3,990 research outputs found
Using survey participants to estimate the impact of nonparticipation
The authors evaluate the effectiveness of two models often used to measure the extent of nonparticipation bias in survey estimates. The first model establishes a "continuum of resistance" to being surveyed, placing people who were interviewed after one phone call on one end and nonparticipants on the other. The second assumes that there are "classes" of nonparticipants and that similar classes can be found among participants; it identifies groups of participants thought to be like nonparticipants and uses them as "proxies" to estimate the characteristics of nonparticipants. The authors use these models to examine how accurately they estimate the characteristics of nonparticipants and the impact of nonparticipation on survey estimates of means of child support awards and payments in Wisconsin. They find that neither model detects the true extent of nonparticipation bias.
Coûts environnementaux du développement périurbain : impact des configurations urbaines et des choix résidentiels
[Departement_IRSTEA]Territoires [TR1_IRSTEA]DTAM [Axe_IRSTEA]DTAM1-REPRO [Axe_IRSTEA]DTAM-QT1-INEGALITESCe projet de recherche part du constat que la littĂ©rature existante sur la durabilitĂ© des espaces pĂ©riurbains n'a pas apportĂ© de rĂ©ponse sur deux points particuliers. En premier lieu, la question du transport est gĂ©nĂ©ralement considĂ©rĂ©e du seul point de vue du transport de personnes, dans une optique d'Ă©quilibre partiel dans laquelle le transport des biens produits et consommĂ©s dans la ville n'est pas pris en compte. Or la thĂ©orie Ă©conomique rĂ©cente, dans le cadre des modĂšles d'Ă©conomie gĂ©ographique, montre que la localisation des mĂ©nages est Ă©troitement liĂ©e Ă celle des entreprises, et que les configurations existant Ă l'Ă©quilibre dĂ©pendent fortement des interrelations entre ces deux catĂ©gories d'agents Ă©conomiques. En d'autres termes, s'il est indispensable de considĂ©rer les choix rĂ©sidentiels des mĂ©nages pour analyser les flux de transport engendrĂ©s par ces derniers, il est tout aussi indispensable de tenir compte des consĂ©quences de ces localisations rĂ©sidentielles sur la localisation des entreprises, et aussi des effets en retour des localisations des entreprises sur la distribution spatiale des mĂ©nages. Cette question fait l'objet du premier axe de notre recherche. En second lieu, les travaux existants nĂ©gligent en gĂ©nĂ©ral le fait que les espaces pĂ©riurbains accueillent des mĂ©nages de catĂ©gories sociales variĂ©es qui ont des comportements diffĂ©rents en termes de dĂ©placement. Or, il semble important de proposer une analyse du dĂ©veloppement pĂ©riurbain intĂ©grant la question du choix rĂ©sidentiel des mĂ©nages en fonction de leur catĂ©gorie sociale, ceci afin de dresser des pistes d'Ă©volution possible des flux de transport engendrĂ©s par les espaces pĂ©riurbains. C'est ce qui est dĂ©veloppĂ© dans le second axe de notre recherche. Enfin, ces analyses portant sur la localisation rĂ©sidentielle des diffĂ©rentes catĂ©gories socio-professionnelles nous amĂšnent aussi Ă analyser la sĂ©grĂ©gation rĂ©sidentielle dans les zones pĂ©riurbaines, en lien avec les dĂ©terminants des choix de localisation rĂ©sidentielle des mĂ©nages. / This research starts from the premise that the existing literature on the sustainability of suburban areas has not provided answers to two specific points. Firstly, the issue of transport is generally considered from the point of view of the transport of persons, in a partial equilibrium framework in which the transport of goods produced and consumed in the city is not taken into account. But the recent economic theory, with the new economic geography models, shows that the location of households is closely linked to the location of firms, and that the existing equilibrium configurations depend strongly on the interrelationships between these two categories of agent. In other words, it is essential to consider the residential choices of households to analyze the traffic flows they generate, but it is also necessary to take into account the consequences of these residential locations on the location of firms and the feedback effects of corporate locations on the spatial distribution of households. This question is the subject of the first axis of our research. Second, existing studies generally neglect the fact that the suburban areas host various social groups of households that have different behaviors in terms of mobility. However, it seems important to provide an analysis of suburban development incorporating the issue of residential choices of households according to their social class, in order to establish avenues for possible evolution of transport flows generated by the suburban areas. This is what is developed in the second focus of our research. Finally, the residential location of the different socio-professional categories is also analyzed in terms of urban segregation, in relation with the determinants of householdsâ choices
MACOC: a medoid-based ACO clustering algorithm
The application of ACO-based algorithms in data mining is growing over the last few years and several supervised and unsupervised learning algorithms have been developed using this bio-inspired approach. Most recent works concerning unsupervised learning have been focused on clustering, showing great potential of ACO-based techniques. This work presents an ACO-based clustering algorithm inspired by the ACO Clustering (ACOC) algorithm. The proposed approach restructures ACOC from a centroid-based technique to a medoid-based technique, where the properties of the search space are not necessarily known. Instead, it only relies on the information about the distances amongst data. The new algorithm, called MACOC, has been compared against well-known algorithms (K-means and Partition Around Medoids) and with ACOC. The experiments measure the accuracy of the algorithm for both synthetic datasets and real-world datasets extracted from the UCI Machine Learning Repository
Program on Earth Observation Data Management Systems (EODMS)
An assessment was made of the needs of a group of potential users of satellite remotely sensed data (state, regional, and local agencies) involved in natural resources management in five states, and alternative data management systems to satisfy these needs are outlined. Tasks described include: (1) a comprehensive data needs analysis of state and local users; (2) the design of remote sensing-derivable information products that serve priority state and local data needs; (3) a cost and performance analysis of alternative processing centers for producing these products; (4) an assessment of the impacts of policy, regulation and government structure on implementing large-scale use of remote sensing technology in this community of users; and (5) the elaboration of alternative institutional arrangements for operational Earth Observation Data Management Systems (EODMS). It is concluded that an operational EODMS will be of most use to state, regional, and local agencies if it provides a full range of information services -- from raw data acquisition to interpretation and dissemination of final information products
Full sphere hydrodynamic and dynamo benchmarks
Convection in planetary cores can generate fluid flow and magnetic fields, and a number of sophisticated codes exist to simulate the dynamic behaviour of such systems. We report on the first community activity to compare numerical results of computer codes designed to calculate fluid flow within a whole sphere. The flows are incompressible and rapidly rotating and the forcing of the flow is either due to thermal convection or due to moving boundaries. All problems defined have solutions that allow easy comparison, since they are either steady, slowly drifting or perfectly periodic. The first two benchmarks are defined based on uniform internal heating within the sphere under the Boussinesq approximation with boundary conditions that are uniform in temperature and stress-free for the flow. Benchmark 1 is purely hydrodynamic, and has a drifting solution. Benchmark 2 is a magnetohydrodynamic benchmark that can generate oscillatory, purely periodic, flows and magnetic fields. In contrast, Benchmark 3 is a hydrodynamic rotating bubble benchmark using no slip boundary conditions that has a stationary solution. Results from a variety of types of code are reported, including codes that are fully spectral (based on spherical harmonic expansions in angular coordinates and polynomial expansions in radius), mixed spectral and finite difference, finite volume, finite element and also a mixed Fourierâfinite element code. There is good agreement between codes. It is found that in Benchmarks 1 and 2, the approximation of a whole sphere problem by a domain that is a spherical shell (a sphere possessing an inner core) does not represent an adequate approximation to the system, since the results differ from whole sphere results
Communities as Well Separated Subgraphs With Cohesive Cores: Identification of Core-Periphery Structures in Link Communities
Communities in networks are commonly considered as highly cohesive subgraphs
which are well separated from the rest of the network. However, cohesion and
separation often cannot be maximized at the same time, which is why a
compromise is sought by some methods. When a compromise is not suitable for the
problem to be solved it might be advantageous to separate the two criteria. In
this paper, we explore such an approach by defining communities as well
separated subgraphs which can have one or more cohesive cores surrounded by
peripheries. We apply this idea to link communities and present an algorithm
for constructing hierarchical core-periphery structures in link communities and
first test results.Comment: 12 pages, 2 figures, submitted version of a paper accepted for the
7th International Conference on Complex Networks and Their Applications,
December 11-13, 2018, Cambridge, UK; revised version at
http://141.20.126.227/~qm/papers
Random tree growth by vertex splitting
We study a model of growing planar tree graphs where in each time step we
separate the tree into two components by splitting a vertex and then connect
the two pieces by inserting a new link between the daughter vertices. This
model generalises the preferential attachment model and Ford's -model
for phylogenetic trees. We develop a mean field theory for the vertex degree
distribution, prove that the mean field theory is exact in some special cases
and check that it agrees with numerical simulations in general. We calculate
various correlation functions and show that the intrinsic Hausdorff dimension
can vary from one to infinity, depending on the parameters of the model.Comment: 47 page
Observational Mass-to-Light Ratio of Galaxy Systems: from Poor Groups to Rich Clusters
We study the mass-to-light ratio of galaxy systems from poor groups to rich
clusters, and present for the first time a large database for useful
comparisons with theoretical predictions. We extend a previous work, where B_j
band luminosities and optical virial masses were analyzed for a sample of 89
clusters. Here we also consider a sample of 52 more clusters, 36 poor clusters,
7 rich groups, and two catalogs, of about 500 groups each, recently identified
in the Nearby Optical Galaxy sample by using two different algorithms. We
obtain the blue luminosity and virial mass for all systems considered. We
devote a large effort to establishing the homogeneity of the resulting values,
as well as to considering comparable physical regions, i.e. those included
within the virial radius. By analyzing a fiducial, combined sample of 294
systems we find that the mass increases faster than the luminosity: the linear
fit gives M\propto L_B^{1.34 \pm 0.03}, with a tendency for a steeper increase
in the low--mass range. In agreement with the previous work, our present
results are superior owing to the much higher statistical significance and the
wider dynamical range covered (about 10^{12}-10^{15} M_solar). We present a
comparison between our results and the theoretical predictions on the relation
between M/L_B and halo mass, obtained by combining cosmological numerical
simulations and semianalytic modeling of galaxy formation.Comment: 25 pages, 12 eps figures, accepted for publication in Ap
Formation of Disk Galaxies: Warm Dark Matter and the Angular Momentum problem
We have performed TreeSPH simulations of disk galaxy formation in various
warm dark matter (WDM) cosmologies. Our results indicate that for a range of
WDM free-streaming masses, the disk galaxy formation angular momentum problem
can be completely resolved by going to the WDM structure formation scenario,
without having to invoke stellar feedback processes at all. We also confirm our
previous suspicion, that part of the angular momentum problem is due to
numerical effects, most likely related to the shock capturing, artificial
viscosity used in SPH. Furthermore we find that we can match the observed
I-band Tully-Fisher (TF) relation, provided that the I-band mass-to-light ratio
of disk galaxies is about 0.8. We argue that this is quite a reasonable value
in comparison with various dynamical and spectrophotometric estimates,
including one given in this paper. We speculate that our success in matching
the TF relation may be due to WDM halos being less centrally concentrated than
CDM halos and suggest to check this exciting possibility with high resolution
simulations, in particular in low Omega_M, WDM cosmologies. Finally, we discuss
possible physical candidates for WDM particles extensively. We find that the
most promising are neutrinos with weaker or stronger interactions than normal,
majorons (light pseudogoldstone bosons) or mirror or shadow world neutrinos.Comment: 50 pages incl. 17 figures. Accepted for publication in Ap
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