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- Alfvén, Hannes, et al.
(author)
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Inter-stellar clouds and formation of stars
- 1978
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In: Astrophysics and Space Science. - : Springer Nature. - 0004-640X .- 1572-946X. ; 55:2, s. 487-509
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Journal article (peer-reviewed)abstract
- Part I gives a survey of the drastic revision of cosmic plasma physics which is precipitated by the exploration of the magnetosphere throughin situ measurements. The ‘pseudo-plasma formalism’, which until now has almost completely dominated theoretical astrophysics, must be replaced by an experimentally based approach involving the introduction of a number of neglected plasma phenomena, such as electric double layers, critical velocity, and pinch effect. The general belief that star light is the main ionizer is shown to be doubtful; hydromagnetic conversion of gravitational and kinetic energy may often be much more important.In Part II the revised plasma physics is applied to dark clouds and star formation. Magnetic fields do not necessarily counteract the contraction of a cloud; they may just as well ‘pinch’ the cloud. Magnetic compression may be the main mechanism for forming interstellar clouds and keeping them together.Part III treats the formation of stars in a dusty cosmic plasma cloud. Star formation is due to an instability, but it is very unlikely that it has anything to do with the Jeans instability. A reasonable mechanism is that the sedimentation of ‘dust’ (including solid bodies of different size) is triggering off a gravitationally assisted accretion. A ‘stellesimal’ accretion analogous to the planetesimal accretion leads to the formation of a star surrounded by a very low density hollow in the cloud. Matter falling in from the cloud towards the star is the raw material for the formation of planets and satellites.The study of the evolution of a dark cloud leads to a scenario of planet formation which is reconcilable with the results obtained from studies based on solar system data. This means that the new approach to cosmical plasma physics discussed in Part I logically leads to a consistent picture of the evolution of dark clouds and the formation of solar systems.
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| 5. |
- Branneby, Cecilia, et al.
(author)
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Aldol Additions with Mutant Lipase : Analysis by Experiments and Theoretical Calculations
- 2004
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In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 31:4-6, s. 123-128
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Journal article (peer-reviewed)abstract
- A Ser105Ala mutant of Candida antarctica lipase B has previously been shown to catalyze aldol additions. Quantum chemical calculations predicted a reaction rate similar to that of natural enzymes, whereas experiments showed a much lower reaction rate. Molecular dynamics simulations, presented here, show that the low reaction rate is a consequence of the low frequencies of near attack complexes in the enzyme. Equilibrium was also considered as a reason for the slow product formation, but could be excluded by performing a sequential reaction to push the reaction towards product formation. In this paper, further experimental results are also presented, highlighting the importance of the entire active site for catalysis.
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| 6. |
- Branneby, Cecilia, et al.
(author)
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Carbon-Carbon Bonds by Hydrolytic Enzymes
- 2003
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 125:4, s. 874-875
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Journal article (peer-reviewed)abstract
- Enzymes are efficient catalysts in synthetic chemistry, and their catalytic activity with unnatural substrates in organic reaction media is an area attracting much attention. Protein engineering has opened the possibility to change the reaction specificity of enzymes and allow for new reactions to take place in their active sites. We have used this strategy on the well-studied active-site scaffold offered by the serine hydrolase Candida antarctica lipase B (CALB, EC 3.1.1.3) to achieve catalytic activity for aldol reactions. The catalytic reaction was studied in detail by means of quantum chemical calculations in model systems. The predictions from the quantum chemical calculations were then challenged by experiments. Consequently, Ser105 in CALB was targeted by site-directed mutagenesis to create enzyme variants lacking the nucleophilic feature of the active site. The experiments clearly showed an increased reaction rate when the aldol reaction was catalyzed by the mutant enzymes as compared to the wild-type lipase. We expect that the new catalytic activity, harbored in the stable protein scaffold of the lipase, will allow aldol additions of substrates, which cannot be reached by traditional aldolases
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| 8. |
- Carlqvist, Per
(author)
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A new mechanism for the crab fingers
- 2004
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In: Astrophysics and Space Science. - 0004-640X .- 1572-946X. ; 289:1-2, s. 47-53
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Journal article (peer-reviewed)abstract
- Images of the outer filamentary parts of the Crab Nebula, earlier obtained with the Hubble Space Telescope WFPC2, are reconsidered. On inspection of the images it is found that most of the mainly radially oriented fingers possess an internal structure, usually in the form of two or more filaments. For some of the fingers there are clear signs that the filaments are twisted around each other. A mechanism for the fingers taking the internal structure into account is proposed. The mechanism is based on the reshaping of magnetized filaments under the influence of inertia and magnetic forces. When interacting with an expanding shell, driven by the pressure of the synchrotron nebula, part of such a filament may develop into a double helix pointing radially inwards. For this transformation to take place it is required that the magnetic field within the filament is sufficiently twisted and that the filament contains a mass condensation. The finger is identified with the double helix. Similar structures of double helices are found to be present also in other environments.
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| 9. |
- Carlqvist, Per
(author)
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A remarkable double helix in the V838 Mon nebula
- 2005
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 436:1, s. 231-239
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Journal article (peer-reviewed)abstract
- In the beginning of 2002 the previously unnoted star V838 Mon had a powerful outburst. The star is surrounded by pre-existing, dusty clouds which are illuminated by the star in an expanding, parabolic layer. Spectacular images captured by the Hubble Space Telescope Advanced Camera for Surveys show that the clouds are to a great extent built up by filaments and concentric shells. One of the most remarkable features is a filamentary structure forming a double helix. The structure, which has a projected length and width of similar to 9 '' and similar to 1.'' 4, respectively, points almost radially towards V838 Mon. In order to reveal the geometry of the double helix in some more detail, a three-dimensional computer model of the structure has been constructed. The model also assists in determining the expansion rate of the light echoes along the double helix. By means of the expansion rate and the tilt of the double helix the distance to V838 Mon is determined to be 2.4 +/- 0.5 kpc. A theory of the double helix, based on a magnetized and twisted filament, is presented. Dynamic and magnetic forces play an essential role in the shaping of the double helix. The theory is supported by a mechanical analogy model. Double helices in other cosmic environments are also discussed.
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| 10. |
- Carlqvist, Per, et al.
(author)
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Benchmark of High Level Programming : Pilot Case Vibration Control
- 2009
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In: Proceedings of the 9th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2009. - 9780955308260 ; , s. 361-364
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Conference paper (peer-reviewed)abstract
- The advancement of technology of laser pattern generators needs to meet demands of the rapid product development pace in the display and semiconductor markets. A hypothesis is that efficiency in the development process of complex systems can be improved by introducing a higher level programming approach. This will make a model and simulation based development (MBD) strategy more easy to adapt leading to 1) higher technical performance at shorter development time from idea to product introduction phase, 2) lower cost of goods, 3) shorter production-, installations- & upgrade time and 4) possibility of very efficient field support & service, etc. The success of an MBD approach is dependent on the simulation software capability to express the behavior of a real system. Consequently, as a first step towards an MBD approach, the investigation covers a pilot-study where results from simulations are compared to an existing controlled system.
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