An adaptive mesh refinement algorithm for compressible two-phase flow in porous media

We describe a second-order accurate sequential algorithm for solving two-phase multicomponent flow in porous media. The algorithm incorporates an unsplit second-order Godunov scheme that provides accurate resolution of sharp fronts. The method is implemented within a block structured adaptive mesh refinement (AMR) framework that allows grids to dynamically adapt to features of the flow and enables efficient parallelization of the algorithm. We demonstrate the second-order convergence rate of the algorithm and the accuracy of the AMR solutions compared to uniform fine-grid solutions. The algorithm is then used to simulate the leakage of gas from a Liquified Petroleum Gas (LPG) storage cavern, demonstrating its capability to capture complex behavior of the resulting flow. We further examine differences resulting from using different relative permeability functions.     

Resolution of 2D Wenner resistivity imaging as assessed by numerical modelling

Modelling of 2D resistivity imaging was done in order to understand the principle resolution of the technique in different geological situations, and for assessing the behaviour of the interpretation methods under controlled circumstances. The Wenner array was used throughout. The results show that the 1D approximation only provides reasonable results in environments with very gradual lateral resistivity changes, otherwise the result may be strongly misleading. Inversion using the 2D quasi-Newton technique results in adequate resolution of the structures in moderately complex environments, but the Gauss–Newton method holds a significant advantage in some complicated cases. The data density can also be of crucial importance for the resolution capability, notably of narrow structures.     

The contribution to IHY from the COST296 Action MIERS: Mitigation of Ionospheric Effects on Radio Systems

The objective of the COST296 Action MIERS (Mitigation of Ionospheric Effects on Radio Systems) is to develop an increased knowledge of the effects imposed by the ionosphere on practical radio systems, and for the development and implementation of techniques to mitigate the deleterious effects of the ionosphere on such systems (http://www.cost296.rl.ac.uk). The COST296 Community contributes to the international efforts of IHY with scientific and outreach activities as well. After the realization of a web site hosted by Istituto Nazionale di Geofisica e Vulcanologia (INGV), developed also to promote the ionospheric physics to the open public, the COST296 Community supported an initiative addressed to the pupils of the primary school of several European Countries: the realization of a school-calendar dedicated to the Sun and to the Sun-Earth connections.     

Extraction of agar from Eucheuma cottonii and Gelidium amansii seaweeds with sonication pretreatment using autoclaving method

The effect of sonication pretreatment condition on Eucheuma cottonii and Gelidium amansii seaweed towards agar extraction wae studied.Four parameters were changed during sonication to investigate the effects on agar yield and quality.These parameters include the time interval,concentration ratio,frequency,and intensity.The highest amount of agar extracted from Eucheuma cottonii species could be obtained from the time interval of 30min,seaweed weight to solvent volume ratio of 1:20,the frequency of 35Hz,and the sonication power intensity of 30%.For Gelidium amansii species,the best agar yield also could be obtained from the time interval of 30 min,1:20 of seaweed weight to water volume ratio,the frequency of 35Hz,and power intensity of 30%.From the experiment,sonication pretreatment signifi cantly influenced the yield and properties of extracted agar.The sonication with autoclaved seaweed produced agar containing less sulfate content,which is an excellent chemical property for gel electrophoresis applications.The gelstrength of sonication with autoclaving for both seaweeds,Eucheuma and Gelidium species was the highest among those by sonication with direct heating,which proved that sonication pretreatment with autoclaving could enhance the physical properties of the agar.     

A proposal for boundary delimitation for integrated coastal zone management initiatives

ICZM relies heavily on the definition of major multidisciplinary characteristics/elements of the coastal area of interest. Usually, only terrestrial boundaries are considered, which tend to respond to a specific sectoral problem and can be determined by administrative limits. In this study, we propose a method for establishing a decision-making tool to inform boundary delimitation for ICZM initiatives that is proactive and widely applicable as opposed to reactive and problem specific. This method integrates environmental, economic and societal characteristics of the marine and terrestrial boundaries of the coastal zone, starting at the boundary of the jurisdictional zone of influence (shoreline units), increasing in detail through the definition of their influential areas from jurisdictional, environmental or socio-economic perspectives (functional areas) and, within them, specifying the finest scale at which relevant indicator data may be obtained (analysis units).     

Positive Charge Region in Lower Part of Thunderstorm and Preliminary Breakdown Process of Negative Cloud-to-Ground Lightning

A new lightning locating technology, called Lightning Mapping Array （LMA）, has been developed. The system takes advantage of GPS technology to measure the times of arrival （TOA） of lightning impulsive very high frequency （VHF） radiation events at each remote location. The spatiotemporal development processes of lightning are described in three-dimension by measurement of the system with high time resolution （50 ns） and space precision （50-100 m）. The charge structures in thunderstorm and their relationship with lightning discharge processes are revealed. The temporal and spatial characteristics of preliminary breakdown process involved in negative cloud-to-ground （CG） lightning discharges are analyzed based on the data of lightning VHF radiation events. The effect of positive charge region in lower part of thunderstorm on the occurrence of negative CG lightning discharge is discussed. The results indicate that the preliminary breakdown process with longer duration in negative CG lightning discharges is an intracloud discharge process. It occurs between negative and positive charge regions located in middle and lower parts of thunderstorm respectively. It initiates from the negative charge region and propagates downward. After propagating into the positive charge region, the lightning channel develops horizontally. The characteristics of the preliminary breakdown process are consistent with that of intracloud lightning discharges. The stepped leaders are initiated by the K type breakdown which occurs in the last stage of the preliminary breakdown process and develops downward through the positive charge region. The existence of positive charge region in lower part of thunderstorm results in the occurrence of preliminary breakdown process with longer duration before the return stroke of negative CG lightning discharges.     

Discrete cosine transform for parameter space reduction in Bayesian electrical resistivity tomography

Electrical resistivity tomography is a non-linear and ill-posed geophysical inverse problem that is usually solved through gradient-descent methods. This strategy is computationally fast and easy to implement but impedes accurate uncertainty appraisals. We present a probabilistic approach to two-dimensional electrical resistivity tomography in which a Markov chain Monte Carlo algorithm is used to numerically evaluate the posterior probability density function that fully quantifies the uncertainty affecting the recovered solution. The main drawback of Markov chain Monte Carlo approaches is related to the considerable number of sampled models needed to achieve accurate posterior assessments in high-dimensional parameter spaces. Therefore, to reduce the computational burden of the inversion process, we employ the differential evolution Markov chain, a hybrid method between non-linear optimization and Markov chain Monte Carlo sampling, which exploits multiple and interactive chains to speed up the probabilistic sampling. Moreover, the discrete cosine transform reparameterization is employed to reduce the dimensionality of the parameter space removing the high-frequency components of the resistivity model which are not sensitive to data. In this framework, the unknown parameters become the series of coefficients associated with the retained discrete cosine transform basis functions. First, synthetic data inversions are used to validate the proposed method and to demonstrate the benefits provided by the discrete cosine transform compression. To this end, we compare the outcomes of the implemented approach with those provided by a differential evolution Markov chain algorithm running in the full, un-reduced model space. Then, we apply the method to invert field data acquired along a river embankment. The results yielded by the implemented approach are also benchmarked against a standard local inversion algorithm. The proposed Bayesian inversion provides posterior mean models in agreement with the predictions achieved by the gradient-based inversion, but it also provides model uncertainties, which can be used for penetration depth and resolution limit identification.     

台湾海峡及其邻近海域鱼类生活史特征及其变化研究

世界范围内,海洋渔业资源广泛面临着过度捕捞的压力.鱼类的不同生活史特征可表征不同的生活史对策,其变化可揭示鱼类种群对渔业捕捞压力的响应.台湾海峡及其邻近海域的主要渔场30多年来面临着过度捕捞的压力,导致了鱼类群落结构发生改变.本研究分析了该海域51种主要经济鱼类的生态参数,系统研究了其生活史特征及其变化.采用主成分分析法可将51种鱼类分成5个不同的生活史对策组,分组结果表明超过60%的鱼类被归纳入第5组,即近r对策组,且多为中上层鱼类.在此基础上收集相关历史数据,对其中25种经济鱼类进行生活史变化分析,讨论不同鱼类种群对渔业开发的响应.分析结果表明,在长期的渔业开发活动下多数鱼类表现出小型化、低龄化、早熟和生长率加快等趋势.此外,本研究计算了每种鱼类的开发率以进一步研究渔业捕捞压力对鱼类种群的影响,发现其中4种底层和近底层鱼类的生活史特征变化显著,提示某些物种可能对捕捞压力更敏感.本研究可为渔业管理和保护提供重要的科学依据.     

Salt-water intrusion mapping by geoelectrical imaging surveys

The geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore-water salinity. A new field survey technique that can be used for environmental and geotechnical investigations has been developed. This study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt-water intrusion boundary in Yan, State of Kedah, northwest Malaysia. The technique was incorporated into these surveys, and it has proved to be a robust method for accurately mapping the fresh-water/saline-water boundary. The resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the Geological Survey of Malaysia at those sites.     

Quadtree-guided 3-D interpolation of irregular sonar data sets

Bottom-penetrating sonar can be used to visualize large areas, for example by normal logging and printing of collected pings. In many applications, it is necessary to obtain an impression of three-dimensional (3-D) structures, but this is not easy because of the irregular spatial sampling due to coarse ship trajectories. Normally, the ping map and the ping data, cover only a very small part of a region of interest. In this paper, we describe a new method for interpolating irregularly spaced sonar data. The basic idea is to use a two-dimensional quadtree of the ping map in order to guide the 3-D interpolation process: since gaps between pings become smaller at higher tree levels, the volume can be filled by marking neighborhood relations in the quadtree and interpolating available pings when they become neighbors. Different marking schemes and their central processing unit times are compared. In the interpolation process, we apply cross correlations of ping data in order to construct continuity of sloping reflections. Our results show that excellent results can be obtained on real sonar data sets, even for volumes filled for less than 7%, for which processing times are reasonable even for large areas, and that the interpolated data can be used for volumetric interactive visualization.