS17 light curve fitter, together with the Baryon Acoustic Oscillation(BAO)
and strong gravitational lenses(SGL), we investigate the constraints on the
dark energy equation-of-state parameter in the flat universe, especially
for the time-varying case . The constraints from SNe data
alone are found to be: (a) as the best-fit
results; (b) for
the two parameters in the time-varying case after marginalizing the parameter
; (c) the likelihood of parameter has a high non-Gaussian
distribution; (d) an extra restriction on is necessary to improve
the constraint of the SNe Ia data on the parameters (, ). A joint
analysis of SNe Ia data and BAO is made to break the degeneracy between and
, and leads to the interesting maximum likelihoods and
. When marginalizing the parameter , the fitting results are
found to be . After
adding the splitting angle statistic of SGL data, a consistent constraint is
obtained and the constraints on time-varying
dark energy are further improved to be , which indicates that the phantom type models are
disfavored.Comment: 24 pages, 9 figures, to be published in JCA
Counting Chiral Operators in Quiver Gauge Theories
We discuss in detail the problem of counting BPS gauge invariant operators in
the chiral ring of quiver gauge theories living on D-branes probing generic
toric CY singularities. The computation of generating functions that include
counting of baryonic operators is based on a relation between the baryonic
charges in field theory and the Kaehler moduli of the CY singularities. A study
of the interplay between gauge theory and geometry shows that given geometrical
sectors appear more than once in the field theory, leading to a notion of
"multiplicities". We explain in detail how to decompose the generating function
for one D-brane into different sectors and how to compute their relevant
multiplicities by introducing geometric and anomalous baryonic charges. The
Plethystic Exponential remains a major tool for passing from one D-brane to
arbitrary number of D-branes. Explicit formulae are given for few examples,
including C^3/Z_3, F_0, and dP_1.Comment: 75 pages, 22 figure
Counting BPS Operators in Gauge Theories: Quivers, Syzygies and Plethystics
We develop a systematic and efficient method of counting single-trace and
multi-trace BPS operators with two supercharges, for world-volume gauge
theories of D-brane probes for both and finite . The
techniques are applicable to generic singularities, orbifold, toric, non-toric,
complete intersections, et cetera, even to geometries whose precise field
theory duals are not yet known. The so-called ``Plethystic Exponential''
provides a simple bridge between (1) the defining equation of the Calabi-Yau,
(2) the generating function of single-trace BPS operators and (3) the
generating function of multi-trace operators. Mathematically, fascinating and
intricate inter-relations between gauge theory, algebraic geometry,
combinatorics and number theory exhibit themselves in the form of plethystics
and syzygies.Comment: 59+1 pages, 7 Figure
Typicality, Black Hole Microstates and Superconformal Field Theories
We analyze the structure of heavy multitrace BPS operators in N = 1
superconformal quiver gauge theories that arise on the worldvolume of D3-branes
on an affine toric cone. We exhibit a geometric procedure for counting heavy
mesonic operators with given U(1) charges. We show that for any fixed linear
combination of the U(1) charges, the entropy is maximized when the charges are
in certain ratios. This selects preferred directions in the charge space that
can be determined with the help of a piece of string. We show that almost all
heavy mesonic operators of fixed U(1) charges share a universal structure. This
universality reflects the properties of the dual extremal black holes whose
microstates they create. We also interpret our results in terms of typical
configurations of dual giant gravitons in AdS space.Comment: 40 pages + 3 appendices, 11 figure
The Cosmological Slingshot Scenario: Myths and Facts
We generalize the Cosmological Slingshot Scenario for a Slingshot brane
moving in a Klebanov-Strassler throat. We show that the horizon and isotropy
problems of standard cosmology are avoided, while the flatness problem is
acceptably alleviated. Regarding the primordial perturbations, we identify
their vacuum state and elucidate the evolution from the quantum to the
classical regimes. Also, we calculate their exact power spectrum showing its
compatibility with current data. We discuss the bouncing solution from a four
dimensional point of view. In this framework the radial and angular motion of
the Slingshot brane are described by two scalar fields. We show that the
bouncing solution for the scale factor in String frame is mapped into a
monotonically increasing (in conformal time) solution in the Einstein frame. We
finally discuss about the regularity of the geometry in Einstein frame.Comment: 16 pages, 2 figs. Major clarifications and references added, version
accepted in Gen. Rel. Grav. (2009
Recommended from our members
Track A Basic Science
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd
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