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Microwave radar absorbers are widely used in the strategic sector and wireless communication systems to reduce the radar cross-section of a target and electromagnetic interferences, respectively. For airborne stealth platforms, it is desired to have wide bandwidth RAS with minimum thickness and adequate structural rigidity. However, the classical RAS structures are thicker with a narrowband of absorption. So the demand of thin and broadband absorber for a modern stealth platform can be accomplished by designing metallic or resistive frequency selective surfaces (FSSs) based radar absorbing structures (RAS). In view of this, a technological assessment on frequency selective surface (FSS)-based radar absorbing structure are presented in this paper, which includes historical review on radar absorber development, design techniques, physical models, and optimization techniques. Ultra-wideband absorbers with essentially thin structures can be realized by optimizing FSS and dielectric parameters. The genetic algorithm (GA) is identified as one of the effective searching algorithms among several numerical algorithms, which are discussed in detail for single and multi-layered FSS–RAS. The fabrication techniques of resistive FSS by printing the periodic pattern using resistivity-controlled ink is also addressed. For proof-of-the concept, a prototype of cross-dipole FSS based RAS is fabricated and measured.

Numerical and experimental investigation on free and forced vibration of honeycomb core sandwich structure using the equivalent two-dimensional (2D) model is presented. Initially, a three-dimensional (3D) honeycomb core sandwich structure is converted to a 2D panel with equivalent properties obtained based on the honeycomb plate theory. Following this, the 2D panel is modelled using a layered structural shell element to obtain the vibration response using commercial element software. An experiment on harmonic analysis is carried out on the honeycomb core sandwich structure. The results obtained based on numerical results of free- and forced-vibration responses match well with experimental results. Further, from the forced-vibration response of both experimental and numerical results, it is noticed that the second mode is not observed. This can be attributed to the excitation location corresponding to the nodal point of the second mode and this is verified with the mode shape obtained based on numerical and experimental analysis.

The Soil Water Assessment Tool (SWAT) was applied to the 2,530 km2 Chaliyar river basin in Kerala, India to investigate the influence of scale on the model parameters. The study was carried out in this river basin at two scales. Parameters such as land use, soil type, topography and management practices are similar at these scales. The model was initially calibrated for streamflow and then validated. Critical parameters were the curve number (CN2), soil evaporation compensation factor (ESCO), available water holding capacity (SOL_AWC), average slope length (SLSUBBSN), and base flow alpha factor (ALPHA_BF). Using the optimized value of various parameters, stream flow was estimated from parts of the basin at two different scales—an area of 2,361.58 km2 and an area of 1,013.15 km2. The streamflow estimates at both these scales were statistically analysed by computing the coefficient of determination (R 2) and the Nash–Sutcliffe efficiency (ENS). Results indicate that the SWAT model could simulate streamflow at both scales reasonably well with very little difference between the observed and computed values. However, the results also indicate that there may be greater uncertainty in SWAT streamflow estimates as the size of the watershed increases.

Cysts of the tunica albuginea are uncommon lesions of the testis which in all reported cases have been benign. Complex cysts of the tunica albuginea can mimic intratesticular lesions, thus necessitating orchiectomy. We present a case of a complex tunica albuginea cyst which mimicked an intratesticular lesion at sonography, as well as at magnetic resonance imaging (MRI). Tangential views, however, suggested that this was in fact an extratesticular lesion. The use of tangential views, as well as knowledge of the appearance of the tunica albuginea at MRI, are important to make this differentiation in order to guide the management of these lesions. To our knowledge, this is the first case in which the appearance of a tunica albuginea cyst at MRI has been described.