THEORETICAL EXPRESSION AND MONTE CARLO SIMULATION OF DIFFUSION BEHAVIORS IN NMR WITH NONLINEAR FIELD GRADIENTS

利用传播子方法研究了在一般非线性场梯度下NMR信号的扩散衰减 .在自由扩散和平板间的限制扩散情况下获得了扩散衰减因子的理论表达式 .该表达式适用范围宽 ,且具有较简单的数学形式和明确的物理意义 .文中还将理论预测与蒙特卡罗模拟结果进行了比较 .结果表明 :文中所采用的理论方法适合于表述自由扩散和短脉冲近似下的受限扩散 ;蒙特卡罗模拟提供了一种定性研究MRI和NMR中非均匀场梯度扩散衰减的方法A propagator method was used to calculate diffusion attenuation of the NMR signal under general nonlinear field gradients. Theoretical expressions of the attenuation factor were obtained for free and restricted diffusion between two plates. Monte Carlo simulation was performed and the results were compared with the theory. It shows that the theoretical method is appropriate for the free diffusion, as well as the restricted diffusion under the short gradient pulse approximation. Monte Carlo simulation provides an alternate way to quantify the effects of inhomogeneous field gradients used in MRI and NMR.ProjectSupportedbytheNationalNaturalScienceFoundationofChina( 1 0 0 0 5 0 0 6,1 0 1 0 40 1 1and1 0 2 3 40 70

Theoretical Expression and Computer Simulation of Diffusion Behaviors in Multiple-Quantum Coherence NMR

改进了Warren所提出的CRAZED脉冲序列以研究分子间多量子相干的扩散过程 ,讨论了利用核磁共振测量分子内和分子间多量子相干表观自扩散系数的理论表述 ,采用粒子的随机行走模型模拟其扩散行为 .在短脉冲近似和长脉冲梯度场两种实验条件下 ,分别获得了因扩散引起的不同相干阶数的相对信号衰减强度随梯度场脉冲间隔时间的变化曲线 ,由此得到分子内多量子相干和分子间多量子相干的表观扩散率与溶液分子扩散系数的关系 .还将计算机模拟结果与理论预测进行分析和比较 ,发现二者能很好地吻合 .研究结果表明 ,分子间多量子相干的表观扩散率与常规的分子内多量子相干的表观扩散率明显不同 ,因此 ,分子间多量子相干的表观扩散率可能提供一种新的核磁共振成像的对比度机理Self-diffusion is one of the most fundamental motions of particles in liquid. Nuclear magnetic resonance (NMR) provides a convenient and noninvasive means for accurately measuring the self-diffusion coefficient of molecules in solution. The theoretical expressions of apparent diffusion rates of MQCs are given and computer simulation based on the method to measure the self-diffusion coefficient by NMR was discussed and the random walk model of particles is used to simulate the apparent diffusion behaviors of intra-molecular and inter-molecular multiple-quantum coherences (MQCs). The results of computer simulation agree well with theoretical predictions.ProjectsupportedbytheNationalNaturalScienceFoundationofChina (10 2 340 70and 10 10 4 0 11)andtheNaturalScienceFoundationofFujianprovince (A0 2 10 0 0 3

Theoretical Calculation of B arrier Height of Metal-semiconductor Contacts

【中文文摘】采用平均键能作为参考能级计算了十种金属 -半导体接触势垒高度 ,其计算结果与实验值的符合程度不亚于 Tersoff和 M o¨ nch所采用的电中性能级方法 ,计算结果表明平均键能方法和 Tersoff提出的电中性能级方法一样 ,可作为金属 -半导体接触势垒高度的一种理论计算方法 【英文文摘】Taken the average -bond-energy as the reference level,ten barrier heights of metal-semiconductor c ontacts are calculated.The coincident de gree of our calculational values and exp erimental values is not less than that o f charge-neutrality point method,adopted by Tersoff and M o¨ nc h.It shows that the average-bond-energy method,similar to Tersoff's charge-neutr ality point method,can be used as one of the methods in theoretical calculation of metal-semiconductor contacts.厦门大学校级自选课题 (Y0 70 10 )资

磁共振成像中背景不均匀场去除方法研究

磁敏感加权成像(susceptibility weighted imaging,SWI)是近年来新开发的磁共振成像技术,最早由E.Mack Haacke等于1997发明[1],并最初被称作"高分辨率血氧水平依赖静脉成像"(high resolution blood oxygenation level dependent venographic imaging)。中央高校基本科研业务费专项资金(2010121101);国家自然科学基金(81171331

基于分子间多量子相干的不均匀磁场下高分辨核磁共振方法的研究进展

高分辨核磁共振(nuclear magnetic resonance,NMR)通常需要高度均匀的强静磁场,然而在活体实验等情况下,样品的磁化率差异将不可避免地导致磁场的不均匀,并且这种不均匀性难以通过匀场等传统方法消除.最近,分子间多量子相干被利用来消除活体等样品中由磁场不均匀引起的谱线增宽以获得高分辨NMR谱.和其他高分辨NMR方法相比,分子间多量子相干方法具有独特的特征与优势,它能同时保留化学位移、峰的裂分模式、偶合常数和相对峰面积等信息.这些信息在传统的一维NMR中通常用于分析和表征分子结构.国家自然科学基金资助项目(批准号:20573084,10575085和10774125

NMR Studies on Interactions between Oxalate-oxodiperoxovanadate and Arginine

【中文文摘】应用多核 (1H ,13 C ,15N和51V)NMR、二维扩散排序谱 (2DDOSY)、变温NMR以及电喷雾质谱 (ESI MS)等谱学方法研究草酸双过氧钒配合物与精氨酸 (Arg)的相互作用 ,发现该相互作用体系可生成以氨基配位的新过氧钒物种[OV(O2 ) 2 Arg] -,研究结果表明综合利用上述谱学方法有助于揭示此类相互作用体系的反应过程和配位机制 【英文文摘】Coordination interactions between oxalate-oxodiperoxovanadate {K 3[VO(O 2) 2(C 2O 4)]·H 2O, abbr. bpV~(oxa)} and arginine (abbr. Arg) in solution were studied by 1D multinuclear ( 1H, 13C, 15N, and 51V) NMR, 2D diffusion ordered spectroscopy (DOSY), variable temperature NMR, and electrospray ionization mass spectrometry (ESI-MS). Spectroscopic results indicated that a new peroxovanadate species [OV(O 2) 2Arg] - was formed in which Arg coordinates to vanadium through amino group. It is proved that these methods are useful for analyzing and characterizing the reaction processes and coordination modes in this kind of the interaction systems.国家自然科学基金 (Nos.1 0 2 340 70,1 0 0 0 50 0 6 ,1 0 1 0 4 0 1 1 );固体表面物理化学国家重点实验室资助项

Interactions between Diperoxovanadate and 2-Methyl-imidazole Studied by NMR Spectroscopy

为探讨过氧钒配合物上有机配体对反应平衡的影响,在模拟生理条件下(0.15MOl/lnACl溶液)应用多核(1H,13C,和51V)多维(COSy和dOSy)nMr以及变温技术等谱学方法研究双过氧钒配合物[OV(O2)2l]n-{n=1~3,l=OXAlATE(缩写为OXA),PICOlInATE(缩写为PIC),bIPyrIdInE(缩写为bIPy),和1,10-PHEnAnTHrOlInE(缩写为PHEn),与它们配位的含钒物种分别缩写为bPV(OXA),bPV(PIC),bPV(bIPy)和bPV(PHEn)}与2-甲基咪唑(缩写为2-ME-IMI)的相互作用,实验结果表明2-ME-IMI与4种双过氧钒配合物的反应性从强到弱的顺序为:bPV(OXA)>bPV(PIC)>bPV(bIPy)>bPV(PHEn).研究表明金属中心上配体的配位能力和空间位阻都对反应平衡产生较大的影响关,键同词时:竞争配位的结果导致新的六配位的过氧物种[OV(O2)2(2-ME-IMI)]-的生成.To understand the effects of organic ligands on reaction equilibrium,the interactions between diperoxovanadate complexes [OV(O2)2LL']n-(n=1--3; LL'=oxalate,picolinate,2,2'-bipyridine,and 1,10-phenanthroline) and 2-methyl-imidazole in 0.15 mol/L NaCl ionic medium,which was used to mimick physiological conditions,were explored using multinuclear (1H,13C,and 51V) NMR spectroscopy and variable temperature experiments.The experimental results indicated the reactivities of the four diperoxovanadate complexes with 2-methyl-imidazole were as follows:bpV(oxalate)>bpV(picolinate)>bpV(2,2'-bipyridine)>bpV(1,10-phenanthroline).Both the coordination capability and the steric effects of the organic ligands affected reaction equilibrium.New six-coordinated peroxovanadate species [OV(O2)2(2-methyl-imidazole)]-were formed due to competitive coordination.supportedbyKeyProjectofHealthandScienceandTechnologyofXiamen(3502Z20051027);ScienceResearchFoundationofMinistryofHealth&UnitedFujianProvincialHealthandEducationProjectforTackilingtheKeyResearch(WKJ2008-2-36);NationalNatu-ralScienceFoundationofChina(20803

Valence-band offsets of strained heterojunction ZnS/ZnSe

采用基于lMTO-ASA的平均结合能计算方法，研究了在znSXSE1-X衬底上沿（001）方向外延生长的应变层异质结znS/znSE的价带带阶值。研究表明，应变的结果使价带带阶随衬底组分（X）的变化呈非线性且单调的关系；与其他理论计算和实验结果比较，本文的计算结果比较理想The valence-band offsets (VBO) of strained heterojunction ZnS/ZnSe as a function of the alloy composition x of ZnS x Se 1- x substrates are studied using the average-bond-energy theory based on LMTO-ASA method.It is shown that the strain leads to the nonlinear and monotonous variation of VBO's with x .The calculation results are more desirable compared with the theoretical and experimental data previously reported.国家和福建省自然科学基

VALENCE BAND ofFSETS of TERNARY ALLOY HETEROJUNCTIONS (AlP) x (Si 2) 1-x /GaP AND (GaP) x (Si 2) 1-x /GaP

采用基于lMTOASA的平均键能计算方法和原子集团展开方法，研究了两组晶格匹配三元合金异质结（AlP）X（SI2）1-X/gAP和（gAP）X（SI2）1-X/gAP的价带带阶ΔEV（X）值。研究表明，两组异质结的ΔEV（X）值随合金组分X的变化都是非线性的，且表现出非单调的关系。The valence band ofFsets Δ E v(x) as a Function of the alloy compositon x of two typical lattice matched ternary alloy heterojunctions (AlP) x (Si 2) 1-x /GaP and (GaP) x (Si 2) 1-x /GaP are studied by using the average bond energy theory in conjunction with the cluster expansion method.It is shown that the variations of Δ E v(x) at (AlP) x (Si 2) 1-x /GaP and (GaP) x (Si 2) 1-x /GaP are nonlinear and non monotonous.The calculated results of Δ E v are in very good agreement with the data previously reported.国家和福建省自然科学基