Spatial variability of the barotropic M2 constituent tidal current over the Rías Baixas Galician shelf (NW Spain)

Using current meters and systematically repeated vessel mounted ADCP data legs, we describe the role of the semidiurnal and diurnal constituents in the tidal currents and investigate the mesoscale variability of the M₂ tidal currents field along three cross-shelf legs over the Galician shelf. We found that the estimated values of the semi-major axes of the main semidiurnal tidal constituents are closely related to those obtained in previous research and that the tidal currents are predominantly semidiurnal. Amplitudes of the M₂ and S₂ semi-major axes constituents are comparable, and important fortnightly variability should thus be expected in the amplitude of the semidiurnal tidal currents. Vertical profiles of the semi-major axes of the main tidal constituents reveal that, in the absence of stratification, and far from the bottom frictional effects, the tidal currents are mostly barotropic. Over the slope, the tidal ellipses tilt from a north–south orientation toward the northeast–southwest direction and, as we go further into the shelf, their amplitude is increased, a feature that is reasonably explained by the transition from the dynamics of a Poincaré wave offshore to the dynamics of a northward alongshore propagating Kelvin wave over the shelf. The Ría de Vigo exerts a notable influence over the tidal currents, acting as an extension of the shelf and introducing a meridional variation in the orientation of the ellipses from the alongshore direction in the southern straight coast toward the northeast–southwest direction at the latitude of the Rías. Finally, the spatial fitting methods we tried have proved to be successful in VMADCP data detiding in this region.     

Primary productivity and export fluxes on the Canadian shelf of the Beaufort Sea: A modelling study

We present a coupled sea ice–ocean-biological (including ice algae) model in the Arctic Ocean. The 1D model was developed and implemented on the Canadian Beaufort Sea shelf to examine the importance of different physical processes in controlling the timing and magnitude of primary production and biogenic particle export over an annual cycle (1987). Our results show that the snow and sea ice cover melt and/or break-up controls the timing of the phytoplankton bloom but primary producers (ice algae and phytoplankton) on the outer shelf are essentially nutrient limited. The total annual primary production (22.7 to 27.7 g-C m^? 2) is thus controlled by nutrient “pre-conditioning” in the previous fall and winter and by the depth of wind mixing that is controlled in part by the supply of fresh water at the end of spring (ice melt or runoff). The spring bloom represents about 40% of the total annual primary production and occurs in a period of the year when sampling is often lacking. Time interpolation of observed values to obtain total annual primary production, as done in many studies, was shown to lead to an underestimation of the actual production. Our simulated ratios of export to primary production vary between 0.42 and 0.44.     

Socio-demographic and built environment influences on the odds of being overweight or obese: The Atlanta experience

This paper explores the association of socio-demographic and built environment characteristics on the odds of being overweight and obese using data from the Atlanta SMARTRAQ travel survey. A new methodological framework based on a multinomial logit (MNL) model and an enhanced odds ratio plot is presented. The use of an MNL model overcomes limitations of many prior studies that employ a sequence of binary logit models to examine multiple weight categories. The use of an enhanced odds ratio plot provides important information into the relative importance of socio-demographic and built environment characteristics. Several new findings for the Atlanta area result from this study. Socio-demographic variables, including age and educational attainment, exhibit a non-linear relationship with the odds of being overweight or obese. Gender, age, ethnicity, and educational attainment are strongly associated with the odds of being overweight or obese, while income and number of students between 5 and 16 years old in the household have smaller effects. Built environment characteristics such as increased net residential densities and enhanced street connectivity are associated with reductions in the odds of being overweight and/or obese. Relative to socio-demographic variables, however, such built environment characteristics have a much smaller impact on describing the odds of being overweight or obese.     

Competition and disruption in a dynamic urban supply chain

Rapid changes and complexities in business environments have stressed the importance of interactions between partners and competitors, leading supply chains to become the most important element of contemporary business environments. There is a concomitant need for foresight in describing supply chain performance in all operating environments, including those involving punctuated disruptions. Furthermore, the urban metropolis is now widely recognized to be an environment which is especially vulnerable to supply chain disruptions and for which integrated supply chain decisions can produce very substantial net benefits. Accordingly, this paper presents a dynamic supply chain network model formulated as a differential variational inequality; the model is fashioned to allow consideration of supply chain disruption threats to producers, freight carriers, and retail enterprises. The DVI is solved using a fixed-point algorithm, and a simple numerical example, introduced to illustrate how the impacts of supply chain disruptions may be quantified, is presented.     

Approximate network loading and dual-time-scale dynamic user equilibrium

In this paper we present a dual-time-scale formulation of dynamic user equilibrium (DUE) with demand evolution. Our formulation belongs to the problem class that Pang and Stewart (2008) refer to as differential variational inequalities. It combines the within-day time scale for which route and departure time choices fluctuate in continuous time with the day-to-day time scale for which demand evolves in discrete time steps. Our formulation is consistent with the often told story that drivers adjust their travel demands at the end of every day based on their congestion experience during one or more previous days. We show that analysis of the within-day assignment model is tremendously simplified by expressing dynamic user equilibrium as a differential variational inequality. We also show there is a class of day-to-day demand growth models that allow the dual-time-scale formulation to be decomposed by time-stepping to yield a sequence of continuous time, single-day, dynamic user equilibrium problems. To solve the single-day DUE problems arising during time-stepping, it is necessary to repeatedly solve a dynamic network loading problem. We observe that the network loading phase of DUE computation generally constitutes a differential algebraic equation (DAE) system, and we show that the DAE system for network loading based on the link delay model (LDM) of Friesz et al. (1993) may be approximated by a system of ordinary differential equations (ODEs). That system of ODEs, as we demonstrate, may be efficiently solved using traditional numerical methods for such problems. To compute an actual dynamic user equilibrium, we introduce a continuous time fixed-point algorithm and prove its convergence for effective path delay operators that allow a limited type of nonmonotone path delay. We show that our DUE algorithm is compatible with network loading based on the LDM and the cell transmission model (CTM) due to Daganzo (1995). We provide a numerical example based on the much studied Sioux Falls network.     

规范城市桥梁检测与维修养护工作

近几年,很多建成的桥梁中出现了大量的病害和破坏现象,一旦发生事故,将会造成经济损失和不良影响。因此,为了更好地防止病害发生、减少桥梁隐患,必须加强对桥梁的检测和维修加固工作。     

基于纸纤维改性的隧道工程透水砂浆性能研究北大核心CSCD

为提出一种适用于隧道初期支护基面找平并且具有一定透水性能的砂浆,将纸纤维加入砂浆试块中对其性能进行改性。通过分析纸纤维的降解原理,并将不同掺量的纸纤维加入砂浆试块中,对其体积密度、吸水率、抗压强度等基本性能指标及微观结构进行测试和分析。由试验结果可知:在碱性环境中,纸纤维具有可降解的性能特点;纸纤维可以使普通砂浆试块的吸水率提升2~3倍,同时也会造成砂浆试块的体积密度和抗压强度降低;对砂浆试块吸水率和抗压强度进行线性拟合后发现其吸水率和抗压强度呈现负相关关系。研究结果表明,通过纸纤维对砂浆进行透水性能的提升是可行的,但是纸纤维掺量对砂浆其他性能的影响还有待进一步研究。     

Use of GIS-Based Models for Integrating and Developing Marine Fish Cages within the Tourism Industry in Tenerife (Canary Islands)

Site selection is a key factor in any aquaculture operation, affecting both success and sustainability. Moreover, it can solve conflicts between different coastal activities, making a rational use of the coastal space. Geographical information systems (GIS) have become of increased significance for environmental planning and assessment mainly because of the need to compare a great number of spatially related data, and because it can be used to couple these spatial data with their attributes and overlay them. This study used GIS and related technology to build a spatial database using those criteria which were considered to have any influence in integrating marine fish-cage culture within the tourism industry in Tenerife. Criteria were grouped in three submodels (distance to beaches, nautical sports, and viewshed), which were combined to generate a final output showing the most suitable areas for cage culture development in coexistence with tourism. Most areas of the coastline of Tenerife were identified as being suitable (56%) or very suitable (46%), suggesting that marine cage aquaculture could be developed on the island in coexistence with the well-established tourism industry.     

Experimental study of drillship resistance performance in open and closed state of moonpool北大核心CSCD

[Objective] This paper carries out an experimental study of a multi-function dirllship model with moonpool structure in towing tank, aiming at analyzing the effects of the moonpool structure on the ship resistance in open and closure condition.[Methods]Taking a dirllship as the research object, the ship motion response in regular and irregular waves is investigated. The resistance of the ship in hydrostatic water and waves is measured with tension sensors, and the acceleration characteristics of the bow, midship and stern are analyzed by acceleration sensors.[Results]The results indicate that hull resistance under light load conditions is greater when open moonpool, while hydrostatic water resistance with closed moonpool is greater under design load conditions. The closed moonpool in regular waves reduces stern acceleration by 58.2%, bow resistance by 46.7% and heave response by 41.8%. The peak of resistance at the bow in irregular waves is about ten times higher than that at the stern, and the peak of resistance occurs more often when the moonpool is open at the same time.[Conclusions]The experimental study shows that the difference in load conditions changes the waterplane area and affects the hull resistance in hyrostatic water. In contrast, the closure of the moonpool not only reduces acceleration and resistance, but also improves surge and heave. As such, this paper can provide references for the structural design of drillships with moonpools. © 2023 Journal of Nanjing Agricultural University. All rights reserved.