Minimum trajectory sensitivity design of systems with random parameters†

A method is presented for designing control systems with uncertain plant parameters and initial states. The open-loop part of a semi-closed loop control guarantees a proper behaviour under the most likely circumstances and a neighbouring feedback is augmented so that trajectory dispersion under random perturbation is minimized. It is shown that the resulting optimization problem is similar to the optimal regulator problem with incomplete state feedback. An original numerical method based on imbedding techniques is proposed to provide a suboptimal control which avoids solving a complicated two-point boundary-value problem. An example exhibits the trajectory sensitivity reduction achieved.     

An ethanol spray at veraison enhances colour in red wines

Aqueous ethanol (5% v/v) was sprayed onto bunches of Vitis vinifera L. cv. Cabernet Sauvignon 8–9 weeks following full flowering (controls were sprayed with water). Internal ethylene concentration in treated berries increased to a maximum within 6 hours, and berry colour subsequently increased substantially (maximum attained 2–3 weeks after spraying). Berry fresh weight at harvest was unaffected by ethanol treatment, but wine made from treated grapes showed greater colour intensity compared with control grapes.     

Determination of maintenance floats using Buzen's algorithm

This paper applies Buzen's algorithm to the problem of determining the maintenance float needed to support an operating system with N circulating units. A maintenance network with load-independent servers is assumed. The operating system availability and maintenance floats are obtained using this iterative algorithm. It is shown that the normalizing constant used in the algorithm can easily be computed for the maintenance float problem by using geometric series. This result is further used to obtain a simple model for the expected number of operating units, thus making it easy to compute the operating system availability for any given N. Buzen's algorithm therefore provides a simple solution to the maintenance float problem.     

Free-transfer lines with unreliable assembly stations and small buffers

This paper describes the arrangement in series of assembly stations that are linked by storage places. The distribution of the stations and of the number of places in the stocks affects the efficiency of the assembly. The results of the continuous model show that grouping stations by two or three does not improve the effectiveness of the line when the number of places is limited. On the other hand, the discrete synchronous model proved that it is profitable to group stations when a low capacity of storage is experienced; these results have been confirmed using a simulation software which processes the components in a discrete manner.     

Oxidation of ZnO thin films during pulsed laser deposition process

Pulsed laser deposition of ZnO thin films, using KrF laser, is analysed. The films were deposited on (001) sapphire substrates at 400 °C, at two different oxygen pressures (0·3 and 0·4 mbar) and two different target–substrate distances (30 and 40 mm). It is observed that in order to obtain good quality in the photoluminescence of the films, associated with oxygen stoichiometry, it is needed to maximize the time during which the plasma remains in contact with the growing film (plasma residence time), which is achieved by selecting suitable combinations of oxygen pressures and target to substrate distances. It is also discussed that for the growth parameters used, the higher probability for ZnO films growth results from the oxidation of Zn deposited on the substrate and such process takes place during the time that the plasma is in contact with the substrate. Moreover, it is observed that maximizing the plasma residence time over the growing film reduces the rate of material deposition, favouring the surface diffusion of adatoms, which favours both Zn–O reaction and grain growth.     

MECHANICAL CLEANING EFFECT AND PRESSURE DROP OF AIR-WATER-FLOW IN HORIZONTAL GLASS TUBES (VACUUM DAIRY PIPELINES)

Mathematical models are presented which make it possible to calculate pressure drop and mechanical cleaning effect for plant design of vacuum dairy milking pipes. Experimentally, air-water mixtures were sent through a test plant, consisting of glass pipes 0.034 m in diameter and 60 m in length (93 m in some experiments), where a soiled piece of pipe could be inserted without disturbing the flow. The soiling was milk-based and dried on application. Light absorption of the soiled glass tube was measured before and after the cleaning operation, which was performed for 45 s with plain water at room temperature. To calculate the pressure drop, the so-called Dukler constant-slip-method was used. A holdup correlation according to Hughmark was improved to fit the pipe system used. Through linear regression analysis an equation was obtained, describing the cleaning effect as influenced by the Reynold number and the liquid fraction of the air-water mixture.