Design of Sliding Mode Techniques for a CMG-based Testbed Attitude Control System

Precise pointing accuracy and rapid maneuvering are two key features for attitude control missions of small spacecraft. Control moment gyroscopes (CMGs) are applied as ideal actuator for large torque output capability but are usually limited due to the problem of inherent mechanical singularity. This paper proposes a robust attitude control methodology, based on Sliding Mode Control (SMC) techniques, in presence of CMG practical restrictions and disturbances. Two second-order SMC techniques are designed, to guarantee accuracy and limited convergence time. Moreover, attitude control torques are generated by means of four single gimbal CMGs in pyramidal configuration, considering the design of an experimental testbed. The effectiveness of the proposed methodologies are shown in simulations, for different mission scenarios, including singularity points

Quantification of the water boiling heat transfer in micro-structures by image analysis

The heat transfer performance of a micro-vaporizer has been measured by conventional methods (using temperatures, flow rates, effective power input). The study was carried out for laminar flow in channels (5 mm×3 cm×200 μm) micro-structured with square obstacles to increase the specific area. The results show that high heat transfer coefficients (1300– 2500 W m−2/C−1) can be reached in such a micro-structured channel. Image analysis was done to estimate the volume vapour fraction, which can be converted into the mass vapour fraction using a slip ratio and avoids the need for any temperature or electric power input measurements. The estimation of this slip ratio is discussed in this paper

Introduction of image analysis for the quantification of the boiling flow heat transfer

Heat transfer performances for non-boiling and boiling flow of a micro-vaporizer have been measured by standard methods (temperatures, flow rates, effective power input). The study was carried out for laminar flow (Re<25) in silicon micro-channels (5 mm×3 cm×200 μm) filled with ordered obstacles to increase the specific area. The results obtained show a strong dependence of the heat transfer on the Reynolds number for the non-boiling flow and pretty high heat transfer coefficients (1300–2500 W/m2 K) for the boiling flow. Image analysis was introduced to estimate the volume vapour fraction, which can be converted into the mass vapour fraction using the slip ratio. The estimation of this slip ratio is discussed in this paper

COAPT-Like Profile Predicts Long-Term Outcomes in Patients With Secondary Mitral Regurgitation Undergoing MitraClip Implantation

Objectives: The aim of this study was to evaluate whether fulfilling COAPT (Cardiovascular Outcomes Assessment of the MitraClip Percutaneous Therapy for Heart Failure Patients With Functional Mitral Regurgitation) criteria identifies patients with better outcomes after MitraClip treatment for secondary mitral regurgitation (SMR). Background: To date, COAPT is the only trial showing a prognostic benefit of MitraClip implantation compared with conservative management. Methods: Three hundred four patients with SMR undergoing MitraClip placement in addition to optimal medical therapy at 3 European centers were analyzed. A COAPT-like profile was defined as absence of all the following criteria: severe left ventricular impairment, moderate to severe right ventricular dysfunction, severe tricuspid regurgitation, severe pulmonary hypertension, and hemodynamic instability. Freedom from all-cause death and from a composite endpoint (cardiovascular death and heart failure hospitalization) were evaluated at 2- and 5-year follow-up. Results: A COAPT-like profile was observed in 65% of the population. Compared with non-COAPT-like patients, those fulfilling COAPT criteria had greater survival free from all-cause death and from the composite endpoint at both 2 year (75% vs. 55% and 67% vs. 47%; p < 0.001 for both) and 5-year (49% vs. 25% and 40% vs. 19%; p < 0.001 for both) follow-up. Among the non-COAPT-like patients, similar outcomes were observed in those fulfilling 1 or ≥1 criterion. Left ventricular impairment had a late impact on outcomes, while right ventricular impairment, pulmonary hypertension, and hemodynamic instability had early effects. COAPT-like profile was an independent predictor of long-term outcomes, as well as administration of neurohormonal antagonists, European System for Cardiac Operative Risk Evaluation II score, and previous heart failure hospitalization. Conclusions: A COAPT-like profile, including specific echocardiographic and clinical criteria, identifies patients with SMR who have a better prognosis after MitraClip implantation