Spectrum Challenges and Solutions by Cognitive Radio: An Overview

This paper provides an overview of major problems that are confronting wireless communication with regard to spectrum use in general i.e. by all sectors, government, private, other telecom service providers and military communication. It is commonly believed that there is a crisis of spectrum availability due to tremendous growth in the wireless based systems and the evolution of the radio communication technologies. In fact, there is no shortage of radio spectrum, only a dearth of affordable communications infrastructure. There is potential to make considerably better usage of the radio-spectrum. There are many areas of the radio spectrum which are not fully utilized. Cognitive radios (CR) have been proposed as a way to reuse this underutilized spectrum in an opportunistic manner. A CR is an autonomous unit in a communications environment that senses its environment, tracks changes, and reacts upon its findings and frequently exchanges information with the networks. We show the how the radio frequency is being managed in India and what India is doing to face the challenges to improve the spectrum management. The radio Communication Assembly of ITU is also studying the plan for implementation of CR systems including technical and regulatory issues.

Thermal slip and radiative heat transfer effects on electro‐osmotic magnetonanoliquid peristaltic propulsion through a microchannel

A mathematical study is described to examine the concurrent influence of thermal radiation and thermal wall slip on the dissipative magnetohydrodynamic electro‐osmotic peristaltic propulsion of a viscous nanoliquid in an asymmetric microchannel under the action of an axial electric field and transverse magnetic field. Convective boundary conditions are incorporated in the model and the case of forced convection is studied, that is, thermal and species (nanoparticle volume fraction) buoyancy forces neglected. The heat source and sink effects are also included and the diffusion flux approximation is employed for radiative heat transfer. The transport model comprises the continuity, momentum, energy, nanoparticle volume fraction, and electric potential equations with appropriate boundary conditions. These are simplified by negating the inertial forces and invoking the Debye–Hückel linearization. The resulting governing equations are reduced into a system of nondimensional simultaneous ordinary differential equations, which are solved analytically. Numerical evaluation is conducted with symbolic software (MATLAB). The impact of different control parameters (Hartmann number, electro‐osmosis parameter, slip parameter, Helmholtz–Smoluchowski velocity, Biot numbers, Brinkman number, thermal radiation, and Prandtl number) on the heat, mass, and momentum characteristics (velocity, temperature, Nusselt number, etc) are presented graphically. Increasing Brinkman number is found to elevate temperature magnitudes. For positive Helmholtz–Smoluchowski velocity (reverse axial electrical field) temperature is strongly reduced, whereas for negative Helmholtz–Smoluchowski velocity (aligned axial electrical field), it is significantly elevated. With increasing thermal slip, nanoparticle volume fraction is also increased. Heat source elevates temperatures, whereas heat sink depresses them, across the microchannel span. Conversely, heat sink elevates nanoparticle volume fraction, whereas heat source decreases it. Increasing Hartmann (magnetic) parameter and Prandtl number enhance the nanoparticle volume fraction. Furthermore, with increasing radiation parameter, the Nusselt number is reduced at the extremities of the microchannel, whereas it is elevated at intermediate distances. The results reported provide a good insight into biomimetic energy systems exploiting electromagnetics and nanotechnology, and, furthermore, they furnish a useful benchmark for experimental and more advanced computational multiphysics simulations.     

Swift heavy ion irradiation effect on Cu-doped CdS nanocrystals embedded in PMMA

Semiconductor nanocrystals (NCs) have received much interest for their optical and electronic properties. When these NCs dispersed in polymer matrix, brightness of the light emission is enhanced due to their quantum dot size. The CdCuS NCs have been synthesized by chemical route method and then dispersed in PMMA matrix. These nanocomposite polymer films were irradiated by swift heavy ion (SHI) (100 MeV, Si⁺⁷ ions beam) at different fluences of 1 × 10¹⁰ and 1 × 10¹² ions/cm² and then compared their structural and optical properties by XRD, atomic force microscopy, photoluminescence, and UV-Vis spectroscopy before and after irradiation. The XRD spectra showed a broad hump around 2θ ≈ 11·83° due to amorphous PMMA and other peaks corresponding to hexagonal structure of CdS nanocrystals in PMMA matrix. The photoluminescence spectra shows a broad peak at 530 nm corresponding to green emission due to Cu impurities in CdS. The UV-Vis measurement showed red shift in optical absorption and bandgap changed from 4·38–3·60 eV as the irradiation fluency increased with respect to pristine CdCuS nanocomposite polymer film.     

Accumulation of chromium and zinc from aqueous solutions using water hyacinth (Eichhornia crassipes)

Under present investigation Eichhornia crassipes (water hyacinth) has been tested for removal of two important heavy metals chromium (Cr) and zinc (Zn) from metal solution. This species was grown at four concentrations of Cr and Zn, i.e. 1.0, 5.0, 10.0 and 20.0 mg l(-1) in single metal solution. This plant has performed extremely well in removing the Cr and Zn from their solution and was capable of removing up to 95% of zinc and 84% of chromium during 11 days incubation period. Removal of Cr at lower concentrations (1.0 and 5.0 mg l(-1)) was found harmless, without any symptom of toxicity but at 10.0 and 20.0 mg l(-1), plants have shown some morphological symptoms of toxicity. On the other hand E. crassipes removed Zn safely at all the four concentrations, i.e. 1.0, 5.0, 10.0 and 20.0 mg l(-1). In this case morphological symptoms of toxicity were not evident in the test plant. Biochemical parameters viz. protein, sugar and chlorophyll in experimental plants have shown a decreasing trend due to accumulation of Zn and Cr. Overall this methodology is safe for the removal of Zn and Cr and can be utilized at large scale after few further investigation.     

Efficacy of application of vegetable seed oils as grain protectant against infestation by Callosobruchus chinensis and its effect on milling fractions and apparent degree of dehusking of legume-pulses

The solvent extracted vegetable seed oils of Cucurbitaceae family viz. Bitter gourd (Momordica charentia), Small bitter gourd (Momordica dioica), Bottle gourd (Lagenaria siscraria) and Ridge gourd (Luffa acutangula) were evaluated as grain protectant against callosobruchus chinensis on the stored legume-pulse grains. All the vegetable seed oils were found effective as legume-pulse grain protectant, which provided, negligible weight loss at the oil-application rate of 6-8 mL/kg in legume-pulse grain after 60 days storage at laboratory conditions. The milling yield and degree of dehusking gets improved after the oil application. The use of solvent extracted Small bitter gourd seed oil at the level of 6-8 mL/kg of legume-pulse grain sample resulted in the improved apparent degree of dehusking from 40.0 to 72.59, 59.88 to 92.44, 63.39 to 87.50 and 57.0 to 79.43 for Pigeonpea (Canjanus cajan), Chickpea (Cicer arietinum), Urdbean (Phaseolus mungo) and Mungbean (Phaseolus radiatus), respectively.     

Thermal modeling of passive and active solar stills for different depths of water by using the concept of solar fraction

This communication presents the thermal analysis of passive and active solar distillation system by using the concept of solar fraction inside the solar still with the help of AUTOCAD 2000 for given solar azimuth and altitude angle and latitude, longitude of the place. Experiments have been conducted for 24 h (9 am to 8 am) for New Delhi climatic conditions (latitude 28°35′N, longitude 77°12′E) during the months of November and December for different water depths in the basin (0.05, 0.1 and 0.15 m) for passive as well as active solar distillation system. Analytical expressions for water and glass cover temperatures and yield have been derived in terms of design and climatic parameters. It is observed that

(i) the solar fraction plays a very important role at lower values of solar altitude angle;

(ii) the internal convective heat transfer coefficient decreases with the increase of water depth in the basin due to decrease in water temperature;

(iii) there is a fair agreement between the experimental observation and theoretical prediction during daytime as compared to that during the night.

Grain growth and structural transformation in ZnS nanocrystalline thin films

Fabrication of ZnS thin films having similar stoichiometry at different substrate temperatures (T_S) e.g. 200 °C, 300 °C and 400 °C by means of RF magnetron sputtering method is presented. The films grown at T_S of 200 °C are in cubic zinc-blende phase and textured along (111) plane. The films deposited at T_S of 300 °C and 400 °C are in hexagonal wurtzite phase. The surface roughness and grain size of the films increase with increasing T_S. The ultra-violet and visible absorption studies show that the bandgap of films can be tailored by varying T_S, taking advantage of the structural transformation.     

Investigations on the photocatalytic activity of sol–gel derived plain and Fe/Nb-doped titania coatings on glass substrates

Plain and doped (Fe³⁺ and Nb⁵⁺) titania coatings were deposited by dip coating on soda lime glass substrates using titania sol synthesized by sol–gel route in combination with commercial nanoparticle dispersions. The dopant concentrations were fixed at 0.07 wt% and the coatings heat treated at 400 °C were characterized with respect to their thickness, phase composition, hydrophilicity/hydrophobicity and microstructure. Photocatalytic activity testing was carried out on the coatings by following up the degradation of methylene blue dye for up to 4 h at 1 h time intervals after exposure to sunlight. The effect of a trivalent and pentavalent doping of Ti⁴⁺ sites on photocatalytic activity of TiO₂ was investigated.     

Swift heavy ion induced structural modifications in indium oxide films

Sub-stoichiometric indium oxide (In_xO_y) films were fabricated by electron-beam evaporation method. One set of films was irradiated with 120 MeV Ag⁹⁺ ions of varying fluences. Another set was thermally annealed and subsequently irradiated. Irradiation of the as-deposited In_xO_y films leads to a phase separation resulting in In and In₂O₃ and the formation of nanometer crystalline In clusters. The In cluster size is in the range of 35-45 nm. Elastic recoil detection analysis indicates a decrease in the O/In ratio with an increase in ion fluence, suggesting oxygen loss during irradiation. On the other hand, thermal annealing of the as-deposited In_xO_y films leads to a complete conversion into stoichiometric In₂O₃. The structure of the stoichiometric films is further resistant to irradiation. Preliminary electrical investigations indicate a decrease in the resistivity of the as-deposited sub-stoichiometric In_xO_y films with irradiation, but a very large increase after irradiation of the stoichiometric thermally annealed films. Thus, structural and electrical modifications induced by swift heavy ions depend upon the stoichiometry of the film.