Microwave-assisted green synthesis of silver nanostructures

Over the past 25 years, microwave (MW) chemistry has moved from a laboratory curiosity to a well-established synthetic technique used in many academic and industrial laboratories around the world. Although the overwhelming number of MW-assisted applications today are still performed on a laboratory (mL) scale, we expect that this enabling technology may be used on a larger, perhaps even production, scale in conjunction with radio frequency or conventional heating. Microwave chemistry is based on two main principles, the dipolar mechanism and the electrical conductor mechanism. The dipolar mechanism occurs when, under a very high frequency electric field, a polar molecule attempts to follow the field in the same alignment. When this happens, the molecules release enough heat to drive the reaction forward. In the second mechanism, the irradiated sample is an electrical conductor and the charge carriers, ions and electrons, move through the material under the influence of the electric field and lead to polarization within the sample. These induced currents and any electrical resistance will heat the sample. This Account summarizes a microwave (MW)-assisted synthetic approach for producing silver nanostructures. MW heating has received considerable attention as a promising new method for the one-pot synthesis of metallic nanostructures in solutions. Researchers have successfully demonstrated the application of this method in the preparation of silver (Ag), gold (Au), platinum (Pt), and gold-palladium (Au-Pd) nanostructures. MW heating conditions allow not only for the preparation of spherical nanoparticles within a few minutes but also for the formation of single crystalline polygonal plates, sheets, rods, wires, tubes, and dendrites. The morphologies and sizes of the nanostructures can be controlled by changing various experimental parameters, such as the concentration of metallic salt precursors, the surfactant polymers, the chain length of the surfactant polymers, the solvents, and the operation reaction temperature. In general, nanostructures with smaller sizes, narrower size distributions, and a higher degree of crystallization have been obtained more consistently via MW heating than by heating with a conventional oil-bath. The use of microwaves to heat samples is a viable avenue for the greener synthesis of nanomaterials and provides several desirable features such as shorter reaction times, reduced energy consumption, and better product yields.     

Potential nutraceutical food beverage with antioxidant properties from banana plant bio-waste (pseudostem and rhizome)

Banana plant biomass waste, viz. pseudostem (BPS) and rhizome (BR), contribute 30.81 and 12.67 per cent respectively. A negligible percentage of these were used for fresh consumption, otherwise they are waste and incinerated. In order to utilize these bio-wastes in a bioactive perspective, nutritional and nutraceutical components were studied from the juices and its Ready-To-Serve (RTS) beverage. When compared to BPS juice, BR juice showed higher total phenolic content (TPC) and total flavonoid content (TFC) of 341.44 mgGAE and 87.60 mgCE/200 μL, respectively, and concomitantly exhibited high antioxidant activity (AOA) in all the assays tested, viz. DPPH radical scavenging activity (82.93%), superoxide radical scavenging activity (49.45%), metal chelation activity (48.32%) total reducing power (0.846 OD at 700 nm) and total antioxidant capacity (928 mmol ascorbic acid equivalents). High quantity of polyphenols present in BR juice resulted high AOA. Strong positive correlations were observed between TPC and TFC of BPS and BR juice with AOA assays. Among the different concentrations of RTS beverages prepared, 25% BPS juice and 20% BR juice with 15°brix TSS and 0.3% acidity were adjudged as best by sensory panelists. Thus, BPS and BR juice can be effectively used to produce new generation functional beverages.     

Status of Bioactive Compounds in Foods,with Focus on Fruits and Vegetables

Components of cereals, legumes, pulses, proteins, sea food, milk, carbohydrates and lipids are being evaluated for their influence on human health, as biofunctional compounds. However, references dealing with fruits and vegetables exceed any other food group and accordingly their focus. Fruits and vegetables abound in a spectacular range of such health influencing compounds and thus, study of their bioactivity, in lieu of their consumption in fresh or processed form. Anti-cancerous phenolics from Phyllanthus, radioprotective Litchi phenolics/flavonoids, hypoglycemic Sygium, quercitin and hydroxyl cinnamates of Sweet cherries, xanthones of Mangosteen, ellagitannins of Pomegranate, ursolic acid of Sea buckthorn, muscle relaxative watermelon, anti-cholesterolemic soluble fibre and sterols, cardioprotective saponins, ACE-inhibitory potato hydrolysates, anti-pancreatic cancerous ascorbic acid, carotenoids including pro-vitamin A are few examples unraveled. Thus, the imminent scope to obviate their structural chemistry, influence on storage and processing conditions, factors favoring their bio-accessibility/bio-availability in the food formulations, influencing human health. It is the meticulous combination of these compounds in daily consumption that determines their usefulness to human body. What is of paramount importance is the actual health benefits accrued from consumption of such functional- compound based fresh/processed fruits,vegetables or other foods.     

Multiple Linear Correlation Analysis of Daily Reference Evapotranspiration

An accurate estimation of reference evapotranspiration (ET₀) is of paramount importance for many studies such as hydrologic water balance, irrigation system design and management, crop yield simulation, and water resources planning and management. Simple regression techniques, may sometimes, provide adequate estimation of ET₀. Implementation of regression methods considering all the predictor variables may, however, lead to overfit and consequent reduction in the predictive capability. The regression models for ET₀ have been developed in the present study for Tirupati, Nellore, Rajahmundry, Anakapalli and Rajendranagar regions of Andhra Pradesh, India by following step-wise procedure, eliminating superfluous predictor variables based on statistical criteria. The sunshine hours, wind velocity, temperature and relative humidity influenced ET₀ in the study area. The linear regression models developed in terms of predictor variables may conveniently be applied in the regions selected for the present study and, in the regions with similar climatic conditions for satisfactory ET₀ estimation.     

Navigation of non-holonomic mobile robot using neuro-fuzzy logic with integrated safe boundary algorithm

In the present work, autonomous mobile robot (AMR) system is intended with basic behaviour, one is obstacle avoidance and the other is target seeking in various environments. The AMR is navigated using fuzzy logic, neural network and adaptive neuro-fuzzy inference system (ANFIS) controller with safe boundary algorithm. In this method of target seeking behaviour, the obstacle avoidance at every instant improves the performance of robot in navigation approach. The inputs to the controller are the signals from various sensors fixed at front face, left and right face of the AMR. The output signal from controller regulates the angular velocity of both front power wheels of the AMR. The shortest path is identified using fuzzy, neural network and ANFIS techniques with integrated safe boundary algorithm and the predicted results are validated with experimentation. The experimental result has proven that ANFIS with safe boundary algorithm yields better performance in navigation, in particular with curved/irregular obstacles.     

Effect of cross-sectional warping of anisotropic sandwich laminates due to dynamic loads using a refined theory and C° finite elements

An attempt has been made to study the effect of cross-sectional warping in the symmetrically laminated anisotropic composite sandwich plates for transient loads. A higher-order shear deformation theory (HOST) is used in conjunction with the simple displacement based C° finite element method (FEM). As is well-known, the classical first-order theories hitherto considered were inadequate to describe the propagation of waves in the highly orthotropic sandwich laminates. The present theory, which is more accurate than the Reissner-Mindlin theory, is applied herein, for the evaluation of plate response to different types of dynamic loads. An explicit central difference scheme is employed for the integration of dynamic equations of equilibrium with a diagonalized mass matrix obtained by a special procedure applicable to quadrilateral isoparametric elements. The numerical results of the present investigation have been compared with the first-order shear deformation theory (FOST) and the differences between HOST and FOST are examined. The results presented here should be useful in obtaining better correlation between theory and experiment, and to numerical analysts in verifying their results.     

An important note on symmetry line boundary conditions in fibre-reinforced laminated anisotropic composites

Symmetry line boundary conditions of symmetrical and unsymmetrical laminated fibrereinforced anisotropic composite structures are discussed. A simple C⁰ isoparametric finite element formulation based on the Reissner-Mindlin first-order shear deformation theory is used. The effects of boundary conditions on the laminated scheme and the orientation of fibres are studied. Numerical results for deflections presented herein should be of interest to composite-structure designers, experimentalists, and numerical analysts in verifying their results.     

A set of pathological tests to validate new finite elements

The finite element method entails several approximations. Hence it is essential to subject all new finite elements to an adequate set of pathological tests in order to assess their performance. Many such tests have been proposed by researchers from time to time. We present an adequate set of tests, which every new finite element should pass. A thorough account of the patch test is also included in view of its significance in the validation of new elements.     

Optical electronegativity, bulk modulus and electronic polarizability of materials

Correlations between the energy gap, optical electronegativity and bulk modulus are given for compound and ternary chalcopyrite semiconductors. Bulk modulus and electronic polarizability values have been evaluated from the optical electronegativity. The estimated values of these parameters are in good agreement with the available experimental data.