Comparative studies of the underlying local order corresponding to different radial distribution functions of disordered materials

We have investigated characteristics of the local symmetry, such as cosine distribution of bond angles and second-order invariants of spherical harmonics for simple disordered systems with systematically varied radial distributions. Two types of variation were used at three different packing fraction values. None of the perturbations affected the basic features, but the extent of local order changed considerably. The most significant alterations were found for the case with the lowest packing fraction. The results presented in this paper may be used as guidelines for assessing the quality of agreement between radial distribution functions from different sources, such as that of simulations and diffraction experiments.     

Preparative-scale chromatography of ecdysteroids of Serratula wolffli andrae

Numerous ecdysteroids are isolated from the herb of Serratula wolffii Andrae, a cultivated plant. The isolation procedure includes a variety of low-pressure liquid chromatography, thin-layer chromatography (TLC), gel chromatography, and high-performance liquid chromatography (HPLC) methods. The progress of separation is monitored by TLC, and the final proof of purity is carried out by HPLC. The isolation process involves the removal of proteins, flavonoids, chlorophylls, other sterines, etc. The purification also includes the separation of the target ecdysteroids from each other. Isolation of the pure compounds requires 2-8 chromatographic steps. The consecutive steps are based on the different physicochemical properties of the ecdysteroids. In some cases, a special peak-cut method employing a flush of dichloromethane into the dichloromethane-isopropanol-water mobile phase is used. This flush of dichloromethane leads to an almost perfect separation of otherwise unresolved peaks. Two ecdysteroids, 25-hydroxydacryhainansterone and 14-epi-20-hydroxyecdysone, are identified as natural products for the first time. The structure-chiroptical relationships for some ecdysteroids are also discussed.     

Solid Contact Micropipette Ion Selective Electrode for Potentiometric SECM

New solid contact ammonium micropipette electrodes (ISE), well applicable in scanning electrochemical microscopy are reported. The solid contact was made of a PEDOT nanowire coated carbon fiber, lowered down close to the orifice, and dipped inside the cocktail being in the pipette tip. This configuration provided low electrical resistance and good potential stability. Submicron tip size, usual in case of micropipette ISE‐s easily can be fabricated in this way. The applicability of the electrode in SECM has been proved in SG/TC mode imaging urease enzyme active spots in urea solutions.     

Microcalorimetric Studies of the Surface Reactivity of Pollutant Gas Atmospheres on Supported SnO2 and Ga2O3 Catalysts

The surface properties of gallium oxide and tin dioxide supported on alumina or titania have been studied by adsorption microcalorimetry. The differential heats of adsorption of various pollutant adsorbates such as sulfur dioxide, nitrogen monoxide, nitrogen dioxide and also ammonia were measured on these catalytic surfaces. NH₃, SO₂, NO₂ are strongly adsorbed while NO is only physisorbed. The supported Ga₂O₃ samples show a slight decrease in acidity as probed by ammonia adsorption, compared to alumina or titania. The addition of SnO₂ decreases the number of strong acid sites but creates a few weak and medium strength acid sites on alumina and does not modify the acidity of titania. In all cases, the basicity, probed by SO₂ adsorption, is very strongly affected by the deposition of Ga₂O₃ or SnO₂. The differential heats of NO₂ adsorption remain nearly constant on all samples. The heats of adsorption are discussed as a function of the coverage and of the amount of guest oxide. This revised version was published online in August 2006 with corrections to the Cover Date.     

Auger spectrometric studies on fracture surfaces of tool steel

The fracture surfaces of tool steel K-13 (Hungarian Standard) were studied by Auger electron spectroscopy. Notched specimens of 3 × 3 mm² were fractured in UHV (6 × 10⁻⁸ Pa) with a fracturer (Riber FR 100) and studied with a CMA analyser (Riber OPC 103). With our modification the fracturer was operated within the −150°C −+230°C temperature range. The fracture surfaces were tested with a scanning electron microscope (JEOL JSM 35). The evaluation of Auger spectra was based on the PHI (PALMBERG et al.). Handbook, however the backscattering correction of Jablonski was applied in some cases. The choice of adequate fracturing temperature proved to be very important. Low temperature fracture of this steel alloy is producing very rigid transgranular fracture. The effects of sample heat treatment and of fracturing temperature as well were studied in details. The Auger spectra of fracture surfaces are strongly affected by the heat treatment of the samples. The grain boundary fracture surface of a sample austenitized at 1100°C quenched and tempered at 600°C exhibited a strong enrichment of P, correlating with the enrichment of Cr, V and Mo. The transgranular fracture surface of the same sample but without tempering corresponded to the bulk composition. In some cases and spots on the fracture surfaces, giant S or P peaks were associated with secondary phases (inclusions) on the SEM pictures.     

Harmonisation of coupled calibration curves to reduce correlated effects in the analysis of natural gas by gas chromatography

Quantitative analysis of natural gas depends on the calibration of a gas chromatograph with certified gas mixtures and the determination of a response relationship for each species by regression analysis. The uncertainty in this calibration is dominated by variations in the amount of the sample used for each analysis that are strongly correlated for all species measured in the same run. The "harmonisation" method described here minimises the influence of these correlations on the calculated calibration curves and leads to a reduction in the root-mean-square residual deviations from the fitted curve of a factor between 2 and 5. Consequently, it removes the requirement for each run in the calibration procedure to be carried out under the same external conditions, and opens the possibility that new data, measured under different environmental or instrumental conditions, can be appended to an existing calibration database.     

Persistence,Permanence and Global Stability for an n-Dimensional Nicholson System

For a Nicholson’s blowflies system with patch structure and multiple discrete delays, we analyze several features of the global asymptotic behavior of its solutions. It is shown that if the spectral bound of the community matrix is non-positive, then the population becomes extinct on each patch, whereas the total population uniformly persists if the spectral bound is positive. Explicit uniform lower and upper bounds for the asymptotic behavior of solutions are also given. When the population uniformly persists, the existence of a unique positive equilibrium is established, as well as a sharp criterion for its absolute global asymptotic stability, improving results in the recent literature. While our system is not cooperative, several sharp threshold-type results about its dynamics are proven, even when the community matrix is reducible, a case usually not treated in the literature.     

Surface Modification of Gold Nanoprisms and Their Self-Assembly with Nanospheres

Controlled surface modification of gold particles is of central importance for the preparation of functional nano-objects, which can be used both in fundamental research and in advanced photonic or nanomedicine applications. In this study, the surface modification of gold nanoprisms using different thiols, namely cysteamine, (16-mercaptohexadecyl)trimethylammonium bromide (MTAB), and α-methoxy-ω-mercapto polyethylene glycol (mPEG-SH (5000 Da)) is investigated. The aim is to prepare binary surface-modified thiol/PEG patchy gold nanoprisms, where the tips/edges and the face regions of the particles are covered by different thiol moieties. By investigating the time evolution of the prisms’ extinction spectra at different capping ligand concentration levels, the conditions to prepare such “patchy” particles are identified. While significantly faster adsorption kinetics are observed for MTAB compared to cysteamine, both molecule types can be used to prepare binary surface-modified thiol/PEG particles. Prisms modified with only MTAB or PEG and subsequently assembled with negatively charged spheres show that MTAB forms hetero-aggregates with the spheres, while PEG prevents particle attachment. For thiol (cysteamine or MTAB)/PEG binary surface-modified prisms, it is found that the efficiency of sphere attachment at the tip/side region during self-assembly is rather low, most likely due to the presence of PEG.     

Sincov’s and other functional equations and negative interest rates

Aequationes mathematicae - Investigating the future value F(K, s, t) of a capital K invested between dates s and t, the “natural” condition $$F(K,s,t)ge K$$ has lost...     

Global dynamics of an epidemiological model with age-of-infection dependent treatment rate

We revisit a previously established model for influenza transmission dynamics, in which antiviral treatment as a single containment strategy was administered within a specified window of opportunity for initiating treatment. We extend this model to a more general framework with age-of-infection dependent treatment rates. The resulting age structured model can be transformed into a closed system of delay differential equations, for which we perform a complete global stability analysis. By constructing suitable Lyapunov functions, we show that the effective reproduction number fully characterizes the possible outcomes of disease dynamics. Our results allow us to evaluate treatment strategies and examine the impact of treatment delays on the potential success of disease control.