Performance improvement in decentralized adaptive control: amodified model reference scheme

A modified decentralized model reference adaptive controller is proposed for a continuous time large scale system composed of N interconnected linear subsystems with unknown parameters. In the case where the high frequency gain of the transfer function of each of the isolated subsystems is known, the modified scheme can be used to improve the bad transient behaviour that typically results from poor knowledge of the subsystem parameters. The transient performance improvement, however, has to be traded off against the “size” of the allowable unmodeled interconnections in such a way that as the unmodeled interconnections disappear, the improvement in transient performance can be made arbitrary. Each local adaptive scheme uses “approximate differentiators,” and so possible sensor noise amplification is expected to be an additional limitation of the proposed scheme     

Low-temperature preparation of polycrystalline silicon from silicon tetrachloride

Polycrystalline silicon has been prepared by zinc reduction of silicon tetrachloride at a low temperature (≈550° C) in a vertical vapour phase reactor. Characterisation of the remelted polycrystalline ingot by X-ray, SEM and electrical methods shows that the material is p-type with an average grain size of 0.5 μm having a room-temperature resistivity in the range 1.0–1.5 Ω cm suitable for solar cell fabrication.     

Acoustic studies of heterophase systems: styrene-butadiene-styrene

Acoustic absorption and velocity measurements are reported over a temperature range from 213 to 293 K on a series of linear and four-arm star styrene-butadiene-styrene triblock copolymers. The loss peak associated with the segmental motion of the butadiene block was studied in detail. Its position, shape and width were found to be sensitive to the composition (styrene-butadiene ratio) and structure of the copolymer. The data is discussed in terms of the effects of morphology and micro-structure on the observed dynamics.     

Hall effects on hydromagnetic flow over an impulsively started porous plate

Summary An exact solution has been obtained for the problem of Hall effects on the hydromagnetic flow due to an impulsive start of a porous flat plate. It is observed that in the initial stages there is no inertial oscillation while at large time the steady state is reached through inertial oscillations. The time to attain the steady state increases with increase in Hall parameter.

---

Hall-Effekte bei hydromagnetischer Strömung über eine impulsartig gestartete Platte

Zusammenfassung Für das Problem der Hall-Effekte bei der hydromagnetischen Strömung, durch den impulsartigen Start einer porösen, ebenen Platte, wurde eine exakte Lösung erhalten. Es wird beobachtet, daß im Anfangszustand keine Trägheitsschwingung auftritt, wogegen nach längerer Zeit der stationäre Zustand durch Trägheitsschwingungen erreicht wird. Die Zeit um den stationären Zustand zu erreichen, wächst mit dem Anwachsen der Hall-Parameter an.

---

---

With 2 Figures     

Studies on the reduction of nitrobenzene to aniline catalysed by pd(acac)2-pyridine system

The complex, bis(acetylacetonato)palladium(II) in pyridine, is used as a homogeneous catalyst for the conversion of nitrobenzene to aniline. From a study of various operational parameters the optimum reduction was found to occur at 1 atm pressure and at room temperature in petroleum ether (b.p. 100–120°C) solvent, yielding 90% of aniline on input nitrobenzene basis. The complex [Pd¹¹(acac)H(C₆H₅NO₂)Py] was isolated under similar experimental conditions and was characterised by elemental analysis, magnetic, thermal and spectral studies. Formation of a phenylnitrene metal complex has been suggested as a hypothetical intermediate in the reduction process.     

On the role of mass transport in high rate dissolution of iron and nickel in ECM electrolytes—I. Chloride solutions

High rate anodic dissolution of iron and nickel in 5 M NaCl was studied in a flow channel cell under controlled hydrodynamic conditions. Galvanostatic experiments were aimed at investigating the influence of current density and electrolyte flow rate on anode potential, current efficiency for metal dissolution and surface texture resulting from dissolution. Active dissolution at low current densities leads to surface etching and transpassive dissolution at high current densities leads to surface brightening. Transition from active to transpassive dissolution is mass transport controlled and is accompanied by a change in anode potential, surface microtexture and in case of iron by a change in the valence of metal dissolution.