Quadraphase demodulation

A received, suppressed carrier, quadraphase shift key modulated (QPSK)signal is demodulated with a phase locked loop including a variable frequency, coherent reference that drives first and second channels also responsive to the QPSK signal. The channels respectively derive first and second replicas of binary signals that modulated the suppressed carrier. The replicas are combined to derive a variable amplitude error signal for controlling the coherent reference frequency. The frequency of the coherent reference is dithered at a low rate so that there is derived a relatively low level tracking error phase from the locked loop. The frequency of the coherent reference is swept when the phase of the error signal differs from the dithering phase by a predetermined value that is appreciably less than 90 degrees

Analysis of β-globin chromatin micro-environment using a novel 3C variant, 4Cv

Copyright: © 2010 Pink et al.Higher order chromatin folding is critical to a number of developmental processes, including the regulation of gene expression. Recently developed biochemical techniques such as RNA TRAP and chromosome conformation capture (3C) have provided us with the tools to probe chromosomal structures. These techniques have been applied to the β-globin locus, revealing a complex pattern of interactions with regions along the chromosome that the gene resides on. However, biochemical and microscopy data on the nature of β-globin interactions with other chromosomes is contradictory. Therefore we developed a novel 4C variant, Complete-genome 3C by vectorette amplification (4Cv), which allows an unbiased and quantitative method to examine chromosomal structure. We have used 4Cv to study the microenvironment of the β-globin locus in mice and show that a significant proportion of the interactions of β-globin are inter-chromosomal. Furthermore, our data show that in the liver, where the gene is active, β-globin is more likely to interact with other chromosomes, compared to the brain where the gene is silent and is more likely to interact with other regions along the same chromosome. Our data suggest that transcriptional activation of the β-globin locus leads to a change in nuclear position relative to the chromosome territory.Ryan Pink is supported by a grant from Action Medical Research; Daniel Caley is supported by a grant from The Dunhill Medical Trust; David Carter is supported by a grant from the British Society for Haematology

Galaxy pairs in the Sloan Digital Sky Survey - XII: The fuelling mechanism of low excitation radio-loud AGN

We investigate whether the fuelling of low excitation radio galaxies (LERGs) is linked to major galaxy interactions. Our study utilizes a sample of 10,800 spectroscopic galaxy pairs and 97 post-mergers selected from the Sloan Digital Sky Survey with matches to multi-wavelength datasets. The LERG fraction amongst interacting galaxies is a factor of 3.5 higher than that of a control sample matched in local galaxy density, redshift and stellar mass. However, the LERG excess in pairs does not depend on projected separation and remains elevated out to at least 500 kpc, suggesting that major mergers are not their main fuelling channel. In order to identify the primary fuelling mechanism of LERGs, we compile samples of control galaxies that are matched in various host galaxy and environmental properties. The LERG excess is reduced, but not completely removed, when halo mass or D4000 are included in the matching parameters. However, when BOTH M_halo and D4000 are matched, there is no LERG excess and the 1.4 GHz luminosities (which trace jet mechanical power) are consistent between the pairs and control. In contrast, the excess of optical and mid-IR selected AGN in galaxy pairs is unchanged when the additional matching parameters are implemented. Our results suggest that whilst major interactions may trigger optically and mid-IR selected AGN, the gas which fuels the LERGs has two secular origins: one associated with the large scale environment, such as accretion from the surrounding medium or minor mergers, plus an internal stellar mechanism, such as winds from evolved stars.Comment: Accepted for publication in MNRAS Letters; 5 page

A Survey of Analogs to Weak MgII Absorbers in the Present

We present the results of a survey of the analogs of weak MgII absorbers (rest frame equivalent width W(2796) < 0.3 A) at 0 < z < 0.3. Our sample consisted of 25 HST/STIS echelle quasar spectra (R = 45,000) which covered SiII 1260 and CII 1335 over this redshift range. Using those similar transitions as tracers of MgII facilitates a much larger survey, covering a redshift pathlength of g(z) = 5.3 for an equivalent width limit of MgII corresponding to W(2796) > 0.02 A, with 30% completeness for the weakest lines. We find the number of weak MgII absorber analogs with 0.02 < W(2796) < 0.3 to be dN/dz = 1.00 +/- 0.20 for 0 < z < 0.3. This value is consistent with cosmological evolution of the population. We consider the expected effect on observability of weak MgII absorbers of the decreasing intensity of the extragalactic background radiation eld from z~1 to z~0. Assuming that all the objects that produce absorption at z~1 are stable on a cosmological timescale, and that no new objects are created, we would expect dN/dz of 2-3 at z~0. About 30-50% of this z~0 population would be decendants of the parsec-scale structures that produce single-cloud, weak MgII absorbers at z~1. The other 50-70% would be lower density, kiloparsec-scale structures that produce CIV absorption, but not detectable low ionization absorption, at z~1. We conclude that at least one, and perhaps some fraction of both, of these populations has evolved away since z~1, in order to match the z~0 dN/dz measured in our survey. This would follow naturally for a population of transient structures whose generation is related to star-forming processes, whose rate has decreased since z~1.Comment: 45 pages, 12 figures, 7 tables ApJ accepte

Geophysical and astronomical models applied in the analysis of very long baseline interferometry

Very long baseline interferometry presents an opportunity to measure at the centimeter level such geodetic parameters as baseline length and instantaneous pole position. In order to achieve such precision, the geophysical and astronomical models used in data analysis must be as accurate as possible. The Mark-3 interactive data analysis system includes a number of refinements beyond conventional practice in modeling precession, nutation, diurnal polar motion, UT1, solid Earth tides, relativistic light deflection, and reduction to solar system barycentric coordinates. The algorithms and their effects on the recovered geodetic, geophysical, and astrometric parameters are discussed