Trapping and recombination processes via deep level T3 in semi-insulating gallium arsenide

Trapping and recombination of free carriers by deep level T₃ has been studied. Occupancy of the level by electrons and dynamics of its filling and emptying as a function of illumination with monoenergetic photons in 0.69–1.55 eV range has been monitored by the thermally stimulated currents method. We have found that level T₃ behaves more like a recombination center than like an ordinary electron trap. Besides trapping free electrons from conduction band, this trap can also communicate with valence band, trapping holes. The capture cross section for trapping a hole is estimated to be comparable or even larger than the capture cross section for trapping an electron. However, in many experimental conditions free electrons are generated more abundantly than free holes, and free carrier mobility and thermal velocity are both much higher for electrons than for holes. Therefore, electron trapping often prevails, so that this frequently detected defect, has been up to now most often perceived as a deep electron trap.     

Pulse and frequency response of a p-i-n photodiode with absorption layer fabricated in two-valley semiconductor

Starting from the transport equations of the phenomenological model for a two-valley semiconductor, we obtained the pulse response of a p-i-n photodiode with the absorption layer fabricated in a two-valley semiconductor (GaAs, InGaAs...). The pulse response was determined for the case when it was possible to linearize the transport equations. It was shown that the nonstationary effects influence significantly the intensity and speed of the response. The frequency response was obtained by applying the fast Fourier transform (FFT) to the pulse response.     

Miscibility of poly(2,6-dimethyl-1,4-phenylene oxide)/poly(vinyl pyrrolidone) blends

The miscibility of blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and poly(vinylpyrrolidone) (PVP) was studied by differential scanning calorimetry (DSC) through the analysis of the glass transition temperature Tg. The dependence of Tg with the annealing temperature was determined for PPO and PVP samples of different molecular weights. The phase diagrams for blends containing three different PVP samples were established. Blends of PPO and PVP were found to be miscible for composition lower than 30% and higher than 65% of PVP. A inmiscibility window between 30 and 65% of PVP is also described.     

A single crystal of YALO3: Ce3+ as a fast scintillator in SEM

A new single-crystal scintillator intended for applications in a scanning electron microscope (SEM) is presented. It is a single-crystal disc of yttrium aluminium perovskite activated by trivalent cerium free of traces of Fe ions. The single crystals of YAlO₃: Ce³⁺ (YAP: Ce³⁺) were prepared by the Czochralski method in a reducing atmosphere of Ar and H₂ with an excess amount of Y³⁺ ions. Effective methods of purification and purity control of the raw material are described. The highest achievable concentration of Ce³⁺ ions in as grown crystals amounted to 0.3 wt%, concentration in the melt was 8–9 times higher. The best properties were found with samples of the maximum possible concentration of Ce³⁺. Compared with the previous aluminate Y₃ Al₅ O₁₂: Ce³⁺ (YAG: Ce³⁺) these samples showed higher efficiency, a shorter decay time of luminescence (40 ns) and an emission band in a more advantageous spectral region (378 nm). Because of high resistance to radiation damage, high chemical resistance and applicability to ultra-high vacuum it is also suitable for detection of other kinds of ionizing radiation.     

Antioxidants in spring leaves of Oxalis acetosella L.

Oxalis acetosella L. is a common, edible wild plant native to the northern hemisphere. The contents of selected antioxidants, and the antioxidant capacity of young and old spring leaves of O. acetosella, were evaluated. The present study reports foliar contents of ascorbic acid, tocopherols, carotenoids, chlorophyll, flavonoids, phenolic acids and total phenolics, and compares the nutritional value of O. acetosella with other cultivated and wild plants. The composition of foliar antioxidants was found to depend on leaf age. On the other hand, the antioxidant capacity of old leaves were in the same range as young leaves. A comparison between O. acetosela with lettuce analysed in our study, and with numerous cultivated and wild edible plants from other studies, showed that O. acetosella is very rich in β-carotene, ascorbic acid, tocopherols and xanthophylls, and that it is one of the best sources of flavonoids (flavonol glycosides and flavan-3-ols), especially rutin. Therefore, O. acetosella is a potentially important dietary source of antioxidants.     

The effect of ripening and storage conditions on the distribution of tyramine,putrescine and cadaverine in Edam-cheese

The aim of the work was to describe the development of selected biogenic amines (histamine, tyramine, putrescine and cadaverine) in 4 layers of Dutch-type cheese (Edam-cheese) depending on 3 ripening/storage regimes during a 98-day period. Biogenic amines were analysed by means of ion-exchange chromatography. A further goal was to identify microbial sources of biogenic amines in the material analysed. Phenotype characterization and repetitive sequence-based PCR fingerprinting were used to identify the isolated bacteria. The highest content of tyramine, putrescine and cadaverine was determined in cheeses stored in a ripening cellar at a temperature of 10 °C during the whole observation period. Lower biogenic amines content was determined in samples which were moved into a cold storage device (5 °C) after 38 days of storage in a ripening cellar (10 °C). The lowest concentrations of biogenic amines were detected in cheeses which were moved into a cold storage device (5 °C) after 23 days of storage in a ripening cellar (10 °C). During the 98-day period, histamine was not detected in any of the regimes. Within the cheeses analysed, non-starter lactic acid bacteria Lactobacillus curvatus, Lactobacillus casei/paracasei and Lactobacillus plantarum were detected as the main producers of the biogenic amines tested. In starter bacteria Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris the decarboxylase activity tested was not detected.     

The influence of monoacylglycerol and L‐glutamic acid on the viscoelastic properties of wheat flour dough and sensory characteristics of French loaf product

BACKGROUND: The influence of monoacylglycerol Rimulsoft Super(V) and L ‐glutamic acid added to wheat flour dough was studied. Properties of the doughs were evaluated on the basis of chemical analysis and rheological measurements on a farinograph. Bakery products made from these doughs were subsequently subjected to sensory analyses. RESULTS: It was found that L ‐glutamic acid influenced the water absorption in dough more (50.0 g kg^?1; water absorption 56.6%) than monoacylglycerol Rimulsoft Super(V) (50.0 g kg^?1; water absorption 55.0%). Farinograph measurements showed that doughs with the addition of L ‐glutamic acid resembled flour containing high‐quality gluten, but dough with the addition of monoacylglycerol Rimulsoft Super(V) corresponded to ‘weak’ flour. Sensory analyses revealed that, in comparison with the control sample of French loaf, the saliva‐absorbing capacity increased in the French loaf with the highest addition of L ‐glutamic acid (30.0 g kg^?1). Deterioration in quality and texture in French loaf with addition of L ‐glutamic acid (8.0 g kg^?1, 30.0 g kg^?1) was noted. No other statistically significant differences were found. CONCLUSION: It is acceptable to add both additives to dough in order to modify its rheological properties. Copyright © 2010 Society of Chemical Industry