共查询到20条相似文献,搜索用时 62 毫秒
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采用装配有疏水铜网的新型喷头研究了超细纳米纤维的制备.静电纺丝实现之前,首先对铜网进行了疏水处理,并将其安装于喷头前端.静电纺丝过程中,聚合物溶液由精密注射泵输送至喷头处.安装于喷头的铜网可将管道内的聚合物溶液分成多股细流从铜网网孔中流出.从铜网网孔流出的溶液细流受电场力作用被拉伸成多股独立射流,并从喷头携带走聚集的正电荷.受铜网表面疏水性和射流间电荷排斥力的影响,从铜网喷射出的多股射流都将保持其独立的轨迹而不会产生聚集.疏水铜网有利于减小纺丝射流的初始直径,并获得均匀的超细纳米纤维.利用新型的电纺丝喷头成功制备了直径20~80 nm的聚氧化乙烯(PEO)和聚乙烯醇(PVA)超细纳米纤维.实验结果表明,超细纳米纤维的直径随着电纺丝溶液浓度的增加而变大. 相似文献
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陈瑞红 《中国新技术新产品》2010,(10):4-4
预制短桩因桩端截面形状的不同可分为敞口桩与闭口桩。对于不同的地质条件,闭口桩桩端几何形状多种多样。工程中也常对预制桩加桩尖,从而有效减小沉桩阻力,加快施工进度。本文对三种桩端形状(平底、锥角为90°的锥形、半球形)的短桩模型进行了室内静载试验,揭示了不同桩端形状对短桩垂直承载性状的影响。 相似文献
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在大型丝印机上大幅面丝网网版的出现,是人们对在不同的承印物上印出更大更好图像的追求.只有不断地在材料和技术上进行创新,才能保证丝网印刷始终处于大幅面成像领域的中心地位.手工丝网制作已经在许多工厂中被自动化设备取代了,同样,丝网涂布也被自动涂布机所取代.本文将对制作大幅面网版的主要步骤——丝目准备、上胶、干燥、曝光、显影和回收技术进行介绍. 相似文献
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熔铸法生产的钛合金,存在内部偏析,加工性差的缺点.而金属粉末注射成形(MIM)法,容易加工为最终产品形状.但是,对β稳定型Ti-(10%~15%)Mo合金采用混合粉的MIM加工时,要得到相对密度96%以上的烧结体,就应在1300℃以上烧结2h,这样导致晶粒变得粗大,引起力学性能的下降. 相似文献
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Sedmak G 《Applied optics》1998,37(21):4605-4613
Fast-Fourier-transform-based simulators of atmospheric wave fronts with a von Kármán turbulence spectrum were tested with reference to the phase-structure function and phase variance over a pupil on large square and rectangular formats. The symmetry and the accuracy of the phase-structure function were found to be limited by the aspect ratio and the size of the phase screen. The phase variance over a pupil is less sensitive to the aspect ratio than the phase-structure function and is dependent mainly on the size of the phase screen. Several tests are reported and discussed together with a method of compensation for the negative effects of rectangular formats. 相似文献
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屏风是中国传统物质文化和精神文化的重要传承,随着人文社会的发展,人们的审美意趣及需求都发生了改变,屏风的形式也在发生着变化,因此,如何使屏风的设计迎合现代审美需求,以及如何实现屏风的多功能创新设计,也就有着重要的意义。主要在结构和功能等方面对屏风展开创新设计。在结构方面,将传统家具中的榫卯结构引入其中;而在功能方面,将置物与展示等功能融合。同时结合实际案例,分析屏风创新设计应该遵循的原则。在结构和功能上的创新设计,不仅增强了屏风结构的稳定性,满足了人们多变的需求,而且易于拆卸和运输,迎合了现代化的发展趋势。屏风的多功能设计,不仅可以从结构和功能方面进行,而且可以从材料等方面切入。当然,这些都要坚持以创新性、安全性、装饰性为原则,并且兼顾人性化。 相似文献
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模块化设计与控制在药品包装机械中的应用 总被引:1,自引:1,他引:0
介绍了现代药品包装的特点,提出对铝塑泡罩包装机采用模块化设计的方法,实现一机多用的功能;并通过PLC和触摸屏结合,完成对该设备的模块化控制,提高了控制的自动化程度. 相似文献
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We measured the modulation transfer function (MTF) of a lens in the visible region using a random test target generated on a computer screen. This is a simple method to determine the entire MTF curve in one measurement. The lens was obscured by several masks so that the measurements could be compared with the theoretically calculated MTF. Excellent agreement was obtained. Measurement noise was reduced by use of a large number of targets generated on the screen. 相似文献
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The approximate analytical formula of the focal shift has been derived for an elliptical diffracting screen that consists of a circular lens and an elliptical aperture. It is found that the focal shift of the beam focused by this elliptical diffraction screen depends not only on the product of the Fresnel number of the focusing geometry and the standard deviation of a mapped function, but also on the ellipticity (the ratio between the minor and the major axes) of the elliptical aperture. The focal shift increases as the decrease in the ellipticity of elliptical aperture. By using an approximate analytical formula and the diffraction integral formula, some numerical simulation comparisons are done. The presented analyses show that the actual analytical expression for the focal shift of a rotationally asymmetric diffraction screen cannot generally be obtained by using the azimuthal average of the screen amplitude transmittance. 相似文献
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丝网印刷样板种类和样式多,每片样板上待测目标也较多,不宜采用一致的梯度阈值参数定位边缘实施测量;此外,传统视觉检测采用定位矩形框建立测量坐标系的方式会引入测量误差,因此,提出一种基于机器视觉的丝网印刷样板的尺寸测量方法。采用一种由粗到细的测量策略,借助每一类待测目标的模板进行信息统计,针对性地设置阈值参数,改善测量精度。在测量阶段,利用基于图像金字塔和归一化互相关函数相结合的分层匹配算法实现多个待测目标的粗糙定位,再使用由模板信息统计获取的阈值参数进行边缘精细定位,建立局部坐标系,完成测量。实验结果表明:在同等实验条件下,此方法能够有效提高测量精度,算法改进后测量结果的平均相对误差由原来的4.02%降到1.47%,并且无需用户介入调整测量参数,适用于不同种类丝网印刷样板的灵活测量。 相似文献
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A high-end drum film digitiser (Tango, Germany) and a calibrated linear microdensitometer developed by PTB were used to assess the modulation transfer function (MTF) and the noise power spectra (NPS) of 3 mammographic screen film systems at optical density levels of 0.8, 1.5 and 2.5. The use of a drum scanner to assess MTF and NPS data appears to be adequate but requires an appropriate characterisation of the scanner to verify its internal noise level and its MTF. It is further necessary to calibrate the scanner output in terms of visual diffuse optical densities. Processing of two-dimensional digital data of grating images need to be more strictly defined for accurate MTF measurements of screen-film systems. Nevertheless, even now it seems to be feasible to use commercially available high-end and well calibrated scanners to assess screen film systems. This is especially important for quality assurance purposes because important parameters of screen film systems such like MTF and NPS can now be determined without using sophisticated microdensitometers which are not commercially available. 相似文献