Families of Line-Graphs and Their Quantization

Any directed graph G with N vertices and J edges has an associated line-graph L(G) where the J edges form the vertices of L(G). We show that the non-zero eigenvalues of the adjacency matrices are the same for all graphs of such a family L ⁿ (G). We give necessary and sufficient conditions for a line-graph to be quantisable and demonstrate that the spectra of associated quantum propagators follow the predictions of random matrices under very general conditions. Line-graphs may therefore serve as models to study the semiclassical limit (of large matrix size) of a quantum dynamics on graphs with fixed classical behaviour.     

NMR frequency and magnetic dipole moment of (3)He nucleus

We present new gas-phase NMR spectra which relate the resonance frequency of (3)He nucleus to the resonance frequency of the proton in tetramethylsilane (TMS). We discuss the dependence of (3)He resonance frequency on the density of the solvent gas, and we consider in detail the absolute shielding scales of both nuclei. Finally, we analyse the accuracy of the results, using the relationship between the resonance frequencies, absolute shielding constants and magnetic dipole moments of (1)H and (3)He nuclei.     

Thermodynamic properties of a diluted Heisenberg ferromagnet with interaction anisotropy—Magnetocaloric point of view

The thermodynamics of a site-diluted ferromagnetic Heisenberg model for spin S=1/2 with interaction anisotropy in spin space is investigated. The study is aimed at presenting the magnetocaloric properties of such a model, including the entropy and temperature changes in magnetization/demagnetization processes, generalized Grüneisen ratio as well as the quantities characterizing the efficiency of magnetic cooling cycles. The results are obtained using pair approximation (PA) method and extensively compared with the molecular field approximation (MFA) calculations. The importance of interaction anisotropy and site-dilution is discussed. The inadequacy of the MFA approach (even on the qualitative level) is found for selected quantities, while PA provides the results which are consistent with the experimentally observed behavior.     

TiO2 thick films supported on reticulated macroporous Al2O3 foams and their photoactivity in phenol mineralization

TiO₂ thick films deposited on macroporous reticulated Al₂O₃ foams with pore size of 10 ppi and 15 ppi were prepared using dip coating from slurries of Aeroxide^® P25 nanopowder and precipitated titania. All prepared films have sufficiently good adhesion to the surface of the substrate also in case of strongly cracked films. No measurable release of deposited TiO₂ after repeated photocatalytic cycles was observed. The photocatalytic activity was characterized as the rate of mineralization of aqueous phenol solution under irradiation of UVA light by TOC technique. The best activity was obtained with Aeroxide^® P25 coated Al₂O₃ foam with the pore size of 10 ppi, annealed at 600 °C. The optimal annealing temperature for preparation of films from precipitated titania could be determined at 700 °C. Films prepared by sol-gel deposition technique were considerably thinner compared to coatings made of suspensions and their photocatalytic activity was significantly smaller.     

Transient Spark Discharge Generated in Various N2/O2 Gas Mixtures: Reactive Species in the Gas and Water and Their Antibacterial Effects

Reactive species generated in the gas and in water by cold air plasma of the transient spark discharge in various N₂/O₂ gas mixtures (including pure N₂ and pure O₂) have been examined. The discharge was operated without/with circulated water driven down the inclined grounded electrode. Without water, NO and NO₂ are typically produced with maximum concentrations at 50% O₂. N₂O was also present for low O₂ contents (up to 20%), while O₃ was generated only in pure O₂. With water, gaseous NO and NO₂ concentrations were lower, N₂O was completely suppressed and HNO₂ increased; and O₃ was lowered in O₂ gas. All species production decreased with the gas flow rate increasing from 0.5 to 2.2 L/min. Liquid phase species (H₂O₂, NO₂￣, NO₃￣, ^·OH) were detected in plasma treated water. H₂O₂ reached the highest concentrations in pure N₂ and O₂. On the other hand, nitrites NO₂￣ and nitrates NO₃￣ peaked between 20 and 80% O₂ and were associated with pH reduction. The concentrations of all species increased with the plasma treatment time. Aqueous ^·OH radicals were analyzed by terephthalic acid fluorescence and their concentration correlated with H₂O₂. The antibacterial efficacy of the transient spark on bacteria in water increased with water treatment time and was found the strongest in the air-like mixture thanks to the peroxynitrite formation. Yet, significant antibacterial effects were found even in pure N₂ and in pure O₂ most likely due to high ^·OH radical concentrations. Controlling the N₂/O₂ ratio in the gas mixture, gas flow rate, and water treatment time enables tuning the antibacterial efficacy.

     

A New Protocol for Ash Wood Modification: Synthesis of Hydrophobic and Antibacterial Brushes from the Wood Surface

The article presents the modification of ash wood via surface initiated activators regenerated by electron transfer atom transfer radical polymerization mediated by elemental silver (Ag⁰ SI-ARGET ATRP) at a diminished catalyst concentration. Ash wood is functionalized with poly(methyl methacrylate) (PMMA) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) to yield wood grafted with PMMA-b-PDMAEMA-Br copolymers with hydrophobic and antibacterial properties. Fourier transform infrared (FT-IR) spectroscopy confirmed the covalent incorporation of functional ATRP initiation sites and polymer chains into the wood structure. The polymerization kinetics was followed by the analysis of the polymer grown in solution from the sacrificial initiator by proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC). The polymer layer covalently attached to the wood surface was observed by scanning electron microscopy (SEM). The hydrophobic properties of hybrid materials were confirmed by water contact angle measurements. Water and sodium chloride salt aqueous solution uptake tests confirmed a significant improvement in resistance to the absorption of wood samples after modification with polymers. Antibacterial tests revealed that wood-QPDMAEMA-Br, as well as wood-PMMA-b-QPDMAEMA-Br, exhibited higher antibacterial activity against Gram-positive bacteria (Staphylococcus aureus) in comparison with Gram-negative bacteria (Escherichia coli). The paper presents an economic concept with ecological aspects of improving wood properties, which gives great opportunities to use the proposed approach in the production of functional hybrid materials for industry and high quality sports equipment, and in furniture production.     

Epidemiological impact of waning immunization on a vaccinated population

This is an epidemiological SIRV model based study that is designed to analyze the impact of vaccination in containing infection spread, in a 4-tiered population compartment comprised of susceptible, infected, recovered and vaccinated agents. While many models assume a lifelong protection through vaccination, we focus on the impact of waning immunization due to conversion of vaccinated and recovered agents back to susceptible ones. Two asymptotic states exist, the “disease-free equilibrium” and the “endemic equilibrium” and we express the transitions between these states as function of the vaccination and conversion rates and using the basic reproduction number. We find that the vaccination of newborns and adults have different consequences on controlling an epidemic. Also, a decaying disease protection within the recovered sub-population is not sufficient to trigger an epidemic at the linear level. We perform simulations for a parameter set mimicking a disease with waning immunization like pertussis. For a diffusively coupled population, a transition to the endemic state can proceed via the propagation of a traveling infection wave, described successfully within a Fisher-Kolmogorov framework.     

Study of radon exhalation from the soil

The influence of meteorological parameters on radon exhalation rate was analyzed. The analyses show a significant influence of precipitation on radon exhalation rate. The highest exhalation rate was found during dry periods and the lowest during the periods of strong precipitation. We also tested two different types of detectors for the measurement of radon exhalation rate—the ionization chamber (AlphaGUARD) and the scintillation chamber of Lucas type. The exhalation rates measured by these detectors were in a good agreement. Likewise, there was an agreement in radon exhalation rates determined from short term and long term increases in radon activity concentration.