Thermodynamic Equilibrium Temperature Research Articles

Plasma screening effect in warm solid-density iron plasma

We study a plasma screening effect in a warm solid-density iron plasma. All the calculations are done using the average atom model in the muffin-tin approximation using the density functional theory in local density approximation at finite temperature in local thermodynamic equilibrium. Between temperatures equal to 15 and 20 eV, the system undergoes a huge change due to the 3d orbital becoming bound. In clear, four electrons become bound. Various average ionizations are defined to see this effect. At temperature equal to 20 eV, all the average ionizations agree to predict a Fermi energy and a plasma frequency that are close to the temperature of the medium. The density of states show a prominent resonance due to d orbital just below temperature equal to 15 eV. We show that the spectral opacity is drastically modified near the L shell threshold due to the appearance of a 2p→3d absorption line.

A Physical Basis for Kinetic Compensation.

Kinetic compensation is a strong, positive correlation between the Arrhenius activation energy E and the frequency factor A for a reaction between the same reactants under similar experimental conditions or similar reactants under the same conditions, even though these parameters are supposed to be independent. The kinetic compensation effect (KCE) is demonstrated by a linear relationship between ln[A] and E/R in the eponymous Constable plot and has been the subject of more than 50 000 publications over the past 100 years, with no consensus opinion about the cause of this effect. In this paper, it is suggested that the linear relationship between ln[A] and E is the result of a real or spurious path dependence of the reaction history between the initial state of the pure reactant(s) and the final state of the pure product(s) having standard enthalpy and entropy differences, ΔH° and ΔS°, respectively. The single-step rate law approximation of a reversible reaction leads to T0 = H°/ΔS° as the dynamic thermal (thermodynamic) equilibrium temperature and 1/T0 = (ln[A̅/k0])/(E̅/R) as the slope of a Constable/KCE plot or the crossover temperature of Arrhenius lines in an isokinetic relationship (IKR), where A̅ and E̅ are mean values for the ensemble of compensating {Ei, Ai} pairs and k0 is a constant that accounts for the path dependence of the reaction history and reconciles the KCE with the IKR. This proposed physical basis for the KCE and IKR is supported by qualitative agreement between ΔH° and ΔS° calculated from the statistics of compensating {Ei, Ai} pairs in the literature, and the difference in the standard enthalpies and entropies of formation of the products and reactants for thermal decomposition of organic peroxides, calcium carbonate, and poly(methyl methacrylate).

Role of Focusing Distance in Picosecond Laser-Induced Cu Plasma Spectra

To study the effects of focusing distance on the characteristics of copper plasma, a picosecond laser is utilized to ablate a pure copper plate to generate a plasma spectrum. Following numerous experiments on the subject, three significant factors are determined: lens focal length, pulse energy, and the lens-to-sample distance. These factors are employed to analyze the spectral intensity, plasma temperature, and electron density in the local thermodynamic equilibrium (LTE) and optically thin condition. Due to the shielding effects of mixed plasma, the strongest spectral intensity is achieved in the prefocused case, no matter how much beam irradiance is employed. The more intensive the beam irradiance is, the more the optimal position is distant from the focal point. The variation of plasma temperature and electron density showed a peak in the prefocused case, which is consistent with the trend of spectral intensity. For the case of extremely high irradiance (on the focus), the shielding effects become seriously, and the resultant above three factors decreased sharply. When a longer-focal-length lens is employed, the spectral intensity exhibited an obvious bimodal trend. In the prefocused case, a longer-focal-length lens is helpful to eliminate the effects of the roughness of the target surface compared with a shorter one. Finally, the assumed LTE is validated by McWhirter relation, plasma relaxation time, and diffusion length, and the optically thin condition was also validated by spectral intensity ratio. We hope that this work could be an important reference for the future design of highly optimized experiments for Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS).

Photo-thermo catalytic dry reforming of methane over Ni-Ir/SiO<sub>2</sub> catalyst

Photo-thermo catalysis can effectively reduce the reaction temperature of dry reforming of methane (DRM) and increase the reaction efficiency. The development of a new type of high-efficiency photo-thermo catalyst and the exploration of its catalytic mechanism are the focuses of current research. A self-confinement strategy was used to prepare nickel-iridium bimetallic catalyst (Ni-Ir/SiO2). Catalyst physicochemical properties and photo-thermo catalytic performances on DRM were both studied. The results show that the bimetal nanoparticle has an average size of less than 3.5 nm and is evenly distributed on the substrate. The light absorption ability of the constructed ultra-small nickel-iridium bimetal is significantly enhanced. At the same time, the electrical field is also enhanced to effectively promote the hot electron excitation and realize its activation of methane and carbon dioxide molecules, especially their dissociation below the thermodynamic equilibrium temperature. In addition, the external heating of the system can further improve DRM reaction rate. Under the conditions of 700℃ and light intensity of 5 W/cm2, the H2 yield reaches 861 mmol/(g h), equivalent to that of the pure noble metal-based catalysts. Also, the catalyst shows good repeatability in the photo-thermo catalytic DRM reaction.

Emissions in short-gated ns/ps/fs-LIBS for fuel-to-air ratio measurements in methane-air flames.

A study of short-gated 10 nanosecond (ns), 100 picosecond (ps), and 100 femtosecond (fs) laser induced breakdown spectroscopy (LIBS) was conducted for fuel-to-air ratio (FAR) measurements in an atmospheric Hencken flame. The intent of the work is to understand which emission lines are available near the optical range in each pulse width regime and which emission ratios may be favorable for generating equivalence ratio calibration curves. The emission spectra in the range of 550-800 nm for ns-LIBS and ps-LIBS are mostly similar with slightly elevated atomic oxygen lines by ps-LIBS. Spectra from fs-LIBS show the lowest continuum background and prominent individual atomic lines, though have significantly weaker ionic emission from nitrogen. A qualitative explanation based on assumed local thermodynamic equilibrium and electron temperatures calculated by the ${{\rm{N}}_{\rm{II}}}({{565}}\;{\rm{nm}})$ and ${{\rm{N}}_{\rm{II}}}({{594}}\;{\rm{nm}})$ emissions is presented. In studying line emission ratios for FAR calculation, it is found that ${{\rm{H}}_\alpha}({{656}}\;{\rm{nm}})/{{\rm{N}}_{\rm{II}}}({{568}}\;{\rm{nm}})$ is best for FAR measurements with ns-LIBS and remains viable for ps-LIBS, while ${{\rm{H}}_\alpha}({{656}}\;{\rm{nm}})/{{\rm{O}}_{\rm I}}({{777}}\;{\rm{nm}})$ is optimal for the ps-LIBS and fs-LIBS cases. Due to low continuum background and short time delay for spectra collection, fs-LIBS is very promising for high-speed FAR measurements using short-gated LIBS.

The GTFSampler: A new downhole equipment for geothermal fluid sampling and its testing results in the Chingshiu geothermal field, Ilan, Taiwan

A new downhole sampler, GTFSampler, is designed to collect in-situ geothermal fluids and preserve the conditions of the sampling depth. The GTFSampler is mainly composed of a stainless sampling cylinder and a gas driven shut-in valve, which are hosted in an equipment protector. The sampler assembly connects to a stainless tube for hoisting in a borehole and switching the shut-in valve by changing the inner pressure of the stainless tube on surface. Selected gas (e.g., N2 or noble gas) is pre-filled to the sampling cylinder at a fixed pressure before sampling. The GTFSampler is also equipped with a traditional mercury maximum thermometer. The comparison between the measured temperature and calculated thermodynamic equilibrium temperature from saturation degree of minerals is used to verify the representativeness of downhole sample collection, on-site sample separation and laboratory analysis.In the borehole IC-19 deployment in Chingshui geothermal field, Ilan, Taiwan, the measured temperature at 800 m are ca. 190∼198 °C. Three downhole samplings were conducted in this study, i.e., the first and second samplings were deployed in discharged borehole condition and the third sampling in closed borehole condition. The first and second samplings showed that the theoretical equilibrium temperature calculated by geochemical modeling from fluid composition is very close to the measured temperature at the sampling depth. However, no convergence solution for equilibrium temperature is obtained for the third sampling, indicating certain interference in geothermal water quality by the natural convection inside the borehole as the control valve is closed. In summary, the GTFSampler and its corresponding sampling procedures successfully collect the downhole geothermal fluids.

Generation of methane gas hydrate equilibrium curve for the thermodynamic gas hydrate inhibitor propylene glycol

Use of thermodynamic hydrate inhibitors (THIs) for prevention of gas hydrate formation in the oil and gas field operations is a well-known and accepted process all over the world. Although glycols are reported as THIs, but only monoethylene glycol is studied in detail and applied conventionally. In this study, gas hydrate inhibition efficiency of propylene glycol is determined. The data is acquired using a stirred cryogenic PVT sapphire cell and the hydrate dissociation temperature measured at isobaric condition (constant pressure) is considered as the thermodynamic equilibrium temperature, because although dissociation temperature depends on hydrate particle size and heat flux, but, it is unlike the random nature and unpredictability of formation temperature. The key objective of this study is to establish the equilibrium condition of methane hydrate in presence of 20 wt% propylene glycol as thermodynamic inhibitor. The identification of dissociation temperature is based on visual method. The gas hydrate equilibrium curve for 20 wt% propylene glycol in methane-water system is established by determining the hydrate equilibrium dissociation temperatures for a pressure range 70–190 bar. Also performance comparison of propylene glycol with monoethylene glycol is done to gauge the inhibition efficiency of propylene glycol, the results of which have shown better inhibition efficiency of propylene glycol. Hydrate equilibrium curve of 20 wt% propylene glycol system showed an average of 10.42 °C deviation towards lower temperature compared to that of the system without the inhibitor. The fitted curve for hydrate dissociation temperatures showed co-efficient of determinants (R2) value ≥ 0.97, suggesting the reliability of the experimental observations.

Enhanced activity of co-precipitated NiFeAlOx in CO2 methanation by segregation and oxidation of Fe

Commercial application of the CO2 methanation reaction demands for the development of catalysts that feature an enhanced stability to increase catalyst lifetime. By time-resolved aging studies, we show that the improved deactivation resistance of co-precipitated NiFeAlOx catalysts compared to NiAlOx is obtained by a temporal increase of the intrinsic catalytic activity of NiFeAlOx, provoked by aging at elevated temperature and pressure in thermodynamic equilibrium. Detailed structural characterization of reduced and aged catalysts resolves that aging triggers the partial segregation of (γFe,Ni) nanoparticles initially formed during activation, accompanied by the oxidation of Fe. Thereby, the intrinsic catalytic activity increases, which can be explained by the generation of redox-active Fe2+ sites that offer an additional reaction pathway for CO2 activation. The deactivation behavior of NiFeAlOx can be described by a superimposition of activity increase related to Fe2+ site formation and decrease due to the loss of active sites by sintering processes.

SN 2010kd: Photometric and Spectroscopic Analysis of a Slow-decaying Superluminous Supernova

Abstract This paper presents data and analysis of SN 2010kd, a low-redshift (z = 0.101) H-deficient superluminous supernova (SLSN), based on ultraviolet/optical photometry and optical spectroscopy spanning between −28 and +194 days relative to B-band maximum light. The B-band light-curve comparison of SN 2010kd with a subset of well-studied SLSNe I at comparable redshifts indicates that it is a slow-decaying PTF12dam-like SLSN. Analytical light-curve modeling using the Minim code suggests that the bolometric light curve of SN 2010kd favors circumstellar matter interaction for the powering mechanism. SYNAPPS modeling of the early-phase spectra does not identify broad H or He lines, whereas the photospheric-phase spectra are dominated by O i, O ii, C ii, C iv, and Si ii, in particular the presence of both low- and high-velocity components of O ii and Si ii lines. The nebular-phase spectra of SN 2010kd are dominated by O i and Ca ii emission lines similar to those seen in other SLSNe I. The line velocities in SN 2010kd exhibit flatter evolution curves similar to SN 2015bn but with comparatively higher values. SN 2010kd shows a higher single-zone local thermodynamic equilibrium temperature in comparison to PTF12dam and SN 2015bn, and it has an upper O i ejected mass limit of ∼10 M ⊙. The host of SN 2010kd is a dwarf galaxy with a high star formation rate (∼0.18 ± 0.04 M ⊙ yr−1) and extreme emission lines.

Phase transition and emergence of active temperature in an active Brownian system in underdamped background

We explore the role of inertia in the properties of active Brownian particles (ABPs) immersed in an underdamped background in two dimensions using Langevin dynamics computer simulation. Similar to an equilibrium two-dimensional passive interacting particle system, the system of ABPs transits from a liquid phase to a solid phase with the change in the coupling parameter, which is the ratio of interaction potential energy and thermal energy of the background solvent. Important qualitative and quantitative differences are found in the liquid-solid phase transition with increasing strength of activity as compared to those found in the conventional overdamped background limit. In the underdamped background, inherent activity is found to lead to a temperature, called the active temperature and defined by average velocity fluctuations of the ABPs, that is different from the fixed background solvent temperature. A new scaling law for active temperature as a function of activity strength is found near the liquid-solid boundary. Active temperature, which behaves similar to the thermodynamic equilibrium temperature, is also found to depend upon the interaction strength between the active particles and the strength of the background dissipation. With an increase in background dissipation, the difference between active temperature and the background solvent temperature decreases and the difference is found to eventually vanish in the overdamped limit, demonstrating the correctness of the calculation.

Infrared and sub-mm observations of outbursting young stars with Herschel and Spitzer

Context. Episodic accretion plays an important role in the evolution of young stars. Although it has been under investigation for a long time, the origin of such episodic accretion events is not yet understood. Aims. We investigate the dust and gas emission of a sample of young outbursting sources in the infrared to get a better understanding of their properties and circumstellar material, and we use the results in a further work to model the objects. Methods. We used Herschel data, from our PI program of 12 objects and complemented with archival observations to obtain the spectral energy distributions (SEDs) and spectra of our targets. We report here the main characteristics of our sample, focussing on the SED properties and on the gas emission lines detected in the PACS and SPIRE spectra. Results. The SEDs of our sample show the diversity of the outbursting sources, with several targets showing strong emission in the far-infrared from the embedded objects. Most of our targets reside in a complex environment, which we discuss in detail. We detected several atomic and molecular lines, in particular rotational CO emission from several transitions from J = 38−37 to J = 4−3. We constructed rotational diagrams for the CO lines, and derived in three domains of assumed local thermodynamic equilibrium (LTE) temperatures and column densities, ranging mainly between 0−100 K and 400−500 K. We confirm correlation in our sample between intense CO J = 16−15 emission and the column density of the warm domain of CO, N(warm). We notice a strong increase in luminosity of HH 381 IRS and a weaker increase for PP 13 S, which shows the beginning of an outburst.

A strategy of designing high-entropy alloys with high-temperature shape memory effect

Shape memory effect, the ability to recover a pre-deformed shape on heating, results from a reversible martensitic transformation between austenite and martensite phases. Here, we demonstrate a strategy of designing high-entropy alloys (HEAs) with high-temperature shape memory effect in the CrMnFeCoNi alloy system. First, we calculate the difference in Gibbs free energy between face-centered-cubic (FCC) and hexagonal-close-packed (HCP) phases, and find a substantial increase in thermodynamic equilibrium temperature between the FCC and HCP phases through composition tuning, leading to thermally- and stress-induced martensitic transformations. As a consequence, the shape recovery temperature in non-equiatomic CrMnFeCoNi alloys can be increased to 698 K, which is much higher than that of conventional shape memory alloys (SMAs) and comparable to that of B2-based multi-component SMAs containing noble metals (Pd, Pt, etc.) or refractory metals (Zr, Hf, etc.). This result opens a vast field of applications of HEAs as a novel class of cost-effective high-temperature SMAs.

Methylamine and other simple N-bearing species in the hot cores NGC 6334I MM1–3

Context. In the search for the building blocks of life, nitrogen-bearing molecules are of particular interest since nitrogen-containing bonds are essential for the linking of amino acids and ultimately the formation of larger biological structures. The elusive molecule methylamine (CH3NH2) is thought to be a key pre-biotic species but has so far only been securely detected in the giant molecular cloud Sagittarius B2. Aims. We identify CH3NH2 and other simple nitrogen-bearing species involved in the synthesis of biologically relevant molecules towards three hot cores associated with the high-mass star-forming region NGC 6334I, located at a distance of 1.3 kpc. Column density ratios are derived in order to investigate the relevance of the individual species as precursors of biotic molecules. Methods. High sensitivity, high angular and spectral resolution observations obtained with the Atacama Large Millimeter/ submillimeter Array were used to study transitions of CH3NH2, CH2NH, NH2CHO, and the 13C- and 15N-methyl cyanide (CH3CN) isotopologues, detected towards NGC 6334I. Column densities are derived for each species assuming local thermodynamic equilibrium and excitation temperatures in the range 220–340 K for CH3NH2, 70–110 K for the CH3CN isotopologues and 120–215 K for NH2CHO and CH2NH. Results. We report the first detections of CH3NH2 towards NGC 6334I with column density ratios with respect to CH3OH of 5.9 × 10−3, 1.5 × 10−3 and 5.4 × 10−4 for the three hot cores MM1, MM2, and MM3, respectively. These values are slightly lower than the values derived for Sagittarius B2 but higher by more than an order of magnitude as compared with the values derived for the low-mass protostar IRAS 16293–2422B. The column density ratios of NH2CHO, 13CH3CN, and CH3C15N with respect to CH3OH are (1.5 – 1.9) × 10−4, (1.0 – 4.6) × 10−3 and (1.7 – 3.0) × 10−3 respectively. Lower limits of 5.2, 1.2, and 3.0 are reported for the CH3NH2 to CH2NH column density ratio for MM1, MM2, and MM3 respectively. These limits are largely consistent with the values derived for Sagittarius B2 and higher than those for IRAS 16293–2422B. Conclusions. The detections of CH3NH2 in the hot cores of NGC 6334I hint that CH3NH2 is generally common in the interstellar medium, albeit that high-sensitivity observations are essential forthe detection of the species. The good agreement between model predictions of CH3NH2 ratios and the observations towards NGC 6334I indicate a main formation pathway via radical recombination on grain surfaces. This process may be stimulated further by high grain temperatures allowing a lager degree of radical mobility. Further observations with ALMA will help evaluate the degree to which CH3NH2 chemistry depends on the temperature of the grains in high- and low-mass star-forming regions respectively.

Temperature range definition of phase transformation in experimental biocompatible Ti-Nb-Zr system alloys by various methods

Abstract The calculated dependences of the α- and β-phases volume fractions change in the 300–600 °C temperature range and thermodynamic equilibrium temperatures of polymorphic α + β-β-transformations (β-transus temperature, Tβ) for biocompatible alloys of the Ti-39%Nb-xZr system, where x ≈ 5; 7; 9 wt% were defined by thermodynamic calculations using ThermoCalc software package. It is established the zirconium in Ti-Nb-Zr system behaves as a β-stabilizer rather than a neutral element, and provides a Tβ decreasing with an increase of its content in the alloy. An equation is proposed for calculating Tβ in ternary alloys of the Ti-Nb-Zr system, where Ci – chemical element concentration, at.%: Tβ = 882.5 − 12.68CNb − 5.56CZr. The equation was obtained from the data on the change of Tβ in the equilibrium binary Ti-Nb, Ti-Zr systems. The Tβ values, calculated according to this equation, were close to those obtained by thermodynamic calculation (the difference does not exceed 4 °C). It was shown that the temperature of the endothermic peak minimum on the DSC heating curves of the Ti-Nb-Zr system alloys caused by the α + β-β-transformation corresponds to the Tβ determined using the ThermoCalc software. The endothermic peak intensity was found to decrease with an increase of the zirconium content, which additionally confirms the β-stabilizing effect of zirconium.

Low levels of methanol deuteration in the high-mass star-forming region NGC 6334I

Context. The abundance of deuterated molecules in a star-forming region is sensitive to the environment in which they are formed. Deuteration fractions, in other words the ratio of a species containing D to its hydrogenated counterpart, therefore provide a powerful tool for studying the physical and chemical evolution of a star-forming system. While local low-mass star-forming regions show very high deuteration ratios, much lower fractions are observed towards Orion and the Galactic centre. Astration of deuterium has been suggested as a possible cause for low deuteration in the Galactic centre. Aims. We derive methanol deuteration fractions at a number of locations towards the high-mass star-forming region NGC 6334I, located at a mean distance of 1.3 kpc, and discuss how these can shed light on the conditions prevailing during its formation. Methods. We use high sensitivity, high spatial and spectral resolution observations obtained with the Atacama Large Millimeter/ submillimeter Array to study transitions of the less abundant, optically thin, methanol-isotopologues: 13CH3OH, CH318OH, CH2DOH and CH3OD, detected towards NGC 6334I. Assuming local thermodynamic equilibrium (LTE) and excitation temperatures of ~120–330 K, we derive column densities for each of the species and use these to infer CH2DOH/CH3OH and CH3OD/CH3OH fractions. Results. We derive column densities in a range of (0.8–8.3) × 1017 cm−2 for 13CH3OH, (0.13–3.4) × 1017 cm−2 for CH318OH, (0.03–1.63) × 1017 cm−2 for CH2DOH and (0.15–5.5) × 1017 cm−2 for CH3OD in a ~1″ beam. Interestingly, the column densities of CH3OD are consistently higher than those of CH2DOH throughout the region by factors of 2–15. We calculate the CH2DOH to CH3OH and CH3OD to CH3OH ratios for each of the sampled locations in NGC 6334I. These values range from 0.03% to 0.34% for CH2DOH and from 0.27% to 1.07% for CH3OD if we use the 13C isotope of methanol as a standard; using the 18 O-methanol as a standard, decreases the ratios by factors of between two and three. Conclusions. All regions studied in this work show CH2DOH/CH3OH as well as CH2DOH/CH3OD values that are considerably lower than those derived towards low-mass star-forming regions and slightly lower than those derived for the high-mass star-forming regions in Orion and the Galactic centre. The low ratios indicate a grain surface temperature during formation ~30 K, for which the efficiency of the formation of deuterated species is significantly reduced. Therefore, astration of deuterium in the Galactic centre cannot be the explanation for its low deuteration ratio but rather the high temperatures characterising the region.

Isomorph theory of physical aging.

This paper derives and discusses the configuration-space Langevin equation describing a physically aging R-simple system and the corresponding Smoluchowski equation. Externally controlled thermodynamic variables like temperature, density, and pressure enter the description via the single parameter Ts/T, in which T is the bath temperature and Ts is the "systemic" temperature defined at any time t as the thermodynamic equilibrium temperature of the state point with density ρ(t) and potential energy U(t). In equilibrium, Ts ≅ T with fluctuations that vanish in the thermodynamic limit. In contrast to Tool's fictive temperature and other effective temperatures in glass science, the systemic temperature is defined for any configuration with a well-defined density, even if it is not close to equilibrium. Density and systemic temperature define an aging phase diagram, in which the aging system traces out a curve. Predictions are discussed for aging following various density-temperature and pressure-temperature jumps from one equilibrium state to another, as well as for a few other scenarios. The proposed theory implies that R-simple glass-forming liquids are characterized by the dynamic Prigogine-Defay ratio being equal to unity.

The importance of supersaturation on determining the solid-liquid equilibrium temperature of waxy oils

Crystallization is a process where an ordered solid structure is formed from a disordered phase. This event is divided in two main stages, namely nucleation and crystals growth. As paraffin nucleation is a stochastic process, a supercooling is needed to initiate the process. In other words, the beginning of crystal precipitation does not coincide with the highest thermodynamic solid-liquid equilibrium temperature. Therefore, during the cooling it is required that the fluid reaches a certain temperature below saturation, i.e., a metastable state, to initiate the crystal nucleation process. The difference between the saturation temperature and the crystallization temperature is called degree of supercooling. As this metastable condition may exist during not only the crystallization but also the dissolution of crystals, this work proposes a procedure to determine consistently the highest solid-liquid thermodynamic equilibrium temperature by using the results of rheometer and DSC experiments. It can be anticipated that the proposed protocol states that the highest solid-liquid thermodynamic equilibrium temperature is considered to approach the dissolution temperature when the material is heated at a very low heating rate.

Three-dimensional, non-isothermal phase-field modeling of thermally and stress-induced martensitic transformations in shape memory alloys

The transition between austenite and martensite provides shape memory alloys (SMAs) with many unique properties. A three-dimensional, non-isothermal phase-field model was employed to comprehensively investigate the latent heat and elastocaloric effects in SMAs, which are originated from the thermoelastic martensitic transformations (MTs). We analyzed thermally induced MTs upon cooling and heating and stress-induced MTs at different temperatures in Mn–Cu alloys. It was observed that the size of twinned martensitic domain varied with temperature and large internal stresses resulted in thermoelastic equilibrium between austenite and martensite. The evolution of temperature field, caused by the latent heat effect, was obtained and the maximum temperature was found nearby the phase interface during the transformation. Twinned and single-variant martensites formed upon uniaxial tension and compression, respectively. Above the thermodynamic equilibrium temperature between austenite and martensite, with the occurring of reverse MT during unloading, superelasticity was realized. The localized temperature change and global elastocaloric effect during uniaxial loading and unloading were obtained and discussed. This model helps understand and explain the uniformity of temperature, stress and microstructural fields in the phase-field method.

Selection of the optimal combination of water vapor absorption lines for detection of temperature in combustion zones of mixing supersonic gas flows by diode laser absorption spectrometry

Determination of a gas medium temperature by diode laser absorption spectrometry (DLAS) is based on the measurement of integral intensities of the absorption lines of a test molecule (generally water vapor molecule). In case of local thermodynamic equilibrium temperature is inferred from the ratio of the integral intensities of two lines with different low energy levels. For the total gas pressure above 1 atm the absorption lines are broadened and one cannot find isolated well resolved water vapor absorption lines within relatively narrow spectral interval of fast diode laser (DL) tuning range (about 3 cm −1 ). For diagnostics of a gas object in the case of high temperature and pressure DLAS technique can be realized with two diode lasers working in different spectral regions with strong absorption lines. In such situation the criteria of the optimal line selection differs significantly from the case of narrow lines. These criteria are discussed in our work. The software for selection the optimal spectral regions using the HITRAN-2012 and HITEMP data bases is developed. The program selects spectral regions of DL tuning, minimizing the error of temperature determination δТ/T , basing on the attainable experimental error of line intensity measurement δS . Two combinations of optimal spectral regions were selected – (1.392 & 1.343 μm) and (1.392 & 1.339 μm). Different algorithms of experimental data processing are discussed.

Atomic Ordering and Sn Segregation in Pt–Sn Nanoalloys Supported on CeO2 Thin Films

The stability and atomic ordering in Pt–Sn nanoalloys supported on CeO2 thin films have been studied by means of synchrotron radiation photoelectron spectroscopy and density functional calculations. Using CO molecules as a probe, we explored the development of the surface structure of supported Pt–Sn nanoalloys with respect to a reference Pt/CeO2 model system. We found a significant decrease in the density of CO adsorption sites on supported Pt–Sn nanoalloys caused by Sn segregation to the surface upon annealing. Additionally, we found that atomic ordering in Pt–Sn nanoalloys is driven by the balance between the surface segregation energy of Sn atoms and the energy of heteroatomic bond formation. Our calculations demonstrate a clear tendency for Sn segregation to the nanoalloy surface. For Pt105Sn35 and Pt1097Sn386 nanoparticles, we calculated a surface stoichiometry of Pt2Sn which is only slightly dependent on temperature in thermodynamic equilibrium. The analysis of Bader charges in Pt–Sn nanoalloys revealed a strong correlation between the charge and the coordination number of Sn atoms with respect to Pt neighbors. In particular, the magnitude of the charge transfer from Sn to Pt increases as a function of the Sn coordination number.