Dynamic maneuverability is an inherent skill of any legged animal locomotion. Thus it is useful and challenging for a physical four-legged robot that runs in open-loop control. This paper presents a ...concept of dynamic maneuverability in a four-legged system that can alter its morphology through leg reconfiguration, i.e., voluntary morphosis 1 . By exploiting this unique feature of the robot body, we designed a dynamic maneuverability control in open-loop that changes the leg length of the ipsilateral pairs of legs to smoothly control the turning of the robot on a particular gait. We verified our control approach on trot gait locomotion. Our results demonstrate that the maneuverability in a four-legged robot is mainly the result of an active change in robot morphology.
Compliant actuation contributes enormously in legged locomotion robotics since it is able to alleviate control efforts in improving the robot's adaptability and energy efficiency. In this paper, we ...present a novel design of a variable stiffness rotary actuator, called MESTRAN, which was especially targeted to address the limitations in terms of the amount of energy and time required to vary the stiffness of an actuated joint. We have constructed a mechanical model in simulation and a physical prototype. We conducted a series of experiments to validate the performance of the MESTRAN actuator prototype. The results from the simulation and experiments show that MESTRAN allows independent control of stiffness and position of an actuated rotary joint with a large operational range and high speed. The torque-displacement relationship is close to linear. Lastly, the MESTRAN actuator is energy-efficient since a certain stiffness level is maintained without energy input.
Abstract Background Exposure of skin to ultraviolet (UV) radiation, an environmental stressor induces number of adverse biological effects (photodamage), including cancer. The damage induced by ...UV-irradiation in skin cells is initiated by the photochemical generation of reactive oxygen species (ROS) and induction of endoplasmic reticulum (ER) stress and consequent activation of unfolded protein response (UPR). Objective To decipher cellular and molecular events responsible for UV-B mediated ER stress and UPR activation in skin cells. Methods The study was performed on human skin fibroblast (Hs68) and keratinocyte (HaCaT) cells exposed to UV-B radiations in lab conditions. Different parameters of UVB induced cellular and molecular changes were analyzed using Western-blotting, microscopic studies and flow cytometry. Results Our results depicted that UV-B induces an immediate ROS generation that resulted in emptying of ER Ca2+ stores inducing ER stress and activation of PERK-peIF2α-CHOP pathway. Quenching ROS generation by anti-oxidants prevented Ca2+ release and subsequent induction of ER stress and UPR activation. UV-B irradiation induced PERK dependent G2/M phase cell cycle arrest in Hs68 and G1/S phase cell cycle arrest in HaCaT. Also our study reflects that UV-B exposure leads to loss of mitochondrial membrane potential, activation of apoptotic cascade as evident by AnnexinV/PI staining, decreased expression of Bcl-2 and increased cleavage of PARP-1 protein. Conclusion UV-B induced Ca2+ deficit within ER lumen was mediated by immediate ROS generation. Insufficient Ca2+ concentration within ER lumen developed ER stress leading to UPR activation. These changes were reversed by use of anti-oxidants which quench ROS.
Thermal loading of fiber reinforced composites during traditional machining is inevitable. This is due to the fact that most of the mechanical energy utilized in material removal is converted into ...heat, which is subsequently dissipated into the workpiece and the cutter, and is carried away by the chips. Heat conduction into the workpiece during machining might cause thermal damage due to matrix softening and decomposition if the generated temperatures exceeded the glass transition temperature of the epoxy resin. In this work, the amount of heat flux applied to the machined edge and the temperature distribution in multidirectional CFRP and GFRP composite laminates was determined using an iterative inverse heat conduction method. The transient heat conduction problems in the laminate and cutter were simulated independently using the finite element method and the amount of heat flux applied to each was determined. It was also found that the heat flux conducted to the workpiece represented only a small fraction of the total heat and is more influenced by the feed speed than the spindle speed. The temperature of the machined surface was estimated and correlations with the resulting machined surface texture were made.
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