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The degeneracy of the genetic code confers a wide array of properties to coding sequences. Yet, its origin is still unclear. A structural analysis has shown that the stability of the Watson–Crick base pair at the second position of the anticodon–codon interaction is a critical parameter controlling the extent of non-specific pairings accepted at the third position by the ribosome, a flexibility at the root of degeneracy. Based on recent cryo-EM analyses, the present work shows that residue A1493 of the decoding center provides a significant contribution to the stability of this base pair, revealing that the ribosome is directly involved in the establishment of degeneracy. Building on existing evolutionary models, we show the evidence that the early appearance of A1493 and A1492 established the basis of degeneracy when an elementary kinetic scheme of translation was prevailing. Logical considerations on the expansion of this kinetic scheme indicate that the acquisition of the peptidyl transferase center was the next major evolutionary step, while the induced-fit mechanism, that enables a sharp selection of the tRNAs, necessarily arose later when G530 was acquired by the decoding center.

With the aim of modeling the vanadium partitioning behavior in iron and steelmaking process, the steelmaking slags model/database was extended for covering the vanadium. In this paper, the binary CaO-VOx, SiO2-VOx and ternary CaO-SiO2-VOx systems were assessed and optimized based upon available phase equilibrium and thermodynamic data. The Generalized Central Atom (GCA) Model was used for describing the liquid slag phase while all intermediate vanadium containing solid phases are treated as stoichiometric compounds. During the optimization, effort was focused on the slag liquidus and its primary solid phases. The obtained model parameters can represent the reliable experimental data reasonably well. The sub-solidus regions at low temperature are not well assessed.

In conventional RNA high-throughput sequencing, modified bases prevent a large fraction of tRNA transcripts to be converted into cDNA libraries. Recent proposals aiming at resolving this issue take advantage of the interference of base modifications with RT enzymes to detect and identify them by establishing signals from aborted cDNA transcripts. Because some modifications, such as methyl groups, do almost not allow RT bypassing, demethylation and highly processive RT enzymes have been used to overcome these obstacles. Working with Escherichia coli as a model system, we show that with a conventional (albeit still engineered) RT enzyme and key optimizations in library preparation, all RT-impairing modifications can be highlighted along the entire tRNA length without demethylation procedure. This is achieved by combining deep-sequencing samples, which allows to establish aborted transcription signal of higher accuracy and reproducibility, with the potential for differentiating tiny differences in the state of modification of all cellular tRNAs. In addition, our protocol provides estimates of the relative tRNA abundance.

In conventional RNA high-throughput sequencing, modified bases prevent a large fraction of tRNA transcripts to be converted into cDNA libraries. Recent proposals aiming at resolving this issue take advantage of the interference of base modifications with RT enzymes to detect and identify them by establishing signals from aborted cDNA transcripts. Because some modifications, such as methyl groups, do almost not allow RT bypassing, demethylation and highly processive RT enzymes have been used to overcome these obstacles. Working with Escherichia coli as a model system, we show that with a conventional (albeit still engineered) RT enzyme and key optimizations in library preparation, all RT-impairing modifications can be highlighted along the entire tRNA length without a demethylation procedure. This is achieved by combining deep-sequencing samples, which allows to establish aborted transcription signal of higher accuracy and reproducibility, with the potential for differentiating tiny differences in the state of modification of all cellular tRNAs. In addition, our protocol provides estimates of the relative tRNA abundance.

International audience; In conventional RNA high-throughput sequencing, modified bases prevent a large fraction of tRNA transcripts to be converted into cDNA libraries. Recent proposals aiming at resolving this issue take advantage of the interference of base modifications with RT enzymes to detect and identify them by establishing signals from aborted cDNA transcripts. Because some modifications, such as methyl groups, do almost not allow RT bypassing, demethylation and highly processive RT enzymes have been used to overcome these obstacles. Working with Escherichia coli as a model system, we show that with a conventional (albeit still engineered) RT enzyme and key optimizations in library preparation, all RT-impairing modifications can be highlighted along the entire tRNA length without demethylation procedure. This is achieved by combining deep-sequencing samples, which allows to establish aborted transcription signal of higher accuracy and reproducibility, with the potential for differentiating tiny differences in the state of modification of all cellular tRNAs. In addition, our protocol provides estimates of the relative tRNA abundance.

International audience; The catalytic site of most enzymes can efficiently handle only one substrate. In contrast, the ribosome is capable of polymerizing at a similar rate at least 20 different kinds of amino acids from aminoacyl-tRNA carriers while using just one catalytic site, the peptidyl-transferase center (PTC). An induced-fit mechanism has been uncovered in the PTC, but a possible connection between this mechanism and the uniform handling of the substrates has not been investigated. We present an analysis of published ribosome structures supporting the hypothesis that the induced-fit eliminates unreactive rotamers predominantly populated for some A-site aminoacyl esters before induction. We show that this hypothesis is fully consistent with the wealth of kinetic data obtained with these substrates. Our analysis reveals that induction constrains the amino acids into a reactive conformation in a side-chain independent manner. It allows us to highlight the rationale of the PTC structural organization, which confers to the ribosome the very unusual ability to handle large as well as small substrates.

Amino acid availability in Gram-positive bacteria is monitored by T-box riboswitches. T-boxes directly bind tRNAs, assess their aminoacylation state, and regulate the transcription or translation of downstream genes to maintain nutritional homeostasis. Here, we report co-crystal and cryo-EM structures of Geobacillus kaustophilus and Bacillus subtilis T-box-tRNA complexes detailing their multivalent, exquisitely selective interactions. The T-box forms a U-shaped molecular vise that clamps the tRNA, captures its 3’-end using an elaborate “discriminator” structure, and interrogates its aminoacylation state using a steric filter fashioned from a wobble base pair. In the absence of aminoacylation, T-boxes clutch tRNAs and form a continuously stacked central spine, permitting transcriptional readthrough or translation initiation. A modelled aminoacyl disrupts tRNA-T-box stacking, severing the central spine and blocking gene expression. Our data establish a universal mechanism of amino acid sensing on tRNAs and gene regulation by T-box riboswitches, and exemplify how higher-order RNA-RNA interactions achieve multivalency and specificity.

The possible mechanism(s) by which ribosomes make peptide bonds during protein synthesis have been explored for decades. Yet, there is no agreement on how the catalytic site, the peptidyl transferase center (PTC), promotes this reaction. Here, we discuss the results of recent investigations of translation with D amino acids that provide fresh insights into that longstanding question.

Proteins assembled by the cell are made up of approximately 20 different kinds of amino acids which are encoded in the genome in accordance with the rules of the genetic code. The structure of each expressed protein, which can count up to several thousand amino acids, is the result of a long evolution during which the composition in amino acids has more or less changed following mutations within the coding sequences and the adaptation of mutants. Thus, the composition in amino acids of a protein reflects the requirements of its specific function. Therefore, we could speculate that no statistical trend should emerge from the analysis of proteomes, which comprise all the proteins of an organism, a genus or even all living beings.

International audience; Nowadays, depending on the steel grade, Ca treatment with the aim of modifying the morphology and melting temperature of non-metallic inclusions is performed in the secondary steelmaking process. The addition of calcium to steel melts rises a technological challenge because at steelmaking temperatures Ca has the tendency to vaporize from the ladle. Efforts are actively pursued in developing solutions that increase Ca yield and improve repeatability of results from treatment to treatment. This work presents a two-phase Euler-Euler flow model of a steel ladle with gas stirring through bottom porous plugs. The model considers that before gas exits through the ladle top, some Ca is transferred from the gas to the liquid steel. The yield is thus defined as the ratio between the Ca transferred to the steel and the total calcium injected into the ladle. The fluid-dynamic calculations are coupled with ArcelorMittal thermodynamic software CEQCSI to get the evolution of the local concentration of dissolved species and non-metallic inclusions assuming local thermodynamic equilibrium. Industrial trials have been performed at one of ArcelorMittal’s facilities with the aim of obtaining data to validate the model. Samples of steel were taken before, during, and after the Ca injection treatment. The total Ca content and the inclusion populations in the steel samples can be compared against the results given by the model, as well as the measured and calculated Ca yield.

In order to diminish the harmful effects of aluminate inclusions and improve the castability of molten steel, calcium treatment is widely used in Aluminum killed steels. However, calcium treatment gives irregular results. Even with many efforts done to understand the behavior of calcium in liquid steel, it is not yet accurately predicted. Therefore, the mechanism by which the calcium dissolves into the liquid steel and transforms the solid inclusions must be understood to optimize the process conditions such as injection speed, injection depth, injection wire diameter, stirring time, etc. In order to understand the mechanism by which the calcium dissolves into the liquid steel, laboratory scale experiments have been performed in a small induction furnace of 2.5 kg metal capacity. The calcium injections are performed at the temperature below and above the boiling point of calcium. Then, the corresponding yields (calcium recovery) are compared. Rise of calcium droplet or bubble in liquid steel is a three-phase problem (calcium droplet or calcium bubble/liquid steel/air at the top). Therefore, an in-house scientific computational platform (ICI-tech) based on finite element methods is adapted to allow the modeling of such three-phase flows, which is validated using the classical benchmark issued from the literature. The dissolution model has been implemented in our software, and their validation has been performed. Thereafter, the rise of Calcium droplets and bubbles are studied in the liquid steel, and their respective average mass transfer coefficient in the liquid steel is reported. In order to study the calcium liquid/gas phase change, the nucleation model has been implemented in the code (ICI-tech). A typical test is performed where the growth of a bubble (water vapor) in uniformly superheated water and growth of a calcium bubble in uniformly superheated Ca liquid is computed.

The published phase diagrams of some key P2O5-containing systems which are relevant to the steelmaking slag and the available experimental data on phosphorus partitioning between liquid iron and slags consisting of SiO2-Al2O3-Fe2O3-FeO-MnO-MgO-CaO-Na2O have been reviewed and assessed. A set of data under carefully controlled experimental conditions, which was considered to be more reliable based on the assessment, was selected for optimising the generalised central atom (GCA) model parameters of phosphorus-containing slag systems. The developed model database is proved to be able to represent the liquidus temperature of some key P2O5-containing systems and the phosphorus distribution ratio between the steelmaking slags and liquid iron reasonably well. With the developed GCA model database, the dephosphorization reaction in the steelmaking process was modelled under various operating conditions such as slag chemistry and temperature. The results show that the phosphorus distribution ratio between the slags and liquid iron displays a maximum point with variation of the FeOx content in the slag. It also shows that the phosphorus deportment to the slag is favored by decreasing the operating temperature and MgO content, and increasing the CaO/SiO2 ratio in the slag. Comparison with the model of the phosphorus distribution data from a commercial BOS furnace shows that operating conditions do not permit to reach P equilibrium contents. The dis-equilibrium degree of P was found to be increased with increasing slag viscosities.

International audience; The structure and function of conserved motifs constituting the apex of Stem I in T-box mRNA leaders are investigated. We point out that this apex shares striking similarities with the L1 stalk (helices 76-78) of the ribosome. A sequence and structure analysis of both elements shows that, similarly to the head of the L1 stalk, the function of the apex of Stem I lies in the docking of tRNA through a stacking interaction with the conserved G19:C56 base pair platform. The inferred structure in the apex of Stem I consists of a module of two T-loops bound together head to tail, a module that is also present in the head of the L1 stalk, but went unnoticed. Supporting the analysis, we show that a highly conserved structure in RNAse P formerly described as the J11/12-J12/11 module, which is precisely known to bind the elbow of tRNA, constitutes a third instance of this T-loop module. A structural analysis explains why six nucleotides constituting the core of this module are highly invariant among all three types of RNA. Our finding that major RNA partners of tRNA bind the elbow with a same RNA structure suggests an explanation for the origin of the tRNA L-shape.

CEQCSI is an ArcelorMittal in-house built thermodynamic equilibrium calculation software which is used both at high temperatures typically for slag-metal reactions but also at “low” temperatures to study solid phase transformations and precipitation in solid steel. It has been built to accommodate different thermodynamic models for slag (the Cell model, the Generalized Central Atom model - product of a collaboration between ArcelorMittal Global R&D Maizieres and CSIRO Melbourne), for steel (sublattice model, Wagner Interaction Parameter Formalism) as well as for oxide, sulfide, carbide… solid solutions. Examples of application concern Si, Mn, S slag-metal equilibrium in Blast-Furnace, P partition in BOF slags, slag-metal equilibrium for flat and long products in ladle… Apart from data relating to mass transfer between different phases at equilibrium, CEQCSI proposes several estimates for slag viscosities with among them one delivered by a new model based on the Generalized Central Atom thermodynamic model for slags. CEQCSI conception allows also handling some kinetic problems such as desulfurization in ladle or slag/metal reaction in mold.

International audience; We examine whether the frequency of amino acids across an organism's proteome is primarily determined by optimization to function or others factors, such as the structure of the genetic code. Considering all available proteins together, we first point out that the frequency of amino acid in a proteome negatively correlates with its mass, suggesting that the genome preserves a fundamental distribution ruled by simple energetics. Given the universality of such distributions, one can use outliers, cysteine and, leucine, to identify amino acids that deviate from this simple rule for functional purposes and examine those functions. We quantify the strength of such selection as the entropic cost outliers pay to defy the mass-frequency relation. Codon degeneracy of an amino acid partially explains the correlation between mass and frequency: light amino acids being typically encoded by highly degenerate codon families, with the exception of arginine. While degeneracy may be a factor in hard wiring the relationship between mass and frequency in proteomes, it does not provide a complete explanation. By examining extremophiles, we are able to show that this law weakens with temperature, likely due to protein stability considerations, thus the environment is essential.

In steelmaking, secondary metallurgy steps are crucial for the quality of the final product. Adjusting the steel-grade composition and deoxidation of the liquid metal generate inclusions that can be harmful to downstream processes and to the product itself (occurrence of defects during rolling process). We present in this paper a numerical model to predict the kinetics of the elimination of inclusions by entrapment by the different phases present in the ladle (slag, bubbles injected in the liquid metal, top layer of gas). We show results for a 3D configuration, and a comparison with industrial data is performed.

Knowledge of the partitioning behavior of sulfur between molten metals and silicates is of interest for understanding processes in the early solar system and in the deep Earth at the mantle/core boundary, but also in technical applications such as the production and purification of steel. Thermodynamic aspects relevant to processes in the Earth and in the early solar system are presented by Baker and Moretti (2011) and Ebel (2011) of this review volume. Here we focus on interactions between molten metals and slags which are the basis for desulfurization of molten metals during steel production. Desulfurization is an important step in the refining of high-quality steels for various applications. The production of liquid steel can be described schematically as follows. Steel can be produced directly from iron ore which is reduced to hot metal in a blast furnace (BF) or by melting scraps in an electric arc furnace (EAF). The hot metal is transformed into steel by oxidizing dissolved carbon in a basic oxygen furnace (BOF). During this process, the phosphorus content is reduced as well. Before the BOF operations, a first desulfurization is performed in the transfer vessel from BF to BOF. After scrap melting or refining in the BOF, steel is “tapped” in a ladle for secondary steelmaking operations, i.e., further decarburization (especially for Ultra-Low Carbon steels), deoxidation (to reduce the oxygen content), alloying (to reach the target composition) and further desulfurization, if needed. In solid steel, sulfur is mainly present as manganese sulfide (MnS) inclusions. MnS inclusions affect the processing and properties of steel. Their volume fraction, size, shape and distribution depend on many factors. The most important factors are the S-content, the solidification rate, the degree of hot and cold deformation and the hot working temperatures. Since the inclusions are more plastic than steel, they act …

The Cell model developed at ArcelorMittal Global R&D Maizieres Process (formerly IRSID) during the 80's was the first comprehensive thermodynamic model for metallurgical slags. A more recent development in this domain, conducted jointly by ArcelorMittal Global R&D Maizieres Process and CSIRO Process Science and Engineering, is the Generalized Central Atom model. This model is a generalization of the Central Atom model proposed in the 1970's by Lupis and co-workers for modelling solid steel, which has now been extended to cover molten oxides and alloys. Recent work has shown how this model could greatly improve the performances of the Cell model for slags and how promising its application to liquid steel is, especially for high alloyed grades or segregated solutions.

This paper gives an overview of the last advances at ArcelorMittal Global R&D Maizieres Process in physical-chemistry modelling applied to steel elaboration. In thermochemistry, progress is expected to come from the development of more precise solution models with higher extrapolability potential. Incentive for this research field is coming from the development of new grades and from the necessity of a better control of the steel composition. The Generalized Central Atom statistical thermodynamic model is an example of development in this domain and is used both to improve and to extend to new components the Cell model for slags as well as to model high alloyed and segregated liquid steels. The driving force for the development of precipitation kinetics models is the necessity to identify actuators able to optimize the precipitates characteristics so as to minimize defects occurrence or to improve in-use properties of the final products. The software MIPPHASOLACIDO dedicated to this research field has been recently improved in terms of computing times by the adoption of a recent mathematical technique: the DQMOM. The very last development consists in a description of interfacial tension of precipitates as function of their composition. It suggests that trace elements entering in precipitates could have a large impact on the precipitates characteristics. The challenge in the development of coupled models associating thermodynamics and fluid dynamics is to have a description taking into account all the phenomena necessary to get a realistic representation of the reactors while keeping computing times under reasonable limits. The example presented corresponds to the very first steps of a modeling of the desulfurization process in a secondary metallurgy ladle.

With an analysis of the structural constraints of the anticodon–codon interaction within the decoding center of the ribosome, we show that the extent of degeneracy at the third position of the anticodon is determined by the level of stability of the base pair at the second position.

Variants of a previously described small self-aminoacylating ribozyme are tested in order to uncover the potentialities of a 3′ extension responsible for the esterification. The base-composition and the length of this specific part of the ribozyme are investigated. Very short extensions can still reach the active site, reflecting the small persistence length of RNA. The yield of aminoacylation is particularly high for ribozymes with extensions made up of a poly-U, for which a maximum of efficiency is observed for a total length of about 10 nucleotides. A simple model describing the behavior of this region of the ribozyme can account for the data.

Theoretical arguments and statistical analyses of present-day coding sequences have long suggested the existence of primitive patterns in RNA sequences, which were thought to have been predominant at the time of the origin of the genetic code. The main propositions were centered around the base-patterns GNC and RNY, where R=A or G, Y=C or U and N=A, G, C or U. A theoretical model of the primitive process of translation explaining the origin of this type of pattern was recently published in the Journal of Theoretical Biology. On the basis of this previous analysis, and on physico-chemical evidence supporting the idea of the GNC base-pattern as the most primitive one, the present paper shows the results of folding simulations of small RNA strands displaying this pattern, which enabled us to specify the characteristics of the suggested primitive form of tRNA. This analysis is notably based on a conjecture of Eigen and Schuster of an early structural (or pattern) similarity between mRNA and tRNA, and, more specifically, of a “joint function of messenger and adaptor”. Working with this conjecture, we show that the convergence of the primitive pool of RNAs toward a system containing a high proportion of sequences displaying the GNC base-pattern (according to the evolutionary model) is accompanied by a significant gain in stability of the translation process. In particular, it is demonstrated how the reading frame would be automatically discriminated without the presence of a start codon.

A RT-PCR method is developed to isolate RNA aminoacylated on their 3’ end from large pools of RNA. The method is being applied in two separate projects. We are interested in isolating a new class of ribozymes that could successively catalyze the two chemical reactions leading to their own 3’ aminoacylation (ATP activation of an amino acid followed by 3' esterification of the RNA). The catalysis of each of the two reactions has independently been demonstrated for some RNA isolated with the SELEX methodology [1-2]. However, the coupling of both reactions on a same molecule has not been achieved yet. The identification of these still hypothetical ribozymes may help understand how the former translation system started in the absence of the aminoacyltRNA Synthetase, which catalyzes the above two reactions on tRNA in modern cells. In another project, we would like to identify the whole repertoire of aminoacylated RNA (the “aminoacylome”) in cells. There are strong indications that other RNA besides tRNA and tmRNA may be aminoacylated for biological purposes [3-4].

CALPHAD method for the calculation of phase diagrams and thermodynamic phase equilibria has been drastically improved over the last 4 decades. In order to accurately describe the complex thermodynamic properties of

International audience; Deoxidation and refining of liquid steel is the site of many complex phenomena, such as liquid–gas–solid multiphase flow, turbulence, precipitation, agglomeration, and extraction of multicomponent inclusions. The steel industry is very interested in developing a framework to integrate these different mechanisms. This is based on three pillars: chemical thermodynamics, population balance, and transport phenomena. Accordingly, a homebrewed thermo-kinetics code is interfaced with a commercial Computer Fluid Dynamic code through a population balance module. The population balance module resorts to the classic Quadrature Method of Moments extended to multicomponent inclusions. This paper is focused on a comparison between three-dimensional numerical results obtained with or without taking into account precipitation kinetics. This distinction is important since under an assumption of local equilibrium, harmful inclusions are completely dissolved before the continuous casting occurs, whereas when using precipitation kinetics, harmful inclusions can be present in the final product. This is consistent with industrial samples.

The computational thermodynamic databases have been applied to various pyrometallurgy processes to understand the complex chemical reaction and improve the process. In this chapter, the ferrous and nonferrous examples are presented.

In this chapter, the reader will find details about the formalisms of the most utilized Gibbs energy models used in thermodynamic computer models. The emphasis is put on models used in iron- and steelmaking areas. The previous chapter is devoted to the presentation of the main features of the thermodynamic computer packages.

A bibliographical review of the most recent developments in slag modelling approaches is presented. It covers the period posterior to the publication in the 2 nd edition of Slag Atlas of the comprehensive review by Kowalski, Spencer and Neuschutz of thermodynamic models and databases for calculation of phase diagrams and thermodynamic properties of slags. The trends in using this information in computational thermodynamics software/database packages are outlined. Industrial applications based on examples pertaining to various iron-and steelmaking reactors are discussed. These applications made essentially with the Irsid slag model and the CEQCSI software concern steel refining or microalloying by slag-metal reactions in the ladle, steel-refractories interactions, and inclusions control in steels.

A numerical simulation which describes precipitation of non-metallic inclusions (liquid or solid oxides, nitrides) during steel solidification is proposed. Its aim is to predict the compositions and size distributions of these precipitates. The model takes into account microsegregation and includes homogeneous nucleation in the interdendritic liquid, and a mixed-controlled growth stage combining transport of solute elements in the boundary layer around precipitates and interfacial kinetics. We have observed that the calculated compositions of oxide inclusions differ from those of inclusions precipitating at equilibrium and are close to industrial observations on semi-killed steels.

The precipitation of non-metallic inclusions in Ti-deoxidised steels is analysed with the multiphase equilibrium code CEQCSI which is based on the IRSID slag model. For that purpose, the slag model has been extended to systems containing titanium oxides, using data available in the literature, and validated with industrial results obtained on various steel grades. Applications concerning slag-metal reactions in ladle metallurgy are described. 2 applications concerning inclusions in Ti-deoxidised steels are also presented: (a) experimental study of the effect of steel contamination by magnesia refractory lining on the composition of oxide inclusions in a Ti-deoxidised steel: there is a good correlation between analysed oxide compositions and compositions predicted by the model; (b) evaluation of the optimised steel composition to obtain Al 2 O 3 -TiO 2 inclusions during solidification for steels pertaining to the so-called metallurgy of oxides in steels.

New insights on the origin of the genetic code, based on the analysis of the physico-chemical properties of its molecular constituents (RNA and amino acids), are reported in this paper. We point out a symmetry in the genetic code table and show that it can be explained by the nature of the anticodon-codon interaction. The importance of the strength of this interaction is examined and a correlation is found between the free-energy change (DeltaG(0)) of anticodon-codon association and the volume of the corresponding amino acids. This correlation is investigated in conjunction with the well-known one linking the hydrophobicity of the anticodons with that of the amino acids. We show that they can be considerated separately and that the energy vs. volume correlation may be explained by the process implicating the peptide bond formation between two successive amino acids during translation. This interpretation is supported by a statistical pattern of bases (purines or pyrimidines), observed in present coding genes, and by considerations involving the availability of the different kinds of amino acids. Finally, we try to explain the hydrophobicity correlation when reconstructing the events at the time of the so-called "RNA World". The whole of our investigation shows that the genetic code might be sufficiently robust to exist without the participation of pre-existing proteins, and that this robustness is a consequence of the physico-chemical properties of the four bases of the genetic system.

The precipitation of non-metallic inclusions (complex oxides, sulphides, nitrides ...) during steel solidification is analysed using the multiphase equilibrium code CEQCS and a nucleation and growth model. The CEQCSI code is based in part on the Irsid slag model, and it provides an evaluation of the composition of inclusions formed at equilibrium, as well as guidelines for industrial treatments in order to reach desirable compositions in semi-killed steel grades. The nucleation and growth model can be applied to the formation, during steel solidification, of stoichiometric compounds or liquid oxide inclusions. Two particularities of this kinetic model are that nucleation and growth are treated simultaneously, and they compete in consuming the supersaturation at each moment, and that a mixed controlled growth model transport/interfacial kinetics at the precipitate/liquid steel interface is considered. The predicted size distribution of TiN precipitates formed in two steel grades is in good agreement with the results of laboratory experiments. In the case of liquid oxide precipitation, the lirst calculations indicate that the composition of inclusions can be significantly different from that of inclusions assumed to precipitate under equilibrium conditions.

A numerical simulation which describes precipitation of non-metallic inclusions during steel solidification is proposed. The model includes nucleation laws in the homogeneous phase, growth controlled by diffusion of solute elements and kinetics of interfacial reaction, as well as microsegregation. The calculated results, i.e., the total amount, size and number of inclusions, were compared to experimental observations obtained in the laboratory on TiN precipitation by quenching during unidirectional solidification. Sulphur content of the steel was observed to influence the kinetics of precipitation.

Considering the three codonic positions as independent, it is possible to explain the grouping of the 64 trinucleotides (without AAA , TTT , CCC and GGG ) into three equal sets T 0 , T 1 and T 2 according to their preferable reading frame (0, 1 or 2) in coding sequences. Supposing that the two complementarity strands of DNA are coding, it is demonstrated that the complementary of a codon is classified in to the same set, which has been observed statistically (with a few exceptions) in the coding sequences by Arques & Michel [(1996) J. theor. Biol. 182, 45–58] and Arques et al . [(1997) J. theor. Biol. 185, 241–253]. Finally, the circular property of the code pointed out by these authors is demonstrated, and a direct consequence to biological considerations of these properties is discussed.

An original model for the calculation of the precipitation of non-metallic inclusions during solidification has been developed at IRSID. The microsegregation equations and the equilibrium conditions between liquid steel and oxide, sulphide, nitride, carbide inclusions are combined in a general multiphase equilibrium code.Sulphide precipitation in several steel grades: plate grades, medium carbon and bearing steels has been analyzed in laboratory samples quenched from a partially solidified state. For the various steel grades investigated, the computed results of sulphides (Mn, Fe)S or (Mn, Fe, Cr)S compositions are in good agreement with the results of the experimental study.Another example concerns the precipitaion of oxide inclusions in semi-killed high-carbon steels: The calculation represents very precisely the observed heterogeneous population of oxide inclusions formed at different stages of the industrial process.

Adequate physical and mechanical properties, for numerous steel grades, can be obtained only with a precise control of the composition, morphology and plasticity of oxide and sulphide inclusions that remain in the product. In liquid metal, the composition of complex inclusions can be monitored by appropriate deoxidation practice, calcium treatment and/or slag-metal reaction. Further transformation may occur during solidification or heat treatments prior to hot-rolling: reaction between oxides and sulphides, as well as crystallization of oxides. An analysis of these factors, and of tools (thermodynamic models and laboratory experiments) which have been developed to comprehend and control them is presented

The topic of this paper is the study of inclusion properties and behaviour inside a ladle containing liquid steel. A new numerical tool tracks the size and the composition of inclusions during the oxygen removal and the steel refining. Commercial CFD codes (Fluent™), home-made thermo-kinetics code and population balance model have been associated to follow oxide precipitates. The long-term scientific goal of this study consists in proposing actuators to prevent or to eliminate harmful inclusions based on results predicted by the numerical model.

A variant of the quadrature method of moments (QMOM) for solving multiple population balance equations (PBE) is developed with the objective of application to steel industry processing. During the process of oxygen removal in a steel ladle, a large panel of oxide inclusions may be observed depending on the type of oxygen removal and addition elements. The final quality of the steel can be improved by accurate numerical simulation of the multi-component precipitation. The model proposed in this article takes into account the interactions between three major aspects of steelmaking modeling, namely fluid dynamics, thermo-kinetics and population balance. A commercial CFD code is used to predict the liquid steel hydrodynamics, whereas a home-made thermo-kinetic code adjusts chemical composition with nucleation and diffusion growth, and finally a set of PBE tracks the evolution of inclusion size with emphasis on particle aggregation. Each PBE is solved by QMOM, the first PBE/QMOM system describing the clusters and each remaining PBE/QMOM system being dedicated to the elementary particles of each inclusion species. It is shown how this coupled model can be used to investigate the cluster size and composition of a particular grade of steel (i.e., Fe-Al-Ti-O). © 2010 American Institute of Chemical Engineers AIChE J, 2010

The origin of the genetic code in the context of an RNA world is a major problem in the field of biophysical chemistry. In this paper, we describe how the polymerization of amino acids along RNA templates can be affected by the properties of both molecules. Considering a system without enzymes, in which the tRNAs (the translation adaptors) are not loaded selectively with amino acids, we show that an elementary translation governed by a Michaelis-Menten type of kinetics can follow different polymerization regimes: random polymerization, homopolymerization and coded polymerization. The regime under which the system is running is set by the relative concentrations of the amino acids and the kinetic constants involved. We point out that the coding regime can naturally occur under prebiotic conditions. It generates partially coded proteins through a mechanism which is remarkably robust against non-specific interactions (mismatches) between the adaptors and the RNA template. Features of the genetic code support the existence of this early translation system.

Publisher Summary This chapter discusses the inclusion cleanness in calcium-treated steel grades. The aim of calcium treatment performed during secondary metallurgy operations on aluminum-killed steels is to avoid nozzle clogging problems. The success of such a treatment can be evaluated from the ratio of the calcium content to the total oxygen content of the grade. To ensure good castability, the Ca content must be high enough to assure complete transformation of solid alumina oxides into completely liquid calcium aluminates, but low enough to avoid precipitation of calcium sulfides at high temperature. The upper limit depends on the sulfur content of the steel grade. It has been shown that the type and, more specifically, the size of the samples taken in the tundish to qualify the Ca treatment are important. Oxide inclusion composition might evolve during cooling by reaction with elements that remain dissolved in the steel or with other precipitated phases such as sulfides. This evolution depends on the cooling rate and the cooling rate is in turn directly linked to the size of the sample.

The synthesis of bis(organostannyl)ethanes of the types (Ph 2 XSnCH 2 ) 2 ( 1 , X = Ph; 2 , X = Cl; 3 , X = Br; 4 , X = I) and (Ph 2 XSnCH 2 ) 2 ( 5 , X = Br, 6 , X = I) is described. The compounds have been investigated by means of 1 H, 13 C and 119 Sn NMR spectroscopy. 2 reacts with HMPA, [Ph 3 P = N = PPh 3 ] + Cl − , and Ph 4 PBr, respectively, to give the 1/1 complexes (Ph 2 ClSnCH 2 ) 2 · HMPA ( 7 ), [Ph 2 ClSnCH 2 ) 2 · Cl] − [Ph 3 PNPPh 3 ] + ( 8 ), and [(Ph 2 ClSnCH 2 ) 2 · Br] − [Ph 4 P] + ( 9 ). The formation constant K a for 8 in CDCl 3 solution is 2260 M −1 . The structures of 7 and 8 have been determined by X-ray diffraction. That of 7 shows that the two tin atoms are pentacoordinate but are inequivalent as a result of having different coordination sphere; one tin atom is coordinated by the monodentate HMPA (SnO 2.255(3) A) whereas the other interacts with a bridging Cl (Sn(1); Cl(2) 3.000(1) A). In the anion of 8 , the bis(chlorodiphenylstannyl)ethane may be regarded as an unsymmetrical chelate ligand towards Cl(12) (Sn(1)-Cl(12) 2.83(1), Sn(2)-Cl(12) 2.70(1) A).