Amontonian frictional behaviour of nanostructured surfaces

With nanotextured surfaces and interfaces increasingly being encountered in technological and biomedical applications, there is a need for a better understanding of frictional properties involving such surfaces. Here we report friction measurements of several nanostructured surfaces using an Atomic Force Microscope (AFM). These nanostructured surfaces provide well defined model systems on which we have tested the applicability of Amontons' laws of friction. Our results show that Amontonian behaviour is observed with each of the surfaces studied. However, no correlation has been found between measured friction and various surface roughness parameters such as average surface roughness (R(a)) and root mean squared (rms) roughness. Instead, we propose that the friction coefficient may be decomposed into two contributions, i.e., μ = μ(0) + μ(g), with the intrinsic friction coefficient μ(0) accounting for the chemical nature of the surfaces and the geometric friction coefficient μ(g) for the presence of nanotextures. We have found a possible correlation between μ(g) and the average local slope of the surface nanotextures.     

2D autocovariance function for comprehensive analysis of two-way GC-MS data matrix: application to environmental samples

This paper describes a signal processing method for comprehensive analysis of the large data set generated by hyphenated GC-MS technique. It is based on the study of the 2D autocovariance function (2D-EACVF) computed on the raw GC-MS data matrix, extending the procedure previously developed for 1D to 2D signals. It appears specifically promising for GC-MS investigation, in particular to single out ordered patterns in complex data: such patterns can be simply identified by visual inspection from deterministic peaks in the 2D-EACVF plot.A case of order along the retention time axis (x = t_R) is represented by a horizontal sequence of peaks, located at the same interdistance Δt_R = b_x, e.g., b_x is the CH₂ retention time increment between subsequent terms of an homologous series. The order along the fragment mass axis (y = m/z) contains information on analyte fragmentation patterns. Deterministic peaks appear in the 2D-EACVF plot at Δm/z values corresponding to the most abundant ion fragments - dominating fragments in MS spectrum - or to ions generated by repetitive loss of the same ion fragment, i.e., Δm/z = 14 amu produced by the [CH₂] group loss in n-alkanes.Method applicability was tested by processing GC-MS data of organic extracts of atmospheric aerosol samples: attention is focused on identifying and characterizing homologous series of organics, i.e., n-alkanes and n-alkanoic acids, since they are considered molecular tracers able to track the origin and fate of different organics in the environment.     

Shedding Light Onto the Nature of Iron Decorated Graphene and Graphite Oxide Nanohybrids for CO2 Conversion at Atmospheric Pressure

We report on the design and testing of new graphite and graphene oxide-based extended π-conjugated synthetic scaffolds for applications in sustainable chemistry transformations. Nanoparticle-functionalised carbonaceous catalysts for new Fischer Tropsch and Reverse GasWater Shift (RGWS) transformations were prepared: functional graphene oxides emerged from graphite powders via an adapted Hummer's method and subsequently impregnated with uniform-sized nanoparticles. Then the resulting nanomaterials were imaged by TEM, SEM, EDX, AFM and characterised by IR, XPS and Raman spectroscopies prior to incorporation of Pd(II) promoters and further microscopic and spectroscopic analysis. Newly synthesised 2D and 3D layered nanostructures incorporating carbon-supported iron oxide nanoparticulate pre-catalysts were tested, upon hydrogen reduction in situ, for the conversion of CO₂ to CO as well as for the selective formation of CH₄ and longer chain hydrocarbons. The reduction reaction was also carried out and the catalytic species isolated and fully characterised. The catalytic activity of a graphene oxide-supported iron oxide pre-catalyst converted CO₂ into hydrocarbons at different temperatures (305, 335, 370 and 405 °C), and its activity compared well with that of the analogues supported on graphite oxide, the 3-dimensional material precursor to the graphene oxide. Investigation into the use of graphene oxide as a framework for catalysis showed that it has promising activity with respect to reverse gas water shift (RWGS) reaction of CO₂ to CO, even at the low levels of catalyst used and under the rather mild conditions employed at atmospheric pressure. Whilst the γ-Fe₂O₃ decorated graphene oxide-based pre-catalyst displays fairly constant activity up to 405 °C, it was found by GC-MS analysis to be unstable with respect to decomposition at higher temperatures. The addition of palladium as a promoter increased the activity of the iron functionalised graphite oxide in the RWGS. The activity of graphene oxide supported catalysts was found to be enhanced with respect to that of iron-functionalised graphite oxide with, or without palladium as a promoter, and comparable to that of Fe@carbon nanotube-based systems tested under analogous conditions. These results display a significant step forward for the catalytic activity estimations for the iron functionalised and rapidly processable and scalable graphene oxide. The hereby investigated phenomena are of particular relevance for the understanding of the intimate surface morphologies and the potential role of non-covalent interactions in the iron oxide-graphene oxide networks, which could inform the design of nano-materials with performance in future sustainable catalysis applications.     

Receptor-based high-throughput screening and identification of estrogens in dietary supplements using bioaffinity liquid-chromatography ion mobility mass spectrometry

A high-throughput bioaffinity liquid chromatography-mass spectrometry (BioMS) approach was developed and applied for the screening and identification of recombinant human estrogen receptor α (ERα) ligands in dietary supplements. For screening, a semi-automated mass spectrometric ligand binding assay was developed applying ¹³C_2, ¹⁵?N-tamoxifen as non-radioactive label and fast ultra-high-performance–liquid chromatography–electrospray ionisation–triple-quadrupole-MS (UPLC-QqQ-MS), operated in the single reaction monitoring mode, as a readout system. Binding of the label to ERα-coated paramagnetic microbeads was inhibited by competing estrogens in the sample extract yielding decreased levels of the label in UPLC-QqQ-MS. The label showed high ionisation efficiency in positive electrospray ionisation (ESI) mode, so the developed BioMS approach is able to screen for estrogens in dietary supplements despite their poor ionisation efficiency in both positive and negative ESI modes. The assay was performed in a 96-well plate, and all these wells could be measured within 3 h. Estrogens in suspect extracts were identified by full-scan accurate mass and collision-cross section (CCS) values from a UPLC-ion mobility-Q-time-of-flight-MS (UPLC-IM-Q-ToF-MS) equipped with a novel atmospheric pressure ionisation source. Thanks to the novel ion source, this instrument provided picogram sensitivity for estrogens in the negative ion mode and an additional identification point (experimental CCS values) next to retention time, accurate mass and tandem mass spectrometry data. The developed combination of bioaffinity screening with UPLC-QqQ-MS and identification with UPLC-IM-Q-ToF-MS provides an extremely powerful analytical tool for early warning of ERα bioactive compounds in dietary supplements as demonstrated by analysis of selected dietary supplements in which different estrogens were identified.

Using mixed-integer programming to solve power grid blackout problems

We consider optimization problems related to the prevention of large-scale cascading blackouts in power transmission networks subject to multiple scenarios of externally caused damage. We present computation with networks with up to 600 nodes and 827 edges, and many thousands of damage scenarios.