| 1. |
- Srinivas, V., et al.
(författare)
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Electronic transport properties of high-resistivity icosahedral AlPdRe below 1 K
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:9
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the conductivity, sigma(T), and the magnetoresistance up to B = 6 T have been studied in the temperature range 0.01 Kless than or equal toTless than or equal to1 K for two differently prepared i-AlPdRe samples on the insulating side of the metal-insulator transition. sigma(T) for both samples was observed to saturate in zero magnetic field below about 20 mK. With increasing magnetic field the temperature dependence of the conductivity increased, and at 6 T, or(T,B = 6 T) was found to decrease linearly with decreasing temperature down to the lowest measurement temperature of 10 mK. The estimated value of the conductivity at T=0 K, sigma(0 K), was found to decrease strongly with increasing resistance ratio R [ = rho(4 K)/rho(295 K)] over a wide range of R values and for differently prepared samples, suggesting that a finite sigma(0,R) is a characteristic property of the icosahedral phase of high-resistivity i-AlPdRe. The magnetoresistance is positive below 1 K. The relation Deltarho(B)/rhosimilar toB(2) is followed at larger fields by a B-2/3 dependence. With decreasing temperature these characteristic field regions are successively depressed towards smaller magnetic fields and eventually become unobservable. A scaling of the magnetoresistance is found for data in the region Tless than or equal to1 K, Bless than or equal to6 T of the form [Deltarho(B)/rho]/T-alpha=f(B/T) for each sample, with alpha about 0.3 for both samples.
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| 2. |
- Stranden, M., et al.
(författare)
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(-)-germacrene D receptor neurones in three species of heliothine moths : structure-activity relationships
- 2003
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Ingår i: Journal of Comparative Physiology A. Sensory, neural, and behavioral physiology. - : Springer Science and Business Media LLC. - 0340-7594 .- 1432-1351. ; 189:7, s. 563-577
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Tidskriftsartikel (refereegranskat)abstract
- Specificity of olfactory receptor neurones plays an important role in food and host preferences of a species, and may have become conserved or changed in the evolution of polyphagy and oligophagy. We have identified a major type of plant odour receptor neurones responding to the sesquiterpene germacrene D in three species of heliothine moths, the polyphagous Heliothis virescens and Helicoverpa armigera and the oligophagous Helicoverpa assulta. The neurones respond with high sensitivity and selectivity to (-)-germacrene D, as demonstrated by screening via gas chromatography with numerous mixtures of plant volatiles. Germacrene D was present in both host and non-host plants, but only in half of the tested species. The specificity of the neurones was similar in the three species, as shown by the 'secondary' responses to a few other sesquiterpenes. The effect of (-)-germacrene D was about ten times stronger than that of the (+)-enantiomer, which again was about ten times stronger than that of (-)-alpha-ylangene. Weaker effects were obtained for (+)-beta-ylangene, (+)-alpha-copaene, beta-copaene and two unidentified sesquiterpenes. The structure-activity relationship shows that the important properties of (-)-germacrene D in activating the neurones are the ten-membered ring system and the three double bonds acting as electron-rich centres, in addition to the direction of the isopropyl-group responsible for the different effects of the germacrene D enantiomers.
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