167 research outputs found

    The seasonal and spatial variability of small-scale turbulence at the Iberian margin

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    Turbulence measurements were made off the northwest coast of Spain in January and August 1998. In winter the water column was vertically mixed to about 100 to 150 m, due to the combined effects of the vertical convection of warm northward-moving water and wind stress. A highly dissipative surface boundary layer was present at all times to a depth (of about 20 m) that correlated well with the local wind and wave amplitude. Below this layer dissipation levels decreased from about 10-7 m2 s-3 at a rate that was commensurate with 'law of the wall' boundary theory. Near the coast local brackish surface stratification served to depress mixing below the pycnocline. In summer, when the water column was thermally stratified, average dissipation levels were typically an order of magnitude smaller than in winter, even though the wind stress in the ocean was of similar magnitude. Bursts of enhanced mixing were occasionally observed in an internal wave field on the shelf. Dissipation levels were higher on the northern side of an upwelling filament (up to 10-7 m2 s-3) than in other parts of the ocean. Although eddy viscosity levels on the shelf and in the ocean were almost identical (about 8 cm2 s-1), eddy diffusion on the shelf (0.37 cm2 s-1) was about three times larger than in the ocean. This may indicate a higher frequency of mixing events on the shelf. The summer data were used to determine a mixing length (of about 0.3 ± 0.05 m) using an algorithm that mimicked the way that turbulence closure models compute dissipation from vertical shear and buoyancy over grid scales of several meters. The correlation between dissipation and the gradient Richardson number was poor and it is suggested that at the scales of the observations, and of some models, buoyancy is just as likely to act as a source of mixing as it is to act as a sink

    Vertical structure, turbulent mixing and fluxes during Lagrangian observations of an upwelling filament system off Northwest Iberia

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    In August 1998, a recurrent filament located near 42°N off Galicia was sampled as part of the OMEX-II project. Lagrangian and other observations were made on the shelf where the filament arose and offshore in the filament itself under upwelling favourable but fluctuating winds. The shelf drift experiment monitored a change from southward to weak northward net flow as the winds decreased to zero. Shipborne {ADCP} measurements showed that the shelf was supplying decreasing volumes of water to the filament as the wind speeds decreased. At the shelf edge the internal tide was larger than can be explained by local forcing and there were many unusually large high frequency internal waves with a quasi-sinusoidal form. Turbulence observations revealed enhanced dissipation rates and vertical eddy diffusion coefficients within the shelf thermocline (of order 1 cm2 s�1), which appeared to be caused by the breaking of internal wave. A second Lagrangian experiment was executed in the filament some 120 km offshore, which again coincided with a period of wind relaxation. Cross-sections revealed a double cold core and that the offshore flow was limited to a thin surface layer. Substantial onshore flow occurred below 50 m in the centre of the filament, while the strongest and deepest offshore flow coincided with its northern boundary. Turbulent kinetic energy dissipation rate measurements showed very weak mixing below 15 m in the filament core, but enhanced mixing at its boundaries. Four mixed layer drifters released in the filament initially indicated convergence at its southern boundary, marked by strong temperature and salinity contrasts. After the wind became more favourable for upwelling, the drifters accelerated. One drifter traced the full extent of the filament, while the other three escaped from it and began to circulate cyclonically over 28 days in a 100 km diameter loop back towards their release point. Although strong mesoscale activity linked the shelf and ocean regimes, offshore transport in the filament was weak at the time of the experiment and vertical and horizontal re-circulations on a variety of time scales were important. There was sufficient vertical mixing in the thermocline to cause it to thicken and draw some heat into the lower layers during the summer months on the shelf. The amount of heat involved was too little to have a significant impact on the development of a filament over a typical lifetime of a week

    Performance of [(18)F]flutemetamol amyloid imaging against the neuritic plaque component of CERAD and the current (2012) NIA-AA recommendations for the neuropathologic diagnosis of Alzheimer's disease

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    INTRODUCTION: Performance of the amyloid tracer [(18)F]flutemetamol was evaluated against three pathology standard of truth (SoT) measures including neuritic plaques (CERAD "original" and "modified" and the amyloid component of the 2012 NIA-AA guidelines). METHODS: After [(18)F]flutemetamol imaging, 106 end-of-life patients who died underwent postmortem brain examination for amyloid plaque load. Blinded positron emission tomography scan interpretations by five independent electronically trained readers were compared with pathology measures. RESULTS: By SoT, sensitivity and specificity of majority image interpretations were, respectively, 91.9% and 87.5% with "original CERAD," 90.8% and 90.0% with "modified CERAD," and 85.7% and 100% with the 2012 NIA-AA criteria. DISCUSSION: The high accuracy of either CERAD criteria suggests that [(18)F]flutemetamol predominantly reflects neuritic amyloid plaque density. However, the use of CERAD criteria as the SoT can result in some false-positive results because of the presence of diffuse plaques, which are accounted for when the positron emission tomography read is compared with the 2012 NIA-AA criteria

    Kestenbaum procedure with posterior fixation suture for anomalous head posture in infantile nystagmus

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    The purpose of this study was to report the effect of combining the Kestenbaum procedure with posterior fixation suture for infantile horizontal nystagmus with anomalous head posture (AHP) in children. Nine consecutive patients who underwent combined Kestenbaum procedure plus posterior fixation suture to the recessed muscles at the same time were retrospectively studied. All patients were orthotropic before surgery and were followed for at least 6 months. Pre- and postoperative AHP and binocular corrected visual acuity (BCVA), and ocular alignment were assessed. Mean age at surgery was 4.8 ± 1.5 years. The average follow-up was 29.7 months. The average head turn preoperatively was 27.4° and postoperatively 7.2°. The average net change in AHP was 24.8° (P = 0.008). Seven of 9 patients (78%) achieved a residual head turn of 10° or less. The average Log Mar BCVA was 0.33 preoperatively and 0.31 postoperatively (P = 0.68). Only 1 patient needed additional surgery for residual horizontal AHP. No patient developed strabismus. Combined Kestenbaum procedure with posterior fixation suture was an effective and stable procedure in reducing AHP of the range of 20° to 35° in children with infantile nystagmus

    Observer-Based State Feedback for Enhanced Insulin Control of Type ‘I’ Diabetic Patients

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    During the past few decades, biomedical modeling techniques have been applied to improve performance of a wide variety of medical systems that require monitoring and control. Diabetes is one of the most important medical problems. This paper focuses on designing a state feedback controller with observer to improve the performance of the insulin control for type ‘I’ diabetic patients. The dynamic model of glucose levels in diabetic patients is a nonlinear model. The system is a typical fourth-order single-input-single-output state space model. Using a linear time invariant controller based on an operating condition is a common method to simplify control design. On the other hand, adaptive control can potentially improve system performance. But it increases control complexity and may create further stability issues. This paper investigates patient models and presents a simplified control scheme using observer-based feedback controllers. By comparing different control schemes, it shows that a properly designed state feedback controller with observer can eliminate the adaptation strategy that the Proportional-Integral-Derivative (PID) controllers need to improve the control performance. Control strategies are simulated and their performance is evaluated in MATLAB and Simulink

    Influence of phenological barriers and habitat differentiation on the population genetic structure of the balearic endemic Rhamnus ludovici-salvatoris Chodat and R. alaternus L

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    [EN] Rhamnus ludovici-salvatoris, endemic to the Gymnesian Islands, coexists with the related and widespread R. alaternus in Mallorca and Menorca. In both species, the population genetic structure using RAPD, and flowering during a 3-year period to check for possible phenological barriers, were analyzed. Rhamnus ludovici-salvatoris showed lower genetic diversity and stronger population structure than R. alaternus, the Cabrera population being less diverse and the most differentiated. Rhamnus ludovici-salvatoris flowered one month later, although flowering of both species coincided sporadically. These congeners seem to have diverged through isolation by time and differentiation in habitat. The population genetic structure of R. ludovici-salvatoris could mainly be due to the existence of small populations on the one hand, and a gene flow caused by rare hybridization events on the other, which may also explain the presence of morphologically intermediate individuals in Menorca. 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    Potential antiproteolytic effects of L-leucine: observations of in vitro and in vivo studies

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    The purpose of present review is to describe the effect of leucine supplementation on skeletal muscle proteolysis suppression in both in vivo and in vitro studies. Most studies, using in vitro methodology, incubated skeletal muscles with leucine with different doses and the results suggests that there is a dose-dependent effect. The same responses can be observed in in vivo studies. Importantly, the leucine effects on skeletal muscle protein synthesis are not always connected to the inhibition of skeletal muscle proteolysis. As a matter of fact, high doses of leucine incubation can promote suppression of muscle proteolysis without additional effects on protein synthesis, and low leucine doses improve skeletal muscle protein ynthesis but have no effect on skeletal muscle proteolysis. These research findings may have an important clinical relevancy, because muscle loss in atrophic states would be reversed by specific leucine supplementation doses. Additionally, it has been clearly demonstrated that leucine administration suppresses skeletal muscle proteolysis in various catabolic states. Thus, if protein metabolism changes during different atrophic conditions, it is not surprising that the leucine dose-effect relationship must also change, according to atrophy or pathological state and catabolism magnitude. In conclusion, leucine has a potential role on attenuate skeletal muscle proteolysis. Future studies will help to sharpen the leucine efficacy on skeletal muscle protein degradation during several atrophic states
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