Speed limit reduction in urban areas: A before–after study using Bayesian generalized mixed linear models

In fall 2009, a new speed limit of 40 km/h was introduced on local streets in Montreal (previous speed limit: 50 km/h). This paper proposes a methodology to efficiently estimate the effect of such reduction on speeding behaviors. We employ a full Bayes before–after approach, which overcomes the limitations of the empirical Bayes method. The proposed methodology allows for the analysis of speed data using hourly observations. Therefore, the entire daily profile of speed is considered. Furthermore, it accounts for the entire distribution of speed in contrast to the traditional approach of considering only a point estimate such as 85th percentile speed. Different reference speeds were used to examine variations in the treatment effectiveness in terms of speeding rate and frequency. In addition to comparing rates of vehicles exceeding reference speeds of 40 km/h and 50 km/h (speeding), we verified how the implemented treatment affected “excessive speeding” behaviors (exceeding 80 km/h). To model operating speeds, two Bayesian generalized mixed linear models were utilized. These models have the advantage of addressing the heterogeneity problem in observations and efficiently capturing potential intra-site correlations. A variety of site characteristics, temporal variables, and environmental factors were considered. The analyses indicated that variables such as lane width and night hour had an increasing effect on speeding. Conversely, roadside parking had a decreasing effect on speeding. One-way and lane width had an increasing effect on excessive speeding, whereas evening hour had a decreasing effect. This study concluded that although the treatment was effective with respect to speed references of 40 km/h and 50 km/h, its effectiveness was not significant with respect to excessive speeding-which carries a great risk to pedestrians and cyclists in urban areas. Therefore, caution must be taken in drawing conclusions about the effectiveness of speed limit reduction. This study also points out the importance of using a comparison group to capture underlying trends caused by unknown factors.     

Evaluation of pressure coefficients and estimation of air flow rates in buildings employing wind towers

Wind pressure coefficients at various openings of a wind tower were determined by testing a scale model of the building in a boundary layer wind tunnel. Wind towers (or Baud-Geers) are structures which have been employed in Iran and neighbouring countries for natural ventilation and passive cooling. Tests were conducted on an isolated tower, the tower and adjoining house, and the tower and house surrounded by a courtyard. The wind pressure coefficients at the tower and house openings were determined at various wind angles for two types of terrain: suburban and open country. The air flow rates were then estimated from a knowledge of the wind pressure coefficients at the building apertures. It was concluded that the presence of a courtyard around the structure and the angle of incidence of the wind influence the rate and the direction of air flowing from the tower to the house. If leeward openings of the tower can be closed (for example, by automatic dampers) restricting the air leaving these apertures, the air flow rate from the tower to the house can be greatly increased. The results of this investigation are believed to provide assistance to architects and engineers in the design of wind towers for desired ventilation rates in buildings.     

Natural production, storage, and utilization of ice in deep ponds for summer air conditioning

A design is proposed to improve the performance of wind towers (or Baud-Geers) for natural ventilation and passive cooling. Under similar climatological and design conditions, the new design is capable of delivering air to the building at higher flow rates. It can also cool the air evaporatively to lower temperatures. Higher airflow rates and the evaporative cooling capability of the new Baud-Geer design can be fully utilized at nigh in summer to cool the building mass to lower temperatures.Momentum, mass and energy analyses are carried out for the proposed design. The results are presented in graphical forms which may be used as guidelines for employing the design for specific applications in the hot, arid areas of the world. An example is worked out to show the use of the results.     

Tensile behaviour of patch-repaired CFRP laminates

The present study examines the tensile behaviour of composite structures repaired by bonding external patches. Various patches of different stacking sequences placed on both sides of the parent plate were considered. Damage development and the failure process of the repaired plates were analyzed and a parent plate fracture model has been proposed. Optimised patch repairs were calculated by finite element modelling. It was found that high stress concentration along the longitudinal edges of circular patches and/or at the transverse edges of the hole leads to early damage initiation in the parent plate. However, the position of damage initiation and the process of damage progression depend particularly on the properties of repair patches. In order to optimise patch repairs, finite element modelling was used and it was founded possible to attain over 90% of the strength of an unnotched specimen. The optimised patch design can be characterised by an optimal strength ratio R^*, which should be minimized when selecting repair parameters.     

Highly efficient dye-sensitized solar cell prepared by electrophoretic deposition method: the effect of TiO<Subscript>2</Subscript> films thickness on the performance of cells

In this work, nanocrystalline P25 TiO₂ films with different thicknesses were deposited on FTO coated glass substrates by an electrophoretic deposition technique (EPD) and applied as the work electrode for dye-sensitized solar cells (DSSC) using cis-bis(isothiocyanato)(2,2'-bipyridyl-4,4'-dicarboxylato)(4,4'di-nonyl-2'-bipyridyl) ruthenium(II) (Z907, Dyesol) as sensitizing dye.The results showed that the increasing the thickness of TiO₂ films lead to increase the adsorption of the dye on the TiO₂ layers which in turns improved the short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc), respectively. Furthermore, it was found that the effects of the surface states on the recombination of the photo-injected electrons (electron–hole pairs) in the TiO₂ films strongly depend on theTiO₂ electrode annealing temperature. Finally, a DSSC with a 32.82 μm thickness for TiO₂ film annealed at 600°C produced the highest conversion efficiency with an incident solar energy of 100 mW/cm² (η = 8.23%, J_sc = 15.98, V_oc = 0.73, FF = 0.7).     

Stability problems in universal current-mode filters

Analog circuit designers have usually focused on the design of circuits employing a minimum number of components, occupying less area and dissipating less power. However, some important issues such as signal limitations and especially stability problems of the analog circuits have not received considerable attention in the literature. Hence, the work described in this paper deals with the stability problems of two new current-mode analog filters employing multiple output current controlled conveyors (MOCCCIIs). Toward that end, a single pole model is replaced for each non-ideal current gain of the MOCCCIIs. Both of the novel universal current-mode active-C filters can simultaneously realize low-pass, band-pass and high-pass/notch filter responses. SPICE and MATLAB simulation results are given to verify the theoretical analysis.     

Nonintrusive diagnostic techniques for measurements on coal-combustion systems

We present an overview of non-intrusive diagnostic techniques that are suitable for measurements on coal-combustion systems. In situ measurements require the use of procedures with high penetration depths in optically opaque two- or three-phase systems. Useful non-intrusive procedures are available for measurements of atomic constituents. Acoustic and microwave techniques have been employed and provide data on solid-phase mass flows, temperatures, velocities, and species concentrations. Data of the type needed for combustor modeling in order to effect real-time process control or combustor scaling have not been obtained and will require the development of new diagnostic tools such as X-ray and microwave or long-wavelength infrared tomography.     

Blind separation of piecewise stationary non-Gaussian sources

We address independent component analysis (ICA) of piecewise stationary and non-Gaussian signals and propose a novel ICA algorithm called Block EFICA that is based on this generalized model of signals. The method is a further extension of the popular non-Gaussianity-based FastICA algorithm and of its recently optimized variant called EFICA. In contrast to these methods, Block EFICA is developed to effectively exploit varying distribution of signals, thus, also their varying variance in time (nonstationarity) or, more precisely, in time-intervals (piecewise stationarity). In theory, the accuracy of the method asymptotically approaches Cramér–Rao lower bound (CRLB) under common assumptions when variance of the signals is constant. On the other hand, the performance is practically close to the CRLB even when variance of the signals is changing. This is demonstrated by comparing our algorithm with various methods that are asymptotically efficient within ICA models based either on the non-Gaussianity or the nonstationarity. The benefit of our algorithm is demonstrated by examples with real-world audio signals.     

Trade-offs in the OTA-based analog filter design

Operational transconductance amplifiers (OTAs) are widely used in the design of electronically tunable circuits. However, electronic tunability ranges of the OTA based filters are restricted by the limited bandwidth of the transconductance gain of the OTA. Furthermore, stability conditions and the linearity of the OTA which depends on the control current restrict the tunability. In this paper, some trade-offs in the electronically tunable filters are investigated. In addition, the tunability ranges of some first and second order OTA-C and OTA-RC filters are comparatively examined. Moreover, an OTA-C all-pass filter circuit is presented. SPICE simulations are performed and stability analyses are given for both of the OTA-C and OTA-RC filters. Operation of the presented all-pass filter is verified experimentally.     

All‐pass sections with rich cascadability and IC realization suitability

In this paper, two new circuit configurations for realizing voltage‐mode (VM) all‐pass sections (APSs) are presented. The proposed circuits employ only two differential voltage current conveyors (DVCCs) and are cascadable with other VM circuits due to their high‐input and low‐output impedances. The first configuration uses a grounded resistor and a grounded capacitor without requiring matching constraints, whereas the second employs two grounded resistors and a grounded capacitor with a single matching condition. While the first configuration can realize only one all‐pass response, the second can provide inverting and non‐inverting all‐pass responses with selection of appropriate input port. Adding two grounded resistors to the proposed filters, variable gain APSs can also be obtained. As applications, two quadrature oscillators, each of which using one of the proposed all‐pass circuits, one grounded resistor and one grounded capacitor are presented. SPICE simulation results are included to verify the theory. Copyright © 2010 John Wiley & Sons, Ltd.