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71.
通过树型菜单,用户可以对资源的结构、类型有直观的了解,但目前很多B/S系统的菜单还是通过代码生成的。为此,基于.NET技术,通过开源项目Peta Poco实现代码,设计并实现了动态导航菜单系统;介绍了数据库设计、算法思想。该技术避免了静态目录树下因数据源经常性改变而频繁修改程序代码的弊端,导航菜单通过数据库进行控制,提高了系统的安全性,使管理变得更加灵活、高效。 相似文献
72.
Teija Vainio 《Digital Creativity》2013,24(1):26-39
While there have been many studies of navigation design guidelines for integrating maps in mobile devices, we argue that the research focus should turn more towards the design of multimodal navigation aids, which would reflect the impact of typical human wayfinding behaviour. Therefore, we suggest an interdisciplinary design approach, i.e. building on urban design practice that focuses on supporting the navigation of pedestrians in urban areas. The design implications are explored in this study with the subjects being pedestrians accomplishing wayfinding tasks in an unfamiliar, urban area. The main areas that this paper contributes to are: investigating the design implications of multimodal navigation aids; evaluating these in the context of mobile wayfinding tasks; and reflecting the results according to the user's wayfinding strategies and spatial anxiety. It is concluded that through designing multimodal tracks into mobile navigation applications we can help users to find their way in unfamiliar, urban environments. 相似文献
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Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
77.
简要介绍水口坝下枢纽工程兴建,从工程选址、通航标准、枢纽主要建筑物设计、自然条件对拟建工程的影响、施工期通航条件、安全保障措施等方面进行了分析论证和安全评估. 相似文献
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79.
Nikos D. Lagaros Manolis Papadrakakis 《Computer Methods in Applied Mechanics and Engineering》2008,198(1):28-41
Performance-Based Design (PBD) methodologies is the contemporary trend in designing better and more economic earthquake-resistant structures where the main objective is to achieve more predictable and reliable levels of safety and operability against natural hazards. On the other hand, reliability-based optimization (RBO) methods directly account for the variability of the design parameters into the formulation of the optimization problem. The objective of this work is to incorporate PBD methodologies under seismic loading into the framework of RBO in conjunction with innovative tools for treating computational intensive problems of real-world structural systems. Two types of random variables are considered: Those which influence the level of seismic demand and those that affect the structural capacity. Reliability analysis is required for the assessment of the probabilistic constraints within the RBO formulation. The Monte Carlo Simulation (MCS) method is considered as the most reliable method for estimating the probabilities of exceedance or other statistical quantities albeit with excessive, in many cases, computational cost. First or Second Order Reliability Methods (FORM, SORM) constitute alternative approaches which require an explicit limit-state function. This type of limit-state function is not available for complex problems. In this study, in order to find the most efficient methodology for performing reliability analysis in conjunction with performance-based optimum design under seismic loading, a Neural Network approximation of the limit-state function is proposed and is combined with either MCS or with FORM approaches for handling the uncertainties. These two methodologies are applied in RBO problems with sizing and topology design variables resulting in two orders of magnitude reduction of the computational effort. 相似文献
80.
In the paper, the approximate controllability of linear abstract second-order infinite-dimensional dynamical systems is considered. It is proved using the frequency-domain method, that approximate controllability of second-order system can be verified by the approximate controllability conditions for the corresponding simplified first-order system. General results are then applied for approximate controllability investigation of a vibratory dynamical system modeling flexible mechanical structure. Some special cases are also considered. Moreover, remarks and comments on the relationships between different concepts of controllability are given. The paper extends earlier results on approximate controllability of second-order abstract dynamical systems. 相似文献