Friction-induced vibration considering multiple types of nonlinearities

Nonlinear Dynamics - The friction-induced vibration of a novel 5-DoF (degree-of-freedom) mass-on-oscillating-belt model considering multiple types of nonlinearities is studied. The first type of...     

Curvature investigation in tapered fibers and its application to sensing and mode conversion

Non-adiabatic tapered fibers are basic photonic components used in a wide range of applications. Here we investigate a way to increase their utility through the controllable bending of one of their tapered sections. The experiments carried out explain, for the first time, the mechanics of this approach showing how these tapers can be used to build more sensitive sensors. Their use as highly efficient mode converters is also discussed.     

Analytical study of the Middle Kingdom group of gold jewellery from tomb 124 at Riqqa,Egypt

The jewellery from tomb 124 at Riqqa, consisting of one pectoral and one winged beetle in gold and cloisonné work, one gold shell pendant decorated with wires and granulation, and one hollow gold amulet in the form of god Min, was analysed by handheld X-ray fluorescence and scanning electron microscopy with energy-dispersive X-ray spectroscopy. This group of jewellery, dated to the second half of the 12th Dynasty (c. 1900–1840 B.C.), was excavated inside the coffin of an adult male, which had been crushed after burial by the collapse of the chamber roof during an episode of looting. Both the male and the looter's body were found inside the chamber, evidencing that the group of jewellery was intact. Despite having been highly restored in the past, as referenced in the correspondence between the excavator Flinders Petrie and the curators of the Manchester Museum, it could be shown that the jewellery was produced using Ag-rich electrum alloys containing platinum group element inclusions that indicate the use of alluvial gold. The analysis of some joins has confirmed the use of hard-soldering, with solders obtained by addition of Cu to the base-alloy. Data obtained for the jewellery of tomb 124 were compared with data previously obtained for tomb 296, also excavated at Riqqa, but dated to the 18th Dynasty. The comparison demonstrates the continuity of the workshop traditions in one location between the Middle Kingdom and the New Kingdom but also reveals discrepancies in the alloys employed in those two periods.     

Attacking and defending multiple valuable secrets in a big data world

This paper studies the attack-and-defence game between a web user and a whole set of players over this user’s ‘valuable secrets.’ The number and type of these valuable secrets are the user’s private information. Attempts to tap information as well as privacy protection are costly. The multiplicity of secrets is of strategic value for the holders of these secrets. Users with few secrets keep their secrets private with some probability, even though they do not protect them. Users with many secrets protect their secrets at a cost that is smaller than the value of the secrets protected. The analysis also accounts for multiple redundant information channels with cost asymmetries, relating the analysis to attack-and-defence games with a weakest link.     

Factorial Hypersurfaces

The codimension of the complement of the set of factorial hypersurfaces of degree d in P^N is estimated for d ≥ 4 and N ≥ 7.     

Evidence for Multiple Binding Modes in the Initial Contact Between SARS-CoV-2 Spike S1 Protein and Cell Surface Glycans**

Infection of host cells by SARS-CoV-2 begins with recognition by the virus S (spike) protein of cell surface heparan sulfate (HS), tethering the virus to the extracellular matrix environment, and causing the subunit S1-RBD to undergo a conformational change into the ‘open’ conformation. These two events promote the binding of S1-RBD to the angiotensin converting enzyme 2 (ACE2) receptor, a preliminary step toward viral-cell membrane fusion. Combining ligand-based NMR spectroscopy with molecular dynamics, oligosaccharide analogues were used to explore the interactions between S1-RBD of SARS CoV-2 and HS, revealing several low-specificity binding modes and previously unidentified potential sites for the binding of extended HS polysaccharide chains. The evidence for multiple binding modes also suggest that highly specific inhibitors will not be optimal against protein S but, rather, diverse HS-based structures, characterized by high affinity and including multi-valent compounds, may be required.     

Enantioselective Rhodium-Catalyzed Pauson–Khand Reactions of 1,6-Chloroenynes with 1,1-Disubstituted Olefins

An enantioselective rhodium(I)-catalyzed Pauson–Khand reaction (PKR) using 1,6-chloroenynes that contain challenging 1,1-disubstituted olefins is described. In contrast to the previous studies with these types of substrates, which are only suitable for a single type of tether and alkyne substituent, the new approach results in a more expansive substrate scope, including carbon and heteroatom tethers with polar and non-polar substituents on the alkene. DFT calculations provide critical insight into the role of the halide, which pre-polarizes the alkyne to lower the barrier for metallacycle formation and provides the proper steric profile to promote a favorable enantiodetermining interaction between substrate and chiral diphosphine ligand. Hence, the chloroalkyne enables the efficient and enantioselective PKR with 1,6-enynes that contain challenging 1,1-disubstituted olefins, thereby representing a new paradigm for enantioselective reactions involving 1,6-enynes.     

New Polyurethane/Docosane Microcapsules as Phase‐Change Materials for Thermal Energy Storage

Polyurethane microcapsules were prepared by mini‐emulsion interfacial polymerization for encapsulation of phase‐change material (n‐docosane) for energy storage. Three steps were followed with the aim to optimize synthesis conditions of the microcapsules. First, polyurethane microcapsules based on silicone oil core as an inert template with different silicone oil/poly(ethylene glycol)/4,4′‐diphenylmethane diisocyanate wt % ratio were synthesized. The surface morphology of the capsules was analyzed by scanning electronic microscopy (SEM) and the chemical nature of the shell was monitored by Fourier transform infrared spectroscopy (FT‐IR). Capsules with the silicone oil/poly(ethylene glycol)/4,4′‐diphenylmethane diisocyanate 10/20/20 wt % ratio showed the best morphological features and shell stability with average particle size about 4 μm, and were selected for the microencapsulation of the n‐docosane. In the second stage, half of the composition of silicone oil was replaced with n‐docosane and, finally, the whole silicone oil content was replaced with docosane following the same synthetic procedure used for silicone oil containing capsules. Thermal and cycling stability of the capsules were investigated by thermal gravimetric analysis (TGA) and the phase‐change behavior was evaluated by differential scanning calorimetry (DSC).     

A multi-scale simulation of tungsten film delamination from silicon substrate

To bridge the different spatial scales involved in the process of tungsten (W) film delaminating from silicon (Si) substrate, a multi-scale simulation procedure is proposed via a sequential approach. In the proposed procedure, a bifurcation-based decohesion model, which represents the link between molecular and continuum scales, is first formulated within the framework of continuum mechanics. Molecular dynamics (MD) simulation of a single crystal W block under tension is conducted to investigate the effect of specimen size and loading rate on the material properties. The proposed decohesion model is then calibrated by using MD simulation of a single crystal W block under tension and using available experimental data, with a power scaling law to account for the size effect. A multi-scale model-based simulation of W film delamination from Si substrate is performed by using the proposed procedure within the framework of the material point method. The simulated results provide new insights into the mechanisms of the film delamination process.