A numerical approach to modelling size effects on the flexural ductility of RC beams

The problem of evaluating the rotation capacity of reinforced concrete (RC) beams in bending has been largely investigated from both the experimental and the analytical point of view during the last decades. Since the development of ductility is influenced by several design parameters, it is difficult to develop a predictive model that can fully describe the mechanical behaviour of RC beams. In particular, the role of the size-scale effect, which has been evidenced by some experimental tests, is not yet completely understood. One of the main reasons is the inadequacy of the traditional models based on ad hoc stress–strain constitutive laws. In the present paper, a new model based on the concept of strain localization is proposed, which is able to describe both cracking and crushing growths in RC beams during the loading process. In particular, the nonlinear behaviour of concrete in compression is modelled by the Overlapping Crack Model, which describes the strain localization due to crushing by means of a material interpenetration. With this algorithm in hand, it is possible to effectively capture the flexural behaviour of RC beams by varying the reinforcement percentage and/or the beam depth. An extensive comparison with experimental results demonstrates the effectiveness of the proposed approach.     

A Phenomenological Model of the Peroxide Value’s Rise and Fall During Lipid Oxidation

During isothermal lipid oxidation at relatively high temperatures, the peroxide concentration frequently peaks while at relatively low temperatures it only rises slowly. These are two manifestations of a process where formation and degradation happen simultaneously on different time scales. A phenomenological mathematical model, comprising a decay factor superimposed on an accumulation term can describe these scenarios. Each has a characteristic time constant shortened by raising the temperature and a rate constant that increases with it. The model’s mathematical structure and the magnitude of its coefficients depend on the particular system. However, regardless of the chosen expressions, if the degradation characteristic time falls within or just beyond the experiment’s duration, a peak peroxide value will be observed whose height and shape will primarily depend on the other model’s parameters. If this characteristic time is far outside the time of the experiment , no peak will be recorded. The model need not be unique and no detailed knowledge of the oxidation mechanisms is required for its formulation. Consequently it can be derived directly from experimental peroxide value versus time relationships, without the need to monitor the intermediate reactions by specialized instrumental methods such as DSC. Through the formation term adjustment, the model can also account for the temperature dependent lag in the rise of the peroxide value and/or the appearance of its peak.     

Patulin in apple-based foods: occurrence and safety evaluation

Patulin is a mycotoxin produced by certain species of Penicillium and Aspergillus, often detectable in mouldy fruits and their derivatives. On the basis of a PMTDI of 0.4 mu g/kg bw, limit values of 50 mu g/kg or 50 mu g/l of patulin have been set in fruit derivatives. To estimate the quantity of patulin that can be taken in with the diet, we analysed by HPL C samples of apples and apple derivatives which are most likely to be contaminated with patulin. In apple juices and in homogenized babyfoods, the mycotoxin concentration was always below the established limits, while in some samples of juice with pulp the mycotoxin content exceeded the safe levels. In rotten apples, not only was the amount of patulin extraordinarily high in the rotten area, but the mycotoxin had also spread to the part unaffected by mould. The data presented in this study indicate that the intake of patulin with apple derivatives is usually below the tolerable level of 0.4 mu g/kg bw/day, but since the patulin content in apples can vary considerably, the quality of fruits used in the production of apple derivatives should be strictly controlled in order not to exceed the safe limits.     

Nucleation and Crystallization of a Lithium Aluminosilicate Glass

An aluminosilicate glass of composition 61SiO₂6Al₂O₃10MgO6ZnO·12Li₂O·5TiO₂ (mol%) has been prepared by a melting process and investigated as far as crystallization is concerned. Glass-ceramic is easily obtained because glass shows a high tendency to crystallize starting from 700°C. The crystalline phases evolve with temperature, showing the aluminosilicates to be the main phase up to 1050°C, followed by metasilicates and silicates, some of which have lower melting points. The titanates of Mg and Zn develop from the phase-separated glass, soon after T _g, and grow to form nucleation centers for the other crystalline phases. The evolution from phase-separated glass to glass-ceramic has been followed by many thermal, diffractometric, spectroscopic, and microscopic techniques.     

Human gallbladder mucosal function: effects on intraluminal fluid and lipid composition in health and disease

OBJECTIVES: Fructose-1,6-diphosphate is a glycolytic intermediate that has been shown experimentally to cross the cell membrane and lead to increased glycolytic flux. Because glycolysis is an important energy source for myocardium during early reperfusion, we sought to determine the effects of fructose-1,6-diphosphate on recovery of postischemic contractile function. METHODS: Langendorff-perfused rabbit hearts were infused with fructose-1,6-diphosphate (5 and 10 mmol/L, n = 5 per group) in a nonischemic model. In a second group of hearts subjected to 35 minutes of ischemia at 37 degrees C followed by reperfusion (n = 6 per group), a 5 mmol/L concentration of fructose-1,6-diphosphate was infused during the first 30 minutes of reperfusion. We measured contractile function, glucose uptake, lactate production, and adenosine triphosphate and phosphocreatine levels by phosphorus 31-nuclear magnetic resonance spectroscopy. RESULTS: In the nonischemic hearts, fructose-1,6-diphosphate resulted in a dose-dependent increase in glucose uptake, adenosine triphosphate, phosphocreatine, and inorganic phosphate levels. During the infusion of fructose-1,6-diphosphate, developed pressure and extracellular calcium levels decreased. Developed pressure was restored to near control values by normalizing extracellular calcium. In the ischemia/reperfusion model, after 60 minutes of reperfusion the hearts that received fructose-1,6-diphosphate during the first 30 minutes of reperfusion had higher developed pressures (83 +/- 2 vs 70 +/- 4 mm Hg, p < 0.05), lower diastolic pressures (7 +/- 1 vs 12 +/- 2 mm Hg, p < 0.05), and higher phosphocreatine levels than control untreated hearts. Glucose uptake was also greater after ischemia in the hearts treated with fructose-1,6-diphosphate. CONCLUSIONS: We conclude that fructose-1,6-diphosphate, when given during early reperfusion, significantly improves recovery of both diastolic and systolic function in association with increased glucose uptake and higher phosphocreatine levels during reperfusion.     

Automatic verification of distributed systems: The process algebra approach

A survey of tools for the analysis of distributed systems represented through process algebras is presented. The tools are compared with respect to a set of qualitative parameters. From this analysis, the properties which are desirable for concurrency tools are investigated. Criteria to evaluate the suitability of a tool with respect to a particular user are proposed.