Analysis of social networks,social interactions,and out-of-home leisure activity generation: Evidence from Japan

Transportation - This article analyses the connection between social networks, social interactions and out-of-home leisure activity generation in the context of Japanese society. A multilevel...     

Estimating micro-scale intermittency of fluorescence fields from conventional CTD measurements

A free-fall microstructure profiler (TurboMAP) reveals highly intermittent features in the fluorescence field. Conventional CTDs that mount a fluorometer are usually deployed with a tethered cable, and the data are averaged or smoothed over a given time or water depth. Because of the nature of the operation and the data processing involved, intermittent features of fluorescence fields are masked. We have developed a statistical technique to extrapolate the intermittency using a lognormal mixture probability density function (mixture pdf). The statistics obtained from the mixture pdf are consistent with microstructure data, thus the conventional CTD can provide statistics appropriate to a micro-scale fluorescence field.     

Phytoplankton patch patterns: Seascape anatomy in a turbulent ocean

Marine phytoplankton experience competition, predation, infection and aggregation occurring across distances of micrometres to centimetres. However, the consequences of these interactions influence global processes, such as climate and fisheries productivity. There is a long-standing default assumption that these global processes cannot be traced to plankton distributions and interactions below a few metres because of the homogenising effect of turbulence [Hutchinson, G.E., 1961. The paradox of the plankton. Am. Nat. 95, 137–146.; Siegel, D.A., 1998. Resource competition in a discrete environment: Why are plankton distributions paradoxical? Limnol. Oceanogr. 43, 1133–1146.]. We show that, in active turbulence, phytoplankton patches, on the order of 10 cm, have repeatable asymmetry and regular spacing over distances of centimetres to tens of metres. The regularity and hierarchical nature of the patches in mixed ocean water means that phytoplankton are distributed in a dynamic, but definite seascape topography, where groups of patches coalesce between intermittent turbulent eddies. These patches may link large scale processes and microscale interactions, acting as fundamental components of marine ecosystems that influence grazing efficiency, taxonomic diversity, and the initiation of aggregation and subsequent carbon flux.     

Apparent phytoplankton bloom due to island mass effect

A continuous monitoring of temperature and chlorophyll-a (Chl-a) concentration from a surface water monitoring system and a towed free fall instrument (MVP) around a small island in the Kuroshio showed low sea surface temperature (SST) and high surface Chl-a concentration (SCC) distribution in the lee of the island that indicates typical “island mass effect” phenomena. When the observed Chl-a profiles (0 to 250 m) were integrated, the total amounts in the lee side data were slightly smaller than those of the upstream side of the island. The difference was statistically significant at the 95% confidence level. The cross section diagram of Chl-a indicated the diffusion of subsurface Chl-a maximum (SCM) from the upstream to the downstream flanks of the island. The diffusivity of SCM and the change of potential energy require the same level of strong turbulent dissipation rate at the flanks of the island. That is consistent with our previous direct measurement in a similar hydrodynamic condition. Therefore, the observed high SCC is due to turbulent diffusion of SCM, and clearly showed that high SCC does not require any new production. Although a high fluorescence field behind an isolated island in a strong flow is often visible from satellite images, the images do not necessarily indicate an enhanced primary production at that moment.     

基于非线性鲁棒控制原理的防滑控制

为了在高速区有效操纵列车,无论列车长度如何都需要控制系统能够提供稳定的制动力.在设计制动控制系统过程中,由于粘着和制动材料的摩擦系数变化而导致的模型不确定性是一个需要首先考虑的问题.提出利用滑模控制原理设计一种全新防滑控制系统.相比于常规控制方式,仿真结果证明,在非线性制动动力学方面,基于滑模控制的防滑控制系统具有良好的性能.     

Effect of wheel-slip prevention based on sliding mode control theory for railway vehicles

It is important to consider the robustness when designing brake control systems, because of the model's uncertainties that result from the nonlinear characteristics of wheel-to-rail adhesion forces and brake material friction coefficients. This paper presents the experimental results from the new wheel-slip prevention control using nonlinear robust control theory. The authors performed experiments for the proposed wheel-slip prevention control to compare it with the conventional control laws. The experimental results proved the comparative effectiveness of the proposed control and showed high brake performance under nonlinear characteristics of brake dynamics.