4,611 research outputs found
The fluctuation of year-classes and the regulation of fisheries
There are three sources of variation of recruitment; first that due to
random fluctuations alone, secondly that, due to variations in stock and
thirdly variations which are extreme at low and high levels of stock and
if these occur sequentially can cause catastrophic declines or sharp
increases in stock density. From a study of stock/recruitment curves of a
number of fish species, it appears that the curve for herring-like fishes
differs markedly from those, for example, of cod-like fishes or in more
general terms that the shape of the stock/recruitment curve is really a
function of its fecundity. That for the herring-like fishes is a near linear
curve whereas that for the cod-like fishes is markedly dome-shaped. It
follows that the herring-like fishes are very vulnerable to long-term
climatic changes and that the cod-like fishes are able to stabilize their
populations through long-term climatic changes merely because the
increased recruitment when stock is slightly reduced is very much greater
than that for the herring-like fishes. If stocks of fish are to be managed
then the stock/recruitment relatioilship has to be taken into account; a
form of self regenerating yield curve combining stock/recruitment and
yield-per-recruit was in fact put forward by BEVERTON and HOLT. A
development of such a curve is needed and one of the uses of such a curve
would he that management need not take too much notice of environmental
change, because if it occurred the stock would have been exploited
at its best rate before any environmental collapse took place
The fluctuation of year-classes and the regulation of fisheries
There are three sources of variation of recruitment; first that due to
random fluctuations alone, secondly that, due to variations in stock and
thirdly variations which are extreme at low and high levels of stock and
if these occur sequentially can cause catastrophic declines or sharp
increases in stock density. From a study of stock/recruitment curves of a
number of fish species, it appears that the curve for herring-like fishes
differs markedly from those, for example, of cod-like fishes or in more
general terms that the shape of the stock/recruitment curve is really a
function of its fecundity. That for the herring-like fishes is a near linear
curve whereas that for the cod-like fishes is markedly dome-shaped. It
follows that the herring-like fishes are very vulnerable to long-term
climatic changes and that the cod-like fishes are able to stabilize their
populations through long-term climatic changes merely because the
increased recruitment when stock is slightly reduced is very much greater
than that for the herring-like fishes. If stocks of fish are to be managed
then the stock/recruitment relatioilship has to be taken into account; a
form of self regenerating yield curve combining stock/recruitment and
yield-per-recruit was in fact put forward by BEVERTON and HOLT. A
development of such a curve is needed and one of the uses of such a curve
would he that management need not take too much notice of environmental
change, because if it occurred the stock would have been exploited
at its best rate before any environmental collapse took place
FeH Absorption in the Near-Infrared Spectra of Late M and L Dwarfs
We present medium-resolution z-, J-, and H-band spectra of four late-type
dwarfs with spectral types ranging from M8 to L7.5. In an attempt to determine
the origin of numerous weak absorption features throughout their near-infrared
spectra, and motivated by the recent tentative identification of the E 4\Pi- A
^4\Pi system of FeH near 1.6 microns in umbral and cool star spectra, we have
compared the dwarf spectra to a laboratory FeH emission spectrum. We have
identified nearly 100 FeH absorption features in the z-, J-, and H-band spectra
of the dwarfs. In particular, we have identified 34 features which dominate the
appearance of the H-band spectra of the dwarfs and which appear in the
laboratory FeH spectrum. Finally, all of the features are either weaker or
absent in the spectrum of the L7.5 dwarf which is consistent with the weakening
of the known FeH bandheads in the spectra of the latest L dwarfs.Comment: accepted by Ap
Waste Not, Want Not: The Potential for Urban Water Conservation in California
The largest, least expensive, and most environmentally sound source of water to meet California's future needs is the water currently being wasted in every sector of our economy. This report, "Waste Not, Want Not," strongly indicates that California's urban water needs can be met into the foreseeable future by reducing water waste through cost-effective water-saving technologies, revised economic policies, appropriate state and local regulations, and public education
The Unusual Object IC 2144/MWC 778
IC 2144 is a small reflection nebula located in the zone of avoidance near
the Galactic anticenter. It has been investigated here largely on the basis of
Keck/HIRES optical spectroscopy (R ~ 48,000) and a SpeX spectrogram in the
near-IR (R = 2000) obtained at the NASA IRTF. The only star in the nebula that
is obvious in the optical or near-IR is the peculiar emission-line object MWC
778 (V = 12.8), which resembles a T Tauri star in some respects. What appear to
be F- or G-type absorption features are detectable in its optical region under
the very complex emission line spectrum; their radial velocity agrees with the
CO velocity of the larger cloud in which IC 2144 is embedded. There are
significant differences between the spectrum of the brightest area of the
nebula and of MWC 778, the presumed illuminator, an issue discussed in some
detail. The distance of IC 2144 is inferred to be about 1.0 kpc by reference to
other star-forming regions in the vicinity. The extinction is large, as
demonstrated by [Fe II] emission line ratios in the near-IR and by the strength
of the diffuse interstellar band spectrum; a provisional value of A_V of 3.0
mag was assumed. The SED of MWC 778 rises steeply beyond about 1 m, with a
slope characteristic of a Class I source. Integration of the flux distribution
leads to an IR luminosity of about 510 L_solar. If MWC 778 is indeed a F- or
G-type pre--main-sequence star several magnitudes above the ZAMS, a population
of faint emission Halpha stars would be expected in the vicinity. Such a
search, like other investigations that are recommended in this paper, has yet
to be carried out.Comment: 36 pages, 13 figures, accepted by A
Echo traces associated with thermoclines
Echoes received from the depth of the thermocline in Windermere, the North Sea, the Barents Sea and off Spitsbergen have been associated with aggregations of plankton organisms: zooplankton at a density of 25/litre in Windermere and phytoplankton at a density of 100,000 cells/litre (Thalassiosira gravida and Chaetoceros sp.) in the Barents Sea
Quantum mechanics is about quantum information
I argue that quantum mechanics is fundamentally a theory about the
representation and manipulation of information, not a theory about the
mechanics of nonclassical waves or particles. The notion of quantum information
is to be understood as a new physical primitive -- just as, following
Einstein's special theory of relativity, a field is no longer regarded as the
physical manifestation of vibrations in a mechanical medium, but recognized as
a new physical primitive in its own right.Comment: 17 pages, forthcoming in Foundations of Physics Festschrift issue for
James Cushing. Revised version: some paragraphs have been added to the final
section clarifying the argument, and various minor clarifying remarks have
been added throughout the tex
59Co-NMR Knight Shift of Superconducting Three-Layer NaxCoO2.yH2O
The superconducting state of NaxCoO2.yH2O with three CoO2 layers in a unit
cell has been studied by 59Co-NMR. The Knight shift measured for a peak of the
NMR spectra corresponding to the external magnetic field H along one of the
principal directions within the CoO2 plane, exhibits a rapid decrease with
decreasing temperature T below the superconducting transition temperature Tc,
indicating that the spin susceptibility is suppressed in the superconducting
phase, at least, for this field direction. Because differences of the
superconducting properties are rather small between this three-layer
NaxCoO2.yH2O and previously reported NaxCoO2.yH2O with two CoO2 layers within a
unit cell, the present result of the Knight shift studies indicates that the
Cooper pairs of the former system are in the singlet state as in the latter,
for which the spin susceptibility is suppressed for both directions of H
parallel and perpendicular to the CoO2 plane.Comment: 5 page
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