1,095 research outputs found
Ecology of Juvenile Walleye Pollock, Theragra chalcogramma: Papers from the workshop "The Importance of Prerecruit Walleye Pollock to the Bering Sea and North Pacific Ecosystems" Seattle, Washington, 28-30 October 1993
The Alaska Fisheries Science Center (AFSC), National
Marine Fisheries Service (NMFS), hosted an international
workshop, 'The Importance of Prerecruit Walleye Pollock to the Bering Sea and North Pacific Ecosystems," from 28 to 30 October 1993. This workshop was held in conjunction with the annual International North Pacific Marine Science Organization (PICES) meeting held in Seattle. Nearly 100 representatives from government agencies, universities, and the fishing industry in Canada, Japan, the People's Republic of China, Russia, and the United States took part in the workshop to review and discuss current knowledge on juvenile pollock from the postlarval period to the time they recruit to the fisheries. In addition to its importance to humans as a major commercial species, pollock also serves as a major forage species for many marine fishes, birds, and mammals in the North Pacific region.
(PDF file contains 236 pages.
Control of the Onset of Filamentation in Condensed Media
Propagation of intense, ultrashort laser pulses through condensed media like
crystals of BaF and sapphire results in the formation of filaments. We
demonstrate that the onset of filamentation may be controlled by rotating the
plane of polarization of incident light. We directly visualize filamentation in
BaF_2 via six-photon absorption-induced fluorescence and, concomitantly, by
probing the spectral and spatial properties of white light that is generated.Comment: To appear in Phys. Rev.
Interactions of gelatinous zooplankton within marine food webs
Gelatinous zooplankton (GZ) comprise a taxonomically and functionally diverse group of marine organisms which includes ctenophores, cnidarians and pelagic tunicates, sharing a soft, mostly transparent body texture, a high body water content and a lack of exoskeleton. They range in size from less than a millimetre to nearly 2 m for the cnidarian jellyfish Nemopilema nomurai, and comprise some of the fastest growing metazoans on Earth (Hopcroft et al., 1998), sometimes surpassing crustacean zooplankton in their contribution to secondary production (i.e. in subtropical waters; Jaspers et al., 2009). They feed on a wide range of prey sizes, with predator–prey ratios comparable in some cases to those of baleen whales and krill (Deibel and Lee, 1992), and with prey removal rates which are similar to those of their non-gelatinous competitors (Acuña et al., 2011). In spite of early work pointing to gelatinous zooplankton as a trophic dead end (Verity and Smetacek, 1996), evidence is rapidly accumulating which shows that they may potentially channel energy from the picoplankton-sized, microbial loop organisms up to the higher trophic levels, including fish (Llopiz et al., 2010). However, this pathway is still largely neglected in most food web investigations even though it is now becoming clear that GZ represent a major fraction of the diet of several commercially important fish species such as bluefin tuna (Thunnus thynnus) (Cardona et al., 2012)
Trapped-ion decay spectroscopy towards the determination of ground-state components of double-beta decay matrix elements
A new technique has been developed at TRIUMF's TITAN facility to perform
in-trap decay spectroscopy. The aim of this technique is to eventually measure
weak electron capture branching ratios (ECBRs) and by this to consequently
determine GT matrix elements of decaying nuclei. These branching
ratios provide important input to the theoretical description of these decays.
The feasibility and power of the technique is demonstrated by measuring the
ECBR of Cs.Comment: 9 pages, 9 figure
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Influence of a Coastal Riverine Plume on the Cross-shelf Variability in Hydrography, Zooplankton, and Juvenile Salmon Diets
Riverine plumes in nearshore coastal waters are areas of enhanced production and accumulation of prey and may increase availability of food during a critical period of juvenile salmon survival and hence serve as a nursery area for these juveniles. Physical and biological sampling was conducted along a cross-shelf transect through the Columbia River plume during May 1999. Based on cluster analyses of physical variables, stations considered to be within the core of the plume, at 27.8–46.3 km from shore, were distinct from inshore (7.4–18.5 km) and offshore (55.6–92.7 km) stations. Five variables (temperature at 10 m, salinity at 3 and 10 m, silicate, and chlorophyll) accounted for 92 % of this difference. Both surface neuston and subsurface plankton tows revealed differences in plankton composition at the plume core stations compared to non-plume stations. However, stomach contents of juvenile Chinook salmon were not significantly different inside and outside the plume core. Comparison of similarity indices showed that the stomach composition was more similar to the catch composition in the neuston than the meter net. Fishes, decapod larvae, and hyperiid amphipods occurred in greater proportions and copepods and euphausiids in lesser proportions in the stomachs than in the plankton. There appeared to be a distinctive plume signal, evident in both the physical environment and zooplankton resources sampled inside and outside the plume core, but the plume signature was not as evident in the salmon diets, possibly due to their higher mobility and shorter residence time within the plume.Keywords: Habitat, Oceanography, Riverine plume, Feeding habits, Juvenile salmon, Zooplankto
First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He
The first direct mass-measurement of He has been performed with the
TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the
mass of He was determined with improved precision over our previous
measurement. The obtained masses are (He) = 6.018 885 883(57) u and
(He) = 8.033 934 44(11) u. The He value shows a deviation from
the literature of 4. With these new mass values and the previously
measured atomic isotope shifts we obtain charge radii of 2.060(8) fm and
1.959(16) fm for He and He respectively. We present a detailed
comparison to nuclear theory for He, including new hyperspherical harmonics
results. A correlation plot of the point-proton radius with the two-neutron
separation energy demonstrates clearly the importance of three-nucleon forces.Comment: 4 pages, 2 figure
Precision mass measurements on neutron-rich rare-earth isotopes at JYFLTRAP - reduced neutron pairing and implications for the -process calculations
The rare-earth peak in the -process abundance pattern depends sensitively
on both the astrophysical conditions and subtle changes in nuclear structure in
the region. This work takes an important step elucidating the nuclear structure
and reducing the uncertainties in -process calculations via precise atomic
mass measurements at the JYFLTRAP double Penning trap. Nd, Pm,
Sm, and Gd have been measured for the first time and the
precisions for Nd, Pm, Eu, Gd, and
Tb have been improved considerably. Nuclear structure has been probed
via two-neutron separation energies and neutron pairing energy metrics
. The data do not support the existence of a subshell closure at .
Neutron pairing has been found to be weaker than predicted by theoretical mass
models. The impact on the calculated -process abundances has been studied.
Substantial changes resulting in a smoother abundance distribution and a better
agreement with the solar -process abundances are observed.Comment: 8 pages, 4 figures, accepted for publication in Physical Review
Letter
Elucidation of the anomalous A = 9 isospin quartet behaviour
Recent high-precision mass measurements of Li and Be, performed
with the TITAN Penning trap at the TRIUMF ISAC facility, are analyzed in light
of state-of-the-art shell model calculations. We find an explanation for the
anomalous Isobaric Mass Multiplet Equation (IMME) behaviour for the two = 9
quartets. The presence of a cubic = 6.3(17) keV term for the =
3/2 quartet and the vanishing cubic term for the excited =
1/2 multiplet depend upon the presence of a nearby = 1/2 state in
B and Be that induces isospin mixing. This is contrary to previous
hypotheses involving purely Coulomb and charge-dependent effects. = 1/2
states have been observed near the calculated energy, above the = 3/2
state. However an experimental confirmation of their is needed.Comment: 5 pages, 2 figure
First Penning-trap mass measurement in the millisecond half-life range: the exotic halo nucleus 11Li
In this letter, we report a new mass for Li using the trapping
experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived
nuclide, , for which a mass measurement has ever been
performed with a Penning trap. Combined with our mass measurements of
Li we derive a new two-neutron separation energy of 369.15(65) keV: a
factor of seven more precise than the best previous value. This new value is a
critical ingredient for the determination of the halo charge radius from
isotope-shift measurements. We also report results from state-of-the-art
atomic-physics calculations using the new mass and extract a new charge radius
for Li. This result is a remarkable confluence of nuclear and atomic
physics.Comment: Formatted for submission to PR
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