4,726 research outputs found
Survey- and fishery-derived estimates of Pacific cod (Gadus macrocephalus) biomass: implications for strategies to reduce interactions between groundfish fisheries and Steller sea lions (Eumetopias jubatus)
Survey- and fishery-derived biomass estimates have
indicated that the harvest indices for Pacific cod (Gadus macrocephalus) within a portion of Steller sea lion (Eumetopias jubatus) critical habitat in February and March 2001 were five to 16 times greater than the annual rate for the entire Bering Sea-Aleutian Islands stock. A bottom
trawl survey yielded a cod biomass estimate of 49,032 metric tons (t) for the entire area surveyed, of which
less than half (23,329 t) was located within the area used primarily by the commercial fishery, which caught 11,631 t of Pacific cod. Leslie depletion analyses of fishery data yielded biomass estimates of approximately 14,500 t (95% confidence intervals of approximately 9,000–25,000 t), which
are within the 95% confidence interval on the fished area survey estimate (12,846–33,812 t). These data indicate
that Leslie analyses may be useful in estimating local fish biomass and harvest indices for certain marine fisheries that are well constrained spatially and relatively short in duration (weeks). In addition, fishery effects on prey availability within the time and space scales relevant
to foraging sea lions may be much greater than the effects indicated by annual harvest rates estimated from stock assessments averaged across the range of the target spe
Influence network linkages across implementation strategy conditions in a randomized controlled trial of two strategies for scaling up evidence-based practices in public youth-serving systems.
BackgroundGiven the importance of influence networks in the implementation of evidence-based practices and interventions, it is unclear whether such networks continue to operate as sources of information and advice when they are segmented and disrupted by randomization to different implementation strategy conditions. The present study examines the linkages across implementation strategy conditions of social influence networks of leaders of youth-serving systems in 12 California counties participating in a randomized controlled trial of community development teams (CDTs) to scale up use of an evidence-based practice.MethodsSemi-structured interviews were conducted with 38 directors, assistant directors, and program managers of county probation, mental health, and child welfare departments. A web-based survey collected additional quantitative data on information and advice networks of study participants. A mixed-methods approach to data analysis was used to create a sociometric data set (n = 176) to examine linkages between treatment and standard conditions.ResultsOf those network members who were affiliated with a county (n = 137), only 6 (4.4%) were directly connected to a member of the opposite implementation strategy condition; 19 (13.9%) were connected by two steps or fewer to a member of the opposite implementation strategy condition; 64 (46.7%) were connected by three or fewer steps to a member of the opposite implementation strategy condition. Most of the indirect steps between individuals who were in different implementation strategy conditions were connections involving a third non-county organizational entity that had an important role in the trial in keeping the implementation strategy conditions separate. When these entities were excluded, the CDT network exhibited fewer components and significantly higher betweenness centralization than did the standard condition network.ConclusionAlthough the integrity of the RCT in this instance was not compromised by study participant influence networks, RCT designs should consider how influence networks may extend beyond boundaries established by the randomization process in implementation studies.Trial registrationNCT00880126
Relativistic Effects in Nuclear Matter and Nuclei
The status of relativistic nuclear many-body calculations of nuclear systems
to be built up in terms of protons and neutrons is reviewed. In detail,
relativistic effects on several aspects of nuclear matter such as the effective
mass, saturation mechanism, and the symmetry energy are considered. This review
will especially focus on isospin asymmetric issues, since these aspects are of
high interest in astrophysical and nuclear structure studies. Furthermore, from
the experimental side these aspects are experiencing an additional boost from a
new generation of radioactive beam facilities, e.g. the future GSI facility
FAIR in Germany or SPIRAL2 at GANIL/France. Finally, the prospects of studying
finite nuclei in microscopic calculations which are based on realistic
interactions by including relativistic effects in calculations of low momentum
interactions are discussed.Comment: 57 pages, 16 figure
Strain-stiffening in random packings of entangled granular chains
Random packings of granular chains are presented as a model polymer system to
investigate the contribution of entanglements to strain-stiffening in the
absence of Brownian motion. The chain packings are sheared in triaxial
compression experiments. For short chain lengths, these packings yield when the
shear stress exceeds a the scale of the confining pressure, similar to packings
of spherical particles. In contrast, packings of chains which are long enough
to form loops exhibit strain-stiffening, in which the effective stiffness of
the material increases with strain, similar to many polymer materials. The
latter packings can sustain stresses orders-of-magnitude greater than the
confining pressure, and do not yield until the chain links break. X-ray
tomography measurements reveal that the strain-stiffening packings contain
system-spanning clusters of entangled chains.Comment: 4 pages, 4 figures. submitted to Physical Review Letter
Shear thickening in densely packed suspensions of spheres and rods confined to few layers
We investigate confined shear thickening suspensions for which the sample
thickness is comparable to the particle dimensions. Rheometry measurements are
presented for densely packed suspensions of spheres and rods with aspect ratios
6 and 9. By varying the suspension thickness in the direction of the shear
gradient at constant shear rate, we find pronounced oscillations in the stress.
These oscillations become stronger as the gap size is decreased, and the stress
is minimized when the sample thickness becomes commensurate with an integer
number of particle layers. Despite this confinement-induced effect, viscosity
curves show shear thickening that retains bulk behavior down to samples as thin
as two particle diameters for spheres, below which the suspension is jammed.
Rods exhibit similar behavior commensurate with the particle width, but they
show additional effects when the thickness is reduced below about a particle
length as they are forced to align; the stress increases for decreasing gap
size at fixed shear rate while the shear thickening regime gradually
transitions to a Newtonian scaling regime. This weakening of shear thickening
as an ordered configuration is approached contrasts with the strengthening of
shear thickening when the packing fraction is increased in the disordered bulk
limit, despite the fact that both types of confinement eventually lead to
jamming.Comment: 21 pages, 14 figures. submitted to the Journal of Rheolog
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