Health benefits of physical activity are well known, yet available physical activity data is limited from children living in African and Asian countries. The purpose of the cross-sectional study was ...to evaluate and compare physical activity and sedentary behavior patterns, particularly hourly variations, among children in Kenya and Japan. Participants included 298 primary school students (122 Kenyan, 176 Japanese) aged 9–12 years. Physical activity and sedentary behavior were measured with accelerometers. Domain-specific physical activity, screen time, and proportion of children using active transport to school were measured by questionnaire. A two-way ANOVA (countries × time) was used to examine the differences in the activity patterns between Kenyan and Japanese children. The results from the present study demonstrated that Kenyan children spent more time in moderate-to-vigorous physical activity compared to Japanese children (p < 0.05) with the greatest differences found for weekday evenings (for boys and girls) and weekend afternoons (for girls). This suggests that these were ‘critical periods’ to differentiate the physical activity levels between Kenyan and Japanese children. However, a higher proportion of the children from Japan used active transport to school and spent less time in television viewing and computer gaming. The results suggest that both countries have successes and challenges that can aid in developing effective and country-specific intervention strategies for promoting physical activity.
The multiplex (MUX) control system of subsea blowout preventer (BOP) plays a vital role in providing safe working conditions for the subsea drilling activities. According to the working states and ...critical failure modes of the MUX control system, this paper presents its stochastic Petri nets (SPN) model, taking into account the imperfect fault detection capacity. The numerical analysis method is proposed based on the isomorphic continuous-time Markov chain of the model. The reliability indexes, namely reliability, availability and MTTF of the MUX control system and pilot hydraulic control system are obtained and compared. In addition, the effects of fault coverage factor on state probabilities and availability of the MUX control system are researched and the uncertainty analysis of the firing rates related to MTTF is also performed.
► A LRFD-based design procedure for subsea composite pressure vessel subjected to external hydrostatic pressure is presented. ► The sensitivity of the partial safety factors to the changes in the ...characterization of various random variables is studied. ► The longitudinal modulus, inside radius, unsupported length and external pressure significantly affect the design results.
A reliability-based load and resistance factor design procedure for subsea composite pressure vessel subjected to external hydrostatic pressure is presented. The failure criterion for defining the performance function is considered as buckling. A sensitivity analysis is conducted to research influences of statistical characteristics of variables on the partial safety factors and the thickness of pressure vessel. The results shows the longitudinal modulus, inside radius of composite layers, unsupported length and external pressure significantly affect the design results, whereas transversal modulus, Poisson’s ratio, shear modulus and winding angle have little effects. In order to validate the design results, a filament-wound composite pressure vessel is manufactured, and the buckling test is performed. It is observed that when the applied external hydrostatic pressure is a little more than the designed critical buckling pressure, the buckling and subsequent burst behaviours occur, which shows a good agreement between the experimental and analytical results.
Electrical discharge machining (EDM) has been wildly used in the modern manufacture industry due to its advantage over the traditional manufacture method of some hard-to-cut materials. However, ...compared with the traditional manufacture method, the EDM process was inefficient and environmentally hazardous due to the decomposition of the dielectrics, especially in the case of sinking EDM which used oil-based dielectric. In order to improve the EDM performance, and for the other hand, alleviate the environmental impact of the process, a new type of dielectric, water in oil (W/O) emulsion was proposed as the working fluid. This work presents a systematical study on the performance of this new type dielectric based on the orthogonal and additional single factor experiments. Statistical analysis of the results show that discharge current (I) and water content of the emulsion significantly influence the machining performance of sinking EDM. The study also analyzed the influence of the emulsion temperature and flushing condition on its EDM performance. It was observed that both MRR and EWR decrease with increasing temperature of the emulsion. Experiments results indicated that W/O emulsion can be used as the working fluid of sinking EDM and alleviated the environmental impact of the process.
Renewable fuels or chemicals from lignocellulosic biomass have the potential to be a substitute for fossil fuels, thereby reducing greenhouse gas emissions and diversifying energy supplies. ...Integrating torrefaction and pyrolysis is a feasible and promising technology that converts biomass into fuels or chemicals. Understanding of the relevant process designs and mechanisms is favorable to the cohesion and optimization of these two processes and the innovation of reactors for commercial-scale biorefineries. First, biomass properties and their corresponding pyrolysis behaviors have been discussed in consideration of the challenge presented by complex biomass structures that limit the in-depth research on torrefaction or pyrolysis. Second, torrefaction fundamentals are illustrated in detail, and many kinetic models with comprehensive mechanism schemes, such as pseudo-mechanistic model and one-, two-, or multi-step models, are summarized. The effect of torrefaction on biomass characteristics and subsequent pyrolysis is reviewed to further elucidate the integrated process. The novel integration of torrefaction and up-to-date pyrolysis techniques is also outlined to improve product quality. Finally, future directions and technological challenges associated with the integrated process are proposed and its economic potential is also evaluated.
•Different torrefaction kinetic models have been developed to guide the reactor design and optimize the parameters.•Torrefaction significantly affects characteristics of biomass feedstock and improves the pyrolysis behavior.•Integrating torrefaction and developing pyrolysis techniques is promising to utilize the biomass energy effectively.•Pyproduct reuse and r heat recovery can enhance the economic competitiveness of the integrated process.•The self-catalysis mechanism of light organic acid and economic evaluation need to be studied further.
An extremely reliable remote control system for subsea blowout preventer stack is developed based on the off-the-shelf triple modular redundancy system. To meet a high reliability requirement, ...various redundancy techniques such as controller redundancy, bus redundancy and network redundancy are used to design the system hardware architecture. The control logic, human–machine interface graphical design and redundant databases are developed by using the off-the-shelf software. A series of experiments were performed in laboratory to test the subsea blowout preventer stack control system. The results showed that the tested subsea blowout preventer functions could be executed successfully. For the faults of programmable logic controllers, discrete input groups and analog input groups, the control system could give correct alarms in the human–machine interface.
► The hardware architecture is developed based on various redundancy techniques. ► The BOP system voting algorithm is designed based on the 2-out-of-3 voting. ► The results show that the developed system and voting algorithm are correct.
An analytical optimization approach of the submersible solenoid valve constrained in a specific small volume is presented. In order to maximum the electromagnetic force, thermal model and ...electromagnetic model are constructed, and five radial dimensions are optimized when the main limiting quantity is the maximum allowed temperature. A numerical optimization calculation is performed in order to verify the proposed analytical approach. The optimal solution of the numerical calculation is compared with the solution of the analytical approach, which shows a good agreement between the two methods. A thermal analysis of the optimal submersible solenoid valve based on AYSYS is also performed to verify the thermal model. A comparative study between the experimental and simulated static characteristics of the optimal submersible solenoid valve is also performed. The results show that the proposed analytical approach is correct.
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•The most suitable method (OFW method) for activation energy calculation was found.•The most suitable methods (KAS and DAEM methods) for pre-exponential factor calculation were ...found.•The optimal torrefaction condition of corncob (240 °C) was determined.•Torrefaction enhanced the aromaticity of corncob.
The effects of torrefaction pretreatment on corncobs properties and its pyrolysis kinetic parameters were investigated in this study. Proximate and ultimate analyses indicated that torrefaction increased the H/Ceff ratio and higher heating value of corncobs, and reduced its oxygen content. Although the mass yield was also reduced, the corresponding energy yield was relatively higher. The crystallinity index of biomass showed a first upward and then downward trend with the torrefaction temperature. Kinetic parameters obtained from three models indicated that both the activation energy and the pre-exponential factor increased with the elevated torrefaction temperature and it's better to calculate the activation energy by the OFW method and to use the KAS and DAEM methods to calculate the pre-exponential factor. In addition, it was found that the optimum pretreatment temperature of corncobs was 240 °C.
Aiming at the problems that many watermarking schemes cannot adapt to the image copyright protection with large amount of information, and the copyright protection of color images faces severe ...challenges, this paper proposes a robust dual color image blind watermarking scheme in the frequency domain. The scheme uses nonsubsampled contourlet transform (NSCT)’s good multi-directivity and multi-scale, translation invariance and Schur decomposition stability and anti-aggression to balance the invisibility and robustness of the watermarking scheme. Firstly, the host image is transformed by layered NSCT to obtain the layered low frequency coefficient matrix, and non-overlapping 4 × 4 coefficient blocks are selected in the layered low-frequency coefficient matrix, and the maximum eigenvalue of the coefficient block is obtained by Schur decomposition, and Quantized index modulation (QIM) is applied to the maximum eigenvalue to embed watermark information. When extracting watermarks, if watermarked image is attacked by geometry, and use image correction algorithm based on perspective transform to preprocess the image, which mainly includes feature point detection, image correction and sawtooth processing. The simulation results show that the proposed scheme has strong robustness to common signal processing attacks, and stronger and more effective robustness to common geometric attacks. Compared with the existing dual color image blind watermarking schemes, the proposed scheme has better performance.
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