Hydrophobicity and Charge Distribution Effects in the Formation of Bioorganoclays

Interactions of bioorganic moieties with clay minerals have attracted attention not only from the perspective of novel bioclay materials but also because they play a crucial role in our understanding of physical and chemical processes in soils. The aim of the present article is to explore the interactions responsible for the formation of a phosphatidylcholine-kaolinite bioclay by employing a series of classical molecular dynamic simulations. Detailed analysis of the structure and energies of the resulting bioclays reveals that the phosphatidylcholine molecules bind to the kaolinite surface either via their zwitterionic heads or hydrophobic aliphatic tails, depending on the kaolinite surface characteristics and the density of organic coating. The phosphatidylcholine molecules have a tendency to form irregular layers with a preferred parallel orientation of molecules with respect to the kaolinite surface. The tails exhibit varying degrees of flexibility and disorder depending on their distance from the surface and the density of surface coating. Significant differences in the binding can be spotted with respect to the two types of kaolinite basal surfaces, i.e., the hydrophobic siloxane surface, which possesses a considerable dispersion character, and the hydrophilic alumina surface, polarized by the surface hydroxyl groups.

BODIPY dimers: structure, interaction, and absorption spectrum

The object of the present study are BODIPY molecules obtained previously by Piskorz et al. (Dyes Pigm. 178:108322, 2020) for their antimicrobial activity. Structural analysis of the BODIPY dimers is presented in context of the aggregation influence on the photophysical properties. The thorough investigation of the nature of intermolecular interaction in the representative BODIPY dimers is provided together with the decomposition of the interaction energy into the components of well-defined origin according to SAPT procedure. For the model BODIPY systems the careful examination of the interaction nature for the dimer structure based on experimental crystal study as well as fully optimized is given. The tendencies observed in the model dimers are further on investigated for two pairs of BODIPY systems designed for biomedical application. The analyzed molecules are shown to maximize the mutual interaction by the optimization of the stacking dispersion contacts between the aromatic rings of the molecules, therefore producing stable dimers. The estimation of SAPT0 interaction energy components confirms the dominating dispersion character arising from mutual BODIPY core contacts. The influence of the dimerization process on the photophysical properties of the systems studied theoretically depends to the high extend on the dimerization mode and is significant for parallel and antiparallel dispersion-governed dimers.

Aluminum adsorption on graphene: Theoretical study of dispersion effects

The interaction between a single atom and graphene is an example in which the density functional theory (DFT) presents serious difficulties in giving an appropriate description of the adsorbate–substrate interaction, giving also different predictions according to the chosen approximation. The present calculations sustain that the inclusion of dispersion interactions in the framework of DFT for the Al/graphene system lead to potential energy curves of different nature according to the theoretical approach employed. The adsorption of an Al atom on the graphene surface was studied using both cluster and slab models. Cluster DFT–PBE calculations show the presence of a minimum at hollow site at an Al–graphene distance of about 2.1–2.3 Å corresponding to an exothermic state. Conversely, under B3LYP the same adsorption mode is endothermic. In comparison, our MP2 reference calculations predict the formation of two minima, both of exothermic nature, separated by an important energy barrier (about 0.2–0.4[Formula: see text]eV). The incorporation of empirical van der Walls (vdW) corrections to B3LYP changes the original behavior, giving an exothermic adsorption; furthermore, it produces a second, more external minimum. Slab calculations with PBE, and specially using the vdW-DF2 functional, predict also the formation of a minimum of very low depth at about 3.1 Å. The analysis of results obtained with cluster and slab models sustains that the bonding of the inner minima is of ionic character while that of the external ones is of dispersion character.

Оптические свойства нестехиометрического оксида кремния SiO-=SUB=-x-=/SUB=- (x<2)

The optical properties of amorphous nonstoichiometric silicon oxide (SiO_ x ) films of variable composition ( x = 0 . 62–1 . 92) formed by plasma-enhanced chemical vapor deposition are studied in the spectral range of 1 . 12–4 . 96 eV. Spectral ellipsometry showed that the refractive index dispersion character allows one to assign the formed SiO_ x films to silicon-like films, dielectrics, or intermediate-conductivity-type films depending on the content of oxygen in the gas phase during synthesis. A model of the SiO_ x structure for ab initio calculations is proposed and describes well the experimental optical spectra. Ab initio calculations of the dependences of the SiO_ x refractive index and band gap on stoichiometry parameter x are performed.

Cardinal functions of the hyperspace of convergent sequences

The symbol 𝓢c(X) denotes the hyperspace of all nontrivial convergent sequences in a Hausdorff space X. This hyperspace is endowed with the Vietoris topology. In the current paper, we compare the cellularity, the tightness, the extent, the dispersion character, the net weight, the i-weight, the π-weight, the π-character, the pseudocharacter and the Lindelöf number of 𝓢c(X) with the corresponding cardinal function of X. We also answer a question posed by the authors in a previous paper.

Improved properties and reduced metal content conductive powders for high temperature sensor applications

High temperature sensor applications have specific demands for the conductive materials used to construct devices. Traditional materials, such as platinum, palladium, and alloys impart qualities suited to their nature. However, these metals are expensive and alternative materials are generally not suited to the demands of the high temperature sensor devices. This work introduces and compares core-shell materials that impart the desirable qualities of the traditional conductive materials with improved characteristics such as thermal processability and dispersion character through engineered particulate surfaces.

Impact of Relative Humidity on Cooling Tower Plume Dispersion

The SACTI model (Seasonal Annual Cooling Tower Impact) as the environmental impact assessment of cooling tower was applied in this paper, which was used to simulate the plume characters under different kinds of relative humidity. The three kinds of relative humidity were 70%, 80% and 90% and it was analyzed that the plume character under these three kinds of relative humidity. Results showed that the plume length, plume height and plume radius will present different change trend when relative humidity changed. Additionally, the plume dispersion character in different seasons presented obviously variations and the different wind direction also play important role in prediction of cooling tower plume dispersion.

The Effect of Wind Speed on Cooling Tower Plume Dispersion

Wind speed was an important impact factor when simulating the cooling tower plume dispersion. The SACTI model was selected in this paper and this model was used to predict the plume dispersion character discharging from cooling tower under normal operation and three different kinds of wind speeds. The three kinds of wind speeds were 2 m/s, 4 m/s and 6 m/s and it was analyzed that the plume character under these three wind speeds. Results showed that the plume length, plume height and plume radius will present different change trend when wind speed changed.