Ankita Pandey

Flow-induced nonequilibrium self-assembly in suspensions of stiff, apolar, active filaments.

Active bodies in viscous fluids interact hydrodynamically through self-generated flows. A stiff, apolar, active filament generates symmetric fluid flow around it and thus cannot self-propel. Here we study the mobility and aggregation induced by hydrodynamic flow in a suspension of stiff, apolar, active filaments. We consider two types of active filaments, with those producing extensile or contractile flows along their long axis. Lateral hydrodynamic attractions in extensile filaments lead, independent of the volume fraction, to anisotropic aggregates which translate and rotate ballistically. Lateral hydrodynamic repulsions in contractile filaments lead to microstructured states, where the degree of clustering increases with the volume fraction and the filament motion is always diffusive. Our results demonstrate that the interplay between active hydrodynamic flows and anisotropic excluded volume interactions provides a generic nonequilibrium mechanism for hierarchical self-assembly of active soft matter.

Optimization and thermoluminescence study of the nanophosphor BaSO4:Eu

In this work, first and foremost optimization of the nanocrystalline BaSO4:Eu has been presented by primarily varying the concentration of the rare earth element Europium (0.05, 0.10, 0.20, 0.50 and 1.00u2005mol %). Further, a comparative study of the nanophosphor with a well-established dosimeter i.e. TLD-100 (and by extension to CaSO4:Dy (TLD-900)) has also been reported here as a step towards finding an ideal TL dosimeter. The various batches of the said phosphor prepared by the chemical co-precipitation method have been investigated for their TL sensitivity property and it has been observed that BaSO4:Eu doped with 0.2u2005mol% Europium showed the highest sensitivity out of the lot. Moreover, when compared to the standard dosimeter, the optimized BaSO4:Eu (0.2u2005mol%) showed a higher sensitivity of about 28.52 times that of the Standard TLD-100 and 1.426 times higher than standard CaSO4:Dy (TLD-900). An extraordinary linear TL response curve over an extensive range of doses (10Gy to 2kGy) is yet another integra...

A study of Co-doping effect on thermoluminescence properties of potassium calcium sulphate

In this study nanocrystalline K2Ca2(SO4)3:Cu, K2Ca2(SO4)3:Mg and K2Ca2(SO4)3:Cu,Mg were prepared by co-precipitation method and were further annealed at 700°C for two hours. The XRD shows the cubic structure with crystallite size around 40-50u2005nm. The concentrations of the dopants Cu and Mg (Cu alone, Mg alone and Cu, Mg co-doped) were 0.1u2005mol % in each of the sample (0.1 % mol in Cu alone, 0.1% mol in Mg alone and 0.05% mol of each Cu and Mg in Cu,Mg co-doped). The samples were irradiated by gamma radiation over a dose range of 10u2005Gy to 2 kGy. TL glow curves of the irradiated samples were recorded and studied on Harshaw TLD Reader 3500. Glow curves of irradiated samples reveal that the sample which is co-doped with Cu,Mg shows more intense peak at 120°C as compared with the other samples. The sample which is doped with Mg alone shows a major peak at 116°C and another peak of low intensity at 163°C. The corresponding peaks’ temperatures for sample doped with Cu alone are 116°C (major peak) and 168°C respec...

Nanocrystalline K2Ca2(SO4)3: Eu for proton beam dosimetry

This paper investigates the Thermoluminescent response of nanocrystalline K2Ca2(SO4)3: Eu, prepared by Co-precipitation technique to 150 MeV proton beam. The particle size was calculated to be 45 nm by the broadening of the XRD peaks using Scherrers formula. Samples in the form of pellets were irradiated by 150 MeV proton beam with dose range of 0.1 Gy to 325 Gy. Thermoluminescence (TL) glow curves of the irradiated samples were recorded and studied. It has been found that the phosphor shows a characteristic single peak at around 420 K. The TL response is linear in the range upto 200 Gy and then saturates for higher doses. The wider linear TL response of nanocrystalline K2Ca2(SO4)3: Eu and low fading makes it a superior candidate as a dosimeter to be used for detecting the doses of protons beams for its various applications in the field of space, therapy and research.

Minimal polar swimmer at low Reynolds number

We propose a minimal model for a polar swimmer, consisting of two spheres connected by a rigid slender arm, at low Reynolds number. The propulsive velocity for the proposed model is the maximum for any swimming cycle with the same variations in its two degrees of freedom and its displacement in a cycle is achieved entirely in one step. The stroke averaged flow field generated by the contractile swimmer at large distances is found to be dipolar. In addition, the changing radius of one of the spheres generates the field of a potential doublet centered at its initial position.

Estimation of the fibre-composition of Verhoff-stained fascia using colour-image processing

This paper reports the results of our work on assessing the composition of abdominal fascia based on microscopic images of specimen stained by Verhoff’s method, using colour-image processing. Verhoff’s method of staining results in collagen fibres appearing red, and elastic fibres and speckle-like artefacts appearing black (elastic fibres being darker), in a yellowish background. The basic idea involves segmenting the red-coloured collagen first, followed by segmenting the black elastic fibres. We use the YIQ colour model for the purpose. Collagen is extracted by thresholding a contrast-enhanced version of the I-image, and elastic fibres are extracted by thresholding the Y-image based on an empirically estimated threshold-value. Results of experiments on real microscopic images are encouraging.