Minority carrier lifetime in silicon photovoltaics : the effect of oxygen precipitation

Single-crystal Czochralski silicon used for photovoltaics is typically supersaturated with interstitial oxygen at temperatures just below the melting point. Oxide precipitates therefore can form during ingot cooling and cell processing, and nucleation sites are typically vacancy-rich regions. Oxygen precipitation gives rise to recombination centres, which can reduce cell efficiencies by as much as 4% (absolute). We have studied the recombination behaviour in p-type and n-type monocrystalline silicon with a range of doping levels intentionally processed to contain oxide precipitates with a range of densities, sizes and morphologies. We analyse injection-dependent minority carrier lifetime measurements to give a full parameterisation of the recombination activity in terms of Shockley–Read–Hall statistics. We intentionally contaminate specimens with iron, and show recombination activity arises from iron segregated to oxide precipitates and surrounding defects. We find that phosphorus diffusion gettering reduces the recombination activity of the precipitates to some extent. We also find that bulk iron is preferentially gettered to the phosphorus diffused layer rather than to oxide precipitates

Regurgitant leak from the area between the stent post and the sewing ring of a stented bovine pericardial valve implanted in the aortic valve position

Biologic valves can sometimes have a small closure or leakage backflow jet originating from the central coaptation point. This is physiologic regurgitation that usually only requires monitoring, and not treatment

A Stabilization Technique for Intermediate Power Level in Stacked-Vdd ICs using Parallel I/O Signal Coding

2013 International Conference on Solid State Devices and Materials (SSDM 2013), September 24-27, 2013, Fukuoka, Japa

Anther-specific carbohydrate supply and restoration of metabolically engineered male sterility

Male-sterile plants are used in hybrid breeding as well as for gene confinement for genetically modified plants in field trials and agricultural production. Apart from naturally occurring mutations leading to male sterility, biotechnology has added new possibilities for obtaining male-sterile plants, although so far only one system is used in practical breeding due to limitations in propagating male-sterile plants without segregations in the next generation or insufficient restoration of fertility when fruits or seeds are to be harvested from the hybrid varieties. Here a novel mechanism of restoration for male sterility is presented that has been achieved by interference with extracellular invertase activity, which is normally specifically expressed in the anthers to supply the developing microspores with carbohydrates. Microspores are symplastically isolated in the locular space of the anthers, and thus an unloading pathway of assimilates via the apoplasmic space is mandatory for proper development of pollen. Antisense repression of the anther-specific cell wall invertase or interference with invertase activity by expressing a proteinacious inhibitor under the control of the anther-specific invertase promoter results in a block during early stages of pollen development, thus causing male sterility without having any pleiotropic effects. Restoration of fertility was successfully achieved by substituting the down-regulated endogenous plant invertase activity by a yeast invertase fused to the N-terminal portion of potato-derived vacuolar protein proteinase II (PiII–ScSuc2), under control of the orthologous anther-specific invertase promoter Nin88 from tobacco. The chimeric fusion PiII–ScSuc2 is known to be N-glycosylated and efficiently secreted from plant cells, leading to its apoplastic location. Furthermore, the Nin88::PiII-ScSuc2 fusion does not show effects on pollen development in the wild-type background. Thus, such plants can be used as paternal parents of a hybrid variety, thereby the introgression of Nin88::PiII-ScSuc2 to the hybrid is obtained and fertility is restored. In order to broaden the applicability of this male sterility/restoration system to other plant species, a phylogenic analysis of plant invertases(β-fructofuranosidases) and related genes of different species was carried out. This reveals a specific clustering of the cell wall invertases with anther-specific expression for dicotyl species and another cluster for monocotyl plants. Thus, in both groups of plants, there seems to be a kind of co-evolution, but no recent common ancestor of these members of the gene family. These findings provide a helpful orientation to classify corresponding candidate genes in further plant species, in addition to the species analysed so far (Arabidopsis, tobacco, tomato, potato, carrots, rice, and wheat)

A male sterility-associated cytotoxic protein ORF288 in Brassica juncea causes aborted pollen development

Cytoplasmic male sterility (CMS) is a widespread phenomenon in higher plants, and several studies have established that this maternally inherited defect is often associated with a mitochondrial mutant. Approximately 10 chimeric genes have been identified as being associated with corresponding CMS systems in the family Brassicaceae, but there is little direct evidence that these genes cause male sterility. In this study, a novel chimeric gene (named orf288) was found to be located downstream of the atp6 gene and co-transcribed with this gene in the hau CMS sterile line. Western blotting analysis showed that this predicted open reading frame (ORF) was translated in the mitochondria of male-sterile plants. Furthermore, the growth of Escherichia coli was significantly repressed in the presence of ORF288, which indicated that this protein is toxic to the E. coli host cells. To confirm further the function of orf288 in male sterility, the gene was fused to a mitochondrial-targeting pre-sequence under the control of the Arabidopsis APETALA3 promoter and introduced into Arabidopsis thaliana. Almost 80% of transgenic plants with orf288 failed to develop anthers. It was also found that the independent expression of orf288 caused male sterility in transgenic plants, even without the transit pre-sequence. Furthermore, transient expression of orf288 and green fluorescent protein (GFP) as a fused protein in A. thaliana protoplasts showed that ORF288 was able to anchor to mitochondria even without the external mitochondrial-targeting peptide. These observations provide important evidence that orf288 is responsible for the male sterility of hau CMS in Brassica juncea