The mass and dynamical state of Abell 2218

Abell 2218 is one of a handful of clusters in which X-ray and lensing analyses of the cluster mass are in strong disagreement. It is also a system for which X-ray data and radio measurements of the Sunyaev-Zel'dovich decrement have been combined in an attempt to constrain the Hubble constant. However, in the absence of reliable information on the temperature structure of the intracluster gas, most analyses have been carried out under the assumption of isothermality. We combine X-ray data from the ROSAT PSPC and the ASCA GIS instruments, enabling us to fit non-isothermal models, and investigate the impact that this has on the X-ray derived mass and the predicted Sunyaev-Zel'dovich effect. We find that a strongly non-isothermal model for the intracluster gas, which implies a central cusp in the cluster mass distribution, is consistent with the available X-ray data and compatible with the lensing results. At r<1 arcmin, there is strong evidence to suggest that the cluster departs from a simple relaxed model. We analyse the dynamics of the galaxies and find that the central galaxy velocity dispersion is too high to allow a physical solution for the galaxy orbits. The quality of the radio and X-ray data do not at present allow very restrictive constraints to be placed on H_0. It is apparent that earlier analyses have under-estimated the uncertainties involved. However, values greater than 50 km/s/Mpc are preferred when lensing constraints are taken into account.Comment: 16 pages, 9 postscript figures, accepted for publication in MNRA

Scanning system, infrared noise equivalent temperature difference: Measurement procedure

A procedure is described for determining the noise equivalent difference temperature for infrared electro-optical instruments. The instrumentation required, proper measurements, and methods of calculation are included

Mechanism of CDW-SDW Transition in One Dimension

The phase transition between charge- and spin-density-wave (CDW, SDW) phases is studied in the one-dimensional extended Hubbard model at half-filling. We discuss whether the transition can be described by the Gaussian and the spin-gap transitions under charge-spin separation, or by a direct CDW-SDW transition. We determine these phase boundaries by level crossings of excitation spectra which are identified according to discrete symmetries of wave functions. We conclude that the Gaussian and the spin-gap transitions take place separately from weak- to intermediate-coupling region. This means that the third phase exists between the CDW and the SDW states. Our results are also consistent with those of the strong-coupling perturbative expansion and of the direct evaluation of order parameters.Comment: 5 pages(REVTeX), 5 figures(EPS), 1 table, also available from http://wwwsoc.nacsis.ac.jp/jps/jpsj/1999/p68a/p68a42/p68a42h/p68a42h.htm

Plans for phase coherent long baseline interferometry for geophysical applications using the Anik-B communications satellite

A pilot project to establish an operational phase stable very long baseline interferometer (VLBI) for geophysical studies is described. Methods for implementation as well as practical applications are presented

Agricultural Communications: A National Portrait of Undergraduate Courses

Considerable research has been conducted regarding competencies needed by agricultural communication program graduates during the past four decades. However, no studies have considered actual program offerings. This study used a qualitative approach to analyze courses offered in agricultural communication programs in the United States. Using content analysis methods, researchers analyzed published course descriptions and discovered 21 categories among 172 courses. Most popular were writing courses, followed by courses introducing students to the major, internship courses, and writing for publication and graphic design courses. Categories with the fewest offerings included research, study abroad, and international focused courses. Findings from this analysis are consistent with previous literature noting the variety existing in agricultural communication programs at the national level. With the current growth of agricultural communication as an academic discipline and the fundamental role agricultural communicators play in sharing information about key societal issues at a time when agriculture has never been under greater pressure, this study is a first step in creating a national portrait of curricular offerings in agricultural communication programs

Agricultural Communications: A National Portrait of Undergraduate Courses

Considerable research has been conducted regarding competencies needed by agricultural communication program graduates during the past four decades. However, no studies have considered actual program offerings. This study used a qualitative approach to analyze courses offered in agricultural communication programs in the United States. Using content analysis methods, researchers analyzed published course descriptions and discovered 21 categories among 172 courses. Most popular were writing courses, followed by courses introducing students to the major, internship courses, and writing for publication and graphic design courses. Categories with the fewest offerings included research, study abroad, and international focused courses. Findings from this analysis are consistent with previous literature noting the variety existing in agricultural communication programs at the national level. With the current growth of agricultural communication as an academic discipline and the fundamental role agricultural communicators play in sharing information about key societal issues at a time when agriculture has never been under greater pressure, this study is a first step in creating a national portrait of curricular offerings in agricultural communication programs

Agricultural Communications: A National Portrait of Undergraduate Courses

Considerable research has been conducted regarding competencies needed by agricultural communication program graduates during the past four decades. However, no studies have considered actual program offerings. This study used a qualitative approach to analyze courses offered in agricultural communication programs in the United States. Using content analysis methods, researchers analyzed published course descriptions and discovered 21 categories among 172 courses. Most popular were writing courses, followed by courses introducing students to the major, internship courses, and writing for publication and graphic design courses. Categories with the fewest offerings included research, study abroad, and international focused courses. Findings from this analysis are consistent with previous literature noting the variety existing in agricultural communication programs at the national level. With the current growth of agricultural communication as an academic discipline and the fundamental role agricultural communicators play in sharing information about key societal issues at a time when agriculture has never been under greater pressure, this study is a first step in creating a national portrait of curricular offerings in agricultural communication programs

Relative Hyperbolicity, Trees of Spaces and Cannon-Thurston Maps

We prove the existence of continuous boundary extensions (Cannon-Thurston maps) for the inclusion of a vertex space into a tree of (strongly) relatively hyperbolic spaces satisfying the qi-embedded condition. This implies the same result for inclusion of vertex (or edge) subgroups in finite graphs of (strongly) relatively hyperbolic groups. This generalises a result of Bowditch for punctured surfaces in 3 manifolds and a result of Mitra for trees of hyperbolic metric spaces.Comment: 27pgs No figs, v3: final version, incorporating referee's comments, to appear in Geometriae Dedicat

The S2 VLBI Correlator: A Correlator for Space VLBI and Geodetic Signal Processing

We describe the design of a correlator system for ground and space-based VLBI. The correlator contains unique signal processing functions: flexible LO frequency switching for bandwidth synthesis; 1 ms dump intervals, multi-rate digital signal-processing techniques to allow correlation of signals at different sample rates; and a digital filter for very high resolution cross-power spectra. It also includes autocorrelation, tone extraction, pulsar gating, signal-statistics accumulation.Comment: 44 pages, 13 figure