An automated simultaneous measurement of thickness and wave velocity by ultrasound

The measurement of wave velocity in a sample requires an accurate determination of the sample thickness at the points of interrogation. The theory of an automated technique is presented. In its application, the thickness of the sample is first calculated by the knowledge of the wave velocity in the immersion fluid. This thickness is then used to calculate the wave velocity in the sample. The results of the application of the technique to isotropic and anisotropic materials are presented.     

Synthesis and Characterization of Cardo Polysulfonates of 1,1′-Bis(4-Hydroxy Phenyl)Cyclohexane with 1,3-Benzene and 2,4-Toluene Disulfonyl Chlorides

Abstract

Cardo polysulfonates (PSBCB and PSBCT) of 1,1′-bis(4-hydroxy phenyl)cyclohexane with benzene-1,3 and toluene-2,4-disulfonyl chlorides have been synthesized by interfacial polycondensation of 1,1′-bis(4-hydroxy phenyl)cyclohexane (0.005 mol) with benzene-1,3/toluene-2,4-disulfonyl chlorides (0.005 mol) using water-chloroform (4:1, v/v) as interphase, alkali (0.015 mol) as acid acceptor, and cetyl trimethyl ammonium bromide (0.125 g) as emulsifier at 0°C for 3 hours. The structures of the polymers were supported by IR and NMR spectral data. The PSBCT was fractionated into several fractions by using 1,2-dichloroethane as solvent and n-butanol as precipitant. The fractions were characterized by GPC and viscometry in different solvents at four different temperatures. Viscosity studies showed that the PSBCT is flexible in solutions and has a specific solvent effect. PSBCB and PSBCT have good biological activity against E. coli and S. citrus organisms, and they possess excellent hydrolytic stability toward acids and alkalis.     

Nondestructive evaluation of helicopter rotor blades using guided Lamb modes

This paper presents an application for turning and direct modes in a complex composite laminate structure. The propagation and interaction of turning modes and fundamental Lamb modes are investigated in the skin, spar and web sections of a helicopter rotor blade. Finite element models were used to understand the various mode conversions at geometric discontinuities such as web-spar joints. Experimental investigation was carried out with the help of air coupled ultrasonic transducers. The turning and direct modes were confirmed with the help of particle displacements and velocities. Experimental B-Scans were performed on damaged and undamaged samples for qualitative and quantitative assessment of the structure. A strong correlation between the numerical and experimental results was observed and reported.     

Synthesis and Mechanistic Study of Triheterocyclic 4H‐Pyrimido[2,1‐b]benzothiazole derivatives,One‐Pot Three‐component Reaction under Solvent‐Free Conditions

An efficient method has been developed for the preparation of 4H‐pyrimido[2,1‐b]benzothiazole derivatives by the condensation of aldehydes, β‐ketoester, and 2‐amino benzothiazole under solvent and solvent‐free conditions using various catalysts. The reaction uses benzothiazole as a new component, and good yield is obtained at 60–65°C under solvent‐free conditions. Atom economies, good yield, environmentally benign, and easy to work‐up are some of the important features of this protocol. The present study suggests that acetic acid and metal catalysts follow different mechanism. In acetic acid, 2‐amino benzothiazole reacts with benzaldehyde, and resultant intermediate reacts with ethyl acetoacetate to give final product, whereas in the presence of metal catalysts, 2‐amino benzothiazole first reacts with ethyl acetoacetate, and resultant intermediate reacts with benzaldehyde to give pyrimido[2,1‐b]benzothiazole.     

Effect of the Functionalization of the Axial Phthalocyanine Ligands on the Energy Transfer in QD-based Donor–Acceptor Pairs

This study examines the electronic coupling between quantum dots (QDs) and molecules on their surfaces as a function of the modality of their interaction. As a probe, the energy transfer (ET) between CdSe QDs and phthalocyanines (Pcs) was monitored and evaluated with regard to the functionalization of the axial phthalocyanine ligand, bulkiness of the functional group bridging the QD donor and Pc acceptor, and the number of the functionalized axial ligands. New silicon PCs and their conjugates with CdSe QDs were synthesized. The ET efficiency and kinetics were studied by steady state and femtosecond time-resolved absorption spectroscopy. We observed a decrease in ET efficiency with the increase in functional group bulkiness, which could be explained by increasing steric hindrance between the ET pair. In addition, a higher ET efficiency was observed for amino and thiol functionalized Pcs compared to Pcs without functional group on the axial alkyl chain.     

Crystalline-amorphous interaction in relation to the phase diagrams of binary polymer blends containing a crystalline constituent

The present article describes an equilibrium theory for determining binary phase diagrams of various crystalline-amorphous polymer blends by taking into account the contributions from both liquid-liquid phase separation between the constituents and solid-liquid phase transition of the crystalline component. An analytical expression for determining a crystal-amorphous interaction parameter is deduced based on the solid-liquid transition, involving the solidus and liquidus lines in conjunction with the coexistence curve of an upper critical solution temperature type. Of particular importance is that the crystalline-amorphous interaction parameter can be determined directly from the melting point depression data. The present analysis is therefore different from the conventional Flory-Huggins interaction parameter, which is associated with the liquid-liquid phase separation. The validity of the present theory is tested with the experimental phase diagrams of blends of poly(ethylene oxide)/diacrylate and poly(vinyl alcohol)/cellulose.     

Quantum dot-based energy transfer: perspectives and potential for applications in photodynamic therapy

Quantum dots have emerged as an important class of material that offers great promise to a diverse range of applications ranging from energy conversion to biomedicine. Here, we review the potential of using quantum dots and quantum dot conjugates as sensitizers for photodynamic therapy (PDT). The photophysics of singlet oxygen generation in relation to quantum dot-based energy transfer is discussed and the possibility of using quantum dots as photosensitizer in PDT is assessed, including their current limitations to applications in biological systems. The biggest advantage of quantum dots over molecular photosensitizers that comes into perspective is their tunable optical properties and surface chemistries. Recent developments in the preparation and photophysical characterization of quantum dot energy transfer processes are also presented in this review, to provide insights on the future direction of quantum dot-based photosensitization studies from the viewpoint of our ongoing research.     

Energetic nitrogen-rich salts and ionic liquids

Energetic salts offer many advantages over conventional energetic molecular compounds. The use of nitrogen containing anions and cations contributes to high heats of formations and high densities. Their low carbon and hydrogen content gives rise to a good oxygen balance. The decomposition of these compounds is predominantly through the generation of dinitrogen which makes them very promising candidates for highly energetic materials for industrial or military applications.