A dynamic reduced order model for simulating entrained flow gasifiers: Part I: Model development and description

The development of accurate, flexible and robust dynamic reduced order models (ROMs) is an important step towards greater commercialization of entrained flow gasifiers (EFGs). This two-part series of papers describes the development of such a ROM. Part I, below, describes the model, while Part II presents its validation for four EFG designs and sensitivity analysis. The ROM employs a reactor network model (RNM) that approximates fluid mixing and recirculation using a series of idealized chemical reactors; well-stirred reactors and 1-D plug flow reactors. The RNM is constructed such that the ROM is capable of simulating the operation of a range of commercial or research gasifiers and syngas cooler configurations. The ROM incorporates submodels for multiple feedstocks, mixing and recirculation, particle properties, drying and devolatilization, chemical kinetics, fluid dynamics, heat transfer, pollutant formation, slag behavior and syngas cooling. It is the first experimentally-validated gasifier simulator to incorporate all of the above submodels as well as possess dynamic capability. Modifications to some of the submodels from their original form to improve ROM accuracy, flexibility and robustness are also discussed. The ROM performs the steady-state simulations presented in Part II of this series in 1–5 min on a desktop personal computer, compared to multiple days on multiple processors for more detailed CFD-based simulations.     

The Effect of Sulfur Concentration in Liquid Iron on Mineral Layer Formation During Coke Dissolution

The effects of sulfur concentration in liquid iron on mineral layer development between coke and iron as coke dissolves in a 2 mass pct carbon-iron liquid have been investigated at 1773 K (1500 °C). The initial sulfur in iron concentrations used ranged from 0.006 to 0.049 mass pct. Key findings include that the two-stage dissolution behavior exhibited in the carbon transfer from coke to iron, as reported in a previous study by the authors, at low initial sulfur in iron contents, was also apparent at the higher values used in this study. This two-stage behavior was attributed to a change in the mineral layer density as a result of changes in mineral morphology at the interface. In addition to confirming the two-stage behavior of the carbon-transfer kinetics at the higher sulfur concentration in iron levels, after a period of time, a solid calcium sulfide layer formed on the mineral layer. The sulfide layer formed after approximately 40 minutes, and the proportion of sulfide in the mineral layer increased with increased experimental time and initial sulfur concentration in iron. It was usually found at the iron side of the mineral layer and was associated with calcium-enriched calcium aluminates. Thermodynamic analysis of this layer confirmed that the sulfide is stabilized as the mineral layer is enriched by calcium.     

The hormonal receptor status of uterine carcinosarcomas (mixed müllerian tumours): an immunohistochemical study

Guidelines for cardiac anaesthesia could reduce irrational variation in practice and so improve cardiac surgical outcome. In October 1994, a postal survey was undertaken to determine the views and attitudes of consultant cardiac anaesthetists in the United Kingdom towards guidelines. One hundred and forty correctly completed questionnaires were returned (minimum response rate 64%). Eighty-nine per cent believed that guidelines were of value in medicine whilst only 21% wanted national guidelines for cardiac anaesthesia. Responses to other parts of the questionnaire showed that those against guidelines for cardiac anaesthesia were less positive towards their advantages and more negative to their disadvantages compared with those in their favour. The majority of cardiac anaesthetists, although believing them to be valuable in medicine, do not want guidelines for cardiac anaesthesia because they are concerned that guidelines would be inflexible and would neither reduce variation in, nor improve the quality of, cardiac anaesthesia.     

Less invasive surgery for gynecologic tumors

The majority of cancers of the female genital tract are managed primarily by surgery in Western communities. Surgical techniques have developed during the 20th century with a tendency toward increasing radicality in order to deal with those cancers with a propensity for locoregional spread. On occasions during the past 100 years, individual surgeons have made efforts to tailor surgical practice to more appropriately deal with the true risks of spread. In recent times this search for more accurate tailoring has moved on apace and has coincided with the burgeoning interest in minimal access surgical techniques. This review is designed to cover the past year's developments in the quest toward less invasive surgery for gynecologic tumors. A major drawback to tailoring of surgical technique with its inevitable reduction in radicality for some patients is the risk of undertreating the cancer. The temptation for the less experienced or less skilled clinician to reduce radicality because such a move more closely matches his or her level of skill will result in poor results, with the risk that the surgical technique being given a bad name rather than the situation being recognized as a decision to use inappropriate therapy.     

High-pressure freezing for immunocytochemistry

Ultrastructural immunocytochemistry requires that minimal damage to antigens is imposed by the processing methods. Immersion fixation in cross-linking fixatives with their potential to damage antigens is not an ideal approach and rapid freezing as an alternative sample-stabilization step has a number of advantages. Rapid freezing at ambient pressure restricts the thickness of well-frozen material obtainable to ≈ 15 μm or less. In contrast, high-pressure freezing has been demonstrated to provide ice-crystal-artefact-free freezing of samples up to 200 μm in thickness. There have been few reports of high-pressure freezing for immunocytochemical studies and there is no consensus on the choice of post-freezing sample preparation. A range of freeze-substitution time and temperature protocols were compared with improved tissue architecture as the primary goal, but also to compare ease of resin-embedding, polymerization and immunocytochemical labelling. Freeze-substitution in acetone containing 2% osmium tetroxide followed by epoxy-resin embedding at room temperature gave optimum morphology. Freeze-substitution in methanol was completed within 18 h and in tetrahydrofuran within 48 h but the cellular morphology of the Lowicryl-embedded samples was not as good as when samples were substituted in pure acetone. Acetone freeze-substitution was slow, taking at least 6 days to complete, and gave blocks which were difficult to embed in Lowicryl HM20. Careful handling of frozen samples avoiding rapid temperature changes reduced apparent ice-crystal damage in sections of embedded material. Thus a slow warm-up to freeze-substitution temperature and a long substitution time in acetone gave the best results in terms of freezing quality and cellular morphology. No clear differences emerged between the different freeze-substitution media from immunocytochemical labelling experiments.     

The arbitrariness of the sign: Learning advantages from the structure of the vocabulary.

Recent research has demonstrated that systematic mappings between phonological word forms and their meanings can facilitate language learning (e.g., in the form of sound symbolism or cues to grammatical categories). Yet, paradoxically from a learning viewpoint, most words have an arbitrary form-meaning mapping. We hypothesized that this paradox may reflect a division of labor between 2 different language learning functions: arbitrariness facilitates learning specific word meanings and systematicity facilitates learning to group words into categories. In a series of computational investigations and artificial language learning studies, we varied the extent to which the language was arbitrary or systematic. For both the simulations and the behavioral studies, we found that the optimal structure of the vocabulary for learning incorporated this division of labor. Corpus analyses of English and French indicate that these predicted patterns are also found in natural languages. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Transesophageal echocardiography in the detection and surgical management of a papillary fibroelastoma of the mitral valve causing partial mitral valve obstruction

Duchenne muscular dystrophy (DMD) is an X-chromosome-linked myopathy caused by a defect in the DMD gene. Intragenic deletions appear to be the most common gene defect leading to DMD, and the deletion frequency has been estimated to be 66%. Results of this study using a group of 24 DMD patients of Sri Lankan origin employing the technique of multiplex DNA amplification using the polymerase chain reaction indicated a deletion frequency of 62.5%. Eighty per cent of these deletions were localized in a region of the DMD gene regarded as a 'hot spot' for DMD deletions. Our results are in agreement with the results of other studies carried out on Caucasian populations.     

Kinetic analysis of silicothermic process under flowing argon atmosphere

The Pidgeon process, a silicothermic reduction of calcined dolomite under vacuum, is the dominant process to make magnesium metal. Experimental data from Morsi et al., were utilised for kinetics analysis of silicothermic reduction of calcined dolomite under argon atmosphere. A number of kinetic models were assessed to evaluate the rate-controlling step in the process. The results suggest that the reaction is controlled by the solid-state diffusion of reactants with the Jander and Ginstling–Brounshtein model providing the best representation of the process kinetics. Mass transfer effects of magnesium vapour from the surface to the bulk gas phase was also analysed. These results suggest that gas–film mass transfer is not the limiting step of the kinetics. Pore diffusion through briquettes is postulated to have some effect on the kinetics but solid-state diffusion is the major rate-limiting step.

Le procédé Pidgeon, une réduction silicothermique sous vide de dolomie calcinée, est le procédé dominant de production de magnésium métallique. On a utilisé les données expérimentales de Morsi et al pour l’analyse cinétique de la réduction silicothermique de dolomie calcinée sous une atmosphère d’argon. On a estimé un certain nombre de modèles cinétiques afin d’évaluer l’étape du procédé cinétiquement limitante. Les résultats suggèrent que la diffusion à l’état solide des réactants contrôle la réaction, le modèle de Jander et Ginstling-Brounshtein fournissant la meilleure représentation de la cinétique du procédé. On a également analysé les effets du transfert massique de la vapeur de magnésium de la surface vers le c?ur de la phase gazeuse. Ces résultats suggèrent que le transfert de masse gaz-film n’est pas l’étape limitante de la cinétique. On postule que la diffusion par pore à travers les briquettes a un certain effet sur la cinétique mais la diffusion à l’état solide est l’étape majeure cinétiquement limitante.     

Mutations in the Lcb2p subunit of serine palmitoyltransferase eliminate the requirement for the TSC3 gene in Saccharomyces cerevisiae

Serine palmitoyltransferase catalyses the committed step in sphingolipid synthesis, the condensation of serine with palmitoyl-CoA to form 3-ketosphinganine. Two proteins, Lcb1p and Lcb2p, are essential for enzyme activity and a third protein, the 80-amino acid Tsc3p, stimulates the activity of serine palmitoyltransferase several-fold. Tsc3p physically associates with a complex of Lcb1p-Lcb2p and stimulates enzyme activity posttranslationally, but its precise function is not known. Tsc3p is essential for cell viability only at elevated temperatures, although serine palmitoyltransferase activity is reduced in the tsc3 delta mutant, even at permissive growth temperatures. Tsc3p is apparently not required for any essential process besides stimulation of serine palmitoyltransferase at 37 degrees C, since providing sphingoid bases to the growth medium reverses the temperature-sensitive growth phenotype of the tsc3 delta mutant. To gain further insight into the function of Tsc3p, suppressor mutants that eliminate the Tsc3p requirement for growth at 37 degrees C were isolated and characterized. These studies show that dominant mutations in the Lcb2p subunit of serine palmitoyltransferase suppress the temperature-sensitive growth phenotype of the tsc3 delta null mutant by increasing the Tsc3p-independent serine palmitoyltransferase activity.