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| 2. |
- Dujon, B, et al.
(författare)
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The nucleotide sequence of Saccharomyces cerevisiae chromosome XV
- 1997
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 387:6632, s. 98-102
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Tidskriftsartikel (refereegranskat)abstract
- Chromosome XV was one of the last two chromosomes of Saccharomyces cerevisiae to be discovered(1). It is the third-largest yeast chromosome after chromosomes XII and IV, and is very similar in size to chromosome VII. It alone represents 9% of the yeast genome (8% if ribosomal DNA is included). When systematic sequencing of chromosome XV was started, 93 genes or markers were identified, and most of them were mapped(2). However, very little else was known about chromosome XV which, in contrast to shorter chromosomes, had not been the object of comprehensive genetic or molecular analysis. It was therefore decided to start sequencing chromosome XV only in the third phase of the European Yeast Genome Sequencing Programme, after experience was gained on chromosomes III, XI and II (refs 3-5). The sequence of chromosome XV has been determined from a set of partly overlapping cosmid clones derived from a unique yeast strain, and physically mapped at 3.3-kilobase resolution before sequencing. As well as numerous new open reading frames (ORFs) and genes encoding tRNA or small RNA molecules, the sequence of 1,091,283 base pairs confirms the high proportion of orphan genes and reveals a number of ancestral and successive duplications with other yeast chromosomes.
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| 3. |
- Dutta, Joydeep, 1964-, et al.
(författare)
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Cluster-induced crystallization of nano-silicon particles
- 1997
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Ingår i: Nanostructured materials. - : Elsevier BV. - 0965-9773 .- 1872-9150. ; 9:1-8, s. 359-362
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of producing from 20 nm to 100 nm sized silicon powders by plasma-induced reactions of silane including the formation of high-mass hydrogenated silicon anion clusters has been recently demonstrated. Careful HREM imaging showed circular contrast features, 1.5 to 2.5 nm in size, embedded in the amorphous particles which was attributed to the presence of medium range order in these regions. This non-homogeneous atomic distribution with partially ordered regions of a couple of nanometer dimension became more pronounced upon annealing upto the onset of crystallization. This observation and the formation of fivefold crystallites thereafter indicate that the clusters serve as seeds in the amorphous-to-crystalline transition.
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| 4. |
- Dutta, Joydeep, 1964-, et al.
(författare)
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Crystallization of nanosized silicon powder prepared by plasma-induced clustering reactions
- 1997
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Ingår i: AIChE Journal. - 0001-1541 .- 1547-5905. ; 43:11 A, s. 2610-2615
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Tidskriftsartikel (refereegranskat)abstract
- Nanosized silicon powders were prepared by gas-phase cluster agglomeration reactions in a low-pressure silane plasma. The formation and agglomeration of clusters leading to the growth of primary particles of powder were studied by in-situ techniques including mass spectroscopy and laser light-scattering experiments. These powders, generally amorphous and crystallized in a reducing atmosphere, were studied in detail by Raman spectroscopy and high-resolution electron microscopy, which revealed a very rough surface of as-prepared single powder particles with structures of 1 to 2 nm. Upon 1-h annealing at temperatures between 300 and 600 °C, circular contrast features, 1.5 to 2.5 nm in size, are observed in the amorphous particles, which show medium-range order. A distinct onset of crystallization is observed at 700 °C with structures ranging from very small crystalline ordered regions of 2.5-3.5 nm in size to fast-grown multiple-twinned crystallites. The crystallization behavior is influenced by the clusters that form primary particles. Observed sintering behavior cannot be explained by a classical approach; hence, theoretical models need to be adapted to nanosized powders.
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| 5. |
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| 6. |
- Hofmeister, H., et al.
(författare)
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Atomic structure of amorphous nanosized silicon powders upon thermal treatment
- 1996
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society (APS). - 0163-1829 .- 1095-3795. ; 54:4, s. 2856-2862
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous silicon powders prepared by plasma-enhanced chemical vapor deposition, of 8-24-nm-sized particles agglomerated into larger aggregates were annealed in a reducing atmosphere to study the phase transformation behavior of these particles. High-resolution electron microscopy revealed a very rough surface, with structural details of 1 to 2 nm, of the as-prepared single powder particles. Upon l h annealing at temperatures between 300 and 600 °C circular contrast features, 1.5-2.5 nm in size, are observed in the amorphous particles, hinting to the formation of a medium-range order. A distinct onset of crystallization is achieved at 700 °C, with structures ranging from very small crystalline ordered regions of 2.5-3.5 nm in size, to fast-grown multiply twinned crystallites. Rapid progress of crystallization, mainly caused by growth twinning, is observed upon annealing at 800 °C. At 900 °C, almost completely crystalline particles are formed. The particles having lattice characteristics of diamond cubic silicon frequently exhibit a faulted structure, because of multiple twinning events. They are covered by an amorphous oxide shell of a 1.5 to 2 nm thickness, which is found to develop with the onset of crystallization. Size and surface roughness of the as-prepared powders are widely preserved throughout all stages of heating, and practically no sintering occurs up to 900 °C.
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| 7. |
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| 8. |
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| 9. |
- Scholz, S. M., et al.
(författare)
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Raman spectroscopic study of silicon nanopowders
- 1997
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Ingår i: Journal of Materials Science & Technology. - : Chinese Society of Metals. - 1005-0302. ; 13:4, s. 327-332
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Tidskriftsartikel (refereegranskat)abstract
- Vibrational properties of silicon nanopowders are discussed with reference to Raman spectroscopic measurements. The powders were produced in a low pressure rf plasma from the cluster induced agglomeration of positive ions formed during the dissociation of silane. Influence of thermal treatment and the crystallization phenomena of the powder were studied. Raman spectroscopic measurements reveal size quantization effects for the particles as well as the existence of partially ordered regions in the apparently amorphous primary particles. The crystalline and amorphous volume fraction in the material were calculated from the relative spectral intensities. The results obtained in these experiments are consistent with the observations from recent high resolution transmission electron microscopy studies of these powders.
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| 10. |
- Bossel, C., et al.
(författare)
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Processing of nano-scaled silicon powders to prepare slip cast structural ceramics
- 1995
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Ingår i: Journal of Materials Science and Engineering. - : Elsevier BV. - 2161-6213 .- 0921-5093. ; 204:1-2, s. 107-112
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Tidskriftsartikel (refereegranskat)abstract
- For slip casting of ceramic powders it is necessary to have a well-defined and thus disagglomerated colloidal suspension. Proper selection of the solvent is required in order to achieve separation of the particles to obtain a homogenous mixture of the powders which is necessary for shaping complex geometrical structures, often used in structural ceramics. Here we report a preliminary investigation of the deagglomeration phenomena of nano-scaled silicon powders obtained by plasma induced dissociation of silane and compare it with silicon nitride powders prepared by laser induced condensation reactions and a commercial product (UBE SE E-10). The size dispersion of aggregates in colloidal suspensions, determined by photon correlation spectroscopy and sedimentation particle size analysis techniques, varies from 20 to 500 nm. Variation in the deagglomeration properties of the particles in different solvents depends on the surface property of the powders, and on the inter-particle interactions. These are studied with respect to the variations in the surface property of the powders in different solvents. Ethanol was found to be a suitable solvent for the colloidal suspension as the average aggregate radii of the silicon powders could be reduced to 80 nm.
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