1,244 research outputs found

    Decomposing Identification Gains and Evaluating Instrument Identification Power for Partially Identified Average Treatment Effects

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    This paper examines the identification power of instrumental variables (IVs) for average treatment effect (ATE) in partially identified models. We decompose the ATE identification gains into components of contributions driven by IV relevancy, IV strength, direction and degree of treatment endogeneity, and matching via exogenous covariates. Our decomposition is demonstrated with graphical illustrations, simulation studies and an empirical example of childbearing and women's labour supply. Our analysis offers insights for understanding the complex role of IVs in ATE identification and for selecting IVs in practical policy designs. Simulations also suggest potential uses of our analysis for detecting irrelevant instruments

    Solar radiation forecasting using ad-hoc time series preprocessing and neural networks

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    In this paper, we present an application of neural networks in the renewable energy domain. We have developed a methodology for the daily prediction of global solar radiation on a horizontal surface. We use an ad-hoc time series preprocessing and a Multi-Layer Perceptron (MLP) in order to predict solar radiation at daily horizon. First results are promising with nRMSE < 21% and RMSE < 998 Wh/m2. Our optimized MLP presents prediction similar to or even better than conventional methods such as ARIMA techniques, Bayesian inference, Markov chains and k-Nearest-Neighbors approximators. Moreover we found that our data preprocessing approach can reduce significantly forecasting errors.Comment: 14 pages, 8 figures, 2009 International Conference on Intelligent Computin

    Cultural differences in microblogging:How Western IT Companies adapt Twitter (X) activities to the Chinese Weibo context

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    Companies worldwide use microblogs to communicate with stakeholders, but there may be cultural differences in how they do it. A content analysis was conducted comparing Twitter (currently known as X) and Weibo accounts of four Western IT companies; Weibo accounts of four similar Chinese companies served as benchmarks. Results show that Western microblog activities differed in many respects from Chinese practices. Specifically, they focused more on technology and less on marketing and community-building. In their localization strategies, Western companies chose to adapt (e.g., paying attention to community building), not adapt (e.g., keeping their technological profile), or cautiously adapt (e.g., using somewhat more emojis or reluctantly experimenting with sweepstakes). Cultural differences on microblogging platforms are comprehensive and multifaceted and cannot be easily reduced to established cultural dimensions. Processes of cultural adaptation, therefore, depend on profound knowledge of the business environment and cultural differences.</p

    X-Ray Diffuse Scattering Study on Ionic-Pair Displacement Correlations in Relaxor Lead Magnesium Niobate

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    Ionic-pair equal-time displacement correlations in relaxor lead magnesium niobate, Pb(Mg1/3Nb2/3)O3Pb(Mg_{1/3}Nb_{2/3})O_{3}, have been investigated at room temperature in terms of an x-ray diffuse scattering technique. Functions of the distinct correlations have been determined quantitatively. The results show the significantly strong rhombohedral-polar correlations regarding Pb-O, Mg/Nb-O, and O-O' pairs. Their spatial distribution forms an ellipse or a sphere with the radii of 30-80AËš\AA. This observation of local structure in the system proves precursory presence of the polar microregions in the paraelectric state which leads to the dielectric dispersion.Comment: 11 pages, 3 figure

    Drum vortons in high density QCD

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    Recently it was shown that high density QCD supports of number of topological defects. In particular, there are U(1)_Y strings that arise due to K^0 condensation that occurs when the strange quark mass is relatively large. The unique feature of these strings is that they possess a nonzero K^+ condensate that is trapped on the core. In the following we will show that these strings (with nontrivial core structure) can form closed loops with conserved charge and currents trapped on the string worldsheet. The presence of conserved charges allows these topological defects, called vortons, to carry angular momentum, which makes them classically stable objects. We also give arguments demonstrating that vortons carry angular momentum very efficiently (in terms of energy per unit angular momentum) such that they might be the important degrees of freedom in the cores of neutron stars.Comment: 11 pages, accepted for publication in Physical Review

    The association between patella alignment and knee pain and function: an MRI study in persons with symptomatic knee osteoarthritis

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    SummaryObjectiveThe aim of the study was to examine the association between patellofemoral (PF) alignment (using standard magnetic resonance imaging (MRI) images of extended knees) and knee pain and function.DesignSubjects were recruited to participate in a natural history study of symptomatic knee osteoarthritis, called the Boston Osteoarthritis of the Knee Study (BOKS). The association of predictive variable (patellar alignment in sagittal and transverse planes) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and function were examined using a linear regression model while adjusting for age, sex, body mass index (BMI), Center for Epidemiologic Studies Depression Scale (CES-D) score and Kellgren and Lawrence score.ResultsIncreasing trochlear angle (TA) was associated with both WOMAC (P=0.06) pain and WOMAC function subscale (P=0.04). Increasing lateral patellar title angle (LPTA) and decreasing bisect offset (increasing lateral subluxation) appeared to be associated with increasing WOMAC pain. However, no such an association was observed for other predictors.ConclusionsThe findings of the present study suggest that increasing TA is associated with increased functional impairment. Other measures of PF malalignment were not significantly associated with either knee pain or functional impairment

    Thermodynamic Potential for Superfluid 3He in Aerogel

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    We present a free energy functional for superfluid 3He in the presence of homogeneously distributed impurity disorder which extends the Ginzburg-Landau free energy functional to all temperatures. We use the new free energy functional to calculate the thermodynamic potential, entropy, heat capacity and density of states for the B-phase of superfluid 3He in homogeneous, isotropic aerogel.Comment: 10 pages, 4 figure
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