Artificial neural networks and geostatistical models for housing valuations in urban residential areas

Property valuation studies often use classical statistics techniques. Among these techniques, the Artificial Neural Networks are the most applied, overcoming the inflexibility and the linearity of the hedonic models. Other researchers have used Geostatistics techniques, specifically the Kriging Method, for interpreting spatial-temporal variability and to predict housing unit prices. The innovation of this study is to highlight how the Kriging Method can help to better understand the urban environment, improving the results obtained by classical statistics. This study presents two different methods that share the general objective of extracting information regarding a city’s housing from datasets. The procedures applied are Ordinary Kriging (Geostatistics) and Multi-Layer Perceptron algorithm (Artificial Neural Networks). These methods were used to predict housing unit prices in the municipality of Pozuelo de Alarcon (Madrid). The implementation of both methods provides us with the urban characteristics of the study area and the most significant variables related to price. The main conclusion is that the Ordinary Kriging models and the Neural Networks models, applied to predicting housing unit prices are necessary methodologies to improve the information obtained in classical statistical techniques.

Abbreviations: ANN: Artificial Neural Networks; OK: ordinary Kriging; MLP: multi-layer perceptron     

Models of local governing coalitions: city politics and policy effects in Spanish municipalities

Local governance involves coalitions between public and private actors on policy issues. Actors participating in these coalitions may vary according to the issue in question, even within the same city. Based on a survey carried out among actors from different sectors of the local political community in four Spanish cities, governance networks are analyzed across five different issues: public housing, cultural tourism, urban regeneration, social policy, and citizen participation. Using network analysis and indexes in a comparative examination of 20 policy networks, we show that variations across networks are explained by policy issue content and supra-municipal regulations, regardless of the cities’ political characteristics.     

Scholte waves on fluid-solid interfaces by means of an integral formulation

The present work shows the propagation of Scholte interface waves at the boundary of a fluid in contact with an elastic solid, for a broad range of solid materials. It has been demonstrated that by an analysis of diffracted waves in a fluid it is possible to infer the mechanical properties of the elastic solid medium, specifically, its propagation velocities. For this purpose, the diffracted wave field of pressures and displacements, due to an initial wave of pressure in the fluid, are expressed using boundary integral representations, which satisfy the equation of motion. The source in the fluid is represented by a Hankel’s function of second kind and zero order. The solution to this wave propagation problem is obtained by means of the Indirect Boundary Element Method, which is equivalent to the well-known Somigliana representation theorem. The validation of the results is carried out by using the Discrete Wave Number Method and the Spectral Element Method. Firstly, we show spectra of pressures that illustrate the behavior of the fluid for each solid material considered, then, we apply the Fast Fourier Transform to show results in time domain. Snapshots to exemplify the emergence of Scholte’s waves are also included.     

Sediment and Water Discharge Assessment on Santiago and Pánuco Rivers (Central Mexico): The Importance of Topographic and Climatic Factors

This study explores the main factors controlling sediment and water discharge in the Santiago and Pánuco Rivers, the two largest rivers of central Mexico. Both Santiago and Pánuco Rivers are sourced in the Central Plateau of Mexico and flow in an opposite direction. Santiago River flows over a tectonically active margin draining to the Pacific Ocean, and Pánuco River flows into the passive margin of the Gulf of Mexico. Mean annual and monthly values of suspended sediment load and water discharge spanning around 50 years were used to evaluate sediment load and water discharge in these two rivers. Our findings indicated that Santiago River delivers to the ocean around 45% more sediment than Pánuco River. However, we found that Santiago River has about half the water discharge of Pánuco River. The high river gradient along Santiago River is likely to enhance the net erosion and sediment transport capacity. Water discharge at Pánuco Basin is higher than in Santiago Basin because the annual rainfall is higher for the former. The difference in sediment and water discharge for both rivers are also related to El Niño Southern Oscillation events. Our results indicated that water discharge in Santiago River increases during El Niño and La Niña events. In contrast, Pánuco River is mostly affected by La Niña events.     

Analytic hierarchy process approach for the selection of stream-gauging sites

ABSTRACT

This investigation proposes the use of the analytic hierarchy process (AHP) to evaluate potential sites for stream monitoring and broadcast of flood warnings. The methodology adopts variables established by the World Meteorological Organization (WMO) for the selection of stream-monitoring sites and incorporates new variables associated with the stream morphometry and hydraulics. The proposed approach quantifies subjective valuations through pairwise comparisons of judgements within the selection criteria. The uncertainty of expert judgement was assessed via Monte Carlo simulations and its effects on the resulting priority vector were analysed. This approach was applied on three main mountain watershed streams at which 11 alternative stream-gauging sites were evaluated and scored. According to our findings, six variables explain 0.711 of the total weight in the priority vector for the evaluation of a candidate site. Our approach is suitable for selecting the most stable alternative location based on a multi-criteria analysis in an inter-comparison arrangement.     

Climate changes and their impacts on water resources in semiarid regions: a case study of the Wei River basin,China

Understanding the impacts of climate change and human activity on the hydrological processes in river basins is important for maintaining ecosystem integrity and sustaining local economic development. The objective of this study was to evaluate the impact of climate variability and human activity on mean annual flow in the Wei River, the largest tributary of the Yellow River. The nonparametric Mann–Kendall test and wavelet transform were applied to detect the variations of hydrometeorological variables in the semiarid Wei River basin in the northwestern China. The identifications were based on streamflow records from 1958 to 2008 at four hydrological stations as well as precipitation and potential evapotranspiration (PET) data from 21 climate stations. A simple method based on Budyko curve was used to evaluate potential impacts of climate change and human activities on mean annual flow. The results show that annual streamflow decreased because of the reduced precipitation and increased PET at most stations. Both annual and seasonal precipitation and PET demonstrated mixed trends of decreasing and increasing, although significant trends (P < 0.05) were consistently detected in spring and autumn at most stations. Significant periodicities of 0.5 and 1 year (P < 0.05) were examined in all the time series. The spectrum of streamflow at the Huaxian station shows insignificant annual cycle during 1971–1975, 1986–1993 and 1996–2008, which is probably resulted from human activities. Climate variability greatly affected water resources in the Beiluo River, whereas human activities (including soil and water conservation, irrigation, reservoirs construction, etc.) accounted more for the changes of streamflow in the area near the Huaxian station during different periods. The results from this article can be used as a reference for water resources planning and management in the semiarid Wei River basin. Copyright © 2012 John Wiley & Sons, Ltd.     

A noniterative design procedure for supplemental brace–damper systems in single‐degree‐of‐freedom systems

In this paper, a method for designing supplemental brace–damper systems in single‐degree‐of‐freedom (SDOF) structures is presented. We include the effects of the supporting brace stiffness in the dynamic response by using a viscoelastic Maxwell model. On the basis of the study of an SDOF under ground excitation, we propose a noniterative design procedure for simultaneously specifying both the damper and the brace while assuring a desired structural performance. It is shown that to increase the damper size beyond the value delivered by the proposed criteria will not provide any improvement but actually worsen the structural response. The design method presented here shows excellent agreement with the FEMA 273 design approach but offers solutions closer to optimality. Copyright © 2013 John Wiley & Sons, Ltd.     

Sub-arcsecond radio and optical observations of the likely counterpart to the gamma-ray source 2FGL J2056.7+4939

We have searched and reviewed all multi-wavelength data available for the region towards the gamma-ray source 2FGL J2056.7+4939 in order to constrain its possible counterpart at lower energies. As a result, only a point-like optical/infrared source with flat-spectrum radio emission is found to be consistent with all X-ray and gamma-ray error circles. Its structure is marginally resolved at radio wavelengths at the sub-arcsecond level. An extragalactic scenario appears to be the most likely interpretation for this object.     

A multiwavelength study of the supernova remnant G296.8-0.3

We report XMM-Newton observations of the Galactic supernova remnant G296.8-0.3, together with complementary radio and infrared data. The spatial and spectral properties of the X-ray emission, detected towards G296.8-0.3, was investigated in order to explore the possible evolutionary scenarios and the physical connexion with its unusual morphology detected at radio frequencies. G296.8-0.3 displays diffuse X-ray emission correlated with the peculiar radio morphology detected in the interior of the remnant and with the shell-like radio structure observed to the northwest side of the object. The X-ray emission peaks in the soft/medium energy range (0.5–3.0 keV). The X-ray spectral analysis confirms that the column density is high (N _H∼0.64×10²² cm⁻²) which supports a distant location (d>9 kpc) for the SNR. Its X-ray spectrum can be well represented by a thermal (PSHOCK) model, with kT∼0.86 keV, an ionization timescale of 6.1×10¹⁰ cm⁻³ s, and low abundance (∼0.12 Z _⊙). The 24 μm observations show shell-like emission correlated with part of the northwest and southeast boundaries of the SNR. In addition a point-like X-ray source is also detected close to the geometrical center of the radio SNR. The object presents some characteristics of the so-called compact central objects (CCO). Its X-ray spectrum is consistent with those found at other CCOs and the value of N _H is consistent with that of G296.8-0.3, which suggests a physical connexion with the SNR.     

撞击坑识别方法综述

目前国内外有多种撞击坑识别方法,在一定程度上实现了对撞击坑的识别提取,但是其准确性以及对数据的适应性不尽相同。首先对撞击坑识别研究进展进行概述,再对撞击坑识别方法进行归纳总结,指出不同方法的优缺点和适用条件。最后,对撞击坑识别研究存在的问题进行分析,提出了研究撞击坑识别的重点及解决途径。