| 1. |
- Appelgren, Patrik, et al.
(författare)
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Experimental Study of Electromagnetic Effects on Solid Copper Jets
- 2010
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 77:1, s. 011010-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a study of the interaction between all electric current pulse and a solid copper jet. Experiments were performed using a dedicated pulsed power supply delivering a current pulse of such amplitude, rise little, and duration that the jet is efficiently affected. The copper jet was created by using a shaped charge warhead. All electrode configuration consisting of two aluminum plates with a separation distance of 150 mm was used. The discharge current pulse and the voltages at the capacitors and at the electrodes were measured to obtain data oil energy deposition in and the resistance of the jet and electrode contact region. X-ray diagnostics were used to radiograph the jet, and by analyzing the radiograph, the degree of disruption of the electrified jet could be obtained. It was found that a current pulse with an amplitude of 200-250 kA and a rise time of 16 mu s could strongly enhance the natural fragmentation of the jet. In this case, the initial electric energy was 100 kJ and about 90% of the electric energy was deposited in the jet and electrodes. At the exit of the electrode region, the jet fragments formed rings with a radial velocity of up to 200 m/s, depending oil the initial electric energy in the pulsed power supply. [DOI: 10.1115/1.3172251]
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| 2. |
- Appelgren, Patrik, et al.
(författare)
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Interaction between solid copper jets and powerful electrical current pulses
- 2011
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 78:2
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between a solid copper jet and an electric current pulse is studied. Copper jets that were created by a shaped-charge device were passed through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. The electrodes were connected to a pulsed-power supply delivering a current pulse with amplitudes up to 250 kA. The current and voltages were measured, providing data on energy deposition in the jet and electrode contact region, and flash X-ray diagnostics were used to depict the jet during and after electrification. The shape of, and the velocity distributions along, the jet has been used to estimate the correlation between the jet mass flow through the electrodes and the electrical energy deposition. On average, 2.8 kJ/g was deposited in the jet and electrode region, which is sufficient to bring the jet up to the boiling point. A model based on the assumption of a homogenous current flow through the jet between the electrodes underestimates the energy deposition and the jet resistance by a factor 5 compared with the experiments, indicating a more complex current flow through the jet. The experimental results indicate the following mechanism for the enhancement of jet breakup. When electrified, the natural-formed necks in the jet are subjected to a higher current density compared with other parts of the jet. The higher current density results in a stronger heating and a stronger magnetic pinch force. Eventually, the jet material in the neck is evaporated and explodes electrically, resulting in a radial ejection of vaporized jet material.
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| 3. |
- Hrastinski, Stefan, et al.
(författare)
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Encouraging participation in an intra - organizational online idea community : A case study of a Swedish municipality
- 2011
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Ingår i: First Monday. - : University of Illinois Libraries. - 1396-0466. ; 16:10
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Tidskriftsartikel (refereegranskat)abstract
- Online communities have flourished in organizations in recent years, but large numbers of them fail. A deeper understanding of how participation can be promoted in online idea communities (OIC) is essential, because the most common reason of failure is low levels of participation. In this paper, we investigated how participation could be encouraged in an intra-organizational OIC. Our case organization was Sollentuna municipality in Sweden. They decided to introduce an OIC to collect ideas from staff as input when developing the municipality's forthcoming IT strategy. We used the theory of online identity-based communities (Ren, et al., 2007) as a lens and a mixed research method comprising interviews and an analysis of the content of the OIC. While this theoretical perspective certainly has merits on its own, the study topic at hand made it necessary to complement the theory with more specific design principles that take the unique characteristics of intra-organiztional OIC into account. These included that managers were expected by staff to be core members of the community, frequent and complementing promotion activities were necessary in order for the OIC to be used, very low entry barriers were expected, and the employees expected the discussion to be focused, both in terms of content and time. The design principles need to be tested and further developed, by conducting studies on other OIC.
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| 4. |
- Larsson, Anders Olof, 1979-, et al.
(författare)
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Blogs and blogging : Current trends and future directions
- 2011
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Ingår i: First Monday. - : University of Illinois Libraries. - 1396-0466. ; 16:3
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Tidskriftsartikel (refereegranskat)abstract
- Adopting an interdisciplinary scope, this paper presents a review of research on blogs and blogging within the social sciences and the humanities. It maps out what kind of research has been completed, how it has been performed and what gaps that might need to be filled in this relatively new area of research. More specifically, the paper will analyze all articles on blogs and blogging published until 2009 and indexed by the ISI Web of Knowledge.
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| 5. |
- Appelgren, Patrik, et al.
(författare)
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Disruption mechanisms in electrified solid copper jets
- 2011
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 78:2
-
Tidskriftsartikel (refereegranskat)abstract
- Interaction between a solid copper jet and an electric current pulse is a complex process that has been experimentally studied by letting a jet created by a shaped charge device pass through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. When the jet bridged the electrodes, which are connected to a charged pulsed power supply, current pulses with amplitude up to 250 kA were passed through the jet. By using flash X-ray diagnostics, the disruption of the electrified jets could be studied. In this paper, the disruption of the electrified jets is discussed and compared with disruption phenomena observed in electrically exploded metal rods in a static setup. Necks are naturally formed along a stretching jet, and in the experiments with current interaction these necks explode electrically. In the static experiments, the metal rods have small notches distributed along the rod to resemble the necks of the jet. When two neighboring necks or notches explode, the shock of the explosion compresses the intermediate jet or rod segment axially and the material is forced out radially. The disruption phenomena in the jet and rod experiments are similar with rapid expansion of the metal at explosion and at comparable velocities.
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| 6. |
- Möller, Cecilia, et al.
(författare)
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Experimental Studies of the Influence of a Resonance Cavity in an Axial Vircator
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:6, s. 1318-1324
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Tidskriftsartikel (refereegranskat)abstract
- Experiments on an axial virtual-cathode oscillator (vircator) with a resonance cavity enclosing the virtual cathode are reported. The vircator is driven by a repetitive Marx generator operating in a single-shot mode. To be able to separate different radiation mechanisms, the design of the vircator allows adjustment of the cavity depth as well as the way microwave radiation is extracted. The microwave radiation is measured with a pair of free-field B-dot sensors. The maximum field strengths were registered when the bandwidth was very narrow.
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| 7. |
- Möller, Cecilia, et al.
(författare)
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Proof of Principle Experiments on Direct Generation of the TE11 Mode in a Coaxial Vircator
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:1, s. 26-31
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Tidskriftsartikel (refereegranskat)abstract
- Experiments on a coaxial vircator with a sectioned emitter are reported. The emitting area is sectioned to form two opposing emitters in order to favor growth of the TE11 mode and inhibit growth of the TM01 mode that is usually excited in a coaxial vircator. Experiments are performed using a compact 320-J 400-kV Marx generator and a compact coaxial vircator built in a standard 8 '' vacuum tube. The radiated magnetic-field strength is measured by means of four free-field (B-dot) probes, and experiments show that sectioning the emitter does, in fact, lead to generation of the TE11 mode.
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