Spinel-Corundum Phase Equilibria in the Systems Mn-Cr-Al-O and Co-Cr-Al-O at 1373 K

The tie lines delineating ion-exchange equilibria between MCr2O4-MAl2O4 spinel solid solution, where M is either Mn or Co, and Cr2O3-Al2O3 solid solution with the corundum structure were determined at 1373 K by electron microprobe and E0AX point count analysis of the oxide phases equilibrated with metallic Co and Au-5% Mn. The component activities in the spinel solid solutions are derived from the tie lines and the thernodynamic data for Cr2O3-Al2O3 soiid solutions available hi the literature. The Gibbs free energies of mixing calculated from the experimental data are discussed in relation to the values derived from the cation distribution a.odel based on the site preference energies and assuming random mixing on both tetrahedral and octahedral sites. Positive deviations from ideality observed in this study suggest a miscibility gap for both series of spinel solid solutions at low temperatures in the absence of oxidation.

A reconsideration of phase relations in the Ti-Al-Mo and Ti-Al systems

A microstructural and X-ray investigation of Ti-AI-Mo alloys Ti-31 Al-15 Mo, Ti-31 Al-13 Mo, Ti-31Al-9Mo and Ti-35Al-9Mo (containing the Ti3Al, TiAl and β phases) indicates that the existing phase diagram of the ternary system for this composition range published by Ge Dhzhi-Min and Pylaeva is in error above 1473 K. An analysis of phase relations reveals that the error has arisen from their use of the Ti-AI diagram due to Bumps, Kessler and Hansen as a basis for generating the ternary. It is shown that a phase diagram of the ternary, consistent with the experimental results, can be generated using a version of the Ti-AI system due to Margolin. Simple geometric arguments are used to build up a new semi-quantitative description of the Ti-AI-Mo system which can be used as a basis for a detailed investigation of phase equilibria in this system.

Hydrothermal phase equilibria studies in Ln2O3---H2O systems and synthesis of cubic lanthanide oxides

Phase diagrams for the systems Ln2O3---H2O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) studied at 5000 to 10,000 psi and temperature range of 200–900°C, show that Ln(OH)3 hexagonal and LnOOH monoclinic are the only stable phases from Nd to Ho. The cubic oxide phase (C---Ln2O3) is stable for systems of Er, Tm, Yb and Lu, with no evidence of its equilibrium in the systems of lighter lanthanides. Using strong acids, HNO3 and HCOOH, as mineralisers the cubic oxides could be stabilised from Eu down to Lu. Solid solution phases of CeO2---Y2O3 and Eu2O3---Y2O3 have also been synthesised with HNO3 as mineraliser, since these compounds have promising use as solid electrolyte and phosphor materials respectively.

Mesoscale description of an asymmetric lamellar phase

The relationship between the parameters in a description based on a mesoscale free energy functional for the concentration field and the macroscopic properties, such as the bending and compression moduli and the permeation constant, are examined for an asymmetric lamellar phase where the mass fractions of the hydrophobic and hydrophilic parts are not equal. The difference in the mass fractions is incorporated using a cubic term in the free energy functional, in addition to the usual quadratic and quartic terms in the Landau–Ginsburg formulation. The relationship between the coefficient of the cubic term and the difference in the mass fractions of the hydrophilic and hydrophobic parts is obtained. For a lamellar phase, it is important to ensure that the surface tension is zero due to symmetry considerations. The relationship between the parameters in the free energy functional for zero surface tension is derived. When the interface between the hydrophilic and hydrophobic parts is diffuse, it is found that the bending and compression moduli, scaled by the parameters in the free energy functional, do increase as the asymmetry in the bilayer increases. When the interface between the hydrophilic and hydrophobic parts is sharp, the scaled bending and compression moduli show no dependence on the asymmetry in the bilayer. The ratio of the permeation constant in between the water and bilayer in a molecular description and the Onsager coefficient in the mesoscale description is O(1) for both sharp and diffuse interfaces and it increases as the difference in the mass fractions is increased.

A fluctuation-based probe to athermal phase transitions

We focus on athermal phase transitions where in discrete and dissipative avalanches are observed in physical observables as the system jumps from one metastable state to another, when driven by an external field. Using higher order statistics of time dependent avalanches, or noise, in electrical resistivity during temperature-driven martensite transformation in thin nickel-titanium films, we demonstrate evidence suggesting the existence of a singular `global instability' or divergence of the correlation length as a function of temperature at the transition. These results not only establish a mapping of non-equilibrium first order phase transition and equilibrium critical phenomena, but perhaps also call for a re-evaluation of many existing experimental claims of self-organized criticality.

Kaveriporukasta liiketoiminnaksi : Tuotannon häiriöt ja organisaation oppiminen nopeasti muuttuvassa yrityksessä

In the 1990 s the companies utilizing and producing new information technology, especially so-called new media, were also expected to be forerunners in new forms of work and organization. Researchers anticipated that new, more creative forms of work and the changing content of working life were about to replace old industrial and standardized ways of working. However, research on actual companies in the IT sector revealed a situation where only minor changes to existing organizational forms were seen .Many of the independent companies faced great difficulties trying to survive the rapid changes in the products and production forms in the emerging field. Most of the research on the new media field has been conducted as surveys, and an understanding of the actual everyday work process has remained thin. My research is a longitudinal study of the early phases of one new media company in Finland. The study is an analysis of the challenges the company faced in a rapidly changing business field and the attempts to overcome these challenges. The two main analyses in the study focus on the developmental phases of the company and the disturbances in the production process. Based on these analyses, I study changes and learning at work using the methodological framework of developmental work research. Developmental work research is a Finnish variant of the cultural-historical activity theory applied to the study of learning and transformations at work. The data was gathered over a three-year period of ethnographic fieldwork. I documented the production processes and everyday life in the company as a participant observer. I interviewed key persons, video and audio-taped meetings, followed e-mail correspondence and collected various documents, such as agreements and memos. I developed a systematic method for analyzing the disturbances in the production process by combining the various data sources. The systematic analysis of the disturbances depicted a very complex and only partly managed production process. The production process had a long duration, and no single actor had an understanding of it as a whole. Most of the disturbances had to do with the customer relationships. The nature of the disturbances was latent; they were recognized but not addressed. In the particular production processes that I analyzed, the ending life span of a particular product, a CD-ROM, became obvious. This finding can be interpreted in relation to the developmental phase of the production and the transformation of the field as a whole. Based on the analysis of the developmental phases and the disturbances, I formulate a hypothesis of the contradictions and developmental potentials of the activity studied. The conclusions of the study challenge the existing understanding of how to conceptualize and study organizational learning in production work. Most theories of organizational learning do not address qualitative changes in production nor historical challenges of organizational learning itself. My study opens up a new horizon in understanding organizational learning in a rapidly changing field where a learning culture based on craft or mass production work is insufficient. There is a need for anticipatory and proactive organizational learning. Proactive learning is needed to anticipate the changes in production type, and the life cycles of products.

Heat transfer with solid liquid phase change initiating at a point in a semi infinite mold

Short-time analytical solutions of temperature and moving boundary in two-dimensional two-phase freezing due to a cold spot are presented in this paper. The melt occupies a semi-infinite region. Although the method of solution is valid for various other types of boundary conditions, the results in this paper are given only for the prescribed flux boundary conditions which could be space and time dependent. The freezing front propagations along the interior of the melt region exhibit well known behaviours but the propagations along the surface are of new type. The freezing front always depends on material parameters. Several interesting results can be obtained as particular cases of the general results.

Theoretical study of the optimum performance of a two-phase flow CO2 gasdynamic laser

Theoretical optimization studies of the performance of a combustion driven premixed two-phase flow gasdynamic laser are presented. The steady inviscid nonreacting quasi-one-dimensional two-phase flow model including appropriate finite rate vibrational kinetic rates has been used in the analysis. The analysis shows that the effect of the particles on the optimum performance of the two-phase laser is very small. The results are presented in graphical form. Applied Physics Letters is copyrighted by The American Institute of Physics.

On prequantization to reduce errors in double phase holograms

Prequantization has been forwarded as a means to improve the performance of double phase holograms (DPHs). We show here that any improvement (even under the best of conditions) is not large enough to help the DPH to compete favourably with other holograms.

Esr study of (SO4)2- dynamics in relation to the ferroelectric phase transition in ammonium sulfate

Ferroelectric phase transition in ammonium sulfate has been studied by ESR of CrO43- radical substituting for SO42- ion in (NH4)2SO4. In addition to discontinuous changes at Tc, certain continuous changes are observed in ESR parameters of this probe below Tc, which reflect the role of the sulfate ion in the phase transition. A microscopic mechanism of the phase transition is proposed and discussed in terms of the change of orientation of the sulfate tetrahedron through a finite angle. The degree of the change of orientation below Tc is thought to be the possible order parameter of the phase transition.

Pole placement in multi-input systems via elementary transformations

This paper is concerned with the development of an algorithm for pole placement in multi-input dynamic systems. The algorithm which uses a series of elementary transformations is believed to be simpler, computationally more efficient and numerically stable when compared with earlier methods. In this paper two methods have been presented.

Predicting a new phase (T′′) of two-dimensional transition metal di-chalcogenides and strain-controlled topological phase transition

Single layered transition metal dichalcogenides have attracted tremendous research interest due to their structural phase diversities. By using a global optimization approach, we have discovered a new phase of transition metal dichalcogenides (labelled as T′′), which is confirmed to be energetically, dynamically and kinetically stable by our first-principles calculations. The new T′′ MoS2 phase exhibits an intrinsic quantum spin Hall (QSH) effect with a nontrivial gap as large as 0.42 eV, suggesting that a two-dimensional (2D) topological insulator can be achieved at room temperature. Most interestingly, there is a topological phase transition simply driven by a small tensile strain of up to 2%. Furthermore, all the known MX2 (M = Mo or W; X = S, Se or Te) monolayers in the new T′′ phase unambiguously display similar band topologies and strain controlled topological phase transitions. Our findings greatly enrich the 2D families of transition metal dichalcogenides and offer a feasible way to control the electronic states of 2D topological insulators for the fabrication of high-speed spintronics devices.

Pressure effect on the phase transition of trissarcosine calcium chloride

The dielectric measurement of ferroelectric trissarcosine calcium chloride (TSCC) was made under various pressures up to 6 kbar. A striking decrease in the peak value of the permittivity, epsilon r, at the transition temperature, Tc, was observed with increasing pressure. The value of Tc increases linearly with a pressure coefficient dTc/dp=11.1K kbar-1 at low pressures. This increase in Tc supports the suggestion that the ferroelectric transition is of the pure order-disorder type. It is suggested on the basis of the behaviour of epsilon r with pressure that the order of the ferroelectric transition changes from second to first order on application of pressure.

Internal nitride formation during gas-phase thermal nitridation of titanium

Titanium nitride surface layers were prepared by gas-phase thermal nitridation of pure titanium in an ammonia atmosphere at 1373 K for different times. In addition to the surface nitride layer, nitride/hydride formation was observed in the bulk of the specimen. The cross-section of the specimen was characterized by various techniques such as optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, secondary ion mass spectrometry and nanomechanical testing, and the mechanism of formation of these phases is discussed.

Stress-induced phase transformation and pseudo-elastic/pseudo-plastic recovery in intermetallic Ni-Al nanowires

Extensive molecular dynamics (MD) simulations have been performed in a B2-NiAl nanowire using an embedded atom method (EAM) potential. We show a stress induced B2 -> body-centered-tetragonal (BCT) phase transformation and a novel temperature and cross-section dependent pseudo-elastic/pseudo-plastic recovery from such an unstable BCT phase with a recoverable strain of similar to 30% as compared to 5-8% in polycrystalline materials. Such a temperature and cross-section dependent pseudo-elastic/pseudo-plastic strain recovery can be useful in various interesting applications of shape memory and strain sensing in nanoscale devices. Effects of size, temperature, and strain rate on the structural and mechanical properties have also been analyzed in detail. For a given size of the nanowire the yield stress of both the B2 and the BCT phases is found to decrease with increasing temperature, whereas for a given temperature and strain rate the yield stress of both the B2 and the BCT phase is found to increase with increase in the cross-sectional dimensions of the nanowire. A constant elastic modulus of similar to 80 GPa of the B2 phase is observed in the temperature range of 200-500 K for nanowires of cross-sectional dimensions in the range of 17.22-28.712 angstrom, whereas the elastic modulus of the BCT phase shows a decreasing trend with an increase in the temperature.