Adaptive control of large space structures using recursive lattice filters

The use of recursive lattice filters for identification and adaptive control of large space structures is studied. Lattice filters were used to identify the structural dynamics model of the flexible structures. This identification model is then used for adaptive control. Before the identified model and control laws are integrated, the identified model is passed through a series of validation procedures and only when the model passes these validation procedures is control engaged. This type of validation scheme prevents instability when the overall loop is closed. Another important area of research, namely that of robust controller synthesis, was investigated using frequency domain multivariable controller synthesis methods. The method uses the Linear Quadratic Guassian/Loop Transfer Recovery (LQG/LTR) approach to ensure stability against unmodeled higher frequency modes and achieves the desired performance

Effect of Clamping Rigidity of the Armour on Ballistic Performance

Influence of the manner in which the armour plates are held during their ballistic testing on the armour performance, has been evaluated. One armour plate was clamped rigidly to the test stand while a second plate of identical composition, hardness, and dimensions was hung loosely from the target holder. Both these plates were impacted with the same type of projectiles and over the same impact velocity range. The nature of ballistic damage evaluated indicates that the manner in which the armour is held during ballistic testing has a negligible influence on its performance at least when the mass of the plate is substantially higher than that of the projectile

The dynamic indentation behavior of steel at large depths of penetration

The objective of the present study is to investigate the dynamic indentation behavior of steel plate material when impacted by ogive-shaped projectiles and in particular under indentation conditions involving large depths of penetration (i.e., depth of penetration greater than projectile radius). Toward the above purpose, dynamic indentation of steel plates of thickness 20, 40, and 80 mm have been carried out using projectiles of diameter 6.2 and 20 mm, and over a range of impact velocities so as to attain depths of penetration in the range 1.4 to 3.6 times the projectile radius. The results indicate that the dynamic hardness, the plastic zone size, specific energy consumed in plastic deformation within the plastic zone, and the average plastic strain within the plastic zone increases continuously with increasing values of depth of penetration normalized by projectile radius. Certain subtle differences regarding the nature of plastic deformation between indentation at large and shallow depths of penetration are presented. However, on a macroscopic scale, the indentation mechanisms and processes are broadly similar and show continuity in terms of behavior across the whole penetration depth range

The Dimensions of Reputation in Electronic Markets

We present a framework for identifying the different dimensions of online reputation and characterizing their influence on the pricing power of sellers. Our theory predicts that sellers with better recorded online reputation can successfully charge higher prices than competing sellers of identical products, and that their pricing power increases with their recorded level of experience. We develop and implement a new text mining technique that identities and quantitatively assesses dimensions of importance in reputation profiles, and use this technique to create a new data set containing detailed reputation profiles and prices for sellers in over 9,500 transactions for consumer software on Amazon.com's online secondary marketplace. The estimation of a set of econometric models on this data set validates the predictions of our theory, and further, ranks these dimensions of reputation based on their effect on measured seller value, identifying those that have the most significant impact on reputation. This paper is the first study that integrates econometric and text mining techniques toward a more complete analysis of the information captured by reputation systems, and it presents new evidence of the importance of their effective and judicious design.Information Systems Working Papers Serie

Shrimp farming by private enterprise- A case study

In view of the encouraging results shown by the research organisations of India and other countries in prawn culture on scientific methods, a commercial research and development project on prawn culture was established by the TATA Oil Mills Co. Ltd., at Pulicat. Experiments were conducted in aarthern ponds of size ranging from 0.4 to 1.25 ha- Stocking rates ranging from 6.5 to 15 prawns/mz were attempted and production to the tune of 0.5 to 1.0 tonne/ha/crop was achieved. Survival rate over 80% could be maintained in all the crops. An artificial feed formulated with shrimp meal, trash fish and vitamin mineral mix along with other usual ingredients, with a protein content of 40%, proved to be better than the other conventional feed. Effect of design of a pond, aging of pond, stocking density, stocking size and various hydrobioiogical parameters viz. salinity, dissolved oxygen and pH were also studied. The intensive stocking rate, the successful feed formula and the effective water managements adopted were the important reasons for the successful production of shrimps in this farm. The cost of production of 1 kg of shrimps considering the variable cost, varied from Ks 20.00 to 34.00 and thus a net revenue of Rg. 8000.00 to 20,000.00/ha/crop was achieved

Corrosion of Aircraft Aluminium Alloys in Acid Solutions & its Prevention by Inhibitors

THE corrosion of metals is a serious problem confronting the industrially advanced countries of the world. Modern developments and war-time experiences have made it possible to manufacture metals at lower costs than before. Secondly, new sources of minerals have been discovered, thereby enabling each nation to increase its capacity for the production of metals. Iron and steel, aluminium, copper and zinc are amongst the metals in common use. In practice all of them are liable to corrode in various environments : atmosphere, soil and liquid medium. The loss of metal due to corrosion necessitating repair or removal of metal parts is one of fundamental importance affecting the economy of a country. The cost of corrosion control is rather high, the estimated figures per annum for some of the countries being U.S.A.' close to 10 billion dollars, U.K.2 600 million pounds, Canada3 500 million dollars, Australia4 100 million pounds. and India5 154 crore rupees. It becomes incre-asingly important to preserve available metals in use since a time may come when some of them approach exhaus-tion. From the available figures it has been indicated that immediate attention should be given to the non- ferrous metals, and greater attention to ferrous res-ources. In the case of iron the losses due to corrosion are estimated to be about 7.6 per cent a year. Corrosion control methods, therefore, assume great importance6

The hardness-flow stress correlation in metallic materials

Hardness is a measure of the resistance of a material to indentation and a wide variety of indentation tests have been devised to measure the hardness of materials. In the case of hardness tests which utilize spherical balls as the indentor, it is also possible to derive flow stress-strain relationships from hardness tests carried out either over a range of loads (static test) or over a range of impact velocities (dynamic test). This paper first describes the experimental procedure for obtaining stress-strain curves from hardness tests. In addition, the paper also analyzes in detail, the indentation test conditions under which the conversion of the hardness-average strain data to flow stress-strain data is simple and straightforward in the sense that the constraint factor which is the correlating parameter for the above conversion is not only independent of strain but also easily computable on the basis of known mechanical property data of the test material

Measuring the quantum efficiency of single radiating dipoles using a scanning mirror

Using scanning probe techniques, we show the controlled manipulation of the radiation from single dipoles. In one experiment we study the modification of the fluorescence lifetime of a single molecular dipole in front of a movable silver mirror. A second experiment demonstrates the changing plasmon spectrum of a gold nanoparticle in front of a dielectric mirror. Comparison of our data with theoretical models allows determination of the quantum efficiency of each radiating dipole.Comment: 4 pages, 4 figure