A unified IMEX Runge-Kutta approach for hyperbolic systems with multiscale relaxation

In this paper we consider the development of Implicit-Explicit (IMEX) Runge-Kutta schemes for hyperbolic systems with multiscale relaxation. In such systems the scaling depends on an additional parameter which modifies the nature of the asymptotic behavior which can be either hyperbolic or parabolic. Because of the multiple scalings, standard IMEX Runge-Kutta methods for hyperbolic systems with relaxation loose their efficiency and a different approach should be adopted to guarantee asymptotic preservation in stiff regimes. We show that the proposed approach is capable to capture the correct asymptotic limit of the system independently of the scaling used. Several numerical examples confirm our theoretical analysis

Implicit-Explicit Runge-Kutta schemes for hyperbolic systems and kinetic equations in the diffusion limit

We consider Implicit-Explicit (IMEX) Runge-Kutta (R-K) schemes for hyperbolic systems with stiff relaxation in the so-called diffusion limit. In such regime the system relaxes towards a convection-diffusion equation. The first objective of the paper is to show that traditional partitioned IMEX R-K schemes will relax to an explicit scheme for the limit equation with no need of modification of the original system. Of course the explicit scheme obtained in the limit suffers from the classical parabolic stability restriction on the time step. The main goal of the paper is to present an approach, based on IMEX R-K schemes, that in the diffusion limit relaxes to an IMEX R-K scheme for the convection-diffusion equation, in which the diffusion is treated implicitly. This is achieved by an original reformulation of the problem, and subsequent application of IMEX R-K schemes to it. An analysis on such schemes to the reformulated problem shows that the schemes reduce to IMEX R-K schemes for the limit equation, under the same conditions derived for hyperbolic relaxation. Several numerical examples including neutron transport equations confirm the theoretical analysis

Semi-Implicit-type order-adaptive CAT2 schemes for systems of balance laws with relaxed source term

In this paper we present two semi-implicit-type second order Compact Approximate Taylor (CAT2) numerical schemes and blend them with a local a posteriori Multi-dimensional Optimal Order Detection (MOOD) paradigm to solve hyperbolic systems of balance laws with relaxed source term. The resulting scheme presents high accuracy when applied to smooth solutions, essentially non-oscillatory behavior for irregular ones, and offers a nearly fail-safe property in terms of ensuring positivity. The numerical results obtained from a variety of test cases, including smooth and non-smooth well-prepared and unprepared initial condition, assessing the appropriate behavior of the semi-implicit-type second order CATMOOD schemes. These results have been compared in accuracy and efficiency with a second order semi-implicit Runge-Kutta (RK) method

Implicit and semi-implicit well-balanced finite-volume methods for systems of balance laws

The aim of this work is to design implicit and semi-implicit high-order well-balanced finite-volume numerical methods for 1D systems of balance laws. The strategy introduced by two of the authors in some previous papers for explicit schemes based on the application of a well-balanced reconstruction operator is applied. The well-balanced property is preserved when quadrature formulas are used to approximate the averages and the integral of the source term in the cells. Concerning the time evolution, this technique is combined with a time discretization method of type RK-IMEX or RK-implicit. The methodology will be applied to several systems of balance laws.This work is partially supported by projects RTI2018-096064-B-C21 funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”, projects P18-RT-3163 of Junta de Andalucía and UMA18-FEDERJA-161 of Junta de Andalucía-FEDER-University of Málaga. G.Russo and S.Boscarino acknowledge partial support from the Italian Ministry of University and Research (MIUR), PRIN Project 2017 (No. 2017KKJP4X) entitled “Innovative numerical methods for evolu-tionary partial differential equations and applications”. I. Gómez-Bueno is also supported by a Grant from “El Ministerio de Ciencia, Innovación y Universidades”, Spain (FPU2019/01541) funded by MCIN/AEI/10.13039/501100011033 and “ESF Invest-ing in your future”. // Funding for open access charge: Universidad de Málaga/CBUA

CWI at TREC 2012, KBA track and Session Track

We participated in two tracks: Knowledge Base Acceleration (KBA) Track and Session Track. In the KBA track, we focused on experi- menting with different approaches as it is the first time the track is launched. We experimented with supervised and unsupervised re- trieval models. Our supervised approach models include language models and a string-learning system. Our unsupervised approaches include using: 1)DBpedia labels and 2) Google-Cross-Lingual Dic- tionary (GCLD). While the approach that uses GCLD targets the central and relvant bins, all the rest target the central bin. The GCLD and the string-learning system have outperformed the oth- ers in their respective targeted bins. The goal of the Session track submission is to evaluate whether and how a logic framework for representing user interactions with an IR system can be used for improving the approximation of the relevant term distribution that another system that is supposed to have access to the session infor- mation will then calculate. the documents in the stream corpora. Three out of the seven runs used a Hadoop cluster provide by Sara.nl to process the stream cor- pora. The other 4 runs used a federated access to the same corpora distributed among 7 workstations

Mental Health in New York City After the September 11 Terrorist Attacks: Results From Two Population Surveys

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/40345/2/Galea_Mental Health in New York city After_2002.pd

Mental Health Service and Medication Use in New York City After the September 11, 2001, Terrorist Attack

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/40261/2/Boscarino_Mental Health Service and Medication Use_2004.pd

Uncertainty quantification for kinetic models in socio-economic and life sciences

Kinetic equations play a major rule in modeling large systems of interacting particles. Recently the legacy of classical kinetic theory found novel applications in socio-economic and life sciences, where processes characterized by large groups of agents exhibit spontaneous emergence of social structures. Well-known examples are the formation of clusters in opinion dynamics, the appearance of inequalities in wealth distributions, flocking and milling behaviors in swarming models, synchronization phenomena in biological systems and lane formation in pedestrian traffic. The construction of kinetic models describing the above processes, however, has to face the difficulty of the lack of fundamental principles since physical forces are replaced by empirical social forces. These empirical forces are typically constructed with the aim to reproduce qualitatively the observed system behaviors, like the emergence of social structures, and are at best known in terms of statistical information of the modeling parameters. For this reason the presence of random inputs characterizing the parameters uncertainty should be considered as an essential feature in the modeling process. In this survey we introduce several examples of such kinetic models, that are mathematically described by nonlinear Vlasov and Fokker--Planck equations, and present different numerical approaches for uncertainty quantification which preserve the main features of the kinetic solution.Comment: To appear in "Uncertainty Quantification for Hyperbolic and Kinetic Equations

Alert but less alarmed: a pooled analysis of terrorism threat perception in Australia

<p>Abstract</p> <p>Background</p> <p>Previous Australian research has highlighted disparities in community perceptions of the threat posed by terrorism. A study with a large sample size is needed to examine reported concerns and anticipated responses of community sub-groups and to determine their consistency with existing Australian and international findings.</p> <p>Methods</p> <p>Representative samples of New South Wales (NSW) adults completed terrorism perception questions as part of computer assisted telephone interviews (CATI) in 2007 (N = 2081) and 2010 (N = 2038). Responses were weighted against the NSW population. Data sets from the two surveys were pooled and multivariate multilevel analyses conducted to identify health and socio-demographic factors associated with higher perceived risk of terrorism and evacuation response intentions, and to examine changes over time.</p> <p>Results</p> <p>In comparison with 2007, Australians in 2010 were significantly more likely to believe that a terrorist attack would occur in Australia (Adjusted Odd Ratios (AOR) = 1.24, 95%CI:1.06-1.45) but felt less concerned that they would be directly affected by such an incident (AOR = 0.65, 95%CI:0.55-0.75). Higher perceived risk of terrorism and related changes in living were associated with middle age, female gender, lower education and higher reported psychological distress. Australians of migrant background reported significantly lower likelihood of terrorism (AOR = 0.52, 95%CI:0.39-0.70) but significantly higher concern that they would be personally affected by such an incident (AOR = 1.57, 95%CI:1.21-2.04) and having made changes in the way they live due to this threat (AOR = 2.47, 95%CI:1.88-3.25). Willingness to evacuate homes and public places in response to potential incidents increased significantly between 2007 and 2010 (AOR = 1.53, 95%CI:1.33-1.76).</p> <p>Conclusion</p> <p>While an increased proportion of Australians believe that the national threat of terrorism remains high, concern about being personally affected has moderated and may reflect habituation to this threat. Key sub-groups remain disproportionately concerned, notably those with lower education and migrant groups. The dissonance observed in findings relating to Australians of migrant background appears to reflect wider socio-cultural concerns associated with this issue. Disparities in community concerns regarding terrorism-related threat require active policy consideration and specific initiatives to reduce the vulnerabilities of known risk groups, particularly in the aftermath of future incidents.</p