We present the framework for the ab initio no-core nuclear shell model and apply it to obtain properties of {sup 12}C. We derive two-body effective interactions microscopically for specific model ...spaces from the realistic CD-Bonn and the Argonne V8' nucleon-nucleon (NN) potentials. We then evaluate binding energies, excitation spectra, radii, and electromagnetic transitions in the 0{Dirac_h}{Omega}, 2{Dirac_h}{Omega}, and 4{Dirac_h}{Omega} model spaces for the positive-parity states and the 1{Dirac_h}{Omega}, 3{Dirac_h}{Omega}, and 5{Dirac_h}{Omega} model spaces for the negative-parity states. Dependence on the model-space size, on the harmonic-oscillator frequency, and on the type of the NN potential, used for the effective interaction derivation, are studied. In addition, electromagnetic and weak neutral elastic charge form factors are calculated in the impulse approximation. Sensitivity of the form-factor ratios to the strangeness one-body form-factor parameters and to the influence of isospin-symmetry violation is evaluated and discussed. Agreement between theory and experiment is favorable for many observables, while others require yet larger model spaces and/or three-body forces. The limitations of the present results are easily understood by virtue of the trends established and previous phenomenological results.
We report the microscopic origins of the anomalously suppressed beta decay of 14C to 14N using the ab initio no-core shell model (NCSM) with the Hamiltonian from chiral effective field theory (EFT) ...including three-nucleon force (3NF) terms. The 3NF induces unexpectedly large cancellations within the p-shell between contributions to beta decay, which reduce the traditionally large contributions from the NN interactions by an order of magnitude, leading to the long lifetime of 14C.
We discuss some of the challenges that future nuclear modeling may face in order to improve the description of the nuclear structure. One challenge is related to the need for A-body nuclear ...interactions justified by various contemporary nuclear physics studies. Another challenge is related to the discrepancy in the NNN contact interaction parameters for 3He and 3H that suggests the need for accurate proton and neutron masses in the future precision calculations. MSC2010 Classification: 17B81 Applications to physics, 17B80 Applications to integrable systems, 81R12 Relations with integrable systems, 81V70 Many-body theory, 81V35 Nuclear physics, 81U15 Exactly and quasi-solvable systems, 82B23 Exactly solvable models; Bethe ansatz.
J.Phys.G36:085103,2009 We report the first no-core shell model results for $^{48}Ca$, $^{48}Sc$ and
$^{48}Ti$ with derived and modified two-body Hamiltonians. We use an oscillator
basis with a ...limited $\hbar\Omega$ range around $45/A^{1/3}-25/A^{2/3} = 10.5
MeV$ and a limited model space up to $1\hbar\Omega$. No single-particle
energies are used. We find that the charge dependence of the bulk binding
energy of eight A=48 nuclei is reasonably described with an effective
Hamiltonian derived from the CD-Bonn interaction while there is an overall
underbinding by about 0.4 MeV/nucleon. However, the resulting spectra exhibit
deficiencies that are anticipated due to: (1) basis space limitations and/or
the absence of effective many-body interactions; and, (2) the absence of
genuine three-nucleon interactions. We then introduce additive
isospin-dependent central terms plus a tensor force to our Hamiltonian and
achieve accurate binding energies and reasonable spectra for all three nuclei.
The resulting no-core shell model opens a path for applications to the
double-beta ($\beta\beta$) decay process.
This contribution reviews a number of applications of the ab initio no-core shell model (NCSM) within nuclear physics and beyond. We will highlight a nuclear-structure study of the A = 12 isobar ...using a chiral NN + 3NF interaction. In the spirit of this workshop we will also mention the new development of the NCSM formalism to describe open channels and to approach the problem of nuclear reactions. Finally, we will illustrate the universality of the many-body problem by presenting the recent adaptation of the NCSM effective-interaction approach to study the many-boson problem in an external trapping potential with short-range interactions.
A simple methodology was used for calculating the equivalent strain values during forming the sample alternately in two mutually perpendicular directions. This method reflects an unexpected material ...flow out of the nominal deformation zone when forming on the MAXStrain II device. Thus it was possible to perform two temperature variants of the simulation of continuous rolling and cooling of a long product made of steel containing 0.17% C and 0.80% Mn. Increasing the finishing temperature from 900°C to 950°C and decreasing the cooling rate from 10°C/s to 5°C/s led to a decrease in the content of acicular ferrite and bainite and an increase in the mean grain size of proeutectoid ferrite from about 8 µm to 14 µm. The result was a change in the hardness of the material by 15%.
Barrier discharges (BDs) can be operated in so-called diffuse modes. In contrast to the usual filamentary regime, which is characterized by a large number of individual microdischarges, the plasma of ...a diffuse BD covers the entire electrode area uniformly. Depending on the operation conditions (gas composition, amplitude and frequency of applied voltage), different diffuse modes can be investigated, namely, the atmospheric pressure Townsend discharge (APTD) and the atmospheric pressure glow discharge (APGD)). The subject of the paper is the study of the transition between APTD and APGD as well as between diffuse and filamentary BD modes. Therefore, BDs were studied in the gas mixtures N@d2/H@d2, N@d2/He, N@d2/Ne and N@d2/Ar. It is shown that APGD in the noble gases helium and neon is formed due to high ionization rate at a comparatively low electric field, assisted by indirect ionization mechanisms involving metastable states of inert gases and nitrogen impurities, while the existence of APTD is coupled to the existence of metastable states of molecular nitrogen. Furthermore, a similar memory effect of residual surface charges on the dielectric barriers as described for filamentary BDs was observed in diffuse BDs.
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