Reinforcement Q-learning based on Multirate Generalized Policy Iteration and Its Application to a 2-DOF Helicopter

International Journal of Control, Automation and Systems - In this paper, we propose a novel Q-learning method based on multirate generalized policy iteration (MGPI) for unknown discrete-time (DT)...     

Experimental investigation on the piezo-composite actuator with piezoelectric single-crystal layer

Studies on muscle mimicking actuators have increased in the last two decades due to the possibility of various applications for compact lightweight actuators including small unmanned aircrafts, missile, and biomimetic robots. Piezoelectric materials have been used in a variety of applications ranging from shape control of structure and active vibration control of structure to noise suppression due to compact size and good frequency response. Conventional polycrystal piezoelectric ceramic materials, however, have limited actuating strains and displacement, hindering their use in actuators for small aerospace vehicles. In this study, the design and fabrication method of an actuator with a piezoelectric single-crystal layer were investigated to increase the actuation strain and displacement. From a comparison of the performance of the LIPCA-C2 and LIPCA-S prototypes, it was found that the new LIPCA-S2, which has much higher coefficient of the unimorph actuator, can generate an actuating displacement more than twice that of LIPCA-C2.     

Effects of Color,Scouring Method,and Age on the Visual Sensibility of Naturally Colored Organic Cotton (NaCOC)

In parallel to the social trend of green consumerism and well‐being, the demand for naturally colored organic cotton (NaCOC) continually increases in the textile and clothing industry. The present study examined the effects of NaCOC color, scouring method, and age on the visual sensibility of NaCOC. Two age groups (20s and 30s; 40s and 50s) of women rated three color sets of NaCOC specimens (ivory, green, and coyote brown) treated by two chemical scouring methods (Na₂CO₃ and NaOH) and two bioscouring methods (enzyme and boiling water) using 7‐point scales of nine visual sensibilities (bright‐dark; clear‐murky; heavy‐light; vivid‐subdued; warm‐cool; fresh‐stale; strong‐weak; showy‐plain; and luxurious‐cheap). Preferred scouring methods by NaCOC color and/or age group were recommended for each visual sensibility (e.g., preferred scouring methods for fresh sensibility are Na₂CO₃ for ivory NaCOC, Na₂CO₃ and NaOH for green NaCOC, and boiling water for coyote brown NaCOC). In addition, the representative visual sensibilities of each NaCOC color (e.g., those of coyote brown NaCOC are dark, murky, heavy, vivid, warm, stale, strong, plain, and luxurious sensibilities) were identified for the women participants. Last, it was demonstrated that a bioscouring method can replace the traditional chemical methods for selected visual sensibilities (e.g., boiling water for luxurious sensibility). © 2012 Wiley Periodicals, Inc.     

A study on comparisons of composite and conventional steel bogie frames

In this study, the dynamic characteristics of three different bogie configurations, a conventional Steel bogie (SB), a composite bogie without primary suspension (CB1), and a composite bogie with primary suspensions of conical rubber type (CB2), were compared. The CB1 shows the highest critical speed while the CB2 shows the lowest. The SB configuration showed the highest ride index value while the CB2 showed the lowest. Both of the composite configurations showed better ride comfort index than that of the steel configuration. The trend of the derailment index was opposite to that of the critical speed. In the derailment index measuring test, the CB1 bogie configuration had a 12.3 % higher derailment index than that of the SB. These results show good agreement in overall trends with the simulation results.     

Hypoxia Suppresses Spontaneous Mineralization and Osteogenic Differentiation of Mesenchymal Stem Cells via IGFBP3 Up-Regulation

Hypoxia has diverse stimulatory effects on human adipose-derived stem cells (ASCs). In the present study, we investigated whether hypoxic culture conditions (2% O₂) suppress spontaneous mineralization and osteogenic differentiation of ASCs. We also investigated signaling pathways and molecular mechanisms involved in this process. We found that hypoxia suppressed spontaneous mineralization and osteogenic differentiation of ASCs, and up-regulated mRNA and protein expression of Insulin-like growth factor binding proteins (IGFBPs) in ASCs. Although treatment with recombinant IGFBPs did not affect osteogenic differentiation of ASCs, siRNA-mediated inhibition of IGFBP3 attenuated hypoxia-suppressed osteogenic differentiation of ASCs. In contrast, overexpression of IGFBP3 via lentiviral vectors inhibited ASC osteogenic differentiation. These results indicate that hypoxia suppresses spontaneous mineralization and osteogenic differentiation of ASCs via intracellular IGFBP3 up-regulation. We determined that reactive oxygen species (ROS) generation followed by activation of the MAPK and PI3K/Akt pathways play pivotal roles in IGFBP3 expression under hypoxia. For example, ROS scavengers and inhibitors for MAPK and PI3K/Akt pathways attenuated the hypoxia-induced IGFBP3 expression. Inhibition of Elk1 and NF-κB through siRNA transfection also led to down-regulation of IGFBP3 mRNA expression. We next addressed the proliferative potential of ASCs with overexpressed IGFBP3, but IGFBP3 overexpression reduced the proliferation of ASCs. In addition, hypoxia reduced the osteogenic differentiation of bone marrow-derived clonal mesenchymal stem cells. Collectively, our results indicate that hypoxia suppresses the osteogenic differentiation of mesenchymal stem cells via IGFBP3 up-regulation.     

Effects of amplitude modulation on perception of wind turbine noise

Wind turbine noise is considered to be easily detectable and highly annoying at relatively lower sound levels than other noise sources. Many previous studies attributed this characteristic to amplitude modulation. However, it is unclear whether amplitude modulation is the main cause of these properties of wind turbine noise. Therefore, the aim of the current study is to identify the relationship between amplitude modulation and these two properties of wind turbine noise. For this investigation, two experiments were conducted. In the first experiment, 12 participants determined the detection thresholds of six target sounds in the presence of background noise. In the second experiment, 12 participants matched the loudness of modified sounds without amplitude modulation to that of target sounds with amplitude modulation. The results showed that the detection threshold was lowered as the modulation depth increased; additionally, sounds with amplitude modulation had higher subjective loudness than those without amplitude modulation.     

Reactive flash sintering: MgO and α-Al2O3 transform and sinter into single-phase polycrystals of MgAl2O4

We show that flash experiments with three phase mixed-powders of yttria-stabilized zirconia (8YSZ), MgO, and α-Al₂O₃ not only produce polycrystals of high density, but also the transformation of magnesia and alumina into single-phase spinel. The presence of zirconia facilitates the onset of the flash. The sintering experiments in the laboratory were extended to live experiments at the National Synchrotron Light Source II at Brookhaven National Laboratory in order to measure the time-dependent evolution of single-phase spinel. The phase transformation occurred in <3 seconds during Stage II. Later, during Stage III the cubic zirconia transformed partly into the monoclinic phase, which reverted back to the cubic phase when the flash was extinguished by turning off the current to the specimen. The results underpin a recent report on the synthesis of single-phase bismuth ferrite from constituent oxides in reactive flash experiments, raising the specter of flash as a method for synthesis as well as sintering of complex oxide ceramics. The role of zirconia in catalyzing the flash in the present study is discussed.