172,706 research outputs found
An Extended Isgur-Paton Model: Agreement With the Lattice?
The spectrum for the pure gauge sector is calculated for an extended
Isgur-Paton model in 2+1 and 3+1 dimensions and compared to recent lattice
calculations of the glueball spectrum. The IP model is extended by inclusion of
a rigidity (curvature) term and, in D=2+1, mixing through a higer topological
contribution. For a choice of parameterizations, near quantitative agreement is
found for SU(3) in D=2+1, but in D=3+1 the extensions fail to remedy the
qualitative disagreement.Comment: 3 pages, LaTeX2e, uses espcrc2.sty, 2 eps figures included, talk
given at LATTICE9
Excitation energies, polarizabilities, multipole transition rates, and lifetimes of ions along the francium isoelectronic sequence
Relativistic many-body perturbation theory is applied to study properties of
ions of the francium isoelectronic sequence. Specifically, energies of the 7s,
7p, 6d, and 5f states of Fr-like ions with nuclear charges Z = 87 - 100 are
calculated through third order; reduced matrix elements, oscillator strengths,
transition rates, and lifetimes are determined for 7s - 7p, 7p - 6d, and 6d -
5f electric-dipole transitions; and 7s - 6d, 7s - 5f, and 5f_5/2 - 5f_7/2
multipole matrix elements are evaluated to obtain the lifetimes of low-lying
excited states. Moreover, for the ions Z = 87 - 92 calculations are also
carried out using the relativistic all-order single-double method, in which
single and double excitations of Dirac-Fock wave functions are included to all
orders in perturbation theory. With the aid of the SD wave functions, we obtain
accurate values of energies, transition rates, oscillator strengths, and the
lifetimes of these six ions. Ground state scalar polarizabilities in Fr I, Ra
II, Ac III, and Th IV are calculated using relativistic third-order and
all-order methods. Ground state scalar polarizabilities for other Fr-like ions
are calculated using a relativistic second-order method. These calculations
provide a theoretical benchmark for comparison with experiment and theory.Comment: 13 figures, 11 table
Adams operations on the Green ring of a cyclic group of prime-power order
We consider the Green ring for a cyclic -group over a field
of prime characteristic and determine the Adams operations in
the case where is not divisible by . This gives information on the
decomposition into indecomposables of exterior powers and symmetric powers of
-modules.Comment: 23 page
Excitation energies, polarizabilities, multipole transition rates, and lifetimes in Th IV
Excitation energies of the ns_{1/2} (n=7-10), np_j (n=7-9), nd_j (n=6-8),
nf_{j} (n=5-7), and ng_{j} (n=5-6) states in Th IV are evaluated. First-,
second-, third-, and all-order Coulomb energies and first- and second-order
Coulomb-Breit energies are calculated. Reduced matrix elements, oscillator
strengths, transition rates, and lifetimes are determined for the 96 possible
nl_j-n'l'_j' electric-dipole transitions. Multipole matrix elements
(7s_{1/2}-6d_j, 7s_{1/2}-5f_j, and 5f_{5/2}-5f_{7/2}) are evaluated to obtain
the lifetimes of the and 7s_{1/2}$ states. Matrix elements are
calculated using both relativistic many-body perturbation theory, complete
through third order, and a relativistic all-order method restricted to single
and double (SD) excitations. Scalar and tensor polarizabilities for the
5f_{5/2} ground state in Th3+ are calculated using relativistic third-order and
all-order methods. These calculations provide a theoretical benchmark for
comparison with experiment and theory.Comment: 9 pages, 9 figure
Fabrication of slender struts for deployable antennas
A procedure for manufacturing long slender graphite tubing is desired. Such tubing has considerable application in truss supported spacecraft applications. The motivation for the selection of the tubing size developed in this program is for use as struts in a NASA, Langley Research Center truss supported antenna concept. The manufacturing procedure uses the LMSC vertical winding machine. A procedure for fabricating graphite epoxy tubing with an aluminum foil inner and outer wrap was also developed. The aluminum foil provides a vapor barrier, significantly improves the thermal conductivity, and provides an excellent thermal control surface
Application of numerical optimization to the design of advanced supercritical airfoils
An application of numerical optimization to the design of advanced airfoils for transonic aircraft showed that low-drag sections can be developed for a given design Mach number without an accompanying drag increase at lower Mach numbers. This is achieved by imposing a constraint on the drag coefficient at an off-design Mach number while minimizing the drag coefficient at the design Mach number. This multiple design-point numerical optimization has been implemented with the use of airfoil shape functions which permit a wide range of attainable profiles during the optimization process. Analytical data for the starting airfoil shape, a single design-point optimized shape, and a double design-point optimized shape are presented. Experimental data obtained in the NASA Ames two-by two-foot wind tunnel are also presented and discussed
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