Variable Structure System Simulation via Predefined Acausal Components

This article outlines a new approach of the experimental open-source modeling and simulation system Modia to simulate systems where the number of variables and equations can be changed after compilation and also during simulation, without having to re-generate and re-compile the code. Details are given for heat transfer in an insulated rod, where the discretisation of the rod is completely hidden from the symbolic engine. It is discussed how this approach could also be used in a future version of Modelica and/or FMI. Furthermore, this feature is also used in various variants to speed up collision handling in 3D mechanical systems. For example, by rigidly fixing an object after it has been gripped, with or without calculating the elastic response, and thereby dynamically changing the number of degrees of freedom

Modelling and Simulation of Physical Systems with Dynamically Changing Degrees of Freedom

A new approach is introduced to model and simulate equation-based systems where variables can appear and disappear during simulation without re-generation and re-compilation of code when the numbers of equations and states change during events. The method is presented in a generic, mathematical way and can be in principle applied to all types of declarative, equation-based modelling languages, such as Modelica. A concrete implementation is given for the Julia-based experimental modelling language Modia, which is similar to Modelica. However, Modia features far simpler semantics based on hierarchical collections of name/value pairs and has the ability to support domain-specific algorithms, especially for multibody systems with collision handling. The new method is demonstrated with heat-transfer in a rod, separation of stages of a rocket and gripping operations of a robot

Modia3D: Modeling and Simulation of 3D-Systems in Julia

Modia3D is an experimental Julia package to model and simulate 3D mechanical systems. Ideas from modern game engines are used to achieve a highly flexible setup and features of multi-body algorithms are used to get a rigid mathematical formulation and support, for example, of closed kinematic loops. Collision handling is performed on convex geometries with elastic response calculation. A Modia3D model is solved with a variable-step solver. This is important to combine Modia3D with the equation-based modeling system Modia in the future

A Prospective Study on the Impact and Out-of-Pocket Costs of Dengue Illness in International Travelers.

Although the costs of dengue illness to patients and households have been extensively studied in endemic populations, international travelers have not been the focus of costing studies. As globalization and human travel activities intensify, travelers are increasingly at risk for emerging and reemerging infectious diseases, such as dengue. This exploratory study aims to investigate the impact and out-of-pocket costs of dengue illness among travelers. We conducted a prospective study in adult travelers with laboratory-confirmed dengue and recruited patients at travel medicine clinics in eight different countries from December 2013 to December 2015. Using a structured questionnaire, we collected information on patients and their health-care utilization and out-of-pocket expenditures, as well as income and other financial losses they incurred because of dengue illness. A total of 90 patients participated in the study, most of whom traveled for tourism (74%) and visited countries in Asia (82%). Although 22% reported hospitalization and 32% receiving ambulatory care while traveling, these percentages were higher at 39% and 71%, respectively, after returning home. The out-of-pocket direct and indirect costs of dengue illness were US$421 (SD 744) and US$571 (SD 1,913) per episode, respectively, averaging to a total out-of-pocket cost of US$992 (SD 2,052) per episode. The study findings suggest that international travelers incur important direct and indirect costs because of dengue-related illness. This study is the first to date to investigate the impact and out-of-pocket costs of travel-related dengue illness from the patient's perspective and paves the way for future economic burden studies in this population

Sentinel surveillance of imported dengue via travellers to Europe 2012 to 2014: TropNet data from the DengueTools Research Initiative.

We describe the epidemiological pattern and genetic characteristics of 242 acute dengue infections imported to Europe by returning travellers from 2012 to 2014. The overall geographical pattern of imported dengue (South-east Asia > Americas > western Pacific region > Africa) remained stable compared with 1999 to 2010. We isolated the majority of dengue virus genotypes and epidemic lineages causing outbreaks and epidemics in Asia, America and Africa during the study period. Travellers acted as sentinels for four unusual dengue outbreaks (Madeira, 2012-13; Luanda, 2013; Dar es Salaam, 2014; Tokyo, 2014). We were able to characterise dengue viruses imported from regions where currently no virological surveillance data are available. Up to 36% of travellers infected with dengue while travelling returned during the acute phase of the infection (up to 7 days after symptom onset) or became symptomatic after returning to Europe, and 58% of the patients with acute dengue infection were viraemic when seeking medical care. Epidemiological and virological data from dengue-infected international travellers can add an important layer to global surveillance efforts. A considerable number of dengue-infected travellers are viraemic after arrival back home, which poses a risk for dengue introduction and autochthonous transmission in European regions where suitable mosquito vectors are prevalent

Comparison of different drug regimens for the treatment of loiasis-A TropNet retrospective study

Loa loa infection is endemic in limited areas of West-Central Africa. Loiasis has been associated with excess mortality, but clinical studies on its treatment are scant, particularly outside endemic areas, due to the rarity of cases diagnosed.; With this retrospective TropNet (European Network for Tropical Medicine and Travel Health) study, we aimed at outlining the treatment schedules followed by different reference centers for tropical medicine across Europe. We gathered information about 238 cases of loiasis, 165 of which had follow up data. The regimens followed by the different centers were heterogeneous. The drugs most frequently administered were: diethylcarbamazine alone (74/165, 45.1%), ivermectin alone (41/165, 25%), albendazole + ivermectin (21/164, 11.6%), ivermectin + diethylcarbamazine (16/165, 9.7%).; The management of loiasis substantially differs across specialized travel clinics in Europe. These discrepancies could be due to different local protocols as well as to (un)availability of the drugs. An harmonization of clinical protocols for the treatment of loiasis would be suggested across reference centers for tropical medicine in Europe

Algorithms for Component-Based 3D Modeling

The experimental modeling environment Modia3D is used to test and evaluate ideas to model and simulate larger and more complex 3-dimensional systems than is possible with a pure equation-based modeling system such as current Modelica. The goal is to closely combine equation-based modeling with component-based 3D modeling as used in modern game engines. In this article some key algorithms are discussed that have been developed for Modia3D. The overall objective is to utilize the results for the design of the next Modelica language generatio

Collision Handling with Variable-Step Integrators

This paper deals with collision handling of many convex shapes in offline simulations of Modelica-like object-oriented models,unsing variable-step Integrators with error control. Hereby, it is assumed that collisions appear only from time to time and/or that path planning algorithm shall utilize the provided information for collision avoidance. If a collision occurs, the collision force is computed with a spring/damper force element depending on the Penetration depth. Improvements to existing algorithms and methods are proposed: The Minikowski Protal Refinement (MPR) algorithm is enhanced so that not only Penetration depths but also closet distances between convex shapes are computed and that Special collision situations are treated properly. The broad and narrow phases of collision detection algorithms are enhanced as well, so that zero-crossing functions can be provided for the Integrator in order to Trigger Events when contact starts and Ends