Photoluminescence Studies of Lateral Composition Modulated Short-Period AlAs/InAs Superlattices

We present low temperature photoluminescence data for a series of spontaneous lateral composition modulation in (AlAs){sub m}/(InAs){sub n} short period superlattices on InP with differing average lattice constants, i.e., varying global strain. The low temperature photoluminescence peak energies were found to be much lower than the corresponding energy expected for the equivalent In{sub x}Al{sub 1{minus}x}As alloy. The bandgap energy reductions are found to approach 500 meV and this reduction is found to correlated with the strength of the composition modulation wave amplitude

Influence of Neonatal Hypothyroidism on Hepatic Gene Expression and Lipid Metabolism in Adulthood

Thyroid hormones are required for normal growth and development in mammals. Congenital-neonatal hypothyroidism (CH) has a profound impact on physiology, but its specific influence in liver is less understood. Here, we studied how CH influences the liver gene expression program in adulthood. Pregnant rats were given the antithyroid drug methimazole (MMI) from GD12 until PND30 to induce CH in male offspring. Growth defects due to CH were evident as reductions in body weight and tail length from the second week of life. Once the MMI treatment was discontinued, the feed efficiency increased in CH, and this was accompanied by significant catch-up growth. On PND80, significant reductions in body mass, tail length, and circulating IGF-I levels remained in CH rats. Conversely, the mRNA levels of known GH target genes were significantly upregulated. The serum levels of thyroid hormones, cholesterol, and triglycerides showed no significant differences. In contrast, CH rats showed significant changes in the expression of hepatic genes involved in lipid metabolism, including an increased transcription of PPARα and a reduced expression of genes involved in fatty acid and cholesterol uptake, cellular sterol efflux, triglyceride assembly, bile acid synthesis, and lipogenesis. These changes were associated with a decrease of intrahepatic lipids. Finally, CH rats responded to the onset of hypothyroidism in adulthood with a reduction of serum fatty acids and hepatic cholesteryl esters and to T3 replacement with an enhanced activation of malic enzyme. In summary, we provide in vivo evidence that neonatal hypothyroidism influences the hepatic transcriptional program and tissue sensitivity to hormone treatment in adulthood. This highlights the critical role that a euthyroid state during development plays on normal liver physiology in adulthood

Creep effect modelling and operation simulation for selected steam superheater elements in pressure part of boiler with supercritical working parameters

Przedstawiono wybrane wyniki badań uzyskane w projekcie rozwojowym pt. „Ocena zachowania się i prognoza długotrwałej pracy stali nowej generacji na elementy kotłów eksploatowanych powyżej temperatury granicznej” [1], w zakresie zbudowania modeli zjawiska pełzania, które to modele wraz z zaproponowaną analizą numeryczną posłużyły do opracowania sposobu wyznaczania trwałości eksploatacyjnej elementów o zróżnicowanej geometrii do pracy w części ciśnieniowej kotłów o parametrach nadkrytycznych (ciśnienie do 28,5 MPa; temperatura do 620oC) wykonanych z wybranych stali, a w szczególności: wysokochromowych stali martenzytycznych o zawartości 9 i 12% Cr w gatunkach X10CrMoVNb9-1 (P91), X12CrCoWVNb12-2-2 (VM12SHC) oraz austenitycznej stali chromowo-niklowej w gatunku X10CrNiCuNb18-9-3 (Super 304H), co jest drugą częścią opracowania. W pierwszej części przedstawiono sporządzone charakterystyki materiałowe badanych stali, omówiono zaproponowaną metodologię oceny stanu materiału i jego stopnia wyczerpania (zmiany obrazu mikrostruktury, zmiany składu fazowego wydzieleń, model ewolucji mikrostruktury, klasyfikacja mikrostruktury) oraz narzędzia do jego oceny [2]. W omawianej części opracowania zaprezentowano zbudowane dla badanych stali modele zjawiska pełzania: – Garofalo (Soderberga) opisujące I i II etap pełzania przy stałym naprężeniu oraz w stałej temperaturze, – własne modele opisujące odkształcenie pełzania dla I, II i III etapu pełzania przy stałym naprężeniu i w stałej temperaturze, – modele opisujące zależności czasu do zniszczenia od naprężenia dla wybranych stali, – modele opisujące prędkości pełzania w stanie ustalonym od wartości naprężenia dla wybranych stali. Na ich podstawie zaproponowano matematyczne modele odkształcenia pełzania w funkcji czasu i naprężenia dla wszystkich trzech analizowanych stali. Przedstawiono analizę wytężenia wybranych elementów konstrukcyjnych o zróżnicowanej geometrii: kolektora wylotowego wykonanego ze stali P91, przegrzewacza SH3 wykonanego ze stali Super 304H i przegrzewacza SH3 wykonanego ze stali VM12SHC, w oparciu o uprzednio wykonaną przez wytwórcę kotłów dokumentację projektową. Wykonana analiza przy wykorzystaniu metody elementów skończonych pozwoliła na wskazanie miejsc koncentracji naprężeń w tych elementach konstrukcyjnych. Przeprowadzona analiza numeryczna pozwoliła na określenie rozkładu odkształceń i naprężeń w nowych elementach konstrukcyjnych oraz takich, w których jest już widoczny wpływ postępującego procesu pełzania, a ponadto na symulację pracy wybranych elementów krytycznych w czasie znacznie przekraczającym czas przeprowadzonych prób pełzania. Modelowano pracę elementów urządzeń do 200 000 godzin pracy, podczas gdy najdłuższe próby pełzania zrealizowane w ramach projektu trwały około 25 000 godzin.This paper presents selected investigation results obtained in the development project “The assessment of behaviour and forecast about long-term operation of new-generation steel for components of boilers operated above limit temperature” with regard to building the creep effect models which, along with proposed numerical analysis, were used for development of the method for determination of life time of elements with different geometry intended for operation in the pressure part of boilers with supercritical parameters (pressure up to 28.5 MPa; temperature up to 620oC) made of selected steels, in particular: high-chromium martensitic steels containing 9 and 12% of Cr – grades X10CrMoVNb9-1 (P91) and X12CrCoWVNb12-2-2 (VM12SHC), and austenitic chromium-nickel steel – grade X10CrNiCuNb18-9-3 (Super 304H), which is the second part of the study. In the first part, the material characteristics developed for selected steels were presented, the proposed methodology for the assessment of material condition and exhaustion extent (changes in the image of microstructure, changes in phase composition of precipitates, microstructure evolution model, microstructure classification) and the assessment tools were discussed [1]. In this part of the study, the following creep effect models built for the examined steels were presented: – Garofalo (Soderberg) model describing stage I and II of the creep at constant stress and constant temperature, – own models describing creep strain for stage I, II and III of the creep at constant stress and constant temperature, – models describing the relationships between time to destruction and strain for selected steels, – models describing steady-state creep rates depending on stress values for selected steels. On the basis of these, the mathematical models of creep strain as a function of time and stress for all the three analysed steels were proposed. The effort analysis for selected structural components with different geometry: discharge collector made of P91 steel, SH3 superheater made of Super 304H steel and SH3 superheater made of VM12SHC steel, was presented based on the design documentation prepared previously by the boiler manufacturer. The analysis made using the finite-element method allowed the points of stress concentration in these structural components to be indicated. The numerical analysis allowed the determination of strain and stress distribution in new structural components as well as those where the effect of progressing creep process was already visible, and moreover the operation simulation for selected critical elements within the time significantly exceeding that of completed creep tests. The operation of the equipment elements was modelled for up to 200,000 hours, while the longest creep tests performed as a part of the project were approx. 25,000 hours

Digital Repeat Analysis; Setup and Operation

Since the emergence of digital imaging, there have been questions about the necessity of continuing reject analysis programs in imaging departments to evaluate performance and quality. As a marketing strategy, most suppliers of digital technology focus on the supremacy of the technology and its ability to reduce the number of repeats, resulting in less radiation doses given to patients and increased productivity in the department. On the other hand, quality assurance radiographers and radiologists believe that repeats are mainly related to positioning skills, and repeat analysis is the main tool to plan training needs to up-skill radiographers. A comparative study between conventional and digital imaging was undertaken to compare outcomes and evaluate the need for reject analysis. However, digital technology still being at its early development stages, setting a credible reject analysis program became the major task of the study. It took the department, with the help of the suppliers of the computed radiography reader and the picture archiving and communication system, over 2 years of software enhancement to build a reliable digital repeat analysis system. The results were supportive of both philosophies; the number of repeats as a result of exposure factors was reduced dramatically; however, the percentage of repeats as a result of positioning skills was slightly on the increase for the simple reason that some rejects in the conventional system qualifying for both exposure and positioning errors were classified as exposure error. The ability of digitally adjusting dark or light images reclassified some of those images as positioning errors

Characterizing Composition Modulations in InAs/AIAs Short-Period Superlattices

The formation of quantum wires has much interest due to their novel electronic properties which may lead to enhanced optoelectronic device performance and greater photovoltaic efficiencies. One method of forming these structures is through spontaneous lateral modulation found during the epitaxial growth of III/V alloys. In this paper, we report and summarize our investigations on the formation of lateral moduation in the MBE grown InAlAs/InP(001) system. This system was grown as a short-period superlattice where n-monolayers of InAs are deposited followed by m-Monolayers of AlAs (with n and m~2) and this sequence is repeated to grown a low strain InAlAs ternary alloy on InP(001) that exhibits lateral modulation. Films were grown under a variety of condition (growth temperature, effective alloy composition, superlattice period, and growth rate). These films have been extensively analyzed using X-ray diffraction, atomic force microscopy, and transmission electron microscopy (TEM) and microcharacterization, in addition to photon-based spectroscopes. Here we present results of several microstructural characterizations using a wide range of TEM-based techniques, and compare them to results from the other methods to obtain a unified understanding of composition modulation. Two strong points consistently emerge: 1) The lateral modulation wavelength is insensitive to growth temperature and effective alloy composition, but the strength of the lateral modulation is greatest near an effective alloy composition of In(0.46)Al(0.54)As, which corresponds to a slightly tensile global strain with respect to InP. 2) The composition variation for the strongly modulated films is as much as 0.38 InAs mole fraction. In addition, for these strongly modulated films, the modulation wave is asymmetric showing strongly peaked, narrower InAs-rich regions separated by flat AlAs-rich regions. We discuss these results and their possible implications in addition to detailing the techniques used to obtain them

Reciprocal-space and real-space analyses of compositional modulation in InAs/AlAs short-period superlattices

The microstructure of lateral composition modulation in InAs/AlAs superlattices grown by MBE on InP is examined. The use of x-ray diffraction, TEM, AFM, and STEM to characterize the modulations is discussed. Combining the information from these techniques gives increased insight into the phenomenon and how to manipulate it. Diffraction measures the intensity of modulation and its wavelength, and is used to identify growth conditions giving strong modulation. The TEM and STEM analyses indicate that local compositions are modulated by as much as 0.38 InAs mole fraction. Plan-view images show that modulated structures consists of short ({approx_lt}0.2 {micro}m) In-rich wires with a 2D organization in a (001) growth plane. However, growth on miscut substrates can produce a single modulation along the miscut direction with much longer wires ({approx_gt}0.4 {micro}m), as desired for potential applications. Photoluminescence studies demonstrate that the modulation has large effects on the bandgap energy of the superlattice