Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect the effect of topographic dynamic forcing on the atmosphere. In wavelength space, topographic spectra...Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect the effect of topographic dynamic forcing on the atmosphere. In wavelength space, topographic spectral energy decreases with decreasing wavelength, in spite of several departures. This relationship is approximated by an exponential function. A power law relationship between the terrain height spectra and wavelength is fitted by the least-squares method, and the fitting slope is associated with grid-size selection for mesoscale models. The monotonicity of grid size is investigated, and it is strictly proved that grid size increases with increasing fitting exponent, indicating that the universal grid size is determined by the minimum fitting exponent. An example of landslide-prone areas in western Sichuan is given, and the universal grid spacing of 4.1 km is shown to be a requirement to resolve 90% of terrain height variance for mesoscale models, without resorting to the parameterization of subgrid-scale terrain variance. Comparison among results of different simulations shows that the simulations estimate the observed precipitation well when using a resolution of 4.1 km or finer. Although the main flow patterns are similar, finer grids produce more complex patterns that show divergence zones, convergence zones and vortices. Horizontal grid size significantly affects the vertical structure of the convective boundary layer. Stronger vertical wind components are simulated for finer grid resolutions. In particular, noticeable sinking airflows over mountains are captured for those model configurations.展开更多
In most domain decomposition (DD) methods, a coarse grid solve is employed to provide the global coupling required to produce an optimal method. The total cost of a method can depend sensitively on the choice of the c...In most domain decomposition (DD) methods, a coarse grid solve is employed to provide the global coupling required to produce an optimal method. The total cost of a method can depend sensitively on the choice of the coaxse grid size H. In this paper, we give a simple analysis of this phenomenon for a model elliptic problem and a variant of Smith's vertex space domain decomposition method [11, 3]. We derive the optimal value Hopt which asymptotically minimises the total cost of method (number of floating point operations in the sequential case and execution time in the parallel case), for subdomain solvers with different complekities. Using the value of Hopt, we derive the overall complexity of the DD method, which can be significantly lower than that of the subdomain solver展开更多
Forward modeling of elastic wave propagation in porous media has great importance for understanding and interpreting the influences of rock properties on characteristics of seismic wavefield. However,the finite-differ...Forward modeling of elastic wave propagation in porous media has great importance for understanding and interpreting the influences of rock properties on characteristics of seismic wavefield. However,the finite-difference forward-modeling method is usually implemented with global spatial grid-size and time-step; it consumes large amounts of computational cost when small-scaled oil/gas-bearing structures or large velocity-contrast exist underground. To overcome this handicap,combined with variable grid-size and time-step,this paper developed a staggered-grid finite-difference scheme for elastic wave modeling in porous media. Variable finite-difference coefficients and wavefield interpolation were used to realize the transition of wave propagation between regions of different grid-size. The accuracy and efficiency of the algorithm were shown by numerical examples. The proposed method is advanced with low computational cost in elastic wave simulation for heterogeneous oil/gas reservoirs.展开更多
The spatial resolution of source data, the impact factor selection on the grid model and the size of the grid might be the main limitations of global land datasets applied on a regional scale. Quantitative studies of ...The spatial resolution of source data, the impact factor selection on the grid model and the size of the grid might be the main limitations of global land datasets applied on a regional scale. Quantitative studies of the impacts of rasterization on data accuracy can help improve data resolution and regional data accuracy. Through a case study of cropland data for Jiangsu and Anhui provinces in China, this research compared data accuracy with different data sources, rasterization methods, and grid sizes. First, we investigated the influence of different data sources on gridded data accuracy. The temporal trends of the History Database of the Global Environment(HYDE), Chinese Historical Cropland Data(CHCD), and Suwan Cropland Data(SWCD) datasets were more similar. However, different spatial resolutions of cropland source data in the CHCD and SWCD datasets revealed an average difference of 16.61% when provincial and county data were downscaled to a 10 × 10 km^2 grid for comparison. Second, the influence of selection of the potential arable land reclamation rate and temperature factors, as well as the different processing methods for water factors, on accuracy of gridded datasets was investigated. Applying the reclamation rate of potential cropland to grid-processing increased the diversity of spatial distribution but resulted in only a slightly greater standard deviation, which increased by 4.05. Temperature factors only produced relative disparities within 10% and absolute disparities within 2 km^2 over more than 90% of grid cells. For the different processing methods for water factors, the HYDE dataset distributed 70% more cropland in grid cells along riverbanks, at the abandoned Yellow River Estuary(located in Binhai County, Yancheng City, Jiangsu Province), and around Hongze Lake, than did the SWCD dataset. Finally, we explored the influence of different grid sizes. Absolute accuracy disparities by unit area for the year 2000 were within 0.1 km^2 at a 1 km^2 grid size, a 25% improvement over the 10 km^2 grid size. Compared to the outcomes of other similar studies, this demonstrates that some model hypotheses and grid-processing methods in international land datasets are truly incongruent with actual land reclamation processes, at least in China. Combining the model-based methods with historical empirical data may be a better way to improve the accuracy of regional scale datasets. Exploring methods for the above aspects improved the accuracy of historical cropland gridded datasets for finer regional scales.展开更多
AIM:To verify the performance of a lesion size measurement system through a clinical study.METHODS:Our proposed system,which consists of a conventional endoscope,an optical device,an optical probe,and a personal compu...AIM:To verify the performance of a lesion size measurement system through a clinical study.METHODS:Our proposed system,which consists of a conventional endoscope,an optical device,an optical probe,and a personal computer,generates a grid scale to measure the lesion size from an endoscopic image.The width of the grid scale is constantly adjusted according to the distance between the tip of the endoscope and lesion because the lesion size on an endoscopic image changes according to the distance.The shape of the grid scale was corrected to match the distortion of the endoscopic image.The distance was calculated using the amount of laser light reflected from the lesion through an optical probe inserted into the instrument channel of the endoscope.The endoscopist can thus measure the lesion size without contact by comparing the lesion with the size of the grid scale on the endoscopic image.(1)A basic test was performed to verify the relationship between the measurement error eM and the tilt angle of the endoscope;and(2)The sizes of three colon polyps were measured using our system during endoscopy.These sizes were immediately measured by scale after their removal.RESULTS:There was no error atα=0°.In addition,the values of eM(mean±SD)were 0.24±0.11 mm(α=10°),0.90±0.58 mm(α=20°)and 2.31±1.41mm(α=30°).According to these results,our system has been confirmed to measure accurately when the tilt angle is less than 20°.The measurement error was approximately 1 mm in the clinical study.Therefore,it was concluded that our proposed measurement system was also effective in clinical examinations.CONCLUSION:By combining simple optical equipment with a conventional endoscope,a quick and accurate system for measuring lesion size was established.展开更多
Workload of each service class varies dynamically in the grid environment, making the static service pool size allocation scheme unable to guarantee the QoS requirement of each service class. In this paper, we link th...Workload of each service class varies dynamically in the grid environment, making the static service pool size allocation scheme unable to guarantee the QoS requirement of each service class. In this paper, we link the issue of dynamical service pool size allocation scheme with QoS requirement under the varying workload, and formulate the QoS performance of service requests in the grid environment by queue theory. Combined Lagrangian optimization with a bisearch approach, the problem of optimally allocating service pool size scheme is resolved. Simulation results show efficiency of the optimal service pool size allocation scheme.展开更多
The stability of the grid is jeopardized with the large percentage of non-dispatchable renewables like wind power and also with increasing solar power. This creates various problems because these forms of energy are v...The stability of the grid is jeopardized with the large percentage of non-dispatchable renewables like wind power and also with increasing solar power. This creates various problems because these forms of energy are very volatile and difficult to predict. In most countries the in-feed of these sources must not be curtailed. In addition most of the renewables do not provide short circuit capacity and inertia in the same way as classical units and so further worsen the stability of the grid. The growing exploitation of wind and solar might be limited due to grid stability problems. In order to compensate those problems a large amount of reserve capacity is needed and therefore new technologies for electricity storage are required. Hydraulic pumped storage—the classical storage technology—has some disadvantages. These plants are in mountain regions often far away from wind farms. The distance to the wind farms mean additional loading for the already stressed grid and additional transmission losses. To compensate the very volatile wind energy, the pump input power should be varied continuously. This is so far only possible with variable speed units. Up to now double-fed asynchronous motor-generators are used which are rather expensive. In order to provide a solution for the described situation, ANDRITZ HYDRO has developed a new innovative concept of decentralized pump storage plants. Small standardized pump turbines are combined with a synchronous motor-generator and a full size converter which allows speed variation in pump and turbine mode over a wide range. These plants can be built locally close to wind farms and other sources to be balanced, allowing the increase of renewable energy without increasing the transmission line capacity. For the future smart grids this will be a key storage technology. This concept is reliable, innovative and more economic than other storage technologies.展开更多
基金supported by the Key Research Program of the Chinese Academy of Sciences (Grant No. KZZD-EW-05-01)the special grant (Grant No. 41375052) from the National Natural Science Foundation of Chinafunded by an open project of the State Key Laboratory of Severe Weather (Grant No. 2013LASW-A06)
文摘Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect the effect of topographic dynamic forcing on the atmosphere. In wavelength space, topographic spectral energy decreases with decreasing wavelength, in spite of several departures. This relationship is approximated by an exponential function. A power law relationship between the terrain height spectra and wavelength is fitted by the least-squares method, and the fitting slope is associated with grid-size selection for mesoscale models. The monotonicity of grid size is investigated, and it is strictly proved that grid size increases with increasing fitting exponent, indicating that the universal grid size is determined by the minimum fitting exponent. An example of landslide-prone areas in western Sichuan is given, and the universal grid spacing of 4.1 km is shown to be a requirement to resolve 90% of terrain height variance for mesoscale models, without resorting to the parameterization of subgrid-scale terrain variance. Comparison among results of different simulations shows that the simulations estimate the observed precipitation well when using a resolution of 4.1 km or finer. Although the main flow patterns are similar, finer grids produce more complex patterns that show divergence zones, convergence zones and vortices. Horizontal grid size significantly affects the vertical structure of the convective boundary layer. Stronger vertical wind components are simulated for finer grid resolutions. In particular, noticeable sinking airflows over mountains are captured for those model configurations.
文摘In most domain decomposition (DD) methods, a coarse grid solve is employed to provide the global coupling required to produce an optimal method. The total cost of a method can depend sensitively on the choice of the coaxse grid size H. In this paper, we give a simple analysis of this phenomenon for a model elliptic problem and a variant of Smith's vertex space domain decomposition method [11, 3]. We derive the optimal value Hopt which asymptotically minimises the total cost of method (number of floating point operations in the sequential case and execution time in the parallel case), for subdomain solvers with different complekities. Using the value of Hopt, we derive the overall complexity of the DD method, which can be significantly lower than that of the subdomain solver
基金supported by the National Basic Research Program of China (No. 2013CB228604)the National Science and Technology Major Project (No. 2011ZX05030-004-002,2011ZX05019-003)the National Natural Science Foundation (No. 41004050)
文摘Forward modeling of elastic wave propagation in porous media has great importance for understanding and interpreting the influences of rock properties on characteristics of seismic wavefield. However,the finite-difference forward-modeling method is usually implemented with global spatial grid-size and time-step; it consumes large amounts of computational cost when small-scaled oil/gas-bearing structures or large velocity-contrast exist underground. To overcome this handicap,combined with variable grid-size and time-step,this paper developed a staggered-grid finite-difference scheme for elastic wave modeling in porous media. Variable finite-difference coefficients and wavefield interpolation were used to realize the transition of wave propagation between regions of different grid-size. The accuracy and efficiency of the algorithm were shown by numerical examples. The proposed method is advanced with low computational cost in elastic wave simulation for heterogeneous oil/gas reservoirs.
基金Under the auspices of National Natural Science Foundation of China(No.41471156,41501207)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA05080102)Special Fund of National Science and Technology of China(No.2014FY130500)
文摘The spatial resolution of source data, the impact factor selection on the grid model and the size of the grid might be the main limitations of global land datasets applied on a regional scale. Quantitative studies of the impacts of rasterization on data accuracy can help improve data resolution and regional data accuracy. Through a case study of cropland data for Jiangsu and Anhui provinces in China, this research compared data accuracy with different data sources, rasterization methods, and grid sizes. First, we investigated the influence of different data sources on gridded data accuracy. The temporal trends of the History Database of the Global Environment(HYDE), Chinese Historical Cropland Data(CHCD), and Suwan Cropland Data(SWCD) datasets were more similar. However, different spatial resolutions of cropland source data in the CHCD and SWCD datasets revealed an average difference of 16.61% when provincial and county data were downscaled to a 10 × 10 km^2 grid for comparison. Second, the influence of selection of the potential arable land reclamation rate and temperature factors, as well as the different processing methods for water factors, on accuracy of gridded datasets was investigated. Applying the reclamation rate of potential cropland to grid-processing increased the diversity of spatial distribution but resulted in only a slightly greater standard deviation, which increased by 4.05. Temperature factors only produced relative disparities within 10% and absolute disparities within 2 km^2 over more than 90% of grid cells. For the different processing methods for water factors, the HYDE dataset distributed 70% more cropland in grid cells along riverbanks, at the abandoned Yellow River Estuary(located in Binhai County, Yancheng City, Jiangsu Province), and around Hongze Lake, than did the SWCD dataset. Finally, we explored the influence of different grid sizes. Absolute accuracy disparities by unit area for the year 2000 were within 0.1 km^2 at a 1 km^2 grid size, a 25% improvement over the 10 km^2 grid size. Compared to the outcomes of other similar studies, this demonstrates that some model hypotheses and grid-processing methods in international land datasets are truly incongruent with actual land reclamation processes, at least in China. Combining the model-based methods with historical empirical data may be a better way to improve the accuracy of regional scale datasets. Exploring methods for the above aspects improved the accuracy of historical cropland gridded datasets for finer regional scales.
基金Supported by The Special Coordination Fund(SCF)for Pro-moting Science and Technology commissioned by the Ministry of Education,Culture,Sports,Science and Technology(MEXT)of Japan
文摘AIM:To verify the performance of a lesion size measurement system through a clinical study.METHODS:Our proposed system,which consists of a conventional endoscope,an optical device,an optical probe,and a personal computer,generates a grid scale to measure the lesion size from an endoscopic image.The width of the grid scale is constantly adjusted according to the distance between the tip of the endoscope and lesion because the lesion size on an endoscopic image changes according to the distance.The shape of the grid scale was corrected to match the distortion of the endoscopic image.The distance was calculated using the amount of laser light reflected from the lesion through an optical probe inserted into the instrument channel of the endoscope.The endoscopist can thus measure the lesion size without contact by comparing the lesion with the size of the grid scale on the endoscopic image.(1)A basic test was performed to verify the relationship between the measurement error eM and the tilt angle of the endoscope;and(2)The sizes of three colon polyps were measured using our system during endoscopy.These sizes were immediately measured by scale after their removal.RESULTS:There was no error atα=0°.In addition,the values of eM(mean±SD)were 0.24±0.11 mm(α=10°),0.90±0.58 mm(α=20°)and 2.31±1.41mm(α=30°).According to these results,our system has been confirmed to measure accurately when the tilt angle is less than 20°.The measurement error was approximately 1 mm in the clinical study.Therefore,it was concluded that our proposed measurement system was also effective in clinical examinations.CONCLUSION:By combining simple optical equipment with a conventional endoscope,a quick and accurate system for measuring lesion size was established.
基金Project supported by the National-High-Technology Research and Development Program of China (Grant No.2004AA111110)
文摘Workload of each service class varies dynamically in the grid environment, making the static service pool size allocation scheme unable to guarantee the QoS requirement of each service class. In this paper, we link the issue of dynamical service pool size allocation scheme with QoS requirement under the varying workload, and formulate the QoS performance of service requests in the grid environment by queue theory. Combined Lagrangian optimization with a bisearch approach, the problem of optimally allocating service pool size scheme is resolved. Simulation results show efficiency of the optimal service pool size allocation scheme.
文摘The stability of the grid is jeopardized with the large percentage of non-dispatchable renewables like wind power and also with increasing solar power. This creates various problems because these forms of energy are very volatile and difficult to predict. In most countries the in-feed of these sources must not be curtailed. In addition most of the renewables do not provide short circuit capacity and inertia in the same way as classical units and so further worsen the stability of the grid. The growing exploitation of wind and solar might be limited due to grid stability problems. In order to compensate those problems a large amount of reserve capacity is needed and therefore new technologies for electricity storage are required. Hydraulic pumped storage—the classical storage technology—has some disadvantages. These plants are in mountain regions often far away from wind farms. The distance to the wind farms mean additional loading for the already stressed grid and additional transmission losses. To compensate the very volatile wind energy, the pump input power should be varied continuously. This is so far only possible with variable speed units. Up to now double-fed asynchronous motor-generators are used which are rather expensive. In order to provide a solution for the described situation, ANDRITZ HYDRO has developed a new innovative concept of decentralized pump storage plants. Small standardized pump turbines are combined with a synchronous motor-generator and a full size converter which allows speed variation in pump and turbine mode over a wide range. These plants can be built locally close to wind farms and other sources to be balanced, allowing the increase of renewable energy without increasing the transmission line capacity. For the future smart grids this will be a key storage technology. This concept is reliable, innovative and more economic than other storage technologies.
