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S F Yoon - One of the best experts on this subject based on the ideXlab platform.
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characteristics of non annealed λ 1 35 μm closely lattice matched gainnas gaas p i n photodetector structures grown by solid source molecular beam epitaxy
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2006Co-Authors: W K Loke, S F Yoon, Satrio Wicaksono, B K NgAbstract:Abstract The electrical and optical characteristics of planar non-annealed GaInNAs/GaAs p-i-n photodetector structures with 0.5 μm thick GaInNAs i-layer with Nitrogen Composition higher than 3% and detection wavelength up to 1.35 μm are reported. Soft-breakdown behavior in the reverse biased characteristic was observed under non-illuminated condition. Analysis of the reverse biased current dependence on detector diameter under non-illuminated condition shows a more significant contribution from the bulk generation current compared to surface recombination current. Under forward bias, the ideality factor value of 1.35 is found to be temperature independent. This suggests that the recombination current in the depletion region contributes significantly to the forward biased current besides the diffusion current. Low-temperature (4 K) photoluminescence (PL) from the GaInNAs layer shows an emission peak at λ = 1.29 μm. From curve fitting of the photoresponsivity spectrum, the room-temperature bandgap of E g,RT = 0.92 eV (or λ = 1.35 μm) is deduced. The room-temperature photoresponsivity spectrum shows a broad wavelength detection range of up to λ = 1.4 μm.
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comparison of electronic band structure and optical transparency conditions of in x ga 1 x as 1 y n y ga as quantum wells calculated by 10 band 8 band and 6 band k p models
Physical Review B, 2005Co-Authors: W J Fan, Y X Dang, S F YoonAbstract:We have investigated the electronic band structure and optical transparency conditions of ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{As}}_{1\ensuremath{-}y}{\mathrm{N}}_{y}∕\mathrm{Ga}\mathrm{As}$ quantum well (QW) using 10-band, 8-band and 6-band $\mathbf{k}∙\mathbf{p}$ models. The transition energy calculated by the 8-band model agrees very well with the values calculated by the 10-band model, especially in the range of high indium Composition (35%). Electron effective mass $({m}_{e}^{*})$ predicated by band anticrossing model, with Nitrogen-related enhancement weakened as indium Composition increases, was used in the 8-band model and was favored compared to the heavier value predicted by the phenomenological relationship. We have calculated the optical transition matrix element $({Q}_{i}^{{n}_{c}{n}_{v}})$ using the Bloch wave functions for the $\mathbf{k}∙\mathbf{p}$ models and discovered that the inclusion of Nitrogen-related energy level $({E}_{N})$ into the calculation of the conduction band by the 10-band $\mathbf{k}∙\mathbf{p}$ model yields lower differential gain $(dG∕dN)$ than that calculated by the 8-band $\mathbf{k}∙\mathbf{p}$ model on the same structure. Contrary to earlier reports that the reduction of $dG∕dN$ in ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{As}}_{1\ensuremath{-}y}{\mathrm{N}}_{y}∕\mathrm{Ga}\mathrm{As}$ QW and thus the lower obtainable optical gain is due to the increase in ${m}_{e}^{*}$, we have concluded that the reduction was due to the increased interaction between the $\ensuremath{\mid}S⟩$ conduction-band state and $\ensuremath{\mid}{S}_{N}⟩$ Nitrogen-related energy state, which weaken the optical transition matrix elements between valence band and conduction band. Our results also show that if ${m}_{e}^{*}$ is very large (as predicted by the phenomenological model), $dG∕dN$ will increase monotonously with Nitrogen Composition. Moreover, neglecting valence band and conduction band interaction in $\mathbf{k}∙\mathbf{p}$ models will result in the prediction of higher $dG∕dN$ which is not accurate.
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effects of surface nitridation during Nitrogen plasma ignition on optical quality of gainasn grown by solid source molecular beam epitaxy
Journal of Applied Physics, 2003Co-Authors: S Z Wang, S F Yoon, Wan Khai LokeAbstract:This article reports the reflection high-energy electron diffraction (RHEED) results during the growth of GaInAsN by solid source molecular beam epitaxy using a plasma-assisted radio frequency Nitrogen source. The results show that at sufficiently low Nitrogen Composition, the surface RHEED reconstruction is the same as that of GaAs. However, increase in Nitrogen Composition causes transformation of the RHEED pattern to (3×1) or (3×3) reconstruction, depending on the coverage of Nitrogen radicals on the growth surface. This fundamental characteristic of the Nitrogen-stabilized surface is accompanied by surface nitridation, which results in the formation of nonradiative recombination centers, hence deteriorating the GaInAsN quality. An overpressure of arsenic flux could, to some extent, minimize surface nitridation during Nitrogen plasma ignition, and therefore provide an important means for quality improvement in GaInAsN. Keeping the GaInAsN quantum well away from the nitridated surface by employing a GaA...
Frederic Bigey - One of the best experts on this subject based on the ideXlab platform.
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Relief from Nitrogen starvation entails quick unexpected down-regulation of glycolytic/lipid metabolism genes in enological Saccharomyces cerevisiae
PLoS ONE, 2019Co-Authors: Catherine Tesniere, Chloé Bessiere, Martine Pradal, Isabelle Sanchez, Bruno Blondin, Frederic BigeyAbstract:Nitrogen Composition of the grape must has an impact on yeast growth and fermentation kinetics as well as on the organoleptic properties of the final product. In some technological processes, such as white wine/rose´ winemaking, the yeast-assimilable Nitrogen content is sometimes insufficient to cover yeast requirements, which can lead to slow or sluggish fermentations. Growth is nevertheless quickly restored upon relief from nutrient starvation, e.g. through the addition of ammonium Nitrogen, allowing fermentation completion. The aim of this study was to determine how Nitrogen repletion affected the transcriptional response of a Saccharomyces cerevisiae wine yeast strain, in particular within the first hour after Nitrogen addition. We found almost 4800 genes induced or repressed, sometimes within minutes after nutrient changes. Some of these responses to Nitrogen depended on the TOR pathway, which controls positively ribosomal protein genes, amino acid and purine biosynthesis or amino acid permease genes and negatively stress-response genes, and genes related to the retrograde response (RTG) specific to the tricarboxylic acid (TCA) cycle and Nitrogen catabolite repression (NCR). Some unexpected transcriptional responses concerned all the glycolytic genes, carbohydrate metabolism and TCA cycle-related genes that were downregulated,as well as genes from the lipid metabolism.
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Relief from Nitrogen starvation entails quick unexpected down-regulation of glycolytic/lipid metabolism genes in enological Saccharomyces cerevisiae
2019Co-Authors: Catherine Tesniere, Chloé Bessiere, Martine Pradal, Isabelle Sanchez, Bruno Blondin, Frederic BigeyAbstract:Nitrogen Composition of the grape must has an impact on yeast growth and fermentation kinetics as well as on the organoleptic properties of the final product. In some technological processes, such as white wine/rosé winemaking, the yeast-assimilable Nitrogen content is sometimes insufficient to cover yeast requirements, which can lead to slow or sluggish fermentations. Growth is nevertheless quickly restored upon relief from nutrient starvation, e.g. through the addition of ammonium Nitrogen, allowing fermentation completion. The aim of this study was to determine how Nitrogen repletion affected the transcriptional response of a Saccharomyces cerevisiae wine yeast strain, in particular within the first hour after Nitrogen addition. We found almost 4800 genes induced or repressed, sometimes within minutes after nutrient changes. Some of these responses to Nitrogen depended on the TOR pathway, which controls positively ribosomal protein genes, amino acid and purine biosynthesis or amino acid permease genes and negatively stress-response genes, and genes related to the retrograde response (RTG) specific to the tricarboxylic acid (TCA) cycle and Nitrogen catabolite repression (NCR). Some unexpected transcriptional responses concerned all the glycolytic genes, carbohydrate metabolism and TCA cycle-related genes that were down-regulated, as well as genes from the lipid metabolism.
Wan Khai Loke - One of the best experts on this subject based on the ideXlab platform.
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effects of surface nitridation during Nitrogen plasma ignition on optical quality of gainasn grown by solid source molecular beam epitaxy
Journal of Applied Physics, 2003Co-Authors: S Z Wang, S F Yoon, Wan Khai LokeAbstract:This article reports the reflection high-energy electron diffraction (RHEED) results during the growth of GaInAsN by solid source molecular beam epitaxy using a plasma-assisted radio frequency Nitrogen source. The results show that at sufficiently low Nitrogen Composition, the surface RHEED reconstruction is the same as that of GaAs. However, increase in Nitrogen Composition causes transformation of the RHEED pattern to (3×1) or (3×3) reconstruction, depending on the coverage of Nitrogen radicals on the growth surface. This fundamental characteristic of the Nitrogen-stabilized surface is accompanied by surface nitridation, which results in the formation of nonradiative recombination centers, hence deteriorating the GaInAsN quality. An overpressure of arsenic flux could, to some extent, minimize surface nitridation during Nitrogen plasma ignition, and therefore provide an important means for quality improvement in GaInAsN. Keeping the GaInAsN quantum well away from the nitridated surface by employing a GaA...
Lamson Phan Tran - One of the best experts on this subject based on the ideXlab platform.
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approaches for enhancement of n2 fixation efficiency of chickpea cicer arietinum l under limiting Nitrogen conditions
Plant Biotechnology Journal, 2014Co-Authors: Maryam Nasr Esfahani, Saad Sulieman, Joachim Schulze, Kazuko Yamaguchishinozaki, Kazuo Shinozaki, Lamson Phan TranAbstract:Chickpea (Cicer arietinum) is an important pulse crop in many countries in the world. The symbioses between chickpea and Mesorhizobia, which fix N₂ inside the root nodules, are of particular importance for chickpea's productivity. With the aim of enhancing symbiotic efficiency in chickpea, we compared the symbiotic efficiency of C-15, Ch-191 and CP-36 strains of Mesorhizobium ciceri in association with the local elite chickpea cultivar 'Bivanij' as well as studied the mechanism underlying the improvement of N₂ fixation efficiency. Our data revealed that C-15 strain manifested the most efficient N₂ fixation in comparison with Ch-191 or CP-36. This finding was supported by higher plant productivity and expression levels of the nifHDK genes in C-15 nodules. Nodule specific activity was significantly higher in C-15 combination, partially as a result of higher electron allocation to N₂ versus H⁺. Interestingly, a striking difference in nodule carbon and Nitrogen Composition was observed. Sucrose cleavage enzymes displayed comparatively lower activity in nodules established by either Ch-191 or CP-36. Organic acid formation, particularly that of malate, was remarkably higher in nodules induced by C-15 strain. As a result, the best symbiotic efficiency observed with C-15-induced nodules was reflected in a higher concentration of the total and several major amino metabolites, namely asparagine, glutamine, glutamate and aspartate. Collectively, our findings demonstrated that the improved efficiency in chickpea symbiotic system, established with C-15, was associated with the enhanced capacity of organic acid formation and the activities of the key enzymes connected to the nodule carbon and Nitrogen metabolism.
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approaches for enhancement of n fixation efficiency of chickpea cicer arietinum l under limiting Nitrogen conditions
Plant Biotechnology Journal, 2014Co-Authors: Maryam Nasr Esfahani, Saad Sulieman, Joachim Schulze, Kazuko Yamaguchishinozaki, Kazuo Shinozaki, Lamson Phan TranAbstract:Chickpea (Cicer arietinum) is an important pulse crop in many countries in the world. The symbioses between chickpea and Mesorhizobia, which fix N2 inside the root nodules, are of particular importance for chickpea’s productivity. With the aim of enhancing symbiotic efficiency in chickpea, we compared the symbiotic efficiency of C-15, Ch-191 and CP-36 strains of Mesorhizobium ciceri in association with the local elite chickpea cultivar ‘Bivanij’ as well as studied the mechanism underlying the improvement of N2 fixation efficiency. Our data revealed that C-15 strain manifested the most efficient N2 fixation in comparison with Ch-191 or CP-36. This finding was supported by higher plant productivity and expression levels of the nifHDK genes in C-15 nodules. Nodule specific activity was significantly higher in C-15 combination, partially as a result of higher electron allocation to N2 versus H+. Interestingly, a striking difference in nodule carbon and Nitrogen Composition was observed. Sucrose cleavage enzymes displayed comparatively lower activity in nodules established by either Ch-191 or CP-36. Organic acid formation, particularly that of malate, was remarkably higher in nodules induced by C-15 strain. As a result, the best symbiotic efficiency observed with C-15-induced nodules was reflected in a higher concentration of the total and several major amino metabolites, namely asparagine, glutamine, glutamate and aspartate. Collectively, our findings demonstrated that the improved efficiency in chickpea symbiotic system, established with C-15, was associated with the enhanced capacity of organic acid formation and the activities of the key enzymes connected to the nodule carbon and Nitrogen metabolism.
Hugh P Duncan - One of the best experts on this subject based on the ideXlab platform.
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Nitrogen Composition in urban runoff implications for stormwater management
Water Research, 2005Co-Authors: Geoff Desmond Taylor, Tim D Fletcher, Tony Hoong Fatt Wong, Peter F Breen, Hugh P DuncanAbstract:Abstract A study was conducted to characterise the Composition of Nitrogen in urban stormwater in Melbourne, Australia, during baseflows and storm events, and to compare the results with international data. Nitrogen in Melbourne stormwater was predominantly dissolved (∼80%), with ammonia the least-abundant form (∼11%). Concentrations of Nitrogen species did not vary significantly between baseflow and storms, although the proportion of Nitrogen in particulate form was higher during storm events ( p = 0.04 ). Whilst the Composition of Nitrogen in Melbourne was broadly consistent with international data, the level of dissolved inorganic Nitrogen was higher in Melbourne ( μ = 48 % during baseflows and 49% during storms) than in the international literature ( μ = 29 % ). Limitations in the international dataset precluded comparison of total dissolved Nitrogen. The results have implications for stormwater management. Whilst Nitrogen species concentrations are variable, they are not strongly related to flow conditions, so treatment systems must be designed to cope with stochastic inflow concentrations at all times. To optimise their performance, stormwater treatments should be designed to improve dissolved Nitrogen removal. Further research is needed to improve the ability of treatment systems to achieve this aim.