| 1. |
- Crenshaw, D. M., et al.
(författare)
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Multiwavelength observations of short-timescale variability in NGC 4151. I. Ultraviolet observations
- 1996
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 322-335335
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Tidskriftsartikel (refereegranskat)abstract
- Presents the results of an intensive ultraviolet monitoring campaign on the Seyfert 1 galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously with the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 Aring went through four significant and well-defined ldquoeventsrdquo of duration 2-3 days during the continuous-monitoring period. The authors find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines
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| 2. |
- Edelson, R. A., et al.
(författare)
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Multiwavelength observations of short-timescale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
- 1996
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 364-377377
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Tidskriftsartikel (refereegranskat)abstract
- For pt.III see ibid., vol.470, no.1, p.349-63 (1996). Combines data from the three preceding papers in order to analyze the multi wave-band variability and spectral energy distribution of the Seyfert 1 galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA=6%) variations (uncorrelated with those at lower energies) were seen at soft gamma-ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 Aring. These data do not probe extreme ultraviolet (1200 Aring to 0.1 keV) or hard X-ray (250 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of lsim0.15 day between 1275 Aring and the other ultraviolet bands, lsim0.3 day between 1275 Aring and 1.5 keV, and lsim1 day between 1275 and 5125 Aring. These tight limits represent more than an order of magnitude improvement over those determined in previous multi-wave-band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (ales-2.5)
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| 3. |
- Akselsson, Roland, et al.
(författare)
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Computer Aided Participatory Planning
- 1990
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Ingår i: Ergonomics of Hybrid Automated Systems II. ; , s. 69-76
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Konferensbidrag (refereegranskat)abstract
- A computer aided action research method for design of work places is presented. A project group of researchers, managers, union representatives, supervisors, shop-floor workers and representatives from the health-and-safety department analyse different aspects of the physical and organizational work environment. Factory layouts and the flow of raw materials and goods, truck routes and overhead crane movements are shown on a computer screen by means of simulation and animation techniques. Field studies at four companies strongly suggest that the animation helps the members in the project group to develop a common language and to better comprehend what a future factory design and work organization would look like.
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| 4. |
- Asratian, Armen, et al.
(författare)
-
Bipartite graphs and their applications
- 1998
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Bipartite graphs constitute one of the most intensively investigated classes of graphs, yet this book appears to be the first devoted entirely to their study. It provides a comprehensive introduction to the subject, with considerable emphasis on applications. In fact most of the chapters have at least one section devoted to applications in other fields of study. Although the grammar is sometimes in need of repair (for example, sentences are occasionally spliced together with commas), the book is clearly written. Many of the exercises are quite challenging. As the basic concepts of graph theory are carefully explained in Chapter 1, this book can be warmly recommended not only to experts but also to those seeking an accesible yet rigorous introduction to bipartite graphs, or indeed to graphs in general.
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| 5. |
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| 6. |
- Hager, J, et al.
(författare)
-
Modelling steam drying of a single porous ceramic sphere: Experiments and simulations
- 1997
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Ingår i: Chemical Engineering Science. - 0009-2509. ; 52:8, s. 1253-1264
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate and describe the drying kinetics occurring in a porous material during superheated steam drying, a model was developed based on the fundamental transport equations for mass and heat. The driving forces in the model are gradients of moisture, temperature and pressure. The transport coefficients employed were either measured experimentally or were derived theoretically from the pore size distribution of the material. The porous material was viewed as having cylindrical pores that wind according to a tortuosity factor, which was the only adjustable parameter used in the simulations. Local thermodynamic equilibrium was assumed to be present throughout the material. To describe this, an experimental sorption isobar was measured. Single ceramic spheres (10 mm diameter), which served as the porous model material, were dried in a thermobalance which enabled weight changes during drying to be determined very accurately. All the experiments were carried out under atmospheric conditions, but both the steam temperature and the steam mass flux were varied within a broad range. Internal temperatures in the sphere were also measured by use of thin thermocouples (0.5 mm), in order to determine the shape of the internal temperature rise and obtain an indication of the temperature gradient. Good agreement was obtained between results of the experiments and of the simulations, both for the drying rate and for internal temperature under varying external conditions, providing support for the model. The model was also used to study the magnitude and influence of the different transport mechanisms during steam drying. (C) 1997 Elsevier Science Ltd.
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| 7. |
- Johansson, Gerd, et al.
(författare)
-
Computer-Aided Planning of Working and Living Environments for Disabled People
- 1992
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Ingår i: Computer Applications in Ergonomics, Occupational Safety and Health. ; , s. 137-144
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Konferensbidrag (refereegranskat)abstract
- A research program for the development of a method for computer-aided planning of homes and working environments for disabled people has recently started. The method is being tested at rehabilitation centres in realistic planning situations and has obtained positive response from both the disabled persons and the professionals such as occupational therapists. The requirements and features of the computer modelling techniques are discussed, and future improvements to the planning tool are suggested.
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| 8. |
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| 9. |
- Petersson, Nils F, et al.
(författare)
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A Master of Ergonomics Programme in Sweden
- 1997
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Ingår i: Contents of Ergonomics, Labour Protection and Work Safety Educational Programs, Poznan 1997. ; , s. 225-231
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Konferensbidrag (refereegranskat)abstract
- A new master programme in ergonomics is being developed by the Swedish National Institute for Working life in co-operation with the Institutes of Technology in Linköping and Lund. The course runs at ‘half-speed’ and with extensive use of IT. The course takes advantage of the students’ different professional backgrounds.
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| 10. |
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