偏置磁场强度对交叉线圈式扭转导波换能器换能效率的影响

交叉线圈式带状磁致伸缩扭转导波换能器偏置磁场强度直接影响换能器换能效率,为获得较佳的检测效果,需要研究偏置磁场强度对该换能器换能效率的影响。首先,从磁致伸缩效应出发,分析交叉线圈式带状磁致伸缩扭转导波换能器的工作原理。其次,在模态验证实验的基础上,分别对激励和接收换能器换能过程中偏置磁场的作用进行研究。实验结果表明随着偏置磁场强度的增大激励端和接收端换能器换能效率均先增大后减小。最后进行缺陷检测实验,当激励端和接收端均选择最佳换能区域时,对比模态验证实验,缺陷信号明显增大。该研究结果可为换能器的现场应用提供技术支持。     

Effect of magnetic field on a spin-peierls cuprate,CuGeO3

We measured the static magnetization of polycrystalline CuGeO₃, which exhibits the spineierls transition around 14.0 K in the absence of the magnetic field. The field dependence of the magnetization below 14.0 K shows a characteristic nonlinear process associated with a phase transition, and phase boundaries between the dimerized phases and other phases were obtained. The magnetic phase diagram qualitatively agrees with that of an organic spin-Peierls material. The phase transition is of first order below 10.0 K, and of second order above 10.0 K. Above 10.0 K, the critical field decreases from 13 to 0 T with increasing temperature. On the other hand, it is nearly independent of temperature below 10.0 K.     

Comparative study on structural transformation of low-melting pure Al and high-melting stainless steel under external pulsed magnetic field

A comparative study on the structural transformation of low-melting pure Al and high-melting 1Cr18Ni9Ti stainless steel under external pulsed magnetic field was carried out. The results showed that totally equiaxed grains were produced for pure Al, however, only thin columnar grains were generated for stainless steel even treated with higher magnetic intensity. It is deemed that grain refinement can be attributed to the heterogeneous nucleus created on the mould wall as well as their falling by the oscillating resulting from the magnetic field. In contrast, a dense chilling layer was generated at the primary solidification stage of the stainless steel due to the large temperature gradient between the high temperature melt and the mould and accordingly the nucleus falling was prevented. Therefore, only dendrites refinement possibly occurred.     

磁场对聚苯胺结构、掺杂行为及热稳定性的影响

在恒定磁场(0.8T) 和无磁场环境下,采用化学氧化聚合法合成了分别用磺基水杨酸(SSA)、对甲基苯磺酸(TSA)以及用十二烷基苯磺钠/盐酸(SDBS HCl)掺杂的聚苯胺盐,并采用X射线光电子能谱(XPS)、傅立叶红外光谱(FT-IR)、X粉末衍射(XRD),热重分析(TGA)等手段研究了磁场对聚苯胺结构、掺杂行为及热稳定性的影响.结果表明在合成聚苯胺的过程中,作为表面活性剂的十二烷基苯磺酸钠在无机酸存在条件下转变成十二烷基苯磺酸并与无机酸共同掺杂进入聚苯胺链;磁场环境下合成的聚苯胺盐比无磁场下合成的聚苯胺盐的链更加规整,热稳定性更好,掺杂程度以及结晶性能也有所提高;从红外光谱分析中可知,磁场取向作用使分子链更加伸展,分子链离域程度更大,但磁场没有明显地改变聚苯胺的基本单元结构.     

The effect of the strength and direction of magnetic field on the assembly of magnetic nanoparticles into higher structures

The self-assembly of magnetic nanoparticles into higher-order organizations upon external magnetic stimulation has critical importance for the fabrication of discrete microstructures. In this study, the tuning of self-assembly behavior of magnetic Fe3O4 nanoparticles (MNPs), with an average size of 6 nm, under the enhanced magnetic force upon changing the applied field strength and direction is explored. Upon evaporation of the solvent where the MNPs are suspended, formation of particular micrometer sized structures is achieved with a surface constructed from sub-micrometer size magnetic beads in between the applied magnetic field and MNPs. In this study, three different surfaces fabricated using sub-micrometer size magnetic beads in between the applied magnetic field and MNPs are used and the effect of the template pattern, applied field strength and direction are explored.     

Comparative study on strength,sorptivity, and chloride ingress characteristics of air-cured and water-cured concretes modified with metakaolin

This paper reports an investigation in which the performance of plain and metakaolin (MK)-modified concretes were studied under two different curing regimes. The purpose of this study is to evaluate the effectiveness of MK in enhancing the strength and permeation properties of concrete. MK was used to replace 0–20% of Portland cement by weight in concrete with two water-binder (w/b) ratios of 0.35 and 0.55. The change in compressive strength, sorptivity, and chloride ingress with age at all cement replacement levels under both air and water curing are compared with those of the control concrete. The results indicated that the inclusion of MK greatly reduced sorptivity and chloride permeability of concrete in varying magnitudes, depending mainly on replacement level of MK, w/b ratio, curing condition, and chloride exposure period. It was found that under the inadequate or poor curing, MK-modified concretes suffered a more severe loss of compressive strength and permeability-related durability than the plain concretes.     

Effect of magnetic field on a spin-peierls cuprate, CuGeO3

We measured the static magnetization of polycrystalline CuGeO₃, which exhibits the spineierls transition around 14.0 K in the absence of the magnetic field. The field dependence of the magnetization below 14.0 K shows a characteristic nonlinear process associated with a phase transition, and phase boundaries between the dimerized phases and other phases were obtained. The magnetic phase diagram qualitatively agrees with that of an organic spin-Peierls material. The phase transition is of first order below 10.0 K, and of second order above 10.0 K. Above 10.0 K, the critical field decreases from 13 to 0 T with increasing temperature. On the other hand, it is nearly independent of temperature below 10.0 K.     

Effect of magnetic properties of a composite superconductor on losses in variable magnetic field. Part 2: Experiment

The theory developed in Part 1 of this paper is compared with the results of experimental measurements of losses in multi-filamentary superconductors in a transverse field. The losses have been measured for different magnetic field variation patterns (sinusoidal, triangular, trapezoidal, single pulses). The numerical results obtained with the aid of the theory are in fairly good agreement with the experimental data. In the majority of the actual cases, analytical expressions for losses can be used.     

外磁场对Ni-Mn-Ga磁性形状记忆合金相变应变及显微组织的影响

研究了外磁场对Ni52Mn24.6Ga23.4(%,原子分数)单晶马氏体相变及其相变应变的影响,并对磁场增强相变应变的微观机制进行了探讨。研究结果表明无外加磁场时,NiMnGa合金发生马氏体相变时可产生约0.3%的收缩形变,沿单晶[100]方向施加外磁场,其相变应变随磁场的增加而呈近线性增加。当外磁场强度为6.37×105A/m时,应变量达到最大值(3.5%)。磁场作用下冷却形成的马氏体虽然孪晶亚结构不变,但自协作组态消失,并伴随有孪晶板条的增厚。磁场对马氏体相变应变的增强效应来自于磁场作用下的马氏体变体的择优取向。     

Effect of annealing in external magnetic field on the microstructure and magnetic properties of FePt films

We have studied the influence of annealing in an external magnetic field on the microstructure and magnetic properties of a multilayer Si/Fe(2 nm)/Fe₅₀Pt₅₀(20 nm)/Pt(2 nm) structure synthesized by means of sequential RF magnetron sputtering of the components. The magnetic field was oriented perpendicular to layers of the structure. It is established that annealing in the external magnetic field leads to the formation of predominant (001) texture in the multilayer structure with L1₀-FePt phase. Thus, a method of obtaining multilayer structures based on FePt films required for the perpendicular magnetic recording has been developed.     

Studying the effect of direction and strength of magnetic field on fluidization of nanoparticles by recurrence analysis

Effect of the intensity and direction of the magnetic field was studied on fluidization of titanium oxide nanoparticles (anatase phase) mixed with ferromagnetic Iron (III) oxide nanoparticles using the recurrence analysis. The bed expansion and visual observation revealed that these particles operate in the ABF regime in all cases. Minimum fluidization velocities were obtained through the standard deviation of pressure fluctuations. Agglomerates samples were taken to study the effect of the magnetic field on the size of agglomerates. It was observed that at low field strength, the vibration has a major effect on fluidization than the magnetic force. At field strengths less than 400 Gauss, the vibration of solenoid improved the quality of fluidization by decreasing the size of agglomerate and minimum fluidization velocity, regardless of the field direction. At field strengths greater than 400 Gauss, the upward direction increases the interaction of agglomerate which results in a stochastic pattern of fluidization and lower ABF characteristics. At high magnetic field strengths, the effect of field direction becomes more noticeable. At high field strengths, the downward field results in less movement of the bed material and resistance against fluidization as well as the formation of larger bubbles and their deterministic effect on the bed.     

Comparative study of conductometric glucose biosensor based on gold and on magnetic nanoparticles

The aim of this study was to show the feasibility and the performances of nanoparticle biosensing. A glucose conductometric biosensor was developed using two types of nanoparticles (gold and magnetic), glucose oxidase (GOD) being adsorbed on PAH (poly(allylamine hydrochloride)) modified nanoparticles, deposited on a planar interdigitated electrode (IDEs). The best sensitivities for glucose detection were obtained with magnetic nanoparticles (70 μM/mM and 3 μM of detection limit) compared to 45 μM/mM and 9 μM with gold nanoparticles and 30 μM/mM and 50 μM with GOD directly cross-linked on IDEs. When stored in phosphate buffer (20 mM, pH 7.3) at 4 °C, the biosensor showed good stability for more than 12 days.     

Effects of high magnetic field strength and direction on pearlite formation in Fe–0.12%C steel

The effect of a magnetic field on the formation of pearlite in a Fe–0.12%C steel was investigated. The results show that pearlite colonies elongate and align along the field direction, and that this tendency increases with increasing magnetic field strength. The possible preferential nucleation of ferrite between existing ferrite grains aligned along field direction at the later stage of proeutectoid transformation promotes carbon diffusion into the austenite areas between the ferrite chains accounts for the phenomena. Moreover, the field effect is dependent on the specimen position with respect to the field direction.     

Effect of a magnetic field on a liquid crystal film and study of the frederiks transition using molecular dynamics

We discuss the results of a molecular-dynamics study of the lattice model of a liquid crystal.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 3, pp. 387–394, March, 1987.     

Effect of magnetic field and temperature on the voltage-current characteristics of YBCO superconductor

Voltage-current characteristics of YBCO superconductor was studied under magnetic field up to 0.4 T at different temperatures below T_c. The critical temperature decreases and the transition width broadens under magnetic field. V-I data below T_c were fitted to a power law expression V I^(T,B) in which (T,B) is found to decrease with increase of magnetic field and temperature, gradually approaching unity as T approaches T_c, being independent of magnetic field. Similarly, (T,B) approaches unity as magnetic field increases being independent of temperature.     

Effect of magnetic field treated water on mortar and concrete containing fly ash

This research investigates the workability and compressive strength of mortar and concrete, which were mixed with magnetic field treated water (MFTW) and contained fly ash. MFTW was obtained by passing tap water through a magnetic field. Test variables included the magnetic strength of water, fly ash content in place of cement, water-to-cementitious material ratio (W/CM) and curing age.Results show that the compressive strength of mortar samples mixed with MFTW is higher than those prepared with tap water. The best compressive strength increase of concrete is achieved when the magnetic strength of treated water is of 0.8 and 1.2 T. The compressive strength increase of concrete prepared with MFTW is more significant at early age.     

Effect of throughflow and magnetic field on Bénard convection in micropolar fluids

Summary The effect of throughflow and magnetic field on the onset of Bénard convection in a horizontal layer of micropolar fluid permeated between two rigid, isothermal and micro-rotation free boundaries is studied. The determination of the critical Rayleigh number entails in solving the eigenvalue problem numerically for which the single-term Galerkin method is employed. It is established that both stabilizing and destabilizing factors can be enhanced by throughflow.