On the Origin of the Clustered QSO Metal Absorption Lines

Observations show that there is significant clustering of QSO metal absorption lines within the range of velocity dispersion between 200km/sec and 600 km/sec. With a reasonable supernova rate, it is shown that high velocity gases driven by SNe and/or strong stellar winds could explain the clustered absorptions, provided that QSO metal-line absorbers are galactic halos or dwarf galaxies. Rich clusters of galaxies, on the other hand, cannot yield the observed clustering of QSO metal absorption lines.Comment: Revtex 15 pages, 2 ps figures available at ftp://astro.queensu.ca/pub/shi/, or at http://astro.queensu.ca/~shi/, or by request. Submitted to Ap. J

Testing Cold Dark Matter Models Using Hubble Flow Variations

COBE-normalized flat (matter plus cosmological constant) and open Cold Dark Matter (CDM) models are tested by comparing their expected Hubble flow variations and the observed variations in a Type Ia supernova sample and a Tully Fisher cluster sample. The test provides a probe of the CDM power spectrum on scales of $0.02h$ Mpc^{-1}\la k\la 0.2h Mpc$^{-1}$, free of the bias factor $b$. The results favor a low matter content universe, or a flat matter-dominated universe with a very low Hubble constant and/or a very small spectral index $n_{ps}$, with the best fits having $\Omega_0\sim 0.3$ to 0.4. The test is found to be more discriminative to the open CDM models than to the flat CDM models. For example, the test results are found to be compatible with those from the X-ray cluster abundance measurements at smaller length scales, and consistent with the galaxy and cluster correlation analysis of Peacock and Dodds (1994) at similar length scales, if our universe is flat; but the results are marginally incompatible with the X-ray cluster abundance measurements if our universe is open. The open CDM results are consistent with that of Peacock and Dodds only if the matter density of the universe is less than about 60% of the critical density. The shortcoming of the test is discussed, so are ways to minimize it.Comment: 8 pages, 10 figures, submitted to MNRA

Expectations for the Difference Between Local and Global Measurements of the Hubble Constant

There are irreducible differences between the Hubble constant measured locally and the global value. They are due to density perturbations and finite sample volume (cosmic variance) and finite number of objects in the sample (sampling variance). We quantify these differences for a suite of COBE-normalized CDM models that are consistent with the observed large-scale structure. For small samples of objects that only extend out to 10,000 km/sec, the variance can approach 4%. For the largest samples of Type Ia supernovae (SNeIa), which include about 40 objects and extend out to almost 40,000 km/sec, the variance is 1-2% and is dominated by sampling variance. Sampling and cosmic variance may be an important consideration in comparing local determinations of the Hubble constant with precision determinations of the global value that will be made from high-resolution maps of CBR anisotropy.Comment: 10 pages, Latex, 2 figures, version accepted for Ap.

Observing the Birth of Supermassive Black Holes with the Planned ICECUBE Neutrino Detector

It has been suggested that the supermassive black holes, at the centers of galaxies and quasars, may initially form in single collapses of relativistic star clusters or supermassive stars built-up during the evolution of dense star clusters. We show that it may be possible for ICECUBE (a planned 1 km^3 neutrino detector in Antarctica) to detect the neutrino bursts associated with those collapses at redshift z\la 0.2 with a rate of $\sim$ 0.1 to 1 burst per year. Such detections could give new insights into the formation of structure in the universe, especially when correlated with gravitational wave signatures or even gamma-ray bursts.Comment: replaced with the version published in PRL. 11 Revtex pages + 2 figure

Suitability for Global Maize Production: A Methodology Based on Spatial Analysis

A methodology based on spatial analysis is proposed to investigate suitability of crop, and then applied to analyzing the suitability for global maize production. The suitable and unsuitable maize cultivated regions are given based on the analysis, and maize cultivated regions sensitive to economic incentive is also illustrated and discussed.Crop Production/Industries,