Effects of metal cations on betanin stability in aqueous-organic solutions

An effect of metal cations on betanin stability was investigated in aqueous and organic-aqueous solutions. The presence of organic solvents (methanol, ethanol, and acetonitrile) affects substantially the pigments decomposition in acidic media induced by metal cations whose degrading action in such media is significantly higher than in aqueous solutions. The influence of Cu²⁺ on the stability was studied by spectrophotometry in more detailed manner, because of its ability to form complexes with betanin. The possibility of a complex formation between betanin and Ni²⁺ was also stated at pH 7–8; its relatively high stability in aqueous samples was observed. A presence of numerous products of betanin decomposition was detected in the wavelength range 380–500 nm in spectra obtained for most of metal cations investigated, especially for higher concentrations of the organic solvents.     

Dynamic modelling for thermal micro-actuators using thermal networks

Thermal actuators are extensively used in microelectromechanical systems (MEMS). Heat transfer through and around these microstructures are very complex. Knowing and controlling them in order to improve the performance of the micro-actuator, is currently a great challenge. This paper deals with this topic and proposes a dynamic thermal modelling of thermal micro-actuators. Thermal problems may be modelled using electrical analogy. However, current equivalent electrical models (thermal networks) are generally obtained considering only heat transfers through the thickness of structures having considerable height and length in relation to width (walls). These models cannot be directly applied to micro-actuators. In fact, micro-actuator configurations are based on 3D beam structures, and heat transfers occur through and around length. New dynamic and static thermal networks are then proposed in this paper. The validities of both types of thermal networks have been studied. They are successfully validated by comparison with finite elements simulation and analytical calculations.     

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.     

Theoretical comparison of a new and the traditional method to calculate Clostridium botulinum survival during thermal inactivation

When published isothermal survival data of Clostridium botulinum spores in the range 101–121 °C were plotted in the form of logS(t) vs t relationships, where S(t) is the momentary survival ratio, they were all non‐linear. They had a noticeable upward concavity, in violation of the assumption that sporal inactivation is a process that follows first‐order reaction order kinetics. They could be described by the power law model logS(t) = ? b(T)t ^n(T), where b(T) and n(T) are temperature‐dependent coefficients of the order of 0.1–6 and about 0.4 respectively. These coefficients were used to construct simulated survival curves under different heating regimes with a recently proposed model. The model is based on the assumption that the local slope of the non‐isothermal survival curve, or the momentary inactivation rate, is determined solely by the momentary temperature and survival ratio, which in turn are functions of the population thermal history. The survival curves calculated with this model differ considerably from those produced by the standard method based on the traditional D and Z values. The shortcomings of the standard model are that these values depend on the number of points taken for the regression, and that its predicted survival ratios depend on the selected reference temperature. The differential equation which is proposed to replace it can be solved numerically using a program such as Mathematica®. Its predictions solely depend on the observed survival patterns under isothermal conditions and not on any preconceived kinetic model. Nevertheless, the method still needs verification with experimental non‐isothermal survival data, as has already been done with Listeria and Salmonella cells. © 2001 Society of Chemical Industry     

A two-scale approach for trabecular bone microstructure modeling based on computational homogenization procedure

In this paper the numerical implementation of two-scale modelling of bone microstructure is presented. The study is a part of long-term project on bone remodelling which drives bone microstructure change based directly on trabeculae surface energy. The proposed approach is based on a first-order computational homogenization technique. The coincidence of macro- and micro-model kinematics is done with the use of uniform displacement and traction boundary conditions. The computational homogenization procedure is driven by a self-prepared manager which is coded in Python. The computation on real bone structure (a piece of female Wistar rat bone) is performed as well.     

Development and characterisation of nanowire-based FETs

Development of Si nanowire-based FETs, suitable for sensor applications is reported. Process sequences for SOI and bulk p-channel FinFETs are described. SEM observations of the fabricated devices (180 nm wide, 87 nm or 175 nm high) are presented and discussed. Electrical characteristics measurements and basic characterisation results obtained for these devices are described. A procedure for serial resistance extraction has been mentioned in more detail, due to its high value inherent in the process used. Several aspects of the device sensitivity to front- and back-gate control have been discussed from the point of view of its application in biochemical detectors.     

Investigations on printed elastic resistors containing carbon nanotubes

This paper presents the results of authors investigations on elaboration of a new thick film composition filled with carbon nanotubes (CNTs). The polymer composition consists of polymer vehicle, which is the solution of organic resin in certain combination of solvents, and functional phase—carbon nanotubes well dispersed in the vehicle. The pastes were applied with screen-printing on several substrates and temperature cured. The properties of obtained layers were characterized. Series of samples were prepared with different amount of CNTs to evaluate electrical properties. Changes in resistance were investigated during periodic mechanical and temperature stresses, realized through cyclical bending and rapid temperature change. Tensometric effect was also investigated. Investigations have proved that polymer composites based on carbon nanotubes exhibit high resilience to stress factors. Resistance change in function of temperature was also investigated to evaluate temperature coefficient of resistance (TCR). All this aspects are important for elastic resistors fabrication in printed electronics microcircuits. Resistance and noise measurements in cryostats have also been involved. 1/f type noise has been observed. Noise intensity, calculated in decade frequency bands, rises significantly with increasing temperature. Activation energies of thermally activated noise sources (TANS) have been revealed using low-frequency noise spectroscopy. Relatively large value of negative TCR has been obtained from resistance versus temperature curve. Calculated dimensionless sensitivity is similar to that observed in cryogenic temperature sensors. However, bulk noise intensity of resistive layer is larger than obtained for lead containing RuO₂ based resistive layers.     

A method for fast simulation of multiple catastrophic faults in analogue circuits

The paper offers an efficient method for simulation of multiple catastrophic faults in linear AC circuits. The faulty elements are either open circuits or short circuits. The method exploits the well‐known Householder formula in matrix theory to find the node voltages deviations due to the perturbations of some circuit elements. The main achievement of the paper is a systematic method for performing the simulation of all combinations of the multiple catastrophic faults. The method includes two new procedures enabling us to find very efficiently the node impedance matrix of the nominal circuit and inverses of some matrices corresponding to different fault combinations. The procedures are the crucial point of this approach and make it very efficient. Consequently, the amount of the computing power needed to carry out all the simulations is significantly reduced. Numerical examples illustrating the proposed approach are provided. Copyright © 2008 John Wiley & Sons, Ltd.