Path methods for strong shift equivalence of positive matrices

In the early 1990's, Kim and Roush developed path methods for establishing strong shift equivalence (SSE) of positive matrices over a dense subring U of the real numbers R. This paper gives a detailed, unified and generalized presentation of these path methods. New arguments which address arbitrary dense subrings U of R are used to show that for any dense subring U of R, positive matrices over U which have just one nonzero eigenvalue and which are strong shift equivalent over U must be strong shift equivalent over U_+. In addition, we show positive real matrices on a path of shift equivalent positive real matrices are SSE over R_+; positive rational matrices which are SSE over R_+ must be SSE over Q_+; and for any dense subring U of R, within the set of positive matrices over U which are conjugate over U to a given matrix, there are only finitely many SSE-U_+ classes.Comment: This version adds a 3-part program for studying SEE over the reals. One part is handled by the arxiv post "Strong shift equivalence and algebraic K-theory". This version is the author version of the paper published in the Kim memorial volume. From that, my short lifestory of Kim (and more) is on my web page http://www.math.umd.edu/~mboyle/papers/index.htm

Quasar Parallax: a Method for Determining Direct Geometrical Distances to Quasars

We describe a novel method to determine direct geometrical distances to quasars that can measure the cosmological constant, Lambda, with minimal assumptions. This method is equivalent to geometric parallax, with the `standard length' being the size of the quasar broad emission line region (BELR) as determined from the light travel time measurements of reverberation mapping. The effect of non-zero Lambda on angular diameter is large, 40% at z=2, so mapping angular diameter distances vs. redshift will give Lambda with (relative) ease. In principle these measurements could be made in the UV, optical, near infrared or even X-ray bands. Interferometers with a resolution of 0.01mas are needed to measure the size of the BELR in z=2 quasars, which appear plausible given reasonable short term extrapolations of current technology.Comment: 13 pages, with 3 figures. ApJ Letters, in press (Dec 20, 2002

Labelling and Diagnosis

This is the author accepted manuscript. The final version is available from the British Psychological SocietyGuest editoria

Compact Nuclei in Galaxies at Moderate Redshift:II. Their Nature and Implications for the AGN Luminosity Function

This study explores the space density and properties of active galaxies to z=0.8. We have investigated the frequency and nature of unresolved nuclei in galaxies at moderate redshift as indicators of nuclear activity such as Active Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged galaxies with multi-component models using maximum likelihood estimate techniques to determine the best model fit. We select those galaxies requiring an unresolved point-source component in the galaxy nucleus, in addition to a disk and/or bulge component, to adequately model the galaxy light. We have searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies containing compact nuclei. In our survey of 1033 galaxies, the fraction containing an unresolved nuclear component greater than 5% of the total galaxy light is 9+/-1% corrected for incompleteness. In this second of two papers in this series, we discuss the nature of the compact nuclei and their hosts. We present the upper limit luminosity function (LF) for low-luminosity AGN (LLAGN) in two redshift bins to z=0.8. Mild number density evolution is detected for nuclei at -18 -16 and this flatness, combined with the increase in number density, is inconsistent with pure luminosity evolution. Based on the amount of density evolution observed for these objects, we find that almost all present-day spiral galaxies could have hosted a LLAGN at some point in their lives. We also comment on the likely contribution of these compact nuclei to the soft X-ray background.Comment: 50 pages, 14 figures, to appear in ApJ, April 199

Conjugatable water-soluble Pt(ii) and Pd(ii) porphyrin complexes: Novel nano- and molecular probes for optical oxygen tension measurement in tissue engineering

Measurement of oxygen tension in compressed collagen sheets was performed using matrix-embedded optical oxygen sensors based on platinum(II) and palladium(II) porphyrins supported on polyacrylamide nanoparticles. Bespoke, fully water-soluble, mono-functionalised Pt(II) and Pd(II) porphyrin complexes designed for conjugation under mild conditions were obtained using microwave-assisted metallation. The new sensors display a linear response (1/τ vs. O₂) to varying oxygen tension over a biologically relevant range (7.0 × 10⁻⁴ to 2.7 × 10⁻¹ mM) in aqueous solutions; a behaviour that is maintained following conjugation to polyacrylamide nanoparticles, and following embedding of the nanosensors in compressed collagen sheets, paving the way to innovative approaches for real-time resolution of oxygen gradients throughout 3D matrices useful for tissue regeneration

Trends in cancer mortality in the European Union and accession countries, 1980-2000

Cancer mortality rates and trends over the period 1980-2000 for accession countries to the European Union (EU) in May 2004, which include a total of 75 million inhabitants, were abstracted from the World Health Organization (WHO) database, together with, for comparative purposes, those of the current EU. Total cancer mortality for men was 166/100 000 in the EU, but ranged between 195 (Lithuania) and 269/100 000 (Hungary) in central and eastern European accession countries. This excess related to most cancer sites, including lung and other tobacco-related neoplasms, but also stomach, intestines and liver, and a few neoplasms amenable to treatment, such as testis, Hodgkin's disease and leukaemias. Overall cancer mortality for women was 95/100 000 in the EU, and ranged between 100 and 110/100 000 in several central and eastern European countries, and up to 120/100 000 in the Czech Republic and 138/100 000 in Hungary. The latter two countries had a substantial excess in female mortality for lung cancer, but also for several other sites. Furthermore, for stomach and especially (cervix) uteri, female rates were substantially higher in central and eastern European accession countries. Over the last two decades, trends in mortality were systematically less favourable in accession countries than in the EU. Most of the unfavourable patterns and trends in cancer mortality in accession countries are due to recognised, and hence potentially avoidable, causes of cancer, including tobacco, alcohol, dietary habits, pollution and hepatitis B, plus inadequate screening, diagnosis and treatment. Consequently, the application of available knowledge on cancer prevention, diagnosis and treatment may substantially reduce the disadvantage now registered in the cancer mortality of central and eastern European accession countrie

The Gravitational Lensing in Redshift-space Correlation Functions of Galaxies and Quasars

The gravitational lensing, as well as the velocity field and the cosmological light-cone warp, changes the observed correlation function of high-redshift objects. We present an analytical expression of 3D correlation function, simultaneously including those three effects. When two objects are separated over several hundreds Mpc along a line of sight, the observed correlation function is dominated by the effect of gravitational lensing rather than the intrinsic clustering. For a canonical lambda-CDM model, the lensing signals in the galaxy-galaxy and galaxy-QSO correlations are beyond noise levels in large-scale redshift surveys like the Sloan Digital Sky Survey.Comment: 10 pages, 1 figure, submitted to ApJ

Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf

We report the detection of periodic (p = 1.96 hours) bursts of extremely bright, 100% circularly polarized, coherent radio emission from the M9 dwarf TVLM 513-46546. Simultaneous photometric monitoring observations have established this periodicity to be the rotation period of the dwarf. These bursts, which were not present in previous observations of this target, confirm that ultracool dwarfs can generate persistent levels of broadband, coherent radio emission, associated with the presence of kG magnetic fields in a large-scale, stable configuration. Compact sources located at the magnetic polar regions produce highly beamed emission generated by the electron cyclotron maser instability, the same mechanism known to generate planetary coherent radio emission in our solar system. The narrow beams of radiation pass our line of sight as the dwarf rotates, producing the associated periodic bursts. The resulting radio light curves are analogous to the periodic light curves associated with pulsar radio emission highlighting TVLM 513-46546 as the prototype of a new class of transient radio source.Comment: 12 pages, 3 figures, accepted for publication in ApJ Letter

ROSAT Blank Field Sources I: Sample Selection and Archival Data

We have identified a population of blank field sources (or `blanks') among the ROSAT bright unidentified X-ray sources with faint optical counterparts. The extreme X-ray over optical flux ratio of blanks is not compatible with the main classes of X-ray emitters except for extreme BL Lacertae objects. From the analysis of ROSAT archival data we found no indication of variability and evidence for only three sources, out of 16, needing absorption in excess of the Galactic value. We also found evidence for an extended nature for only one of the 5 blanks with a serendipitous HRI detection; this source (1WGAJ1226.9+3332) was confirmed as a z=0.89 cluster of galaxies. Palomar images reveal the presence of a red (O-E~2) counterpart in the X-ray error circle for 6 blanks. The identification process brought to the discovery of another high z cluster of galaxies, one (possibly extreme) BL Lac, two ultraluminous X-ray sources in nearby galaxies and two apparently normal type1 AGNs. These AGNs, together with 4 more AGN-like objects seem to form a well defined group: they present unabsorbed X-ray spectra but red Palomar counterparts. We discuss the possible explanations for the discrepancy between the X-ray and optical data, among which: a suppressed big blue bump emission, an extreme dust to gas (~40-60 the Galactic ratio), a high redshift (z>3.5) QSO nature, an atypical dust grain size distribution and a dusty warm absorber. These AGN-like blanks seem to be the bright (and easier to study) analogs of the sources which are found in deep Chandra observations. Three more blanks have a still unknown nature.Comment: 23 pages, 8 figures, accepted by ApJ main journa