| 1. |
- Crenshaw, D. M., et al.
(författare)
-
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. |
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| 3. |
- Svensson, C. E., et al.
(författare)
-
Decay Out of the Doubly Magic Superdeformed Band in the N=Z Nucleus 60Zn
- 1999
-
Ingår i: Physical Review Letters. - 1079-7114. ; 82:17, s. 3400-3403
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Tidskriftsartikel (refereegranskat)abstract
- The doubly magic superdeformed band in the N = Z nucleus Zn-60 has been identified. Linking transitions connecting this band to the yrast line provide the first spin, parity, and excitation energy measurements for superdeformed states in the A similar to 60 region. The stretched-E2 character and relatively large B(E2) values of these transitions suggest a nonstatistical decay-out process.
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| 4. |
- Asztalos, S J, et al.
(författare)
-
Spin yields of neutron-rich nuclei from deep inelastic reactions
- 1999
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 60:4
-
Tidskriftsartikel (refereegranskat)abstract
- The potential for using deep inelastic reactions to populate high-spin states in neutron-rich nuclei is studied in a series of experiments using GAMMASPHERE for gamma-ray detection and a silicon strip detector for measuring the angles of projectilelike and targetlike fragments. In three experiments 61 new transitions up to a maximum spin of 22 (h) over bar in 12 neutron-rich rare-earth nuclei were found. We observe that gamma-ray yields as a function of spin are flatter for all neutron transfer products than for inelastic excitation of either the projectile or target nucleus. Calculations are presented which indicate that this difference cannot be accounted for by quasielastic processes, but more likely are the result of larger energy loss processes, such as deep inelastic reactions. [S0556-2813(99)06009-4].
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| 5. |
- LaFosse, D R, et al.
(författare)
-
Search for hyperdeformation in Gd-146,Gd-147
- 1996
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 54:4, s. 1585-1588
-
Tidskriftsartikel (refereegranskat)abstract
- A search was undertaken to look for evidence of hyperdeformation in Gd-146,Gd-147. Three experiments employing Gammasphere for gamma-ray detection coupled with the Microball for channel selection via charged particle detection were carried out with increasing detection sensitivity and statistics. No definitive evidence for band structures that could be assigned to hyperdeformation could be found. Candidates previously reported are shown not to have properties consistent with a band structure.
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| 6. |
- Aberg, Jan, et al.
(författare)
-
Multialphabet coding with separate alphabet description
- 1997
-
Ingår i: Proceedings. Compression and Complexity of SEQUENCES 1997. - 0818681322 ; , s. 56-65
-
Konferensbidrag (refereegranskat)abstract
- For lossless universal source coding of memoryless sequences with an a priori unknown alphabet size (multialphabet coding), the alphabet of the sequence must be described as well as the sequence itself. Usually an efficient description of the alphabet can be made only by taking into account some additional information. We show that these descriptions can be separated in such a way that the encoding of the actual sequence can be performed independently of the alphabet description, and present sequential coding methods for such sequences. Such methods have applications in coding methods where the alphabet description is made available sequentially, such as PPM.
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| 7. |
- Aberg, J., et al.
(författare)
-
Non-uniform PPM and context tree models
- 1998
-
Ingår i: Proceedings DCC '98 Data Compression Conference. - 0818684062 ; , s. 279-288
-
Konferensbidrag (refereegranskat)abstract
- The problem of optimizing PPM with the help of different choices of estimators and their parameters for different subsets of nodes in the context tree is considered. Methods of such optimization for Markov chain and context tree models for individual files and over given sets of files are presented, and it is demonstrated that the extension from Markov chain models to context tree models is necessary to receive significant improvements of the compression ratio.
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| 8. |
- Aberg, J., et al.
(författare)
-
Towards understanding and improving escape probabilities in PPM
- 1997
-
Ingår i: Proceedings DCC '97. Data Compression Conference. - 0818677619 ; , s. 22-31
-
Konferensbidrag (refereegranskat)abstract
- The choice of expressions for the coding probabilities in general, and the escape probability in particular, is of great importance in the family of PPM algorithms. We present a parameterized version of the escape probability estimator which, together with a 'compactness' criterion, provides guidelines for the estimator design given a 'representative' set of files. This parameterization also makes it possible to adapt the expression of the escape probability during one-pass coding. Finally, we present results for one such compression scheme that illustrates the usefulness of our approach.
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| 9. |
- Lee, I Y, et al.
(författare)
-
Study of neutron-rich nuclei using deep-inelastic reactions
- 1997
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 56:2, s. 753-759
-
Tidskriftsartikel (refereegranskat)abstract
- We have used the Ca-48+Yb-176 reaction to study the population of high-spin states in neutron-rich nuclei by deep-inelastic reactions. Using Gammasphere, we observed gamma transitions from nuclei several neutrons richer than the target. Yrast states with spin up to 20 were populated in this reaction. High-spin states in Yb-175,Yb-177,Yb-178 were observed. In this region of reduced pairing, a reference based on experimental data was used to derive experimental Routhians. Systematics of experimental Routhians in neutron-rich Yb nuclei compare well with cranked shell-model calculations.
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| 10. |
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