Design of microstrip hyperbolic line to match a complex impedance to a standard coaxial transmission line

Based on the solution of the Riccati equation, a hyperbolically tapered microstrip transmission line for matching a complex load to a standard coaxial cable is designed. An iterative procedure is used to yield the phase constant leading to an accurate design. A numerical example is considered. The result shows that a tremendous reduction in the size of matching components can be achieved if hyperbolic instead of uniform transmission lines are used. This is highly advantageous in the miniaturization of solid state circuits.     

Effect of pretreatment with salt and sucrose on the quality and stability of dehydrated cauliflower

Dehydrated cauliflower was prepared by soaking the blanched pieces in solutions of different concentrations of common salt and sucrose (cane sugar), alone and in combination, prior to drying in a cabinet drier and evaluated for sensory, rehydration, storage, microbiological, histological and sorption characteristics. While sucrose alone produced considerable improvement, salt supplemented its effect. The optimum treatment was soaking in 3% salt and 6% sucrose for 12–16h at 4°C it markedly reduced shrinkage and improved rehydration without affecting palatability. It was necessary to boil the soak solution for 3 min and cool prior to soaking to reduce microbial contamination. The treatment increased ascorbic acid loss by 8%. Monolayer moisture content calculated from BET equation was 6.5% (moisture-free) basis for treated and 5.3% for untreated. The treatment increased the shelf-life of the product from 3 to 12 months at ambient temperature when packaged in paper-foil-polythene laminate.     

T6热处理对共晶Al-Si合金力学性能、耐磨和抗蚀性能的影响(英文)

对共晶Al-Si合金的耐磨、抗蚀性能进行研究。通过控制T6热处理参数来改变共晶Al-Si合金的组织,研究组织变化对合金的硬度、强度和拉伸性能的影响,以及对抗冲蚀和腐蚀性能的影响。采用Al-Si合金制备了一典型的农机零部件。并将Al-Si合金与常用的农机用铝材的性能进行比较。结果表明,合金的化学成分、显微组织、载荷、滑动距离和试验环境对材料的耐磨、抗冲蚀和腐蚀性能有很大的影响。铸态Al-Si合金的性能要明显优于传统的铝材,而且T6热处理能够改善Al-Si合金的性能。因此,可采用Al-Si合金来替代传统的铝材制造农机。     

Enhanced corrosion performance of magnesium phosphate conversion coating on AZ31 magnesium alloy

Magnesium phosphate conversion coating (MPCC) was fabricated on AZ31 magnesium alloy for corrosion protection by immersion treatment in a simple MPCC solution containing Mg²⁺ and PO^3?₄ ions. The MPCC on AZ31 Mg alloy showed micro-cracks structure and a uniform thickness with the thickness of about 2.5 µm after 20 min of phosphating treatment. The composition analyzed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the coating consisted of magnesium phosphate and magnesium hydroxide/oxide compounds. The MPCC showed a significant protective effect on AZ31 Mg alloy. The corrosion current of MPCC was reduced to about 3% of that of the uncoated surface and the time for the deterioration process during immersion in 0.5 mol/L NaCl solution improved from about 10 min to about 24 h.     

Stochastic analysis of a priority unit standby system with repair machine failure

This paper deals with the analysis of reliability characteristics of a two-unit (priority ‘p’ and ordinary V) cold standby system model under a very practicable assumption that the repair machine may also fail during the process of system effectiveness. The analysis is obtained by using a regenerative point technique.     

A differential-difference equations model of a dynamic aquatic ecosystem†

This paper presents a differential-difference equations model of a dynamic aquatic ecosystem. This paper departs from other models by considering : (a) specific phyla of phytoplankton, zooplankton and nekton ; (b) their prey—predation relationships ; (c) both allelochemic and antotoxic effects of algae upon zooplankton and other algae ; (d) inter-phyla competition for nutrients. Other factors included are : limiting effects of phosphates, nitrates, silicates, photoperiod, turbidity, temperature, and time lag, as they affect growth and reproduction of the biota. The model uses the western basin of Lake Erie as a test example, but any shallow basin that does not experience thermoclines could be used.     

RECENT ADVANCES IN ADAPTIVE CONTROL

Abstract

A survey of the design techniques and applications of adaptive control has been presented. Two approaches to adaptive control have been considered, with greater emphasis on the model reference adaptive systems including the new ideas introduced in this area during the past decade. A typical example of the design of a two-level model-reference adaptive controller for a continuous stirred tank reactor is discussed in detail. A number of other examples with applications are also briefly presented, and a list of references is given for further details.     

ON THE DESIGN OF AN ADAPTIVE CONTROLLER FOR UNCERTAIN PLANTS VIA LIAPUNOV SIGNAL SYNTHESIS METHOD

This paper presents an adaptive design approach for controlling a class of unknown nonlinear multivariable plants operating in an uncertain environment. The approach uses a “two-level” control technique, with a feedforward controller on its first-level, and a conditional feedback controller on its second-level. The procedure employs a Liapunov type signal synthesis approach. By introducing a characteristic vector, which is characteristic of the unknown plant and its environment, the design of the controller bypasses the rigid requirements of explicit identification of the plant and its environment as needed in the implementation of a controller using conventional techniques.

The applicability of this control approach is demonstrated by means of hybrid computer simulation studies which were carried out on a number of unknown plants; however, in this paper we present some simulation results for an exothermic chemical reactor.     

A robust test of uncertain linear systems

In this paper, it is shown that for low-order uncertain systems, there is no need to calculate all the minimum and maximum values of the coefficients for a perturbed system which is expressed in terms of polynomials and hence no need to formulate and test all the four Kharitonov＇s polynomials. Furthermore, for higher-order systems such as n ≥ 5, the usual four Kharitonov＇s polynomials need not be tested initially for sufficient condition of perturbed systems; rather, the necessary condition can be checked before going for sufficient condition. In order to show the effectiveness of the proposed method, numerical examples are shown and computational efficiency is highlighted.     

The Use of Legendre Polynomial Expansions in Solving Optimal Control Problems in the Space l 2

A method for solving a class of general deterministic optimal control problems is presented here. The method consists of relating the functions involved in the problem to sequences and then converting the problem to one which deals with these sequences alone. The function-sequence correspondence is defined by representing each function by its Legendre polynomial expansion and then relating the function to the sequence of coefficients in this expansion. After this is done, the problem is converted to one in l ²; by determining the equivalents in l ²; of differentiation, inner multiplication, and multiplication.

The resulting problem in l ²; is a non-linear programming problem which consists of an infinite array of equations, inequalities, and expressions, each of which involves infinite polynomial expressions. To solve a problem of this type it must be approximated by a finite non-linear programming problem. After this is done various methods can bo used for solving the final problem.