“影响扩散快慢的主要因素”演示实验的改进

"在一个烧杯中装半杯热水,另一个同样的烧杯中装等量的凉水.用滴管分别在两个杯底注入一滴墨水,比较两杯中墨水的扩散现象."是义务教育课程标准实验教科书<物理>九年级全一册(人教版2006年3月第3版)里的演示实验.     

"电感和电容对交变电流的影响"演示实验的改进

"电感和电容对交变电流的影响"演示实验的操作难度大且现象不明显,为此介绍了2种演示该实验的方法,一是通过将电灯分别与电感(电容)和电阻串联对比进行实验来演示电感和电容对交变电流的影响;二是通过信号发生器和示波器来研究交流电对电感(电容)的影响.2种方法演示效果均较好.     

驻波实验中"二分频"现象的探讨

在大学物理实验教材中常用音叉弦振动形成共振驻波来测量音叉的振动频率,但对其中的"二分频"现象无相关的理论解释,本文在建立与‘‘二分频"现象相似的模型中,用数值计算的方法演示了这一结果.     

确定"曲线运动速度的方向"实验的改进

1原教材中实验 曲线运动速度的方向可通过实验现象笼统地来说明，如砂轮打磨物体产生的火星、飞出的链球、由转动的雨伞边缘飞出的雨滴，等等．如何通过实验确定做曲线运动的物体在某一时刻的速度方向？按照人教版教材“演示”的实验思想，在教学过程中，老师们多用“管”作轨道进行实验设计，有两种常见情况．一是软管喷墨实验，把弯曲的软管置于水平面内，用注射器使墨水沿软管做曲线运动，并从管口喷出，喷出的墨迹显示出喷出点瞬时速度方向；     

用注射器做的几个演示实验

用演示实验在给学生表明各种现象时,比口头叙述更直观、更清楚、更明确、更易于理解和记忆.但是由于目前许多乡镇中学仪器设备不足,使一些演示实验不能进行.由于注射器是一个既透明又透热的"气缸活塞"装置,用来演示各种现象便于观察;内部空腔的体积、压强、温度便于调节;可吸气也可排气.     

气体扩散现象演示的改进

高中二年级物理学第一分册图81,以空气和二氧化碳来演示气体的扩散现象,然后以石灰水来检验在盛空气的圆玻璃筒中也有二氧化碳,这一实验的优点是二氧化碳比重较空气大,但它的分子能反抗重力作用而向上扩散,很有力地说明了扩散现象是分子运动的结果。但这一演示也有一定的缺陷:因为二氧化碳和空气都是无色的气体,在扩散过程中看不出什么现象,又在扩散后还要进行石灰水检验的手续。     

关于“光的偏振”教学的一些尝试

在大学物理教学中,让学生更好地接受知识,是每一名教师的职责。根据物理是实验科学的特点,课堂教学应更多地强调演示实验和实际应用。按照这一想法,笔者在2018年秋季学期对"光的偏振"部分做了新的教学尝试。课堂教学以演示实验开始,结合实验现象来讲授物理知识,分析实验条件对实验现象的影响,并通过实际应用来加深对物理知识的理解。实践表明,教学效果还是很好的,大部分学生对这种教学模式持肯定态度。本文介绍新教学模式的指导思想、实施方案和学生反馈。     

喷墨打印量子点薄膜的形貌控制

基于微流体理论,对采用聚合物量子点墨水打印薄膜的干燥过程进行了研究,并通过优化溶剂配比、聚合物含量及干燥温度克服"咖啡环"现象,改善薄膜形貌.研究结果表明:墨水中添加高沸点溶剂有助于延缓外向流动;调节聚合物含量可改变墨水的物理性质,有利于在诱发内向流动的同时阻碍外向流动,二者均可明显改善"咖啡环"形貌,另外聚合物的流平作用可提高薄膜的平整度;调节干燥温度可优化液滴与基板的接触线钉扎,从而进一步改善"咖啡环"形貌.最终,在量子点浓度为12mg/mL,墨水中氯苯/环己基苯体积比为8∶2,聚丙烯酸酯质量百分比为11wt%,干燥温度为25℃时制备了直径约为169μm,高度约为65nm的均匀量子点薄膜及量子点点阵,为QLED器件的制备及Micro-LED面板的全彩化提供了技术支持.     

谈"圆驻波"演示实验中的思维误区

指出了对“圆驻波”演示实验在认识上的两个误区，并在理论上分析了在该装置中实现圆环驻波的条件，得到了和实验现象相一致的理论结果。     

混沌现象的仿真演示

利用Matlab GUI模拟演示了混沌现象的演化细节,通过界面布局的优化,可以直接在界面中输入和改变实验参量,形象直观地演示出变化的参数对实验结果的影响.     

Diffusion anisotropy in a toroidal (ring) vortex in water

Diffusion of paint (ink) particles in a toroidal (ring) vortex in a density-homogeneous liquid (water) was experimentally studied. Particle diffusion anisotropy in rotating water of the vortex was detected. The effect consists in the fact that the particle diffusivity in the direction perpendicular to the rotation axis of the torus core is much lower than that in the direction parallel to the rotation axis.     

薄层色谱法检验喷墨打印机墨水的种类

用薄层色谱法对88种国内外不同品牌的喷墨打印机墨水进行了种类的鉴定。根据色谱中所得斑点个数及比移值Rf的不同,可将88种不同品牌的墨水分为11类。     

Patterns of Ink in Water and Air: Creating Radial Spreads of Ink in Water

Radial spreads are made by placing different types of ink and paint over each other. Then, when gravity ‘activates’ the spread, causing the ink to move outward, the resulting patterns of ink are photographed. Recent work shows how different types of ink react to the force of the spread (by, for instance, forming thin films, or becoming filamentous). Different types of ink can be used in conjunction to reveal different parts of the spread. Regular shapes in tessellations, underwater 3D forms, and airborne radial spreads have been observed. Radial spreads of ink in water can be seen in terms of both art and science. Artistic aspects include an exploration of ink textures, and comparisons are made with other natural and man-made materials. Parallels between radial spreads and organic life forms are made, and new juxtapositions of the ‘birth, life and death’ of the spreads are found. Connections are made between the small-scale world of ink in water, and large-scale objects, e.g. cosmic phenomena. Ambiguous imagery, requiring an imaginative contribution from the viewer, is explored. Long-term aims are to collaborate with those interested in the science of diffusion to build up visual profiles of inks, and also to develop 3D chromatography. Artistically, links with other natural forms will be explored. More images are at www.chronoscapes.co.uk.     

环周进汽两相流喷射升压过程实验研究

本文用实验方法研究了环周进汽/中心进水的超音速两相流喷射升压过程,得到混合腔内压力随进水温度、进汽压力和出水流量的变化趋势,研究了整体升压性能随实验参数的变化规律,揭示了环周进汽汽液两相流喷射升压装置的升压机理。这些工作对该装置的进一步研究有重要的理论指导意义。     

Temperature effects on the diffusion of water and monovalent counterions in the hydrated montmorillonite

We investigate here the effect of temperature on the diffusion of water and cations in the Wyoming-type montmorillonite clay. The considered cations are monovalent compensating ions, such as Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ in one-, two- and three-hydration states. For this purpose, molecular dynamics simulations have been performed to obtain the dynamic behaviour regarding the interlayer ions and water molecules under a temperature range between 260 and 400 K. The diffusion coefficient of water and cations in different hydrated clays increases with temperature. The influence of temperature on the diffusion of water is much greater than that of cations in one-, two- or three-hydrated clay. The degree of hydration plays an important role on the diffusion behaviour of water and counterions. We found that the effect of temperature is negligible in weakly hydrated clay, whereas it became significant in highly hydrated one. Besides, the size and mass of cations’ hydrate also affect the diffusion behaviour of water and cations in the interlayer space of hydrated clay.     

High-fidelity chemical patterning on oxide-free germanium

Oxide-free germanium can be chemically patterned directly with self-assembled monolayers of n-alkanethiols via submerged microcontact printing. Native germanium dioxide is water soluble; immersion activates the germanium surface for self-assembly by stripping the oxide. Water additionally provides an effective diffusion barrier that prevents undesired ink transport. Patterns are stable with respect to molecular exchange by carboxyl-functionalized thiols.     

Synthesis and characterization of conductive silver ink for electrode printing on cellulose film

Silver nanoparticles with size less than 50 nm were synthesized from silver nitrate, polyvinylpyrrolidone (PVP) and ethylene glycol, where these chemicals acted as metal precursor, stabilizer and reducing agent, respectively. Then a conductive silver ink was prepared with a suitable solvent by adding a viscosifier, hydroxyethyl-cellulose (HEC), and a surfactant, diethylene glycol (DEG). The combined effect of both viscosifier and surfactant on the physical property of the silver ink was analyzed by measuring the contact angle of the silver ink on a cellulose film. Moreover, the influences of PVP molecular weight and reaction temperature on the size of the silver nanoparticles were analyzed. Then the silver ink was coated on the cellulose film by spin coating and the effects of different solvents, sintering temperatures and solid contents on its electrical resistivity were examined. It was found that, with 50 % co-solvent of deionized water and DEG and solid content of around 50 %, the silver ink exhibited the lowest resistivity. This ink can be used for inkjet printing of conductive patterns on cellulose films.     

Influence of un-cured PDMS chains in stamp using PDMS-based lithography

We present the compatibility of elastomeric stamp, poly(dimethylsiloxane) (PDMS), with inks for non-photolithography. This ink limitation is important in considering the lamination of hydrophilic solution on the patterned ink surface using an elastomeric stamp. We focus on an increase of the hydrophobicity of the patterned surface due to diffusion of low molecular weight (LMW) silicone polymer chains. This hydrophobicity increases inversely with the PDMS–ink interaction parameter (χ), which is correlated with the solubility parameter (δ). This study's results translate into proposed design factors for ink used in the patterned functional layer for PDMS-based lithography. Both the XPS and the contact angle measurement show that the hydrophobicity can be increased by LMW PDMS chains transfer from stamps, and this increase can cause the expansion of the free volume in PDMS pores through a swelling effect.     

三股互击式喷注器及燃烧室流场的数值模拟

结合旋涡耗散模型及Arrhenius化学反应速率系数来描述燃烧室内的化学反应, 对三股互击式喷注器及燃烧室的冷流场及有反应流场进行了三维的数值模拟研究. 引入螺旋度及混合长度参量分析了三股互击式喷注器的混合机理和混合效果, 获取了燃烧室的关键特征参数, 如总温、总温的空间分布、气流在燃烧室内的驻留时间等. 对燃料组合分别采用F-O-F, O-F-O的喷注器及燃烧室的流场特性进行了比较分析. 对于一定的燃料配比和燃烧室特征长度, 燃料组合采用O-F-O时, 在燃烧室出口的F₂解离度比F-O-F要高出13.5%. 实验证实激光器出光功率提升了17%.     

Simultaneous magnetic resonance imaging of diffusion anisotropy and diffusion gradient

The theory of diffusion gradient-weighted MRI (DGWI) is presented in this paper. The Bloch-Torrey equation was modified to include the effect of intravoxel spatial-location variation of water diffusion (diffusion gradient) on MRI signal, in addition to the effect of intravoxel spatial-direction variation of water diffusion (diffusion anisotropy). An analytical solution for a diffusion-encoding spin-echo pulse sequence was derived. Unlike water diffusion which attenuates the image signal intensity, this newly derived solution relates the spatial gradient of the water diffusion with the phase of the image signal. This novel MRI technique directly measures both the water diffusion and its spatial gradient, and thus offers a noninvasive imaging tool to simultaneously investigate the intravoxel inhomogeneity and anisotropy of tissue structures. In addition, as demonstrated with our preliminary data, this new method may be utilized to delineate the interfaces of tissues with different diffusion. This method is an extension of the successful diffusion tensor MRI (DTI), but requires no additional data acquisition. In addition to the measured diffusion tensor, this new method provides measurements of the spatial derivatives of the three principal diffusivities of the tensor, thereby providing additional information for improving white matter fiber tractography.