Anomalous magnetic susceptibility and inhomogeneous magnetic state in lanthanum strontium manganites

Anomalous magnetic susceptibility χ has been observed in mono-and polycrystalline (ceramic) samples of lanthanum strontium manganites. The oscillations of χ observed for single crystal samples in the vicinity of the Curie temperature (and in the paramagnetic region) are explained by the existence of magnetic clusters. The appearance of susceptibility oscillations in ceramic samples is attributed to the formation of magnetic clusters, which may occur both in grains (at the interface between ferro-and antiferromagnetic phases) and at the grain boundaries.     

Semi-empirical modelling of the di-interstitial defect in silicon

Previous infrared spectroscopy studies of the defect spectrum of neutron irradiated Czochralski grown silicon (Cz-Si) revealed a band at 533 cm^?1, which disappears from the spectra at ~170 °C and exhibits a similar thermal stability with the Si-P6 Electron paramagnetic resonance (EPR) spectrum correlated with the di-interstitial defect. The proposed structural model for this defect consists of two self-interstitial atoms located symmetrically around a lattice site Si atom. The calculations reveal that the previously suggested structure of the Si-P6 defect has a vibrational frequency at about 513 cm^?1, which is close to the experimental value of 533 cm^?1. The modeling results indicate that the 533 cm^?1 infrared band originates from the same structure as that of the Si-P6 EPR spectrum.     

Nuclear magnetic resonance-based current-voltage source

A solenoid geometry for producing magnetic fields is introduced. A 1-A current has been stabilized using nuclear magnetic resonance techniques. A pair of tandem solenoids produces two uniform magnetic fields in opposite directions, and these fields are not affected by external magnetic shielding. The current and background field are controlled to within 0.1 ppm over an 8-h period     

Multiscale modelling of defect kinetics in irradiated iron.

Changes in microstructure and mechanical properties of nuclear materials are governed by the kinetics of defects produced by irradiation. The population of vacancies, interstitials and their clusters can however be followed only indirectly, for example by macroscopic resistivity measurements. The information on the mobility, recombination, clustering or dissociation of defects provided by such experiments is both extremely rich and difficult to interpret. By combining ab initio and kinetic Monte Carlo methods, we successfully reproduce the abrupt resistivity changes-so-called recovery stages-observed upon annealing at increasing temperatures after electron irradiation in alpha-iron. New features in the mechanisms responsible for these stages are revealed. We show that di-vacancies and tri-interstitials contribute to the stages attributed to mono-vacancy and di-interstitial migration respectively. We also predict the effect of the unexpected low migration barriers found for tri- and quadri-vacancies, and discuss the challenging questions raised by the mobility of larger defect clusters.     

Anomalous magnetic properties of mechanically milled cobalt oxide nanoparticles

Defect induced magnetic properties of CoO nanoparticles produced via mechanical ball milling have been assessed by detailed magnetic measurements. A progressive decrease in the particle size and a concomitant increase in the induced strain have been observed with the milling times. The mechanically milled nanoparticles of CoO exhibit anomalous magnetic properties such as FM hysteresis when compared with the unmilled CoO sample. The presence of weak ferromagnetism, with a highest value of magnetization of 0.532 emu/g at 10 K in the 100 h milled sample, is attributed to the uncompensated surface spins resulting from induced surface defects via mechanical milling. The ZFC coercive force, measured at 10 K, increases with milling time reaching a maximum value of 1066 Oe for the 100 h milled sample. The temperature dependent field-cooled (FC) and zero-field-cooled (ZFC) magnetic measurements indicate a presence of an exchange bias field arising from uncompensated moments generated by mechanical strain and the antiferromagnetic (AFM) core. The exchange bias field measured at 10 K reaches a value 210 Oe for the 50 h milled sample and decreases upon prolonged milling. The exchange bias field vanishes at a temperature approximately 200 K, a temperature much lower than the Neel temperature of CoO (TN approximately 291 K). The observed anomalous magnetic behavior of CoO could be interpreted in terms of the exchanged bias FM-AFM model.     

阳极磁屏蔽霍尔离子源磁场的数值模拟

为了提高离子束电流和离子束能量,进一步增加霍尔离子源的效率,对霍尔离子源阳极进行磁屏蔽,达到优化磁场位形,增强磁场对放电等离子体的约束。由磁场的数值模拟结果可知:阳极磁屏蔽后,有明显凸向阳极表面的弯曲磁场线,并且提高了磁镜磁场的磁镜比;大的正梯度磁场的存在,增强了磁场的径向分量,相对减弱了放电等离子体的震荡;不仅保留原有鞍形场的作用,而且还充分发挥了另外两个鞍形场的优势。最后通过实验结果和数值模拟结果的比较,验证了此数值模拟结果的正确性。     

A magnetic field source system for magnetic refrigeration and its interaction with magnetocaloric material

The magnetic field source system constitutes an important component of magnetic refrigeration. A specific methodology for its' dimensioning is proposed in this paper. It is based on analytical calculation models and takes into account the geometry of the system, the magnetic properties of the magnetocaloric material and the magnetothermal cycle (direct or active magnetic regenerative refrigeration). The analytical calculation of the field is first developed and applied to usual permanent magnet-based field sources with and without soft magnetic materials. Then the forces generated by the interaction between the field and the magnetocaloric effect material are analytically evaluated considering the real field distribution. All calculations are validated thanks to two- or three-dimensional finite element method simulations.     

Ion source with magnetic field for time-of-flight mass spectrometry

A new ion source for the time-of-flight mass spectrometer (TOFMS) with electron-impact ionization and built-in permanent magnet for electron-beam focusing is described. The focusing of electrons in a homogeneous field leads to an increase in the resolving power and sensitivity of the TOFMS. A spectrometer with the proposed source can operate at electron energies within the 7–100-eV range. The method of suppressing spurious lines in the mass spectrum is described, which is based on a decrease in the energy of ionizing electrons.     

Reference magnetic field source based on a four-wire line

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 51–52, May, 1990.     

小型磁偏转质谱计离子源设计与验证

离子源是质谱计的"心脏",其很大程度上直接决定了质谱计的灵敏度、分辨率等主要性能指标,因此需要对其结构和供配电关系等精心设计。针对空间环境探测应用目标,开展了小型磁偏转质谱计离子源的设计、仿真分析和试验测试。阐述了离子源的设计结构、供配电关系以及仿真分析和试验验证情况。通过分析得到了电压参数对离子束引出能力和束发散角的影响结果,通过试验验证了离子源的主要性能指标和抗力学环境能力满足设计要求。     

S—枪磁控溅射源的研制及其特性

Ｓ－枪是一种先进的真空溅射镀膜器件，可用于进行多种真空镀膜工艺。详细介绍了研制Ｓ－枪的结构状况及其工作特性。     

Diagnostics of NV defect structure orientation in diamond using optically detected magnetic resonance with a modulated magnetic field

Technical Physics Letters - A method for determining the orientation of nitrogen-vacancy (NV) defect structure orientation in diamond crystals and nanodiamonds is proposed, which is based on the...     

A comparative study of explicit and implicit modelling of subsegmental speaker-specific excitation source information

In this paper, the explicit and implicit modelling of the subsegmental excitation information are experimentally compared. For explicit modelling, the static and dynamic values of the standard Liljencrants–Fant (LF) parameters that model the glottal flow derivative (GFD) are used. A simplified approximation method is proposed to compute these LF parameters by locating the glottal closing and opening instants. The proposed approach significantly reduces the computation needed to implement the LF model. For implicit modelling, linear prediction (LP) residual samples considered in blocks of 5 ms with shift of 2.5 ms are used. Different speaker recognition studies are performed using NIST-99 and NIST-03 databases. In case of speaker identification, the implicit modelling provides significantly better performance compared to explicit modelling. Alternatively, the explicit modelling seem to be providing better performance in case of speaker verification. This indicates that explicit modelling seem to have relatively less intra and inter-speaker variability. The implicit modelling on the other hand, has more intra and inter-speaker variability. What is desirable is less intra and more inter-speaker variability. Therefore, for speaker verification task explicit modelling may be used and for speaker identification task implicit modelling may be used. Further, for both speaker identification and verification tasks the explicit modelling provides relatively more complimentary information to the state-of-the-art vocal tract features. The contribution of the explicit features is relatively more robust against noise. We suggest that the explicit approach can be used to model the subsegmental excitation information for speaker recognition.     

Anomalous phenomena

The laws of large departures from equilibrium and the laws governing structural transitions indicated previously by the author are used as the basis for discussing anomalous phenomena. Their main properties are described, a classification is put forward, a simple model is proposed to describe an anomalous phenomenon, and several families of possible phenomena are indicated. Pis’ma Zh. Tekh. Fiz. 25, 57–63 (April 12, 1999)     

端部霍尔离子源的磁场设计与数值模拟

首先简单介绍了用于离子束辅助沉积的端部霍尔离子源的工作原理，然后分析了其性能对磁场的要求，据此介绍了磁路组件的设计。最后,采用ANSYS大型有限元分析软件对一个条形的端部霍尔离子源的磁场进行了模拟计算，并与实验结果进行了比较，获得了满意的结果。通过对模拟结果的分析，获得了对该离子源磁场分布的直观深入的认识，为具体的端部霍尔离子源的改进设计提供了理论指导。     

Electric and magnetic combined source integral equations for electromagnetic transmission problems

Various combined source integral equation (CSIE) formulations are developed for the analysis of electromagnetic scattering by three-dimensional arbitrarily shaped homogeneous penetrable objects. The considered CSIE formulations include the classical “electric” CSIE proposed by Mautz and Harrington in 1979, and its dual “magnetic” CSIE as well as mixed “electric–magnetic” and “magnetic–electric” CSIE formulations. Novel discretization schemes by utilizing the primary (Rao–Wilton–Glisson, RWG) and the dual (Buffa–Christiansen, BC) functions are applied to convert the integral equations into matrix equations. These schemes avoid the numerical problems that would appear if the CSIE formulations were discretized with the conventional Galerkin method using the RWG functions only.