4,921 research outputs found
Probing CP violation with the electric dipole moment of atomic mercury
The electric dipole moment of atomic Hg induced by the nuclear Schiff
moment and tensor-pseudotensor electron-nucleus interactions has been
calculated. For this, we have developed and employed a novel method based on
the relativistic coupled-cluster theory. The results of our theoretical
calculations combined with the latest experimental result of Hg
electric dipole moment, provide new bounds on the T reversal or CP violation
parameters , the tensor-pseudotensor coupling constant
and . This is the most accurate
calculation of these parameters to date. We highlight the the crucial role of
electron correlation effects in their interplay with the P,T violating
interactions. Our results demonstrate substantial changes in the results of
earlier calculations of these parameters which can be attributed to the more
accurate inclusion of important correlation effects in the present work.Comment: 4 pages and 1 figur
Calculation of isotope shifts and relativistic shifts in CI, CII, CIII and CIV
We present an accurate ab initio method of calculating isotope shifts and
relativistic shifts in atomic spectra. We test the method on neutral carbon and
three carbon ions. The relativistic shift of carbon lines may allow them to be
included in analyses of quasar absorption spectra that seek to measure possible
variations in the fine structure constant, alpha, over the lifetime of the
Universe. Carbon isotope shifts can be used to measure isotope abundances in
gas clouds: isotope abundances are potentially an important source of
systematic error in the alpha-variation studies. These abundances are also
needed to study nuclear reactions in stars and supernovae, and test models of
chemical evolution of the Universe
Relativistic many-body calculation of low-energy dielectronic resonances in Be-like carbon
We apply relativistic configuration-interaction method coupled with many-body
perturbation theory (CI+MBPT) to describe low-energy dielectronic
recombination. We combine the CI+MBPT approach with the complex rotation method
(CRM) and compute the dielectronic recombination spectrum for Li-like carbon
recombining into Be-like carbon. We demonstrate the utility and evaluate the
accuracy of this newly-developed CI+MBPT+CRM approach by comparing our results
with the results of the previous high-precision study of the CIII system
[Mannervik et al., Phys. Rev. Lett. 81, 313 (1998)].Comment: 6 pages, 1 figure; v2,v3: fixed reference
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
Relativistic calculations of pionic and kaonic atoms hyperfine structure
We present the relativistic calculation of the hyperfine structure in pionic
and kaonic atoms. A perturbation method has been applied to the Klein-Gordon
equation to take into account the relativistic corrections. The perturbation
operator has been obtained \textit{via} a multipole expansion of the nuclear
electromagnetic potential. The hyperfine structure of pionic and kaonic atoms
provide an additional term in the quantum electrodynamics calculation of the
energy transition of these systems. Such a correction is required for a recent
measurement of the pion mass
Evidence for the absence of regularization corrections to the partial-wave renormalization procedure in one-loop self energy calculations in external fields
The equivalence of the covariant renormalization and the partial-wave
renormaliz ation (PWR) approach is proven explicitly for the one-loop
self-energy correction (SE) of a bound electron state in the presence of
external perturbation potentials. No spurious correctio n terms to the
noncovariant PWR scheme are generated for Coulomb-type screening potentia ls
and for external magnetic fields. It is shown that in numerical calculations of
the SE with Coulombic perturbation potential spurious terms result from an
improper treatment of the unphysical high-energy contribution. A method for
performing the PWR utilizing the relativistic B-spline approach for the
construction of the Dirac spectrum in external magnetic fields is proposed.
This method is applied for calculating QED corrections to the bound-electron
-factor in H-like ions. Within the level of accuracy of about 0.1% no
spurious terms are generated in numerical calculations of the SE in magnetic
fields.Comment: 22 pages, LaTeX, 1 figur
Long-range forces between two excited mercury atoms and associative ionization
The long-range quadrupole-quadrupole () and leading dispersion
() interactions between all pairs of excited Hg() ,
, , and atoms are determined. The quadrupole moments are
calculated using the {\it ab initio} relativistic configuration-interaction
method coupled with many-body perturbation theory. The van der Waals
coefficients are approximated using previously calculated static
polarizabilities and expressions for the dispersion energy that are validated
with similar systems. The long-range interactions are critical for associative
ionization in thermal and cold collisions, and are found to be quite different
for different pairs of interacting states. Based on this knowledge and the
short-range parts of previously calculated potential curves, improved estimates
of the chemi-ionization cross sections are obtained.Comment: accepted in Phys Rev
Ab initio study of alanine polypeptide chains twisting
We have investigated the potential energy surfaces for alanine chains
consisting of three and six amino acids. For these molecules we have calculated
potential energy surfaces as a function of the Ramachandran angles Phi and Psi,
which are widely used for the characterization of the polypeptide chains. These
particular degrees of freedom are essential for the characterization of
proteins folding process. Calculations have been carried out within ab initio
theoretical framework based on the density functional theory and accounting for
all the electrons in the system. We have determined stable conformations and
calculated the energy barriers for transitions between them. Using a
thermodynamic approach, we have estimated the times of characteristic
transitions between these conformations. The results of our calculations have
been compared with those obtained by other theoretical methods and with the
available experimental data extracted from the Protein Data Base. This
comparison demonstrates a reasonable correspondence of the most prominent
minima on the calculated potential energy surfaces to the experimentally
measured angles Phi and Psi for alanine chains appearing in native proteins. We
have also investigated the influence of the secondary structure of polypeptide
chains on the formation of the potential energy landscape. This analysis has
been performed for the sheet and the helix conformations of chains of six amino
acids.Comment: 24 pages, 10 figure
'Raising the bar' : improving the standard and utility of weed and invasive plant research
Fil: Murray, Justine V.. Water for Healthy Country Flagship; AustraliaFil: Lehnhoff, Erik A.. Montana State University; Estados UnidosFil: Neve, Paul. University of Warwick; Reino UnidoFil: Poggio, Santiago Luis. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de AgronomÃa; ArgentinaFil: Webber, Bruce L.. CSIRO Ecosystems Sciences; Australia. The University of Western Australia; Australi
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