Who performs better? AVMs vs hedonic models

Purpose: In the literature there are numerous tests that compare the accuracy of automated valuation models (AVMs). These models first train themselves with price data and property characteristics, then they are tested by measuring their ability to predict prices. Most of them compare the effectiveness of traditional econometric models against the use of machine learning algorithms. Although the latter seem to offer better performance, there is not yet a complete survey of the literature to confirm the hypothesis. Design/methodology/approach: All tests comparing regression analysis and AVMs machine learning on the same data set have been identified. The scores obtained in terms of accuracy were then compared with each other. Findings: Machine learning models are more accurate than traditional regression analysis in their ability to predict value. Nevertheless, many authors point out as their limit their black box nature and their poor inferential abilities. Practical implications: AVMs machine learning offers a huge advantage for all real estate operators who know and can use them. Their use in public policy or litigation can be critical. Originality/value: According to the author, this is the first systematic review that collects all the articles produced on the subject done comparing the results obtained

Direct measurement of riverine particulate organic carbon age structure

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 39 (2012): L19703, doi:10.1029/2012GL052883.Carbon cycling studies focusing on transport and transformation of terrigenous carbon sources toward marine sedimentary sinks necessitate separation of particulate organic carbon (OC) derived from many different sources and integrated by river systems. Much progress has been made on isolating and characterizing young biologically-formed OC that is still chemically intact, however quantification and characterization of old, refractory rock-bound OC has remained troublesome. Quantification of both endmembers of riverine OC is important to constrain exchanges linking biologic and geologic carbon cycles and regulating atmospheric CO2 and O2. Here, we constrain petrogenic OC proportions in suspended sediment from the headwaters of the Ganges River in Nepal through direct measurement using ramped pyrolysis radiocarbon analysis. The unique results apportion the biospheric and petrogenic fractions of bulk particulate OC and characterize biospheric OC residence time. Compared to the same treatment of POC from the lower Mississippi-Atchafalaya River system, contrast in age spectra of the Ganges tributary samples illustrates the difference between small mountainous river systems and large integrative ones in terms of the global carbon cycle.This work was partially supported by U.S. National Science Foundation (NSF) Cooperative Agreement OCE-228996 to NOSAMS and NSF grants OCE-0851015 & OCE-0928582 to VG.2013-04-0

Global patterns of radiocarbon depletion in subsoil linked to rock-derived organic carbon

Organic matter stored in sedimentary rocks is one of the largest stocks of carbon at Earth’s surface. The fate of this rock organic carbon (OCpetro) during weathering in soils influences the geological carbon cycle, and impacts soil radiocarbon content that is used to quantify soil carbon turnover. Here, we assess the potential contribution of OCpetro to soils, using a mixing model generated by a global dataset of soil radiocarbon measurements (14C). Soils developed on sedimentary rocks (rather than on igneous substrate) have a paired OC content and 14C values consistent with OCpetro input, giving rise to apparent increase in soil residence time. We call for renewed assessment of OCpetro input to soils, in terms of its impact on soil radiocarbon inventories, and its potential to release carbon dioxide

Economic liberalism, social disparities and poverty in underdeveloped countries

Following the radical programs of economic adjustment, international agencies and governments in Latin America have been shaping their policies to protect the very poor, either by compensating for a deterioration in standards of living to which they themselves had contributed to, or simply to avoid further social unrest. Today, the idea that the government should intervene to resol ve problems of poverty and disparity is accepted; but it is accepted from a liberalstandpoint, that is to say, expeling politics from the equation and giving the market free rein to regulate society. In this view, policy to protect the poor makes the State some kind of charitable organization, a safety-net for those shut out of the market. This is based on two principIes: be patient, wait till tomorrow. These principIes are to be found in Rawls and in Hayek, who differ on some matters but agree on four main themes: the decisive role of the market in forming society, the justification of the fetishism of commodities, the creative disparities and the social exclusion as an individual phenomenon.Luego de los programas de ajustes radicales, las entidades internacionales y los gobiernos de los países latinoamericanos vienen adoptando políticas en defensa de los más pobres, bien sea para compensar el deterioro del nivel de vida que aquellos originaron o bien para evitar un mayor descontento social. Hoy se acepta la intervención del Estado para afrontar los problemas de la pobreza y las desigualdades sociales, aunque desde una óptica liberal, es decir, expulsando la política y dando prioridad al mercado como entidad reguladora de la sociedad. Así, las políticas en la defensa de los pobres adquiere un carácter de mera beneficencia o de red de seguridad para quienes son excluidos por el mercado, y se basan en dos principios: hay que ser pacientes y esperar hasta mañana. Sus fundamentos filosóficos se encuentran en Rawls y Hayek, quienes aunque difieren en algunas cuestiones comparte cuatro temas fundamentales: el papel determinante del mercado en la formación de la sociedad, la apología del fetichismo de la mercancía, las desigualdades creadoras y la exclusión social como fenómeno individual

BOÎTES ET FILS DE GE SUR SI(001) ORDONNÉS À LONGUE DISTANCE PAR DES RÉSEAUX DE DISLOCATIONS DE FLEXION

The growth of ordered semiconductor nanostrucutres, with a controlled size and position, is an major technologic challenge. In this study, we propose an original method to grow by molecular beam epitaxy ordered germanium nanostructures on silicon (001). A periodic array of tilt dislocations is obtained by molecular bounding, and induces a periodic strain field at the surface of the substrate. The observed organization of germanium nanostructures is due to the strain field generated on the silicon surface by an interfacial tilt dislocation array.L'élaboration de nanostructures semi-conductrices ordonnées, contrôlées en taille et en position, est un enjeu technologique important pour satisfaire les besoins de miniaturisation des circuits actuels de la micro/nano-électronique. Dans cette thèse, une méthode originale d'organisation latérale de nanostructures a été explorée et appliquée au cas de nanostructures de germanium épitaxiées sur silicium (001). Cette technique utilise un réseau de dislocations de flexion proche de la surface libre du substrat, obtenu par collage moléculaire. Un champ de déformation élastique, périodique, se propageant de l'interface de collage jusqu'à la surface des échantillons, nous avons pu obtenir une croissance organisée de nanostructures de germanium

Experimental evidence of isotropic transparency and complete band gap formation for ultrasounds propagating in stealth hyperuniform media

Following on recent experimental characterization of the transport properties of stealth hyperuniform media for electromagnetic and acoustic waves, we report here measurements at ultrasonic frequencies of the multiple scattering of waves by 2D hyperuniform distributions of steel rods immersed in water. The transparency, for which the effective attenuation of the medium is cancelled, is first evidenced by measuring the transmission of a plane wave propagating in a highly correlated and relatively dense medium. It is shown that a band gap occurs in the vicinity of the first Bragg frequency. The isotropy of both transparency and bang gap are also evidenced for the case of waves generated by a point source in differently ordered and circular shaped distributions. In other words, we thus obtain a representation of the Green's function. Our results demonstrate the huge potential of hyperuniform as well as highly correlated media for the design of functional materials

A Primary Study of Attributes of Innovations during the Prediffusion Stage

We provide a theoretical model for testing the adoption of information technology during the prediffusion stage (research and development and early trials) of an innovation. The model was tested using Linux based applications of Open Source Software (OSS). The results of surveying 1000 members of the Linux User Groups WorldWide (LUGWW) are presented. This study is significant because it provides empirical evidence that attributes of innovations correlate with adoption during the prediffusion stage (research and development) of an innovation. This extends diffusion of innovations research and has important implications for DOI theory and practice

Hydrologic controls on seasonal and inter-annual variability of Congo River particulate organic matter source and reservoir age

We present dissolved organic carbon (DOC) concentrations, particulate organic matter (POM) composition (δ13C, δ15N, ∆14C, N/C), and particulate glycerol dialkyl glycerol tetraether (GDGT) distributions from a 34-month time-series near the mouth of the Congo River. An end-member mixing model using δ13C and N/C indicates that exported POM is consistently dominated by C3 rainforest soil sources, with increasing contribution from C3 vegetation and decreasing contribution from phytoplankton at high discharge. Large C4 inputs are never observed despite covering ≈ 13% of the catchment. Low and variable ∆14C values during 2011 [annual mean = (− 148 ± 82) ‰], when discharge from left-bank tributaries located in the southern hemisphere reached record lows, likely reflect a bias toward pre-aged POM derived from the Cuvette Congolaise swamp forest. In contrast, ∆14C values were stable near − 50‰ between January and June 2013, when left-bank discharge was highest. We suggest that headwater POM is replaced and/or diluted by C3 vegetation and pre-aged soils during transit through the Cuvette Congolaise, whereas left-bank tributaries export significantly less pre-aged material. GDGT distributions provide further evidence for seasonal and inter-annual variability in soil provenance. The cyclization of branched tetraethers and the GDGT-0 to crenarchaeol ratio are positively correlated with discharge (r ≥ 0.70; p-value ≤ 4.3 × 10− 5) due to the incorporation of swamp-forest soils when discharge from right-bank tributaries located in the northern hemisphere is high. Both metrics reach record lows during 2013, supporting our interpretation of increased left-bank contribution at this time. We conclude that hydrologic variability is a major control of POM provenance in the Congo River Basin and that tropical wetlands can be a significant POM source despite their small geographic coverage