Abnormality of Magnetic Behavior and Resistivity of La_(0.7-x)Dy_x Sr_(0.3)MnO_3 (0.00≤x≤0.30)System at Low Temperature

通过测量样品的磁化强度-温度曲线、电阻率-温度曲线及磁电阻-温度曲线.研究了 Dy 掺杂(0.00≤x≤0.30)对 La_(0.7-x)Dy_xSr_(0.3)MnO_3 体系磁电性质的影响.实验发现,随 Dy 掺杂量的增加,体系磁结构从长程铁磁有序向自旋团簇玻璃态、反铁磁状态转变；x=0.20、0.30时的低温磁行为发生异常,电行为存在低温电阻率极小值现象.这些奇特现象不仅来源于掺杂引起的晶格效应,也来源于掺杂引起的额外磁性耦合.

Hepatic abnormal perfusion visible by magnetic resonance imaging in acute pancreatitis

AIM:to study the prevalence and patterns of hepatic abnormal perfusion(HAP)visible by magnetic resonance imaging(MRI)in acute pancreatitis(AP).METHODS:Enhanced abdominal MRI was performed on 51 patients with AP.these patients were divided into two groups according to the MRI results:those with signs of gallstones,cholecystitis,common bile duct(CBD)stones or dilatation of the CBD on MRI and those without.the prevalence,shape and distribution of HAP in the two groups were analyzed and compared.the severity of AP was graded using the MR severity index(MRSI).the correlation between the MRSI and HAP was then analyzed.RESULTS:Of the 51 patients with AP,32(63%)showed at least one sign of gallbladder and CBD abnormalities on the MR images,while 19(37%)showed no sign of gallbladder or CBD abnormalities.Nineteen patients(37%)had HAP visible in the enhanced images,including strip-,wedge-or patch-shaped HAP distributed in the hepatic tissue adjacent to the gallbladder and left and right liver lobes.there were no significant differences in the prevalence of HAP(χ2=0.305,P=0.581>0.05)or HAP distribution in the liver(χ2=2.181,P=0.536>0.05)between patients with and without gallbladder and CBD abnormalities.there were no significant differences in the MRSI score between patients with and without HAP(t=0.559,P=0.552>0.05).HAP was not correlated with the MRSI score.CONCLUSION:HAP is common in patients with AP and appears strip-,patch-or wedge-shaped on MRI.HAP on MRI cannot be used to indicate the severity of AP.

Transcraneal Magnetic Stimulation Improves Sleep Parameters in Patients Affected with Imsomnia Associated to Electroencephalographic Abnormalities

Insomnia is one of the most frequently observed sleep disorders, affecting nearly 10% of the general population. It has multiple etiological factors. Recently, it has been reported that EEG abnormalities are associated with insomnia in patients previously diagnosed as idiopathic insomniacs. In addition, transcranial magnetic stimulation (TMS) has shown to be effective in the treatment of disorders characterized by neural hyper-excitability. Method: In the present study, patients with insomnia and EEG abnormalities were submitted to slow repetitive trans-cranial magnetic stimulation, for 15 minutes daily during 10 days. Polysomnographic recordings were performed before and after TMS. Results: The results indicate that the presence of EEG abnormalities significantly decreased after TMS. In addition, most of the sleep parameters showed significant improvement. Conclusions: These data support the notion that TMS is a reliable therapeutic tool for patients affected with abnormalities linked to neuronal hyper-excitability.

Stress induced magnetic field abnormality

Residual stresses in ferromagnetic material affect the direction and structure of domains and generate magnetic field abnormality on the surface. In the formation of stress induced magnetic field, the influence of geomagnetic field is unclear. Residual stress specimen was produced by tight matching of a round ring and a peg. The magnetic fields of contrast specimens, which were produced in geomagnetic field or in shielding geomagnetic field, were inspected with 8 mm lift-off. The results show that mean amplitude of magnetic field of the specimen produced in geomagnetic field is 0.85% larger than that of specimen produced in shielding geomagnetic field. So the formation of stress induced magnetic field abnormality above the surface of inspected ferromagnetic material geomagnetic field gives little contribution.

Effect of Mirror Magnetic Field on Abnormal Glow Discharge of Four-Anode Device

Abstract In the four-anode device, the mirror magnetic field affects the characteristics of charged particles motion, so that the current-voltage relations of glow discharge are changed. Firstly, the discharge device is introduced, and the distribution of mirror magnetic field generated by the loops surrounding the discharge chamber is presented. Both the discharge current-voltage characteristics and the radial distributions of electron density are measured, respectively, with/without the magnetic field. When the discharge occurs in a 99.99% helium with a pressure ranging from 100 Pa to 800 Pa without magnetic field, the voltage, sustaining a certain abnormal glow discharge current, decreases with the increase in gas pressure. With a mirror magnetic field of certain intensity, the discharge voltage increases with the current in a rate slower than that without the magnetic field. Moreover, when the magnetic field intensity increases, the discharge voltage first decreases then increases. Simultaneously, the mirror magnetic field affects the moving characteristics of charged particles, and causes a more inhomogeneous electron density.

Investigation of Abnormal Grain Growth in Sintered Nd-Fe-B Permanent Magnet

The abnormal growth of grains of sintering Nd13.6 Dy0.4 Fe79.5 B6.5 magnets were investigated in low oxygen manufacturing process.The abnormal growth of grains occurs easily when the sintering temperature is higher than 1080℃ during the manufacture process.In the magnets, the oxygen content is less than 700 × 10-6 and the average particle size of powder is smaller than 4 μm.The squareness of demagnetization curve of magnet is deteriorated.For high performance magnets, the abnormal growth grain should be avoided by selecting a suitable sintering temperature.

用数字示波器探究光磁共振实验中反常共振信号的机理

本文根据拟合得到的gF因子大小,确定了光磁共振实验中的反常共振信号;用数字示波器测量了反常共振射频信号的频谱,计算了反常共振射频信号各高次谐波的大小;通过线性拟合,得到了正常共振信号幅度与射频信号幅度的关系。利用此关系,计算了各高次谐波产生的反常共振信号大小,计算结果与测量值基本一致。频率计连接射频信号源后,射频信号波形和频谱发生明显变化,反常共振信号随着射频信号频谱的变化发生相应改变,进一步证明了反常共振信号由射频信号的高次谐波共振所引起。这些结果表明,用数字示波器探究光磁共振实验中反常共振信号的机理不仅可行,还能定量估算和预测射频信号波形对反常共振信号大小的影响。

孤立性直肠溃疡综合征患者的X线排粪造影和MR排粪造影的影像学表现

目的 回顾性总结分析孤立性直肠溃疡综合征(SRUS)患者的X线排粪造影(XRD)和MR排粪造影(MRD)的影像学表现,为临床诊疗提供重要信息。方法 19例经临床、病理和肠镜检查证实的SRUS患者纳入本研究,15例行XRD,7例行MRD,3例患者同时进行了XRD和MRD检查。收集所有患者的数据并进行盆底功能测量。结果 在XRD结果中,3例(20%)表现直肠内套叠,8例(53.3%)直肠外脱垂,2例(13.3%)中度直肠前突。另外耻骨直肠肌肥厚患者有2例,膀胱脱垂和子宫脱垂患者各有1例。在MRD结果中,3例(42.9%)表现直肠黏膜脱垂(部分性脱垂),4例(57.1%)直肠前突患者中,3例(均为女性)为中度直肠前突,1例为轻度直肠前突。3例患者同时观察到相关的前、中腔室器官下降,2例耻骨直肠肌肥厚,没有患者表现乙状结肠疝。结论 排粪造影可以评估SRUS患者的直肠外脱垂、直肠前突、直肠黏膜脱垂、直肠内套叠等盆底结构及功能异常,对SRUS患者的治疗具有指导意义。

高精度磁测在内蒙古额济纳旗苦泉山铁矿区勘查中的应用

为了高效地在内蒙古额济纳旗苦泉山地区寻找深部隐伏的磁铁矿体,评价该区铁多金属矿的资源潜力,在预查的基础上开展了1∶10000地面高精度磁测工作,识别出了5条断裂,圈定了2个磁异常(C1和C2),经探槽工程验证,在C2磁异常揭露了2个磁铁矿体,取得了较好的找矿效果。勘查结果表明:通过ΔT磁异常化极运算能较好地推测铁矿体的分布范围,ΔT水平方向导数运算能有效识别区域构造格架;初步确立“接触带+断裂+高磁异常区”是区域铁矿成矿的有利靶区;磁铁矿体在经历构造改造作用后会在地表引起强负磁异常,在磁铁矿勘查中要重视这种非正常的磁化现象。研究可为北山地区的矽卡岩型铁矿勘查提供经验借鉴。

交叉异位融合肾影像学表现

目的 观察交叉异位融合肾影像学表现。方法 回顾性分析12例交叉异位融合肾资料,分析该病影像学表现。结果 12例交叉异位融合肾包括L型5例,下异位型(Ii型)、S型及块状型(O型)各2例,甜甜圈型或盘状型(C-C型)1例;均表现为一侧肾窝空虚而对侧肾形态、位置大致正常,异位肾跨过中线与对侧肾融合,8例右向左、4例左向右融合;异位肾输尿管均跨过中线,11例开口于对侧膀胱三角区、1例异位开口于前列腺。3例合并生殖系统畸形,其中单角子宫、双角子宫、隐睾各1例;2例合并下腔静脉异常,包括双下腔静脉、左下腔静脉各1例。结论 交叉异位融合肾具有特征性影像学表现;完整显示肾融合、输尿管走行及开口有助于准确诊断及分型。

漏磁检测在管道损伤探测中的应用

漏磁检测技术是油气管道损伤检测中最常用的方法之一。其是一种利用磁敏传感器检测漏磁信号进而探测管道缺陷的无损检测技术。首先介绍了漏磁检测的原理和操作流程,而后综述了近年来漏磁检测技术在信号预处理、异常识别以及缺陷量化3方面取得的重要成果。其中,重点介绍了基于深度学习的异常识别和缺陷量化方法,并分析了这些方法存在的不足。最后,对管道漏磁检测的未来发展进行了展望。

河北及周边地区岩石圈磁场变化模值的分析

为更好地开展地磁异常变化与地震的关系,通过对河北及周边地区2017—2021年流动地磁矢量资料,采用模值量化的计算方法,研究发生在测区范围内震级M_(L)≥4.0地震震中位置变化模值的分布特征。结果表明:H模和F模的图像分布形态极为相似。测区主要异常形态与测区地质构造对岩石圈磁场变化的控制作用不强。测区岩石圈磁场时间变化总体稳定,局部地区存在起伏波动变化。80%的震例均发生在H模和F模的低值区,且震中模值与模值测区均值的比值ρ的取值集中在0.2~0.9区间范围内,M_(L)和ρ不具备线性相关性。将标准模作为研究地区模值异常的参考阈值,得到H模和F模的参考异常阈值分别为3.10和3.54。采用改进的R值评估方法,得到基于模值测区均值的R为0.3。可见,基于模值异常的地震预测水平还很低,流动地磁的异常研判工作仍处于探索阶段。

南北地震带历史地震与岩石圈磁场空间分布特征分析

利用2016—2020年南北地震带流动地磁矢量观测资料,结合2017年6月1日至2021年7月1日发生在测区范围内MS≥5.0地震,对该地区2015.0年代岩石圈磁场空间分布与地震的特征进行分析和归纳。结果表明,南北地震带地区大部分MS≥5.0地震在岩石圈磁场中表现出较明确的位置特征,尤其是“0”值线附近、水平矢量H幅值弱化这2个位置,是南北地震带地区中强及以上地震的易发部位。高梯度带和水平矢量H方向转向这些位置亦需格外关注。

Characterization of the Elastic-plastic Region Based on Magnetic Memory Effect

Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further research to evaluate stress concentration quantitatively due to ambiguous physical mechanism, though it has potential to detect early defects in ferromagnetic materials. Mild Q235 steel defective specimens in demagnetization state were loaded in tension up to visible necking, with magnetic memory signals measurement made at increasing stress levels. Magnetic signals varied greatly under first several loadings and subsequently tended to stability in the elastic region, which showed that the magnetization always approaches the anhysteretic magnetization curve and was explained by the theory of magnetomechanical effect. In the plastic stage, an abnormal wave occurred in the stress concentration zone and its height value was sensitive to plastic deformation levels and dependent on the distance between the probe and defect, in accordance with the simulation results based on the magnetic dipole model. Different magnetic signal characteristics in the elastic-plastic region indicate that the magnetic memory technique can identify macroyielding and early damage, which is of profound significance for ensuring safe operation of equipment in service.

Regional brain structural abnormality in ischemic stroke patients:a voxel-based morphometry study

Our previous study used regional homogeneity analysis and found that activity in some brain areas of patients with ischemic stroke changed significantly. In the current study, we examined structural changes in these brain regions by taking structural magnetic resonance imaging scans of 11 ischemic stroke patients and 15 healthy participants, and analyzing the data using voxel-based morphometry. Compared with healthy participants, patients exhibited higher gray matter density in the left inferior occipital gyrus and right anterior white matter tract. In contrast, gray matter density in the right cerebellum, left precentral gyrus, right middle frontal gyrus, and left middle temporal gyrus was less in ischemic stroke patients. The changes of gray matter density in the middle frontal gyrus were negatively associated with the clin- ical rating scales of the Fugl-Meyer Motor Assessment （r = -0.609, P = 0.047） and the left middle temporal gyrus was negatively correlated with the clinical rating scales of the nervous functional deficiency scale （r = -0.737, P = 0.010）. Our findings call objectively identify the functional abnormality in some brain regions of ischemic stroke patients.

Statistical model of magnetization reversal in Nd-Fe-B sintered magnets

Statistical model of magnetization reversal was used to simulate the magnetization reversal behavior in the sintered Nd-Fe-B magnets with double grain-size distributions due to the abnormal grain growth (AGG). The magnetic properties and mechanical properties due to the formation of AGG grains in Nd-Fe-B sintered magnets were tested. The results show that the magnetic properties, especially the rectangularity were severely deteriorated after the formation of the AGG grains and a step was shown on the demagnetization curve, and the occurrence of AGG may account for the poor rectangularity and existence of the step on demagnetization curve according to the statistical model of magnetization reversal. The fracture toughness and bending strength are lowered because of the stress concentration in the AGG grains. The SEM images show that the formation of AGG grains is caused by the solid sintering due to the absence of RE-rich phase. Statistical model of magnetization reversal can qualitative by explain the dependence of the magnetization reversal behavior on the grain size in the Nd-Fe-B sintered magnets.

A Classification Algorithm for Ground Moving Targets Based on Magnetic Sensors

A novel classification algorithm based on abnormal magnetic signals is proposed for ground moving targets which are made of ferromagnetic material. According to the effect of diverse targets on earth's magnetism,the moving targets are detected by a magnetic sensor and classified with a simple computation method. The detection sensor is used for collecting a disturbance signal of earth magnetic field from an undetermined target. An optimum category match pattern of target signature is tested by training some statistical samples and designing a classification machine. Three ordinary targets are researched in the paper. The experimental results show that the algorithm has a low computation cost and a better sorting accuracy. This classification method can be applied to ground reconnaissance and target intrusion detection.

Factors Affecting the Squareness of Hysteresis Loops of Sintered NdFeB Magnets

Investigation into the magnets with different squareness of hysteresis loop(SHL) reveals that the microstructure of sintered NdFeB magnets has great effects on the SHL of the magnets. The abnormal grain growth deteriorates the SHL seriously. The shape of the grain and the grain boundary affect the intensity of demagnetization field, and consequently on the SHL. The added elements have effects on the phase structures and distributions in the magnets, which influences the uniform of demagnetization field.

Exploring the Abnormal Brain Regions and Abnormal Functional Connections in SZ by Multiple Hypothesis Testing Technique

Schizophrenia(SZ)is one of the most common mental diseases.Its main characteristics are abnormal social behavior and inability to correctly understand real things.In recent years,the magnetic resonance imaging(MRI)technique has been popularly utilized to study SZ.However,it is still a great challenge to reveal the essential information contained in the MRI data.In this paper,we proposed a biomarker selection approach based on the multiple hypothesis testing techniques to explore the difference between SZ and healthy controls by using both functional and structural MRI data,in which biomarkers represent both abnormal brain functional connectivity and abnormal brain regions.By implementing the biomarker selection approach,six abnormal brain regions and twenty-three abnormal functional connectivity in the brains of SZ are explored.It is discovered that compared with healthy controls,the significantly reduced gray matter volumes are mainly distributed in the limbic lobe and the basal ganglia,and the significantly increased gray matter volumes are distributed in the frontal gyrus.Meanwhile,it is revealed that the significantly strengthened connections are those between the middle frontal gyrus and the superior occipital gyrus,the superior occipital gyrus and the middle occipital gyrus as well as the middle occipital gyrus and the fusiform gyrus,and the rest connections are significantly weakened.

术前磁共振评价腹腔镜手术治疗剖宫产切口瘢痕缺陷相关异常子宫出血的价值及影响因素

目的:剖宫产率逐年上升,而剖宫产切口瘢痕缺陷的治疗具有较大挑战性。本研究旨在评估术前磁共振成像技术对于腹腔镜手术治疗剖宫产切口瘢痕缺陷相关异常子宫出血患者的临床价值并分析相关影响因素。方法:选择2018年至2022年在中南大学湘雅三医院妇科接受腹腔镜手术治疗剖宫产切口瘢痕缺陷相关异常子宫出血的患者共计57例,进行回顾性队列分析。将57例患者根据腹腔镜手术治疗剖宫产切口瘢痕缺陷相关异常子宫出血的术后临床治愈情况分为临床治愈组(n=28,49.1%)及非临床治愈组(n=29,50.9%)。对所有的受试者进行术后3个月的随访调查,通过logistic回归分析探讨患者的年龄、临床症状、孕产史、剖宫产史等基本临床信息、术前磁共振成像参数以及术后月经情况等与腹腔镜手术治疗剖宫产切口瘢痕缺陷相关异常子宫出血的临床治愈率的相关性。结果:2组患者的年龄、前次剖宫产年龄、怀孕次数、前次剖宫产时间、腹腔镜术前T2信号磁共振评估的子宫位置、缺陷长度、缺陷宽度、缺陷残余肌层厚度、缺陷邻近子宫肌层厚度及缺陷距宫颈外口距离等参数的差异均无统计学意义(均P>0.05)。患者的异常子宫出血症状出现时间(P=0.036,OR=1.019,95%CI 1.002~1.038)和术前磁共振成像的缺陷深度(P=0.010,OR=5.793,95%CI 1.635~25.210)是影响临床治愈率的危险因素。结论:患者异常子宫出血症状出现时间及术前磁共振评估的缺陷深度是腹腔镜手术治疗剖宫产切口瘢痕缺陷相关异常子宫出血临床治愈的影响因素,术前磁共振对于判断本病预后具有一定的临床意义。