Microbial community structure in the marginal ice zone of the Bellingshausen Sea

Phytoplankton, bacteria and microzooplankton were investigated on a transect in the Bellingshausen Sea during the ice melt period in November–December 1992. The transect along the 85°W meridian comprised seven stations that progressed from solid pack-ice (70°S), through melting ice into open water (67°S). The abundance, biomass and taxonomic composition were determined for each component of the microbial community. The phytoplankton was mostly dominated by diatoms, particularly small (<20 μm) species. Diatom abundance ranged from 66 000 cells l⁻¹ under the ice to 410 000 cells l⁻¹ in open water. Phytoplankton biomass varied from <1 to 167 mg C m⁻³, with diatoms comprising 89–95% of the total biomass in open water and autotrophic nanoflagellates comprising 57% under the ice. The standing stocks of autotrophs in the mixed layer ranged from 95 mg C m⁻² under the pack-ice to 9478 mg C m⁻² in open waters. Bacterial abundance in ice-covered and open water stations varied from 1.1 to 5.5×10⁸ cells l⁻¹. Bacterial biomass ranged from 2.4 mg C m⁻³ under pack-ice to an average of 14 mg C m⁻³ in open water. The microzooplankton consisted mainly of aloricate oligotrich ciliates and heterotrophic dinoflagellates and these were most abundant in open waters. Their biomass varied between 0.2 and 54 mg C m⁻³ with a minimum at depth under the ice and maximum in open surface waters. Microheterotrophic standing stocks varied between 396 mg C m⁻² under pack-ice and 3677 mg C m⁻² in the open waters. The standing stocks of the total microbial community increased consistently from 491 mg C m⁻² at the ice station to 13 155 mg C m⁻² in open waters, reflecting the productive response of the community to ice-melt. The composition of the microbial community also shifted markedly from one dominated by heterotrophs (82% of microbial stocks) at the ice station to one dominated by autotrophs (73% of microbial stocks) in the open water. Our estimates suggest that the microbial community comprised >100% of the total particulate organic carbon (POC) under the ice and 62–66% of the measured POC in the open waters.     

欧洲最新城市快速铁路电动车组

对瑞士的Flirt、奥地利的Elektro-Talent和波兰的EN95 3种动车组的技术性能和价格进行了比较.     

用特性模型分析IGBT功耗

文章介绍了IGBT特性模型的建模技术.通过特性模型简化了IGBT功耗的分析和计算,评估了正弦电路应用中IGBT的结温和损耗.仿真结果证实了特性模型的可行性.     

An Optimal Continuous Time Control Strategy for Active Suspensions with Preview

A continuous time control strategy for an active suspension with preview, based on optimal control theory, is presented. No approximation is needed to model the time delay between the excitation of the front and the rear wheels. The suspension is applied to a two DOF model of the rear side of the tractor of a tractor-semitrailer. The purpose of the suspension is to reduce either the required suspension working space or the maximum absolute acceleration of the sprung mass, without an increase of the dynamic tire force variation. For a step function as road input, reductions of 65% and 55%, respectively, are possible compared with a passive suspension.     

The state-of-the-art in urban transportation planning or how we got here

This paper traces the development of urban transportation planning in the United States, focusing particularly on the influence that three previous conferences -Sagamore (1958), Hershey (1962), and Williamsburg (1965) - have had on the course of this development. Included also are comments on the current state of the art of urban transportation planning and observations as to its future direction.The Federal-Aid Highway Act of 1934, which authorized the use of 1 percent funds for highway planning is identified as the progenitor of urban transportation planning in the U.S., and two reports based on information developed by the highway planning surveys first funded under the 1934 Act, Toll Roads and Free Roads (1939) and Interregional Highways (1944), are credited with preparing the ground for much of the urban transportation planning that was to follow.The rapid development of home interview survey techniques in the late 1940's and the full-scale introduction of computer technology in the Detroit Area Transportation Study are noted, as is the work of the National Committee on Urban Transportation, which was initiated in 1954 under sponsorship of the Automotive Safety Foundation. In addition to its substantial technical contributions, the NCUT, through its success in mobilizing the cooperative efforts of virtually every major group concerned with urban transportation, stimulated significant gains in Federal-State-local relationships and paved the way for increased Federal aid to cities in solving their local transportation problems.The impact of the 1956 and 1962 Federal-Aid Highway Acts on urban transportation planning is assessed. The substantial contributions, of the Hartford, Sagamore, Hershey, and Williamsburg conferences are discussed, as are their shortcomings. It is noted that many of our present concerns — environmental impacts, relationships between transportation and land use, need for cooperation among all levels of government, the multi-modal nature of urban transportation, and the need for citizen involvement, to name a few — were incorporated in the provisions of either one or another of the Federal-Aid statutes in the 1950's and 60's or appear in the recommendations of the several conferences. That these matters still concern us today is given as evidence that planning has not fully lived up to its promise and responsibility, that more rather than less planning is needed, and that, above all, new leadership to pick up where the old has left off must soon assert itself.     

Microscopic decision model for pedestrian route choice at signalized crosswalks

In this paper, two‐tier mathematical models were developed to simulate the microscopic pedestrian decision‐making process of route choice at signalized crosswalks. In the first tier, a discrete choice model was proposed to predict the choices of walking direction. In the second tier, an exponential model was calibrated to determine the step size in the chosen direction. First, a utility function was defined in the first‐tier model to describe the change of utility in response to deviation from a pedestrian's target direction and the conflicting effects of neighboring pedestrians. A mixed logit model was adopted to estimate the effects of the explanatory variables on the pedestrians' decisions. Compared with the standard multinomial logit model, it was shown that the mixed logit model could accommodate the heterogeneity. The repeated observations for each pedestrian were grouped as panel data to ensure that the parameters remained constant for individual pedestrians but varied among the pedestrians. The mixed logit model with panel data was found to effectively address inter‐pedestrian heterogeneity and resulted in a better fit than the standard multinomial logit model. Second, an exponential model in the second tier was proposed to further determine the step size of individual pedestrians in the chosen direction; it indicates the change in walking speed in response to the presence of other pedestrians. Finally, validation was conducted on an independent set of observation data in Hong Kong. The pedestrians' routes and destinations were predicted with the two‐tier models. Compared with the tracked trajectories, the average error between the predicted destinations and the observed destinations was within an acceptable margin. Copyright © 2016 John Wiley & Sons, Ltd.     

Efficient solution algorithm for finding spatially dependent reliable shortest path in road networks

Travel times are generally stochastic and spatially correlated in congested road networks. However, very few existing route guidance systems (RGS) can provide reliable guidance services to aid travellers planning their trips with taking account explicitly travel time reliability constraint. This study aims to develop such a RGS with particular consideration of travellers' concern on travel time reliability in congested road networks with uncertainty. In this study, the spatially dependent reliable shortest path problem (SD‐RSPP) is formulated as a multi‐criteria shortest path‐finding problem in road networks with correlated link travel times. Three effective dominance conditions are established for links with different levels of travel time correlations. An efficient algorithm is proposed to solve SD‐RSPP by adaptively using three established dominance conditions. The complexities of road networks in reality are also explicitly considered. To demonstrate the applicability of proposed algorithm, a comprehensive case study is carried out in Hong Kong. The results of case study show that the proposed solution algorithm is robust to take account of travellers' multiple routing criteria. Computational results demonstrate that the proposed solution algorithm can determine the reliable shortest path on real‐time basis for large‐scale road networks. Copyright © 2016 John Wiley & Sons, Ltd.