1,178 research outputs found
Constraints on Beta Functions from Duality
We analyze the way in which duality constrains the exact beta function and
correlation length in single-coupling spin systems. A consistency condition we
propose shows very concisely the relation between self-dual points and phase
transitions, and implies that the correlation length must be duality invariant.
These ideas are then tested on the 2-d Ising model, and used towards finding
the exact beta function of the -state Potts model. Finally, a generic
procedure is given for identifying a duality symmetry in other single-coupling
models with a continuous phase transition.Comment: LaTeX, 6 page
Genetic identity determines risk of post-settlement mortality of a marine fish
Author Posting. © Ecological Society of America, 2007. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecology 88 (2007): 1263â1277, doi:10.1890/06-0066.Longitudinal sampling of four cohorts of Neopomacentrus filamentosus, a common tropical damselfish from Dampier Archipelago, Western Australia, revealed the evolution of size structure after settlement. Light traps collected premetamorphic individuals from the water column (âsettlersâ) to establish a baseline for each cohort. Subsequently, divers collected benthic juveniles (ârecruitsâ) at 1â3-month intervals to determine the relative impacts of post-settlement mortality during the first three months. Growth trajectories for individual fish were back-calculated from otolith records and compared with nonlinear mixed-effects models. Size-selective mortality was detected in all cohorts with the loss of smaller, slower growing individuals. Three months after settlement, recruits showed significantly faster growth as juveniles, faster growth as larvae, and larger sizes as hatchlings. The timing and intensity of post-settlement selection differed among cohorts and was correlated with density at settlement. The cohort with the greatest initial abundance experienced the strongest selective mortality, with most of this mortality occurring between one and two months after settlement when juveniles began foraging at higher positions in the water column. Significant genetic structure was found between settlers and three-month-old recruits in this cohort as a result of natural selection that changed the frequency of mtDNA haplotypes measured at the control region. The extent of this genetic difference was enlarged or reduced by artificially manipulating the intensity of size-based selection, thus establishing a link between phenotype and haplotype. Sequence variation in the control region of the mitochondrial genome has been linked to mitochondrial efficiency and weight gain in other studies, which provides a plausible explanation for the patterns observed here.The project was funded by the Australian Institute of
Marine Science, the Australian European Award Program, le
Ministe` re francž ais des Affaires Etrange` res, ARC-DEET,
Boston University, and the National Science Foundation
(Biological Oceanography, OCE 0349177)
Measuring the three-dimensional shear from simulation data, with applications to weak gravitational lensing
We have developed a new three-dimensional algorithm, based on the standard
PM method, for computing deflections due to weak gravitational lensing. We
compare the results of this method with those of the two-dimensional planar
approach, and rigorously outline the conditions under which the two approaches
are equivalent. Our new algorithm uses a Fast Fourier Transform convolution
method for speed, and has a variable softening feature to provide a realistic
interpretation of the large-scale structure in a simulation. The output values
of the code are compared with those from the Ewald summation method, which we
describe and develop in detail. With an optimal choice of the high frequency
filtering in the Fourier convolution, the maximum errors, when using only a
single particle, are about 7 per cent, with an rms error less than 2 per cent.
For ensembles of particles, used in typical -body simulations, the rms
errors are typically 0.3 per cent. We describe how the output from the
algorithm can be used to generate distributions of magnification, source
ellipticity, shear and convergence for large-scale structure.Comment: 22 pages, latex, 11 figure
Weak gravitational lensing in the standard Cold Dark Matter model, using an algorithm for three-dimensional shear
We investigate the effects of weak gravitational lensing in the standard Cold
Dark Matter cosmology, using an algorithm which evaluates the shear in three
dimensions. The algorithm has the advantage of variable softening for the
particles, and our method allows the appropriate angular diameter distances to
be applied to every evaluation location within each three-dimensional
simulation box. We investigate the importance of shear in the distance-redshift
relation, and find it to be very small. We also establish clearly defined
values for the smoothness parameter in the relation, finding its value to be at
least 0.88 at all redshifts in our simulations. From our results, obtained by
linking the simulation boxes back to source redshifts of 4, we are able to
observe the formation of structure in terms of the computed shear, and also
note that the major contributions to the shear come from a very broad range of
redshifts. We show the probability distributions for the magnification, source
ellipticity and convergence, and also describe the relationships amongst these
quantities for a range of source redshifts. We find a broad range of
magnifications and ellipticities; for sources at a redshift of 4, 97{1/2}% of
all lines of sight show magnifications up to 1.3 and ellipticities up to 0.195.
There is clear evidence that the magnification is not linear in the
convergence, as might be expected for weak lensing, but contains contributions
from higher order terms in both the convergence and the shear.Comment: 14 pages, LaTeX, 15 figures include
Quality of private and public ambulatory health care in low and middle income countries: systematic review of comparative studies
Paul Garner and colleagues conducted a systematic review of 80 studies to compare
the quality of private versus public ambulatory health care in low- and
middle-income countries
Structurally diverse hamigerans from the New Zealand marine sponge Hamigera tarangaensis: NMR-directed isolation, structure elucidation and antifungal activity
The NMR-directed investigation of the New Zealand marine sponge Hamigera tarangaensis has afforded ten new compounds of the hamigeran family, and a new 13-epi-verrucosane congener. Notably, hamigeran F (6) possesses an unusual carbonâcarbon bond between C-12 and C-13, creating an unprecedented skeleton within this class. In particular, the structural features of 6, hamigeran H (10) and hamigeran J (12) imply a diterpenoid origin, which has allowed the putative biogenesis of three hamigeran carbon skeletons to be proposed based on geranyl geranyl pyrophosphate. All new hamigerans exhibited micromolar activity towards the HL-60 promyelocytic leukaemic cell line, and hamigeran G also selectively displayed antifungal activity in the budding yeast Saccharomyces cerevisiae. Homozygous deletion profiling (HOP) analysis suggests Golgi apparatus function as a potential target of this unusual class of sponge-derived terpenoids
Corner Exponents in the Two-Dimensional Potts Model
The critical behavior at a corner in two-dimensional Ising and three-state
Potts models is studied numerically on the square lattice using transfer
operator techniques. The local critical exponents for the magnetization and the
energy density for various opening angles are deduced from finite-size scaling
results at the critical point for isotropic or anisotropic couplings. The
scaling dimensions compare quite well with the values expected from conformal
invariance, provided the opening angle is replaced by an effective one in
anisotropic systems.Comment: 11 pages, 2 eps-figures, uses LaTex and eps
Research protocol â Assessing Post-Stroke Psychology Longitudinal Evaluation (APPLE) study : A prospective cohort study in stroke
Acknowledgements The following experts provided advice on the design and conduct of the APPLE study: Prof Jonathan Evans (University of Glasgow); Prof Gillian Mead (University of Edinburgh); Prof Sarah T Pendlebury (University of Oxford) Funding This work was supported by the Chief Scientist Office and Stroke Association (funders reference PPA 2015/01_CSO).Peer reviewedPublisher PD
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