Using three-layer vector field model,the dispersion characteristics and spectral response of long-period fiber gratings(LPFGs)with different cladding radii are analyzed.Both the numerical and experimental results demo...Using three-layer vector field model,the dispersion characteristics and spectral response of long-period fiber gratings(LPFGs)with different cladding radii are analyzed.Both the numerical and experimental results demonstrate that LPFG’s resonant wavelengths shift towards much longer wavelength and the transmission depth is strengthened significantly by decreasing cladding radius.When the cladding radius is less than 20μm,only a single resonant peak over a wavelength range of 600 nm(from 1200 nm to 1800 nm)is achieved,and the sensitivity of LPFG to external refractive index is enhanced significantly.展开更多
目的:评估术中磁共振成像(intraoperative magnetic resonance imaging,i MRI)联合神经导航在切除岛叶胶质瘤中的应用价值。方法:回顾性分析2014年8月至2017年10月中山大学附属第一医院采用3.0T i MRI联合神经导航辅助手术的41例岛叶胶...目的:评估术中磁共振成像(intraoperative magnetic resonance imaging,i MRI)联合神经导航在切除岛叶胶质瘤中的应用价值。方法:回顾性分析2014年8月至2017年10月中山大学附属第一医院采用3.0T i MRI联合神经导航辅助手术的41例岛叶胶质瘤患者的临床资料,对切除程度、并发症及预后进行评价。结果:通过i MRI发现肿瘤次全切除21例,大部分切除20例;i MRI后再次切除。术后MRI示肿瘤全切16例,次全切18例,大部分切除7例。对比i MRI前后肿瘤切除程度,差异有统计学意义(P<0.05)。41例患者在3个月至3年的随访期间,症状有所好转。结论:i MRI联合神经导航可以及时纠正脑漂移,准确评估肿瘤切除程度,最大安全范围内切除岛叶胶质瘤。展开更多
基金the National Natural Science Foundation of China(No.61007007)the Talents of North China University of Technology(No.CCXZ201307)+1 种基金the Foundation of Beijing Municipal Committee of CPC Organization Department(No.2012D005002000001)the Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions
文摘Using three-layer vector field model,the dispersion characteristics and spectral response of long-period fiber gratings(LPFGs)with different cladding radii are analyzed.Both the numerical and experimental results demonstrate that LPFG’s resonant wavelengths shift towards much longer wavelength and the transmission depth is strengthened significantly by decreasing cladding radius.When the cladding radius is less than 20μm,only a single resonant peak over a wavelength range of 600 nm(from 1200 nm to 1800 nm)is achieved,and the sensitivity of LPFG to external refractive index is enhanced significantly.
文摘氮化铝(AlN)作为一种宽带隙半导体,具有优异的物理和化学性能,在紫外发光二极管(Light Emitting Diode,LED)领域有着广泛的应用。同样,发展较为成熟的氮化镓(GaN)在该领域也有着不可替代的作用。而高性能的器件需要有良好的外延层。AlGaN基紫外LED外延层的传统制备方法是采用金属有机化学气相沉积法(Metal Organic Chemical Vapor Deposition,MOCVD),但是由于该方法中存在着强烈的预反应和Al原子本身迁移速率慢等原因,导致外延层中出现大量缺陷,使得紫外LED器件的性能降低。此外,由于不同材料以及材料与空气的折射率存在差异,使得光难以逃逸到外界,大部分光被局域在芯片内部,从而降低光提取效率以及光强。为了提高器件的光学性能,一种新的紫外LED结构被提出,文章采用时域有限差分模拟(Finite Difference Time Domain,FDTD)软件对该外延结构的光提取效率和出光强度进行了仿真。研究发现,与传统的LED结构相比,新型紫外LED结构的横磁波(TM)光模式和横电波(TE)光模式的光提取效率分别提高了19.1%和29.3%,最大出光强度分别提高了42.78%和47.18%,对器件的光学性能有着显著的改善。另外,文章还研究了新型紫外LED外延层的结构参数对器件整体光学性能的影响,在光源、物理模型尺寸和仿真条件等因素不变的情况下,获得了光学性能最佳的结构参数。
