Mn掺杂LiFePO4的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 计算了不同Mn掺杂浓度LiFe_1-xMn_xPO₄ (x=0,0.25,0.50,0.75) 的电子结构. 同时采用流变相辅助高温固相碳热还原法制备了LiFe_1-xMn_xPO₄ (x= 0,0.25,0.50,0.75) 材料. 理论计算表明: LiFePO₄具有E_g = 0.725 eV的带隙宽度, 为半导体材料. 通过Fe位掺杂25%的Mn离子可最大程度地 减小材料带隙宽度、降低Fe---O键及Li---O键键能, 进而提高材料的电子电导率及锂离子扩散速率. 实验结果亦表明, 当Mn掺杂量x=0.25时, 材料具有最优的电化学性能, 其具有约为158 mAh· g^-1的放电比容量以及551 Wh· kg^-1的能量密度. 理论计算与实验结果非常符合.     

锂离子蓄电池正极材料LiFePO4研究进展

锂离子电池正极材料正在向着高比能量、长寿命、低成本、环境友好的方向发展,而具有橄榄石结构的LiFePO_4正极材料以其结构稳定、成本低、无污染等优点成为21世纪最理想的绿色电源,但自身也存在缺点。综述了锂离子电池正极材料LiFePO_4的研究进展。系统地阐述了LiFePO_4的晶体结构特征及性能、多种合成方法以及掺杂多种导电材料和控制晶体生长制备纳米粉体对材料性能的影响。对该材料的应用前景进行了展望,并提出了下一步可能的研究趋势。     

Forward and inverse problem for cardiac magnetic field and electric potential using two boundary element methods

This paper discusses the forward and inverse problem for cardiac magnetic fields and electric potentials.A torso-heart model established by boundary element method(BEM) is used for studying the distributions of cardiac magnetic fields and electric potentials.Because node-to-node and triangle-to-triangle BEM can lead to discrepant field distributions,their properties and influences are compared.Then based on constructed torso-heart model and supposed current source functional model-current dipole array,the magnetic and electric imaging by optimal constrained linear inverse method are applied at the same time.Through figure and reconstructing parameter comparison,though the magnetic current dipole array imaging possesses better reconstructing effect,however node-to-node BEM and triangleto-triangle BEM make little difference to magnetic and electric imaging.     

LiAl0.03Mn1.97O4的流变相辅助微波合成以及电化学性能

采用一种特殊微波合成法，流变相辅助微波合成法，制备了结晶度好、纯度高的尖晶石相的锂离子电池正极材料LiAl0.03Mn1.97O4。对其进行了XRD分析和SEM研究，并就结构、形貌与传统固相法制备的LiMn2O4、LiAl0.03Mn1.97O4进行了比较。采用这种流变相辅助微波合成法制备的LiAl0.03Mn1.97O4具有优良的电化学性能，电化学性能测试表明，这种材料具有比较高的首次放电容量（115mAh／g）以及良好的可逆性、优异的循环性能，25次循环结束比容量几乎不变，保持在115mAh／g左右，衰减性得到很好的改善。     

锂离子蓄电池正极材料LiFePO4研究进展

锂离子电池正极材料正在向着高比能量、长寿命、低成本、环境友好的方向发展，而具有橄榄石结构的LiFePO4正极材料以其结构稳定、成本低、无污染等优点成为21世纪最理想的绿色电源，但自身也存在缺点。综述了锂离子电池正极材料LiFePO4的研究进展。系统地阐述了LiFePO4的晶体结构特征及性能、多种合成方法以及掺杂多种导电材料和控制晶体生长制备纳米粉体对材料性能的影响。对该材料的应用前景进行了展望，并提出了下一步可能的研究趋势。     

基于心磁信号的心脏电流偶极子阵列成像及相关性质的研究

超导量子干涉器（SQUID）能探测到微弱的心脏磁场信号. 通过对所得的心磁信号进行分析,可为许多心脏疾病的诊断提供依据. 利用心磁信号,采用极小范数最小二乘法（MNLS）对心脏的电流偶极子阵列进行重建,从而实现了对心脏内部等效电流源的成像. 在使用MNLS进行电流偶极子阵列反演重建的过程中,反演所需的心磁信号,分别由单电流偶极子和电流多极子作为激发源模拟得到,以及由SQUID实际测量得到. 同时,对不同心磁信号反演得到的电流偶极子的分布规律进行了分析. 此外,还给模拟的人体外心磁信号施加了均匀噪声和随机噪声,研究不同信噪比的均匀噪声和随机噪声对电流偶极子阵列重建的影响.     

Cardiac magnetic source imaging based on current multipole model

It is widely accepted that the heart current source can be reduced into a current multipole. By adopting three linear inverse methods, the cardiac magnetic imaging is achieved in this article based on the current multipole model expanded to the first order terms. This magnetic imaging is realized in a reconstruction plane in the centre of human heart, where the current dipole array is employed to represent realistic cardiac current distribution. The current multipole as testing source generates magnetic fields in the measuring plane, serving as inputs of cardiac magnetic inverse problem. In the heart-torso model constructed by boundary element method, the current multipole magnetic field distribution is compared with that in the homogeneous infinite space, and also with the single current dipole magnetic field distribution. Then the minimum-norm least-squares (MNLS) method, the optimal weighted pseudoinverse method (OWPIM), and the optimal constrained linear inverse method (OCLIM) are selected as the algorithms for inverse computation based on current multipole model innovatively, and the imaging effects of these three inverse methods are compared. Besides, two reconstructing parameters, residual and mean residual, are also discussed, and their trends under MNLS, OWPIM and OCLIM each as a function of SNR are obtained and compared.     

A new magneto-cardiogram study using a vector model with a virtual heart and the boundary element method

A cardiac vector model is presented and verified, and then the forward problem for cardiac magnetic fields and electric potential are discussed based on this model and the realistic human torso volume conductor model, including lungs. A torso-cardiac vector model is used for a 12-lead electrocardiographic (ECG) and magneto-cardiogram (MCG) simulation study by using the boundary element method (BEM). Also, we obtain the MCG wave picture using a compound four-channel HTc ·SQUID system in a magnetically shielded room. By comparing the simulated results and experimental results, we verify the cardiac vector model and then do a preliminary study of the forward problem of MCG and ECG. Therefore, the results show that the vector model is reasonable in cardiac electrophysiology.     

乳液法制备球形锰酸锂及其影响因素

文章介绍了目前锂离子电池正极材料球形化制备的情况，对乳液法二次造粒的方法及其机理进行了初步探讨。以微波合成法制备的LiMn2O4作为一次颗粒，采用一种特殊的乳液法二次造粒，初步制备了球形LiMn2O4正极材料。对二次造粒的产物进行了SEM、XRD分析，测试了其振实密度，发现在二次造粒过程中一次颗粒有一定生长，二次颗粒球状形貌还不够理想，分析了原因，为进一步研究打下基础。     

The forward and inverse problem of cardiac magnetic fields based on concentric ellipsoid torso-heart model

<正>This paper constructs a concentric ellipsoid torso-heart model by boundary element method and investigates the impacts of model structures on the cardiac magnetic fields generated by both equivalent primary source—a current dipole and volume currents.Then by using the simulated magnetic fields based on the torso-heart model as input,the cardiac current sources—an array of current dipoles by optimal constrained linear inverse method are constructed.Next, the current dipole array reconstruction considering boundaries are compared with that in an unbounded homogeneous medium.Furthermore,the influence of random noise on reconstruction is also considered and the reconstructing effect is judged by several reconstructing parameters.