11,395 research outputs found
Effects of commercial fishing on local abundance of Pacific cod (Gadus macrocephalus) in the Bering Sea
Groundfish fisheries in the southeast Bering Sea in Alaska
have been constrained in recent years by management measures to protect the endangered Steller sea lion (Eumetopias jubatus). There is concern that the present commercial harvest may produce a localized depletion
of groundfish that would affect the foraging success of Steller sea lions or other predators. A three-year field experiment was conducted to determine whether an intensive
trawl fishery in the southeast Bering Sea created a localized depletion in the abundance of Pacific cod (Gadus
macrocephalus). This experiment produced strongly negative results; no difference was found in the rate of seasonal change in Pacific cod abundance between stations within a
regulatory no-trawl zone and stations in an immediately adjacent trawled area. Corollary studies showed that
Pacific cod in the study area were highly mobile and indicated that the geographic scale of Pacific cod movement
was larger than the spatial scale used as the basis for current no-trawl zones. The idea of localized depletion
is strongly dependent on assumed spatial and temporal scales and contains an implicit assumption that there is
a closed local population. The scale of movement of target organisms is critical in determining regional effects of
fishery removals
Entanglement and its Role in Shor's Algorithm
Entanglement has been termed a critical resource for quantum information
processing and is thought to be the reason that certain quantum algorithms,
such as Shor's factoring algorithm, can achieve exponentially better
performance than their classical counterparts. The nature of this resource is
still not fully understood: here we use numerical simulation to investigate how
entanglement between register qubits varies as Shor's algorithm is run on a
quantum computer. The shifting patterns in the entanglement are found to relate
to the choice of basis for the quantum Fourier transform.Comment: 15 pages, 4 eps figures, v1-3 were for conference proceedings (not
included in the end); v4 is improved following referee comments, expanded
explanations and added reference
General practitioners' reasons for removing patients from their lists: postal survey in England and Wales
The removal of patients from doctors' lists causes conÂ
siderable public and political concern, with speculation
that patients are removed for inappropriate, including
financial, reasons. In 1999 the House of Commons
Select Committee on Public Administration noted that
little evidence was available on either the frequency of,
or the reasons for, removal of patients. National statistics do not distinguish between patients removed after
moving out of a practice area and those removed for
other reasons. Two postal surveys have reported why
general practitioners might, in general, remove
patients, and one small study has described the
reasons doctors give for particular removals. We
therefore determined the current scale of, and doctors'
reasons for, removal of patients from their lists in EngÂ
land and Wales
What is Philosophy?
What is philosophy? Thatâs a good questionânot because thereâs no answer, but because whatâs involved in posing it points up something essential to philosophy. ¶ In the *Treatise on the Emendation of the Intellect,* Spinoza sets out whatâs required by a definition. A circle, a typical definition might run, is a figure in which all lines drawn from the center to the circumference are equal. The problem with this definition, what makes it merely verbal, is that it defines a circle by way of one of its properties, not by way of its essence. Definition, for Spinoza, gets at the essence (from which all properties follow): A complete definition demonstrates how what it defines comes about. The definition of a circle as a figure that is described by any line of which one end is fixed and the other movable, as one commentator has pointed out, âliterally generates the circle by providing a procedure whereby we âmakeâ the thing to be defined.â ¶ Philosophy is defined by what takes place in the question of philosophy itself. What Auden said of poetry could also be said of philosophy: it makes nothing happen. *Nothing* happens, or nothing *happens*âand in the space of the same few words both *can.* Philosophy operates that displacement and is defined by it: âwhat is *philosophy*?â become â*what is* philosophy?ââthe question persists, but everything has changed
Signatures of the collapse and revival of a spin Schr\"{o}dinger cat state in a continuously monitored field mode
We study the effects of continuous measurement of the field mode during the
collapse and revival of spin Schr\"{o}dinger cat states in the Tavis-Cummings
model of N qubits (two-level quantum systems) coupled to a field mode. We show
that a compromise between relatively weak and relatively strong continuous
measurement will not completely destroy the collapse and revival dynamics while
still providing enough signal-to-noise resolution to identify the signatures of
the process in the measurement record. This type of measurement would in
principle allow the verification of the occurrence of the collapse and revival
of a spin Schr\"{o}dinger cat state.Comment: 5 pages, 2 figure
Upper Bound on the region of Separable States near the Maximally Mixed State
A lower bound on the amount of noise that must be added to a GHZ-like
entangled state to make it separable (also called the random robustness) is
found using the transposition condition. The bound is applicable to arbitrary
numbers of subsystems, and dimensions of Hilbert space, and is shown to be
exact for qubits. The new bound is compared to previous such bounds on this
quantity, and found to be stronger in all cases. It implies that increasing the
number of subsystems, rather than increasing their Hilbert space dimension is a
more effective way of increasing entanglement. An explicit decomposition into
an ensemble of separable states, when the state is not entangled,is given for
the case of qubits.Comment: 2 figures. accepted J. Opt. B: Quantum Semiclass. Opt. (2000
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