Quadruply coupled linear free vibrations of thin-walled beams with a generic open section

The coupled vibration of thin-walled beams with a generic open section induced by the boundary conditions is investigated using the finite element method. If the axial displacement of the pin end is restrained at another point rather than the centroid of the asymmetric cross section, the axial vibration, two bending vibrations, and torsional vibration may be all coupled. The element developed here has two nodes with seven degrees of freedom per node. The shear center axis is chosen to be the reference axis and the element nodes are chosen to be located at the shear centers of the end cross sections of the beam element. Different sets of element nodal degrees of freedom corresponding to different pin ends are considered here. The relation between element matrices referred to different sets of element nodal degrees of freedom is derived.

Numerical examples are presented to demonstrate the accuracy of the proposed method and to investigate the effects of different pin ends on the coupled vibrations of the thin-wall beam.     

Surface oxidation of molten Sn(Ag,Ni, In,Cu) alloys

The surface oxidations of molten Sn(Ag, Ni, In, Cu) alloys are studied. We conclude that the microstructure (phase and density) of the surface oxide layer is the key factor for the surface oxidation formation. Also, we found that the microstructure (phase and density) of the Sn surface oxide layer is highly influenced by the additives in the solder alloys, which can be roughly anticipated from the additives’ electromagnetic field values and Gibbs free energies of oxide formation. The detailed effect (either retarding or enhancing) of the additives on the surface oxidation is discussed in this paper.     

Low Area/Power Synthesis Using Hybrid Pass Transistor/CMOS Logic Cells in Standard Cell-Based Design Environment

This brief presents a logic synthesis flow that depends on the popular Synopsys Design Compiler to perform logic translation and minimization based on the standard cell library with both pass transistor logic (PTL) and CMOS logic cells. The hybrid PTL/CMOS logic synthesis can generate appropriate circuits considering various design constraints. The proposed multilevel PTL logic cells are automatically constructed from only a few basic cells. Postlayout simulations with UMC 90-nm technology are presented based on the standard cell library with pure PTL, pure CMOS, or hybrid PTL/CMOS cells. Experimental results show that, in most cases, pure PTL circuits have smaller area and power, whereas CMOS circuits, in general, have smaller delay.      

受火钢结构非线性性能的向量式有限元分析

采用向量式有限元分析,对受火钢结构的非线性响应进行研究。通过与已公布的钢结构试验数据及分析结果相比较,验证数字模型。对Williamstoggle框架和钢框架在地震荷载和火荷载下的非线性性能响应进行研究。数值结果显示:当温度低于临界值时,随着温度增加,Williamstoggle框架的承载力显著增大;然而,当温度高于临界值时,随着温度增加,Williamstoggle框架的承载力显著减少,但当温度达到1000℃时,承载力仍大于室内温度时的弹性屈服强度。此外,随着温度增加,屈服前浅拱向上偏转,而且其挠度远小于同样跨度的梁结构。屈曲后,结构的挠度向下,当重新平衡时,显示出悬链线作用。在地震诱发的火灾中,结构变形受余震、火、结构单元的破坏影响较大。     

Deformation Structure of Unidirectionally Compressed Ultrafine-Grained Mg-3Al-1Zn Alloy

Ultrafine-grained (UFG) Mg-3Al-1Zn (AZ31) alloys with gain sizes ranging from 0.46 to 3.22 μm were prepared by equal channel angular pressing (ECAP) and annealing. The deformation structure of UFG AZ31 alloy resulting from uniaxial compression was studied by optical and electron microscopy. The deformation was noted to proceed with the development of shear bands (SBs), which has not been reported in an UFG hcp metal. Characterization of these SBs was performed, and comparison with the SBs formed in UFG bcc and fcc metals was given. { 10[`1]2} \{ 10\bar{1}2\} tension twins inside SBs were found in all specimens compressed, irrespective of the grain size. Discussion on the limiting grain size of twinning in the UFG AZ31 alloy is also given.     

The significance of telemedicine in a rural emergency department

Telemedicine is evolving into an important tool in delivering services to emergency departments (EDs) in rural areas. However, we do not yet know what kinds of services can be effectively delivered or the degree to which these services might be useful. In this pilot study, a high-speed, high-quality video, 24-hour ATM (asynchronous transfer mode) network linked a rural ED to an ED of a major medical center. The objective was to measure the utilization of telemedical consulting services. Specifically, this one-year study examined the significance of telemedicine in changing diagnosis and treatment and the influence on patient transfers     

Processable and colorless fluorinated poly(ether imide)s based on an isopropylidene‐containing bis(ether anhydride) and various aromatic bis(ether amine)s bearing trifluoromethyl groups

A series of novel organosoluble and light‐colored fluorinated poly(ether imide)s (PEIs) ( IV ) having inherent viscosities of 0.43–0.59 dL/g were prepared from 4,4′‐[1,4‐phenylenbis(isopropylidene‐1,4‐phenyleneoxy)]diphthalic anhydride ( I ) and various trifluoromethyl‐substituted aromatic bis(ether amine)s by a standard two‐step process with thermal and chemical imidization of poly(amic acid) precursors. These PEIs showed excellent solubility in many organic solvents and could be solution‐cast into transparent and tough films. These films were essentially colorless, with an UV–visible absorption edge of 361–375 nm and a very low b* value (a yellowness index) of 15.3–17.0. They also showed good thermal stability with glass‐transition temperature of 191–248°C, 10% weight loss temperature in excess of 494°C, and char yields at 800°C in nitrogen more than 39%. The thermally cured PEI films showed good mechanical properties with tensile strengths of 83–96 MPa, elongations at break of 8–11%, and initial moduli of 1.7–2.0 GPa. They possessed lower dielectric constants of 3.25–3.72 (1 MHz). In comparison with the V series nonfluorinated PEIs, the IV series showed better solubility, lower color intensity, and lower dielectric constants. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 620–628, 2007     

Synthesis and properties of new aromatic polyimides containing redox‐active anthraquinone moieties

A novel anthraquinone‐containing bis(ether amine) monomer, 2,6‐bis(4‐aminophenoxy)anthraquinone, was synthesized from readily available reagents. A series of novel aromatic polyimides were prepared from the newly synthesized diamine monomer with various aromatic tetracarboxylic dianhydrides. The intermediate poly(amic acid)s had inherent viscosities of 0.67–1.12 dL g^?1, and those derived from less stiff dianhydrides could be solution‐cast and thermally cyclodehydrated into flexible and tough polyimide films. The polyimides exhibited glass transition temperatures between 270 and 297 °C, and they were fairly stable up to a temperature of 500 °C in air or nitrogen. The electrochemical and electrochromic properties of one of the polyimides were investigated. The polymer could undergo two reversible steps of electrochemical reduction, with a color change from a colorless neutral state to pink and rose‐red reduced states. © 2012 Society of Chemical Industry     

Numerical analyses and experiment investigations of an annular micro gas turbine power system using fuels with low heating values

This study investigates the effects of using fuels with low heating values on the performance of an annular micro gas turbine (MGT) experimentally and numerically. The MGT used in this study is MW-54, whose original fuel is liquid (Jet A1). Its fuel supply system is re-designed to use biogas fuel with low heating value (LHV). The purpose is to reduce the size of a biogas distributed power supply system and to enhance its popularization. This study assesses the practicability of using fuels with LHVs by using various mixing ratios of methane (CH₄) and carbon dioxide (CO₂). Prior to experiments, the corresponding simulations, aided by the commercial code CFD-ACE+, were carried out to investigate the cooling effect in a perforated combustion chamber and combustion behavior in an annular MGT when LHV gas was used. The main purposes are to confirm that there are no hot spots occurring in the liners and the exhaust temperatures of combustor are lower than 700°C when MGT is operated under different conditions. In experiments, fuel pressure and mass flow rate, turbine rotational speed, generator power output, and temperature distribution were measured to analyze MGT performance. Experimental results indicate that the presented MGT system operates successfully under each tested condition when the minimum heating value of the simulated fuel is approximately 50% of pure methane. The power output is around 170 W at 85000 r/min as 90% CH₄ with 10% CO₂ is used and 70 W at 60000 r/min as 70% CH₄ with 30% CO₂ is used. When a critical limit of 60% CH₄ is used, the power output is extremely low. Furthermore, the best theoretical Brayton cycle efficiency for such MGT is calculated as 23% according to the experimental data while LHV fuel is used. Finally, the numerical results and experiment results reveal that MGT performance can be improved further and the possible solutions for performance improvement are suggested for the future studies.