On sufficient conditions for the stability of interval matrices

Using Gershgorin's diagonal dominance theorem, new sufficient conditions for the stability of interval matrices are obtained. The new conditions remove a restriction in Heinen's (1983) analysis and are applicable to a wider class of problems than previously possible.     

CONTAMINATION OF PATULIN IN CLEAR APPLE JUICE IN MASHHAD, IRAN

Patulin is a frequent contaminant of moldy and rotten apples and apple products. The aim of this study was to evaluate patulin contamination in 58 apple juices collected from a retail market in Mashhad during winter and spring of 2006.
Samples were assayed for patulin by high-performance liquid chromatography. Fifty-four samples were positive for patulin at levels that ranged from 10.5 to 121.8 µg/L, and six samples had patulin levels higher than 50 µg/L. The overall mean of patulin concentration was 29.2  ±  19.5 µg/L. Forty-eight samples had patulin concentration between 5 and 50 µg/L. Although the mean concentration of patulin samples was lower than Iranian maximum tolerated level of 50 µg/L, contamination of 10% of the samples at levels higher than 50 µg/L indicated the need for improving production techniques by the industry.

PRACTICAL APPLICATIONS

Studies have shown that the concentration of patulin may exceed the determined limits in apple juice and in other fruit products. Its presence can be a potential threat to the health of consumers, particularly children. The results may help us in understanding what should be the level of patulin in apple juice. The awareness of the apple industry of patulin contamination in fruit and the implementation of improved techniques for the production of apple products with reduced patulin concentrations have contributed to the quality of apple juice that are available on the Iranian market.     

核电结构材料应力腐蚀开裂初始阶段裂尖驱动力的研究

裂尖力学状态是影响核电结构材料应力腐蚀开裂(SCC)扩展速率的主要因素之一。为了搞清SCC不同扩展阶段裂尖驱动力的变化及其对SCC扩展速率的影响,本文建立了SCC扩展不同阶段的有限元模型,详细分析了裂纹初始阶段影响裂尖应力状态的工作载荷、残余应力,以及氧化膜形成过程中产生的膜致应力。结果表明,在SCC裂纹初始阶段,裂尖氧化膜形成所产生的“锲入张力”是SCC的主要驱动力;随着裂纹的扩展,工作载荷和残余应力逐渐成为SCC裂纹扩展的主要驱动力。     

冷轧加工纳米结构Ti_(50)Ni_(48)Co_2形状记忆合金的超弹性行为（英文）

研究冷轧后退火对Ti_(50)Ni_(48)Co_2形状记忆合金显微组织演化和超弹性性能的影响。结果表明,在冷轧制过程中,合金的显微组织经历了应力诱导马氏体相变和马氏体塑性变形、变形孪晶、马氏体中沿孪晶和不同晶界的位错堆积、纳米晶化、非晶化以及马氏体向奥氏体的可逆相变6个基本阶段。在400℃退火1 h后,冷轧样品中形成的非晶相完全晶化,生成了一个完全纳米晶体的结构。这种纳米晶体合金的峰应力高达730 MPa,明显高于粗晶Ni_(50)Ti_(50)和Ti_(50)Ni_(48)Co_2合金。而且,纳米晶Ti_(50)Ni_(48)Co_2合金具有较高的阻尼容量和较好的储能效率。     

A simulation study on autonomous decentralized mechanism in fish behaviour model

The behaviour of a fish school is considered an interesting phenomenon because a fish school behaves differently in various situations. The paper considers a fish school as an autonomous decentralized system and constructs a mathematical model for the autonomous decentralized mechanism. Simulation results show that, by varying the quantity of information exchange among members in school, the present model describes fish behaviour not only for a school with fixed configuration but also for that with variable form. Furthermore, a remarkable difference in fish trajectory is found between the two schools.     

On the design of observers for generalized state space systems using singular value decomposition

In this paper a method is developed for the design of Luenberger-type observers for linear time-invariant control systems whose state equation is of the form Ex= Ax+ Bu where E is a singular square matrix. The method is based on the singular-value decomposition of the matrix E, and on the reduction of the equation Ex= Ax +Bu to a system consisting of a differential equation of the form w₁, = F₁w₁ + F₂ + w₂ +G₁u and an algebraic equation of the form H₁w₁ +H₂w₂ + G₁u = 0. If w₂ can be eliminated from the differential equation by the aid of the algebraic equation and the original output equation of the system, the method yields a reduced-order observer for the generalized state space system.     

减少离散大系统两级镇定控制的保守性

The aim of this paper is to propose a new algorithm for multilevel stabilization of large scale systems. In two-level stabilization method, a set of local stabilizers for the individual subsystems in a completely decentralized environment is designed. The solution of the control problem involves designing of a global controller on a higher hierarchical level that provides corrective signals to account for interconnections effect. The principle feature of this paper is to reduce conservativeness in global controller design. Here, the key point is to reduce the effect of interactions instead of neutralizing them. In fact, unlike prior methods, our idea does not ignore the possible beneficial aspects of the interactions and does not try to neutralize them.     

Effect of process parameters on coating composition of cathodic-plasma-electrolysis-treated copper

Cathodic plasma electrolysis is a novel technique to form nanostructured layers on metallic surfaces by application of high voltage in a suitable aqueous electrolyte. In the present study, copper is treated by plasma electrolysis in 50 vol% ethanol electrolyte and coatings comprising carbon nanostructure and copper oxide are formed on the copper. The effect of some process parameters such as electrical conductivity, volume and temperature of electrolyte and ratio of anode to cathode surface area on current–voltage behaviour and subsequently coating compositions are investigated at 150 V deposition voltage. The composition and morphology of these coatings are characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Different current–voltage behaviours, temperatures of substrate and the contents and energies of radicals and ions around the substrate by changes in the mentioned parameters cause different compositions from 100 vol% copper oxide to different ratios of copper oxide to carbon, the structure changing from amorphous to graphitic structure in carbon and amorphous to cubic morphology in copper oxide on the substrate. Therefore, the understanding of cathodic plasma electrolysis can be developed.     

Influence of starter culture type and incubation temperatures on rheology and microstructure of low fat set yoghurt

The effects of different cultures and incubation temperatures on the physical properties of low fat yoghurts were investigated. The samples were incubated with exopolysaccharide (EPS)-producing and non-EPS-producing cultures at 37, 42 and 45°C. All measured parameters except firmness were influenced by culture type and incubation temperature. Firmness, G' and G" were maximised at 42°C for both cultures. Increased incubation temperature and EPS culture led to a higher water-holding capacity but lower syneresis, G' and G". The EPS treatment incubated at 37°C showed even lower syneresis than non-EPS treatments incubated at higher temperatures.