Influence of Surface Stress on Frequency of Microcantilever-Based Biosensors (vol 10, pg 307, 2004)

Microcantilever-based biosensors have been found increasing applications in physical, chemical, and biological fields in recent years. When biosensors are used in those fields, surface stress and mass variations due to bio-molecular binding can cause the microcantilever deform or the shift of frequency. These simple biosensors allow biologists to study surface biochemistry on a micro or nano scale and offer new opportunities in developing microscopic biomedical analysis with unique characteristics. To compare and illustrate the influence of the surface stress on the frequency and avoid unnecessary and complicated numerical solution of the resonance frequency, some dimensionless numbers are derived in this paper by making governing equations dimensionless. Meanwhile, in order to analyze the influence of the general surface stress on the frequency, a new model is put forward, and the frequency of the microcantilever is calculated by using the subspace iteration method and the Rayleigh method. The sensitivity of microcantilever is also discussed. (19 refs.)

Influence of Forced Convection on Columnar Microstructure During Directional Solidification of Al-Ni Alloys

This paper presents a summary of cellular and dendritic morphologies resulting from the upward directional solidification of Al - Ni alloys in a cylindrical crucible. We analysed the coupling of solid-liquid interface morphology with natural and forced convection. The influence of natural convection was first analyzed as a function of growth parameters (solute concentration, growth rate and thermal gradient). In a second step, the influence of axial vibrations on solidification microstructure was investigated by varying vibration parameters (amplitude and frequency). Experimental results were compared to preliminary numerical simulations and a good agreement is found for natural convection. In this study, the critical role of the mushy zone in the interaction between fluid flow and solidification microstructure is pointed out.

An experimental study of the influence of weak convection on perikinetic coagulation

A remarkably increased coagulation rate for 2-mu m PS spheres was previously reported for a perikinetic coagulation experiment performed under microgravity conditions (1998, R. Folkersma, A. J. G. van Diemen, and H. N. Stein, J. Colloid Interface Sci. 206, 482); from this experiment, it was assumed that the leading factor slowing the coagulation process under normal gravitation was free convection due to gravity (1998, R. Folkersma, and H. N. Stein, J. Colloid Interface Sci. 206, 494). To test the influence of free convection as a single-effect factor on the coagulation process, a ground-based experiment was constructed. The coagulation rate of 2-mu m PS spheres dispersed in water was determined by measuring the turbidity of the dispersion solution while convection-driven flows in the solution were checked with a visual magnification system. We found that it was possible to cease free convection-driven particle flows on the ground, as long as the experiments were carefully operated. The strength of convection was controlled by changing the temperature gradient applied to the sample cell. By monitoring both the coagulation rate and convection-driven flows simultaneously, our experiments showed that weak free convection (maximum speed <150 mu m/s) actually has negligible effects on the coagulation rate.

The influence of stacks on flow patterns and stratification associated with natural ventilation

We investigate the steady state natural ventilation of an enclosed space in which vent A, located at height hA above the floor, is connected to a vertical stack with a termination at height H, while the second vent, B, at height hB above the floor, connects directly to the exterior. We first examine the flow regimes which develop with a distributed source of heating at the base of the space. If hBhB>hA, then two different flow regimes may develop. Either (i) there is inflow through vent B and outflow through vent A, or (ii) the flow reverses, with inflow down the stack into vent A and outflow through vent B. With inflow through vent A, the internal temperature and ventilation rate depend on the relative height of the two vents, A and B, while with inflow through vent B, they depend on the height of vent B relative to the height of the termination of the stack H. With a point source of heating, a similar transition occurs, with a unique flow regime when vent B is lower than vent A, and two possible regimes with vent B higher than vent A. In general, with a point source of buoyancy, each steady state is characterised by a two-layer density stratification. Depending on the relative heights of the two vents, in the case of outflow through vent A connected to the stack, the interface between these layers may lie above, at the same level as or below vent A, leading to discharge of either pure upper layer, a mixture of upper and lower layer, or pure lower layer fluid. In the case of inflow through vent A connected to the stack, the interface always lies below the outflow vent B. Also, in this case, if the inflow vent A lies above the interface, then the lower layer becomes of intermediate density between the upper layer and the external fluid, whereas if the interface lies above the inflow vent A, then the lower layer is composed purely of external fluid. We develop expressions to predict the transitions between these flow regimes, in terms of the heights and areas of the two vents and the stack, and we successfully test these with new laboratory experiments. We conclude with a discussion of the implications of our results for real buildings.

Influence of Obstacle-Produced Turbulence on Development of Premixed Flames

An investigation into influence of obstructions on premixed flame propagation has been carried out in a semi-open tube. It is found that there exists flame acceleration and rising overpressure along the path of flame due to obstacles. According to the magnitude of flame speeds, the propagation of flame in the tube can be classified into three regimes: the quenching, the choking and the detonation regimes. In premixed flames near the flammability limits, the flame is observed first to accelerate and then to quench itself after propagating past a certain number of obstacles. In the choking regime, the maximum flame speeds are somewhat below the combustion product sound speeds, and insensitive to the blockage ratio. In the more sensitive mixtures, the transition to detonation (DDT) occurs when the equivalence ratio increases. The transition is not observed for the less sensitive mixtures. The dependence of overpressure on blockage ratio is not monotonous. Furthermore, a numerical study of flame acceleration and overpressure with the unsteady compressible flow model is performed, and the agreement between the simulation and measurements is good.

INFLUENCE OF MICROSTRUCTURE ON THE TOUGHNESS OF CARBON FIBRE/PLASTIC COMPOSITES.

A preliminary study is presented of the relationship between the microstructural aspects of failure and the fracture energy G//1//C for cracking parallel to the fibres in long-fibre/thermoplastic matrix composites. Fracture energies are measured by a new technique, and fracture surfaces generated by the test are examined by scanning electron microscopy.

The influence of corrosion on the erosion of aluminium by aqueous silica slurries

The slurry erosion-corrosion behaviour of aluminium in aqueous silica slurries containing 0.5 M NaCl, acetic acid and 0.1 M Na2CO3 at open circuit has been investigated using a modified slurry erosion rig. The erosion rates of aluminium in the NaCl and acetic acid slurries were much higher than those in an aqueous slurry without electrolyte additives even though the pure corrosion component was very small. Eroded specimens were examined by scanning electron and optical microscopy. In pure aqueous slurry erosion, the basic mechanism leading to mass loss was the ductile fracture of flakes formed on the eroded surface. In corrosive slurries, however, the mass loss was enhanced by cracking of the flakes induced by stress and corrosion. © 1995.

INFLUENCE OF MICROSTRUCTURE ON THE TOUGHNESS OF CARBON FIBRE/PLASTIC COMPOSITES.

A preliminary study is presented of the relationship between the microstructural aspects of failure and the fracture energy G//l//C for cracking parallel to the fibres in long-fibre/thermoplastic matrix composites. Fracture energies are measured by a new technique, and fracture surfaces generated by the test are examined by scanning electron microscopy.

Static Study of Cantilever Beam stiction under Electrostatic Force Influence

The model and analysis of the cantilever beam adhesion problem under the action of electrostatic force are given. Owing to the nonlinearity of electrostatic force, the analytical solution for this kind of problem is not available. In this paper, a systematic method of generating polynomials which are the exact beamsolutions of the loads with different distributions is provided. The polynomials are used to approximate the beam displacement due to electrostatic force. The equilibrium equation offers an answer to how the beam deforms but no information about the unstuck length. The derivative of the functional with respect to the unstuck length offers such information. But to compute the functional it is necessary to know the beam deformation. So the problem is iteratively solved until the results are converged. Galerkin and Newton-Raphson methods are used to solve this nonlinear problem. The effects of dielectric layer thickness and electrostatic voltage on the cantilever beamstiction are studied.The method provided in this paper exhibits good convergence. For the adhesion problem of cantilever beam without electrostatic voltage, the analytical solution is available and is also exactly matched by the computational results given by the method presented in this paper.

Influence of liquid bridge volume on instability of floating half zone convection

Thermocapillary instabilities on floating half zone convection in microgravity environment were investigated by linear instability analysis method. The critical Marangoni numbers were obtained and compared with the experimental ones. The influences of the liquid bridge volume and the aspect ratio on the critical Marangoni number were analyzed. It is found that the liquid bridge volume and the aspect ratio have great influence on the critical Marangoni number. There was a gap region where the oscillatory convection will not be observed in present analyses and in experiments in the curve of the critical Marangoni number vs the liquid bridge volume for the case of large Prandtl number and small aspect ratio.

The Influence of Strain Gradient on the shear Band in a Saturated Soil

The dynamic localization of saturated soil is investigated by considering the influence of higher strain gradient. It is shown that the strain gradient has a significant influence on the evolution of shear band in saturated soil and that the width of shear band is proportional to the square root of the strain gradient softening coefficient. The numerical simulation is processed to investigate the influences of shear strain gradient and other factors on the evolution of shear band.

Influence of Coriolis force on bulk flows during horizontal Bridgman growth on a centrifuge: a numerical study

Three-dimensional and time-dependent numerical simulations are performed For melt convection in horizontal Bridgman crystal growth tinder high gravity conditions by means of a centrifuge. The numerical results show that Coriolis Force can cause a stabilizing effect on the fluctuations of the melt flow under a specific relation direction and relation rates of the centrifuge as reported in previous experiments (Ma et al., Materials Processing in High Gravity, Plenum Press, New York, 1994, p. 61). The present simulation provides details of the now features associated with the effect of the Coriolis force. There are also some differences between the present three-dimensional and former two-dimensional numerical solutions particularly in the prediction of the critical conditions and flow patterns.

Influence of Indenter Tip Roundness on Hardness Behavior in Nanoindentation

In this paper. the effect of indenter tip roundness on hardness behavior for two typical elastic perfectly plastic materials is studied by means of finite element simulation. A rigid conical indenter of semi apex angle 70.3 degrees fitted smoothly with a spherical tip is employed. It is shown that as the indentation depth increases hardness first rises from zero, reaches a maximum and then decreases slowly approaching asymptotically the limiting value equal to that due to a conical indenter of ideally sharp tip. The range within which hardness varies appreciably is comparable to the radius of the indenter tip. The difference between the maximum value and the limiting value depends on the yield stress over the Young's modulus ratio. The smaller this ratio the greater the difference is. Numerical simulation also provides an opportunity for checking the accuracy and limitations of the widely used Oliver-Pharr method.

Influence of liquid bridge volume on the onset of oscillation in floating-zone convection III. Three-dimensional model

An unsteady and three-dimensional model of the floating-half-zone convection on the ground is studied by the direct numerical simulation for the medium of 10 cSt silicon oil, and the influence of the liquid bridge volume on the critical applied temperature difference is especially discussed. The marginal curves for the onset of oscillation are separated into two branches related, respectively, to the slender liquid bridge and the fat liquid bridge. The oscillatory features of the floating-half-zone convection are also discussed.