5,067 research outputs found
Gamma ray spectrometry of LDEF samples at SRL
A total of 31 samples from the Long Duration Exposure Facility (LDEF), including materials of aluminum, vanadium, and steel trunnions were analyzed by ultra-low-level gamma spectrometry. The study quantified particle induced activations of Na-22, Sc-46, Cr-51, Mn-54, Co-56, Co-57, Co-58, and Co-60. The samples of trunnion sections exhibited increasing activity toward the outer end of the trunnion and decreasing activity toward its radial center. The trunnion sections did not include end pieces, which were reported to collect noticeable Be-7 on their leading surfaces. No significant Be-7 was detected in the samples analyzed
Two-Variable Wilson Polynomials and the Generic Superintegrable System on the 3-Sphere
We show that the symmetry operators for the quantum superintegrable system on
the 3-sphere with generic 4-parameter potential form a closed quadratic algebra
with 6 linearly independent generators that closes at order 6 (as differential
operators). Further there is an algebraic relation at order 8 expressing the
fact that there are only 5 algebraically independent generators. We work out
the details of modeling physically relevant irreducible representations of the
quadratic algebra in terms of divided difference operators in two variables. We
determine several ON bases for this model including spherical and cylindrical
bases. These bases are expressed in terms of two variable Wilson and Racah
polynomials with arbitrary parameters, as defined by Tratnik. The generators
for the quadratic algebra are expressed in terms of recurrence operators for
the one-variable Wilson polynomials. The quadratic algebra structure breaks the
degeneracy of the space of these polynomials. In an earlier paper the authors
found a similar characterization of one variable Wilson and Racah polynomials
in terms of irreducible representations of the quadratic algebra for the
quantum superintegrable system on the 2-sphere with generic 3-parameter
potential. This indicates a general relationship between 2nd order
superintegrable systems and discrete orthogonal polynomials
Generalized Modeling Approaches to Risk Adjustment of Skewed Outcomes Data
There are two broad classes of models used to address the econometric problems caused by skewness in data commonly encountered in health care applications: (1) transformation to deal with skewness (e.g., OLS on ln(y)); and (2) alternative weighting approaches based on exponential conditional models (ECM) and generalized linear model (GLM) approaches. In this paper, we encompass these two classes of models using the three parameter generalized gamma (GGM) distribution, which includes several of the standard alternatives as special cases OLS with a normal error, OLS for the log normal, the standard gamma and exponential with a log link, and the Weibull. Using simulation methods, we find the tests of identifying distributions to be robust. The GGM also provides a potentially more robust alternative estimator to the standard alternatives. An example using inpatient expenditures is also analyzed.
Separation of variables and the XXZ Gaudin magnet
In this work we generalise previous results connecting (rational) Gaudin
magnet models and classical separation of variables. It is shown that the
connection persists for the case of linear r-matrix algebra which corresponds
to the trigonometric 4x4 r-matrix (of the XXZ type). We comment also on the
corresponding problem for the elliptic (XYZ) r-matrix. A prescription for
obtaining integrable systems associated with multiple poles of an L-operator is
given.Comment: 11 pages, AMS-Te
- …