TiC System Research Articles

Origins, function, and regulation of the TOC-TIC general protein import machinery of plastids.

The evolution of chloroplasts from the original endosymbiont involved the transfer of thousands of genes from the ancestral bacterial genome to the host nucleus, thereby combining the two genetic systems to facilitate coordination of gene expression and achieve integration of host and organelle functions. A key element of successful endosymbiosis was the evolution of a unique protein import system to selectively and efficiently target nuclear-encoded proteins to their site of function within the chloroplast after synthesis in the cytoplasm. The chloroplast TOC-TIC (translocon at the outer chloroplast envelope-translocon at the inner chloroplast envelope) general protein import system is conserved across the plant kingdom, and is a system of hybrid origin, with core membrane transport components adapted from bacterial protein targeting systems, and additional components adapted from host genes to confer the specificity and directionality of import. In vascular plants, the TOC-TIC system has diversified to mediate the import of specific, functionally related classes of plastid proteins. This functional diversification occurred as the plastid family expanded to fulfill cell- and tissue-specific functions in terrestrial plants. In addition, there is growing evidence that direct regulation of TOC-TIC activities plays an essential role in the dynamic remodeling of the organelle proteome that is required to coordinate plastid biogenesis with developmental and physiological events.

Investigation into the Influence of the Structure Dispersion and Homogeneity on the Properties of Powder Metastable Austenitic Carbide Steels and Diamond Tools

Diffusion and homogenization in “iron (5 μm–nickel (5 μm or 50 nm)” powder systems of various degrees of dispersion during sintering (900 and 1000°C), as well as spark plasma sintering, are investigated using the Matano–Boltzmann method. Calculated diffusivities in pairs of micron powders sintering without applying pressure (900°C, 6 h) and by the spark plasma method (900°C, 5 min) in these systems are equal to 7 × 10–10 cm2/s. It is shown that the use of nanodispersed nickel powder in diffusion pairs based on finely dispersed iron powder promotes a twofold increase in diffusivity at 900°C in contrast to the pair with the microdispersed nickel powder. Constants in the Ivensen sintering kinetics equation are calculated for the “iron–nickel” powder systems, by which the factors activating sintering of these systems are established. The dependences of the structural phase composition and physicomechanical properties of carbide steels of the Fe(base)–14 wt % Ni–8 wt % TiC system on the sintering temperature in range t = 900–1200°C and structure dispersity and homogeneity are determined. The dependences of the grain size, porosity, hardness, microhardness, fracture toughness, and bending ultimate strength on the sintering temperature are shown. Dependences of tribotechnical properties on the degree of homogeneity of the solid solution and volume of the phase transformation of metastable austenite into deformation martensite during abrasive friction turn out similar for carbide steels and diamond tools based on carbide steel. Optimal values of the variation coefficient of the nickel concentration in austenite and carbide steels of the same chemical composition but with different degrees of dispersity, which provide the maximal volume of the austenite decomposition and high values of the diamond-tool grinding coefficient, turn out equal to 5 in both systems, but the sintering parameters are different. It is shown that the physicomechanical properties of the studied systems depend on the structure porosity and dispersity, while tribotechnical properties depend on the structural homogeneity of steels.

Distribution of Tourette's verbal tics produced during active speech

Tourette syndrome causes individuals to produce unwanted movements and vocalizations called tics. Verbal tics are those tics that closely mimic words/phrases—their execution requires the same set of articulators needed to produce speech. Tics respond to a preceding urge to tic and are akin to other urge-based actions like cough. Urges to tic can arise at any time but speech and tics must be deployed sequentially as they cannot be produced simultaneously. How are conflicts between the speech and tic motor systems resolved? This study tests the prediction that tics interfere with production of words and intonational phrases less frequently than expected by chance. As predicted, pilot data from one subject showed that the expected probability of words and tics co-occurring were these events independent was significantly higher than the observed likelihood of tics interrupting words. Correspondingly, the likelihood of intonational phrase-final boundaries co-occurring with tics if these events were independent was significantly lower than the observed probability of tics given intonational phrase-final boundaries. Data from multiple people with Tourette’s will be presented. Results suggest that utterances are “protected” from tic interruptions, providing evidence that the tic and speech motor systems are linked in production. [Work supported by NIH and NSF.]

Strengthening and toughening of laminated TiAl composite sheets by titanium alloy layers and carbide particles

AbstractLaminated sheets with Ti2AlC/TiAl composite layers synthesized from the Ti–Al–TiC system and TC4 titanium alloy as the toughening layer were fabricated by spark plasma sintering. Their phase composition and microstructure were analyzed and flexural strength and fracture toughness measured. The composite layers mainly comprised Ti2AlC, TiC, TiAl, and Ti3Al phases. The flexural strength and fracture toughness of the sheets perpendicular to the laminated direction were 455.74 MPa and 21.65 MPa · m1/2, respectively. The TC4 layers provided a strengthening–toughening effect by changing the crack propagation model and weakening the fracture energy. Ti2AlC particles provided a strengthening effect. The synergistic effect of the two components enhanced the mechanical properties of these TiAl-based laminated composite sheets.

The in-situ synthesis of TiC in Cu melts based on Ti–C–Si system and its mechanism

Introduction of carbon into metal melts, especially those with limited carbon solubility, for composites preparation by casting method is very difficult due to the poor wettability between carbon and melts. In this work, carbon in various forms has been effectively introduced into Cu melts and TiC has been in-situ synthesized based on Ti–C–Si system, and its mechanism has been investigated. It is found that, after the addition of TiC mixture into Cu melts, carbon can be wetted by Cu through TiC reaction. However, because of the TiC interconnected network formation, the mixture tends to become the block which cannot be dispersed into the melts. Using Ti–C–Si instead of TiC system is an effective way to wet carbon and in-situ synthesize TiC while prevent the formation of TiC network. It is considered that Si changes the reaction pathway of the system. The Ti5Si3 which is prior to be formed in Ti–C–Si system can prevent the following formed TiC from interconnecting and its subsequently dissolution due to TiC formation can further help the products to distribute more uniformly in Cu melts.

Study of the effect of dispersion and homogeneity of the structure on the properties of powder metastable austenitic carbide steels and diamond tools

Diffusion and homogenization in powder systems of varying degrees of dispersion «iron (5 μm) – nickel (5 μm or 50 nm)» during sintering (900 and 1000 °C), as well as spark plasma sintering using the Matano-Boltzmann method were studied. In these systems, the calculated diffusion coefficients in pairs of micron powders, sintered without application of pressure (900 °C, 6 h) and the spark plasma method (900 °C, 5 min), were equal to 7·10–10 cm2/s. It is shown that in diffusion pairs based on microdispersed iron powder, the use of nanodispersed nickel powder instead of microdispersed one contributes to an increase in the diffusion coefficient at a temperature of 900 °C by a factor of 2. The constants in the sintering kinetics equation of V.A. Ivensen are calculated for iron–nickel powder systems. Through them the factors activating the sintering of these systems were established. The dependences of the structure-phase composition and physicomechanical properties of carbides of the Fe (base) system — 14 wt.% Ni – 8 wt.% TiC system on the sintering temperature in the interval t = 900÷1200 °C, dispersion and homogeneity of the structure were determined. The dependences of grain size, porosity, hardness, microhardness, toughness, bending strength on sintering temperature are shown. The established dependences of the tribotechnical properties on the degree of homogeneity of the solid solution and the volume of the phase transformation of the metastable austenite to deformation martensite during friction on the abrasive were similar for carbide steels and diamond tools based on carbide steels. The optimal values of the coefficient of variation of nickel concentration in austenite in carbidostils of the same chemical composition, but different dispersion, providing the maximum amount of austenite decomposition and high values of the diamond tool grinding coefficient were 5 in both systems, but the sintering parameters differed. It is shown that the physicomechanical properties of the studied systems depend on the porosity and dispersion of the structure, and the tribotechnical properties are subjected to the homogeneity of the structure of the steel.

Oxidation behavior of in situ synthesized (TiB + TiC)/Ti–6Al–4V composites from Ti–B4C–C and Ti–TiB2–TiC systems

Abstract

Automated Sensitivity Computations for Bayesian Markov Chain Monte Carlo Inference: A New Approach for Prior Robustness and Convergence Analysis

Infinitesimal perturbation analysis is a widely used approach to assess the input sensitivities of stochas- tic dynamic systems in the classical simulation context. In this paper, we introduce an efficient nu- merical approach to undertake Infinitesimal perturbation analysis in the context of dependent Markov Chain Monte Carlo simulations widely used in Bayesian inference. Building on recent developments, we develop a scheme based on automatic differentiation to compute posterior sensitivities based on exact (up to computer floating point error) first-order derivatives of draws (Jacobians) with respect to prior input parameters alongside the estimation algorithm. Assessing such local robustness of posterior inference poses a challenge for existing methods such as finite differencing, symbolic differentiation, and likelihood ratio methods due to the complex stochastic dependence structure and computational intensity of dependent sample draws. The proposed methods allow for a comprehensive and exact local sensitivity analysis of Markov Chain Monte Carlo output with respect to all input parameters, i.e., prior hyper-parameters (prior robustness) and chain starting values (convergence). Our imple- mentation focuses on methods for Gibbs-based algorithms widely used for inference and forecasting in complex high-dimensional settings. We illustrate how the methods can help practitioners assess convergence and prior robustness in an application of Bayesian Vector Autoregression with shrinkage priors for US macroeconomic time series data and forecasting.

Review of phase stability in the group IVB and VB transition‐metal carbides

AbstractThis review summarizes the phase stability in the group IVB (Ti‐C; Zr‐C; Hf‐C) and group VB (V‐C; Nb‐C; Ta‐C) transition‐metal carbides. The order parameter functional (OPF) method and density functional theory (DFT) method have been used to predict phase equilibria in these systems. Extensive experimental investigations have attempted to determine both phase stability as a function of composition as well the crystal structures present using X‐ray diffraction, neutron diffraction, electron backscatter detection, and selected area electron diffraction. These investigations have demonstrated that the structures that form are based on the close‐packing of the metal atoms and the arrangement of the carbon atoms in the octahedral interstices. In general, the rocksalt B1 phase is stable for all of the transition‐metal carbides, with their substoichiometry tolerance increasing with temperature; vanadium carbide is the exception due to its negative vacancy formation energy. Vacancy‐ordered M6C5 phases have been predicted and experimentally confirmed in both groups of carbides; however, kinetic limitations often inhibit the formation of vacancy‐ordered phases, which has contributed to controversy in phase identification. The vacancy‐ordered M4C3 phase has been predicted for select carbides and has only been observed in zirconium carbide. In contrast, the stacking fault phase ζ‐M4C3−x has been readily reported in the group VB carbides (but not in the group IVB carbides). The vacancy‐ordered M3C2 has been predicted by DFT for the group IVB carbides but not in the group VB carbides, whereas OPF predicts its stability in both carbides. Vacancy‐ordered M3C2 phases have been experimentally observed in the Ti‐C and Hf‐C systems. Finally, the M2C phase has been predicted in both group carbides, except for hafnium carbide, with an order‐disorder transition with temperature. These factors result in phase diagrams that are similar among all the carbides, but each phase diagram is unique due to subtle differences in bonding that result in slight differences in thermodynamically stable phases.

A first-principles investigation on mechanical and metallic properties of titanium carbides under pressure

The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0GPa, 30GPa and 50GPa. A phase diagram of the Ti-C system at 0K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system.

Optical methods to quantify amorphous carbon in carbide-based nanocomposite coatings

We report how the total carbon content and the amorphous carbon (a-C) phase fraction in transition metal carbide/a-C nanocomposite coatings can be obtained using optical methods, which are much more practical for industrial use than conventional X-ray photoelectron spectroscopy. A large set of carbon-containing nanocomposite coatings deposited using different magnetron sputtering techniques were analyzed by X-ray photoelectron spectroscopy, reflectance spectrophotometry, and spectroscopic ellipsometry. The chemical composition and the a-C phase fraction were determined by X-ray photoelectron spectroscopy for each coating and results are presented for the TiC, CrC, and NbC systems. The composition and the a-C phase fraction are correlated to optical reflectance in the visible range, by parametrization in L*a*b* color space, and by ellipsometry primary data. Results show that it is possible to rapidly estimate the composition and the a-C fraction using these optical methods. We propose that optical methods have promising use in the industry as a cost-efficient technique for characterization of carbide-based coatings.

Microstructure and wear resistance of in-situ TiC surface composite coating on copper matrix synthesized by SHS and Vacuum-Expendable Pattern Casting

An in-situ TiC surface composite coating was synthesized upon a copper matrix, using Self-Propagating High-temperature Synthesis (SHS) and Vacuum-Expendable Pattern Casting (V-EPC). Ti, C and Cu, as raw powders, were mixed at various ratios and pasted on the surface of an Expandable Polystyrene (EPS) pattern after compacted. They were placed into the silica sands after being brushed fireproof coating and then casting copper under vacuum condition. The in-situ TiC surface composite coating was synthesized with cast-cooper simultaneously when cooled down. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscope (TEM) equipped with energy dispersive X-Ray spectroscopy (EDX), scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and Raman spectroscopy are used for investigating the phase constituents and microstructure of coatings and wear property. The hardness of coatings were obtained. The wear behavior of the coating was assessed by using a pin-on-disc tribometer under various loads. Appropriate amount of Cu can enhance the SHS reaction of Ti-C system. The wear resistance of coating with 5wt% Cu added is relatively better than that of other specimens.

Heat transfer and diffusion-controlled kinetics of liquid–solid phase in titanium matrix composite during selective laser melting

This study describes a self-consistent theoretical model of simulating diffusion-controlled kinetics on the liquid–solid phase boundary during high-speed solidification in the melt pool after the selective laser melting (SLM) process for titanium matrix composite based on Ti–TiC system. The model includes the heat transfer equation to estimate the temperature distribution in the melt pool and during crystallization process for some deposited layers. The temperature field is used in a micro region next to solid–liquid boundary, where solute micro segregation and dendrite growth are calculated by special approach based on transient liquid phase bonding. The effect of the SLM process parameters (laser power, scanning velocity, layer thickness and substrate size) on the microstructure solidification is being discussed.

Bonding-restricted structure search for novel 2D materials with dispersed C2 dimers.

Currently, the available algorithms for unbiased structure searches are primarily atom-based, where atoms are manipulated as the elementary units, and energy is used as the target function without any restrictions on the bonding of atoms. In fact, in many cases such as nanostructure-assembled materials, the structural units are nanoclusters. We report a study of a bonding-restricted structure search method based on the particle swarm optimization (PSO) for finding the stable structures of two-dimensional (2D) materials containing dispersed C2 dimers rather than individual C atoms. The C2 dimer can be considered as a prototype of nanoclusters. Taking Si-C, B-C and Ti-C systems as test cases, our method combined with density functional theory and phonon calculations uncover new ground state geometrical structures for SiC2, Si2C2, BC2, B2C2, TiC2, and Ti2C2 sheets and their low-lying energy allotropes, as well as their electronic structures. Equally important, this method can be applied to other complex systems even containing f elements and other molecular dimers such as S2, N2, B2 and Si2, where the complex orbital orientations require extensive search for finding the optimal orientations to maximize the bonding with the dimers, predicting new 2D materials beyond MXenes (a family of transition metal carbides or nitrides) and dichalcogenide monolayers.

REACTION KINETICS SELF-PROPOGATION REGIME DURING PRE-IGNITION PERIOD

Self-propagation high temperature synthesis (SHS) technological regulations application is mainly limited by transformation processes taking place in the pre-ignition period. Zn-S, Zn-Se, Ti-C and 3Ni-Al small sample systems ignition experimental study was carried out under heating conditions in inert atmosphere with temperature values T = 1200K.It was shown that at this temperature level a chemical reaction can be initiated, turning into a self-sustaining mode. Wherein the reaction limiting factors can be mass transfer processes. Ignition temperatures were determined and plotted via the samples size. A physical ignition model was developed assuming the pre-ignition period limiting reaction Arrhenius law.The inverse combustion problem solution made it possible to calculate the low-temperature (T = 800 ÷ 1200K) reaction kinetic constant values. Comparison thus obtained values with the known data of other researchers showed their good agreement.Activation energy values for the Zn-S system were used to calculate the heat wave propagation speed. This value appeared to coincide with experimental values.Obtained results analysis leads to the conclusion about the availability and justification for the proposed method of express-analysis of presupposed, but previously not studied SHS systems. The results thus obtained allow us to estimate conditions for the SHS technology implementation, the reactor characteristic sizes and the thermal wave’s propagation speed.

Critical Evaluation and Thermodynamic Optimization of the Ti-C-O System and Its Applications to Carbothermic TiO2 Reduction Process

Based on the critical evaluation of available phase diagram, thermodynamic, and crystal structure data, the ternary Ti-C-O system is thermodynamically assessed using the Calculation of Phase Diagram method. Both binary Ti-C and Ti-O systems are reassessed to obtain the successful description of ternary Ti-C-O system for the first time. The liquid phase is described by the modified quasichemical model, which takes short-range ordering in liquid solution into account. All solid solutions are described using compound energy formalism. In particular, a completed solid solution between TiC x and TiO y with the excess solubilities of Ti, C, and O is accurately described with the (Ti, Va)1(C, O, Va)1 solution structure. The thermodynamic models with a set of optimized self-consistent model parameters can reproduce available reliable experimental data within experimental error limits. The results are also applied to the thermodynamic analysis of complex carbothermic TiO2 reduction process.

Problem of the expansion of judicial control at the pre-trial stage of criminal proceedings

Abstract: In the article analyzed possibility of expansion of judicial control within the framework of criminal trial. Proceeding possibility of introduction of new position is examined within the framework of the court. Keywords: judicial control, expansion of judicial control, criminal trial, department judicial, pre-trial production, judicial reform, functions of justice, legality, court, criminal procedure, inquisitional judge, law and order, criminal case, justice, Law, office of public prosecutor, Supreme court, plenary powers of court, Constitution, rights and freedoms, complaint, reform, state, investigation, investigation, crime, citizen, investigator, organs of inquest. At its substantive purpose judiciary is a specific form of state activities in their respective spheres of society. The need of the state in the judiciary is defined as the necessity to re-solve recurrent disputes and the necessity to protect the con-stitutional order, rights and freedoms, the legitimate interests of man and of civil society.The Constitution of the Republic of Kazakhstan as a key priority determines the rights, freedom and legitimate interests of man and citizen, thus perpetuating the importance of judicial protection, one of the mechanisms which is judicial control.As a general rule the essence of judicial control is to ver-ify compliance with the objectives of monitoring results: the courts verify that the activities of state bodies and their of-ficials and the laws of their tasks; record deviations from the goals and ways to achieve them; take measures to prevent and bring to responsibility the guilty persons.Judicial control is primarily aimed at improving the ef-ficiency of criminal investigations, as well as raising the level of citizens’ rights protection in criminal procedures, which provide optimal conditions for the investigator to perform the main functions, consisting in the prevention and investigation of crimes.It is believed that the expansion of judicial control at the pre-trial stage of the criminal process in the proposed form would serve a greater enforcement of constitutional rights guar -anteed by the investigating authorities, which generally serve to strengthen the rule of law in the Republic of Kazakhstan [1].The current Criminally-Remedial Law of the Republic of Kazakhstan in art. 139 CPC RK has determined that a preven-tive measure is elected to prevent the possibility to the accused person to escape from the inquiry, preliminary investigation or trial, to prevent the objective investigation and trial pro-ceedings, to continue to engage in criminal activities and, to ensure its execution after sentencing. The list of mentioned circumstances in the theory either called “misconduct” or pur -pose, which is achieved by the institute of preventive measures.In accordance with Art. 140 CPC RK, the Preventive mea -sures are the following: recognizance not to leave and proper conduct; personal surety; placing a serviceman under the supervision of the commander of a military unit; the return of the minor under the supervision; pledge; house arrest; deten-tion [2]. Before turning to the issue of arrest sanctioning, it is necessary to find out what the arrest is a preventive measure.Detention is the strictest kind of procedural measures of restraint. Preventive measures are a form of coercive measures that apply to a person involved in the commission of a crime, in order to ensure his presence in the criminal process. Preven-tive measure is to limit the personal freedom of the accused approved by the prosecutor or the court decision by placing it in the pre-trial detention in the course of criminal proceedings Detention as a preventive measure — it is not a criminal of-fense the accused (alleged criminal). In this case it does not have punitive value and it has only preventive tone, it applies not to the guilty but to the accused (in exceptional cases — to the alleged). Detention creates optimal conditions for the participation of the accused in criminal proceedings, to sup-press his opposing to the normal course of an investigation or proceedings before a court, in order to prevent the defendant attempts to hide from the inquiry, investigation, trial, to prevent the establishment of truth on criminal case, re-engage in crimi -nal activity, as well as to ensure the execution of the sentence.The principal direction of the current criminal procedural legislation is to further the implementation of the criminal jus -tice system of additional procedural means and mechanisms to ensure the rights, freedom and interests of the individual. A number of theorists and practitioners believe that one of these mechanisms could serve as a further extension of judi-cial control over the pre-trial activity. However, the expansion

Low Temperature Combustion Synthesis of TiC Powder Induced by PTFE

TiC powders were prepared at low temperature from the Ti-C system with polytetrafluoroethylene (PTFE) as a chemical activator. The reaction temperature, phase composition and morphology were determined via differential scanning calorimetry (DSC), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) to explore the reaction mechanism, respectively. The FESEM result shows that TiC powders with average particle size less than 100 nm are synthesized via low-temperature combustion synthesis at 530 °C by adding 3wt% PTFE into Ti-C system. Based on the most intensive diffraction peak (200) of the XRD pattern, the crystallite size of prepared TiC powders is calculated to be about 81 nm by the Scherrer formula, which is close to the average particle size observed from the FESEM image. It indicates that TiC particles consist of a single crystal as the result of fast, low-temperature, solid-state synthesis process. According to DSC results, the combustion synthesis mainly includes two reaction processes. Firstly, the initial reaction between titanium and PTFE particles releases a great amount of heat, and subsequently, the heat induced combustion reaction between titanium and carbon particles.

Reply to the ‘Comment on “Stable phase domains of the TiO2–Ti3O5–Ti2O3–TiO–Ti(CxOy)–TiC system examined experimentally and via first principles calculations”’ by P. Pistorius and F. Fatollahi-Fard, J. Mater. Chem. A, 2015, 3, DOI: 10.1039/c4ta04469j

This article contains a reply to the comment by Pistorius and Fatollahi-Fard.

Interfacial Phenomena in Fe/Stainless Steel–TiC Systems and the Effect of Mo

AbstractTitanium carbide is used as reinforcement particles in composites due to its hardness, wear resistance and stability. This work is a part of the study in which titanium carbides are formed in stainless steel castings in the mold to improve the wear resistance of a certain surface of the casting. Such local reinforcement is a very potential method but it is a quite demanding task requiring profound knowledge of interfacial phenomena in the system, wettability, stability, dissolution and precipitation of new phases in production of these materials. Good wetting between different constituents in the material is a key factor to attain maximal positive effects. Mo is used with TiC or Ti(C,N) reinforcement in composites to improve wettability. In this work the effect of Mo on the phenomena in Fe/stainless steel–TiC systems was examined by wetting experiments between the substrate and the alloy. Wetting was not significantly improved by adding Mo to the systems. Core-rim type carbides as well as more homogenous carbide particles were observed. Overall the carbide particles are very complex regarding to their chemistry, size and shape which aspects have to be taken into account in the development of these materials and manufacturing processes.