An analytic function f in the unit disk D ：= {z ∈ C ： ｜z｜ 〈 1}, standardly normalized, is called close-to-convex with respect to the Koebe function k（z） ：= z/（1-z）2, z ∈ D, if there exists δ ∈ （-π/2,...An analytic function f in the unit disk D ：= {z ∈ C ： ｜z｜ 〈 1}, standardly normalized, is called close-to-convex with respect to the Koebe function k（z） ：= z/（1-z）2, z ∈ D, if there exists δ ∈ （-π/2,π/2） such that Re {eiδ（1-z）2f′（z）} 〉 0, z ∈ D. For the class C（k） of all close-to-convex functions with respect to k, related to the class of functions convex in the positive direction of the imaginary axis, the Fekete-Szego problem is studied.展开更多
The particularity and practicality of harmony operations of close-coupling multiple helicopters indicate that the researches on it are urgent and necessary, Using the model that describes two hovering helicopters carr...The particularity and practicality of harmony operations of close-coupling multiple helicopters indicate that the researches on it are urgent and necessary, Using the model that describes two hovering helicopters carrying one heavy load, an inertia coordinate system and body coordinate systems of each sub-system are established. A nonlinear force model is established too. The equilibrium computation results can be regarded as the reference control inputs of the flight control system under hovering or low-speed flight condition. After the establishment of a translation kinematics model and a posture kinematics model, a coupling dynamics model of the multiple helicopter system is set up. The results can also be regarded as the base to analyze stabilization and design a controller for a close-coupling multiple helicopters harmony operation system.展开更多
This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at t...This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at three positions: contact detonation in the center, contact detonation above the web and close-in detonation in the center. The external and internal breach parameters of the panels were evaluated by measuring the diameter of the ejection crater, spalling crater and breach hole created by the charge detonation. The experimental results were compared to predict values obtained by the analytical models proposed by McVay, Morishita and Remennikov. A modified breach with crater limit line and breach without crater limit line were put forward based on the experimental results. The maximum cross-sectional destruction area ratio(MCDAR) values were used to evaluate the damage degree. The maximum value of MCDAR reached 0.331 corresponding to the C5 experimental condition, of which explosion occurred above the web.展开更多
Oriental Beech is the most important commercial tree species in northern Iran. In recent years wood production companies interested in felling large beech trees for profit have challenged advocates of close-to-nature ...Oriental Beech is the most important commercial tree species in northern Iran. In recent years wood production companies interested in felling large beech trees for profit have challenged advocates of close-to-nature silviculture who favor conservation. Our study objective was to assess the economic value of over-mature beech trees by relating tree diameter （DBH） to amount of decay. Based on the location of onset of decay, we categorized three types of decay as stump, stem, and crown decay. Trees of greater diameter （age） typically showed greater decay in the stem. Percent of decayed volume, diameter of decayed tissue, and length of decay in tree stems varied between 0.5%-64.3%, 15 cm-75 cm, and 2.0-19.5 m, respectively. With increasing trunk diameter, the propor- tion of truck decay increased. Red heart and dark red heart constituted 25% and 14.3% of sampled trees, respectively. However, we found no correlation between intensity of stem decay and morphological charac- teristics of trees. Seedlings were not abundant around the bases of over-mature trees, suggesting that the trees did not contribute to regeneration of the stand. Beech trees of diameter 〉1 m do not provide valu- able round wood for industries and cause to raise wood production costs. We recommend that these trees 〉1 m DBH should be retained in forest stands because of their low commercial value but high ecological and conservational values such as maintaining biodiversity in forest ecosystems.展开更多
The reinforced concrete(RC) structural component might suffer a great damage under close-in explosion.Different from distant explosions, blast loads generated by the close-in explosion are non-uniformly distributed on...The reinforced concrete(RC) structural component might suffer a great damage under close-in explosion.Different from distant explosions, blast loads generated by the close-in explosion are non-uniformly distributed on the structural component and may cause both local and structural failure. In this study,an experimental study was conducted to investigate the dynamic responses of RC beams under doubleend-initiated close-in explosions. The experimental results show that the distribution of blast loads generated by the double-end-initiated explosion is much more non-uniform than those generated by single-point detonation, which is caused by the self-Mach-reflection effects. A 3 D finite element model was developed and validated in LS-DYNA by employing the modified K&C model. Intensive numerical calculations were conducted to study the influences of the initiation way, scaled distance and longitudinal reinforcement ratio on the dynamic responses and failure modes of RC beams. Numerical results show that the RC beam suffers greater damage as the cylindrical explosive is detonated at its double ends than the scenario in which the cylindrical explosive is detonated at its central point. RC beams mainly suffer flexural failure and flexure-shear failure under the double-end close-in explosion, and the failure modes of RC beams change from the flexural damage to flexure-shear damage as the scaled distance or the longitudinal reinforcement ratio decreases. The direct shear failure mode is not usually observed in the double-end-initiated explosion, since the intense blast loads is basically concentrated in the midspan of RC beam, which is due to self-Mach-reflection enhancement.展开更多
Fresh Pd/CeO/AlOclose coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these...Fresh Pd/CeO/AlOclose coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these pretreated catalysts were aged at 1000 °C for 3 h to study their anti-aging properties. The catalytic activities of the catalysts were investigated detailedly, and the results showed that the catalyst pretreated at 800 °C before aging treatment possessed the best anti-aging performance for CHoxidation. XRD and XPS results indicated that well-crystallized CeOparticles were formed during calcinations at 800 °C, which made CeOan effective promoter. HRTEM revealed that Pd particles found on the edge of CeOover the aged catalyst pretreated at 800 °C were relatively smaller than those over the catalysts without pretreatment. H-TPR and XPS results also implied that the interaction between well-crystallized CeOand Pd suppressed the deactivation of PdO sites and further enhanced the catalytic performance.展开更多
New photometric observations of NS VS 01286630 were performed and two sets of fourcolor（B, V, Rc, Ic） light curves（LCs） were obtained. Using the 2013 version of the Wilson-Devinney（W-D） code, we analyzed these d...New photometric observations of NS VS 01286630 were performed and two sets of fourcolor（B, V, Rc, Ic） light curves（LCs） were obtained. Using the 2013 version of the Wilson-Devinney（W-D） code, we analyzed these data. The photometric solutions reveal that NS VS 01286630 is an active detached eclipsing binary（EB） with a high orbital inclination（nearly 90°）. Remarkably, the temperature of the primary component（the hotter star） is higher than the secondary one, but the value of mass ratio q（M2/M1）for NS VS 0128663 is more than 1, which can be explained in that the surface of the secondary component of NSVS 01286630 is covered with big cool starspots. Based on our new CCD mid-eclipse times and the data published until now, variations in the mid-eclipse times were reanalyzed in detail using a weighted least-squares method. It is discovered that the（O-C） diagram of the system shows a cyclic oscillation with a period of 3.61 yr and an amplitude of 0.001 d. The cyclic variation may be caused by the light-travel time effect（LTTE） due to the presence of a third companion, whose mass we calculated as M3 sin（i3） =0.11 M（⊙）. The third body may affect the orbital evolution of the central binary system by transferring angular momentum.展开更多
The performance of multilayered thin steel plates subjected to close-range air blasts has been experimentally studied and compared with that of monolithic plates made of the same material and having equal mass. In pre...The performance of multilayered thin steel plates subjected to close-range air blasts has been experimentally studied and compared with that of monolithic plates made of the same material and having equal mass. In present experiments, multilayered plates are in-contact four-layered thin steel plates and two types of deformation/failure modes were observed for them. Comparisons concerning deformation/failure modes, strain distributions and energy absorptions between the multilayered plate and its monolithic counterpart were conducted. It is found that the multilayered plate is much superior to its monolithic counterpart in the ability to deform against blast loading. Furthermore, under intense airblast loading, the multilayered plate can not only absorb much more energy but also effectively reduce the secondary destruction ability of structural fragments in comparison with its monolithic counterpart.展开更多
A new identification method for a linear discrete-time closed-loop system is proposed based on an output over-sampling scheme. When the system outputs are over-sampled the new output sequences would contain more infor...A new identification method for a linear discrete-time closed-loop system is proposed based on an output over-sampling scheme. When the system outputs are over-sampled the new output sequences would contain more information about the plant structure. Using general least squares method （GLS） the plant over-sampled model should be recognized. Then the original plant model should be obtained by its relationship with the over-sampled model. Compared with conventional approaches the advantage of the new method is that even if the ordinary identifiability conditions are not satisfied, a close-loop system can be identified by using the oversampled output without utilizing any external test signal. Accuracy analysis shows the relationship between the estimation error and the over-sampling rate. Numerical simulation illnstrates its effectiveness.展开更多
On the basis of fractal theory, one of the nonlinear theories, this paper studies the validity of Chinese fund market fractal time sequence through Hurst exponent, calculates the H value and proposes a new close-end f...On the basis of fractal theory, one of the nonlinear theories, this paper studies the validity of Chinese fund market fractal time sequence through Hurst exponent, calculates the H value and proposes a new close-end fund mean reversion model. Meanwhile, this paper validates the mean reversion time sequence for consecutive 54 week data of fund market. The result indicates that this model can effectively prove that Chinese close-end fund market follows the biased random walk. The research also proves that the fund discount does have mean reversion tendency and averagely the fund with high discount has a higher excess yield than that of the fund with low discount. The mean excess yield and the ratio between discount rate deviation and standard deviation demonstrate a descending relationship. The optimum investment period based on ＂mean reversion＂ is one month. Consequently this model provides a new arbitrage method through the discount of close-end fund.展开更多
In this paper, a new physically based constitutive model is developed for hexagonal close-packed metals, especially the Ti-6Al-4V alloy, subjected to high strain rate and different temperatures based on the microscopi...In this paper, a new physically based constitutive model is developed for hexagonal close-packed metals, especially the Ti-6Al-4V alloy, subjected to high strain rate and different temperatures based on the microscopic mechanism of plastic deformation and the theory of thermally activated dislocation motion. A global analysis of constitutive parameters based on the Latin Hypercube Sampling method and the Spearman＇s rank correlation method is adopted in order to improve the identification efficiency of parameters. Then, an optimal solution of constitutive parameters as a whole is obtained by using a global genetic algorithm composed of an improved niche genetic algorithm, a global peak determination strategy and the local accurate search techniques. It is concluded that the proposed constitutive modal can accurately describe the Ti-6Al-4V alloy＇s dynamic behavior because the prediction results of the model are in good agreement with the experimental data.展开更多
This paper proposes a thorough scheme, by virtue of camera zooming descriptor with two-level threshold, to automatically retrieve close-ups directly from moving picture experts group （MPEG） compressed videos based o...This paper proposes a thorough scheme, by virtue of camera zooming descriptor with two-level threshold, to automatically retrieve close-ups directly from moving picture experts group （MPEG） compressed videos based on camera motion analysis. A new algorithm for fast camera motion estimation in compressed domain is presented. In the retrieval process, camera-motion-based semantic retrieval is built. To improve the coverage of the proposed scheme, close-up retrieval in all kinds of videos is investigated. Extensive experiments illustrate that the proposed scheme provides promising retrieval results under real-time and automatic application scenario.展开更多
One of the main causes of rear-end crashes is attributed to close-following and hazardous driving behavior. A study was conducted to investigate the close-following behavior of heavy vehicle under various heavy vehicl...One of the main causes of rear-end crashes is attributed to close-following and hazardous driving behavior. A study was conducted to investigate the close-following behavior of heavy vehicle under various heavy vehicle categories, travel speeds and gross vehicle weights (GVW). Investigation is based on data obtained from simulation and empirical observations. A safety performance assessment of close-following behavior of heavy vehicles by using empirical-simulation technique is proposed. The simulation, which incorporates vehicle dynamics, is to generate the minimum safe time gap (MSTG) for truck-following-car situations. MSTG is defined as the minimum time required by the following vehicle to decelerate and stop without hitting the leading vehicle when both leading and following vehicles apply the emergency brakes. Based on comparison between the actual time gap data and the MSTG, a safety performance assessment technique that considers vehicle type, vehicle braking characteristics, truck GVW and speed is proposed for truck-following-car situation.展开更多
In order to solve the problem of difficult modeling and identification caused by time-variable parameters,multiple inputs and outputs and unstable open loop,a subsystem model-based close-loop grey-box identification m...In order to solve the problem of difficult modeling and identification caused by time-variable parameters,multiple inputs and outputs and unstable open loop,a subsystem model-based close-loop grey-box identification method was put forward when consider the main coupling effects of hydraulic Stewart platform.Firstly,the whole system is divided into three TITO(Two Input Two Output) subsystems according to the characteristics of the pseudo-mass matrix,hence transfer function matrix model of the subsystem can also be found.Secondly,since the Stewart platform is unstable,the close-loop transfer model of the subsystem is derived under the proportional controllers.The inverse M serial is adopted as the identification signal to get the experimental data.All parameters of the subsystem are determined in close-loop indirect identification by PEM(Prediction Error Method).Finally,a case study validates the correctness and effectiveness of the subsystem model-based close-loop grey-box identification method for hydraulic Stewart platform.展开更多
In close-coupled gas atomization(CCGA), the influences of melt superheat on breakup process are fundamental to obtain desired or finer powder. Based on a series of Cu atomization experiment under different superheatin...In close-coupled gas atomization(CCGA), the influences of melt superheat on breakup process are fundamental to obtain desired or finer powder. Based on a series of Cu atomization experiment under different superheating conditions, the influences of melt superheat on breakup process were studied. Experimental results indicate that as the melt superheat is increased to 150, 200, 250 and 300 K, the mean particle size (D50) decreases consequently to 34.9, 32.3, 30.9 and 19.7 μm. Theoretical analysis reveals that the primary breakup and secondary breakup processes are close coupled, and the melt superheat radically influences the melt properties, and plays a crucial role on governing the filming process of primary breakup and the atomization modes of secondary breakup. There exists a strong nonlinear decrease of contact angle of melt to nozzle orifice wall when the superheat is increased from 250 K to 300 K, leading to a marked fall of the film thickness formed in primary breakup, and D50 of copper powders is therefore sharply reduced. However, the log-normal distribution feature of particle size has not been substantially improved.展开更多
The gas atomization is the process that a liquid mass is disintegrated into a collection of liquid melt droplets by the impact of high velocity gas stream and solidified into metal particles. However, the liquid melt ...The gas atomization is the process that a liquid mass is disintegrated into a collection of liquid melt droplets by the impact of high velocity gas stream and solidified into metal particles. However, the liquid melt sheet breaking mechanism has not been fully understood. So the experimental research was carried out under the condition of lower melt superheat. The results reveal that there are three approaches about melt metal sheet’s breakage: from the edges of sheets, from inner surface of sheets, and disrupted by other droplets and sheets. The approach of melt sheet breakage is dependent on its thickness. The thicker sheets (above 25μm) are disintegrated mainly by the way of droplet’s departing from edges, and the thinner sheets (below 10μm) are chiefly breaking from the inner surface.展开更多
In order to provide the model point accuracy of ±2 mm,an extra high accuracy industrial control net with four surveying piers with accuracy ±0.1 mm was set up around the model.Tens of orientation marks have ...In order to provide the model point accuracy of ±2 mm,an extra high accuracy industrial control net with four surveying piers with accuracy ±0.1 mm was set up around the model.Tens of orientation marks have been placed on the different parts and measured with accuracy ±0.2 mm from the above_mentioned piers.The main four stereopairs taken with the P31 camera around the model are simultaneously processed on the BC2 analytical plotter.The accuracy of absolute orientation is better than ±0.9 mm.Finally,about 300 sections construction drawings have been directly offered,and the close_range photogrammetric data has been used for the design and construction of the statue.展开更多
文摘An analytic function f in the unit disk D ：= {z ∈ C ： ｜z｜ 〈 1}, standardly normalized, is called close-to-convex with respect to the Koebe function k（z） ：= z/（1-z）2, z ∈ D, if there exists δ ∈ （-π/2,π/2） such that Re {eiδ（1-z）2f′（z）} 〉 0, z ∈ D. For the class C（k） of all close-to-convex functions with respect to k, related to the class of functions convex in the positive direction of the imaginary axis, the Fekete-Szego problem is studied.
基金National Natural Science Foundation of China(60475039)
文摘The particularity and practicality of harmony operations of close-coupling multiple helicopters indicate that the researches on it are urgent and necessary, Using the model that describes two hovering helicopters carrying one heavy load, an inertia coordinate system and body coordinate systems of each sub-system are established. A nonlinear force model is established too. The equilibrium computation results can be regarded as the reference control inputs of the flight control system under hovering or low-speed flight condition. After the establishment of a translation kinematics model and a posture kinematics model, a coupling dynamics model of the multiple helicopter system is set up. The results can also be regarded as the base to analyze stabilization and design a controller for a close-coupling multiple helicopters harmony operation system.
基金supported by The National Natural Science Foundation of China under Grant No.11390362 and No. 11221202
文摘This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at three positions: contact detonation in the center, contact detonation above the web and close-in detonation in the center. The external and internal breach parameters of the panels were evaluated by measuring the diameter of the ejection crater, spalling crater and breach hole created by the charge detonation. The experimental results were compared to predict values obtained by the analytical models proposed by McVay, Morishita and Remennikov. A modified breach with crater limit line and breach without crater limit line were put forward based on the experimental results. The maximum cross-sectional destruction area ratio(MCDAR) values were used to evaluate the damage degree. The maximum value of MCDAR reached 0.331 corresponding to the C5 experimental condition, of which explosion occurred above the web.
文摘Oriental Beech is the most important commercial tree species in northern Iran. In recent years wood production companies interested in felling large beech trees for profit have challenged advocates of close-to-nature silviculture who favor conservation. Our study objective was to assess the economic value of over-mature beech trees by relating tree diameter （DBH） to amount of decay. Based on the location of onset of decay, we categorized three types of decay as stump, stem, and crown decay. Trees of greater diameter （age） typically showed greater decay in the stem. Percent of decayed volume, diameter of decayed tissue, and length of decay in tree stems varied between 0.5%-64.3%, 15 cm-75 cm, and 2.0-19.5 m, respectively. With increasing trunk diameter, the propor- tion of truck decay increased. Red heart and dark red heart constituted 25% and 14.3% of sampled trees, respectively. However, we found no correlation between intensity of stem decay and morphological charac- teristics of trees. Seedlings were not abundant around the bases of over-mature trees, suggesting that the trees did not contribute to regeneration of the stand. Beech trees of diameter 〉1 m do not provide valu- able round wood for industries and cause to raise wood production costs. We recommend that these trees 〉1 m DBH should be retained in forest stands because of their low commercial value but high ecological and conservational values such as maintaining biodiversity in forest ecosystems.
基金supported by the National Natural Science Foundations of China(Nos. 51622812, and 51427807)National Basic Research Program of China(No. 2015CB058003)China Postdoctoral Science Foundation(No. 2017M613379)
文摘The reinforced concrete(RC) structural component might suffer a great damage under close-in explosion.Different from distant explosions, blast loads generated by the close-in explosion are non-uniformly distributed on the structural component and may cause both local and structural failure. In this study,an experimental study was conducted to investigate the dynamic responses of RC beams under doubleend-initiated close-in explosions. The experimental results show that the distribution of blast loads generated by the double-end-initiated explosion is much more non-uniform than those generated by single-point detonation, which is caused by the self-Mach-reflection effects. A 3 D finite element model was developed and validated in LS-DYNA by employing the modified K&C model. Intensive numerical calculations were conducted to study the influences of the initiation way, scaled distance and longitudinal reinforcement ratio on the dynamic responses and failure modes of RC beams. Numerical results show that the RC beam suffers greater damage as the cylindrical explosive is detonated at its double ends than the scenario in which the cylindrical explosive is detonated at its central point. RC beams mainly suffer flexural failure and flexure-shear failure under the double-end close-in explosion, and the failure modes of RC beams change from the flexural damage to flexure-shear damage as the scaled distance or the longitudinal reinforcement ratio decreases. The direct shear failure mode is not usually observed in the double-end-initiated explosion, since the intense blast loads is basically concentrated in the midspan of RC beam, which is due to self-Mach-reflection enhancement.
基金Project supported by the National Natural Science Foundation of China(21173153)the National Hi-tech Research Development Program of China(863 Program,2013AA065304)the Sichuan Science and Technology Agency Supported Project(2012FZ0008)
文摘Fresh Pd/CeO/AlOclose coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these pretreated catalysts were aged at 1000 °C for 3 h to study their anti-aging properties. The catalytic activities of the catalysts were investigated detailedly, and the results showed that the catalyst pretreated at 800 °C before aging treatment possessed the best anti-aging performance for CHoxidation. XRD and XPS results indicated that well-crystallized CeOparticles were formed during calcinations at 800 °C, which made CeOan effective promoter. HRTEM revealed that Pd particles found on the edge of CeOover the aged catalyst pretreated at 800 °C were relatively smaller than those over the catalysts without pretreatment. H-TPR and XPS results also implied that the interaction between well-crystallized CeOand Pd suppressed the deactivation of PdO sites and further enhanced the catalytic performance.
基金supported by the National Natural Science Foundation of China(Nos.11573063,11611530685)the Key Science Foundation of Yunnan Province(No.2017FA001)+1 种基金support from the staff of the Xinglong 85 cm telescopepartially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences
文摘New photometric observations of NS VS 01286630 were performed and two sets of fourcolor（B, V, Rc, Ic） light curves（LCs） were obtained. Using the 2013 version of the Wilson-Devinney（W-D） code, we analyzed these data. The photometric solutions reveal that NS VS 01286630 is an active detached eclipsing binary（EB） with a high orbital inclination（nearly 90°）. Remarkably, the temperature of the primary component（the hotter star） is higher than the secondary one, but the value of mass ratio q（M2/M1）for NS VS 0128663 is more than 1, which can be explained in that the surface of the secondary component of NSVS 01286630 is covered with big cool starspots. Based on our new CCD mid-eclipse times and the data published until now, variations in the mid-eclipse times were reanalyzed in detail using a weighted least-squares method. It is discovered that the（O-C） diagram of the system shows a cyclic oscillation with a period of 3.61 yr and an amplitude of 0.001 d. The cyclic variation may be caused by the light-travel time effect（LTTE） due to the presence of a third companion, whose mass we calculated as M3 sin（i3） =0.11 M（⊙）. The third body may affect the orbital evolution of the central binary system by transferring angular momentum.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 51179200 and 51209211)the Innovation Research Foundation for Ph. D Candidates of Naval University of Engineering, China (Grant No. HGYJSJJ2012001)
文摘The performance of multilayered thin steel plates subjected to close-range air blasts has been experimentally studied and compared with that of monolithic plates made of the same material and having equal mass. In present experiments, multilayered plates are in-contact four-layered thin steel plates and two types of deformation/failure modes were observed for them. Comparisons concerning deformation/failure modes, strain distributions and energy absorptions between the multilayered plate and its monolithic counterpart were conducted. It is found that the multilayered plate is much superior to its monolithic counterpart in the ability to deform against blast loading. Furthermore, under intense airblast loading, the multilayered plate can not only absorb much more energy but also effectively reduce the secondary destruction ability of structural fragments in comparison with its monolithic counterpart.
基金Project supported by National Natural Science Foundation ofChina (Grant No .60174030)
文摘A new identification method for a linear discrete-time closed-loop system is proposed based on an output over-sampling scheme. When the system outputs are over-sampled the new output sequences would contain more information about the plant structure. Using general least squares method （GLS） the plant over-sampled model should be recognized. Then the original plant model should be obtained by its relationship with the over-sampled model. Compared with conventional approaches the advantage of the new method is that even if the ordinary identifiability conditions are not satisfied, a close-loop system can be identified by using the oversampled output without utilizing any external test signal. Accuracy analysis shows the relationship between the estimation error and the over-sampling rate. Numerical simulation illnstrates its effectiveness.
基金Supported by Chenguang Plan Project of Science and Technology Bureau in Wuhan (20065004116-11)
文摘On the basis of fractal theory, one of the nonlinear theories, this paper studies the validity of Chinese fund market fractal time sequence through Hurst exponent, calculates the H value and proposes a new close-end fund mean reversion model. Meanwhile, this paper validates the mean reversion time sequence for consecutive 54 week data of fund market. The result indicates that this model can effectively prove that Chinese close-end fund market follows the biased random walk. The research also proves that the fund discount does have mean reversion tendency and averagely the fund with high discount has a higher excess yield than that of the fund with low discount. The mean excess yield and the ratio between discount rate deviation and standard deviation demonstrate a descending relationship. The optimum investment period based on ＂mean reversion＂ is one month. Consequently this model provides a new arbitrage method through the discount of close-end fund.
基金the financial support by the National Natural Science Foundation of China Academy of Engineering Physicsthe jointly set-up"NSAF"joint fund under Contract No.U1430119
文摘In this paper, a new physically based constitutive model is developed for hexagonal close-packed metals, especially the Ti-6Al-4V alloy, subjected to high strain rate and different temperatures based on the microscopic mechanism of plastic deformation and the theory of thermally activated dislocation motion. A global analysis of constitutive parameters based on the Latin Hypercube Sampling method and the Spearman＇s rank correlation method is adopted in order to improve the identification efficiency of parameters. Then, an optimal solution of constitutive parameters as a whole is obtained by using a global genetic algorithm composed of an improved niche genetic algorithm, a global peak determination strategy and the local accurate search techniques. It is concluded that the proposed constitutive modal can accurately describe the Ti-6Al-4V alloy＇s dynamic behavior because the prediction results of the model are in good agreement with the experimental data.
基金This work was supported by European IST FP6 Research Programme as funded for the Integrated Project:LIVE(No.IST-4-027312).
文摘This paper proposes a thorough scheme, by virtue of camera zooming descriptor with two-level threshold, to automatically retrieve close-ups directly from moving picture experts group （MPEG） compressed videos based on camera motion analysis. A new algorithm for fast camera motion estimation in compressed domain is presented. In the retrieval process, camera-motion-based semantic retrieval is built. To improve the coverage of the proposed scheme, close-up retrieval in all kinds of videos is investigated. Extensive experiments illustrate that the proposed scheme provides promising retrieval results under real-time and automatic application scenario.
文摘One of the main causes of rear-end crashes is attributed to close-following and hazardous driving behavior. A study was conducted to investigate the close-following behavior of heavy vehicle under various heavy vehicle categories, travel speeds and gross vehicle weights (GVW). Investigation is based on data obtained from simulation and empirical observations. A safety performance assessment of close-following behavior of heavy vehicles by using empirical-simulation technique is proposed. The simulation, which incorporates vehicle dynamics, is to generate the minimum safe time gap (MSTG) for truck-following-car situations. MSTG is defined as the minimum time required by the following vehicle to decelerate and stop without hitting the leading vehicle when both leading and following vehicles apply the emergency brakes. Based on comparison between the actual time gap data and the MSTG, a safety performance assessment technique that considers vehicle type, vehicle braking characteristics, truck GVW and speed is proposed for truck-following-car situation.
文摘In order to solve the problem of difficult modeling and identification caused by time-variable parameters,multiple inputs and outputs and unstable open loop,a subsystem model-based close-loop grey-box identification method was put forward when consider the main coupling effects of hydraulic Stewart platform.Firstly,the whole system is divided into three TITO(Two Input Two Output) subsystems according to the characteristics of the pseudo-mass matrix,hence transfer function matrix model of the subsystem can also be found.Secondly,since the Stewart platform is unstable,the close-loop transfer model of the subsystem is derived under the proportional controllers.The inverse M serial is adopted as the identification signal to get the experimental data.All parameters of the subsystem are determined in close-loop indirect identification by PEM(Prediction Error Method).Finally,a case study validates the correctness and effectiveness of the subsystem model-based close-loop grey-box identification method for hydraulic Stewart platform.
基金Projects(10476043 50574103) supported by National Natural Science Foundation of China
文摘In close-coupled gas atomization(CCGA), the influences of melt superheat on breakup process are fundamental to obtain desired or finer powder. Based on a series of Cu atomization experiment under different superheating conditions, the influences of melt superheat on breakup process were studied. Experimental results indicate that as the melt superheat is increased to 150, 200, 250 and 300 K, the mean particle size (D50) decreases consequently to 34.9, 32.3, 30.9 and 19.7 μm. Theoretical analysis reveals that the primary breakup and secondary breakup processes are close coupled, and the melt superheat radically influences the melt properties, and plays a crucial role on governing the filming process of primary breakup and the atomization modes of secondary breakup. There exists a strong nonlinear decrease of contact angle of melt to nozzle orifice wall when the superheat is increased from 250 K to 300 K, leading to a marked fall of the film thickness formed in primary breakup, and D50 of copper powders is therefore sharply reduced. However, the log-normal distribution feature of particle size has not been substantially improved.
文摘The gas atomization is the process that a liquid mass is disintegrated into a collection of liquid melt droplets by the impact of high velocity gas stream and solidified into metal particles. However, the liquid melt sheet breaking mechanism has not been fully understood. So the experimental research was carried out under the condition of lower melt superheat. The results reveal that there are three approaches about melt metal sheet’s breakage: from the edges of sheets, from inner surface of sheets, and disrupted by other droplets and sheets. The approach of melt sheet breakage is dependent on its thickness. The thicker sheets (above 25μm) are disintegrated mainly by the way of droplet’s departing from edges, and the thinner sheets (below 10μm) are chiefly breaking from the inner surface.
文摘In order to provide the model point accuracy of ±2 mm,an extra high accuracy industrial control net with four surveying piers with accuracy ±0.1 mm was set up around the model.Tens of orientation marks have been placed on the different parts and measured with accuracy ±0.2 mm from the above_mentioned piers.The main four stereopairs taken with the P31 camera around the model are simultaneously processed on the BC2 analytical plotter.The accuracy of absolute orientation is better than ±0.9 mm.Finally,about 300 sections construction drawings have been directly offered,and the close_range photogrammetric data has been used for the design and construction of the statue.
