In situ evaluation of contact stiffness in a slip interface with different roughness conditions using ultrasound reflectometry.

Understanding the dynamic condition of the interface between a railway wheel and rail is important to reduce the risks and consider the effectiveness of countermeasures for tribological problems. Traditionally the difficulty in obtaining accurate non-destructive interfacial measurements has hindered systematic experimental investigations. Recently, an ultrasound reflectometry technique has been developed as a direct observation method of a rolling-sliding interface; however, the topography dependence under the high contact pressures in a wheel-rail contact has not been clarified. For this reason, a novel in situ measurement of the contact stiffness using ultrasound reflectometry was carried out for three different levels of roughness. A contact pressure equivalent to that in a wheel-rail interface was achieved by using a high-pressure torsion test approach. The dynamic change of contact stiffness with slip was measured using ultrasound and the influence of roughness was investigated. The measured changes were validated using a newly developed numerical simulation, and mechanisms to explain the observed behaviour were proposed in terms of fracture and plastic deformation of the asperity bonds. These findings could help in understanding the traction characteristics for different roughness conditions and also assist in understanding damage mechanisms better, such as wear and rolling contact fatigue.

Non-contact measurement of the thickness of a surface film using a superimposed ultrasonic standing wave.

Most methods used to measure the thickness of thin liquid or solid surface films and coatings need access to the coated surface. In this work reflected ultrasonic pulses were used to measure a coating thickness from a solid back face. Piezoelectric transducers on the solid back face emitted ultrasound waves and received the waves that bounced off the front face. The magnitude of the reflected wave was dependent on the film thickness at the front face. Most pulse-echo ultrasonic approaches use the time-of-flight through the surface layer to determine its thickness. However, as the film becomes thinner, the reflected echoes overlap and there is often an acoustic mismatch between the solid and the surface film that reduces the signal strength. In this work, we propose the use of an ultrasonic continuously repeated chirp longitudinal wave to amplify the effect of the surface film. Multiple reflections interfere within the solid to form a superimposed standing wave whose amplitude spectrum is highly dependent on the surface film thickness thus overcoming the acoustic mismatch problem. Two bare 10 MHz piezoelectric elements were bonded to a 10 mm thick aluminium solid in a pitch-catch arrangement such that one continuously sends repeating chirp ultrasound waves and the other acts as the receiver. The transmitter was set to send a repeating chirp wave of 4 ms duration corresponding to the bandwidth of the transducer in order to maximise signal amplitude. The incident and reflected waves constructively and destructively interfere to form a superimposed standing wave within the solid. The solid/surface film to solid/air boundary condition frequency spectra ratio showed the film resonant frequency modes as minima. Using this technique epoxy coatings ranging from 70 µm to 350 µm were measured and showed a good correlation with independent measurements using a surface profilometer.

Characterization and correction of cupping effect artefacts in cone beam CT.

OBJECTIVE: The purpose of this study was to demonstrate and correct the cupping effect artefact that occurs owing to the presence of beam hardening and scatter radiation during image acquisition in cone beam CT (CBCT). METHODS: A uniform aluminium cylinder (6061) was used to demonstrate the cupping effect artefact on the Planmeca Promax 3D CBCT unit (Planmeca OY, Helsinki, Finland). The cupping effect was studied using a line profile plot of the grey level values using ImageJ software (National Institutes of Health, Bethesda, MD). A hardware-based correction method using copper pre-filtration was used to address this artefact caused by beam hardening and a software-based subtraction algorithm was used to address scatter contamination. RESULTS: The hardware-based correction used to address the effects of beam hardening suppressed the cupping effect artefact but did not eliminate it. The software-based correction used to address the effects of scatter resulted in elimination of the cupping effect artefact. CONCLUSION: Compensating for the presence of beam hardening and scatter radiation improves grey level uniformity in CBCT.

Protein adsorption on novel acrylamido-based polymeric ion-exchangers. III. Salt concentration effects and elution behavior.

The effect of salt concentration on the adsorption and desorption of BSA has been determined for a polymeric anion-exchanger based on acrylamido monomers. The material investigated possesses a high adsorption capacity at low salt concentration and the bound protein can be recovered quantitatively at high salt concentrations. The effects of salt on adsorption and desorption rates were evaluated from batch and shallow-bed experiments, and a model was developed to describe the data quantitatively. The adsorption capacity decreases as the salt concentration is increased, but both adsorption and desorption rates increase at higher salt concentrations. The predictability of the behavior of columns packed with this material was examined by comparing model predictions and experimental results obtained in laboratory columns. In general, a good agreement was obtained between predicted and experimental breakthrough and elution profiles, especially in shorter columns. Thus, the model allows a prediction of the effects of column length, mobile phase flow-rate, protein feed concentration, and salt concentration on dynamic capacity, productivity, and on the concentration of product fractions.

Effects of bovine serum albumin heterogeneity on frontal analysis with anion-exchange media.

The presence of dimers in commercial bovine serum albumin (BSA) samples of nominal high purity is investigated along with their effects on the frontal analysis behavior of preparative anion-exchange media. Size-exclusion and analytical anion-exchange chromatography are used to determine the relative amounts of monomer and dimer for two samples of BSA. While the amount of dimer was generally low, its impact on adsorptive behavior is significant. Equilibrium experiments demonstrate that the anion-exchange media binds the dimer more strongly, leading to an unequal distribution of the monomer and dimer between the two phases. Analysis of the breakthrough behavior of BSA reveals that the monomer breaks through prior to the dimer. This leads to the characteristic tailing breakthrough curve often seen with BSA. Breakthrough experiments carried out using dimer-free BSA confirm that the extreme tailing observed with the commercial samples is curtailed by removing the dimer.

Protein adsorption on novel acrylamido-based polymeric ion-exchangers. I. Morphology and equilibrium adsorption.

The protein uptake equilibrium and particle morphology are determined for novel polymeric ion-exchange media based on acrylamido monomers with a high density of functional groups and a variety of morphological characteristics. The study considers two anion-exchangers and a cation-exchanger. Physical properties determined experimentally include particle density, ion-exchange capacity, particle size distribution, and equilibrium isotherms for model proteins. The pore structure was evaluated using size exclusion chromatography with neutral probe molecules and transmission electron microscopy. For the anion-exchangers, two types of structures were inferred. The first is comprised of particles that contain a low-density gel supported by denser polymer aggregates. This material had a very low size-exclusion limit for neutral probes, but exhibited an extremely high and reversible protein adsorption capacity (280-290 mg BSA/ml). The second structure is comprised of particles with large, open macropores. While the size-exclusion limit was very high, the protein adsorption capacity was low (60 mg BSA/ml). Moreover, the adsorption was nearly irreversible. The physical structure of the cation-exchanger appeared to be intermediate between those of the anion-exchangers, containing both large pores and smaller pores yielding an intermediate, but reversible, protein uptake capacity (120-130 mg alphaCHY/ml). The different behavior of these materials with regards to protein adsorption correlates well with their physical structure. For these ion-exchangers, high protein adsorption capacities are attained when a low-density polymer gel with a high concentration of functional groups is present.

Protein adsorption on novel acrylamido-based polymeric ion exchangers. II. Adsorption rates and column behavior.

Uptake kinetics and breakthrough behavior were determined for bovine serum albumin (BSA) and alpha-chymotrypsinogen (alphaCHY) in new polymeric ion-exchange media based on acrylamido monomers. Two anion exchangers and a cation exchanger were investigated. As shown in Part I of this work, the two anion exchangers have different morphologies. The first one, BRX-Q, comprises a low-density gel with a matrix of denser polymeric aggregates. While this material has a very low size-exclusion limit for neutral probes, it exhibits an extremely high binding capacity for BSA. The second anion exchanger, BRX-QP, comprises large open pores but has a very low binding capacity. The cation exchanger, BRX-S, also comprises large open pores but exhibits an intermediate capacity; likely as a result of the presence of smaller pores. Dynamic protein uptake experiments showed that the highest mass transfer rates are obtained with BRX-Q. The apparent diffusivity is also highest for this material and increases substantially as the protein concentration is reduced. For these particles, the external film resistance is dominant at very low protein concentrations. Much lower rates and apparent diffusivities are obtained for BRX-QP. Finally intermediate rates and apparent diffusivities are found with BRX-S. The concentration dependence of the apparent pore diffusivity is much less pronounced in this case. The apparently paradoxical result that mass transfer rates are highest for the material with the smallest neutral-probe size-exclusion limit can be explained in terms of a general conceptual model where parallel pore and adsorbed-phase diffusion paths exist in these particles. In the first case, adsorbed phase diffusion in gel pores is dominant, while in the second transport is dominated by diffusion in a macroporous network. In the third case, both contributions are important. The conceptual model provides an accurate prediction of the breakthrough behavior of columns packed with these media using independently determined rate parameters. Dynamic binding capacities of 80-140 mg/ml were observed for BSA on BRX-Q in ca. 1.5 cm columns operated at 300-900 cm/h in agreement with theoretical predictions.

Phylogenetic analysis of three lipocalin-like proteins present in the milk of Trichosurus vulpecula (Phalangeridae, Marsupialia).

Three proteins have been identified in the milk of the common brush tail possum. Trichosurus vulpecula that from sequence analysis are members of the lipocalin family. They include beta-lactoglobulin, which appears to have two forms; a homologue to the late-lactation protein found in tammar, Macropus eugenii; milk; and a novel protein termed trichosurin. Whereas beta-lactoglobulin and trichosurin are both expressed throughout lactation, the late-lactation protein is not detected in samples taken before days 100-110 of lactation. The cDNAs encoding each of these proteins have been isolated from cDNA libraries prepared using possum mammary mRNA and sequenced. Phylogenetic analysis showed that the T. vulpecula beta-lactoglobulin, along with two other macropod beta-lactoglobulins, forms a subclass of beta-lactoglobulins distinct from those for eutherian mammals; both marsupial late-lactation proteins appear to have similarities to a family of odorant-binding proteins, whereas trichosurin has similarities to the major urinary proteins of rodents.