The Epontic Algal Community of the Ice Edge Zone and Its Significance to the Davis Strait Ecosystem

The ice algae community in the dynamic outer edge zone of the Davis Strait pack ice was investigated in April-May 1978. Surveys of the epontic community were made using a remote camera system, a fibrescope, an ice corer, and in situ C14 incubation chambers. The undersurfaces of the floes were generally flat, containing slight undulations and small depressions of up to 10 cm. In the bottom few centimetres a transition was noted from hard ice to more fragile, but still firm, crystalline ice. Epontic flora was highly patchy and almost entirely restricted to the bottom few centimetres of the floes. Average concentrations in the bottom 6 cm of ice was 10.24 mg chl a/cu m. The pack ice bloom occurred in April and May with a peak occurring in May. The maximum primary production rates of 2.4 mg C/sq m/d occurred at a light intensity of 1.8 mu epsilon/sq m/s. Photosynthesis appeared to be inhibited at light levels above 20 mu epsilon/sq m/s. The dominant genera of the epontic flora were Navicula, Nitzschia, and Pleurosigma; species composition of the epontic algal community differed significantly from that of the plankton. Two other ice algae communities were noted; a "sandwich" community in the middle of an ice floe, dominated by Asteromphalus hookeri and Thalassiosira gravida; and a floe surface community which was on one occasion observed being seeded from the plankton. The total contribution of the epontic algae to the primary production of the Davis Strait was estimated to be approximately 7x10**7g C/y, or less than 1% that of the phytoplankton. The contribution may still be important, however, as it precedes the phytoplankton bloom and is the only algal concentration under heavy pack ice.Key words: Davis Strait, pack ice, epontic, primary production, ice algaeMots clés: détroit de Davis, banquise, production primaire, algue glacial

Misdiagnosis of hereditary amyloidosis as AL (Primary) amyloidosis

Background: Hereditary, autosomal dominant amyloidosis, caused by mutations in the genes encoding transthyretin, fibrinogen A -chain, lysozyme, or apolipoprotein A-I, is thought to be extremely rare and is not routinely included in the differential diagnosis of systemic amyloidosis unless there is a family history. Methods: We studied 350 patients with systemic amyloidosis, in whom a diagnosis of the light-chain (AL) type of the disorder had been suggested by clinical and laboratory findings and by the absence of a family history, to assess whether they had amyloidogenic mutations. Results: Amyloidogenic mutations were present in 34 of the 350 patients (9.7 percent), most often in the genes encoding fibrinogen A -chain (18 patients) and transthyretin (13 patients). In all 34 of these patients, the diagnosis of hereditary amyloidosis was confirmed by additional investigations. A low-grade monoclonal gammopathy was detected in 8 of the 34 patients (24 percent). Conclusions: A genetic cause should be sought in all patients with amyloidosis that is not the reactive systemic amyloid A type and in whom confirmation of the AL type cannot be obtained

An alternative architecture and control strategy for hexapod positioning systems to simplify structural design and improve accuracy

Hexapod systems (6 legged Stewart Platforms), offer advantages in accuracy over other positioning systems and are finding applications in numerous telescopes. However, instruments with increased sophistication for modern telescopes continue to grow in size and required positioning accuracy. This paper details an alternative hexapod configuration and design approach, particularly focused on relatively large, high precision hexapod systems supporting high mass payloads. The new configuration improves accuracy, reduces actuator mass, simplifies design, and reduces system cost but requires modest additional control algorithm sophistication.Center for Electromechanic

Counter-propagating entangled photons from a waveguide with periodic nonlinearity

The conditions required for spontaneous parametric down-conversion in a waveguide with periodic nonlinearity in the presence of an unguided pump field are established. Control of the periodic nonlinearity and the physical properties of the waveguide permits the quasi-phase matching equations that describe counter-propagating guided signal and idler beams to be satisfied. We compare the tuning curves and spectral properties of such counter-propagating beams to those for co-propagating beams under typical experimental conditions. We find that the counter-propagating beams exhibit narrow bandwidth permitting the generation of quantum states that possess discrete-frequency entanglement. Such states may be useful for experiments in quantum optics and technologies that benefit from frequency entanglement.Comment: submitted to Phys. Rev.

Correction to: “Constraining climate forecasts: The role of prior assumptions”

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Quantum Loops in the Resonance Chiral Theory: The Vector Form Factor

We present a calculation of the Vector Form Factor at the next-to-leading order in the 1/N_C expansion, within the framework of Resonance Chiral Theory. The calculation is performed in the chiral limit, and with two dynamical quark flavours. The ultraviolet behaviour of quantum loops involving virtual resonance propagators is analyzed, together with the kind of counterterms needed in the renormalization procedure. Using the lowest-order equations of motion, we show that only a few combinations of local couplings appear in the final result. The low-energy limit of our calculation reproduces the standard Chiral Perturbation Theory formula, allowing us to determine the resonance contribution to the chiral low-energy couplings, at the next-to-leading order in 1/N_C, keeping a full control of their renormalization scale dependence.Comment: 27+1 pages, 9 figure

The Development of high-precision hexapod actuators for the Hobby-Eberly Telescope Wide Field Upgrade

Hexapods are finding increased use in telescope applications for positioning large payloads. Engineers from The University of Texas at Austin have been working with engineers from ADS International to develop large, high force, highly precise and controllable hexapod actuators for use on the Wide Field Upgrade (WFU) as part of the Hobby Eberly Telescope Dark Energy Experiment (HETDEX)‡. These actuators are installed in a hexapod arrangement, supporting the 3000+ kg instrument payload which includes the Wide Field Corrector (WFC), support structure, and other optical/electronic components. In addition to force capability, the actuators need to meet the tracking speed (pointing) requirements for accuracy and the slewing speed (rewind) requirements, allowing as many observations in one night as possible. The hexapod actuator stroke (retraction and extension) was very closely monitored during the design phase to make sure all of the science requirements could be met, while minimizing the risk of damaging the WFC optical hardware in the unlikely event of a hexapod actuator or controller failure. This paper discusses the design trade-offs between stiffness, safety, back-drivability, accuracy, and leading to selection of the motor, high ratio worm gear, roller screw, coupling, end mounts, and other key components.Center for Electromechanic