两株抗氧化活性酵母的鉴定及对乳成分的影响

为获得有抗氧化活性的工业用酵母菌株,对2株来源于原料乳中有较强抗氧化活性的酵母菌进行鉴定.根据菌株的表型、生理生化特征和基因型的特性,初步将这2株菌鉴定为毕赤氏发酵酵母(Pichia fermentans).将这2株酵母菌在高温灭菌(UHT)牛乳中培养以研究其对牛乳主要成分的影响,结果表明:这2株酵母能在UHT牛乳中产乙醇,具有促进蛋白水解活性与脂肪水解活性的能力,能有效提高乳中的游离氨基酸和脂肪酸的含量.     

ON THE DYNAMIC PROPERTIES OF THE EXTENSIVE VARIABLE CONTROL STRUCTURES

The purpose of this paper is to investigate the dynamic properties of controller structures synthesized using extensive thermodynamic variables of a process. Several state-space and frequency domain multivariable techniques, including INA, and Modal Interaction Analysis, are used in order to evaluate the dynamic properties of these control structures. These structures show zero steady state interaction and minimal dynamic interaction for all processes examined. Dynamic simulation of several application examples, including distillation columns and a network of two stirred tank heaters in series, shows that the loops in these structures can also be tuned with minimum effort. Comparison of the proposed structures, with the conventional parallel single-input single-output control structures, shows the advantages of the proposed method.     

The time dependent strain potential function for a polymeric glass

Torsion and normal force measurements were made during single step stress relaxation experiments on a polymeric glass (PMMA). Isochronal data were analysed using an approach adapted from that developed by Penn and Kearsley¹ (for incompressible elastic materials) to determine the derivatives $\text{?W}\text{?I}{}_1$, and $\text{?W}\text{?I}{}_2$ of the time dependent strain potential function. $\text{?W}\text{?I}{}_1$ and $\text{?W}\text{?I}{}_2$ are determined from existing solution to the torsion of an incompressible cylinder. A special solution to the torsion of a compressible cylinder is presented and it is shown that the values of $\text{?W}\text{?I}{}_1$ and $\text{?W}\text{?I}{}_2$ obtained using this solution to analyse the data do not differ greatly from those obtained using the incompressible solution. It is found from both solutions that $\text{?W}\text{?I}{}_1$ is negative and increases towards zero with increasing time and deformation while $\text{?W}\text{?I}{}_2$ is positive, greater in magnitude than $\text{?W}\text{?I}{}_1$ and decreases towards zero with increasing time and deformation. These results were unexpected and a full understanding of their meaning has yet to be reached.     

A new contribution to the finite line-source model for geothermal boreholes

Heat transfer around vertical ground heat exchangers is a common problem for the design and simulation of ground-coupled heat pump (GCHP) systems. Most models are based on step response of the heat transfer rate, and the superposition principle allows the final solution to be in the form of the convolution of these contributions. The step response is thus a very important tool. Some authors propose numerical tabulated values while others propose analytical solutions for purely radial problem as well as axisymmetric problems. In this paper we propose a new analytical model that yields results very similar to the tabulated numerical ones proposed in the literature. Analytical modeling offers better flexibility for a parameterized design.     

Modelling of growth, growth/no-growth interface and nonthermal inactivation areas of Listeria in foods

Growth, growth boundary and inactivation models have been extensively developed in predictive microbiology and are commonly applied in food research nowadays. Few studies though report the development of models which encompass all three areas together. A tiered modelling approach, based on the Gamma hypothesis, is proposed here to predict the behaviour of Listeria.Datasets of Listeria spp. behaviour in laboratory media, meat, dairy, seafood products and vegetables were collected from literature, unpublished sources and from the databases ComBase and Sym'Previus. The explanatory factors were temperature, pH, water activity, lactic and sorbic acids. For the growth part, 697 growth kinetic datasets were fitted. The estimated growth rates and 2021 additional growth primary datasets were used to fit the secondary growth models. In a second step, the fitted model was used to predict the growth/no-growth boundary. For the inactivation modelling phase, 535 inactivation curves were used.Gamma models with and without interactions between the explanatory factors were used for the growth and boundary models. The correct prediction percentage (predicted growth when growth is observed + predicted inactivation when inactivation is observed) varied from 62% to 81% for the models without interactions, and from 85% to 87% for the models with interactions. The median error for the predicted population size was less than 0.34 log₁₀(CFU/mL) for all models. The kinetics of inactivation were fitted with modified Weibull primary models and the estimated bacterial resistance was then modelled as a function of the explanatory factors. The error for the predicted microbial population size was less than 0.71 log₁₀(CFU/mL) with a median value of less than 0.21 for all foods.The model enables the quantification of the increase or decrease in the bacterial population for a given formulation or storage condition. It might also be used to optimise a food formulation or storage condition in the case of a targeted increase or decrease of the bacterial population.     

Elastic–plastic cracking analysis for brittle–ductile rocks using manifold method

In this study, the formation of localized deformation band and failure processes of brittle–ductile materials (coarse and medium marbles) containing pre-existing flaws under various loading conditions are simulated numerically. By incorporating the modified Mohr–Coulomb crack initiation criterion and the crack evolution techniques, the cracking processes, such as crack initiation, propagation and coalescence are successfully modeled by the developed numerical manifold method. According to the results, the development of macro-shear cracks is preceded by the development of localized deformation bands, which are underlain by damage accumulation and material deterioration. The numerical results are comparable to the laboratory test results.     

An innovative approach to identify the knowledge diffusion path: the case of resource-based theory

This study presents an innovative approach for identifying the knowledge diffusion path of a target research field. We take the resource-based theory (RBT) as an example to demonstrate the usefulness of this methodology. Several survey studies have provided valuable summarization and commentaries to the RBT from different perspectives. These analyses are useful and pertinent for understanding the development of RBT. However, limited by the methodologies they used, previous scholars can only select part of the RBT literature to conduct the survey work. To eliminate the limitation, this study develops an innovative approach which can handle thousands of articles. This study analyzes a dataset including 2,105 theoretical developments, empirical studies, and review papers to explore the knowledge diffusion path of the RBT. Citation data are used to build the citation network. Main paths are then probed and visualized via social network analysis methodology. To figure out the total picture of the knowledge diffusion path, this study integrates various main path analyses to supplement the traditional approach. The traditional main path analysis investigates the knowledge diffusion from a local view. The global analysis provides a main path from a macro view. The key-route analysis helps explore and clarify a complete picture of the convergence-divergence phenomena. We believe that through this novel tool, new researchers can easily identify the papers that have made major contributions to RBT knowledge diffusion and uncover the interrelationships among them.     

Thermochromic composite fibres containing liquid crystals formed via melt extrusion

A three-layered composite fibre has been generated via a modified wire-coating melt co-extrusion process. The continuous fibre consists of a thermochromic liquid crystalline (TLC) layer encapsulated between a transparent polypropylene outer sheath and a black polyether ether ketone inner core. The fibres exhibit clear thermochromic behaviour consistent with the behaviour of unincorporated TLCs, and have been formed into a textile. The presence of the black inner core was found to be the key for the clear retention of colour within the fibres against both white and black backgrounds. The temperature-sensitive fibres and textiles can be applied to a variety of thermal mapping applications, such as in the medical and engineering fields, due to the tunable nature of TLCs.