Frequency interference between two mesa-shaped quartz crystal microbalances

The multichannel quartz crystal microbalance (MQCM) is very attractive for biosensor applications. The principle of the MQCM design involves fabricating arrays of quartz microbalances on a single substrate, and it is important that the individual sensor performance is not influenced by the neighboring devices. Feasible ways to control the coupling of acoustical energy within a MQCM structure are to increase the difference in the resonance frequency between the electroded and unelectroded portions of the substrate; and a practical way to achieve this is to use mesa structures. In this paper, the frequency interference between two mesa-shaped quartz crystal microbalances is investigated using Mindlin's theory. The results show that even a very small mesa height (/spl sim/5% of the plate thickness) can greatly reduce the frequency interference and more effectively trap the acoustic energy. This allows for a broader design window and higher packing density for MQCM applications.     

Preliminary study of a polycaprolactone membrane utilized as epidermal substrate

Solvent-cast sheets of polycaprolactone were biaxially stretched to produce 10–15 m thick films. PCL films were found to have a tensile strength of 55 MPa which is about two and a half times stronger than native skin. One of our previous studies using non-coated PCL membranes showed that only 36% of the membrane surface was covered with keratinocytes after 9 days of culture. The present study examined the effects of coating the surface of PCL membranes with fibrin on the proliferation of keratinocytes. Qualitative analysis revealed that the cells attached and proliferated better on coated PCL films. Keratinocytes exhibited healthy cobblestone morphology and proliferated as continuous monolayers over a period of 16 days. The results indicated that fibrin coated PCL films would support the attachment and proliferation of human keratinocytes and have the potential to be applied as a matrix material for tissue engineering an epidermal equivalent.     

Performance enhancement of DS-CDMA system using overlapping sectors with interference avoidance

A cellular system with overlapping sectors is proposed to enhance system performance through interference avoidance. Due to the overlapping effect, each user is allowed to select one sector out of many for operation. It is shown that the mutual interference among users in different regions within a cell can be minimized by choosing a good sector combination. The potential benefits of the proposed technique are investigated in two scenarios: orthogonal and nonorthogonal code division multiple access systems. In the former case, it is shown that when compared with the traditional nonoverlapping sectors system, one is able to reduce the number of spreading codes required to support all users by using appropriate code allocation in the proposed system. A theoretical framework based on combinatorial enumeration is developed to assess the performance of the proposed system. For the latter case, the enhancement takes the form of multiple access interference reduction. Simulation results show that its improvement is significant and can be further enhanced by increasing the number of overlapping sectors.     

The role of mechanical twinning on microcrack nucleation and crack propagation in a near-γ TiAl alloy

The role of mechanical twinning on microcrack nucleation and crack propagation in a near-γ TiAl alloy was investigated in 4-point bend specimens using selected area channeling patterns and electron channeling contrast imaging to obtain the true crystal orientation image crystal defects. Two types of bend specimens were used, a conventional specimen that was deformed to a surface strain of about 1.4%, but not fractured, and a bi-layer notched specimen with an aluminum backing that prevented catastrophic fracture so that crack arrest features could be examined. Most grains showed activity of 1–4 twinning systems, and their activity correlated closely with the Schmid factor. Grain boundary microcracks were most frequently found where twins interacted with the grain boundary, and crystallographic analysis indicated that the twinning shear caused these cracks to open. In the crack growth specimen, extensive twinning and dislocation activity occurred in the grain with the arrested crack tip, but with continued straining, these same twins caused grain boundary microcracks to form and link-up to form full intergranular cracks, resulting in renucleation of the primary failure crack.     

The biodegradation of N-methyl-2-pyrrolidone in water by sewage bacteria

The biodegradability of N-methyl-2-pyrrolidone was studied using a static die-away system and a semi-continuous activated sludge system. The biodegradation was followed by gas-liquid chromatographic analysis as well as by monitoring the change in chemical oxygen demand of the culture mixture. Results show that N-methyl-2-pyrrolidone is readily degradable under these conditions. However, the metabolite has an appreciable oxygen demand and is shown by infra-red spectroscopy to be a carbonyl compound.     

Fabrication of Single-Crystal α-Al2O3 Nanorods by Displacement Reactions

Nanometer-sized Al₂O₃ rods are fabricated by sintering a powder mixture of Al and SiO₂. The sintered product is leached in HF–HNO₃ solution, followed by rinsing and washing before the nanorods are collected. The yield of the product is about 50 wt%. Transmission electron microscopy reveals that these rods are 1 to 2 μm long and have a diameter of 20 to 100 nm, while electron diffraction confirms that these rods are single crystals of α-Al₂O₃. It is observed that these rods have either round or slightly sharp tips, which is different from those having droplet-like tips that are usually found in products fabricated by catalytic reactions.     

Synthesis of dysprosium oxide by homogeneous precipitation

Nanocrystals of uniform dysprosium oxide (Dy₂O₃) particles have been prepared by homogeneous precipitation technique. The particles were produced by aging DyCl₃solution in presence of urea at elevated temperature. The particles were characterized with respect to their size, shape, and thermal decomposition behavior. It was found that the precipitated particles were spherical, uniform in size, and amorphous in nature. Upon heating in air, these particles decomposed into oxide and no change in morphology was observed. The dysprosium ion concentration was found to have significant effect on the particle size and its distribution.     

Optimal experiment design for autoregressive model with output power constraints

The output power constraint problem of optimal experiment design for an autoregressive model is considered. It is shown that besides the known minimum variance control law design, aD- optimal experiment consisting of sinusoidai input test signals without feedback can be obtained by solving a set of nonlinear equations. Two examples are also given to illustrate this design methodology.     

Synthesis and characterization of functional diene oligomers in view of their practical applications

An overview is given on the preparation and characterization of hydroxyl terminated liquid polybutadienes and polyisoprenes which are potential alternative backbones for polyurethanes. After stating the requirements for such precursors, selected routes to their production are discussed, taken from more recent literature and from own experience. Characterization encompasses new methods of end group determination, problems of functionality and fractionation. In spite of the progress achieved in various aspects, outstanding properties of e.g. carbon black-filled polyurethanes have been reported rarely and on a larger scale commercial realization of such oligomers for high quality products seems somewhat uncertain at the moment.     

Point matching computation of transverse resonances

Point matching (collocation) methods are reviewed and the conditions under which they break down are examined. The detailed treatment applies to complex-valued solutions of the two-dimensional Helmholtz equation with either Neumann or Dirichlet boundary conditions. Point matching methods (when they are valid) can have very real computational advantages. It is shown, by a combination of analysis and computational example, how to estimate whether the cross-section of any particular resonant system is suitable for the application of an existing point matching method. An extended point matching method is introduced to handle cases for which previous methods fail. The method is illustrated with several computational examples. The discussion is specifically concerned with electromagnetic wave guides, but the results can be applied to a wide range of physical systems.