Initial Stages Of Transition Research Articles

On the Theory of Structural Transformations in Magnetic Fluids

Results of studying a new scenario of condensation phase transition in the ensemble of ferrofluid particles are reported. Phase transition in this ensemble starts with the formation of chain clusters. Chains whose length exceeds a certain critical value dependent on temperature and magnetic field undergo collapse and are transformed into very dense globules. The globule evolution leads to the separation of ferrofluid into two phases with different particle density. Initial (chain collapse) and final (equilibrium) stages of phase transition are investigated. Calculations of the critical length of a chain corresponding to its collapse, as well as the characteristics of dense phase at the final separation stage are in good agreement with the results of known experiments.

Inactivation and aggregation of beta-galactosidase in lyophilized formulation described by Kohlrausch-Williams-Watts stretched exponential function.

To examine whether the empirical Kohlrausch-Williams-Watts (KWW) equation is applicable not only to protein aggregation but also to protein denaturation in lyophilized formulations. Lyophilized beta-galactosidase (beta-GA) formulations containing polyvinylalcohol and methylcellulose were used as model formulations. The possibility of predicting storage stability based on the temperature dependence of the estimated parameters of inactivation/aggregation--time constant (tau) and its distribution (beta) is discussed. Protein aggregation in lyophilized beta-GA formulations at 10-70 degrees C and 6-43% relative humidity was determined as a function of time by size exclusion chromatography. Enzyme activity was also determined using 2-nitrophenyl-beta-D-galactopyranoside as a substrate. Inactivation and aggregation of beta-GA were describable with the empirical KWW equation, regardless of whether the temperature was above or below the NMR relaxation-based critical mobility temperature (Tmc) or whether protein molecules with different degrees of deformation resulting from stresses during lyophilization exist in formulation. The estimated beta parameter for protein aggregation creased rapidly as temperature increased beyond Tmc becausethe mobility of polymer molecules increased in the initial stages of glass transition. The time required for 10% enzyme to aggregate (t90) calculated from the tau and beta parameters exhibited a change in temperature dependence gradient near Tmc. In contrast, t90 for protein inactivation exhibited temperature dependence patterns varying withthe excipients. The t90 calculated from the estimated tau and beta parameters was found to be a useful parameter for evaluating the stability of lyophilized beta-GA formulations. The prediction of t90 by extrapolation was possible in the temperature range in which beta did not rapidly vary with temperature.

Investigation of relaxations in polystyrene–polyoxyethylene copolymer by thermally stimulated current

The diblock copolymer containing 43.5 wt.% of polystyrene (PS) (M w =15 000) and polyoxyethylene (POE) (M w =19 500) was investigated by integral and by partial thermally stimulated depolarization current (TSDC) measurements in the temperature range of 173–293 K. The first peak P 1, widely distributed from 183 to 213 K, was a dipolar peak attributed to the initial stage of glass transition in POE. The second peak P 2, with a maximum at 273 K, was due to glass transition. The third peak P 3, with a maximum at about 263 K, was caused by the space charge relaxation localized at the interfaces between the ordered and nonordered phases in POE, Maxwell–Wagner relaxation, representing a precursor in melting of POE crystals. The results were supported by determination of activation energy E a of the partial peaks, which covered the whole range of investigation, and by differential scanning calorimetry (DSC) measurements. The E a( T) distribution showed a maximum in entropy change at 219±4 K. Some runs with samples containing different amounts of the PS component were considered. All the relaxations were coming from the POE block. The current due to PS slightly overlapped the total spectra without interaction. The influence of the repeated runs was observed and discussed.

Returning a Favor: Reciprocity Between Female Education and Fertility in India

In this paper, an attempt has been made to show that while at the initial stages of demographic transition it is the education of females that exerts significant negative effect on fertility, as the transition progresses, this effect tends to weaken, and the dominant pattern changes to one wherein it is the fertility level that exerts significant negative influence on educational attainment of children, especially of girls. By using crosstabular data from censuses and surveys, it is shown that much of the recent reduction in fertility and the rise in contraceptive levels in India has come, not from more women becoming literate over time, but from the changes in the reproductive behavior of illiterate women themselves. Further, using micro-level data from a national survey, it is shown that illiterate parents, while regulating their fertility, send more of their children to school. The first-born daughter appears to be the greatest beneficiary of the changing emphasis on quality over quantity in reproductive outcomes, as she is released from the burden of attending to younger siblings.

Self-similar states in turbulent mixing layers

Large-eddy simulations of temporally evolving turbulent mixing layers have been carried out. The effect of the initial conditions and the size of the computational box on the turbulent statistics and structures is examined in detail. A series of calculations was initialized using two different realizations of a spatially developing turbulent boundary-layer with their free streams moving in opposite directions. Computations initialized with mean flow plus random perturbations with prescribed moments were also conducted. In all cases, the initial transitional stage, from boundary-layer turbulence or random noise to mixing-layer turbulence, was followed by a self-similar period. The self-similar periods, however, differed considerably: the growth rates and turbulence intensities showed differences, and were affected both by the initial condition and by the computational domain size. In all simulations the presence of quasi-two-dimensional spanwise rollers was clear, together with ‘braid’ regions with quasi-streamwise vortices. The development of these structures, however, was different: if strong rollers were formed early (as in the cases initialized by random noise), a well-organized pattern persisted throughout the self-similar period. The presence of boundary layer turbulence, on the other hand, inhibited the growth of the inviscid instability, and delayed the formation of the roller–braid patterns. Increasing the domain size tended to make the flow more three-dimensional.

Modelling of the thermal history of a non-spherical molten metal droplet during solidification

A mathematical model to describe the thermal history of an atomised non-spherical droplet during solidification is formulated. Four distinct solidification stages, the initial transition stage, the rapid solidification stage, the slow solidification stage, and the final transition stage, have been identified. As the initial undercooling increases, the extent of the initial transition stage is smaller, and the recalescence temperature range becomes larger. The extent of the rapid solidification stage is larger, and the extents of the slow solidification and the final transition stages are smaller for larger initial undercooling. The final recalescence temperature is lower for larger initial undercooling. The release rate of the latent heat is smaller and the cooling rate is more dominant for the elliptical metal droplets than for the spherical droplets. The extent of the initial transition stage is smaller and the final recalescence temperature is lower for elliptical droplets.

Initiation systems using secondary explosives

The paper reports the main results of the work on designing initiation systems and firing devices for industrial use, primarily in metal working, that was begun in 1961 at the Institute of Hydrodynamics and headed for a long time by Academician M. A. Lavrent’ev. Within the framework of this work, basic research on the initial stages of detonation transition was performed and the ablative mechanism of combustion of melting explosives, which, in particular, distinguishes them from smokeless powders, was revealed and studied. A dynamic initiation studies have been used to design industrial explosive devices for metal working and initiation systems for mechanized priming in hydroexplosive forming and synthesis of ultradisperse diamonds.

Effect of grain size on friction and wear behavior of Ti 3SiC 2

The effects of grain size on the sliding friction, sliding wear, and two-body abrasive wear behavior of Ti 3SiC 2 were investigated. Samples with two different grain sizes, namely, 5 μm (`fine') and 100 μm (`coarse'), were used as discs in pin-on-disc sliding wear tests against a 440C steel pin and as rectangular pins in diamond belt abrasion tests. In the pin-on-disc test, irrespective of the grain size, it was found that the material undergoes an initial transition stage where the friction coefficient, μ, increases linearly to 0.15 to 0.45. After this transition stage, μ rises to steady state values, of about 0.83 for both coarse- and the fine-grained materials. It was concluded that the transition from the low to high μ is due to accumulation of debris entrapped between the disc and the pin, resulting in third-body abrasion. The average sliding wear rates in the pin-on-disc tests were 4.25×10 −3 and 1.34×10 −3 mm 3/N m for the fine and the coarse grains, respectively. In the diamond belt abrasion tests, the average wear rates were much higher: 6.14×10 −2 and 3.96×10 −2 mm 3/N m for the fine and the coarse grains, respectively. In the fine-grained material, it was concluded that the wear mechanisms include grain pre-fracture and removal. Delamination, crack bridging, grain deformation, microcracking, and grain fracture are the operative wear mechanisms observed in the case of the coarse-grained material. It is this multitude of possible sliding energy dissipation mechanisms that is believed to enhance the wear resistance of the coarse-grained material relative to the fine-grained one.

605 管内流の遷移初期に発生する乱流パフ及びスラグの構造

605 管内流の遷移初期に発生する乱流パフ及びスラグの構造

Nonlinear spectral dynamics of hypersonic laminar boundary layer flow

The nonlinear interactions of the instability modes in a hypersonic laminar boundary layer undergoing natural transition are examined using bispectral analysis. The data are from an experiment of a boundary layer flow on a cooled-wall cone in a low-level free-stream disturbance hypersonic wind tunnel, and thus, the bispectral measurements are a good representation of the natural transition processes. The bispectral analysis shows that in the initial stages of transition the dominant nonlinear interaction is forcing by the fundamental to generate a harmonic. Subsequently, mutual forcing of the fundamental and harmonic yield a second harmonic. Difference interactions within the band of unstable disturbances centered on the fundamental and harmonic also generate a low frequency nonlinear interaction. At high amplitudes of the fundamental and harmonic a nonlinear interaction characterized by a low frequency modulation of the fundamental and harmonic then follows. This nonlinear interaction is then the most dominant and precedes the breakdown of the laminar flow.

Job Rights in Russian Firms: Endangered or Extinct Institution?

Did the Soviet institution of job rights, guaranteed employment despite individual or firm performance, survive the initial stages of transition in the Russian economy? This paper employs survey data collected in 1992 and 1995 to evaluate the extent to which job rights continued to influence the behavior of firms and households three years after Russia inititated its reform program. Using a variety of measures, the results indicate that, while job rights might have been an endangered institution in 1995, the institution does not appear to have been rendered extinct.

Real-Time Observation of a Metastable State during the Phase Transition in Shocked Cadmium Sulfide

A method was developed to perform ps time-resolved electronic spectroscopy in shock wave experiments, and used to examine the initial stages of the phase transition in CdS. Changes in the electronic spectra were observed with 100 ps resolution in single crystals shocked to stresses between 3.6--8.8 GPa. The absorption results suggest that the initial stage of the transition is characterized by a very rapid transformation to an indirect band gap material. Along with earlier ns continuum data, these results make a strong case for a metastable state during the phase transition in shocked CdS.

Effect of colour singletness of quark-gluon plasma in quark-hadron phase transition

Consequences of the constraint of SU(3) colour singletness of quark-gluon plasma are studied. This restriction increases the free energy barrier for the formation of hadronic bubble in supercooled phase and influences significantly the dynamics of the initial stage of quark-hadron phase transition. It also introduces terms dependent on the volume occupied by the plasma in the energy density and the pressure. These modifactions vanish in the limit of an infinite volume. The last stage of the hadronization of the QGP likely to be formed in relativistic heavy ion collisions is necessarily characterized by a decreasing volume containing the quark matter, and thus these corrections become important. The nucleation of plasma droplets at AGS energies is also seen to be strongly affected by the requirement of colour singletness, and the choice of prefactor.

Effect of colour singletness of quark-gluon plasma in quark-hadron phase transition

Consequences of the constraint of SU(3) colour singletness of quark-gluon plasma are studied. This restriction increases the free energy barrier for the formation of hadronic bubble in supercooled phase and influences significantly the dynamics of the initial stage of quark-hadron phase transition. It also introduces terms dependent on the volume occupied by the plasma in the energy density and the pressure. These modifactions vanish in the limit of an infinite volume. The last stage of the hadronization of the QGP likely to be formed in relativistic heavy ion collisions is necessarily characterized by a decreasing volume containing the quark matter, and thus these corrections become important. The nucleation of plasma droplets at AGS energies is also seen to be strongly affected by the requirement of colour singletness, and the choice of prefactor.

Central Bank Independence, Inflation, and Growth in Transition Economies

In this paper, we document two empirical relationships that have emerged as the former communist countries have taken steps to transform their economies from command systems to market-based systems. First, increased central bank independence has tended to improve inflation performance. Second, high inflation has adversely affected real activity. More specifically, in the first section of this paper, we develop indices of central bank independence (CBI) for twelve transition economies and examine the relationship between CBI and inflation performance across these countries. Statistical evidence suggests that the transition economies with more independent central banks have achieved lower inflation than their counterparts. The second section of this paper studies the relationship between inflation and growth in twenty-six transition economies. We present econometric evidence indicating that reducing inflation helps stabilize economic activity, following the sharp output declines that occur during the initial stages of transition. The paper conc1udes that establishing an independent central bank is a concrete institutional reform that may reduce inflation and thus facilitate economic growth.

High-temperature oxidation of Al-deposited stainless-steel foils

The oxidation resistance of Al-deposited Fe−Cr−Al foils containing small amounts of La and Ce was assessed by a cyclic oxidation test with temperature varying between room temperature and 1323 K to 1423 K in static air. (1) The Al content of Fe−Cr−Al−La, Ce foils can be increased by depositing an Al layer from the vapor phase. The deposition of a 1-μm-thick Al layer on both sides of the 50-μm-thick foil is equivalent to a 1.5 mass% increase in the Al content. The deposited Al diffuses into the foil during heat treatment. The uniform distribution of Al is obtained by heating at 1273 K for 18 ks. (2) After the initial transition stage the oxidation follows the parabolic law until breakaway sets in. The scale consists mainly of α-Al2O3 during the parabolic period. (3) The increase in the Al content by more than 5 mass% by the Al-deposition remarkably improves high-temperature oxidation resistance (smaller parabolic rate constant and longer protection time). (4) The Al-deposited foils have better oxidation resistance than the conventional foils with the same contents of Al and rare-earth elements. This is attributable to the different nature of the initially formed oxide on the Al-deposited foil. (5) The so-called rare-earth element effect was also observed for the Al-deposited foils. Predominant diffusion of oxygen through the Al2O3 scale and vacancy-sink mechanism are applicable to the present results.

Central Bank Independence, Inflation and Growth in Transition Economies

In this paper, we document two empirical relationships that have emerged as the former communist countries have taken steps to transform their economies from command systems to market-based systems. First, increased central bank independence has tended to improve inflation performance. Second, high inflation has adversely affected real activity. More specifically, in the first section of this paper, we develop indices of central bank independence (CBI) for twelve transition economies and examine the relationship between CBI and inflation performance across these countries. Statistical evidence suggests that the transition economies with more independent central banks have achieved lower inflation than their counterparts. The second section of this paper studies the relationship between inflation and growth in twenty-six transition economies. We present econometric evidence indicating that reducing inflation helps stabilize economic activity, following the sharp output declines that occur during the initial stages of transition. The paper conc1udes that establishing an independent central bank is a concrete institutional reform that may reduce inflation and thus facilitate economic growth.

Critical layer thickness for self-assembled InAs islands on GaAs.

Using atomic force microscopy (AFM), we have directly observed the progression of surface morphology of InAs deposited by molecular-beam epitaxy on GaAs(100). InAs self-assembled dots (coherent) or relaxed InAs islands (incoherent) are formed depending on the InAs coverage. The InAs coverage was varied continuously and AFM was used to monitor in detail the nucleation and resulting size and shape transition of the InAs self-assembled dots. Dots of uniform size were observed only at the initial stages of this Stranski-Krastanow growth-mode transition. The self-assembled dot density increased very abruptly with total deposited amount of InAs. Treating this InAs growth-mode transition as a first-order phase transition with InAs total coverage as the critical parameter, we extract a critical thickness for surface elastic relaxation of 1.50 ML.

Multiple instabilities of three-dimensional boundary layers along a concave wall

The initial stage of laminar turbulent transition in boundary layers on a swept wing is governed by two types of instability, namely, the Tollmien-Schlichting instability based on the effect of viscosity and the cross-flow instability associated with the twisted velocity distribution of three-dimensional boundary layers. If the flow is along a locally concave surface, there is another possibility, that of Taylor–Görtler instability induced by centrifugal force. The strength of these instabilities mainly depends upon local Reynolds number, magnitude and direction of the cross-flow, and local curvature of the wall. Thus a model system of linear equations is proposed to describe the initial development of disturbances through the three instabilities, and its eigensolutions are used to evaluate stability limits of the Falkner Skan-Cooke flow to those disturbances. The three types of disturbances can be distinguished from each other by definite differences in the wavenumber and frequency regions. Three subregions in the parameter plane of cross-flow magnitude and wall curvature are determined in correspondence to the three instabilities, each of which gives the lowest value of critical Reynolds numbers in its own Subregion.

Identification of the laminar-turbulent transition process in a plasma plume

This paper illustrates the complete dynamics of the laminar-turbulent transition process in a plasma plume using a simple measurement of the magnation-point heat flux correlated with acoustic, optical, and voltage drop fluctuations. In the laminar flow regime a steady jet is produced and the heat fluxes are accurately predicted hr laminar correlations. The initial stage of transition is characterized by the formation of axisymmetric structures and velocity fluctuations which increase the heat flux over laminar correlations. This is followed by a rapid decrease in heat flux as the vortex structures become more intense and rapidly entrain external air into the plume. The plume oscillations (acoustical and voltage drop) become most intense and are identical in frequency at the point of minimum heat flux. The transition is complete which the transition to small-scale turbulence in the exiting boundary layer which results in dec reased entrainment and increased heat flux.