Automatic Verification of Erlang-Style Concurrency

This paper presents an approach to verify safety properties of Erlang-style, higher-order concurrent programs automatically. Inspired by Core Erlang, we introduce Lambda-Actor, a prototypical functional language with pattern-matching algebraic data types, augmented with process creation and asynchronous message-passing primitives. We formalise an abstract model of Lambda-Actor programs called Actor Communicating System (ACS) which has a natural interpretation as a vector addition system, for which some verification problems are decidable. We give a parametric abstract interpretation framework for Lambda-Actor and use it to build a polytime computable, flow-based, abstract semantics of Lambda-Actor programs, which we then use to bootstrap the ACS construction, thus deriving a more accurate abstract model of the input program. We have constructed Soter, a tool implementation of the verification method, thereby obtaining the first fully-automatic, infinite-state model checker for a core fragment of Erlang. We find that in practice our abstraction technique is accurate enough to verify an interesting range of safety properties. Though the ACS coverability problem is Expspace-complete, Soter can analyse these verification problems surprisingly efficiently.Comment: 12 pages plus appendix, 4 figures, 1 table. The tool is available at http://mjolnir.cs.ox.ac.uk/soter

Spreading in Social Systems: Reflections

In this final chapter, we consider the state-of-the-art for spreading in social systems and discuss the future of the field. As part of this reflection, we identify a set of key challenges ahead. The challenges include the following questions: how can we improve the quality, quantity, extent, and accessibility of datasets? How can we extract more information from limited datasets? How can we take individual cognition and decision making processes into account? How can we incorporate other complexity of the real contagion processes? Finally, how can we translate research into positive real-world impact? In the following, we provide more context for each of these open questions.Comment: 7 pages, chapter to appear in "Spreading Dynamics in Social Systems"; Eds. Sune Lehmann and Yong-Yeol Ahn, Springer Natur

Survival of Medicare Patients After Enrollment in Hospice Programs

Background: Each year more than 220,000 Medicare beneficiaries receive care from hospice programs designed to enhance the quality of the end of life. Enrollment requires certification by a physician that the patient has a life expectancy of less than six months. We examined how long before death patients enrolled in hospice programs. Methods: Using 1990 Medicare claims data, we analyzed the characteristics and survival of 6451 hospice patients followed for a minimum of 27 months with respect to mortality. Results: The patients' mean age was 76.4 years; 92.4 percent were white. Half the patients were women, and 80.2 percent had cancer of some type. The most common diagnoses were lung cancer (21.4 percent), colorectal cancer (10.5 percent), and prostate cancer (7.4 percent). The median survival after enrollment was only 36 days, and 15.6 percent of the patients died within 7 days. At the other extreme, 14.9 percent of the patients lived longer than six months. Survival varied substantially according to diagnosis, even after adjustment for age and coexisting conditions. The unadjusted survival after enrollment was shortest for those with renal failure, those with leukemia or lymphoma, and those with liver or biliary cancer; it was longest for those with chronic lung disease, those with dementia, and those with breast cancer. Patients at for-profit, larger, outpatient, or newer hospices lived longer after enrollment than those in other types of hospice programs. Conclusions: Most patients who enter hospice care do so late in the course of their terminal illnesses. The timing of enrollment in hospice programs varies substantially with the characteristics of the patients and the hospices.Sociolog

An Experimental Evaluation of Deliberate Unsoundness in a Static Program Analyzer

Abstract. Many practical static analyzers are not completely sound by design. Their designers trade soundness in order to increase automa-tion, improve performance, and reduce the number of false positives or the annotation overhead. However, the impact of such design decisions on the effectiveness of an analyzer is not well understood. In this pa-per, we report on the first systematic effort to document and evaluate the sources of unsoundness in a static analyzer. We present a code in-strumentation that reflects the sources of deliberate unsoundness in the.NET static analyzer Clousot. We have instrumented code from several open source projects to evaluate how often concrete executions violate Clousot’s unsound assumptions. In our experiments, this was the case in 8–29 % of all analyzed methods. Our approach and findings can guide users of static analyzers in using them fruitfully, and designers in finding good trade-offs.

Dynamics of Locally Coupled Oscillators with Next-Nearest-Neighbor Interaction

A theoretical description of decentralized dynamics within linearly coupled, one-dimensional oscillators (agents) with up to next-nearest-neighbor interaction is given. Conditions for stability of such system are presented. Our results indicate that the stable systems have response that grow at least linearly in the system size. We give criteria when this is the case. The dynamics of these systems can be described with traveling waves with strong damping in the high frequencies. Depending on the system parameters, two types of solutions have been found: damped oscillations and reflectionless waves. The latter is a novel result and a feature of systems with at least next-nearest-neighbor interactions. Analytical predictions are tested in numerical simulations

Predicting the academic underachievement in high school in Spain over the next few years: A dynamic modelling approach

[EN] In this paper we propose a dynamic model to understand the evolution of the academic underachievement in a high school in Spain. This model is based on ideas of Christakis and Fowler where individual habits may be transmitted by social contact. Thus, to build the model we suppose that a student has academic failure when she/he gets into study habits transmitted by students with bad academic habits. From the available academic results of the Spanish high school educational system during the period 1999 2008, we fit the model to the data in order to obtain the parameters of the model. Then, we predict the academic underachievement evolution over the next few years.This work has been partially supported by the Spanish M.C.Y.T. grant MTM2009-08587 and the Universitat Politecnica de Valencia grant PAID06-09-2588Camacho Vidal, FJ.; Cortés, J.; Micle, RM.; Sánchez-Sánchez, A. (2013). Predicting the academic underachievement in high school in Spain over the next few years: A dynamic modelling approach. Mathematical and Computer Modelling. 57(7):1703-1708. https://doi.org/10.1016/j.mcm.2011.11.011S1703170857

Television viewing, computer use, obesity, and adiposity in US preschool children

Professor.Background: There is limited evidence in preschool children linking media use, such as television/video viewing and computer use, to obesity and adiposity. We tested three hypotheses in preschool children: 1) that watching > 2 hours of TV/videos daily is associated with obesity and adiposity, 2) that computer use is associated with obesity and adiposity, and 3) that > 2 hours of media use daily is associated with obesity and adiposity. Methods: We conducted a cross-sectional study using nationally representative data on children, aged 2�5 years from the National Health and Nutrition Examination Survey, 1999-2002. Our main outcome measures were 1) weight status: normal versus overweight or at risk for overweight, and 2) adiposity: the sum of subscapular and triceps skinfolds (mm). Our main exposures were TV/video viewing (= 2 or > 2 hours/day), computer use (users versus non-users), and media use (= 2 or > 2 hours/day). We used multivariate Poisson and linear regression analyses, adjusting for demographic covariates, to test the independent association between TV/video viewing, computer use, or overall media use and a child's weight status or adiposity. Results: Watching > 2 hours/day of TV/videos was associated with being overweight or at risk for overweight (Prevalence ratio = 1.34, 95% CI [1.07, 1.66]; n =1340) and with higher skinfold thicknesses ([Beta] = 1.08, 95% CI [0.19, 1.96]; n = 1337). Computer use > 0 hours/day was associated with higher skinfold thicknesses ([Beta] = 0.56, 95% CI [0.04, 1.07]; n = 1339). Media use had borderline significance with higher skinfold thicknesses ([Beta] = 0.85, 95% CI [-0.04, 1.75], P=0.06; n = 1334) Conclusion: Watching > 2 hours/day of TV/videos in US preschool-age children was associated with a higher risk of being overweight or at risk for overweight and higher adiposity-findings in support of national guidelines to limit preschool children's media use. Computer use was also related to higher adiposity in preschool children, but not weight status. Intervention studies to limit preschool children's media use are warranted.USDA/ARS under Cooperative Agreement No. 58-6250-6001

A Study of Concurrency Bugs and Advanced Development Support for Actor-based Programs

The actor model is an attractive foundation for developing concurrent applications because actors are isolated concurrent entities that communicate through asynchronous messages and do not share state. Thereby, they avoid concurrency bugs such as data races, but are not immune to concurrency bugs in general. This study taxonomizes concurrency bugs in actor-based programs reported in literature. Furthermore, it analyzes the bugs to identify the patterns causing them as well as their observable behavior. Based on this taxonomy, we further analyze the literature and find that current approaches to static analysis and testing focus on communication deadlocks and message protocol violations. However, they do not provide solutions to identify livelocks and behavioral deadlocks. The insights obtained in this study can be used to improve debugging support for actor-based programs with new debugging techniques to identify the root cause of complex concurrency bugs.Comment: - Submitted for review - Removed section 6 "Research Roadmap for Debuggers", its content was summarized in the Future Work section - Added references for section 1, section 3, section 4.3 and section 5.1 - Updated citation