A new approach to simulate positional error of line segment in GIS

To determine the distribution of positional error of a line segment, Monte Carlo approach is applied to simulate the probability density function of a line segment with the assumption that the error of endpoints in a line segment follows a two-dimensional normal distribution. For such purpose, a stochastic generator used for uncertain endpoints with the two-dimensional normal distribution is presented. This forms the basis of the generation of random line segment for the simulation of the error model of a whole line segment. The error models cover the cases where two endpoints are either independent or dependent to each other, also including a special case that the distance between two random endpoints in a line segment is close enough.     

Spatial conjunctive analysis of (crime) case configurations: Using Monte Carlo methods for significance testing

While research has repeatedly demonstrated how spatial distributions of crime can be shaped by the presence of facilities such as bars and public transport hubs, the joint influence of different facility types has rarely been explored. Spatial conjunctive analysis of case configurations (also known as qualitative comparative analysis) offers a means to identify the combinations of facility types that are most commonly found around crime events, and has been used in a small number of studies focusing on street robbery. This study extends this limited evidence base by implementing a significance test based on the Monte Carlo method using street robbery data for Austin, Texas. The results show that some of the top-ranking facility type combinations had observed frequencies that were not significantly greater than chance expectations. The accurate identification of the highest-risk environments has important implications for crime prevention.     

大气折射母函数方法、大气折射解析解和映射函数

回顾了作为实用天文学和大地测量学中基本研究课题之一的大气折射映射函数研究的进展。介绍了近几年上海天文台发展的大气折射母函数方法 ,以及由此导出的大气折射解析解。对如今广泛地应用在空间测量技术中的几种映射函数做出评述 ;分析了NMF模型的优点和不足之处。介绍了由大气折射母函数方法引出的大气延迟新连分式映射函数和天文大气折射的映射函数方法。利用VLBI实验中高度截止角与基线长度重复率的关系、探空气球 (radiosonde)观测资料、PRARE资料比较了各种映射函数的结果。特别指出了映射函数方法对天文大气折射和光学波段测距精度的改进。讨论了大气折射计算中的主要误差源。     

Prediction of climate change effects on the runoff regime of a forested catchment in northern Iran

ABSTRACT

The southern coast of the Caspian Sea in northern Iran is bordered by a mountain range with forested catchments which are susceptible to droughts and floods. This paper examines possible changes to runoff patterns from one of these catchments in response to climate change scenarios. The HEC-HMS rainfall–runoff model was used with downscaled future rainfall and temperature data from 13 global circulation models, and meteorological and hydrometrical data from the Casilian (or “Kassilian”) Catchment. Annual and seasonal predictions of runoff change for three future emissions scenarios were obtained, which suggest significantly higher spring rainfall with increased risk of flooding and significantly lower summer rainfall leading to a higher probability of drought. Flash floods arising from extreme rainfall may become more frequent, occurring at any time of year. These findings indicate a need for strategic planning of water resource management and mitigation measures for increasing flood hazards.

EDITOR M.C. Acreman ASSOCIATE EDITOR not assigned     

Changes in climatic variability and maize yield inNortheast China

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Maritime piracy confrontations across the globe: Can crew action shape the outcomes?

The recent tightening of military budget constraints has called into question the feasibility of costly multilateral naval intervention used to combat maritime piracy off the eastern coast of Africa. Though past studies agree that the transformation of the Somali economy and government is crucial for a long-term solution to piracy in this part of the world, short to medium-run solutions are needed to bridge the gap. Such solutions should be fiscally sensible and serve as effective deterrents, as well as be applicable in addressing the problem of piracy and maritime armed robbery in other parts of the globe. This paper builds upon the foundations laid in Mejia et al. [12] and Mileski et al. [13] by examining the following question: given that a ship is engaged by pirates, what factors help shape the outcome of the confrontation? This study finds that observable action taken on the part of a ship's crew is extremely effective in decreasing the risk of a ship being successfully robbed or hijacked. There has yet (as of May 2014) to be a reported incident where pirates successfully hijacked a vessel that had a security team on board, and so though the effectiveness of security in this matter can be inferred, it cannot be empirically tested (the same is true – in this study's dataset – of the effect of onboard security on deterring robberies). This may provide some guidance for policymakers; if naval intervention is to be scaled back, the encouragement and oversight of shipping companies’ crew response procedures (and perhaps of onboard security measures) by international governments could pose a valid alternative.     

Numerical study on the flow characteristics of tidal jets induced by a tidal-jet-generator

The flow characteristics of tidal jets induced by a Tidal-Jet Generator (TJG) are investigated using a finite-difference numerical scheme, named Navier–Stokes (NS)–Marker and Cell (MAC)-TIDE, based on the fully 3D NS equations. The TJG is an enclosed rectangular breakwater, which has vertical opening and a large enclosed volume inside. During both phases of tide, strong and uni-directional jets can be obtained locally from the inlet of the TJG, due to the water level difference between the inner and outer sides of TJG.The computed results are extensively compared with three other independently developed numerical models; 3D-ADI, DVM, and CIP-CSF. These models are based on quasi-3D, 2D depth-averaged, and fully 3D NS equations, respectively. It is seen that the present fully 3D numerical model NS–MAC-TIDE can predict the maximum intensity of inlet velocity with higher accuracy than the other numerical models when compared with the empirical function proposed from the experiments. The numerical simulations based on NS–MAC-TIDE can reproduce successfully the processes of generation, development, and dissipation of tidal jets. The effects of gap opening on the main characteristics of the tidal jet flow are assessed. Through numerical assessment, it is also clearly demonstrated that the residual time of a pollutant distributed around the front of the TJG can be decreased by significant amount due to the locally induced tidal jet. The TJG can thus utilize tidal energy for water purification in local marine environment by providing a flushing mechanism.     

Inverse flood risk modelling under changing climatic conditions

One of the most significant anticipated consequences of global climate change is the increased frequency of hydrologic extremes. Predictions of climate change impacts on the regime of hydrologic extremes have traditionally been conducted using a top‐down approach. The top‐down approach involves a high degree of uncertainty associated with global circulation model (GCM) outputs and the choice of downscaling technique. This study attempts to explore an inverse approach to the modelling of hydrologic risk and vulnerability to changing climatic conditions. With a focus targeted at end‐users, the proposed approach first identifies critical hydrologic exposures that may lead to local failures of existing water resources systems. A hydrologic model is used to transform inversely the main hydrologic exposures, such as floods and droughts, into corresponding meteorological conditions. The frequency of critical meteorological situations is investigated under present and future climatic scenarios by means of a generic weather generator. The weather generator, linked with GCMs at the last step of the proposed methodology, allows the creation of an ensemble of different scenarios, as well as an easy updating, when new and improved GCM outputs become available. The technique has been applied in Ontario, Canada. The results show significant changes in the frequency of hydro‐climatic extremes under future climate scenarios in the study area. Copyright © 2007 John Wiley & Sons, Ltd.     

单片机低频信号发生器

介绍利用单片机控制,采用频率锁相技术实现的低频信号发生器的软硬件结构及工作原理。该信号发生器能输出正弦波、方波、三角波、锯齿波四种波形,具有频率和幅值控制方便、准确、稳定度好的优点。     

具有井下自发电及自传感功能的随钻测量新方法研究——以用于振动测量的井下摩擦纳米发电机为例

现有随钻测量系统的供电方式均有各自的适用条件,因此有必要探索新型的井下供电方式作为对现有方式的补充,或联合现有供电方式共同使用。摩擦纳米发电机源于接触起电及静电感应现象（即生活中常见的静电）,具有发电机和传感器的双重功能。基于此,本文将摩擦纳米发电机原理引入地质勘探领域,提出了一种可用于井下自供电（也叫自发电）及自传感的随钻测量新方法,并以自供电式井下振动传感器的研制为例对该方法进行阐述,同时通过大量的试验验证了传感器的高信噪比及良好的发电特性,且进一步通过280 ℃范围内的高温测试表明了基于该方法具有研制超高温井下传感器及超高温井下实时发电机的优势。还指出了下一步的重点研究方向及其解决途径。