Femtosecond pump-probe spectroscopy of intersubband relaxation dynamics in narrow InGaAs/AlAsSb quantum well structures

Intersubband relaxation dynamics in InGaAs/AlAsSb multiquantum wells (QWs) is studied by single-color femtosecond pump-probe measurements. At early delay times, all samples show an exponential decay of the transient transmission occurring with time constants of the order of a picosecond. The relaxation dynamics at later delay times strongly depend on both QW thickness and doping location. A non-single-exponential decay behavior indicates extra competing relaxation channels, as further confirmed by solving three-level rate equations. It is shown that slowly decaying components are due to electron transfer to states related to indirect valleys in the wells or in the barriers

Intersubband relaxation dynamics in narrow InGaAs/AlAsSb quantum well structures studied by femtosecond pump-probe spectroscopy

Intersubband relaxation dynamics in modulation doped InGaAs/AlAsSb multiquantum well (QW), with different QW thicknesses was investigated by femtosecond pump-probe spectroscopy. At early delay times, the samples show an exponential decay of the transient transmission with picosecond time constants. At later delay times, the relaxation dynamics depends on QW thickness. The presence of a slowly decaying component indicates the transfer of electrons to states related to indirect valleys in the barriers. This result is further confirmed by solving three-level rate equations

Mortality and utilisation of Sclerocarya birrea subsp. caffra between 2001 and 2008 in the Kruger National Park, South Africa

A resurvey of a sample of marula trees (n=474) in the Kruger National Park (KNP) originally documented in 2001, was conducted in 2008 to determine the response of this population segment to the conditions prevalent during that time. These included an increasing elephant population and changes to the KNP fire policy. The overall mortality rate was estimated to be 2.6% per annum, with the mortality rate for individuals N5 m in height being 3.7% per annum. The highest level of mortality was found in the 5–8 m height class (7.1% per annum), while the highest number of dead individuals occurred in the 11–15 m height class (25). In addition minimal recruitment into the seedling size class was observed (n=6). No growth of saplings less than 2 m in height to heights greater than 2 m was observed. Almost half the individuals that were heavily damaged in 2001 had died by 2008. Heavy elephant utilisation and tree mortality was concentrated in the Sabie thorn thickets ecozone on granites where marula density was highest. Utilisation levels on the surviving individuals throughout the sampled area had almost tripled between 2001 and 2008, with individuals between 5 and 8 m in height accumulating the most additional elephant utilisation. It was concluded that the sampled marula population was not sustaining itself under the conditions prevalent between 2001 and 2008. Since sampled trees N5 m in height were strongly biased towards the Sabie thorn thickets, any projections for the likely fate of marulas in terms of adult mortality would mainly apply to this ecozone. The spatial variability described in this study suggests that further sampling is needed to adequately represent trends elsewherePeer reviewe

Determination of aspartate kinase in maize tissues.

Lysine, threonine, methionine and isoleucine are synthesized from aspartate in a branched pathway in higher plants. Aspartate kinase plays a key role in the control of the aspartate pathway. The enzyme is very sensitive to manipulation and storage and the hydroxamate assay normally used to determine aspartate kinase activity has to be altered according to the plant species and tissue to be analyzed. We have optimized the assay for the determination of aspartate kinase in maize plants callus cell cultures. Among all the assay parameters tested, the concentration of ATP/Mg and temperature were critical for enzyme activity. In the case of temperature, 35°C was shown to be the optimum temperature for aspartate kinase activity

Caracterização nutricional de grãos integrais e descascados de cultivares de cevada Chemical characterization of covered and hulness barley cultivars

O objetivo deste trabalho foi determinar a composição de nutrientes de grãos de diferentes cultivares de cevada, na forma integral e descascada, e classificá-los em grupos com características nutricionais distintas. Foram utilizadas amostras de 17 cultivares, da Embrapa Trigo, Passo Fundo, RS, da safra de 2005. As determinações químicas foram realizadas de acordo com os métodos de análise oficial da AOAC Internacional. Foram observadas diferenças significativas entre grãos integrais de cultivares para proteína bruta, cinzas, extrato etéreo, fibra total e carboidratos não-fibrosos, porém, os teores de fibra insolúvel e fibra solúvel não diferiram. Em grãos descascados, foram observadas diferenças em todos os parâmetros analisados. Com exceção da fração de carboidratos não-fibrosos, o processo de descascamento promoveu redução em todas as frações avaliadas, em especial nos teores de fibra total e fibra insolúvel. Diferenças na composição bromatológica ocorreram devido à variabilidade genética das cultivares e ao descascamento.<br>The objective of this work was to determine the chemical composition of different covered and hulness barley cultivars grains and to classify them according to distinctive nutritional groups. Seventeen cultivars from 2005 crop of Embrapa Trigo, Passo Fundo, RS, Brazil, were utilized. The chemical determinations were based on Official Methods of Analysis of the AOAC International. Significative differences between integral cultivars in relation to crude protein, ash, ether extract, total fiber and non-fibrous carbohydrate were observed, however, there were no differences for fiber content and soluble fiber. In the hulness grain, differences were observed. The non-fibrous carbohydrate was an exception and, in this case, the hull's process promoted the fraction's reduction, specially in the total fiber and insoluble fiber content. Variation in the bromatological composition occurs because of the genetic variability of cultivars and due to the hulness