测量磁致伸缩系数实验的改进

采用电阻应变片配合UJ31型电位差计进行镍的磁致伸缩系数的测定,使学生在初步掌握“电位差计”及“灵敏电流计特性研究”两实验基础上进一步熟练掌握基本测量方法。一、原理与装置置于磁场中的铁磁体,随磁场H值的变化,长度会有微小改变Δl。     

电容法测量磁性材料的磁致伸缩系数

磁致伸缩系数λ是表征磁性材料磁化状态变化引起弹性变性的参量,经典的测量是用光杠杆法和光干涉法,前者的灵敏度较低而且误差较大,后者则设备较复杂也不便于对λ值较大的材料进行测量,而电容法则可方便地进行测量且灵敏度较高。     

单缝衍射法测量磁致伸缩系数

根据单缝衍射原理设计光路,通过数字图样处理方法处理高清摄像头采集的衍射图像,搭建一套精确测量铁磁材料在弱磁场中磁致伸缩系数的实验装置.该装置具有测量方法简单,精确度高,能够快捷测量的特点.     

磁致伸缩系数的测量

为了避免非平衡电桥法测量磁致伸缩系数出现的漂移现象，本文提出了一种用光学干涉法间接测量磁致伸缩系数的实验方法。     

超磁致伸缩材料性能测量实验

采用比较法和电桥法测量了Terfenol-D样品的磁致伸缩系数,并采用共振法测量了Terfenol-D样品的磁机械耦合系数.将超磁致伸缩材料特性测量实验引入本科实验教学,可以使学生在近代物理实验课程的学习中接触到材料科学研究前沿领域的技术与知识,有助于提高学生的创新意识和创新能力,激发学生的学习兴趣.     

铁基非晶合金磁致伸缩的温度效应

本文研究了Fe_80-xCu_xSi₅B₁₅,(Fe_1-xCo_x)₈₂Cu_0.4Si_4.4B_13.2两系列非晶合金的磁致伸缩系数λ₄随温度T的变化关系,温度范围分别为室温至非晶态居里点和室温至晶在居里点。分析了Fe基非晶合金随温度变化所产生的结构变化,并讨论了其磁致伸缩的单离子微观机制。 关键词：     

七种非晶铁磁合金的体积磁致伸缩研究

 强制体积磁致伸缩的数量级极小（10^-10~10^-9[(10³/4π)(A/m)]^-1），如通过测量三个互成直角方向的线磁致伸缩（10^-6[(10³/4π)(A/m)]^-1）再正负迭加则很难测准。本文利用热力学关系：(dω/dH)_T,p=-(dM_s/dp)_T,H，用静水压法在0.000 1~2.4 GPa范围测得七种非晶合金Fe_81.6Si_4.6B_13.8、Fe_46.3Co_0.03Ni_46.5Si_3.75V_0.92B_2.5、Fe₇₅Cr₅Si₅B₁₅、Fe_73.9Co_8.3Si_4.4B_13.4、Fe₇₅Ni₅Si₅B₁₅、Fe_78.75Cu_1.25Si₅B₁₅和(Fe_0.85Co_0.15)₈₂Cu_0.4Si_4.4B_13.2的强制体积磁致伸缩及其随静水压p的变化。结果表明：（1）其中六种属于第一类压磁效应。(dω/dH)_T,p在大部分压力下为正，p增加时M_s不断减小；(dω/dH)_T,p仅在几个狭窄的压力范围为负。可归因于磁性原子与非磁性原子的化学短程序在压力下的变化。（2）非晶合金Fe_78.75Cu_1.25Si₅B₁₅属于第二类压磁效应。(dω/dH)_T,p在绝大部分压力下为负。M_s反常升高与Cu的特殊作用有关。     

用迈克耳孙干涉仪测量磁致伸缩系数

借助迈克耳孙干涉仪可以精密测量长度变化这一条件，对铁磁物质的磁致伸缩系数进行测量。     

甩带Fe85Ga15合金的巨磁致伸缩研究

利用甩带快淬方法制备了Fe85Ga1 5合金样品 .测量了样品在沿带片长度方向和厚度方向上的磁致伸缩 ,发现其值分别高达 - 1 30 0ppm和 1 1 0 0ppm .巨大磁致伸缩的获得来源于甩带样品的形状各向异性和合金内部生成的大量短程应变有序以及它们的择优取向 .样品温度特性的测量表明 ,在室温附近约 6 0℃宽的温度范围 ,合金的磁致伸缩数值基本保持不变 ;而在高温条件下 ,合金具有更大的磁致伸缩     

用恒流法自制仪器精确测定液体的黏度

介绍了用恒流法自制仪器精确测定液体的黏度.该自制仪器,能有效地保证底部的密封性、液体水位恒定和可操作性.另外,还增设一个玻璃管连通器,并附加一根标尺和游标,可使液体水位的测量精确度提高.在接毛细管输出液体的量筒处加上光电计时,可使测量液体的流速的精确度提高.再将相关数据送入已编好程序的电子仪器进行计算并显示出黏度.另外该仪器可调换不同管径的毛细管,因此应用本方法能快速准确地测量多种液体的黏度.     

高能氮离子轰击对四面体非晶碳膜的表面改性和摩擦系数影响的研究

利用过滤阴极真空电弧技术制备了sp³键含量不小于80%的四面体非晶碳(ta-C)膜.利用冷阴极潘宁离子源产生不同能量的氮离子对制备的ta-C薄膜进行轰击,通过X射线光电子能谱和原子力显微镜对薄膜表面结构与形貌进行分析研究.研究表明,随着氮离子的轰击能量的增大,薄膜中的CN键结构略有增大,形成了轻N掺杂;同时,在薄膜表层发生了sp³键结构向sp²键结构的转化;薄膜的表面粗糙度在经过氮离子轰击后从0.2 nm减小至0.18 nm,然后随着轰击能 关键词： 四面体非晶碳 X射线光电子能谱 摩擦系数     

小角X射线散射表征非晶合金纳米尺度结构非均匀

表征纳米尺度结构非均匀对于理解非晶合金的变形、弛豫等动力学行为至关重要.受时空尺度限制,非晶合金纳米尺度结构非均匀的实验表征具有很大的挑战性.本文针对一种典型的锆基非晶合金,开展了同步辐射小角X射线散射原位拉伸实验.通过对散射曲线的定量分析,揭示了非晶合金在纳米尺度的非均匀结构图像.首先,Porod散射曲线呈现正偏离行为,表明非晶合金属于非理想两相散射体系,两相界面弥散且任一相内都存在电子密度涨落.基于散射曲线的Guinier定律分析,进一步揭示非晶合金中散射体形状远偏离球形,其特征尺度主要分布在0.8—1.6 nm之间,且在弹性变形阶段几乎不变.最后,通过Debye相关函数分析,发现这些纳米尺度散射体仅在1 nm之内存在强关联,符合非晶合金短程有序、长程无序的结构特征.研究结果表明非晶合金中存在具有复杂空间分布的纳米尺度非均匀结构.     

Further study of the phase-recovering algorithm for saturated fringe patterns with a larger saturation coefficient in the projection grating phase-shifting profilometry

The phase error will occur when captured fringe patterns are saturated in the projection grating phase-shifting profilometry. The phase-recovering algorithm corresponding to seven-frame phase-shifting method is deduced. The applicability ranges of phase-recovering algorithms corresponding to different phase-shifting methods are studied with different intensity saturation coefficients by a simulative method. Simulative results indicate that the phase error caused by the intensity saturation can be effectively decreased by the phase-recovering algorithm when the saturation coefficient of fringe patterns is within the applicability range of the corresponding phase-recovering algorithm. Furthermore, the applicability range of the phase-recovering algorithm will be extended with the increase of phase-shifting steps. An experimental result is presented to prove the availability of the phase-recovering algorithm.     

Improvement of a new rotation function for molecular replacement by designing new scoring functions and dynamic correlation coefficient

A previously published new rotation function has been improved by using a dynamic correlation coefficient as well as two new scoring functions of relative entropy and mean-square-residues to make the rotation function more robust and independent of a specific set of weights for scoring and ranking. The previously described new rotation function calculates the rotation function of molecular replacement by matching the search model directly with the Patterson vector map. The signal-to-noise ratio for the correct match was increased by averaging all the matching peaks. Several matching scores were employed to evaluate the goodness of matching. These matching scores were then combined into a single total score by optimizing a set of weights using the linear regression method. It was found that there exists an optimal set of weights that can be applied to the global rotation search and the correct solution can be ranked in the top 100 or less. However, this set of optimal weights in general is dependent on the search models and the crystal structures with different space groups and cell parameters. In this work, we try to solve this problem by designing a dynamic correlation coefficient. It is shown that the dynamic correlation coefficient works for a variety of space groups and cell parameters in the global search of rotation function. We also introduce two new matching scores: relative entropy and mean-square-residues. Last but not least, we discussed a valid method for the optimization of the adjustable parameters for matching vectors.     

Measurement of the structure coefficient of refractive index fluctuations in a turbulent premixed butane-air flame by means of a laser-based interferometer technique

With a view to measuring the structure coefficient of refractive index fluctuations in a turbulent premixed butane-air flame, a thin laser beam is sent into the flame perpendicular to the flow direction. The laser beam generally undergoes fluctuations of direction, phase, and amplitude. Only the random deflections of the laser beam may be taken into account. After having traversed the flame, the perturbed laser beam enters into an interferometric system. Materials and experimental procedure are described. In the unperturbed interference pattern, the zones only sensitive to fluctuations of the angle-of-arrival of the laser beam are detected. From the random displacements of the central bright fringe, the structure coefficient of refractive index fluctuations in the flame is measured. To prove that the method of measurement is satisfactory, the result obtained is applied for computing the power spectral density of the angle-of-arrival of the laser beam from the formula of correlations of the laser beam deflection angles which we have demonstrated in previous works. This computed power spectral density is compared to that measured from the effective position of the detector. A good agreement is observed between the two results.     

Photonic generation of ultrawideband signals by exploiting gain saturation of dark pump pulse with double undershoots in a highly nonlinear fiber

We have proposed and theoretically demonstrated an alternative photonic scheme to generate ultrawideband (UWB) doublet pulses based on gain saturation effect in one piece of highly nonlinear fiber (HNLF). A flexible format swap between UWB doublet and monocycle pulses can be successfully realized by properly tuning the optical tunable delay line (ODL). Moreover, the key parameters for UWB pulse, including the center frequency (Fc), 10 dB bandwidth (BW_10dB), and fractional bandwidth (FBW), are also investigated with Fc being Einstein shift when the doublet pulse transforms into the monocycle pulse. Finally, our proposed scheme exhibits good performance that the obtained UWB pulse can have a FBW of > 100% at the Fc of ~ 7 GHz and UWB-over-fiber technology is also implemented without dispersion management.     

Determination of aerosol extinction coefficient and mass extinction efficiency by DOAS with a flashlight source

With the method of differential optical absorption spectroscopy （DOAS）, average concentrations of aerosol particles along light path were measured with a flashlight source in Chiba area during the period of one month. The optical thickness at 550 nm is compared with the concentration of ground-measured suspended particulate matter （SPM）. Good correlations are found between the DOAS and SPM data, leading to the determination of the aerosol mass extinction efficiency （MEE） to be possible in the lower troposphere. The average MEE value is about 7.6m^2.g^-1 , and the parameter exhibits a good correlation with the particle size as determined from the wavelength dependence of the DOAS signal intensity.     

Persistence length for a model semirigid polyelectrolyte as seen by small angle neutron scattering: a relevant variation of the lower bound with ionic strength

In a SANS experiment, we have directly determined for the first time the conformation of hyaluronan, a model semirigid polyelectrolyte. At high ionic strength, this is completely possible, where the scattered intensity crosses over (when decreasing q) from a q(-1) rod variation to a q(-2) and, where fitting to the "wormlike" chain model gives the backbone, intrinsic, persistence length: L0 = 86.5 A. At low ionic strength, we can safely check that the measured persistence length appears increased by at least the amount predicted by Odijk for the electrostatic contribution, L(e) (approximately kappa(-2), square of the Debye screening length). However, the intensity at the lowest q is not only due to the single chain, since it crosses over from a q(-1) to a q(-4) variation, characteristic of polymer associations.