In the phase of the study reported, the sol-gel technique was followed in the preparation of cobalt ferrite amorphous powder following the same procedure which was selected as the best approach as described in a previous study. It was assumed that there must be a correlation between the heat treatment operational parameters and the structural properties of the material being synthesized. Similarly, it was understood that some heat treatment is necessary to completely decompose the organic and nitrate contents present in the amorphous powder. Having ensured that the heat treatment parameters could be changed without producing a material with poorer properties, it was then possible to produce batches of powders using milder conditions in the heat treatment operation. The particle size distributions of these new batches of nanoparticles were estimated to be in the range 7-28 nm and since the results showed promise, their magnetic properties were also determined.

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Inspired by the morphology of Coscinodiscus species diatom, bi-layered photonic structures comprised of dielectric-filled nano-holes of varying diameters have been designed and analyzed to enhance and tune absorption characteristics of GaAs-based thin-film photonic devices. Finite difference time domain-based numerical analysis and effective medium approximation based theoretical calculations show that by adjusting diameter and areal density of the nano-holes of the two layers, the peak absorption wavelength can be tuned over a wide spectral range, while attaining a maximum peak-absorptance value of about 97% and a maximum absorption bandwidth of ∼ 190 nm. The maximum enhancement factor of the bi-layered structure is about 11% higher than the value obtained for its equivalent single-layered counterpart over the near-ultraviolet to visible regime of the spectra. High absorptance over a wide-angle for TM polarization and tunable angle-dependent absorption characteristics for TE polarization are also obtained for the proposed ultra-thin absorbers. It has been shown that instead of having misaligned pore-centers as in Coscinodiscus species diatoms, a bi-layered structure designed with layers of identical lattice constant offers significant flexibility in terms of design and practical realization of thin-film photonic devices.

A good number of infrastructure projects are implemented in Bangladesh during the last decade and many more are still in pipeline. In the financial year 2017-18 approximately 12.7 million tons of aggregate are used by the construction industries. Local sources could supply only 11% of those aggregate and rest 89% are collected from foreign sources. Due to the wide variation of aggregate sources performance of concrete become unpredictable. Therefore, in the present study influence of commonly used coarse aggregate characteristics for building sustainable infrastructure are investigated by evaluating the performance of concrete with various aggregate types. To evaluate performance, six mostly used coarse aggregate sources are selected for this study. A series of laboratory test are conducted to evaluate the ACV, TFV, LAA, EI, FI, specific gravity, water absorption and unit weight for all six aggregates. Additionally, chemical composition and petrographic properties are also explored. Keeping the gradation of aggregate constant, two types of concrete mix (w/c ratio 0.3 and 0.4) were prepared to cast concrete cylinders and beams by using six sources of coarse aggregate. Concrete properties including compressive, tensile and flexural strength are determined. The study finds that physical properties of aggregate generally influence the properties of concrete. However, the influence is significant in case of concrete requiring compressive strength higher than 50 MPa. The outcomes of the study will help the engineers to select appropriate sources of aggregate depending on concrete strength requirements.

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Macroporous alkali resistant glass has been developed by making additions of zirconia (ZrO 2 ) and zircon (ZrSiO 4 ) to the sodium borosilicate glass system SiO 2 -B 2 O 3 -Na 2 O. The glass was made using a traditional high temperature fusion process. Differential thermal analysis (DTA) was carried out to identify the glass transition temperature (T g ) and crystallisation temperature (T x ). Based on these findings, controlled heattreatments were implemented to separate the glass into two-phases; a silica-rich phase, and an alkali-rich borate phase. X-ray diffraction (XRD) was used to identify any crystal phases present in the as-quenched and heat-treated glasses. Fourier transform infrared (FTIR) spectroscopy also proved effective in investigating phase separation and crystallisation behaviour. After leaching, a silica-rich skeleton with an interconnected pore structure and a uniform pore distribution was observed. Pore characterisation was carried out using mercury porosimetry. The size and shape of the pores largely depended on the heattreatment temperature and time. ZrO 2 /ZrSiO 4 additions increased the alkali resistance of the porous glass 3-4 times.