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Sökning: WAKA:ref > Chalmers tekniska högskola > (1970-1979) > (1977)

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1.
  • Davidsson, A., et al. (författare)
  • Electric Dichroism Spectroscopy
  • 1977
  • Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 10:6, s. 447-454
  • Tidskriftsartikel (refereegranskat)abstract
    • Legrand-Grosjean circular dichroism spectrometers are easily converted to detect electric dichroism (ELD), i.e. anisotropic absorption due to an external electric field. The sensitivity enables the studying of small molecules with dipole moments or anisotropic polarisabilities. The observed ELD is in part due to the orientation of the absorbing transition dipole (the orientational distribution being given by the interaction between the dipole and the electric field) but contributions due to perturbations (type Stark) may generally not be neglected. The method is predicted to become an important complement to LD studies in oriented matrix, to evaluate directions of transitions moments, but other applications are also possible. The experimental qualifications are demonstrated on two different species, nitrobenzene and Cu(II) ethylenediamine (acetylacetone)2.
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  • Hakansson, R., et al. (författare)
  • Magnetic circular dichroism of heterocycles: thiophene
  • 1977
  • Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 50:2, s. 305-308
  • Tidskriftsartikel (refereegranskat)abstract
    • The existence of two transitions with opposite MCD in the 38000–45000 cm−1 absorption of thiophene is demonstrated. The B-term for the lowest transition is negative, while it is positive for the higher one. Quantum mechanical calculations in the π-electron approximation resulted in energies, oscillator strengths and MCD terms in good agreement with the observed spectra.
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7.
  • Jeppson, Kjell, 1947, et al. (författare)
  • Negative bias stress of MOS devices at high electric fields and degradation of MNOS devices
  • 1977
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 48:5, s. 2004-2014
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the most important degradation effects observed in MNOS memory transistors is a negative shift of the threshold window. This negative shift is caused by a strong increase of the density of Si‐SiO2 surface traps. This effect has been proposed to be caused by the same effect that is observed in MOS devices subjected to negative‐bias stress (NBS). In this paper, a detailed study of the increase of the number of surface traps in MOS structures after NBS at temperatures (25–125°C) and fields (400–700 MV/m) comparable to those used in MNOS devices is presented. Two different behaviors are observed. At low fields the surface‐trap density increases as t^1/4 and at high fields it increases linearly with the stress time t. The low‐field behavior is temperature and field dependent and the zero‐field activation energy is determined to be 0.3 eV. The high‐field behavior is strongly field dependent but independent of temperature. A physical model is proposed to explain the surface‐trap growth as being diffusion controlled at low fields and tunneling limited at high fields. A comparison with MNOS degradation is made and it was found to be related to the t^1/4 behavior mentioned above.
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  • Johansson, Mats H., et al. (författare)
  • Reducing end groups in brich xylan and their alkaline degradation
  • 1977
  • Ingår i: Wood Science and Technology. - 1432-5225 .- 0043-7719. ; 11:4, s. 251-263
  • Tidskriftsartikel (refereegranskat)abstract
    • The structure of the reducing end group in xylan can be written: -β-D-Xylp-(1→4)-β-D-Xylp-(1→3)-α-L-Rhap-(1→2)--α-D-GalpA-(1→4)-D-XylIn alkaline media the reducing xylose group is easily isomerized and removed by a β-elimination which leads to a reducing galacturonic acid end group. The 1, 2-linkage between rhamnose and the galacturonic acid explains the retarding effect on the alkaline peeling. Even under fairly mild conditions the galacturonic acid group is converted to other groups which are very stable in alkaline media. Model experiments permit the conclusion that OH-3 in the reducing group is subjected to β-hydroxyelimination. The 3-deoxy-2-O-α-L-rhamnopyranosyl-D-threo-hex-2-enuronic acid group formed is unstable in acid medium and escapes observation by the techniques employed for determination of the end groups.Upon prolonged alkaline treatment and increased proportion of these groups is lost and a rapid peeling proceeds until a xylose group with a 4-O-methylglucuronic acid substituent is liberated. The consecutive reactions of this group are similar to those of the galacturonic acid groups.The formation of 3-deoxyaldonic acid end groups, an important stopping reaction in cellulose, is of minor importance in xylan.The financial support from the 1959 Års Fond för Teknisk och Skoglig Forskning samt Utbildning is gratefully acknowledged.
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10.
  • Jonas, I., et al. (författare)
  • Orientation Studies of Probe Molecules in Lamellar Liquid Crystalline Lipid Systems by Linear Dichroism
  • 1977
  • Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 10:6, s. 501-506
  • Tidskriftsartikel (refereegranskat)abstract
    • The LD-method of inclined incidence was found useful in the study of the orientations of probe chromophores (carotene, anthracene) solubilized in lamellar mesophases of the systems sodium octanoate/decanol/water and sodium di-2-ethylhexylsulphosuccinate/water, respectively. The results suggest the existence of two competing molecular orientation mechanisms aligning the longest axis of the probe molecule either parallel with the lamellar surface or perpendicular to it.
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  • Resultat 1-10 av 37

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