Synthetic Observations of Simulated Radio Galaxies I: Radio and X-ray Analysis

We present an extensive synthetic observational analysis of numerically- simulated radio galaxies designed to explore the effectiveness of conventional observational analyses at recovering physical source properties. These are the first numerical simulations with sufficient physical detail to allow such a study. The present paper focuses on extraction of magnetic field properties from nonthermal intensity information. Synchrotron and inverse-Compton intensities provided meaningful information about distributions and strengths of magnetic fields, although considerable care was called for. Correlations between radio and X-ray surface brightness correctly revealed useful dynamical relationships between particles and fields. Magnetic field strength estimates derived from the ratio of X-ray to radio intensity were mostly within about a factor of two of the RMS field strength along a given line of sight. When emissions along a given line of sight were dominated by regions close to the minimum energy/equipartition condition, the field strengths derived from the standard power-law-spectrum minimum energy calculation were also reasonably close to actual field strengths, except when spectral aging was evident. Otherwise, biases in the minimum- energy magnetic field estimation mirrored actual differences from equipartition. The ratio of the inverse-Compton magnetic field to the minimum-energy magnetic field provided a rough measure of the actual total energy in particles and fields in most instances, within an order of magnitude. This may provide a practical limit to the accuracy with which one may be able to establish the internal energy density or pressure of optically thin synchrotron sources.Comment: 43 pages, 14 figures; accepted for publication in ApJ, v601 n2 February 1, 200

Chemical control of Heterodera schachtii on sugarbeet in California

RESP-790

The economic and innovation contribution of universities: a regional perspective

Universities and other higher education institutions (HEIs) have come to be regarded as key sources of knowledge utilisable in the pursuit of economic growth. Although there have been numerous studies assessing the economic and innovation impact of HEIs, there has been little systematic analysis of differences in the relative contribution of HEIs across regions. This paper provides an exploration of some of these differences in the context of the UK’s regions. Significant differences are found in the wealth generated by universities according to regional location and type of institution. Universities in more competitive regions are generally more productive than those located in less competitive regions. Also, traditional universities are generally more productive than their newer counterparts, with university productivity positively related to knowledge commercialisation capabilities. Weaker regions tend to be more dependent on their universities for income and innovation, but often these universities under-perform in comparison to counterpart institutions in more competitive regions. It is argued that uncompetitive regions lack the additional knowledge infrastructure, besides universities, that are more commonly a feature of more competitive regions

Quasi-Periodic Occultation by a Precessing Accretion Disk and Other Variabilities of SMC X-1

We have investigated the variability of the binary X-ray pulsar, SMC X-1, in data from several X-ray observatories. We confirm the ~60-day cyclic variation of the X-ray flux in the long-term monitoring data from the RXTE and CGRO observatories. X-ray light curves and spectra from the ROSAT, Ginga, and ASCA observatories show that the uneclipsed flux varies by as much as a factor of twenty between a high-flux state when 0.71 second pulses are present and a low-flux state when pulses are absent. In contrast, during eclipses when the X-rays consist of radiation scattered from circumsource matter, the fluxes and spectra in the high and low states are approximately the same. These observations prove that the low state of SMC X-1 is not caused by a reduction in the intrinsic luminosity of the source, or a spectral redistribution thereof, but rather by a quasi-periodic blockage of the line of sight, most likely by a precessing tilted accretion disk. In each of two observations in the midst of low states a brief increase in the X-ray flux and reappearance of 0.71 second pulses occurred near orbital phase 0.2. These brief increases result from an opening of the line of sight to the pulsar that may be caused by wobble in the precessing accretion disk. The records of spin up of the neutron star and decay of the binary orbit are extended during 1991-1996 by pulse-timing analysis of ROSAT, ASCA, and RXTE PCA data. The pulse profiles in various energy ranges from 0.1 to >21 keV are well represented as a combination of a pencil beam and a fan beam. Finally, there is a marked difference between the power spectra of random fluctuations in the high-state data from the RXTE PCA below and above 3.4 keV. Deviation from the fitted power law around 0.06 Hz may be QPO.Comment: Accepted to ApJ. 33 pages including 11 figure

A Uniform Analysis of the Ly-alpha Forest at z=0 - 5: V. The extragalactic ionizing background at low redshift

In Paper III of our series "A Uniform Analysis of the Ly-alpha forest at z=0 - 5", we presented a set of 270 quasar spectra from the archives of the Faint Object Spectrograph on the Hubble Space Telescope. A total of 151 of these spectra, yielding 906 lines, are suitable for using the proximity effect signature to measure J(\nu_0), the mean intensity of the hydrogen-ionizing background radiation field, at low redshift. Using a maximum likelihood technique and the best estimates possible for each QSO's Lyman limit flux and systemic redshift, we find J(\nu_0)= 7.6^+9.4_-3.0 x 10^-23 ergs s^-1 cm^-2 Hz^-1 sr^-1 at at 0.03 < z < 1.67. This is in good agreement with the mean intensity expected from models of the background which incorporate only the known quasar population. When the sample is divided into two subsamples, consisting of lines with z 1, the values of J(\nu_0) found are 6.5^+38._-1.6 x 10^-23 ergs s^-1 cm^-2 Hz^-1 sr^-1, and 1.0^+3.8_-0.2 x 10^-22 ergs s^-1 cm^-2 Hz^-1 sr^-1, respectively, indicating that the mean intensity of the background is evolving over the redshift range of this data set. Relaxing the assumption that the spectral shapes of the sample spectra and the background are identical, the best fit HI photoionization rates are found to be 6.7 x 10^-13 s^-1 for all redshifts, and 1.9 x 10^-13 s^-1 and 1.3 x 10^-12 s^-1 for z 1, respectively. This work confirms that the evolution of the number density of Ly-alpha lines is driven by a decrease in the ionizing background from z ~ 2 to z ~ 0 as well as by the formation of structure in the intergalactic medium. (Abridged)Comment: 71 LaTeX pages, 20 encapsulated Postscript figures, Accepted for publication in ApJ, Figure 4 available at http://lithops.as.arizona.edu/~jill/QuasarSpectra/ or http://hea-www.harvard.edu/QEDT/QuasarSpectra

Study of relativistic bound states for scalar theories in Bethe-Salpeter and Dyson-Schwinger formalism

The Bethe-Salpeter equation for Wick-Cutkosky like models is solved in dressed ladder approximation. The bare vertex truncation of the Dyson-Schwinger equations for propagators is combined with the dressed ladder Bethe-Salpeter equation for the scalar S-wave bound state amplitudes. With the help of spectral representation the results are obtained directly in Minkowski space. We give a new analytic formula for the resulting equation simplifying the numerical treatment. The bare ladder approximation of Bethe-Salpeter equation is compared with the one with dressed ladder. The elastic electromagnetic form factors is calculated within the relativistic impulse approximation.Comment: 30 pages, 10 figures, accepted for publication in Phys. Rev.

Martian Atmospheric Methane Plumes from Meteor Shower Infall: A Hypothesis

Methane plumes in the martian atmosphere have been detected using Earth-based spectroscopy, the Planetary Fourier Spectrometer on the ESA Mars Express mission, and the NASA Mars Science Laboratory. The methane's origin remains a mystery, with proposed sources including volcanism, exogenous sources like impacts and interplanetary dust, aqueous alteration of olivine in the presence of carbonaceous material, release from ancient deposits of methane clathrates, and/or biological activity. To date, none of these phenomena have been found to reliably correlate with the detection of methane plumes. An additional source exists, however: meteor showers could generate martian methane via UV pyrolysis of carbon-rich infall material. We find a correlation between the dates of Mars/cometary orbit encounters and detections of methane on Mars. We hypothesize that cometary debris falls onto Mars during these interactions, depositing freshly disaggregated meteor shower material in a regional concentration. The material generates methane via UV photolysis, resulting in a localized "plume" of short-lived methane

On the interpretation of spin-polarized electron energy loss spectra

We study the origin of the structure in the spin-polarized electron energy loss spectroscopy (SPEELS) spectra of ferromagnetic crystals. Our study is based on a 3d tight-binding Fe model, with constant onsite Coulomb repulsion U between electrons of opposite spin. We find it is not the total density of Stoner states as a function of energy loss which determines the response of the system in the Stoner region, as usually thought, but the densities of Stoner states for only a few interband transitions. Which transitions are important depends ultimately on how strongly umklapp processes couple the corresponding bands. This allows us to show, in particular, that the Stoner peak in SPEELS spectra does not necessarily indicate the value of the exchange splitting energy. Thus, the common assumption that this peak allows us to estimate the magnetic moment through its correlation with exchange splitting should be reconsidered, both in bulk and surface studies. Furthermore, we are able to show that the above mechanism is one of the main causes for the typical broadness of experimental spectra. Finally, our model predicts that optical spin waves should be excited in SPEELS experiments.Comment: 11 pages, 7 eps figures, REVTeX fil