Element sets for high-order Poincaré mapping of perturbed Keplerian motion     

David J. Gondelach  Roberto Armellin 《Celestial Mechanics and Dynamical Astronomy》2018,130(10):65

The propagation and Poincaré mapping of perturbed Keplerian motion is a key topic in Celestial Mechanics and Astrodynamics, e.g., to study the stability of orbits or design bounded relative trajectories. The high-order transfer map (HOTM) method enables efficient mapping of perturbed Keplerian orbits using the high-order Taylor expansion of a Poincaré or stroboscopic map. The HOTM is only accurate close to the expansion point and therefore the number of revolutions for which the map is accurate tends to be limited. The proper selection of coordinates is of key importance for improving the performance of the HOTM method. In this paper, we investigate the use of different element sets for expressing the high-order map in order to find the coordinates that perform best in terms of accuracy. A new set of elements is introduced that enables extremely accurate mapping of the state, even for high eccentricities and higher-order zonal perturbations. Finally, the high-order map is shown to be very useful for the determination and study of fixed points and center manifolds of Poincaré maps.  相似文献   

涉密矢量数字地图中敏感要素几何信息量的测度方法     

李安波  陈楹  姚蒙蒙  吴赛松 《地球信息科学学报》2018,20(1):7-16

涉密矢量数字地图中敏感要素几何信息的定量测度,是实现定量化密级评定的基础和前提。如何进行敏感要素几何信息量的计算,目前尚缺乏相关研究。在现有地图信息论研究成果的基础上,论文主要开展了3方面的研究工作：首先,从地理对象的敏感性入手,探讨了地图要素敏感性的定义与要素集合的敏感性表征指标;然后,基于任意发生元的Voronoi构建方法,实现了对点要素集、线要素集、部分覆盖面要素集及综合要素集的信息单元自动化剖分;最后,基于长度系数、面积系数和角度系数,提出了线、面要素图形复杂度的计算方法,并在此基础上形成了涉密矢量数字地图中敏感几何信息量的测度方法。实验表明,该方法的计算结果遵循了信息量的非负性、连续性、可加性等特点,较为合理地反映了相关因素（地图比例尺、要素空间分布、要素图形复杂度、要素敏感系数等）对计算结果的影响。相关成果将支持矢量数字地图的定量化密级评定,并有助于完善地理信息安全监管的理论和方法体系。  相似文献   

Design of Buoys for Mounting Wind Turbines at Exposed Sites     

ERDO?AN Beytullah  ?EL?KKOL Barbaros  SWIFT Robinson 《中国海洋大学学报(英文版)》2018,17(2):257-266

In this study, two designs for a buoy capable of supporting a 10 kW wind turbine and its tower were developed to operate at the University of New Hampshire’s Center of Ocean Renewable Energy testing site located off the Isles of Shoals, New Hampshire. The buoys are to be moored by a catenary chain system. To evaluate wave response, two Froude-scaled models were constructed, tested, and compared at the Ocean Engineering wave tank at the University of New Hampshire. These buoys have been implemented and compared with wave tank measurements of the spar displacement at a reference elevation 2.44 m above the mean water level.  相似文献   

A terrain openness index for the extraction of karst Fenglin and Fengcong landform units from DEMs   总被引：1，自引：0，他引：1  

Xin Meng  Li-yang Xiong  Xian-wu Yang  Bi-sheng Yang  Guo-an Tang 《山地科学学报》2018,15(4):752-764

The Fenglin and Fengcong landform units are considered to be an important representation for defining the degree of development of Karst landforms. However, these terrain features have been proven difficult to delineate and extract automatically because of their complex morphology. In this paper, a new method for identifying the Fenglin and Fengcong landform units is proposed. This method consists of two steps: (1) terrain openness calculation and (2) toe line extraction. The proposed method is applied and validated in the Karst case area of Guilin by using ASTER GDEM with one arc-second resolution. The openness of both the positive and negative terrain and a threshold were used to extract toe lines for segmenting depressions and pinnacles in Fenglin and Fengcong landforms. A comparison between the extracted Fenglin and Fengcong landform units and their real units from high resolution images was carried out to evaluate the capability of the proposed method. Results show the proposed method can effectively extract the Fenglin and Fengcong landform units, and has an overall accuracy of 93.28%. The proposed method is simple and easy to implement and is expected to play an important role in the automatic extraction of similar landform units in the Karst area.  相似文献   

Exact solution of anisotropic compact stars via mass function     

S. K. Maurya  Ayan Banerjee  Y. K. Gupta 《Astrophysics and Space Science》2018,363(10):208

Studying relativistic compact objects is important in modern astrophysics to understand several astrophysical issues. It is therefore natural to ask for an internal structure and physical properties of specific classes of compact stars from astrophysical observations. We obtain a class of new relativistic solutions with anisotropic distribution of matter for compact stars. More specifically, stellar models, described by an anisotropic fluid, establishing a relation between metric potentials and generating a specific form of mass function, are explicitly constructed within the framework of General Relativity. New solutions can be used to model compact objects, which adequately describe compact strange star candidates like SMC X-1, Her X-1 and 4U 1538-52, with observational data taken from Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431:3216, 2013). As a possible astrophysical application the obtained solutions could explain the physics of selfgravitating objects, and might be useful for strong-field regimes where data are currently inadequate.  相似文献   

Study of some chaotic inflationary models in $$ gravity     

M. Sharif  Iqra Nawazish 《Astrophysics and Space Science》2018,363(4):73

In this paper, we discuss an inflationary scenario via scalar field and fluid cosmology for an anisotropic homogeneous universe model in \(f(R)\) gravity. We consider an equation of state which corresponds to a quasi-de Sitter expansion and investigate the effect of the anisotropy parameter for different values of the deviation parameter. We evaluate potential models like linear, quadratic and quartic models which correspond to chaotic inflation. We construct the observational parameters for a power-law model of \(f(R)\) gravity and construct the graphical analysis of tensor–scalar ratio and spectral index which indicates the consistency of these parameters with Planck 2015 data.  相似文献   

一种由粗到精的地面激光点云多层级配准方法     

王英  张云生 《测绘与空间地理信息》2020,(2):156-159

提出了一种综合利用快速点特征直方图(FPFH)描述符和同名点引导ICP优化的地面激光扫描(TLS)点云配准方法。该方法包括3个步骤:1)点云金字塔构建;2)基于FPFH的粗配准;3)同名点引导的ICP精配准。首先使用体素网格滤波器构造点云的金字塔结构,在粗配准时,FPFH描述符用于金字塔顶层上点云的鲁棒匹配,在此基础上,再进行两层级同名点引导的ICP精配准优化,使用3组典型TLS点云对进行实验,结果表明本文方法可以高效地完成TLS点云的配准。  相似文献   

Effects of stocking density on the growth and immunity of Atlantic salmon salmo salar reared in recirculating aquaculture system (RAS)     

Wang  Yanfeng  Chi  Liang  Liu  Qinghua  Xiao  Yongshuang  Ma  Daoyuan  Xiao  Zhizhong  Xu  Shihong  Li  Jun 《中国海洋湖沼学报》2019,37(1):350-360

Atlantic salmon reared in recirculating aquaculture system (RAS) may lead to inappropriately high stocking density, because fish live in a limited space. Finding the suitable stocking density of Atlantic salmon reared in RAS is very important for RAS industry. In this paper, the influence of stocking density on growth and some stress related physiological factors were investigated to evaluate the effects of stocking density. The fish were reared for 220 days at five densities (A: 24 kg/m³; B: 21 kg/m³; C: 15 kg/m³; D: 9 kg/ m³ and E: 6 kg/m³ ). The results show that 30 kg/m³ might be the maximum density which RAS can afford in China. The stocking densities under 30 kg/m³ have no effect on mortality of Atlantic salmon reared in RAS. However, the specific growth rate (SGR), final weight and weight gain in the high density group were significantly lower than the lower density groups and middle density groups. Moreover, feed conversion rate (FCR) had a negative correlation with density. Plasma hormone T₃ and GH showed significant decrease with the increase of the stocking density of the experiment. Furthermore, thyroid hormone (T₃), GH (growth hormone) activities were decreased with stocking density increase. However, plasma cortisol, GOT (glutamic oxalacetic transaminase) and GPT (glutamic pyruvic transaminase) activities were increase with stocking density increase. And the stocking density has no effects on plasma lysozyme of Atlantic salmon reared in RAS. These investigations would also help devise efficient ways to rear adult Atlantic salmon in China and may, in a way, help spread salmon mariculture in China.

  相似文献   

Projections of the impacts of climate change on the water deficit and on the precipitation erosive indexes in Mantaro River Basin,Peru     

Sly C. Wongchuig  Carlos R. Mello  Sin C. Chou 《山地科学学报》2018,15(2):264-279

Projections of climate change are essential to guide sustainable development plans in the tropical Andean countries such as Peru. This study assessed the projections of precipitation and potential evaporation, rain erosive potential, and precipitation concentration in the Mantaro River Basin, in the Peruvian Andes, which is important for agriculture and energy production in Peru. We assumed the Intergovernmental Panel on Climate Change (IPCC) A1B greenhouse gas emission scenario and simulated the global climate change by the HadCM3 global climate model. Due to the steepness of the mountain slopes and the narrowness of the river valley, this study uses the downscaling of the global model simulations by the regional Eta model down to 20-km resolution. The downscaling projections show decrease in the monthly precipitation with respect to the baseline period, especially during the rainy season, between February and April, until the end of the 21st century. Meanwhile, a progressive increase in the monthly evaporation from the baseline period is projected. The Modified Fournier Index (MFI) shows a statistically significant downward trend in the Mantaro River Basin, which suggests a possible reduction in the rain erosive potential. The Precipitation Concentration Index (PCI) shows a statistically significant increasing trend, which indicates increasingly more irregular temporal distribution of precipitation towards the end of the century. The results of this study allow us to conclude that there should be a gradual increase in water deficit and precipitation concentration. Both changes can be negative for agriculture, power generation, and water supply in the Mantaro River Basin in Peru.  相似文献   

Review of pre-processing technologies for ice cores     

Wen-tao Du  Shi-chang Kang  Xiang Qin  Wei-jun Sun  Yu-lan Zhang  Yu-shuo Liu  Ji-zu Chen 《山地科学学报》2018,15(9):1950-1960

High-resolution ice core records covering long time spans enable reconstruction of the past climatic and environmental conditions allowing the investigation of the earth system’s evolution. Preprocessing of ice cores has direct impacts on the data quality control for further analysis since the conventional ice core processing is time-consuming, produces qualitative data, leads to ice mass loss, and leads to risks of potential secondary pollution. However, over the past several decades, preprocessing of ice cores has received less attention than the improvement of ice drilling, the analytical methodology of various indices, and the researches on the climatic and environmental significance of ice core records. Therefore, this papers reviews the development of the processing for ice cores including framework, design as well as materials, analyzes the technical advantages and disadvantages of the different systems. In the past, continuous flow analysis (CFA) has been successfully applied to process the polar ice cores. However, it is not suitable for ice cores outside polar region because of high level of particles, the memory effect between samples, and the filtration before injection. Ice core processing is a subtle and professional operation due to the fragility of the nonmetallic materials and the random distribution of particles and air bubbles in ice cores, which aggravates uncertainty in the measurements. The future developments of CFA are discussed in preprocessing, memory effect, challenge for brittle ice, coupling with real-time analysis and optimization of CFA in the field. Furthermore, non-polluting cutters with many different configurations could be designed to cut and scrape in multiple directions and to separate inner and outer portions of the core. This system also needs to be coupled with streamlined operation of packaging, coding, and stacking that can be implemented at high resolution and rate, avoiding manual intervention. At the same time, information of the longitudinal sections could be scanned and identified, and then classified to obtain quantitative data. In addition, irregular ice volume and weight can also be obtained accurately. These improvements are recorded automatically via user-friendly interfaces. These innovations may be applied to other paleomedias with similar features and needs.  相似文献