Stellar disk destruction by dynamical interactions in the Orion Trapezium star cluster

We compare the observed size distribution of circum stellar disks in the Orion Trapezium cluster with the results of $N$-body simulations in which we incorporated an heuristic prescription for the evolution of these disks. In our simulations, the sizes of stellar disks are affected by close encounters with other stars (with disks). We find that the observed distribution of disk sizes in the Orion Trapezium cluster is excellently reproduced by truncation due to dynamical encounters alone. The observed distribution appears to be a sensitive measure of the past dynamical history of the cluster, and therewith on the conditions of the cluster at birth. The best comparison between the observed disk size distribution and the simulated distribution is realized with a cluster of $N = 2500\pm500$ stars with a half-mass radius of about 0.5\,pc in virial equilibrium (with a virial ratio of $Q = 0.5$, or somewhat colder $Q \simeq 0.3$), and with a density structure according to a fractal dimension of $F \simeq 1.6$. Simulations with these parameters reproduce the observed distribution of circum stellar disks in about 0.2--0.5\,Myr.Comment: submitted to MNRA

On Using Active Learning and Self-Training when Mining Performance Discussions on Stack Overflow

Abundant data is the key to successful machine learning. However, supervised learning requires annotated data that are often hard to obtain. In a classification task with limited resources, Active Learning (AL) promises to guide annotators to examples that bring the most value for a classifier. AL can be successfully combined with self-training, i.e., extending a training set with the unlabelled examples for which a classifier is the most certain. We report our experiences on using AL in a systematic manner to train an SVM classifier for Stack Overflow posts discussing performance of software components. We show that the training examples deemed as the most valuable to the classifier are also the most difficult for humans to annotate. Despite carefully evolved annotation criteria, we report low inter-rater agreement, but we also propose mitigation strategies. Finally, based on one annotator's work, we show that self-training can improve the classification accuracy. We conclude the paper by discussing implication for future text miners aspiring to use AL and self-training.Comment: Preprint of paper accepted for the Proc. of the 21st International Conference on Evaluation and Assessment in Software Engineering, 201

Quality Measures in Uncertain Data Management

Many applications deal with data that is uncertain. Some examples are applications dealing with sensor information, data integration applications and healthcare applications. Instead of these applications having to deal with the uncertainty, it should be the responsibility of the DBMS to manage all data including uncertain data. Several projects do research on this topic. In this paper, we introduce four measures to be used to assess and compare important characteristics of data and systems

Photometric Accretion Signatures Near the Substellar Boundary

Multi-epoch imaging of the Orion equatorial region by the Sloan Digital Sky Survey has revealed that significant variability in the blue continuum persists into the late-M spectral types, indicating that magnetospheric accretion processes occur below the substellar boundary in the Orion OB1 association. We investigate the strength of the accretion-related continuum veiling by comparing the reddening-invariant colors of the most highly variable stars against those of main sequence M dwarfs and evolutionary models. A gradual decrease in the g band veiling is seen for the cooler and less massive members, as expected for a declining accretion rate with decreasing mass. We also see evidence that the temperature of the accretion shock decreases in the very low mass regime, reflecting a reduction in the energy flux carried by the accretion columns. We find that the near-IR excess attributed to circumstellar disk thermal emission drops rapidly for spectral types later than M4. This is likely due to the decrease in color contrast between the disk and the cooler stellar photosphere. Since accretion, which requires a substantial stellar magnetic field and the presence of a circumstellar disk, is inferred for masses down to 0.05 Msol we surmise that brown dwarfs and low mass stars share a common mode of formation.Comment: 37 pages, 14 figures, accepted by A

IMPrECISE: Good-is-good-enough data integration

IMPrECISE is an XQuery module that adds probabilistic XML functionality to an existing XML DBMS, in our case MonetDB/XQuery. We demonstrate probabilistic XML and data integration functionality of IMPrECISE. The prototype is configurable with domain knowledge such that the amount of uncertainty arising during data integration is reduced to an acceptable level, thus obtaining a "good is good enough" data integration with minimal human effort

Sensitivity of Building Loss Estimates to Major Uncertain Variables

This paper examines the question of which sources of uncertainty most strongly affect the repair cost of a building in a future earthquake. Uncertainties examined here include spectral acceleration, ground-motion details, mass, damping, structural force-deformation behavior, building-component fragility, contractor costs, and the contractor's overhead and profit. We measure the variation (or swing) of the repair cost when each basic input variable except one is taken at its median value, and the remaining variable is taken at its 10th and at its 90th percentile. We perform this study using a 1960s highrise nonductile reinforced-concrete moment-frame building. Repair costs are estimated using the assembly-based vulnerability (ABV) method. We find that the top three contributors to uncertainty are assembly capacity (the structural response at which a component exceeds some damage state), shaking intensity (measured here in terms of damped elastic spectral acceleration, Sa), and details of the ground motion with a given Sa

Urban Field Geology for K-8 Teachers

Geologists have long recognized the value of field trips, and the National Science Education Standards recommend them for K-8 science curricula. However, many teachers avoid running field trips. This article presents the results of a series of summer institutes for urban geoscience teachers in Milwaukee, Wisconsin, in which field and laboratory activities were developed in the context of local geology and field trip practices of "Teaming Up", reducing novelty space, and pre- and post-trip activities were encouraged. Teachers were also introduced to the use of the Action Planning model to assist in implementing curricular changes within their schools to encourage the use of field trips. The researchers determined that the teachers in these workshops increased their personal belief in their ability to teach earth science more effectivly. They also felt more comfortable with content material and found that action plans were an effective way to enact change regarding the role of field trips in their schools and in their earth science curricula. Educational levels: Graduate or professional

Clinical picture and risk prediction of short-term mortality in cardiogenic shock

AIMS: The aim of this study was to investigate the clinical picture and outcome of cardiogenic shock and to develop a risk prediction score for short-term mortality. METHODS AND RESULTS: The CardShock study was a multicentre, prospective, observational study conducted between 2010 and 2012. Patients with either acute coronary syndrome (ACS) or non-ACS aetiologies were enrolled within 6 h from detection of cardiogenic shock defined as severe hypotension with clinical signs of hypoperfusion and/or serum lactate >2 mmol/L despite fluid resuscitation (n = 219, mean age 67, 74% men). Data on clinical presentation, management, and biochemical variables were compared between different aetiologies of shock. Systolic blood pressure was on average 78 mmHg (standard deviation 14 mmHg) and mean arterial pressure 57 (11) mmHg. The most common cause (81%) was ACS (68% ST-elevation myocardial infarction and 8% mechanical complications); 94% underwent coronary angiography, of which 89% PCI. Main non-ACS aetiologies were severe chronic heart failure and valvular causes. In-hospital mortality was 37% (n = 80). ACS aetiology, age, previous myocardial infarction, prior coronary artery bypass, confusion, low LVEF, and blood lactate levels were independently associated with increased mortality. The CardShock risk Score including these variables and estimated glomerular filtration rate predicted in-hospital mortality well (area under the curve 0.85). CONCLUSION: Although most commonly due to ACS, other causes account for one-fifth of cases with shock. ACS is independently associated with in-hospital mortality. The CardShock risk Score, consisting of seven common variables, easily stratifies risk of short-term mortality. It might facilitate early decision-making in intensive care or guide patient selection in clinical trials