Economic Evaluation of Computerized Structural Analysis

This completed effort involved a technical and economic study of the capabilities of computer programs in the area of structural analysis. The applicability of the programs to NASA projects and to other users was studied. The applications in other industries was explored including both research and development and applied areas. The costs of several alternative analysis programs were compared. A literature search covered applicable technical literature including journals, trade publications and books. In addition to the literature search, several commercial companies that have developed computerized structural analysis programs were contacted and their technical brochures reviewed. These programs include SDRC I-DEAS, MSC/NASTRAN, SCADA, SUPERSAP, NISA/DISPLAY, STAAD-III, MICAS, GTSTRUDL, and STARS. These programs were briefly reviewed as applicable to NASA projects

Collider Constraints on Dipole-Interacting Dark Matter

Dark matter which interacts through a magnetic or electric dipole moment is an interesting possibility which may help to resolve the discrepancy between the DAMA annual modulation signal and the null results of other searches. In this article we examine relic density and collider constraints on such dark matter, and find that for couplings needed to explain DAMA, the thermal relic density is generically in the right ballpark to account for cosmological measurements. Collider constraints are relevant for light WIMPs, but less constraining that direct searches for masses above about 10 GeV.Comment: 11 pages, 2 figures, extended discussion, added references, conclusion unchange

VSAERO analysis of tip planforms for the free-tip rotor

The results of a numerical analysis of two interacting lifting surfaces separated in the spanwise direction by a narrow gap are presented. The configuration consists of a semispan wing with the last 32 percent of the span structurally separated from the inboard section. The angle of attack of the outboard section is set independently from that of the inboard section. In the present study, the three-dimensional panel code VSAERO is used to perform the analysis. Computed values of tip surface lift and pitching moment coefficients are correlated with experimental data to determine the proper approach to model the gap region between the surfaces. Pitching moment data for various tip planforms are also presented to show how the variation of tip pitching moment with angle of attack may be increased easily in incompressible flow. Calculated three-dimensional characteristics in compressible flow at Mach numbers of 0.5 and 0.7 are presented for new tip planform designs. An analysis of sectional aerodynamic center shift as a function of Mach number is also included for a representative tip planform. It is also shown that the induced drag of the tip surface is reduced for negative incidence angles relative to the inboard section. The results indicate that this local drag reduction overcomes the associated increase in wing induced drag at high wing lift coefficients

Task-based Augmented Contour Trees with Fibonacci Heaps

This paper presents a new algorithm for the fast, shared memory, multi-core computation of augmented contour trees on triangulations. In contrast to most existing parallel algorithms our technique computes augmented trees, enabling the full extent of contour tree based applications including data segmentation. Our approach completely revisits the traditional, sequential contour tree algorithm to re-formulate all the steps of the computation as a set of independent local tasks. This includes a new computation procedure based on Fibonacci heaps for the join and split trees, two intermediate data structures used to compute the contour tree, whose constructions are efficiently carried out concurrently thanks to the dynamic scheduling of task parallelism. We also introduce a new parallel algorithm for the combination of these two trees into the output global contour tree. Overall, this results in superior time performance in practice, both in sequential and in parallel thanks to the OpenMP task runtime. We report performance numbers that compare our approach to reference sequential and multi-threaded implementations for the computation of augmented merge and contour trees. These experiments demonstrate the run-time efficiency of our approach and its scalability on common workstations. We demonstrate the utility of our approach in data segmentation applications

Characters of graded parafermion conformal field theory

The graded parafermion conformal field theory at level k is a close cousin of the much-studied Z_k parafermion model. Three character formulas for the graded parafermion theory are presented, one bosonic, one fermionic (both previously known) and one of spinon type (which is new). The main result of this paper is a proof of the equivalence of these three forms using q-series methods combined with the combinatorics of lattice paths. The pivotal step in our approach is the observation that the graded parafermion theory -- which is equivalent to the coset osp(1,2)_k/ u(1) -- can be factored as (osp(1,2)_k/ su(2)_k) x (su(2)_k/ u(1)), with the two cosets on the right equivalent to the minimal model M(k+2,2k+3) and the Z_k parafermion model, respectively. This factorisation allows for a new combinatorial description of the graded parafermion characters in terms of the one-dimensional configuration sums of the (k+1)-state Andrews--Baxter--Forrester model.Comment: 36 page

Rotating neutron stars with exotic cores: masses, radii, stability

A set of theoretical mass-radius relations for rigidly rotating neutron stars with exotic cores, obtained in various theories of dense matter, is reviewed. Two basic observational constraints are used: the largest measured rotation frequency (716 Hz) and the maximum measured mass ($2\;M_\odot$). Present status of measuring the radii of neutron stars is described. The theory of rigidly rotating stars in general relativity is reviewed and limitations of the slow rotation approximation are pointed out. Mass-radius relations for rotating neutron stars with hyperon and quark cores are illustrated using several models. Problems related to the non-uniqueness of the crust-core matching are mentioned. Limits on rigid rotation resulting from the mass-shedding instability and the instability with respect to the axisymmetric perturbations are summarized. The problem of instabilities and of the back-bending phenomenon are discussed in detail. Metastability and instability of a neutron star core in the case of a first-order phase transition, both between pure phases, and into a mixed-phase state, are reviewed. The case of two disjoint families (branches) of rotating neutron stars is discussed and generic features of neutron-star families and of core-quakes triggered by the instabilities are considered.Comment: Matches published version. Minor modifications and reference adde

SM(2,4k) fermionic characters and restricted jagged partitions

A derivation of the basis of states for the $SM(2,4k)$ superconformal minimal models is presented. It relies on a general hypothesis concerning the role of the null field of dimension $2k-1/2$. The basis is expressed solely in terms of $G_r$ modes and it takes the form of simple exclusion conditions (being thus a quasi-particle-type basis). Its elements are in correspondence with $(2k-1)$-restricted jagged partitions. The generating functions of the latter provide novel fermionic forms for the characters of the irreducible representations in both Ramond and Neveu-Schwarz sectors.Comment: 12 page

The Impact of Reducing Greenhouse Gas Emissions in Crop Agriculture: A Spatial- and Production-Level Analysis

With the Waxman-Markey Bill passing the House and the administration’s push to reduce carbon emissions, the likelihood of the implementation of some form of a carbon emissions policy is increasing. This study estimates the greenhouse gas (GHG) emissions of the six largest row crops produced in Arkansas using 57 different production practices predominantly used and documented by the University of Arkansas Cooperative Extension Service. From these GHG emission estimates, a baseline state “carbon footprint†was estimated and a hypothetical GHG emissions reduction of 5, 10, and 20 percent was levied on Arkansas agriculture using a cap-and-trade method. Using current production technology and traditional land use choices, results show that the trading of carbon-emitting permits to reduce statewide GHG emissions by 5 percent from the baseline would enhance GHG emissions efficiency measured as net crop farm income generated per unit of carbon emissions created. The 5 percent reduction in GHG emissions does cause marginal reductions in acres farmed and has marginal income ramifications. Beyond the 5 percent reduction target, gains in GHG emissions efficiency decline but remain positive in most counties through the 10 percent GHG reduction target. However, with a 10 percent GHG reduction, acreage and income reductions more than double compared to the 5 percent level. When GHG emissions are reduced by 20 percent from the baseline, the result is a major cropping pattern shift coupled with significant reductions in traditional row crop acreage, income, and GHG emissions efficiency.greenhouse gas emissions, carbon equivalents, sustainability, cap and trade, Environmental Economics and Policy, Resource /Energy Economics and Policy,

Is the decoherence of a system the result of its interaction with the environment?

According to a usual reading, decoherence is a process resulting from the interaction between a small system and its large environment where information and energy are dissipated. The particular models treated in the literature on the subject reinforce this idea since, in general, the behavior of a particle immersed in a large "bath" composed by many particles is studied. The aim of this letter is to warn against this usual simplified reading. By means of the analysis of a well-known model, we will show that decoherence may occur in a system interacting with an environment consisting of only one particle.Comment: 4 Pages, 5 Figure