12,065 research outputs found
Comparison of life history parameters for landed and discarded fish captured off the southeastern United States
Commercial fisheries that are managed with minimum size limits protect small fish of all ages and may affect size-selective mortality by the differential removal of fast growing fish. This differential removal may decrease the average size at age, maturation, or sexual transition of the exploited population. When fishery-independent data are
not available, a comparison of life history parameters of landed with those of discarded fish (by regulation) will
indicate if differential mortality is occurring with the capture of young but large fish (fast growing phenotypes).
Indications of this differential size-selective mortality would include the following: the discarded portion of the target fish would have similar age ranges but smaller sizes at age, maturation, and sexual transition as that of landed fish. We examined three species with minimum size limits but different exploitation histories. The known heavily exploited species (Rhomboplites aurorubens [vermilion snapper] and Pagrus pagrus [red porgy]) show signs of this
differential mortality. Their landed catch includes many young, large fish, whereas discarded fish had a similar age range and mean ages but smaller sizes at age than the landed
fish. The unknown exploited species, Mycteroperca phenax (scamp), showed no signs of differential mortality due
to size-selective fishing. Landed catch consisted of old, large fish and discarded scamp had little overlap in age ranges, had significantly different mean ages, and only small differences in size at age when compared to comparable
data for landed fish
Dynamic Decomposition of Spatiotemporal Neural Signals
Neural signals are characterized by rich temporal and spatiotemporal dynamics
that reflect the organization of cortical networks. Theoretical research has
shown how neural networks can operate at different dynamic ranges that
correspond to specific types of information processing. Here we present a data
analysis framework that uses a linearized model of these dynamic states in
order to decompose the measured neural signal into a series of components that
capture both rhythmic and non-rhythmic neural activity. The method is based on
stochastic differential equations and Gaussian process regression. Through
computer simulations and analysis of magnetoencephalographic data, we
demonstrate the efficacy of the method in identifying meaningful modulations of
oscillatory signals corrupted by structured temporal and spatiotemporal noise.
These results suggest that the method is particularly suitable for the analysis
and interpretation of complex temporal and spatiotemporal neural signals
Positive representations of finite groups in Riesz spaces
In this paper, which is part of a study of positive representations of
locally compact groups in Banach lattices, we initiate the theory of positive
representations of finite groups in Riesz spaces. If such a representation has
only the zero subspace and possibly the space itself as invariant principal
bands, then the space is Archimedean and finite dimensional. Various notions of
irreducibility of a positive representation are introduced and, for a finite
group acting positively in a space with sufficiently many projections, these
are shown to be equal. We describe the finite dimensional positive Archimedean
representations of a finite group and establish that, up to order equivalence,
these are order direct sums, with unique multiplicities, of the order
indecomposable positive representations naturally associated with transitive
-spaces. Character theory is shown to break down for positive
representations. Induction and systems of imprimitivity are introduced in an
ordered context, where the multiplicity formulation of Frobenius reciprocity
turns out not to hold.Comment: 23 pages. To appear in International Journal of Mathematic
MHV, CSW and BCFW: field theory structures in string theory amplitudes
Motivated by recent progress in calculating field theory amplitudes, we study
applications of the basic ideas in these developments to the calculation of
amplitudes in string theory. We consider in particular both non-Abelian and
Abelian open superstring disk amplitudes in a flat space background, focusing
mainly on the four-dimensional case. The basic field theory ideas under
consideration split into three separate categories. In the first, we argue that
the calculation of alpha'-corrections to MHV open string disk amplitudes
reduces to the determination of certain classes of polynomials. This line of
reasoning is then used to determine the alpha'^3-correction to the MHV
amplitude for all multiplicities. A second line of attack concerns the
existence of an analog of CSW rules derived from the Abelian Dirac-Born-Infeld
action in four dimensions. We show explicitly that the CSW-like perturbation
series of this action is surprisingly trivial: only helicity conserving
amplitudes are non-zero. Last but not least, we initiate the study of BCFW
on-shell recursion relations in string theory. These should appear very
naturally as the UV properties of the string theory are excellent. We show that
all open four-point string amplitudes in a flat background at the disk level
obey BCFW recursion relations. Based on the naturalness of the proof and some
explicit results for the five-point gluon amplitude, it is expected that this
pattern persists for all higher point amplitudes and for the closed string.Comment: v3: corrected erroneous statement about Virasoro-Shapiro amplitude
and added referenc
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