713 research outputs found
The role of visual and spatial working memory informing mental models derived from survey and route descriptions
No full textThis study examines the involvement of spatial and visual working memory (WM) in the
construction of flexible spatial models derived from survey and route descriptions. Sixty
young adults listened to environment descriptions, 30 from a survey perspective and the
other 30 from a route perspective, while they performed spatial (spatial tapping [ST]) and
visual (dynamic visual noise [DVN]) secondary tasks – believed to overload the spatial and
visual working memory (WM) components, respectively – or no secondary task (control,
C). Their mental representations of the environment were tested by free recall and a
verification test with both route and survey statements. Results showed that, for both
recall tasks, accuracy was worse in the ST than in the C or DVN conditions. In the
verification test, the effect of both ST and DVN was a decreasing accuracy for sentences
testing spatial relations from the opposite perspective to the one learnt than if the
perspective was the same; only ST had a stronger interference effect than the C condition
for sentences from the opposite perspective from the one learnt. Overall, these findings
indicate that both visual and spatial WM, and especially the latter, are involved in the
construction of perspective-flexible spatial models
A command governor approach to plasma shape control
No full textThe paper deals with the application of the socalled Command Governor (CG) approach to the shape control of plasmas in thermonuclear fusion reactors. A primal internal loop controlling the plasma-wall gaps is designed first and a CG device is then tuned to modify, whenever necessary, the reference to the primal loop, taking into account constraints due to voltages saturations on the converters, currents limitations in the active coils, force limits on the mechanical structures, minimum clearance between the plasma and the vacuum chamber wall, maximum induced forces on coils. The reference signal modification is accomplished through an online optimization procedure which embodies plasma model forecasts computed along a finite time virtual receding horizon as usual in model predictive paradigms. The ITER (International Thermonuclear Experimental Reactor) tokamak is assumed as a case study. Numerical simulations are carried out on a numerical nonlinear model taking into account almost a hundred of constraints. ©2009 IEEE
Constrained plasma shape control in ITER
No full textThis paper presents an application of a novel constrained control methodology known as Command Governor (CG) to the shape control of plasmas in thermonuclear fusion reactors. The CG strategy is based on predictive control ideas and consists in modifying, whenever necessary, the reference signal supplied to a primal internal loop controlling the plasma distance from the internal walls of the tokamak, taking into account constraints due to voltages saturations on the converters, currents limitations in the active coils for magnetic confinement, force limits on the mechanical structures, minimum clearance between the plasma and the vacuum chamber wall, maximum induced forces on coils. The reference signal modification is accomplished through an on-line optimization procedure which embodies plasma model forecasts computed along a finite time virtual receding horizon. A numerical example with about a hundred of constraints, is developed with reference to ITER
A Command Governor Approach to Plasma Shape Control
No full textThe paper deals with the application of the socalled Command Governor (CG) approach to the shape control of plasmas in thermonuclear fusion reactors. A primal internal loop controlling the plasma-wall gaps is designed first and a CG device is then tuned to modify, whenever necessary, the reference to the primal loop, taking into account constraints due to voltages saturations on the converters, currents limitations in the active coils, force limits on the mechanical structures, minimum clearance between the plasma and the vacuum chamber wall, maximum induced forces on coils. The reference signal modification is accomplished through an online optimization procedure which embodies plasma model forecasts computed along a finite time virtual receding horizon as usual in model predictive paradigms. The ITER (International Thermonuclear Experimental Reactor) tokamak is assumed as a case study. Numerical simulations are carried out on a numerical nonlinear model taking into account almost a hundred of constraints
A constrained control strategy for the shape control in thermonuclear fusion tokamaks
No full textThe paper deals with the application of the so-called Reference (or Command) Governor constrained control strategy to the shape control of plasmas in thermonuclear fusion reactors with the main scope of optimizing tokamak operations also in conditions very close to the operating envelope limits. A primal inner loop controlling the plasma-wall distance is first designed; the Reference Governor device is then tuned to modify, whenever necessary, the reference signals to the inner loop, on the basis of constraints due to voltage saturations on the power supply converters, limitations of currents in the active control coils, minimum clearance between the plasma surface and the vacuum chamber wall, maximum induced magnetic fields and forces on coils. As usual in model predictive paradigms, the reference signal modification is accomplished through an on-line optimization procedure which embodies plasma model forecasts computed along a finite time virtual receding horizon. The ITER (International Thermonuclear Experimental Reactor) tokamak is assumed as the case study. Numerical simulations are carried out on a finite elements nonlinear model taking into account induced currents in the passive structures. The proposed application shows how almost a hundred constraints can be managed on-line by the Reference Governor. © 2012 Elsevier Ltd. All rights reserved
MTHFR C677T mutation, factor II G20210A mutation and factor V Leiden as risks factor for youth retinal vein occlusion.
No full textObjective: To determine whether methylene tetrahydrofolate reductase (MTHFR) C677T mutation, factor II G20210A mutation and factor V Leiden are risk factors for retinal vein occlusion (RVO) in patients under fifty years of age. Methods: Comparison of 29 patients, under 50 years old of age, as affected RVO and 62 age matched normal controls. Plasma MTHFR C677T genotype, Factor II G20210A genotype, Factor V Leiden genotype, S protein level, C protein level, APCR presence (Actived Protein C Resistance), homocysteine level and Beta-thromboglobulin level were determined. Results: Seventeen RVO patients and twenty-one controls were heterozygous for the MTHFR C677T mutation. Three RVO patients and twenty-three controls were homozygous for the MTHFR C677T mutation. Three RVO patients and two controls were heterozygous for the factor II G20210A mutation. One control was heterozygous for the factor V Leiden. Conclusions: This study fails to demonstrate that these mutations are risk factors for RVO in patients under fifty years of age
Neutrophil gelatinase-associated lipocalin immunoexpression in colorectal carcinoma: A stage-specific prognostic factor?
No full textTNM post-surgical staging is considered to be one of the most powerful prognosticators for colorectal carcinoma. Although patient survival mostly decreases concomitantly to stage increase, in a percentage of cases TNM stage appears only to express the anatomic extent of the neoplasia with no correlation with clinical outcome. Thais, the identification of additional prognostic markers for colorectal cancer is required. Neutrophil gelatinase-associated lipocalin (NGAL) is a 25-kDa protein that appears to play an important role in colorectal cancer progression. In order to evaluate whether NGAL expression may be considered as a predictor of colorectal cancer progression, we analyzed its correlation with clinicopathological characteristics, as well as with patient progression-free survival in a series of surgically resected colorectal carcinomas. A variable NGAL immunoexpression was found in 24 out of the 64 analyzed cases. When only the positive cases were considered, a significant association was found between a high NGAL expression and the presence of distant metastases or high tumor stage. In addition, the presence of NGAL was a significant negative prognostic marker correlated with a shorter progression-free survival in stage I colorectal carcinoma, but not in the remaining TNM stages. If our findings are confirmed in more extensive analyses on stage I colorectal carcinoma, NGAL assessment may be used in order to select those patients with a higher progression risk and to submit them to adjuvant therapies useful to prevent adverse outcome
Exercise oscillatory breathing and NT-proBNP levels in stable heart failure provide the strongest prediction of cardiac outcome when combining biomarkers with cardiopulmonary exercise testing
No full textN-Terminal pro-brain natriuretic peptide (NT-proBNP) and cardiopulmonary exercise testing (CPET)-derived variables are gold standards for assessing prognosis in heart failure (HF) patients. We sought to refine cardiac events prediction by performing a combined analysis of NT-proBNP with markers of exercise ventilatory efficiency.
Methods and Results: A total of 260 stable HF patients underwent measurements of plasma NT-proBNP levels before, at peak exercise, and at I-minute CPET recovery phase along with peak oxygen uptake (VO2), ventilation to CO2 production (VE/VCO2) slope, and exercise periodic breathing (EPB) determinations. After a median follow-up period of 20.6 months, there were 54 cardiac-related deaths. Univariate analysis including NT-proBNP at rest, at peak exercise, and at 1 minute recovery, peak VO2, VE/VCO2 slope, and EPB showed NT-proBNP to be the strongest independent predictor with equivalent performance for rest, peak, and recovery levels. Thus, only NT-proBNP at rest was considered (Harrel C 0.783, 95% confidence interval [CI] 0.722-0.844) with VE/VCO2 slope (Harrel C 0.720, 95% Cl 0.646-0.794), EPB (Harrel C 0.685, 95% CI 0.619-0.751), and peak VO2 (Harrel C 0.618, 95% Cl 0.533-0.704). With bivariate stepwise analyses, NT-proBNP along with EPB emerged as the strongest prognosticators (Harrel C 0.800, 95% Cl 0.737-0.862).
Conclusions: In the refinement for robust outcome predictors in HE patients, NT-proBNP levels together with EPB led to the most powerful definition. VE/VCO2 slope and peak VO2 did not provide any prognostic adjunct. A biomarker/CPET approach seems very promising to warrant the continuous implementation in the prognostic work-up of HE patients
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