768 research outputs found
Condensates of p-wave pairs are exact solutions for rotating two-component Bose gases
We derive exact analytical results for the wave functions and energies of
harmonically trapped two-component Bose-Einstein condensates with weakly
repulsive interactions under rotation. The isospin symmetric wave functions are
universal and do not depend on the matrix elements of the two-body interaction.
The comparison with the results from numerical diagonalization shows that the
ground state and low-lying excitations consists of condensates of p-wave pairs
for repulsive contact interactions, Coulomb interactions, and the repulsive
interactions between aligned dipoles.Comment: 4 pages, 1 figure; revised version explains exact solutions in terms
of isospin symmetry and Hund's rul
Density-functional theory for fermions in the unitary regime
In the unitary regime, fermions interact strongly via two-body potentials
that exhibit a zero range and a (negative) infinite scattering length. The
energy density is proportional to the free Fermi gas with a proportionality
constant . We use a simple density functional parametrized by an effective
mass and the universal constant , and employ Kohn-Sham density-functional
theory to obtain the parameters from fit to one exactly solvable two-body
problem. This yields and a rather large effective mass. Our approach
is checked by similar Kohn-Sham calculations for the exactly solvable Calogero
model.Comment: 5 pages, 2 figure
Medium-mass nuclei from chiral nucleon-nucleon interactions
We compute the binding energies, radii, and densities for selected
medium-mass nuclei within coupled-cluster theory and employ the "bare" chiral
nucleon-nucleon interaction at order N3LO. We find rather well-converged
results in model spaces consisting of 15 oscillator shells, and the doubly
magic nuclei 40Ca, 48Ca, and the exotic 48Ni are underbound by about 1 MeV per
nucleon within the CCSD approximation. The binding-energy difference between
the mirror nuclei 48Ca and 48Ni is close to theoretical mass table evaluations.
Our computation of the one-body density matrices and the corresponding natural
orbitals and occupation numbers provides a first step to a microscopic
foundation of the nuclear shell model.Comment: 5 pages, 5 figure
Complex coupled-cluster approach to an ab-initio description of open quantum systems
We develop ab-initio coupled-cluster theory to describe resonant and weakly
bound states along the neutron drip line. We compute the ground states of the
helium chain 3-10He within coupled-cluster theory in singles and doubles (CCSD)
approximation. We employ a spherical Gamow-Hartree-Fock basis generated from
the low-momentum N3LO nucleon-nucleon interaction. This basis treats bound,
resonant, and continuum states on equal footing, and is therefore optimal for
the description of properties of drip line nuclei where continuum features play
an essential role. Within this formalism, we present an ab-initio calculation
of energies and decay widths of unstable nuclei starting from realistic
interactions.Comment: 4 pages, revtex
Comment on "Ab Initio study of 40-Ca with an importance-truncated no-core shell model"
In a recent Letter [Phys. Rev. Lett. 99, 092501 (2007)], Roth and Navratil
present an importance-truncation scheme for the no-core shell model. The
authors claim that their truncation scheme leads to converged results for the
ground state of 40-Ca. We believe that this conclusion cannot be drawn from the
results presented in the Letter. Furthermore, the claimed convergence is at
variance with expectations of many-body theory. In particular, coupled-cluster
calculations indicate that a significant fraction of the correlation energy is
missing.Comment: 1 page, comment on arXiv:0705.4069 (PRL 99, 092501 (2007)
Bremsstrahlung Spectrum in alpha Decay
Using our previous approach to electromagnetic emission during tunneling, an
explicit, essentially classical, formula describing the bremsstrahlung spectrum
in alpha decay is derived. The role of tunneling motion in photon emission is
discussed. The shape of the spectrum is a universal function of the ratio Eg/Eo
, where Eg is the photon energy and Eo is a characteristic energy depending
only on the nuclear charge and the energy of the alpha particle.Comment: 8 pages, 3 figure
Enzymatic activity of the Arabidopsis sulfurtransferase resides in the C-terminal domain but is boosted by the N-terminal domain and the linker peptide in the full-length enzyme
Sulfurtransferases/rhodaneses are a group of enzymes widely distributed in plants, animals, and bacteria that catalyze the transfer of sulfur from a donor molecule to a thiophilic acceptor substrate. Sulfurtransferases (STs) consist of two globular domains of nearly identical size and conformation connected by a short linker sequence. In plant STs this linker sequence is exceptionally longer than in sequences from other species. The Arabidopsis ST1 protein (AJ131404) contains five cysteine residues: one residue is universally conserved in all STs and considered to be catalytically essential; a second one, closely located in the primary sequence, is conserved only in sequences from eukaryotic species. Of the remaining three cysteine residues two are conserved in the so far known plant STs and one is unique to the Arabidopsis ST1. The aim of our study was to investigate the role of the twodomain structure, of the unique plant linker sequence and of each cysteine residue. The N and C-terminal domains of the Arabidopsis ST1, the fulllength protein with a shortened linker sequence and several pointmutated proteins were overexpressed in E. coli, purified and used for enzyme activity measurements. The C-terminal domain itself displayed ST activity which could be increased by adding the separately prepared N-terminal domain. The activity of an ST1 derivative with a shortened linker sequence was reduced by more than 60% of the wild-type activity, probably because of a drastically reduced protein stability. The replacement of each cysteine residue resulted in mutant forms which differed significantly in their stability, in the specific ST activities, and in their kinetic parameters which were determined for 3-mercaptopyruvate as well as thiosulfate as sulfur substrates: mutation of the putative active site cysteine (C332) essentially abolished activity; for C339 a crucial role at least for the turnover of thiosulfate could be identified.DFG/PA/764/1-1DFG/PA/764/1-2Fonds der Chemischen Industri
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