Ferromagnetic resonance in Sr doped rare earth orthocobaltites, Ln1−xSrxCoO3†

FMR measurements have been carried out on several members of the Ln_1−xSrxCoO₃ (Ln = Rare earth) system. The results show that g_eff in these systems is around 1.25 independent of x as well as the rare earth ion. It is suggested that this unusual value of g_eff is due to the localized intermediate-spin Co³⁺ ions (t⁵_2g e¹_g) located at the top of the π^* band.     

Steady state and transient fluorescence studies of CaF2: Dy single crystals

The steady state and transient fluorescence spectra of CaF₂: Dy³⁺ have been studied using Ar⁺ and N₂ lasers in the temperature range 77–673 K and in the wavelength region 4500–9000 Å. The spectra show the presence of two types of centers (type A and type B) with decay times of 1.3 and 3.5 ms. The observed spectrum is mostly due to type A centers. Three new groups of fluorescence ⁴F_9/2−⁶H_11/2, ⁴F_9/2−(⁶H_9/2, ⁶F_11/2) and ⁴F_9/2−(⁶H_7/2, ⁶F_9/2) have been observed for type A centers, and a tentative assignment of the positions of the Stark levels of ⁶H_11/2, (⁶H_9/2, ⁶F_11/2) and (⁶H_7/2, ⁶F_9/2) has been made. The change in the intensity of the transitions with temperature and excitation wavelength are discussed.     

Majumdar-Papapetrou class of nonstatic cylindrically symmetric Brans-Dicke-Maxwell fields

We have obtained relations between certain components of the metric and the electromagnetic potentials for source-free Brans-Dicke-Maxwell fields described by a nonstatic cylindrically symmetric Einstein-Rosen metric. These are important, in the sense that they generate a class of solutions that in a way can be said to belong to the class generated by similar relations obtained by Majumdar [1] and Papapetrou [2] for generalized static Einstein-Maxwell fields. The relations have further been used to reduce the B-D Maxwell equations to B-D vacuum equations and vice versa.     

Indentation studies of alkali halides at elevated temperatures

The hardness of NaCl and KCl crystals has been estimated from the lengths of dislocation rosette formed around indentation at various temperatures up to 400°C. The hardness decreases with increasing temperature. This is due to the softening of the crystals at elevated temperatures which results in the easy movement of dislocations. The results are discussed using a few available relations which connect hardness to temperature. Arms of indentation dislocation rosette are well defined up to 300°C but around 400°C the rosette pattern is spread over a circular region. A possible mechanism is discussed.     

Thermal neutron polarisation

The basic principle for the production of polarised thermal neutrons is discussed and the choice of various crystal monochromators surveyed. Brief mention of broad-spectrum polarisers is made. The application of polarised neutrons to the study of magnetisation density distributions in magnetic crystals, the dynamic concept of polarisation, principle and use of polarisation analysis, the neutron spin-echo technique are discussed.     

High pressure transport behaviour of AgI-Ag2O-MoO3 glasses and the cluster model

The effect of pressure on the conductivity of fast ion conducting AgI-Ag₂O-MoO₃ glasses has been investigated down to 150 K. The observed variation of conductivities appears to support the application of cluster model to the ionic glasses. Contribution No. 258 from the Solid State and Structural Chemistry Unit.     

温度/应变/扭曲三参量同时测量低成本传感系统

提出了一种利用布喇格光纤光栅反射光作信号源、高频CO2激光脉冲写入的长周期光纤光栅和超周期光纤光栅作传感器实现温度、应变和扭曲同时测量的全光栅型低成本强度解调传感方案.文中利用长周期光纤光栅边缘滤波效应实现了温度、应变和扭曲传感信号的实时解调.实验结果表明,其温度和应变的测量灵敏度分别为－0.211 dB/℃和－0.012 dB/10με;而扭曲率的测量灵敏度为0.4394 dB/(rad·m－1),是该法写入普通LPFG的4倍以上.     

Measurement of storage time, estimation of ion number and study of absorption line profile in a Paul trap

Europium (Eu⁺) ions were confined in a Paul trap and detected by non-destructive method. Storage time of Eu⁺ ions achieved in vacuum was improved by orders of magnitude employing buffer gas cooling. The experimentally detected signal was fitted to the ion response signal and the total number of ions trapped was estimated. It is found that the peak signal amplitude as well as the product of FWHM and the peak signal amplitude is proportional to the total number of trapped ions. The trapped ion secular frequency was swept at different rates and its effect on the absorption line profile was studied both experimentally and theoretically.     

长距离分布式光纤传感技术研究进展

分布式光纤传感技术是光纤传感领域的重要组成部分,具有以下突出优势:无需在光纤上制作传感器,传感光纤集传感与传输于一体,可实现远距离、大范围的传感与组网;可连续感知光纤传输路径上每一点的温度、应变、振动等物理参量的空间分布和变化信息,单根光纤上能获得多达数万点的传感信息.由于在长距离连续传感方面具有不可替代的优势,分布式光纤传感技术在周界安防、石油电力、大型结构等领域的安全监控方面具有非常广阔的应用前景.本文主要介绍电子科技大学光纤传感与器件研究团队在长距离分布式光纤静(布里渊光时域分析仪)、动(相位敏感型光时域反射仪)态参量传感技术取得的研究进展,包括基础与应用研究两个方面.