Analysis of the temperature-induced transition to current self-oscillations in doped GaAs/AlAs superlattices

We observed the decrease of the hysteresis effect and the transition from the stable to the dynamic domain regime in doped superlattices with increasing temperature. The current-voltage characteristics and the behaviours of the domain boundary are dominated by the temperature-dependent lineshape of the electric field dependence of the drift velocity (V(F)), As the peak-valley ratio in the V(F) curve decreases with increasing temperature, the hysteresis will diminish and temporal current self-oscillations will occur. The simulated calculation, which takes the difference in V(F) curves into consideration, gives a good agreement with the experimental results.

Formation and magnetic properties of Fe16N2 films prepared by ion-beam-assisted deposition

Fe-N films containing the Fe16N2 phase were prepared in a high-vacuum system of ion-beam-assisted deposition (IBAD). The composition and structure of the films were analysed by Auger electron spectroscopy (AES) and X-ray diffraction (XRD), respectively. Magnetic properties of the films were measured by a vibrating sample magnetometer (VSM). The phase composition of Fe-N films depend sensitively on the N/Fe atomic arrival ratio and the deposition temperature. An Fe16N2 film was deposited successfully on a GaAs (1 0 0) substrate by IBAD at a N/Fe atomic arrival ratio of 0.12. The gram-saturation magnetic moment of the Fe16N2 film obtained is 237 emu/g at room temperature, the possible cause has been analysed and discussed. Hysteresis loops of Fe16N2 have been measured, the coercive force H-c is about 120 Oe, which is much larger than the value for Fe, this means the Fe16N2 sample exhibits a large uniaxial magnetocrystalline anisotropy. (C) 1998 Elsevier Science B.V. All rights reserved.

Geomagnetic paleointensity dating of South China Sea sediments for the last 130 kyr

Relative paleointensity records from the northern South China Sea, northwest Pacific Ocean were studied in two gravity piston cores. Continuous mineral magnetic and paleomagnetic measurements were made using discrete sediment samples. Detailed rock magnetic parameters, such as thermomagnetic and high-field hysteresis data, indicate that pseudo-single domain magnetite in a narrow range of grain-size and concentration is the main contributor to the remanent magnetization. The uniform magnetic mineralogy meets the commonly accepted criteria for establishing relative paleointensity records. The relative paleointensity (RPI) curves were constructed by normalizing the natural remanent magnetization (NRM) with isothermal remanent magnetization (IRM), both in the 20-60 mT demagnetization state. Dating constraints have been provided by radiocarbon ages in the upper 400 cm of both cores. Furthermore, we have correlated our paleointensity records with NAPIS-75, S.Atlantic-1089, Sint-200 and NOPAPIS-250 to determine the chronological RPI framework for the South China Sea (SCS-PIS). Although some temporal offsets of paleointensity features between the different records have been recognized, their similar shape suggests that relative paleointensity on the 10(3)-10(4) year scale is globally coherent and can provide an age framework for sediments independent of delta O-18 ages.

Ferromagnetic MnSb Films Consisting of Nanorods and Nanoleaves

Ferromagnetic MnSb films were synthesized on Si wafers by physical vapor deposition. X-ray diffraction revealed that the films primarily consisted of MnSb alloy. Nanorods and nanoleaves were observed in the MnSb films by field-emission scanning electron microscopy. These nanorods had an average diameter of 20nm and a length of up to hundreds of nanometers. The nanoleaves had a width and thickness of about 100 and 20nm, respectively. Magnetic hysteresis loops were measured by an alternative gradient magnetometer, and the loops showed strong geometrical anisotropy.

Formation and magnetic properties of Fe16N2 films prepared by ion-beam-assisted deposition

Fe-N films containing the Fe16N2 phase were prepared in a high-vacuum system of ion-beam-assisted deposition (IBAD). The composition and structure of the films were analysed by Auger electron spectroscopy (AES) and X-ray diffraction (XRD), respectively. Magnetic properties of the films were measured by a vibrating sample magnetometer (VSM). The phase composition of Fe-N films depend sensitively on the N/Fe atomic arrival ratio and the deposition temperature. An Fe16N2 film was deposited successfully on a GaAs (1 0 0) substrate by IBAD at a N/Fe atomic arrival ratio of 0.12. The gram-saturation magnetic moment of the Fe16N2 film obtained is 237 emu/g at room temperature, the possible cause has been analysed and discussed. Hysteresis loops of Fe16N2 have been measured, the coercive force H-c is about 120 Oe, which is much larger than the value for Fe, this means the Fe16N2 sample exhibits a large uniaxial magnetocrystalline anisotropy. (C) 1998 Elsevier Science B.V. All rights reserved.

Molecular-dynamics investigation on polarization retention of barium titanate nanofilm arising from ordered oxygen vacancy

Molecular-dynamics simulations have been carried out to investigate the electric hysteresis of barium titanate nanofilm containing oxygen vacancy ordering array parallel to the {101} crystal plane. The results obtained show a significant weakening of polarization retention from non-zero value to zero as the size of the array was reduced to a critical level, which was attributed to the formation and motion of head-to-head domain wall structure under external field loading process. By comparing with materials containing isolated oxygen vacancies, it was found that the zero retention was due to the oxygen vacancy ordering array rather than to the concentration of oxygen vacancy. Copyright (C) EPLA, 2010

兰州重离子加速器深层治癌扫描电源研究与设计

This paper describes the technique targets and operation principle of the scanning power supply for the deep tumor therapy facility with heavy ions in Cooler-Storage-Ring of the Heavy Ion Research Facility in Lanzhou(HIRFL-CSR).To ensure the specified accuracy of the current,the hysteresis loop control strategy was adopted,and tracking error was constrained in the specified tolerance.One prototype was designed and installed.And the simulation results and test results were listed in the paper.The results sho...中文摘要：阐述了用于兰州重离子深层治癌装置的扫描电源的技术指标和工作原理,为保证该电源输出电流的精度,采用滞环控制策略,将跟踪误差限制在设计要求的误差范围内。研制了1台扫描电源样机,并给出了电路仿真和测试结果。测试结果显示各项指标均达到了设计要求,表明所选电路结构和滞环控制方案是切实可行的。

Loess magnetic properties in the Ili Basin and their correlation with the Chinese Loess Plateau

     Over the past two decades, magnetoclimatological studies of loess-paleosol sequences in the Chinese Loess Plateau (CLP) have made outstanding achievements, which greatly promote the understanding of East Asian paleomonsoon evolution, inland aridification of Asia, and past global climate changes. Loess magnetic properties of the CLP have been well studied. In contrast, loess magnetic properties from outside the CLP in China have not been fully understood. We have little knowledge about the magnetic properties of loess in the Ili Basin, an intermontane depression of the Tianshan (or Tien Shan) Mountains. Here, we present the results of rock magnetic measurements of the Ili loess including mass magnetic susceptibility (χ) and anhysteretic remanent magnetization (ARM), high/low temperature dependence of susceptibility (TDS) and hysteresis, as well as X-ray diffraction (XRD) for mineral analysis. Based on the comparison with loess-paleosol sequences in the CLP (hereafter referred to as the Chinese loess), we discuss the possible magnetic susceptibility enhancement mechanism of the Ili loess. The results show that 1) the total magnetic mineral concentration of the Ili loess is far lower than that of the Chinese loess, though they have similar magnetic mineral compositions. The ferrimagnetic minerals in the Ili loess are magnetite and maghemite, and the antiferromagnetic mineral is hematite; XRD analysis also identifies the presence of ilmenite. The ratio of maghemite is lower in the Ili loess than in the Chinese loess, but the ratios of magnetite and hematite are higher in the Ili loess than in the Chinese loess. 2) The granularity of magnetic minerals in the Ili loess, dominated by pseudo-single domain (PSD) and multi-domain (MD) grains, is generally much coarser than that of the Chinese loess. Ultrafine pedogenically-produced magnetic grains have a very limited contribution to the susceptibility enhancement. Rather, PSD and MD particles of magnetite and maghemite are the main contributors to the enhancement of susceptibility in the Ili loess. 3) The susceptibility enhancement mechanism for the Ili loess is complicated and superimposes both a wind velocity/vigor model (Alaskan or Siberian model) and the in situ ultrafine grain pedogenic model; the former might play an important role in the Ili loess. 4) Magnetic susceptibility enhancements of the Ili loess are related not only to the eolian input of the source area, but also to the local climate, landform, and geological background. Therefore, great care should be taken when reconstructing paleoclimate using magnetic susceptibility data from the Ili loess.

Structural analysis of nickel doped cobalt ferrite nanoparticles prepared by coprecipitation route

Magnetic nanoparticles of nickel substituted cobalt ferrite (NixCo1-xFe2O4:0 <= x <= 1) have been synthesized by co-precipitation route. Particles size as estimated by the full width half maximum (FWHM) of the strongest X-ray diffraction (XRD) peak and transmission electron microscopy (TEM) techniques was found in the range 18-28 +/- 4 nm. Energy dispersive X-ray (EDX) analysis confirms the presence of Co, Ni, Fe and oxygen as well as the desired phases in the prepared nanoparticles. The selective area electron diffraction (SAED) analysis confirms the crystalline nature of the prepared nanoparticles. Data collected from the magnetization hysteresis loops of the samples show that the prepared nanoparticles are highly magnetic at room temperature. Both coercivity and saturation magnetization of the samples were found to decrease linearly with increasing Ni-concentration in cobalt ferrite. Superparamagnetic blocking temperature as determined from the zero field cooled (ZFC) magnetization curve shows a decreasing trend with increasing Ni-concentration in cobalt ferrite nanoparticles. (C) 2009 Elsevier B.V. All rights reserved.

V5+-doped Bi3.4Yb0.6Ti3O12 fatigue resistant ferroelectric thin films

In this paper, a serial of Bi3.4Yb0.6Ti3-xVxO12 (BYTV) thin film with different V5+ contents were deposited on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD). The crystallized phase and electrical properties of the films were investigated using X-ray diffraction, polarization hysteresis loops, leakage current-voltage, and fatigue test. From our experimental results, it can be found that the ferroelectric properties can be improved greatly using V5+-doped in Bi3.4Yb0.6Ti3O12 (BYT) thin film, compared with the reported BYT thin film. The remanent polarization was enhanced and excellent leakage current characteristic with 10(-11)A at the bias voltage of 4V, which is much lower than the BYT thin film or some reported bismuth layer-structure ferroelectric films. Fatigue test shows that the fabricated films have good anti-fatigue characteristic after 10(10) switching cycles. (c) 2008 Published by Elsevier B.V.

Friction phenomena and phase transition in the underdamped two-dimensional Frenkel-Kontorova model

Locked-to-sliding phase transition has been studied in the driven two-dimensional Frenkel-Kontorova model with the square symmetric substrate potential. It is found that as the driving force increases, the system transfers from the locked state to the sliding state where the motion of particles is in the direction different from that of driving force. With the further increase in driving force, at some critical value, the particles start to move in the direction of driving force. These two critical forces, the static friction or depinning force, and the kinetic friction force for which particles move in the direction of driving force have been analyzed for different system parameters. Different scenarios of phase transitions have been examined and dynamical phases are classified. In the case of zero misfit angle, the analytical expressions for static and kinetic friction force have been obtained.

黄土区考虑滞后作用的坡地水量转化模型

建立了考虑滞后作用的坡地水量转化数学模型，并对模型不同情况下的定解条件进行了分析。利用陕西长武王东沟小流域坡地天然降雨－入渗－产流的实测资料对模型进行了系统检验，结果表明该模型具有较高精度，考虑滞后作用时的模拟值更加接近实测值。在降雨入渗过程中，滞后作用对土壤含水率、入渗速率、径流过程、产流量都有相当大的影响。

黄土区坡地降雨入渗产流过程中的滞后效应

利用黄土高原沟壑区典型小流域坡地天然降雨入渗 -产流的实测资料分别对考虑滞后效应与不考虑滞后效应的情况进行了模拟研究 ,结果表明 :在降雨入渗 -产流过程中 ,滞后效应加快入渗速率 ,减少径流量 ;滞后模型使土壤含水量、产流过程更加接近实测值。由此可见 ,土壤水滞后效应对土壤含水量、入渗速率、产流过程及产流量都有相当大的影响 ,因此在水量转化研究工作中考虑滞后效应的影响是必要的

Ordered magnetic core-manganese oxide shell nanostructures and their application in water treatment

In this paper, we have reported a facile method for the synthesis of ordered magnetic core-manganese oxide shell nanostructures. The process included two steps. First, manganese ferrite nanoparticles were obtained through a solvothermal method. Then, the manganese ferrite nanoparticles were mixed directly with KMnO4 solution without any additional modified procedures of the magnetic cores. It has been found that Mn element in the core can react with KMnO4 to form manganese oxide which acts as a seed for the in-situ growth of manganese oxide shells. This is significant for the controllable fabrication of symmetrical ordered manganese oxide shell structures. The shell thickness can be easily controlled through the reaction time. Transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction and energy-dispersive X-ray spectroscopy have been employed to characterize the products at different reaction time.

Organic Thin-Film Transistor Memory With Nanoparticle Floating Gate

Organic thin-film transistor memory devices were realized by inserting a layer of nanoparticles (such as Ag or CaF2) between two Nylon 6 gate dielectrics as the floating gate. The transistor memories were fabricated on glass substrates by full thermal deposition. The transistors exhibit significant hysteresis behavior in current-voltage characteristics, due to the separated Ag or CaF2 nanoparticle islands that act as charge trap centers. The mechanism of the transistor memory operation was discussed.