642 research outputs found
A complete sample of radio sources in the North Ecliptic Cap, selected at 38 MHz -- III. further imaging observations and the photometric properties of the sample
Further imaging observations of a sample of radio sources in the North
Ecliptic Cap are presented and a number of new identifications are made. Using
redshifts from spectroscopic data presented in a companion paper (Lacy et al.\
1999b), the photometric properties of the galaxies in the sample are discussed.
It is shown that: (1) out to at least z~0.6 radio galaxies are good standard
candles irrespective of radio luminosity; (2) for 0.6~<z~<1 a large fraction of
the sample have magnitudes and colours consistent with a non-evolving giant
elliptical, and (3) at higher redshifts, where the R-band samples the
rest-frame UV flux, most objects have less UV luminosity than expected if they
form their stellar populations at a constant rate from a high redshift to
in unobscured star-forming regions (assuming an Einstein -- de Sitter
cosmology). The consequences of these observations are briefly discussed.Comment: 10 pages, 6 figures, accepted by MNRA
A Suggested Criterion for Selecting between E-V and Stochastic Dominance Analysis Tools
Research Methods/ Statistical Methods,
Winter Body Mass and Over-Ocean Flocking as Components of Danger Management by Pacific Dunlins
Background: We compared records of the body mass and roosting behavior of Pacific dunlins (Calidris alpinapacifica) wintering on the Fraser River estuary in southwest British Columbia between the 1970s and the 1990s.‘Over-ocean flocking’ is a relatively safe but energetically-expensive alternative to roosting during the high tideperiod. Fat stores offer protection against starvation, but are a liability in escape performance, and increase flightcosts. Peregrine falcons (Falco peregrinus) were scarce on the Fraser River estuary in the 1970s, but their numbershave since recovered, and they prey heavily on dunlins. The increase has altered the balance between predationand starvation risks for dunlins, and thus how dunlins regulate roosting behavior and body mass to manage thedanger. We therefore predicted an increase in the frequency of over-ocean flocking as well as a decrease in theamount of fat carried by dunlins over these decades.Results: Historical observations indicate that over-ocean flocking of dunlins was rare prior to the mid-1990s andbecame common thereafter. Residual body masses of dunlins were higher in the 1970s, with the greatestdifference between the decades coinciding with peak peregrine abundance in October, and shrinking over thecourse of winter as falcon seasonal abundance declines. Whole-body fat content of dunlins was lower in the 1990s,and accounted for most of the change in body mass.Conclusions: Pacific dunlins appear to manage danger in a complex manner that involves adjustments both in fatreserves and roosting behavior. We discuss reasons why over-ocean flocking has apparently become morecommon on the Fraser estuary than at other dunlin wintering sites
Diode laser array
A diode laser array comprises a substrate of a semiconductor material having first and second opposed surfaces. On the first surface is a plurality of spaced gain sections and a separate distributed Bragg reflector passive waveguide at each end of each gain section and optically connecting the gain sections. Each gain section includes a cavity therein wherein charge carriers are generated and recombine to generate light which is confined in the cavity. Also, the cavity, which is preferably a quantum well cavity, provides both a high differential gain and potentially large depth of loss modulation. Each waveguide has a wavelength which is preferably formed by an extension of the cavity of the gain sections and a grating. The grating has a period which provides a selective feedback of light into the gain sections to supporting lasing, which allows some of the light to be emitted from the waveguide normal to the surface of the substrate and which allows optical coupling of the gain sections. Also, the grating period provides an operating wavelength which is on the short wavelength side of the gain period of the gain sections required for laser oscillation. An RF pulse is applied so as to maximize the magnitude of the loss modulation and the differential gain in the gain sections. The array is operated by applying a DC bias to all the gain sections at a level just below the threshold of the gain sections to only one of the gain sections which raises the bias in all of the gain sections to a level that causes all of the gain sections to oscillate. Thus, a small bias can turn the array on and off
Using radio galaxies to find super-structures
Radio galaxies are excellent at tracing large-scale structure due to their
high bias. We present new results from the TONS08 radio galaxy redshift survey.
We find unequivocal evidence for a huge (at least 80 x 80 x 100 Mpc^3)
super-structure at redshift z=0.27, confirming tentative evidence for such a
structure from the 7C redshift survey (7CRS). A second, newly discovered
super-structure is also tentatively found at redshift 0.35 (of dimensions at
least 100 x 100 x 100 Mpc^3). Out of the total sample size of 84 radio
galaxies, at least 25 are associated with the two super-structures. We use
quasi-linear structure formation theory to estimate the number of such
structures expected in the TONS08 volume if the canonical value for radio
galaxy bias is assumed. Under this assumption, the structures represent ~ 4-5
sigma peaks in the primordial density field and their expected number is low
(10^{-2}-10^{-4}). Fortunately, there are several plausible explanations (many
of which are testable) for these low probabilities in the form of potential
mechanisms for boosting the bias on large scales. These include: the
association of radio galaxies with highly biased rich clusters in
super-structures, enhanced triggering by group/group mergers, and enhanced
triggering and/or redshift space distortion in collapsing systems as the growth
of super-structures moves into the non-linear regime. Similar structures could
have been missed in previous surveys because of the effects of Poisson-sampling
fluctuations.Comment: 6 pages, 3 figures. To appear in "Radio galaxies: past, present and
future", eds M. Jarvis et al., Leiden, Nov 200
Cosmology without cosmic variance
We examine the improvements in constraints on the linear growth factor G and
its derivative f=d ln G / dln a that are available from the combination of a
large-scale galaxy redshift survey with a weak gravitational lensing survey of
background sources. In the linear perturbation theory limit, the
bias-modulation method of McDonald & Seljak allows one to distinguish the
real-space galaxy clustering from the peculiar velocity signal in each Fourier
mode. The ratio of lensing signal to galaxy clustering in transverse modes
yields the bias factor b of each galaxy subset (as per Pen 2004), hence
calibrating the conversion from galaxy real-space density to matter density in
every mode. In combination these techniques permit measure of the growth rate f
in each Fourier mode. This yields a measure of the growth rate free of sample
variance, i.e. the uncertainty in f can be reduced without bound by increasing
the number of redshifts within a finite volume. In practice, the gain from the
absence of sample variance is bounded by the limited range of bias modulation
among dark-matter halos. Nonetheless, the addition of background weak lensing
data to a redshift survey increases information on G and f by an amount
equivalent to a 10-fold increase in the volume of a standard redshift-space
distortion measurement---if the lensing signal can be measured to sub-percent
accuracy. This argues that a combined lensing and redshift survey over a common
low-redshift volume is a more powerful test of general relativity than an
isolated redshift survey over larger volume at high redshift. An example case
is that a survey of ~10^6 redshifts over half the sky in the redshift range
can determine the growth exponent \gamma for the model
to an accuracy of , using only modes with
k<0.1h/Mpc, but only if a weak lensing survey is conducted in concert.
[Abridged]Comment: 9 pages, 3 figures, accepted by MNRAS, minor changes to match the
accepted versio
Effect of changing data size on eigenvalues in the Korean and Japanese stock markets
In this study, we attempted to determine how eigenvalues change, according to
random matrix theory (RMT), in stock market data as the number of stocks
comprising the correlation matrix changes. Specifically, we tested for changes
in the eigenvalue properties as a function of the number and type of stocks in
the correlation matrix. We determined that the value of the eigenvalue
increases in proportion with the number of stocks. Furthermore, we noted that
the largest eigenvalue maintains its identical properties, regardless of the
number and type, whereas other eigenvalues evidence different features
Intraspecific Variation in Commuting Distance of Marbled Murrelets (Brachyramphus marmoratus): Ecological and Energetic Consequences of Nesting Further Inland
Estimating the Range of Obesity Treatment Response Variability in Humans: Methods and Illustrations
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