Consistent Set Of Parameters Research Articles

Cube slip and non-Schmid effects in single crystal Ni-base superalloys

An advanced constitutive model incorporating two specific aspects of Ni-base superalloy deformation behaviour is proposed. Several deformation mechanisms are active in these two-phase materials. In the matrix phase, cube slip plays an important role in the orientation dependence of the material. Moreover, inelastic deformation of the precipitate phase leads to non-Schmid effects in the material response. Macroscopic cube slip is modelled here by incorporating a zig-zag cross slip mechanism into the constitutive relations for the matrix phase. A cross slip factor is proposed that quantifies the amount of cross slip and consequently represents the orientation dependence of the cube slip. Further, a detailed precipitate phase constitutive model is proposed, which enables the simulation of non-Schmid effects, like the tension–compression asymmetry. The cross slip mechanism and the associated splitting of partial dislocations in the γ′-phase, which are responsible for the anomalous yield behaviour, are incorporated in the model. The proposed formulations are implemented in a recently developed crystal plasticity framework for single crystal Ni-base superalloys and a consistent set of model parameters for the commercial alloy CMSX-4 is determined. The model is shown to reasonably predict the material tensile response and creep behaviour for a range of temperatures and stress or strain rate levels. The incorporation of the cross slip mechanisms in the matrix and precipitate results in an adequate simulation of the material orientation dependence and the experimentally determined tension–compression asymmetry.

Importance of adsorption for CCN activity and hygroscopic properties of mineral dust aerosol

This study uses published data on dust‐water interactions to examine the importance of including water adsorption effects when describing the hygroscopic and cloud condensation nuclei (CCN) behavior of mineral dust aerosol. Adsorption activation theory (AT) better represents fresh dust‐water interactions than Köhler theory (KT), as i) a consistent set of adsorption parameters can describe the hygroscopic behavior of dust (under both sub and supersaturated conditions), and ii) the dependence of critical supersaturation, sc, with particle dry diameter, Ddry, is closer to observations. The long adsorption timescale could also contribute to the large differences observed between dry and wet generated dust hygroscopicity. If KT and AT are consistently applied to the same dust size distribution, KT predicts up to tenfold higher CCN and 40% higher droplet number concentration than AT. This profoundly different behavior between the theories suggests that both may be required for a comprehensive description of atmospheric dust CCN activity.

Development of ReflEXAFS data analysis for deeper surface structure studies

An analytical approach to the analysis of ReflEXAFS data collected from complex multilayer samples, at a range of angles above and below the critical angle is presented. The aim of the technique is to generate a structural model of the investigated system that is consistent with the variable depth sensitivity of the experimental data. The procedure follows three main steps (i) the determination of the free atom reflectivity background for the multilayer system, (ii) the estimation of the depth dependent EXAFS signals and (iii) the calculation of the corresponding ReflEXAFS components. By iterating between steps (ii) and (iii), and varying the estimates of the EXAFS signals, a consistent set of structural parameters is extracted that reflects the bulk structure of the multilayer system through the basic reflectivity signals, and the depth dependent local atomic structure through the estimated EXAFS components. An example of the depth dependent structure of copper in a copper-chromium multilayer stack is presented to illustrate the capabilities of the method.

Experimental investigation and thermodynamic modeling of the Al–P–Zn ternary system

The 450 ∘C isothermal section of the Al–P–Zn ternary system has been determined using optical microscopy, scanning electronic microscopy coupled with energy dispersive x-ray spectroscopy, and x-ray diffractometry. No true ternary compound was found in the present study. The optimized descriptions of the phase diagram and thermodynamic properties of the Al–P and P–Zn binary systems were obtained from experimental data by means of the CALPHAD technique. On the basis of the literature data for thermodynamic assessment of Al–Zn and the present work on Al–P and P–Zn systems, the phase diagram calculation for Al–P–Zn was carried out. A consistent set of thermodynamic parameters for each phase was derived. The optimized results and the experimental data are in good agreement.

Average neutron parameters for hafnium

The neutron transmission of natural hafnium samples have been measured within the 2 eV to 50 keV energy range at the white neutron source GELINA of the Institute for Reference Materials and Measurements (IRMM) in Geel, Belgium. Data sets for two temperatures (77 K and 300 K) and three sample thicknesses (1 mm, 2 mm, 15 mm) have been simultaneously analyzed in terms of Reich–Moore parameters. The ESTIMA technique in association with the generalized SPRT method were used to obtain a consistent set of l-dependent average resonance parameters. For each hafnium isotope, scattering radius R ′ , neutron strength function S l , distant level parameter R l ∞ , mean level spacing D l and average radiation width 〈 Γ γ 〉 are given and compared with results reported in the literature. The capture and total cross sections calculated by the CONRAD code using this set of average parameters were successfully compared to experimental data retrieved from EXFOR.

Thermodynamic assessment of the CoO x–CrO 1.5 system

By application of the CALPHAD method, a consistent set of thermodynamic model parameters is optimized for the oxide phases in the Co–Cr–O system. Cobalt chromium spinel is described as a normal spinel at room temperature and with cation redistribution at high temperature. All the solid oxide solution phases are described using the compound energy model, and the liquid phase is described using the two-sublattice model for ionic liquids. Calculated phase diagrams are presented, and values for the thermodynamic properties are compared with experimental data.

Logarithmic corrections in(4+1)-dimensional directed percolation

We simulate directed site percolation on two lattices with four spatial and one timelike dimensions (simple and body-centered hypercubic in space) with the standard single cluster spreading scheme. For efficiency, the code uses the same ingredients (hashing, histogram reweighing, and improved estimators) as described by Grassberger [Phys. Rev. E 67, 036101 (2003)]. Apart from providing the most precise estimates for p_{c} on these lattices, we provide a detailed comparison with the logarithmic corrections calculated by [Janssen and Stenull [Phys. Rev. E 69, 016125 (2004)]. Fits with the leading logarithmic terms alone would give estimates of the powers of these logarithms which are too big by typically 50%. When the next-to-leading terms are included, each of the measured quantities (the average number of sites wetted at time t , their average distance from the seed, and the probability of cluster survival) can be fitted nearly perfectly. But these fits would not be mutually consistent. With a consistent set of fit parameters, one obtains still much improvement over the leading log approximation. In particular we show that there is one combination of these three observables which seems completely free of logarithmic terms.

Thermodynamic modeling of the Mg–Pu and Cu–Pu systems

The thermodynamic assessment of the Mg–Pu and Cu–Pu systems was carried out by using the calculation of phase diagrams (CALPHAD) method on the basis of experimental data including thermodynamic properties and phase equilibria. The Gibbs free energies of the liquid, fcc, hcp, αPu, βPu, γPu, δPu, δ′Pu, and εPu phases were described by the subregular solution model with a Redlich–Kister equation, and those of the intermetallic compounds in the Mg–Pu and Cu–Pu binary systems were described by the sublattice model. A consistent set of thermodynamic parameters were derived for describing the Gibbs free energies of solution phases and intermetallic compounds in the Mg–Pu and Cu–Pu binary systems. An agreement between the calculated results and experimental data is obtained.

Impact ionization in semiconductors: recent progress on non‐local effects

AbstractA model of the ionization pathlength PDF is reformulated with new parameters that have more physical significance and allow further investigation. The transition from the dead space effect to the dead space plus resonance effect is investigated and a new measure, the overshoot factor, is suggested as the method for indicating the degree of resonant behaviour. The non‐local model is extended for non‐uniform electric field profiles. When this extended model is fitted to Monte Carlo data derived for four different electric field profiles, a fairly consistent set of parameters is found. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Use of autocatalytic kinetics to obtain composition of lignocellulosic materials

Non-isothermal thermogravimetric analysis (TGA) data of biomasses and pulps originating from non-wood and alternatives materials (i.e., Tagasaste or rice straw) have been fitted with refined models, which include autocatalytic kinetics. Data sets were obtained for different experimental conditions, such as variations of heating rate and atmosphere, i.e., inert (pyrolysis) versus oxidative atmosphere (combustion). Besides the access to classical kinetic parameters (pre-exponential factor, activation energy, and reaction order), the improved data analysis enabled the determination of the chemical composition of the samples (cellulose, hemicellulose, extractives, lignin). The latter compared very well with those obtained by conventional methods (chemical analysis, HPLC). Given the reduced environmental impact and rapidness of the method, potential applications for research related to new biomasses and industrial processes can be foreseen. The herein implemented method is based on the assumption that samples contain pseudo-components, which independently degrade, and that combustion is the combination of an initial volatilization process (similar to pyrolysis) and a subsequent char oxidation process. Further, it was found that for a reliable modeling of the volatilization stage, extractives should be considered as well, together with the classical pseudo-components: hemicellulose, cellulose and lignin. The char oxidation stage has been simulated as a sum of the oxidation of three char types, one for each main pseudo-component. Importantly, fitting of TGA curves under consideration of autocatalytic kinetics allows the determination of a consistent set of kinetic parameters at different heating rates and leads to significant suppression of the compensation effect. While autocatalysis (characterized by the nucleation order) is not very significant for pyrolysis of biomasses, it can reach high levels for combustion, especially when high heating rates are used. In cellulosic char oxidation a nucleation order larger than one was fitted. The autocatalysis level of the char oxidation can rapidly increase with small modifications of the heating rate (i.e. to pass from 5 to 10 °C/min). In this case, the classically applied nth-order kinetic is particularly insufficient to fit experimental data with the same set of the kinetic parameters.

Positive and negative analyte ion yield in matrix-assisted laser desorption/ionization revisited

The most commonly accepted model for the formation of analyte ions in MALDI-MS assumes a primary ionization of the matrix e.g., by photoionization, leading among others to stable protonated and deprotonated matrix ions, respectively. Peptide and protein ions are then formed by secondary proton transfer reactions in the expanding plume. This model had been checked experimentally by comparing the yield of positive to negative ions of three peptides (Bradykinin, Angiotensin I and Fibrinopeptide A) and six matrices (α-cyano-4-hydroxycinnamicacid (CHCA), 2,5-dihydroxybenzoicacid (DHB), 6-aza-2-thiothymine (ATT), 4-nitroaniline (4-NA), 2-amino-5-nitro-4-picoline (ANP), 5-aminoquinolione (5-AQ)), differing in gas-phase basicity by about 100 kJ/mole [M. Dashtiev, E. Wäfler, U. Röhling, M. Gorshkov, F. Hillenkamp, R. Zenobi, Int. J. Mass Spetrom. 268 (2007) 122]. The data have been revisited for a more general and in-depth analysis. Model predictions are presented for a wide range of experimental parameters, in particular for ranges of the gas-phase basicity and acidity of analyte and matrix and for different molar ratios of analyte to matrix as well as the yield of primary matrix ions. It is shown that the observed ion yields cannot be explained by any single and consistent set of parameters. It is concluded that the existing simple model needs be modified to fully explain the experimental findings. Such modifications should primarily address the formation of negative matrix and analyte ions.

Experimental investigation and thermodynamic calculation of the phase equilibria in the Co–Mo–W system

The isothermal sections in the Co–Mo–W ternary system at 600 °C, 800 °C, 1000 °C, 1100 °C, 1200 °C and 1300 °C have been determined using the Electron probe micro-analyzer (EPMA) and X-ray diffraction (XRD) techniques. A thermodynamic assessment of the Co–Mo–W ternary system was carried out by the CALPHAD ( Calculation of Phase Diagrams) method. The Gibbs free energies of the liquid and solution phases were described by the subregular solution models, and those of intermetallic compounds were described by the sublattice model. A consistent set of thermodynamic parameters has been derived for describing the Gibbs free energies of each solution phase and intermetallic compound in the Co–Mo–W ternary system. The calculated phase diagrams and thermodynamic properties in the Co–Mo–W ternary system are in good agreement with experimental data.

Thermodynamic assessment of the Molybdenum–Rhenium system

A thermodynamic optimization of the Mo–Re system by the Calphad method is proposed, taking into account new experimental data obtained in this work. According to recent crystal chemistry work, the χ and σ Frank–Kasper phases were modeled using two independent sublattices of variable occupation. This was made possible by including experimental site fractions in the different sublattices as input data for the parameter optimization. A consistent set of parameters is proposed. Good agreement is found between calculated and selected experimental values for different kinds of data: phase diagram, thermodynamic and crystallographic data.

Recent advances on kinetic analysis of electromigration enhanced intermetallic growth and damage formation in Pb-free solder joints

A comprehensive kinetic analysis was established to investigate the electromigration (EM) enhanced intermetallic compound (IMC) growth and void formation for Sn-based Pb-free solder joints with Cu under bump metallization (UBM). The kinetic model takes into account Cu–Sn interdiffusion and current stressing. Derivation of the diffusion coefficients and the effective charge numbers for the intermetallic compounds is an essential but challenging task for the study of this multi-phase multi-component intermetallic system. A new approach was developed to simultaneously derive atomic diffusivities and effective charge numbers based on simulated annealing (SA) in conjunction with the kinetic model. A consistent set of parameters were obtained, which provided important insight into the diffusion behaviors driving the IMC growth. The parameters were used in a finite difference model to numerically solve the IMC growth problem and the result accurately correlated with the experiment. EM reliability test revealed that the ultimate failure of the solder joints was caused by extensive void formation and subsequent crack propagation at the intermetallic interface. This damage formation mechanism was analyzed by first considering vacancy transport under current stressing. This was followed by a finite element analysis on the crack driving force induced by void formation. This paper is concluded with a future perspective on applying the kinetic analysis and damage mechanism developed to investigate the structural reliability of the through-Si-via in 3D interconnects.

Experimental determination and thermodynamic calculation of the phase equilibria in the Cu–Cr–Nb and Cu–Cr–Co systems

Phase equilibria in the Cu–Cr–Nb and Cu–Cr–Co systems were, respectively, determined by metallography, X-ray diffraction (XRD) and scanning electron microscopy–energy dispersive X-ray (SEM–EDX) techniques. The thermodynamic assessments of the Cu–Cr–Nb and Cu–Cr–Co systems were carried out by using CALPHAD (CALculation of PHAse Diagrams) method on the basis of the experimental data measured by the present and previous works. The Gibbs free energies of the liquid and solid solution phases were described by the subregular solution model, and those of intermetallic compounds were described by the sublattice model. A consistent set of the thermodynamic parameters has been obtained, and the evaluated thermodynamic parameters lead to a better fit between calculated results and experimental data in both the Cu–Cr–Nb and Cu–Cr–Co systems.

The composition of dust in Jupiter-family comets inferred from infrared spectroscopy

We review the composition of Jupiter-family comet (JFC) dust as inferred from infrared spectroscopy. We find that JFCs have 10 μ m silicate emission features with fluxes roughly 20–25% over the dust continuum (emission strength 1.20–1.25), similar to the weakest silicate features in Oort Cloud (OC) comets. We discuss the grain properties that alter the silicate emission feature (composition, size, and structure/shape), and emphasize that thermal emission from the comet nucleus can have significant influence on the derived silicate emission strength. Recent evidence suggests that grain porosity is the is different between JFCs and OC comets, but more observations and models of silicates in JFCs are needed to determine if a consistent set of grain parameters can explain their weak silicate emission features. Models of 8 m telescope and Spitzer Space Telescope observations have shown that JFCs have crystalline silicates with abundances similar to or less than those found in OC comets, although the crystalline silicate mineralogy of comets 9P/Tempel and C/1995 O1 (Hale-Bopp) differ from each other in Mg and Fe content. The heterogeneity of comet nuclei can also be assessed with mid-infrared spectroscopy, and we review the evidence for heterogeneous dust properties in the nucleus of comet 9P/Tempel. Models of dust formation, mixing in the solar nebula, and comet formation must be able to explain the observed range of Mg and Fe content and the heterogeneity of comet 9P/Tempel, although more work is needed in order to understand to what extent do comets 9P/Tempel and Hale-Bopp represent comets as a whole.

Thermodynamic description of the C-Fe-Mn system with key experiments and its practical applications

Abstract Based on the critically reviewed experimental data available in the literature, new phase transition temperatures and phase equilibria at 800 °C close to the Cu-Fe side of the Cu-Fe-Mn system were measured in the present work. The composition-invariant (γFe, γMn) → (αFe) massive transformations were observed in the two quenched alloys in the Fe-rich region. A set of consistent thermodynamic parameters of the Cu-Fe-Mn system was then obtained by taking into account all kinds of experimental data. Comparisons between the calculated and measured phase diagrams indicate that most of the experimental information is satisfactorily described by the present thermodynamic modeling. The liquidus isolines, liquidus projection and reaction scheme of this ternary system are also presented. Significant improvements have been made, compared with the previous assessments. The presently obtained parameters were applied in successfully solving the !surface fissure" during hot rolling of steel and controlling the micro-structure of the Cu-Fe based alloys in rapid solidification.

Absolute line intensities measurements and calculations for the 5.7 and 3.6 μm bands of formaldehyde

The goal of this study is to achieve absolute line intensities for the strong 5.7 and 3.6 μm bands of formaldehyde and to generate, for both spectral regions, an accurate list of line positions and intensities. Both bands are now used for the infrared measurements of this molecule in the atmosphere. However, in the common access spectroscopic databases there exists, up to now, no line parameters for the 5.7 μm region, while, at 3.6 μm, the quality of the line parameters is quite unsatisfactory. High-resolution Fourier transform spectra were recorded for the whole 1600–3200 cm −1 spectral range and for different path-length-pressure products conditions. Using these spectra, a large set of H 2CO individual line intensities was measured simultaneously in both the 5.7 and 3.6 μm spectral regions. From this set of experimental line strength which involve, at 5.7 μm the ν 2 band and, at 3.6 μm, the ν 1 and ν 5 bands together with nine dark bands, it has been possible to derive a consistent set of line intensity parameters for both the 5.7 and 3.6 μm spectral regions. These parameters were used to generate a line list in both regions. For this task, we used the line positions generated in [Margulés L, Perrin A, Janeckovà R, Bailleux S, Endres CP, Giesen TF, et al. Can J Phys, accepted] and [Perrin A, Valentin A, Daumont L, J Mol Struct 2006;780–782:28–42] for the 5.7 and 3.6 μm, respectively. The calculated band intensities derived for the 5.7 and 3.6 μm bands are in excellent agreement with the values achieved recently by medium resolution band intensity measurements. It has to be mentioned that intensities in the 3.6 μm achieved in this work are on the average about 28% stronger than those quoted in the HITRAN or GEISA databases. Finally, at 3.6 μm the quality of the intensities was significantly improved even on the relative scale, as compared to our previous study performed in 2006.

Excitonic polarons in quasi-one-dimensional LH1 and LH2 bacteriochlorophyll a antenna aggregates from photosynthetic bacteria: A wavelength-dependent selective spectroscopy study

Spectral characteristics of the optically excited states in the ring-shaped quasi-one-dimensional aggregates comprising 18 and 32 tightly coupled bacteriochlorophyll a molecules have been investigated using selective spectroscopy methods and theoretical modelling of the data. Distinguished by the lowest electronic transition energies in the LH2 and LH1 antenna complexes these aggregates govern the functionally important ultrafast funneling of solar excitation energy in the photosynthetic membranes of purple bacteria. It was found by using a sophisticated differential fluorescence line narrowing method that exciton–phonon coupling in terms of the dimensionless Huang–Rhys factor is strong in these systems, justifying an excitonic polaron theoretical approach for the data analysis. Although we reached this qualitative conclusion already previously, in this work essential dependence of the exciton–phonon coupling strength and reorganization energy on excitation wavelength as well as on excitation light fluence has been established. We then show that these results corroborate with the properties of excitonic polarons in diagonally disordered ensembles of the aggregates. Furthermore, the weighted density of states of the phonon modes, which is an important characteristic of dynamical systems interacting with their surroundings, was derived. Its shape, being similar for all studied circular aggregates, deviates significantly from a reference profile describing local response of a protein to the Q y electronic transition in a single bacteriochlorophyll a molecule. Similarities of the data for regular and B800 deficient mutant LH2 complexes indicate that the B800 pigments have no direct influence on the electronic states of the B850 aggregate system. Consistent set of model parameters was determined, unambiguously implying that excitonic polarons, rather than bare excitons are proper lowest-energy optical excitations in the LH1 and LH2 antenna complexes.

Conduction mechanisms during the growth of Pd thin films: Experiment and model

The conduction mechanisms in different growth stages of Pd thin films are investigated in detail. Special attention is paid to the transition regions between the different stages of film growth and the dominant conduction mechanisms. Mechanisms of thermally activated tunneling, percolation conduction, and continuous film conduction are considered and a consistent set of model parameters is deduced. This is done by also varying the substrates. Activation energies of tunneling on the order of 50 meV, percolation thresholds ${p}_{c}=0.70\ifmmode\pm\else\textpm\fi{}0.01$, and conduction exponents $\ensuremath{\mu}=2.43\ifmmode\pm\else\textpm\fi{}0.12$ were achieved. The physical meaning of the model parameters is discussed and connected mechanisms are proposed. The minimal film thicknesses of continuous RT-sputtered Pd films were found to be on the order of 1.5 nm.