12,349 research outputs found
Microscopic Restoration of Proton-Neutron Mixed Symmetry in Weakly Collective Nuclei
Starting from the microscopic low-momentum nucleon-nucleon interaction V{low
k}, we present the first systematic shell model study of magnetic moments and
magnetic dipole transition strengths of the basic low-energy one-quadrupole
phonon excitations in nearly-spherical nuclei. Studying in particular the
even-even N=52 isotones from 92Zr to 100Cd, we find the predicted evolution of
the predominantly proton-neutron non-symmetric state reveals a restoration of
collective proton-neutron mixed-symmetry structure near mid-shell. This
provides the first explanation for the existence of pronounced collective
mixed-symmetry structures in weakly-collective nuclei.Comment: 5 Pages, 3 figure
Shell model description of the 14C dating beta decay with Brown-Rho-scaled NN interactions
We present shell model calculations for the beta-decay of the 14C ground
state to the 14N ground state, treating the states of the A=14 multiplet as two
0p holes in an 16O core. We employ low-momentum nucleon-nucleon (NN)
interactions derived from the realistic Bonn-B potential and find that the
Gamow-Teller matrix element is too large to describe the known lifetime. By
using a modified version of this potential that incorporates the effects of
Brown-Rho scaling medium modifications, we find that the GT matrix element
vanishes for a nuclear density around 85% that of nuclear matter. We find that
the splitting between the (J,T)=(1+,0) and (J,T)=(0+,1) states in 14N is
improved using the medium-modified Bonn-B potential and that the transition
strengths from excited states of 14C to the 14N ground state are compatible
with recent experiments.Comment: 4 pages, 5 figures Updated to include referee comments/suggestion
Dynamic Elasticities and Flexibilities in a Quarterly Model of the U.S. Pork Sector
It has long been recognized that usual elasticity and flexibility concepts are of limited value in a multi-equation setting. This is because the response caused by a change in an exogenous variable will have feedback effects as the system obtains a new equilibrium. Consequently, it is necessary to examine total response measures in a system framework. In spite of this recognition there has been no known attempt to examine the structural implications of an econometric model by using total elasticities and flexibilities. This paper extends the results from Cavas, Hassan, and Johnson (1981) to obtain total elasticity and flexibility measures in a general dynamic model, using a quarterly model of the U.S. pork sector. The results indicate that supply elasticities are generally smaller than those reported previously
Rapid, Precise, and High-Sensitivity Acquisition of Paleomagnetic and Rock-Magnetic Data: Development of a Low-Noise Automatic Sample Changing System for Superconducting Rock Magnetometers
Among Earth sciences, paleomagnetism is particularly linked to the statistics of large sample sets as a matter of historical development and logistical necessity. Because the geomagnetic field varies over timescales relevant to sedimentary deposition and igneous intrusion, while the fidelity of recorded magnetization is modulated by original properties of rock units and by alteration histories, "ideal" paleomagnetic results measure remanent magnetizations of hundreds of samples at dozens of progressive demagnetization levels, accompanied by tests of magnetic composition on representative sister specimens.
We present an inexpensive, open source system for automating paleomagnetic and rock magnetic measurements. Using vacuum pick-and-place technology and a quartz-glass sample holder, the system can in one hour measure remanent magnetizations, as weak as a few pAm2, of ~30 specimens in two vertical orientations with measurement errors comparable to those of the best manual systems. The system reduces the number of manual manipulations required per specimen ~8 fold
Aggregating available soil water holding capacity data for crop yield models
The total amount of water available to plants that is held against gravity in a soil is usually estimated as the amount present at -0.03 MPa average water potential minus the amount present at -1.5 MPa water potential. This value, designated available water-holding capacity (AWHC), is a very important soil characteristic that is strongly and positively correlated to the inherent productivity of soils. In various applications, including assessing soil moisture status over large areas, it is necessary to group soil types or series as to their productivity. Current methods to classify AWHC of soils consider only total capacity of soil profiles and thus may group together soils which differ greatly in AWHC as a function of depth in the profile. A general approach for evaluating quantitatively the multidimensional nature of AWHC in soils is described. Data for 902 soil profiles, representing 184 soil series, in Indiana were obtained from the Soil Characterization Laboratory at Purdue University. The AWHC for each of ten 150-mm layers in each soil was established, based on soil texture and parent material. A multivariate clustering procedure was used to classify each soil profile into one of 4, 8, or 12 classes based upon ten-dimensional AWHC values. The optimum number of classes depends on the range of AWHC in the population of oil profiles analyzed and on the sensitivity of a crop to differences in distribution of water within the soil profile
Structure of the lightest tin isotopes
We link the structure of nuclei around Sn, the heaviest doubly magic
nucleus with equal neutron and proton numbers (), to nucleon-nucleon
() and three-nucleon () forces constrained by data of few-nucleon
systems. Our results indicate that Sn is doubly magic, and we predict
its quadrupole collectivity. We present precise computations of Sn
based on three-particle--two-hole excitations of Sn, and reproduce the
small splitting between the lowest and states. Our
results are consistent with the sparse available data.Comment: 8 pages, 4 figure
Chiral three-nucleon forces and pairing in nuclei
We present the first study of pairing in nuclei including three-nucleon
forces. We perform systematic calculations of the odd-even mass staggering
generated using a microscopic pairing interaction at first order in chiral
low-momentum interactions. Significant repulsive contributions from the leading
chiral three-nucleon forces are found. Two- and three-nucleon interactions
combined account for approximately 70% of the experimental pairing gaps, which
leaves room for self-energy and induced interaction effects that are expected
to be overall attractive in nuclei.Comment: 4 pages, 3 figure
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