5,137 research outputs found
A survey of selected coastal vegetation communities of Florida
A survey of coastal vegetation around Florida
was conducted during 1973 and 1974. Seventeen sites were selected and sampled
using the transect method to determine species occurrence, relative densities, and
habitat development and structure. Sites were sampled quarterly except where high
tides prevented data gathering. Species occurrence was compared within and
between sites using Sarensen's Index of Similarity (IS,) as a basis for determining
similarity of species inhabiting selected sites. Indices ranged from 4 to 61%, the
former representing only one plant common to two sites. Results show
environmental factors acting upon species alter species composition in seemingly
similar habitats. Instead of the term "community", the term "association" is used to
better reflect the concept of a taxonomically unrelated group of plants occupying a
particular habitat. (Document has 40 pages.
Squeezing more out of a laser
A laser's intensity can be stabilized by negative feedback from a conventional photodetector. I propose extraction of sub-shot-noise light from the feedback loop at a beam splitter by illuminating the back side of the beam splitter with squeezed-state light
Predicting Future Duration from Present Age: A Critical Assessment
Using a temporal version of the Copernican principle, Gott has proposed a
statistical predictor of future longevity based on present age [J. R. Gott III,
Nature 363, 315 (1993)] and applied the predictor to a variety of examples,
including the longevity of the human species. Though Gott's proposal contains a
grain of truth, it does not have the universal predictive power that he
attributes to it.Comment: 17 pages, standard LaTeX; to be published in Contemporary Physic
Particle-Number-Conserving Bogoliubov Approximation for Bose-Einstein Condensates Using Extended Catalytic States
We encode the many-body wavefunction of a Bose-Einstein condensate (BEC) in
the -particle sector of an extended catalytic state. This catalytic state is
a coherent state for the condensate mode and an arbitrary state for the modes
orthogonal to the condensate mode. Going to a time-dependent interaction
picture where the state of the condensate mode is displaced to the vacuum, we
can organize the effective Hamiltonian by powers of . Requiring the
terms of order to vanish gives the Gross-Pitaevskii equation. Going
to the next order, , we derive equations for the number-conserving
Bogoliubov approximation, first given by Castin and Dum [Phys. Rev. A
, 3008 (1998)]. In contrast to other approaches, ours is well
suited to calculating the state evolution in the Schr\"{o}dinger picture;
moreover, it is straightforward to generalize our method to multi-component
BECs and to higher-order corrections.Comment: 29 pages, 1 figur
Entangling power of the quantum baker's map
We investigate entanglement production in a class of quantum baker's maps.
The dynamics of these maps is constructed using strings of qubits, providing a
natural tensor-product structure for application of various entanglement
measures. We find that, in general, the quantum baker's maps are good at
generating entanglement, producing multipartite entanglement amongst the qubits
close to that expected in random states. We investigate the evolution of
several entanglement measures: the subsystem linear entropy, the concurrence to
characterize entanglement between pairs of qubits, and two proposals for a
measure of multipartite entanglement. Also derived are some new analytical
formulae describing the levels of entanglement expected in random pure states.Comment: 22 pages, 11 figure
Quantum wideband traveling-wave analysis of a degenerate parametric amplifier
We develop a wideband traveling-wave formalism for analyzing quantum mechanically a degenerate parametric amplifier. The formalism is based on spatial differential equations-spatial Langevin equations-that propagate temporal Fourier components of the field operators through the nonlinear medium. In addition to the parametric nonlinearity, the Langevin equations include absorption and associated fluctuations, dispersion (phase mismatching), and pump quantum fluctuations. We analyze the dominant effects of phase mismatching and pump quantum fluctuations on the squeezing produced by a degenerate parametric amplifier
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