CONDITION OF THE TREATED SURFACE OF NIOBIUM-BASED ALLOY WHEN GRINDING FROM SILICON CARBIDE

The study of the surface of silicon carbide after grinding niobium was carried out on a Versa 3D electronic microscope. It is shown that as a result of the grinding, traces of the grinding wheel material are formed on the treated surface, and the ground material itself is prone to adhesion to the grinding wheel. As a result of cohesive interaction, the metal adhering to the grinding wheel is transferred, and vice versa. And, as a result of adhesion-fatigue processes, mechanical action, there is a hanging wear of the grinding wheel and the indentation of individual crystals of silicon carbide into the surface of the metal being processed. This article examines such features of the behavior of niobium, when grinding it with silicon wheels and is considered from the standpoint of the electronic structure of the metal atom.

Nonconventional driving force for selective oxidative C–C coupling reaction due to concurrent and curious formation of Ag0

Is it possible to ‘explore’ metal’s intrinsic property—a cohesive interaction—which naturally transform M0 into an aggregate or a particle or film for driving oxidative C–C bond formation? With this intention, reduction of [Ag(NH3)2]+ to Ag0 with concurrent oxidation of different phenols/naphthols to biphenyls was undertaken. The work is originated during careful observation of an undergraduate experiment—Tollens’ test—where silver mirror film deposition takes place on the walls of borosilicate glass test tube. When the same reaction was carried out in polypropylene (plastic-Eppendorf) tube, we observed aggregation of Ag0 leading to floating Ag-particles but not silver film deposition. This prompted us to carry out challenging cross-coupling reaction by ONLY changing the surface of the reaction flask from glass to plastic to silicones. To our surprise, we observed good selective oxidative homo-coupling on Teflon surface while cross-coupling in Eppendorf vial. Thus, we propose that the formation of biphenyl is driven by the macroscopic growth of Ag0 into [Ag-particle] orchestrated by Ag…Ag cohesive interaction. To validate results, experiments were also performed on gram scale. More importantly, oxidation of β-naphthol carried out in quartz (chiral) tube which yielded slight enantioselective excess of BINOL. Details are discussed.

Molecular recognition of human islet amyloid polypeptide assembly by selective oligomerization of thioflavin T

Selective oligomerization is a common phenomenon existing widely in the formation of intricate biological structures in nature. The precise design of drug molecules with an oligomerization state that specifically recognizes its receptor, however, remains substantially challenging. Here, we used scanning tunneling microscopy (STM) to identify the oligomerization states of an amyloid probe thioflavin T (ThT) on hIAPP8–37 assembly to be exclusively even numbers. We demonstrate that both adhesive interactions between ThT and the protein substrate and cohesive interactions among ThT molecules govern the oligomerization state of the bounded ThT. Specifically, the work of the cohesive interaction between two head/tail ThTs is determined to be 6.4 kBT, around 50% larger than that of the cohesive interaction between two side-by-side ThTs (4.2 kBT). Overall, our STM imaging and theoretical understanding at the single-molecule level provide valuable insights into the design of drug compounds using the selective oligomerization of molecular probes to recognize protein self-assembly.

2D Runout Modelling of Hillslope Debris Flows, Based on Well-Documented Events in Switzerland

In mountain areas, mass movements, such as hillslope debris flows, pose a serious threat to people and infrastructure, although size and runout distances are often smaller than those of debris avalanches or in-channel-based processes like debris floods or debris flows. Hillslope debris-flow events can be regarded as a unique process that generally can be observed at steep slopes. The delimitation of endangered areas and the implementation of protective measures are therefore an important instrument within the framework of a risk analysis, especially in the densely populated area of the alpine region. Here, two-dimensional runout prediction methods are helpful tools in estimating possible travel lengths and affected areas. However, not many studies focus on 2D runout estimations specifically for hillslope debris-flow processes. Based on data from 19 well-documented hillslope debris-flow events in Switzerland, we performed a systematic evaluation of runout simulations conducted with the software Rapid Mass Movement Simulation: Debris Flow (RAMMS DF)—a program originally developed for runout estimation of debris flows and snow avalanches. RAMMS offers the possibility to use a conventional Voellmy-type shear stress approach to describe the flow resistance as well as to consider cohesive interaction as it occurs in the core of dense flows with low shear rates, like we also expect for hillslope debris-flow processes. The results of our study show a correlation between the back-calculated dry Coulomb friction parameters and the percentage of clay content of the mobilised soils. Considering cohesive interaction, the performance of all simulations was improved in terms of reducing the overestimation of the observed deposition areas. However, the results also indicate that the parameter which accounts for cohesive interaction can neither be related to soil physical properties nor to different saturation conditions.

Physicochemical Properties of African Catfish Mucus and Its Effect on the Stability of Soya Milk Emulsions

Mucus, a waste product produced when African catfish undergoes stress, has lubricating effects and could be a potential emulsifier. Emulsions are thermodynamically unstable; researchers have documented synthetic bio-polymers as emulsifiers, but its sustainability is in question. This research aims to establish some physicochemical properties of African catfish mucus (ACM) and its effect in soya milk emulsions. A Zetasizer and Turbiscan were used to measure stability, morphology was determined with Transmission electron microscopy (TEM), while functional groups in ACM and ACM-stabilized soya milk emulsions were determined using Attenuated Total Reflection Fourier Transform Infra-red spectroscopy. ACM is a stable hydrogel with negatively charged (−36.2 mV) loosely bound electrons with polar and non-polar portions. ACM concentrations of 1, 3, and 5 g w/w stabilized soya milk emulsions after 180 min of storage. The spectra of stabilized emulsion revealed interactions with soya milk droplets. ACM encapsulated the stabilized emulsion and conferred a kind of cohesive interaction and stability. Turbiscan revealed that the mucin formed strong cohesive connections with stabilized emulsions and the mucin exhibited adhesive properties. ACM is an excellent natural emulsifier with mucoadhesive properties as it encapsulates soya milk to enhance stability.

Mechanical Behavior of Bio-Inspired Wavy Adhesive Bonding Under Shear

Inspired by biological suture joints with wavy morphology, wavy adhesive joints were designed and the shear resistance of the designs were explored via finite element (FE) simulations. The influences of waviness and material properties of the layer on the mechanical behaviors of the adhesive joints were quantified. Both adhesive and cohesive failure mechanisms were explored: (1) delamination along the interface between the softer layer and the harder substrates, and (2) layer material failure. In the FE models, both cohesive interaction and ductile damage mechanics models were used to capture the two failure mechanisms. The effects of Young’s modulus and damage evolution parameters on the force-displacement relation were studied. Both failure mechanisms were observed by varying the material properties in the adhesive layer. It was found that, the stiffness, strength and the failure mechanisms of the wavy adhesive joints are largely dependent on the geometry and material properties of the layer.