Feedback control and optimization for the production of commercial fuels by blending

International audienceThis paper presents a control algorithm for blending systems. Such systems are used in refining to produce mixtures having specified properties from several components. The underlying control problem is multi-variable, with constraints on the inputs and outputs, and involves large uncertainties. To address this complexity, a constrained optimization problem is formulated, while the uncertainties are treated in closed-loop by an estimator of the components properties. Besides a theoretical study of the main algorithm and a study of convergence, the paper presents numerous technical details that are needed to solve blending problems as they appear in refining operations. Among them are a general lack of measurements, variable delays, measurement synchronization, infeasibilities management, hydraulic constraints, and pre-blends. Industrial case-studies are provided and stress the relevance of the approach

Screening effect in Spin-Hall Devices

The stationary state of the spin-Hall bar is studied in the framework of a variational approach that includes non-equilibrium screening effects. The minimization of the power dissipated in the system is performed with taking into account the spin-flip relaxation and the global constrains due to the electric generator and global charge conservation. The calculation is performed in both approximations of negligible spin-flip scattering and strong spin-flip scattering. In both cases, the expressions of the spin-accumulation and the longitudinal and transverse pure spin-currents are derived analytically. Due to the small value of the Debye-Fermi screening length, the spin-accumulation is shown to be linear in $y$ (across the device), linear in the electric field imposed by the generator, and inversely proportional to the temperature for non-degenerate conductors

Surface currents in Hall devices

One hundred and forty years after his discovery, the Hall effect still deserves attention. If it is well-known that the Hall voltage measured in Hall bar devices is due to the electric charges accumulated at the edges in response to the magnetic field, the nature of the corresponding boundary conditions is still problematic. In order to study this out-of-equilibrium stationary state, the Onsager's least-dissipation principle is applied. It is shown that, beside the well-known expression of the charge accumulation and the corresponding Hall voltage, a longitudinal surface current proportional to the charge accumulation is generated. An expression of the surface current is given. The surface currents allow the Hall voltage to be stabilized at a stationary state, despite, e.g., the presence of leakage of charges at the edges

Citrulline malate supplementation does not improve German Volume Training performance or reduce muscle soreness in moderately trained males and females

Background Use of supplements to aid performance is common practice amongst recreationally active individuals, including those without a sufficient evidence base. This investigation sought to assess whether acute supplementation with 8 g of citrulline malate (CM) (1.11: 1 ratio) would improve anaerobic performance. Methods A randomised double blind placebo control trial was employed, using a counterbalanced design. We recruited recreationally active men and women to take part in an isokinetic chair protocol, based on German Volume Training (GVT) whereby participants attempted to perform 10 sets of 10 repetitions against a force representing 70% of their peak concentric force. Results The number of repetitions achieved over the course of the GVT was 94.0 ± 7.9 and 90.9 ± 13.9 for placebo and CM respectively. There was no significant difference between the placebo and CM treatment for number of repetitions (P = 0.33), isometric (P = 0.60), concentric (P = 0.38), or eccentric (P = 0.65) peak force following the GVT. Total muscle soreness was significantly higher in the CM compared to the placebo treatment following the GVT protocol over 72 h (P = 0.01); although this was not accompanied by a greater workload/number of repetitions in the CM group. Conclusions We conclude that an acute dose of CM does not significantly affect anaerobic performance using an isokinetic chair in recreational active participants. Practical implications include precaution in recommending CM supplementation. Coaches and athletes should be aware of the disparity between the chemical analyses of the products reviewed in the present investigation versus the manufacturers’ claims

Handling parameter ranking, equalities and bounds in adaptive control of blending systems

International audienceThis paper presents solutions to handle ranking, equalities and bounds for the parameter estimates of a linear adaptive controller scheme used in the production of commercial fuels by blending. The control problem under consideration is a multi-variable output regulation problems with large uncertainties in the plant parameters. It can be solved using a specifically designed adaptive controller which combines constrained optimization and a closed-loop estimator of the plant parameters. As in numerous applications of adaptive control, while output convergence is usually guaranteed under feasibility assumptions, little is known about the asymptotic behavior of the parameter estimates themselves. Yet, from an application view-point, it is desired that these estimates satisfy some physical properties. In particular, parameters ranking, equalities and bounds are of practical importance and assert the consistency of the estimation. In this paper we expose techniques that guarantee this desired behavior

Effet d'écrantage dans l'effet Hall de spin

International audienceThe stationary state of the spin Hall bar is studied in the framework of a variational approach that includes nonequilibrium screening effects at the edges. The minimization of the power dissipated in the system is performed taking into account the spin-flip relaxation and the global constraints due to the electric generator and global charge conservation. The calculation is performed within the approximations of negligible spin-flip scattering and strong spin-flip scattering. In both cases, simple expressions of the spin accumulation and the longitudinal and transverse pure spin currents are derived analytically. In usual conditions, the maximum amplitude of the spin accumulation is expected to be of the order of 1% of the equilibrium density carriers