The northern limit of spawning by Atlantic eels (Anguilla spp.) in the Sargasso Sea in relation to thermal fronts and surface water masses

American and European eels (Anguilla rostrata and A. anguilla) spawn in a large poorly defined area east of the Bahamas between about longitude 50W and 75W in the Sargasso Sea. We use the distribution of tiny Anguilla larvae taken in ichthyoplankton collections and associated characterizations of hydrography to test two hypotheses concerning distribution of water masses and the northern limit of spawning by both species. Data are presented from four transects of closely spaced stations conducted during February and April 1983 which refute our hypothesis that a positive correlation exists between the distribution of the Subtropical Underwater and spawning by Anguilla. Larvae ≤5.5 mm were taken on both sides of fronts at the northern edge of the Subtropical Underwater. This result was supported by data from two longer transects conducted during March 1985. Though Subtropical Underwater was not encountered along these transects tiny Anguilla larvae were present. Our second hypothesis, that fronts along the northern edge of the warm, saline surface water mass of the southern Sargasso Sea form the northern limit of spawning by Anguilla, was strongly supported by the March 1985 collections. Tiny Anguilla larvae were taken in all collections south of fronts separating southern Sargasso Sea surface water from mixed Subtropical Convergence Zone water to the north. Anguilla larvae ≤5.5 mm TL were not taken in collections at stations where mixed Subtropical Convergence zone water was present

Single-photon optomechanics in the strong coupling regime

We give a theoretical description of a coherently driven opto-mechanical system with a single added photon. The photon source is modeled as a cavity which initially contains one photon and which is irreversibly coupled to the opto-mechanical system. We show that the probability for the additional photon to be emitted by the opto-mechanical cavity will exhibit oscillations under a Lorentzian envelope, when the driven interaction with the mechanical resonator is strong enough. Our scheme provides a feasible route towards quantum state transfer between optical photons and micromechanical resonators.Comment: 14 pages, 6 figure

Design, fabrication, and characterization of deep-etched waveguide gratings

One-dimensional (1-D) deep-etched gratings on a specially grown AlGaAs wafer were designed and fabricated. The gratings were fabricated using state-of-the-art electron beam lithography and high-aspect-ratio reactive ion etching (RIE) in order to achieve the required narrow deep air slots with good accuracy and reproducibility. Since remarkable etch depths (up to 1.5 /spl mu/m), which completely cut through the waveguide core layer, have been attained, gratings composed of only five periods (and, thus, shorter than 6 /spl mu/m) have a bandgap larger than 100 nm. A defect was introduced by increasing the width of the central semiconductor tooth to create microcavities that exhibit a narrow transmission peak (less than 7 nm) around the wavelength of 1530 nm. The transmission spectra between 1460 and 1580 nm have been systematically measured, and the losses have been estimated for a set of gratings, both with and without a defect, for different periods and air slot dimensions. Numerical results obtained via a bidirectional beam propagation code allowed the evaluation of transmissivity, reflectivity, and diffraction losses. By comparing experimental results with the authors' numerical findings, a clear picture of the role of the grating's geometric parameters in determining its spectral features and diffractive losses is illustrated

Creating and Verifying a Quantum Superposition in a Micro-optomechanical System

Micro-optomechanical systems are central to a number of recent proposals for realizing quantum mechanical effects in relatively massive systems. Here we focus on a particular class of experiments which aim to demonstrate massive quantum superpositions, although the obtained results should be generalizable to similar experiments. We analyze in detail the effects of finite temperature on the interpretation of the experiment, and obtain a lower bound on the degree of non-classicality of the cantilever. Although it is possible to measure the quantum decoherence time when starting from finite temperature, an unambiguous demonstration of a quantum superposition requires the mechanical resonator to be in or near the ground state. This can be achieved by optical cooling of the fundamental mode, which also provides a method to measure the mean phonon number in that mode. We also calculate the rate of environmentally induced decoherence and estimate the timescale for gravitational collapse mechanisms as proposed by Penrose and Diosi. In view of recent experimental advances, practical considerations for the realization of the described experiment are discussed.Comment: 19 pages, 8 figures, published in New J. Phys. 10 095020 (2008); minor revisions to improve clarity; fixed possibly corrupted figure

Macroscopic superpositions via nested interferometry: finite temperature and decoherence considerations

Recently there has been much interest in optomechanical devices for the production of macroscopic quantum states. Here we focus on a proposed scheme for achieving macroscopic superpositions via nested interferometry. We consider the effects of finite temperature on the superposition produced. We also investigate in detail the scheme's feasibility for probing various novel decoherence mechanisms.Comment: 12 pages, 2 figure

Polychromatic photonic quasicrystal cavities

Quantum Matter and Optic

Diffraction-limited high-finesse optical cavities

Quantum Matter and Optic

Ileorectal anastomosis for ulcerative and Crohn\u27s colitis.

Except in the presence of severe perineal suppuration or sphincter damage by previous surgery for fistulas, the rectum was preserved in all patients considered candidates for surgery for inflammatory disease of the bowel. A primary anastomosis with a single-layer 5-0 monofilament stainless steel wire was carried out when a relatively healthy rectum with erythema and granularity presented. For patients with more severe disease of the rectum, a two-stage operation with intensive interval treatment of the rectum stump with topical corticosteroids was carried out. Of a total of eighty-six patients with involvement of the colon and rectum with either Crohn\u27s disease or chronic ulcerative colitis, fifty-six patients were treated by local abdominal colectomy and ileorectal anastomosis. Twenty-four had primary anastomosis and thiry-two had a two-stage operation. One anastomotic dehiscence developed. A mean follow-up of 8.4 years (6 months to 20 years) has been satisfactory. Only three anastomoses have been taken down for unsatisfactory results. With the proper selection of patients and with appropriate treatment of the diseased rectal segment, a large majority of patients with inflammatory disease of the bowel can have long-term salutory results after colectomy and ileorectal anastomosis

Helicity conservation by flow across scales in reconnecting vortex links and knots

The conjecture that helicity (or knottedness) is a fundamental conserved quantity has a rich history in fluid mechanics, but the nature of this conservation in the presence of dissipation has proven difficult to resolve. Making use of recent advances, we create vortex knots and links in viscous fluids and simulated superfluids and track their geometry through topology-changing reconnections. We find that the reassociation of vortex lines through a reconnection enables the transfer of helicity from links and knots to helical coils. This process is remarkably efficient, owing to the antiparallel orientation spontaneously adopted by the reconnecting vortices. Using a new method for quantifying the spatial helicity spectrum, we find that the reconnection process can be viewed as transferring helicity between scales, rather than dissipating it. We also infer the presence of geometric deformations that convert helical coils into even smaller scale twist, where it may ultimately be dissipated. Our results suggest that helicity conservation plays an important role in fluids and related fields, even in the presence of dissipation

Decoherence of a Pointer by a Gas Reservoir

We study the effect of the environment on the process of the measurement of a state of a microscopic spin half system. The measuring apparatus is a heavy particle, whose center of mass coordinates can be considered at the end of the measurement as approximately classical, and thus can be used as a pointer. The state of the pointer, which is the result of its interaction with the spin, is transformed into a mixed state by the coupling of the pointer to the environment. The environment is considered to be a gas reservoir, whose particles interact with the pointer. This results in a Fokker-Planck equation for the reduced density matrix of the pointer. The solution of the equation shows that the quantum coherences, which are characteristic to the entangled state between the probabilities to find the pointer in one of two positions, decays exponentially fast in time. We calculate the exponential decay function of this decoherence effect, and express it in terms of the parameters of the model.Comment: 41 pages, 1 figur