A study on the temperature sensitivity of NMR porosity in porous media based on the intensity of magnetization Dedicated to the special issue “Magnetic Resonance in Porous Media”

The measurement of nuclear magnetic resonance(NMR)porosity is affected by temperature.Without considering the impact of NMR logging tools,this phenomenon is mainly caused by variations in magnetization intensity of the measured system due to temperature fluctuations and difference between the temperature of the porous medium and calibration sample.In this study,the effect of temperature was explained based on the thermodynamic theory,and the rules of NMR porosity responses to temperature changes were identified through core physics experiments.In addition,a method for correcting the influence of temperature on NMR porosity measurement was proposed,and the possible factors that may affect its application were also discussed.

High repetition granular Co/Pt multilayers with improved perpendicular remanent magnetization for high-density magnetic recording

Thanks to the strong perpendicular magnetic anisotropy(PMA), excellent processing compatibility as well as novel spintronic phenomenon, Co/Pt multilayers have been attracting massive attention and widely used in magnetic storage.However, reversed magnetic domains come into being with the increasing layer repetition ‘N’ to reduce magneto-static energy, resulting in the remarkable diminishment of the remanent magnetization(Mr). As a result, the product of Mrand thickness(i.e., the remanent moment-thickness product, Mrt), a key parameter in magnetic recording for reliable data storing and reading, also decreases dramatically. To overcome this issue, we deposit an ultra-thick granular [Co/Pt]80multilayer with a total thickness of 68 nm on granular SiNxbuffer layer. The Mrt value, Mrto saturation magnetization(Ms) ratio as well as out of plane(OOP) coercivity(Hcoop) are high up to 2.97 memu/cm^(2), 67%, and 1940 Oe(1 Oe = 79.5775 A·m^(-1)),respectively, which is remarkably improved compared with that of continuous [Co/Pt]80multilayers. That is because large amounts of grain boundaries in the granular multilayers can efficiently impede the propagation and expansion of reversed magnetic domains, which is verified by experimental investigations and micromagnetic simulation results. The simulation results also indicate that the value of Mrt, Mr/Msratio, and Hcoopcan be further improved through optimizing the granule size, which can be experimentally realized by manipulating the process parameter of SiNxbuffer layer. This work provides an alternative solution for achieving high Mrt value in ultra-thick Co/Pt multilayers, which is of unneglectable potential in applications of high-density magnetic recording.

Microstructure and magnetic properties of granularFePt/(FePt)_(27)Ti_(73) films for ultrahigh-density recording media

FePt granular films were prepared by direct current facing-target magnetron sputtering system onto glass substrates and subsequently in-situ annealed in vacuum. Vibrating sample magnetometer, X-ray diffraction and scanning probe microscope were applied to study the magnetic properties, microstructures, morphologies and domain structures of the samples. （FePt）27Ti73 bilayer films were fabricated at various conditions to investigate the effect of Ti on FePt grains. The results show that without Ti matrix layer, FePt films deposited onto the glass substrates are fcc disordered; with addition of Ti matrix layer, FePt/Ti films form a ternary （FePt）27Ti73 alloy possessing fcc and L10 （111） mixed texture. FePt/（FePt）27Ti73 films with perfectly ordered L10（111） structure and unique magnetic properties can be obtained at Ti thickness of 35nm and substrate temperature of 250℃. The maximum coercivity is more than 240kA/m and the squareness ratio is more than 0.9. The obtained results suggest that the granular FePt/（FePt）27Ti73 films can be applicable to ultrahigh-density magnetic recording media.

Writability issues in high-anisotropy perpendicular magnetic recording media

Challenges and recent developments associated with writability issues in high-anisotropy perpendicular recording media are reviewed. The writing field is limited by the high coercivity caused by the high anisotropy. Some new alterna- tives are proposed to solve the writability issues, including texture-tilting-assisted, domain-wall-assisted, energy-assisted magnetic recording technologies, and so on, In addition, we propose new alternatives for the next-generation of magnetic recording media.

Magnetic properties of soft layer/FePt-MgO exchange coupled composite perpendicular recording media

The magnetic properties of exchange coupled composite （ECC） media that are composed of perpendicular magnetic recording media FePt MgO and two kinds of soft layers have been studied by using an x-ray diffractometer, a polar Kerr magneto-optical system （PMOKE） and a vibrating sample magnetometer （VSM）. The results show that ECC media can reduce the coercivities of perpendicular magnetic recording media FePt-MgO. The ECC media with granular-type soft layers have weaker exchange couplings between magnetic grains and the magnetization process, for ECC media of this kind mainly follow the Stoner Wohlfarth model.

Magnetic property and microstructure of SmCo magnetic recording films

Cr/SmCo/Cr thin films with Sm concentration of 37.7 at.% were deposited on glass substrates by magnetron sputtering. Measurement of magnetic properties showed that the SmCo film possessed good magnetic anisotropy, a high coercivity of 3019 kA/m and low magnetic exchange coupling. Microstructure analysis showed that crystallized SmCo5 magnetic phase, non-magnetic SmCo2 phase and Sm2Co7 phase co-existed in the film. The non-magnetic SmCo2 phase might function as isolator of SmCo grains, leading to a decrease of magnetic exchange coupling. Moreover, a Cr2O3 oxide layer which could protect the SmCo layer from oxidation formed at the surface of the Cr cap layer.

Endolymphatic hydrops in Meniere's disease secondary to otitis media and visualized by gadolinium-enhanced magnetic resonance imaging

Aimed to test the hypothesis that endolymphatic hydrops in Meniere's disease(MD) may be secondary to otitis media, history of a patient who developed MD as a complication of otitis media was reviewed. The inner ear was imaged using a 3.0 Tesla MR system post-intravenous injection of gadolinium-tetraazacyclododecane-tetraacetic acid(Gd-DOTA) in a standard single dosage(0.1 mmol/kg). Both t2-spc-rst-tra-iso(T2-weighted) and heavily T2-weighted 3-dimensional fluid-attenuated inversion recovery magnetic resonance imaging [h T(2)W-3D-FLAIR] sequences were applied. As a result, in the T2-weighted images, the perilymph and endolymph, cerebrospinal fluid surrounding the eighth nerve(N8), and middle ear granulation tissue showed intense signals. In the h T(2)W-3D-FLAIR images, evident enhancement by Gd-DOTA was observed in the middle ear cavity and the perilymphatic compartments of the cochlea. Cochlear endolymphatic hydrops was implicated by the enlarged scala media in the basalturn. In general, the Gd-DOTA uptake in the vestibule was weak, and signs of vestibular endolymphatic hydrops were obvious. The N8 on the diseased side was also significantly enhanced. To conclude, endolymphatic hydrops in MD may be induced by otitis media. Cochlear endolymphatic hydrops in MD secondary to otitis media may not follow the classical pattern.

NANO-MULTILAYERS WITH HIGH PERPENDICULAR ANISOTROPY FOR MAGNETIC RECORDING

(FePt/Ag)n nano-multilayers were deposited on MgO (100) single crystal with laser ablation and then subjected to annealing. FePt L1o grains with (001) texture and thus a large perpendicular magnetic anisotropy constant Ku of the order of 106 J/m3 were formed. A thick Ag layer is found to be favorable for decreasing the dispersion of the easy axis for magnetization. The measurement of time decay of magnetization gave rise to a small activation volume of the order of 10-25m3, showing the promising of being the recording medium for future high density perpendicular recording.

A NEW FORMULA FOR INDUCTANCE OF ANISOTROPIC MAGNETIC MEDIA

By solving the basic equations of magnetic field in the anisotropic magnetic mediain which the tensor μik is symmetric,an integral formula for anisotropic vector potential A isobtained.By which the characteristic formulae for self and mutual inductances are derived inscalar and tensor forms,and their transformation formula are also derived.Finally,the formulais checked by practical examples.

First-order reversal curves of magnetic recording tapes

The interaction and its variation between magnetic grains in two kinds of magnetic recording tapes are investigated by first-order reversal curves （FORC） and the 5M method. The composition and microstructure of the samples are characterised by x-ray diffraction and scanning electron microscope. The FORC diagram can provide more accurate information of the interaction and its variation, but the 5M curves cannot. The positive interaction field and the large variation of the interaction field have opposite effects on the δM curve.

Dynamical System of Three Magnetic Layers in the Presence of Porous Media

This paper concerns the linear stability of three viscous fluid layers in porous media. The system is composed of a middle fluid embedded between two semi-infinite fluids, in which the effect of the normal magnetic field is to introduce. The principle aim of this work is to investigate the influence of fluid viscosity and the porosity effect on the growth rate in the presence of normal magnetic field. The parameters governing the layers flow system, the magnetic properties and porosity effects strongly influence the wave forms and their amplitudes and hence the stability of the fluid. The stability criteria are discussed theoretically and numerically and stability diagrams are obtained, where regions of stability and instability are identified. It is found that the stabilizing role for the magnetic field is retarded when the flow is in porous media. Moreover, the increase in the values of permeability parameters plays a dual role, in stability behavior. It has been found that the phenomenon of the dual (to be either stabilizing or destabilizing) role is found for increasing the permeability parameter. It is established that both the viscosity coefficient and the magnetic permeability damps the growth rate, introducing stabilizing influence. The role of the magnetic field and Reynolds number is to increase the amplitude of the disturbance leading to the destabilization state of the flow system, promote the oscillatory behavior. Influence of the various parameters of the problem on the interface stability is thoroughly discussed.

Induced Dipoles in Electromagnetic Media in Motion

We present a non-relativistic approach to the equivalent polarization Peq=(1/c2)v×Meq, that appears in a magnetized medium in motion. We apply an analogous method to that used by Panofsky and Phillips to calculate the symmetric effect, the equivalent magnetization that appears in a polarized dielectric in motion, Meq=P×v,?This method is based on a particular expression of Maxwell’s equations and the application of the convective derivative. These authors argue, however, that the equivalent polarization can be obtained only with a relativistic approach. We show that with the same method, but with a different and equivalent expression of Maxwell’s equations, this effect can also be calculated. In this way both effects can be considered relativistic effects to first order in v/c.

An iterative ITI cancellation method for multi-head multi-track bit-patterned magnetic recording systems

Bit-Pattemed Magnetic Recording(BPMR)is one of the emerging data storage technologies,which promises an Areal Density(AD)of about 4 Tb/in2.However,a major problem practically encountered in a BPMR system is Inter-Track Interference(ITI)that can deteriorate the overall system performance,especially at high ADs.This paper proposes an iterative ITI cancellation method for an m-head m-track BPMR system,which uses m heads to read m adjacent tracks and decodes them simultaneously.To cancel the ITI,we subtract the weighted readback signals of adjacent tracks,acting as the ITI signals,from the readback signal of the target track,before passing the refined readback signal to a turbo decoder.Then,the decoded data will be employed to reconstruct the ITI signal for the next turbo iteration.Experimental results indicate that the proposed system performs better than the conventional system that uses one head to read one data track.Furthermore,we also find out that the proposed system is more robust to media noise and track misregistration than the conventional system.

基于地震学的天山地区地震动衰减关系研究

选取天山地区3171条矩震级为3.5~4.5级测震记录,通过计算S波段速度傅里叶幅值谱,采用微遗传算法,反演得到5个区域地壳介质参数,即应力降Δσ为18.206 MPa,品质因子参数Q 0为444.20,η值为0.35,几何衰减参数R 1和R 2分别为74.30 km和106.59 km。根据地壳介质参数计算加速度傅氏谱,再配合随机相位谱,得到某一震级、震中距下地震动时程,提取其PGA,建立区域地震动峰值加速度衰减关系。研究结果显示,矩震级为5级和6级中远场地震动衰减关系与强震动记录符合较好,尤其是5级结果,在选取的5条经验值衰减关系中,其均值和标准差均为最小,结果最优;矩震级为7级的地震动衰减关系,远场结果高于大多数强震动记录。

基于钆塞酸二钠增强肝胆期MRI构建影像组学模型评估肝纤维化临床病理分期

目的 观察基于钆塞酸二钠(Gd-EOB-DTPA)增强肝胆期(HBP)MRI构建的影像组学模型评估肝纤维化(HF)临床病理分期的价值。方法 回顾性分析接受Gd-EOB-DTPA增强MR检查并经病理/临床评估HF临床病理分期的240例患者资料,测量HBP肝脏-肌肉信号强度比值(SIR1)及肝脏-脾脏信号强度比值(SIR2);提取并筛选HBP影像组学特征,构建影像组学模型;基于信号强度比值(SIR)及影像组学标签构建SIR-影像组学联合模型;以受试者工作特征(ROC)曲线分析各模型评估HF临床病理分期的效能。结果 SIR1与SIR2评估HF临床病理分期的曲线下面积(AUC)分别为0.63~0.70及0.65~0.71。评估HF、显著HF、进展期HF及早期肝硬化效能最高的影像组学模型分别为支持向量机(SVM)、SVM、轻量梯度提升机及K邻近法模型(验证集AUC分别为0.87、0.82、0.81及0.80)。SIR-影像组学联合模型评估验证集上述HF临床病理分期的AUC分别为0.88、0.82、0.82及0.81。结论 基于GdEOB-DTPA增强HBP MRI构建的影像组学模型有助于评估HF临床病理分期;联合HBP SIR可提高评估其效能。

化学交换饱和转移磁共振对比剂及其影像学特性

目的:寻找具有合适化学交换位点的小分子化合物作为磁共振对比剂并探讨其CEST特性和潜在应用价值。方法:初步筛选18种小分子化合物,通过磷酸盐缓冲液制备成试管模型。利用7.0 T磁共振成像仪上的CEST序列进行数据采集。利用MATLAB平台上工程师编辑的程序脚本进行数据后处理。采用GraphPad Prism软件中的pearson相关性分析方法对数据结果进行统计学分析。结果:除生物素外,所测试的一系列小分子物质均具有CEST特性。L-苯丙氨酸、盐酸多巴胺和奥沙拉秦钠的最佳化学交换位点分别为2.65 ppm、2.6 ppm和9.8 ppm,CEST效应的大小与饱和能量呈正相关,与pH值呈负相关(P<0.05)。3-硝基-4氨基苯酚和硫普罗宁的化学位移偏移位点分别位于1.65 ppm和-2.5 ppm,其CEST效应的大小与pH值无显著相关性(P>0.05)。2,5-二羟基苯酚和5-氨基水杨酸具有2个化学交换位点,分别为1.8 ppm、8.5 ppm和1.0 ppm、8.0 ppm,最适pH值为6.8。其它小分子物质,如丙烯酰胺(2.75 ppm)、L-半胱氨酸(-2.75 ppm)、内消旋-2,3-二巯基丁二酸(-2.5 ppm)、血卟啉(-12.5 ppm)、水杨酸(9.3 ppm)、环糊精(0.5 ppm)、透明质酸(1.0 ppm)、叶酸(1.8 ppm)、3,5-二羟基苯甲酰胺(1.8 ppm)和谷胱甘肽(-2.75 ppm和3.0 ppm),由于分子结构不同,各自的CEST特性亦不同。结论:我们通过一小群初步筛选的候选物,证明了具有CEST效应的一类小分子化合物具有作为非金属依赖性磁共振对比剂的潜力。水杨酸及其类似物是一类非常理想的外源性CEST对比剂候选物。总之,每种小分子物质都有其独特的CEST特性,未来可以有针对性设计其潜在应用价值。

TSE-DWI在显示及鉴别胆脂瘤型中耳炎中的价值

目的 探讨MR自旋回波扩散加权成像(turbo spin-echo diffusion-weighted imaging,TSE-DWI)在显示和鉴别胆脂瘤型中耳炎中的应用价值。方法 选取经手术证实的中耳炎患者99例,术前行常规MRI序列及TSE-DWI序列检查。根据手术及病理结果将患者分为胆脂瘤组56例及非胆脂瘤组43例。利用syngo. via后处理软件分别定量测量并计算胆脂瘤及非胆脂瘤病变的信号强度(signal intensity,SI)、信号强度比(signal intensity ratios,SIR)、ADC值。采用统计学方法检验两组中各参数的差异。采用受试者工作特征曲线(ROC)分析评估SI、SIR、和ADC值鉴别胆脂瘤和非胆脂瘤病变的最佳截断值。结果 胆脂瘤组的SI、SIR均值明显高于非胆脂瘤组,ADC均值明显低,差异有统计学意义(P<0.05)。ROC曲线分析将SI、SIR、ADC值的截断值分别确定为226.0、0.8、2.5×10^(-3)mm^(2)/s时,诊断胆脂瘤的灵敏度、特异度分别为100%、97.7%;98.2%、97.7%;100%、97.7%。结论 TSE-DWI技术在鉴别诊断胆脂瘤与非胆脂瘤病变中具有很大优势,定量指标SI、SIR、ADC值可以帮助提高诊断的准确率。

Influence of Ti on Microstructure and Magnetic Properties of FePt Granular Films

在室温下,应用对靶直流磁控溅射设备在普通玻璃基片上制备了FePt(30 nm)／Ti(t nm)颗粒膜样品,随后,在真空中进行了原位退火。详细研究了Ti衬底层对FePt颗粒膜的微结构和磁特性的影响。X射线衍射图谱表明样品形成了较有序的L10织构,Ti和FePt形成了三元FePtTi合金。当Ti层厚度t=5 nm、退火温度Ta=500℃时,样品具有高度有序的L10织构、小的颗粒尺寸和优异的磁特性。矫顽力超过了6．7 kOe,饱和磁化强度为620emu／cc。并且具有较小的开关场分布。结果表明FePt／Ti颗粒膜系统可作为超高密度磁记录介质的候选者。

平环强磁选机聚磁介质齿板开发研究

选用酒钢自产含碳量低,含铬量适中的超纯铁素体不锈钢,通过改良工艺、自行研制、加工平环强磁选机聚磁介质齿板开发出一种导磁性能好,工作场强高,耐磨、耐腐蚀性能好,分选指标优良的聚磁介质齿板。完成新开发聚磁介质齿板实验室、生产现场导磁性能、选别指标测试试验。在精矿品位相当的前提下,新开发聚磁介质齿板平均金属回收率比外购聚磁介质齿板金属回收率提高4.36个百分点。