Modeling the response function of dual-enzyme microbiosensors

A general theoretical model for competitive dual-enzyme microbiosensors based on self-assembled monolayers (SAM) is presented. The model is derived for amperometric dual-enzyme ATP sensors and provides excellent agreement with experimental ATP measurements at 25 microm diameter microelectrodes. In this model, the statistical probability of a glucose molecule in competition between two enzymes, glucose oxidase (GOD)/hexokinase (HEX), at the ATP sensor surface is combined with the enzymatic reaction rate. Thereby, a simple model predicting the sensor signal for varying surface concentrations of GOD and HEX, glucose concentration, and ATP concentration is obtained. Excellent agreement of the predicted current signal with experimentally obtained sensor signals was achieved at ATP concentrations between 10 and 300 microM in a buffer containing glucose at physiologically relevant levels. Consequently, the development time for new dual-enzyme biosensors can be reduced, and an analytical model for the sensor response function is provided facilitating the calibration of enzymatic biosensors.     

Amperometric biosensor for lactate analysis in wine and must during fermentation

A lactate oxidase-based amperometric biosensor is designed for lactate determination. Two methods of lactate oxidase immobilization on the surface of commercial SensLab platinum printing electrodes are compared. The sensor with lactate oxidase immobilized by physical adsorption in Resydrol polymer is shown to have both narrower dynamic range (0.004–0.5 mМ lactate) and higher sensitivity (320 nA/mM) as compared with that immobilized in poly(3,4-ethylenedioxythiophene) by electrochemical polymerization (0.05–1.6 mM and 60 nA/mM respectively). The operational stability of the biosensors developed is studied; the immobilization method is shown to be of no influence. The lactate content in wine and in wine material during fermentation is analyzed. The data obtained by amperometric lactate biosensor correlated with those of standard chromatography. The biosensor developed can be used in food industry for control and optimization of process of wine fermentation as well as for control of wine quality.     

Numerical analysis of stress singularity at singular points of three-dimensional elastic bodies

A numerical method of constructing eigensolutions for arbitrary elastic conical bodies with smooth and non-smooth lateral surfaces is considered. Different variants of its numerical implementation based on the finite element method are discussed. The results of numerical experiments demonstrating the efficiency and reliability of the proposed method are presented. The character of stress responses (the character of stress singularities) in the vicinity of vertices of circular and non-circular cones, composite and hollow cones, cones with non-smooth lateral surfaces, trihedral wedge, one and two intersecting wedge-shaped cracks is estimated based on the obtained solutions.     

Amperometric determination of hydrazine at manganese hexacyanoferrate modified graphite-wax composite electrode

Fabrication, characterization and application of a manganese hexacyanoferrate (MnHCF) modified graphite-wax composite electrode are described. The MnHCF mixed with graphite powder was dispersed into molten paraffin wax to yield a conductive composite, which was used as electrode material to construct a renewable three-dimensional MnHCF modified electrode. The characterization of the modified electrode has been studied by electrochemical techniques. The cyclic voltammogram of the MnHCF modified graphite-wax composite electrode prepared under optimum composition, showed a well-defined redox couple due to Fe(CN)(6)(4-)/Fe(CN)(6)(3-) system. The electrocatalytic oxidation of hydrazine by MnHCF modified graphite-wax composite electrode has been investigated in an attempt to develop a new sensor for its determination. It was found that the mediator catalyzed the oxidation of hydrazine. The electrocatalytic oxidation of hydrazine was also studied under hydrodynamic and chronoamperometric conditions. The anodic current increases linearly with increase in the concentration of hydrazine in the range of 3.33x10(-5)M to 8.18x10(-3)M. The detection limit was found to be 6.65x10(-6)M (S/N=3). The modified electrode can also be used for on-line detection of hydrazine. The proposed method has also been applied for the determination of hydrazine in photographic developer solution.     

A three-dimensional boundary element formulation for the elastoplastic analysis of cracked bodies

In this paper a general boundary element formulation for the three-dimensional elastoplastic analysis of cracked bodies is presented. The non-linear formulation is based on the Dual Boundary Element Method. The continuity requirements of the field variables are fulfilled by a discretization strategy that incorporates continuous, semi-discontinuous and discontinuous boundary elements as well as continuous and semi-discontinuous domain cells. Suitable integration procedures are used for the accurate integration of the Cauchy surface and volume integrals. The explicit version of the initial strain formulation is used to satisfy the non-linearity. Several examples are presented to demonstrate the application of the proposed method. © 1998 John Wiley & Sons, Ltd.     

Amperometric immunosensor for the detection of anti-West Nile virus IgG

An amperometric immunosensor for the detection of West Nile virus (WNV) IgG was developed. This device was based on the immobilization of T7 phages, which were modified by an additional peptide sequence taken from the virus and used as antigen. The electropolymerization of a phage-amphiphilic pyrrole ammonium mixture previously adsorbed on the electrode surface provided an efficient entrapment of phages in a polypyrrole film. After incubation with a secondary peroxidase-labeled antibody, the immunosensors were applied to the quantitative amperometric determination of WNV-antibody at 0 V vs Ag/AgCl via the reduction of the enzymically generated quinone in the presence of hydroquinone and H2O2. The optimum immunosensor configuration detected low WNV-antibody dilutions down to a titer of 1:10(7) with an excellent regeneration of the immunosensor response by glycine treatment.     

A numerical method for the analysis of flexible bodies in unsteady viscous flows

A two‐dimensional numerical model for unsteady viscous flow around flexible bodies is developed. Bodies are represented by distributed body forces. The body force density is found at every time‐step so as to adjust the velocity within the computational cells occupied by the body to a prescribed value. The method combines certain ideas from the immersed boundary method and the volume of fluid method. The main advantage of this method is that the computations can be effected on a Cartesian grid, without having to fit the grid to the body surface. This is particularly useful in the case of flexible bodies, in which case the surface of the object changes dynamically, and in the case of multiple bodies moving relatively to each other. The capabilities of the model are demonstrated through the study of the flow around a flapping flexible airfoil. The novelty of this method is that the surface of the airfoil is modelled as an active flexible skin that actually drives the flow. The accuracy and fidelity of the model are validated by reproducing well‐established results for vortex shedding from a stationary as well as oscillating rigid cylinder. Copyright © 2006 John Wiley & Sons, Ltd.     

A finite element model for contact analysis of multiple Cosserat bodies

The objective of this paper is to develop a finite element model for multi-body contact analysis of Cosserat materials. Based on the parametric virtual work principle, a quadratic programming method is developed for finite element analysis of contact problems. The contact problem with friction between two Cosserat bodies is treated in the same way as in plastic analysis. The penalty factors, that are normally introduced into the algorithm for contact analysis, have a direct influence on accuracy of solution. There is no available rule for choosing a reasonable value of these factors for simulation of contact problems of Cosserat materials, and they are therefore cancelled through a special technique so that the numerical results can be of high accuracy. Compared with the conventional work on Cosserat elasticity, the newly developed model is on the contact analysis of the Cosserat materials and is seldom found in the existing literatures. Four examples are computed to illustrate the validity and importance of the model developed.     

A numerical analysis of the unsteady flow past bluff bodies

The paper describes in detail a relatively sophisticated numerical approach, using the Boundary Element Method in conjunction with the Discrete Vortex Model, to represent the complex unsteady flow field around a bluff body with separating shear layers. Important steps in the numerical analysis of this challenging problem are discussed and a performance evaluation algorithm established. Of considerable importance is the effect of computational parameters such as number of elements representing the geometry, time-step size, location of the nascent vortices, etc., on the accuracy of results and the associated cost.As an example, the method is applied to the analysis of the flow around a stationary Savonius rotor. A detailed parametric study provides fundamental information concerning the starting torque time histories, evolution of the wake, Strouhal number, etc. A comparison with the wind tunnel test data shows remarkable correlation suggesting considerable promise for the approach.     

Continuum coupled cohesive zone elements for analysis of fracture in solid bodies

Embedding cohesive surfaces into finite element models is a widely used technique for the numerical simulation of material separation (i.e. crack propagation). Typically, a traction-separation law is specified that relates the magnitude of the cohesive traction to the distance between the separating surfaces. Thus the characterization of fracture in such models is not directly coupled to the bulk constitutive response, in the sense that the cohesive traction does not explicitly depend on material stretching in the plane of the fracture surface. In this work, an initially-rigid cohesive-traction formulation that is coupled to the surrounding continuum is introduced as a further development of the cohesive zone idea. In this model, the traction-separation law - and therefore the fracture phenomenology - derives directly from the bulk constitutive law. The immediate goal is an improved cohesive zone framework that naturally and logically initiates cohesive separation behavior, and couples its evolution to the material state in the region of the crack tip. A cohesive element based on this model is implemented in an explicit three-dimensional finite element code. Proof-of-concept analyses using both linear elastic and Gurson void growth constitutive relations are presented. A three-point bend simulation is found to give good agreement with experimental results.     

Stress and fracture analysis in periodic contact problem for coated bodies

The periodic contact problem for the system of dies and two‐layered elastic foundation is considered. The imperfect adhesion between the layer and the substrate is taken into account by the boundary conditions at the interface. The solution of the problem is based on Hankel transform and the methods of localisation and superposition. The results are used to evaluate internal stresses in coated bodies which are in contact with rough surface and to analyse the influence of mechanical and geometrical characteristics of the coatings and the roughness parameters on the maximum stress value and its location, and on the types of coating fracture.     

Nonsteady,heat-flux distribution in semiinfinite bodies in the presence of a finite heat source at the contact boundary of the bodies

On the basis of solving the heat-conduction boundary problem, the nonsteady character of the heat-flux distribution in semiinfinite bodies is analyzed, in the presence of a heat source at the contact boundary of the bodies.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 2, pp. 303–309, February, 1986.     

Transient elastodynamic analysis of nonhomogeneous anisotropic plane bodies

A boundary-only BEM procedure is employed to solve the transient dynamic analysis of nonhomogeneous anisotropic plane elastic bodies. The response of such bodies is governed by two coupled linear, second-order hyperbolic PDEs with spatially dependent coefficients. The lack of a reliable 2D time-domain elastodynamic fundamental solution is overcome using the principle of the Analog Equation, a method by which the equations of motion of the problem are substituted by two coupled quasi-static Poisson-type equations having as nonhomogeneous terms the components of a fictitious time-dependent load distribution in the specified domain. The standard BEM is employed for the solution of the substitute equations. To avoid the appearance of the domain integral in the integral representation of the solution, the fictitious load distribution is approximated by multiquadrics with unknown time-dependent expansion coefficients, which are calculated at discrete timepoints by collocating the equations of motion at a predefined set of domain interpolation nodes. The obtained numerical results by the proposed method demonstrate its stability and accuracy over other numerical methods.     

On the analysis of rotation and stress rate in deforming bodies

Summary When a solid element experience large deformations, the components of stress will, in general, vary as a result of material rotation. These changes occur even in the absence of additional strain, and need to be accounted for in formulating constitutive laws that involve the rate of change of stress. In this paper the correction terms are extended to the case when material axes become strongly skewed. An expression for the rate of material rotation as an explicit function of vorticity, rate of deformation and stretch is derived. It is then shown that the rate of change of stress depends on the rate of material rotation. As an example, expressions for material rotation and stress are derived for a hypoelastic material undergoing uniform, rectilinear, shear. The shear stress is compared with a solution that neglects skewing of the axes, and it is found that, for the example, skewing may be neglected for strains less than 0.4. Finally, the use of these relations in numerical calculations involving finite deformation is discussed.

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Zur Untersuchung der Rotations-und Spannungsgeschwindigkeit in sich deformierenden Körpern

Zusammenfassung Wenn ein Festkörper große Verformungen erfährt, werden sich die Spannungskomponenten im allgemeinen als Folge der Materialrotation ändern. Diese Veränderungen treten sogar in Abwesenheit zusätzlicher Verzerrung auf, und müssen bei der Formulierung der Zustandsgleichungen, welche die Rate der Spannungsänderung berücksichtigen, in Betracht gezogen werden. In dieser Arbeit werden die Korrekturglieder erweitert zu dem Fall, wenn die materialachsen stark schräg zueinander werden. Abgeleitet wird ein Ausdruck für die Werkstoffrotationsgeschwindigkeit als eine explizite Funktion der Wirbel, Verformungs-und Ausdehnungsgeschwindigkeit. Es wird dann gezeigt, daß die Änderung der Spannung von der Materialrotationsgeschwindigkeit abhängig ist. Als Beispiel werden Ausdrücke für Werkstoffrotation und Spannung für einen hypo-elastischen Werkstoff, der gleichförmigen, geradlinigen Schub aufweist, hergeleitet. Die Schubspannung wird mit einer Lösung verglichen, die die Schräge der Achsen vernachlässigt, und es ergibt sich, daß, für dieses Beispiel, die Schräge für Verzerrungen weniger als 0,4 zu vernachlässigen ist. Abschließend wird die Anwendung dieser Beziehungen in numerischen Rechnungen für endliche Deformationen erörtert.

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With 1 Figure     

超薄金修饰的钯电极用于乙醇安培传感研究

超薄贵金属膜具有独特的结构和功能,创新其制备方法,拓展其电 化学应用具有重要意义。通过在镀 Pd 的玻碳电极（GCE）上电沉积欠导电 Se 超薄膜并作为模板,再与 HAuCl 4 进行原电池置换反应,制备了超薄 Au 膜修饰的镀 Pd 电极（Au Se /Pd/GCE）,并在碱性条件下采用循环伏安法研究 了 Au Se /Pd/GCE 对乙醇的电催化氧化性能影响,并构建了乙醇安培传感器。 研究表明,与裸 Pd 电极相比,Au Se /Pd/GCE 对乙醇的电催化氧化活性更高; 在最优条件下,修饰电极对乙醇的线性检测范围为 0.025~10.000 mmol·L -1,灵敏度为 0.94 (mA·cm -2)/(mmol·L-1),优于多数已报道的方法。此种以欠导电物质均匀电沉积薄膜为模板,采用原电池置换反应制备超薄贵金属膜的新 方法有望在纳米电催化剂的制备及电催化与电分析研究中广泛应用。     

A method for linear elasto-static analysis of multi-layered axisymmetrical bodies using Hankel's transform

 A method to determine the distribution of stresses and displacements in an infinite, linear, elastic, multi-layered medium subjected to static axisymmetric loading is presented in this work. By using axisymmetric governing equations, Hankel's transform and matrix analysis, the methodology gives a clearly arranged way to calculate the stresses and displacements in the medium. A numerical method for Hankel's transform is employed to perform the calculation. Two representative examples are studied. The results can be utilized as a fundamental solution for boundary element methods for the linear, elasto-static, axisymmetric multi-layered problem with a little modification.