Swedish Defence Research Agency

About: Swedish Defence Research Agency is a government organization based out in Stockholm, Sweden. It is known for research contribution in the topics: Radar & Laser. The organization has 1413 authors who have published 2731 publications receiving 56083 citations. The organization is also known as: Totalförsvarets forskningsinstitut.

A framework for fault-tolerance in HLA-based distributed simulations

Abstract: The widespread use of simulation in future military systems depends, among others, on the degree of reuse and availability of simulation models. Simulation support in such systems must also cope with failure in software or hardware. Research in fault-tolerant distributed simulation, especially in the context of the High Level Architecture (HLA), has been quite sparse. Nor does the HLA standard itself cover fault-tolerance extensively. This paper describes a framework, named Distributed Resource Management System (DRMS), for robust execution of federations. The implementation of the framework is based on Web Services and Semantic Web technology, and provides fundamental services and a consistent mechanism for description of resources managed by the environment. To evaluate the proposed framework, a federation has been developed that utilizes time-warp mechanism for synchronization. In this paper, we describe our approach to fault tolerance and give an example to illustrate how DRMS behaves when it faces faulty federates.

Solid Propellants based on ADN and HTPB

Abstract: The aim of this work was to perform an initial evaluation of ammonium dinitramide, ADN, as substitute for ammonium perchlorate, AP, in solid rocket propellants for large space launch boosters. This paper includes performance evaluation, curing and compatibility assessments, propellant formulation and determination of ballistic properties. The results show that the theoretical specific impulse increases from 262 s to 270 s by replacing AP with the same volume ADN in a typical HTPB/Al-based formulation. ADN is found to be chemically compatible with HTPB. However, ADN seems to accelerate the oxidative degradation of HTPB and thus a suitable antioxidant is required. ADN/HTPB/Albased propellants have been formulated and cured successfully using isocyanates. The formulations were found to be thermally stable. Ballistic properties were determined using a strand burner. ADN/Al/HTPB propellant with a solid loading of 80% had a burn rate of 12.8 mm/s at 6 MPa and a pressure exponent of 0.9. The pressure exponent was high, but no burn rate modifiers or ballistic additives were used.

A framework for simulation-based optimization of business process models

Abstract: The Assignment Problem is a classical problem in the field of combinatorial optimization, having a wide range of applications in a variety of contexts. In general terms, the Assignment Problem consists of determining the best assignment of tasks to agents according to a predefined objective function. Different variants of the Assignment Problem have been extensively investigated in the literature in the last 50 years. In this work, we introduce and analyze the problem of optimizing a business process model with the objective of finding the most beneficial assignment of tasks to agents. Despite similarities, this problem is distinguished from the traditional Assignment Problem in that we consider tasks to be part of a business process model, being interconnected according to defined rules and constraints. In other words, assigning a business process to agents is a more complex form of the Assignment Problem. Two main categories of business processes, assignment-independent and assignment-dependent, are distinguished. In the first category, different assignments of tasks to agents do not affect the flow of the business process, while processes in the second category contain critical tasks that may change the workflow, depending on who performs them. In each category several types of processes are studied. Algorithms for finding optimal and near-optimal solutions to these categories are presented. For the first category, depending on the type of process, the Hungarian algorithm is combined with either the analytical method or simulation to provide an optimal solution. For the second category, we introduce two algorithms. The first one finds an optimal solution, but is feasible only when the number of critical tasks is small. The second algorithm is applicable to large number of critical tasks, but provides a near-optimal solution. In the second algorithm a hill-climbing heuristic method is combined with the Hungarian algorithm and simulation to find an overall near-optimal solution. A series of tests is conducted which demonstrates that the proposed algorithms efficiently find optimal solutions for assignment-independent and near-optimal solutions for assignment-dependent processes.

Ka-band RF MEMS phase shifters for energy starved millimetre-wave radar sensors

Abstract: Low-loss millimetre-wave RF MEMS phase shifters made on quartz are assessed with respect to a Ka-band low-power multifunctional radar sensor application. A loaded line type of phase shifter circuit presents a phase shift of 22.3° and a loss of 0.4 dB at 35 GHz. A switched line phase shifter gives 187° of phase shift and 1.5 dB of loss at 30 GHz (i.e. a FoM=122°/dB). We estimate that a 5-bit loaded line/switched line MEMS phase shifter circuit can achieve a loss of 4 dB at 35 GHz which could reduce by a factor 2 the required transmit DC power level in a Ka-Band energy starved phased array radar system.

Multilevel model for airborne transmission of foot-and-mouth disease applied to Swedish livestock

Abstract: The foot-and-mouth disease is an ever-present hazard to the livestock industry due to the huge economic consequences following an outbreak that necessitates culling of possibly infected animals in vast numbers. The disease is highly contagious and previous epizootics have shown that it spreads by many routes. One such route is airborne transmission, which has been investigated in this study by means of a detailed multilevel model that includes all scales of an outbreak. Local spread within an infected farm is described by a stochastic compartment model while the spread between farms is quantified by atmospheric dispersion simulations using a network representation of the set of farms. The model was applied to the Swedish livestock industry and the risk for an epizootic outbreak in Sweden was estimated using the basic reproduction number of each individual livestock-holding farm as the endpoint metric. The study was based on comprehensive official data sets for both the current livestock holdings and regional meteorological conditions. Three species of farm animals are susceptible to the disease and are present in large numbers: cattle, pigs and sheep. These species are all included in this study using their individual responses and consequences to the disease. It was concluded that some parts of southern Sweden are indeed preconditioned to harbor an airborne epizootic, while the sparse farm population of the north renders such events unlikely to occur there. The distribution of the basic reproduction number spans over several orders of magnitudes with low risk of disease spread from the majority of the farms while some farms may act as very strong disease transmitters. The results may serve as basic data in the planning of the national preparedness for this type of events.