Spatial and temporal variation of bacterioplankton in a sub-Antarctic coastal area (Kerguelen Archipelago)

Bacterial abundance and production were measured monthly for one year along cross-shore transects in 3 sub-Antarctic fjords of the Kerguelen Archipelago (seven stations each). Mean values of the 3 most coastal (inside) and most offshore (outside) stations were used to describe the relationship between temperature, phytoplankton biomass, bacterial abundance and bacterial production over a one year annual cycle. The entire sampling protocol was repeated twice during each cruise: once at noon and once at midnight. Over the whole sampling period, the temperature ranged from 2.1 to 7.4 °C, while chlorophyll a concentrations varied by a factor of 10, and bacterial abundance and production varied by factors of 12 and 30, respectively. Within one day, all of these parameters sometimes varied by a factor of 4 between noon and midnight. A clear seasonality was observed for all of the parameters. However, while variations of phytoplankton and bacterial production paralleled those of temperature, bacterial abundance was low in midsummer and maximum in autumn. While no general pattern could be observed from the total data set, spatial gradients could interfere strongly with temporal changes.     

整体式转向梯形的设计方法研究

为了在整体式转向梯形设计过程中考虑轮胎侧偏的影响,采用了百分比阿克曼校正率对阿克曼转角关系进行了修正。设计过程中使用了MATLAB数学工具箱以及空间运动分析的方法分析转向梯形的空间运动规律,并且考虑四轮定位参数对转角关系的影响。分析结果表明,通过考虑轮胎侧偏影响设计的转向梯形与现有车型的转向梯形参数比较接近,同时通过灵敏度分析发现,梯形参数中的梯形底角对车轮转角关系的影响很大。     

轿车内部凸出物试验方法

为加强车内乘员保护,进一步改善和优化汽车仪表板及结构部件设计,文章通过分析汽车内部凸出物标准有关技术要求,探讨了相关试验方法,通过不同试验方法对比得出了试验设备与实际测量碰撞点空间位置重合法,能更好地模拟乘员在事故中的碰撞;该方法能更好地考核乘员在事故中受到的伤害,同时能更好地验证仪表板及其结构部件的质量。因此,建议试验机构或生产厂家应按照该方法进行汽车内部凸出物静态吸能试验。     

The maximum approximate composite marginal likelihood (MACML) estimation of multinomial probit-based unordered response choice models

The likelihood functions of multinomial probit (MNP)-based choice models entail the evaluation of analytically-intractable integrals. As a result, such models are usually estimated using maximum simulated likelihood (MSL) techniques. Unfortunately, for many practical situations, the computational cost to ensure good asymptotic MSL estimator properties can be prohibitive and practically infeasible as the number of dimensions of integration rises. In this paper, we introduce a maximum approximate composite marginal likelihood (MACML) estimation approach for MNP models that can be applied using simple optimization software for likelihood estimation. It also represents a conceptually and pedagogically simpler procedure relative to simulation techniques, and has the advantage of substantial computational time efficiency relative to the MSL approach. The paper provides a “blueprint” for the MACML estimation for a wide variety of MNP models.     

Spatial structure and mobility

The aim of this paper is to contribute to a clearer understanding of the extent to which the spatial structure and planning of the residential environment can explain mobility, in general, and the choice of mode of transport, in particular, and what spatial planning and traffic management aspects play a significant role in this. The research showed that certain aspects of the planned environment do indeed have a clear impact on mobility. These effects are particularly apparent in trips made for shopping and social or recreational purposes. It is mainly personal characteristics that largely or almost entirely determine commuter traffic. An integral approach to the planning of residential areas is required to achieve any great changes in mobility. Only then may we expect spatial planning to have any significant impact on car use.     

The value of transportation accessibility in a least developed country city – The case of Rajshahi City,Bangladesh

Little appears to be known about the capitalization of transportation accessibility in South Asian housing markets, which typically differ from those of industrialized countries. This study starts addressing this gap by providing empirical evidence about the nature and the magnitude of the value of accessibility as reflected by residential rents in Rajshahi City, Bangladesh. Results of our SARAR spatial hedonic model estimated on 526 observations from a random sample collected via in-person interviews indicate that the rent of a multi-unit dwelling decreases by 0.0239% for every 1% increase in network access distance to the nearest major road. Moreover, proximity (within 400 m) to a primary school and to a healthcare facility commands rent premiums of respectively 93.55 BDT ($1.40) and 109.45 BDT ($1.64). Surprisingly, whether access roads are paved or not does not statistically impact rents, probably because of the dominance of walking, rickshaws use, and biking, combined with the rarity of personal cars. Likewise, proximity to bus stops and to train stations is not reflected in rents of multi-family dwellings, likely because buses and trains in Rajshahi City only provide regional and national service. Differences in estimates of our spatial models between maximum likelihood (ML) and generalized spatial two-stage-least-squares illustrate the danger of relying on ML in the presence of heteroskedasticity. These results should be useful for planning transportation infrastructure funding measures in least developed country cities like Rajshahi City.     

基于改进TOPSIS模型的地铁网络节点重要性评价方法

对城市地铁网络节点重要性进行评价在城市交通体系的运营和管理中具有重要意义。TOPSIS法是一种节点重要程度多指标综合评价方法。已有的TOPSIS法在评价地铁网络节点重要程度时存在贴近度评价不合理,权重算法没有考虑网络空间特性两方面问题。针对上述不足,提出相应的改进措施:(1)结合垂面距离和灰色关联度综合评价方案与理想解的贴近度;(2)设计适用于空间网络的局部熵赋权法。最后,以北京地铁网络为例,利用改进的TOPSIS法测算了节点的重要性程度。结果表明:该方法确定的结果符合实际情况并且优于现有的TOPSIS法,说明该方法具有较高的准确性和较强的应用性。     

宁安铁路小角度斜交桥异形刚架空间分析研究

南京至安庆铁路新建工程需跨越321省道,线路与既有道路夹角仅为16.45°。为解决结构高度受限、斜交角度过小的问题,通过多方案比选确定采用(39.6+18.7+41.3+18.7+39.6)m的异形刚架桥,着重介绍开天窗和侧窗异形刚架的布置和设计。基于空间分析和动力特性分析总结异形刚架的受力行为和特点,对比分析空间和平面两种计算方法的差异性。计算结果表明,该结构能够满足无砟轨道桥梁的各项强度及刚度要求。     

物流通道的空间溢出效应检验——基于中国11 条物流通道的实证

以中国11 条物流通道为实证对象,综合测算物流通道技术水平,构造基于地理距 离的空间邻接权重矩阵,检验相关变量的空间自相关性,构建空间杜宾面板数据模型验证了 中国物流通道的空间溢出效应.研究表明：中国物流通道总体上具有显著的正向空间溢出效 应,但从分布于不同空间的物流通道看,长江、沿海、京九、陇海兰新和沪昆物流通道正向空间 溢出效应显著;而京沪、京广和宝昆物流通道研究期内空间溢出效应不显著.我国物流通道的 空间溢出效应具有显著的空间差异,应因地制宜地合理化建设物流通道.