The effect of nanoscale vanadium pentoxide on the electrical and mechanical properties of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) loaded with vanadium pentoxide (V₂O₅) nanoparticles was successfully prepared at room temperature and ambient pressure. Transmission electron microscopy was used to characterize the final product. It was found that V₂O₅ nanoparticles were well dispersed and uniform in shape and that the diameter of the particles was confined to within 8 nm. Addition of small amounts (0.2–1 wt%) of nanoparticulate V₂O₅ to PVA increased the electrical conductivity as well as the modulus of elasticity. The deformation behaviour after preparing the nanocomposites, irrespective of V₂O₅ concentration, is similar to that of the unfilled elastomer, implying that the mechanism of large deformation is mainly governed by the matrix. Copyright © 2007 Society of Chemical Industry     

Formation of metastable solid solutions in the Pb-Ge system

The formation and decomposition behaviours of metastable solid solutions in liquid-quenched and vapour-quenched Pb-Ge alloys were studied using X-ray diffraction, transmission electron microscopy (TEM), differential thermal analysis (DTA) and resistance measurement techniques. It is shown that the Pb-rich fcc phase can retain upto about 13 at% Ge on liquid-quenching and upto about 5 at% Ge on vapour-quenching. Decomposition of the Pb-rich fcc phase occurs in the temperature range 220 to 300° C and it is a temperature dependent nucleation and growth phenomenon. Upto about 7.5 at% Pb can be retained in Ge-rich compositions in an amorphous Ge matrix on vapour-quenching but there is no detectable solubility of Pb in crystalline Ge retained by liquid-quenching. On heating, the amorphous Ge-Pb films crystallize to a Ge-rich solid solution which decomposes to equilibrium constituents at higher temperatures. Stability of amorphous Ge-Pb films decreases on increasing metal concentration.     

Differential nm23 gene expression at the fetal-maternal interface

The product of the nm23 gene has been proposed as a candidate tumour metastasis suppressor protein. A strong association has been observed between reduced expression of the nm23 gene and acquisition of metastatic behaviour in some tumour cells, including breast cancer and melanoma, but not in others, such as neuroblastoma and colon, cervical and thyroid cancers. During the early gestation period both human and murine trophoblast cells exhibit in vitro invasive properties similar to those of neoplastic cells. Such invasive properties, however, disappear in the late stage of gestation. In the present study, we examined the abundance of nm23 mRNA from various fetal-maternal interface tissues (uterus, decidua, placenta and embryo) during early (day 8), mid (day 14) and late (day 18) stages of gestation in CD1 mice, in order to determine whether nm23 plays any anti-invasive and/or biological roles during gestation. nm23 was found to be expressed in all the tissues during the early and mid stages of gestation. The expression levels were, however, variable among different tissues and development stages. In the early stage, nm23 mRNA levels were the highest and similar among tissues from the uterus, decidua, placenta and embryo. In the mid stage, the mRNA levels were reduced significantly in the uterus, decidua and placenta, but not in the embryo. In the late stage, nm23 mRNA was further reduced to the extent that it could not be seen in the decidua, was barely seen in the uterus and was weakly present in the placenta. However, the mRNA level of the embryo in the late stage was still high and similar to the early stage. We also examined nm23 expression in trophoblast cells from normal human term placenta and a highly metastatic human choriocarcinoma cell line, JAR. nm23 expression was significantly higher in JAR than in normal placenta, indicating that nm23 does not appear to have an anti-metastatic function in this cell line. Several cytokines--interleukin 2 (IL-2), tumour necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma)--and prostaglandin E2 (PGE2) known to modulate tumour growth and metastasis were examined to determine whether they regulate nm23 expression in JAR in vitro. The B16F10 melanoma cell line was used as control. No effect was found in the JAR cell line, whereas TNF-alpha, IFN-gamma and PGE2 down-regulated nm23 expression in the B16F10 cell line.(ABSTRACT TRUNCATED AT 400 WORDS)     

Reliability of k-out-of-n:G systems with imperfect fault-coverage

k-out-of-n:G systems are modeled to determine their reliability and availability. Markov models are obtained to examine the fault-tolerant operation of the system. From the Markov chains, reliability and availability measures are found as state probabilities. Recursive expressions for mean time-between-failures and mean time-to-failure are obtained for repairable systems, considering perfect and imperfect fault-coverage     

Preparation, physico-chemical characterization and electrical conductivity measurement studies of an organic-inorganic nanocomposite cation-exchanger: Poly-o-toluidine Zr(IV) phosphate

An organic-inorganic nanocomposite cation-exchanger, i.e. poly-o-toluidine Zr(IV) phosphate was synthesized via sol-gel mixing of an electrical conducting polymer poly-o-toluidine into the matrices of inorganic precipitate of Zr(IV) phosphate. The ion-exchange capacity, chemical stability, effect of eluant concentration, elution behavior, pH titration and thermal studies were also carried out to understand the ion-exchange capabilities. The physico-chemical properties of the material were determined using AAS, CHN elemental analysis, FTIR, TGA-DTA, XRD, TEM and SEM studies. On the basis of distribution studies, the material was found to be highly selective for Hg(II). Its selectivity was examined by achieving some important binary separations like Hg(II)-Pb(II), Hg(II)-Cu(II), Hg(II)-Co(II), Hg(II)-Fe(III), Hg(II)-Sr(II), etc. on its column. This material possessed d.c. electrical conductivity in the semi-conducting range, i.e. 10⁻³ to 10⁻² S cm⁻¹; measured by four-in-line probe d.c. electrical conductivity-measuring technique. The d.c. electrical conductivity of the composite material was found stable upto 110 °C for the composites under ambient conditions.     

Detection of helicopters using neural nets

Artificial neural networks (ANNs), in combination with parametric spectral representation techniques, are applied for the detection of helicopter sound. Training of the ANN detectors was based on simulated helicopter sound from four helicopters and a variety of nonhelicopter sounds. Coding techniques based on linear prediction coefficients (LPCs) have been applied to obtain spectral estimates of the acoustic signals. Other forms of the LPC parameters such as reflection coefficients, cepstrum coefficients, and line spectral pairs (LSPs) have also been used as feature vectors for the training and testing of the ANN detectors. We have also investigated the use of wavelet transform for signal de-noising prior to feature extraction. The performance of various feature extraction techniques is evaluated in terms of their detection accuracy     

Finite difference time domain methods for piezoelectric crystals

The numerical simulation of acoustic wave propagation through piezoelectric crystals using the finite-difference time-domain (FDTD) method is introduced. The update equations for the velocity and stress fields are derived and applied to the propagation of ultrasonic waves in three substrates. The concept of the perfectly matched layer (PML), first introduced for the simulation of electromagnetic waves, is extended to the simulation of mechanical waves. The technique is shown to be effective for some crystals, but the PML is found to exhibit numerical instabilities for others.     

Size effects on the mechanical behavior of nanoporous Au

Recent nanomechanical tests on submicron metal columns and wires have revealed a dramatic increase in yield strength with decreasing sample size. Here, we demonstrate that nanoporous metal foams can be envisioned as a three-dimensional network of ultrahigh-strength nanowires, thus bringing together two seemingly conflicting properties: high strength and high porosity. Specifically, we characterized the size-dependent mechanical properties of nanoporous gold using a combination of nanoindentation, column microcompression, and molecular dynamics simulations. We find that nanoporous gold can be as strong as bulk Au, despite being a highly porous material, and that the ligaments in nanoporous gold approach the theoretical yield strength of Au.