290 research outputs found
Program in C for studying characteristic properties of two-body interactions in the framework of spectral distribution theory
We present a program in C that employs spectral distribution theory for
studies of characteristic properties of a many-particle quantum-mechanical
system and the underlying few-body interaction. In particular, the program
focuses on two-body nuclear interactions given in a JT-coupled harmonic
oscillator basis and calculates correlation coefficients, a measure of
similarity of any two interactions, as well as Hilbert-Schmidt norms specifying
interaction strengths. An important feature of the program is its ability to
identify the monopole part (centroid) of a 2-body interaction, as well as its
'density-dependent' one-body and two-body part, thereby providing key
information on the evolution of shell gaps and binding energies for larger
nuclear systems. As additional features, we provide statistical measures for
'density-dependent' interactions, as well as a mechanism to express an
interaction in terms of two other interactions. This, in turn, allows one to
identify, e.g., established features of the nuclear interaction (such as
pairing correlations) within a general Hamiltonian. The program handles the
radial degeneracy for 'density-dependent' one-body interactions and together
with an efficient linked list data structure, facilitates studies of nuclear
interactions in large model spaces that go beyond valence-shell applications.Comment: 22 pages, 3 figure
Ab initio Folding Potentials for Nucleon-Nucleus Scattering based on NCSM One-Body Densities
Calculating microscopic optical potentials for elastic nucleon-nucleus
scattering has already led to large body of work in the past. For folding
first-order calculations the nucleon-nucleon (NN) interaction and the one-body
density of the nucleus were taken as input to rigorous calculations in a
spectator expansion of the multiple scattering series.
Based on the Watson expansion of the multiple scattering series we employ a
nonlocal translationally invariant nuclear density derived from a chiral
next-to-next-to-leading order (NNLO) and the very same interaction for
consistent full-folding calculation of the effective (optical) potential for
nucleon-nucleus scattering for light nuclei.
We calculate scattering observables, such as total, reaction, and
differential cross sections as well as the analyzing power and the
spin-rotation parameter, for elastic scattering of protons and neutrons from
He, He, C, and O, in the energy regime between 100 and
200~MeV projectile kinetic energy, and compare to available data.
Our calculations show that the effective nucleon-nucleus potential obtained
from the first-order term in the spectator expansion of the multiple scattering
expansion describes experiments very well to about 60 degrees in the
center-of-mass frame, which coincides roughly with the validity of the NNLO
chiral interaction used to calculate both the NN amplitudes and the one-body
nuclear density.Comment: 10 pages, 14 figures, 1 tabl
Ab initio symmetry-adapted emulator for studying emergent collectivity and clustering in nuclei
We discuss emulators from the ab initio symmetry-adapted no-core shell-model framework for studying the formation of alpha clustering and collective properties without effective charges. We present a new type of an emulator, one that utilizes the eigenvector continuation technique but is based on the use of symplectic symmetry considerations. This is achieved by using physically relevant degrees of freedom, namely, the symmetry-adapted basis, which exploits the almost perfect symplectic symmetry in nuclei. Specifically, we study excitation energies, point-proton root-mean-square radii, along with electric quadrupole moments and transitions for 6Li and 12C. We show that the set of parameterizations of the chiral potential used to train the emulators has no significant effect on predictions of dominant nuclear features, such as shape and the associated symplectic symmetry, along with cluster formation, but slightly varies details that affect collective quadrupole moments, asymptotic normalization coefficients, and alpha partial widths up to a factor of two. This makes these types of emulators important for further constraining the nuclear force for high-precision nuclear structure and reaction observables
Avalanche precursors of failure in hierarchical fuse networks
We study precursors of failure in hierarchical random fuse network models
which can be considered as idealizations of hierarchical (bio)materials where
fibrous assemblies are held together by multi-level (hierarchical) cross-links.
When such structures are loaded towards failure, the patterns of precursory
avalanche activity exhibit generic scale invariance: Irrespective of load,
precursor activity is characterized by power-law avalanche size distributions
without apparent cut-off, with power-law exponents that decrease continuously
with increasing load. This failure behavior and the ensuing super-rough crack
morphology differ significantly from the findings in non-hierarchical
structures
The Heine-Stieltjes correspondence and the polynomial approach to the standard pairing problem
A new approach for solving the Bethe ansatz (Gaudin-Richardson) equations of
the standard pairing problem is established based on the Heine-Stieltjes
correspondence. For pairs of valence nucleons on different
single-particle levels, it is found that solutions of the Bethe ansatz
equations can be obtained from one (k+1)x(k+1) and one (n-1)x(k+1) matrices,
which are associated with the extended Heine-Stieltjes and Van Vleck
polynomials, respectively. Since the coefficients in these polynomials are free
from divergence with variations in contrast to the original Bethe ansatz
equations, the approach thus provides with a new efficient and systematic way
to solve the problem, which, by extension, can also be used to solve a large
class of Gaudin-type quantum many-body problems and to establish a new
efficient angular momentum projection method for multi-particle systems.Comment: ReVTeX, 4 pages, no figur
Synergistic regulation of cerebellar Purkinje neuron development by laminin epitopes and collagen on an artificial hybrid matrix construct
Cataloged from PDF version of article.The extracellular matrix (ECM) creates a dynamic environment around the cells in the developing central nervous system, providing them with the necessary biochemical and biophysical signals. Although the functions of many ECM molecules in neuronal development have been individually studied in detail, the combinatorial effects of multiple ECM components are not well characterized. Here we demonstrate that the expression of collagen and laminin-1 (lam-1) are spatially and temporally correlated during embryonic and post-natal development of the cerebellum. These changes in ECM distribution correspond to specific stages of Purkinje neuron (PC) migration, somatic monolayer formation and polarization. To clarify the respective roles of these ECM molecules on PC development, we cultured cerebellar neurons on a hybrid matrix comprised of collagen and a synthetic peptide amphiphile nanofiber bearing a potent lam-1 derived bioactive IKVAV peptide epitope. By systematically varying the concentration and ratio of collagen and the laminin epitope in the matrix, we could demonstrate a synergistic relationship between these two ECM components in controlling multiple aspects of PC maturation. An optimal ratio of collagen and IKVAV in the matrix was found to promote maximal PC survival and dendrite growth, while dendrite penetration into the matrix was enhanced by a high IKVAV to collagen ratio. In addition, the laminin epitope was found to guide PC axon development. By combining our observations in vivo and in vitro, we propose a model of PC development where the synergistic effects of collagen and lam-1 play a key role in migration, polarization and morphological maturation of PCs. This journal is © the Partner Organisations 2014
Ab initio Folding Potentials for Proton-Nucleus Scattering with NCSM Nonlocal One-Body Densities
Based on the spectator expansion of the multiple scattering series we employ a nonlocal translationally invariant nuclear density derived from a chiral next-to-next-to-leading order (NNLO) and the very same interaction for consistent full-folding calculations of the effective (optical) potential for nucleon-nucleus scattering for light nuclei
Electromagnetic Excitations and Responses in Nuclei from First Principles
We discuss the role of clustering on monopole, dipole, and quadrupole
excitations in nuclei in the framework of the ab initio symmetry-adapted
no-core shell model (SA-NCSM). The SA-NCSM starts from nucleon-nucleon
potentials and, by exploring symmetries known to dominate the nuclear dynamics,
can reach nuclei up through the calcium region by accommodating ultra-large
model spaces critical to descriptions of clustering and collectivity. The
results are based on calculations of electromagnetic sum rules and discretized
responses using the Lanczos algorithm, that can be used to determine response
functions, and for 4He are benchmarked against exact solutions of the
hyperspherical harmonics method. In particular, we focus on He, Be, and O
isotopes, including giant resonances and monopole sum rules.Comment: 6 pages, 4 figures, Proceedings of the Fourth International Workshop
on State of the Art in Nuclear Cluster Physics, Galveston, TX, USA, May
13-18, 201
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