Measuring the Distance of VX Sagittarii with SiO Maser Proper Motions

We report on 43 GHz v=1, J=1-0 SiO maser proper motions in the circumstellar envelope of the M-type semi-regular variable star VX Sgr, observed by Very Long Baseline Array （VLBA） at 3 epochs during 1999 April-May. Applying the statistical parallax analysis to these proper motions, we estimated a distance of VX Sgr of 1.57±0.27kpc, which is consistent with that based on the proper motions of H20 masers, or on the assumption that VX Sgr belongs to the Sgr OB1 association. At this distance, VX Sgr can be classified as a red supergiant. Comparing the statistical parallax method with those of model fitting and annual parallax, we think that the statistical parallax method may be a good way of estimating SiO maser distances at present.

支流入汇对干流航道通航条件影响模拟研究

自然河流由于支流的汇入,在交汇区与干流相互混掺顶托,改变了原有的水流形态,形成复杂的水流结构,对内河船舶航运的操纵性和安全性均造成一定影响。采用数值模拟试验方法,基于分离式(MMG)水动力模型,系统地研究了不同交汇角、汇流比以及干支流河道宽度比情况下交汇区船舶通航条件,即船舶航行时的漂角和偏航距离因素,并以此为基础,基于Design-Export响应面分析软件,得出了无量纲化后的最大偏航距离与交汇角、汇流比以及干支流宽度比之间的响应函数。

Simulation of unsteady aerodynamic loads on high-speed trains in fluctuating crosswinds

To study the unsteady aerodynamic loads of high-speed trains in fluctuating crosswinds, the fluctuating winds of a moving point shifting with high-speed trains are calculated in this paper based on Cooper theory and harmonic superposition method. The computational fluid dynamics method is used to obtain the aerodynamic load coefficients at different mean yaw angles, and the aero- dynamic admittance function is introduced to calculate unsteady aerodynamic loads of high-speed trains in fluctuating winds. Using this method, the standard deviation and maximum value of the aerodynamic force （moment） are simulated. The results show that when the train speed is fixed, the varying mean wind speeds have large impact on the fluctuating value of the wind speeds and aerodynamic loads; in contrast, when the wind speed is fixed, the varying train speeds have little impact on the fluctuating value of the wind speeds or aerodynamic loads. The ratio of standard deviation to 0.SpKU2, or maximum value to 0.5pKU2, can be expressed as the function of mean yaw angle. The peak factors of the side force and roll moment are the same （ - 3.28）, the peak factor of the lift force is - 3.33, and the peak factors of the yaw moment and pitch moment are also the same （- 3.77）.

An application of the KNND method for detecting nearby open clusters based on Gaia-DR1

This paper presents a preliminary test of the k-th nearest neighbor distance （KNND） method for detecting nearby open clusters based on Gaia-DR1. We select 38 386 nearby stars （〈 100 pc） from the Gaia-DR1 catalog, and then use the KNND method to detect overdense regions in three-dimensional space. We find two overdense regions （the Hyades and Coma Berenices （Coma Ber） open clusters）, and obtain 57 reliable cluster members. Based on these cluster members, the distances to the Hyades and Coma Ber clusters are determined to be 46.0±0.2 and 83.5±0.3 pc, respectively. Our results demonstrate that the KNND method can be used to detect open clusters based on a large volume of astrometry data.

Evaluation of the asset＇s value by using fuzzy two-stage discounted cash flow model

This paper establishes the fuzzy discounted cash flow model to settle the uncertainties of the cash flow and discount rate in two-stage DCF model, to take the imprecise of the time period of the supernormal growth phase with considering the investor＇s attitude to risk. Firstly, the discount rate and the growth rate are fuzzified as triangular fuzzy numbers in this fuzzy discounted cash flow model. Then the intrinsic value of an asset can be evaluated by the arithmetic operation on interval and λ- signed distance method under the framework of DCF approach. Finally, a listed company at Shanghai Stock Exchange is analyzed as the case to demonstrate the process of stock value calculation by the fuzzy discounted cash flow model.

Super-Large-Scale Structures in the Sloan Digital Sky Survey

We study the super-large-scale structures in the Sloan Digital Sky Survey by cluster analysis, and examine the geometry and the properties of the member galaxies. Two subsamples are selected from the SDSS, Subsample 1 at the celestial equator and Subsample 2 further north. In Subsample 1 we discover two compact super-large-scale structures： the Sloan Great Wall and the CfA Great Wall. The Sloan Great Wall, located at a median redshift of z= 0.07804, has a total length of about 433 Mpc and a mean galaxy density of about six times that of the whole sample. Most of its member galaxies are of medium size and brightness. The CfA Great Wall, located at a median redshift of z = 0.03058, has a total length of about 251 Mpc and includes large percentages of faint and small galaxies and relatively fewer early-type galaxies.

基于PWPF调制技术的飞机飞行姿态控制系统软件设计

为实现飞机行进轨迹多波段同时调节,使其飞行姿态能够受到软件程序的有效控制,设计基于PWPF调制技术的飞机飞行姿态控制系统软件程序;根据时钟配置情况,设置CAN通信接口,并以此为基础,完成对导航仪与舵机状态的检测,再联合偏航距离校正结果,规范核心控制程序的编写形式,实现系统各软件模块功能的设计;建立自抗扰闭环,按照PWPF调制技术的静态作用需求,求解二次规划函数,完成基于PWPF调制技术的控制机制定义;在反步控制器运行过程中,推导非线性建模表达式,实现对飞机飞行姿态控制行为的建模,完成基于PWPF调制技术的飞机飞行姿态控制系统软件设计;实验结果表明,基于PWPF调制技术所设计的软件程序,在X波、C波、S波、L波的波频范围内,均能有效控制飞机的飞行姿态,与多波段调节飞机行进轨迹的实际应用诉求相符合。

基于数值天气预报的输电线路风偏闪络预警方法

现有输电线路风偏预警一般是采用在线监测装置实现,且没有对风偏后空气间隙的闪络风险进行有效评估,导致工程上适用性不强、预警效果不理想等问题。利用传统的风偏研究成果,提出了一种基于数值天气预报的输电线路风偏闪络预警方法。首先,采用反距离加权的插值算法进行格点预报风速映射处理,并依据风向与线路走向的夹角完成垂直于线路风速分量的计算。然后,以典型的酒杯塔为例,运用刚体直棒法计算线路与杆塔的最小空气间隙。最后,对间隙击穿电压进行空气密度、湿度、降水量的修正,得到预报天气条件下的闪络电压值,并与系统运行电压进行对比完成风偏闪络预警。该方法可为安装在线装置困难而又处于强风区的重要输电线路提供一种可行、有效的风偏闪络风险管控手段,对电网防风减灾工作具有重要的实用意义。

海上GPS导航系统的参数计算

根据当前船位和预置的航路点位置计算航路点导航参数是海上导航的基本问题。本文简要介绍了航路点导航的基本原理,提出了海上GPS导航参数的一种计算方法,对大圆航法导航参数的推导、计算进行了讨论,最后给出了软件设计流程图。

桥墩紊流对船舶艏摇力矩作用的定量分析

为了定量分析桥墩流场对临近船舶作用机理,文中引入经典的湍流模型建立了单桥墩的船舶运动数值模拟方案,设定船舶顺流下水航行的计算边界条件,运用FLUENT模拟无船通过情况下的单圆柱桥墩流场变化特征.运用DES模型及动网格技术,选取不同船舶与桥墩横向距离参数下,模拟船舶通过单圆柱桥墩时的紊流和船舶艏摇力矩的变化.多工况下的数值模拟结果表明:船舶驶近桥墩时,船舶艏摇力矩受到桥墩流场的影响显著化;随着船舶与桥墩横距的增加,桥墩流场对船舶艏摇力矩的影响逐渐减弱.计算示例表明,当横向距离达到桥墩直径1.5倍时,两者之间作用可以忽略.

船舶操纵术语之商榷

对各种《船舶操纵》教材中的一些术语的不同解释提出疑问，并阐述了作者本人的观点，以期理顺概念，统一解释，更好地指导操船实践。

电动车辆对开路面再生制动仿真研究

分析电动车辆在对开路面上紧急制动时的整车受力情况,在前后轴制动力比例分配情况下,对比分析左右轮制动力分别采用低选控制、独立控制和修正独立控制3种不同制动控制策略时的制动稳定性、制动距离和制动能量回收效率。仿真结果表明,采用修正独立控制策略的电动车辆在对开路面上紧急制动时能降低横摆力矩、横摆角加速度和制动距离,且具有较高的制动能量回收效率。

Two Novel Approaches for Photometric Redshift Estimation based on SDSS and 2MASS

We investigate two training-set methods; support vector machines （SVMs） and Kernel Regression （KR） for photometric redshift estimation with the data from the databases of Sloan Digital Sky Survey Data Release 5 and Two Micron All Sky Survey. We probe the performances of SVMs and KR for different input patterns. Our experiments show that with more parameters considered, the accuracy does not always increase, and only when appropriate parameters are chosen, the accuracy can improve. For different approaches, the best input pattern is different. With different parameters as input, the optimal bandwidth is dissimilar for KR. The rms errors of photometric redshifts based on SVM and KR methods are less than 0.03 and 0.02, respectively. Strengths and weaknesses of the two approaches are summarized. Compared to other methods of estimating photometric redshifts, they show their superiorities, especially KR, in terms of accuracy.

单回转双回开断塔下方的工频电场分布及其影响因素研究

单回转双回架空线路开断塔可将单回线路开断后,转角90°形成不同相序的双回线路继续走线,这种杆塔的使用可有效减少塔基占地面积,节约线路成本。为研究开断塔下方的电场分布特征,文章对110 kV单回转双回架空线路开断塔进行了三维电场计算,对比了常规直线塔与开断塔下方电场强度,分析了导线相序组合、导线水平相间距离、横担高度、风偏对开断塔下方电场强度的影响。结果表明:相同影响因素下,开断塔下方电场强度大于直线塔下方电场强度;逆相序布置下的开断塔下方电场强度最小;开断后的双回架空线水平相间距离减小,开断塔下方电场强度随之减小;横担高度增加,开断塔下方电场强度随之减小;随着风偏致跳线串偏移角的增大,地电位作业人员体表电场强度随之增大,开断塔下方距地面1.5 m高水平截面电场分布近乎不变。该文研究结果能够为开断塔的优化设计提供参考。

Multicolor photometry of the galaxy cluster A98: substructures and star formation properties

An optical photometric observation with the Beijing-Arizona-Taiwan- Connecticut （BATC） multicolor system is carried out for A98 （z =0.104）, a galaxy cluster with two large enhancements in X-ray surface brightness. Spectral energy distributions （SEDs） covering 15 intermediate bands are obtained for all sources detected down to V - 20 mag in a field of 58′× 58′. After star-galaxy separation with colorcolor diagrams, a photometric redshift technique is applied to the galaxy sample for further membership determination. The color-magnitude relation is taken as a further restriction of the early-type cluster galaxies. As a result, a list of 198 faint member galaxies is achieved. Based on the newly generated sample of member galaxies, the dynamical substructures, A98N, A98S, and A98W, are investigated in detail. A separate galaxy group, A98X, is also found to the south of the main concentration of A98, which is gravitationally unbound to A98. For 74 spectroscopically confirmed member galaxies, the environmental effect on the star formation history is investigated. The bright galaxies in the core region are found to have shorter time scales of star formation, longer mean stellar ages, and higher interstellar medium metallicities, which can be interpreted in the context of the hierarchical cosmological scenario.

基于大地主题解算方法的无人机偏航距修正探讨

无人机航空摄影在飞行作业时经常受气流等环境因素影响导致飞行航线与计划航线出现偏差,这时操作人员需要实时修正偏航距离。介绍了基于大地主题解算方法,利用计算机数值快速逼近的计算优势,精确计算偏航距,消除利用地图投影进行直角坐标系下点线距离计算引起的投影误差,不仅提高了偏航距计算精度,同时增强了高精度偏航距计算功能的适应性。

A Critical Review of the Evidence for M32 being a Compact Dwarf Satellite of M31 rather than a More Distant Normal Galaxy

Since Baade＇s photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our investigation into the nature of the existing evidence. We find that the case for M32 being a satellite of M31 rests upon Hubble Space Telescope （HST） based stellar population studies which have resolved red-giant branch （RGB） and red clump stars in M32 as well as other nearby galaxies. Taken in isolation, this recent evidence could be considered to be conclusive in favour of the existing view. However, the conventional scenario does not explain M32＇s anomalously high central velocity dispersion for a dwarf galaxy （several times that of either NGC 147, NGC 185 or NGC 205） or existing planetary nebula observations （which suggest that M32 is more than twice as distant as M31） and also requires an elaborate physical explanation for M32＇s inferred compactness. Conversely, we find that the case for M32 being a normal galaxy, of the order of three times as distant as M31, is supported by： （1） a central velocity dispersion typical of intermediate galaxies, （2） the published planetary nebula observations, and （3） known scaling relationships for normal early-type galaxies. However, this novel scenario cannot account for the high apparent luminosities of the RGB stars resolved in the M32 direction by HST observations. We are therefore left with two apparently irreconcilable scenarios, only one of which can be correct, but both of which suffer from potentially fatal evidence to the contrary.This suggests that current understanding of some relevant fields is still very far from adequate.

The Peak Luminosity of Type Ia Supernovae and its Implications for the Cosmic Expansion Rate

Supernovae of type Ia (SNe Ia) are confirmed to be the best distance indicators to derive the cosmic expansion rate. The dispersion of their peak luminosity at optical bands (BVI) is approximate to 0.13 mag, after taking into account the effects of the second parameters (i.e., the Antial decline rate m15(B) and (B - V) color at maximum light). The local calibrations from HST indicate an absolute magnitude of 19.48 ± 0.08mag (in V band) for SNe Ia in spiral galaxies. The current expansion rate, Ho, is found to be 63.6 ± 1.8 (random) ±5.7 (systematic) kms-1 Mpc-1. This Value will decrease by 3% when the metallicity effect on the cepheid distances is considered. In addition, a marginal local outward flow of 4.0 ± 4.5% within the velocity-distance of 7000 km s-1 can be inferred from SNe Ia for the Einstein-de Sitter universe; however, this outward flow is only 2.2 ± 4.4% for an accelerating expansion universe (which is supported by high-z SNe Ia).

Concordance of Kinematics and Lensing of Elliptical Galaxies with WMAP Cosmology

We explore degeneracies in strong lensing model so to make time delay data consistent with the WMAP （Wilkinson Microwave Anisotropy Probe） cosmology. Previous models using a singular isothermal lens often yield a time delay between the observed multiple images too small than the observed value if we ＂hardwire＂ the now widely quoted post-WMAP ＂high＂ value of the Hubble constant （Ho ～71 ± 4km s^-1 Mpc^-1）. Alternatively, the lens density profile （star plus dark matter） is required to be locally steeper than r-2 （isothermal） profile near the Einstein radius （of the order 3 kpc） to fit the time delays; a naive extrapolation of a very steep profile to large radius would imply a lens halo with a scale length of the order only 3 kpc, too compact to be consistent with CDM. We explore more sophisticated, mathematically smooth, positive lens mass density profiles which are consistent with a large halo and the post-WMAP H0. Thanks to the spherical monopole degeneracy, the ＂reshuffling＂ of the mass in a lens model does not affect the quality of the fit to the image positions, amplifications, and image time delays. Even better, unlike the better-known mass sheet degeneracy, the stellar mass-to-light and the H0 value are not affected either. We apply this monopole degeneracy to the quadruple imaged time-delay system PG 1115＋080. Finally we discuss the implications of the time delay data on the newly proposed relativistic MOND theory.

The Feasibility of Constraining Dark Energy Using LAMOST Redshift Survey

We consider using future redshift surveys with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） to constrain the equation of state of dark energy w. We analyze the Alcock ＆ Paczynski （AP） effect imprinted on the two-point correlation function of galaxies in redshift space. The Fisher matrix analysis is applied to estimate the expected error bounds of w0 and wα from galaxy redshift surveys, w0 and wα being the two parameters in the equation of state parametrization w（z） = w0 ＋ wαz/（1 ＋ z）. Strong degeneracies between w0 and wα are found. The direction of the degeneracy in w0 - wα plane, however, rotates counter-clockwise as the redshift increases. LAMOST can potentially contribute in the redshift range up to 0.5. In combination with other high redshift surveys, such as the proposed Kilo-Aperture Optical Spectrograph project （KAOS）, the joint constraint derived from galaxy surveys at different redshift ranges is likely to efficiently break the degeneracy of w0 and wα. We do not anticipate that the nature of dark energy can be well constrained with LAMOST alone, but it may help to reduce the error bounds expected from other observations, such as the Supernova/Acceleration Probe （SNAP）.