467 research outputs found
Comparison of potential models of nucleus-nucleus bremsstrahlung
At low photon energies, the potential models of nucleus-nucleus
bremsstrahlung are based on electric transition multipole operators, which are
derived either only from the nuclear current or only from the charge density by
making the long-wavelength approximation and using the Siegert theorem. In the
latter case, the bremsstrahlung matrix elements are divergent and some
regularization techniques are used to obtain finite values for the
bremsstrahlung cross sections. From an extension of the Siegert theorem, which
is not based on the long-wavelength approximation, a new potential model of
nucleus-nucleus bremsstrahlung is developed. Only convergent integrals are
included in this approach. Formal links between bremsstrahlung cross sections
obtained in these different models are made. Furthermore, three different ways
to calculate the regularized matrix elements are discussed and criticized. Some
prescriptions for a proper implementation of the regularization are deduced. A
numerical comparison between the different models is done by applying them to
the bremsstrahlung.Comment: submitted to Phys. Rev.
Transcriptome-based reconstructions from the murine knockout suggest involvement of the urate transporter, URAT1 (slc22a12), in novel metabolic pathways.
URAT1 (slc22a12) was identified as the transporter responsible for renal reabsorption of the medically important compound, uric acid. However, subsequent studies have indicated that other transporters make contributions to this process, and that URAT1 transports other organic anions besides urate (including several in common with the closely related multi-specific renal organic anion transporters, OAT1 (slc22a6) and OAT3 (slc22a8)). These findings raise the possibility that urate transport is not the sole physiological function of URAT1. We previously characterized mice null for the murine ortholog of URAT1 (mURAT1; previously cloned as RST), finding a relatively modest decrement in urate reabsorptive capacity. Nevertheless, there were shifts in the plasma and urinary concentrations of multiple small molecules, suggesting significant metabolic changes in the knockouts. Although these molecules remain unidentified, here we have computationally delineated the biochemical networks consistent with transcriptomic data from the null mice. These analyses suggest alterations in the handling of not only urate but also other putative URAT1 substrates comprising intermediates in nucleotide, carbohydrate, and steroid metabolism. Moreover, the analyses indicate changes in multiple other pathways, including those relating to the metabolism of glycosaminoglycans, methionine, and coenzyme A, possibly reflecting downstream effects of URAT1 loss. Taken together with the available substrate and metabolomic data for the other OATs, our findings suggest that the transport and biochemical functions of URAT1 overlap those of OAT1 and OAT3, and could contribute to our understanding of the relationship between uric acid and the various metabolic disorders to which it has been linked
Relativistic semiempirical-core-potential calculations in Ca, Sr, and Ba ions on Lagrange meshes
Relativistic atomic structure calculations are carried out in
alkaline-earth-metal ions using a semiempirical-core-potential approach. The
systems are partitioned into frozen-core electrons and an active valence
electron. The core orbitals are defined by a Dirac-Hartree-Fock calculation
using the grasp2k package. The valence electron is described by a Dirac-like
Hamiltonian involving a core-polarization potential to simulate the
core-valence electron correlation. The associated equation is solved with the
Lagrange-mesh method, which is an approximate variational approach having the
form of a mesh calculation because of the use of a Gauss quadrature to
calculate matrix elements. Properties involving the low-lying metastable
states of Ca, Sr, and Ba are studied, such as
polarizabilities, one- and two-photon decay rates, and lifetimes. Good
agreement is found with other theory and observation, which is promising for
further applications in alkali-like systems.Comment: 15 pages, accepted for publication in Phys. Rev.
Towards an ab initio description of the light-nuclei radiative captures
The and astrophysical factors are evaluated at low
collision energies (less than 2.5 MeV in the centre-of-mass frame) within the
no-core shell model with continuum approach using a renormalized chiral
nucleon-nucleon interaction.Comment: 4 pages, submitted as a proceeding of the 21st International
Conference on Few-Body Problems in Physic
and astrophysical factors from the no-core shell model with continuum
The and astrophysical factors are calculated within
the no-core shell model with continuum using a renormalized chiral
nucleon-nucleon interaction. The
astrophysical factors agree reasonably well with the experimental data
while the ones are overestimated. The
seven-nucleon bound and resonance states and the elastic scattering are also studied and compared with experiment. The
low-lying resonance properties are rather well reproduced by our approach. At
low energies, the -wave phase shift, which is non-resonant, is
overestimated.Comment: 8 pages, submitted to Phys. Lett.
Exchange effects in nucleus-nucleus reactions
We present a scattering model for nuclei with similar masses. In this
three-body model, the projectile has a core+valence structure, whereas the
target is identical to the core nucleus. The three-body wave functions must be
symmetrized for the exchange of the cores. This property gives rise to
non-local potentials, which are computed without approximation. The present
model is an extension of the Continuum Discretized Coupled Channel (CDCC)
formalism, with an additional treatment of core exchange. We solve the
coupled-channel system, including non-local terms, by the -matrix method
using Lagrange functions. This model is applied to the C,
C and C systems. Experimental
scattering cross sections are fairly well reproduced without any parameter
fitting. The backward-angle enhancement of the elastic cross sections is due to
the non-local potential. We discuss in more detail the various non-local
contributions and present effective local potentials.Comment: 13 pages, 11 figures, submitted to Physical Review
- …