水轮机下环铸件凝固过程热应力模拟分析

采用数值模拟方法对水轮机下环铸件凝固过程中的应力场进行了模拟和分析。模拟中采用接触单元法处理铸件与砂芯之间力的作用,改进了传统的铸件/铸型边界条件处理方法。文中重点分析了下环凝固过程中准固相区的受力情况,根据准固相区受力特点建立了适当的热裂判据,对下环凝固过程热裂倾向性进行预测。实际生产结果与预测结果相符合。     

连续通电条件下触点接触电阻劣化的初步分析

电器长期通电后可使触点表面劣化,具体体现为接触电阻稳定增大、无规律增大、周期性变化、瞬时变化等电接触失效形式。本文以银镍触点材料为例,试验研究了接触压力、通电时间和通电电流对接触电阻的影响,并分析了接触电阻劣化失效的物理机制。     

pHEMA: An Overview for Biomedical Applications

Poly(2-hydroxyethyl methacrylate) (pHEMA) as a biomaterial with excellent biocompatibility and cytocompatibility elicits a minimal immunological response from host tissue making it desirable for different biomedical applications. This article seeks to provide an in-depth overview of the properties and biomedical applications of pHEMA for bone tissue regeneration, wound healing, cancer therapy (stimuli and non-stimuli responsive systems), and ophthalmic applications (contact lenses and ocular drug delivery). As this polymer has been widely applied in ophthalmic applications, a specific consideration has been devoted to this field. Pure pHEMA does not possess antimicrobial properties and the site where the biomedical device is employed may be susceptible to microbial infections. Therefore, antimicrobial strategies such as the use of silver nanoparticles, antibiotics, and antimicrobial agents can be utilized to protect against infections. Therefore, the antimicrobial strategies besides the drug delivery applications of pHEMA were covered. With continuous research and advancement in science and technology, the outlook of pHEMA is promising as it will most certainly be utilized in more biomedical applications in the near future. The aim of this review was to bring together state-of-the-art research on pHEMA and their applications.     

圆坯连铸GCr15SiMn的成分偏析和接触疲劳寿命研究

利用金属原位分析技术和钻孔化学分析方法对高淬透性轴承钢GCr15SiMn的Φ450 mm连铸圆坯和Φ130 mm圆钢的C、Si、Mn、Cr元素横截面的分布情况进行分析。采用推力片式接触疲劳试验机进行了材料的接触疲劳寿命测试。结果表明：GCr15SiMn连铸圆坯C元素的偏析倾向较大,易产生中心正偏析,而Cr、Si、Mn元素的偏析倾向较小。通过采取稳定低过热度浇铸、三段强电磁搅拌等措施,铸坯的中心碳偏析得以改善。采用(1240±20)℃×5 h高温扩散、初轧首道次变形量≥90 mm大变形轧制的Φ130 mm圆钢的碳偏析可以得到进一步的改善,试验钢在5.3GPa高应力负载下的接触疲劳额定寿命L₁₀达到3.58×10⁶次,接近电渣重熔钢的水平。     

接触器特征参数测试仪

本文详细介绍了微机型接触器特征参数测试仪工作原理，软硬件及调试、运行和故障处理。     

Surface contact degradation of multilayer ceramics under cyclic subcritical loads and high number of cycles

Alumina/alumina–zirconia ceramic laminated composites produced by tape casting present a compressive residual stress at the alumina surface due to the thermal expansion mismatch between layers developed during processing. Because of this residual stress, the mechanical properties at the surface, such as wear or surface fracture, have proven to be better than the properties of a monolithic stress-free alumina. In a previous work, it was shown that this laminate composite has better resistance to the development of a ring crack when loaded with a spherical indenter, under both cyclic and static loads below the critical load for cone cracking. In this work, cyclic Hertzian indentations with subcritical loads are performed on the same laminate ceramic and a monolithic alumina, but with a higher number of cycles than the necessary to provoke the first damage (ring crack). Results show that for low and intermediate number of cycles, the laminated composite presents better resistance to damage than the monolithic alumina. However, for high number of cycles, spalling at the surface of the laminate material appears, whereas the monolithic alumina develops secondary cone cracking. This difference is attributed to the fact that laminate ceramics present an enhanced apparent fracture toughness of the material, which implies a higher quasi-plasticity due to shear driven microcracking. For a high number of cycles, these microcracks grow until coalescence at the surface, provoking exfoliation of the material at the contact area, enhanced by the fact that the indented and the indenter material have different elastic properties.     

The role of the surface free energy in the selection of a suitable excipient in the course of a wet-granulation method

Pellets containing metronidazole were produced in a centrifugal granulator, with hydroxypropylcellulose (Klucel LF®) as binding agent, and corn starch, microcrystalline cellulose (Vivapur 101®) and lactose as excipients. The wettability of the pharmaceutical powders was assessed by means of contact angle measurements, and the dispersive and polar surface energies were determined. The spreading coefficients, the work of adhesion and the work of cohesion were calculated and correlated with the pellet properties (friability, bulk and tapped density, and porosity). The aim was to investigate the role of the surface free energy of one- and two-component powder compositions in pellet production. The interactions between the particles were found to be connected with the measured pellet parameters. It was concluded that, in the course of the growth of the pellets, the particle sizes of the pharmaceutical powders and the interactions between them are important. If the work of cohesion of the binder is lower than the work of cohesion of the substrate and the work of adhesion, then the optimal amount of the binding agent is that which coats the particles uniformly in minimal quantity and in continuous layer.     

Tasting green leaf volatiles by larvae and adults of Colorado potato beetle,Leptinotarsa decemlineata

Larvae and adults of the Colorado potato beetle,Leptinotarsa decemlineata (Say), are shown to have galeal gustatory cells that are highly sensitive to distillate of potato leaf extracts, (E)-2-hexen-1-ol, (E)-2-hexenal, and other saturated and unsaturated six-carbon alcohols. In larvae and adults, the sensory response patterns elicited by leaf homogenate, leaf distillate and a mixture of these two extracts differ in subtle ways. Beetle larvae feed most readily on Millipore disks treated with leaf homogenate and the mixture, but they did not feed on disks treated with leaf distillate. The differences in behavioral response and sensory input are used to derive a potential gustatory code that may stimulate different levels of feeding. This code may be disrupted by compounds present in nonhost leaves, thus leading to reduced feeding. Possible interactions of sapid leaf volatiles, amino acids, sugars, and potentially deterrent plant compounds are discussed.     

HEAT TRANSFER BETWEEN ROUGH SURFACES IN CONTACT OVER A HIGHLY ELLIPTICAL CONTOUR AREA: COMPARISON OF EXPERIMENTAL AND NUMERICAL RESULTS

This paper describes experimental and numerical studies of heat transfer between surfaces in contact over a highly elliptical area in a gas or in vacuum. Measurements of the steady-state thermal resistance of a high aspect ratio contact formed between cylindrical steel surfaces with widely different radii of curvature (76 cm vs 0.95 cm) are reported for two levels of surface roughness (0.05 μm and 1.0 μm rms) and compared to 3-D numerical results obtained with the multigrid method. Theoretical results obtained by evaluating the contact conductance acting over each surface element within the contour area with a method developed previously for rough but nominally flat surfaces are shown to be in excellent agreement with the rough surface experimental data.     

超高密度磁记录的课题与展望

介绍了超高密度记录的研究开发状况 ,论述了垂直磁记录技术的课题以及采用TMR磁头的、记录密度为Subterabit in2 的记录 读出特性。作为高密度记录所必需的头 盘界面技术 ,提出了接触记录技术的课题 ,还就STM (Scanningtunnelingmicroscopy)存储器论述了未来超高密度技术