267 research outputs found
Relativistic and correlation effects in atoms
This review article deals with some case studies of relativistic and
correlation effects in atomic systems. After a brief introduction to
relativistic many-electron theory, a number of applications ranging from
correlation energy to parity non-conservation in atoms are considered. There is
a special emphasis on relativistic coupled-cluster theory as most of the
results presented here are based on it.Comment: Review article, 4 eps figures, latex 2
Relativistic coupled-cluster calculations of Ne, Ar, Kr and Xe: correlation energies and dipole polarizabilities
We have carried out a detailed and systematic study of the correlation
energies of inert gas atoms Ne, Ar, Kr and Xe using relativistic many-body
perturbation theory and relativistic coupled-cluster theory. In the
relativistic coupled-cluster calculations, we implement perturbative triples
and include these in the correlation energy calculations. We then calculate the
dipole polarizability of the ground states using perturbed coupled-cluster
theory.Comment: 10 figures, 6 tables, submitted to PR
Optical frequency standard with : A theoretical many-body approach
Demands from several areas of science and technology have lead to a worldwide
search for accurate optical clocks with an uncertainty of 1 part in ,
which is times more accurate than the present day cesium atomic clocks
based on microwave frequency regime. In this article we discuss the electric
quadrupole and the hyperfine shifts in the clock transition in , one of the most promising
candidates for next generation optical clocks. We have applied relativistic
coupled cluster theory for determining the electric quadrupole moment of the
state of and the magnetic dipole ()
and electric quadrupole () hyperfine constants for the and
states which are important in the study of frequency standards
with . The effects of electron correlation which are very
crucial for the accurate determination of these quantities have been discussed.Comment: TC-2005 Conference, India, 2 EPS figures, Latex 2
Electric quadrupole moment of the state in : A relativistic coupled-cluster analysis
The electric quadrupole moment for the state of
, has been calculated using the relativistic
coupled-cluster method. Earlier a similar calculation was performed for the 4d
state of which is the most accurate
determination to date {[}PRL, \textbf{96}, 193001 (2006)]. The present
calculation of the electric quadrupole moment of
yielded a value where the experimental value is
; is the Bohr radius and the elementary charge.
We discuss in this paper our results in detail for and
highlight the dominant correlation effects present. We have presented the
effect of inner core excitations and their contribution to the electric
quadrupole moment, which is a property sensitive to regions away from the
nucleus.Comment: 5 pages, 1 figure. Accepted in Phys.Rev.
Facts and Treatment of Bullous Pemphigoid: A Review
Bullous pemphigoid (a type of pemphigoid) is an autoimmune pruritic skin disease that typically occurs in people aged over 60, that may involve the formation of blisters (bullae) in the space between the epidermal and dermal skin layers. It is classified as a type II hypersensitivity reaction, which involves formation of anti-hemidesmosome antibodies, causing a loss of keratinocytes to basement membrane adhesion. Pemphigus and bullous pemphigoid are autoantibody-mediated blistering skin diseases. In pemphigus, keratinocytes in epidermis and mucous membranes lose cell-cell adhesion, and in pemphigoid, the basal keratinocytes lose adhesion to the basement membrane. Pemphigus lesions are mediated directly by the autoantibodies, whereas the autoantibodies in pemphigoid fix complement and mediate inflammation. In both diseases, the autoantigens have been cloned and characterized; pemphigus antigens are desmogleins (cell adhesion molecules in desmosomes), and pemphigoid antigens are found in hemidesmosomes (which mediate adhesion to the basement membrane). This knowledge has enabled diagnostic testing for these diseases by enzyme-linked immunosorbent assays and dissection of various pathophysiological mechanisms, including direct inhibition of cell adhesion, antibody-induced internalization of antigen, and cell signaling. Understanding these mechanisms of disease has led to rational targeted therapeutic strategies
New Distributional Records for Cardinalfishes (Perciformes/ Apogonidae) from North East Arabian Sea, Western Indian Ocean
Fishes of family Apogonidae popularly known as cardinalfishes are of high ecological importance owing to its trophic role. Though
the presence of apogonids from the coastal waters of the northeastern Arabian sea are reflected in diets of predatory fishes of the
region and bycatch of trawls, limited reports are available on species composition. Three species namely Apogonichthyoides
pseudotaeniatus (Gon, 1986), Jaydia queketti (Gilchrist, 1903) and Jaydia lineata (Temmink& Schlegal, 1842) have been reported
for the first time from the region, adding to the apogonids diversity of the region. Ostorhinchus fasciatus (White, 1790) is also
reported for the first time from the coastal waters of Gujarat. Morphometric assessment of the four species revealed several
discriminating attributes capable of separating the species from each other
Highly Conducting pi-Conjugated Molecular Junctions Covalently Bonded to Gold Electrodes
We measure electronic conductance through single conjugated molecules bonded
to Au metal electrodes with direct Au-C covalent bonds using the scanning
tunneling microscope based break-junction technique. We start with molecules
terminated with trimethyltin end groups that cleave off in situ resulting in
formation of a direct covalent sigma bond between the carbon backbone and the
gold metal electrodes. The molecular carbon backbone used in this study consist
of a conjugated pi-system that has one terminal methylene group on each end,
which bonds to the electrodes, achieving large electronic coupling of the
electrodes to the pi-system. The junctions formed with the prototypical example
of 1,4-dimethylenebenzene show a conductance approaching one conductance
quantum (G0 = 2e2/h). Junctions formed with methylene terminated oligophenyls
with two to four phenyl units show a hundred-fold increase in conductance
compared with junctions formed with amine-linked oligophenyls. The conduction
mechanism for these longer oligophenyls is tunneling as they exhibit an
exponential dependence of conductance with oligomer length. In addition,
density functional theory based calculations for the Au-xylylene-Au junction
show near-resonant transmission with a cross-over to tunneling for the longer
oligomers.Comment: Accepted to the Journal of the American Chemical Society as a
Communication
Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation
The current status of electric dipole moments of diamagnetic atoms which
involves the synergy between atomic experiments and three different theoretical
areas -- particle, nuclear and atomic is reviewed. Various models of particle
physics that predict CP violation, which is necessary for the existence of such
electric dipole moments, are presented. These include the standard model of
particle physics and various extensions of it. Effective hadron level combined
charge conjugation (C) and parity (P) symmetry violating interactions are
derived taking into consideration different ways in which a nucleon interacts
with other nucleons as well as with electrons. Nuclear structure calculations
of the CP-odd nuclear Schiff moment are discussed using the shell model and
other theoretical approaches. Results of the calculations of atomic electric
dipole moments due to the interaction of the nuclear Schiff moment with the
electrons and the P and time-reversal (T) symmetry violating
tensor-pseudotensor electron-nucleus are elucidated using different
relativistic many-body theories. The principles of the measurement of the
electric dipole moments of diamagnetic atoms are outlined. Upper limits for the
nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained
combining the results of atomic experiments and relativistic many-body
theories. The coefficients for the different sources of CP violation have been
estimated at the elementary particle level for all the diamagnetic atoms of
current experimental interest and their implications for physics beyond the
standard model is discussed. Possible improvements of the current results of
the measurements as well as quantum chromodynamics, nuclear and atomic
calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for
EPJ
CP violation in sbottom decays
We study CP asymmetries in two-body decays of bottom squarks into charginos
and tops. These asymmetries probe the SUSY CP phases of the sbottom and the
chargino sector in the Minimal Supersymmetric Standard Model. We identify the
MSSM parameter space where the CP asymmetries are sizeable, and analyze the
feasibility of their observation at the LHC. As a result, potentially
detectable CP asymmetries in sbottom decays are found, which motivates further
detailed experimental studies for probing the SUSY CP phases.Comment: 29 pages, 7 figure
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