| 1. |
- Jansson, M, et al.
(författare)
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Effects of luminal stimuli on polyamine metabolism in the small intestine of the rat : the role of enteric nerves
- 1993
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 149:4, s. 90-483
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate to what extent polyamine metabolism in the small intestine of the rat is controlled by the enteric nervous system. Polyamine metabolism was followed by measuring the activity of ornithine decarboxylase (ODC) and in some instances also the content of polyamines (putrescine, spermidine and spermine). ODC activity in the intestine was increased when intraluminal pressure was increased and 3 h after placing cholera toxin in the intestinal lumen. Cholera toxin also increased the tissue putrescine content. Atropine or hexamethonium given i.v. did not influence the evoked changes of ODC activity. The pressure induced changes were not decreased by placing lidocaine on the serosal surface. On the other hand, the ODC activity of control segments were decreased by hexamethonium or atropine. The presence of glucose in the intestinal perfusate did not augment tissue ODC activity, neither did the heat stable enterotoxin from Escherichia coli (STa). It is concluded that the effect on polyamine metabolism evoked by luminal pressure or cholera toxin seems not to be mediated via nerves, while nerves seem to influence ODC activity during control conditions. The experiments with enterotoxins suggest that cAMP is the intracellular second messenger controlling intestinal ODC activity.
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| 2. |
- Jansson, Erik V., et al.
(författare)
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On eigenmodes of the violin—Electronic holography and admittance measurements
- 1994
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 95:2, s. 1100-1105
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Tidskriftsartikel (refereegranskat)abstract
- The present experimental investigation, using recently assembled advanced electro-optical equipment for vibration analysis of three violins, was conducted to seek answers to three questions. A general or global question: Which parts of the violin body are vibrating the most? And two questions related to tonal quality: Are basic low-frequency vibration modes of a musically superior instrument different from those of an inferior violin? Can some special vibration properties be found to support the ``bridge hill?'' Optically obtained vibration modes were recorded as well as frequency responses in the form of admittance measurements. The investigation showed that the vibration modes found earlier are representative both for the inferior violin and the musically superior instruments, although discrepancies can be seen, both in eigenmode shapes and admittance responses. The experimental results are also in quite good agreement with published results of the modal analysis of a violin. Further, the experimental results indicate that the transversal vibrations are mainly within the plates, but at low frequencies, the vibrations of the edges and of the ribs can be large and in-plane as well as transversal. At higher frequencies, the transversal vibration amplitudes are small at the plate edges and larger inside. The top plate tends to have the largest amplitude of vibrations. In the 2.5-kHz range the violin with the most clear ``bridge hill'' tends to have the largest vibrations of the plates.
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| 3. |
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| 4. |
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| 5. |
- Jansson, Magnus, et al.
(författare)
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Efficient Implementation of a Submodel for Composite Materials to be Combined with the FDTD-Algorithm
- 1994
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Ingår i: IEEE Transactions on Magnetics. - : IEEE Magnetics Society. - 0018-9464 .- 1941-0069. ; 30:5, s. 3188-3191
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Tidskriftsartikel (refereegranskat)abstract
- A submodel to be used for thin sheets of semiconducting materials in combination with the finite difference time domain algorithm for solving Maxwell's equations is derived. Emphasis is concentrated on accomplishing an efficient and robust algorithm. Stability properties of the combined model are also investigated
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| 6. |
- Molin, Nils-Erik, et al.
(författare)
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Transient wave response of the violin body
- 1990
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 88:5, s. 2479-2481
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, the dispersive, transient wave propagation field of a complete violin excited by a mechanically induced impulse at the top of the bridge is presented. By means of double pulsed holographic interferometry with a ruby laser as light source the propagating wave field is recorded. From presented interferograms, it is seen that initially the top plate acts mainly as a nonsymmetric dipole with centers at the two bridge feet. The back plate is strongly coupled to the motion of the top plate by the sound post and acts more like a monopole. Thus the position of the sound post is crucial to the performance of the instrument. The free edges at the f-holes are very early reached by the dispersive bending waves of high amplitude probably giving a significant contribution to the sound of the violin family instruments
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