| 1. |
- Lindgren, Per, et al.
(författare)
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Robust real-time applications in Timber
- 2006
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Ingår i: 2006 IEEE International Conference on Electro/information Technology. - Piscataway, NJ : IEEE Communications Society. - 0780395921 ; , s. 191-196
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Konferensbidrag (refereegranskat)abstract
- Embedded systems are often operating under hard real-time constraints, for example in automotive applications. For such systems, robustness and reliability are crucial, which calls for rigorous system design and methodologies for validation. In this paper we advocate a design methodology for robust, realtime systems, based on Timber; a pure reactive system model that allows for formal reasoning about various system properties. We outline how system specifications in Timber can be "compiled" into efficient standalone executables for general light-weight microcontroller platforms. Methods for resource analysis and implications to system dimensioning and validation are further discussed.
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| 2. |
- Kero, Johan, et al.
(författare)
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Determination of meteoroid physical properties from tristatic radar observations
- 2008
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Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 26, s. 2217-2228
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Tidskriftsartikel (refereegranskat)abstract
- In this work we give a review of the meteor head echo observations carried out with the tristatic 930MHz EISCAT UHF radar system during four 24 h runs between 2002 and 2005 and compare these with earlier observations. A total number of 410 tristatic meteors were observed. We describe a method to determine the position of a compact radar target in the common volume monitored by the three receivers and demonstrate its applicability for meteor studies. The inferred positions of the meteor targets have been utilized to estimate their velocities, decelerations and directions of arrival as well as their radar cross sections with unprecedented accuracy. The velocity distribution of the meteoroids is bimodal with peaks at 35–40 km/s and 55–60 km/s, and ranges from 19–70 km/s. The estimated masses are between 10−9–10−5.5 kg. There are very few detections below 30 km/s. The observations are clearly biased to high-velocity meteoroids, but not so biased against slow meteoroids as has been presumed from previous tristatic measurements. Finally, we discuss how the radial deceleration observed with a monostatic radar depends on the meteoroid velocity and the angle between the trajectory and the beam. The finite beamwidth leads to underestimated meteoroid masses if radial velocity and deceleration of meteoroids approaching the radar are used as estimates of the true quantities in a momentum equation of motion.
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| 3. |
- Kero, Johan, 1978-
(författare)
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High-resolution meteor exploration with tristatic radar methods
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A meteor observed with the naked eye is colloquially called a shooting star. The streak of light is generated by an extra-terrestrial particle, a meteoroid, entering the Earth’s atmosphere. The term meteor includes both luminosity detectable by optical means and ionization detectable by radar. The radar targets of meteor head echoes have the same motion as the meteoroids on their atmospheric flight and are relatively independent of aspect angle. They appear to be compact regions of plasma created at around 100 km altitude and have no appreciable duration. This thesis reviews the meteor head echo observations carried out with the tristatic 930 MHz EISCAT UHF radar system during four 24h runs between 2002 and 2005, and a 6h run in 2003 with the monostatic 224 MHz EISCAT VHF radar. It contains the first strong observational evidence of a submillimeter-sized meteoroid breaking apart into two distinct fragments. This discovery promises to be useful in the further understanding of the interaction processes of meteoroids with the Earth’s atmosphere and thus also the properties of interplanetary/interstellar dust. The tristatic capability of the EISCAT UHF system makes it a unique tool for investigating the physical properties of meteoroids and the meteor head echo scattering process. The thesis presents a method for determining the position of a compact radar target in the common volume of the antenna beams and demonstrates its applicability for meteor studies. The inferred positions of the meteor targets are used to estimate their velocities, decelerations, directions of arrival and radar cross sections (RCS) with unprecedented accuracy. The head echoes are detected at virtually all possible aspect angles all the way out to 130° from the meteoroid trajectory, limited by the antenna pointing directions. The RCS of individual meteors simultaneously observed with the three receivers are equal within the accuracy of the measurements with a very slight trend suggesting that the RCS decreases with increasing aspect angle. A statistical evaluation of the measurement technique shows that the determined Doppler velocity agrees with the target range rate. This demonstrates that no contribution from slipping plasma is detected and that the Doppler velocities are unbiased within the measurement accuracy. The velocities of the detected meteoroids are in the range of 19-70 km/s, but with very few detections at velocities below 30 km/s. The thesis compares observations with a numerical single-body ablation model, which simulates the physical processes during meteoroid flight through the atmosphere. The estimated meteoroid masses are in the range of 10-9 - 10-5.5 kg.
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| 4. |
- Kero, Johan, et al.
(författare)
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On the meteoric head echo radar cross section angular dependence
- 2008
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35, s. 5-
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Tidskriftsartikel (refereegranskat)abstract
- We present radar cross section (RCS) measurements of meteor head echoes observed with the tristatic 930 MHz EISCAT UHF radar system. The three receivers offer a unique possibility to accurately compare the monostatic RCS of a meteor target with two simultaneously probed bistatic RCSs at different aspect angles. Meteoroids from all possible directions entering the common volume monitored by the three receivers are detected, out to an aspect angle of 130° from the meteoroid trajectories. The RCS of individual meteors as observed by the three receivers are equal within the accuracy of the measurements. This is consistent with an essentially isotropic scattering process as has previously been inferred from polarization measurements by S. Close et al. (2002). There is a very weak trend present in our data suggesting that the RCS may decrease at a rate of 0.2 dB per 10° with increasing aspect angle.
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| 5. |
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| 6. |
- Kero, Johan, et al.
(författare)
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Three-dimensional radar observation of a submillimeter meteoroid fragmentation
- 2008
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35, s. 5-
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Tidskriftsartikel (refereegranskat)abstract
- We present and discuss two examples of pulsating meteor events observed with the tristatic 930 MHz EISCAT UHF radar system. One of them provides the first strong observational evidence of a submillimeter-sized meteoroid breaking apart into two distinct fragments. The received power fluctuates regularly in the time profiles of all three receivers, but the fluctuation frequencies are different. The pulsations are interpreted as being due to interference from two distinct scattering centers and the three detected pulsation rates are utilized to calculate the differential velocity of the fragments. The result is consistent with interference from two fragments of unequal cross-sectional area over mass ratio, separating from each other due to different deceleration along the trajectory of their parent meteoroid. The other meteor event is an example of a meteoroid undergoing quasi-continuous disintegration. This manifests itself as simultaneous pulsations at all three receivers. Both observations indicate a head echo target upper size limit of the order of half the 32 cm radar wavelength.
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| 7. |
- Kero, Martin, et al.
(författare)
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A correct and useful incremental copying garbage collector
- 2007
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Ingår i: Proceedings of the the 2007 International Symposium on Memory Management. - New York : ACM Digital Library. - 9781595938930 ; , s. 129-140
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Konferensbidrag (refereegranskat)abstract
- Designing a garbage collector with real-time properties is a particularly difficult task, involving the construction of both an incremental run-time algorithm as well as methods enabling a priori reasoning about schedulability in two dimensions (time and memory usage in conjunction). In order to comply with such ambitious goals with any amount of formal rigor, a comprehensive understanding of the actual algorithm used is of course a fundamental requirement. In this paper we present a formal model of an incremental copying garbage collector, where each atomic increment is modeled as a transition between states of a heap process. Soundness of the algorithm is shown by proving that the garbage collecting heap process is weakly bisimilar to a non-collecting heap with infinite storage space. In addition, we show that our collector is both terminating and useful, in the sense that it actually recovers the unreachable parts of any given heap in a finite number of steps.
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| 8. |
- Kero, Martin, et al.
(författare)
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Timber as an RTOS for small embedded devices
- 2005
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Ingår i: PREALWSN 2005. - Kista : Swedish Institute of Computer Science.
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Konferensbidrag (refereegranskat)abstract
- Software development for small, real-time and resource constrained, embedded systems is becoming increasingly complex. To be able to guarantee robustness and reliability, the underlying infrastructure should not be based upon ad hoc solutions. In this paper we identify three key features of a minimalistic Real-Time Operating System (RTOS), and presents the run-time system of Timber, a reactive deadlinedriven programming language. We scrutinize the functionalities of the run-time system in the light of real-time requirements, and emphasize the importance of integrating an adequate notion of time, both semantically in the programming interface as well as part of the run-time system.
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| 9. |
- Kero, Timo, 1973, et al.
(författare)
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ASSESSING METHODS FOR MANAGEMENT OF R&D PROCESS INFORMATION
- 2009
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Ingår i: International Association for Management of Technology, IAMOT 2009 Proceedings.
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Konferensbidrag (refereegranskat)abstract
- In this paper a new method incorporating flexible collection of process information along with an intuitive manner of presenting the processes along with the process information is presented and compared to a standard DSM process chart. A prototype tool implementing the proposed method is also presented.A bio-medical process is mapped using interviews and available documentation from Nobel Biocare as the main method to collect process information. The complete model is documented applying a DSM tool. The proposed interactive process modeling (IPM) method has been developed in parallel with the mapped process, along with a prototype process documentation tool, to map the same process and compare the two mapping cases.The studied process contains 101 process activities that have been mapped and described using the two methods (DSM and the new interactive process mapping (IPM)). It has been found that the IPM method enables a more complete approach to process improvement since it can be applied and updated easier because of features such as: version control, higher level of user interactivity, alternative representations of process properties using links between information objects, IT-resources and organizational roles within the process chart.A flexible approach using the IPM method ensures rich and easily accessible process information that is easier to interpret, communicate and maintain over time than the standard DSM model.
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| 10. |
- Meisel, David D., et al.
(författare)
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Physical Characteristics of Kazan Minor Showers as Determined by Correlations with the Arecibo UHF radar
- 2008
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Ingår i: Advances in Meteoroid and Meteor Science. - New York, NY : Springer. - 9780387784182
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Bokkapitel (refereegranskat)abstract
- In the northern hemisphere, the month of February is characterized by a lack of major meteor shower activity yet a number of weak minor showers are present as seen bythe Kazan radar. Using the Feller transformation to obtain the distribution of true meteor velocities from the distribution of radial velocities enables the angle of incidence to be obtained for the single beam AO (Arecibo Observatory) data. Thus the loci of AO radiants become beam-centered circles on the sky and one can, with simple search routines, find where these circles intersect on radiants determined by other means. Including geocentric velocity as an additional search criterion, we have examined a set of February radiants obtained at Kazan for coincidence in position and velocity. Although some may be chance associations, only those events with probabilities of association[0.5 have been kept. Roughly 90 of the Kazan showers have been verified in this way with mass, radius anddensity histograms derived from the AO results. By comparing these histograms with those of the ‘‘background’’ in which the minor showers are found, a qualitative scale of dynamical minor shower age can be formulated. Most of the showers are found outside the usual ‘‘apex’’ sporadic source areas where it is easiest to detect discrete showers with less confusion from the background.
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