Easy and affordable energy is one of the great boons of modern industrial civilization and is considered the basis for standard living. Energy makes people's lives brighter, safer, comfortable and more mobile. The ever-increasing demand and overexploitation of energy sources (electricity, petroleum products, etc.) is one of the major causes of environmental degradation.

Coal-burning power plants and automobiles are the largest source of carbon dioxide pollutionthey produce 6 billion tons every year. Carbon dioxide and other polluting gases that are collecting in the atmosphere like a thick blanket trap the sun's heat and cause the planet to warm up (global warming). The whole world is worried about global warming and is looking for clean-green energy sources as well as means of increasing energy efficiency. New policies and measures are being evolved to improve efficiency in energy production and use, enhance the energy security and mitigate emissions. These measures include efforts to increase efficiency of energy utilization and increase reliance on non-fossil fuel energies that are clean and green, such as hydropower, wind, solar or bio energy. The first three papers in this issue deal with these aspects.

Hydropower is a clean energy that does not contribute to pollution and global warming. A large potential is available in the small hydropower sources that can be harnessed to meet the increasing energy demand. The disadvantages associated with large hydropower like large displacement of population, vast submerged areas, heavy deforestation and change in ecology are not there with small hydropower. Several low head turbines are available, out of which the bulb turbine is found to be the most suitable for low head sites. Bulb turbine has a compact form and good hydraulic features, resulting in low civil costs and less hydraulic losses compared to other types of turbines available for similar site conditions. In the review paper, "Installation of Bulb Turbines in Small Hydropower Plants: A Review", the authors Sunil Kumar Singal, Anurag Kumar and R P Saini have presented the technical and operational aspects of the bulb turbines. The paper lists bulb turbine installations in India and other countries and reviews research work in improving the efficiency and reliability, use of CFD and other software in modeling and simulation, cavitation issues and comparison of bulb turbine with other turbines used for similar site conditions.

The second paper "Modified Entry System to Enhance the Performance of Stratified Solar Energy Storage", by V V R L S Gangadhar, V Vasudeva Rao and K Mohan Rao, has experimentally studied thermal stratification in energy storage systems. The experiments were conducted on two tanksone lined inside with rubber and the other lined with fiber glassto study the effect of thermal conductivity of the lining material. It is found that the mild steel tank lined inside with fiber glass performs better than the rubber-lined tank, which was superior to Plexiglass tank. The authors have found through extensive experiments, carried out in both static and dynamic modes, that the rate of filling the tank and the design of the distributor affect the process of stratification. Lower rate of filling improves the thermoclines and distributor producing smaller disturbances assures better stratification. They also observed that heat losses increase as the temperature difference between cold and hot water increases.

The third paper, "Optimization of Fin Geometry in the Internal Finned Tube by Numerical Method", by R Palanichamy, P Nagaraj and S Muthu Somasundaram, presents a numerical simulation of laminar heat transfer in circular tube flows with internal longitudinal fins using finite difference numerical code. Laminar heat transfer systems for maximum heat transfer-minimum weight are crucial in applications such as electronic systems, compact heat exchangers, automotive and aerospace applications. The authors have considered three types of fin models with three different half-included angles, two types of fluids (water and engine oil), and Aluminium as tube/fin material. The variation of thermal conductivity of the tube materials, fluids and viscosity of the fluids with temperature is taken into account in the solution procedure. The results show that the inclusion of fins enhanced the heat transfer rate significantly. Engine oil is found to be the more effective coolant. The fin with half-included angle of 14º is found to be the best profile for the internal fin for heat transfer enhancement.

The fourth paper, "Numerical Analysis for Development of Hertz Contact Stresses in Cylindrical Roller Bearing and Their Distribution Using MATLAB", by P H Darji and D P Vakharia, on rolling bearing analysis is about a tool developed in MATLAB to analyze the subsurface stress before applying the real load on the body. In the program, just by changing the required parameters, the user can rapidly get the contours of stress distribution in the contact patch. On the basis of the results, the designer can do the required modifications in the dimensions of the contact body or in material so that the induced stresses are within limits. The paper uses Hertzian contact theory to compute local contact stresses and surface stresses caused by a concentrated force applied perpendicular to the surface. A complete numerical analysis is carried out for calculation of distribution of stresses under the surface induced in the cylindrical roller bearing.

The fifth paper, "Effect of Weld Pool Oscillation on Mechanical Properties of Carbon Steel Weldments", by S P Tiwari, describes the influence of oscillation on mechanical properties of carbon steel welds. For the study, workpieces were welded on an oscillatory table under different frequencies (0-400 Hz) and amplitudes (0-40 µm) of oscillations. Test specimens for impact test, hardness test and microstructure examination were made from the welded workpieces under stationary and oscillatory conditions. The specimens were tested for impact strength and hardness. Significant improvement in impact strength and hardness of oscillatory-prepared welds was observed when compared with these properties of stationary-prepared welds. Microstructure studies revealed that the grain structure is fine for oscillatory-prepared weld when compared with stationary-prepared weld. Maximum improvement in mechanical properties is obtained at 400 Hz-5 µm oscillatory condition of welding.

The last paper in this issue, "Structural Comparison of In-Parallel Robotic Manipulators on the Basis of Compactness", by A B Srinivasa Rao and M K Prasad, is on Multi Degree of Freedom (MDOF) planar kinematic chains. MDOF planar kinematic chains can be considered for application as parallel manipulators in view of their greater rigidity. The paper presents a simple and logical method to accomplish the selection of chains for specific tasks like workspace and rigidity. A large number of distinct chains are possible with the same number of links and DOF for consideration as parallel structures. Hence, it becomes necessary to know which of these chains possesses the desirable characteristics, such as greater rigidity, large workspace, less accumulation of joints, etc., and suits the particular application. A measure of compactness is proposed in the paper that enables comparison of distinct chains for specific characteristics. The conclusions drawn by the authors include: parallelism is high in the case of chains consisting of low connectivity links. For example, the same DOF chains containing ternary and binary links lead to greater parallelism compared to chains with quaternary and ternary links; parallelism increases when higher connectivity links are separated by binary links and direct joining of high connectivity links reduces compactness and parallelism.

- - R K Mittal
Consulting Editor