No description available.

<p>In this thesis, the microstructure of organic photovoltaic APFO-3:PC₆₁BM bulk-heterojunction blends was examined. Earlier studies have focused on the microstructure after spin coating. This thesis aims to give a better insight into microstructural degradation as the films are annealed above the glass transition temperature, T_g, and the mixture approaches thermodynamic equilibrium. Electro- and photoluminescence studies indicate that the polymer and PC₆₁BM are intermixed on a scale shorter than the exciton diffusion length of 10 nm, even when annealed above T_g. The temperature stability of APFO-3:PC₆₁BM was also investigated with respect to the molecular weight of the polymer. The photovoltaic performance of these blends was found to be stable up to temperatures approaching the glass transition temperature, especially if a high molecular-weight APFO-3 grade was used.</p><p> </p><p>The crystallization of PC₆₁BM was also investigated. Above T_g, PC₆₁BM crystallization was found to commence, albeit slowly at temperatures close to T_g. At elevated temperatures instead, micrometer sized crystals were observed to form. It was also noted that illumination while annealing APFO-3:PC₆₁BM thin films above T_g affected PC₆₁BM crystallization, the origin of which is so far unclear although chemical degradation could be largely excluded.</p>

In this thesis, the microstructure of organic photovoltaic APFO-3:PC61BM bulk-heterojunction blends was examined. Earlier studies have focused on the microstructure after spin coating. This thesis aims to give a better insight into microstructural degradation as the films are annealed above the glass transition temperature, Tg, and the mixture approaches thermodynamic equilibrium. Electro- and photoluminescence studies indicate that the polymer and PC61BM are intermixed on a scale shorter than the exciton diffusion length of 10 nm, even when annealed above Tg. The temperature stability of APFO-3:PC61BM was also investigated with respect to the molecular weight of the polymer. The photovoltaic performance of these blends was found to be stable up to temperatures approaching the glass transition temperature, especially if a high molecular-weight APFO-3 grade was used.   The crystallization of PC61BM was also investigated. Above Tg, PC61BM crystallization was found to commence, albeit slowly at temperatures close to Tg. At elevated temperatures instead, micrometer sized crystals were observed to form. It was also noted that illumination while annealing APFO-3:PC61BM thin films above Tg affected PC61BM crystallization, the origin of which is so far unclear although chemical degradation could be largely excluded.

In this diploma thesis there is elaborated design of low-voltage power supply block using I3T25 technology. The theoretical part describes the basic structures used in the design, using CMOS and bipolar devices. Furthermore, the properties and the analysis used in the evaluation are described. In the design part there is an elaborated design of individual parts, including voltage references, current references, DAC converter, operational amplifier. In the last part, the power supply block is subjected to simulations for verification of temperature compensated output variables and analyzed circuit functionality.

The paper describes the comparison and the difference of modern hydraulic fluids compared to conventional hydraulic fluids. A comparison of different base oil groups, solvent neutrals, group I and comparison with hydrotreated/hydroprocessed group II and/or group III base oils is presented. The influence on oxidation stability, elastomer compatibility, carbon distribution and physical properties is outlined.

The paper describes the comparison and the difference of modern hydraulic fluids compared to conventional hydraulic fluids. A comparison of different base oil groups, solvent neutrals, group I and comparison with hydrotreated/hydroprocessed group II and/or group III base oils is presented. The influence on oxidation stability, elastomer compatibility, carbon distribution and physical properties is outlined.

Additive manufacturing (AM) techniques are being studied for their application in the aerospace industry. Numerous benefits come from the already in shape final piece, which needs reduced amount of prime material for its production and can have its shape numerically optimized for weight reduction. Austenitic stainless steels (AuSS) are widely used in aerospace and their manufacturing through AM is a popular research topic in order to accelerate their effective incorporation in air-crafts and spaceships. The special microstructures of AM has been observed with characterization techniques. The present work studies the high temperature stability of three AuSS (316L, MOD-316 and 21-6-9) considering two approaches; surface corrosion and microstructure evolution. First, for high temperature corrosion, thermogravimetric analysis has been performed from 850°C to 1150°C. From the results, kinetic analysis were performed and the activation energy was extracted from Arrhenius fits. Two mechanism were found for alloy 316L (first 435.41 kJ/mol and second 593.24 kJ/mol) and MOD-316 (first 740.01 kJ/mol and second 495.58 kJ/mol). Further SEM observations on the scales have shown Ni diffusion through the chromia scale in MOD-316 alloy, which could explain the higher oxidation rates at 1150°C. Alloy 21-6-9 has the best passivation behaviour with an activation energy of 190.47 kJ/mol. Secondly, long heat treatment (HT) at 725°C in air atmosphere has been performed, for 24 and 240h. Samples were initially as-built or annealed (900°C for 1h), to compare the effect of the HT on the microstructure evolution and precipitates formation. LOM observation showed preferable nucleation in grain boundaries (GB), an increment of the number of precipitates and a growth towards elongated shapes following GB with increased time. It was also observed a reduction in precipitates number with the annealing HT for all the alloys. XRD, SEM and EDS analysis has been carried out to identify the structure and composition of the precipitates. Various chromium, tungsten, copper, molybdenum and niobium carbides and oxides have been found in MOD-316. Higher porosity is observed in 21-6-9, that presented mainly chromium oxides, carbides and nitrides in GB and surrounding the AM defects. / SeSSA

No description available.

This thesis describes the incorporation within a semiconductor laser of a multiple quantum well InGaAsP/InP Electron Bragg Reflector (EBR). The EBR is intended to improve laser performance by inhibiting the escape of hot electrons from the laser active region by quantum mechanical Bragg reflection. To the author's knowledge, this investigation represents the first attempt to realize an EBR in the InGaAsP/InP material system. Computer models based on a transfer matrix method for the solution of Schrodinger's equation were written to obtain the EBR design. The transfer matrix method is described. Extensions to the transfer matrix method for optics are presented and are demonstrated to provide more than an order of magnitude improvement in computational efficiency for the calculation of the complex TE-mode propagation constant for planar graded-index waveguides with absorption or gain. The EBR designed for this work incorporates several new features. Deleterious band bending in the vicinity of the EBR is minimized by exploiting material strain to reduce the density of hole states in the EBR quantum wells. To maximize reflection bandwidth and relax fabrication tolerances, the EBR design used well widths that decreased with increasing depth into the p-type InP cladding. By the placement of the EBR adjacent to the separate confinement region, a return path was provided for electrons that scattered inelastically within the EBR. Moreover, the EBR structure was designed to support no bound electron states, so that the recombination of electrons with holes in the EBR would be minimal. To the author's knowledge, the EBR-equipped laser fabricated for this work represents the first attempt to exploit electron state exclusion. To explore the effectiveness of EBRs in the InGaAsP/InP material system, two nearly identical ridge waveguide lasers (one with an EBR, and one without) were designed, fabricated, and tested. The EBR-equipped lasers exhibited an anomalous threshold current temperature dependence which featured a "negative-To" regime (in which the threshold current decreases with increasing temperature), attaining a minimum in threshold current between T=150 K and T=200 K. These lasers had a threshold current temperature stability superior to that of standard lasers within a ~70 K window around the minimum threshold temperature. Experimental evidence suggests that the improved stability is not due to quantum mechanical Bragg reflection provided by the EBR, but is attributable to the temperature-dependent rate of hole escape from the EBR quantum wells into the separate confinement region. The proposed mechanism is described in detail and is supported by theoretical and experimental evidence. The results have implications for device design, because the mechanism by which the superior temperature stability is achieved does not rely on the electron coherence effects; the mathematical model suggests that the mechanism can be exploited to provide superior temperature stability in semiconductor lasers at 300 K or above. / Thesis / Master of Engineering (ME)

In this thesis, optimization of production of lipolytic enzymes by submerzed cultivation of Bacillus subtilis (BS) was studied. Production of lipolytic enzymes was tested in three nutrient media, which differed mainly in main sources of carbon, respectively of nitrogen. The first medium contained mainly extract from calf brain and beef heart (BHIB), the second medium contained peptone and yeast extract (NB) and the third one contained peptone and yeast extract with the addition of 2% (w/v) glucose (NBG). The highest lipolytic activity (0.0784 Uml-1) was measured in NBG medium. Maximum of lipolytic activity was observed before the end of the exponential phase of BS growth in all the media. Temperature optimum in NBG medium was determined from 30 to 50 °C, pH optimum in the range of 5 to 11 and subsequently the temperature stability of lipolytic enzymes produced by the BS was estimated. The activity value was determined spectrometrically using p-nitrophenyllaurate as a substrate. Produced lipolytic enzymes showed maximum activity at 37 °C in the alkaline pH of 8.0. Measurement of temperature stability showed that lipolytic enzymes are relatively thermostable enzymes retaining 100 % of the activity even after 1 hour of cultivation at 30 - 50 °C. The presence of 1% (w/v) olive oil in medium NBG caused a decrease in lipolytic activity by 65 % as well as in pH from 6.5 to 5.4 after 14 days of cultivation. After substitution of glucose by fructose in medium NBG, lipolytic activity showed comparable values during the first week of cultivation. On the other hand, the decrease of lipolytic activity by 29 % in the medium with fructose was observed after 14 days of cultivation. A procedure for the identification of lipolytic enzymes of BS by peptide massfingerprinting was developed to understand the potential of synthetic polyester - poly(e-caprolactone) as a lipase inductor. Degradation study of commercial polyester poly(e-caprolactone) was carried out by submerged cultivation of Bacillus subtilis in NBG medium at initial pH 7.0 and 30 °C for 14 days. PCL (Mn = 10,000, Mw = 14 000) was studied in the form of films (1.0 x 1.0 cm), which were prepared by melt-pressing, rapid cooling of the melt to 4 °C and evaporation of the solvent from 2 % dichlormethane solution. The evaluation of the films shown occurrence of weight loss (7.8 - 17.0 wt.%) together with the formation of numerous holes and cracks in the sample surface in relation to the method of the films preparation. Lipolytic activity values increased by 9 - 17 % in the degradation media compared to control samples. Densitometric monitoring showed also higher increase in cell mass in the degradation medium compared with control samples. Based on the results obtained, the degradation process induced by BS could be suggested.