Synthesis of sampled feedback systems for prescribed time domain tolerance

This paper presents a design procedure for single-loop sampled feedback systems in which the plant transfer function has prescribed bounds on its parameters. The plant is imbedded in a ‘ two-degree-of-freedom system’, which is to be designed such that the system time response to a deterministic input lies within specified boundaries. The design procedure is based on frequency concepts. The time-domain tolerances are translated into equivalent frequency response tolerances. The latter lead to bounds on the loop-transmission L(jv) [v =tang (π/WS)[, in the form of continuous curves on the Nichols chart. However, due to inherent theoretical difficulties existing in sampled feedback systems, it might happen that no L(jv) can be found so that the design specifications of the problem are achieved. The design procedure is transparent enough to guide the designer in which direction to change the specifications of the problem so that the next trial design will be successful.     

Moisture, Total Fat and Cholesterol in Goat Organ and Muscle Meat

Moisture, total fat and cholesterol of goat liver, kidney, heart, Longissimus dorsi (LD) and Biceps femoris (BF) muscles were determined. Samples were taken from 10 Alpine and 10 Nubian post-weaned goat kids that were fed a complete diet treated with 4 levels of Ca for 12 wk before slaughter. Mean moisture (%), total fat (%) and cholesterol (mg/100g wet tissue) for the respective tissues were: 75.9, 3.26, 214.2; 82.0, 3.14, 276.7; 79.2, 4.32,167.5; 79.2, 2.27, 57.8; 80.4, 2.03, 69.5. These goats contained less cholesterol in liver and more cholesterol in kidney and heart than the same organs in mutton samples reported previously. Fat and cholesterol were significantly (P < 0.01) influenced by dietary Ca, breed and tissue, while moisture was affected only by tissue.     

A new approach for the design of multivariable feedback systems

A new design technique for multivariable feedback systems is presented. In this approach, n —1 open-loop transfer functions at different inputs of the plant, with all other feedback paths closed, are specified in advance, and are achieved exactly. The nth open-loop transfer function is a by-product of the design process, such that the overall feedback system is stabilized. The design approach is fitted to solve problems in which the plant elements can have non-stable poles and non-minimum phase zeros. The design process is straightforward, no iterations are necessary, and the achieved design copes exactly with the design specifications. The gainbandwidths of the different lis and the overall loop gain l* might be constrained due to non-stable poles and zeros of the plant elements. Based on the obtained different loop gains, any input output matrix T can bo achieved with the aid of an appropriate prefilter matrix F.     

NATURAL CHEDDAR CHEESE TEXTURE VARIATION AS A RESULT OF MILK SEASONALITY

A set of standard testing conditions using the TA-XT2 Texture Analyser were established to monitor cheddar cheese texture variation. Cheddar cheese was produced in the standard commercial practice and sampled at monthly intervals throughout the milk production season (August - June), and monitored for textural and compositional changes occurring during ripening. The composition, based on fat and protein levels, of the cheese was relatively constant during the period, which was expected as the commercial process aims for that outcome. A reduction in the force and degree of compression at fracture with time, indicative of a reduction in cheese firmness and an increase in cheese crumbliness, was recorded as the milk production season progressed. The degree of proteolysis and changes in milk fat in late season milk are primarily responsible for the changes recorded in cheese texture. The differences observed between cheeses produced at different times during the season indicate that the current fat and protein standardization employed by cheese-makers is not adequate to provide cheddar cheese with consistent textural characteristics year round.     

INVESTIGATIONS INTO THE INFLUENCE OF WATER ACTIVITY, pH AND HEAT TREATMENT ON THE VELOCITY OF THE MAILLARD REACTION IN FOODS

This work was conducted in conjunction with a research project (Fox 1980) investigating the feasibility of using a combination of mild processing methods to produce microbiologically stable product and at the same time minimize some of the adverse effects associated with accepted preservation techniques. The purpose of this research was to determine the influence of the four process parameters: (1) temperature and (2) time of heat treatment, (3) pH-value and (4) water activity (a_w) on an undesirable reaction which often occurs in foods—the formation of brown pigments in the progressive phase of the Maillard reaction. In this work, investigations were undertaken with a model product consisting of the reducing sugar, Glucose, and the amino acid, Alanine. From the data developed, it was determined that the lag time necessary before this reaction produced brown pigment was so long that this reaction was insignificant in a combination processing method using the parameters under investigation.     

INVESTIGATIONS INTO THE INFLUENCE OF WATER ACTIVITY, pH AND HEAT TREATMENT ON THE BREAKDOWN OF 5'-RIBONUCLEOTIDES IN FOODS

Conventional food preservation methods frequently have adverse effects on the flavor of the finished product. Recent research has been conducted (Fox 1980) to determine the feasibility of using a combination of mild processing methods which will produce microbiologically stable product and at the same time reduce the undesirable effect on flavor associated with accepted preservation techniques. The purpose of this research was to determine the optimum combination of process parameters with respect to minimizing flavor loss in the product. A 5′-ribonucleotide flavor enhancer was added to a model product as the test substance and after undergoing a series of combination processes consisting of a mild heat treatment, reduced pH and reduced water activity (a_w), the amount of breakdown of the flavor enhancer was determined. From the data produced, one can see the strong influence of the time and temperature of the heat treatment, the lesser but still significant influence of pH and the lack of influence of water activity on the breakdown of the 5′-ribonucleotide.     

FUZZY MODELS FOR ENERGY DEMAND MANAGEMENT

Abstract

Energy planning is a management and control tool meant to deal medium- and long-term with the interaction process between the economic development and efficient resource allocation of a given country. The paper gives a complementary approach to an econometric model which by means of fuzzy sets theory enables the social planner to estimate the energy vector at a given moment within the content of a given industrial structure. The fuzzy approach is used to quantify the preferences and/or the given information states that are neither deterministic in use nor certain and so they have to be dynamically approached. This approach is used to compute and evaluate end use energy demand on a time scale. The management-oriented results illuminate further dimensions of the complex problem of energy use management by means of models and the interaction with the social planner, its way of thinking and preferences.     

Hybrid design method for dead-beat regulators†

Since the works of Kalman (1963) and Tou (1964) it is known that an nth-order sampled-data system needs n control signals to reach equilibrium if taken in an arbitrary initial state. These control signals may be applied either in open loop, through linear feedback channels when all the state variables are accessible or with a digital compensator if only the output is available. A computational procedure for solving this problem is described. This method uses the analogue simulation of the process in order to form a linear system which is then solved on a digital computer giving directly the open-loop control signals. Then, with the open-loop control signals one sees how the feedback coefficients or the digital compensator can be found in a very simple way in order to get dead-beet response. The method has the advantage of keeping all the tedious work (matrix integration and matrix multiplication) to a minimum by using the analogue computer, the digital computer only having to solve two linear systems. The method may be applied to scalar systems or to multi-input systems. The authors think that the design of dead-beat compensators is thus greatly simplified mid two examples are displayed with numerical results.