Micellar size and shape in solutions of calcium stearate in cetane from optical depolarization data

Observations at a series of temperatures of the changes in viscosities and depolarization factors of 1% and 18% solutions of calcium stearate in cetane to which varying amounts of water have been added can be interpreted in terms of the existence of anisometric micelles. In general, changes in the size of the micelles inferred from values of ρh agree with those deduced from the viscosity data. The correlation between anisometry of micelles from rheological and optical observations is much poorer in the case of ρν, presumably because of the difficulty in differentiating the contribution of anisometry and anisotropy to ρν.

Approximate multipole coefficients of RF ion traps as functions of aperture size

In this study we present approximate analytical expressions for estimating the variation in multipole expansion coefficients as a function of the size of the apertures in the electrodes in axially symmetric (3D) and two-dimensional (2D) ion trap ion traps. Following the approach adopted in our earlier studies which focused on the role of apertures to fields within the traps, here too, the analytical expression we develop is a sum of two terms, A(n,noAperiure), the multipole expansion coefficient for a trap with no apertures and A(n,dueToAperture), the multipole expansion coefficient contributed by the aperture. A(n,noAperture) has been obtained numerically and A(n,dueToAperture) is obtained from the n th derivative of the potential within the trap. The expressions derived have been tested on two 3D geometries and two 2D geometries. These include the quadrupole ion trap (QIT) and the cylindrical ion trap (CIT) for 3D geometries and the linear ion trap (LIT) and the rectilinear ion trap (RIT) for the 2D geometries. Multipole expansion coefficients A(2) to A(12), estimated by our analytical expressions, were compared with the values obtained numerically (using the boundary element method) for aperture sizes varying up to 50% of the trap dimension. In all the plots presented, it is observed that our analytical expression for the variation of multipole expansion coefficients versus aperture size closely follows the trend of the numerical evaluations for the range of aperture sizes considered. The maximum relative percentage errors, which provide an estimate of the deviation of our values from those obtained numerically for each multipole expansion coefficient, are seen to be largely in the range of 10-15%. The leading multipole expansion coefficient, A(2), however, is seen to be estimated very well by our expressions, with most values being within 1% of the numerically determined values, with larger deviations seen for the QIT and the LIT for large aperture sizes. (C) 2010 Elsevier B.V. All rights reserved.

Effects of molecular size in solvation dynamics

The effects of molecular size on the dynamics of polar solvation are studied by using a microscopic theory which includes the translational relaxation modes of the solvent consistently. It is shown that while in the absence of the translational contribution the solvation rate increases with the size of the solute (in agreement with the conclusions of the nonequilibrium MSA theory),a complete reversal of the solute size dependence occurs when translational modes make a significant contribution to the solvent polarization relaxation.

Effect of morphology and particle size on the ionic conductivities of composite solid electrolytes

A model incorporating the surface conductivity and morphology of the composite solid electrolytes is envisaged to explain their conduction behaviour. The conductivity data on LinX−50 m/o Al2O3 (X = F−, Cl−, Br−, CO32−, SO42−, PO43−) composites prepared by thermal decomposition of LinX·2nAl(OH)3·mH2O salts and Li2SO4−A (A=Al2O3, CeO2, Y2O3, Yb2O3, Zr2O3, ZrO2 and BaTiO3) composites prepared by mechanical mixing of the components are examined in the light of this model. It is surmised that the particle size of both the dispersoids and the hosts not only influence the ionic conductivity of the host matrix but also affect its bulk properties.

Taking Multiple Infections of Cells and Recombination into Account Leads to Small Within-Host Effective-Population-Size Estimates of HIV-1

Whether HIV-1 evolution in infected individuals is dominated by deterministic or stochastic effects remains unclear because current estimates of the effective population size of HIV-1 in vivo, N-e, are widely varying. Models assuming HIV-1 evolution to be neutral estimate N-e similar to 10(2)-10(4), smaller than the inverse mutation rate of HIV-1 (similar to 10(5)), implying the predominance of stochastic forces. In contrast, a model that includes selection estimates N-e>10(5), suggesting that deterministic forces would hold sway. The consequent uncertainty in the nature of HIV-1 evolution compromises our ability to describe disease progression and outcomes of therapy. We perform detailed bit-string simulations of viral evolution that consider large genome lengths and incorporate the key evolutionary processes underlying the genomic diversification of HIV-1 in infected individuals, namely, mutation, multiple infections of cells, recombination, selection, and epistatic interactions between multiple loci. Our simulations describe quantitatively the evolution of HIV-1 diversity and divergence in patients. From comparisons of our simulations with patient data, we estimate N-e similar to 10(3)-10(4), implying predominantly stochastic evolution. Interestingly, we find that N-e and the viral generation time are correlated with the disease progression time, presenting a route to a priori prediction of disease progression in patients. Further, we show that the previous estimate of N-e>10(5) reduces as the frequencies of multiple infections of cells and recombination assumed increase. Our simulations with N-e similar to 10(3)-10(4) may be employed to estimate markers of disease progression and outcomes of therapy that depend on the evolution of viral diversity and divergence.

Size dependence of the bulk modulus of semiconductor nanocrystals from first-principles calculations

The variation in the bulk modulus of semiconductor nanoparticles has been studied within first-principles electronic-structure calculations using the local density approximation (LDA) for the exchange correlation. Quantum Monte Carlo calculations carried out for a silicon nanocrystal Si87H76 provided reasonable agreement with the LDA results. An enhancement was observed in the bulk modulus as the size of the nanoparticle was decreased, with modest enhancements being predicted for the largest nanoparticles studied here, a size just accessible in experiments. To access larger sizes, we fit our calculated bulk moduli to the same empirical law for all materials, the asymptote of which is the bulk value of the modulus. This was found to be within 2-10% of the independently calculated value. The origin of the enhancement has been discussed in terms of Cohen's empirical law M.L. Cohen, Phys. Rev. B 32, 7988 (1985)] as well as other possible scenarios.

Grain size effect on the phase transformation temperature of nanostructured CuFe2O4

We report a large decrease in tetragonal to cubic phase transformation temperature when grain size of bulk CuFe2O4 is reduced by mechanical ball milling. The change in phase transformation temperature was inferred from in situ high temperature conductivity and x-ray diffraction measurements. The decrease in conductivity with grain size suggests that ball milling has not induced any oxygen vacancy while the role of cation distribution in the observed decrease in phase transformation temperature is ruled out from in-field Fe-57 Mossbauer and extended x-ray absorption fine structure measurements. The reduction in the phase transformation temperature is attributed to the stability of structures with higher crystal symmetry at lower grain sizes due to negative pressure effect. (C) 2011 American Institute of Physics. doi: 10.1063/1.3493244]

Dependence of the strength of interaction of carbon monoxide with transition metal clusters on the cluster size

The interaction of CO with Cu, Pd, and Ni at different coverages of the metals on solid substrates has been investigated by He II and core-level spectroscopies, after the nature of variation of the metal core-level binding energies with the coverage or the cluster size is established. The separation between the (1 pi + 5 sigma) and 4 sigma levels of CO increases with a decrease in the size of the metal clusters, accompanied by an increase in the desorption temperature. In the case of Cu, the intramolecular shakeup satellite of CO disappears on small clusters. More importantly, CO dissociates on small Ni clusters, clearly confirming that metal-CO interaction strength increases with a decrease in the cluster size.

Size effect on the superconducting transition of embedded lead particles in an Al-Cu-V amorphous matrix

We have synthesized specimens of nanometric lead dispersion in a glassy Al-Cu-V matrix by rapid solidification of the corresponding melt. The microstructure has been designed to avoid superconducting percolation due to coupling of the neighboring particles by the proximity effect. Using these specimens, we have determined quantitatively the effect of size of the ultrafine lead particles on the superconducting transition. (C) 1999 American Institute of Physics. [S0003-6951(99)02037-9].

The effect of SiC particles on the size and morphology of eutectic silicon in cast A356/SiCp composites

Properties of cast aluminium matrix composites are greatly influenced by the nature of distribution of reinforcing phase in the matrix and matrix microstructural length scales, such as grain size, dendrite arm spacing, size and morphology of secondary matrix phases, etc. Earlier workers have shown that SIC reinforcements can act as heterogeneous nucleation sites for Si during solidification of Al-Si-SiC composites. The present study aims at a quantitative understanding of the effect of SiC reinforcements on secondary matrix phases, namely eutectic Si, during solidification of A356 Al-SiC composites. Effect of volume fraction of SiC particulate on size and shape of eutectic Si has been studied at different cooling rates. Results indicate that an increase in SiC volume fraction leads to a reduction in the size of eutectic Si and also changes its morphology from needle-like to equiaxed. This is attributed to the heterogeneous nucleation of eutectic Si on SiC particles. However, SiC particles are found to have negligible influence on DAS. Under all the solidification conditions studied in the present investigation, SiC particles are found to be rejected by the growing dendrites. (C) 1999 Elsevier Science Ltd. All rights reserved.

Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy

InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.

Evolution of sub-micron grain size and weak texture in magnesium alloy Mg-3Al-0.4Mn by a modified multi-axial forging process

This is the first successful attempt to produce simultaneously ultrafine grain size and weak texture in a single-phase magnesium alloy Mg-3Al-0.4Mn through an optimal choice of processing parameters in a modified multi-axial forging (MAF) process. An average grain size of similar to 0.4 mu m and a weak texture could be achieved. This has led to an increase in the strength as well as room-temperature ductility (55%). The plot of the yield loci shows a decrease in anisotropy after MAF. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Size-mediated cytotoxicity of nanocrystalline titanium dioxide, pure and zinc-doped hydroxyapatite nanoparticles in human hepatoma cells

Nanoparticles are highly used in biological applications including nanomedicine. In this present study, the interaction of HepG2 hepatocellular carcinoma cells (HCC) with hydroxyapatite (HAp), zinc-doped hydroxyapatite, and titanium dioxide (TiO2) nanoparticles were investigated. Hydroxyapatite, zinc-doped hydroxyapatite and titanium dioxide nanoparticles were prepared by wet precipitation method. They were subjected to isochronal annealing at different temperatures. Particle morphology and size distribution were characterized by X-ray diffraction and transmission electron microscope. The nanoparticles were co-cultured with HepG2 cells. MTT assay was employed to evaluate the proliferation of tumor cells. The DNA damaging effect of HAp, Zn-doped HAp, and TiO2 nanoparticles in human hepatoma cells (HepG2) were evaluated using DNA fragmentation studies. The results showed that in HepG2 cells, the anti-tumor activity strongly depend on the size of nanoparticles in HCC cells. Cell cycle arrest analysis for HAp, zinc-doped HAp, and TiO2 nanoparticles revealed the influence of HAp, zinc-doped HAp, and titanium dioxide nanoparticles on the apoptosis of HepG2 cells. The results imply that the novel nano nature effect plays an important role in the biomedicinal application of nanoparticles.

Estimation of the shear transformation zone size fin a bulk metallic glass through statistical a analysis of the first pop-in stresses during spherical nanoindentation

The size of the shear transformation zone (STZ) that initiates the elastic to plastic transition in a Zr-based bulk metallic glass was estimated by conducting a statistical analysis of the first pop-in event during spherical nanoindentation. A series of experiments led us to a successful description of the distribution of shear strength for the transition and its dependence on the loading rate. From the activation volume determined by statistical analysis the STZ size was estimated based on a cooperative shearing model. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Strain induced phase transition in CdSe nanowires: Effect of size and temperature

Using all-atom molecular dynamics simulation, we have studied the effect of size and temperature on the strain induced phase transition of wurtzite CdSe nanowires. The wurtzite structure transforms into a five-fold coordinated structure under uniaxial strain along the c axis. Our results show that lower temperature and smaller size of the nanowires stabilize the five-fold coordinated phase which is not a stable structure in bulk CdSe. High reversibility of this transformation with a very small heat loss will make these nanowires suitable for building efficient nanodevices. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4734990]