采用涡度相关技术对南方"双季稻-冬闲田"生态系统CO_2通量进行了一年的连续监测,分析了"双季稻-冬闲田"生态系统碳交换[净碳交换量(NEE)、总初级生产力(GPP)和生态系统总呼吸(Reco)]的动态变化及其影响因子。结果表...采用涡度相关技术对南方"双季稻-冬闲田"生态系统CO_2通量进行了一年的连续监测,分析了"双季稻-冬闲田"生态系统碳交换[净碳交换量(NEE)、总初级生产力(GPP)和生态系统总呼吸(Reco)]的动态变化及其影响因子。结果表明:南方"双季稻-冬闲田"生态系统NEE具有明显的日变化和季节变化,NEE月平均日变化在生长季表现为较明显的"U"型曲线,不同月份"U"型高度不同;NEE季节变化存在明显的两个吸收期(NEE为负)和三个排放期(NEE为正),NEE在早稻和晚稻的生长季有两个明显的碳吸收期,早稻平均值为-0.58 g C·m^(-2)·d^(-1),最大值出现在2015年6月20日,为-1.77 g C·m^(-2)·d^(-1),晚稻平均值为-1.28 g C·m^(-2),最大值出现在2015年9月19日,为-2.23 g C·m^(-2)·d^(-1);冬闲期存在两个碳排放期,平均值为2.68 g C·m^(-2)·d^(-1)。水稻种植期间白天的净碳交换受光合有效辐射的影响显著,夜间的净碳交换受5 cm土壤温度的显著影响,温度低时的冬闲期温度敏感性高于温度高时的双季稻种植期。全年的NEE总和表现为碳排放,达778.4 g C·m^(-2),GPP为1 643.7 g C·m^(-2),Reco为2 425.8 g C·m^(-2)。因此,南方"双季稻-冬闲田"生态系统有可观的固碳减排潜力。展开更多
Objective:To investigate the feasibility of a 4D-CT reconstruction method based on the similarity principle of spatial adjacent images and mutual information measure. Methods:A motor driven sinusoidal motion platform ...Objective:To investigate the feasibility of a 4D-CT reconstruction method based on the similarity principle of spatial adjacent images and mutual information measure. Methods:A motor driven sinusoidal motion platform made in house was used to create one-dimensional periodical motion that was along the longitudinal axis of the CT couch. The amplitude of sinusoidal motion was set to an amplitude of ±1 cm. The period of the motion was adjustable and set to 3.5 s. Phantom objects of two eggs were placed in a Styrofoam block, which in turn were placed on the motion platform. These objects were used to simulate volumes of interest undergoing ideal periodic motion. CT data of static phantom were acquired using a multi-slice general electric (GE) LightSpeed 16-slice CT scanner in an axial mode. And the CT data of periodical motion phantom were acquired in an axial and cine-mode scan. A software program was developed by using VC++ and VTK software tools to resort the CT data and reconstruct the 4D-CT. Then all of the CT data with same phase were sorted by the program into the same series based on the similarity principle of spatial adjacent images and mutual information measure among them, and 3D reconstruction of different phase CT data were completed by using the software. Results:All of the CT data were sorted accurately into different series based on the similarity principle of spatial adjacent images and mutual information measures among them. Compared with the unsorted CT data, the motion artifacts in the 3D reconstruction of sorted CT data were reduced significantly, and all of the sorted CT series result in a 4D-CT that reflected the characteristic of the periodical motion phantom. Conclusion:Time-resolved 4D-CT reconstruction can be implemented with any general multi-slice CT scanners based on the similarity principle of spatial adjacent images and mutual information measure.The process of the 4D-CT data acquisition and reconstruction were not restricted to the hardware or software of the CT scanner and has the feasibility ,which extensive applicability.展开更多
Objective:To investigate the influences of motion artifacts on three-dimensional (3D) reconstruction volume and conformal radiotherapy planning. Methods:A phantom which can mimic the clip motion of lung tumor along th...Objective:To investigate the influences of motion artifacts on three-dimensional (3D) reconstruction volume and conformal radiotherapy planning. Methods:A phantom which can mimic the clip motion of lung tumor along the cranial-caudal direction is constructed by step motor, small ball of polyethylene and potato. Ten different scan protocols were set and CT data of the phantom were acquired by using a commercial GE LightSpeed16 CT scanner. The 3D reconstruction of the CT data was implemented by adopting volume-rendering technology of GE AdvantageSim 6.0 system. The reconstructed volumes of each target in different scan protocols were measured through 3D measuring tools. Thus, relative deviations of the reconstruction volumes between moving targets and static ones were determined. The three-dimensional conformal radiation therapy (3D-CRT) plans and conformal fields were created and compared for a static/moving target with the WiMRT treatment planning system (TPS). Results:For a static target, there was no obvious difference among the 3D reconstruction volumes when the CT data were acquired with different pitches and slices. The appearance of 3D reconstruction volume and 3D conformal field of a moving target was quite different from that of static one. The maximum relative deviation is nearly 90% for a moving target scanned with different scan protocols. The relative deviations are variable among the different targets, about from -39.8% to 89.5% for a smaller target and from -18.4% to 20.5% for a larger one. Conclusion:The motion artifacts have great effects on 3D-CRT planning and reconstruction volume, which will greatly induce distorted conformal radiation fields and false DVHs for a moving target.展开更多
Objective: Neurons in the cochlear nucleus show different response patterns to the short tone bursts. Because of the limitations of animal experiments, it is hard to explore the principle. Therefore, using a model to ...Objective: Neurons in the cochlear nucleus show different response patterns to the short tone bursts. Because of the limitations of animal experiments, it is hard to explore the principle. Therefore, using a model to simulate CN neurons will be a feasible way. Methods: Based on the initial model mentioned in the previous study, we proposed an improved CN model in MATLAB R2012b. Results: By modifying the parameters of the model we found the interchanges among "primary-like", "chopper",and "onset" response patterns. Furthermore, we simulated the "pauser" response pattern by adding an extra input in our model. Conclusion: The results indicate that the synaptic integrations and the input modes can give rise to different characteristics of CN neurons, which eventually determine the response patterns of CN neurons.展开更多
Computed tomography(CT) plays an important role in the field of modern medical imaging. Reducing radiation exposure dose without significantly decreasing image's quality is always a crucial issue. Inspired by the ...Computed tomography(CT) plays an important role in the field of modern medical imaging. Reducing radiation exposure dose without significantly decreasing image's quality is always a crucial issue. Inspired by the outstanding performance of total variation(TV) technique in CT image reconstruction, a TV regularization based Bayesian-MAP(MAP-TV) is proposed to reconstruct the case of sparse view projection and limited angle range imaging. This method can suppress the streak artifacts and geometrical deformation while preserving image edges. We used ordered subset(OS) technique to accelerate the reconstruction speed. Numerical results show that MAP-TV is able to reconstruct a phantom with better visual performance and quantitative evaluation than classical FBP,MLEM and quadrate prior to MAP algorithms. The proposed algorithm can be generalized to cone-beam CT image reconstruction.展开更多
文摘采用涡度相关技术对南方"双季稻-冬闲田"生态系统CO_2通量进行了一年的连续监测,分析了"双季稻-冬闲田"生态系统碳交换[净碳交换量(NEE)、总初级生产力(GPP)和生态系统总呼吸(Reco)]的动态变化及其影响因子。结果表明:南方"双季稻-冬闲田"生态系统NEE具有明显的日变化和季节变化,NEE月平均日变化在生长季表现为较明显的"U"型曲线,不同月份"U"型高度不同;NEE季节变化存在明显的两个吸收期(NEE为负)和三个排放期(NEE为正),NEE在早稻和晚稻的生长季有两个明显的碳吸收期,早稻平均值为-0.58 g C·m^(-2)·d^(-1),最大值出现在2015年6月20日,为-1.77 g C·m^(-2)·d^(-1),晚稻平均值为-1.28 g C·m^(-2),最大值出现在2015年9月19日,为-2.23 g C·m^(-2)·d^(-1);冬闲期存在两个碳排放期,平均值为2.68 g C·m^(-2)·d^(-1)。水稻种植期间白天的净碳交换受光合有效辐射的影响显著,夜间的净碳交换受5 cm土壤温度的显著影响,温度低时的冬闲期温度敏感性高于温度高时的双季稻种植期。全年的NEE总和表现为碳排放,达778.4 g C·m^(-2),GPP为1 643.7 g C·m^(-2),Reco为2 425.8 g C·m^(-2)。因此,南方"双季稻-冬闲田"生态系统有可观的固碳减排潜力。
基金Guangzhou Municipal Medicine &Health ProgramGrant number:2006-YB-177+1 种基金Guangdong Province Medicine Scientific Research ProgramGrant number:A2007290
文摘Objective:To investigate the feasibility of a 4D-CT reconstruction method based on the similarity principle of spatial adjacent images and mutual information measure. Methods:A motor driven sinusoidal motion platform made in house was used to create one-dimensional periodical motion that was along the longitudinal axis of the CT couch. The amplitude of sinusoidal motion was set to an amplitude of ±1 cm. The period of the motion was adjustable and set to 3.5 s. Phantom objects of two eggs were placed in a Styrofoam block, which in turn were placed on the motion platform. These objects were used to simulate volumes of interest undergoing ideal periodic motion. CT data of static phantom were acquired using a multi-slice general electric (GE) LightSpeed 16-slice CT scanner in an axial mode. And the CT data of periodical motion phantom were acquired in an axial and cine-mode scan. A software program was developed by using VC++ and VTK software tools to resort the CT data and reconstruct the 4D-CT. Then all of the CT data with same phase were sorted by the program into the same series based on the similarity principle of spatial adjacent images and mutual information measure among them, and 3D reconstruction of different phase CT data were completed by using the software. Results:All of the CT data were sorted accurately into different series based on the similarity principle of spatial adjacent images and mutual information measures among them. Compared with the unsorted CT data, the motion artifacts in the 3D reconstruction of sorted CT data were reduced significantly, and all of the sorted CT series result in a 4D-CT that reflected the characteristic of the periodical motion phantom. Conclusion:Time-resolved 4D-CT reconstruction can be implemented with any general multi-slice CT scanners based on the similarity principle of spatial adjacent images and mutual information measure.The process of the 4D-CT data acquisition and reconstruction were not restricted to the hardware or software of the CT scanner and has the feasibility ,which extensive applicability.
基金Grant sponsor:Guangzhou Municipal Medicin &Health ProgramGrant number:2006-YB-177
文摘Objective:To investigate the influences of motion artifacts on three-dimensional (3D) reconstruction volume and conformal radiotherapy planning. Methods:A phantom which can mimic the clip motion of lung tumor along the cranial-caudal direction is constructed by step motor, small ball of polyethylene and potato. Ten different scan protocols were set and CT data of the phantom were acquired by using a commercial GE LightSpeed16 CT scanner. The 3D reconstruction of the CT data was implemented by adopting volume-rendering technology of GE AdvantageSim 6.0 system. The reconstructed volumes of each target in different scan protocols were measured through 3D measuring tools. Thus, relative deviations of the reconstruction volumes between moving targets and static ones were determined. The three-dimensional conformal radiation therapy (3D-CRT) plans and conformal fields were created and compared for a static/moving target with the WiMRT treatment planning system (TPS). Results:For a static target, there was no obvious difference among the 3D reconstruction volumes when the CT data were acquired with different pitches and slices. The appearance of 3D reconstruction volume and 3D conformal field of a moving target was quite different from that of static one. The maximum relative deviation is nearly 90% for a moving target scanned with different scan protocols. The relative deviations are variable among the different targets, about from -39.8% to 89.5% for a smaller target and from -18.4% to 20.5% for a larger one. Conclusion:The motion artifacts have great effects on 3D-CRT planning and reconstruction volume, which will greatly induce distorted conformal radiation fields and false DVHs for a moving target.
基金National Natural Science Foundation of Chinagrant number:31171059
文摘Objective: Neurons in the cochlear nucleus show different response patterns to the short tone bursts. Because of the limitations of animal experiments, it is hard to explore the principle. Therefore, using a model to simulate CN neurons will be a feasible way. Methods: Based on the initial model mentioned in the previous study, we proposed an improved CN model in MATLAB R2012b. Results: By modifying the parameters of the model we found the interchanges among "primary-like", "chopper",and "onset" response patterns. Furthermore, we simulated the "pauser" response pattern by adding an extra input in our model. Conclusion: The results indicate that the synaptic integrations and the input modes can give rise to different characteristics of CN neurons, which eventually determine the response patterns of CN neurons.
基金National Natural Science Foundation of Chinagrant number:30970866+3 种基金Guangzhou Municipal Science and Technology Projectgrant number:llBppZLjj2120029Guangdong Strategic Emerging Industry Core Technology Researchgrant number:2011A081402003
文摘Computed tomography(CT) plays an important role in the field of modern medical imaging. Reducing radiation exposure dose without significantly decreasing image's quality is always a crucial issue. Inspired by the outstanding performance of total variation(TV) technique in CT image reconstruction, a TV regularization based Bayesian-MAP(MAP-TV) is proposed to reconstruct the case of sparse view projection and limited angle range imaging. This method can suppress the streak artifacts and geometrical deformation while preserving image edges. We used ordered subset(OS) technique to accelerate the reconstruction speed. Numerical results show that MAP-TV is able to reconstruct a phantom with better visual performance and quantitative evaluation than classical FBP,MLEM and quadrate prior to MAP algorithms. The proposed algorithm can be generalized to cone-beam CT image reconstruction.