Further results on the design of multivariable regulators under structure and robustness constraints

Parameter optimization methods are known to be an efficient tool for synthesizing multivariable regulators, especially when constraints are present on both their structure and the robustness of the control system. However, most of the underlying numerical algorithms first require the selection of a regulator satisfying all the assigned constraints, which is often non-trivial. This paper aims at presenting some new results on this subproblem. Specifically, constructive sufficient conditions are given for the existence of simple low-gain centralized and decentralized regulators supplying the closed-loop system with asymptotic stability as well as robust zero-error regulation in the face of ramp-type exogenous signals. Next, solutions are presented to two design problems incorporating constraints on the robustness of the control system with respect to large plant parameter variations.     

AN ATM-LIKE SYSTEM ARCHITECTURE FOR SATELLITE COMMUNICATIONS INCLUDING ON-BOARD SWITCHING

In this paper, an ATM system architecture for satellite communications is described. The proposed architecture includes an on-board switch and implements the adaptation of real-time services (e.g. voice and video) and non-real-time services (e.g. data) to the satellite communication link, while achieving statistical advantage. To this end, the ATM traffic categories defined in recent specifications^1,2 are utilized. Real-time and non-real-time traffic components are simultaneously supported by a TDMA/TDM on the satellite uplink/downlink, respectively. By exploiting the burstiness of real-time traffic, the proposed satellite system architecture achieves a significant increase of the overall system throughput. After describing the satellite system architecture and addressing scheme, we derive analytical models, by using sophisticated queueing models that allow a very accurate performance evaluation and an easy dimensioning of the data buffers. The proposed model is validated with simulations. The main result is the assessed feasibility of on-board buffers with current technology, even under very strict performance requirements on cell loss ratio and for quite high load values (e.g. 80 per cent of the downlink capacity). Finally, a congestion control scheme, based on a combination of preventive and reactive strategies, is proposed and analysed.     

The effect of post-veraison water deficit on yield components and maturation of irrigated Shiraz (Vitis vinifera L.) in the current and following season

Given their perennial nature, grapevines can respond to deficit irrigation during both the current season as well as during the following season, even though full irrigation may have been restored during that second season. To define the cropping responses involved, three post-veraison irrigation treatments were imposed on spur, mechanically and minimally pruned Shiraz vines that were already receiving restricted water application using Partial Rootzone Drying (PRD). The treatments resulted in the vines receiving 1.25 ML per hectare pre veraison and the three irrigation treatments receiving 1.25, 0.65 and 0 ML of water per hectare in the post-veraison period. Water deficit during the current season reduced berry and bunch weight, and yield. Sugar concentration was reduced, and phenolic concentration increased when less water was applied, but anthocyanin concentration was unaffected. Although irrigation was returned to standard practice (PRD) in the following season, yield was reduced in accordance with deficit irrigation treatments the previous season. This reduction in yield was primarily caused by fewer bunches per vine, which in turn was a direct consequence of fewer shoots per vine (lower budburst). The lower crop load on the vines that had received restricted irrigation post-veraison in the previous season resulted in higher sugar and antho-cyanin concentrations in fruit the following season. Lighter pruning resulted in a greater number of smaller bunches comprising smaller berries. In both seasons the minimal pruning treatment delayed fruit maturity as measured by sugar accumulation. Post-veraison water deficit thus has the potential to impact on both yield and fruit composition during the current season as well as during the subsequent season.     

ADHESION CHARACTERISTICS OF ISOLATED WAX SUBSTANCES FROM FRUIT CUTICLES RELATED TO OSMOTIC DEHYDRATION OF WHOLE FRUITS I. EFFECT OF TEMPERATURE AND PRELIMINARY TREATMENT

Adhesion behavior of cuticular wax isolated from cherries, plums and grapes, in a 70% sucrose solution, is the subject of discussion in the present work. Criterion is suggested for estimation of the effectiveness of preliminary treatment and temperature conditions in osmotic treatment of whole fruits. An apparatus is described for the determination of the contact angle θ_slv according to the method of the lying drop. Calculations are made of the energy characteristics, the energy of wetting Wslv and the adhesion work A_slv, of the three phase contact, isolated cuticular wax/70% sucrose solution/air, at temperatures from 20°C to 80°C.     

Optimal improvement in bistable measurement device performance via stochastic resonance

The notion of noise-activated systems has been well known since the 1950s. A number of natural phenomena have been investigated by means of this theory and an improvement in the performance of several systems has also been achieved. Recently the stochastic resonance (SR) phenomenon was introduced as an innovative approach for both understanding the behaviour and improving the performance of several classes of systems. In the present work some new results regarding the influence of forcing signal parameters on the persistence of the SR condition are given. Both theoretical results and numerical simulations have been carried out to emphasize the suitability of the proposed noise tuning methodology.     

INTEGRATING SENSORY ANALYSIS AND HEDONIC EVALUATION FOR APPLE QUALITY ASSESSMENT

ABSTRACT

Apple cultivars were subjected to a consumer test in order to appreciate individual preferences and set up a protocol for a practical hedonic‐sensory evaluation. Cultivars subjected to the test were “Golden Delicious,”“Modì,”“Pink Lady” and “Fuji” of two different origins. Apples had the sensory profile defined by a trained panel and were evaluated by 154 consumers. According to their preferences, consumer population could be divided in six clusters. Consumer preference responses clearly associated the two “Fuji” and showed “Modì” and “Pink Lady” to have appeal on the same consumers groups. Besides expressing hedonic judgment, consumers were requested to indicate the positive sensory attributes determining their choice. Consumers appreciated “Golden Delicious” and “Fuji” on the basis of sweetness and aroma, while preferences for “Pink Lady” and “Modì” were expressed by consumers appreciating crispness, juiciness and a certain degree of acidity. The involvement of consumers in defining attributes driving preferences provides details useful for weighing up the consistency between consumers' response and sensory panel profile.

PRACTICAL APPLICATIONS

This work contributes to the knowledge on consumer preferences and concerning apple sensory quality. In particular, the tested varieties could be divided in three groups on the basis of perceived attributes. Knowledge of consumer preferences related to apple qualities can be a key point in planning production and marketing strategies. A protocol integrating sensory characteristics defined by a trained panel, hedonic consumer judgments and sensory preference drivers is proposed.