The early stage of phase separation for the system polydimethylsiloxane-diethyl carbonate

The time evolution of a ring formed by the forward scattered light in the phase separation process was found to be divided into an early and a late stage. The effective concentration diffusivity D¹ estimated within the linearized approximation in the unstable region was found to be approximately represented by -D¹∝?^v1 with v¹ ≈0.6₂, where ?=| (T-T_c)/T_c|.     

Molecular phase separation and cluster size in GeSe2 glass

The local vibrational modes and the microscopic nature of Te sites in GeSe₂-_xTe_x alloy glasses have been examined using Raman and¹²⁹I Mossbauer emission spectroscopy. Two distinct types (A, B) of chalcogen (Te) sites are observed. The Mossbauer site intensities I_B/I_A(x) reveal a power-law variation which on statistical grounds requires that these sites be formed in a cluster. The characteristic size of the cluster is found to be 60–75 A.     

Bubble size distribution in acoustic droplet vaporization via dissolution using an ultrasound wide-beam method

Performance and efficiency of numerous cavitation enhanced applications in a wide range of areas depend on the cavitation bubble size distribution. Therefore, cavitation bubble size estimation would be beneficial for biological and industrial applications that rely on cavitation. In this study, an acoustic method using a wide beam with low pressure is proposed to acquire the time intensity curve of the dissolution process for the cavitation bubble population and then determine the bubble size distribution. Dissolution of the cavitation bubbles in saline and in phase-shift nanodroplet emulsion diluted with undegassed or degassed saline was obtained to quantify the effects of pulse duration (PD) and acoustic power (AP) or peak negative pressure (PNP) of focused ultrasound on the size distribution of induced cavitation bubbles. It was found that an increase of PD will induce large bubbles while AP had only a little effect on the mean bubble size in saline. It was also recognized that longer PD and higher PNP increases the proportions of large and small bubbles, respectively, in suspensions of phase-shift nanodroplet emulsions. Moreover, degassing of the suspension tended to bring about smaller mean bubble size than the undegassed suspension. In addition, condensation of cavitation bubble produced in diluted suspension of phase-shift nanodroplet emulsion was involved in the calculation to discuss the effect of bubble condensation in the bubble size estimation in acoustic droplet vaporization. It was shown that calculation without considering the condensation might underestimate the mean bubble size and the calculation with considering the condensation might have more influence over the size distribution of small bubbles, but less effect on that of large bubbles. Without or with considering bubble condensation, the accessible minimum bubble radius was 0.4 or 1.7 μm and the step size was 0.3 μm. This acoustic technique provides an approach to estimate the size distribution of cavitation bubble population in opaque media and might be a promising tool for applications where it is desirable to tune the ultrasound parameters to control the size distribution of cavitation bubbles.     

Influence of selective heating on the kinetics of the late stage of first-order phase transitions

The effect of radiation on the kinetics of the late stage of first-order phase transitions (Ostvald ripening) was studied. In particular, features of the growth kinetics of nuclei were revealed in relation to their size and time of exposure to radiation. Possible approaches to controlling the nucleus growth kinetics were shown.     

Difference in the dynamic scaling behavior of droplet size distribution for coalescence under pulsed and continuous vapor delivery

Dynamic scaling behavior of the droplet size distribution in the coalescence regime for growth by pulsed laser deposition is studied experimentally and by computer simulation, and the same is compared with that for continuous vapor deposition. The scaling exponent for pulsed deposition is found to be (1.2 +/- 0.1), which is significantly lower as compared to that for continuous deposition (1.6 +/- 0.1). Simulations reveal that this dramatic difference can be traced to the large fraction of multiple droplet coalescence under pulsed vapor delivery. A possible role of the differing diffusion fields in the two cases is also suggested.     

The phase separation line in the two-dimensional Ising model

We prove that, at low temperature, the line of separation between the two pure phases shows large fluctuations in shape. This implies the translation invariance of the correlation functions associated with some non translation invariant boundary conditions and should be a peculiarity of the dimensionality of the model.This work has been partially supported by the Consiglio Nazionale delle Ricerche (Gruppo Nazionale per l'Analisi Funzionale): CNR(GNAFA).     

Ultrasound emulsification: effect of ultrasonic and physicochemical properties on dispersed phase volume and droplet size

Ultrasonic emulsification of oil and water was carried out and the effect of irradiation time, irradiation power and physicochemical properties of oil on the dispersed phase volume and dispersed phase droplet size has been studied. The increase in the irradiation time increases the dispersed phase volume while decreases the dispersed phase droplets size. With an increase in the ultrasonic irradiation power, there is an increase in the fraction of volume of the dispersed phase while the droplet size of the dispersed phase decreases. The fractional volume of the dispersed phase increases for the case of groundnut oil-water system while it is low for paraffin (heavy) oil-water system. The droplet size of soyabean oil dispersed in water is found to be small while that of paraffin (heavy) oil is found to be large. These variations could be explained on the basis of varying physicochemical properties of the system, i.e., viscosity of oil and the interfacial tension. During the ultrasonic emulsification, coalescence phenomenon which is only marginal, has been observed, which can be attributed to the collision of small droplets when the droplet concentration increases beyond a certain number and the acoustic streaming strength increases.     

The droplet in the tube: A case of phase transition in the canonical ensemble

We consider the 2-dimensional Ising model with ferromagnetic nearest neighbour interaction at inverse temperature. LetS _N = _t be the total magnetization inside anN×N square box, ^per be the Gibbs state in with periodic b.c., andm() be the spontaneous magnetization. We show the existence of the limit

The rigidity of the surface of phase separation in the ising ferromagnet

A model due to Onsager and Temperley for the interface between thermodynamic phases in classical lattice gases is examined. It is found that a field is needed for stabilisation in two dimensions; in three dimensions, on the other hand, the interface is localised, unlike the drumhead model without cutoff.     

The temporal evolution of the city size distribution

We present an application of a growth model for a system of cities. This computer model simulates the evolution of systems with measurable entities (e.g. city size), and takes into account the growth of the entities in terms of size and number. It includes a random multiplicative process for the growth of individual entities and for the creation of new ones. We use a new mathematical expression with a positive exponent α (which we call the ‘shape exponent’) and additional three parameters, to describe the dynamics of the systems’ size distributions through time. We compare the changes of a real system of cities and the model’s results quantitatively and qualitatively. Our findings suggest that there is a good agreement at the macro level between the model and the real data.     

The grain size distribution in nanocomposite films

The grain size distributions and related mechanisms in nanocomposite films with nanostructures comprising a nanocrystalline (nc) phase surrounded by an amorphous (a) matrix under different amorphous phase amounts (V _a) have been analyzed by using a Monte Carlo grain growth model. The results show that with the V _a value increasing to a critical value of ～28%, the grain size distribution approaches lognormality, and it becomes off-lognormal when the V _a value is larger or smaller than ～28%. The simulated results are in a good agreement with the experiment. It is shown that the homogenous or inhomogeneous grain growth mode, determined by the energy exerted on the grain boundary, originates in lognormal or off-lognormal grain size distributions in nanocomposite films. Also, in a system with lognormal grain size distribution, the amorphous phase just covers all grain boundaries (GBs) and the length obtained by summing the boundary circumference of all nanograins is the longest. It is expected that this microstructure can result in exceptional properties of nanocomposite films.     

Correlations to predict droplet size in ultrasonic atomisation.

In conventional two fluid nozzles, the high velocity air imparts its energy to the liquid and disrupts the liquid sheet into droplets. If the energy for liquid sheet fragmentation can be supplied by the use of ultrasonic energy, finer droplets with high sphericity and uniform size distribution can be achieved. The other advantage of ultrasound induced atomisation process is the lower momentum associated with ejected droplets compared to the momentum carried by the droplets formed using conventional nozzles. This has advantage in coating and granulation processes. An ultrasonic probe sonicator was designed with a facility for liquid feed arrangement and was used to atomise the liquid into droplets. An ingenious method of droplet measurement was attempted by capturing the droplets on a filter paper (size variation with regard to wicking was uniform in all cases) and these are subjected to image analysis to obtain the droplet sizes. This procedure was evaluated by high-speed photography of droplets ejected at one particular experimental condition and these were image analysed. The correlations proposed in the literature to predict droplet sizes using ultrasound do not take into account all the relevant parameters. In this work, a truly universal correlation is proposed which accounts for the effects of physico-chemical properties of the liquid (flow rate, viscosity, density and surface tension), and ultrasonic properties like amplitude, frequency and the area of vibrating surface. The significant contribution of this work is to define dimensionless numbers incorporating ultrasonic parameters, taking cue from the conventional numbers that define the significance of different forces involved in droplet formation. The universal correlations proposed are robust and can be used for designing ultrasonic atomisers for different applications. Among the correlations proposed here, those ones that are based on the dimensionless numbers and Davies approach predict droplet sizes within acceptable limits of deviation. Also, an empirical correlation from experimental data has been proposed in this work.     

Experimental studies on droplet characteristics in a microfluidic flow focusing droplet generator: effect of continuous phase on droplet encapsulation

The European Physical Journal E - Interaction of cytoskeletal filaments, motor proteins, and crosslinking proteins drives important cellular processes such as cell division and cell movement....     

On the dynamics of phase separation

A new framework is developed for a treatment of the unmixing of an alloy or another system undergoing a phase transition after a quench into the coexistence region. Expanding around a suitably chosen reference equilibrium state new order parameter fields are introduced by a regrouping of diagrams. In a path integral representation the action of the new fields is constructed in a renormalized form and calculated by expansion ind=4– dimensions. As a first application the timedependence of the structure factor is computed using a simple factorization. It is found that unmixing takes place in the whole coexistence régime with a lifetime of metastable states which diverges at the coexistence curve and with no sharp boundary between the spinodale and nucleation régime.     

The atomization current and droplet size of ethanol in two different small-scale electro-spraying systems

An experimental study on electro-spraying from small-scale combustors is carried out using liquid ethanol as fuel. Two systems of electro-spraying are employed in the present study; one is a nozzle system (without a ring electrode) and the other is a nozzle-ring system (with a ring electrode). The photos of electro-spraying at the cone-jet mode are taken by a digital camera. The voltage drop across the resistance in the loop is measured by a data acquisition instrument, and the atomization current is calculated according to Ohm's Law. The size and velocity of electro-spraying droplets are measured by a Phase Doppler Anemometer. A non-dimensional analysis on atomization current is completed to explain the electro-spraying phenomena of liquid at the stable cone-jet mode. The results show that, the lower atomization current and droplet velocity corresponds to smaller size of droplet. Based on the results of non-dimensional analysis, it is found that the dimensionless atomization current in both the nozzle system and nozzle-ring system obeys the scaling law as square root of the dimensionless flow rate. The charge density is of a −1.5 power dependence on droplet diameter. Both of the nozzle and the nozzle-ring systems show a good agreement with Rayleigh instability.     

Constraining the initial phase in water-fat separation

An algorithm is described for use in chemical shift-based water-fat separation to constrain the phase of both species to be equal at an echo time of zero. This constraint is physically reasonable since the initial phase should be a property of the excitation pulse and receiver coil only. The advantages of phase constrained water-fat separation, namely, improved noise performance and/or reduced data requirements (fewer echos), are demonstrated in simulations and experiments.     

Electronic phase separation in La-Cuprates

The mechanisms driving the phase separation in high-T _c La cuprates is studied by magnetic susceptibility and electrical resistivity measurements. The experiments are performed under different thermal treatment. Three temperature ranges can be resolved characteristic for different physical processes: At 150T170K a space limited diffusion of superparamagnetic clusters (single hole clusters) occurs leading to the formation of a small but rather tight percolative subphase which at highT _c values becomes superconducting. Above 180 K the cluster motion becomes unrestricted in space and a more extended subphase is built up, however, with lowerT _c values. Above 230 K oxygen diffusion starts leading to an unexpected destruction of the conducting/superconducting phase.