Free volume study of poly(chlorotrifluoroethylene) using positron annihilation spectroscopy as a microanalytical tool

Positron lifetimes and X-ray diffraction measurements were carried out on poly(chlorotrifluoroethylene) films annealed between 25 and 215 degrees C. The positron lifetime results were used to determine the free volume and XRD data were used to determine the apparent crystallite size and crystallinity. The glass transition temperature (T-g) of 52 degrees C obtained from positron results is in agreement with that obtained by thermal analysis. The average free volume cell size is 74 Angstrom(3) in films annealed below T-g, and increases to 84 Angstrom(3) in samples annealed above T-g. Although the observed changes in positron lifetime parameters as a function of annealing temperature are small, they are significant for the kind of material investigated. Our observations are explained in terms of thermally activated chain mobility, local relaxations and long-range motions. We further estimate, for the first time, the activation energies in the amorphous and crystalline regions of the polymer using the Goldanskii kinetic relations. Copyright (C) 1996 Elsevier Science Ltd

NANOTECHNOLOGICAL APPROACH TO ENHANCE THE STABILITY AND BIOAVAILABILITY OF THE HERBAL DRUG "MURVA"

Murva (Maerua oblongifolia) contains numerous bioactive compounds that may provide multiple health benefits, including anti-microbial, anti-fungal, anti-pyretic and anti-diabetic. Most of the therapeutic effects of murva have been attributed due to the presence of triterpenoids and alkaloids, in their composition. Although these compounds have been shown promising therapeutic effects under in-vitro conditions, they met with limited efficacy in clinical settings due to various reasons such as poor oral absorption and bioavailability. Different techniques have been proposed to improve the stability and bioavailability of the herbal drugs. Among such strategies, nanoparticulate based drug delivery systems are novel and promising tools. In this study, chitosan nanoparticles containing Murva (CNP1-CNP3) were synthesized by ionic gelation technique, which resulting in particles size smaller than 650nm. The encapsulation efficiency of nanoformulations was over 41.5%. The nanoformulations exhibited slow and sustained in vitro release over 99% of drug from the Murva encapsulated chitosan nanoparticles after 24 hours. The synthesized nanoformulations were found to be a promising system for oral sustained administration of murva and also enhances its stability and bioavailability. Keywords: Nanoparticles, Murva, chitosan, stability, bioavailability

Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6

The superconductor YB6 has the second highest critical temperature Tc among the boride family MBn. We report measurements of the specific heat, resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K, using a single crystal with Tc = 7.2 K. The superconducting gap is characteristic of medium-strong coupling. The specific heat, resistivity and expansivity curves are deconvolved to yield approximations of the phonon density of states, the spectral electron-phonon scattering function and the phonon density of states weighted by the frequency-dependent Grueneisen parameter respectively. Lattice vibrations extend to high frequencies >100 meV, but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of yttrium ions in oversized boron cages, appears to provide most of the superconducting coupling and gives rise to an unusual temperature behavior of several observable quantities. A surface critical field Hc3 is also observed.Comment: 29 pages, 5 tables, 17 figures. Accepted for publication in Phys. Rev.

Diffusing-wave spectroscopy of nonergodic media

We introduce an elegant method which allows the application of diffusing-wave spectroscopy (DWS) to nonergodic, solid-like samples. The method is based on the idea that light transmitted through a sandwich of two turbid cells can be considered ergodic even though only the second cell is ergodic. If absorption and/or leakage of light take place at the interface between the cells, we establish a so-called "multiplication rule", which relates the intensity autocorrelation function of light transmitted through the double-cell sandwich to the autocorrelation functions of individual cells by a simple multiplication. To test the proposed method, we perform a series of DWS experiments using colloidal gels as model nonergodic media. Our experimental data are consistent with the theoretical predictions, allowing quantitative characterization of nonergodic media and demonstrating the validity of the proposed technique.Comment: RevTeX, 12 pages, 6 figures. Accepted for publication in Phys. Rev.

The Lifetime of FRIIs in Groups and Clusters: Implications for Radio-Mode Feedback

We determine the maximum lifetime t_max of 52 FRII radio sources found in 26 central group galaxies from cross correlation of the Berlind SDSS group catalog with the VLA FIRST survey. Mock catalogs of FRII sources were produced to match the selection criteria of FIRST and the redshift distribution of our parent sample, while an analytical model was used to calculate source sizes and luminosities. The maximum lifetime of FRII sources was then determined via a comparison of the observed and model projected length distributions. We estimate the average FRII lifetime is 1.5x10^7 years and the duty cycle is ~8x10^8 years. Degeneracies between t_max and the model parameters: jet power distribution, axial ratio, energy injection index, and ambient density introduce at most a factor of two uncertainty in our lifetime estimate. In addition, we calculate the radio active galactic nuclei (AGN) fraction in central group galaxies as a function of several group and host galaxy properties. The lifetime of radio sources recorded here is consistent with the quasar lifetime, even though these FRIIs have substantially sub-Eddington accretion. These results suggest a fiducial time frame for energy injection from AGN in feedback models. If the morphology of a given extended radio source is set by large-scale environment, while the lifetime is determined by the details of the accretion physics, this FRII lifetime is relevant for all extended radio sources.Comment: 18 pages, 7 figures. Accepted for publication in ApJ. High resolution paper available at http://www.astronomy.ohio-state.edu/~bird/BMK07.pd

Possible unconventional superconductivity in iron-based layered compound LaFePO: Study of heat capacity

Heat capacity measurements were performed on recently discovered iron based layered superconductors, non doped LaFePO and fluorine doped LaFePO. A relatively large electronic heat capacity coefficient and a small normalized heat capacity jump at Tc = 3.3 K were observed in LaFePO. LaFePO0.94F0.06 had a smaller electronic heat capacity coefficient and a larger normalized heat capacity jump at Tc = 5.8 K. These values indicate that these compounds have strong electron electron correlation and magnetic spin fluctuation, which are the signatures of unconventional superconductivity mediated by spin fluctuation.Comment: 15 Pages, 3 Figure

S=−1S=-1 Meson-Baryon Unitarized Coupled Channel Chiral Perturbation Theory and the S01−S_{01}- Λ\Lambda(1405) and −Λ- \Lambda(1670) Resonances

The $s-$wave meson-baryon scattering is analyzed for the strangeness $S=-1$ and isospin I=0 sector in a Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry. Four channels have been considered: $\pi \Sigma$, $\bar K N$, $\eta \Lambda$ and $K \Xi$. The required input to solve the Bethe-Salpeter equation is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. There appear undetermined low energy constants, as a consequence of the renormalization of the amplitudes, which are obtained from fits to the $\pi\Sigma\to\pi\Sigma$ mass-spectrum, to the elastic $\bar K N \to \bar K N$ and $\bar K N\to \pi \Sigma$ $t$--matrices and to the $K^- p \to \eta \Lambda$ cross section data. The position and residues of the complex poles in the second Riemann Sheet of the scattering amplitude determine masses, widths and branching ratios of the $S_{01}-$ $\Lambda$(1405) and $-\Lambda$(1670) resonances, in reasonable agreement with experiment. A good overall description of data, from $\pi \Sigma$ threshold up to 1.75 GeV, is achieved despite the fact that three-body channels have not been explicitly included.Comment: 23 pages, Latex, 10 Figures. In this revised version a new subsection 3.6 on Heavy Baryon Expansion and new references have been adde

Dislocation Driven Chromium Precipitation in Fe-9Cr Binary Alloy: A Positron Lifetime Study

The influence of initial heat treatment on anomalous Cr precipitation within high temperature solubility region in Fe-9Cr alloy has been investigated using positron lifetime studies. Air-quenched samples with pre-existing dislocations exhibited a distinct annealing stage in positron lifetime between 800 and 1100 K corresponding to Cr-precipitation. During this stage, Transmission Electron Microscopy showed fine precipitates of average size 4 nm, dispersed throughout the sample and from EDS analysis they are found to be Cr-enriched. The existence of dislocations is found to be responsible for Cr precipitation.Comment: Revised version Submitted to Phys. Rev.

Low Temperature Transport and Specific Heat Studies of Nd_{1-x}Pb_{x}MnO_{3} Single Crystals

Electrical transport and specific heat properties of Nd_{1-x}Pb_{x}MnO_{3} single crystals for 0.15 < x 0.5 have been studied in low temperature regime. The resistivity in the ferromagnetic insulating (FMI) phase for x < 0.3 has an activated character. The dependence of the activation gap Delta on doping x has been determined and the critical concentration for the zero-temperature metal-insulator transition was determined as x_{c} ~ 0.33. For a metallic sample with x=0.42, a conventional electron-electron (e-e) scattering term proportional T^{2} is found in the low-temperature electrical resistivity, although the Kadowaki-Woods ratio is found to be much larger for this manganite than for a normal metal. For a metallic sample with x=0.5, a resistivity minimum is observed for x= 0.5. The effect is attributed to weak localization and can be described by a negative T^{1/2} weak-localization contribution to resistivity for a disordered three-dimensional electron system. The specific heat data have been fitted to contributions from free electrons (gamma), spin excitations (beta_{3/2}), lattice and a Schottky-like anomaly related to the rare-earth magnetism of the Nd ions. The value of gamma is larger than for normal metals, which is ascribed to magnetic ordering effects involving Nd. Also, the Schottky-like anomaly appears broadened and weakened suggesting inhomogeneous molecular fields at the Nd-sites.Comment: 14 pages, 8 figure