25CrNi2MoV钢的微动磨损性能

采用微动摩擦磨损试验机在干摩擦条件下对新型高速重载传动轴用25CrNi2MoV钢进行微动磨损试验,研究了不同载荷(50~200N)和频率(15~30Hz)下该钢的微动磨损性能。结果表明:在频率为20Hz条件下,当载荷由50N增至200N时,25CrNi2MoV钢的平均摩擦因数由0.766减至0.661,磨损体积由19.65×10^-3 mm^3增至75.83×10^-3 mm^3;在载荷为30N条件下,当频率由15Hz增至30Hz时,平均摩擦因数由0.790增至0.905,磨损体积由11.43×10^-3 mm^3增至23.88×10^-3 mm^3;在不同试验参数下,25CrNi2MoV钢磨损表面均出现了氧化和犁沟现象,磨损机制包含氧化磨损和磨粒磨损;在频率为20Hz条件下,载荷为50,100N时,25CrNi2MoV钢的磨损机制以黏着磨损为主,载荷为150,200N时,主要磨损机制为疲劳磨损;在载荷为30N条件下,频率为15~25Hz时,磨损机制以磨粒磨损为主,当频率增至30Hz时,磨损机制以疲劳磨损为主。     

从系统安全设计角度剖析Therac-25医疗事件

Therac-25事件到今已有20年的历史,往事不堪回首,针对事故的复杂性,利用系统工程的观点和现代软件工程原理,从系统安全设计角度对事故的复杂性未重视、系统工程被漠视、软件工程被忽视、用户界面被藐视和软件测试被轻视等五个方面进行了剖析,并对系统总体安全设计在软件开发过程中的重要性作了论证。     

铸态Al_(63)Cul_(25)Fel_(12)准晶材料的相分析及微观结构研究

采用普通铸造法在真空中频熔炼炉中制备了Al63Cu25Fe12准晶合金试样,利用光学显微镜、扫描电镜、能谱分析仪和X衍射衍射仪,分析了准晶相和其它类似相的微观组织及相的变化。结果表明:铸态Al63Cu25Fe12准晶合金主要由λ相、I相、β相和其它微量相组成;采用各部位冷却速度不同的圆台式浇铸模具对合金进行浇铸,冷却速度较快的铸锭底部准晶I相的含量低于冷却速度较慢的铸锭顶部;Al63Cu25Fe12准晶合金经过750℃×8 h的退火处理后,λ相、β相及其它微量相有向准晶I相变化的趋势。     

P25对TiO_2镀膜光催化活性的影响

通过向钛酸四正丁酯溶胶中添加纳米级TiO2粉末（P25）,来提高煅烧TiO2镀层的光催化活性。用不锈钢丝网作为煅烧TiO2镀层载体,以甲基橙降解效果来衡量TiO2镀层的光催化活性。实验结果表明,当溶胶中P25添加量为1g／L、镀膜次数为4次时,镀层光催化活性达到最大,150min内甲基橙降解率达到69．8％。     

Vitamin D and Death by Sunshine

Exposure to sunlight is the major cause of skin cancer. Ultraviolet radiation (UV) from the sun causes damage to DNA by direct absorption and can cause skin cell death. UV also causes production of reactive oxygen species that may interact with DNA to indirectly cause oxidative DNA damage. UV increases accumulation of p53 in skin cells, which upregulates repair genes but promotes death of irreparably damaged cells. A benefit of sunlight is vitamin D, which is formed following exposure of 7-dehydrocholesterol in skin cells to UV. The relatively inert vitamin D is metabolized to various biologically active compounds, including 1,25-dihydroxyvitamin D3. Therapeutic use of vitamin D compounds has proven beneficial in several cancer types, but more recently these compounds have been shown to prevent UV-induced cell death and DNA damage in human skin cells. Here, we discuss the effects of vitamin D compounds in skin cells that have been exposed to UV. Specifically, we examine the various signaling pathways involved in the vitamin D-induced protection of skin cells from UV.     

BRIGADIER JOHN TILTMAN: ONE OF BRITAIN'S FINEST CRYPTOLOGISTS

Biography of Brigadier John Tiltman, who worked as a cryptologist for the British and American governments from 1920 to 1980.     

A viscous titania paste with a single coating-sintering step for 8–24 μm thick,high-haze,high-quality TiO2 films of dye-sensitized solar cells

A viscous TiO₂ paste was prepared by ball-milling commercially available P25 with ethylene glycol and citric acid. The conventional three- or four-fold deposition process was replaced by a single coating-sintering step of TiO₂ compound. That is coating the paste on Fluorine-doped SnO₂ conductive glass, followed by sintering at high temperature. TiO₂ films varying from 8 μm to 24 μm could be fabricated by this single coating-sintering step. The high viscosity of the paste, the esterification between ethylene glycol and citric acid and the subsequently polyester decomposition in the sintering process were the reasons to make high-quality thick film without cracking and delamination. 7.36% photoelectrical-conversion efficiency was achieved by using the photoelectrode with its P25 film thickness of 14.3 μm. Therefore, the paste would have promising applications for industrial production because of its low-price and simple process.     

Pilot-scale gasification of woody biomass

The gasification of pine and mixed-hardwood chips has been carried out in a pilot-scale system at a range of gas flow rates. Consuming ∼17-30 kgh⁻¹ of feedstock, the producer gas was composed of ∼200 dm³ m⁻³ carbon monoxide, 12 dm³ m⁻³ carbon dioxide, 30 dm³ m⁻³ methane and 190 dm³ m⁻³ hydrogen, with an energy content of ∼6 MJ m⁻³ for both feedstocks. It was found that the efficiency of the system was enhanced at higher flow rates.