172 research outputs found
The physiology of circulation during swimming activity in rainbow trout
From Introduction: Rainbow trout (Salmo gairdneri) were introduced into Europe from North America in the latter half of the last century. They can tolerate higher water temperatures and lower oxygen concentrations than the native brown trout
(Salmo trutta). Rainbows grow faster than brown trout under similar conditions and are thus particularly attractive for artificial rearing methods. In Denmark there is a thriving rainbow trout farming industry producing about
9,000 metric tons annually which is largely exported for table use (Mills 1971).
In Britain production of rainbow trout for food is not on such a large scale but they form the basis of a considerable sport fishery. In Scotland and Northern England although rainbow trout reach sexual maturity they do not generally
breed so the population is entirely dependent on restocking with hatchery reared fish, thus although living more or less wild in many British waters , this species is essentially an artificially managed resource upon which man can impose genetic selection (Donaldson and Olson 1957) as well as normal fishery controls. A detailed understanding of the biology and physiology of this species is hence of particular importance
Paradox of inductionless magnetorotational instability in a Taylor-Couette flow with a helical magnetic field
We consider the magnetorotational instability (MRI) of a hydrodynamically
stable Taylor-Couette flow with a helical external magnetic field in the
inductionless approximation defined by a zero magnetic Prandtl number
(\Pm=0). This leads to a considerable simplification of the problem
eventually containing only hydrodynamic variables. First, we point out that the
energy of any perturbation growing in the presence of magnetic field has to
grow faster without the field. This is a paradox because the base flow is
stable without the magnetic while it is unstable in the presence of a helical
magnetic field without being modified by the latter as it has been found
recently by Hollerbach and Rudiger [Phys. Rev. Lett. 95, 124501 (2005)]. We
revisit this problem by using a Chebyshev collocation method to calculate the
eigenvalue spectrum of the linearized problem. In this way, we confirm that MRI
with helical magnetic field indeed works in the inductionless limit where the
destabilization effect appears as an effective shift of the Rayleigh line.
Second, we integrate the linearized equations in time to study the transient
behavior of small amplitude perturbations, thus showing that the energy
arguments are correct as well. However, there is no real contradiction between
both facts. The linear stability theory predicts the asymptotic development of
an arbitrary small-amplitude perturbation, while the energy stability theory
yields the instant growth rate of any particular perturbation, but it does not
account for the evolution of this perturbation.Comment: 4 pages, 3 figures, submitted to Phys. Rev.
Single-magnet rotary flowmeter for liquid metals
We present a theory of single-magnet flowmeter for liquid metals and compare
it with experimental results. The flowmeter consists of a freely rotating
permanent magnet, which is magnetized perpendicularly to the axle it is mounted
on. When such a magnet is placed close to a tube carrying liquid metal flow, it
rotates so that the driving torque due to the eddy currents induced by the flow
is balanced by the braking torque induced by the rotation itself. The
equilibrium rotation rate, which varies directly with the flow velocity and
inversely with the distance between the magnet and the layer, is affected
neither by the electrical conductivity of the metal nor by the magnet strength.
We obtain simple analytical solutions for the force and torque on slowly moving
and rotating magnets due to eddy currents in a layer of infinite horizontal
extent. The predicted equilibrium rotation rates qualitatively agree with the
magnet rotation rate measured on a liquid sodium flow in stainless steel duct.Comment: 15 pages, 6 figures, revised version, to appear in J. Appl. Phy
Enhancement of primary production in the North Atlantic outside of the spring bloom, identified by remote sensing of ocean colour and temperature
Peer reviewedPublisher PD
Putative fishery-induced changes in biomass and population size structures of demersal deep-sea fishes in ICES Sub-area VII, Northeast Atlantic Ocean
This work was supported by a series of NERC grants to the principal investigators including NE/C512961/1. The results of the early joint SAMS and IOS surveys were digitized with support from EU MAST Contract MAS2-CT920033 1993–1995, and data analyses was supported by EU FP7 Projects HERMES and HERMIONE. We thank Alain Zuur from Highland Statistics Ltd. for advice with the statistical analyses and Odd Aksel Bergstad for valuable comments that helped to improve the manuscript. We thank the ships’ companies of the RRS Challenger and RRS Discovery.Peer reviewedPublisher PD
A modified BlÄzka–type respirometer for the study of swimming metabolism in fishes having deep, laterally compressed bodies or unusual locomotor modes
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73888/1/j.1095-8649.2000.tb00890.x.pd
Acoustic and optical variations during rapid downward motion episodes in the deep north-western Mediterranean Sea
An Acoustic Doppler Current Profiler (ADCP) was moored at the deep-sea site
of the ANTARES neutrino telescope near Toulon, France, thus providing a unique
opportunity to compare high-resolution acoustic and optical observations
between 70 and 170 m above the sea bed at 2475 m. The ADCP measured downward
vertical currents of magnitudes up to 0.03 m s-1 in late winter and early
spring 2006. In the same period, observations were made of enhanced levels of
acoustic reflection, interpreted as suspended particles including zooplankton,
by a factor of about 10 and of horizontal currents reaching 0.35 m s-1. These
observations coincided with high light levels detected by the telescope,
interpreted as increased bioluminescence. During winter 2006 deep dense-water
formation occurred in the Ligurian subbasin, thus providing a possible
explanation for these observations. However, the 10-20 days quasi-periodic
episodes of high levels of acoustic reflection, light and large vertical
currents continuing into the summer are not direct evidence of this process. It
is hypothesized that the main process allowing for suspended material to be
moved vertically later in the year is local advection, linked with topographic
boundary current instabilities along the rim of the 'Northern Current'.Comment: 30 pages, 7 figure
Notes on age determination, size and age structure, longevity, and growth of co-occurring macrourid fishes
ACKNOWLEDGEMENTS We are grateful to crew and colleagues who sampled and processed macrourids on the MARECO and ECOMAR cruise, to Ms Hege Ø Hansen for assistance in the otolith laboratory, and to home institutions and the Alfred P Sloan Foundation for financial support. An early version of the results was submitted in partial fulfilment of the requirements for the MSc degree of R.H. Fundings: Data for this paper were collected on cruises funded by Norway and the United Kingdom (Natural Environment Research Council). In addition to institutional funding, the work benefitted from a grant to the ecosystems of the mid-atlantic ridge (MAR-ECO) Programme from the Alfred P. Sloan Foundation, New York, USA.Peer reviewedPublisher PD
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