Phase transition and bulk properties of some polonide compounds: a comparative study

In the present paper the structural and electronic properties of polonides of lead, barium and calcium polonide (PbPo, BaPo and CaPo) have been reported. These properties have been studied using first principles calculations as well as the interionic potential model modified with the covalency effect. Gibbs free energy and enthalpy calculations show that these compounds undergo a structural phase transition from NaCl-type structure to CsCl-type structure. The electronic band structure and density of states of the PbPo, BaPo and CaPo have also been reported. The calculated equilibrium structural parameters are in good agreement with the available experimental results.     

Adhesion and stress of magnesium oxide thin films: Effect of thickness, oxidation temperature and duration

Nanoscale magnesium oxide thin films have been deposited on glass substrate by thermal oxidation (in air) of vacuum evaporated magnesium films. X-ray diffraction (XRD) showed orientation along (2 0 0) and (2 2 0) directions. The mechanical properties of the MgO thin films were found to be the function of thickness (300, 450 and 600 nm), oxidation temperature (573, 623 and 673 K) and oxidation duration (90 and 180 min). As oxidation temperature and oxidation duration increases, adhesion and intrinsic stress were found to increase. Intrinsic stress decreased whereas adhesion increased due to increase in thin film thickness. The value of intrinsic stress was in range 28.902-73.212 (×10⁷ N/m²) and that of adhesion was 12.1-27.4 (×10⁴ N/m²) for the thin film of thickness 300 nm.     

Synthesis of combinatorial libraries based on terpenoid scaffolds

Triterpenoid-based scaffolds betulinic acid (1a) and ursolic acid (1b), have been used for the generation of combinatorial libraries in parallel format using solid phase organic synthesis method. These templates have the potential for the synthesis and amplification of triterpenoid-based compounds with one and two-point diversity. This has been demonstrated by the synthesis of two small libraries comprising 18 derivatives each of betulinic acid and ursolic acid with structural diversity at C-3 and C-28 positions. The primary screening of antimalarial activity of these libraries against P. falciparum in vitro led to the identification of four compounds with 5 fold increase in the activity compared to betulinic and ursolic acids.     

Optical and room temperature sensing properties of highly oxygen deficient flower-like ZnO nanostructures

Oxygen deficient zinc oxide (ZnO) thin films were deposited electrochemically on glass substrates which are pre-sputtered with pure zinc (Zn) metal. Well-arranged flower-like nanostructures are observed from the SEM micrographs. The purity and crystallinity of the deposited films were confirmed from X-ray diffraction studies supported by Raman studies. The broad and intense defect induced green emission confirms the high oxygen deficiency in the nanostructures. The flower-like structures as well as the oxygen defects present in the system are indeed very suitable for gas and chemical sensing applications. These films were used for room temperature sensing of three different chemicals viz. acetone, ethanol and ammonia. The sensor was found to be insensitive to the change in different concentrations of acetone while it was found to be sensitive to different concentrations of ethanol and ammonia. The sensor is most suitable for sensing ammonia at room temperature.     

Reliability of fluctuation-induced transport in a Maxwell-demon-type engine

We study the transport properties of an overdamped Brownian particle which is simultaneously in contact with two thermal baths. The first bath is modeled by an additive thermal noise at temperature T _A . The second bath is associated with a multiplicative thermal noise at temperature T _B . The analytical expressions for the particle velocity and diffusion constant are derived for this system, and the reliability or coherence of transport is analyzed by means of their ratio in terms of a dimensionless Péclet number. We find that the transport is not very coherent, though one can get significantly higher currents.     

Law of the iterated logarithm for perturbed empirical distribution functions evaluated at a random point for nonstationary random variables

We consider perturbed empirical distribution functions , where {Ginn, n1} is a sequence of continuous distribution functions converging weakly to the distribution function of unit mass at 0, and {X _{i, i}1} is a non-stationary sequence of absolutely regular random variables. We derive the almost sure representation and the law of the iterated logarithm for the statistic whereU _n is aU-statistic based onX ₁,...,X _n . The results obtained extend or generalize the results of Nadaraya,⁽⁷⁾ Winter,⁽¹⁶⁾ Puri and Ralescu,^(9,10) Oodaira and Yoshihara,⁽⁸⁾ and Yoshihara,⁽¹⁹⁾ among others.Research supported by the Office of Naval Research Contract N00014-91-J-1020.     

Lens epithelial cell response to polymer stiffness and polymer chemistry

Posterior capsule opacification (PCO) is the most common complication of cataract surgery, and intraocular lens (IOL) implantation is the standard of care for cataract patients. Induction of postoperative epithelial-mesenchymal transition (EMT) in residual lens epithelial cells (LEC) is the main mechanism by which PCO forms. Previous studies have shown that IOLs made with different materials have varying incidence of PCO. The aim of this paper was to study the interactions between human (h)LEC and polymer substrates. Polymers and copolymers of 2-hydroxyethyl methacrylate (HEMA) and 3-methacryloxypropyl tris(trimethylsiloxy)silane (TRIS) were synthesized and evaluated due to the clinical use of these materials as ocular biomaterials and implants. The chemical properties of the polymer surfaces were evaluated by contact angle, and polymer stiffness and roughness were measured using atomic force microscopy. In vitro studies showed the effect of polymer mechanical properties on the behavior of hLECs. Stiffer polymers increased α-smooth muscle actin expression and induced cell elongation. Hydrophobic and rough polymer surfaces increased cell attachment. These results demonstrate that attachment of hLECs on different surfaces is affected by surface properties in vitro, and evaluating these properties may be useful for investigating prevention of PCO.