磁力共振在磁致伸缩光纤磁场传感器中的应用

给出了影响共振频率的因素及解决频率漂移的办法 ,从而得到既有很高灵敏度又有很好稳定性的光纤直流弱磁场传感器。

扭转Alfvén波共振的数学描述

提出完备正交函数基(OFSE)展开方法,求解冕环中无耗散扭转Alfvn波。每个基函数对应冕环中每根磁力线的一个固有角频率ω_n,当冕环足点驱动频率等于磁力线的固有频率时,Alfvn波将在这根磁力线处发生共振。采用OFSE方法求解了双足点驱动时冕环Alfvn波的时变演化问题,给出了时变解析解的新形式,其中包含共振项,从共振项可以发现,在共振角频率为ω的共振磁力线附近,在时间t为π/ω的整数倍时,出现δ型间断;在t为π/(2ω)的奇数倍时,出现1/x间断。共振磁力线振幅随时间线性增加,增加的斜率正比于Alfvn波速,反比于冕环长度,与驱动频率无关。

Effects of Fe_(2)O_(3) content on microstructure and mechanical properties of CaO-Al_(2)O_(3)-SiO_(2) system

The effects of Fe2O3 content on the microstructure and mechanical properties of the CaO-Al2O3-SiO2 system were investigated by differential thermal analysis（DTA）, X-ray diffraction（XRD）, scanning electron microscopy（SEM）, electron spin resonance（ESR）, and Mssbauer spectroscopy. The results show that the addition of Fe2O3 does not affect the main crystalline phase in the prepared glasses, but it reduces the crystallisation peak temperature, increases the crystallisation activation energy, and reduces the crystal granularity. The ESR results indicate that Fe2O3 can promote crystallization, as it leads to the phase separation of the CaO-Al2O3-SiO2 system due to axial distortion. Moreover, Fe2O3 alters the network structure of the CaO-Al2O3-SiO2 system, allowing Fe3＋ to enter octahedral sites that exhibit higher symmetry than tetrahedral sites. All of these factors are favourable to increasing the bending strength. The Mssbauer results reveal that there are two types of coordination for both Fe3＋ and Fe2＋ and the bending strength of the CaO-Al2O3-SiO2 system increases with the amount of six-coordinate Fe3＋. The increasing interaction between Fe3＋ and Fe2＋ can also enhance the bending strength of the CaO-Al2O3-SiO2 system. The microhardness of the CaO-Al2O3-SiO2 system was determined to be HV 896.9 and the bending strength to be 217 MPa under the heat treatment conditions of nucleation temperature of 700 °C and nucleation time of 2 h, crystallization temperature of 910 °C and crystallization time of 3 h.

Microscopic damage and dynamic mechanical properties of rock under freeze-thaw environment

For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were conducted. After freezethaw, nuclear magnetic resonance(NMR) tests and impact loading tests were carried out, from which microscopic damage characteristics of sandstone and dynamic mechanical parameters were obtained. The results indicate that the porosity increases with the increase of cycle number, the rate of porosity growth descends at the beginning of freeze-thaw, yet accelerates after a certain number of cycles. The proportion of pores with different sizes changes dynamically and the multi-scale distribution of pores tends to develop on pore structure with the continuing impact of freeze-thaw and thawing. Dynamic compressive stress-strain curve of sandstone undergoing freeze-thaw can be divided into four phases, and the phase of compaction is inconspicuous compared with the static curve. Elastic modulus and dynamic peak intensity of sandstone gradually decrease with freeze-thaw cycles, while peak strain increases. The higher the porosity is, the more serious the degradation of dynamic intensity is. The porosity is of a polynomial relationship with the dynamic peak intensity.

三小时制立体器官模型

医疗科技除讲求先进,快捷省时也很重要,上月底在香港举行的第一届“BioLTWorld生物科技会议及展览2002”,便见证了这个趋势,医生翻查病历,一点击便一目了然,显示医疗科技已进入另一新天地。

英国科学家发现孕妇怀孕期间失去记忆的原因

英国科学家发现孕妇怀孕期间失去记忆的原因据英国科学家宣称，孕妇在怀孕期间偶尔失去记忆和精神不集中，这可能是脑部收缩所致。这种症状要在产后６个月才能消退。负责这项研究的麻醉师费尔德克罗夫特在《新科学》杂志上撰文说，１０例接受试验的健康孕妇，其脑代体积分...

BLOOD FLOW PATTERN AND QUANTITATIVE STUDY IN SOLITARY PULMONARY NODULES WITH DYNAMIC CONTRAST-ENHANCED MRI

Objective To evaluate the efficacy of contrast enhanced dynamic MRI in differentiating solitary pulmonary nodules（SPNs）. Methods Eighty-three patients with SPNs undertaken contrast enhanced dynamic MRI. Time-signal intensity curve （T-SI Curve） was made. Peak height （PH） , steepest slope （SS）, maximum enhancement （ Emax ） and the enhancement rates of signal intensity were recorded at the frst （ E1 ）, second （ E2 ）, third （ E3 ） , fourth （ E4 ） , fifth （E5）, and sixth （ E6 ） minute after injection. Results Malignant nodules and inflammatory nodules enhanced significantly higher than benign nodules, and malignant nodules and inflammatory nodules showed obviously higher PH, SS, Emax, El-E6 values than benign nodules （ P 〈 0. 01 ）. There were no sig- nificant differences in PH, SS, Emax, E1-E6 values between malignant nodules and inflammatory nodules （P 〉 0. 05）. Conclusion Contrast enhanced dynamic MR imaging can provide SPNs＇ hemodynamic information and is helpful in differentiating SPNs.

Assessment of hemodynamics in precancerous lesion of hepatocellular carcinoma:Evaluation with MR perfusion

AIM: To investigate the hemodynamic changes in a precancerous lesion model of hepatocellular carcinoma (HCC). METHODS: Hemodynamic changes in 18 Wistar rats were studied with non-invasive magnetic resonance (MR) perfusion. The changes induced by diethylnitrosamine (DEN) developed into liver nodular lesions due to hepatic cirrhosis during the progression of carcinogenesis. The MR perfusion data [positive enhancement integral (PEI)] were compared between the nodular lesions corresponding well with MR images and pathology and their surrounding hepatic parenchyma. RESULTS: A total of 46 nodules were located by MR imaging and autopsy, including 22 dysplastic nodules (DN), 9 regenerative nodules (RN), 10 early HCCs and 5 overt HCCs. Among the 22 DNs, 6 were low-grade DN (lGDN) and 16 were high-grade DN (HGDN). The average PEI of RN, DN, early and overt HCC was 205.67 ± 31.17, 161.94 ± 20.74, 226.09 ± 34.83, 491.86 ± 44.61 respectively, and their liver parenchyma nearby was 204.84 ± 70.19. Comparison of the blood perfusion index between each RN and its surrounding hepatic parenchyma showed no statistically significant difference (P = 0.06). There were significant differences in DN (P = 0.02). During the late hepatic arterial phase, the perfusion curve in DN declined. DN had an iso-signal intensity at the early hepatic arterial phase and a low signal intensity at the portal venous phase. Of the 10early HCCs, 4 demonstrated less blood perfusion and 6 displayed minimally increased blood flow compared to the surrounding parenchyma. Five HCCs showed significantly increased blood supply compared to the surrounding parenchyma (P = 0.02). CONCLUSION: Non-invasive MR perfusion can detect changes in blood supply of precancerous lesions.

Theoretical and Experimental Studies on Interactions of Cationic-Anionic Surfactants

Typical cationic and anionic surfactants were chosen and their interactions were calculated by quantum chemical method. Interaction energies are -0.2378 kJ·mol-1, -3.3394kJ·mol-1 and 0.1204kJ·mol-1 for the molecular pairs with fluocarbon and hydrocarbon chain: C4H10/C5H12, C4F10/C5H12, and C4F10 /C5F12, respectively. When hydrophilic group with cationic and anionicions is introduced, interaction energies are -287.40kJ·mol-1, -311.18kJ·mol-1 and -345.83kJ·mol-1. The results show that there is strong static interaction between cationic and anionic surfactants. It has been predicted that mixed monolayer may be formed and surface activity is enhanced favorably, especially for mixtures of cationic and anionic surfactants with fluocarbon and hydrocarbon chains. The anionic surfactants, sodium octadecylbenzenesulfonate perfluopolyetherbenzenesulonate(ANF-I) was synthesized, mixture effects of ANF-I with sodium octadecylbenzenesulfonate or dodecyldimethyl benzylammonium bromide were studied. The results indicate that the efficiency of mixing increased and the theoretical prediction was testified. These results can provide useful information for the design of new surfactants.

Transsphenoidal microsurgical treatment of infradiaphragmatic craniopharyngioma

Objective Typically,the transcranial approach has been used for the treatment of craniopharyngiomas with suprasellar extension,whereas the transsphenoidal approach has been used mostly for infradiaphragmatic craniopharyngioma.Total resection of craniopharyngioma can reduce the recurrence rate,especially in young children,but it may lead to severe complications.Therefore,any benefit of the degree of resection must be weighed against the risk of complications by the surgeons.The purpose of this study was to explore the therapeutic outcome after transsphenoidal microsurgical treatment of infradiaphragmatic craniopharyngioma and share our experiences.Methods Between January 2003 and June 2013,30 patients with infradiaphragmatic craniopharyngioma underwent transsphenoidal microsurgical resection in our hospital.The neurological,visual,and endocrine functions,and extent of resection were analyzed retrospectively.Recurrence or growth of residual tumor tissue during follow-up was assessed using magnetic resonance imaging(MRI).Results Total resection was achieved in 25 patients(83.3%),subtotal resection was achieved in 4 patients(13.3%),and partial resection was achieved in 1 patient(3.4%).There were no perioperative deaths.Cerebrospinal fluid(CSF) leakage occurred in 6 patients,and among them,2 required surgical repair of the sella.New-onset postoperative diabetes insipidus(DI) developed in 8 patients.Vision and visual fields were improved at different levels in 13 out of 16 patients who had sight impediments before treatment.Tumor recurrence and regrowth was observed in 2 patients;1 patient underwent transsphenoidal reoperation,the condition of the other patient who had undergone several craniotomies grew worse over the 6-month follow-up period.Conclusion Transsphenoidal surgery is an ideal choice in treating infradiaphragmatic craniopharyngioma.The transsphenoidal approach,which preserves pituitary function and avoids damage to the hypothalamic structures and optic nerve,is associated with fewer complications than the transcranial approach and a low mortality rate.

Theoretical Studies of Electron Paramagnetic Resonance Parameters for Cr^4＋ Ions in Ca2GeO4 Crystals

The electron paramagnetic resonance (EPR) parameters (zero-Geld splitting Dand g factors g_‖, g_⊥) of Cr~(4+) ions in Ca_2 GeO_4 crystals have been calculated from thecomplete high-order perturbation formulas of EPR parameters for a 3d~2 ion in trigonal MX_4clusters. In these formulas, in addition to the contributions to EPR parameters from the widely usedcrystal-field (CF) mechanism, the contributions from the charge-transfer (CT) mechanism (which areoften neglected) are included. From the calculations, it is found that for the high valence state3d~n ions in crystals, the reasonable explanation of EPR parameters (in particular, the g factors)should take both the CF and CT mechanisms into account.

Obstacles Facing the Implementation of Functional Magnetic Resonance Imaging （fMRI） of Brain in Jeddah City

fMRI （Functional Magnetic Resonance Imaging） is a relatively new technique that uses MRI （Magnetic Resonance Imaging） to measure the hemodynamic response （change in blood flow） related to neural activity in the brain. This paper aims to explore and identify the obstacles facing the implementation and applications of IMRI in radiology departments within Jeddah city by analyzing related data received by direct questionnaires and interviews with all the people working in MRI units in Jeddah city and finds that the major obstacle is lacking of awareness of fMRI among medical professionals and their training.

ULF波及其与能量粒子相互作用研究进展

地球磁层中的超低频波(ultra low frequencywave,简称ULF波)的全球分布特性以及与能量粒子之间的相互作用,如ULF波和粒子之间的共振调制、对能量粒子的加速等问题一直是空间物理研究中的热门问题.深入研究这些问题对于理解太阳风和磁层之间的能量传输,能量粒子加速等机制问题有着很重要的意义.本文简要介绍有关ULF波的全球分布及其与能量粒子之间共振调制的最新观测研究进展,并对将来研究工作中的问题和方向做一个简单的总结和展望.

磁暴时ULF波多卫星联合观测研究

利用Cluster C1,GOES10,12和Polar四颗卫星的观测数据,研究了在2003年10月31日21:00～23:00 UT磁暴恢复相期间,地球磁层内大尺度ULF波的全球分布特征.数据分析结果表明,位于磁层不同区域的卫星观测到的ULF波的幅度、周期等性质差别很大.对ULF波幅度的全球分布来说,ClusterC1观测到的环向模最强,这可以解释为Cluster C1所在区域内发生了磁力线共振:空腔共振的压缩波模将能量耦合传递给磁力线共振的剪切阿尔芬波,从而观测到了到的很强的环向模.对ULF波周期的全球分布来说,ClusterC1观测到的波的频谱峰值周期最短,同步轨道高度的GOES卫星观测到的峰值周期较长,而位于更远处的Polar卫星观测到的峰值周期最长.Cluster C1在L=11.7～5.3范围内观测到环向模的周期几乎相同.GOES10和Cluster C1的三种波模的平方小波相关分析表明磁力线共振区域在向日面磁层至少扩展了四个地方时的宽度范围.Polar卫星观测的环向模是驻波,而极向模是行波,这可能是开放的磁尾波导模作用的结果.由于在时段内的太阳风速度很高而动压变化不明显,因此推测观测到的ULF波是高速太阳风在磁层顶激发的Kelvin-Helmholtz不稳定性激发的.

巴西 VR进入医学界

巴西研究人员日前尝试以虚拟现实(VR)和3D打印技术相结合,呈现胎儿的模样。据报道,新技术融合超声波及磁力共振,扫描出胎儿的影像,然后利用3D技术建构一个立体的胎儿模型,以VR方式呈现,让父母预先看看胎儿的模样,更可探听其心跳。此外,新技术可让医生预先监察胎儿的健康情况,尽早发现一些难以察觉的疾病,并早作准备。同时,研究人员指出,新技术可让父母知悉胎儿是否畸形,为儿女做前期医疗决定。

太阳风正负动压脉冲激发磁层ULF波的数值模拟

磁层中的超低频波动(Ultra Low Frequency Wave,简称ULF波)通常被认为是由外界太阳风/行星际磁场扰动或者磁层内部的等离子体不稳定性激发的.当太阳风动压脉冲作用于磁层顶时,可能在磁层内部激发ULF波,从而将太阳风能量输运到地球磁层中.本文利用磁流体力学(MHD)数值模拟研究不同形式的太阳风动压脉冲作用下,在磁层中激发的ULF波的性质.我们主要关注地球磁层对太阳风动压正/负脉冲以及太阳风动压正-负脉冲对的响应.模拟结果表明,幅度和周期均相同的太阳风动压正脉冲和负脉冲,在磁层中所激发的ULF波幅度,周期均相同,然而相位相差180°.另外,对一个太阳风动压正-负脉冲对作用于偶极磁层的情况,在地球磁层内的某些特定区域仍可观察到磁力线共振(FLRs)现象,磁力线共振的区域分布和动压脉冲的周期以及动压脉冲对之间的时间间隔有关.同时模拟计算结果还表明,与单一脉冲相比较而言,在动压脉冲对的作用下,太阳风能量可以传递到地球磁层中更低纬度的区域.因此本文结果可以帮助我们更好地理解太阳风能量通过ULF波形式输运到地球磁层的机制;同时,还可以为研究有关内磁层中能量粒子对不同的行星际激波的响应方式提供线索.

行星际激波引发的电离层总电子含量波动的观测研究

行星际激波能使近地空间发生剧烈扰动.本文使用高时间分辨率(1 s)的地面GPS接收机数据,分析了2015年3月17日行星际激波事件中电离层总电子含量(TEC)的扰动.研究发现,激波到达地球后, TEC扰动呈现出超低频波动的特征,且不同纬度区域的波动特征不同:极区台站观测到的TEC波动幅度为~0.4 TECU,持续时间10 min以上,波动周期2~3 min,随穿刺点纬度的升高而增大;中低纬地区台站观测到的TEC波动幅度为~0.2 TECU,持续时间5~10 min,波动周期均为2 min左右.我们认为等离子体层的存在可能是导致这种TEC波动差异的原因,同时我们认为极区的TEC波动可能与磁力线共振有关,中低纬地区的TEC波动可能与空腔模振荡有关.本工作利用GPS TEC技术探测到了由行星际激波引发的电离层TEC波动,这将有助于进一步理解超低频波动在地球磁层-电离层系统中的性质,同时也进一步显示出GPS TEC技术在近地空间环境研究中的重要作用.

Janus γ-Fe2O3/SiO2-based nanotheranostics for dual-modal imaging and enhanced synergistic cancer starvation/chemodynamic therapy

Multimodal cancer synergistic therapy exhibited remarkable advantages over monotherapy in producing an improved therapeutic efficacy. In this work, Janus-type γ-Fe2 O3/SiO2 nanoparticles(JFSNs) are conjugated with glucose oxidase(GOx) for synergistic cancer starvation/chemodynamic therapy. The γ-Fe2O3 hemisphere of JFSNs can perform photoacoustic/T2 magnetic resonance dual-modal imaging of tumors.GOx on the surface of JFSNs catalyzes the decomposition of glucose and produces H2O2 for cancer starvation therapy. Subsequently, the γ-Fe2O3 hemisphere catalyzes the disproportionation of H2O2 to generate highly reactive hydroxyl radicals in an acidic tumor microenvironment. The close distance between GOx and JFSNs ensures adequate contact between the γ-Fe2O3 hemisphere and its substrate H2O2, thus enhancing the catalytic efficiency. This synergy of glucose depletion, biotoxic H2O2 and hydroxyl radicals significantly suppresses 4 T1 mammary tumor growth with minimal adverse effects.

Thickness effects on magnetoelectric coupling for Metglas/PZT/Metglas laminates

Thickness effects on the ME coefficient αME and electromechanical resonance frequency of Metglas/PZT/Metglas tri-layered laminates are investigated. The thickness of the magnetic plate is changed by assembling different numbers of the Metglas thin sheets （30μm for each layer） while the PZT plate is maintained at constant thickness （0.5 mm）. At 1 kHz of the applied alter- nating magnetic field, only one peak presents in the ME coefficient （OCME） versus static magnetic field （Hs） curve. As the thickness ratio n increases, the peak value of αME first increases and reaches a maximum at approximately n = 0.519, and then decreases afterward. The peak position （Hoptim） moves steadily toward a higher value as n increases. It is suggested that the re- laxation factor k of the magnetic phase is reduced as n increases, causing the decrease of the piezomagnetic coefficient d11,m and the increase of Hoptim. By employing the micromechanics model and considering the degradation of dll,m with n, an opti- mized thickness ratio of 0.5 is predicted, which is in agreement with the experimental observations. The resonance frequency of the laminate increases with n, which is consistent with the calculation using a straightforward mixture law.