Identification of a class of nonlinear state-space models using RPEtechniques

The RPE (recursive prediction error) method in state-space form is developed in the nonlinear systems and extended to include the exact form of a nonlinearity, thus enabling structure preservation for certain classes of nonlinear systems. Both the discrete and the continuous-discrete versions of the algorithm in an innovations model are investigated, and a nonlinear simulation example shows a quite convincing performance of the filter as combined parameter and state estimator     

Optical networks for local loop applications

Some of the options for optical technology within the local loop environment are examined. In particular, passive shared access networks have been considered in some detail. These networks show great promise for delivering existing telephone services to small to medium business customers (4-30 lines) economically by the early 1990s. Extending fiber to the home will also be possible by virtue of a similar passive network infrastructure for customers requiring new broadband services beyond the single telephone line. For one-line plain old telephone service (POTS) customers, an intermediate approach of terminating the fiber network at the final network distribution point, with copper retained for the final leg, may be used prior to the provision of broadband services. A key feature of the passive optical network architecture is the use of wavelength-division multiplexing (WDM) as an upgrade strategy, allowing graceful upgrading from telephone services to multichannel high-definition television (HDTV) on gigabit/second bearers and full two-way switched broadband services employing wavelength routing across the network     

Kinematic nonuniqueness of elastoplastic structures

Lack of uniqueness of the kinematic solution of structures, analyzed as an assemblage of discretized elements assuming nonholonomic linearly-elastic/perfectly-plastic behaviour and a linearized yield surface, is studied. The occurrence of an elastoplastic mechanism leads to nonuniqueness; an elastoplastic mechanism is defined as a kinematically-admissible strain rate field made up of an admissible elastoplastic solution of the governing conditions and an add-on variable component consisting of a linear combination of plastic (collapse) mechanisms. The scalar multipliers of this linear combination are bounded, except at plastic collapse in which case the elastoplastic mechanism degenerates to a plastic mechanism. In the space of loads, the load paths that could coexist with nonuniqueness are restricted to a hyperplane or a crease of intersection of hyperplanes, defined by the equilibrium equations arising from the associated plastic mechanisms of the elastoplastic mechanism. The difference between any two competing displacement vectors would be normal to that hyperplane or crease, in the same manner plastic strain rates are to the yield surface according to the flow rule.     

Comfort limits for asymmetric thermal radiation

Groups of 32 and 16 subjects of both sexes were exposed in an environmental chamber to radiant asymmetry caused by a cool wall, a warm wall, and a cool ceiling. Each subject was tested individually while seated and clothed at 0.6 clo. During each 3.5-hour experiment the subject was exposed to six radiant temperature asymmetries. He was asked whether and where he experienced any local cool or warm sensation, and whether it was felt to be uncomfortable. During the entire experiment he was kept thermally neutral by changing the air temperature according to his wishes.For cool walls, warm walls, and cool ceilings curves have been established showing the percentage of dissatisfied subjects as a function of the radiant asymmetry. Radiant asymmetry at a warm wall caused less discomfort than a cool wall. A cool ceiling caused less discomfort than a warm ceiling. Accepting that 5% of the subjects may feel uncomfortable. a radiant temperature asymmetry of 10°C is allowable at a cool wall, 23°C at a warm wall, and 14°C under a cool ceiling. A previous study showed that 4°C is allowable under a warm ceiling. Radiant asymmetry had no significant impact on the operative temperatures preferred by the subjects. No significant differences were observed between the responses of men and women exposed to radiant asymmetry.     

Hydrologic regionalisation impacts on wet-weather control selection.

Continuous simulation is performed using the US Environmental Protection Agency (USEPA) Storm Water Management Model (SWMM) to evaluate regional differences around the United States in hydrologic and water quality performance of wet-weather controls. Controls are characterised as being limited by peak inflow rate (i.e. any device with little or no storage, such as screens, filters and some proprietary devices) or by storage capacity (e.g., ponds, tanks). For flow-limited devices, results are presented in the form of percentage of annual runoff volume captured (passing through the device) for a given inflow capacity. For storage-limited devices, results are presented in two forms: percentage of annual runoff volume captured as a function of unit basin size and drawdown (drain) time, and as a percentage of total suspended solids captured, for the same two variables. Regional differences are apparent, driven mainly by variations in rainfall patterns around the country.     

Effects of alloy additions on the microstructures and tensile properties of cast Co-Cr-Mo alloy used for surgical implants

The composition of the Co-Cr-Mo alloy has been modified by additions of nickel and some trace elements aluminium, titanium and boron. In this paper, the first part of the present study, the effects of alloy additions on the microstructures and tensile properties of the as-cast Co-Cr-Mo alloy are discussed. The effects of alloy additions on the fatigue behaviour of the alloy will be discussed in the second part of the present study. It is found that alloy additions do not seem to result in changes in the nature of the casting structure. A directional, coarse dendritic cast structure is produced in the modified alloys as in the base alloY. However, the alloy additions affect the carbide precipitations and the formation of some fine details of the microstructure such as dislocations, stacking faults and twins produced during the solidification. A considerable improvement in the transient mechanical properties, especially in the tensile ductility, is achieved by modifying the base alloy with alloy additions.     

THEORETICAL STUDY OF A NEW MATERIAL FOR FILTERS: AEROGELS

Aerogels are highly porous materials made by removing the liquid phase of a dilute suspension of solids by taking off the vapor under super-critical temperature and pressure conditions. The aerogel structure has a skeleton of nanometer-size elements forming pores that are tens of nanometers in dimension. In some cases the structure of the aerogel arises from clusters having fractal geometry. The collection efficiency and pressure drop for such material is predicted here from models in the literature. A quality factor is used to compare aerogel material with other filter materials. The quality factor relating gas filtration efficiency with pressure drop is predicted to be unusually high for these materials in comparison with other common fibrous filter media, predicting lower flow resistance for aerogels at equivalent particle collection efficiency levels.     

A finite elastostatic analysis of bimaterial interface cracks

A numerical method is developed to study the bimaterial interface problem in Neo-Hookean materials under plane stress conditions. Comparison is made with the analytical predictions for the asymptotic field of the problem. The range of dominance of the asymptotic solution at different load levels is established and the amplitudes of the crack-tip asymptotic field are related to the far field loading. The numerical model is extended to analyze the experiments conducted on specimens with an edge crack at the interface between two dissimilar Solithane plates that are characterized by Mooney-Rivlin material behavior.

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Résumé On met au point une méthode numérique pour l'étude d'un problème d'interfaces entre deux matériaux néo-Hookiens sollicités en état plan de tension. On compare les résultats avec les prédictions analytiques étabiies pour un champ asymptotique. On établit la gamme dans laquelle la solution asymptotique est dominante, à différents niveaux de charge, et on met en relation l'ampleur du champ asymptotique à l'extrémité de la fissure avec celle du champ de contraintes à une certaine distance. Le modèle numérique est étendu à l'analyse d'essais sur éprouvettes comportant une fissure de bord à l'interface de deux tôles de Solithane caractérisée par un comportement de matériau de Mooney-Rivlin.

     

Admiral John A. B. Dahlgren (1809–1870): His life, times and technical work in U.S. naval ordnance

John Dahlgren served in the U.S. Navy for nearly 35 years, sometimes in a sea-keeping capacity but mostly developing large naval artillery. To-day, his name, when recognised by students of naval ordnance, is associated with teh Dahlgren or ‘soda bottle shaped’ gun of 9 to 11 inch calibre. He designed, developed and lived to see his guns installed aboard warships and used to considerable effect, especially in the American Civil War. However, a nearly indistinguishable external design of gun was developed for the Army by T. J. Rodman, an officer now even less known than Dahlgren and whose researches and contributions are virtually forgotten. This paper and that in Ref. [1] attempt to appreciate (along with other technical questions of the period) the different ways pursued by these men towards the final development of the ‘soda bottle shaped’ gun, though it is a matter still not entirely understood.

Both names are totally omitted from several ‘classic’ books on artillery and this is a grave misfortune. Besides trying to throw factual light on the Dahlgren-Rodman controversy and the priority issue (though not one pursued with acrimony by the men themselves at the time), the paper describes Admiral Dahlgren's general career, the books he wrote, the technical problems he attacked and the problematic ordnance discussions of his day, to which he gave his life.

The work of Dahlgren and Rodman, in particular, saw the elevation of American gun design from the level of mere copying (of early Columbiads in the first decades of the century) to that which compelled attention from, and study by, the super-powers of the day, Great Britain, France and Russia.