共查询到20条相似文献，搜索用时 828 毫秒
1.
黄学根 《中学物理教学参考》1995,(8)
1、用卡尺观察光的衍射现象时,可顺便观察“小缝成像”。将测脚间狭缝调至1.5mm左右,眼睛靠近缝看课本,出现了几行小字的倒立群像;看远近景物也都是倒像。 现象的解释:可将狭缝视为一个个针孔紧紧排列连通而成,于是小孔成像延伸变成了小缝成像(观察时倒像位于物的上方或下方)。 2、将氦氖激光器发出的红色激光束沿直径横穿钱 相似文献
2.
吴善勇 《中学物理教学参考》2004,33(11):34-34
高中《物理》第三册(必修加选修)第二十章第二节“光的衍射”中有较多的实验插图，阅读材料还有泊松亮斑的介绍．波发生明显衍射的条件是缝、孔的宽度或障碍物的尺寸跟波长相差不多或比波长更小．光也是一种波，在一定条件下也会发生明显的衍射现象．教材上给出单色光通过狭缝和小孔发生衍射的照片，一般学校还可以用2513(GY-1型)激光光学演示仪在课堂上对单缝衍射、三缝衍射、光栅衍射、圆孔衍射和方孔衍射、矩形孔衍射、三角孔衍射等实验进行演示。 相似文献
3.
《实验室研究与探索》2018,(10)
提出了一种液体中超声声强的光电测量方法。在传统的光学法测量液体中超声声强实验中,一般通过显微镜观察超声光栅引起的衍射光场中某个衍射级的缺失来推算超声强度。这种测量方式的明显缺点是无法连续测量声强变化,只能测量几个特殊声强点。光电测量方法在传统光学法基础上,利用光电图像传感器CCD采集超声光栅衍射光场的图像,通过数字图像处理提取声强值。通过构建光电测量实验系统,测量了随机变化的声强,验证了新方法的可行性。实验系统为声学测量实验教学提供了一个技术先进、演示性强、功能全面的平台。 相似文献
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CCD和其透镜作为逆付里叶变换系统,输入面为两个狭缝,改变正、负付里叶变换透镜的距离,自动比较CCD上两个波峰的间隔变化来控制CCD移动定焦。用付里叶变换原理和几何光学成像原理进行理论分析,并进行了实验研究和误差分析,这种方法有较高的定位精度。 相似文献
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徐汉屏 《中学物理教学参考》2001,(9)
物理学是一门以实验为基础的学科 ,历届高考对物理实验一直比较重视 .2 0 0 1年全国物理卷有实验题 3道 ,共 2 0分 ,占总分的 1 3 .3(若将第 4题选择题也算在内 ,则占分比例为1 6 ) ;全国理科综合卷有物理实验题 1道 ,共2 0分 ,占物理内容分值的 1 6.7 ;上海物理卷有实验题 5道 ,共 3 0分 ,占总分的 2 0 .上述三份试卷中的 9道实验题 ,大体可分为以下三大类型 :一、基于大纲规定实验 (包括学生实验和演示实验 )的试题这部分试题不超越大纲规定的学生实验和演示实验范围 ,主要考查考生对实验基本原理、仪器使用、操作过程等知识、技能的掌握程度以及实验观察、分析能力 .全国物理卷第 1 4题、上海物理卷第 1 4和第 1 5题 ,便属于这一类型 .全国物理卷第 1 4题是有关“用卡尺观察光的衍射现象”的实验 ,这一实验在大纲中规定为学生实验 ,试题要求从提供的四点表述中选出正确的结论 .考生根据实验时的观察结果 ,结合光的衍射规律 ,不难作出如下正确判断 :不论狭缝与灯丝平行还是垂直 ,衍射条纹与狭缝都是平行的 ;衍射条纹的疏密程度或间距与狭缝的宽度和光的波长均有... 相似文献
8.
余小英 《南宁师范高等专科学校学报》2013,(3)
CCD技术是现代光电技术的一个重要分支，其在非接触领域有着非常广泛的应用。在阐述光的衍射原理的基础上，将热学与光学的实验原理、仪器的综合利用，通过CCD成像系统实现衍射法测金属线胀系数。实验结果表明，通过CCD成像系统提高微小形变量的测量精度，可以实现金属线胀系数的非接触测量，且精度较高。 相似文献
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《实验室研究与探索》2015,(11):26-29
利用超声光栅测量液体中的声速实验中,由于光波通过超声光栅产生的衍射条纹数量较少,不能很好地进行多级衍射条纹间距的测量,而且无法测量具有腐蚀性的液体。为此,在超声槽及增加超声波功率等方面,进行了一些实验方法和仪器的改进设计与制作,主要是给超声波传感器(压电陶瓷片)增加了一个功率放大器,并将超声槽全部用玻璃制作,便于产生更多级衍射条纹,然后将超声传感器用耦合剂紧贴在全玻璃矩形超声槽外侧,再将全玻璃超声槽与控温系统相连接,控温系统是在传统的蒸汽喷射加热仪的基础上,组合黏滞系数实验部分仪器和温度传感器而做成的。结果表明,改进后的实验装置不仅拓展了实验中所用液体的范围,而且可方便研究声速与被测液体的浓度及温度的关系。利用CCD测量技术实现超声波速度的自动化测量,以减少测量误差。 相似文献
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两步投影法校正图像采集中的梯形畸变 总被引：1，自引：0，他引：1
图像采集中的梯形畸变是工程中最常见的畸变之一,但少有文献对此进行论述,为此文章提出一种简便的校正方法,在已知摄像机的镜头焦距和CCD大小的情况下,仅需要知道摄像机中轴线与地面(或被拍摄平面)的倾角一个参数,不需要控制点,就可以恢复原始图像.基本方法是利用小孔成像原理,先将CCD上的点投影到地面上,同时假设平行于地面一定高度有一虚拟CCD平面,再将地面上相应的点投影到虚拟CCD上,当所有点都遍历后,虚拟CCD平面上获得的图像就是梯形校正后的图像.实验证明,这种方法简洁有效,适应性强,效果理想,在工程上具有较高的应用价值. 相似文献
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为了抑制多载波通信中发送信号相对较高的峰值功率,提出了一种新的基于交织的选择性映射方案.在该方案中,采用一组交织跨度仅为几个比特的比特级交织器来产生多个表示相同信息的序列,从中选择对应信号峰均比最低的序列作为发送的序列.描述了该方案的实现方式以及这种短跨度交织器的结构.通过仿真考察了该映射方案在降低多载波信号峰均比方面的性能.结果表明该方案在抑制峰均比方面呈现出很好的性能,对于高阶调制信号,如16QAM和64QAM,它甚至达到选择性映射所能实现的最佳性能.与传统的基于交织的选择性映射方案相比较,这种基于短跨度交织的选择性映射方案产生非常短的时间延迟,只需要很少的缓冲寄存器,且易于用硬件实现. 相似文献
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Progress in selective laser melting equipment,related biomedical metallic materials and applications
Yu-chao Bai Fan Fu Ze-feng Xiao Ming-kang Zhang Di Wang Yong-qiang Yang Chang-hui Song 《浙江大学学报(A卷英文版)》2018,19(2):122-136
This paper introduces the latest achievements of the South China University of Technology in basic research on selective laser melting (SLM), applications of SLM manufacturing equipment, and biomedical metallic materials manufactured by SLM. First, we describe the use of DiMetal-100 equipment to study the process parameters, microstructure, and mechanical properties of three kinds of metal medical materials manufactured by SLM, including 316L stainless steel, CoCrMo, and Ti6Al4V. Second, we describe the application of 316L stainless steel manufactured by SLM to personalized lingual orthodontic brackets and surgical guide plates, the application of CoCrMo manufactured by SLM to knee prostheses and dental crowns and bridges, and the research results of Ti6Al4V manufactured by SLM in the treatment of pelvic fracture bone plates and personalized cranial prostheses. Finally, we introduce the development directions and research plans for SLM technology at the South China University of Technology, including the manufacture of a new porous structure by SLM directly, the manufacture by SLM of various material products simultaneously, SLM + material-reducing hybrid manufacturing, improving the negative feedback systems of SLM equipment, and developing SLM manufacturing processes using ceramics and new metals. 相似文献
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Obtaining an electrocorticograms （ECoG） signal requires an invasive procedure in which brain activity is recorded from the cortical surface. In contrast, obtaining electroencephalograms （EEG） recordings requires the non-invasive procedure of recording the brain activity from the scalp surface, which allows EEG recordings to be performed more easily on healthy humans. In this work, a technique previously used to study spatial-temporal patterns of brain activity on animal ECoG was adapted for use on EEG. The main issues are centered on solving the problems introduced by the increment on the interelectrode distance and the procedure to detect stable frames. The results showed that spatial patterns of beta and gamma activity can also be extracted from the EEG signal by using stable frames as time markers for feature extraction. This adapted technique makes it possible to take advantage of the cognitive and phenomenological awareness of a normal healthy subject. 相似文献
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Hendrik Dubbe Elena Holl Adriaan Spierings Konrad Wegener Ulrich Nieken 《浙江大学学报(A卷英文版)》2018,19(10):735-745
Examples of the use of additive manufacturing and rapid prototyping in a range of applications are of great interest in order to emphasize their role in development and production technology. In this study, a catalytic low temperature burner for H2 on a lab scale with an integrated flow distributor was designed, manufactured, and tested for functionality. Based on a theoretical approach, a flow distributor for the burner was designed and a prototype was built using fused deposition modeling (FDM). Based on test results, an optimized version of the burner was then designed and manufactured using selective laser melting (SLM). The functionality of the designed catalytic burner was proven. Several advantages were found in comparison to conventional non-catalytic burners. In particular, flameless uniform low temperature heat generation with temperatures of about 200 °C could be realized. This contribution highlights the potential of additive manufacturing in chemical engineering. Not only was the final product built using SLM, but also during the development process, FDM was used for rapid prototyping. 相似文献
15.
Power Quality （PQ） combined disturbances become common along with ubiquity of voltage flickers and harmonics. This paper presents a novel approach to classify the different patterns of PQ combined disturbances. The classification system consists of two parts, namely the feature extraction and the automatic recognition. In the feature extraction stage, Phase Space Reconstruction （PSR）, a time series analysis tool, is utilized to construct disturbance signal trajectories. For these trajectories, several indices are proposed to form the feature vectors. Support Vector Machines （SVMs） are then implemented to recognize the different patterns and to evaluate the efficiencies. The types of disturbances discussed include a combination of short-term disturbances （voltage sags, swells） and long-term disturbances （flickers, harmonics）, as well as their homologous single ones. The feasibilities of the proposed approach are verified by simulation with thousands of PQ events. Comparison studies based on Wavelet Transform （WT） and Artificial Neural Network （ANN） are also reported to show its advantages. 相似文献
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Mohammed K. Khalil Loren D. Nelson Jonathan D. Kibble 《Anatomical sciences education》2010,3(5):219-226
This study used qualitative and quantitative approaches to evaluate the effectiveness of self‐learning modules (SLMs) developed to facilitate and individualize students' learning of basic medical sciences. Twenty physiology and nineteen microanatomy SLMs were designed with interactive images, animations, narrations, and self‐assessments. Of 41 medical students, 40 students voluntarily completed a questionnaire with open‐ended and closed‐ended items to evaluate students' attitudes and perspectives on the learning value of SLMs. Closed‐ended items were assessed on a five‐point Likert scale (5 = high score) and the data were expressed as mean ± standard deviation. Open‐ended questions further evaluated students' perspectives on the effectiveness of SLMs; student responses to open‐ended questions were analyzed to identify shared patterns or themes in their experience using SLMs. The results of the midterm examination were also analyzed to compare student performance on items related to SLMs and traditional sessions. Students positively evaluated their experience using the SLMs with an overall mean score of 4.25 (SD ± 0.84). Most students (97%) indicated that the SLMs improved understanding and facilitated learning basic science concepts. SLMs were reported to allow learner control, to help in preparation for subsequent in‐class discussion, and to improve understanding and retention. A significant difference in students' performance was observed when comparing SLM‐related items with non‐SLM items in the midterm examination (P < 0.05). In conclusion, the use of SLMs in an integrated basic science curriculum has the potential to individualize the teaching and improve the learning of basic sciences. Anat Sci Educ 3: 219–226, 2010. © 2010 American Association of Anatomists. 相似文献
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AlSi12 samples were prepared by selective laser melting (SLM) under different processing conditions in order to obtain different top surface morphologies, where single tracks were produced using a fixed processing parameter to reveal the mechanism of the single track on different morphologies. The results show that the morphologies of single tracks changed with roughness of the top surface (Top Ra) of SLM parts, reflected in the variation of wetting angles on the surface processed previously as well as in dimensions of height, width, and depth at the cross-section of each single track. These changes were mainly caused by different wettability and flow behavior of the molten metal under various solidification environments of the single track during SLM. A poor solidification environment in which numerous balls existed limited an effective wetting behavior of molten metal on a previously processed surface of a SLM sample because of an increasing solid-liquid contact area, thus causing dramatical instability of the melt pool and attendant inferior processability of the single track. Meanwhile, under the action of surface tension, the molten metal had a high tendency to transfer into a pore near the single track to form an extending track or flow toward an upper region of melt to form a balling track, hence showing various morphologies of single tracks. This study proposes a theory of the solidification mechanism of single track on the non-ideal surface to provide a better understanding of the SLM processing of Al-Si alloy. 相似文献
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Selective laser melting (SLM) is one type of additive manufacturing which produces metal parts by powder bed fusion. Since the materials undergo repeated and sharp heating/cooling cycles, the SLMed parts have unique microstructures. The relations among SLM processing parameters, resultant microstructures, and mechanical properties have been investigated by many researchers. However, the wear performance of SLMed materials under various contact conditions has not been carried out until recently. This paper is a presentation of previous and recent research related to wear performance. This is a crucial aspect if SLM is to be expanded to produce friction pairs. Wear rates and mechanisms of the SLMed materials under dry, boundary lubrication, cavitation erosion, and corrosion conditions are discussed and compared with conventionally processed (CP) materials. SLMed materials benefit from fine grains and high hardness, which have higher wear resistance than CP materials. Moreover, a unique tribo-layer on the surface of the SLMed part is found to protect the bulk material under boundary lubrication conditions. An optimized combination of processing parameters increases part density, which further improves the wear resistance. Future work includes studying the influence of pores on the deforming and lubricating behaviors from dry conditions to different lubrication regimes. The final target is to actively control the processing parameters to obtain desirable material properties for improving wear performance. 相似文献
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Due to e-business's variety of customers with different navigational patterns and demands, multi-class queuing network is a natural performance model for it. The open multi-class queuing network(QN) models are based on the assumption that no service center is saturated as a result of the combined loads of all the classes. Several formulas are used to calculate performance measures, including throughput, residence time, queue length, response time and the average number of requests. The solution technique of closed multi-class QN models is an approximate mean value analysis algorithm (MVA) based on three key equations, because the exact algorithm needs huge time and space requirement. As mixed multi-class QN models, include some open and some closed classes, the open classes should be eliminated to create a closed multi-class QN so that the closed model algorithm can be applied. Some corresponding examples are given to show how to apply the algorithms mentioned in this article. These examples indicate that multi-class QN is a reasonably accurate model of e-business and can be solved efficiently. 相似文献
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朱逸韬黄卫东 《福建工程学院学报》2020,(6):570-575
设计了以激光功率、扫描速度、扫描间距、铺粉厚度为因素的正交实验,研究了SLM 成型18Ni-300 模具钢粉末过程中各个工艺参数对成型件致密度的影响规律,并进行了工艺参数优化。实验表明,在选定范围内,成型件致密度随激光功率的增加先增大后减小?随扫描速度的增加持续减小?随扫描间距的增加先增加后减小?随铺粉厚度的增加持续减小。最优工艺参数组为激光功率260 W、扫描速度500 mm/ s、扫描间距0.11 mm、铺粉厚度0.02 mm 时,成型件致密度99.99%,为所有实验中的最优值。 相似文献