Taylor Dispersion of Contaminants by Dual-peak Spectral Random Waves

Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can affect various water quality considerations such as the distribution of suspended sediments in the water column as well as the potential of eutrophication. Comparatively, how the presence of waves influences the horizontal diffusivity/dispersivity has received only scant attention in the literature. Our previous works investigated the role played by the Taylor mechanism due to the wave-induced drift profile which leads to the longitudinal dispersion of contaminants in the horizontal direction, under regular sinusoidal waves and random waves with single-peak spectra.Natural waves in the coastal environment, however, often possess dual-peak spectra, comprising both higher frequency wind waves and lower frequency swells. In this study, the Taylor dispersion of contaminants under random waves with dual-peak spectra is examined through analytical derivation and numerical calculations. The effects of various dual-peak spectral parameters on the horizontal dispersion, including the proportion of lower frequency energy, peak frequency ratio and spectral shape parameter, are investigated. The results show that the relative energy distribution between the dual peaks has the most significant effect. Compared with single-peak spectra with equivalent energy, the Taylor dispersion with dual-peak spectra is stronger when the lower frequency is close to the peak frequency of the single-peak spectrum, and weaker with the higher frequency instead. Thus, it can be concluded that with a dual-peak wave spectrum, wind-dominated seas with higher frequency lead to stronger dispersion in the horizontal direction than swell-dominated seas with lower frequency.     

Environmental and socioeconomic dynamics of the Indian Ocean tsunami in Penang,Malaysia

This paper addresses some of the environmental and socioeconomic dimensions of the 2004 Indian Ocean tsunami on Penang, Malaysia. We aim to offer wide access to unique and perishable data, while at the same time providing insight to ongoing debates about hazards, vulnerability and social capital. Our social survey examines some of the dynamics that shaped the tsunami impact, response and recovery process. While in terms of lives lost Penang may not conform to arguments surrounding vulnerable environments, the recovery process is more marked by social disparities in terms of the ability to access resources. Our physical survey records local topography, flow depth and flow direction, and charts the differential impact of the tsunami. Yet measuring hazards is not a straightforward process, and relies on reflexive methodologies and eyewitness accounts.     

A Bayesian probabilistic approach for structure damage detection

A Bayesian probabilistic approach is presented for the damage detection of multistorey frame structures. In this paper, a Bayesian probabilistic approach is applied to identify multiple damage locations using estimated modal parameters when (1) the measurement data are potentially corrupted with noise, (2) only a small number of degrees of freedom are measured, and (3) a few fundamental modes are estimated. To reduce the potentially intensive computational cost of the proposed method, a branch-and-bound search scheme is proposed and a simplified approach for the modelling of multistorey frame structures is employed. A six-storey shear frame example and two multistorey frame examples, with multiple damage locations, are presented to illustrate the applicability of the proposed approach. © 1997 John Wiley & Sons, Ltd.     

An experimental study of temperature effect on modal parameters of the Alamosa Canyon Bridge

Damage detection techniques have been proposed to exploit changes in modal parameters and to identify the extent and location of damage in large structures. Most of such techniques, however, generally neglect the environmental effects on modal parameters. Such environmental effects include changes in loads, boundary conditions, temperature, and humidity. In fact, the changes due to environmental effects can often mask more subtle structural changes caused by damage. This paper examines a linear adaptive model to discriminate the changes of modal parameters due to temperature changes from those caused by structural damage or other environmental effects. Data from the Alamosa Canyon Bridge in the state of New Mexico were used to demonstrate the effectiveness of the adaptive filter for this problem. Results indicate that a linear four-input (two time and two spatial dimensions) filter to temperature can reproduce the natural variability of the frequencies with respect to time of day. Using this simple model, we attempt to establish a confidence interval of the frequencies for a new temperature profile in order to discriminate the natural variation due to temperature. Copyright © 1999 John Wiley & Sons, Ltd.     

A Lagrangian biogeochemical study of an eddy in the Northeast Atlantic

We report the results of an experiment in the Northeast Atlantic in which sulphur hexafluoride (SF₆) was released within an eddy and the behaviour of trace gases, nutrients and productivity followed within a Lagrangian framework over a period of 24 days. Measurements were also made in the air above the eddy in order to estimate air-sea exchange rates for some components. The physical, biological and biogeochemical properties of the eddy resemble those of other eddies studied in this area, suggesting that the results we report may be applicable beyond the specific eddy studied. During a period of low wind speed at the start of the experiment, we are able to quantitatively describe and balance the nutrient and carbon budgets for the eddy. We also report concentrations of various trace gases in the region which are similar to those observed in other studies and we estimate exchange rates for several trace gases. We show that the importance of gas exchange over other loss terms varies with time and also varies for the different gases. We show that the various trace gases considered (CO₂, dimethyl sulphide (DMS), N₂O, CH₄, non-methane-hydrocarbons, methyl bromide, methyl iodide and volatile selenium species) are all influenced by physical and biological processes, but the overall distribution and temporal variability of individual gases are different to one another. A storm disrupted the stratification in the eddy during the experiment, resulting in enhanced nutrient supply to surface waters, enhanced gas exchange rates and a change in plankton community, which we quantify, although overall productivity was little changed. Emphasis is placed on the regularity of storms in the temperate ocean and the importance of these stochastic processes in such systems.     

Wave effects in global ocean modeling: parametrizations vs. forcing from a wave model

One of the main challenges of the Copernicus Marine Service is the implementation of coupled ocean/waves systems that accurately estimate the momentum and energy fluxes provided by the atmosphere to the ocean. This study aims to investigate the impact of forcing the Nucleus for European Modelling of the Ocean (NEMO) ocean model with forecasts from the wave model of Météo-France (MFWAM) to improve classical air-sea flux parametrizations, these latter being mostly driven by the 10-m wind. Three wave-related processes, namely, wave-state-dependent stress, Stokes drift-related effects (Stokes-Coriolis force, Stokes drift advection on tracers and on mass), and wave-state-dependent surface turbulence, are examined at a global scale with a horizontal resolution of 0.25°. Three years of sensitivity simulations (2014–2016) show positive feedback on sea surface temperature (SST) and currents when the wave model is used. A significant reduction in SST bias is observed in the tropical Atlantic Ocean. This is mainly due to the more realistic momentum flux provided by the wave model. In mid-latitudes, the most interesting impact occurs during the summer stratification, when the wind is low and the wave model produces a reduction in the turbulence linked with wave breaking. Magnitudes of the large-scale currents in the equatorial region are also improved by 10% compared to observations. In general, it is shown that using the wave model reduces on average the momentum and energy fluxes to the ocean in tropical regions, but increases them in mid-latitudes. These differences are in the order of 10 to 20% compared with the classical parametrizations found in stand-alone ocean models.     

Street-Frontage-Net: urban image classification using deep convolutional neural networks

ABSTRACT

Quantifying aspects of urban design on a massive scale is crucial to help develop a deeper understanding of urban designs elements that contribute to the success of a public space. In this study, we further develop the Street-Frontage-Net (SFN), a convolutional neural network (CNN) that can successfully evaluate the quality of street frontage as either being active (frontage containing windows and doors) or blank (frontage containing walls, fences and garages). Small-scale studies have indicated that the more active the frontage, the livelier and safer a street feels. However, collecting the city-level data necessary to evaluate street frontage quality is costly. The SFN model uses a deep CNN to classify the frontage of a street. This study expands on the previous research via five experiments. We find robust results in classifying frontage quality for an out-of-sample test set that achieves an accuracy of up to 92.0%. We also find active frontages in a neighbourhood has a significant link with increased house prices. Lastly, we find that active frontage is associated with more scenicness compared to blank frontage. While further research is needed, the results indicate the great potential for using deep learning methods in geographic information extraction and urban design.     

Uncertainties in gas exchange parameterization during the SAGE dual-tracer experiment

A dual tracer experiment was carried out during the SAGE experiment using the inert tracers SF₆ and ³He, in order to determine the gas transfer velocity, k, at high wind speeds in the Southern Ocean. Wind speed/gas exchange parameterization is characterised by significant variability and we examine the major measurement uncertainties that contribute to that scatter. Correction for the airflow distortion over the research vessel, as determined by computational fluid dynamics (CFD) modelling, had the effect of increasing the calculated value of k by 30%. On the short time scales of such experiments, the spatial variability of the wind field resulted in differences between ship and satellite QuikSCAT winds, which produced significant differences in transfer velocity. With such variability between wind estimates, the comparison between gas exchange parameterizations from diverse experiments should clearly be made on the basis of the same wind product. Uncertainty in mixed layer depth of ∼10% arose from mixed layer deepening at high wind speed and limited resolution of vertical sampling. However the assumption of equal mixing of the two tracers is borne out by the experiment. Two dual tracer releases were carried out during SAGE, and showed no significant difference in transfer velocities using QuikSCAT winds, despite the differences in wind history. In the SAGE experiment, duration limitation on the development of waves was shown to be an important factor for Southern Ocean waves, despite the presence of long fetches.     

Genealogy of the Singaporean black‐and‐white house

The distinctive black‐and‐white houses from Singapore's colonial era that survive in enclaves as fine dwellings for the present‐day elite have been recognized and documented as a type. In this paper we tell the story of their cultural formation, which is one of remarkable hybridity. Various influences were brought to bear and resolved into the black‐and‐white house‐type, which was not invented ‘all at once’ in Singapore, but developed over the course of more than two centuries. We begin the story in India, when British settlers learnt from local Bengali practices to make serviceable dwellings for a climate that they found difficult. The overhanging roofs that shaded walls and the tall internal volumes were formalized with reference to European expectations of geometry and finish, and the bungalow was born. In British Malaya the bungalow was further hybridized with the house on stilts that was well known to the indigenous tradition. This produced the spatial configuration that is to be found also in the Singapore houses, with their extensive verandas on an upper floor level. Their distinctive colouring comes from a different tradition: the black‐and‐white Tudoresque style that was very popular in Britain and sometimes called ‘Old English’. This was used by the British colonizers so that they could feel more at home in surroundings that were in a far‐off foreign cultural environment.     

Biofilms and Size Sorting of Fine Sediment During Erosion in Intertidal Sands

The goal of this research was to investigate size-specific retention of clay and silt-sized grains by biofilms in sandy intertidal sediments. Sediment cores were collected from an intertidal flat in Cole Harbour, NS, and eroded at increasing shear stresses (0.08–0.60 Pa) with a Gust microcosm. Half of the cores were eroded without undergoing prior treatment, while sodium hypochlorite was added to the other cores to destroy biofilms. The disaggregated inorganic grain size distribution of sediment resuspended by the Gust microcosm was then obtained with a Multisizer^? 3 Coulter Counter®, and each treated core was compared with its corresponding untreated core. Overall, significantly less total sediment mass was resuspended from untreated cores than from treated cores. At intermediate shear stresses, the sediment resuspended from treated cores contained a greater proportion of fine and medium silts than the sediment resuspended from untreated cores. Very fine silts and clays were not retained preferentially by biofilms. The results show that biofilms stabilize the sediment, but they do not necessarily enhance the proportion of finest sediment sizes, as previously proposed.