10,574 research outputs found
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
Dynamical Spin Response Functions for Heisenberg Ladders
We present the results of a numerical study of the 2 by L spin 1/2 Heisenberg
ladder. Ground state energies and the singlet-triplet energy gaps for L =
(4-14) and equal rung and leg interaction strengths were obtained in a Lanczos
calculation and checked against earlier calculations by Barnes et al. (even L
up to 12). A related moments technique is then employed to evaluate the
dynamical spin response for L=12 and a range of rung to leg interaction
strength ratios (0 - 5). We comment on two issues, the need for
reorthogonalization and the rate of convergence, that affect the numerical
utility of the moments treatment of response functions.Comment: Revtex, 3 figure
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
Expression of beta human chorionic gonadotrophin by non-trophoblastic non-endocrine 'normal' and malignant epithelial cells.
Expression of hCG and its free subunits by non-trophoblastic tumours is well recognised. Previously we reported hCG secretion by normal and malignant bladder epithelial cells in vitro. Here we examined culture medium from 83 different cell lines derived mainly from common epithelial tumours. Thirty-two of the cell lines were found to secrete hCG-like material into their culture media. Partial immunochemical characterisation showed that of these only choriocarcinoma and fetal tissue cell lines produced intact hCG and alpha subunit. The remaining 28 hCG-expressing epithelial cell lines, which are of mucosal origin, only secreted free beta subunit. Expression of free beta hCG by non-trophoblastic nonendocrine cells would appear to be especially characteristic of mucosal epithelia from the genitourinary and oral/respiratory tracts. Furthermore, this phenomenon may be characteristic of epithelium with transitional and/or squamous cell-like properties
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
Neutron elastic scattering on calcium isotopes from chiral nuclear optical potentials
We formulate microscopic neutron-nucleus optical potentials from many-body
perturbation theory based on chiral two- and three-body forces. The neutron
self energy is first calculated in homogeneous matter to second order in
perturbation theory, which gives the central real and imaginary terms of the
optical potential. The real spin-orbit term is calculated separately from the
density matrix expansion using the same chiral interaction as in the self
energy. Finally, the full neutron-nucleus optical potential is derived within
the improved local density approximation utilizing mean field models consistent
with the chiral nuclear force employed. We compare the results of the
microscopic calculations to phenomenological models and experimental data up to
projectile energies of MeV. Experimental elastic differential
scattering cross sections and vector analyzing powers are generally well
reproduced by the chiral optical potential, but we find that total cross
sections are overestimated at high energies
- …