New evidence on the specification and performance of neoclassical gravity models in the study of urban transportation

Gravity models with power and exponential resistance functions are derived using constrained neoclassical utility maximization. Both equations are then fitted to a set of weekday motor vehicle traffic data describing trips in the Los Angeles, California, area for the year 1966, using multiple linear regression analysis. The equation with the power resistance function gives the better fit for all twenty origin areas analyzed. This result ensues because the reciprocal of the power resistance function is more flexible; it can vary from concave to highly convex, but the exponential cannot. Analysis of estimated regression coefficients shows that the great majority of tripmakers was constrained by a convex time cost function rather than the concave money cost of travel in all but two of the poorest origin areas. The implications of these results for the understanding of automobile travel in urban areas are discussed.     

A complementary metal–oxide semiconductor digitally programmable current conveyor

A second‐generation current conveyor with digitally programmable current gains is presented. A current division network with zero standby power consumption is utilized in two different ways to provide both gain and attenuation of the second‐generation current conveyor's current transfer characteristics. The proposed topology overcomes several drawbacks of the previous solutions through affording a more power and area efficient solution while exhibiting relatively wider tuning range and bandwidth. A variable‐gain amplifier and a two‐integrator‐loop filter biquad providing low‐pass and band‐pass responses are given as application examples. A modified two‐integrator‐loop topology is developed to offer independent control of the pole frequency and quality factor without disturbing the passband gain. Simulation results obtained from a standard 0.18 µm complementary metal–oxide semiconductor process are given. Copyright © 2011 John Wiley & Sons, Ltd.     

A novel hybrid photovoltaics/thermoelectric cooler distillation system

In this paper, a novel hybrid photovoltaics/thermoelectric cooler (PV/TEC) distillation system has been introduced. The limitation for distillation system working under hot arid climate is the heat removal required for the condensation process. The novelty of the proposed system is that it utilizes TEC to improve the condensation process. The proposed system composed of two porous layers separated by an air gap. The upper porous layer is installed at the back of a PV module; the lower porous layer is installed at the top of a TEC modules layer. This system can provide the demand of electricity and potable water for those people who live in rural areas (using one unit or more). The proposed system prevents PV module from overheating and actively enhancing the condensation process of the evaporated water. A steady‐state mathematical model has been proposed. This model was solved and simulated by equation solver software. Wind speed, solar radiation, and ambient temperature effect on the system performance were simulated and discussed. Results showed that the maximum productivity of the system reached an ambient temperature of 298 K, solar radiation of 1000 W/m² and wind speed of 5.5 m/s. The maximum yield of the system was 4.2 kg of distilled water per day with a net electrical output power of 73 W with an overall efficiency of 57.9% and PV cell efficiency of 12.32%.     

A survey of current architectures for connecting wireless mobile ad hoc networks to the Internet

Connecting wired and wireless networks, and particularly mobile wireless ad hoc networks (MANETs) and the global Internet, is attractive in real‐world scenarios due to its usefulness and praticality. Because of the various architectural mismatches between the Internet and MANETs with regard to their communication topology, routing protocols, and operation, it is necessary to introduce a hybrid interface capable of connecting to the Internet using Mobile IP protocol and to MANETs owing to an ad hoc routing protocol. Specifically, the approaches available in the literature have introduced updated versions of Mobile IP agents or access points at the edge of the Internet to help MANET nodes get multi‐hop wireless Internet access. The main differences in the existing approaches concern the type of ad hoc routing protocol as well as the switching algorithm used by MANET nodes to change their current Mobile IP agents based on specific switching criteria. This paper surveys a variety of approaches to providing multi‐hop wireless Internet access to MANET nodes. Copyright © 2006 John Wiley & Sons, Ltd.     

A mathematical model for breast cancer lesion estimation: electrical impedance technique using TS2000 commercial system

We present a mathematical model to analyze transadmittance data for the detection of breast cancer using TransScan TS2000 commercial system. The model was constructed based on the assumption that a lesion exists near the surface of a breast region. The breast region that is considered as a background is assumed to be homogeneous at least near the surface where we attach a planar array of electrodes. Based on the model, we developed a lesion estimation algorithm utilizing single- or multifrequency transadmittance data. The approximate ratio of two conductivity values for the lesion and background needs to be known to estimate the size of the lesion even though the location estimate does not require this ratio. From the results of numerical simulations with added noise, we suggest better ways of interpreting TS2000 transadmittance images for the detection of breast cancer with improved accuracy. Since this study provides a rigorous mathematical modeling of TS2000 commercial system, it will be possible to apply the technique to lesion estimation problems based on more realistic models of breast regions in future studies.     

Assessment of wind-generation potentiality in Jordan using the site effectiveness approach

Wind data gathered over 3–10 years is used for a feasibility analysis of optimum future utilization of wind-generator potentiality in 22 sites covering all landscape types and regions in Jordan. The yearly mean wind speed and the yearly average available wind energy flux were computed for each site. Yearly mean wind speeds at a height of 24 m could reach as high as 7.6 m/s and available wind energy flux close to 3 MWh/m²/year could be attained. Detailed technical assessment for the nine most promising potential wind sites was made using the site effectiveness approach. The maximum site effectiveness and its corresponding cut-in speed were indicated, both of which depended on the site. The investigation was performed assuming three models of small and medium size wind machines representing different ranges of characteristic speeds and rated power suitable for water pumping and electric supply. The results show that small and medium wind turbines could be installed in the highlands and desert regions and utilized for water supply and electrical power generation, provided the correct wind machine-site is selected.     

Promotion effect in Pt–ZnO catalysts for selective hydrogenation of crotonaldehyde to crotyl alcohol: A structural investigation

Pt–ZnO catalysts prepared from different precursors, H₂PtCl₆ and Pt(NH₃)₄(NO₃)₂, and reduced at increased temperatures are used to achieve high selectivity towards crotyl alcohol in hydrogenation of crotonaldehyde. The ex-chloride catalyst shows a higher activity and selectivity than the ex-nitrate one. Transmission electron microscopy, electron diffraction, high-resolution imaging, energy dispersive X-ray spectroscopy and element mapping are used to characterize the catalysts in order to correlate the microstructure to the catalytic behavior. PtZn alloy formation is confirmed for both ex-chloride and ex-nitrate catalysts reduced at 673 K. The metal particles in ex-nitrate catalyst are smaller in size than those in ex-chloride. In most aggregates of the ex-chloride catalyst, chlorine is distributed homogeneously with low concentration (<1%). The higher chlorine concentration in some region leads to local morphology and microstructure changes. Influences of the observed structural features such as alloy formation, particle size difference, formation of ill-defined material, and chlorine distribution are discussed.     

Hybrid Petri Nets for Modeling and Analysis of Microgrid Systems

Hybrid Petri nets (HPNs) are widely used to describe and analyze various industrial hybrid systems that have both discrete-event and continuous discrete-time behaviors. Recently, many researchers attempt to utilize them to characterize power and energy systems. This work proposes to adopt an HPN to model and analyze a microgrid that consists of green energy sources. A reachability graph for such a model is generated and used to analyze the system properties.      

Feature detection and tracking in optical flow on non-flat manifolds

Optical flow is a classical approach to estimating the velocity vector fields associated to illuminated objects traveling onto manifolds. The extraction of rotational (vortices) or curl-free (sources or sinks) features of interest from these vector fields can be obtained from their Helmholtz-Hodge decomposition (HHD). However, the applications of existing HHD techniques are limited to flat, 2D domains. Here we demonstrate the extension of the HHD to vector fields defined over arbitrary surface manifolds. We propose a Riemannian variational formalism, and illustrate the proposed methodology with synthetic and empirical examples of optical-flow vector field decompositions obtained on a variety of surface objects.