2,485 research outputs found
The Antarctic krill fishery : a techno-economic investigation
From a review of recent developments in the harvesting and processing of krill, an analysis is made of the market potential for the main products of a krill fishery, namely whole krill, tail meats, mince (particularly surimi) and meal.
A techno-economic analysis of various catching - processing - product systems is made, in terms of costs and prices applicable in Western countries in 1977. The study finds that in practice the rapid
spoilage rate of- krill after capture effectively determines that it should be processed on board freezer or factory trawlers. However, unless krill is marketed essentially as a crustacean product (even
though in minced form) it is most unlikely to generate sufficient revenue to justify the high costs of its exploitation.
Consideration is also given to the management issues raised by the
exploitation of Antarctic krill in the context of the Southern Ocean.
It is concluded that the quantities of krill likely to be taken by Western countries in the foreseeable future will be comparatively low.
However. should the Soviets continue to expand their activities then even comparatively modest catch levels (of the order of a few million tonnes per year) could have a serious effect on Southern Ocean stocks, if not on krill, then on other species dependent upon this resource
The Three Component Electronic Structure of the Cuprates Derived from SI-STM
We present a phenomenological model that describes the low energy electronic
structure of the cuprate high temperature superconductor Bi2Sr2CaCu2O8+x as
observed by Spectroscopic Imagining Scanning Tunneling Microscopy (SI-STM). Our
model is based on observations from Quasiparticle Interference (QPI)
measurements and Local Density of States (LDOS) measurements that span a range
of hole densities from critical doping, p~0.19, to extremely underdoped,
p~0.06. The model presented below unifies the spectral density of states
observed in QPI studies with that of the LDOS. In unifying these two separate
measurements, we find that the previously reported phenomena, the Bogoliubov
QPI termination, the checkerboard conductance modulations, and the pseudogap
are associated with unique energy scales that have features present in both the
q-space and LDOS(E) data sets
Anti-phase Modulation of Electron- and Hole-like States in Vortex Core of Bi2Sr2CaCu2Ox Probed by Scanning Tunneling Spectroscopy
In the vortex core of slightly overdoped Bi2Sr2CaCu2Ox, the electron-like and
hole-like states have been found to exhibit spatial modulations in anti-phase
with each other along the Cu-O bonding direction. Some kind of
one-dimensionality has been observed in the vortex core, and it is more clearly
seen in differential conductance maps at lower biases below +-9 mV
Charge Ordered RVB States in the Doped Cuprates
We study charge ordered d-wave resonating valence bond states (dRVB) in the
doped cuprates, and estimate the energies of these states in a generalized model by using a renormalized mean field theory. The long range Coulomb
potential tends to modulate the charge density in favor of the charge ordered
RVB state. The possible relevance to the recently observed
checkerboard patterns in tunnelling conductance in high cuprates is
discussed.Comment: 4 pages, 4 figures, 3 table
Global Phase Diagram of the High Tc Cuprates
The high Tc cuprates have a complex phase diagram with many competing phases.
We propose a bosonic effective quantum Hamiltonian based on the projected SO(5)
model with extended interactions, which can be derived from the microscopic
models of the cuprates. The global phase diagram of this model is obtained
using mean-field theory and the Quantum Monte Carlo simulation, which is
possible because of the absence of the minus sign problem. We show that this
single quantum model can account for most salient features observed in the high
Tc cuprates, with different families of the cuprates attributed to different
traces in the global phase diagram. Experimental consequences are discussed and
new theoretical predictions are presented.Comment: 19 pages, 20 figures, with updated references, final versio
Evolution of the electronic excitation spectrum with strongly diminishing hole-density in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}
A complete knowledge of its excitation spectrum could greatly benefit efforts
to understand the unusual form of superconductivity occurring in the lightly
hole-doped copper-oxides. Here we use tunnelling spectroscopy to measure the
T\to 0 spectrum of electronic excitations N(E) over a wide range of
hole-density p in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+/delta}. We
introduce a parameterization for N(E) based upon an anisotropic energy-gap
/Delta (\vec k)=/Delta_{1}(Cos(k_{x})-Cos(k_{y}))/2 plus an effective
scattering rate which varies linearly with energy /Gamma_{2}(E) . We
demonstrate that this form of N(E) allows successful fitting of differential
tunnelling conductance spectra throughout much of the
Bi_{2}Sr_{2}CaCu_{2}O_{8+/delta} phase diagram. The resulting average
/Delta_{1} values rise with falling p along the familiar trajectory of
excitations to the 'pseudogap' energy, while the key scattering rate
/Gamma_{2}^{*}=/Gamma_{2}(E=/Delta_{1}) increases from below ~1meV to a value
approaching 25meV as the system is underdoped from p~16% to p<10%. Thus, a
single, particle-hole symmetric, anisotropic energy-gap, in combination with a
strongly energy and doping dependent effective scattering rate, can describe
the spectra without recourse to another ordered state. Nevertheless we also
observe two distinct and diverging energy scales in the system: the energy-gap
maximum /Delta_{1} and a lower energy scale /Delta_{0} separating the spatially
homogeneous and heterogeneous electronic structures.Comment: High resolution version available at:
http://people.ccmr.cornell.edu/~jcdavis/files/Alldredge-condmat08010087-highres.pd
STM/STS Study on 4a X 4a Electronic Charge Order of Superconducting Bi2Sr2CaCu2O8+d
We performed low-bias STM measurements on underdoped Bi2212 crystals, and
confirmed that a two-dimensional (2D) superstructure with a periodicity of four
lattice constants (4a) is formed within the Cu-O plane at T<Tc. This 4a X 4a
superstructure, oriented along the Cu-O bonding direction, is nondispersive and
more intense in lightly doped samples with a zero temperature pseudogap (ZTPG)
than in samples with a d-wave gap. The nondispersive 4a X 4a superstructure was
clearly observed within the ZTPG or d-wave gap, while it tended to fade out
outside the gaps. The present results provide a useful test for various models
proposed for an electronic order hidden in the underdoped region of high-Tc
cuprates.Comment: 4 pages, submitted to J. Phys. Soc. Jp
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