Great cities look small

Great cities connect people; failed cities isolate people. Despite the fundamental importance of physical, face-to-face social ties in the functioning of cities, these connectivity networks are not explicitly observed in their entirety. Attempts at estimating them often rely on unrealistic over-simplifications such as the assumption of spatial homogeneity. Here we propose a mathematical model of human interactions in terms of a local strategy of maximizing the number of beneficial connections attainable under the constraint of limited individual travelling-time budgets. By incorporating census and openly available online multi-modal transport data, we are able to characterize the connectivity of geometrically and topologically complex cities. Beyond providing a candidate measure of greatness, this model allows one to quantify and assess the impact of transport developments, population growth, and other infrastructure and demographic changes on a city. Supported by validations of gross domestic product and human immunodeficiency virus infection rates across US metropolitan areas, we illustrate the effect of changes in local and city-wide connectivities by considering the economic impact of two contemporary inter- and intra-city transport developments in the UK: High Speed 2 and London Crossrail. This derivation of the model suggests that the scaling of different urban indicators with population size has an explicitly mechanistic origin.     

A Program for Reliability Evaluation of Undirected Networks via Polygon-to-Chain Reductions

This paper discusses the design and implementation of PolyChain, a FORTRAN program for reliability evaluation of undirected networks of a special structure via polygon-to-chain reductions. Theoretical results presented by Satyanarayana & Wood are reviewed. The program's design and its implementation in FORTRAN are described. A small problem is tested illustrating the code's output. Several large problems are run to evaluate the code's performance capabilities.     

Effect of calcination temperature on structure and thermoelectric properties of CuAlO<Subscript>2</Subscript> powders

Copper aluminum oxide (CuAlO₂) with delafossite phase was synthesized by the Pechini method using different calcination temperatures to evaluate its influence on the structure and thermoelectric material properties. X-ray diffraction and Raman spectroscopy confirm that delafossite phase was formed at 1100 °C with the presence of 2H-CuAlO₂ and Al₂O₃ impurities, while at lower calcination temperatures (900 and 1000 °C), a mixture of CuO + CuAl₂O₄ (spinel phase) was observed. Energy-dispersive X-ray elemental maps display an even distribution of copper, aluminum and oxygen in the sample calcined at 1100 °C. Direct optical band gap, E _g = 3.6 eV, was calculated from reflectance diffuse spectra by Kubelka–Munk and Tauc methods. An absorption band at 1.7 eV accounts for defect levels, masking the characteristic indirect transition. The thermoelectric properties, such as Seebeck coefficient, and thermal and electrical conductivities of the sample calcined at 1100 °C were measured at different temperatures. Hall voltage and positive values of the Seebeck coefficient (425.8–434.4 µV K^?1) confirm the material’s p-type character. The independence of the Seebeck coefficient on the operation temperature indicates a small polaron electrical conduction mechanism. Thermal conductivity decreases exponentially with the temperature from 43.45 to 23.9 W m^?1 K^?1, where the principal contribution is due to phonons. Figure of merit ZT of sample calcined at 1100 °C between 100 and 800 °C increases from 1.42 × 10^?8 to 4.94 × 10^?4 in the order of the literature reports. From the Arrhenius plot ln(σT) versus 1000/T, an activation energy E _a = 0.32 eV for the electrical conductivity was calculated.     

Hybridizations of GRASP with path relinking for the far from most string problem

Among the sequence selection and comparison problems, the far from most string problem (FFMSP) is one of the computationally hardest with applications in several fields, including molecular biology where one is interested in creating diagnostic probes for bacterial infections or in discovering potential drug targets. In this paper, we describe several heuristics that hybridize GRASP with different path‐relinking strategies, such as forward, backward, mixed, greedy randomized adaptive forward, and evolutionary path relinking. Experiments on a large set of both real‐world and randomly generated test instances indicate that these hybrid heuristics are both effective and efficient. In particular, the hybrid GRASP with evolutionary path relinking finds slightly better quality solutions compared to the other variants when running for the same number of iterations, while the hybrid with backward path relinking finds better quality solution within a fixed running time.     

Analysis of the correlation structure of square time series

Abstract.  This paper analyses the asymptotic behaviour of the autocorrelation structure exhibited by squares of time series with a Wold expansion where the input error is a sequence of random variables with mean zero and finite kurtosis. Two important cases are discussed: (i) when the errors are independent and, (ii) when the errors are uncorrelated but their squares are correlated. Both situations are addressed when the process exhibits short or long memory. Consequences of these results on certain models widely used in many disciplines are also discussed.     

Selecting feature lines in generalized dissimilarity representations for pattern recognition

Recently, generalized dissimilarity representations have shown their potential for small sample size problems. In generalizations by feature lines, instead of dissimilarities with objects, we have dissimilarities with feature lines. One drawback of such generalization is the high amount of generated lines that increases computational costs and may provide redundant information. To overcome this, the selection of lines based on the length of the line segments has been considered in previous works, showing good results for correlated data. In this paper, we propose a new supervised criterion for the selection of feature lines. Experimental results show that the proposed criterion obtains competitive or better results than those obtained by previous criteria, especially for data with high intrinsic dimension, spherical data and data with outliers. As our proposal provides better results for small representation sets, it allows one to obtain a good trade-off between classification accuracy and computational efficiency.     

Effect of the O2/CO2 ratio and welding current on the geometry of square groove weld joints in low carbon steels obtained with GMAW

Welding with fusible electrode and shielding gas (GMAW) using a shielding mixture based on CO₂ + O₂ is a procedure with high potential for joining low-carbon and low-alloy steels compared with traditional mixtures based on argon. One of the reasons for this is related to the possibility of achieving a high penetration level without the need to increase the heat supply of the electric arc, by employing the shielding mixture of CO₂ + O₂, and the consequent decrease in the consumption of energy carriers. For that reason, the present paper presents a study on the influence of the shielding atmosphere characteristics (O₂/CO₂ ratio) and the welding current in the geometry of square groove weld joints on plates. For this purpose, a factorial experimental design was applied to obtaining regression equations, which would map such a behaviour. The equations were obtained using the O₂/CO₂ ratio and the welding current as independent variables. Nomograms were also plotted in order to make it easier to apply the results of this paper.     

The Use of Elevation Map Histograms for Topographic Heterogeneity Analysis

Surface defects are extremely important in mechanical characterization of several different materials. Therefore, the analysis of surface finishing is essential for a further simulation of surface mechanical properties in a customized project in materials science and technology. One of the methods commonly employed for such purpose is the statistical mapping of different sample surface regions using the depth from focus technique. The analysis is usually performed directly from the elevation maps which are obtained from the digital image processing. In this paper, the possibility of quantifying the surface heterogeneity of Silicon Carbide porous ceramics by elevation map histograms is presented. The advantage of this technique is that it allows the qualitative or quantitative verification of all surface image fields that cannot be done by using the Surface Plot plugin of image J? platform commonly used in digital image processing.     

Luminescent polydibenzothiophene thin film obtained by glow discharge method

This work presents the synthesis by plasma and characterization of luminescent polymer thin films of dibenzothiophene (DBT) by plasma polymerization. The DBT is solid at room conditions and was sublimated and introduced to the plasma reactor to produce the chemical reactions with the vapors. The results indicated the production of polymers with benzene and thiophene rings in the structure as well as methylene groups. The polymer structure was studied by Fourier transform infrared spectroscopy and ¹³C‐CPMAS. The thermal analysis showed a residual mass of 60% at 800°C, which suggests a great thermal resilience in the polymer. The critical superficial tension was calculated with a Zisman plot and was 25 mN/m. The polymer has a fluorescent green emission between 400 and 660 nm and an orange emission between 660 and 850 nm. This effect can be a consequence of the electronic distribution along the structure in aliphatic and aromatic segments with benzene and thiophene rings. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011