Spectral Dependence of Polarized Radiation due to Spatial Correlations

We study the polarization of light emitted by spatially correlated sources. We show that in general polarization acquires nontrivial spectral dependence due to spatial correlations. The spectral dependence is found to be absent only for a special class of sources where the correlation length scales as the wavelength of light. We further study the cross correlations between two spatially distinct points that are generated due to propagation. It is found that such cross correlation leads to sufficiently strong spectral dependence of polarization which can be measured experimentally.Comment: 5 pages, 4 figure

Environmental justice and transportation equity: a review of MPOs

Book ChapterSurface transportation policies at the local, regional, state, and national levels have a direct impact on urban land use and development patterns. The types of transportation facilities and services in which public funds are invested provide varying levels of access to meet basic social and economic needs. The way regions develop land dictates the need for certain types of transportation, and on the other hand, the transportation options in which regions invest influence patterns of urban development. While many lament the trend toward suburban sprawl as damaging to the environment or unaesthetic, those who support social equity should also be concerned about the associated impacts. Substantial investment in highway development and other transportation programs that encourage private automobile use has supported low-density developments that extend increasingly farther and farther from the central city, and to residential and commercial areas that are increasingly spread out, producing "edgeless cities" (Lang 2003). In addition to being costly to state and local governments, transportation policies that encourage these growth patterns play a substantial role in producing some indirect, negative social and economic effects, including perpetuating residential segregation and exacerbating the inability of minorities to access entry-level employment, which is increasingly found in suburban areas. MPOs are well suited to provide leadership in the areas of metropolitan development and civil rights

A preliminary investigation of the use of throttles for emergency flight control

A preliminary investigation was conducted regarding the use of throttles for emergency flight control of a multiengine aircraft. Several airplanes including a light twin-engine piston-powered airplane, jet transports, and a high performance fighter were studied during flight and piloted simulations. Simulation studies used the B-720, B-727, MD-11, and F-15 aircraft. Flight studies used the Lear 24, Piper PA-30, and F-15 airplanes. Based on simulator and flight results, all the airplanes exhibited some control capability with throttles. With piloted simulators, landings using manual throttles-only control were extremely difficult. An augmented control system was developed that converts conventional pilot stick inputs into appropriate throttle commands. With the augmented system, the B-720 and F-15 simulations were evaluated and could be landed successfully. Flight and simulation data were compared for the F-15 airplane

The Wolf effect and the Redshift of Quasars

We consider a simple model, based on currently accepted models for active galactic nuclei, for a quasi-stellar object (QSO or ``quasar'') and examine the influence that correlation- induced spectral changes (``The Wolf Effect'') may have upon the redshifts of the optical emission lines.Comment: 13 pages, 3 figures. To be published in J. European Optical Soc. A: Pure and Applied Optic

IS AGRICULTURAL RESEARCH STILL A PUBLIC GOOD?

The nature of public agricultural research changed in 1980 when the Bayh-Dole Act allowed universities to retain title to inventions that were created with Federal funds, and the court case Diamond v. Chakrabarty allowed patenting of living tissue and eventually other bio-engineered products. In 1997, over 2,300 new licenses and options were executed on academic life-sciences property. This raises the questions agricultural research still be a public good? This paper is a critical first step in understanding how increasingly private ownership of intellectual property affects the agribusiness environment and the evolving role of public agricultural research institutions. The innovative step in this paper is the development of a formal economic model which represents the role of applied biotech research in the agricultural life sciences. The model is built around neo-Schumpeterian ideas of endogenous innovation and growth. The most salient implications for the role of the public sector are(1)The private sector underinvests in applied R&D activity. (2) Concentration in the large-firm, life-science R&D industry increases over time. (3) The life-science revolution is reducing the number of markets, in the short run. This reduction in the number of niche markets diminishes the role of the public sector. (4) There is a role for the public sector in conducting R&D in niche markets. (5) In the long run, the life-science revolution may also create new niche markets. (6) There is a role for the public sector in the provision of basic research which increases the productivity of applied R&D.Research and Development/Tech Change/Emerging Technologies,

Accurate masses for dispersion-supported galaxies

We derive an accurate mass estimator for dispersion-supported stellar systems and demonstrate its validity by analyzing resolved line-of-sight velocity data for globular clusters, dwarf galaxies, and elliptical galaxies. Specifically, by manipulating the spherical Jeans equation we show that the dynamical mass enclosed within the 3D deprojected half-light radius r_1/2 can be determined with only mild assumptions about the spatial variation of the stellar velocity dispersion anisotropy. We find M_1/2 = 3 \sigma_los^2 r_1/2 / G ~ 4 \sigma_los^2 R_eff / G, where \sigma_los^2 is the luminosity-weighted square of the line-of-sight velocity dispersion and R_eff is the 2D projected half-light radius. While deceptively familiar in form, this formula is not the virial theorem, which cannot be used to determine accurate masses unless the radial profile of the total mass is known a priori. We utilize this finding to show that all of the Milky Way dwarf spheroidal galaxies (MW dSphs) are consistent with having formed within a halo of mass approximately 3 x 10^9 M_sun in Lambda CDM cosmology. The faintest MW dSphs seem to have formed in dark matter halos that are at least as massive as those of the brightest MW dSphs, despite the almost five orders of magnitude spread in luminosity. We expand our analysis to the full range of observed dispersion-supported stellar systems and examine their I-band mass-to-light ratios (M/L). The M/L vs. M_1/2 relation for dispersion-supported galaxies follows a U-shape, with a broad minimum near M/L ~ 3 that spans dwarf elliptical galaxies to normal ellipticals, a steep rise to M/L ~ 3,200 for ultra-faint dSphs, and a more shallow rise to M/L ~ 800 for galaxy cluster spheroids.Comment: 20 pages, 13 figures. Accepted to MNRAS on March 27th, 201

Grain boundary energies and cohesive strength as a function of geometry

Cohesive laws are stress-strain curves used in finite element calculations to describe the debonding of interfaces such as grain boundaries. It would be convenient to describe grain boundary cohesive laws as a function of the parameters needed to describe the grain boundary geometry; two parameters in 2D and 5 parameters in 3D. However, we find that the cohesive law is not a smooth function of these parameters. In fact, it is discontinuous at geometries for which the two grains have repeat distances that are rational with respect to one another. Using atomistic simulations, we extract grain boundary energies and cohesive laws of grain boundary fracture in 2D with a Lennard-Jones potential for all possible geometries which can be simulated within periodic boundary conditions with a maximum box size. We introduce a model where grain boundaries are represented as high symmetry boundaries decorated by extra dislocations. Using it, we develop a functional form for the symmetric grain boundary energies, which have cusps at all high symmetry angles. We also find the asymptotic form of the fracture toughness near the discontinuities at high symmetry grain boundaries using our dislocation decoration model.Comment: 12 pages, 19 figures, changed titl

CYCLICAL CONCENTRATION AND CONSOLIDATION IN BIOTECH R&D: A NEO-SCHUMPETERIAN MODEL

Over the past fifteen years, the agricultural biotechnology industry has exhibited cyclical behavior in concentration and consolidation. This paper provides a theoretical model of endogenous R&D, in which industry concentration exhibits cyclical behavior. The model also generates additional testable hypotheses, and policy implications.Industrial Organization, Research and Development/Tech Change/Emerging Technologies,