Measuring accident risk exposure for pedestrians in different micro-environments

Pedestrians are mainly exposed to the risk of road accident when crossing a road in urban areas. Traditionally in the road safety field, the risk of accident for pedestrian is estimated as a rate of accident involvement per unit of time spent on the road network. The objective of this research is to develop an approach of accident risk based on the concept of risk exposure used in environmental epidemiology, such as in the case of exposure to pollutants. This type of indicator would be useful for comparing the effects of urban transportation policy scenarios on pedestrian safety. The first step is to create an indicator of pedestrians’ exposure, which is based on motorised vehicles’ “concentration” by lane and also takes account of traffic speed and time spent to cross. This is applied to two specific micro-environments: junctions and mid-block locations. A model of pedestrians’ crossing behaviour along a trip is then developed, based on a hierarchical choice between junctions and mid-block locations and taking account of origin and destination, traffic characteristics and pedestrian facilities. Finally, a complete framework is produced for modelling pedestrians’ exposure in the light of their crossing behaviour. The feasibility of this approach is demonstrated on an artificial network and a first set of results is obtained from the validation of the models in observational studies.     

Application of an Anisotropic Constitutive Model for Structured Clay to Seismic Slope Stability

The anisotropic nature of response and degradation of shear strength from the undisturbed condition to the remolded state are two fundamental and challenging aspects of response in some clay deposits. This paper presents a comprehensive, yet flexible and practical, version of the SANICLAY model and its application to a seismic slope-stability problem. The model is based on the well-known isotropic modified Cam-Clay model with two additional mechanisms to account for anisotropy and destructuration. The model has been efficiently implemented in a three-dimensional (3D) continuum, coupled, dynamic, finite-difference program. The program has been used to analyze the seismic response of clay slopes to gain better insight into the role of the previously mentioned parameters in real applications. Different aspects of the model, including anisotropy and destructuration, and their effects on the earthquake-induced strains and deformations in the slope have then been explored and presented. By providing a link between the model parameters and the soil’s undrained shear strength, which is a well-known engineering parameter, a benchmark comparison has been made between the results of the present advanced model and those of an engineering approach. To this end, a modified Newmark sliding-block analysis has been used, in which the yield acceleration is gradually reduced as block sliding progresses during the earthquake. It is observed that although the two analyses display the same trends, the modified Newmark sliding-block method provides conservative results compared with those obtained from the developed simulation model.     

A solution to efficient power allocation for H.264/SVC video transmission over a realistic MIMO channel using precoder designs

In this paper we propose a novel scheme for real time SVC-based video transmission over MIMO channels in the context of Joint Source Channel Coding (JSCC). This scheme compares the transmission of the H.264/SVC video over four precoder solutions, namely Max-SNR, WF, QoS and E-d_min. We exploit the high flexibility of the QoS precoder to minimize the total distortion of the received video. The proposed adaptive QoS precoder takes into account the scalability of the H.264/SVC standard jointly with the instantaneous MIMO channel statue. Finally, the proposed scheme is evaluated over both statistical and time varying realistic MIMO channels.This study provides the performance of these four precoder designs in term of BER, ML decoder complexity and the quality of the received video. We show that the precoder solutions providing the best BER performance are not usually the most appropriate for real time video transmission. However, the adaptive QoS precoder which uses three configurations, by considering both the importance of the video bitstream and the channel statue, provides the best Rate-Distortion performance regardless the channel conditions.We assess the accuracy of these four precoder solutions against channel estimation errors over time varying realistic MIMO channel. The results shows that the adaptive QoS precoder remains robust against channel estimation errors even at high mobility speed.     

Hydroforming of anisotropic aluminum tubes: Part II analysis

Part I presented an experimental investigation of hydroforming of Al-6260-T4 tubes and a simple two-dimensional model of the process. Relatively long, extruded circular tubes were formed against a square die with rounded corners, with simultaneous application of axial feeding. Localized wall thinning was reported to occur at mid-span which, accentuated by friction, led to burst. Part II presents fully 3D models of the process that include friction as well as more advanced constitutive models shown in previous studies to be essential for simulation of burst in free hydroforming of aluminum alloy tubes. The models are used to simulate several of the experiments of Part I, emphasizing the prediction of all aspects of the forming process, including wall thinning and its localization that lead to rupture. A shell element model is shown to capture the majority of the structural features of the process very successfully. However, even with the implementation of advanced constitutive models, it fails to reproduce correctly the localization of wall thinning. It is demonstrated that switching to solid elements coupled to non-quadratic yield functions results in accurate predictions of all aspects of the problem, including the onset of rupture. Apparently, slow growing depressions that develop at the interface between the flattened part of the cross section that is in contact with the die and the rounded part that is not, have a complex three dimensional stress state requiring accurate modeling offered by solid elements. Furthermore, the evolution of these depressions is only reproduced with accuracy when in addition non-quadratic yield functions are adopted.     

Raman enhancement of rhodamine adsorbed on Ag nanoparticles self-assembled into nanowire-like arrays

ABSTRACT: This work reports on Raman scattering of rhodamine (R6G) molecules absorbed on either randomly distributed or grating-like arrays of approximately 8-nm Ag nanoparticles developed by inert gas aggregation. Optimal growth and surface-enhanced Raman scattering (SERS) parameters have been obtained for the randomly distributed nanoparticles, while effects related to the aging of the silver nanoparticles were studied. Grating-like arrays of nanoparticles have been fabricated using line arrays templates formed either by fracture-induced structuring or by standard lithographic techniques. Grating structures fabricated by both methods exhibit an enhancement of the SERS signal, in comparison to the corresponding signal from randomly distributed Ag nanoparticles, as well as a preferential enhancement in the areas of the sharp features, and a dependence on the polarization direction of the incident exciting laser beam, with respect to the orientation of the gratings structuring. The observed spectroscopic features are consistent with a line-arrangement of hot-spots due to the self- alignment of metallic nanoparticles, induced by the grating-like templates.     

Martensite Formation in Conventional and Isothermal Tension of 304 Austenitic Stainless Steel Measured by X-ray Diffraction

The temperature above which neither stress nor plastic strain can cause austenite to transform to martensite is determined for 304 austenitic stainless steel by X-ray diffraction measurements on specimens that were previously subjected to isothermal tension tests. The specimens were tested at 273 K, 298 K, 308 K, 333 K, and 373 K (0 °C, 25 °C, 35 °C, 60 °C, and 100 °C). A new isothermal testing technique was used not only for controlling the testing temperature but also for averting deformation-induced heating. Hence, the effect of temperature on the strain-induced martensite is decoupled from that of strain. The diffraction measurements reveal that the martensite volume fraction decreases linearly with the testing temperature up to a critical temperature, which is found by linearly extrapolating to zero martensite volume fraction.     

Plasticity Model for Sand under Small and Large Cyclic Strains

A plasticity constitutive model for sands is proposed, which combines a bounding surface framework for large cyclic strains with a Ramberg-Osgood-type hysteretic formulation for relatively smaller strains. The distinction between small and large cyclic strains is based on the volumetric threshold cyclic shear strain γtv, a well-established geotechnical parameter. The state parameter ψ is used explicitly to interrelate the critical, peak, and dilatancy deviatoric stress ratios. The plastic modulus is expressed as a particular function of accumulated plastic volumetric strain, which simulates empirically the effect of fabric evolution during shearing. Extensive comparisons with experiments show accurate simulation of the basic aspects of cyclic behavior for a wide range of cyclic strain amplitudes, specifically, (1) the degradation of shear modulus and increase of hysteretic damping with cyclic shear strain amplitude; (2) the evolving rates of shear strain and excess pore pressure (or volumetric strain) accumulation with number of cycles; and (3) the resistance to liquefaction. The 14 model parameters are proven independent of initial and drainage conditions, as well as the cyclic shear strain amplitude. The simulation of monotonic shearing is equally accurate.     

Correction to: Classifying MOOC forum posts using corpora semantic similarities: a study on transferability across different courses

Neural Computing and Applications - A correction to this paper has been published: https://doi.org/10.1007/s00521-021-05904-z