A bidirectional path-finding algorithm and data structure for maritime routing

Route planning is an important problem for many real-time applications in open and complex environments. The maritime domain is a relevant example of such environments where dynamic phenomena and navigation constraints generate difficult route finding problems. This paper develops a spatial data structure that supports the search for an optimal route between two locations while minimizing a cost function. Although various search algorithms have been proposed so far (e.g. breadth-first search, bidirectional breadth-first search, Dijkstra’s algorithm, A^*, etc.), this approach provides a bidirectional dynamic routing algorithm which is based on hexagonal meshes and an iterative deepening A^* (IDA^*) algorithm, and a front to front strategy using a dynamic graph that facilitates data accessibility. The whole approach is applied to the context of maritime navigation, taking into account navigation hazards and restricted areas. The algorithm developed searches for optimal routes while minimizing distance and computational time.     

三维地震采集中一致性问题探讨

随着勘探程度的提高,吉林探区的地震采集转向了岩性油藏、隐蔽油藏他和深层火山岩勘探,要求地震采集资料要有较高的分辨率和精度。而由观测系统设计参数产生的采集脚印及激发接收条件差异产生的子波不一致,影响了采集中处理精度的提高和解释中地震属性的精度提高。因此,从影响子波一致性的原因入手,从观测系统设计、激发和接收因素的选择上加以分析和研究,提出了减弱影响子波一致性的技术方法,在很大程度上提高了复杂地表的地震采集资料品质。     

甘肃马衔山北缘断裂西北段几何结构及其新活动

甘肃马衔山北缘断裂在大地构造上属昆仑—祁连—秦岭加里东-华力西造山系,其西北段位于兰州中生代盆地内部。通过对该段的1∶10000条带状地质填图,弄清了其几何结构,获取了新活动时代、活动性质的若干地质地貌证据和年龄证据。结果表明,该段断裂由咸水沟—马泉沟、新城沟和青石咀3小段构成,其中咸水沟—马泉沟小段晚更新世—全新世活动,活动性质以左旋走滑为主,新城沟和青石咀两小段晚更新世以来未见活动。全新世晚期以来,咸水沟—马泉沟小段的左旋位移量5～8m,位移速率0.5～1.72mm/a     

Isotropic Homogeneous Universe with a Bulk Viscous Fluid in Lyra Geometry

Exact solutions are obtained for an isotropic homogeneous universe with a bulk viscous fluid in the cosmological theory based on Lyra’s geometry. The viscosity coefficient of the bulk viscous fluid is assumed to be a power function of the mass density. Cosmological models with time dependent displacement field have been discussed for a constant value of the deceleration parameter. Finally some possibilities of further problems and their investigations have been pointed out.     

Can Lyra geometry explain the singularity free as well as accelerating Universe?

Observations of high red shift supernovae indicate that the Universe is accelerating. Existence of Big-bang singularity is one of the basic failures of general theory of relativity. In this letter we show that within the framework of Lyra geometry, the space-time of the Universe is not only free of Big-bang singularity but also exhibits acceleration during its evolution.     

Impact of GPS satellite and pseudolite geometry on structural deformation monitoring: analytical and empirical studies

Global positioning systems (GPS) have in recent years been increasingly used to monitor the deformations of large structures, particularly the deflections of long suspension bridges. When appropriately employed, and with the presence of a strong satellite geometry, GPS can supply timely and accurate structural deformation information. However, the three-dimensional (3-D) positioning accuracies in a local coordinate system are uneven. For instance, the vertical component of 3-D coordinates is less accurate than the horizontal component. In addition, GPS satellite availability tends to be a function of the latitude of the observation site and its surrounding obstructions. As a consequence, the accuracy of the north–south component is typically worse than that of the east–west component in mid-latitude areas (>45), and in some of the worst situations the horizontal positioning accuracy could even degrade to the same level as that of the vertical component. With such measurements it might not be possible to correctly interpret the real structural deformations. Furthermore, an insufficient number of satellites, caused by signal obstruction, could make it impossible to use GPS alone for kinematic positioning, even when integrated with other sensors such as triaxial accelerometers. With the aim of improving 3-D positioning accuracies for the monitoring of structural deflections, especially in vertical and northern directions, the optimal location selection of an array of ground-based pseudolites to augment GPS satellite geometry using an analytical simulation technique proposed by the authors is considered. Achievable 3-D positioning accuracies are estimated by simulating a real bridge deformation scenario using augmented transmitter geometry and compared with actual positioning accuracies calculated from the measurements gathered from a bridge trial. The results show that with an augmented satellite geometry and multipath mitigation it is possible to achieve uniform 3-D positioning accuracies of a few millimetres.     

辽宁建平朝阳沟破火山口地质特征

朝阳沟破火山口出露面积约８０ｋｍ２，呈椭圆状，受北东与北西两组基底断裂控制，火山活动期为晚侏罗－早白垩世。火山活动以爆发为主，具多期次脉动喷发特点。岩浆演化由早期至晚期呈由中性到酸性，火山喷发序次由外向内由老至新，岩石结构由细至粗，晚期潜火山岩相正长斑岩沿放射状断裂侵入。     

中国黄土分布区多沙曲流发育规律

依据中国黄土分布区多沙曲流的水沙资料、河床平面形态和河床大断面测量资料分析认为：多沙河流来水变率影响河床断面形态和曲流发育;由于窄深的河槽是高含沙水流输沙的必要条件和结果,因此随着含沙量的增加,多沙河流河床断面形态首先出现变窄深的趋势,随着含沙量的进一步增加,水流造床能力增大,河槽会向宽浅方向调整;一定的河床冲淤强度有利于曲流的发育,随着含沙量的增加,多沙河流河床曲率存在先增加后减小的规律。     

Tides in the Mandovi and Zuari estuaries, Goa, west coast of India

Mandovi and Zuari are two estuaries located in Goa, west coast of India. Variation of water level in the estuaries was monitored for a month at 13 locations using tide-poles during March–April 2003. Analysis of this data has provided for the first time, characteristics of how tidal constituents vary in the narrow and shallow estuaries, typical of those found along the west coast of India. At a distance of 45 km from the mouth the tidal range increased in both estuaries by approximately 20%. The tidal range at the upstream end of the two channels at the stations dropped sharply because of the increase in elevation of the channels.