Topological anisotropy of stone-wales waves in graphenic fragments

Stone-Wales operators interchange four adjacent hexagons with two pentagon-heptagon 5|7 pairs that, graphically, may be iteratively propagated in the graphene layer, originating a new interesting structural defect called here Stone-Wales wave. By minimization, the Wiener index topological invariant evidences a marked anisotropy of the Stone-Wales defects that, topologically, are in fact preferably generated and propagated along the diagonal of the graphenic fragments, including carbon nanotubes and graphene nanoribbons. This peculiar edge-effect is shown in this paper having a predominant topological origin, leaving to future experimental investigations the task of verifying the occurrence in nature of wave-like defects similar to the ones proposed here. Graph-theoretical tools used in this paper for the generation and the propagation of the Stone-Wales defects waves are applicable to investigate isomeric modifications of chemical structures with various dimensionality like fullerenes, nanotubes, graphenic layers, schwarzites, zeolites.     

Hierarchical structure formation and pattern replication induced by an electric field

Several techniques based on soft lithography have emerged to replicate micrometre-sized patterns. Similar to most other lithographic methods, these techniques structure a single layer of photo resist. For many applications, however, it is desirable to control the spatial arrangement of more than one component. With traditional methods, this requires an iterative, multistep procedure, making the replication process more complex and less reliable. Here, a replication process is described where multiple materials are processed simultaneously. Using a bilayer formed by two different polymers, electrohydrodynamic instabilities at both polymer surfaces produce a hierarchic lateral structure that exhibits two independent characteristic dimensions. A lateral modulation of the electric field enables replication with a resolution down to 100 nanometres. This approach might provide a simple strategy for large-area, sub-100-nanometre lithography.     

Kinetic data on the polycondensation of tetrachlorobisphenol A with bis(2,3-dichloropropyl) phosphorochloridite

Tetrachlorobisphenol A and bis(2,3 dichloropropyl)phosphorochloridite form a polycondensate with the elimination of HCl and 2,3 dichloropropanol. The polyphosphite formed undergoes an Arbuzov transposition leading to a more stable polyphosphonate. I.r. and ¹H-n.m.r. spectroscopy give support for the described mechanism. From the ¹H-n.m.r. spectral integrals which were registered during the reaction, the separate processes and the rate of consumption of tetrachlorobisphenol A, may be quantitatively determined. The reaction temperature has to be kept below 200°C in order to avoid side reactions.     

Corrosion susceptibility of implant materials Ti-5Al-4V and Ti-6Al-4Fe in artificial extra-cellular fluids

The paper is aimed at detecting the corrosion susceptibility (generated by the potential gradients, due to the pH changes) of implant materials Ti-5Al-4V and Ti-6Al-4Fe alloys exposed in extra-cellular fluids for long term (10 000 exposure hours) in comparison with pure titanium. The titanium and its ternary alloys exhibited spontaneous passivity in Ringer’s solutions of pH=6.98, 4.35 and 2.5, simulating the real situations that can arise in surgical applications. Potential gradients determined in presumptive extreme pH conditions indicate that there is no probability for local corrosion. Impedance spectra were fitted with one time constant equivalent circuit, typically for protective, compact oxide film. The fitting parameters indicate long-term stability of the passive layers in surgical implant conditions. Atomic force microscopy (AFM) and spectral infrared (IR) data are important arguments in supporting the conclusion that titanium and its ternary alloys have a very good corrosion resistance in long-term functional conditions.     

Defect formation in amorphous structures as revealed by computer simulation

Various types of defect in amorphous structures are discussed. It is shown that the formation, migration, redistribution and annihilation of defects in amorphous solids can be fully understood only by using computer simulation. More insight into the physics of amorphous thin films is given by the simulation of columnar growth and of the interface between a crystalline phase and an amorphous phase.     

Coordination polymers

Summary By interfacial polycondensation of Cu,Ni,Co and Mn rezorcylaldehyde-ophenylenediamine sodium salt with terephthalic and isophthalic dichloride respectively, coordination polymers, particularly chelate plyesters, as coloured powders, insoluble in organic solvents, were obtained. The identification of coordination polymers has been carried out by the elementary analysis and IR spectroscopy.     

Optothermal window method for on-line monitoring of decay kinetics of<Emphasis Type="Italic"> trans</Emphasis>-β-carotene in thermally treated vegetable oils

The optothermal window detection method at 488 nm was used to monitor on-line the concentration of trans-ß-carotene that was added to several vegetable oils after treating them at 200 °C in the presence of air for varying amounts of time. Results obtained for extra virgin oil show a direct proportionality between the rate constant describing the disappearance of trans-ß-carotene and the duration of thermal treatment. The rate constant for the decay of trans-ß-carotene in oils treated under identical conditions was also dependent on the type of oil. Trends and individual data are discussed in the light of a possible application of the method for the determination of the oxidative stability of vegetable oils.     

Active vibration control in palletised workholding system for milling

This paper presents the development implementation and testing of an active controlled palletised workholding system for milling operations. The traditional approach to controlling vibration in a machining system is to develop control systems for cutting tools or machine spindles as in the case of milling machines. This work is a deviation from the traditional approach and targets a workholding system for the control of unwanted vibration. Palletised workholding systems, due to their compact design, offer an opportunity to design active control systems that are economical and easier to implement in the case of milling machines. The active control system developed here is based on an adaptive filtering algorithm, the filtered X-LMS, and employs piezo-actuators for dynamic control force. The system has been tested experimentally to demonstrate the reduction in dynamic force due to vibration. Extensive testing has been carried out to validate the performance of the system in terms of parameters of practical importance such as improvement in surface finish and increase in tool life.