13,392 research outputs found
Gamow-Teller GT+ distributions in nuclei with mass A=90-97
We investigate the Gamow-Teller strength distributions in the
electron-capture direction in nuclei having mass A=90-97, assuming a 88Sr core
and using a realistic interaction that reasonably reproduces nuclear
spectroscopy for a wide range of nuclei in the region as well as experimental
data on Gamow-Teller strength distributions. We discuss the systematics of the
distributions and their centroids. We also predict the strength distributions
for several nuclei involving stable isotopes that should be experimentally
accessible for one-particle exchange reactions in the near future.Comment: 9 pages, 10 figures (from 17 eps files), to be submitted to
Phys.Rev.C; corrected typos, minor language change
Theory of Linear Spin Wave Emission from a Bloch Domain Wall
We report an analytical theory of linear emission of exchange spin waves from
a Bloch domain wall, excited by a uniform microwave magnetic field. The problem
is reduced to a one-dimensional Schr\"odinger-like equation with a
P\"oschl-Teller potential and a driving term of the same profile. The emission
of plane spin waves is observed at excitation frequencies above a threshold
value, as a result of a linear process. The height-to-width aspect ratio of the
P\"oschl-Teller profile for a domain wall is found to correspond to a local
maximum of the emission efficiency. Furthermore, for a tailored P\"oschl-Teller
potential with a variable aspect ratio, particular values of the latter can
lead to enhanced or even completely suppressed emission.Comment: added ancillary file
Effective interactions and shell model studies of heavy tin isotopes
We present results from large-scale shell-model calculations of even and odd
tin isotopes from 134Sn to 142}Sn with a shell-model space defined by the
1f7/2,2p3/2,0h9/2,2p1/2,1f5/2,0i13/2 single-particle orbits. An effective
two-body interaction based on modern nucleon-nucleon interactions is employed.
The shell-model results are in turn analyzed for their pairing content using a
generalized seniority approach. Our results indicate that a pairing-model
picture captures a great deal of the structure and the correlations of the
lowest lying states for even and odd isotopes.Comment: 7 pages, revtex latex style, submitted to PR
TDRSS momentum unload planning
A knowledge-based system is described which monitors TDRSS telemetry for problems in the momentum unload procedure. The system displays TDRSS telemetry and commands in real time via X-windows. The system constructs a momentum unload plan which agrees with the preferences of the attitude control specialists and the momentum growth characteristics of the individual spacecraft. During the execution of the plan, the system monitors the progress of the procedure and watches for unexpected problems
Excess nitrogen leaching and C/N decline in the Tillingbourne catchment, southern England: INCA process modelling for current and historic time series
Measurements of nitrate deposition and streamwater chemistry in the Tillingbourne Catchment, in Southern England, made in 1979-1982 and 1999-2001 show a 216% increase in Nitrogen leaching despite a reduction in N inputs. Both the historical and current data sets have been modelled using the Integrated Nitrogen Model in Catchments (INCA). The process-based model is shown to reproduce the historical patterns of N release from the catchment. However, modelling the increased leaching of N during recent years required an increase of the mineralisation control parameter in the model, suggesting enhanced mineralisation rates. Comparing historic and current soils data for C/N ratios shows that there has been a reduction in C/N from 38 to 26% in the humus layer and a reduction from 33 to 26% in the mineral soil horizon. This significant fall in C/N is consistent with the increase in N saturation in the H and Ah horizons of the major catchment soil.</p> <p style='line-height: 20px;'><b>Keywords: </b>acid deposition, recovery, nitrogen, Carbon-Nitrogen ratios, Tillingbourne, Thames, catchment studies, nutrient leaching, modelling</p
A QTL for osteoporosis detected in an F2 population derived from White Leghorn chicken lines divergently selected for bone index
Osteoporosis, resulting from progressive loss of structural bone during the period of egg-laying in hens, is associated with an increased susceptibility to bone breakage. To study the genetic basis of bone strength, an F cross was produced from lines of hens that had been divergently selected for bone index from a commercial pedigreed White Leghorn population. Quantitative trait loci (QTL) affecting the bone index and component traits of the index (tibiotarsal and humeral strength and keel radiographic density) were mapped using phenotypic data from 372 F individuals in 32 F families. Genotypes for 136 microsatellite markers in 27 linkage groups covering ∼80% of the genome were analysed for association with phenotypes using within-family regression analyses. There was one significant QTL on chromosome 1 for bone index and the component traits of tibiotarsal and humeral breaking strength. Additive effects for tibiotarsal breaking strength represented 34% of the trait standard deviation and 7.6% of the phenotypic variance of the trait. These QTL for bone quality in poultry are directly relevant to commercial populations
Primitive Words, Free Factors and Measure Preservation
Let F_k be the free group on k generators. A word w \in F_k is called
primitive if it belongs to some basis of F_k. We investigate two criteria for
primitivity, and consider more generally, subgroups of F_k which are free
factors.
The first criterion is graph-theoretic and uses Stallings core graphs: given
subgroups of finite rank H \le J \le F_k we present a simple procedure to
determine whether H is a free factor of J. This yields, in particular, a
procedure to determine whether a given element in F_k is primitive.
Again let w \in F_k and consider the word map w:G x G x ... x G \to G (from
the direct product of k copies of G to G), where G is an arbitrary finite
group. We call w measure preserving if given uniform measure on G x G x ... x
G, w induces uniform measure on G (for every finite G). This is the second
criterion we investigate: it is not hard to see that primitivity implies
measure preservation and it was conjectured that the two properties are
equivalent. Our combinatorial approach to primitivity allows us to make
progress on this problem and in particular prove the conjecture for k=2.
It was asked whether the primitive elements of F_k form a closed set in the
profinite topology of free groups. Our results provide a positive answer for
F_2.Comment: This is a unified version of two manuscripts: "On Primitive words I:
A New Algorithm", and "On Primitive Words II: Measure Preservation". 42
pages, 14 figures. Some parts of the paper reorganized towards publication in
the Israel J. of Mat
PMH57 SECOND GENERATION ANTIPSYCHOTICS AND HOSPITALIZATION IN BIPOLAR DISORDER: A CLAIMS DATA ANALYSIS
Gamow-Teller transitions and deformation in the proton-neutron random phase approximation
We investigate reliability of Gamow-Teller transition strengths computed in
the proton-neutron random phase approximation, comparing with exact results
from diagonalization in full shell-model spaces. By allowing the
Hartree-Fock state to be deformed, we obtain good results for a wide variety of
nuclides, even though we do not project onto good angular momentum. We suggest
that deformation is as important or more so than pairing for Gamow-Teller
transitions.Comment: 8 pages, 5 figures; added references, clarified discussion with
regards to stabilit
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