Stress corrosion in brass considered against the background of potential/pH diagrams

The paper describes a study of stress corrosion in brass (62·8 per cent Cu, 37·2 per cent Zn) exposed to ammoniacal copper sulphate solution. The relation between the stress corrosion behaviour and the composition of the corrosive medium is discussed against the background of potential/ pH diagrams for the corroding system.

The time to cracking was found to be very dependent on the pH. At pH 2·0 cracking did not take place within 1000 h of exposure. At about pH 7·3 the time to cracking was at its minimum value, 1–2 h. The results indicated that the process is governed by the formation of a black surface coating of copper oxide on the metal, but counteracted by the precipitation of basic copper sulphate. The cracks were generally transgranular in the absence of black oxide but intergranular in the presence of such a coating. It appeared that the shape of the cracks was influenced by the precipitation of basic copper sulphate. Reduction reactions likely to cause metal dissolution during stress corrosion are discussed for different pH ranges. According to the potential/pH diagram the formation of Cu(NH₃)₂⁺ ions is in general important.     

Toward improved catalytic low-temperature NOx removal in diesel-powered vehicles

The potential of different catalytic after treatment techniques to meet future diesel emission standards, which are strongly shifted toward urban driving conditions including cold start, are critically discussed in this Account and evaluated for their suitability for commercial applications. The dominating techniques in this field are NO(x) storage, urea-selective catalytic reduction (SCR), and HC-SCR. Each of these techniques have significant disadvantages such as sulfur sensitiveness and regeneration requirements of NO(x)-storage materials, infrastructure issues and formation of ammonium nitrate (at low temperatures) for urea-SCR, and low-temperature activity of HC-SCR catalysts. Ways to overcome these disadvantages in commercial applications may involve optimized regeneration strategies, reactor modifications, flow reversal, closed-loop NO(x) feedback systems, nonthermal plasma, and/or hydrogen-assisted catalyses, etc.     

Brittle‐to‐Ductile Transition in Uniaxial Compression of Silicon Pillars at Room Temperature

Robust nanostructures for future devices will depend increasingly on their reliability. While great strides have been achieved for precisely evaluating electronic, magnetic, photonic, elasticity and strength properties, the same levels for fracture resistance have been lacking. Additionally, one of the self‐limiting features of materials by computational design is the knowledge that the atomistic potential is an appropriate one. A key property in establishing both of these goals is an experimentally‐determined effective surface energy or the work per unit fracture area. The difficulty with this property, which depends on extended defects such as dislocations, is measuring it accurately at the sub‐micrometer scale. In this Full Paper the discovery of an interesting size effect in compression tests on silicon pillars with sub‐micrometer diameters is presented: in uniaxial compression tests, pillars having a diameter exceeding a critical value develop cracks, whereas smaller pillars show ductility comparable to that of metals. The critical diameter is between 310 and 400 nm. To explain this transition a model based on dislocation shielding is proposed. For the first time, a quantitative method for evaluating the fracture toughness of such nanostructures is developed. This leads to the ability to propose plausible mechanisms for dislocation‐mediated fracture behavior in such small volumes.     

Alternating Cationic-Hydrophobic Peptide/Peptoid Hybrids: Influence of Hydrophobicity on Antibacterial Activity and Cell Selectivity

The influence of hydrophobicity on antibacterial activity versus the effect on the viability of mammalian cells for peptide/peptoid hybrids was examined for oligomers based on the cationic Lys-like peptoid residue combined with each of 28 hydrophobic amino acids in an alternating sequence. Their relative hydrophobicity was correlated to activity against both Gram-negative and Gram-positive species, human red blood cells, and HepG2 cells. This identified hydrophobic side chains that confer potent antibacterial activity (e. g., MICs of 2–8 μg/mL against E. coli) and low toxicity toward mammalian cells (<10 % hemolysis at 400 μg/mL and IC₅₀>800 μg/mL for HepG2 viability). Most peptidomimetics retained activity against drug-resistant strains. These findings corroborate the hypothesis that for related peptidomimetics two hydrophobicity thresholds may be identified: i) it should exceed a certain level in order to confer antibacterial activity, and ii) there is an upper limit, beyond which cell selectivity is lost. It is envisioned that once identified for a given subclass of peptide-like antibacterials such thresholds can guide further optimisation.     

Preclinical Evaluation of 99mTc-ZHER2:41071, a Second-Generation Affibody-Based HER2-Visualizing Imaging Probe with a Low Renal Uptake

Radionuclide imaging of HER2 expression in tumours may enable stratification of patients with breast, ovarian, and gastroesophageal cancers for HER2-targeting therapies. A first-generation HER2-binding affibody molecule [^99mTc]Tc-ZHER2:V2 demonstrated favorable imaging properties in preclinical studies. Thereafter, the affibody scaffold has been extensively modified, which increased its melting point, improved storage stability, and increased hydrophilicity of the surface. In this study, a second-generation affibody molecule (designated ZHER2:41071) with a new improved scaffold has been prepared and characterized. HER2-binding, biodistribution, and tumour-targeting properties of [^99mTc]Tc-labelled ZHER2:41071 were investigated. These properties were compared with properties of the first-generation affibody molecules, [^99mTc]Tc-ZHER2:V2 and [^99mTc]Tc-ZHER2:2395. [^99mTc]Tc-ZHER2:41071 bound specifically to HER2 expressing cells with an affinity of 58 ± 2 pM. The renal uptake for [^99mTc]Tc-ZHER2:41071 and [^99mTc]Tc-ZHER2:V2 was 25–30 fold lower when compared with [^99mTc]Tc-ZHER2:2395. The uptake in tumour and kidney for [^99mTc]Tc-ZHER2:41071 and [^99mTc]Tc-ZHER2:V2 in SKOV-3 xenografts was similar. In conclusion, an extensive re-engineering of the scaffold did not compromise imaging properties of the affibody molecule labelled with ^99mTc using a GGGC chelator. The new probe, [^99mTc]Tc-ZHER2:41071 provided the best tumour-to-blood ratio compared to HER2-imaging probes for single photon emission computed tomography (SPECT) described in the literature so far. [^99mTc]Tc-ZHER2:41071 is a promising candidate for further clinical translation studies.     

Poly(lactic acid)/pulp fiber composites: The effect of fiber surface modification and hydrothermal aging on viscoelastic and strength properties

Poly(lactic acid) (PLA)/kraft pulp fiber (30 wt%) composites were prepared with and without a coupling agent (epoxidized linseed oil, ELO, 1.5 wt%) by injection molding. The non-annealed composite samples, along with lean PLA, were exposed to two hydro-thermal conditions: cyclic 50% RH/90% RH at 23 and 50°C, both up to 42 days. The aging effects were observed by size exclusion chromatography, differential scanning calorimetry, dynamic and tensile mechanical analysis, and fracture surface imaging. ELO temporarily accelerated the material's internal transition from viscous to an increasingly elastic response during the aging at 50°C. ELO also slowed down the tensile strength reduction of the composites at 50°C. These observations were explained with the hydrophobic ELO molecules' coupling and plasticizing effects at fiber/matrix interfaces. No effects were observed at 23°C.     

Evaluation of haptic guidance virtual fixtures and 3D visualization methods in telemanipulation—a user study

Intelligent Service Robotics - This work presents a user-study evaluation of various visual and haptic feedback modes on a real telemanipulation platform. Of particular interest is the potential...     

The influence of surface roughness on friction and wear of machine element coatings

The use of low friction coatings like amorphous carbon or metal-doped carbon coatings on machine elements is constantly increasing. Most often, a surface treatment, e.g. grinding and polishing or honing, is required for optimal performance of the coated machine element. This can be time consuming and costly.In this study, the effect of surface roughness on friction and sliding wear of two different coatings, one tungsten containing and one chromium containing coating, were examined using a ball-on-disc test. Ball bearing steel plates were grinded to different surface roughnesses and coated with the two different coatings.The friction was found to depend on surface roughness where the rougher surfaces gave higher friction coefficients. The wear rate for the a-C:W coating was found to be independent of the roughness, whereas the roughness had a strong influence on the wear rate for the a-C:Cr coating. This could partly be explained by a difference in wear mechanism, where fatigue wear was observed for the a-C:Cr coating but not for the a-C:W coating.     

A combined reflectometry and quartz crystal microbalance with dissipation setup for surface interaction studies

We have developed an instrument for surface interaction studies, which combines a newly invented four detector optical reflectometry setup with quartz crystal microbalance with dissipation (QCM-D) monitoring. The design is such that data from both techniques can be obtained simultaneously on the same sensor surface, with the same signal-to-noise ratio and time resolution, as for the individual techniques. In addition, synchronized information about structural transformations, molecular mass, and the hydration of thin films on solid surfaces can be obtained on the same specimen, as validated by monitoring the formation of supported lipid bilayers on a silica-coated QCM sensor surface. We emphasize that the optical (molecular) mass can be separated from the acoustic mass including hydrodynamically coupled solvent, which means, in turn, that the amount of solvent sensed by the QCM-D technique can be dynamically resolved during adsorption processes. In addition, the advantage/necessity to use four, compared to two, detector reflectometry is emphasized.