Environment-dependent generation of photoacoustic waves from plasmonic nanoparticles

Nanoparticle-augmented photoacoustics is an emerging technique for molecular imaging. This study investigates the fundamental process of the photoacoustic signal generation by plasmonic nanoparticles suspended in a weakly absorbing fluid. The photoacoustic signal of gold nanospheres with varying silica shell thicknesses is shown to be dominated by the heat transfer between the nanoparticles and the surrounding environment.     

Enhanced π-π interactions between a C60 fullerene and a buckle bend on a double-walled carbon nanotube

In situ low-voltage aberration corrected transmission electron microscopy (TEM) observations of the dynamic entrapment of a C₆₀ molecule in the saddle of a bent double-walled carbon nanotube is presented. The fullerene interaction is non-covalent, suggesting that enhanced π-π interactions (van der Waals forces) are responsible. Classical molecular dynamics calculations confirm that the increased interaction area associated with a buckle is sufficient to trap a fullerene. Moreover, they show hopping behavior in agreement with our experimental observations. Our findings further our understanding of carbon nanostructure interactions, which are important in the rapidly developing field of low-voltage aberration corrected TEM and nano-carbon device fabrication.      

Hydrogen gas sensing properties of WO3 sputter-deposited thin films enhanced by on-top deposited CuO nanoclusters

Magnetron-based gas aggregation cluster source (GAS) was used to prepare high-purity CuO (cupric oxide) nanoclusters on top of sputter-deposited thin film of tungsten trioxide (WO₃). The material was assembled as a conductometric hydrogen gas sensor and its response was tested and evaluated. It is demonstrated that addition of CuO clusters noticeably enhances the sensitivity of the pure WO₃ thin film. With an increasing amount of CuO clusters the sensitivity of CuO/WO₃ system rises further. When CuO clusters form a sufficiently thick and compact layer, the resistance response is reversed. Based on the sensorial behavior, conventional and near-ambient pressure X-Ray photoemission spectroscopies, and resistivity measurements, we propose that the sensing mechanism is based on the formation of nano-sized p-n junctions in between p-type CuO and n-type WO₃. The advantages of the GAS technique for preparing sensorial and/or catalytically active materials are emphasized.     

Life-cycle assessment and repair of the railway transition zones of an existing bridge using geocomposite materials

The railway infrastructure is a very important component of the world’s total transportation network. Investment in its construction and maintenance is therefore significant on a global scale. Up to now, some results of the life-cycle assessment (LCA) of open railway line, as well as railway bridges and tunnels, have been published, but detailed analyses of transition zones have not so far been performed. In railway networks, transitional zones are a critical area where the transition from open rail to solid bridge construction can cause significant settlements. The goal of these analyses was to compare two different types of track renewal methods for railway transition zones. In the first method, traditional cement stabilisation is used, whereas the second solution makes use of a geocomposite anchored by steel anchors. The paper presents some results from an environmental study for railway transition zones based on the demonstration case. The results of the performed LCA showed that, in the case of track renewal for transition zones by means of a geocomposite and anchors, the environmental impact is lower than in the case when cement stabilisation works are performed. Less extensive excavation works and thus lower quantities of used material are additional benefits.     

Effect of micro-pores on cracks formation in metallurgical coke

The relationships of micro-pores and cracks in metallurgical coke have been investigated by optical microscope and field emission scanning electron microscope, using surface section samples. The pores have circular, elliptical and irregular shapes with smooth outlines, formed during the thermoplastic stage of the coking process. They often associate with connecting cracks between neighbouring pores. In case of elliptical pores, the connecting cracks are usually oriented along the longer axis of the pore. The connecting cracks can be developed between the pores, depending on their size and the distance between them. The coke with a large number of small pores rather than with a small number of larger pores will have lower strength due to the increased amount of connecting cracks. When compared with circular pores, elliptical and flattened pores have a lower ability to resist load pressure. Nano-sized pores have polygonal outlines, indicating an ‘explosion’-type formation in the solidified matrix.     

Crystal chemistry of mercury oxo- and chalcohalides

The features of mercury oxo- and chalcohalide crystal structure, including Hg₃ Y ₂ X ₂ (Y?=?O, S, Se, Te; X?=?Cl, Br, I), chromates, phosphates and related compounds, are analyzed in terms of building blocks, their symmetry and stability. Building blocks are found, which are rigid atomic groups, namely, oxo-centered [Hg₄O] tetrahedra, [Hg₆O₂] r-octahedra, [Hg₂]²⁺, [Hg₃]⁴⁺, [Hg₃O]²⁺, [Ag₃Hg]⁴⁺ cluster cations, etc. Bonded by the strongest chemical bonds, these groups keep their geometry unchanged in crystal structures of different composition. Thus cluster cations can be considered as single large cations, while their environment may be described by pseudo-coordination polyhedra, constructed around the centroid of each cation. This tendency was found for the example of atoms joined to pairs of [CrO₄] tetrahedra, according to which the geometry of mutual arrangement of rigid atomic groups tends not to change. It is shown that the symmetry of the rigid atomic groups is a subgroup of the space group symmetry, and partly predetermines it. In crystal structures of some Hg₃ Y ₂ X ₂ chalcohalides, the structure-forming role of packing of halogen atoms is revealed.     

Brochosomes protect leafhoppers (Insecta,Hemiptera, Cicadellidae) from sticky exudates

Leafhoppers (Insecta, Hemiptera, Cicadellidae) actively coat their integuments with buckyball-shaped submicron proteinaceous secretory particles, called brochosomes. Here, we demonstrate that brochosomal coats, recently shown to be superhydrophobic, act as non-stick coatings and protect leafhoppers from contamination with their own sticky exudates—filtered plant sap. We exposed 137 wings of Alnetoidia alneti (Dahlbom), from half of which brochosomes were removed, to the rain of exudates under a colony of live A. alneti. One hundred and fifty-two droplets became stuck to the bared wings and only three to the intact wings. Inspection of the wings with a scanning electron microscope confirmed that the droplets that had hit the intact wings had rolled or bounced off the brochosomal coats. This is the first experimental study that tested a biological function of the brochosomal coats of leafhopper integuments. We argue that the production of brochosomes in leafhoppers and production of epidermal wax blooms in other sap-sucking hemipterans are alternative solutions, both serving to protect these insects from entrapment by their exudates.     

Fast simulation-driven design of microwave structures using improved variable-fidelity optimization technique

An improved variable-fidelity optimization algorithm for the simulation-driven design of microwave structures is presented. It exploits a set of electromagnetic-based models of increasing discretization density. These models are sequentially optimized with the optimum of the ‘coarser’ model being the initial design for the ‘finer’ one. The found optimum is further refined using a response surface approximation model constructed from the coarse-discretization simulation data. In this work, the computational efficiency of the variable-fidelity algorithm is enhanced by employing a novel algorithm for optimizing the coarse-discretization models. This allows reduction of the overall design time by up to 50% compared to the previous version. The presented technique is particularly suitable for problems where simulation-driven design is the only option, for example, ultra wideband and dielectric resonator antennas. Operation of the presented approach is demonstrated using two examples of antennas and a microstrip filter. In all cases, the optimal design is obtained at a low computational cost corresponding to a few high-fidelity simulations of the structure.     

Composite polypyrrole-containing particles and electrical properties of thin films prepared therefrom

Preparation of core-shell particles consisting of polystyrene-poly(ethylene glycol) monomethacrylate (PS-PEGMA) core covered with polypyrrole (PPy) shell is described. The thickness of PPy shell, which strongly influences electrical properties of the films prepared from the particles, can be varied by changing pyrrole load, controlling the overall template surface area in the system and by influencing the pyrrole polymerization kinetics in the presence of different oxidants. The type of anions and PPy loading strongly influence the electrical conductivity. Typical value of the resistivity of thin film consisting of core-shell particles was 34 Ωm (PPy oxidized by FeCl₃, shell thickness 3 nm). Current-voltage dependences of low conductivity samples (thin PPy shell layer) are characteristic of contact-limited currents. The conductivity of the particles changes with humidity, which can be utilized in humidity sensors.