Numerical modeling of structural transitions in few-particle confined 2D systems

We study classical strongly correlated few-particle systems in two-dimensional traps. Strong interaction between the particles leads to formation of ordered structure (the Wigner crystal), and the precise configuration of particles is determined by the shape of the confinement. Structural transitions in systems of four to seven particles induced by compression of the confining trap in one of two lateral directions are modeled numerically using the statistical Monte Carlo technique and distributed (grid) computing. We focus on the dependence of the specific heat on the eccentricity of the confinement, and show that rapid variations of the specific heat can be used to detect and classify changes of system configuration. These structural transitions are the finite-size analogues of phase transitions commonly defined for infinite systems.     

The impact of Al2O3 amount on the synthesis of CASH samples and their influence on the early stage hydration of calcium aluminate cement

In this work the impact of Al₂O₃ amount on the synthesis (200?°C; 4–8?h) of calcium aluminium silicate hydrates (CSAH) samples and their influence on the early stage hydration of calcium aluminate cement (CAC) was examined. It was found that the amount of Al₂O₃ plays an important role in the formation of calcium aluminate hydrates (CAH) because in the mixtures with 2.7% Al₂O₃ only calcium silicate hydrates (CSH) intercalated with Al³⁺ ions were formed. While in the mixtures with a higher amount of Al₂O₃ (5.3–15.4%), calcium aluminate hydrate – C₃AH₆, is formed under all experimental conditions. It is worth noting that the largest quantity of mentioned compound was obtained after 4?h of hydrothermal treatment, in the mixtures with 15.4% of Al₂O₃. It was proved that synthesized C₃AH₆ remain stable up to 300?°C and at higher temperature (945?°C) recrystallized to mayenite (Ca₁₂Al₁₄O₃₃), which reacted with the rest part of CaO and amorphous structure compound, resulting in the formation of gehlenite (Ca₂Al₂SiO₇). Moreover, the synthesized C₃AH₆ addition induced the early stage of CAC hydration. Besides, in the samples with an addition, the induction period was effectively shortened: in a case of pure CAC (G70) paste, hydration takes about 6–6.5?h, while with addition – only 2–2.5?h. The synthesized and calcinated compounds was characterized by using XRD and STA analysis.     

A semi-global reaction rate model based on experimental data for the self-hydrolysis kinetics of aqueous sodium borohydride

This work studied the self-hydrolysis kinetics of aqueous sodium borohydride (NaBH₄) for hydrogen generation and storage purposes. Two semi-global rate expressions of sodium borohydride and hydrogen ion consumption were derived from an extensive series of batch process experiments where the following parameters were systematically varied: solution temperature (298 K–348 K), NaBH₄ concentration (0.5 wt% to 25.0 wt%), and sodium hydroxide (NaOH) concentration (0.0 wt% to 4.0 wt%). Transient hydrogen generation rates and transient solution pH were measured during the hydrolysis experiments. Given initial conditions (temperature, NaBH₄ concentration, and H⁺ concentration), the two coupled semi-global rate equations can be integrated to obtain the transient time history of H₂ generation (or NaBH₄ consumption) and solution pH (or H⁺ concentration). Comparing analytical results of transient hydrogen generation rate and transient solution pH with experimental data, good agreement was reached for many conditions, especially for elevated solution pH values, levels at which NaBH₄ solutions are used practically.     

Synthesis of new hole-transporting molecular glasses with pendant carbazolyl-based hydrazone moieties

Synthesis, thermal, optical and photoelectrical properties of new hole-transporting molecular glasses with pendant carbazolyl-based hydrazone moieties, linked by aliphatic linking fragments, are reported. Electron photoemission spectra of the synthesized derivatives have been recorded and the ionization potentials have been established. The hole drift mobility values in compositions of the designed structures with bisphenol Z polycarbonate exceed 10^?5 cm² V^?1 s^?1 at an electric field 10⁶ V/cm.     

Antibacterial performance of polydopamine-modified polymer surfaces containing passive and active components

A growing number of device-related nosocomial infections, elevated hospitalization costs, and patient morbidity necessitate the development of novel antibacterial strategies for clinical devices. We have previously demonstrated a simple, aqueous polydopamine dip-coating method to functionalize surfaces for a wide variety of uses. Here, we extend this strategy with the goal of imparting antifouling and antimicrobial properties to substrates, exploiting the ability of polydopamine to immobilize polymers and induce metal nanoparticle formation. Polydopamine was deposited as a thin adherent film of 4 nm thickness from alkaline aqueous solution onto polycarbonate substrates, followed by grafting of antifouling polymer polyethylene glycol and in situ deposition of silver nanoparticles onto the polydopamine coated polycarbonate substrates. Elemental and morphological surface analyses confirmed successful grafting of polyethylene glycol brushes onto polydopamine-coated substrates, as well as spontaneous silver nanoparticle formation for polydopamine-coated substrates incubated in silver-nitrate solutions. Sustained silver release was observed over at least 7 days from silver-coated substrates, and the release kinetics could be modulated via additional polydopamine overlayers. In vitro functional assays employing gram negative and positive strains demonstrated dual fouling resistance and antibacterial properties of the coatings due to the fouling resistance of grafted polyethylene glycol and antibacterial effect of silver, respectively. Polycarbonate substrates coated only with silver using a method similar to existing commercial coatings provided an antibacterial effect but failed to inhibit bacterial attachment. Taking into account the previously demonstrated substrate versatility of polydopamine coatings, our findings suggest that this strategy could be implemented on a variety of substrate materials to simultaneously improve antifouling and antimicrobial performance.     

Synthesis and characterisation of wollastonite with aluminium and fluoride ions

This work aims to investigate the influence of aluminium and fluoride ions on the mechanism of wollastonite formation during a two-step synthesis. For the synthesis, three mixtures with different chemical compositions were prepared. The first step of the synthesis was carried out under hydrothermal conditions (stirring – 50 rpm; 200 °C, 4–48 h); the second step was carried out in a furnace with a temperature range of 900–1100 °C for 1 h. The chemical composition of the primary mixture has been determined to exert a significant influence on the mineralogical composition of the hydrothermal synthesis products, since tobermorite and xonotlite dominated in the pure system, while tobermorite and cuspidine dominated in the mixture with aluminium and fluoride ions. After calcination of the precursors, pure wollastonite was obtained using a mixture of amorphous silica and calcium oxide, while in the other two mixtures, it was identified together with wollastonite cuspidine and fluormayenite or gehlenite. Dilatometric and BET analyses of the products showed that Al³⁺ and F^? ions caused densification and loss of porosity during the formation of wollastonite. The synthesised products were characterised by STA, XRD, DIL and BET analyses.     

Solution processable C60 fullerene-hydrazone dyads for optoelectronics

Ambipolar, narrow band gap (∼1.35 eV) fullerene-arylhydrazone dyads have been synthesized utilizing the Prato-Maggini-Scorrano reaction followed by the condensation with phenylhydrazines. Room temperature electron and hole mobilities, measured by the xerographic time of flight technique, exceed 10⁻⁴ cm² V⁻¹ s⁻¹ at strong electric fields. The values of ionization potential, measured by the photoemission in air method, are in the range of 5.29–5.36 eV. Good ambipolar charge transport, photosensitivity across the whole visible light region of the spectrum, and solubility in common organic solvents makes these dyads attractive materials for various optoelectronic applications.     

Automatic benthic imagery recognition using a hierarchical two-stage approach

The main objective of this work is to establish an automated classification system of seabed images. A novel two-stage approach to solving the image region classification task is presented. The first stage is based on information characterizing geometry, colour and texture of the region being analysed. Random forests and support vector machines are considered as classifiers in this work. In the second stage, additional information characterizing image regions surrounding the region being analysed is used. The reliability of decisions made in the first stage regarding the surrounding regions is taken into account when constructing a feature vector for the second stage. The proposed technique was tested in an image region recognition task including five benthic classes: red algae, sponge, sand, lithothamnium and kelp. The task was solved with the average accuracy of 90.11% using a data set consisting of 4589 image regions and the tenfold cross-validation to assess the performance. The two-stage approach allowed increasing the classification accuracy for all the five classes, more than 27% for the “difficult” to recognize “kelp” class.     

Determination of the dye penetration rate in porous aluminum oxide using Raman spectroscopy

Oxidised aluminum coatings are useful in various high technology applications to protect surfaces from negative environmental effects. In this study, aluminum discs and foils of industrial alloys were anodised in a sulphuric acid/oxalic acid electrolyte. Scanning electron microscopy was used to determine the pore diameter, distribution and surface porosity. The anodising procedure was adapted to produce near‐hollow templates on aluminium foil, onto which aqueous solutions of commercial chromium‐complexed anionic azodyes were dropped. Raman spectroscopy was used to detect the penetration of dye compounds based on the most intensive vibrational modes. Each dye was successfully monitored to assess its penetration rate and behaviour in the anodised coating. This method could be applied to characterise newly developed organic dyes for aluminum colouring.