On the Motion of Substance in a Channel of a Network: Extended Model and New Classes of Probability Distributions

We discuss the motion of substance in a channel containing nodes of a network. Each node of the channel can exchange substance with: (i) neighboring nodes of the channel, (ii) network nodes which do not belong to the channel, and (iii) environment of the network. The new point in this study is that we assume possibility for exchange of substance among flows of substance between nodes of the channel and: (i) nodes that belong to the network but do not belong to the channel and (ii) environment of the network. This leads to an extension of the model of motion of substance and the extended model contains previous models as particular cases. We use a discrete-time model of motion of substance and consider a stationary regime of motion of substance in a channel containing a finite number of nodes. As results of the study, we obtain a class of probability distributions connected to the amount of substance in nodes of the channel. We prove that the obtained class of distributions contains all truncated discrete probability distributions of discrete random variable ω which can take values 0,1,⋯,N. Theory for the case of a channel containing infinite number of nodes is presented in Appendix A. The continuous version of the discussed discrete probability distributions is described in Appendix B. The discussed extended model and obtained results can be used for the study of phenomena that can be modeled by flows in networks: motion of resources, traffic flows, motion of migrants, etc.     

Dynamic control of volume phase transitions of poly(N‐isopropylacrylamide) based microgels in water using hydrazide‐aldehyde chemistry

We demonstrate that the volume phase transition temperature (VPTT) of copolymer microgel particles made from N‐isopropylacrylamide (NIPAm) and methacryloyl hydrazide (MH) can be tailored in a reversible manner upon the reaction of the hydrazide functional groups with aldehydes. The microgels were synthesized by precipitation polymerization in water. Due to the water‐soluble nature of the MH monomer, the VPTT at which the microgel particles contract shifts to higher values by increasing the incorporated amounts of methacryloyl hydrazide from 0 to 5.0 mol %. The VPTT of the copolymer microgel dispersions in water can be fine‐tuned upon addition of hydrophobic/hydrophilic aldehydes, which react with the hydrazide moiety to produce the hydrazone analogue. This hydrazone formation is reversible, which allows for flexible, dynamic control of the thermo‐responsive behavior of the microgels. The ability to “switch” the VPTT was demonstrated by exposing hydrophilic streptomycin sulfate salt incubated microgel particles to an excess of a hydrophobic aldehyde, that is benzaldehyde. The temperature at which these microgels contracted in size upon heating was markedly lowered in these aldehyde exchange experiments. Transformation into benzaldehyde hydrazone derivatives led to assembly of the microgel particles into small colloidal clusters at elevated temperatures. This control of supracolloidal cluster formation was also demonstrated with polystyrene particles which had a hydrazide functionalised microgel shell. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1745–1754     

Formation of polyketone particle structure by hexafluoroisopropanol solvent evaporation and effects of plasticizer addition

Few solvents are capable of dissolving polyketones (PKs). 1,1,1,3,3,3‐Hexafluoro‐2‐propanol (hexafluoroisopropanol, HFIP) is a better solvent than trifluoroethanol and m‐cresol. When HFIP was evaporated from a PK/HFIP solution, a porous cast‐film with a microparticle structure was formed because the isotactic PKs adopted a helical conformation, and convection during evaporation of the high polarity and low‐boiling‐point HFIP caused aggregation and rolling of the polymer molecules. The addition of plasticizer suppressed particle formation, improving the surface structure and mechanical properties of the film. In particular, the dielectric properties of the film improved significantly. This will enable PKs, which are rigid insulating materials, to be used as dielectric materials, broadening their range of applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 887–892     

Nuclear Versus Side-Chain Bromination of 4-Methoxy Toluene by an Electrochemical Method

The electrochemical bromination of 4-methoxy toluene by two-phase electrolysis yields 3-bromo 4-methoxy toluene at first, which subsequently undergoes side-chain bromination to give 3-bromo 4-methoxy benzyl bromide as a final product in 86% yield. The two-phase electrolysis consists of 25–50% NaBr as aqueous electrolyte and CHCl₃ containing aromatic compound as organic phase. The reaction temperature is maintained at 10–25 °C. The probable orientation of bromine atom in an alkyl aromatic compound (nuclear versus side chain) is explained from the experimental result.     

Design of pincer complexes based on (methylsulfanyl)acetic/propionic acid amides with ancillary S‐ and N‐donors as potential catalysts and cytotoxic agents

Pincer complexes featuring readily tunable tridentate ligand frameworks comprise one of the most actively studied classes of organometallic and metal–organic compounds and find extensive use in catalysis, organic synthesis, materials science, and other fields of chemistry and allied disciplines. Currently growing attention is devoted to non‐classical ligand scaffolds, such as functionalized carboxamides, which offer multiple options for directed structural modifications. In this study, the reactions of (methylsulfanyl)acetyl and propanoyl chlorides with 2‐(aminomethyl)pyridine, 2‐(2‐aminoethyl)pyridine, 8‐aminoquinoline and 2‐(diphenylthiophosphoryl)aniline afford a series of new pincer‐type ligands based on functionalized carboxamides. The ligands obtained readily undergo direct cyclopalladation under the action of PdCl₂(NCPh)₂ in dichloromethane at room temperature, resulting in Pd(II) pincer complexes with N,N,S‐ and S,N,S‐donor sets. Importantly, some of the cyclopalladated derivatives can also be produced efficiently under solvent‐free conditions according to the approach recently developed by our group. The complexes obtained have been tested for cytotoxicity against several human cancer cell lines and catalytic activity in the model Suzuki reaction. The results have been compared to those for the related Pd(II) pincer complexes to define the main structure–activity relationships and to outline the most promising structures for further investigations.     

Development and validation of a simple solid‐phase extraction method coupled with liquid chromatography–triple quadrupole tandem mass spectrometry for simultaneous determination of lincomycin,tylosin A and tylosin B in royal jelly

We have developed an analytical method for the determination of lincomycin, tylosin A and tylosin B residues in royal jelly using liquid chromatography–triple quadrupole tandem mass spectrometry analysis. For extraction and purification, we employed 1% trifluoroacetic acid and 0.1 m Na₂EDTA solutions along with an Oasis HLB cartridge. The target antibiotics were well separated in a Kinetex EVO C₁₈ reversed‐phase analytical column using a combination of 0.1% formate acid in ultrapure water (A) and acetonitrile (B) as the mobile phase. Good linearity was achieved over the tested concentration range (5–50 μg/kg) in matrix‐matched standard calibration. The coefficients of determination (R²) were 0.9933, 0.9933 and 0.996, for tylosin A, tylosin B and lincomycin, respectively. Fortified royal jelly spiked with three different concentrations of the tested antibiotics (5, 10 and 20 μg/kg) yielded recoveries in the range 80.94–109.26% with relative standard deviations ≤4%. The proposed method was applied to monitor 11 brand of royal jelly collected from domestic markets and an imported brand from New Zealand; all the samples tested negative for lincomycin, tylosin A and tylosin B residues. In conclusion, 1% trifluoroacetic acid and 0.1 m Na₂EDTA aqueous solvents combined with solid‐phase extraction could effectively complete the sample preparation process for royal jelly before analysis. The developed approach can be applied for a routine analysis of lincomycin, tylosin A and tylosin B residues in royal jelly.     

A higher resolution edge‐based finite volume method for the simulation of the oil–water displacement in heterogeneous and anisotropic porous media using a modified IMPES method

In this article, we present a higher‐order finite volume method with a ‘Modified Implicit Pressure Explicit Saturation’ (MIMPES) formulation to model the 2D incompressible and immiscible two‐phase flow of oil and water in heterogeneous and anisotropic porous media. We used a median‐dual vertex‐centered finite volume method with an edge‐based data structure to discretize both, the elliptic pressure and the hyperbolic saturation equations. In the classical IMPES approach, first, the pressure equation is solved implicitly from an initial saturation distribution; then, the velocity field is computed explicitly from the pressure field, and finally, the saturation equation is solved explicitly. This saturation field is then used to re‐compute the pressure field, and the process follows until the end of the simulation is reached. Because of the explicit solution of the saturation equation, severe time restrictions are imposed on the simulation. In order to circumvent this problem, an edge‐based implementation of the MIMPES method of Hurtado and co‐workers was developed. In the MIMPES approach, the pressure equation is solved, and the velocity field is computed less frequently than the saturation field, using the fact that, usually, the velocity field varies slowly throughout the simulation. The solution of the pressure equation is performed using a modification of Crumpton's two‐step approach, which was designed to handle material discontinuity properly. The saturation equation is solved explicitly using an edge‐based implementation of a modified second‐order monotonic upstream scheme for conservation laws type method. Some examples are presented in order to validate the proposed formulation. Our results match quite well with others found in literature. Copyright © 2016 John Wiley & Sons, Ltd.     

Phase field crystal study of the crystallization modes within the two-phase region

Using the phase field crystal approach, the crystallization process within the liquid–solid coexistence region is investigated for a square lattice on an atomic scale. Two competing growth modes, i.e., the diffusion-controlled growth through long-range atomic migration in liquid and the diffusionless growth through local atom rearrangement, which give rise to two completely different crystallization behaviors, are compared. In the diffusion-controlled regime, the interface migrates in a layerwise manner, leading to a gradual change of crystal morphology from truncated square to four-fold symmetric dendrite with the increase of driving force. For the diffusionless growth mode, a single crystal with no significant density change occupies the whole system at a faster rate while exhibiting a small growth anisotropy. The competition between these two modes is also discussed from the key input of the phase field crystal model: the correlation function.     

Preparation of hydrophilic poly(vinylidene fluoride) membrane by in-situ grafting of N-vinyl pyrrolidone via a reactive vapor induced phase separation procedure

Increasing hydrophilicity of hydrophobic membrane is one of the strategies to improve its antifouling performance. Herein we report a procedure of reactive-vapor induced phase separation to prepare an N-vinyl pyrrolidone (NVP) modified poly(vinylidene fluoride) (PVDF) membrane to improve its hydrophilicity. PVDF solution containing NVP monomer was cast in ammonia water vapor atmosphere to prepare the modified membrane. During the process, PVDF was dehydrofluorinated by the reactive vapor of ammonia water to generate double bond of FC═CH, and then NVP was grafted. The degree of grafting modification and the microstructure evolution of the membrane were studied by adjusting the amount of NVP addition. A possible mechanism of membrane formation from crystallization gelling to non-crystallization gelling has been proposed to understand the morphology change from nodular sphere to bi-continuous microstructure with fibril matrix. It has been found that rising the degree of modification has changed the polymorph of PVDF from β to α crystalline phase, as well as turned the hydrophobic PVDF membrane into hydrophilic. Moreover, the modified membrane displayed obvious reduction in bovine serum albumin adsorption, suggesting improvement in anti-fouling performance. Therefore, our work provides an easy strategy to prepare hydrophilic PVDF membrane, which may have promising potential applications.     

Impedance Response of a Thin Film on an Electrode: Deciphering the Influence of the Double Layer Capacitance

The different contributions of the interfacial capacitance are identified in the case of passive materials or thin protective coatings deposited on the electrode surface. The method is based on a graphical analysis of the EIS results to determine both the passive-film capacitance in the high-frequency domain and the double-layer capacitance in the low-frequency domain. The proposed analysis is shown to be independent of the physicochemical origins of the frequency dispersion of the interfacial capacitances which results, from an analysis point of view of the experimental results, in the use of a constant-phase element However, for a correct evaluation of the thin-film properties such as its thickness, the high-frequency data must be corrected for the double-layer contribution. In particular, it is shown that if the double-layer capacitance gives a frequency-dispersed response, it is necessary to correct the high-frequency part for the double-layer constant-phase elements. This is first demonstrated on synthetic data and then used for the determination of the thickness of thin oxide film formed on Al in neutral pH solution.