Current techniques of forest inventory rely on manual measurements and are slow and labor intensive.Recent developments in computer vision and depth sensing can produce accurate measurement data at significantly reduc...Current techniques of forest inventory rely on manual measurements and are slow and labor intensive.Recent developments in computer vision and depth sensing can produce accurate measurement data at significantly reduced time and labor costs.We developed the ForSense system to measure the diameters of trees at various points along the stem as well as stem straightness.Time use,mean absolute error(MAE),and root mean squared error(RMSE)metrics were used to compare the system against manual methods,and to compare the system against itself(reproducibility).Depth-derived diameter measurements of the stems at the heights of 0.3,1.4,and 2.7 m achieved RMSE of 1.7,1.5,and 2.7 cm,respectively.The ForSense system produced straightness measurement data that was highly correlated with straightness ratings by trained foresters.The ForSense system was also consistent,achieving sub-centimeter diameter difference with subsequent measures and less than 4%difference in straightness value between runs.This method of forest inventory,which is based on depth-image computer vision,is time efficient compared to manual methods and less computationally and technologically intensive compared to Structure-from-Motion(SFM)photogrammetry and ground-based LiDAR or terrestrial laser scanning(TLS).展开更多
A high-precision method of detecting motion straightness was proposed based on the prin- ciple of plane mirror interference after analyzing the motion straightness error of a linear stage. De- tection experiments were...A high-precision method of detecting motion straightness was proposed based on the prin- ciple of plane mirror interference after analyzing the motion straightness error of a linear stage. De- tection experiments were carried out and the motion straightness errors were separated by the linear regression method. Finally, linear measurement uncertainty of the detection method was estimated. The results showed that this detection method was simple and accurate, and was especially suitable for precision detection of motion straightness error in the small travel movement of ultra-precision machining.展开更多
You can describe a person in many ways.They may be young or old.You can talk about their height.They may be tall,short or average.You can talk about their hair,too.It can be long or short,curly or straight.It may be b...You can describe a person in many ways.They may be young or old.You can talk about their height.They may be tall,short or average.You can talk about their hair,too.It can be long or short,curly or straight.It may be brown,black,gray,,blonde or red.These days,it may be green or purple,too!You can also tell a person's eye color.Most people have black,brown,blue or green eyes.展开更多
Look around you,and you will see many people wearing jeans.They are popular and a favorite fashion choice for men and women of all ages.There are many styles and colors of jeans.But blue is still the most common color...Look around you,and you will see many people wearing jeans.They are popular and a favorite fashion choice for men and women of all ages.There are many styles and colors of jeans.But blue is still the most common color.Some jeans are tight.Some have straight legs,others have wide legs.Jeans with rips in them are in fashion now.展开更多
A slender and flat shaft is a key part of the track recorder in marine vessels. However, the axial straightness of the shaft often exceeds standard measurements after it is machined. It has also been found that its pr...A slender and flat shaft is a key part of the track recorder in marine vessels. However, the axial straightness of the shaft often exceeds standard measurements after it is machined. It has also been found that its precision does not last a long time. After thorough analysis of these problems the main reasons that affect machining quality are identified-and a process modification plan is put forward that meets design requirements of the shaft. The production and practice indicate that the precision of the shaft is stable for a long period and the quality of products improved substantially after new measures were employed, securing the e accuracy of the track recording of the marine vessel.展开更多
An immersed boundary(IB)-lattice Boltzmamm method(LBM)coupled model is utilized to study the particle focusing in a straight microchannel.The LBM is used to solve the incompressible fluid flow over a regular Eulerian ...An immersed boundary(IB)-lattice Boltzmamm method(LBM)coupled model is utilized to study the particle focusing in a straight microchannel.The LBM is used to solve the incompressible fluid flow over a regular Eulerian grid,while the IB method is employed to couple the bead-spring model which represents the fluid-particle interaction.After model validation,the simulations for hydrodynamic focusing of the single and multi particles are performed.The particles can be focused into the equilibrium positions under the pressure gradient and self-rotation induced forces,and the particle radius and Reynolds number are the key parameters influencing the focusing dynamics.This work demonstrates the potential usefulness of the IB-LBM model in studying the particle hydrodynamic focusing.展开更多
Background：This contribution evaluates the effect of forest structure and tree species diversity on plot productivity and individual tree growth in the unique Knysna forests in Southern Africa using mapped tree data ...Background：This contribution evaluates the effect of forest structure and tree species diversity on plot productivity and individual tree growth in the unique Knysna forests in Southern Africa using mapped tree data from an observational study that has been re-measured over a period of 40 years.Methods：The effects of tree species diversity and forest structure on tree growth and forest production are evaluated on three levels of resolution：a） the forest community（canopy,sub-canopy species）,b） the subplots（number of trees per ha,skewness of the diameter distribution,diameter coefficient of variation） and c） the immediate neighborhood of selected reference trees（＂Mingling＂,＂Dominance＂,Aggregation＂ and ＂Size Variation＂）.Results：An analysis of the community level identified two distinct clusters,one including dominant/canopy species with the highest growth rates and a greater variation of growth,and another cluster which includes the remaining subcanopy species which have a smaller maximum size and lower rates of growth.The area-based structure variables on plot level have a highly significant effect on total basal area growth.However,the effects of forest density and species richness on productivity were not straight forward.Maximum basal area production of about 0.75 m^2/ha/year is achieved at medium levels of richness（around 20 species per ha） and medium levels of density（around 30 m^2/ha basal area） using percentile regression estimates.The relative ＂Dominance＂ of a selected reference tree had a highly significant effect on individual tree growth on all investigated species.Other neighbourhood structure variables were only occasionally significant or not significant at all.Conclusion：This contribution presents a new theoretical framework for analysing natural forests that includes community,plot and neighborhood variables of forest structure and diversity,and a first specific analysis of the structure and dynamics of the Knysna Afromontane Forest,based on a unique set of longterm observations.The species-area（SAR） model developed in this study,represents a new general approach that can be used to derive a common standard of tree species diversity for different plot sizes,the species richness per hectare.展开更多
A genuinely three-dimensional spacetime conservation element and solution element(CE/SE)scheme is built as simple,consistent and straightforward extensions of an improved high resolution 2D CE/SE scheme.It is applied ...A genuinely three-dimensional spacetime conservation element and solution element(CE/SE)scheme is built as simple,consistent and straightforward extensions of an improved high resolution 2D CE/SE scheme.It is applied to examine the mechanism of three-dimensional detonation process in rectangular ducts.The simulations clearly show detailed three-dimensional detonation modes,namely a rectangular mode and a diagonal mode.Furthermore,the formation of unreacted pockets with high density and low temperature behind the detonation is observed for the two modes.展开更多
SrTiO_(3)(001) vicinal substrates of miscut 1°, 3°, and 6° toward the (001) plane were annealed at 800-1000°C in pure flowing O_(2) for 6h and examined by atomic force microscopy. The high temperat...SrTiO_(3)(001) vicinal substrates of miscut 1°, 3°, and 6° toward the (001) plane were annealed at 800-1000°C in pure flowing O_(2) for 6h and examined by atomic force microscopy. The high temperature annealed vicinal SiTiO_(3)(001) displayed arrays of straight steps and smooth terraces. The step heights vary from about 2 to 6 unit cell depending on the annealing temperatures. At 1000°C, step bunching becomes obvious. The height steps of 1 unit cell are difficult to be observed by our atomic force microscopy. The YBa2Cu3O7-δ thin film grows epitaxially on the step-terrace surface with c-axis orientation by magnetron sputtering in the two-dimensional island mode. Prospect of step-flow growth is being discussed.展开更多
Pipeline plays an indispensable role in process industries,because the progressing crack-like defects of in it may result in serious accidents and significant economic losses.Therefore,it is essential to detect the cr...Pipeline plays an indispensable role in process industries,because the progressing crack-like defects of in it may result in serious accidents and significant economic losses.Therefore,it is essential to detect the cracks occurred in pipelines.The axial crack-like defects in elbows with different angle are inspected by using the T(0,1)mode guided waves,in which different configurations including 45°,90°,135°and 180°(straight pipe)are considered respectively.Firstly,the detection sensitivity for different defect location is experimentally investigated.After that,finite element simulation is used to explore the propagation behaviors of T(0,1)mode in different bend structures.Simulation and experiment results show that the crack in different areas of the elbow can affect the detection sensitivity.It can be found that the detection sensitivity of crack in the middle area of the elbow is higher compared to the extrados and intrados of the elbow.Finally,the mode conversion is also investigated when the T(0,1)crosses the bend,and the results show that bend is a key factor to the mode conversion phenomenon which presents between the T(0,1)mode and F(1,2)mode.展开更多
In this study,wind tunnel experiment was carried out to investigate the self-staring capability for straight-bladed vertical axis wind turbine.The flow visualization also was been performed at the rest of the rotor.Th...In this study,wind tunnel experiment was carried out to investigate the self-staring capability for straight-bladed vertical axis wind turbine.The flow visualization also was been performed at the rest of the rotor.The effect of the azimuthal angle of blade position relative to wind direction on the self-starting capability was discussed based on the results of flow visualization.The torque and centripetal force of the rotor when the self-starting behavior starts were roughly calculated with the flow visualization results of the rotor.It is suggested that there exists the condition of wind speed and configuration of the blade position of the rotor at the rest of rotor to the reach to situational rotation number.展开更多
High quality silicon on insulator(SOI)materials have been successfully produced using the unibond method,a new member of SOI technology.The quality of SOI samples has been investigated by using cross-section transmiss...High quality silicon on insulator(SOI)materials have been successfully produced using the unibond method,a new member of SOI technology.The quality of SOI samples has been investigated by using cross-section transmission electron microscopy,Rutherford backscattering and channeling spectrometry and spreading resistance probe technology.Experimental results indicate that both the thickness uniformity and the crystalline quality of the top Si layer are good.The interface between the top Si layer and SiO2 buried layer is very sharp and straight.展开更多
A Gunn active layer is used as an X electron probe to detect the X tunnelling current in the GaAs--AlAs heterostructure,from which a new heterostructure intervalley transferred electron(HITE)device is obtained.In the ...A Gunn active layer is used as an X electron probe to detect the X tunnelling current in the GaAs--AlAs heterostructure,from which a new heterostructure intervalley transferred electron(HITE)device is obtained.In the 8 mm band,the highest pulse output power of these diodes is 2.65 W and the highest conversion efficiency is 18%.The dc and rf performance of the HITE devices was simulated by the band mixing resonant tunnelling theory and Monte Carlo transport simulation.The HITE effect has transformed the transit-time dipole-layer mode in the Gunn diode into a relaxation oscillation mode in the HITE device.From the comparison of simulated results to the measured data,the HITE effect is demonstrated straightforwardly.展开更多
基金funded in part by the United States Department of Agriculture Forest Service,Northern Research Station,USDA Hardwood Tree Improvement and Regeneration CenterUSDA National Institute of Food and Agriculture McIntire Stennis project (IND011523MS)。
文摘Current techniques of forest inventory rely on manual measurements and are slow and labor intensive.Recent developments in computer vision and depth sensing can produce accurate measurement data at significantly reduced time and labor costs.We developed the ForSense system to measure the diameters of trees at various points along the stem as well as stem straightness.Time use,mean absolute error(MAE),and root mean squared error(RMSE)metrics were used to compare the system against manual methods,and to compare the system against itself(reproducibility).Depth-derived diameter measurements of the stems at the heights of 0.3,1.4,and 2.7 m achieved RMSE of 1.7,1.5,and 2.7 cm,respectively.The ForSense system produced straightness measurement data that was highly correlated with straightness ratings by trained foresters.The ForSense system was also consistent,achieving sub-centimeter diameter difference with subsequent measures and less than 4%difference in straightness value between runs.This method of forest inventory,which is based on depth-image computer vision,is time efficient compared to manual methods and less computationally and technologically intensive compared to Structure-from-Motion(SFM)photogrammetry and ground-based LiDAR or terrestrial laser scanning(TLS).
基金Supported by National Defense Basic Scientific Research Project(A222013)High Quality CNC Machine Tool and Basic Manufacturing Equipment Scientific Major Project(2012ZX04010-061)
文摘A high-precision method of detecting motion straightness was proposed based on the prin- ciple of plane mirror interference after analyzing the motion straightness error of a linear stage. De- tection experiments were carried out and the motion straightness errors were separated by the linear regression method. Finally, linear measurement uncertainty of the detection method was estimated. The results showed that this detection method was simple and accurate, and was especially suitable for precision detection of motion straightness error in the small travel movement of ultra-precision machining.
文摘You can describe a person in many ways.They may be young or old.You can talk about their height.They may be tall,short or average.You can talk about their hair,too.It can be long or short,curly or straight.It may be brown,black,gray,,blonde or red.These days,it may be green or purple,too!You can also tell a person's eye color.Most people have black,brown,blue or green eyes.
文摘Look around you,and you will see many people wearing jeans.They are popular and a favorite fashion choice for men and women of all ages.There are many styles and colors of jeans.But blue is still the most common color.Some jeans are tight.Some have straight legs,others have wide legs.Jeans with rips in them are in fashion now.
文摘A slender and flat shaft is a key part of the track recorder in marine vessels. However, the axial straightness of the shaft often exceeds standard measurements after it is machined. It has also been found that its precision does not last a long time. After thorough analysis of these problems the main reasons that affect machining quality are identified-and a process modification plan is put forward that meets design requirements of the shaft. The production and practice indicate that the precision of the shaft is stable for a long period and the quality of products improved substantially after new measures were employed, securing the e accuracy of the track recording of the marine vessel.
基金Supported by the National Natural Science Foundation of China under Grant No 91023024the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No 20110092110003the National Science Foundation for Post-doctoral Scientists of China under Grant No 2012M511647。
文摘An immersed boundary(IB)-lattice Boltzmamm method(LBM)coupled model is utilized to study the particle focusing in a straight microchannel.The LBM is used to solve the incompressible fluid flow over a regular Eulerian grid,while the IB method is employed to couple the bead-spring model which represents the fluid-particle interaction.After model validation,the simulations for hydrodynamic focusing of the single and multi particles are performed.The particles can be focused into the equilibrium positions under the pressure gradient and self-rotation induced forces,and the particle radius and Reynolds number are the key parameters influencing the focusing dynamics.This work demonstrates the potential usefulness of the IB-LBM model in studying the particle hydrodynamic focusing.
文摘Background：This contribution evaluates the effect of forest structure and tree species diversity on plot productivity and individual tree growth in the unique Knysna forests in Southern Africa using mapped tree data from an observational study that has been re-measured over a period of 40 years.Methods：The effects of tree species diversity and forest structure on tree growth and forest production are evaluated on three levels of resolution：a） the forest community（canopy,sub-canopy species）,b） the subplots（number of trees per ha,skewness of the diameter distribution,diameter coefficient of variation） and c） the immediate neighborhood of selected reference trees（＂Mingling＂,＂Dominance＂,Aggregation＂ and ＂Size Variation＂）.Results：An analysis of the community level identified two distinct clusters,one including dominant/canopy species with the highest growth rates and a greater variation of growth,and another cluster which includes the remaining subcanopy species which have a smaller maximum size and lower rates of growth.The area-based structure variables on plot level have a highly significant effect on total basal area growth.However,the effects of forest density and species richness on productivity were not straight forward.Maximum basal area production of about 0.75 m^2/ha/year is achieved at medium levels of richness（around 20 species per ha） and medium levels of density（around 30 m^2/ha basal area） using percentile regression estimates.The relative ＂Dominance＂ of a selected reference tree had a highly significant effect on individual tree growth on all investigated species.Other neighbourhood structure variables were only occasionally significant or not significant at all.Conclusion：This contribution presents a new theoretical framework for analysing natural forests that includes community,plot and neighborhood variables of forest structure and diversity,and a first specific analysis of the structure and dynamics of the Knysna Afromontane Forest,based on a unique set of longterm observations.The species-area（SAR） model developed in this study,represents a new general approach that can be used to derive a common standard of tree species diversity for different plot sizes,the species richness per hectare.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10732010 and 10972010.
文摘A genuinely three-dimensional spacetime conservation element and solution element(CE/SE)scheme is built as simple,consistent and straightforward extensions of an improved high resolution 2D CE/SE scheme.It is applied to examine the mechanism of three-dimensional detonation process in rectangular ducts.The simulations clearly show detailed three-dimensional detonation modes,namely a rectangular mode and a diagonal mode.Furthermore,the formation of unreacted pockets with high density and low temperature behind the detonation is observed for the two modes.
文摘SrTiO_(3)(001) vicinal substrates of miscut 1°, 3°, and 6° toward the (001) plane were annealed at 800-1000°C in pure flowing O_(2) for 6h and examined by atomic force microscopy. The high temperature annealed vicinal SiTiO_(3)(001) displayed arrays of straight steps and smooth terraces. The step heights vary from about 2 to 6 unit cell depending on the annealing temperatures. At 1000°C, step bunching becomes obvious. The height steps of 1 unit cell are difficult to be observed by our atomic force microscopy. The YBa2Cu3O7-δ thin film grows epitaxially on the step-terrace surface with c-axis orientation by magnetron sputtering in the two-dimensional island mode. Prospect of step-flow growth is being discussed.
基金supported by the National Natural Science Foundation of China(Nos.51575185,51175178)
文摘Pipeline plays an indispensable role in process industries,because the progressing crack-like defects of in it may result in serious accidents and significant economic losses.Therefore,it is essential to detect the cracks occurred in pipelines.The axial crack-like defects in elbows with different angle are inspected by using the T(0,1)mode guided waves,in which different configurations including 45°,90°,135°and 180°(straight pipe)are considered respectively.Firstly,the detection sensitivity for different defect location is experimentally investigated.After that,finite element simulation is used to explore the propagation behaviors of T(0,1)mode in different bend structures.Simulation and experiment results show that the crack in different areas of the elbow can affect the detection sensitivity.It can be found that the detection sensitivity of crack in the middle area of the elbow is higher compared to the extrados and intrados of the elbow.Finally,the mode conversion is also investigated when the T(0,1)crosses the bend,and the results show that bend is a key factor to the mode conversion phenomenon which presents between the T(0,1)mode and F(1,2)mode.
基金supported in part by International Platform for Dryland Research and Education (IPDRE),Tottori University
文摘In this study,wind tunnel experiment was carried out to investigate the self-staring capability for straight-bladed vertical axis wind turbine.The flow visualization also was been performed at the rest of the rotor.The effect of the azimuthal angle of blade position relative to wind direction on the self-starting capability was discussed based on the results of flow visualization.The torque and centripetal force of the rotor when the self-starting behavior starts were roughly calculated with the flow visualization results of the rotor.It is suggested that there exists the condition of wind speed and configuration of the blade position of the rotor at the rest of rotor to the reach to situational rotation number.
文摘High quality silicon on insulator(SOI)materials have been successfully produced using the unibond method,a new member of SOI technology.The quality of SOI samples has been investigated by using cross-section transmission electron microscopy,Rutherford backscattering and channeling spectrometry and spreading resistance probe technology.Experimental results indicate that both the thickness uniformity and the crystalline quality of the top Si layer are good.The interface between the top Si layer and SiO2 buried layer is very sharp and straight.
基金Support of the National Natural Science Foundation of China under Grant No.69676022.
文摘A Gunn active layer is used as an X electron probe to detect the X tunnelling current in the GaAs--AlAs heterostructure,from which a new heterostructure intervalley transferred electron(HITE)device is obtained.In the 8 mm band,the highest pulse output power of these diodes is 2.65 W and the highest conversion efficiency is 18%.The dc and rf performance of the HITE devices was simulated by the band mixing resonant tunnelling theory and Monte Carlo transport simulation.The HITE effect has transformed the transit-time dipole-layer mode in the Gunn diode into a relaxation oscillation mode in the HITE device.From the comparison of simulated results to the measured data,the HITE effect is demonstrated straightforwardly.
