激光在材料中感生的瞬态光声波和光热波

研究了锁模激光在材料中产生频率达GHz的光声波和相应探测技术,用回波分析法无损坏测量了薄材料的厚度。研究了激光在材料中感生的光热波,热沉测量可用于解释材料的破坏机理。     

用过滤工艺全面提高铸锭质量

探讨了过滤器孔径对6063铝合金铸锭组织和性能的影响规律。在此基础上指出,在过滤工艺恰当时,不仅可以减少铸锭中的夹杂物,而且可以有效地防止裂纹、羽毛晶等连续铸锭中的常见缺陷。     

激光辐照对不同饵料微藻生长的影响

利用Nd:YAG激光(波长1.06μm,功率5W,照射时间0.5-3min)和Ar 激光(波长:488nm,功率70mw,照射时间5-20min)分别照射角毛藻和叉鞭金藻,辐照后进行细胞增殖和生长速率的测定。实验结果表明:照射剂量为1min的Nd:YAG激光及剂量为5min的Ar 激光对叉鞭金藻有较明显的促长效果,这两种激光处理组的细胞增殖量在辐照后的两天内较对照组分别高42.9%和48.1%,但这种促长效果随时间的推移逐渐消失。不同剂量的两种激光辐照角毛藻后,在延滞期均出现生长抑制现象,但进入指数生长期或传代培养后,剂量为1min的Nd:YAG激光及剂量为10min的Ar 激光对角毛藻有明显的促长效果,其中在指数生长期1min剂量的Nd:YAG激光处理可促长27.0%,传代培养后10min的Ar 激光处理组生长速率提高达51.2%。本文对不同激光及不同激光参数条件下,两种饵料藻的耐受性及生长特性的差异也进行分析探讨。本实验结果不仅证实了已有研究的推论,还展示出激光技术在饵料藻种选育中的应用前景。     

Investigation of texture effect on visual colour difference evaluation

The texture effect on visual colour difference evaluation was investigated in this study. Five colour centers were selected and textured colour pairs were generated using scanned textile woven fabrics and colour‐mapping technique. The textured and solid colour pairs were then displayed on a characterized cathode ray tube (CRT) monitor for colour difference evaluation. The colour difference values for the pairs with texture patterns are equal to 5.0 CIELAB units in lightness direction. The texture level was represented by the half‐width of histogram, which is called texture strength in this study. High correlation was found between texture strength and visual colour difference for textured colour pairs, which indicates that an increasing of 10 units of texture strength in luminance would cause a decreasing of 0.25 units visual difference for the five colour centers. The ratio of visual difference between textured and solid colour pairs also indicates a high parametric effect of texture. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 341–347, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.     

Influence of phosphorus element on direct laser sintering of multicomponent Cu-based metal powder

This article presents a detailed investigation on the influence of the phosphorus element upon the laser sintering of a multicomponent Cu-based metal powder system consisting of Cu, Cu-10Sn, and Cu-8.4P. Powder systems containing 0, 10, 15, and 20 wt pct CuP were sintered in atmosphere at room temperature using the following optimal processing parameters: laser power of 350 W, scan speed of 0.04 m/s, scan line spacing of 0.15 mm, and layer thickness of 0.25 mm. It was found that the relative density of the sintered sample with 15 wt pct CuP increased by 24,4 pct as compared with the sample without phosphorus addition. A further increase in the CuP content (≥20 wt pct), however, resulted in a poor densification with a serious delamination. The exact metallurgical roles of the phosphorus element in the laser sintering process were addressed as follows. First, the phosphorus could prevent the sintering system from oxidation by forming CuPO₃, thereby improving the wetting characteristics and the sintering kinetics. Second, the phosphorus could decrease the surface tension of molten materials, leading to a successive transition from highly discontinuous sintered tracks to fairly coherent ones with increasing the phosphorus content. Third, the phosphorus could lower the melt viscosity, thereby improving the microstructural homogeneity of the laser-sintered samples.     

An accurate and practical buffer allocation model for the buffer cache based on marginal gains

A new dynamic buffer allocation strategy based on the notion of marginal gains is presented for the buffer cache that is used by the operating system to store frequently accessed disk blocks in main memory, and the performance of the proposed strategy is compared with those of previous allocation strategies. In the proposed strategy, marginal gain values are predicted by exploiting functions that approximate the expected number of buffer hits per unit time. Experimental results from both trace-driven simulation and an actual implementation in the FreeBSD operating system show that the proposed strategy accurately predicts the marginal gain values for various workloads resulting in significantly improved buffer hit ratios.     

单壁碳纳米管的制备及生长特性研究

采用Fe/MgO作为催化剂 ,催化裂解CH4制备了较纯的单壁碳纳米管 ,用TEM和Raman对碳纳米管进行了表征 ,对不同生长温度下制备的碳纳米管Raman径向呼吸振动峰 (RBM)进行了分析 ,研究了生长温度对单壁碳纳米管生长特性和结构特性的影响     

城市化进程中的小城镇交通初探

通过对小城镇城市结构、路网结构、交通结构和交通管理特征进行详细分析，得出小城镇交通问题症结所在，并初步提出小城镇交通规划和交通治理的对策。     

天铁炼铁技术进步

近十年来，天铁集团炼铁厂通过改善原燃料条件；优化炉料结构，提高入炉品位；采用提高炉顶压力、富氧喷煤、低硅冶炼、炉顶气象系统等多项先进技术，使高炉各项经济技术指标逐年提高。     

A mechanistic analysis of the correlation between overall strength and indentation hardness in discontinuously reinforced aluminum

It is well established that the indentation hardness of metallic alloys shows a reasonable correlation with their yield strength or ultimate strength. Experiments illustrate that such a unique correlation is nonexistent for discontinuously reinforced metal matrix composites, even when the indentation size is much greater than the reinforcement size. For aluminum alloys reinforced with silicon carbide particles, the same composite yield strength and tensile strength with different reinforcement fractions do not lead to similar hardness, or vice versa. Finite element analyses are carried out to rationalize the experimental findings. The modeling utilizes a two-dimensional plane-strain formulation. Discrete particles are included in the material model, and the overall stress-strain response and the indentation response are numerically simulated. The results confirm the lack of unique correspondence between the composite hardness and strength. The alteration of local heterogeneity in the composite is found to affect the indentation response. Effects of the geometrical arrangement of particles and thermal residual stresses on the indentation response are also investigated numerically.