Kirsten Hansen

Specifying and verifying requirements of real-time systems

An approach to specification of requirements and verification of design for real-time systems is presented. A system is defined by a conventional mathematical model for a dynamic system where application specific states denote functions of real time. Specifications are formulas in duration calculus, a real-time interval logic, where predicates define durations of states. Requirements define safety and functionality constraints on the system or a component. A top-level design is given by a control law: a predicate that defines an automation controlling the transition between phases of operation. Each phase maintains certain relations among the system states; this is analogous to the control functions known from conventional control theory. The top-level design is decomposed into an architecture for a distributed system with specifications for sensor, actuator, and program components. Programs control the distributed computation through synchronous events. Sensors and actuators relate events with system states. Verification is a deduction showing that a design implies requirements. >

From safety analysis to software requirements

Software for safety critical systems must deal with the hazards identified by safety analysis. This paper investigates, how the results of one safety analysis technique, fault trees, are interpreted as software safety requirements to be used in the program design process. We propose that fault tree analysis and program development use the same system model. This model is formalized in a real-time, interval logic, based on a conventional dynamic systems model with state evolving over time. Fault trees are interpreted as temporal formulas, and it is shown how such formulas can be used for deriving safety requirements for software components.

Paleozoic paleo-cover of the southern part of the fennoscandian shield-fission track constraints

Abstract Granitic intrusions older than 1200 Ma, from an area west of lake Vanern, south Sweden, show fission track ages of 680 ± 50 Ma (2 σ) (Late Precambrian) for sphene and 220 ± 10 Ma (Late Triassic) for apatite. The samples were taken at the present post-glacial erosion surface which is close to the sub-Cambrian peneplain. The c. 680 Ma sphene fission track ages are thought to be related to the uplift of the area which led to the establishment of this erosion surface at c. 600 Ma ago. The much younger apatite fission track ages and the confined spontaneous track length distributions along with regional stratigraphic constraints suggest that the basement was subsequently buried under 3–4 km of Paleozoic supracrustals. This induced in the basement a rise in temperature which obliterated the older apatite fission tracks, but not those in sphene which has a higher closure temperature. At the beginning of the Mesozoic, the area was uplifted again, the cover rocks were removed, and the basement rocks cooled slowly below the temperature range of fission track annealing in apatite.

Lamprophyres and carbonatitic lamprophyres related to rifting in the Labrador Sea

Abstract Lamprophyre dykes intruded into the Archaean of South West Greenland are believed to coincide with the early stages of rifting in the Labrador Sea area. They yield K/Ar and fission-track ages of 150–115 m.y. which are similar to the apatite fission-track ages from the host rocks but which predate the formation of ocean floor. The strongly undersaturated, often K-rich magmas exhibit the chemical characters of modern rift volcanism with many types present, and the paragenesis and their mineral chemistry reflect the composition and the different physical conditions in the evolution of the lamprophyres. Crystal fractionation and carbonate unmixing are believed to be the main factors in the evolution of the lamprophyre dykes from a primary mantle derived magma. However, the most undersaturated and evolved lamprophyre types cannot be explained in this way, and more complex models must be considered.

Post-orogenic tectonic and thermal history of a rifted continental margin: the Scoresby Sund area, East Greenland

Abstract Fission track (FT) analysis of zircon, sphene and apatite from crystalline basement in the Scoresby Sund area, East Greenland, and FT modelling reveal information about the cooling and uplift paths for individual tectonic blocks since the Caledonian orogeneny. Up to c. 325 Ma the area cooled and behaved as a single unit. However, it subsequently broke into several fault-bounded blocks, each block moving independently of adjacent blocks. Net uplift since 325 Ma was of a similar magnitude (8 km, assuming a geothermal gradient of 30°C/km) along the crest of the Devonian fault zone for the southern blocks, but about 9 km for the Stauning Alper; and these blocks were probably tilted away from the rifted continental margin. The relief evolution accompanying uplift in the Caledonian basement is closely related to Mesozoic basin formation, subsidence and infilling in the area. FT modelling reveals fast cooling from c. 70°C to surface temperatures during the last 55 m.y., probably as a result of Tertiary rifting and magmatic activity in the area.

The Proper Role of Evidence in Complementary/Alternative Medicine

In this article we explore the role evidence ought to play in complementary and alternative medicine (CAM). First, we consider the claim that evidence in the form of randomized controlled trials (RCTs) cannot be obtained for CAMs. Second, we consider various claims to the effect that there are ways of obtaining evidence that do not make use of RCTs. We argue that there is no good reason why CAM should be exempted from the general requirement that treatments undergo evaluation by RCT. Third, we consider two implications for health care policy. First, many activities in conventional medicine have never been rigorously evaluated and are widely in use nonetheless. We argue that this fails to provide a reason for exempting CAM from a demand for evidence. Second, CAM use may be compared to a choice of lifestyle, and this has a significant impact on which requirements of evidence can reasonably be imposed.

A numerical model for the thermal history of rocks based on confined horizontal fission tracks

Abstract A numerical model for determination of the thermal history of rocks is presented. It is shown that the thermal history may be uniquely determined as a piece-by-piece linear function on the basis of etched confined, horizontal fission track length distributions, their surface densities, and the uranium content. The initial track length distribution is taken into account. A relation between the measured track length distribution and age is given which includes correlation for partial annealing. The annealing model used is the fanning Arrhenius plot. It is shown that track length distributions measured in transmitted light are biased favouring short tracks compared with measurements in reflected light. Testing of the model is performed on apatites from a tuffaceous sandstone from Bornholm (Denmark) yielding an estimate of the thermal history for the period of about 280 Ma back in time.

Attitudes to evidence in acupuncture: an interview study

The use of complementary and alternative medicine is increasing in the Western world. However, there is no clear evidence of effect of alternative therapies. Moreover, there is no consensus between practitioners and researchers as to the right way of assessing the efficacy of alternative therapies. To investigate practitioners’ perspective on evidence and ways of assessing efficacy twelve in-depth interviews were conducted in Denmark with acupuncturists, including physicians practising acupuncture, acupuncturists with a health-related background, and acupuncturists without a health-related background. Two themes predominated the study, first, the interviewees’ general reflections on how it is possible to establish knowledge about an effect of acupuncture; and second the interviewees’ reflections on the use of randomized controlled trials in acupuncture, including obstacles and alternatives to conducting randomized controlled trials. Further, two conceptions of what constitutes evidence were identified: a biomedical conception and an experience-based conception. Most interviewees were sceptical about the use of randomized controlled trials in acupuncture. Two reasons, especially, were given for this scepticism. First, practical and instrumental reasons concerning the specific elements of the randomized controlled trial or relating to limited resources; and second, value-based reasons are concerning the nature of acupuncture. However, the interviewees were really opposed only to a certain kind of randomized controlled trial, the so-called explanatory trial. They would actually welcome a pragmatic trial. The study gives valuable insight into an under explored field and provide a platform for further investigation, and a better informed discussion of the subject.

Rare earth abundances in Mesozoic undersaturated alkaline rocks from West Greenland

Abstract Rare earth element analyses from a series of Mesozoic undersaturated lamprophyre dykes from southern West Greenland show concentration levels comparable to similar rock types elsewhere. An earlier published simple fractionation model, describing their evolution, must be modified. A primitive olivine nephelinitic parent magma similar to the most primitive lamprophyre coexisted in the mantle with a fluid phase and evolved — possibly at a higher level — mainly through crystal fractionation and liquid immiscibility. Crustal contamination may have had minor importance for their evolution.

The Use of Fission Track Measurements in Basin Modeling

Forward modeling of fission track annealing of apatites is used together with basin modeling to estimate past heat flow and amount of erosion. For a known uranium concentration the track length histogram and the surface track density, hold information on the thermal history of the minerals. An equation is developed which is used to determine the number of horizontal (relative to prismatic faces) tracks in the histogram that has been generated after deposition. The post-sedimentary thermal history of the sample is calculated by a ID-basin model with an initial estimate on the paleoheat flow. The thermal history then is used to calculate the track length histogram including distribution of track lengths caused by distribution of energy of fission products and anisotropy. Adjustments of the paleoheat flow or the erosion depth are performed to obtain a better match between the calculated and measured track length histograms (post-sedimentary stage).The modeling is applied to the Danish North Sea well D-l.Fission track measurements on apatite are available at three depths.