大型环形可展开天线型面高精度测试方法研究

天线反射器型面精度是衡量、评价天线质量的重要指标之一,天线型面精度的高低将直接影响天线的电性能指标。大型环形可展开天线型面精度测试,目前多采用高精度工业数字化摄影测量技术进行,在使用高精度数字化摄影测量系统对大型环形可展开天线开展型面测试过程中,系统测量精度主要受摄影基准选用、测量距离、测量靶标大小、测量角度、测量拍照数量、相机参数等多项工艺参数影响。就如何使用数字化摄影测量系统对大型环形可展开天线开展高精度型面测试方法开展研究,通过对高精度长基准尺的设计及布局研究,以及对摄影测量系统最优匹配工艺参数研究及验证,得到一种针对大型环形可展开天线开展高精度型面测试的方法。试验证明,该方法可靠有效,能够满足大型环形可展开天线开展型面高精度测试的测量需求。

C语言中浮点数的存储格式及其有效数字位数

总结了C语言中的单精度型(float)、双精度型(double)和长双精度型(long double)浮点数的存储格式,并用简洁的C程序给出了验证;对其表示的十进制数的有效数字位数,从相对误差的角度,给出了判定方法及结论。

对95年自行车产品统检质量问题的分析(续)

下面再分析一下散件包装车部分一般项的情况: 1.螺纹精度:该项目主要是考核前叉立管、前叉上挡、脚蹬、曲柄、后轴身及飞轮等零部件的有关螺纹精度。《分等规定》中规定此项是以该项中最低等级件作为该项目的等级。但95年统检该项目时是执行全国自行车标准化中心“全自标(94)15号文”的有关规定:即在检验中如有三分之二以上的螺纹件达到《分等规定》的某质量等级,则判定螺纹件为相应的质量等级。对螺纹精度件测量,只使用螺纹通端和止端量规。

Combined Method of Datum Transformation Between Different Coordinate Systems

The similarity transformation model between different coordinate systems is not accurate enough to describe the discrepancy of them.Therefore,the coordinate transformation from the coordinate frame with poor accuracy to that with high accuracy cannot guarantee a high precision of transformation.In this paper,a combined method of similarity transformation and regressive approximating is presented.The local error accumulation and distortion are taken into consideration and the precision of coordinate system is improved by using the recommended method

NEW OPTIMIZATION METHOD WITH REGARD TO MACHINING PRECISION

An optimization method of variant step length based on precision and two new concepts “variant step length based on precision” and “one dimensional search based on the sorting” are presented.They make the optimum design closely combined with precision of every design variable.In addition,the authors propose that for a multi peaked one dimensional search problem its optimum solution can be obtained by ordinary optimization methods only when the convexity or concavity of the objective function matches the step length determining the one dimensional search region and the method of finding the optimum step length factor.

Maximal sequence length of exact match between members from a gene family during early evolution

Mutation (substitution, deletion, insertion, etc.) in nucleotide acid causes the maximal sequence lengths of exact match (MALE) between paralogous members from a duplicate event to become shorter during evolution. In this work, MALE changes between members of 26 gene families from four representative species (Arabidopsis thaliana, Oryza sativa, Mus mus- culus and Homo sapiens) were investigated. Comparative study of paralogous’ MALE and amino acid substitution rate (dA<0.5) indicated that a close relationship existed between them. The results suggested that MALE could be a sound evolutionary scale for the divergent time for paralogous genes during their early evolution. A reference table between MALE and divergent time for the four species was set up, which would be useful widely, for large-scale genome alignment and comparison. As an example, de- tection of large-scale duplication events of rice genome based on the table was illustrated.

Exact Solution of D-Dimensional Klein-Gordon Oscillator with Minimal Length

Specific modifications of the usual canonical commutation relations between position and momentumoperators have been proposed in the literature in order to implement the idea of the existence of a minimal observablelength. Here, we study a consequence of this proposal in relativistic quantum mechanics by solving in the momentumspace representation the Klein-Gordon oscillator in arbitrary dimensions. The exact bound states spectrum and thecorresponding momentum space wave function are obtained. Following Chang et al. (Phys. Rev. D 65 (2002) 125027),we discuss constraint that can be placed on the minimal length by measuring the energy levels of an electron in a penningtrap.

The first all-season sample set for mapping global land cover with Landsat-8 data

We report the world's first all-season training and validation sample sets for global land cover classification with Landsat-8 data.Prior to this,such samples were only available at a single date primarily from the growing season.It is unknown how much limitation such a single-date sample has to mapping global land cover in other seasons of the year.To answer this question,we selected available Landsat-8 images from four seasons and collected training and validation samples from them.We compared the performances of training samples in different seasons using Random Forest algorithm.We found that the use of training samples from any individual season would result in the best overall classification accuracy when validated by samples in the same season.The global overall accuracy from combined best seasonal results was 67.2% when classifying the 11 Level-1 classes in the Finer Resolution Observation and Monitoring of Global Land Cover(FROM-GLC) classification system.The use of training samples from all seasons(named all-season training sample set hereafter) produced an overall accuracy of 67.0%.We also tested classification within 10° latitude 60° longitude zones using all-season training subsample within each zone and obtained an overall accuracy of 70.2%.This indicates that properly grouped subsamples in space can help improve classification accuracies.All the results in this study seem to suggest that it is possible to use an all-season training sample set to reach global optimality with universal applicability in classifying images acquired at any time of a year for global land cover mapping.

Preoperative determination of tibial nail length： An anthropometric study

Objective： To assess the correlation between five anthropometric parameters and the distance from tibial tuberosity to medial malleolus in 100 volunteers. Methods： Six anthropometric parameters were measured in 50 male and 50 female medical students using a metallic scale： medial knee joint line to ankle joint line （K-A）, medial knee joint line to medial malleolus （K-MM）, tibial tuberosity to ankle joint （TT-A）, tibial tuberosity to medial malleolus （TT- MM）, olecranon to 5th metacarpal head （O-MH） and body height （BH）. Nail size predicted based upon Tr-MM measurement was chosen as ideal nail size. A constant was derived for each of the six anthropometric parameters which was either added or subtracted to each measurement to derive nail size. A regression equation was applied to BH measurements. Nail sizes calculated were compared with that obtained from TI＇-MM measurement and accuracy was evaluated. Accuracy of O-MH and BH regression equations recommended by other authors were calculated in our data. Results： Adding 11 mm to Tr-A distance had highest accuracy （81%） and correlation （0.966） in predicting nails correctly. Subtracting 33 mm from K-MM measurement and 25 mm from K-A distance derived accurate sizes in 69% and 76% respectively. Adding 6 mm to O-MH distance had a poor accuracy of 51%. Nail size prediction based upon body height regression equation derived correct nail sizes in only 34% of the cases. Regression equation analysis by other authors based on O-MH and BH distances yielded correct sizes in 11% and 5% of the cases respectively. Conclusion： TT-A, K-A and K-MM measurements can be used simultaneously to increase accuracy of nail size prediction. This method would be helpful in determining nail size preoperatively especially when one anatomic landmark is difficult to palpate.

Fertilization increases paddy soil organic carbon density

Field experiments provide an opportunity to study the effects of fertilization on soil organic carbon(SOC) sequestration.We sampled soils from a long-term(25 years) paddy experiment in subtropical China.The experiment included eight treatments:(1) check,(2) PK,(3) NP,(4) NK,(5) NPK,(6) 7F:3M(N,P,K inorganic fertilizers+30% organic N),(7) 5F:5M(N,P,K inorganic fertilizers+50% organic N),(8) 3F:7M(N,P,K inorganic fertilizers+70% or-ganic N).Fertilization increased SOC content in the plow layers compared to the non-fertilized check treatment.The SOC density in the top 100 cm of soil ranged from 73.12 to 91.36 Mg/ha.The SOC densities of all fertilizer treatments were greater than that of the check.Those treatments that combined inorganic fertilizers and organic amendments had greater SOC densities than those receiving only inorganic fertilizers.The SOC density was closely correlated to the sum of the soil carbon converted from organic amendments and rice residues.Carbon sequestration in paddy soils could be achieved by balanced and combined fertilization.Fertilization combining both inorganic fertilizers and organic amendments is an effective sustainable practice to sequestrate SOC.

Pulling growth technique towards rare earth single crystals

Pulling growth technique serves as a popular method to grow congruent melting single crystals with multiscale sizes ranging from micrometers to centimeters.In order to obtain high quality single crystals,the crystal constituents would be arranged at the lattice sites by precisely controlling the crystal growth process.Growing interface is the position where the phase transition of crystal constituents occurs during pulling growth process.The precise control of energy at the growing interface becomes a key technique in pulling growth.In this work,we review some recent advances of pulling technique towards rare earth single crystal growth.In Czochralski pulling growth,the optimized growth parameters were designed for rare earth ions doped Y_3Al_5O_(12)and Ce:(Lu_(1-x)Y_x)_2Si O_5on the basis of anisotropic chemical bonding and isotropic mass transfer calculations at the growing interface.The fast growth of high quality rare earth single crystals is realized by controlling crystallization thermodynamics and kinetics in different size zones.On the other hand,the micro pulling down technique can be used for high throughput screening novel rare earth optical crystals.The growth interface control is realized by improving the crucible bottom and temperature field,which favors the growth of rare earth crystal fibers.The rare earth laser crystal fiber can serve as another kind of laser gain medium between conventional bulk single crystal and glass fiber.The future work on pulling technique might focus on the mass production of rare earth single crystals with extreme size and with the size near that of devices.

On the monitoring model of reference point of VLBI antenna

Some insights and analysis are presented concerning the monitoring model of the VLBI(Very Long Baseline Interferometry) antenna,settings of parameters and selection of constraints to the observation equation,which are verified via data simulation analysis to be reasonable and effective.The effects of the number of targets and antenna orientations,the precision of target positioning observations,the observation outliers detection and deletion on the determination precision of antenna parameters are also analyzed,and some preliminary conclusions are given.