Effect of Fe3+ substitution on the structural modification and band structure modulated UV absorption of hydroxyapatite

The effect of Fe³⁺ ionic substitution in hydroxyapatite (Ca_10-xFe_x(PO₄)₆(OH)₂) was studied using structural modifications, resulting in an improvement in UV absorption through a tailored optical band structure. Ca²⁺ of HA being larger compared to Fe³⁺ contributes to the shrinkage of the lattice. Undoped HA has a peak at 1085 cm⁻¹ (ʋ₃ PO₄³⁻) which is shifted to 1033 cm⁻¹ for Fe-HA, because of the perturbation in HA structure. An improvement of UV absorption in the entire UVA and UVB range with an increase in Fe content because of a decrease in bandgap from 5.9 eV to 2.1 eV with undoped and doped HA. Theoretically obtained band gap and optical behaviour of the systems are well correlated with the experimental findings. Moreover, the use of marine biowaste from cuttlefish bone, as the source of HA; low cost and promising UV absorption can have a potential application as UV protective sunscreen filters.     

Mechanochemical Adhesion and Plasticity in Multifiber Hydrogel Networks

The extracellular matrix (ECM) has force-responsive (i.e., mechanochemical) properties that enable adaptation to mechanical loading through changes in fibrous network structure and interfiber bonding. Imparting such properties into synthetic fibrous materials will allow reinforcement under mechanical load, the potential for material self-adhesion, and the general mimicking of ECM. Multifiber hydrogel networks are developed through the electrospinning of multiple fibrous hydrogel populations, where fibers contain complementary chemical moieties (e.g., aldehyde and hydrazide groups) that form covalent bonds within minutes when brought into contact under mechanical load. These fiber interactions lead to microscale anisotropy, as well as increased material stiffness and plastic deformation. Macroscale structures (e.g., tubes and layered scaffolds) are fabricated from these materials through interfiber bonding and adhesion when placed into contact while maintaining a microscale fibrous architecture. The design principles for engineering plasticity described can be applied to numerous material systems to introduce unique properties, from textiles to biomedical applications.     

Dispersion forces in wetting

tA simple, analytically tractable, model is used to obtain wetting phase diagrams for insulators on insulating and metallic substrates. The phase diagrams are consistent with the general rule that if the vapor phases of A and B are dilute and dispersion forces allow wetting of A on B then, wetting of B on A is not allowed.     

Prism coupling technique: a method for measurement of propagation constant and beat length in single-mode fibres

We report preliminary investigations on the application of the prism coupling technique to the measurement of the mode spectra of conventional and birefringent single-mode fibres (SMFs). Experimental results on the measurement of the propagation constant in normal SMF, and the application of this technique to the measurement of beat length on an elliptic-core SMF, are presented.     

Family pathology and anorexia in the Indian context

Frequent associations have been found between family interaction and anorectic behaviour. Family theorists have viewed anorexia as a manifestation of a dysfunctional family system. We report three families of cases of anorexia (one male and two female) where the symptom was a reflection of family pathology and was being maintained by it. The cases emphasize the need to assess families of anorectics in detail and view them in the cultural context of eating.     

The Weyl correspondence and time-frequency analysis

Describes the Weyl correspondence and its properties, showing how it gives a “window-independent” definition of time-frequency concentration for use in models in signal detection. The definition of concentration is justified by showing that it gives reasonable answers in certain intuitive cases. The Weyl correspondence expresses a linear transformation as a weighted superposition of time-frequency shifts of the signal, and then authors explain why this is not the same as “transforming” a signal into the time-frequency domain, multiplying by a weight in the transform domain and taking the inverse. The investigation into time-frequency concentration and the Weyl correspondence is justified by a new result. The authors show that convolving the Wigner distribution with a general smoothing function is equivalent to evaluating a weighted sum of spectrograms. This is a new interpretation of the process of smoothing the Wigner distribution to reduce cross-terms. It relates smoothing of the Wigner distribution to the “multiple window” technique pioneered by Thomson (1982)     

Forced convection heat transfer from axisymmetric bodies to non-Newtonian fluids

A theoretical analysis for forced convection heat transfer from axisymmetric bodies immersed in non-Newtonian power-law fluids has been performed. Results for the velocity shape factor, local friction coefficient, and the Nusselt number are presented for different values of Prandtl number and the power-law index. The local friction coefficient results are compared with available experimental data and it is shown that asymptotic expressions suffice to get accurate predictions of heat transfer at low and high Prandtl numbers.     

The kosterlitz-thouless transition and vortex dynamics

The physics of the Kosterlitz-Thouless vortex-unbinding transition in two-dimensional superfluids is discussed, and theN ×N Josephson junction array is considered as a prototype system. Dynamical behaviour is considered in two cases: (a) the complex impedance shows structure at a frequency-dependent transition temperature, similar to the dynamic susceptibility of a spin glass; (b) with a perpendicular non-uniform magnetic field, of a particular ‘self-similar’ hierarchical pattern, a scaling argument gives non-exponential relaxational dynamics of a prepared non-equilibrium vortex distribution.