Geometric and algebraic errors in calculating a transducer'sspatial impulse response

Two types of errors resulting from the numerical evaluation of a transducer's spatial impulse response function have been identified, One is geometric and is due to the mismatch between the emulated piston surface (approximated using many small planar elements) and the true surface. The other error is algebraic and is due to the inexact formulation of the response of the emulated surface. The deviations from the true response were calculated for three different pistons. The results indicate that the shape and placement of the elements are important for the computational accuracy     

Receptor-mediated endocytosis of CC-chemokines

Chemokines are chemotactic proteins which play a central role in immune and inflammatory responses. Chemokine receptors are members of the seven transmembrane G-protein coupled family and have recently been shown to be involved in the entry of human immunodeficiency virus (HIV) into target cells. To study chemokine endocytosis in detail we have used novel site-specific chemistry to make a fluorescently labeled CC-chemokine agonist (rhodamine-MIP-1alpha) and antagonist (NBD-RANTES). We have also generated a CHO cell line stably expressing a hemagglutinin-tagged version of the CC-chemokine receptor 1 (CCR1), and using these reagents we have examined the receptor-mediated endocytosis of CC-chemokines by confocal microscopy. Our studies reveal that the agonist was internalized and accumulated in transferrin receptor-positive endosomes whereas the antagonist failed to internalize. However, receptor-bound antagonist could be induced to internalize by co-administration of agonist. Analysis of receptor redistribution following chemokine addition confirmed that sequestration was induced by agonists but not by antagonists.     

Response of hybrid laminated composite plates under low-velocity impact

The response of hybrid laminated composite plates subjected to low velocity impact was investigated using shear deformation theory. As a result, the fractional energy loss of two hybrid composite plates with the same component ratio has different values according to the stacking sequence. A Graphite-Kevlar-Graphite plate has low energy loss and a Kevlar-Graphite-Kevlar plate much higher energy loss. Contact forces between the impactor and plates, center deflections of the plates and velocity changes of the impactor to time have different values according to the material properties of the impacted surface. Various composite plates with the same material in the impacted surface behaved with a similar response.     

Time-constant-based CMOS readout circuit for DNA detection

An RC-to-time constant interface circuit was implemented in 0.18 mum CMOS to characterise the conductive polymer labelled deoxyribonucleic acid (DNA) hybridisation activity on nano-sensor micro-arrays. Measured results show that sub-picomolar DNA (0.1-10 pM) are able to be differentiated with respect to their electrical parameters of 1-23 GOmega resistances parallel with 2.8 down to 0.1 nF capacitances.     

Corrosion resistance and mechanical properties of low-alloy steels under atmospheric conditions

The corrosion resistance and mechanical strength of four newly developed low-alloy steels (LAS) were compared with a carbon steel (SS400) and a weathering steel (Acr-Ten A) using a laboratory-accelerated test that involved cyclic wet/dry conditions in a chloride environment (5 wt.% NaCl). The new LAS were designated 1605A, 1605B, 1604A, and 1604B. After 72 cycles of cyclic corrosion tests, the susceptibility of the steels to corrosion could be listed in the following order based on their weight loss (from high to low): SS400 > Acr-Ten A > 1604B ? 1604A > 1605B ? 1605A. The change in mechanical properties by corrosion was the least for SS400, Acr-Ten A was second, and effects of corrosion on the mechanical properties of the other four low-alloy steels were similar. Finally, the characteristics of the rust layers on each LAS sample were observed by SEM, and analyzed by FTIR and EPMA. The results indicated that most of the rust layers on the test steels were composed of a loose outer rust layer and a dense inner rust layer. The outer rust layer of each steel was composed of α-FeOOH, γ-FeOOH, magnetite (Fe₃O₄), H₂O, and amorphous ferric oxyhydroxide (FeO_x(OH)_3−2x, x=0-1), while the inner rust layer was composed mainly of Fe₃O₄ with a little α-FeOOH. In addition, it was apparent that the copper and chromium alloying additions were enriched, respectively, at the rust-layer/substrate interface and in the rust layers. Finally, combining the results of the accelerated tests and the rust layer analysis showed that low-alloy steels, such as 1605A and 1605B, have better weathering steel properties than Acr-Ten A for use in the humid and salty weather.     

Geometric constraints within feature hierarchies

We study the problem of enabling general 2D and 3D variational constraint representation to be used in conjunction with a feature hierarchy representation, where some of the features may use procedural or other non-constraint based representations. We trace the challenge to a requirement on constraint decomposition algorithms or decomposition-recombination (DR) planners used by most variational constraint solvers, formalize the feature hierarchy incorporation problem for DR-planners, clarify its relationship to other problems, and provide an efficient algorithmic solution. The new algorithms have been implemented in the general, 2D and 3D opensource geometric constraint solver FRONTIER developed at the University of Florida.     

Characterization of synthetic polymers by electrospray-assisted pyrolysis ionization-mass spectrometry

Rapid characterization of synthetic polymers based on the differences in the appearance of the polar pyrolysate ions was achieved by electrospray-assisted pyrolysis ionization-mass spectrometry. The pyrolytical products produced by a commercial Curie point pyroprobe were conducted to the tip of a capillary, where charged methanol droplets were generated continuously by electrospray. Polar components in the pyrolysates may react directly with the protonated methanol ions or fuse with the charged methanol droplets; electrospray ionization proceeds from the fused droplets to generate protonated analyte ions. The mass spectra obtained through this approach were used to rapidly distinguish the polymer standards that differ in the nature of building units, degrees of polymerization, and copolymerization coefficients.     

Crack-tip force method for computing energy release rate in delaminated plates

A new method called the crack-tip force method (CTFM) is derived for computing the energy release rate in delaminated beams and plates. In this method the delaminated plate is divided into two laminates on either side of the plane of delamination. The interaction forces, called crack-tip forces, between the sub-laminates at the crack-tip are computed. The energy release rate is expressed as a quadratic function of the crack-tip forces and the plate compliance coefficients. The CTFM is compared to the virtual crack closure technique (VCCT) as well as to a previously derived method called the strain energy density method using double cantilevered beam specimens as examples. The CTFM is found to be very efficient as the crack-tip forces are part of the solution of finite element analysis of delaminated plates, and they can be readily used to compute the point-wise energy release rate along the delamination front.     

Two distinct fracture modes of copper alloys in fluoride environments

The susceptibility of aluminum brass and aluminum bronze to stress corrosion cracking (SCC) was evaluated in fluoride environments by means of the slow strain rate technique. The effects of fluoride concentration and applied electrochemical potential on the SCC susceptibility were investigated. The SCC mechanism of aluminum brass was found to be dependent upon the de-alloying phenomenon while that of aluminum bronze on the film-rupture mechanism occurring within a certain range of applied electrochemical potentials. For aluminum brass, both the stress ratio and the time-to-fracture ratio were closely related to the logarithmic concentration of F⁻ ions. The fracture modes were ductile dimpled tearing fracture for the aluminum brass at the corrosion potential while intergranular for the aluminum bronze at various anodic potentials. The micro-galvanic effects of the constituent elements were used to estimate the anodic equilibrium potentials of the two alloys.