Nanofiber‐Directed Anisotropic Self‐Assembly of CdSe–CdS Quantum Rods for Linearly Polarized Light Emission Evidenced by Quantum Rod Orientation Microscopy

Hybrid soft materials composed of CdSe–CdS nanorods or “quantum rods” (QRs) and the fluorescent 2,3‐didecyloxyanthracene (DDOA) low molecular weight organogelator are obtained through self‐assembly. Spectroscopy, microscopy, and rheology studies show that the QRs and DDOA coassemble, thereby stabilizing the organogels. Depending on the QR load and excitation wavelength, single nanofibers (NFs) of the hybrid gel display either sharp polarized red luminescence (under green excitation), or dual perpendicularly polarized blue and red emissions (under UV excitation). Transmission electron microscopy, microspectroscopy, and quantum rod orientation microscopy (QROM) reveal that QRs align along the organogel NFs with order parameters reaching 76% and 87%. This paves the way for obtaining surfaces of QR/NF assemblies yielding sharp red linearly polarized emission. In addition, this work demonstrates that QRs can be used more generally to probe nanostructured soft materials, even nonemissive ones. QROM allows to establish maps of the orientation of single QRs dispersed onto or within a gel network by measuring the polarization of the emission of the individual QRs. As occurs within this work in which QRs and NFs interact, the orientation of each QR reveals information on the underlying nanostructure (such as surface striation, bundle formation, and helicity).     

Synthesis of Co3O4/Poly(N‐vinylcarbazole) Core/Shell Composite With Enhanced Optical Property

Co₃O₄/poly(N‐vinylcarbazole) (PNVC) composite with enhanced optical property was synthesized via a simple in situ bulk polymerization of NVC monomers in the presence of Co₃O₄ nanoparticles at an elevated temperature. High‐resolution electron microscopic observations showed that the Co₃O₄ nanoparticles were coated with uniform nanolayer shells of PNVC. Fourier‐transform infrared (FT‐IR) spectroscopy revealed the presence of strong interactions between the PNVC polymer chains with the Co₃O₄ surface in the Co₃O₄/PNVC composite. Raman spectroscopic results supported conclusions based on electron microscopy and FT‐IR spectra. The uniform nanolayer coating of PNVC decreases the inherent bulk conductivity of Co₃O₄, however, significantly increases the fluorescence property of Co₃O₄ nanoparticles.

     

Genetic algorithms for optimality of data hiding in digital images

This paper investigates the scope of usage of Genetic Algorithms (GA) for data hiding in digital images. The tool has been explored in this topic of research to achieve an optimal solution in multidimensional nonlinear problem of conflicting nature that exists among imperceptibility, robustness, security and payload capacity. Two spatial domain data hiding methods are proposed where GA is used separately for (i) improvement in detection and (ii) optimal imperceptibility of hidden data in digital images respectively. In the first method, GA is used to achieve a set of parameter values (used as Key) to represent optimally the derived watermark in the form of approximate difference signal used for embedding. In the second method, GA is used for finding out values of parameters, namely reference amplitude (A) and modulation index (μ) both with linear and non linear transformation functions, for achieving the optimal data imperceptibility. Results on robustness for both the methods against linear, non linear filtering, noise addition, and lossy compression as well as statistical invisibility of the hidden data are reported here for some benchmark images.     

The effect of the carbon nanotubes surface oxidation on the morphology and properties of poly(N-vinylcarbazole) coated multi-walled carbon nanotube nanocables

This article describes the effect of carbon nanotubes (CNTs) outer surface oxidation on the morphology and properties of poly(N-vinylcarbazole) (PNVC)-coated individual multi-walled CNT (MWCNT) nanocables. Surface oxidation of MWCNTs has been carried out by refluxing MWCNTs with 5 M nitric acid (HNO₃) at 80 °C for 1 h. The PNVC-coated MWCNT nanocables are synthesized by in situ solid-state polymerization of N-vinylcarbazole monomers in the presence of oxidised MWCNTs (o-MWCNTs) at an elevated temperature. The PNVC-coated MWCNT nanocables are characterized by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning and transmission electron microscopes, photo-luminescence spectroscopy, and direct-current conductivity measurements. Results show that the uniform nanolayer coating of PNVC decreases the inherent bulk conductivity of MWCNTs, but significantly increases the optical properties of MWCNTs.     

Transient liquid phase diffusion bonding of 6061-15 wt% SiCp in argon environment

Extruded 6061-15 wt% SiCp composite was joined by transient liquid phase diffusion (TLPD) bonding process in argon environment using 50-μm thick copper foil interlayer. The bonding was carried out at 560 °C with two different applied pressures (0.1 and 0.2 MPa) and five different holding times (20 min, 1, 2, 3 and 6 h). Kinetics of the bonding process was significantly accelerated in the presence of reinforcement (SiC). This acceleration is attributed to the increased solute diffusivity through defect-rich SiC particle/matrix interface and porosity. Adequate bond strength (90% of the original composite strength) was achieved for bonding at 0.2 MPa pressure with 6 h of holding. This is very close to the reported highest bond strength achieved (92% of the original composite strength) for joining aluminium-based metal matrix composite by TLPD process in vacuum followed by isostatic pressing. The rejection of oxide at periphery on completion of isothermal solidification, and elimination of void at bond interface through solid state diffusion at higher pressure (0.2 MPa) were the main reasons of achieving high bond strength.     

Ion-solvent interactions - studies on the solvation of electrolytes in mixed solvents

In order to throw light on ion-solvent interactions, the solvation numbers of electrolytes in different mixed solvents (methanol + water and ethanol + water mixtures) have been determined using ultrasonic interferometer. The anomalies in the solvation number of cations (in aqueous solutions) like K⁺, Na⁺ and H⁺ are presented. The changes in the solvation numbers of electrolytes with increasing quantities of alcohol indicates some interesting features and are explained on the basis of:(i) decrease in the solvent molecules.(ii) structural re-arrangement.(iii) preferential solvation of cations and anions.(iv) Approximations in the determination of solvation numbers. The role of the solvents could hardly be explained in absence of a complete knowledge of the nature of solvation of electrolytes and particularly of ions. The subject has attracted considerable attention and the solvation number has been determined using different well-known techniques[1-4].In order to throw light on the ion-solvent interactions, we tried to determine the solvation numbers of different known electrolytes like HCl, NaCl and KCl in water, methanol + water and ethanol + water mixtures by the compressibility method using ultrasonic interferometer. The results are presented in this communication.     

Fluorinated aramid fiber reinforced polypropylene composites and their characterization

Polymer fibers are one of the main substances used for the reinforcement of plastic composites. Surface modification of aramid fiber was performed by direct fluorination. The crystallinity and the decomposition temperature of the modified fiber were increased. Scanning electron microscope shows that the roughness increases in the modified fiber. Composites were prepared by using modified and unmodified fibers. It was shown that the mechanical and thermal properties increase for modified fiber reinforcing composites. To reduce the fiber degradation or breakdown, composites were prepared by solution casting method. POLYM. COMPOS., 28:462–469, 2007. © 2007 Society of Plastics Engineers     

Recent developments in mine hoists drives

This paper presents a comprehensive literature review for mine hoist drives. Both DC and AC drives with their control techniques are discussed with a comparative study on their performance. Many recent control techniques using power electronic based systems are also discussed. The future trend in this area is also addressed. This review paper is the first of its kind information source provider for mine winder drives to be useful for researchers, designers and application engineers in the mining industry.