Magnetic-field-controlled spin valve and spin memory based on single-molecule magnets

A single-molecule magnet is a long-sought-after nanoscale component because it can enable us to miniaturize nonvolatile memory storage devices.The signature of a single-molecule magnet is switching between two bistable magnetic ground states under an external magnetic field.Based on this feature,we theoretically investigate a magnetic-fieldcontrolled reversible resistance change active at low temperatures in a molecular magnetic tunnel junction,which consists of a single-molecule magnet sandwiched between a ferromagnetic electrode and a normal metal electrode.Our numerical results demonstrate that the molecular magnetism orientation can be manipulated by magnetic fields to be parallel/antiparallel to the ferromagnetic electrode magnetization.Moreover,different magnetic configurations can be“read out”based on different resistance states or different spin polarization parameters in the current spectrum,even in the absence of a magnetic field.Such an external magnetic field-controlled resistance state switching effect is similar to that in traditional spin valve devices.The difference between the two systems is that one of the ferromagnetic layers in the original device has been replaced by a magnetic molecule.This proposed scheme provides the possibility of better control of the spin freedom of electrons in molecular electrical devices,with potential applications in future high-density nonvolatile memory devices.

Influence of Magnetic Reluctances of Magnetic Elements on Servo Valve Torque Motors

The current research of electro-hydraulic servo valves mainly focuses on the vibration, pressure oscillating and source of noise. Unfortunately, literatures relating to the study of the influence of the magnetic reluctances of the magnetic elements are rarely available. This paper aims to analyze the influence of the magnetic reluctances of the magnetic elements on torque motor. Considering these magnetic reluctances ignored in previous literatures, a new mathematical model of servo valve torque motor is developed and proposed based on the fundamental laws of electromagnetism. By using this new mathematical model and the previous models, electromagnetic torque constant and magnetic spring stiffness are evaluated for a given set of torque motor parameters. A computer simulation by using AMESim software is also performed for the same set of torque motor parameters to verify the proposed model. The theoretical results of electromagnetic torque constant and magnetic spring stiffness evaluated by the proposed model render closer agreement with the simulation results than those evaluated by the previous models. In addition, an experimental measurement of the magnetic flux densities in the air-gaps is carried out by using SFL218 servo valve torque motor. Compared with the theoretical results of the magnetic flux densities in the air-gaps evaluated by the previous models, the theoretical results evaluated by the proposed model also show better agreement with the experimental data. The proposed model shows the influence of the magnetic reluctances of the magnetic elements on the servo valve torque motor, and offers modified and analytical expressions to electromagnetic torque constant and magnetic spring stiffness. These modified and analytical expressions could provide guidance more accurately for a linear control design approach and sensitivity analysis on electro-hydraulic servo valves than the previous expressions.

Role of TbFe on Perpendicular Magnetic Anisotropy and Giant Magnetoresistance Effect in [Co/Ni]_N-Based Spin Valves

The exchange-coupled [Co/Ni]N/Tb Fe nano-magnetic films can display strong perpendicular magnetic anisotropy(PMA) which depends on the Tb:Fe component ratio, Tb Fe layer thickness and the repetition number N of [Co/Ni]Nmultilayer. Perpendicular spin valves in the nano thickness scale, consisting of a [Co/Ni]3free and a [Co/Ni]5/Tb Fe reference multilayer, show high giant magnetoresistance(GMR) signal of 6.5 % and a large switching field difference over3 k Oe. However, unexpected slanting of the free layer magnetization, accompanied by a reduced GMR ratio, was found to be caused by the presence of a thick Fe-rich or even a thin but Tb-rich Tb Fe layer. We attribute this phenomenon to the large magnetostriction effect of Tb Fe which probably induces strong stress acting on the free layer and hence reduces its interfacial PMA.

Evaluation of Left Ventricular Systolic Function after Pulmonary Valve Replacement Using Cardiovascular Magnetic Resonance Imaging

Following reparative surgery for tetralogy of Fallot or critical pulmonary stenosis(PS),patients frequently present with severe right ventricular(RV)volume overload due to pulmonary regurgitation,resulting in decreased RV function.Surgical pulmonary valve replacement(PVR)is known to improve RV function,but changes in left ventricular(LV)function after PVR have rarely been described.We sought to determine the midterm results regarding LV systolic function after PVR using cardiac MRI in 40 consecutive patients with repaired TOF(31 patients)or PS(9 patients)with an age of 29±9 years who underwent PVR from 2006 to 2011 at a single center.Cardiac MRI RV and LV volumes before and after PVR were analyzed.Demographics,clinical variables,cardiopulmonary bypass duration,and medications were reviewed.LV ejection fraction(LVEF)increased from(54±8)to(57±6)%(P=0.02).Before PVR,26 patients had depressed LVEF of(49±5)%(range 36– 54%).In this group,LVEF increased by(7±7)%(P<0.0001)after PVR.Low LVEF before PVR was correlated with increased LVEF after PVR(regression coefficient-0.7,R 2=0.59,P<0.0001).Demographics,medications,prior pregnancies,and cardiopulmonary bypass duration had no effect on LVEF after PVR.The increase in LVEF was most significant in patients with low pre-PVR LVEF.

Bending sensor based on flexible spin valve

Flexible spin valves were prepared by magnetron sputtering on polyimide substrates. The buffer layer that reduces significantly the effect of the polymer substrate on the spin valve microstructure and magnetoresistive properties was revealed. Bending deformation was applied to the microobjects based on the flexible spin valves in parallel to anisotropy axes. It was revealed that during the bend the magnetoresistance changes due to the joint impact of both the change of the magnetic field projection on the film plane and the change of the magnetic properties of the ferromagnetic layers. The obtained dependences have been used in construction of bending sensor, in which the flexible spin valve microstripes were united into the Wheatstone bridge.

Magnetoresistive behavior and magnetization reversal of NiFe/Cu/CoFe/IrMn spin valve GMRs in nanoscale

The magnetoresistance behavior and the magnetization reversal mode of NiFe/Cu/CoFe/IrMn spin valve giant magnetoresistance （SV-GMR） in nanoscale were investigated experimentally and theoretically by nanosized magnetic simulation methods. Based on the Landau-Lifshitz-Gilbert equation, a model with a special gridding was proposed to calculate the giant magnetoresistance ratio （MR） and investigate the magnetization reversal mode. The relationship between MR and the external magnetic field was obtained and analyzed. Studies into the variation of the magnetization distribution reveal that the magnetization reversal mode, that is, the jump variation mode for NiFe/Cu/CoFe/IrMn, depends greatly on the antiferromagnetic coupling behavior between the pinned layer and the antiferromagnetic layer. It is also found that the switching field is almost linear with the exchange coefficient.

The magnetoresistive effect induced by stress in spin-valve structures

Using a method of free energy minimization, this paper investigates the magnetization properties of a ferromagnetic （FM） monolayer and an FM/antiferromagnetic （AFM） bilayer under a stress field, respectively. It then investigates the magnetoresistance （MR） of the spin-valve structure, which is built by an FM rnonolayer and an FM/AFM bilayer, and its dependence upon the applied stress field. The results show that under the stress field, the magnetization properties of the FM monolayer is obviously different from that of the FM/AFM bilayer, since the coupled AFM layer can obviously block the magnetization of the FM layer. This phenomenon makes the MR of the spin-valve structure become obvious. In detail, there are two behaviors for the MR of the spin-valve structure dependence upon the stress field distinguished by the coupling （FM coupling or AFM coupling） between the FM layer and the FM/AFM bilayer. Either behavior of the MR of the spin-valve structure depends on the stress field including its value and orientation. Based on these investigations, a perfect mechanical sensor at the nano-scale is suggested to be devised experimentally.

Low power linear actuator for direct drive electrohydraulic valves

This paper presents a bi-directional permanent-magnet linear actuator for directly driving electrohydraulic valves with low power consumption. Its static and dynamic performances were analyzed using the 2D finite element method,taking into account the nonlinear characterization and the eddy current loss of the magnetic material. The experiment and simulation results agree well and show that the prototype actuator can produce a force of ±100 N with the maximum power being 7 W and has linear characteristics with a positive magnetic stiffness within a stroke of ±1 mm. Its non-linearity is less than 1.5% and the hysteresis less than 1.5%. The actuator's frequency response(-3 dB) of the displacement reaches about 15 Hz,and the most significant factor affecting the dynamic performance is identified as the eddy current loss of the magnetic material.

Analytical Modelling and Experiment of Novel Rotary Electro-Mechanical Converter with Negative Feedback Mechanism for 2D Valve

The manufacturing of spiral groove structure of two-dimensional valve(2D valve)feedback mechanism has shortcomings of both high cost and time-consuming.This paper presents a novel configuration of rotary electro-mechanical converter with negative feedback mechanism(REMC-NFM)in order to replace the feedback mechanism of spiral groove and thus reduce cost of valve manufacturing.In order to rapidly and quantitative evaluate the driving and feedback performance of the REMC-NFM,an analytical model taking leakage flux,edge effect and permeability nonlinearity into account is formulated based on the equivalent magnetic circuit approach.Then the model is properly simplified in order to obtain the optimal pitch angle.FEM simulation is used to study the influence of crucial parameters on the performance of REMC-NFM.A prototype of REMC-NFM is designed and machined,and an exclusive experimental platform is built.The torque-angle characteristics,torque-displacement characteristics,and magnetic flux density in the working air gap with different excitation currents are measured.The experimental results are in good agreement with the analytical and FEM simulated results,which verifies the correctness of the analytical model.For torque-angle characteristics,the overall torque increases with both current and rotation angle,which reaches about 0.48 N·m with 1.5 A and 1.5°.While for torque-displacement characteristics,the overall torque increases with current yet decrease with armature displacement due to the negative feedback mechanism,which is about 0.16 N·m with 1.5 A and 0.8 mm.Besides,experimental results of conventional torque motor are compared with counterparts of REMC-NFM in order to validate the simplified model.The research indicates that the REMC-NFM can be potentially used as the electro-mechanical converter for 2D valves in civil servo areas.

Patient selection for transcatheter aortic valve replacement:A combined clinical and multimodality imaging approach

Transcatheter aortic valve replacement(TAVR) has been validated as a new therapy for patients affected by severe symptomatic aortic stenosis who are not eligible for surgical intervention because of major contraindication or high operative risk. Patient selection for TAVR should be based not only on accurate assessment of aortic stenosis morphology, but also on several clinical and functional data. Multi-Imaging modalities should be preferred for assessing the anatomy and the dimensions of the aortic valve and annulus before TAVR. Ultrasounds represent the first line tool in evaluation of this patients giving detailed anatomic description of aortic valve complex and allowing estimating with enough reliability the hemodynamic entity of valvular stenosis. Angiography should be used to assess coronary involvement and plan a revascularization strategy before the implant. Multislice computed tomography play a central role as it can give anatomical details in order to choice the best fitting prosthesis, evaluate the morphology of the access path and detect other relevant comorbidities. Cardiovascular magnetic resonance and positron emission tomography are emergent modality helpful in aortic stenosis evaluation. The aim of this review is to give an overview onTAVR clinical and technical aspects essential for adequate selection.

Research of Damping System Characteristics for HVDC Converter Valves

直流换流阀阻尼系统由饱和电抗器铁心电阻和晶闸管级阻尼电阻2部分组成。该文提出了饱和电抗器动态电感和铁心电阻分析计算方法,建立了铁心电阻与磁通密度的函数关系及饱和电抗器等值电路模型。通过对高频电压源激励下端口伏安特性理论计算结果与试验测试结果对比,验证了模型的正确性。提出了阻尼系统抑制振荡电流性能分析方法,给出了晶闸管第1个电流波谷值处于局部极限值的阻尼系统配置方案;分析了阻尼系统冲击电压下辅助限制过电压性能;提出了阻尼系统损耗计算方法,研究了换流阀不同运行状态下的损耗性能。

The Impact of a Bicuspid Aortic Valve on Aortic Geometry and Function in Patients with Aortic Coarctation:A Comprehensive CMR Study

Background:An isolated bicuspid aortic valve(BAV)is associated with structural and functional abnormalities of the aorta and the left ventricle(LV).Although~50%of patients with aortic coarctation(CoA)have a BAV,less is known about its impact on LV function and aortic geometry and function in CoA patients.In this cardiovascular magnetic resonance imaging(CMR)study,we analysed markers of LV and aortic function as well as aortic geometry in a large cohort of CoA patients with a BAVand compared them with CoA patients with a tricuspid aortic valve(TAV).Methods:We included 48 patients with a BAV(18.4±9.3 years)and 45 patients with TAV(20.7±9.9 years).LV volumes,mass and ejection fraction as well as aortic distensibilty,pulse wave velocity(PWV)were measured from standard cine CMR and phase-contrast CMR images.2-dimensional CMR feature tracking(2DCMR-FT)was performed to measure longitudinal,circumferential and radial strain and strain rate of the LV.Aortic arch geometry was classified as romanic,gothic and crenel.Results:LV volumes,mass and ejection fraction as well as aortic distensibility and PWV did not significantly differ between the BAV and the TAV group.There was also no significant difference for LV global longitudinal,radial and circumferential strain and strain rate between both groups.Patients with a BAV had more commonly a gothic aortic arch compared to TAV patients,but this difference was not statistically significant(22 vs.14,p=0.2).Ascending and descending aortic distensibility correlated with LV mass in the entire patient group(p<0.001).Global longitudinal,circumferential and radial strain(GLS,GCS,GRS)and global longitudinal and circumferential strain rate(GLSR,GCSR)correlated with LV ejection fraction(p<0.001).Conclusion:Our data suggest that the presence of a BAV does not adversely impact LV and aortic function in children and young adults with CoA.The correlation of global circumferential,longitudinal and radial strain values with LV ejection fraction demonstrates that 2D-CMR-FT might provide additional information related to ventricular function in CoA patients.

Prevalence of Bicuspid Aortic Valve in Turner Syndrome Patients Receiving Cardiac MRI and CT: A Meta-Analysis

Turner syndrome(TS)is a rare disorder affecting 25–50 in 100000 female newborns.Bicuspid aortic valve(BAV)is assumed to be the most common congenital heart defect(CHD)in TS.In literature,reported BAV prevalence in TS ranges between 14%and 34%.The specific BAV prevalence in TS is still unknown.The aim of this study was to give a more precise estimation of BAV prevalence in TS by conducting a meta-analysis of TS-studies,which detected BAV by either cardiac magnetic resonance imaging(MRI)or cardiac computed tomography(CT).We searched PubMed,Cochrane Library,and Web of Science databases to collect observational studies including the prevalence of BAV identified by cardiac MRI or cardiac CT in TS patients up to June 4th,2021.After screening for inclusion,data extraction,and quality assessment by two independent reviewers,the meta-analysis was performed with R 4.1.1 software.Results are shown as proportion and weighted mean difference with 95%confidence intervals(95%CI).In total,11 studies involving 1177 patients were included.Pooled data showed that the prevalence of BAV in TS patients was 23.7%(95%CI:21.3%to 26.1%).No high heterogeneity was found between the included studies.The current meta-analysis reveals that BAVcan be detected in 23.7%of TS patients receiving cardiac MRI or cardiac CT.Therefore,BAV can be considered as the most common CHD in TS.Compared to TTE,cardiac MRI and cardiac CT might represent superior imaging modalities in BAV assessment of adult TS patients.

Staged Surgery for Bronchobiliary Fistula and Incidental Finding of Mitral Valve Disease

Bronchobiliary fistula (BBF) is defined as abnormal passage between bronchial system and the bile tree which often manifests as presence of bile in the sputum (biloptysis). BBF is a serious complication which requires early diagnosis and well-planned management strategy to avoid the high morbidity and mortality rate. The hydatid cystic disease is still the leading cause of the BBF. In this paper we present a case of 32-year-old man with BBF who was incidentally found to have a mitral valve disease for which he underwent mitral valve replacement during his management course.

Numerical Study on Claw-pole Electric Motors for Electronic Expansion Valves

电子膨胀阀在变频空调系统中能精确调节制冷剂流量，有助于提高空调系统的能效和改善空调环境的热舒适性。研究电子膨胀阀用爪极永磁步进电机有助于提高电子膨胀阀稳定性和可靠性。对电子膨胀阀的电机力矩特性进行数值分析，在保持转子尺寸、通电电流和定转子之间气隙不变的前提下，通过改变爪极形状尺寸，分析了爪极形状参数对电子膨胀阀用爪极式步进电机白定位力矩和保持力矩的影响，认为在满足一定自定位力矩的前提下，保持力矩越大越好，并以此为基础对电机的爪极尺寸进行了优化，认为合理设计爪极尺寸参数，能够使电机的保持力矩和自定位力矩达到最佳，对电子膨胀阀步进电机的研究和设计有借鉴价值。

心血管MRI用于二尖瓣病变进展

随着心血管MRI(CMRI)技术的进步,多模态CMRI已广泛用于评估二尖瓣病变,可显示瓣膜解剖学结构、评估瓣膜病变严重程度、量化心腔容积及心肌纤维化,在二尖瓣狭窄、二尖瓣关闭不全及其危险分层方面取得较多进展。本文围绕CMRI评估二尖瓣病变进展进行综述。

多模态影像评估主动脉瓣置换术后左心室逆重构研究进展

慢性主动脉瓣狭窄及反流可导致左心室重构,这些变化在瓣膜置换术后是否可逆及可逆程度是影响外科手术时机和患者预后的主要决定因素。影像技术是目前常用于评估心肌结构与功能的无创性方法,其中超声心动图及增强CT有助于人工瓣功能评估和左心室形变监测,心脏磁共振及PET/CT有助于识别术后心纤维化的进展及消退,这些技术综合应用可早期诊断和无创检测术后左心室逆重构,从而改善临床结局。本文综述多模态影像学技术对主动脉瓣置换术后左心室逆重构评估及应用进展。

复合磁-电弹簧直动式溢流阀设计与性能分析

为了解决传统机械弹簧因塑性变形、断裂等造成溢流阀工作性能劣化的问题,设计一种复合磁-电弹簧结构应用于直动式溢流阀调压弹簧中,以提高直动式溢流阀的响应速度,实现电控弹簧力。理论分析复合磁-电弹簧磁力特性,利用Maxwell软件对复合磁-电弹簧进行磁力特性仿真;采用AMESim软件对机械弹簧直动式溢流阀和复合磁-电弹簧直动式溢流阀进行动态特性仿真。对复合磁-电弹簧磁力特性及溢流阀的动态特性进行实验测试。结果表明:复合磁-电弹簧设计合理,复合磁-电弹簧直动式溢流阀动态响应特性优于现有机械弹簧直动式溢流阀。

高速燃油电磁阀电磁特性

高速燃油电磁阀作为航空发动机用叶片调节器的关键控制部件,其电磁特性直接影响叶片调节器的控制精度。首先基于Maxwell建立电磁阀数值模型。其次,深入研究磁路材料和外壳壁厚对电磁阀电磁力的影响规律。然后,对比研究极面形状和工作气隙相对位置对电磁力的影响规律。最后,研制了高速燃油电磁阀样机,进行实验验证。结果表明:磁路材料均为1J22时,电磁力最大;外壳壁厚0.75~1.5 mm时,各工作气隙下电磁力几乎不变;厚度小于0.75 mm时,电磁力随外壳壁厚的减小而下降;工作气隙小时,锥形极面衔铁电磁力小于平面极面,反之,锥形极面衔铁电磁力较大;工作气隙相对位置对电磁力影响有限。实验结果与仿真结果具有较好的吻合度,验证了仿真模型的正确性和研究方法的可行性。研究成果对高速燃油电磁阀电磁性能优化提升,提供了理论基础和数据支撑,具有实践意义。

高速开关阀动态响应特性研究及性能优化

为研究某型高速开关阀的动态响应特性并开展参数优化,描述开关阀的结构组成及工作原理,并建立其数学模型;基于电磁铁的有限元模型,重点研究极靴盆口磁分路的作用,并求解电磁力及磁通量离散空间分布;进而建立开关阀的机-电-液联合仿真模型,研究其静态压力控制特性及关键参量的动态响应过程。以单变量作用规律分析为基础,应用(1+1)-ES算法完成多参数迭代优化。最后,测定高速开关阀的动态响应特性,完成对比验证。实验结果表明:所建立的联合仿真模型较好地刻画了开关阀的动态响应特性,并借助进化策略优化算法实现了性能的有效提升。