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.     

Stochastic LQ-optimal control for 2-D systems

Stochastic LQ-optimal control problem is solved for linear 2-D systems via 2-D polynomial techniques. All stabilizing controllers are parameterized and then minimizing one is obtained. Its transfer function results from two 2-D spectral factorizations and a couple of linear equations in formal power series. A practically useful sub-optimal controller is also considered that results from truncated spectral factorizations and a couple of 2-D polynomial equations.     

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.     

Network formation involving epoxide and carboxyl groups

Summary The base catalyzed reaction between epoxide and carboxyl groups was studied using a simple model system phenylglycidyl ether-caproic acid in the presence of triethylamine. The reaction was investigated by mass spectrometry and GPC which provide an overall qualitative and quantitative survey of all the forming reaction products. The addition esterification is followed by etherification and condensation esterification and the main reaction product, monoester, is disproportionated yielding diester and diol. In a polyfunctional system, the latter reaction may cause splitting of the polymer chain and formation of new crosslinks.     

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