Optimal control of delay systems via block pulse functions

The concept of coefficient shift matrix is introduced to represent delay variables in block pulse series. The optimal control of a linear delay system with quadratic performance index is then studied via block pulse functions, which convert the problems into the minimization of a quadratic form with linear algebraic equation constraints. The solution of the two-point boundary-value problem with both delay and advanced arguments is circumvented. The control variable obtained is piecewise constant.     

Thermal degenerate rearramement of 1,2-dimethylenecyclobutane iron tricarbonyl

Vapor phase pyrolysis of $\text{bis}$-1,2-(dideuteriomethylene) cyclobutane iron tricarbonyl at 170° resulted in hydrogen scrambling. Degradation of the rearrangement product indicated that either one exomethylene group was exchanging with one ring methylene or hydrogens were being reversibly transferred from the ring carbons to the exocyclic ones. Mechanisms that would explain either possibility involve the intermediacy of a sigma bonded iron with a π-allyl ligand.     

Lifetimes of unresolved transitions from very high spin states in nuclei nearN=82

Average lifetimes of unresolved transitions deexciting very high spin states populated in²⁸Si(^{136, 129}Xe,xn)^164? x, 157?xEr reactions have been determined by a Doppler shift attenuation method. We find that the yrast bump region between 1.0 and 1.6 MeV contains a majority of strongly collectiveE2 transitions with very short lifetimes (a few tens of fsec) in the well deformed nuclei around¹⁵⁹Er and, with less certainty, almost comparably short lifetimes in the more spherical nuclei around¹⁵²Er. In the high energy region of 2.0–3.2 MeV we observe transitions which depopulate longer lived states in the nuclei nearN=82 than in the well deformed systems.     

Synthetic carbapenem antibiotics III. 1-Methyl thienamycin

Total syntheses of 1α- and 1β-methyl thienamycin are reported. 1β-Methyl thienamycin retains the antibacterial activity of thienamycin and is highly resistant to hydrolysis by DHP-I enzyme.     

On optimal feedback control of a class of linear distributed systems

Journal of Optimization Theory and Applications - Optimal modal feedback control laws are synthesized from the modal equations which are obtained by eigenfunction expansion of the diffusion...     

On the dynamics of liquids in a cylindrical tank with a flexible bottom

Summary The problem of hydroelastic sloshing of a liquid, partially filling a cylindrical tank with rigid side walls and a flat flexible bottom, has been investigated. The liquid is assumed to be inviscid, homogeneous and incompressible; the flexible bottom is assumed to be a stretched membrane. An approximate solution is given and numerical examples are discussed. The data obtained show good agreement with experimental results reported by other authors.

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Übersicht In der vorliegenden Arbeit wird das hydroelastische Problem des Schwappens von flüssigem Treibstoff in einem kreiszylindrischen Tank mit starrer Wand und ebenem, flexiblem Boden untersucht. Die Flüssigkeit wird als reibungsfrei, homogen und inkompressibel, der Boden als gespannte Membran angenommen. Eine Näherungslösung wird angegeben und numerische Rechnungen werden diskutiert. Die erhaltenen Resultate zeigen gute Übereinstimmung mit experimentellen Befunden anderer Autoren.

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Paper presented in part at the Canadian Congress of Applied Mechanics, Centennial Year 1967, 22–26 May 1967, Lavai University at Quebec City. This work was performed under National Aeronautics and Space Administration Grant No. NsG-542 to the University of Florida. Numerical calculations were carried out at the University of Florida computing center.     

Fast turn-on characteristics of tungsten-based dispenser cathodes. II

In the Proceedings of the 1982 Tri-Service Cathode Workshop, the authors described studies of the reactivations of tungsten-based dispenser cathodes following poisonings of the kind expected during shelf storage of a microwave tube [Appl. Surface Sci. 16 (1983) 73]. Further work on the problems of reactivation following such poisoning is described here. In addition to coated (“M”) and uncoated tungsten matrix cathodes, the tungsten-iridium mixed metal matrix (“MM”) cathode has been studied. In general reproducible results have been obtained from different examples of the same type of “M” and uncoated cathodes. However, although some “MM” cathodes have exhibited good reactivation characteristics, a large variation has been observed between different examples of “MM” cathodes. The composition of the impregnant in the dispenser cathodes has been found to be an important factor in determining the reactivation rate of a cathode. As the barium oxide concentration in the impregnant increases, the cathode will recover faster from a poisoning exposure. Studies of the poisoning caused by combinations of different gases suggest that poisoning will occur if there is a sufficient exposure of a poisoning agent, regardless of the total exposure. The exposures necessary to poison a cathode are so small, that poisoning of the cathode appears probable during shelf storage of a microwave tube. The reactivation results have been summarised in terms of the times and temperatures required to achieve both a given current density and a given degree of reactivation from a poisoned cathode. The studies also indicate that the limiting step during the reactivation process involves the dispensing of fresh material to the cathode surface rather than the desorption or conversion of a poisoned surface layer.