7,709 research outputs found
The use of otolith morphology to indicate the stock structure of common coral trout (Plectropomus leopardus) on the Great Barrier Reef, Australia
We investigated the use of otolith morphology to indicate the stock structure of an exploited serranid coral reef fish, Plectropomus leopardus, on the Great Barrier Reef (GBR), Australia. Otoliths were measured by traditional one-and two-dimensional measures (otolith length, width, area, perimeter, circularity, and rectangularity), as well as by Fourier analysis to capture the finer details of otolith shape. Variables were compared among four regions of the GBR separated by hundreds of kilometers, as well as among three reefs within each region, hundreds of meters to tens of kilometers apart. The temporal stability in otolith structure was examined by comparing two cohorts of fully recruited four-year-old P. leopardus collected two years before and two years after a signif icant disturbance in the southern parts of the GBR caused by a large tropical cyclone in March 1997. Results indicated the presence of at least two stocks of P. leopardus, although the structure of each stock varied depending on the cohort considered. The results highlight the importance of incorporating data from several years in studies using otolith morphology to discriminate temporary and possibly misleading signals from those that indicate persistent spatial structure in stocks. We conclude that otolith morphology can be used as an initial step to direct further research on groups of P. leopardus that have lived at least a part of their life in different environments
Discussion of: A statistical analysis of multiple temperature proxies: Are reconstructions of surface temperatures over the last 1000 years reliable?
Discussion of "A statistical analysis of multiple temperature proxies: Are
reconstructions of surface temperatures over the last 1000 years reliable?" by
B.B. McShane and A.J. Wyner [arXiv:1104.4002]Comment: Published in at http://dx.doi.org/10.1214/10-AOAS398F the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Time step rescaling recovers continuous-time dynamical properties for discrete-time Langevin integration of nonequilibrium systems
When simulating molecular systems using deterministic equations of motion
(e.g., Newtonian dynamics), such equations are generally numerically integrated
according to a well-developed set of algorithms that share commonly agreed-upon
desirable properties. However, for stochastic equations of motion (e.g.,
Langevin dynamics), there is still broad disagreement over which integration
algorithms are most appropriate. While multiple desiderata have been proposed
throughout the literature, consensus on which criteria are important is absent,
and no published integration scheme satisfies all desiderata simultaneously.
Additional nontrivial complications stem from simulating systems driven out of
equilibrium using existing stochastic integration schemes in conjunction with
recently-developed nonequilibrium fluctuation theorems. Here, we examine a
family of discrete time integration schemes for Langevin dynamics, assessing
how each member satisfies a variety of desiderata that have been enumerated in
prior efforts to construct suitable Langevin integrators. We show that the
incorporation of a novel time step rescaling in the deterministic updates of
position and velocity can correct a number of dynamical defects in these
integrators. Finally, we identify a particular splitting that has essentially
universally appropriate properties for the simulation of Langevin dynamics for
molecular systems in equilibrium, nonequilibrium, and path sampling contexts.Comment: 15 pages, 2 figures, and 2 table
Exact approximation of Rao-Blackwellised particle filters
Particle methods are a category of Monte Carlo algorithms that have become popular for performing inference in non-linear non-Gaussian state-space models. The class of 'Rao-Blackwellised' particle filters exploits the analytic marginalisation that is possible for some state-
space models to reduce the variance of the Monte Carlo estimates. Despite being applicable to only a restricted class of state-space models, such as conditionally linear Gaussian models, these algorithms have found numerous applications. In scenarios where no such analytical integration is possible, it has recently been proposed in Chen et al. [2011] to use 'local' particle filters to
carry out this integration numerically. We propose here an alternative approach also relying on \local" particle filters which is more broadly applicable and has attractive theoretical properties. Proof-of-concept simulation results are presented
Cancer in Northern Ireland by 2002.
An estimate of cancer deaths and incidence for the years 1997 and 2002, taking account of current trends and population projections for Northern Ireland is presented below. These numbers will be of value to those planning services and, in particular, for those implementing the report "Cancer Services - Investing for the Future". Cancer deaths are expected to rise by almost 13% to 4056 by the year 2002. Marked rises are expected in the number of deaths from cancer of the lung, oesophagus, kidney, bladder and prostate with smaller rises in deaths from breast and pancreatic cancer. The fall in stomach cancer is expected to continue as is the trend of lower deaths from cervical cancer. Deaths from cancer of the colon and rectum are expected to remain static. Estimates of cancer incidence currently and for the years 1997 and 2002 are also included. The impact of tobacco use by the population, which poses a current and future serious threat to public health is highlighted
Species abundance information improves sequence taxonomy classification accuracy.
Popular naive Bayes taxonomic classifiers for amplicon sequences assume that all species in the reference database are equally likely to be observed. We demonstrate that classification accuracy degrades linearly with the degree to which that assumption is violated, and in practice it is always violated. By incorporating environment-specific taxonomic abundance information, we demonstrate a significant increase in the species-level classification accuracy across common sample types. At the species level, overall average error rates decline from 25% to 14%, which is favourably comparable to the error rates that existing classifiers achieve at the genus level (16%). Our findings indicate that for most practical purposes, the assumption that reference species are equally likely to be observed is untenable. q2-clawback provides a straightforward alternative for samples from common environments
The correlation of VLF propagation variations with atmospheric planetary-scale waves
Variations in the received daytime phase of long distance, cesium-controlled, VLF transmission were compared to the height variations of the 10-mb isobaric surface during the first three months of 1965 and 1969. The VLF phase values are also compared to height variations of constant electron densities in the E-region and to variations of f-min which have been shown to be well correlated with planetary-scale variations in the stratosphere by Deland and Cavalieri (1973). The VLF phase variations show good correlation with these previous ionospheric measurements and with the 10-mb surfaces. The planetary scale waves in the stratosphere are shown to be travelling on the average eastward in 1965 and westward in 1969. These correlations are interpreted as due to the propagation of travelling planetary scale waves with westward tilted wave fronts. Upward energy transport due to the vertical structure of those waves is also discussed. These correlations provide further evidence for the coupling between the lower ionosphere at about 70 km altitude (the daytime VLF reflection height and the stratosphere, and they demonstrate the importance of planetary wave phenomena to VLF propagation
Looking For Disoriented Chiral Condensates From Pion Distributions
We suggest two methods for the detection of the formation of disoriented
chiral condensates in heavy ion collisions. We show that the variance in the
number of charged pions (in a suitable range of momentum space) provides a
signature for the observation of a disoriented chiral condensate. The signal
should be observable even if multiple domains of DC form provided the
average number of pions per domain is significantly larger than unity. The
variance of the number charged pions alone provides a signal which can be used
even if the number of neutral pions cannot be measured in a given detector. On
the other hand, the probability distribution in , the proportion of neutral
pions to all pions emitted in heavy ion collisions in certain kinematic
regions, has been suggested as a signal of a disoriented chiral condensate.
Here we note that the signature can be greatly enhanced by making suitable cuts
in the data. In particular, we consider reducing the data set such that the
pions with lowest are all neutral. We find that, given such cuts,
can be substantially different from 1/3. For example, for a single D$\chi$C
domain without contamination due to incoherently emitted pions, is 3/5
given the pion with lowest is neutral, and 5/7 given the two pions with
lowest are both neutral, {\it etc.}. The effects of multi-domain DC
formation and noise due to incoherent pion emission can be systematically
incorporated. Potential applications to experiments and their limitations are
briefly discussed.Comment: 16 pages in REVTeX, 7 figures. Combined and updated version of
nucl-th/9903029 and nucl-th/9904074. Accepted by Phys. Rev.
Scientific Advocacy: A Tool for Assessing the Risks of Engagement
Scientists active in the public sphere recognize the importance of broader communications but sometimes have an incomplete or exaggerated view of the risks to both their public and professional reputations as a function of their advocacy. These risks are connected fundamentally to the degree that the advocacy positions they take are based on values that are shared (or not) with their audiences. An encapsulation of the connections between Risks, Advocacy, and Values in Engagement (RAVE) may help inform choices that public scientists must make
Classical pion fields in the presence of source
Classical pion field similar to Disoriented Chiral Condensate (DCC) is
considered in the presence of the external source. This field is similar to DCC
in the sense that its isotopic orientation is specified with a single vector at
the whole space. We study the classical field solutions in the nonlinear
sigma-model both in the chiral limit with massless pion and for the finite pion
mass. In both cases the field resembles the Coulomb field of charged particle
however the nonlinear pion interactions lead to the existence of several
solutions. In the massless case and for the very small size of the source there
is the lot of classical solutions with finite discrete energies. In the more
realistic situation of large nucleus (heavy ion) there are no stable solutions
of the above type, but there is the possibility for the formation of the
quasistationary states. They can live for a long time slowly decaying through
the emission of very soft pions. The structure and the energies of these
solutions is investigated numerically.Comment: 10 pages, LaTeX, 1 figure, epsfig.sty, corrected typos, added
reference
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