ABSTRACT
In the aspect of further development of investigations in the area of spacecraft modeling and analysis of the control scheme, a new hybrid finite-time robust three-axis cascade attitude control approach is proposed via pulse modulation synthesis. The full quaternion based control approach proposed here is organized in association with both the inner and the outer closed loops. It is shown that the inner closed loop, which consists of the sliding mode finite-time control approach, the pulse width pulse frequency modulator, the control allocation and finally the dynamics of the spacecraft is realized to track the three-axis referenced commands of the angular velocities. The pulse width pulse frequency modulators are in fact employed in the inner closed loop to accommodate the control signals to a number of on-off thrusters, while the control allocation algorithm provides the commanded firing times for the reaction control thrusters in the overactuated spacecraft. Hereinafter, the outer closed loop, which consists of the proportional linear control approach and the kinematics of the spacecraft is correspondingly designed to deal with the attitude angles that are presented by quaternion vector. It should be noted that the main motivation of the present research is to realize a hybrid control method by using linear and nonlinear terms and to provide a reliable and robust control structure, which is able to track time varying three-axis referenced commands. Subsequently, a stability analysis is presented to verify the performance of the overall proposed cascade attitude control approach. To prove the effectiveness of the presented approach, a thorough investigation is presented compared to a number of recent corresponding benchmarks.
ABSTRACT
An elastic solution of cylinder-truncated cone shell intersection under internal pressure is presented. The edge solution theory that has been used in this study takes bending moments and shearing forces into account in the thin-walled shell of revolution element. The general solution of the cone equations is based on power series method. The effect of cone apex angle on the stress distribution in conical and cylindrical parts of structure is investigated. In addition, the effect of the intersection and boundary locations on the circumferential and longitudinal stresses is evaluated and it is shown that how quantitatively they are essential.
ABSTRACT
OBJECTIVE: The aim of this experimental study was to investigate the effects of exercise training on visceral fat and adiponectin levels in ovariectomized (OVX) rats. METHOD: Female Wistar rats were divided into OVX (n = 20) and sham-operated control (SHAM; n = 8) groups. OVX rats were subdivided into a sedentary (OVX-SED; n = 10) and an exercise (OVX-EX; n = 10) group. The exercise consisted of 8 weeks of aerobic exercise (26 m/min, 5 days/week, 60 min/day, 10% slope). RESULTS: In OVX rats, body weight was 21% greater (255.2 +/- 9.31 vs. 211.63 +/- 3.23; p < 0.01) and visceral fat was 29% greater (10.87 +/- 0.66 vs. 8.43 +/- 0.45; p < 0.05) than in SHAM rats. After training, visceral fat was 20% lower in OVX-EX rats than in OVX-SED rats (8.72 +/- 0.46 vs. 10.87 +/- 0.66; p < 0.05). After 8 weeks of running on the treadmill, levels of serum glucose, insulin and serum adiponectin, and the homeostasis model assessment of insulin resistance were not changed significantly in the OVX-EX group. CONCLUSION: These results suggest that 8-week exercise training induces a decrease in visceral fat, and this reduction without weight loss does not change serum adiponectin levels and insulin sensitivity in ovariectomized rats.
