Analytical considerations of flow boiling heat transfer in metal-foam filled tubes

Flow boiling in metal-foam filled tube was analytically investigated based on a modified microstructure model, an original boiling heat transfer model and fin analysis for metal foams. Microstructure model of metal foams was established, by which fiber diameter and surface area density were precisely predicted. The heat transfer model for flow boiling in metal foams was based on annular pattern, in which two phase fluid was composed by vapor region in the center of the tube and liquid region near the wall. However, it was assumed that nucleate boiling performed only in the liquid region. Fin analysis and heat transfer network for metal foams were integrated to obtain the convective heat transfer coefficient at interface. The analytical solution was verified by its good agreement with experimental data. The parametric study on heat transfer coefficient and boiling mechanism was also carried out.Peer reviewedFinal Accepted Versio

Influence of long-range cation order on relaxor properties of doped Pb(Mg1/3Nb2/3)O3 ceramics

The 1:1 B-site cation order in Pb(Mg1/3Nb2/3)O3 relaxor ferroelectric ceramics was significantly enhanced by doping of minor amounts of La3+, Sc3+, or W6+ (less than 3 at. %) combined with a slow cooling procedure. Transmission electron microscopy examination confirmed the size increase of the cation-ordered regions embedded in a disordered matrix in the samples that were slowly cooled after sintering. The average cation ordering parameter (S) determined from x-ray diffraction data in these partially ordered samples was about 0.3–0.4. The ferroelectric properties and dielectric relaxation were compared in partially ordered and disordered (S=0) samples with the same composition. It was found that typical relaxor behavior was preserved in partially ordered ceramics. Furthermore, the temperature and diffuseness of the characteristic relaxor permittivity peak and the parameters of dielectric relaxation (in particular, the distribution of relaxation times and the Vogel-Fulcher freezing temperature) were practically independent of S. In contrast, the diffuseness of the phase transition from the ferroelectric phase (induced by external electric field) to the ergodic relaxor phase appeared to be much larger in the disordered samples than in the partially ordered ones (this diffuseness was assessed using pyroelectric current and ferroelectric hysteresis loops). These results suggest that cation ordering did not influence the behavior of polar nanoregions which are responsible for the dielectric response in the ergodic relaxor phase but significantly influenced the ferroelectric phase transition. The results are interpreted in terms of different types of polar regions in the disordered matrix and cation-ordered domains

Dynamic Stress Analysis of a Composite Electromagnetic Track

The firing of an electromagnetic gun is shown to result in the armature moving along the guide rail, which can cause extrusion, wear, planing and other problems, which set limits on its application. The track properties can be adjusted by changing its composition, so as to obtain good electrical conductivity, corrosive resistance, and strength. For simplicity, the composite track is presented as an elastic foundation beam, and the general solution of composite track deflection at dynamic load is obtained by using the two-dimensional Fourier integral transformation, on this basis, the bending moment distribution and expression for dynamic stress are obtained. The characteristics of dynamic stress distribution and factors that influence them are analyzed, the effect of the proportion of the composite layer and its parameters on the dynamic stress of the track is discussed.Показано, что выстрел электромагнитной пушки приводит к перемещению брони по направляющей, что может вызывать выталкивание, износ, обдирание и другие процессы, которые налагают ограничения на ее применение. Свойства направляющей могут быть модифицированы путем изменения ее состава, что обеспечит хорошую удельную электропроводность, коррозионную стойкость и прочность. Для простоты композиционная направляющая представлена в виде упругой фундаментной балки, общее решение для прогиба направляющей при динамической нагрузке получают с помощью двухмерного интегрального преобразования Фурье, на его основании получают распределение изгибающего момента и выражение для напряжения при динамической нагрузке. Выполнен анализ характеристик распределения напряжений и влияющих на них факторов. Рассмотрено влияние доли композиционного слоя и его параметров на напряжение направляющей при динамической нагрузке

Pilot Testing of Assessment of Capacity for Myoelectric Control (ACMC) in Evaluating Myoelectric Hand Function in Chinese Population

Upper limb amputations cause marked functional disability and lower the individual’s self-body image, with severepsychological implications. Many rehabilitation parameters are involved in the successful rehabilitation of upper limbamputations. The aim of this study was to examine the validity and reliability of the Chinese version of Assessment ofCapacity for Myoelectric Control (Chinese-ACMC) in upper limb amputated subjects and with a myo-electric-poweredprosthetic hand.To validate the Chinese version of Assessment of Capacity for Myoelectric Control (Chinese-ACMC) in upper limbamputee subjects (children and adults) with a myo-electric-powered prosthetic hand. A sample of convenience samplingof 22 subjects (11 males, 11 females) with upper limb amputation and myoelectric prosthetic hands were recordedduring a regular clinical visit for ACMC. Each subject was evaluated according to four criteria: (a) Upper Limb Amputationincluding all levels of amputation; (b) No specific pain type – no matter phantom or pain in the stump; (c) With intactcognitive function; (d) Age ranged from 12 to 40 years. With instruction, occupational therapists and prosthetic-orthoticswith at least twenty years’ clinical experience of myoelectric prosthesis training would conduct the 30-items ChineseACMC for each subject. A serial of errand tasks of activities of daily living were designed for evaluation. Individuals’ratings were repeated after 4 weeks. Through test-retest reliability, internal consistency testing, factor analysis, intra andinter factor correlation analysis. A four-factor structure, namely, “Gripping”, “Holding”, “Releasing” and “Coordinating”are identified