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  • 1
    Electronic Resource
    Electronic Resource
    Detailed kinetics of titanium nitride synthesis (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 377-388 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A thermogravimetric analyzer is used to study the synthesis of TiN from Ti powder over a wide range of temperature, conversion and heating rate, and for two Ti precursor powders with different morphologies. Conversions to TiN up to 99% are obtained with negligible oxygen contamination. Nonisothermal initial rate and isothermal data are used in a nonlinear least-squares minimization to determine the most appropriate rate law. The logarithmic rate law offers an excellent agreement between the experimental and calculated conversions to TiN and can predict afterburning, which is an important experimentally observed phenomenon. Due to the form of the logarithmic rate law, the observed activation energy is a function of effective particle size, extent of conversion, and temperature even when the intrinsic activation energy remains constant. This aspect explains discrepancies among activation energies obtained in previous studies. The frequently used sedimentation particle size is a poor measure of the powder reactivity. The BET surface area indicates the powder reactivity much better.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690410219
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  • 2
    Electronic Resource
    Electronic Resource
    Noncatalytic gas-solid reactions and mechanical stress generation (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 1235-1250 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The reaction rate in gas-solid systems can be affected by mechanical stresses that arise as the reaction proceeds. Stresses develop due to differences between precursor and product molar volumes and thermal expansion coefficients. Experimental evidence on the interaction of reaction rate and mechanical stress for the Ti/N2 and Ti/O2 systems is provided. A detailed and consistent mathematical model is developed for the reaction taking place at the constrained precursor/product interface. An elastic formulation for the stresses is adopted, and stress generation due to mismatches in linear thermal expansion coefficients and equivalent volume (Pilling-Bedworth ratio) for the precursor and product are considered. The effect of surface energy, which becomes significant for particle sizes below 1 μm, is also included in the model. Both experimentally and theoretically, conditions exist where the mechanical stresses exceed the strength of the material, leading to mechanical breakdown of the product layer, thus causing a discontinuity in the observed reaction rate. The entire processing history, including the reaction, temperature, and pressure profiles, plays an important role in determining the overall reaction kinetics of the powder.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690410519
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  • 3
    Electronic Resource
    Electronic Resource
    Reaction rate modeling in noncatalytic gas-solid systems: Species transport and mechanical stress (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2614-2624 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A detailed model to describe the overall reaction rate of the oxidation of titanium is developed. The mathematical model consists of two facets, the first of which involves a detailed description of species transport that accounts for the formation of charged species. This is augmented by a description of the occurrence of mechanical stress due to a Pilling - Bedworth ratio that differs significantly from I as well as differences between precursor and product thermal expansion coefficients. A self imposed electric field is formed across the oxide layer due to different mobilities of the species considered. This field opposes the transport of electrons and enhances the transport of anion vacancies, thus increasing the overall reaction rate compared to a pure diffusion process, while also ensuring that electrical charge is conserved. Large growth stresses result from the unmatched precursor and product volumes, significantly affecting the overall process. These results show that the incorporation of a consistent treatment of mechanical stress forms a necessay part of any accurate description of the overall behavior of a reacting particle.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690411210
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  • 4
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    Impact of genome reduction on bacterial metabolism and its regulation (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-12-08
    Description: To understand basic principles of bacterial metabolism organization and regulation, but also the impact of genome size, we systematically studied one of the smallest bacteria, Mycoplasma pneumoniae. A manually curated metabolic network of 189 reactions catalyzed by 129 enzymes allowed the design of a defined, minimal medium with 19 essential nutrients. More than 1300 growth curves were recorded in the presence of various nutrient concentrations. Measurements of biomass indicators, metabolites, and 13C-glucose experiments provided information on directionality, fluxes, and energetics; integration with transcription profiling enabled the global analysis of metabolic regulation. Compared with more complex bacteria, the M. pneumoniae metabolic network has a more linear topology and contains a higher fraction of multifunctional enzymes; general features such as metabolite concentrations, cellular energetics, adaptability, and global gene expression responses are similar, however.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Yus, Eva -- Maier, Tobias -- Michalodimitrakis, Konstantinos -- van Noort, Vera -- Yamada, Takuji -- Chen, Wei-Hua -- Wodke, Judith A H -- Guell, Marc -- Martinez, Sira -- Bourgeois, Ronan -- Kuhner, Sebastian -- Raineri, Emanuele -- Letunic, Ivica -- Kalinina, Olga V -- Rode, Michaela -- Herrmann, Richard -- Gutierrez-Gallego, Ricardo -- Russell, Robert B -- Gavin, Anne-Claude -- Bork, Peer -- Serrano, Luis -- New York, N.Y. -- Science. 2009 Nov 27;326(5957):1263-8. doi: 10.1126/science.1177263.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Centre for Genomic Regulation (CRG) and Universitat Pompeu Fabra, Avenida Dr. Aiguader 88, 08003 Barcelona, Spain.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19965476" target="_blank"〉PubMed〈/a〉
    Keywords: Adenosine Triphosphate/metabolism ; Bacterial Proteins/*metabolism ; Culture Media ; Energy Metabolism ; Enzymes/genetics/metabolism ; Gene Expression Profiling ; *Gene Expression Regulation, Bacterial ; *Genome, Bacterial ; Glycolysis ; *Metabolic Networks and Pathways ; Mycoplasma pneumoniae/*genetics/growth & development/*metabolism ; RNA, Bacterial/genetics/metabolism ; Signal Transduction ; Systems Biology ; Transcription, Genetic ; rRNA Operon
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Transcriptome complexity in a genome-reduced bacterium (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-12-08
    Description: To study basic principles of transcriptome organization in bacteria, we analyzed one of the smallest self-replicating organisms, Mycoplasma pneumoniae. We combined strand-specific tiling arrays, complemented by transcriptome sequencing, with more than 252 spotted arrays. We detected 117 previously undescribed, mostly noncoding transcripts, 89 of them in antisense configuration to known genes. We identified 341 operons, of which 139 are polycistronic; almost half of the latter show decaying expression in a staircase-like manner. Under various conditions, operons could be divided into 447 smaller transcriptional units, resulting in many alternative transcripts. Frequent antisense transcripts, alternative transcripts, and multiple regulators per gene imply a highly dynamic transcriptome, more similar to that of eukaryotes than previously thought.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Guell, Marc -- van Noort, Vera -- Yus, Eva -- Chen, Wei-Hua -- Leigh-Bell, Justine -- Michalodimitrakis, Konstantinos -- Yamada, Takuji -- Arumugam, Manimozhiyan -- Doerks, Tobias -- Kuhner, Sebastian -- Rode, Michaela -- Suyama, Mikita -- Schmidt, Sabine -- Gavin, Anne-Claude -- Bork, Peer -- Serrano, Luis -- New York, N.Y. -- Science. 2009 Nov 27;326(5957):1268-71. doi: 10.1126/science.1176951.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Centre for Genomic Regulation (CRG), Universitat Pompeu Fabra, Barcelona, Spain.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19965477" target="_blank"〉PubMed〈/a〉
    Keywords: Base Sequence ; *Gene Expression Profiling ; *Gene Expression Regulation, Bacterial ; Genes, Bacterial ; *Genome, Bacterial ; Molecular Sequence Data ; Mycoplasma pneumoniae/*genetics/metabolism ; Oligonucleotide Array Sequence Analysis ; Operon ; RNA, Antisense/genetics/metabolism ; RNA, Bacterial/*genetics/metabolism ; RNA, Messenger/genetics/metabolism ; RNA, Untranslated/analysis/*genetics ; *Transcription, Genetic
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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