Selectivity and efficiency of two otter trawls used to assess estuarine fish and macroinvertebrate populations in North Carolina

Otter trawl surveys are frequently used to assess estuarine fish and macroinvertebrate communities. Although these surveys may have similar objectives and sampling areas and seasons may overlap, the sampling gear is usually unique to the agency conducting the survey. An example of this is the North Carolina Division of Marine Fisheries (NCDMF) and Environmental Monitoring and Assessment Program-Estuaries (EMAP) surveys in North Carolinian estuaries. We estimated experimentally the selectivity and efficiency of the trawls used for these surveys to determine the comparability of data used to estimate community structure and the abundance of dominant species. The catch percent similarity of the trawls was low (12.0%). The NCDMF net (3.2-m flat otter trawl, 6.4-mm mesh body, 3.2-mm cod-end, plus tickle chain) precisely (11.7%) and accurately (4.5%) sampled brown shrimp, Penaeus aztecus, density but overestimated spot, Leiostomus xanthurus, densities (22.8% accuracy), possibly because these fishes had highly contagious distributions. The EMAP net (4.9-m high-rise otter trawl, 38.1-mm mesh body and cod-end) was precise (17.9–37.4%) but inaccurate (76.8–97.2%), probably because of the single large mesh size and the lack of a tickler chain. Our study suggests the EMAP and NCDMF surveys collect different subsamples of the same fish and macroinvertebrate estuarine populations, and therefore could deliver different results and conclusions.     

Compositional dual mesh method for single phase flow in heterogeneous porous media—application to CO<Subscript>2</Subscript> storage

Numerical simulation of fluid flow coupled with chemical reactions has been an active field in the hydrogeology community and many formulations have been programmed into different software. In recent years, this subject has attracted increasing interest in the reservoir simulation community, partly for the application of chemical methods for hydrocarbon extraction but also for research on the geological sequestration of CO₂. In this paper, an extension to the concept of dual mesh for reactive transport modeling is presented. This approach involves two meshes, a low-resolution mesh to resolve the pressure equation and a high-resolution mesh to transport the species and to calculate the geochemical equilibrium. The main objective is to preserve the fine scale heterogeneities to reach a more accurate field behavior simulation than conventional approach which consist in performing simulations on a coarser mesh. The method is applied to a simulation of CO₂ storage in the SPE10 model that keep a high resolution of the heterogeneities.     

手持式X射线荧光光谱分析仪在斑岩铜矿快速勘查中的应用

现场X射线荧光光谱(XRF)测量因样品的不平度效应、不均匀效应和湿度效应等面临的技术难题,使得手持式XRF现场原位分析结果与实验室分析结果存在一定偏差.本文现场手持式X射线荧光光谱分析仪的测试时间、样品含量、测试距离、样品干湿度和样品粒度等测试条件对测试结果的影响进行了定量研究.结果表明:在最佳测试时间90s条件下,得...     

Geometric modelling and object-oriented software concepts applied to a heterogeneous fractured network from the Grimsel rock laboratory

Discrete fracture network simulations are computationally intensive and usually time-consuming to construct and configure. This paper presents a case study with techniques for building a 3D finite element model of an inhomogeneous fracture network for modelling flow and tracer transport, combining deterministic and stochastic information on fracture aperture distributions. The complex intersected fractures represent a challenge for geometrical model design, mesh quality requirements and property allocations. For the integrated and holistic modelling approach, including the application of numerical and analytical simulation techniques, new object-oriented concepts in software engineering are implemented to ensure a resourceful and practicable software environment.     

带岛屿约束的三角形空间剖分算法的改进方法

本文针对数值模拟中三角形有限元网格的具体要求，对经典的Bowyer-watson算法作了局部改进，利用具有岛屿约束的Delaunay剖分方法来构建三角形网格，使其适用于有岛屿、关键点和特征线约束的区域剖分的要求。此方法在（苏州，无锡，常州）以下简称苏锡常地区地下水流数值模拟中得到了应用，结果表明此方法自动生成带岛屿约束的三角形网格是可行的。     

Assessment of Fish Assemblages Before Dredging of the Shipping Channel Near the Mouth of the Savannah River in Coastal Georgia

Evaluating the effects of anthropogenic activities is dependent upon data collection prior to impact, though funds are rarely allocated to conduct an assessment before a critical need arises. The Savannah Harbor Expansion Project is one such activity that includes dredging of the Savannah River. It may potentially change physical conditions of the estuary thereby altering fish assemblages. The purpose of the present study was to characterize pre-impact fish assemblages along a salinity gradient near the mouth of the river and determine which abiotic factors most influence them. One site within the mouth of the Savannah River and two sites immediately outside the river mouth were sampled monthly for 2 years using both a beam trawl and seine net. Salinity, temperature, dissolved oxygen, and sediment grain size were assessed. All four factors had a significant effect on fish assemblages. A total of 3943 fishes representing ≥55 species formed three statistically distinct fish assemblages and at least three seasonal assemblages. Only 24 species (43.6 %) were collected by both gear types indicating the importance of using multiple gear types to assess fish assemblages. We conclude that the fish assemblages near the mouth of the Savannah River may be altered or may shift given the predicted increase in salinity and/or the possible changes in sediment composition from channel dredging. Understanding the abiotic factors that most influence spatial and seasonal fish distributions prior to dredging will be invaluable in predicting how organisms will be impacted by similar public projects elsewhere.     

Mesh size influence on dynamic modeling

Mesh size influence on dynamic modelling in 1-D and 2-D models is investigated by using discrete element code UDEC. It is shown that the modelling with smaller mesh ratio obtains higher accuracy, which agrees well with the common acceptance. Furthermore, it is found that the error, induced by the mesh size, increases with increasing distance from the wave source and also with increasing wave frequency. Therefore, it is suggested that the mesh distortion may resulted by a combination effect of mesh size, wave frequency and distance from the wave source. Comparing the results between 1-D and 2-D models indicates that the 2-D modelling produces higher error than 1-D model, which is explained as due to the error superposition in x and y directions in the 2-D model.     

Perforation of Flexible Rockfall Barriers by Normal Block Impact

Flexible rockfall barriers are a common form of protection against falling blocks of rock and rock fragments (rockfall). These barriers consist of a system of cables, posts, and a mesh, and their capacity is typically quantified in terms of the threshold of impact (kinetic) energy at which the barrier fails. This threshold, referred to here as the “critical energy,” is often regarded as a constant. However, several studies have pointed out that there is no single representative value of critical energy for a given barrier. Instead, the critical energy decreases as the block size decreases, a phenomenon referred to as the “bullet effect.” In this paper, we present a simple analytical model for determining the critical energy of a flexible barrier. The model considers a block that impacts normally and centrally on the wire mesh, and rather than incorporate the structural details of the cables and posts explicitly, the supporting elements are replaced by springs of representative stiffness. The analysis reveals the dependence of the critical energy on the block size, as well as other relevant variables, and it provides physical insight into the impact problem. For example, it is shown that bending of the wire mesh during impact reduces the axial force that can be sustained within the wires, thus reducing the energy that can be absorbed. The formulas derived in the paper are straightforward to use, and the analytical predictions compare favorably with data available in the literature.     

Optimal benthic macrofaunal sampling protocol for detecting differences among four habitats in Willapa Bay,Washington, USA

As part of an effort to estimate estuarine habitat values with respect to ecological indicators of benthic macrofaunal community condition, an optimal (effective and least costly) sampling protocol (sample unit size [area x depth], sieve mesh size, and sample number [n]) was determined. The goal was to use four ecological indicators (number of species, abundance, biomass, and fish and crab prey abundance) to detect differences among four intertidal habitats in Willapa Bay, Washington, United States. The four habitats were eelgrass (Zostera marina), Atlantic cordgrass (Spartina alterniflora), mud shrimp (Upogebia pugettensis), and ghost shrimp (Neotrypaea californiensis). Four sample unit areas (0.005, 0.010, 0.015, and 0.020 m²), two sample unit depths (0–5 and 0–10 cm), and two sieve mesh sizes (1.0 and 0.5 mm) were evaluated. The optimal sampling protocol was defined as the least costly protocol capable of reliably (statistical power, 1?β≥0.80) detecting significant (α=0.05) differences among ≥4 of the 6 pairwise habitat contrasts by ANOVA on all four ecological indicators. The relative cost of each sampling protocol was estimated as a direct function of the sample unit size and number and the cost-in-processing-time ratios of 1 (5 cm deep):1.7 (10 cm deep) and 1 (≥1.0 mm macrofauna size fraction); 2.5 (≥0.5 mm macrofauna size fraction), which were taken from previous studies. The optimal sampling protocol was 15–20, 0.01-m²×5-cm deep, 0.5-mm mesh samples per habitat.     

Numerical upper bounds to the ultimate load bearing capacity of three-dimensional reinforced concrete structures

This contribution is addressing the ultimate limit state design of massive three-dimensional reinforced concrete structures based on a finite-element implementation of yield design theory. The strength properties of plain concrete are modeled either by means of a tension cutoff Mohr Coulomb or a Rankine condition, while the contribution of the reinforcing bars is taken into account by means of a homogenization method. This homogenization method can either represent regions of uniformly distributed steel rebars smeared into the concrete domain, but it can also be extended to model single rebars diluted into a larger region, thereby simplifying mesh generation and mesh size requirements in this region. The present paper is mainly focused on the implementation of the upper bound kinematic approach formulated as a convex minimization problem. The retained strength condition for the plain concrete and homogenized reinforced regions are both amenable to a formulation involving positive semidefinite constraints. The resulting semidefinite programming problems can, therefore, be solved using state-of-the-art dedicated solvers. The whole computational procedure is applied to some illustrative examples, where the implementation of both static and kinematic methods produces a relatively accurate bracketing of the exact failure load for this kind of structures.     

Habitat use and movement of the mummichog (<Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>) in a restored salt marsh

The mummichog,Fundulus heteroclitus, is one of the most abundant macrofaunal components of salt marsh ecosystems along the east coast of the United States. During April–November 1998, we determined the habitat use and movement patterns of young-of-the-year (YOY) and adult mummichogs in a restored marsh, formerly a salt hay farm, and an adjacent creek in order to expand our understanding of the ecology of the species and evaluate the success of the restoration. Four major fish habitat types (large first-order natural creek, second-order created creek, linear drainage ditch, and marsh surface) were identified within the study site. Patterns of relative abundance and mark and recapture using coded wire tags were used to determine the habitat use, tidal movements, home range, and site fidelity of the species within these habitat types. A total of 14,784 fish, ranging from 20–100 mm SL, were captured with wire mesh traps and tagged, and 1,521 (10.3%) fish were recaptured. A variety of gears were used to attempt to recapture fish across all habitat types, including wire mesh traps, push nets, and otter trawls. Based on abundance and recaptures of tagged fish, the YOY and adults primarily used the shallow subtidal and intertidal areas of the created creek, the intertidal drainage ditches, and the marsh surface of the restored marsh but not the larger, first-order natural creek. At low tide, large numbers were found in the subtidal areas of the created creek; these then moved onto the marsh surface on the flooding tide. Elevation, and thus hydroperiod, appeared to influence the microscale use of the marsh surface. We estimated the home range of adults and large YOY (20–100 mm SL) to be 15 ha at high tide, which was much larger than previously quantified. There was strong site fidelity to the created creek at low tide. The habitat use and movement patterns of the mummichog appeared similar to that reported for natural marshes. Coupled with the results of other studies on the feeding, growth, and production of this species in this restoreh, the species appeared to have responded well to the restoration.     

喷锚支护节理岩体的弹性复合单元模型

利用复合单元技术,建立节理岩体喷锚支护的弹性模型。该模型可先不考虑节理、锚杆、喷层等细部结构,生成常规有限元网格,然后根据节理、锚杆、喷层的相关信息,形成复合单元网格信息。该模型可重点考虑锚杆和喷层在节理面上的局部化非线性变形与相互作用关系。算例研究验证了模型的合理性。该复合单元算法同时包含等效模拟和离散模拟的优点,有着较好的应用前景     

起伏地表下的复杂三维地质模型建立与重力异常计算

由于地质体和矿体的形态非常复杂，使用长方体网格离散建立正演模型时可能和真实情况有很大差别，因此计算结果可靠性差。本文提出一种基于约束Delaunay网格剖分的方法对地质体进行离散并进行重力建模，在模型边界等复杂区域使用网格自适应加密技术，将三维地质体离散为有限个四面体；并详细推导出针对四面体网格的重力正演公式，实现了基于约束Delaunay网格剖分技术的三维重力数值模拟；最后，针对一个合成数据模型，将计算解与解析解对比。结果表明，细化网格的模拟结果比粗糙网格更好，满足数值模拟的精度要求。将该方法应用到金川矿区实际地质体建模中，根据局部需要，建立各处网格密度不均匀的三维模型，并计算该模型的地表重力场，而后对比模拟数据与实测数据，结果表明Delaunay网格建模方法具有很强的适用性，能够模拟复杂的地质体重力异常。     

Fish biomass size spectra in Chesapeake Bay

Biomass size spectra of pelagic fish were modeled to describe community structure, estimate potential fish production, and delineate trophic relationships in Chesapeake Bay. Spectra were constructed from midwater trawl collections each year in April, June–August, and October 1995–2000. The size spectra were bimodal: the first spectral dome corresponded to small zooplanktivorous fish, primarily bay anchovyAnchoa mitchilli; the second dome consisted of larger fish from several feeding guilds that are supported by multiple prey-predator linkages. Annual production estimates of pelagic fish, derived from a mean production to biomass ratio, varied nearly three-fold, ranging from 162 × 109 kcal (125 × 103 tons) in 1996 to 457 × 109 kcal (352 × 103 tons) in 2000. Seasonally, the biomass level and mean individual sizes of fish in the first dome increased from April to October, while the biomass level of the second dome was relatively stable. Regionally, biomass levels in the second dome were higher than biomasses in the first dome for the upper and lower Bay, but were minimal in the middle Bay where seasonal and episodic hypoxia occurs. To test a benthic-pelagic coupling hypothesis that could explain the higher biomass in the second domes for the lower and upper Bay, a cyclic size-spectrum model was fit that included only species in the zooplanktivorous-piscivorous fish guilds. The mean, normalized slope equaled ?1, indicating that zooplanktivorous fish may support piscivore production, but that a benthic-pelagic linkage is required to fully support fish production in the second dome. Interannual variability in slopes and intercepts of modeled size spectra was related to salinity, recruitment level of bay anchovy, and the primary axis of a correspondence analysis (salinity effect) on fish community structure. The spectral slope and intercept of normalized spectra were lowest in 1996, a near-record wet year. Results suggest that fish size spectra can be developed as useful indicators of ecosystem state and response to perturbations, especially if prey-predator relationships are explicitly represented.     

Virtual organisation in the SIMDAT meteorological activity: a decentralised access control mechanism for distributed data

The EU funded SIMDAT project is aimed at applying generic grid technology for the solution of complex application problems in several representative fields including automotive, aerospace, pharmaceutical and meteorology. To satisfy the requirements of the World Meteorological Organization (WMO) and the WMO Information Systems (WIS), the partners in the meteorology activity within SIMDAT (ECMWF, Deutscher Wetterdienst, the UK Met office, EUMETSAT and Météo-France), have developed grid-enabled software that provides generic distributed access to distributed meteorological data repositories via web-based portals, through a series of nodes organized in a mesh network. However, granting access to such an infrastructure, especially considering its fully distributed nature, is a serious challenge and a risk to the security of the overall grid infrastructure. SIMDAT solves this problem by implementing a security model based on a decentralized fine-grained access control mechanism that federates data providers and security issues using the notion of “trust domains”. In this paper we highlight the main features of the SIMDAT grid application and describe its security model in detail.     

富钴结壳超细标准物质的加工制备

用气流磨制备了2个具有超细粒度的海山富钴结壳标准物质MCPt-1和MCPt-2。原样先经球磨成74μm(-200目),再用气流磨进行超细加工。样品粒度采用激光粒度仪检测,用粒度分布图和特征粒度来表达测量结果。两个样品的平均粒度分别为1.8μm和1.5μm(约2 000目),是目前粒度最小的标准物质。文章介绍了用于超细加工的流化床式气流磨原理与方法,展示了样品加工后的粒度分析结果,对比了国内外超细标准物质的概况。最后讨论了当前关注样品加工的重要性、超细加工的问题及超细样品分析研究的意义。     

Spatial variation in delaware bay (U.S.A.) marsh creek fish assemblages

Delaware Bay is one of the largest estuaries on the U.S. eastern seaboard and is flanked by some of the most extensive salt marshes found in the northeastern U.S. While physicochemical and biotic gradients are known to occur along the long axis of the bay, no studies to date have investigated how the fish assemblage found in salt marsh creeks vary along this axis. The marshes of the lower portion of the bay, with higher salinity, are dominated bySpartina spp., while the marshes of the upper portion, with lower salinity, are currently composed primarily of common reed,Phragmites australis, S. alterniflora, or combinations of both. Extensive daytime sampling (n=815 tows) during May–November 1996 was conducted with otter trawls (4.9 m, 6 mm mesh) in six intertidal and subtidal marsh creek systems (upper and lower portions of each creek) where creek channel depths ranged from 1.4–2.8 m at high tide. The fish taxa of the marsh creeks was composed of 40 species that were dominated by demersal and pelagic forms including sciaenids (5 species), percichthyids (2), and clupeids (7), many of which are transients that spawn outside the bay but the early life history stages are abundant within the bay. The most abundant species wereMorone americana (24.3% of the total catch),Cynoscion regalis (15.4%),Micropogonias undulatus (15.3%),Anchoa mitchilli (12.0%), andTrinectes maculatus (10.8%). Non-metric Multi-Dimensional Scaling ordination of catch per unit effort (CPUE) data indicated two fish assemblages that were largely independent of the two major vegetation types, but generally corresponded with spatial variation in salinity. This relationship was more complex because some of the species for which we could discriminate different age classes by size had different patterns of distribution along the salinity gradient.     

ICP-AES在新疆哈拉奇地区水系沉积物样品分析中的应用研究

本文采用四酸溶样ICP6300电感耦合等离子体发射光谱法测试了新疆哈拉奇地区水系沉积物样品中的Li P Ti V Cr Mn Co Ni Cu Zn Sr Y Nb Mo Ba La Pb B W Sn Cd 21种微量元素,明确了该方法测试样品中的Li P Ti V Cr Mn Co Ni Cu Zn Sr Y Nb Mo Ba La 16个元素的检出限、准确度、精密度满足规范（DZ/T0130.2006-2006）要求,而Pb B Cd Sn W5个元素测试质量不能满足规范要求,并对新疆哈拉奇地区水系沉积物采样粒度样品进行了分析测试,验证了该区化探扫面选择10-80目粒度是合适的,但在异常查证工作中要选择10-60目采样粒度更合理。     

The modelling of anchors using the material point method

The ultimate capacity of anchors is determined using the material point method (MPM). MPM is a so‐called meshless method capable of modelling large displacements, deformations and contact between different bodies. A short introduction to MPM is given and the derivation of the discrete governing equations. The analysis of a vertically loaded anchor and one loaded at 45° is presented. The load–displacement curves are compared to that obtained from experiments and the effect of soil stiffness and anchor roughness is investigated. The results of the vertically loaded anchor are also compared to an analytical solution. The displacement of the soil surface above the anchor was measured and compared to the numerical predictions. Convergence with mesh refinement is demonstrated and the effect of mesh size and dilatancy angle on the shear band width and orientation is indicated. The results show that MPM can model anchor pull out successfully. No special interface elements are needed to model the anchor–soil interface and the predicted ultimate capacities were within 10% of the measured values. Copyright © 2005 John Wiley & Sons, Ltd.     

A new method in palaeoecology: fish community structure indicates environmental changes

A new method to reconstruct aquatic palaeoenvironments is presented. It is based on a non-metrical ‘fish environment reconstruction index’ (FERI), calculated for the total fish community recorded at an archaeological site. As an example, a FERI is generated for the Baltic Sea using the ecological requirements of northern European fish species. The present study evaluates the proposed method by using fish bone assemblages from a region (the middle Holocene Baltic Sea coast) with well-studied hydrographic history. The bones originate from consecutive human riparian and coastal settlements of hunter-gatherers. The results obtained for the parameters salinity and sediment structure correlate well with geological knowledge. The new method shows a successive change from freshwater to brackish and finally to nearly marine conditions before, during, and towards the end of the marine transgression that created the present Baltic Sea. Additionally, a shift in the sediment structure from muddy to sandy/rocky conditions is recognisable.