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由于乙醇最有可能成为直接甲醇燃料电池(DMFC)的替代燃料,因此近年来。对乙醇的电化学氧化及直接乙醇燃料电池的研究已引起人们的很大兴趣。甲醇毒性较大并且易透过Nafion膜进入阴极造成阴极的混合电位而影响DMFC的阴极性能.这是制约DMFC走向实用化的主要问题之一。因此人们在致力于研究直接甲醇燃料电池的同时.也寻求其它的小分子醇作为甲醇的替代燃料。乙醇是除甲醇以外最简单的醇.它来源广泛.无毒,是可再生和环保型能源.并且也有较高的能量密度和反应活性。但是乙醇在电极上的完全氧化因涉及到C-C键的断裂要比甲醇困难.阳极反应动力学过程也比较缓慢。到目前为止铂基催化剂仍然是乙醇氧化最好的催化剂.虽然也有使用非铂催化剂研究乙醇的电氧化,但催化活性远不如铂基催化剂高。 相似文献
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Accurate attenuation correction is required in dedicated breast PET imaging systems for image artifact removal and quantitative studies. In this study, a method using only emission data based on consistency conditions is proposed for attenuation correction in breast PET imaging systems. The consistency conditions are exploited to evaluate the accuracy of the estimated attenuation distribution and find the appropriate parameters that yield the most consistent attenuation distribution with the measured emission data. We have proved the validity of the method with experimental investigations and single-patient studies using a dedicated breast PET. The results show that the method is capable of accurately estimating the attenuation distribution of a uniform attenuator from the experimental data with various relatively low activities. The results also show that in single-patient studies, the method is robust for the irregular boundary of breast tissue and provides a distinct improvement in image quality. 相似文献
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结构内部爆炸破坏机理和规律是常规武器毁伤效能预测与评估、建筑物和舰船抗爆防护设计的重要支撑。基于结构内爆炸载荷、内部爆炸作用下结构塑性响应、内部爆炸作用下箱壁结构破坏模式、内部爆炸作用下多箱型结构破坏模式和分布四个方面详细论述了箱型结构内部爆炸破坏的研究现状及存在的问题,并对内部爆炸后续研究给出了建议。建议研究并建立更加复杂的结构内部爆炸载荷和破坏效应描述模型、内部爆炸作用下箱壁的动力响应机理、多箱型结构与内部爆炸波产生的耦合效应、内部爆炸作用下结构的破坏模式和破坏范围的快速准确预测方法等。 相似文献
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In fully three-dimensional (3D) positron emission tomography (PET) imaging, the scatter fraction (SF) is about 40%-60%, which may degrade the imaging quality severely. Scatter correction is important for high quality image reconstruction. Model-based scatter correction has been proved to be accurate and available in clinical PET. However, it does not correct the scatter from out of the field of view (OFOV) and multiple scatters. In this study, we demonstrate the radial and axial distribution of scatters from OFOV when the source is located in different radial positions. In order to apply the above conclusions to different PET systems, we characterize the scatters from OFOV as a function of the ratio of the scanner diameter to the length of the axial field of view (AFOV) by modeling several typical whole-body and micro PET systems. The proportions of true events (S0-0), single scatter of one photon (S1-0) , single scatter of both photons (S1-1) , double scatter of one photon (S2-0) and multiple scatter (Sm) are also calculated and compared. Here the 3D-PET Monte Carlo simulations are performed with the Geant4 Application for Tomography Emission (GATE). In summary, the scatters from OFOV tend to be recorded on the lines of response (LOR) far away from the source. They have a much more serious impact on whole-body PET than micro PET depending on the ratio of scanner diameter to the length of AFOV. In whole-body PET, twice scatters including single scatter of both photons (S1-1) and double scatter of one photon (S2-0) add up to about 12% so that twice scatter correction must be taken into account to acquire a high quality reconstruction image. 相似文献
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A fully 3D OSEM reconstruction method for positron emission tomography (PET) based on symmetries and sparse matrix technique is described. Great savings in both storage space and computation time were achieved by exploiting the symmetries of scanner and sparseness of the system matrix. More reduction of storage requirement was obtained by introducing the approximation of system matrix. Iteration-filter was performed to restrict image noise in reconstruction. Performances of simulation data and phantom data got from Micro-PET (Type: Epuls-166) demonstrated that similar image quality was achieved using the approximation of the system matrix. 相似文献
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K8[ZnMg(H2O)W11O39]·15H2O的合成、表征及化学热扩渗 总被引:1,自引:1,他引:1
利用直接法合成未见文献报道的K8[ZnMg(H2O)W11O39]·15H2O,通过ICP,IR和XRD等方法对其结构进行表征,结果表明所合成的配合物具有Keggin结构.采用化学热扩渗法对合成配合物进行稀土扩渗实验,经XPS测试表明,有微量的钆渗进配合物的体相,并与组成元素存在键合作用,导电性测试结果表明,扩渗后试样的导电率提高105倍,是一种优良的固体电解质,有望成为具有实用价值的功能材料. 相似文献
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PET image reconstruction with a system matrix containing point spread function derived from single photon incidence response
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A point spread function(PSF)for the blurring component in positron emission tomography(PET)is studied.The PSF matrix is derived from the single photon incidence response function.A statistical iterative reconstruction(IR)method based on the system matrix containing the PSF is developed.More specifically,the gamma photon incidence upon a crystal array is simulated by Monte Carlo(MC)simulation,and then the single photon incidence response functions are calculated.Subsequently,the single photon incidence response functions are used to compute the coincidence blurring factor according to the physical process of PET coincidence detection.Through weighting the ordinary system matrix response by the coincidence blurring factors,the IR system matrix containing the PSF is finally established.By using this system matrix,the image is reconstructed by an ordered subset expectation maximization(OSEM)algorithm.The experimental results show that the proposed system matrix can substantially improve the image radial resolution,contrast,and noise property.Furthermore,the simulated single gamma-ray incidence response function depends only on the crystal configuration,so the method could be extended to any PET scanner with the same detector crystal configuration. 相似文献