近来,无线电能传输技术受到了越来越广泛的关注,同时,该技术也被尝试应用于电动汽车以实现电动汽车的无线充电。与能量在自由空间传播相比,电动汽车无线充电时的电磁环境有很大不同,而电磁安全问题也变得日益突出。基于上述问题,首先分...近来,无线电能传输技术受到了越来越广泛的关注,同时,该技术也被尝试应用于电动汽车以实现电动汽车的无线充电。与能量在自由空间传播相比,电动汽车无线充电时的电磁环境有很大不同,而电磁安全问题也变得日益突出。基于上述问题,首先分析了该领域的安全限制与标准问题;其次通过仿真分析了电动汽车充电时的参数变化、电磁环境以及对人体的影响;最后通过电动汽车试验来验证仿真结果,系统实现了约为3.5 k W的能量传输。该研究可为无线充电电动汽车的优化设计提供理论依据。展开更多
This paper demonstrates capabilities of low-field nuclear magnetic resonance (NMR) and microfocus X-ray computed tomography (μCT) in advanced, nondestructive, and quantitative characterization of pore types, producib...This paper demonstrates capabilities of low-field nuclear magnetic resonance (NMR) and microfocus X-ray computed tomography (μCT) in advanced, nondestructive, and quantitative characterization of pore types, producible porosity, pore structure, and spatial disposition of pore-fractures in coals. Results show that the NMR transverse relaxation time (T2) at 0.5–2.5, 20–50, and 】100 ms correspond to pores of 【0.1 μm, 】0.1 μm, and fractures, respectively. A much higher T2 spectrum peak reflects a much better development of pores (or fractures) corresponding to the T2, and vice versa. Three basic components in coals, i.e., the pores (or fractures), coal matrix, and minerals have their distinctive range of CT numbers. Among these, the CT number of pores is commonly less than 600 HU. The producible porosity, which is a determination of permeability, can be calculated by T2 cutoff value (T2C) of coal NMR. The coal pore structure can be efficiently estimated by the newly proposed "T2C based model". Finally, μCT scan was proven capable of modeling and spatial visualization of pores and fractures.展开更多
Objective To investigate the rule of the aquaporin 4 (AQP4) expression in acute ischemic brain edema, and to study the correlation between AQP4 expression and diffusion weighted imaging (DWI) Methods Thirty ...Objective To investigate the rule of the aquaporin 4 (AQP4) expression in acute ischemic brain edema, and to study the correlation between AQP4 expression and diffusion weighted imaging (DWI) Methods Thirty six Wistar rats were divided into 2 groups randomly, control group (n=12) and operation group (n=24) in which right middle cerebral artery of each animal had been occluded unilaterally (MCAO) at interval times of: 15 minutes, 30 minutes, 1 hours, 3 hours, 6 hours and 24 hours, respectively The operation process of the control group was the same as the operation group except for the MCAO All groups were examined using DWI The apparent diffusion coefficient (ADC), relative density (rd) and relative area (rs) of the biggest hyperintensity signal layer on DWI were measured After that the animals were sacrificed and perfused with the mixture solution consisting of TTC The biggest layers of the ischemic cerebral tissues in each rat corresponding to the DWI were stained with TTC and examined with immunochemistry (△S) , in situ hybridization (α) and histology Results There was no significant change in the control group In the operation group, a hyperintensity signal was found in the DWI of the right MAC territory at 15 minutes after MCAO The ADC value decreased quickly within one hour after MCAO, while the AQP4 expression, rd DWI and rs DWI increased rapidly during this stage As time progressed, the ADC value decreased further to (2 1±0 6)×10 4 mm 2/s at 3 hours, and then began to increase slowly till 24 hours But the AQP4 expression (△S and α) and rd as well as the rs continuously increased slowly between 1 hour and 6 hours after MCAO, followed a peak after 6 hours The AQP4 expression (α) showed a positive relationship with the rs DWI, they all presented two peaks and a plateau The corresponding sequential pathologic changes were a gradual increase of intracellular edema (within one hour), then an emergence of vasogenic edema (1-6 hours), and fin展开更多
Diffusion weighted magnetic resonance imaging (DWI) is an imaging technique which provides tissue contrast by the measurement of diffusion properties of water molecules within tissues. Diffusion is expressed in an app...Diffusion weighted magnetic resonance imaging (DWI) is an imaging technique which provides tissue contrast by the measurement of diffusion properties of water molecules within tissues. Diffusion is expressed in an apparent diffusion coefficient (ADC), which reflects the diffusion properties unique to each type of tissue. DWI has been originally used in neuroradiology. More recently, DWI has increasingly been used in addition to conventional unenhanced and enhanced magnetic resonance imaging (MRI) in other parts of the body. The reason for this delay was a number of technical problems inherent to the technique, making DWI very sensitive to artifacts, which had to be overcome. With assessment of ADC values, DWI proved to be helpful in characterization of focal liver lesions. However, DWI should always be used in conjunction to conventional MRI since there is considerable overlap between ADC values of benign and malignant lesions. DWI is useful in the detection of hepatocellular carcinoma in the cirrhotic liver and detection of liver metastases in oncological patients. In addition, DWI is a promising tool in the prediction of tumor responsiveness to chemotherapy and the follow-up of oncological patients after treatment, as DWI may be capable of detecting recurrent disease earlier than conventional imaging.This review focuses on the most common applications of DWI in the liver.展开更多
Rapid development of renewable energy in China is driving a major shift in the characteristics and control requirements of the electricity grid.Since the best renewable energy resources are far away from load centers ...Rapid development of renewable energy in China is driving a major shift in the characteristics and control requirements of the electricity grid.Since the best renewable energy resources are far away from load centers in the east and southeast,transmission over long distances is required.Over 20 high-voltage DC(HVDC)transmission lines,with a combined capacity exceeding 150 GW,are in operation or are currently under construction.This rapid expansion of new generation and transmission capacities based on power electronics starts to change the characteristics of the grid,especially in areas where they concentrate,creating new stability problems and operational challenges.New system theories and technologies are required to support the development and operation of a future grid that relies more and more on power electronics.This paper highlights the characteristics of power electronics as used in renewable energy generation and HVDC transmission systems,discusses the impacts of these power-electronics-based assets on grid stability and operational requirements,and identifies opportunities for the development of both new system theories and system technologies to support a national energy policy that emphasizes the use of clean energy.展开更多
Imaging studies are a major component in the evaluation of patients for the screening,staging and surveillance of colorectal cancer.This review presents commonly encountered findings in the diagnosis and staging of pa...Imaging studies are a major component in the evaluation of patients for the screening,staging and surveillance of colorectal cancer.This review presents commonly encountered findings in the diagnosis and staging of patients with colorectal cancer using computed tomography(CT)colonography,magnetic resonance imaging(MRI),and positron emission tomography(PET)/CT colonography.CT colonography provides important information for the preoperative assessment of T staging.Wall deformities are associated with muscular or subserosal invasion.Lymph node metastases from colorectal cancer often present with calcifications.CT is superior to detect calcified metastases.Three-dimensional CT to image the vascular anatomy facilitates laparoscopic surgery.T staging of rectal cancer by MRI is an established modality because MRI can diagnose rectal wall laminar structure.N staging in patients with colorectal cancer is still challenging using any imaging modality.MRI is more accurate than CT for the evaluation of liver metastases.PET/CT colonography isvaluable in the evaluation of extra-colonic and hepatic disease.PET/CT colonography is useful for obstructing colorectal cancers that cannot be traversed colonoscopically.PET/CT colonography is able to localize synchronous colon cancers proximal to the obstruction precisely.However,there is no definite evidence to support the routine clinical use of PET/CT colonography.展开更多
文摘近来,无线电能传输技术受到了越来越广泛的关注,同时,该技术也被尝试应用于电动汽车以实现电动汽车的无线充电。与能量在自由空间传播相比,电动汽车无线充电时的电磁环境有很大不同,而电磁安全问题也变得日益突出。基于上述问题,首先分析了该领域的安全限制与标准问题;其次通过仿真分析了电动汽车充电时的参数变化、电磁环境以及对人体的影响;最后通过电动汽车试验来验证仿真结果,系统实现了约为3.5 k W的能量传输。该研究可为无线充电电动汽车的优化设计提供理论依据。
基金supported by National Major Research Program for Science and Technology of China (Grant Nos. 2008ZX05034-01 and 2008ZX05062-001)National Basic Research Program of China (Grant No. 2009CB219604)+2 种基金National Natural Science Foundation of China (Grant No. 40972107)Petro China Innovation Foundation (Grant No. 2008D-5006-01-04)Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT0864)
文摘This paper demonstrates capabilities of low-field nuclear magnetic resonance (NMR) and microfocus X-ray computed tomography (μCT) in advanced, nondestructive, and quantitative characterization of pore types, producible porosity, pore structure, and spatial disposition of pore-fractures in coals. Results show that the NMR transverse relaxation time (T2) at 0.5–2.5, 20–50, and 】100 ms correspond to pores of 【0.1 μm, 】0.1 μm, and fractures, respectively. A much higher T2 spectrum peak reflects a much better development of pores (or fractures) corresponding to the T2, and vice versa. Three basic components in coals, i.e., the pores (or fractures), coal matrix, and minerals have their distinctive range of CT numbers. Among these, the CT number of pores is commonly less than 600 HU. The producible porosity, which is a determination of permeability, can be calculated by T2 cutoff value (T2C) of coal NMR. The coal pore structure can be efficiently estimated by the newly proposed "T2C based model". Finally, μCT scan was proven capable of modeling and spatial visualization of pores and fractures.
基金theNationalNaturalScienceFoundationofChina (No 3 0 0 70 2 47)
文摘Objective To investigate the rule of the aquaporin 4 (AQP4) expression in acute ischemic brain edema, and to study the correlation between AQP4 expression and diffusion weighted imaging (DWI) Methods Thirty six Wistar rats were divided into 2 groups randomly, control group (n=12) and operation group (n=24) in which right middle cerebral artery of each animal had been occluded unilaterally (MCAO) at interval times of: 15 minutes, 30 minutes, 1 hours, 3 hours, 6 hours and 24 hours, respectively The operation process of the control group was the same as the operation group except for the MCAO All groups were examined using DWI The apparent diffusion coefficient (ADC), relative density (rd) and relative area (rs) of the biggest hyperintensity signal layer on DWI were measured After that the animals were sacrificed and perfused with the mixture solution consisting of TTC The biggest layers of the ischemic cerebral tissues in each rat corresponding to the DWI were stained with TTC and examined with immunochemistry (△S) , in situ hybridization (α) and histology Results There was no significant change in the control group In the operation group, a hyperintensity signal was found in the DWI of the right MAC territory at 15 minutes after MCAO The ADC value decreased quickly within one hour after MCAO, while the AQP4 expression, rd DWI and rs DWI increased rapidly during this stage As time progressed, the ADC value decreased further to (2 1±0 6)×10 4 mm 2/s at 3 hours, and then began to increase slowly till 24 hours But the AQP4 expression (△S and α) and rd as well as the rs continuously increased slowly between 1 hour and 6 hours after MCAO, followed a peak after 6 hours The AQP4 expression (α) showed a positive relationship with the rs DWI, they all presented two peaks and a plateau The corresponding sequential pathologic changes were a gradual increase of intracellular edema (within one hour), then an emergence of vasogenic edema (1-6 hours), and fin
文摘Diffusion weighted magnetic resonance imaging (DWI) is an imaging technique which provides tissue contrast by the measurement of diffusion properties of water molecules within tissues. Diffusion is expressed in an apparent diffusion coefficient (ADC), which reflects the diffusion properties unique to each type of tissue. DWI has been originally used in neuroradiology. More recently, DWI has increasingly been used in addition to conventional unenhanced and enhanced magnetic resonance imaging (MRI) in other parts of the body. The reason for this delay was a number of technical problems inherent to the technique, making DWI very sensitive to artifacts, which had to be overcome. With assessment of ADC values, DWI proved to be helpful in characterization of focal liver lesions. However, DWI should always be used in conjunction to conventional MRI since there is considerable overlap between ADC values of benign and malignant lesions. DWI is useful in the detection of hepatocellular carcinoma in the cirrhotic liver and detection of liver metastases in oncological patients. In addition, DWI is a promising tool in the prediction of tumor responsiveness to chemotherapy and the follow-up of oncological patients after treatment, as DWI may be capable of detecting recurrent disease earlier than conventional imaging.This review focuses on the most common applications of DWI in the liver.
基金supported in part by the State Grid Science and Technology Project“Impedance-Based Modeling and Control of Distributed Generation Systems”(NYB1720170218).
文摘Rapid development of renewable energy in China is driving a major shift in the characteristics and control requirements of the electricity grid.Since the best renewable energy resources are far away from load centers in the east and southeast,transmission over long distances is required.Over 20 high-voltage DC(HVDC)transmission lines,with a combined capacity exceeding 150 GW,are in operation or are currently under construction.This rapid expansion of new generation and transmission capacities based on power electronics starts to change the characteristics of the grid,especially in areas where they concentrate,creating new stability problems and operational challenges.New system theories and technologies are required to support the development and operation of a future grid that relies more and more on power electronics.This paper highlights the characteristics of power electronics as used in renewable energy generation and HVDC transmission systems,discusses the impacts of these power-electronics-based assets on grid stability and operational requirements,and identifies opportunities for the development of both new system theories and system technologies to support a national energy policy that emphasizes the use of clean energy.
文摘Imaging studies are a major component in the evaluation of patients for the screening,staging and surveillance of colorectal cancer.This review presents commonly encountered findings in the diagnosis and staging of patients with colorectal cancer using computed tomography(CT)colonography,magnetic resonance imaging(MRI),and positron emission tomography(PET)/CT colonography.CT colonography provides important information for the preoperative assessment of T staging.Wall deformities are associated with muscular or subserosal invasion.Lymph node metastases from colorectal cancer often present with calcifications.CT is superior to detect calcified metastases.Three-dimensional CT to image the vascular anatomy facilitates laparoscopic surgery.T staging of rectal cancer by MRI is an established modality because MRI can diagnose rectal wall laminar structure.N staging in patients with colorectal cancer is still challenging using any imaging modality.MRI is more accurate than CT for the evaluation of liver metastases.PET/CT colonography isvaluable in the evaluation of extra-colonic and hepatic disease.PET/CT colonography is useful for obstructing colorectal cancers that cannot be traversed colonoscopically.PET/CT colonography is able to localize synchronous colon cancers proximal to the obstruction precisely.However,there is no definite evidence to support the routine clinical use of PET/CT colonography.
