Fast multiple electron capture dissociation in a linear radio frequency quadrupole ion trap

We developed a fast electron capture dissociation (ECD) device using a linear radio frequency-quadrupole (RFQ) ion trap. The device dissociated peptides and proteins using a focused electron beam with an intensity of 0.5 microA and a diameter of 1 mm. The electron capture rate was 13%/ms for doubly charged peptides, and the total amount of ECD products was identical to the theoretical limit, i.e., 50% of incident precursor ions were observed as maximum ECD products by electron irradiation of 7 ms in a pulse counting detection scheme. Coupling this ECD device to a time-of-flight mass spectrometer, we applied multiple ECD. Protonated ubiquitin precursor ions with a charge state of 10 were repeatedly cleaved by ECD, i.e., charge-reduced species and their highly charged fragments were cleaved again and again, creating lower charged products, leaving only singly to triply charged states among the final products. Meanwhile with the amount of electron irradiated, lower charged products increased. Applying an electron beam for 8 ms, we obtained 96% of the total sequence coverage using a 40 fmol sample except at three proline sites. This fast ECD device should be widely applicable to proteomics including post-translational modification analysis and top-down analysis.     

Improvement mechanism of fatigue strength of weld joints by hammer peening on base metal

New peening technology is proposed to improve the fatigue strength of welded joints. By using this technology, compressive residual stress is introduced at weld toe by the developed peening procedure which plastic deformation is only applied to the base material near the weld toe. In this study, improvement mechanism of fatigue strength of weld joints by hammer peening on base metal was clarified by FEA. It was clarified that increasing of stress at weld toe is controlled by depression formed near the weld toe. Not only compressive residual stress at weld toe but also decreasing stress concentration at weld toe by plastic deformation on base metal was indicated as the factor of improving fatigue strength of weld joints.     

Characteristics of powder metallurgy pure titanium matrix composite reinforced with multi-wall carbon nanotubes

By using pure titanium powder coated with un-bundled multi-wall carbon nanotubes (MWCNTs) via wet process, powder metallurgy (P/M) titanium matrix composite (TMC) reinforced with the CNTs was prepared by spark plasma sintering (SPS) and subsequently hot extrusion process. The microstructure and mechanical properties of P/M pure titanium and reinforced with CNTs were evaluated. The distribution of CNTs and in situ formed titanium carbide (TiC) compounds during sintering was investigated by optical and scanning electron microscopy (SEM) equipped with EDS analyzer. The mechanical properties of TMC were significantly improved by the additive of CNTs. For example, when employing the pure titanium composite powder coated with CNTs of 0.35 mass%, the increase of tensile strength and yield stress of the extruded TMC was 157 MPa and 169 MPa, respectively, compared to those of extruded titanium materials with no CNT additive. Fractured surfaces of tensile specimens were analyzed by SEM, and the uniform distribution of CNTs and TiC particles, being effective for the dispersion strengthening, at the surface of the TMC were obviously observed.     

The influence of carbon nanotubes on the corrosion behaviour of AZ31B magnesium alloy

Carbon nanotubes (CNTs) are an effective reinforcement for magnesium (Mg) and its alloys due to their excellent mechanical properties. However, due to their quite different electrical properties compared to other carbon allotropes, the influence of CNTs on the corrosion of Mg is expected to be different. For this reason, the corrosion of AZ31B Mg alloy based composite with CNTs (AZ31B/CNT composite) was investigated with immersion tests, polarization tests and surface potential measurements. The galvanic corrosion between the Mg matrix and CNTs played an important role in the corrosion behaviour of the AZ31B/CNT composite.     

Effect of rubber compounding agent on adhesion strength between rubber and heat-assisted plasma-treated polytetrafluoroethylene (PTFE)

Although heat-assisted plasma treatment enables drastic improvement of the adhesion property of polytetrafluoroethylene (PTFE), plasma-treated PTFE does not strongly adhere to any adherend. To clarify which rubber compounding agents positively affect the adhesion strength of a plasma-treated PTFE/rubber assembly, six types of unvulcanised rubbers were prepared and thermally compressed to a plasma-treated PTFE sheet. Thus, it was found that SiO₂ addition to rubber drastically increased the adhesion strength of a plasma-treated PTFE/rubber assembly and cohesion failure of rubber occurred with large fractions of SiO₂ although no adhesives were used. To confirm the reaction between plasma-treated PTFE and SiO₂ powder, X-ray photoelectron spectroscopy (XPS) measurements were performed for the thermally compressed SiO₂/PTFE assembly after repeated washing. The XPS results indicated that hydrophilic SiO₂ powder strongly adhered to the plasma-treated PTFE, whereas hydrophobic SiO₂ powder did not adhere to the PTFE. In this paper, a model was proposed for a possible mechanism of strong adhesion of a PTFE/rubber assembly through both hydrogen and covalent bonds between silanol groups of the SiO₂ powder surface in the rubber and hydroxyl or carboxyl groups on the plasma-treated PTFE.     

Human oral processing and texture profile analysis parameters: Bridging the gap between the sensory evaluation and the instrumental measurements

Studies in food oral processing are becoming increasingly important with the advent of the aged society. The food oral processing model of Hutchings and Lillford (Journal of Texture Studies, 19, 1988, 103–115) describes the structural breakdown and lubrication of ingested food before the swallowing stage, and has been revisited in the present article. The instrumental technique texture profile analysis (TPA) purports to mimic the first two bites of mastication and its ease of use has lured some researchers to use it without a critical eye. In this article, we consider inconsistencies in the Hutchings and Lillford model with the hope that it might be further refined. With regard to TPA we question the validity of the data generated and urge authors caution before they publish results from the test protocol. If results are published then the x‐axis should be viewed as deformation or strain, and not time. Hardness should be represented by the breaking stress. Adhesiveness should be measured at a medium strain taking into account the surface properties of the plunger. The ratio of the energy estimated by the area under the curve obtained from the second and the first bites (A₂/A₁) should be called recoverability and not cohesiveness.     

Cavitation erosion of aluminum matrix sintered composite with AlN dispersoids

The cavitation erosion resistance of P/M aluminum alloy-sintered composite with AlN dispersoids, prepared via the in situ synthesis and the conventional premixing process, was evaluated by using magnetostrictive-vibration type equipment. In situ synthesized AlN particles were effective for the improvement of the erosion resistance of the composite because of their good bonding with the aluminum matrix. The additive AlN by the premixing process were easily detached from the specimen surface due to the insufficient coherence with the matrix, and caused the poor resistance. The cavitation resistance also depended on the porosity of the sintered composite. The continuously opened pores accelerated the wear phenomena by the cavitation due to the high-pressure attack on the primary particle boundaries of sintered materials in the collapse of the bubbles.     

Rheological study of gum arabic solutions: Interpretation based on molecular self-association

This study deals with the rheological properties of aqueous solutions of gum arabic, the complex arabinogalactan polysaccharide containing about 2% protein. The flow behavior of control gum and a matured gum (EM2), which have different molecular associations, was investigated at different concentrations in water and added urea (6M) by rheological and dynamic light scattering methods. The influence of molecular association on rheological behavior of gum arabic solutions was studied. It was found that though Newtonian behavior was observed across a wide range of concentrations and at high shear rates, gum arabic solutions showed a pronounced shear thinning in low shear rate ranges. The maximum difference in viscosity between shear rate increasing and decreasing processes was observed at 6% for both control gum and EM2 in water, and at 3% for control gum and 9% for EM2 in urea solutions. The results demonstrated macromolecular association of gum arabic occurring in the solutions, and the observed time-dependent flow behavior reflected microstructural breakdown and re-building in the systems. This phenomenon was understood in view of the relationship between rheological properties and microstructural characteristics. A model was presented to interpret the rheological behavior, which is attributed to the occurrence of shear-induced breakdown and re-formation of gum arabic aggregates.