Colonoscopy is the gold standard for colorectal cancer prevention; however, it is still an imperfect modality. Precancerous lesions can be lost during screening examinations, thus increasing the risk of interval cance...Colonoscopy is the gold standard for colorectal cancer prevention; however, it is still an imperfect modality. Precancerous lesions can be lost during screening examinations, thus increasing the risk of interval cancer. A variety of factors either patient-, or endoscopist dependent or even the procedure itself may contribute to loss of lesions. Sophisticated modalities including advanced technology endoscopes and add-on devices have been developed in an effort to eliminate colonoscopy's drawbacks and maximize its ability to detect potentially culprit polyps. Novel colonoscopes aim to widen the field of view. They incorporate more than one cameras enabling simultaneous image transmission. In that way the field of view can expand up to 330°. On the other hand a plethora of add-on devices attachable on the standard colonoscope promise to detect lesions in the proximal aspect of colonic folds either by offering a retrograde view of the lumen or by straightening the haustral folds during withdrawal. In this minireview we discuss how these recent advances affect colonoscopy performance by improving its quality indicators(cecal intubation rate, adenoma detection rate) and other metrics(polyp detection rate, adenomas per colonoscopy, polyp/adenoma miss rate) associated with examination's outcomes.展开更多
A wide-angle beam propagation algorithm based on an oblique coordinate system is presented.A waveguide with tilted structure is simulated in terms of this method and the conventional wide-angle BPM. By comparing the r...A wide-angle beam propagation algorithm based on an oblique coordinate system is presented.A waveguide with tilted structure is simulated in terms of this method and the conventional wide-angle BPM. By comparing the results,it is found that this method is effective especially in tilted structure. The Y-junction has been also simulated in terms of this new method,and the good results are obtained.展开更多
Previous soil-disc force prediction models have considered spherical and concave blades, as used on disc ploughs and harrows, with many simplifying assumptions. This study proposes an approach applying the fundamental...Previous soil-disc force prediction models have considered spherical and concave blades, as used on disc ploughs and harrows, with many simplifying assumptions. This study proposes an approach applying the fundamental equation of earth moving mechanics for calculating the soil passive reaction acting on a rotating fiat disc blade as used on a zero-till single disc seeder. The study considers the effects of disc variable depth of cut, sweep and tilt angles, free rotation and a scrubbing reaction at the beveled edge. This paper outlines the modeling approach and prediction results for a fixed circular blade operating at 90° sweep angle over a range of speeds and at two tilt angles. To account for the varying depth across the circular disc shape width, elemental wide blade force reactions acting on wide blade segments of elemental width were integrated across the disc working width. By including inertia forces due to speed as well as additional bulldozing forces due to the loose soil accumulation in front of the blade the draught and upward vertical forces acting on the vertical disc blade were predicted with a deviation of 6%-19% and 1.5%-14% from measured data, respectively. The model was able to predict the effect of increasing the tilt angle from 0° to 20° on reducing both draught and upward vertical forces. Further development and validation of the model will be described in subsequent papers, reflecting a step by step approach of increasing complexity to model a disc blade as used on a zero-till single disc seeding system.展开更多
In order to establish a new method for measuring the dimensions of coarse aggregates, five different-size flat and elongated (F&E) coarse aggregates were glued into two specimens by epoxy resin, respectively, and ...In order to establish a new method for measuring the dimensions of coarse aggregates, five different-size flat and elongated (F&E) coarse aggregates were glued into two specimens by epoxy resin, respectively, and slice images were obtained by X-ray CT, then the aggregates were extracted by the fuzzy c-means clustering algorithm. Attributions of the particle on different cross-sections were determined by the ‘overlap area method’. And unified three-dimensional Cartesian coordinate system was established based on continuous slice images. The coefficient values of spherical harmonics descriptor representing particles surface profile were gained, then each scanned particle was represented by 60×120 discrete points conformably with spherical harmonics descriptor. The chord length and direction angles were determined by the calculation. With the major axis (L) and orthogonal axis (W and T), the calculated results were compared with those measured by caliper. It is concluded that the new L, W, and T dimension measuring method is able to take the place of the present manual measurement.展开更多
In 2010,a 500-km-long wide-angle reflection/refraction seismic profile was completed,running northwest from the central Sichuan Basin.This profile orthogonally crosses the meizoseismal area of great Wenchuan earthquak...In 2010,a 500-km-long wide-angle reflection/refraction seismic profile was completed,running northwest from the central Sichuan Basin.This profile orthogonally crosses the meizoseismal area of great Wenchuan earthquake of 12 May 2008,which occurred in the central part of the Longmenshan.The profile also passes through the northwestern Sichuan Plateau,along which a new deep seismic sounding observation system was set up that was much improved over previous datasets and enabled abundant observations to be recorded.Seismic wave phase records that reflect the structural characteristics of different tectonic blocks,especially the complicated phase features associated with the Wenchuan earthquake,were calculated and analyzed in detail.A 2D crustal P-wave velocity model for the orogenic belt in the central Longmenshan and its margins was determined,and crustal structure differences between the stable Sichuan Basin and the thickened northwestern Sichuan Plateau were characterized.Lithological variations within the upper and lower crust in the interior of the plateau,especially a great velocity decrease and plastic rheological properties associated with strong lithologic weakening in lower crust,were detected.From west to east in the lower crust beneath the orogenic belt lying between the Sichuan Basin and the northwestern Sichuan Plateau,a giant shovel-like upwelling is observed that dips gently in the lower part and at higher angles in the upper part;this is inferred to be related to the fault systems in the central Longmenshan.An upwelling in the upper-middle crust along the eastern margin of the orogenic belt is associated with steeply dipping thrusts that strongly uplift the upper crust and crystalline basement beneath a central fault system in the Longmenshan.The data,combined with an understanding of the regional tectonic stress field and previous geological results,enable a discussion of basin-and-range coupling,orogenic tectonics,the crustal fault system,and the seismogenic tectonic environment of the central Longmenshan along the eastern margin of the Qinghai-Tibet Plateau.展开更多
The performance of broadband polarizing beam splitters(PBSs) is sensitive to the incident angle.By taking account of the spectrum of the laser source and using the needle optimization method,a large acceptance angle P...The performance of broadband polarizing beam splitters(PBSs) is sensitive to the incident angle.By taking account of the spectrum of the laser source and using the needle optimization method,a large acceptance angle PBS for laser-based displays is designed.The average degrees of polarization in transmission and reflection can reach 0.989 and 0.980 for an acceptance angle of 13.6?in air using two materials,while better results of 0.993 and 0.989 for an acceptance angle of 14.8?in air are attained when three common materials are used.Both designs consist of 40 layers.展开更多
Lithosphere thinning and destruction in the middle-eastern North China Craton(NCC), a region susceptible to strong earthquakes, is one of the research hotspots in solid earth science. All 42 seismic wide-angle reflect...Lithosphere thinning and destruction in the middle-eastern North China Craton(NCC), a region susceptible to strong earthquakes, is one of the research hotspots in solid earth science. All 42 seismic wide-angle reflection/refraction profiles have been completed in the middle-eastern NCC. We collect all the 2-D profiling results and perform gridding of the velocity and interface depth data, building a 3-D crustal velocity structure model for the middle-eastern NCC, named HBCrust1.0, by using the Kriging interpolation method. Our result shows that the first-arrival times calculated by HBCust1.0 fit well with the observations. The result demonstrates that the upper crust is the main seismogenic layer, and the brittle-ductile transition occurs at depths near interface C(the interface between upper and lower crust). The depth of interface Moho varies beneath the source area of the Tangshan earthquake, and a low-velocity structure is found to extend from the source area to the lower crust. Based on these observations, it can be inferred that stress accumulation responsible for the Tangshan earthquake may have been closely related to the migration and deformation of the mantle materials. Comparisons of the average velocities of the whole crust, the upper and the lower crust show that the average velocity of the lower crust under the central part of the North China Basin(NCB) in the east of the craton is obviously higher than the regional average. This high-velocity probably results from long-term underplating of the mantle magma.展开更多
文摘Colonoscopy is the gold standard for colorectal cancer prevention; however, it is still an imperfect modality. Precancerous lesions can be lost during screening examinations, thus increasing the risk of interval cancer. A variety of factors either patient-, or endoscopist dependent or even the procedure itself may contribute to loss of lesions. Sophisticated modalities including advanced technology endoscopes and add-on devices have been developed in an effort to eliminate colonoscopy's drawbacks and maximize its ability to detect potentially culprit polyps. Novel colonoscopes aim to widen the field of view. They incorporate more than one cameras enabling simultaneous image transmission. In that way the field of view can expand up to 330°. On the other hand a plethora of add-on devices attachable on the standard colonoscope promise to detect lesions in the proximal aspect of colonic folds either by offering a retrograde view of the lumen or by straightening the haustral folds during withdrawal. In this minireview we discuss how these recent advances affect colonoscopy performance by improving its quality indicators(cecal intubation rate, adenoma detection rate) and other metrics(polyp detection rate, adenomas per colonoscopy, polyp/adenoma miss rate) associated with examination's outcomes.
文摘A wide-angle beam propagation algorithm based on an oblique coordinate system is presented.A waveguide with tilted structure is simulated in terms of this method and the conventional wide-angle BPM. By comparing the results,it is found that this method is effective especially in tilted structure. The Y-junction has been also simulated in terms of this new method,and the good results are obtained.
文摘Previous soil-disc force prediction models have considered spherical and concave blades, as used on disc ploughs and harrows, with many simplifying assumptions. This study proposes an approach applying the fundamental equation of earth moving mechanics for calculating the soil passive reaction acting on a rotating fiat disc blade as used on a zero-till single disc seeder. The study considers the effects of disc variable depth of cut, sweep and tilt angles, free rotation and a scrubbing reaction at the beveled edge. This paper outlines the modeling approach and prediction results for a fixed circular blade operating at 90° sweep angle over a range of speeds and at two tilt angles. To account for the varying depth across the circular disc shape width, elemental wide blade force reactions acting on wide blade segments of elemental width were integrated across the disc working width. By including inertia forces due to speed as well as additional bulldozing forces due to the loose soil accumulation in front of the blade the draught and upward vertical forces acting on the vertical disc blade were predicted with a deviation of 6%-19% and 1.5%-14% from measured data, respectively. The model was able to predict the effect of increasing the tilt angle from 0° to 20° on reducing both draught and upward vertical forces. Further development and validation of the model will be described in subsequent papers, reflecting a step by step approach of increasing complexity to model a disc blade as used on a zero-till single disc seeding system.
基金Project(51038004) supported by the National Natural Science Foundation of ChinaProject(2009318000078) supported by the Western China Communications Construction and Technology Program, China
文摘In order to establish a new method for measuring the dimensions of coarse aggregates, five different-size flat and elongated (F&E) coarse aggregates were glued into two specimens by epoxy resin, respectively, and slice images were obtained by X-ray CT, then the aggregates were extracted by the fuzzy c-means clustering algorithm. Attributions of the particle on different cross-sections were determined by the ‘overlap area method’. And unified three-dimensional Cartesian coordinate system was established based on continuous slice images. The coefficient values of spherical harmonics descriptor representing particles surface profile were gained, then each scanned particle was represented by 60×120 discrete points conformably with spherical harmonics descriptor. The chord length and direction angles were determined by the calculation. With the major axis (L) and orthogonal axis (W and T), the calculated results were compared with those measured by caliper. It is concluded that the new L, W, and T dimension measuring method is able to take the place of the present manual measurement.
基金supported by the Chinese Mainland Active Fault Exploration Project 2010-Deep Seismic Sounding Profile in the central Longmenshan,CEAthe National Natural Science Foundation of China(Grant No.40974033)
文摘In 2010,a 500-km-long wide-angle reflection/refraction seismic profile was completed,running northwest from the central Sichuan Basin.This profile orthogonally crosses the meizoseismal area of great Wenchuan earthquake of 12 May 2008,which occurred in the central part of the Longmenshan.The profile also passes through the northwestern Sichuan Plateau,along which a new deep seismic sounding observation system was set up that was much improved over previous datasets and enabled abundant observations to be recorded.Seismic wave phase records that reflect the structural characteristics of different tectonic blocks,especially the complicated phase features associated with the Wenchuan earthquake,were calculated and analyzed in detail.A 2D crustal P-wave velocity model for the orogenic belt in the central Longmenshan and its margins was determined,and crustal structure differences between the stable Sichuan Basin and the thickened northwestern Sichuan Plateau were characterized.Lithological variations within the upper and lower crust in the interior of the plateau,especially a great velocity decrease and plastic rheological properties associated with strong lithologic weakening in lower crust,were detected.From west to east in the lower crust beneath the orogenic belt lying between the Sichuan Basin and the northwestern Sichuan Plateau,a giant shovel-like upwelling is observed that dips gently in the lower part and at higher angles in the upper part;this is inferred to be related to the fault systems in the central Longmenshan.An upwelling in the upper-middle crust along the eastern margin of the orogenic belt is associated with steeply dipping thrusts that strongly uplift the upper crust and crystalline basement beneath a central fault system in the Longmenshan.The data,combined with an understanding of the regional tectonic stress field and previous geological results,enable a discussion of basin-and-range coupling,orogenic tectonics,the crustal fault system,and the seismogenic tectonic environment of the central Longmenshan along the eastern margin of the Qinghai-Tibet Plateau.
基金supported by the National Natural Science Foundation of China (No.50802080)the Natural Science Foundation of Fujian Province (No.2010J01349)
文摘The performance of broadband polarizing beam splitters(PBSs) is sensitive to the incident angle.By taking account of the spectrum of the laser source and using the needle optimization method,a large acceptance angle PBS for laser-based displays is designed.The average degrees of polarization in transmission and reflection can reach 0.989 and 0.980 for an acceptance angle of 13.6?in air using two materials,while better results of 0.993 and 0.989 for an acceptance angle of 14.8?in air are attained when three common materials are used.Both designs consist of 40 layers.
基金supported by the National Natural Science Foundation of China (Grant Nos. 90814012, 91014006, 91414301, 41174052 & 41274113)
文摘Lithosphere thinning and destruction in the middle-eastern North China Craton(NCC), a region susceptible to strong earthquakes, is one of the research hotspots in solid earth science. All 42 seismic wide-angle reflection/refraction profiles have been completed in the middle-eastern NCC. We collect all the 2-D profiling results and perform gridding of the velocity and interface depth data, building a 3-D crustal velocity structure model for the middle-eastern NCC, named HBCrust1.0, by using the Kriging interpolation method. Our result shows that the first-arrival times calculated by HBCust1.0 fit well with the observations. The result demonstrates that the upper crust is the main seismogenic layer, and the brittle-ductile transition occurs at depths near interface C(the interface between upper and lower crust). The depth of interface Moho varies beneath the source area of the Tangshan earthquake, and a low-velocity structure is found to extend from the source area to the lower crust. Based on these observations, it can be inferred that stress accumulation responsible for the Tangshan earthquake may have been closely related to the migration and deformation of the mantle materials. Comparisons of the average velocities of the whole crust, the upper and the lower crust show that the average velocity of the lower crust under the central part of the North China Basin(NCB) in the east of the craton is obviously higher than the regional average. This high-velocity probably results from long-term underplating of the mantle magma.
