5,134 research outputs found
Putting pharmaceuticals into the wider context of challenges to fish populations in rivers
The natural range of fish species in our rivers is related to flow, elevation, temperature, local habitat and connectivity. For over 2000 years, humans have altered to varying degrees the river habitat. In the past 200 years, we added to the environmental disruption by discharging poorly treated sewage, nutrients and industrial waste into our rivers. For many rivers, the low point arrived during the period of 1950s–1970s, when rapid economic development overrode environmental concerns and dissolved oxygen concentrations dropped to zero. In these more enlightened times, gross river pollution is a thing of the past in the Developed World. However, persistent legacy chemical contaminants can be found in fish long after their discharge ceased. Changes in habitat quality and morphology caused and continue to cause the disappearance of fish species. The range of fish stressors has now increased as temperatures rise, and non-native fish introductions bring new diseases. The threat from pharmaceuticals to fish populations remains hypothetical, and no studies have yet linked change in fish populations to exposure
Associations between congenital malformations and childhood cancer. A register-based case-control study.
This report describes a population-based case-control study that aimed to assess and quantify the risk of children with congenital malformations developing cancer. Three sources of data were used: the Victorian Cancer Register, the Victorian Perinatal Data Register (VPDR) and the Victorian Congenital Malformations/Birth Defects Register. Cases included all Victorian children born between 1984 and 1993 who developed cancer. Four controls per case, matched on birth date, were randomly selected from the VPDR. Record linkage between registers provided malformation data. A matched case-control analysis was undertaken. Of the 632 cancer cases, 570 (90.2%) were linked to the VPDR. The congenital malformation prevalence in children with cancer was 9.6% compared with 2.5% in the controls [odds ratio (OR) 4.5, 95% CI 3.1-6.7]. A strong association was found with chromosomal defects (OR=16.7, 95% CI 6.1-45.3), in particular Down's syndrome (OR=27.1, 95% CI 6.0-122). Most other birth defect groups were also associated with increased cancer risk. The increased risk of leukaemia in children with Down's syndrome was confirmed, and children with central nervous system (CNS) defects were found to be at increased risk of CNS tumours. The report confirms that children with congenital malformations have increased risks of various malignancies. These findings may provide clues to the underlying aetiology of childhood cancer, as congenital malformations are felt to be a marker of exposures or processes which may increase cancer risk. The usefulness of record linkage between accurate population-based registers in the epidemiological study of disease has also been reinforced
AGN feedback at z~2 and the mutual evolution of active and inactive galaxies
The relationships between galaxies of intermediate stellar mass and moderate
luminosity active galactic nuclei (AGNs) at 1<z<3 are investigated with the
Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample
complemented with public data in the GOODS-South field. Using X-ray data,
hidden AGNs are identified in unsuspected star-forming galaxies with no
apparent signs of non-stellar activity. In the color-mass plane, two parallel
trends emerge during the ~2 Gyr between the average redshifts z~2.2 and z~1.3:
while the red sequence becomes significantly more populated by ellipticals, the
majority of AGNs with L(2-10 keV)>10^42.3 erg s^-1 disappear from the blue
cloud/green valley where they were hosted predominantly by star-forming systems
with disk and irregular morphologies. These results are even clearer when the
rest-frame colors are corrected for dust reddening. At z~2.2, the ultraviolet
spectra of active galaxies (including two Type 1 AGNs) show possible gas
outflows with velocities up to about -500 km s^-1 that are not observed neither
in inactive systems at the same redshift, nor at lower redshifts. Such outflows
indicate the presence of gas that can move faster than the escape velocities of
active galaxies. These results suggest that feedback from moderately luminous
AGNs (logL_X~2 by contributing to
outflows capable of ejecting part of the interstellar medium and leading to a
rapid decrease in the star formation in host galaxies with stellar masses
10<logM<11 M_Sun.Comment: Astrophysical Journal Letters, in press (6 pages, 4 figures
A Study of the Kazakov-Migdal Model
We study numerically the SU(2) Kazakov-Migdal model of `induced QCD'. In
contrast to our earlier work on the subject we have chosen here {\it not} to
integrate out the gauge fields but to keep them in the Monte Carlo simulation.
This allows us to measure observables associated with the gauge fields and
thereby address the problem of the local symmetry present in the model.
We confirm our previous result that the model has a line of first order phase
transitions terminating in a critical point. The adjoint plaquette has a clear
discontinuity across the phase transition, whereas the plaquette in the
fundamental representation is always zero in accordance with Elitzur's theorem.
The density of small monopoles shows very little variation and is always
large. We also find that the model has extra local U(1) symmetries which do not
exist in the case of the standard adjoint theory. As a result, we are able to
show that two of the angles parameterizing the gauge field completely decouple
from the theory and the continuum limit defined around the critical point can
therefore not be `QCD'.Comment: 11 pages, UTHEP-24
Fixed twist dynamics of SO(3) gauge theory
We perform a throughout study of 3+1 dim. SO(3) LGT for any fixed-twist
background. We concentrate in particular on the physically significant trivial
and 1-twist sectors. Introducing a Z(2) monopole chemical potential the 1st
order bulk transition is moved down in the strong coupling region and weakened
to 2nd order in the 4-dim Ising model universality class. In this extended
phase diagram we gain access to a confined phase in every fixed twist sector of
the theory. The Pisa disorder operator is employed together with the Polyakov
loop to study the confinement-deconfinement transition in each sector. Due to
the specific properties of both operators, most results can be used to gain
insight in the ergodic theory, where all twist sectors should be summed upon.
An explicit mapping of each fixed twist theory to effective positive plaquette
models with fixed twisted boundary conditions is applied to better establish
their properties in the different phases.Comment: 20 pages, 11 Figures. Minor changes in text and figures, to appear in
Eur.Phys.J.
Convergence of the Optimized Delta Expansion for the Connected Vacuum Amplitude: Zero Dimensions
Recent proofs of the convergence of the linear delta expansion in zero and in
one dimensions have been limited to the analogue of the vacuum generating
functional in field theory. In zero dimensions it was shown that with an
appropriate, -dependent, choice of an optimizing parameter \l, which is an
important feature of the method, the sequence of approximants tends to
with an error proportional to . In the present paper we
establish the convergence of the linear delta expansion for the connected
vacuum function . We show that with the same choice of \l the
corresponding sequence tends to with an error proportional to . The rate of convergence of the latter sequence is governed by
the positions of the zeros of .Comment: 20 pages, LaTeX, Imperial/TP/92-93/5
Metalanguage in L1 English-speaking 12-year-olds: which aspects of writing do they talk about?
Traditional psycholinguistic approaches to metalinguistic awareness in L1 learners elicit responses containing metalanguage that demonstrates metalinguistic awareness
of pre-determined aspects of language knowledge. This paper, which takes a more ethnographic approach, demonstrates how pupils are able to engage their own focus of metalanguage when reflecting on their everyday learning activities involving written language. What is equally significant is what their metalanguage choices reveal about
their understanding and application of written language concepts
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