Constant Number Density Research Articles

Numerical Simulation of Flashing Flows in a Converging–Diverging Nozzle with Interfacial Area Transport Equation

Flashing flows of initially sub-cooled water in a converging–diverging nozzle is investigated numerically in the framework of the two-fluid model (TFM). The thermal non-equilibrium effect of phase change is considered by an interfacial heat transfer model, while the pressure jump across the interface is ignored. The bubble size distribution induced by nucleation, bubble growth/shrinkage, coalescence, and breakup is described based on the interfacial area transport equation (IATE) and constant bubble number density model (CBND), respectively. The results are compared with the experimental data. Satisfactory prediction of the axial pressure distribution along the nozzle as well as the flashing inception, is achieved by the TFM-IATE coupling method. It was also found that the vapor production in the diverging section was overpredicted, and the radial gas volume fraction distribution deviated from the experiment. The radial diameter profiles exhibit opposite patterns at the nozzle throat and near the outlet, and similar trends can be observed for the superheated degree. A poly-disperse method is suggested to be introduced to describe the evolution of interfacial area concentration.

A Direct Measurement of Galaxy Major and Minor Merger Rates and Stellar Mass Accretion Histories at Z < 3 Using Galaxy Pairs in the REFINE Survey

We measure the role of major and minor mergers in forming the stellar masses of galaxies over redshifts 0 < z < 3 using a combination of ∼3.25 deg2 of the deepest ground-based near-infrared imaging taken to date (Ultra Deep Survey, Ultra-VISTA, and VIDEO) as part of the collated REFINE survey. We measure the pair fraction and merger fractions for galaxy mergers of different mass ratios, and quantify the merger rate with newly measured timescales derived from the Illustris simulation as a function of redshift and merger mass ratio. For a M * > 1011 M ⊙ selection, we find that over 0 < z < 3 major mergers with mass ratios greater than 1:4 occur times on average, while minor mergers down to ratios of 1:10 occur on average times per galaxy. We also quantify the role of major and minor mergers in galaxy formation, whereby the increase in mass due to major mergers is while minor mergers account for an increase of using a M * > 1011 M ⊙ selection. We thus find that major mergers add more stellar mass to galaxies than minor mergers over this epoch. Overall, mergers will more than double the mass of massive galaxies over this epoch when selecting by stellar mass. We however find a lower increase in stellar mass when selecting by a constant number density. Finally, we compare our results to simulations, finding that minor mergers are overpredicted in Illustris and in semi-analytical models, suggesting a mismatch between observations and theory in this fundamental aspect of galaxy assembly.

Effects of adiabatic flame temperature on flames’ characteristics in a gas-turbine combustor

In this study a comparison between the premixed methane oxygen-enriched-air (CH4/O2/N2) and oxy-methane (CH4/O2/CO2) in a gas-turbine model combustor that imitates pre-mixers in operational air-fuel dry low emissions gas turbines is presented. The comparison and analyses that follow in this study are based on the results of experiments conducted. The combustion stability maps were obtained through the estimation of acoustic limits and measurement of blowout limits within the space of equivalence ratio (φ) – oxygen fraction (OF). The stability maps obtained were superimposed on the contour plots of constant adiabatic temperature (Tad), Reynolds number (Re), and power density (PD) of the combustor. Effects of Tad on flame macrostructure, flame stability, flame speed, and blowout mechanism were investigated. The temperature distributions were also measured. The study results indicated that blowout of CO2 as well as N2 flames occur at constant Tad. These results are more pronounced in the case of the multi-hole burner because, such burner is not characterized with sporadic nature of flame lifting and reattachment that dominate the occurrence of a blowout in swirl burner; for a given OF, φ at which CO2 flames blowout is higher than that of N2 flames due to the poorer resistance of oxy-flames to blowout as compared to air flames; the stable combustion zone of CO2 flames is larger than that of N2 flames.

Numerical simulation of flashing using a pressure-based compressible multiphase approach and a thermodynamic cavitation model

A recently published pressure-based compressible multiphase flow model Labois and Narayanan (2017) is validated for applications relevant to safety of pressurized systems, such as flashing of high-pressure water through valves and nozzles. The pressure-based compressible multiphase flow solver is based on non-conservative discretization of the mixture continuity equation and has the advantage of being applicable to interface tracking and n-phase mixture formulations. For simulation of flashing, two well-known cavitation models Singhal et al.(2002), Yuan et al.(2001) have been implemented along with thermodynamic effects such as latent heat of phase change, variable saturation pressure, and heat capacities. The limitations of the well-established cavitation models in terms of their applicability to compressible flows have been clarified. The model was applied to the Super Moby Dick experiment Rousseau (1987). Good flow rates, and pressure and void fraction variations were obtained for three chosen conditions by tuning the cavitation model under incompressible conditions. It was found that the void fraction stops increasing beyond the throat due to thermodynamic effects where the latent heat and heat capacity are functions of pressure and temperature. The reduction of latent heat and rapid changes in liquid and vapour heat capacities close to the saturation line at high pressures was shown to be important. The accuracy, robustness, and efficiency of the pressure-based method has been proven for flashing under strong depressurization conditions. The cavitation model predictions are strongly sensitive to model parameters such as the nucleate density making the models not general enough to be applied to different problems without calibration. It was shown that there is significant room for development of improved cavitation models especially focussing on the constant number density constraint due to the strong sensitivity of the current models to this input parameter. The assumption of incompressibility and homogeneity of the phasic velocities is also identified as serious limitations requiring further study.

"Dense diffusion" in colloidal glasses: short-ranged long-time self-diffusion as a mechanistic model for relaxation dynamics.

Despite decades of exploration of the colloidal glass transition, mechanistic explanation of glassy relaxation processes has remained murky. State-of-the-art theoretical models of the colloidal glass transition such as random first order transition theory, active barrier hopping theory, and non-equilibrium self-consistent generalized Langevin theory assert that relaxation reported at volume fractions above the ideal mode coupling theory prediction φg,MCT requires some sort of activated process, and that cooperative motion plays a central role. However, discrepancies between predicted and measured values of φg and ambiguity in the role of cooperative dynamics persist. Underlying both issues is the challenge of conducting deep concentration quenches without flow and the difficulty in accessing particle-scale dynamics. These two challenges have led to widespread use of fitting methods to identify divergence, but most a priori assume divergent behavior; and without access to detailed particle dynamics, it is challenging to produce evidence of collective dynamics. We address these limitations by conducting dynamic simulations accompanied by experiments to quench a colloidal liquid into the putative glass by triggering an increase in particle size, and thus volume fraction, at constant particle number density. Quenches are performed from the liquid to final volume fractions 0.56 ≤ φ ≤ 0.63. The glass is allowed to age for long times, and relaxation dynamics are monitored throughout the simulation. Overall, correlated motion acts to release dynamics from the glassy plateau - but only over length scales much smaller than a particle size - allowing self-diffusion to re-emerge; self-diffusion then relaxes the glass into an intransient diffusive state, which persists for φ < 0.60. We observe similar relaxation dynamics up to φ = 0.63 before achieving the intransient state. We find that this long-time self-diffusion is short-ranged: analysis of mean-square displacement reveals a glassy cage size a fraction of a particle size that shrinks with quench depth, i.e. increasing volume fraction. Thus the equivalence between cage size and particle size found in the liquid breaks down in the glass, which we confirm by examining the self-intermediate scattering function over a range of wave numbers. The colloidal glass transition can hence be viewed mechanistically as a shift in the long-time self-diffusion from long-ranged to short-ranged exploration of configurations. This shift takes place without diverging dynamics: there is a smooth transition as particle mobility decreases dramatically with concomitant emergence of a dense local configuration space that permits sampling of many configurations via local particle motion.

Unbiased Differential Size Evolution and the Inside-out Growth of Galaxies in the Deep CANDELS GOODS Fields at 1 ≤ z ≤ 7

Abstract We present a size analysis of a sample of ∼49,000 galaxies from the Cosmic Assembly Near-infrared Deep Extragalactic Survey GOODS North and South fields, using redshift-independent relative surface-brightness metrics to determine an unbiased measure of the differential size evolution of galaxies at 1 ≤ z ≤ 7. We introduce a novel method of removing foreground objects from distant galaxy (z &gt; 3) images that makes use of the Lyman break at 912 Å, in what we call “2D Lyman-break imaging.” The images used are in the rest-frame optical at z &lt; 3 and progressively bluer bands at z &gt; 3. They are therefore subject to K-correction and cosmological dimming effects, which are tested and corrected for. We separately consider a mass-selected sample (with masses in the range 109 M ⊙ ≤ M * ≤ 1010.5 M ⊙) and a number-density-selected sample (using a constant number density of n = 1 × 10−4Mpc−3). Instead of utilizing the commonly used, but potentially biased, effective radii for size measurements, we measure the redshift-independent Petrosian radius, defined by the parameter η, for each galaxy for three values of η, and use this as a proxy for size. The evolution of the measured radii can be described by a power law of the form R Petr = α(1+z) β kpc where β &lt; 0. We find that the outer radius increases more rapidly, suggesting that as a galaxy grows, mass is added to its outer regions via an inside-out growth. This growth is stronger for the number-density-selected sample, with a growth rate of nearly three in the outer radii compared to the inner. We test and confirm these results using a series of image simulations.

Stellar Mass Growth of Brightest Cluster Galaxy Progenitors in COSMOS Since z ∼ 3

Abstract We examine the role of environment on the in situ star formation (SF) hosted by the progenitors of the most massive galaxies in the present-day universe, the brightest cluster galaxies (BCGs), from z ∼ 3 to present in the COSMOS field. Progenitors are selected from the COSMOS field using a stellar mass cut motivated by the evolving cumulative comoving number density of progenitors within the Illustris simulation, as well as the Millennium-II simulation and a constant comoving number density method for comparison. We characterize each progenitor using far-ultraviolet–far-infrared observations taken from the COSMOS field and fitting stellar, dust, and active galactic nucleus components to their spectral energy distributions. Additionally, we compare the SF rates of our progenitor sample to the local density maps of the COSMOS field to identify the effects of environment. We find that BCG progenitors evolve in three stages, starting with an in situ SF-dominated phase (z &gt; 2.25). This is followed by a phase until z ∼ 1.25 where mass growth is driven by in situ SF and stellar mass deposited by mergers (both gas rich and poor) on the same order of magnitude independent of local environment. Finally, at low redshift dry mergers are the dominant stellar mass generation process. We also identify this final transition period as the time when progenitors quench, exhibiting quiescent NUVrJ colors.

Investigation of Atmospheric Aerosol Size Distributions from Ground-Based Solar Spectrometer Measurements Synthesized with Satellite Data

Data collected by a ground-based solar spectrometer at Collegeville, MN, was used to generate Aerosol Optical Depths (AODs) throughout the 2017 calendar year. The AOD data was then visualized at 13 selected wavelengths throughout the year and analyzed in comparison to satellite imagery, upper air charts and backwards trajectories of air masses moving towards Central Minnesota in order to determine key dates of interest that correspond to times before (20170615), during (20170729), and at the conclusion of (20170914) forest fires that burned in British Columbia (BC) during the summer of 2017. The data from these specific days were analyzed further by inputting the maximum and minimum AODs for each day into a Parameter Based Particle Swarm Optimization (PBPSO) algorithm in order to generate bimodal lognormal particle size distributions. The bimodal distributions were chosen because they carry more information about the aerosol loads across the entire spectrum of particle radii. The resulting distributions show an increase in number density and decrease in median radius in the Aitken mode during the BC forest fires and a relatively constant (within uncertainty) number density of accumulation mode particles at daily maximum AODs. Comparing the resulting bimodal lognormal distribution for daily minimum AODs (where evaporation and other diurnal effects are at a minimum) shows an increased number density of Aitken mode particles by two orders of magnitude from pre- to post-forest fires. This measured increase in the number density of smaller radii particles due to forest fires illustrates the PBPSO’s capability of distinguishing variations in atmospheric aerosol particle number size distributions in the Aitken mode based on data collected by the Kipp-Zonen PGS-100 solar spectrometer. KEYWORDS: Atmospheric Aerosol; Particle Swarm Optimization; Aerosol Optical Depth; Solar Spectrometer; Size Distributions; Forest Fire; Satellite Imagery; Upper Air Charts; Backward Trajectory

A new equation of state for homo-polymers in dissipative particle dynamics.

A chain-revised Groot-Warren equation of state (crGW-EOS) was developed and tested to describe systems of homo-oligomeric chains in the framework of dissipative particle dynamics (DPD). First, thermodynamic perturbation theory is applied to introduce correction terms that account for the reduction in pressure with an increasing number of bonds at constant bead number density. Then, this EOS is modified by introducing a set of switching functions that yields an accurate second virial coefficient in the low-density limit. The crGW-EOS offers several improvements over the revised Groot-Warren equation of state and Groot-Warren equation of state for chain molecules. We tested the crGW-EOS by using it to predict the pressure of oligomeric systems and the B2 virial coefficient of chain DPD particles for a range of bond lengths. Additionally, a method is developed for determining the strength of cross-interaction parameters between chains of different compositions and sizes and for thermal and athermal mixtures. We explored how different levels of coarse-graining affect the upper-critical solution temperature.

Acetone Tracer Laser-Induced Fluorescence (LIF) at 282 nm Excitation as a Diagnostic Tool in Elevated Pressure and Temperature Systems.

This paper provides new data at constant pressure, variable temperature and constant temperature, variable pressure over the range of temperature (295-750 K) and pressure (0.5-40 atm), in air and nitrogen bath gases at both constant number density and constant mole fraction needed to enable acetone laser-induced fluorescence (LIF) as a diagnostic tool in an elevated temperature and pressure environment. Results clearly indicate that the effect of elevated pressure on the temperature sensitivity of acetone LIF is negligible when the excitation wavelength is chosen near the absorption maximum, making acetone LIF ideal for measuring temperature fields in high-pressure systems. The data also show that the temperature sensitivity of fluorescence is relatively insensitive to changes in pressure at 282 nm excitation. Furthermore, at 282 nm, fluorescence per mole fraction can be used to extract temperature while fluorescence per molecule is relatively insensitive to temperature, making it optimal for concentration or pressure measurements.

Complex transients in power modulated inductively-coupled chlorine plasmas

Time-dependent studies of power-modulated chlorine inductively-coupled plasmas are presented. Power at 13.56 MHz applied to the plasma was modulated between high and low power states. Time-resolved optical emission, power delivery, and Langmuir probe measurements revealed at least two conditions upon switching from high to low power: a ‘normal’ mode in which electron temperature (Te) remains constant, while electron and ion number densities (ne and n+) and optical emission spectroscopic (OES) intensities smoothly drop to a level roughly equal to the fractional drop in power, and an ‘abnormal’ mode in which ne, n+ and OES intensities plummet before the plasma re-ignites and these values rise to levels more commensurate with the drop in power. Whether the plasma operates in the normal or abnormal mode is sensitive to impedance matching conditions and is also a function of pressure and pulsing parameters. This ignition delays in the abnormal mode can be qualitatively understood in terms of a power balance model commonly used to explain instability-induced, self-modulation in highly electronegative plasmas, caused by the slower time response of negative ions compared with electrons. The study indicates that power modulation for added control in processes such as plasma etching will require careful measurement and possibly control of power with microsecond resolution.

Flux effects in precipitation under irradiation – Simulation of Fe-Cr alloys

Radiation-enhanced precipitation of Cr-rich α′ in irradiated Fe-Cr alloys, which results in hardening and embrittlement, depends on the irradiating particle and the displacement per atom (dpa) rate. Here, we utilize a Cahn-Hilliard phase-field based approach, that includes simple models for nucleation, irradiating particle and rate dependent radiation-enhanced diffusion and cascade mixing to simulate α′ evolution under neutrons, heavy ions, and electron irradiations. Different irradiating particles manifest very different cascade mixing efficiencies. The model was calibrated using neutron data. For cascade inducing neutron/heavy-ion dpa rates at 300 °C between 10−8 and 10−6 dpa/s the model predicts approximately constant number density, decreasing radius, decreasing α′ Cr composition, and lower α′ volume fraction. The model then predicts a dramatic transition to no α’ formation above approximately 10−5 dpa/s, while electron irradiation, with weak mixing, has little effect at dpa rates up to 10−3 dpa/s. These model predictions are consistent with experiments. We explain the results in terms of the flux dependence of the radiation-enhanced diffusion, cascade mixing, and their ratio, which all vary significantly in relevant flux ranges for neutron and cascade inducing ion irradiations. These results show that both cascade mixing and radiation-enhanced diffusion must be accounted for when attempting to emulate neutron-irradiation effects using accelerated ion irradiations.

Effect of a Magnetizable Surfactant on the Motion of a Liquid Film on the Horizontal Surface

The motion of a thin liquid film of viscous incompressible fluid on the horizontal surface in the presence of a magnetizable surfactant on the free boundary in the external inhomogeneous magnetic field is investigated. Surfactant diffusion along the free surface and the dependence of the surface tension on the magnetic field strength are taken into account. The system of evolutionary equations is derived in the lubricant approximation and steady-state film flows and their stability in the case of constant film thickness and constant surfactant number density are investigated with regard to the Marangoni effect.

Modeling of bubble flows in vertical pipes with the N-phase compressible algebraic slip model

In the current work, the N-phase compressible algebraic slip model (ASM) framework is presented. The framework is implemented in TransAT© which is a commercial finite-volume CFD solver specialized in the modeling of multiphase flows. It is applied to bubbly flows in vertical pipes where compressibility of the gas phase is important. Effects of compressibility of the gas phase namely, the change in volume of the individual bubbles, the reduction in the liquid volume fraction, and the change in bubble size due to almost constant number density are identified and illustrated with the help of an analytical one-dimensional model. It was shown that the volume effect was the strongest, although the effect of the change in the bubble radius is also important though to a lesser extent.The framework implemented in TransAT© does not solve for the gas number density and assumes a fixed radius for the bubbles. In the first step the implementation is verified with the help of the one-dimensional model. In the next step, the implementation is tested against the selected test cases from the TOPFLOW database for different types of bubbly flow namely the wall-peaked, the transition and the central-peaked. The simulation results are able to predict the overall behavior of the different types of bubbly flow. The radial gas velocity profiles for all the test cases showed a good match with the experimental data. Unrealistic accumulation of small bubbles close to the walls is observed for the wall-peaked test cases. The results showed that the unrealistic behaviour could be removed tuning the wall lubrication force model. The results highlight the inadequacy of the current wall lubrication force models and show that the wall lubrication force should depend on the velocity of the continuous phase probably in an analogous way to the lift force.

Nanoscale morphogenesis of nylon-sputtered plasma polymer particles

Sub-micron polymer particles are highly important in various fields including astrophysics, thermonuclear fusion and nanomedicine. Plasma polymerization offers the possibility to produce particles with tailor-made size, crosslink density and chemical composition to meet the requirements of a particular application. However, the mechanism of nucleation and growth of plasma polymer particles as well as diversity of their morphology remain far from being clear. Here, we prepared nitrogen-containing plasma polymer particles by rf magnetron sputtering of nylon in a gas aggregation cluster source with variable length. The method allowed the production of particles with roughly constant chemical composition and number density but with the mean size changing from 80 to 320 nm. Atomic Force Microscopy with super-sharp probes was applied to study the evolution of the particle surface topography as they grow in size. Height–height correlation and power spectral density functions were obtained to quantify the roughness exponent α = 0.78, the growth exponent β = 0.35, and the dynamic exponent 1/z = 0.50. The set of critical exponents indicates that the particle surface evolves in a self-affine mode and the overall particle growth is caused by the accretion of polymer-forming species from the gas phase and not by coagulation. Redistribution of the incoming material over the surface coupled with the inhomogeneous distribution of inner stress is suggested as the main factor that determines the morphogenesis of the plasma polymer particles.

Numerical calculation of the reflection, absorption and transmission of a nonuniform plasma slab based on FDTD

In this paper, reflection, absorption and transmission characteristics of nonuniform plasma layer with varying electron number density are analyzed. The plasma number density profile is parabolic. Finite-difference time-domain (FDTD) and subslabs approximation methods are utilized and the results are validated. In FDTD, we use auxiliary differential equation (ADE) to simulate the plasma dispersive characteristics. In subslabs method, the plasma layer is divided into several thin subslabs with constant electron number density in each subslab. Partial reflection coefficients at each subslab boundary with different electromagnetic parameters are calculated. The total reflected and transmitted coefficients are then deduced using transmission line method. The reflected, transmitted and absorption power ratio with respect to the incident power is acquired. Their functional dependence on the number density, collision frequency and the distribution of number density, collision frequency is studied.

The VIMOS Public Extragalactic Redshift Survey (VIPERS)

We use the final data from the VIPERS redshift survey to extract an unparalleled sample of more than 2000 massive M > 10^11 M_sun passive galaxies (MPGs) at redshift 0.5 < z < 1.0, based on their NUVrK colours. This enables us to investigate how the population of these objects was built up over cosmic time. We find that the evolution of the number density depends on the galaxy mean surface stellar mass density, Sigma. In particular, dense (Sigma > 2000 M_sun pc^-2) MPGs show a constant comoving number density over this redshift range, whilst this increases by a factor ~ 4 for the least dense objects, defined as having Sigma < 1000 M_sun pc^-2. We estimate stellar ages for the MPG population both fitting the Spectral Energy Distribution (SED) and through the D4000_n index, obtaining results in good agreement. Our findings are consistent with passive ageing of the stellar content of dense MPGs. We show that at any redshift the less dense MPGs are younger than dense ones and that their stellar populations evolve at a slower rate than predicted by passive evolution. This points to a scenario in which the overall population of MPGs was built up over the cosmic time by continuous addition of less dense galaxies: on top of an initial population of dense objects that passively evolves, new, larger, and younger MPGs continuously join the population at later epochs. Finally, we demonstrate that the observed increase in the number density of MPGs is totally accounted for by the observed decrease in the number density of correspondingly massive star forming galaxies (i.e. all the non-passive M > 10^11 M_sun objects). Such systems observed at z ~ 1 in VIPERS, therefore, represent the most plausible progenitors of the subsequent emerging class of larger MPGs.

A consistent measure of the merger histories of massive galaxies using close-pair statistics – I. Major mergers at z &lt; 3.5

We use a large sample of $\sim 350,000$ galaxies constructed by combining the UKIDSS UDS, VIDEO/CFHT-LS, UltraVISTA/COSMOS and GAMA survey regions to probe the major merging histories of massive galaxies ($>10^{10}\ \mathrm{M}_\odot$) at $0.005 < z < 3.5$. We use a method adapted from that presented in Lopez-Sanjuan et al. (2014) using the full photometric redshift probability distributions, to measure pair $\textit{fractions}$ of flux-limited, stellar mass selected galaxy samples using close-pair statistics. The pair fraction is found to weakly evolve as $\propto (1+z)^{0.8}$ with no dependence on stellar mass. We subsequently derive major merger $\textit{rates}$ for galaxies at $> 10^{10}\ \mathrm{M}_\odot$ and at a constant number density of $n > 10^{-4}$ Mpc$^{-3}$, and find rates a factor of 2-3 smaller than previous works, although this depends strongly on the assumed merger timescale and likelihood of a close-pair merging. Galaxies undergo approximately 0.5 major mergers at $z < 3.5$, accruing an additional 1-4 $\times 10^{10}\ \mathrm{M}_\odot$ in the process. Major merger accretion rate densities of $\sim 2 \times 10^{-4}$ $\mathrm{M}_\odot$ yr$^{-1}$ Mpc$^{-3}$ are found for number density selected samples, indicating that direct progenitors of local massive ($>10^{11}\mathrm{M}_\odot$) galaxies have experienced a steady supply of stellar mass via major mergers throughout their evolution. While pair fractions are found to agree with those predicted by the Henriques et al. (2014) semi-analytic model, the Illustris hydrodynamical simulation fails to quantitatively reproduce derived merger rates. Furthermore, we find major mergers become a comparable source of stellar mass growth compared to star-formation at $z < 1$, but is 10-100 times smaller than the SFR density at higher redshifts.

Breakdown of the Stokes-Einstein relation in pure Lennard-Jones fluids: From gas to liquid via supercritical states.

We have examined the conditions under which the breakdown of the Stokes-Einstein (SE) relation occurs in pure Lennard-Jones (LJ) fluids over a wide range of temperatures and packing fractions beyond the critical point. To this end, the temperature and packing-fraction dependence of the self-diffusion coefficient, D, and the shear viscosity, η_{sv}, were evaluated for Xe using molecular dynamics calculations with the Green-Kubo formula. The results showed good agreement with the experimental values. The breakdown was determined in light oftheSE equation which we have recently derived for pure LJ liquids: Dη_{sv}=(k_{B}T/2π)(N/V)^{1/3}, where k_{B} is the Boltzmann constant, T is the temperature, and N is the particle number included in the system volume V. We have found that the breakdown occurs in the lower range of the packing fraction, η<0.2, and derived the SE relation in its broken form as Dη_{sv}=0.007(1-η)^{-5}η^{-4/3}(k_{B}T/ε)^{n}k_{B}T(N/V)^{1/3}, where n increases from 0 up to 1 with the decreasing η. The equation clearly shows that the breakdown mainly occurs because the packing-fraction dependence does not cancel out between D and η_{sv} in this region, which is attributed to the gaseous behavior in the packing-fraction dependence of the shear viscosity under a constant number density. In addition, the gaseous behavior in the temperature dependence of the shear viscosity also partially causes the breakdown.

Effect of gamma radiation on the transport and structural properties of polyacrylonitrile-lithium bis(oxalato)borate films

Different doses of gamma-rays from 5 to 35kGy have been used to irradiate solid polyacrylonitrile (PAN)-lithium bis(oxalato)borate (1:1 ratio) films in order to study their transport and structural characteristics. Impedance data show that with an increase of radiation dose, conductivity (σ) of the complexes increases and exhibits a maximum of 1.02×10−4Scm−1 at γ-ray dose of 15kGy. The obtained conductivity is about 200 times higher than that of the virgin sample (σ=1.74×10−6Scm−1). By fitting the Nyquist plots with the impedance of an equivalent circuit, it is possible to calculate the dielectric constant (εr), diffusion coefficient (D), ionic mobility (μ) and mobile ion number density (n). These parameters are highest for 15kGy irradiated samples indicating that σ, εr, D, μ and n are dependent on radiation dose. FT-IR spectroscopy confirms that ɣ-irradiation causes IR peak shifting, abolishment and reformation of functional groups of PAN-LiBOB indicating bond breaking, bond deformation and/or new bond formation. At 25 and 35kGy doses of ɣ-radiation, new peaks have been observed at 833, 877, 1072, 1160 and 1225cm−1 which may be attributed to the formation of new species. Free and contact ions in irradiated films have been calculated via deconvolution of the FTIR spectra obtained from 1750 to 1850cm−1. The sample irradiated with 15kGy ɣ-radiation contains the highest percentage of free ions and the lowest concentration of contact ions. The number density of free ions is observed to have more control on the conductivity compared to ion mobility and diffusion coefficient. XRD spectrum reveals peaks at 2θ ~16.85°, ~30.5° and ~36.9° for all irradiated samples. The polymer electrolyte irradiated with 15kGy gamma-rays is the most amorphous. The FWHM values increase with ɣ-ray doses showing maximum at 15kGy and then decreases with further increase of radiation dose. Crystallite size decreases with the increase of radiation doses, reaches lowest value at 15kGy followed by additional growths as more radiation is applied. This observation is also conceivable with the EIS and FT-IR results.