Urban Social Media Demographics: An Exploration of Twitter Use in Major American Cities

This article explores intersections between place, race/ethnicity, and gender amongst American Twitter users and makes an argument that studying the intensity of tweets provides insights into how and why particular groups tweet. Given recent events in American political life such as the shooting in Ferguson, Missouri and the reactions by young, urban African Americans on Twitter, understanding the role of race, place, gender, and age is important. We observed the time between tweets of urban American Twitter users and explored whether the medium may be providing traditionally marginalized groups, such as young Black men, with potential avenues for mobilizing communication and access to resources.     

The effect of mother–child separation on the behavior of children experiencing a diagnostic medical procedure.

54 4–6 and 7–10 yr olds were observed having a venal puncture blood sample drawn in a clinical laboratory with or without their mothers being present. Younger Ss exhibited significantly more crying before and during the blood test, more aggression, and more resistance to the procedure than did older Ss, regardless of experimental condition. The mother-present condition only affected crying before the initiation of the blood test. Ss in both age groups displayed significantly more crying when their mothers were present than when their mother remained in the waiting room. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Verhaltensbasierte Verkettung von Internetsitzungen

Die Analyse der Aktivit?ten eines Internet-Nutzers ist über l?ngere Zeit in der Regel nur mit Kenntnis der bei vielen Internet-Zugangsprovidern mindestens einmal t?glich wechselnden IP-Adressen m?glich. Verwendet der Nutzer zudem einen Anonymisierungsdienst, sollte eine Verkettung der Nutzer-Aktivit?ten auch für den Zugangsprovider unm?glich sein. Der Beitrag zeigt, dass eine verhaltensbasierte Verkettung dennoch m?glich ist und verbreitete Anonymisierungsl?sungen in der Praxis einen deutlich geringeren Schutz vor Beobachtung bieten, als bisher angenommen.     

On Discriminative Bayesian Network Classifiers and Logistic Regression

Discriminative learning of the parameters in the naive Bayes model is known to be equivalent to a logistic regression problem. Here we show that the same fact holds for much more general Bayesian network models, as long as the corresponding network structure satisfies a certain graph-theoretic property. The property holds for naive Bayes but also for more complex structures such as tree-augmented naive Bayes (TAN) as well as for mixed diagnostic-discriminative structures. Our results imply that for networks satisfying our property, the conditional likelihood cannot have local maxima so that the global maximum can be found by simple local optimization methods. We also show that if this property does not hold, then in general the conditional likelihood can have local, non-global maxima. We illustrate our theoretical results by empirical experiments with local optimization in a conditional naive Bayes model. Furthermore, we provide a heuristic strategy for pruning the number of parameters and relevant features in such models. For many data sets, we obtain good results with heavily pruned submodels containing many fewer parameters than the original naive Bayes model.Editors: Pedro Larrañaga, Jose A. Lozano, Jose M. Peña and Iñaki Inza     

Using enterprise architecture analysis and interview data to estimate service response time

Insights into service response time is important for service-oriented architectures and service management. However, directly measuring the service response time is not always feasible or can be very costly. This paper extends an analytical modeling method which uses enterprise architecture modeling to support the analysis. The extensions consist of (i) a formalization using the Hybrid Probabilistic Relational Model formalism, (ii) an implementation in an analysis tool for enterprise architecture and (iii) a data collection approach using expert assessments collected via interviews and questionnaires. The accuracy and cost effectiveness of the method was tested empirically by comparing it with direct performance measurements of five services of a geographical information system at a Swedish utility company. The tests indicate that the proposed method can be a viable option for rapid service response time estimates when a moderate accuracy within 15% is sufficient.     

Efficient triangular surface approximations using wavelets and quadtree data structures

We present a method for adaptive surface meshing and triangulation which controls the local level of detail of the surface approximation by local spectral estimates. These estimates are determined by a wavelet representation of the surface data. The basic idea is to decompose the initial data set by means of an orthogonal or semi orthogonal tensor product wavelet transform (WT) and to analyze the resulting coefficients. In surface regions, where the partial energy of the resulting coefficients is low, the polygonal approximation of the surface can be performed with larger triangles without losing too much fine grain details. However, since the localization of the WT is bound by the Heisenberg principle, the meshing method has to be controlled by the detail signals rather than directly by the coefficients. The dyadic scaling of the WT stimulated us to build an hierarchical meshing algorithm which transforms the initially regular data grid into a quadtree representation by rejection of unimportant mesh vertices. The optimum triangulation of the resulting quadtree cells is carried out by selection from a look up table. The tree grows recursively as controlled by detail signals which are computed from a modified inverse WT. In order to control the local level of detail, we introduce a new class of wavelet space filters acting as "magnifying glasses" on the data. We show that our algorithm performs a low algorithmic complexity, so that surface meshing can be achieved at interactive rates, such as required by flight simulators, however, other applications are possible as well.     

Connecting geodesics on smooth surfaces

In this paper, we present a novel method for computing multiple geodesic connections between two arbitrary points on a smooth surface. Our method is based on a homotopy approach that is able to capture the ambiguity of geodesic connections in the presence of positive Gaussian curvature that generates focal curves. Contrary to previous approaches, we exploit focal curves to gain theoretical insights on the number of connecting geodesics and a practical algorithm for collecting these. We consider our method as a contribution to the contemporary debate regarding the calculation of distances in general situations, applying continuous concepts of classical differential geometry which are not immediately transferable in purely discrete settings.     

HUMID AIR EFFECTS ON CRACK TIP PLASTIC WORK IN 1008 STEEL

The cyclic plastic work of fatigue crack propagation, Q_pw, and the effective surface energy, U, were measured for an annealed 1008 steel in humid air and dry nitrogen using calorimetry Q_pw was not significantly affected by the humid air environment suggesting that the hydrogen generated by the oxidation of iron at the crack tip does not strongly affect the cyclic properties for this material U was identical and constant for the two environments for crack growth rates greater than ～ 100 A/cycle. Below da/dN～ 100 A/cycle U decreased rapidly with decreasing δK in the humid air environment It was concluded from these two observations that the main effect of hydrogen on crack growth in this alloy was to lower the atomic surface energy, γ, thereby lowering the local fracture stress.