| 21. |
- Andersson, Pontus, 1971, et al.
(författare)
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Nearly complete isobar suppression by photodetachment
- 2010
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 1089-7550 .- 0021-8979. ; 107:2
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency of selective suppression of negative ions by photodetachment in a gas-filled radio frequency quadrupole ion cooler was investigated with a new detection method. A neodymium doped yttrium aluminum garnet laser beam at 1064 nm was used to remove Co− ions in the radio frequency quadrupole cooler and the remaining ions were then probed by photodetachment and neutral particle detection. More than 99.99% suppression of the Co− ions was observed. Under identical conditions, only 20% of a Ni− beam was suppressed. The results demonstrate that this isobar suppression technique can lead to nearly complete elimination of certain isobaric contaminants in negative ion beams, opening up new experimental possibilities in nuclear and atomic research and accelerator mass spectrometry.
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| 22. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Formation of Highly Rovibrationally Excited Ammonia from Dissociative Recombination of NH4
- 2010
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 1:17, s. 2519-2523
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Tidskriftsartikel (refereegranskat)abstract
- The internal energy distribution of ammonia formed in the dissociative recombination (DR) of NH4+ with electrons has been studied by an imaging technique at the ion storage ring CRYRING. The DR process resulted in the formation of NH3 + H (0.90 ± 0.01), with minor contributions from channels producing NH2 + H2 (0.05 ± 0.01) and NH2 + 2H (0.04 ± 0.02). The formed NH3 molecules were highly internally excited, with a mean rovibrational energy of 3.3 ± 0.4 eV, which corresponds to 70% of the energy released in the neutralization process. The internal energy distribution was semiquantitatively reproduced by ab initio direct dynamics simulations, and the calculations suggested that the NH3 molecules are highly vibrationally excited while rotational excitation is limited. The high internal excitation and the translational energy of NH3 and H will influence their subsequent reactivity, an aspect that should be taken into account when developing detailed models of the interstellar medium and ammonia-containing plasmas.
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| 23. |
- Andersson, Urban, 1965, et al.
(författare)
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Download data versus traditional impact metrics : measuring impact in a sample of biomedical doctoral dissertations
- 2010
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Ingår i: World Library and Information Congress : 76th IFLA General Conference and Assembly : Meeting: 155. Science and Technology Libraries (10-15 August 2010, Gothenburg, Sweden).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Download data and traditional impact metrics such as citation analysis both measure usage and possible impact of research. The case chosen for this analysis is based on dissertations of a cohort at the Sahlgrenska Academy, the faculty of Health Sciences of University of Gothenburg. At the Academy, a committee responsible for the PhD education selects the "Best doctoral thesis" of the year. This made it possible to carry out additional analysis, as examining the relationship between peer judgement and usage data (citations and downloads), and studying how promotional activities influence the usage of the dissertations. This praxis-oriented research investigates how a university library can develop different methods to provide valid user data. Analyses were carried out using field normalized citation scores and aggregated usage log data. Bivariate analysis measured the correlation between the data. The results showed no correlation between downloads and citations. However, there was a positive correlation between the peer judgments and field normalized citation scores, and between PR activities and usage through downloading.
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| 24. |
- Andreasson, Håkan, 1966, et al.
(författare)
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Formation of trapped surfaces for the spherically symmetric Einstein-Vlasov system
- 2010
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Ingår i: Journal of Hyperbolic Differential Equations. - Göteborg : Chalmers University of Technology. - 0219-8916. ; 7:4, s. 707-731
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Tidskriftsartikel (refereegranskat)abstract
- We consider the spherically symmetric, asymptotically flat, non-vacuum Einstein equations, using as matter model a collisionless gas as described by the Vlasov equation. We find explicit conditions on the initial data which guarantee the formation of a trapped surface in the evolution which in particular implies that weak cosmic censorship holds for these data. We also analyze the evolution of solutions after a trapped surface has formed and we show that the event horizon is future complete. Furthermore we find that the apparent horizon and the event horizon do not coincide. This behavior is analogous to what is found in certain Vaidya spacetimes. The analysis is carried out in Eddington-Finkelstein coordinates.
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| 25. |
- Andreasson, Håkan, 1966, et al.
(författare)
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Gravitational collapse and the formation of black holes for the spherically symmetric Einstein-Vlasov system.
- 2010
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Ingår i: Quarterly of Applied Mathematics. - 1552-4485. ; 68, s. 17-42
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Tidskriftsartikel (refereegranskat)abstract
- We review results on the spherically symmetric, asymptotically flat Einstein-Vlasov system. We focus on a recent result where we found explicit conditions on the initial data which guarantee the formation of a black hole in the evolution. Among these data there are data such that the corresponding solutions exist globally in Schwarzschild coordinates. We put these results into a more general context, and we include arguments which show that the spacetimes we obtain satisfy the weak cosmic censorship conjecture and contain a black hole in the sense of suitable mathematical definitions of these concepts which are available in the literature.
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| 26. |
- Andreasson, Håkan, 1966
(författare)
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Regularity Results for the Spherically Symmetric Einstein-Vlasov System
- 2010
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Ingår i: Annales Henri Poincare. - : Springer Science and Business Media LLC. - 1424-0637 .- 1424-0661. ; 11:5, s. 781-803
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Tidskriftsartikel (refereegranskat)abstract
- The spherically symmetric Einstein-Vlasov system is considered in Schwarzschild coordinates and in maximal-isotropic coordinates. An open problem is the issue of global existence for initial data without size restrictions. The main purpose of the present work is to propose a method of approach for general initial data, which improves the regularity of the terms that need to be estimated compared to previous methods. We prove that global existence holds outside the center in both these coordinate systems. In the Schwarzschild case we improve the bound on the momentum support obtained in Rein et al. (Commun Math Phys 168:467-478, 1995) for compact initial data. The improvement implies that we can admit non-compact data with both ingoing and outgoing matter. This extends one of the results in Andreasson and Rein (Math Proc Camb Phil Soc 149:173-188, 2010). In particular our method avoids the difficult task of treating the pointwise matter terms. Furthermore, we show that singularities never form in Schwarzschild time for ingoing matter as long as 3m <= r. This removes an additional assumption made in Andreasson (Indiana Univ Math J 56:523-552, 2007). Our result in maximal-isotropic coordinates is analogous to the result in Rendall (Banach Center Publ 41:35-68, 1997), but our method is different and it improves the regularity of the terms that need to be estimated for proving global existence in general.
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| 27. |
- Andreasson, Håkan, 1966, et al.
(författare)
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The asymptotic behaviour in Schwarzschild time of Vlasov matter in spherically symmetric gravitational collapse
- 2010
-
Ingår i: Mathematical proceedings of the Cambridge Philosophical Society. - 0305-0041 .- 1469-8064. ; 149:1, s. 173-188
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Tidskriftsartikel (refereegranskat)abstract
- Given a static Schwarzschild spacetime of ADM mass M, it is well known that no ingoing causal geodesic starting in the outer domain r > 2M will cross the event horizon r = 2M in finite Schwarzschild time. We show that in gravitational collapse of Vlasov matter this behaviour can be very different. We construct initial data for which a black hole forms and all matter crosses the event horizon as Schwarzschild time goes to infinity, and show that this is a necessary condition for geodesic completeness of the event horizon. In addition to a careful analysis of the asymptotic behaviour of the matter characteristics our proof requires a new argument for global existence of solutions to the spherically symmetric Einstein–Vlasov system in an outer domain, since our initial data have non-compact support in the radial momentum variable and previous methods break down.
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| 28. |
- Angelov, Krasimir, 1978, et al.
(författare)
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PGF: A Portable Run-time Format for Type-theoretical Grammars
- 2010
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Ingår i: Journal of Logic, Language and Information. - : Springer Science and Business Media LLC. - 0925-8531 .- 1572-9583. ; 19:2, s. 201-228
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Tidskriftsartikel (refereegranskat)abstract
- Portable Grammar Format (PGF) is a core language for type-theoretical grammars. It is the target language to which grammars written in the high-level formalism Grammatical Framework (GF) are compiled. Low-level and simple, PGF is easy to reason about, so that its language-theoretic properties can be established. It is also easy to write interpreters that perform parsing and generation with PGF grammars, and compilers converting PGF to other formats. This paper gives a concise description of PGF, covering syntax, semantics, and parser generation. It also discusses the technique of embedded grammars, where language processing tasks defined by PGF grammars are integrated in larger systems.
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| 29. |
- Anguelova, Milena, 1978, et al.
(författare)
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On analytic and algebraic observability of nonlinear delay systems
- 2010
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098. ; 46:4, s. 682-686
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Tidskriftsartikel (refereegranskat)abstract
- The observability of nonlinear delay systems has previously been defined in an algebraic setting by a rank condition on modules over noncommutative rings. We introduce an analytic definition of observability to ensure the local uniqueness of state and initial conditions that correspond to a given input-output behaviour. It is shown that an algebraically observable delay system can be reformulated as a system of ordinary differential equations. Analytic observability is then decided by the local uniqueness of solutions to a boundary value problem for this ODE system. (C) 2010 Elsevier Ltd. All rights reserved.
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| 30. |
- Anguelova, Milena, 1978, et al.
(författare)
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When classical nonlinear time-delay state-space systems admit an input-output equation of neutral type
- 2010
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Ingår i: 9th IFAC Workshop on Time Delay Systems, TDS 2010, Prague, 7 - 9 June 2010. - 1474-6670. - 9783902661715 ; 9:PART 1, s. 200-205
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Konferensbidrag (refereegranskat)abstract
- This paper deals with nonlinear retarded time-delay systems that surprisingly admit an input-output representation of neutral type. It is shown that such an unexpected behaviour represents a strictly nonlinear phenomenon, for it cannot happen in the linear time-delay case where retarded systems always admit an input-output representation of retarded type. A necessary and sufficient condition under which the nonlinear systems admit a neutral input-output representation is given and strategies for finding an inputoutput representation of retarded type are briefly outlined. Some open problems that arise, like minimality and system transformations, are discussed as well.
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