共查询到20条相似文献,搜索用时 88 毫秒
1.
铁磁共振测试是自旋电子学研究的重要手段,为实现简单高效的FMR测试,基于瑞士苏黎世仪器500k MFLI锁相放大器,搭建了微扰型宽频带共面波导式铁磁共振测试系统,并对坡莫合金等材料进行了测试.为了得到材料的真实性质,对影响实验结果的参量进行优化,在深入讨论了这些参量对实验结果的影响及其物理和数学机制后,得到准确铁磁共振测试结果的实验条件为:电磁铁定点增加模式下,锁相放大器的时间常量为100 ms,滤波阶数在2阶以上,微扰线圈驱动信号振幅为1~2 V,频率为33~200 Hz. 相似文献
2.
物理仪器的管理与使用是一项经常性的工作,它直接关系到实验的效果.如何提高仪器的管理水平,使仪器的技术性能保持良好的状态,发挥最佳效能,是物理实验室工作的重要内容.笔者就物理仪器的“管”和“用”谈以下几点看法.1健全管理制度是做好工作的基础仪器设备是学... 相似文献
3.
磁共振扩散张量成像(DTI)是在扩散加权成像(DWI)基础上发展起来的一种新型技术,可以无创伤显示脑白质纤维,诊断脑白质病变. 但是由于各种原因,DTI一般只在超导高场磁共振成像(MRI)仪器上进行,这就限制了这一重要诊断手段临床应用的广泛性. 本文在低场磁共振成像系统上应用线扫描实现了扩散张量成像,并测量了健康志愿者大脑内主要解剖结构的表观扩散系数(ADC)和各项异性分数(FA),得到的数据与高场仪器上的相关数据比较是吻合的. 因此临床上使用在低场强上得到的DTI图像评价脑白质是可行的,而且通常在临床上这也是足够的. 相似文献
4.
5.
6.
7.
8.
多脉冲强流直线感应加速器(LIA)测控系统中仪器设备数量大、种类多、总线类型复杂,其通信和控制直接影响装置运行的可靠性。在硬件上将众多仪器根据功能划分成不同的子系统,每个子系统仪器设备通过必要协议转换后和相应的前端设备服务器连接,然后接入测控系统网络;仪器设备的通信控制软件采用LabVIEW平台进行开发,前端设备服务器中的本地控制程序通过VISA或UDP协议与仪器通信,远程通信采用DataSocket技术;为了应对强烈的电磁干扰和高压冲击,对仪器供电系统以及Marx充电线路进行了多处隔离,同时采取优化网络结构和数据流向、采用UDP协议以及主从模式总线仲裁等措施提高软件的可靠性。这套系统目前应用于多脉冲强流LIA装置的调试试验中,运行稳定可靠,完全满足实验要求。 相似文献
9.
10.
11.
任意波形发生器作为测试测量设备的一种重要仪器,在航空航天的测量与控制技术领域中得到了广泛应用。当前市场成熟任意波形发生器产品多为国外产品或者国内厂商基于国外FPGA和DAC研制的产品。为了打破技术垄断,提高国产任意波形发生器的自主技术保障能力,研制基于国产芯片的任意波形发生器愈发重要。随着国产芯片设计技术提升,国产FPGA和DAC的性能显著提高,并得到了广泛应用。PXI总线作为当前仪器领域的主要总线类型之一,可以满足大部分测试仪器的通讯要求。基于国产FPGA和DAC器件,从硬件设计和软件设计两个方面出发,成功研制了一款采样率为100MSa/s的 PXI总线任意波形发生器模块,实现了43MHz信号输出,通过实验测试了模块的功能和性能,完全满足模块指标要求,充分证明了国产芯片在工程设计中的性能特性。 相似文献
12.
13.
Noam Amir 《Applied Acoustics》2004,65(12):1181-1196
The Australian didjeridu is a unique and interesting instrument. Despite the fact that the bore shape is almost random in nature and varies considerably across different instruments, the didjeridu timbre is readily recognizable. This is also true despite the fact that the player can manipulate the timbre more than in most wind instruments, by changing the shape of his vocal tract. In this study we examine the didjeridu spectrum in detail, in order to determine the characteristics that are similar across different instruments, those that are constant for a given instrument, and those that are readily influenced by the player. To this end we recorded and analyzed the sounds of eight instruments of different quality, all of them played across a range of timbres. Examining the resultant spectra, along with the resonance frequencies of these instruments, leads to a number of interesting conclusions. One of these is that the random nature of the instrument bore is actually conducive to creating its typical timbre. We also give a preliminary explanation of the differences between good and poor instruments. 相似文献
14.
15.
蛋白饲料原料粗蛋白含量近红外光谱模型转移研究 总被引:2,自引:0,他引:2
建立良好的蛋白饲料近红外光谱定量分析模型及实现在不同仪器间的模型共享,能极大提高模型的利用效率,满足饲料行业快速发展的需要。针对蛋白饲料原料粗蛋白含量近红外分析模型适用性问题,首次采用光谱差值转移、直接校正和分段直接校正法进行了三台不同类型的近红外光谱仪之间的模型转移研究。实验样品为四种蛋白饲料原料:玉米蛋白粉、菜粕、酒糟和鱼粉。实验仪器包括MATRIX-Ⅰ傅里叶变换型近红外光谱仪(主仪器),Spectrum 400傅里叶变换型近红外光谱仪(从仪器1)和SupNIR-2750光栅扫描型近红外光谱仪(从仪器2)。研究表明,同一样品体系在主仪器和从仪器2上所得光谱数据的差异性相对较小,且均与从仪器1所得光谱数据的差异性相对较大。除分段直接校正法对玉米蛋白粉从仪器2的预测结果无促进作用之外,其他模型的预测均方根误差和系统偏差均明显低于转移前。玉米蛋白粉、菜粕和酒糟样品采用三种方法转移后的模型预测相对分析误差(RPD)均大于3.0,预测效果良好。鱼粉样品模型转移后的预测RPD均大于2.5,预测效果较好。三种方法对于蛋白饲料原料不同仪器间的光谱差异进行了有效校正。该研究结果对于蛋白饲料品质近红外快速分析模型的广泛应用具有重要意义。 相似文献
16.
B. Heise 《The European physical journal. Special topics》2007,145(1):3-14
Chladni's accomplishments in the field of instrument
making were until recently not nearly as well-respected as his
studies on the modes of vibration of plates and rods. However, he
had developed his own friction instruments based on the glass
harmonica, a popular instrument of his time. The instruments, which
he partially built himself, had keys, which distinguished them from
the glass harmonica. Additionally, these instruments differed from
traditional keyboard instruments as they enabled the crescendo and
decrescendo of individual notes after the key had been struck.
Although Chladni's clavicylinder fascinated audiences and prompted
imitations by many instrument makers, it was largely ignored by
composers and pianists and therefore never became part of standard
orchestration.
The Museum of Musical Instruments of the University of Leipzig
features three rare examples of friction instruments which have
outlasted the centuries. These instruments were built according to
the Chladni principle. After a thorough analysis, including the
production of individual notes, these instruments will be presented
in their cultural-historical as well as their technical context,
followed by a discussion of their advantages and disadvantages.
These originals exhibits allow for a conclusive comprehension of
Chladni's ideas and his quest for new, unusual tone
colors. 相似文献
17.
18.
McLachlan N 《The Journal of the Acoustical Society of America》2011,129(6):3441-3444
The primary oscillators of tuned percussion instruments are rigid structures that exhibit bending waves. Bending waves do not naturally occur at harmonically related frequencies, which may lead to uncertainty associated with the intended pitch of the instrument. Despite millennia of development across many cultures, tuned percussion instruments rarely exhibit harmonic tuning of the first three or more partials. This letter presents three percussion instruments that have three or more harmonically tuned partials, and provides an overview of the methods used to tune the partials and manufacture the instruments at relatively low production costs. These instruments form the basis of new percussion instrument ensembles for educational, recreational, and professional use. 相似文献
19.
20.
近红外光谱分析仪器的发展概况 总被引:5,自引:1,他引:4
近红外光谱分析技术被誉为分析化学领域的“巨人”, 已成为发展最快、最引人注目的光谱分析技术之一。在国外,定性、定量分析所使用的近红外光谱分析仪器已走过了50年的发展历程,并且在不断完善的过程当中;我国的近红外光谱仪器的研制仅仅历经20年的时间,虽然处在起步阶段,但近几年的研究成果还是十分显著的。随着科技的进步,高性能的近红外光谱分析仪器层出不穷。文章就近红外光谱分析仪器从诞生至今的发展史及包括滤光片型、傅里叶变换型、声光可调滤光型等类型在内的五种近红外光谱分析仪的工作原理、特点作了较为详细的评述,并列举了当今国内外主要的近红外光谱分析仪制造商的主流产品。最后,作者展望了近红外光谱分析仪器的发展前景。 相似文献