| 1. |
- Bremer, Kåre, et al.
(författare)
-
An ordinal classification for the families of flowering plants
- 1998
-
Ingår i: ANNALS OF THE MISSOURI BOTANICAL GARDEN. - : MISSOURI BOTANICAL GARDEN. - 0026-6493. ; 85:4, s. 531-553
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Recent cladistic analyses are revealing the phylogeny of flowering plants in increasing detail, and there is support for the monophyly of many major groups above the family level. With many elements of the major branching sequence of phylogeny established
|
|
| 2. |
- Gray, JS, et al.
(författare)
-
Lyme borreliosis awareness
- 1998
-
Ingår i: Zentralblatt fur Bakteriologie : international journal of medical microbiology. - : Elsevier BV. - 0934-8840. ; 287:3, s. 253-265
-
Tidskriftsartikel (refereegranskat)
|
|
| 3. |
- Keeney, Jill B, et al.
(författare)
-
Multiple molecular determinants for retrotransposition in a primer tRNA
- 1995
-
Ingår i: Molecular and Cellular Biology. - : American Society for Microbiology. - 0270-7306 .- 1098-5549. ; 15:1, s. 217-226
-
Tidskriftsartikel (refereegranskat)abstract
- Retroviruses and long terminal repeat-containing retroelements use host-encoded tRNAs as primers for the synthesis of minus strong-stop DNA, the first intermediate in reverse transcription of the retroelement RNA. Usually, one or more specific tRNAs, including the primer, are selected and packaged within the virion. The reverse transcriptase (RT) interacts with the primer tRNA and initiates DNA synthesis. The structural and sequence features of primer tRNAs important for these specific interactions are poorly understood. We have developed a genetic assay in which mutants of tRNA(iMet), the primer for the Ty1 retrotransposon of Saccharomyces cerevisiae, can be tested for the ability to serve as primers in the reverse transcription process. This system allows any tRNA mutant to be tested, regardless of its ability to function in the initiation of protein synthesis. We find that mutations in the T psi C loop and the acceptor stem regions of the tRNA(iMet) affect transposition most severely. Conversely, mutations in the anticodon region have only minimal effects on transposition. Further study of the acceptor stem and other mutants demonstrates that complementarity to the element primer binding site is a necessary but not sufficient requirement for effective tRNA priming. Finally, we have used interspecies hybrid initiator tRNA molecules to implicate nucleotides in the D arm as additional recognition determinants. Ty3 and Ty1, two very distantly related retrotransposons, require similar molecular determinants in this primer tRNA for transposition.
|
|
| 4. |
- Lastras-Martínez, L. F., et al.
(författare)
-
Reflectance difference spectroscopy of GaAs asymmetric surface quantum wells above the fundamental gap
- 1998
-
Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 170:2, s. 317-321
-
Tidskriftsartikel (refereegranskat)abstract
- We report Reflectance Difference (RD) measurement on (001) GaAs surface quantum wells (QW) under Ultra High Vacuum (UHV) conditions from 1.7 to 5.0eV. The QW is embedded between an arsenic-rich reconstructed GaAs surface and an AlAs barrier. The samples, grown by MBE with a protective arsenic cap layer, were heated to 320 and 430°C to desorb the As layer and form c(4 x 4) and (2 x 4) surface reconstructions, respectively. By modifying the surface reconstructure, we are able to separate the contributions to the optical anisotropy from the surface region (mainly associated with the As dimers) from those originating below the surface.
|
|
| 5. |
- Rönnow, Daniel, et al.
(författare)
-
Isotope effects on the electronic critical points of germanium : Ellipsometric investigation of the E1 and E1+ Delta(1) transitions
- 1998
-
Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 5:1, s. 29-35
-
Tidskriftsartikel (refereegranskat)abstract
- Within the past years the optical excitations of electrons have been measured for semiconductor samples of different isotope compositions. The isotope shift observed have been compared with calculations of the effects of electron-phonon interaction on the electronic band structure. While qualitative agreement has been obtained, some discrepancies remain especially concerning the E1 and E1 + Delta(1) transitions. We have remeasured the effect of isotope mass on the E1 and E1 + Delta(1) transitions of germanium with several isotopic compositions. The results, obtained by means of spectroscopic ellipsometry, confirm that the real part of the gap self-energies induced by electron-phonon interaction is larger than found from band structure calculations, while the imaginary part agrees with those calculations, which are based on a pseudopotential band structure and a bond charge model for the lattice dynamics. Our results agree with predictions based on the measured temperature dependence of the gaps. We compare our data for E1 and E1 + Delta(1) with results for the lowest direct (E0) and indirect (E9) gaps. The measured values of Δ0 and Δ1 increase noticeably with increasing isotope mass. Similar effects have been observed in the temperature dependence of Delta(1) in alpha-Sn and GaSb. A microscopic explanation for this effect is not available.
|
|
| 6. |
- Rönnow, Daniel, et al.
(författare)
-
Piezo-optical coefficients of ZnSe and ZnTe above the fundamental gap
- 1999
-
Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 59:8, s. 5581-5590
-
Tidskriftsartikel (refereegranskat)abstract
- The piezo-optical coefficients P11-P12 and P44 have been measured for ZnSe and ZnTe above the fundamental gap (in the energy ranges 2.6-5.5 eV and 2.0-5.5 eV, respectively) by using reflectance difference spectroscopy. The measured spectra of P11-P12 and P44 show good Kramers-Kronig consistency between their real and imaginary parts. Values for the deformation potentials D1 5, D3 3, and D3 5 for the E1 and E1 + Δ1 transitions were estimated by fitting the spectral dependence of P11-P12 and P44 to analytical line shapes based on a one-electron approximation.
|
|
