| 1. |
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Contreras, L, et al.
(author)
-
Time-resolved XRD study of TiC-TiB2 composites obtained by SHS
- 2004
-
In: Acta Materialia. - : Elsevier BV. - 1873-2453 .- 1359-6454. ; 52:16, s. 4783-4790
-
Journal article (peer-reviewed)abstract
- Composites of TiC and TiB2 were prepared by self-propagating high-temperature synthesis (SHS). Two routes were attempted; from the elements and from a mixture of anatase, boron oxide, graphite and magnesium. The reactions were monitored in situ by synchrotron X-ray diffraction ( lambda = 0. 26102 Angstrom). The powder mixtures were compacted as cylindrical pellets and upon ignition diffraction patterns were collected every 65 ms with a CCD camera. TiC was the first phase to form, followed by TiB2. The reactions take place in time scales of 0.1 s. The temperature profile for the first route was established from the peak position and the known thermal expansion coefficients. The microstructure of the final products was different: particles of 10 mum for the first and submicron for the second. The viability of the second route to produce ceramic powders in a cheaper way was confirmed. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
|
|
| 5. |
- Duggan, P, et al.
(author)
-
Gamma-ray bursts and X-ray melting of material to form chondrules and planets
- 2003
-
In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 409:2, s. 9-12
-
Journal article (peer-reviewed)abstract
- Chondrules are millimeter sized objects of spherical to irregular shape that constitute the major component of chondritic meteorites that originate in the region between Mars and Jupiter and which fall to Earth. They appear to have solidified rapidly from molten or partially molten drops. The heat source that melted the chondrules remains uncertain. The intense radiation from a gamma-ray burst (GRB) is capable of melting material at distances up to 300 light years. These conditions were created in the laboratory for the first time when millimeter sized pellets were placed in a vacuum chamber in the white synchrotron beam at the European Synchrotron Radiation Facility (ESRF). The pellets were rapidly heated in the X-ray and gamma-ray furnace to above 1400 degreesC melted and cooled. This process heats from the inside unlike normal furnaces. The melted spherical samples were examined with a range of techniques and found to have microstructural properties similar to the chondrules that come from meteorites. This experiment demonstrates that GRBs can melt precursor material to form chondrules that may subsequently influence the formation of planets. This work extends the field of laboratory astrophysics to include high power synchrotron sources.
|
|
| 6. |
- Krol, M, et al.
(author)
-
Low growth temperature inhibition of photosynthesis in cotyledons of jack pine seedlings (Pinus banksiana) is due to impaired chloroplast development
- 2002
-
In: Canadian Journal of Botany. - 0008-4026 .- 1480-3305. ; 80:10, s. 1042-1051
-
Journal article (peer-reviewed)abstract
- Cotyledons of jack pine seedlings (Pinus banksiana Lamb.) grown from seeds were expanded at low temperature (5degreesC), and total Chl content per unit area of cotyledons in these seedlings was only 57% of that observed for cotyledons on 20degreesC-grown controls. Chl a/b ratio of 5degreesC-grown jack pine was about 20% lower (2.3 +/- 0.1) than 20degreesC controls (2.8 +/- 0.3). Separation of Chl-protein complexes and SDS-PAGE indicated a significant reduction in the major Chl a containing complex of PSI (CP1) and PSII (CPa) relative to LHCII1 in 5degreesC compared to 20degreesC-grown seedlings. In addition, LHCII1/LHCII3 ratio increased from 3.8 in control (20degreesC) to 5.5 in 5degreesC-grown cotyledons. Ultrastructurally, 5degreesC-grown cotyledons had chloroplasts with swollen thylakoids as well as etiochloroplasts with distinct prolamellar bodies. Based on CO2-saturated O-2 evolution and in vivo Chl a fluorescence, cotyledons of 5degreesC jack pine exhibited an apparent photosynthetic efficiency that was 40% lower than 20degreesC controls. Seedlings grown at 5degreesC were photoinhibited more rapidly at 5degreesC and 1200 mumol.m(-2).s(-1) than controls grown at 20degreesC, although the final extent of photoinhibition was similar. Exposure to high light at 5degreesC stimulated the xanthophyll cycle in cotyledons of both controls and 5degreesC-grown seedlings. In contrast to winter cereals, we conclude that growth of jack pine at 5degreesC impairs normal chloroplast biogenesis, which leads to an inhibition of photosynthetic efficiency.
|
|
| 7. |
|
|
| 8. |
- Pocock, T H, et al.
(author)
-
Susceptibility to low-temperature photoinhibition and the acquisition of freezing tolerance in winter and spring wheat : The role of growth temperature and irradiance
- 2001
-
In: Physiologia Plantarum. - 0031-9317 .- 1399-3054. ; 113:4, s. 499-506
-
Journal article (peer-reviewed)abstract
- Five winter and five spring wheat (Triticum aestivum L.) cultivars were grown under either control conditions (20 degreesC/250 photosynthetic photon flux density (PPFD) [mu mol m(-2) s(-1)]), high irradiance (20 degreesC/800 PPFD) or at low temperature (either 5 degreesC/250 PPFD or 5 degreesC/50 PPFD). To eliminate any potential bias, the wheat cultivars were arbitrarily chosen without any previous knowledge of their freezing tolerance or photosynthetic competence. We show that the differential susceptibilities to photoinhibition exhibited between spring and winter wheat cultivars, as assessed by chlorophyll fluorescence cannot be explained on the basis of either growth irradiance or low growth temperature per se. The role of excitation pressure is discussed. We assessed the correlation between susceptibility to low-temperature photoinhibition, maximum ribulose 1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) and NADP-dependent malate dehydrogenase (EC 1.1.1.82) activities, chlorophyll and protein concentrations and freezing tolerance determined by electrolyte leakage. Susceptibility to photoinhibition is the only parameter examined that is strongly and negatively correlated with freezing tolerance. We suggest that the assessment of susceptibility to photoinhibition may be a useful predictor of freezing tolerance and field survival of cereals.
|
|
| 9. |
- Savitch, L V, et al.
(author)
-
Cold acclimation of Arabidopsis thaliana results in incomplete recovery of photosynthetic capacity, associated with an increased reduction of the chloroplast stroma
- 2001
-
In: Planta. - 0032-0935 .- 1432-2048. ; 214:2, s. 295-303
-
Journal article (peer-reviewed)abstract
- The effects of short-term cold stress and long-term cold acclimation on the light reactions of photosynthesis were examined in vivo to assess their contributions to photosynthetic acclimation to low temperature in Arabidopsis thaliana (L.) Heynh.. All photosynthetic measurements were made at the temperature of exposure: 23 degreesC for non-acclimated plants and 5 degreesC for cold-stressed and cold-acclimated plants. Three-day cold-stress treatments at 5 degreesC inhibited light-saturated rates of CO2 assimilation and O-2 evolution by approximately 75%. The 3-day exposure to 5 degreesC also increased the proportion of reduced QA by 50%, decreased the yield of PSII electron transport by 65% and decreased PSI activity by 31%. In contrast, long-term cold acclimation resulted in a strong but incomplete recovery of light-saturated photosynthesis at 5 degreesC. The rates of light-saturated CO2 and O-2 gas exchange and the in vivo yield of PSII activity under light-saturating conditions were only 35-40% lower, and the relative redox state of QA only 20% lower, at 5 degreesC after cold acclimation than in controls at 23 degreesC. PSI activity showed full recovery during long-term cold acclimation. Neither short-term cold stress nor long-term cold acclimation of Arabidopsis was associated with a limitation in ATP, and both treatments resulted in an increase in the ATP/NADPH ratio. This increase in ATP/NADPH was associated with an inhibition of PSI cyclic electron transport but there was no apparent change in the Mehler reaction activity in either cold-stressed or cold-acclimated leaves. Cold acclimation also resulted in an increase in the reduction state of the stroma, as indicated by an increased total activity and activation state of NADP-dependent malate dehydrogenase, and increased light-dependent activities of the major regulatory enzymes of the oxidative pentose-phosphate pathway. We suggest that the photosynthetic capacity during cold stress as well as cold acclimation is altered by limitations at the level of consumption of reducing power in carbon metabolism.
|
|
| 10. |
- Spiers, H, et al.
(author)
-
Self propagating high temperature synthesis of magnesium zinc ferrites (MgxZn1-xFe2O3): thermal imaging and time resolved X-ray diffraction experiments
- 2004
-
In: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501. ; 14:7, s. 1104-1111
-
Journal article (peer-reviewed)abstract
- Spinel ferrites of the form MgxZn1-xFe2O4 ( x = 0. 0.25, 0.50, 0.75, 1.00) were prepared by self-propagating high-temperature synthesis (SHS) from reactions of iron(III), zinc and magnesium oxides, iron powder and sodium perchlorate. The driving force for the reactions is the oxidation of iron powder. Reactions were carried out in the presence of an external magnetic field of 0.2 or 1.1 T. Reaction velocity and temperatures were obtained by thermal imaging camera. The transformation of reactants to products was studied by time resolved X-ray diffraction using Rietveld refinement for determination of phase percentages. Reactions typically reached temperatures in excess of 1150 degreesC with a timescale of complete conversion of reactant to products of 20 s. All materials were characterised by X-ray powder diffraction (XRD), energy dispersive X-ray analysis (EDXA), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Mossbauer spectroscopy and vibrating sample magnetometry (VSM).
|
|
