A comparison of assimilation results from the ensemble Kalman Filter and a reduced-rank extended Kalman Filter

International audienceThe goal of this study is to compare the performances of the ensemble Kalman filter and a reduced-rank extended Kalman filter when applied to different dynamic regimes. Data assimilation experiments are performed using an eddy-resolving quasi-geostrophic model of the wind-driven ocean circulation. By changing eddy viscosity, this model exhibits two qualitatively distinct behaviors: strongly chaotic for the low viscosity case and quasi-periodic for the high viscosity case. In the reduced-rank extended Kalman filter algorithm, the model is linearized with respect to the time-mean from a long model run without assimilation, a reduced state space is obtained from a small number (100 for the low viscosity case and 20 for the high viscosity case) of leading empirical orthogonal functions (EOFs) derived from the long model run without assimilation. Corrections to the forecasts are only made in the reduced state space at the analysis time, and it is assumed that a steady state filter exists so that a faster filter algorithm is obtained. The ensemble Kalman filter is based on estimating the state-dependent forecast error statistics using Monte Carlo methods. The ensemble Kalman filter is computationally more expensive than the reduced-rank extended Kalman filter.The results show that for strongly nonlinear case, chaotic regime, about 32 ensemble members are sufficient to accurately describe the non-stationary, inhomogeneous, and anisotropic structure of the forecast error covariance and the performance of the reduced-rank extended Kalman filter is very similar to simple optimal interpolation and the ensemble Kalman filter greatly outperforms the reduced-rank extended Kalman filter. For the high viscosity case, both the reduced-rank extended Kalman filter and the ensemble Kalman filter are able to significantly reduce the analysis error and their performances are similar. For the high viscosity case, the model has three preferred regimes, each with distinct energy levels. Therefore, the probability density of the system has a multi-modal distribution and the error of the ensemble mean for the ensemble Kalman filter using larger ensembles can be larger than with smaller ensembles

Osteoporosis therapy: an example of putting evidence-based medicine into clinical practice

A major aim of evidence-based medicine is to assist clinical decision-making by providing the most current and reliable medical information. Systematic reviews and meta-analyses are important tools in this process. Systematic reviews identify and compile relevant evidence, while meta-analyses summarize and quantify the results of such reviews. Results from meta-analyses are, at present, the main source of summary evidence for the efficacy of treatments for a specific condition. They are important tools for helping to choose among treatment options, although they cannot be used to directly compare the magnitude of the effect of various therapies. However, the methods used and the consequent clinical value of the results, may be poorly understood by clinicians, who may therefore not take full advantage of the evidence. Recently, a panel of experts in osteoporosis and evidence-based medicine applied rigorous, validated, scientific standards to produce a systematic review and meta-analysis of randomized controlled trials of anti-resorptive agents used to treat osteoporosis. They found that, although several agents reduced the risk of vertebral fracture, only two, alendronate and risedronate, demonstrated convincing evidence for both non-vertebral and vertebral fracture risk reductions. The clinical implication of these results is that there are important differences in anti-fracture efficacy among currently available agents. In the absence of evidence from head-to-head clinical trials and because of the systematic nature and methodological rigor of the analyses, these data provide important information for clinical decision-makin

Overvoltages in DC Urban Light Railway Systems: Statistical Analysis and Possible Causes

In DC light railway systems the equipment in the power substations and certain devices along the lines are protected against lightning overvoltages thanks to surge arresters. This paper analyses the overvoltages occurring on the tram network of Torino, Italy to discover the causes that brought to the explosion of several surge arresters in the past years. The cause is found to be the regenerative breaking of a particular type of vehicles, in conditions of low load in the system. The benefits of regenerative breaking are discussed in the light of the possible problems introduced. Finally, possible solutions are proposed

Federated Learning in Computer Vision

Federated Learning (FL) has recently emerged as a novel machine learning paradigm allowing to preserve privacy and to account for the distributed nature of the learning process in many real-world settings. Computer vision tasks deal with huge datasets often with critical privacy issues, therefore many federated learning approaches have been presented to exploit its distributed and privacy-preserving nature. Firstly, this paper introduces the different FL settings used in computer vision and the main challenges that need to be tackled. Then, it provides a comprehensive overview of the different strategies used for FL in vision applications and presents several different approaches for image classification, object detection, semantic segmentation and for focused settings in face recognition and medical imaging. For the various approaches the considered FL setting, the employed data and methodologies and the achieved results are thoroughly discussed

Heritable and nutritional influences on bone mineral mass

Osteoporosis is the net result of the maximal amount of bone mineral mass achieved by the end of pubertal growth (peak bone mass) minus post-menopausal and elderly bone losses. Peak bone mineral mass is determined from early childhood by both heritable and environmental factors. Recent developments in the molecular epidemiology of osteoporosis have shown the interest, but also the limitations, of specific molecular markers, such as the vitamin D receptor gene polymorphisms Bsm 1 and Fok 1, to explain bone mineral density differences across the population. Importantly, however, interactions between VDR gene polymorphisms and environmental factors, particularly dietary calcium, have provided new insights into the complex determination of bone mineral mas

Modeling distinct vertical biogeochemical structure of the Black Sea: Dynamical coupling of the oxic, suboxic, and anoxic layers

A one-dimensional, vertically resolved, physical-biogeochemical model is used to provide a unified representation of the dynamically coupled oxic-suboxic-anoxic system for the interior Black Sea. The model relates the annual cycle of plankton production in the form of a series of successive phytoplankton, mesozooplankton, and higher consumer blooms to organic matter generation and to the remineralization-ammonification-nitrification-dentrification chain of the nitrogen cycle as well as to anaerobic sulfide oxidation in the suboxic-anoxic interface zone. The simulations indicate that oxygen consumption during remineralixation and nitrification, together with a lack of ventilation of subsurface waters due to the presence of strong stratification, are the two main factors limiting aerobic biogeochemical activity to the upper similar to 75 m of the water column, which approximately corresponds to the level of nitrate maximum. The position of the upper boundary and thus the thickness of the suboxic layer are controlled by upper layer biological processes. The quasi-permanent character of this layer and the stability of the suboxic-anoxic interface within the last several decades are maintained by a constant rate of nitrate supply from the nitrate maximum zone. Nitrate is consumed to, oxidize sinking particulate organic matter as well as hydrogen sulfide and ammonium transported upward from deeper levels

PTH improves titanium implant fixation more than pamidronate or renutrition in osteopenic rats chronically fed a low protein diet

Summary : We evaluated the effects of parathyroid hormone (PTH), pamidronate, or renutrition on osseointegration of titanium implants in the proximal tibia of rats subject to prolonged low-protein diets. PTH improved mechanical fixation, microarchitecture, and increased pull-out strength. Pamidronate or renutrition had lesser effects. PTH can thus improve implant osseointegration in protein-malnourished rats. Introduction: Protein malnutrition impairs implant osseointegration in rats. PTH and pamidronate prevent deleterious effects of protein restriction introduced just prior to implantation. Whether these treatments improve osseointegration after chronic protein deprivation, i.e., in osteopenic bone at time of implantation, is unknown. We evaluated effects of PTH, pamidronate, or renutrition on resistance to pull-out of titanium rods implanted into the rat tibiae following isocaloric low-protein intake. Methods: Forty-one adult female rats received normal or isocaloric low-protein diets. Six weeks later, implants were surgically inserted into proximal tibiae. Following implantation, rats on low-protein diets were treated with PTH (1-34), pamidronate, saline vehicle, or normal protein diets, for another 8weeks. Tibiae were removed for micro-computerised tomographic morphometry and evaluation of pull-out strength. Results: Pull-out strength decreased in rats on isocaloric low-protein diets compared with normal protein group (−33.4%). PTH increased pull-out strength in low-protein group, even compared to controls from the normal protein group. PTH and pamidronate increased bone volume/tissue volume, bone-to-implant contact, and trabecular thickness, whilst trabecular separation was reduced, with a shift to more plate-like bone surrounding the implants. Conclusions: PTH reversed the deleterious effects of long-term protein undernutrition on mechanical fixation and bone microarchitecture and improved implant osseointegration more than pamidronate or renutrition, likely through changes to structure model inde

Zinc increases the effects of essential amino acids-whey protein supplements in frail elderly

Abstract: Protein undernutrition is frequent in the elderly. It contributes to the development of osteoporosis, possibly via lower IGF-I. Dietary zinc can influence IGF-I production. Objectives: To determine the influence of dietary zinc addition on IGF-I and bone turnover responses to essential amino acids-whey (EAA-W) protein supplements in frail elderly. Design and setting: A daily oral protein supplement was given to hospitalized patients for 4 weeks. On a randomized, double-blind basis, patients received either an additional 30 mg/day of zinc or control. Participants: Sixty-one hospitalized elderly aged 66.7 to 105.8, with a mini-nutritional assessment score between 17 and 24 were enrolled. Measurements: Activities of daily living; dietary intakes; serum IGF-I, IGF-BP3, CrossLaps™, osteocalcin and zinc were measured before and after 1, 2 and 4 weeks of protein supplementation. Results: Serum IGF-I rapidly increased in both groups. Zinc accelerated this increase with changes of +48.2±14.3 and +22.4±4.7% (p<.05) by 1 week, in the zinc-supplemented and control groups, respectively. Zinc significantly decreased the serum bone resorption marker CrossLaps™ by already 1 week. Activities of daily living improved by +27.0±3.1 and +18.3±4.5% in zinc-supplemented and control groups, respectively. Conclusion: In the elderly, zinc supplementation accelerated the serum IGF-I response to EAA-W protein by 1 week and decreased a biochemical marker of bone resorptio