Adaptive identification and control of structural dynamics systems using recursive lattice filters

A new approach for adaptive identification and control of structural dynamic systems by using least squares lattice filters thar are widely used in the signal processing area is presented. Testing procedures for interfacing the lattice filter identification methods and modal control method for stable closed loop adaptive control are presented. The methods are illustrated for a free-free beam and for a complex flexible grid, with the basic control objective being vibration suppression. The approach is validated by using both simulations and experimental facilities available at the Langley Research Center

An alternative method to determining optical lever sensitivity in atomic force microscopy without tip-sample contact

Force studies using atomic force microscopy generally require knowledge of the cantilever spring constants and the optical lever sensitivity. The traditional method of evaluating the optical lever sensitivity by pressing the tip against a hard surface can damage the tip, especially sharp ones. Here a method is shown to calculate the sensitivity without having to bring the tip into contact. Instead a sharpened tungsten wire is used to cause a point contact directly onto the cantilever and cause cantilever bending. Using beam theory, the sensitivity thus found can be converted to the equivalent sensitivity that would be obtained using the tip location. A comparison is presented between sensitivity values obtained from the conventional tip contact method and those derived from the wire-based technique for a range of cantilevers in air. It was found that the difference between the calculated sensitivity from the wire-based technique and the sensitivity obtained conventionally was less than 12%. These measurements indicate the presented method offers a simple alternative approach to obtain optical lever sensitivity without compromising the tip shape

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

Binary black hole merger gravitational waves and recoil in the large mass ratio limit

Spectacular breakthroughs in numerical relativity now make it possible to compute spacetime dynamics in almost complete generality, allowing us to model the coalescence and merger of binary black holes with essentially no approximations. The primary limitation of these calculations is now computational. In particular, it is difficult to model systems with large mass ratio and large spins, since one must accurately resolve the multiple lengthscales which play a role in such systems. Perturbation theory can play an important role in extending the reach of computational modeling for binary systems. In this paper, we present first results of a code which allows us to model the gravitational waves generated by the inspiral, merger, and ringdown of a binary system in which one member of the binary is much more massive than the other. This allows us to accurately calibrate binary dynamics in the large mass ratio regime. We focus in this analysis on the recoil imparted to the merged remnant by these waves. We closely examine the "antikick", an anti-phase cancellation of the recoil arising from the plunge and ringdown waves, described in detail by Schnittman et al. We find that, for orbits aligned with the black hole spin, the antikick grows as a function of spin. The total recoil is smallest for prograde coalescence into a rapidly rotating black hole, and largest for retrograde coalescence. Amusingly, this completely reverses the predicted trend for kick versus spin from analyses that only include inspiral information.Comment: 15 pages, 5 figures. Submitted to Phys. Rev.

Electrostatic Force Microscopy and Electrical Isolation of Etched Few-Layer Graphene Nano-Domains

Nanostructured bi-layer graphene samples formed through catalytic etching are investigated with electrostatic force microscopy. The measurements and supporting computations show a variation in the microscopy signal for different nano-domains that are indicative of changes in capacitive coupling related to their small sizes. Abrupt capacitance variations detected across etch tracks indicates that the nano-domains have strong electrical isolation between them. Comparison of the measurements to a resistor-capacitor model indicates that the resistance between two bi-layer graphene regions separated by an approximately 10 nm wide etch track is greater than about 1×1012 Ω with a corresponding gap resistivity greater than about 3×1014 Ω⋅nm . This extremely large gap resistivity suggests that catalytic etch tracks within few-layer graphene samples are sufficient for providing electrical isolation between separate nano-domains that could permit their use in constructing atomically thin nanogap electrodes, interconnects, and nanoribbons