纳米晶粒硬质合金平面磨削表面粗糙度研究

采用树脂结合剂金刚石砂轮对纳米晶粒硬质合金进行平面磨削试验,结合单因素和正交实验研究不同磨削要素即磨削深度ap、工件进给速度vw、砂轮线速度vs 对磨削纳米晶粒硬质合金表面粗糙度的影响。结果表明,磨削深度ap 和工件进给速度vw 增加,表面粗糙度增加?砂轮线速度vs 增加,表面粗糙度减小。磨削3 要素对纳米晶粒硬质合金表面粗糙度影响程度的大小依次是工件进给速度、砂轮线速度、磨削深度。因此,为了获得好的表面质量可以采取小进给、小切深、高砂轮线速度的组合方式进行磨削?同时建立了磨削纳米晶粒硬质合金的表面粗糙度数学模型并验证了模型的可靠性。     

纳米材料的特性及进展

论述了纳米材料的分类和结构特征,介绍了纳米材料的尺寸效应,表面与界面效应,并阐述了纳米材料的进展,包括纳米光学材料,纳米催化材料,纳米敏感材料外,纳米储氢材料,纳米巨磁电阻材料。     

纳米科技与碳纳米管

纳米科技是新兴的前沿学科领域,对碳纳米管的研究是其中最活跃的部分。 本文对纳米科技、纳米材料的制备、纳米材料的特性以及碳纳米管进行了综述。     

走进纳米科技领域

本介绍了纳米科学技术概念和近50年来世界各国纳米技术发展的概况,纳米物理学、纳米机械学、纳米材料学等新型前沿学科所取得的辉煌研究成果和发展方向,分析了纳米材料具有的神奇特性的机理和纳米粒子的物理化学制备方法,并指出高校应当昂首挺进纳米科技领域。     

纳米技术与新型建筑材料

纳米技术是一门崭新的、划时代的科学技术，从一定意义上说，纳米技术是21世纪经济发展的发动机。美国等发达国家都在斥巨资研究开发纳米技术。我国政府也非常关注纳米材料的发展，目前已经建立了10多条纳米材料和技术的生产线，并在纳米复合塑料、橡胶和纤维的改性、纳米功能涂层材料的设计和应用、纳米材料在能源和环保等方面进行了应用研究和开发研究。纳米科技将彻底改变目前的产业结构，无限的科学价值和商业机会，表明纳米技术必将推动人类社会的飞速发展。     

纳米技术与纳米材料(二)

纳米材料是由无数超微粒子组成的聚合体,可分为三大类:一是纳米微粒,指晶粒尺度为1～15纳米的超微粒子;二是纳米固体,是由大量超微粒子在保持新鲜表面的情况下,经过加压成型而获得的固体材料;三是纳米薄膜,是直接依靠成模机制,由在固体表面形成     

新型多功能材料——纳米氧化锌

纳米材料是当今材料科学的热门话题。那么纳米材料主要有什么特征呢？一是改变材料性质。一纳米只有一毫米的百万分之一，在加工过程中，当材料晶粒的线径小于一纳米时，材料的性质就会发生意想不到的变化，如各种块状金属都呈各种不同的颜色，但当其细化到纳米级颗粒时，均变成了黑色。二是熔点极低。如金的熔点是1064℃，而两纳米大小的金粉熔点仅为330℃。这就使低温下烧结制造合金产品成为可能，而且能把通常不可熔的金属冶炼成合金。     

纳米技术与现代化工业

纳米技术是本世纪三大支柱产业之一，介绍了纳米技术的发展及纳米材料包括纳米粉末，纳米纤维，纳米膜及纳米块体在现代化工业相关领域的应用。     

纳米技术与现代化工业

纳米技术是本世纪三大支柱产业之一.介绍了纳米技术的发展及纳米材料包括纳米粉末、纳米纤维、纳米膜及纳米块体在现代化工业相关领域的应用.     

纳米二氧化钛颗粒生物安全性动物模型的评价

纳米材料的毒性分为体内及体外,本文通过使用中性溶液中稳定存在、高分散的纳米二氧化钛,以腹腔注射方式对小鼠进行适量急性中毒测试。通过透射电镜(TEM)、X射线衍射(XRD)和纳米粒度仪(PCS)手段表征纳米颗粒的物化特性;通过激光拉曼显微镜(RAM)、等离子发射光谱(ICP)和能谱仪(EDS)手段观察纳米二氧化钛在肺、肝、肾组织中的富集;通过HE染色组织切片以及生物透射电镜(Bio-TEM)观察其对各组织的破坏。结果发现,肝脏相对于其他组织,纳米颗粒的富集情况严重,且各组织内部细胞结构相对于正常组织均有不同程度的变化。     

Correlation Between Process Parameter and Primary Dendrite Arm Spacing in Laser Welding of Cu and Al

A combined numerical model of thermal field and the primary dendrite arm spacing(PDAS) was proposed to correlate the process parameters and PDAS in laser welding of Cu and Al. The solidification parameters simulated by the finite volume method with commercial software ANASYS FLUENT were applied in the PDAS model to predict the dendrite arm spacing of fusion zone. Dendrite was also examined by the metallographic method to validate the model. Results indicate that the calculated PDAS agrees with metallographic measurements reasonably, especially the Hunt model. PDAS increases apparently with increasing laser power while decreases slightly with increasing welding speed. Increasing laser power increases the secondary dendrite and increasing welding speed increases the microporosity in dendrite.     

超短脉冲激光烧蚀SiO2材料的库仑爆炸模型理论分析

基于动理论Vlasov-Poisson方程,建立了超短脉冲激光引起的SiO2材料表面库仑爆炸烧蚀机理的理论模型,计算了在多光子吸收与雪崩2种电离机制下材料中自由电子的非平衡态分布,并在此基础上定量分析了自洽电场导致的材料表面库仑爆炸的机理及激光参数对材料表面烧蚀的影响.结果表明,在飞秒激光作用下自由电子弛豫时间不是常数...     

室温固相反应合成纳米材料碱式碳酸铝钠

用无水Na2CO3与加有表面活性剂的AlCl3.6H2O室温下进行固相反应,合成得到碱式碳酸铝钠纳米材料和可溶性无机盐,用水洗去可溶性盐,烘干,即得到碱式碳酸铝钠纳米晶体。用均匀试验设计方法安排试验方案,用多元逐步回归法建立数学模型,并用网格优化法确定了最佳的试验条件。产物最终经XRD表征,证实为纳米尺寸晶体。     

基于LabVIEW的作物关键生长参数提取

随着机器视觉技术的发展,图像处理技术在农业方面的应用越来越广,尤其是农作物检测.生长参数的提取是农作物检测的基础,也是重点.本文以LabVIEW及Vision图像处理工具包为平台,研究了作物在不同阶段下生长参数的提取方法.以番茄幼苗为例,通过图像处理和量化分级的方法,研究了幼苗阶段生长参数的提取方法.以油菜为例,研究了成长阶段生长参数的提取方法.通过HSI空间模型参数量化的方式,对植株的缺素情况进行分级,实例验证了方法的有效性和可行性.以图像处理为核心的作物生长参数提取方式将为数字化和智能化的农作物监测系统开发提供新思路.     

SLM成型AlSi10Mg倾斜薄壁件壁厚响应面法优化

针对激光选区熔化成形倾斜薄壁件尺寸精度低、成形质量差等问题,应用响应曲面法研究工艺参数及倾斜角度对薄壁件壁厚的影响,建立倾斜角度、工艺参数与壁厚相对误差关系模型。结果表明:倾斜角度对壁厚的影响最大,激光功率次之。由于倾斜角度改变,薄壁件悬垂面粉末支撑区域不同,导热效果存在差异,激光功率与扫描间距对于不同倾斜角度的薄壁件壁厚影响不同。其中,激光功率对45°倾斜薄壁件壁厚的影响最大,当激光功率选择150~350W时,壁厚相对误差最大差值为24%而扫描间距对90°倾斜薄壁件壁厚的影响最大,当扫描间距选择0.1~0.2mm时,壁厚相对误差最大差值为9.5%,合理的工艺参数能够有效降低壁厚相对误差。     

A novel method for fabricating polydimethylsiloxane microfluidic chip master molds

We proposed a novel method of fabricating polydimethylsiloxane （PDMS） microfluidic chip polymer master molds in this paper. The method mainly includes two steps. First, a stainless steel slice was laser etched to form a metal model. Then, the organic solution of poly（methyl methacrylate） （PMMA） was casted onto the metal model to fabricate the PMMA master which subsequently would be used to fabricate PDMS chips. We systematically researched different laser parameters influencing the surface status of microchannels and obtained optimized etching parameters. We investigated and optimized the organic solution composition of PMMA while casting chip masters, and developed a method to form fine polymer masters using two different viscosity solutions to cast the model in turn, and studied the repeatable replication. Then, we investigated physical performance of this chip and evaluated the practicability by analyzing Rhodamine B. Compared with present methods, the proposed method does not need photolithography on photoresistant and chemical etching. The entire fabricating progress is simple, fast, low-cost and can be controlled easily. Only several minutes are required to make a metal model, 3 hours for a PMMA master, and one day for PDMS chips.     

Evaluating the Accuracy of Judgments Obtained From Item Review Committees

When the item response theory (IRT) model uses the marginal maximum likelihood estimation, person parameters are usually treated as random parameters following a certain distribution as a prior distribution to estimate the structural parameters in the model. For example, both PARSCALE (Muraki &; Bock, 1999) and BILOG 3 (Mislevy &; Bock, 1990) use a standard normal distribution as a default person prior. When the fixed-item linking method is used with an IRT program having a fixed-person prior distribution, it biases person ability growth downward or upward depending on the direction of the growth due to the misspecification of the prior. This study demonstrated by simulation how much biasing impact there is on person ability growth from the use of the fixed prior distribution in fixed-item linking for mixed-format test data. In addition, the study demonstrated how to recover growth through an iterative prior update calibration procedure. This shows that fixed-item linking is still a viable linking method for a fixed-person prior IRT calibration.     

The application of various nonlinear models to describe academic growth trajectories: an empirical analysis using four-wave longitudinal achievement data from a large urban school district

This study introduced various nonlinear growth models, including the quadratic conventional polynomial model, the fractional polynomial model, the Sigmoid model, the growth model with negative exponential functions, the multidimensional scaling technique, and the unstructured growth curve model. It investigated which growth models effectively describe student growth in math and reading using four-wave longitudinal achievement data. The objective of the study is to provide valuable information to researchers especially when they consider applying one of the nonlinear models to longitudinal studies. The results showed that the quadratic conventional polynomial model fit the data best. However, this model seemed to overfit the data and made statistical inference problematic concerning parameter estimates. Alternative nonlinear models with fewer parameters adequately fit the data and yielded consistent significance testing results under extreme multicollinearity. It indicates that the alternative models denoting somewhat simpler models would be selected over the conventional polynomial model with more fixed parameters. Other practical issues pertaining to these growth models are also discussed.     

Versapulse 532nm激光治疗血管性皮肤病的临床观察及实验研究

目的报道Versapulse 532nm激光治疗血管性皮肤病的临床疗效,并以免耳为模型探讨其对血管的作用．方法用美国Coherent 公司生产的Versapulse 532激光,治疗５５６例血管性皮肤病,其中鲜红斑痣１２４例,草莓状血管瘤２３例,樱桃状血管瘤６３例,蜘蛛痣１４５例,毛细血管扩张２０１例,治疗间隔为１～３个月,并选择不同激光参数,用兔耳血管进行动物实验．结果经过１～数次激光治疗,取得明显疗效,痊愈４２２例,显效６３例,有效７１例．动物实验显示激光照射后血管内红细胞变性破坏,继而血栓形成为主要变化,照射能量相对大而脉宽相对小可出现轻度红细胞外渗,对临床选择激光参数具有指导作用,结论 Versapulse 532nm激光治疗血管性皮肤病疗效好,副反应少,其效果与激光参数的选择有关．     

弱氦-氖激光对东北林蛙卵孵化和蝌蚪生长速度的影响

通过卵孵化试验和蝌蚪生长速度试验研究弱氯-氖激光对东北林蛙卵孵化和蝌蚪生长速度的影响．结果表明。弱氯-氖激光可以提高东北林蛙卵孵化率,缩短卵的发育历期,对蝌蚪的生长速度有促进作用,且激光照射时间越长,卵孵化率越高、卵的发育历期越短、蝌蚪生长速度越快．同时,弱氨-氖激光照射在一定范围内可以提高蝌蚪的成活率,适宜照射时间为30min．此试验为东北林蛙人工养殖提供了一定的依据．