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Experimental Study on Interference Effect of Three Risers Arranged in Tandem with Variable Spacing Ratios
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作者 ZHANG Peng LIU Li-hua +2 位作者 LIU Ming REN Xiao-hui WANG Yu 《China Ocean Engineering》 SCIE EI CSCD 2023年第3期408-419,共12页
Taking the three-riser group arranged in tandem as the research subject,an experimental study was carried out on the risers arranged in tandem.The purpose is to explore the sensitivity of the dynamic response of each ... Taking the three-riser group arranged in tandem as the research subject,an experimental study was carried out on the risers arranged in tandem.The purpose is to explore the sensitivity of the dynamic response of each riser to spacing ratio and reveal the physical mechanism of riser groups under the interference effect.The spacing ratios of the adj acent risers are 4.0,5.0,6.0,and 8.0.At the spacing between the risers of 4.0D,the strong feedback effect increases the cross-flow(CF) displacement amplitude of the upstream riser.The shielding effect is the key factor affecting the interference effect on the midstream and downstream risers.At low reduced velocities,the shielding area initially appears,the displacement amplitude of the midstream and downstream risers varies greatly,the vibration of the two risers is still dominated by the first-order mode,and the transition between adjacent vibration modes is restrained.The multi-frequency superposition phenomenon is very significant at high reduced velocities.The most sensitive interference spacing under the test conditions is obtained.Due to the separation of the incoming flow and the double shielding effect of the upstream and midstream risers,the regular vortex-induced vibration in the wake area of the downstream riser is broken,and the vibration in the two directions is weakened.In general,the interference effect is more significant for the CF vibration of the three-riser groups than the in-line(IL) vibration. 展开更多
关键词 three-riser group tandem arrangement vortex-induced vibration wake interference variable spacing ratios
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Design of Linear Functional Noncircular Gear with High Contact Ratio Used in Continuously Variable Transmission
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作者 Yanan Hu Chao Lin +2 位作者 Chunjiang He Yongquan Yu Zhiqin Cai 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2023年第3期205-218,共14页
Continuously variable transmission(CVT)of noncircular gear has the technical advantages of large bearing capacity and high transmission efficiency.The key technology of CVT with noncircular gear has been broken throug... Continuously variable transmission(CVT)of noncircular gear has the technical advantages of large bearing capacity and high transmission efficiency.The key technology of CVT with noncircular gear has been broken through some countries,and is in the stage of deep application research.Although the characteristics and design methods of noncircular gear pairs have been continuously studied in China,the noncircular gear CVT is still in the preliminary exploration and research stage.The linear functional noncircular gear pair,whose transmission ratio is a linear function in the working section,to realize continuously variable transmission was the research object in this paper.According to the required transmission ratio in the working section,the transmission ratio function in the non-working section was constructed by using a polynomial.And then the influence of pitch curve parameters in the working section on which in the non-working section was also analyzed to obtain the pitch curve suitable for transmission of this gear pair.In addition,for improving the stability and bearing capacity of gear transmission,the noncircular gear pair transmission with high contact ratio was designed.Furthermore,the accurate value of the contact tooth length was calculated based on the gear principle and the characteristics of the involute tooth profile,from this the contact tooth length error was calculated by comparing the accurate value with its actual value obtained by the rolling experiment.Finally,an indirect method to verify the contact ratio by detecting the contact length error of the tooth profile was proposed. 展开更多
关键词 Continuously variable transmission Noncircular gear Pitch curve Contact ratio Contact tooth profile
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A Modified Bi-Directional Evolutionary Structural Optimization Procedure with Variable Evolutionary Volume Ratio Applied to Multi-Objective Topology Optimization Problem
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作者 Xudong Jiang Jiaqi Ma Xiaoyan Teng 《Computer Modeling in Engineering & Sciences》 SCIE EI 2023年第4期511-526,共16页
Natural frequency and dynamic stiffness under transient loading are two key performances for structural design related to automotive,aviation and construction industries.This article aims to tackle the multi-objective... Natural frequency and dynamic stiffness under transient loading are two key performances for structural design related to automotive,aviation and construction industries.This article aims to tackle the multi-objective topological optimization problem considering dynamic stiffness and natural frequency using modified version of bi-directional evolutionary structural optimization(BESO).The conventional BESO is provided with constant evolutionary volume ratio(EVR),whereas low EVR greatly retards the optimization process and high EVR improperly removes the efficient elements.To address the issue,the modified BESO with variable EVR is introduced.To compromise the natural frequency and the dynamic stiffness,a weighting scheme of sensitivity numbers is employed to form the Pareto solution space.Several numerical examples demonstrate that the optimal solutions obtained from the modified BESO method have good agreement with those from the classic BESO method.Most importantly,the dynamic removal strategy with the variable EVR sharply springs up the optimization process.Therefore,it is concluded that the modified BESO method with variable EVR can solve structural design problems using multi-objective optimization. 展开更多
关键词 Bi-directional evolutionary structural optimization variable evolutionary volume ratio multi-objective optimization weighted sum topology optimization
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A Class of Estimators for Population Ratio in Simple Random Sampling Using Variable Transformation 被引量:2
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作者 A. C. Onyeka V. U. Nlebedim C. H. Izunobi 《Open Journal of Statistics》 2014年第4期284-291,共8页
This paper is an extension and generalization of the study carried out by [1] on the estimation of the population ratio (R) of the population means of two variables (y and x) under Simple Random Sampling (SRS) scheme,... This paper is an extension and generalization of the study carried out by [1] on the estimation of the population ratio (R) of the population means of two variables (y and x) under Simple Random Sampling (SRS) scheme, using a variable transformation of the auxiliary variable, x. All the six estimators proposed by [1] are easily identified as special cases of the proposed class of estimators. Asymptotic properties of the proposed class of estimators are derived theoretically and subsequently verified using empirical illustrations. Some of the proposed estimators are found to have relatively large gains in efficiency over the customary ratio estimator, ?for the given data set. 展开更多
关键词 variable TRANSFORMATION ratio Product and Regression-Type ESTIMATORS Mean Squared ERROR
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Estimation of Population Ratio in Post-Stratified Sampling Using Variable Transformation
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作者 Aloy Chijioke Onyeka Chinyeaka Hostensia Izunobi Iheanyi Sylvester Iwueze 《Open Journal of Statistics》 2015年第1期1-9,共9页
Extending the work carried out by [1], this paper proposes six combined-type estimators of population ratio of two variables in post-stratified sampling scheme, using variable transformation. Properties of the propose... Extending the work carried out by [1], this paper proposes six combined-type estimators of population ratio of two variables in post-stratified sampling scheme, using variable transformation. Properties of the proposed estimators were obtained up to first order approximations,(on–1), both for achieved sample configurations (conditional argument) and over repeated samples of fixed size n (unconditional argument). Efficiency conditions were obtained. Under these conditions the proposed combined-type estimators would perform better than the associated customary combined-type estimator. Furthermore, optimum estimators among the proposed combined-type estimators were obtained both under the conditional and unconditional arguments. An empirical work confirmed the theoretical results. 展开更多
关键词 variable TRANSFORMATION Combined-Type ESTIMATOR ratio Product and Regression-Type ESTIMATORS Mean Squared Error
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Separate-Type Estimators for Estimating Population Ratio in Post-Stratified Sampling Using Variable Transformation
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作者 Aloy Chijioke Onyeka Chinyeaka Hostensia Izunobi Iheanyi Sylvester Iwueze 《Open Journal of Statistics》 2015年第1期27-34,共8页
The study proposes, along the line of [1], six separate-type estimators for estimating the population ratio of two variables in post-stratified sampling, using variable transformation. Properties of the proposed estim... The study proposes, along the line of [1], six separate-type estimators for estimating the population ratio of two variables in post-stratified sampling, using variable transformation. Properties of the proposed estimators were obtained up to first order approximations, both for achieved sample configurations (conditional argument) and over repeated samples of fixed size n (unconditional argument). Efficiency conditions, under which the proposed separate-type estimators would perform better than the associated customary separate-type estimators in terms of having smaller mean squared errors, were obtained. Furthermore, conditions under which some of the proposed separate-type estimators would perform better than other proposed separate-type estimators were also obtained. The optimum estimators among the proposed separate-type estimators were obtained and an empirical illustration confirmed the theoretical results. 展开更多
关键词 variable Transformation Separate-Type ESTIMATOR OPTIMUM ESTIMATORS ratio Product and Regression-Type ESTIMATORS Mean Squared Error
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Mixture Ratio Estimators Using Multi-Auxiliary Variables and Attributes for Two-Phase Sampling
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作者 Paul Mwangi Waweru John Kung’u James Kahiri 《Open Journal of Statistics》 2014年第9期776-788,共13页
In this paper, we have proposed three classes of mixture ratio estimators for estimating population mean by using information on auxiliary variables and attributes simultaneously in two-phase sampling under full, part... In this paper, we have proposed three classes of mixture ratio estimators for estimating population mean by using information on auxiliary variables and attributes simultaneously in two-phase sampling under full, partial and no information cases and analyzed the properties of the estimators. A simulated study was carried out to compare the performance of the proposed estimators with the existing estimators of finite population mean. It has been found that the mixture ratio estimator in full information case using multiple auxiliary variables and attributes is more efficient than mean per unit, ratio estimator using one auxiliary variable and one attribute, ratio estimator using multiple auxiliary variable and multiple auxiliary attributes and mixture ratio estimators in both partial and no information case in two-phase sampling. A mixture ratio estimator in partial information case is more efficient than mixture ratio estimators in no information case. 展开更多
关键词 ratio ESTIMATOR MULTIPLE AUXILIARY variables MULTIPLE AUXILIARY Attributes TWO-PHASE Sampling Bi-Serial Correlation Coefficient
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Variable Gear Ratio Control Using Vehicle Body Slip Angle
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作者 Takahiko Yoshino Hiromichi Nozaki 《Engineering(科研)》 2014年第8期439-448,共10页
Vehicles with variable steering characteristics have long been studied and compared with those having typical fixed gear ratio steering, and the variable gear ratio properties are reported to have improved maneuverabi... Vehicles with variable steering characteristics have long been studied and compared with those having typical fixed gear ratio steering, and the variable gear ratio properties are reported to have improved maneuverability and stability in high-speed lane changes and on slippery low-friction road surfaces. However, it is not clear how gear ratios should be set for individual vehicle characteristics. Therefore, the present study has investigated a variable steering gear system using body slip angle feedback for the purpose of improved maneuverability and stability in the critical cornering range and upwards, in excess of the critical limit, and into the countersteer range. The results of a driving simulator experiment show that the steering effect improves and maneuverability and stability increase in the critical cornering range and upwards, in excess of the critical limit, and into the countersteer range by applying linear-variable control to the steering ratio from a body slip angle of 5?. This result is seen both in double lane changes, such as in hazard avoidance, and in J-turns with long drifting. Moreover, it shows an improvement in drift controllability through prompt countersteering. Overall, the present system can enhance the driver’s hazard avoidance capability. 展开更多
关键词 Motion CONTROL AUTOMOBILE Vehicle Dynamics MANEUVERABILITY variable GEAR ratio
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New Class of Almost Unbiased Modified Ratio Cum Product Estimators with Knownparameters of Auxiliary Variables
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作者 Jambulingam Subramani Master Ajith S 《Journal of Mathematics and System Science》 2017年第9期248-260,共13页
This manuscript deals with new class of almost unbiased ratio cum product estimators for the estimation of population mean of the study variable by using the known values auxiliary variable. The bias and mean squared ... This manuscript deals with new class of almost unbiased ratio cum product estimators for the estimation of population mean of the study variable by using the known values auxiliary variable. The bias and mean squared error of proposed estimators are obtained. An empirical study is carried out to assess the efficiency of proposed estimators over the existing estimators with the help of some known natural populations and it shows that the proposed estimators are almost unbiased and it perform better than the existing estimators. 展开更多
关键词 Auxiliary variable BIAS Mean squared error Natural populations ratio and Productestimators Simple random sampling.
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Mixture Regression-Cum-Ratio Estimator Using Multi-Auxiliary Variables and Attributes in Single-Phase Sampling
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作者 Teresio Mutembei John Kung’u Christopher Ouma 《Open Journal of Statistics》 2014年第5期367-376,共10页
In this paper, we have proposed a class of mixture regression-cum-ratio estimator for estimating population mean by using information on multiple auxiliary variables and attributes simultaneously in single-phase sampl... In this paper, we have proposed a class of mixture regression-cum-ratio estimator for estimating population mean by using information on multiple auxiliary variables and attributes simultaneously in single-phase sampling and analyzed the properties of the estimator. An empirical was carried out to compare the performance of the proposed estimator with the existing estimators of finite population mean using simulated population. It was found that the mixture regression-cum-ratio estimator was more efficient than ratio and regression estimators using one auxiliary variable and attribute, ratio and regression estimators using multiple auxiliary variables and attributes and regression-cum-ratio estimators using multiple auxiliary variables and attributes in single-phase sampling for finite population. 展开更多
关键词 Regression-Cum-ratio ESTIMATOR Multiple AUXILIARY variableS and Attributes SINGLE-PHASE Sampling
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Generalized Ratio-Cum-Product Estimators for Two-Phase Sampling Using Multi-Auxiliary Variables
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作者 John Kung’u Joseph Nderitu 《Open Journal of Statistics》 2016年第4期616-627,共13页
In this paper, we have proposed estimators of finite population mean using generalized Ratio- cum-product estimator for two-Phase sampling using multi-auxiliary variables under full, partial and no information cases a... In this paper, we have proposed estimators of finite population mean using generalized Ratio- cum-product estimator for two-Phase sampling using multi-auxiliary variables under full, partial and no information cases and investigated their finite sample properties. An empirical study is given to compare the performance of the proposed estimators with the existing estimators that utilize auxiliary variable(s) for finite population mean. It has been found that the generalized Ra-tio-cum-product estimator in full information case using multiple auxiliary variables is more efficient than mean per unit, ratio and product estimator using one auxiliary variable, ratio and product estimator using multiple auxiliary variable and ratio-cum-product estimators in both partial and no information case in two phase sampling. A generalized Ratio-cum-product estimator in partial information case is more efficient than Generalized Ratio-cum-product estimator in No information case. 展开更多
关键词 ratio-Cum-Product Estimator Multiple Auxiliary variables Two-Phase Sampling
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Mechanism of adjusting bypass ratio by front variable area bypass injector for a variable cycle engine
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作者 Qian LI Chen XIA +3 位作者 Guoping HUANG Omer MUSA Linjun LI Zonghan YU 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2024年第10期158-171,共14页
The Front Variable Area Bypass Injector(FVABI)is a key to bypass ratio adjustment for a Variable Cycle Engine(VCE).In order to study the role of the FVABI with the Core Driven Fan Stage(CDFS)duct,firstly,the engine by... The Front Variable Area Bypass Injector(FVABI)is a key to bypass ratio adjustment for a Variable Cycle Engine(VCE).In order to study the role of the FVABI with the Core Driven Fan Stage(CDFS)duct,firstly,the engine bypass with the CDFS duct model and the equivalent engine bypass without the CDFS duct model are designed using the concept of a jet boundary line.By comparing the difference between airflow driving forces in the two engine bypass models,the quantitative effects of the injection from the CDFS duct on the mass flow rate of the engine bypass airflow are obtained under different combinations of pressure difference and area ratios.Then,the CDFS duct injection characteristic map is obtained through the typical experiment of the FVABI.Based on this map,the performance model of the FVABI is developed.Finally,the turbofan engine model with the Variable Inlet Guide Vane(VIGV),the First Variable Cycle Engine model(VCE1)with the CDFS duct and without the VIGV,and the Second Variable Cycle Engine model(VCE2)with the CDFS duct and VIGV are built.The gain on the engine bypass ratio adjustment range caused by the injection from the CDFS duct is clarified by comparing the three engine models.It is concluded that the bypass ratio adjustment range of the variable cycle engine with the FVABI is about twice that of the traditional turbofan engine. 展开更多
关键词 Front variable area bypass injector variable cycle engine Bypass ratio Injection CDFS duct injection characteristic map
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Establishment of Dynamic Model for Axle Box Bearing of High-Speed Trains Under Variable Speed Conditions 被引量:5
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作者 Yongqiang Liu Baosen Wang +1 位作者 Bin Zhang Shaopu Yang 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2022年第4期340-351,共12页
In this study,a dynamic model for the bearing rotor system of a high-speed train under variable speed conditions is established.In contrast to previous studies,the contact stress is simplifed in the proposed model and... In this study,a dynamic model for the bearing rotor system of a high-speed train under variable speed conditions is established.In contrast to previous studies,the contact stress is simplifed in the proposed model and the compensation balance excitation caused by the rotor mass eccentricity considered.The angle iteration method is used to overcome the challenge posed by the inability to determine the roller space position during bearing rotation.The simulation results show that the model accurately describes the dynamics of bearings under varying speed profles that contain acceleration,deceleration,and speed oscillation stages.The order ratio spectrum of the bearing vibration signal indicates that both the single and multiple frequencies in the simulation results are consistent with the theoretical results.Experiments on bearings with outer and inner ring faults under various operating conditions are performed to verify the developed model. 展开更多
关键词 variable speed conditions High-speed train Bearing model Angle iteration Order ratio spectrum
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Cu Secondary Adsorption by Some Variable Charge Soils After Adsorbing SO_4^(2-) 被引量:1
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作者 DONGYUAN-YAN WANGSHU-YU 《Pedosphere》 SCIE CAS CSCD 1993年第2期173-180,共8页
Cu secondary adsorption by three variable charge soils collected from hubei Province and Hunan Province was investigated.The amount of Cu secondary adsorption increased with that of SO4^2- elementary adsorption and co... Cu secondary adsorption by three variable charge soils collected from hubei Province and Hunan Province was investigated.The amount of Cu secondary adsorption increased with that of SO4^2- elementary adsorption and conformed with the Langmuir,freundlich and Temkin isotherms.Desorption of secondary-adsorbed Cu indicated that the hysteresis ratio decreased as Cu secondary adsorption increased,which meant that secondry-adsorbed Cu existed not only in the exchangeable form but also in the bridge form and specifically adsorbed form.The amount of Cu secondary adsorption increased with the temperature. 展开更多
关键词 CU hysteresis ratio secondary adsorption variable charge soils
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Hydro-mechanical Transmit Performance Analysis for a Continuously Variable Transmission 被引量:1
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作者 Liang He Wanlin Guo Sihong Zhu 《Journal of Food Science and Engineering》 2016年第3期121-131,共11页
Based on an exact CAD model of hydro-mechanical continuously variable transmission (HMCVT) gearbox which can transmit 180 horsepower, virtual prototype of the HMCVT was built. Revolution speed of shafts, gears and c... Based on an exact CAD model of hydro-mechanical continuously variable transmission (HMCVT) gearbox which can transmit 180 horsepower, virtual prototype of the HMCVT was built. Revolution speed of shafts, gears and clutches of the HMCVT were calibrated by using results obtained by theoretical calculation and test methods. The needed power and torques of both mechanical power input shaft and hydropower input shaft were calculated by simulation. Hydraulic power distributing ratio and power flow of the system was also studied. The analysis results showed that cycle power was produced inevitably when the output shaft speed of HMCVT change smoothly during mechanical and hydraulic working state HM1 to HM4, and the instantaneous maximum cycle power was 39.5%. Then the overall transmission efficiency of HMCVT was studied, and the maximum overall efficiency of the system was about 87%. The results of the studies gave references to select suited engine and variable displacement pump for the HMCVT, and to develop rational speed control strategies for the HMCVT by changing displacement ratio of variable displacement pump. 展开更多
关键词 Tractor continuously variable transmission displacement ratio rotational speed torque power flow.
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Health status assessment of axial piston pump under variable speed 被引量:1
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作者 Guo Rui Li Hucheng +3 位作者 Zhao Zhiqian Zhang Rongbing Zhao Jingyi Gao Dianrong 《High Technology Letters》 EI CAS 2020年第3期315-322,共8页
The axial piston pump usually works under variable speed conditions.It is important to evaluate the health status of the axial piston pump under the variable speed condition.Aiming at the characteristic signals obtain... The axial piston pump usually works under variable speed conditions.It is important to evaluate the health status of the axial piston pump under the variable speed condition.Aiming at the characteristic signals obtained under different wear levels of the port plate,a feature signal extraction method under variable speed conditions is proposed.Firstly,the combination of complete ensemble empirical mode decomposition with adaptive noise(CEEMDAN)energy spectrum and fast spectral kurtosis principle is used to accurately extract the intrinsic mode function(IMF)component containing the sensitive information of the degraded feature.Then,the aspect ratio analysis method of the angle domain variational mode decomposition(VMD)is used to process the feature index containing the sensitive information of the degraded feature.In order to evaluate the health status of the axial piston pump under variable speed,the vibration reliability analysis method for axial piston pump based on Weibull proportional failure rate model is proposed.The experimental results show that the proposed method can accurately evaluate the health status of the axial piston pump. 展开更多
关键词 axial piston pump variable speed condition order ratio variational mode decomposition(VMD)in angle domain health status assessment
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Diffusion tensor imaging of spinal microstructure in healthy adults: improved resolution with the readout segmentation of long variable echo-trains
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作者 Bu-tian Zhang Meng Li +3 位作者 Li-li Yu Yi-meng Dai Shao-nan Yu Jin-lan Jiang 《Neural Regeneration Research》 SCIE CAS CSCD 2017年第12期2067-2070,共4页
Diffusion tensor imaging plays an important role in the accurate diagnosis and prognosis of spinal cord diseases. However, because of technical limitations, the imaging sequences used in this technique cannot reveal t... Diffusion tensor imaging plays an important role in the accurate diagnosis and prognosis of spinal cord diseases. However, because of technical limitations, the imaging sequences used in this technique cannot reveal the fine structure of the spinal cord with precision. We used the readout segmentation of long variable echo-trains(RESOLVE) sequence in this cross-sectional study of 45 healthy volunteers aged 20 to 63 years. We found that the RESOLVE sequence significantly increased the resolution of the diffusion images and improved the median signal-to-noise ratio of the middle(C4–6) and lower(C7–T1) cervical segments to the level of the upper cervical segment. In addition, the values of fractional anisotropy and radial diffusivity were significantly higher in white matter than in gray matter. Our study verified that the RESOLVE sequence could improve resolution of diffusion tensor imaging in clinical applications and provide accurate baseline data for the diagnosis and treatment of cervical spinal cord diseases. 展开更多
关键词 nerve regeneration diffusion tensor imaging cervical spinal cord MICROSTRUCTURE gray matter white matter readout segmentationof long variable echo-train sequence signal-to-noise ratio fractional anisotropy neural regeneration
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Variable stiffness control algorithm for high-rising buildings of closely spaced frequencies based on wavelet transforms
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作者 滕军 鲁志雄 闫安志 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2010年第5期600-606,共7页
To establish the algorithm of SAT-TMD system with the wavelet transform(WT),the modal mass participation ratio is proposed to distinguish if the high-rising structure has the characteristic of closely distributed freq... To establish the algorithm of SAT-TMD system with the wavelet transform(WT),the modal mass participation ratio is proposed to distinguish if the high-rising structure has the characteristic of closely distributed frequencies.A time varying analytical model of high-rising structure such as TV-tower with the SAT-TMD is developed.The proposed new idea is to use WT to identify the dominant frequency of structural response in a segment time,and track its variation as a function of time to retune the SAT-TMD.The effectiveness of SAT-TMD is investigated and it is more robust to change in building stiffness and damping than that of the TMD with a fixed frequency corresponding to a fixed mode frequency of the building.It is proved that SAT-TMD is particularly effective in reducing the response even when the building stiffness is changed by ±15%;whereas the TMD loses its effectiveness under such building stiffness variations. 展开更多
关键词 variable stiffness control semi-active tunable TMD(SAT-TMD) wavelet transforms closely spaced frequencies modal mass participation ratio
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A New Regression Type Estimator with Two Auxiliary Variables for Single-Phase Sampling 被引量:1
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作者 Everline Chemutai Tum John Kung’u Leo Odongo 《Open Journal of Statistics》 2014年第9期789-796,共8页
In this paper, we have proposed an estimator of finite population mean using a new regression type estimator with two auxiliary variables for single-phase sampling and investigated its finite sample properties. An emp... In this paper, we have proposed an estimator of finite population mean using a new regression type estimator with two auxiliary variables for single-phase sampling and investigated its finite sample properties. An empirical study has been carried out to compare the performance of the proposed estimator with the existing estimators that utilize auxiliary variables for finite population mean. It has been found that the new regression type estimator with two auxiliary variables for to be more efficient than mean per unit, ratio and product estimator and exponential ratio and exponential product estimators and exponential ratio-product estimator. 展开更多
关键词 Regression ESTIMATOR EXPONENTIAL ratio-Product ESTIMATOR AUXILIARY variableS Mean Squared ERROR
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Estimation of Population Variance Using the Coefficient of Kurtosis and Median of an Auxiliary Variable under Simple Random Sampling
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作者 Tonui Kiplangat Milton Romanus Otieno Odhiambo George Otieno Orwa 《Open Journal of Statistics》 2017年第6期944-955,共12页
In this study we have proposed a modified ratio type estimator for population variance of the study variable y under simple random sampling without replacement making use of coefficient of kurtosis and median of an au... In this study we have proposed a modified ratio type estimator for population variance of the study variable y under simple random sampling without replacement making use of coefficient of kurtosis and median of an auxiliary variable x. The estimator’s properties have been derived up to first order of Taylor’s series expansion. The efficiency conditions derived theoretically under which the proposed estimator performs better than existing estimators. Empirical studies have been done using real populations to demonstrate the performance of the developed estimator in comparison with the existing estimators. The proposed estimator as illustrated by the empirical studies performs better than the existing estimators under some specified conditions i.e. it has the smallest Mean Squared Error and the highest Percentage Relative Efficiency. The developed estimator therefore is suitable to be applied to situations in which the variable of interest has a positive correlation with the auxiliary variable. 展开更多
关键词 Modified ratio Type Variance Estimator Study variable AUXILIARY variable KURTOSIS MEDIAN Bias Mean Squared Error (MSE) PERCENTAGE Relative Efficiency (PRE) Simple Random Sampling
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