Colloidal calcium nanoparticles: digestive ripening in the presence of a capping agent and coalescence of particles under an electron beam

The nanochemistry of calcium remains unexplored, which is largely due to the inaccessibility of calcium nanoparticles in an easy to handle form by conventional methods of synthesis as well as its highly reactive and pyrophoric nature. The synthesis of colloidal Ca nanoparticles by the solvated metal atom dispersion (SMAD) method is described. The as-prepared Ca-THF nanoparticles, which are polydisperse, undergo digestive ripening in the presence of a capping agent, hexadecyl amine (HDA) to afford highly monodisperse colloids consisting of 2-3 nm sized Ca-HDA nanoparticles. These are quite stable towards precipitation for long periods of time, thereby providing access to the study of the nanochemistry of Ca. Particles synthesized in this manner were characterized by UV-visible spectroscopy, high resolution electron microscopy, and powder X-ray diffraction methods. Under an electron beam, two adjacent Ca nanoparticles undergo coalescence to form a larger particle.

Nano Al2O3-Pb AND SiO2-Pb cermets by sol-gel technique and the phase transformation study of the embedded Pb particles

Sol-gel processing followed by H2 reduction is used to produce dispersions of nanosized Pb in amorphous SiO2 and ultrafine γ Al2O3 matrices. A depression of 3–5K in Pb melting point is reported. The size and shape of these metastable particles in molten and solid state are discussed in the light of the experimental observations and expectations from the intersection group theory for equilibrium shape.

General classical theory of spinning particles in a meson field

An exact classical theory of the motion of a point dipole in a meson field is given which takes into account the effects of the reaction of the emitted meson field. The meson field is characterized by a constant $\chi =\mu /\hslash $ of the dimensions of a reciprocal length, $\mu $ being the meson mass, and as $\chi \rightarrow $ 0 the theory of this paper goes over continuously into the theory of the preceding paper for the motion of a spinning particle in a Maxwell field. The mass of the particle and the spin angular momentum are arbitrary mechanical constants. The field contributes a small finite addition to the mass, and a negative moment of inertia about an axis perpendicular to the spin axis. A cross-section (formula (88 a)) is given for the scattering of transversely polarized neutral mesons by the rotation of the spin of the neutron or proton which should be valid up to energies of 10$^{9}$ eV. For low energies E it agrees completely with the old quantum cross-section, having a dependence on energy proportional to p$^{4}$/E$^{2}$ (p being the meson momentum). At higher energies it deviates completely from the quantum cross-section, which it supersedes by taking into account the effects of radiation reaction on the rotation of the spin. The cross-section is a maximum at E $\sim $ 3$\cdot $5$\mu $, its value at this point being 3 $\times $ 10$^{-26}$ cm.$^{2}$, after which it decreases rapidly, becoming proportional to E$^{-2}$ at high energies. Thus the quantum theory of the interaction of neutrons with mesons goes wrong for E $\gtrsim $ 3$\mu $. The scattering of longitudinally polarized mesons is due to the translational but not the rotational motion of the dipole and is at least twenty thousand times smaller. With the assumption previously made by the present author that the heavy partilesc may exist in states of any integral charge, and in particular that protons of charge 2e and - e may occur in nature, the above results can be applied to charged mesons. Thus transversely polarised mesons should undergo a very big scattering and consequent absorption at energies near 3$\cdot $5$\mu $. Hence the energy spectrum of transversely polarized mesons should fall off rapidly for energies below about 3$\mu $. Scattering plays a relatively unimportant part in the absorption of longitudinally polarized mesons, and they are therefore much more penetrating. The theory does not lead to Heisenberg explosions and multiple processes.

Effect of charge asymmetry and charge screening on structure of superlattices formed by oppositely charged colloidal particles

Colloidal suspensions made up of oppositely charged particles have been shown to self-assemble into substitutionally ordered superlattices. For a given colloidal suspension, the structure of the superlattice formed from self-assembly depends on its composition, charges on the particles, and charge screening. In this study we have computed the pressure-composition phase diagrams of colloidal suspensions made up of binary mixtures of equal sized and oppositely charged particles interacting via hard core Yukawa potential for varying values of charge screening and charge asymmetry. The systems are studied under conditions where the thermal energy is equal or greater in magnitude to the contact energy of the particles and the Debye screening length is smaller than the size of the particles. Our studies show that charge asymmetry has a significant effect on the ability of colloidal suspensions to form substitutionally ordered superlattices. Slight deviations of the charges from the stoichiometric ratio are found to drastically reduce the thermodynamic stability of substitutionally ordered superlattices. These studies also show that for equal-sized particles, there is an optimum amount of charge screening that favors the formation of substitutionally ordered superlattices. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.3700226]

Tribology of soot suspension in hexadecane as distinguished by the physical structure and chemistry of soot particles

Ethylene gas is burnt to generate soot which is collected thermophoretically from different locations of the flame. Tribological performance of the collected soot in hexadecane suspension is compared with that of carbon black and diesel soot. The soots are analysed to yield a range of mechanical properties, physical structures and chemistry. The paper correlates these property variations with the corresponding variations in friction and wear when the soot suspended in hexadecane is used to lubricate a steel on steel sliding interaction. The particles are dispersed in hexadecane by a non-ionic surfactant, poly-isobutylene succinimide (PIBS), which is mono-functional with no free amine group. The grafting of the surfactant on the soot particles is found to have a profound effect on the dispersion of the soot, in general, while, between the different soot types, the tribology is differentiated by the physical structure and chemistry.

Radiative and non-radiative effects of a substrate on localized plasmon resonance of particles

Experiments have shown strong effects of some substrates on the localized plasmons of metallic nano particles but they are inconclusive on the affecting parameters. Here, we have used discrete dipole approximation in conjunction with Sommerfeld integral relations to explain the effect of the substrates as a function of the parameters of incident radiation. The radiative coupling can both quench and enhance the resonance and its dependence on the angle and polarization of incident radiation with respect to the surface is shown. Non-radiative interaction with the substrate enhances the plasmon resonance of the particles and can shift the resonances from their free-space energies significantly. The non-radiative interaction of the substrate is sensitive to the shape of particles and polarization of incident radiation with respect to substrate. Our results show that the plasmon resonances in coupled and single particles can be significantly altered from their free-space resonances and are quenched or enhanced by the choice of substrate and polarization of incident radiation. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4736544]

Friction between a Steel Ball and a Steel Flat Lubricated by MoS2 Particles Suspended in Hexadecane at 150 degrees C

A steel ball was slid on a steel flat lubricated by molybdenum disulfide (MoS2) particles suspended in hexadecane oil at 150 degrees C. The friction data is compared with that obtained when the ball was slid on the flat sprayed apriori with nominally dry MoS2 particles. The friction in the dry experiment was found to increase with temperature while the friction in wet condition was found to decrease with increasing temperature. Micro-Raman and Fourier transform IR spectroscopy are used to explore the roles of environmental moisture and chemical degradation of oil on the formation of antifriction film on the steel substrate.

SuSeFLAV: A program for calculating supersymmetric spectra and lepton flavour violation

The program SuSeFLAV is introduced for computing supersymmetric mass spectra with flavour violation in various supersymmetric breaking scenarios with/without see-saw mechanism. A short user guide summarizing the compilation, executables and the input files is provided.

Supersymmetric Chern-Simons theories with vector matter

In this paper we discuss SU(N) Chern-Simons theories at level k with both fermionic and bosonic vector matter. In particular we present an exact calculation of the free energy of the N = 2 supersymmetric model (with one chiral field) for all values of the `t Hooft coupling in the large N limit. This is done by using a generalization of the standard Hubbard-Stratanovich method because the SUSY model contains higher order polynomial interactions.

Status of supersymmetric type-I seesaw in SO(10) inspired models

We report on the status of supersymmetric seesaw models in the light of recent experimental results on mu -> e + gamma, theta(13) and the light Higgs mass at the LHC. SO(10)-like relations are assumed for neutrino Dirac Yukawa couplings and two cases of mixing, one large, PMNS-like, and another small, CKM-like, are considered. It is shown that for the large mixing case, only a small range of parameter space with moderate tan beta is still allowed. This remaining region can be ruled out by an order of magnitude improvement in the current limit on BR(mu -> e + gamma). We also explore a model with non-universal Higgs mass boundary conditions at the high scale. It is shown that the renormalization group induced flavor violating slepton mass terms are highly sensitive to the Higgs boundary conditions. Depending on the choice of the parameters, they can either lead to strong enhancements or cancellations within the flavor violating terms. Such cancellations might relax the severe constraints imposed by lepton flavor violation compared to mSUGRA. Nevertheless for a large region of parameter space the predicted rates lie within the reach of future experiments once the light Higgs mass constraint is imposed. We also update the potential of the ongoing and future experimental searches for lepton flavor violation in constraining the supersymmetric parameter space.

Synthesis and characterization of Fe- and Co-based ferrite nanoparticles and study of the T-1 and T-2 relaxivity of chitosan-coated particles

In pursuit of newer and more effective contrast agents for magnetic resonance imaging, we report in this article the use of biocompatible chitosan-coated ferrite nanoparticles of different kinds with a view to determine their potential applications as the contrast agents in the field of nuclear magnetic resonance. The single-phase ferrite particles were synthesized by chemical co-precipitation (CoFe2O4 and Fe3O4) and by applying ultrasonic vibration (CoFe2O4 and Co0.8Zn0.2Fe2O4). Although magnetic anisotropy of CoFe2O4 nanoparticle leads to finite coercivity even for nanoensembles, it has been reduced significantly to a minimum level by applying ultrasonic vibration. Fe3O4 synthesized by chemical co-precipitation yielded particles which already possess negligible coercivity and remanence. Substitution of Co by Zn in CoFe2O4 increases the magnetization significantly with a small increase in coercivity and remanence. Particles synthesized by the application of ultrasonic vibration leads to the higher values of T-2 relaxivities than by chemical coprecipitation. We report that the T-2 relaxivities of these particles are of two orders of magnitude higher than corresponding T-1 relaxivities. Thus, these particles are evidently suitable as contrast agent for T-2 weighted MR images.

Proposal for generalised supersymmetry Les Houches Accord for see-saw models and PDG numbering scheme

The SUSY Les Houches Accord (SLHA) 2 extended the first SLHA to include various generalisations of the Minimal Supersymmetric Standard Model (MSSM) as well as its simplest next-to-minimal version. Here, we propose further extensions to it, to include the most general and well-established see-saw descriptions (types I/II/III, inverse, and linear) in both an effective and a simple gauged extension of the MSSM framework. In addition, we generalise the PDG numbering scheme to reflect the properties of the particles. (c) 2012 Elsevier B.V. All rights reserved.

Study of the Formation of Nano-Networks in Colloidal Particles

The authors studied the formation of a wafer-scale network of connected colloidal beads by reactive ion etching. The dimensions of the connections have been studied as a function of etching time for colloidal beads of different sizes, and could be well controlled. The authors have found that the nano-network forms and disappears for the same time of etching independent of the diameter of the polystyrene beads. With recent interest of connected colloidal networks in various optical sensing applications, such as photonic crystals, as surface-enhanced Raman scattering substrates, the studies have potential uses in the development of wafer-scale nanophotonic sensors.

Clusters of bound particles in the derivative delta-function Bose gas

In this paper we discuss a novel procedure for constructing clusters of bound particles in the case of a quantum integrable derivative delta-function Bose gas in one dimension. It is shown that clusters of bound particles can be constructed for this Bose gas for some special values of the coupling constant, by taking the quasi-momenta associated with the corresponding Bethe state to be equidistant points on a single circle in the complex momentum plane. We also establish a connection between these special values of the coupling constant and some fractions belonging to the Farey sequences in number theory. This connection leads to a classification of the clusters of bound particles associated with the derivative delta-function Bose gas and allows us to study various properties of these clusters like their size and their stability under the variation of the coupling constant. (C) 2013 Elsevier B.V. All rights reserved.

Gene expression in osteoblast cells treated with submicron to nanometer hydroxyapatite-mullite eluate particles

The present research focused on determining the effect of hydroxyapatite-20 wt% mullite (H20M) particle eluates on apoptosis and differentiation of human fetal osteoblast (hFOB) cells. The H20M particles (257 +/- 37 nm) were prepared, starting with the production of a nanocomposite using a unique route of spark plasma sintering, followed by a repeated grinding-cryo treatment and elution process. Tetrazolium based cytotoxicity assay results showed a time-and dose-dependent effect of H20M particle eluates on hFOB cytotoxicity. In particular, the results revealed statistically reduced cell viability after hFOB were exposed to the above 10% H20M (257 +/- 37 nm) eluates for 48 h. The apoptotic cell death triggered by H20M treatment was proven by the analysis of molecular markers of apoptosis, that is, the Bcl-2 family of genes. hFOB expression of Bcl-xL and Bcl-xS significantly increased 25.6- and 25.2-fold for 50% of H20M concentrations, respectively. The ratio of Bcl-xL/Bax (4.01) decreased 2-fold for hFOB exposed to 100% of H20M eluates than that for 10% H20M eluate (7.94) treated hFOB cells. On the other hand, the Bcl-xS/Bax ratio for the 10% H20M eluate was 4.15-fold, whereas for 100% H20M eluates, it was 11.55-fold. Specifically, the anti-apoptotic effect of the H20M particle eluates was corroborated by the up-regulation of bone cell differentiation marker genes such as, collagen type I, cbfa, and osteocalcin. In summary, the present work clearly demonstrated that H20M submicron to nanometer composite particle eluates have a minimal effect on hFOB apoptosis and can even up-regulate the expression of bone cell markers at the molecular level.