316 research outputs found
Almost-zero-energy Eigenvalues of Some Broken Supersymmetric Systems
For a quantum mechanical system with broken supersymmetry, we present a
simple method of determining the ground state when the corresponding energy
eigenvalue is sufficiently small. A concise formula is derived for the
approximate ground state energy in an associated, well-separated, asymmetric
double-well-type potential. Our discussion is also relevant for the analysis of
the fermion bound state in the kink-antikink scalar background.Comment: revised version, to be pubilshed in PR
Use of geostatistical Bayesian updating to integrate airborne radiometrics and soil geochemistry to improve mapping for mineral exploration
Mineral exploration programmes around the world use data from remote
sensing, geophysics, and direct sampling. On a regional scale, the
combination of airborne geophysics and ground-based geochemical
sampling can aid geological mapping and mineral exploration. Since
airborne geophysical and traditional soil-sampling data are generated at
different spatial resolutions, they are not immediately comparable due to
their different sampling density. Several geostatistical techniques,
including indicator cokriging and collocated cokriging, can be used to
integrate different types of data into a geostatistical model. However,
with increasing numbers of variables the inference of the crosscovariance
model required for cokriging can be demanding in terms of
effort and computational time. In this paper a Gaussian-based Bayesian
updating approach is applied to integrate airborne radiometric data and
ground-sampled geochemical soil data to maximize information
generated from the soil survey, enabling more accurate geological
interpretation for the exploration and development of natural resources.
The Bayesian updating technique decomposes the collocated estimate
into two models: prior and likelihood models. The prior model is built
from primary information and the likelihood model is built from
secondary information. The prior model is then updated with the
likelihood model to build the final model. The approach allows multiple
secondary variables to be simultaneously integrated into the mapping of
the primary variable. The Bayesian updating approach is demonstrated
using a case study from Northern Ireland. The geostatistical technique
was used to improve the resolution of soil geochemistry, at a density of
one sample per 2 km2, by integrating more closely measured airborne
geophysical data from the GSNI Tellus Survey, measured over a
footprint of 65 x 200 m. The directly measured geochemistry data were
considered as primary data and the airborne radiometric data were used
as secondary data. The approach produced more detailed updated maps
and in particular enhanced information on the mapped distributions of
zinc, copper, and lead. The enhanced delineation of an elongated
northwest/southeast trending zone in the updated maps strengthened
the potential for discovering stratabound base metal deposits
Deterministic and stochastic descriptions of gene expression dynamics
A key goal of systems biology is the predictive mathematical description of
gene regulatory circuits. Different approaches are used such as deterministic
and stochastic models, models that describe cell growth and division explicitly
or implicitly etc. Here we consider simple systems of unregulated
(constitutive) gene expression and compare different mathematical descriptions
systematically to obtain insight into the errors that are introduced by various
common approximations such as describing cell growth and division by an
effective protein degradation term. In particular, we show that the population
average of protein content of a cell exhibits a subtle dependence on the
dynamics of growth and division, the specific model for volume growth and the
age structure of the population. Nevertheless, the error made by models with
implicit cell growth and division is quite small. Furthermore, we compare
various models that are partially stochastic to investigate the impact of
different sources of (intrinsic) noise. This comparison indicates that
different sources of noise (protein synthesis, partitioning in cell division)
contribute comparable amounts of noise if protein synthesis is not or only
weakly bursty. If protein synthesis is very bursty, the burstiness is the
dominant noise source, independent of other details of the model. Finally, we
discuss two sources of extrinsic noise: cell-to-cell variations in protein
content due to cells being at different stages in the division cycles, which we
show to be small (for the protein concentration and, surprisingly, also for the
protein copy number per cell) and fluctuations in the growth rate, which can
have a significant impact.Comment: 23 pages, 5 figures; Journal of Statistical physics (2012
Quasi-Normal Modes of Schwarzschild Anti-De Sitter Black Holes: Electromagnetic and Gravitational Perturbations
We study the quasi-normal modes (QNM) of electromagnetic and gravitational
perturbations of a Schwarzschild black hole in an asymptotically Anti-de Sitter
(AdS) spacetime. Some of the electromagnetic modes do not oscillate, they only
decay, since they have pure imaginary frequencies. The gravitational modes show
peculiar features: the odd and even gravitational perturbations no longer have
the same characteristic quasinormal frequencies. There is a special mode for
odd perturbations whose behavior differs completely from the usual one in
scalar and electromagnetic perturbation in an AdS spacetime, but has a similar
behavior to the Schwarzschild black hole in an asymptotically flat spacetime:
the imaginary part of the frequency goes as 1/r+, where r+ is the horizon
radius. We also investigate the small black hole limit showing that the
imaginary part of the frequency goes as r+^2. These results are important to
the AdS/CFT conjecture since according to it the QNMs describe the approach to
equilibrium in the conformal field theory.Comment: 2 figure
(1+1)-Dirac particle with position-dependent mass in complexified Lorentz scalar interactions: effectively PT-symmetric
The effect of the built-in supersymmetric quantum mechanical language on the
spectrum of the (1+1)-Dirac equation, with position-dependent mass (PDM) and
complexified Lorentz scalar interactions, is re-emphasized. The signature of
the "quasi-parity" on the Dirac particles' spectra is also studied. A Dirac
particle with PDM and complexified scalar interactions of the form S(z)=S(x-ib)
(an inversely linear plus linear, leading to a PT-symmetric oscillator model),
and S(x)=S_{r}(x)+iS_{i}(x) (a PT-symmetric Scarf II model) are considered.
Moreover, a first-order intertwining differential operator and an
-weak-pseudo-Hermiticity generator are presented and a complexified
PT-symmetric periodic-type model is used as an illustrative example.Comment: 11 pages, no figures, revise
Identifying topological edge states in 2D optical lattices using light scattering
We recently proposed in a Letter [Physical Review Letters 108 255303] a novel
scheme to detect topological edge states in an optical lattice, based on a
generalization of Bragg spectroscopy. The scope of the present article is to
provide a more detailed and pedagogical description of the system - the
Hofstadter optical lattice - and probing method. We first show the existence of
topological edge states, in an ultra-cold gas trapped in a 2D optical lattice
and subjected to a synthetic magnetic field. The remarkable robustness of the
edge states is verified for a variety of external confining potentials. Then,
we describe a specific laser probe, made from two lasers in Laguerre-Gaussian
modes, which captures unambiguous signatures of these edge states. In
particular, the resulting Bragg spectra provide the dispersion relation of the
edge states, establishing their chiral nature. In order to make the Bragg
signal experimentally detectable, we introduce a "shelving method", which
simultaneously transfers angular momentum and changes the internal atomic
state. This scheme allows to directly visualize the selected edge states on a
dark background, offering an instructive view on topological insulating phases,
not accessible in solid-state experiments.Comment: 17 pages, 10 figures. Revised and extended version, to appear in EJP
Special Topic for the special issue on "Novel Quantum Phases and Mesoscopic
Physics in Quantum Gases". Extended version of arXiv:1203.124
Supersymmetrization of Quaternion Dirac Equation for Generalized Fields of Dyons
The quaternion Dirac equation in presence of generalized electromagnetic
field has been discussed in terms of two gauge potentials of dyons.
Accordingly, the supersymmetry has been established consistently and thereafter
the one, two and component Dirac Spinors of generalized quaternion Dirac
equation of dyons for various energy and spin values are obtained for different
cases in order to understand the duality invariance between the electric and
magnetic constituents of dyons.Comment: Key words: Supersymmetry, quaternion, Dirac equation, dyons PACS No.:
11.30.Pb, 14.80.Ly, 03.65.G
A Group-Theoretical Method for Natanzon Potentials in Position-Dependent Mass Background
A new manner for deriving the exact potentials is presented. By making use of
conformal mappings, the general expression of the effective potentials deduced
under su(1,1) algebra can be brought back to the general Natanzon
hypergeometric potentials
hnRNPUL1 ensures efficient Integrator-mediated cleavage of snRNAs and is mutated in amyotrophic lateral sclerosis
Aspectos microscĂłpicos da interação feijoeiro-Colletotrichum lindemuthianum mediados pelo silĂcio
A antracnose, causada pelo fungo Colletotrichum lindemuthianum, Ă© uma das doenças mais destrutivas que afetam a cultura do feijoeiro. Com o objetivo de encontrar alternativas para o controle dessa doença, o presente trabalho investigou, em nĂvel microscĂłpico, o efeito do silĂcio (Si) na resistĂŞncia do feijoeiro Ă infecção por C. lindemuthianum. Plantas de feijoeiro (cv. PĂ©rola) foram cultivadas em solução nutritiva contendo 0 (-Si) ou 2 mM (+Si) de Si e inoculadas no estádio de crescimento V4 com uma suspensĂŁo de conĂdios de C. lindemuthianum. A severidade da antracnose decresceu cerca de 52% nas folhas das plantas supridas com Si (4,4%) em relação Ă s folhas das plantas nĂŁo supridas (8,5%). Observações de folhas de feijoeiro das plantas nĂŁo supridas com Si no microscĂłpio eletrĂ´nico de varredura revelaram alterações morfolĂłgicas nas nervuras em contraste com as folhas de plantas supridas com Si. Utilizando-se a microanálise de raios-X, verificou-se maior concentração dos minerais enxofre, potássio e Si nas folhas das plantas supridas com Si. Em conclusĂŁo, o suprimento de Si em plantas de feijoeiro foi importante para reduzir os sintomas da antracnose
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