Effect of ZnO on phase emergence, microstructure and surface modifications of calcium phosphosilicate glass/glass-ceramics having iron oxide

The effect of ZnO on phase emergence and microstructure properties of glass and glass-ceramics with composition 25SiO₂-50CaO-15P₂O₅-(10 − x)Fe₂O₃-xZnO (where x = 0, 2, 5, 7 mol%) has been studied. They have been characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Surface modifications of these glass-ceramics in simulated body fluid have been studied using Fourier transform infrared reflection spectroscopy (FTIR), XPS and SEM. Results have shown a decrease in the fraction of non-bridging oxygen with increase in zinc oxide content. Emergence of crystalline phases in glass-ceramics at different heat treatment temperatures was studied using XRD. When glass is heat treated at 800 °C calcium phosphate, hematite and magnetite are developed as major phases in the glass-ceramics samples with ZnO up to 5 mol%. In addition to these, calcium silicate (Ca₃Si₂O₇) phase is also observed when glass is heat treated at 1000 °C. The microstructure of the glass-ceramics heat treated at 800 °C exhibits the formation of nano-size (40-50 nm) grains. On heat treatment at 1000 °C crystallites grow to above 50 nm size and more than one phase are observed in the microstructure. The formation of thin flake-like structure with coarse particles is observed at high zinc oxide concentration (x = 7 mol%). In vitro studies have shown the surface modifications and formation of Ca-P-rich layer on the glass-ceramics when immersed in simulated body fluids (SBF) for different durations. The bioactive response was found to depend on ZnO content.     

Solar eclipse effects of 22 July, 2009 on the propagation of radio signals

The results of investigation of the variation of radio signal strengths during the solar eclipse on July 22, 2009 are reported in this paper. Observations of the radio signals transmitted from different radio stations at different frequencies and received at a particular observing site indicate a distinct change in signal strength around the time the eclipse umbra passes the propagation paths. The three types of variations in the eclipse day and particularly during its peak period are different from propagation under normal condition. The phenomena of signal variations, the noted “Inverted U-shape“ at one of the frequencies before the occurrence of the eclipse and 13 to 15 minutes time difference between the enhancement of the signal strength and the onset of eclipse are some interesting characteristics. The results are interpreted by ionospheric D-layer behavior at such times.     

Steady state and time-resolved spectroscopic investigations on the photoreactions involved within the electronically excited electron acceptor 9-cyanoanthracene in presence of benzotriazole and benzimidazole donors

The electrochemical, “steady-state” and “time-resolved” spectroscopic investigations were made on the well-known electron acceptor 9-cyanoanthracene (CNA) when interacted with the electron donors benzotriazole (BZT) and benzimidazole (BMI) molecules. Though electrochemical measurements indicate the thermodynamical possibility of occurrences of photoinduced electron transfer reactions within these reacting systems in the lowest excited singlet state (S₁) of the acceptor CNA but the steady-state and time-resolved measurements clearly demonstrate only the triplet-initiated charge separation reactions. It was reported earlier that in the cases of disubstituted indole molecules the occurrences of photoinduced electron transfer reactions were apparent both in the excited singlet and triplet states of the acceptor 9-cyanoanthracene, but the similarly structured present donor molecules benzotriazole (and benzimidazole) behave differently from indoles. The weak ground state complex formations within the presently studied reacting systems appear to be responsible for the observed static quenching phenomena as evidenced from the time-resolved fluorescence studies. Time-resolved spectroscopic investigations demonstrate the formation of the ground state of the reacting components (donor and acceptor) through recombination of triplet ion-pairs via formations of contact neutral radical produced by H-abstraction mechanism.     

Effects of nematic fluctuations on the elastic properties of iron arsenide superconductors

We demonstrate that the changes in the elastic properties of the FeAs systems, as seen in our resonant ultrasound spectroscopy data, can be naturally understood in terms of fluctuations of emerging nematic degrees of freedom. Both the softening of the lattice in the normal, tetragonal phase as well as its hardening in the superconducting phase are consistently described by our model. Our results confirm the view that structural order is induced by magnetic fluctuations.     

Ising model on self-avoiding walk chains

The phase transitions of nearest-neighbour interacting Ising models on self-avoiding walk (SAW) chains on square and triangular lattices have been studied using Monte Carlo technique. To estimate the transition temperature (T _c) bounds, the average number of nearest-neighbours (Z _eff) of spins on SAWs have been determined using the computer simulation results, and the percolation thresholds (p _c) for site dilution on SAWs have been determined using Monte Carlo methods. We find, for SAWs on square and triangular lattices respectively,Z _eff=2.330 and 3.005 (which compare very well with our previous theoretically estimated values) andp _c=0.022±0.003 and 0.045±0.005. When put in Bethe-Peierls approximations, the above values ofZ _eff givekT _c/J<1.06 and 1.65 for Ising models on SAWs on square and triangular lattices respectively, while, using the semi-empirical relation connecting the Ising modelT _c's andp _c's for the same lattices, we findkT _c/J0.57 and 0.78 for the respective models. Using the computer simulation results for the shortest connecting path lengths in SAWs on both kinds of lattices, and integrating the spin correlations on them, we find the susceptibility exponent =1.024±0.007, for the model on SAWs on two dimensional lattices.     

Measurement of plane wave acoustic fields in flow ducts

The response of a fluid loaded plate is derived as function of the incident pressure in the fluid. The results are compared with full scale measurements made in the aft peak tank on a ship. Propeller induced pressure and hull plate velocity were measured with flush-mounted hydrophones and accelerometers. It is found that for a typical aft body construction the boundaries of the plate elements can be assumed to be simply supported. The plate model agrees well with full scale measurements down to 40 Hz. Below this frequency global vibrations determine the response of the hull. Both theoretical and experimental results indicate that the field induced by the vibrating plate elements can be considerable. The response of a plate can be decreased if the width of the plate is decreased or the plate thickness increased.     

Finite quantum field theory and neutrinodynamics

In quantum neutrinodynamics (photon-neutrino weak coupling) all the renormalization constants vanish and therefore the field equations cannot be expressed in terms of unrenormalized field quantities. This helps us to formulate quantum neutrinodynamics as a convergent quantum field theory. It is also pointed out that from the viewpoint of the unified model of weak and electromagnetic interaction as developed on the basis of the photon-neutrino weak coupling by Bandyopadhyay, quantum electrodynamics also manifests itself as a convergent field theory.