| 1. |
- Le Lay, G., et al.
(författare)
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STM and synchrotron radiation studies of "prototypical" metal{plus 45 degree rule}semiconductor systems
- 1994
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Ingår i: Surface Science. - 0039-6028. ; 307-309:PART A, s. 280-294
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Tidskriftsartikel (refereegranskat)abstract
- Since the origin of surface science noble metal{plus 45 degree rule}elemental semiconductor couples have been considered as "prototypical" systems. After three decades of research their structural and electronic properties remain an intriguing maze despite recent advances made, especially thanks to the development of the near-field microscopies and the extensive use of synchrotron radiation in surface crystallography and in high-resolution photoelectron spectroscopy. In the last few years, lead, as a replacement inert metal, has nearly gained the pole position in the display of exotic behaviour. This paper gives a flavour of this mystery story and highlights some puzzling questions. © 1994.
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| 2. |
- Brenning, Nils, et al.
(författare)
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Critical ionization velocity interaction in the CRIT I rocket experiment
- 1990
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Ingår i: Advances in Space Research. - : Elsevier BV. - 0273-1177. ; 10, s. 63-66
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Tidskriftsartikel (refereegranskat)abstract
- In the rocket experiment CRIT I, launched from Wallops Island on 13 May 1986, two identical Barium shaped charges were fired from distances of 1.3 km and 3.6 km towards the main experiment payload, which was separated from a sub-payload by a couple of km along the magnetic field. The relevance of earlier proposed mechanisms for electron heating in ionospheric critical velocity experiments is investigated in the light of the CRIT I results. It is concluded that both the "homogeneous" and the "ionizing front" models can be applied, in different parts of the stream. It is also possible that a third, entirely different, mechanism may contribute to the electron heating. This mechanism involves direct energization of electrons in the magnetic-field-aligned component of the DC electric field. © 1989.
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| 3. |
- Brenning, Nils, et al.
(författare)
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Interpretation of the Electric Fields Measured in an Ionospheric Critical Ionization Velocity Experiment
- 1991
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 96, s. 9719-9733
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the quasi-dc electric fields measured in the CRIT I ionospheric release experiment, which was launched from Wallops Island on May 13, 1986. The purpose of the experiment was to study the critical ionization velocity (CIV) mechanism in the ionosphere. Two identical barium shaped charges were fired from distances of 1.99 km and 4.34 km towards a main payload, which made full three-dimensional measurements of the electric field inside the streams. There was also a subpayload separated from the main payload by a couple of kilometers along the magnetic field. The relevance of earlier proposed mechanisms for electron heating in CIV is investigated in the light of the CRIT I results. It is concluded that both the “homogeneous” and the “ionizing front” models probably apply, but in different parts of the stream. It is also possible that electrons are directly accelerated by a magnetic-field-aligned component of the electric field; the quasi-dc electric field observed within the streams had a large magnetic-field-aligned component, persisting on the time scale of the passage of the streams. The coupling between the ambient ionosphere and the ionized barium stream in CRIT I was more complicated than is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes. One interpretation of the quasi-dc electric field data is that the internal electric fields of the streams were not greatly modified by magnetic-field-aligned currents, i.e., a state was established where the transverse currents were to a first approximation divergence-free. It is argued that this interpretation can explain both a reversal of the strong explosion-directed electric field in burst 1 and the absence of such a reversal in burst 2.
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| 4. |
- Brenning, Nils, et al.
(författare)
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Electrodynamic interaction between the CRIT I ionized barium streams and the ambient ionosphere
- 1990
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Ingår i: Advances in Space Research. - : Elsevier BV. - 0273-1177. ; 10, s. 67-70
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Tidskriftsartikel (refereegranskat)abstract
- In the CRIT I Critical Velocity experiment, launched from Wallops Island on 13 May, 1986, two fast barium streams were ejected by means of shaped charges. Their electrodynamic interaction with the ambient ionosphere is discussed. An outstanding feature of the DC electric field observed within the streams was a large magnetic-field-aligned component, persisting on the time scale of the passage of the streams. One interpretation of the DC electric field data is that the internal electric fields of the streams is not greatly modified by Birkeland currents, i.e. a state is established, where the transverse currents are to a first approximation divergence-free. It is argued that this interpretation can explain why a reversal of the strong explosion-directed electric field was observed in the first explosion but not in the second (more distant one). © 1989.
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| 5. |
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| 6. |
- Egholm, M., et al.
(författare)
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PNA HYBRIDIZES TO COMPLEMENTARY OLIGONUCLEOTIDES OBEYING THE WATSON-CRICK HYDROGEN-BONDING RULES
- 1993
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 365:6446, s. 566-568
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Tidskriftsartikel (refereegranskat)abstract
- DNA ANALOGUES are currently being intensely investigated owing to their potential as gene-targeted drugs1-3. Furthermore, their properties and interaction with DNA and RNA could provide a better understanding of the structural features of natural DNA that determine its unique chemical, biological and genetic properties3,4. We recently designed a DNA analogue, PNA, in which the backbone is structurally homomorphous with the deoxyribose backbone and consists of N-(2-aminoethyl)glycine units to which the nucleobases are attached5-9. We showed that PNA oligomers containing solely thymine and cytosine can hybridize to complementary oligonucleotides, presumably by forming Watson-Crick-Hoogsteen (PNA)2-DNA triplexes, which are much more stable than the corresponding DNA-DNA duplexes5-7, and bind to double-stranded DNA by strand displacement5,8. We report here that PNA containing all four natural nucleobases hybridizes to complementary oligonucleotides obeying the Watson-Crick base-pairing rules, and thus is a true DNA mimic in terms of base-pair recognition.
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| 7. |
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| 8. |
- Holbech, J. D., et al.
(författare)
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H2* defect in crystalline silicon
- 1993
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 71:6, s. 875-878
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Tidskriftsartikel (refereegranskat)abstract
- Detailed infrared studies have been carried out on proton- and deuteron-implanted Si. A dominant trigonal defect involving a pair of inequivalent hydrogen atoms has been identified, with local modes at 2061.5, 1838.3, 1599.1, and 817.2 cm-1. The structure, the local modes, and the isotopic shifts of the H2* defect have been calculated using ab initio pseudopotential cluster theory. The structure is consistent with channeling and uniaxial stress experiments. The calculated frequencies and isotopic shifts are in close agreement with those observed.
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| 9. |
- Johansson, Anja, et al.
(författare)
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Ergonomic Evaluation of Two Different Locations of the Scales in a Supermarket Checkout System
- 1993
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Ingår i: Advances in Industrial Ergonomics and Safety V. ; , s. 667-674
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Konferensbidrag (refereegranskat)abstract
- The aim of this pilot study was to ergonomically evaluate the effect of the location of the scales in a supermarket checkout system. A location of the scales to the left of the cashier was compared with a location under the conveyor belt. Two cashiers were videotaped while working with the two scale locations, in both sitting and standing working postures. Analysis of the video tapes was performed using the WOPALAS method, the VIRA method, and by noting certain positions of the left arm. The left wrist movements were registered by a two-dimensional goniometer. The results indicate that the location under the conveyor belt is somewhat more ergonomically favourable. The improvement is more pronounced for the cashier with a greater reach.
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| 10. |
- Jones, R, et al.
(författare)
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Identification of the dominant nitrogen defect in silicon
- 1994
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 72:12, s. 1882-1885
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the dominant N pair defect in Si is determined from channeling, infrared local vibrational mode spectroscopy, and ab initio local density functional theory. Channeling experiments show that the N atoms are displaced by 1.1±0.1 Å from lattice sites along 〈100〉. Annealing experiments reveal that this N site is associated with two N-related local vibrational modes originating from the N pair. The ab initio calculations demonstrate that the pair consists of two neighboring 〈100〉 oriented N-Si split interstitials, arranged in an antiparallel configuration, and with four N-Si bonds forming a square lying on {011}.
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