Identification in closed‐loop operation of models for collective pitch robust controller design

To achieve load reduction and power optimization, wind turbine controllers design requires the availability of reliable control‐oriented linear models. These are needed for model‐based controller design. Model identification of wind turbine while operating in closed loop is an appropriate solution that has recently shown its capabilities when linear time‐invariant controllers and complicated control structures are present. However, the collective pitch control loop, one of the most important wind turbine loops, uses non‐linear controllers. Typically, this non‐linear controller is a combination of a linear controller and a gain scheduling. This paper presents a new algorithm for identification in closed‐loop operation that allows the use of this kind of non‐linear controllers. The algorithm is applied for identification the collective pitch demand to generator speed of a wind turbine at various operating points. The obtained models are presented and discussed from a control point of view. The validity of these models is illustrated by their use for the design of a linear fix robust controller. The performance based on simulation data of this linear controller is similar to that obtained with simulations based on a linear controller with gain scheduling, but its design and implementation is much simpler. Copyright © 2012 John Wiley & Sons, Ltd.     

Role of thromboxane and angiotensin in cyclosporine-induced renal vasoconstriction in the dog

Cyclosporine is associated with renal insufficiency characterized by a reduction in glomerular filtration rate that may result from renal vasoconstriction. Injection of cyclosporine in the isolated renal artery perfused at a constant flow induces a potent dose-dependent vasoconstriction of renal arterial vessels in the dog. The present study was designed to investigate the role of thromboxane A2, angiotensin, and endothelial-dependent vasodilation in the cyclosporine-induced renal vasoconstriction. A specific thromboxane A2-receptor antagonist (pinane-thromboxane A2), administered at a dose of 150 micrograms, significantly decreased the renal vasoconstriction response to cyclosporine from 103 +/- 26 mm Hg to 45 +/- 11 mm Hg (p < 0.05), with cyclosporine serum levels at the end of injection averaging 382 +/- 105 and 421 +/- 150 nmol/L before and after injection of the antagonist. In contrast, pharmacologic blockade of angiotensin receptors by saralasin had no effect on the cyclosporine arterial vasoconstriction in the kidney. The endothelium-dependent vasodilation to acetylcholine was not modified during cyclosporine injection. Thus cyclosporine renal vasoconstriction appears independent of the renin-angiotensin system and of endothelium-dependent vasodilation. It is at least partly mediated by thromboxane A2. Prevention of cyclosporine vasoconstriction by thromboxane A2-receptor antagonist may likely be possible, with more potent agents having more affinity to thromboxane A2 renal receptors.     

Hydro-Quebec's concerns related to performances of SF6circuit-breakers

Hydro-Quebec's concerns regarding circuit breaker reliability are presented. Emphasis is placed on two aspects crucial in determining line charging current breaking capacity, i.e., the arc duration and the test circuit configuration. The importance of manufacturing quality for the arcing contacts, nozzles and gasket is discussed. Test criteria at 20°C for simulating breaking tests at -50°C are given. Hydro-Quebec's requirements for testing the tightness of SF₆ breakers are presented together with a reliable leakage-measuring method     

Long-term durability of the interface in FRP composites after exposure to simulated physiologic saline environments

Fiber/matrix interfacial bond strength significantly influences the mechanical behavior of fiber-reinforced polymer (FRP) composites. Interfacial bond strength durability is therefore particularly important in the development of FRP composites for implant applications where diffused moisture may potentially weaken the material over time. In this study, the long-term durability of interfacial bonding in carbon fiber/380 grade polyetheretherketone (C/PEEK) and carbon fiber/polysulfone (C/PSF) composites was investigated after exposure to hygrothermal environments. A single fiber pull-out test was used to quantitatively determine the ultimate bond strength (UBS) of the samples following exposure. Samples were tested at three temperatures (37, 65, and 95 degrees C) for six time periods (0-5000 h) and in two environments (dry and physiologic saline-immersed). A mathematical model based on nth order chemical reaction kinetics was applied to describe the long-term durability of the interface. The results of this study indicate that interfacial bond strengths in C/PSF and C/PEEK (380 grade) composites are significantly decreased by exposure to physiologic saline and are functions of both time and temperature. For each material, the kinetics of degradation analysis predicts further bond strength losses following initial saturation, which then stabilizes at temperature-dependent equilibrium bond strength levels.     

Differential intrinsic enzymatic activity of Syk and Zap-70 protein-tyrosine kinases

Syk and Zap-70 are related protein-tyrosine kinases implicated in antigen and Fc receptor signaling. While Zap-70 is restricted to T-cells and natural killer cells, Syk accumulates in B-cells, mast cells, platelets, and immature T-cells. In addition, we found that an isoform of Syk (SykB), which carries a 23-amino acid deletion in the "linker" region, is prominently expressed in bone marrow. To better understand the relative impact of Syk, SykB, and Zap-70 on signal transduction, we compared their intrinsic enzymatic properties in transiently transfected COS-1 cells and in hemopoietic cells. Using modified versions of these enzymes bearing a common Myc epitope at the amino terminus, we determined that the ability of Syk and SykB to undergo autophosphorylation and to phosphorylate erythrocyte band 3 in immune complex kinase reactions was at least 100-fold greater than that of Zap-70. Similarly, Syk and SykB, but not Zap-70, caused prominent tyrosine phosphorylation of p120(c-)cbl in COS-1 cells. A similar pattern of activity was also noted for endogenous Syk and Zap-70 from hemopoietic cells. To understand the structural basis for these characteristics, we also created and analyzed a series of chimeras between Syk and Zap-70. These studies indicated that the catalytic domain of Syk and Zap-70, but not their SH2 domains, linker region or carboxyl-terminal tail, was responsible for their respective activity. Taken together, these data demonstrated that the intrinsic enzymatic activity of Syk and SykB is superior to that of Zap-70 and that such a distinction relates to structural variations in the catalytic domain.     

Study of fuel efficiency in a direct borohydride fuel cell

In this study, direct borohydride fuel cells (DBFCs) potentialities are evaluated. These emerging systems make it possible to reach maximum powers of about 200 mW cm⁻² at room temperature and ambient air (natural convection) with high concentrated borohydride solutions. On the other hand, a part of borohydride hydrolyses during cell operating which leads to hydrogen formation and fuel loss: the practical capacity represents about only 18% of the theoretical one. In order to improve fuel efficiency, thiourea is tested as an inhibitor of the catalytic hydrolysis associated with BH₄⁻ electro-oxidation on Pt. The practical capacity is drastically improved: it represents about 64% of the theoretical one. Against, electrochemical performances (I–E curves) are affected by the presence of thiourea.     

MFG-E8 Reduces Aortic Intimal Proliferation in a Murine Model of Transplant Vasculopathy

Transplant vasculopathy is characterized by endothelial apoptosis, which modulates the local microenvironment. Milk fat globule epidermal growth factor 8 (MFG-E8), which is released by apoptotic endothelial cells, limits tissue damage and inflammation by promoting anti-inflammatory macrophages. We aimed to study its role in transplant vasculopathy using the murine aortic allotransplantation model. BALB/c mice were transplanted with fully mismatched aortic transplants from MFG-E8 knockout (KO) or wild type (WT) C57BL/6J mice. Thereafter, mice received MFG-E8 (or vehicle) injections for 9 weeks prior to histopathological analysis of allografts for intimal proliferation (hematoxylin and eosin staining) and leukocyte infiltration assessment (immunofluorescence). Phenotypes of blood leukocytes and humoral responses were also evaluated (flow cytometry and ELISA). Mice receiving MFG-E8 KO aortas without MFG-E8 injections had the most severe intimal proliferation (p < 0.001). Administration of MFG-E8 decreased intimal proliferation, especially in mice receiving MFG-E8 KO aortas. Administration of MFG-E8 also increased the proportion of anti-inflammatory macrophages among graft-infiltrating macrophages (p = 0.003) and decreased systemic CD4⁺ and CD8⁺ T-cell activation (p < 0.001). An increase in regulatory T cells occurred in both groups of mice receiving WT aortas (p < 0.01). Thus, the analarmin MFG-E8 appears to be an important protein for reducing intimal proliferation in this murine model of transplant vasculopathy. MFG-E8 effects are associated with intra-allograft macrophage reprogramming and systemic T-cell activation dampening.     

Effects of gamma irradiation,irradiation environment,and postirradiation aging on thermal and tensile properties of ultrahigh molecular weight polyethylene fibers

The effects of gamma irradiation in four types of irradiation environment on the thermal and tensile properties of gel-spun, ultrahigh molecular weight polyethylene fibers (Spectra™ 1000) have been investigated. The gamma irradiation was conducted at 2.5 Mrad and in air, nitrogen, acetylene, and vacuum to study the effects of irradiation media on the aforementioned properties. Thermal and tensile properties of virgin and irradiated fiber samples were examined using differential scanning calorimetry and an Instron tensile tester, respectively. The results indicate that both gamma irradiation and irradiation environment affected the properties of the polyethylene fibers, and substantial changes were observed for the oxygen-containing environment. The tensile-fractured surfaces of the fibers were examined by scanning electron microscopy. The properties of irradiated fibers were further evaluated at 160 days postirradiation and found to be affected, substantially. The postirradiation aging significantly decreased the tensile strength and elongation of the irradiated fibers, indicating that polyethylene fibers should not be exposed to gamma irradiation. © 1996 John Wiley & Sons, Inc.     

Experimental study of convective heat transfer on a finned rotating cylinder

In this study, the local convective heat transfer from a rotating finned cylinder to the surrounding air was evaluated using an infrared thermographic experimental set up. Solving the inverse conduction heat transfer problem allows the local convective heat transfer coefficient to be identified. We used the specification function method, along with spatio-temporal regularization, to develop a model of local convective heat transfer in order to take lateral conduction and 2D geometry into account. This model was tested using rotational Reynolds numbers (based on the cylinder diameter and the peripheral speed) between 4300 and 17 900. The local heat transfer on the fin surface was analyzed to determine the influence of the rotational Reynolds number and the influence of the height and spacing of the fins. In this paper, we propose an efficiency definition that allows the optimal geometrical configuration of the finned cylinder to be identified for the given operating conditions.