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1968年,Leksell在瑞典制造了世界上第一台立体定向放射治疗装置,它以γ射线为破坏手段,能像手术刀一样将病灶消除,所以简称γ刀。另一种X刀是用电子直线加速器产生的X光子来作放射外科手术,它始于80年代,由意大利学者Colombo研制成功,对应于γ刀被称为X刀。γ刀与X刀是一种不需开颅手术,而能治疗脑肿瘤等疾病的无创性新技术,对神经外科治疗起极大推动作用,并形成立体定向放射神经外科学这门新的学科。一、原理X射线与γ射线对生物体的作用基本相同,主要是通过光电效应、康普顿散射、电子对产生3种方式转移能量。 相似文献
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IntroductionThetransportofcontaminantsinunsaturatedzonehascausedmuchattention .Inearly1960s,contaminationproblemsofsoilandgroundwaterhadbeenstudiedathomeandabroad[1].Andinrecentyears ,thetransformationandtransportationofcontaminantshavebeendeeplystudiedinthefieldsofhydrogeology ,petroleumengineering ,environmentalengineeringandsoon[2 ,3].Somecontaminanttransportmodelshavebeenpresentedsofar.Forexample ,Paker[4 ]etal.presentedaconstitutivemodelgoverningparametersofwater,gasandcontaminantswhenth… 相似文献
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污染物在非饱和带内运移的流固耦合数学模型及其渐近解 总被引:3,自引:0,他引:3
污染物在非饱和带中运移过程是多组分多相渗流问题.在考虑气相的存在对水相影响的前提下,基于流固耦合力学理论,建立了污染物在非饱和带内运移的流固耦合数学模型.对该强非线性数学模型采用摄动法及积分变换法进行拟解析求解,得出了解析表达式.对非饱和带内的孔隙压力分布、孔隙水流速以及污染物的浓度在耦合与非耦合气相条件下的分布规律进行解析计算.对该渐近解与Faust模型的计算结果进行了对比分析,结果表明:该模型解与Faust解基本吻合,且气相作用以及介质的变形对溶质的输运过程产生较大的影响,从而验证了解析表达式的正确性和实用性.这为定量化预报预测污染物在非饱和带中迁移转化和实验室确定压力-饱和度-渗透率三者之间的关系提供了可靠的理论依据. 相似文献
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Two coordination polymers(CPs),{[Ag(ADA)_(0.5)(DPE)]·H_2O}_n(1) and {[Ag(ADA)_(0.5)(Bipy)_(0.5)]·H_2O}_n(2),(H_2ADA = 3,3-azodibenzoic acid,DPE = 1,2-di(4-pyridyl)-ethylene,Bipy = 4,4?-bipyridine),have been synthesized via solvothermal reactions of Ag+ with ADA~(2-) and/or DPE,Bipy.CPs 1 and 2 were characterized by elemental analyses,IR spectra,thermal behaviors,and X-ray single-crystal diffraction.CPs 1 and 2 feature "Ag···Ag" subunits.CP 1 shows a 3D construction,in which the "Ag···Ag" subunits extend through ADA~(2-) and DPE ligands using μ6-kO,O;kO;kO;kO,O;kO;kO and μ_2-kO;kO coordination modes,respectively.It crystallizes in triclinic system,space group P1,with a = 0.3808(18),b = 1.2476(6),c = 1.309(6) nm,α = 76.757(5),β = 84.649(5),γ = 86.809(5)o,V = 0.6024(5) nm~3,Z = 2,Mr = 351.11,C_(13)H_(11)AgN_2O_3,Dc = 1.936 g/cm3,F(000) = 348,S = 1.064,R = 0.0323 and w R = 0.0689.CP 2 exhibits a 3 D supramolecular structure,in which the "Ag···Ag" subunits are connected by ADA~(2-) and DPE ligands with μ_6-kO;kO;kO,O;kO;kO and μ_2-kO;kO coordination modes,respectively.Ultimately,through hydrogen bond and π???π interaction,the "Ag···Ag" subunits stabilize the 3D supramolecular structure of 2.It crystallizes in monoclinic,space group C2/c,with a = 25.301(15),b = 13.197(8),c = 6.970(4) nm,β = 102.597(7)o,V = 2.271(2) nm~3,Z = 8,C_(12)H_(10)AgN_2O_(2.50),M_r = 330.09,D_c = 1.931 g/cm~3,F(000) = 1304,S = 1.082,R = 0.1107 and wR = 0.2984.The fluorescence properties of CPs 1 and 2 have been also investigated. 相似文献
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Experimental and computational study of visible light-induced photocatalytic ability of nitrogen ions-implanted TiO_2 nanotubes 下载免费PDF全文
Nitrogen-doped TiO2 nanotubes(TNTs)were prepared by ion implantation and anodic oxidation.The prepared samples were applied in photocatalytic(PC)oxidation of methyl blue,rhodamine B,and bisphenol A under light irradiation.To explore the influence of doped ions on the band and electronic structure of TiO2,computer simulations were performed using the VASP code implementing spin-polarized density functional theory(DFT).Both substitutional and interstitial nitrogen atoms were considered.The experimental and computational results propose that the electronic structure of TiO2 was modified because of the emergence of impurity states in the band gap by introducing nitrogen into the lattice,leading to the absorption of visible light.The synergy effects of tubular structures and doped nitrogen ions were responsible for highly efficient and stable PC activities induced by visible and ultraviolet(UV)light. 相似文献
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正电子发射型计算机断层成像(positronemissioncomputedtomograph简称PET),其原理是将含有发射正电子的放射性核素,如18F、11C、15O、13N等显像剂注入或吸入人体,通过探测正电子放射性核素衰变时产生的正电子与组织内电子湮灭产生两个能量相等、方向相反的γ光子,由计算机重建图像,显示人体代谢和生化等改变,被誉为活体的分了断层图像。因此PET能将人的思维、行为和脑化学联系起来,探讨、解释和定位人脑的功能活动,对于许多精神、情感、功能及运动障碍等功能性疾病,PET具有理论意义和实用价值。 相似文献
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研究了两亲聚合物聚 (2 -丙烯酰胺基十六烷磺酸 ) (PAMC16S)存在下 1 -乙基 -3 ,3 -二甲基螺 [吲哚啉 -萘并口恶嗪 ](SO -E)在水溶液中的增溶作用及PAMC16S对SO -E化学和光化学性质的影响。PAMC16S明显增加了SO -E在水相的溶解性 ,SO -E的最大增溶浓度随PAMC16S浓度增加呈线性增加规律。在PAMC16S存在下 ,新配制的SO -E溶液显示可逆的光致变色性 ,显色体呈红色 ,最大吸收峰位于 5 2 0nm ,在室温下的消色反应速度明显慢于无PAMC16S存在下的兰色显色体。SO -E/PAMC16S溶液是不稳定的 ,配制后较长时间即失去SO -E的正常光致变色性质。盐酸具有与PAMC16S相似的作用 ,SO -E/PAMC16S体系的不稳定性可用氨水中和的方法解决。1H -NMR结果表明SO -E在酸性介质中发生了不可逆的化学反应。 相似文献
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