Foreground separation methods for satellite observations of the cosmic microwave background

A maximum entropy method (MEM) is presented for separating the emission resulting from different foreground components from simulated satellite observations of the cosmic microwave background radiation (CMBR). In particular, the method is applied to simulated observations by the proposed Planck Surveyor satellite. The simulations, performed by Bouchet &38; Gispert, include emission from the CMBR and the kinetic and thermal Sunyaev–Zel'dovich (SZ) effects from galaxy clusters, as well as Galactic dust, free–free and synchrotron emission. We find that the MEM technique performs well and produces faithful reconstructions of the main input components. The method is also compared with traditional Wiener filtering and is shown to produce consistently better results, particularly in the recovery of the thermal SZ effect.     

SOCIAL RELATIONS SPATIALLY FIXED: CONSTRUCTION AND MAINTENANCE OF SCHOOL DISTRICTS IN SAN ANTONIO,TEXAS

ABSTRACT. More than 140 court cases filed in the United States between 1970 and 2003 argued that unacceptable and unconstitutional funding disparities exist among school districts in most states. In those arguments, stories, statistics, and maps are used to compare various school districts to prove that conditions are indeed unequal. Both sides—plaintiff and defendant—use such information to disprove each other's contentions. In so doing, each assumes that the political spaces of the school districts are absolute, timeless, and independent. Failure to recognize that these spaces—the school districts—are not objective but, in fact, constitutive of the class and race relations actually being argued and debated in court further legitimates local geographies of privilege and deprivation. I examine the formation of the school districts around San Antonio, Texas to illustrate that these districts are far from independent of one another and were formed to isolate privileged communities from the rest of the city. A relational view of space‐time allows such spaces as school districts to assume a political role, as opposed to the absolute, independent spaces they now represent.     

Turbulence in the troposphere of Venus: Refined characteristics and new estimates

Based on spaceborne experimental data, characteristics of turbulence are calculated for the Venusian troposphere under conditions corresponding to the planet-averaged flux of solar radiation, which is equal to its value at a solar zenith angle of 66°. Additionally, given experimental data on radiation fluxes and their numerical calculations, turbulence characteristics were calculated for a solar zenith angle of 45°. The turbulence pattern is significantly different for small and large solar zenith angles. At large solar zenith angles, there exist an anomalous downward turbulent heat flux above 7–10 km and a normal upward flux at lower heights. At small zenith angles, the turbulent flux is normal throughout the entire troposphere. The dissipation of turbulent energy contributes significantly to the atmospheric heating in a wide range of altitudes. The spectrum of the time and space scales of dissipative processes in the troposphere is very wide and changes with height.Translated from Astronomicheskii Vestnik, Vol. 39, No. 1, 2005, pp. 38–50.Original Russian Text Copyright © 2005 by Izakov.     

The γ-ray emission mechanism for Fermi Blazars

Fermi Blazars are characterized mainly by the vast effect that relativistic beaming has on their emission spectra. Fermi-LAT has detected more than 1000 blazars which provide us with a good opportunity to study the emission mechanism. In this paper, adopted the Doppler factor δ _γ determined in our previous paper, the γ-ray emission mechanism is discussed using the investigation of dependence of the γ-ray luminosity on the Doppler factor. Our discussions suggest that the γ-ray emission mechanism is SSC for BL Lacs.     

Luminosity function of contact binaries based on the All Sky Automated Survey (ASAS)

The luminosity function for contact binary stars of the W UMa type is evaluated on the basis of the All Sky Automated Survey (ASAS) photometric project covering all stars south of  δ=+ 28°  within a magnitude range  8 < V < 13  . Lack of colour indices enforced a limitation to 3374 systems with   P < 0.562 d  (i.e. 73 per cent of all systems with   P < 1 d  ) where a simplified M_V (log  P ) calibration could be used. The spatial density relative to the main-sequence FGK stars of 0.2 per cent, as established previously from the Hipparcos sample to   V = 7.5  , is confirmed. While the numbers of contact binaries in the ASAS are large and thus the statistical uncertainties small, derivation of the luminosity function required a correction for missed systems with small amplitudes and with orbital periods longer than 0.562 d; the correction, by a factor of 3, carries an uncertainty of about 30 per cent.     

The cooling of flare produced plasmas in the solar corona

Solar flare X-rays, at energies less than 10 keV, are emitted by hot plasmas located in the corona. Three plasma cooling models are examined in detail. The cooling of the electrons by Coulomb collisions with ions at a lower temperature would require the observed material to occupy very large volumes. Cooling could take place by conduction or by radiation and observations are proposed which would allow the dominant cooling mechanism to be established.On leave during a portion of this work as University Research Fellow in Astronomy, University of Leicester, England.     

Fast solar electrons,interplanetary plasma and km-wave type-III radio bursts observed from the IMP-6 spacecraft

IMP-6 spacecraft observations of low frequency radio emission, fast electrons, and solar wind plasma are used to examine the dynamics of the fast electron streams which generate solar type-III radio bursts. Of twenty solar electron events observed between April, 1971 and August, 1972, four were found to be amenable to detailed analysis. Observations of the direction of arrival of the radio emission at different frequencies were combined with the solar wind density and velocity measurements at 1 AU to define an Archimedean spiral trajectory for the radio burst exciter. The propagation characteristics of the exciter and of the fast electrons observed at 1 AU were then conpared. We find that: (1) the fast electrons excite the radio emission at the second harmonic; (2) the total distance travelled by the electrons was between 30 and 70% longer than the length of the smooth spiral defined by the radio observations; (3) this additional distance travelled is the result of scattering of the electrons in the interplanetary medium; (4) the observations are consistent with negligible true energy loss by the fast electrons.     

An imaging spectrometric observatory for spacelab

The capability to measure nearly simultaneously the entire spectrum of atmospheric emission from the extreme ultraviolet to the near infrared, with relatively high spectral resolution and high sensitivity, while also obtaining global and altitude coverage, would provide a database from which significant advances could be made in our current understanding of the atmosphere and its processes. The large payload capacity of the shuttle orbiter offers the first opportunity to put such instrumentation into space. The Imaging Spectrometric Observatory (ISO) comprises an array of five spectrometers designed to make full use of the shuttle as an observing platform for remote sensing of the atmosphere. ISO covers the wavelength range 300–12000 Å at 2–7 Å resolution. Use of area array detectors (intensified-CCD's) permits simultaneous measurements of ～1000 Å at a time. The instrument is capable of scanning the entire wavelength range in less than 20 s, or dwelling on weaker features for longer periods of time. The detectors are two dimensional and permit spectral imaging in one direction and spatial imaging in the other. The spatial imaging and spatial scanning features permit measurement of altitude profiles, or mapping of strongly spatially varying features such as aurorae. The instrument is designed to allow versatility. The various functions are programmable and software controlled. The key subsystems are modular for convenient replacement or upgrading. It is anticipated that the instrument will have applications not only in the area of atmospheric science, but also in studies of the ionosphere and magnetosphere, and in support of active experiments to be performed in space.     

Issues of Spatial and Temporal Variability in Climate Impact Studies

The accuracy of impact estimates relating climate change to regional-scale agricultural production is constrained by the temporal and spatial resolution of climate change projections. Several techniques have been used to compensate for these limitations in order to provide reasonable estimates of the impact of climate change on crop yield. One approach assumes that variability over time can substitute for spatial variability, thereby reducing the need to estimate the impacts at a spatially dense network of stations—an assumption that has not been generally tested. This study evaluates this assumption using methods similar to those employed in the climate impact literature. The findings suggest that current practices are generally defensible if the goal is to provide a range of possible crop responses to climate change. However, the results also show that the assumption is highly sensitive to specific interactions at the soil-plant-atmosphere interface and, consequently, does not hold under certain circumstances.