Numerical study of wave overtopping of a seawall supported by porous structures

This paper presents a VOF-based two-phase flow model for the simulation of wave interactions with seawall supported by a porous terrace. Firstly, the model was verified against laboratory data in a simple case for wave overtopping of a vertical wall. Comparison of computed and measured wave properties showed reasonably good agreement. The model was then applied to study the interactions of waves and a seawall protected by porous structures with a permeable terrace. The application results showed that the overtopping rate was strongly related to the energy dissipation through the drag force; the porous reef and terrace were very effective to produce a low crest type seawall. It is concluded that there exist two optimum values of porosity of the submerged reef, about of 0.25 and 0.7, that give minimum overtopping rates. Whereas, there is an effective range of porosity of the permeable terrace varying from 0.4 to 0.65 for significantly reducing the overtopping rate. The verification results confirm that the VOF-based two-phase flow model is sufficient robust to simulate the wave overtopping of coastal structures with reasonable accuracy.     

Chiral quaternary phosphonium salts: a new class of organocatalysts

Phase-transfer catalysis has widely been used as a prime synthetic tool for both laboratory and industrial processes. During the last twenty years, asymmetric phase-transfer catalysis using chiral organocatalysts has attracted widespread interest. However, the scope of chiral phase-transfer catalysis has been limited mostly to the quaternary ammonium salts. As an emerging area, the recent developments in the application of quaternary phosphonium salts as chiral phase-transfer catalysts are discussed in this article.     

Cyclotron-resonance line-width due to electron-LO-phonon interaction in cylindrical quantum wires

The absorption power due to the electron-LO-phonon interaction in a cylindrical quantum wire (CQW) in the presence of a magnetic field is calculated. The dependence of absorption power on the photon energy is computationally calculated and graphically plotted for a specific CQW. From graphs of the absorption power, we determine cyclotron-resonance line-width (CRLW) as profiles of the curves. The numerical results show that the CRLW increases with increasing of the temperature and magnetic field, and CRLW decreases with increasing of the wire’s radius. The present results are in qualitative agreement with the existing theoretical and experimental results.     

Sulfur-functionalized N-heterocyclic carbene complexes of Pd(II): syntheses, structures and catalytic activities

N-heterocyclic carbenes (NHCs) can be easily modified by introducing functional groups at the nitrogen atoms, which leads to versatile coordination chemistry as well as diverse catalytic applications of the resulting complexes. This article summarizes our contributions to the field of NHCs bearing different types of sulfur functions, i.e., thioether, sulfoxide, thiophene, and thiolato. The experimental evidence for the truly hemilabile coordination behavior of a Pd(II) thioether-NHC complex has been reported as well. In addition, complexes bearing rigid CSC-pincer ligands have been synthesized and the reasons for pincer versus pseudo-pincer formation investigated. Incorporation of the electron-rich thiolato function resulted in the isolation of structurally diverse complexes. The catalytic activities of selected complexes have been tested in Suzuki-Miyaura, Mizoroki-Heck and hydroamination reactions.     

Large time behavior of weakly coupled systems of first-order Hamilton–Jacobi equations

We show a large time behavior result for class of weakly coupled systems of first-order Hamilton–Jacobi equations in the periodic setting. We use a PDE approach to extend the convergence result proved by Namah and Roquejoffre (Commun. Partial. Differ. Equ. 24(5–6):883–893, 1999) in the scalar case. Our proof is based on new comparison, existence and regularity results for systems. An interpretation of the solution of the system in terms of an optimal control problem with switching is given.     

CSC-pincer versus pseudo-pincer complexes of palladium(II): a comparative study on complexation and catalytic activities of NHC complexes

Three thioether bridged diimidazolium dibromides with different steric and electronic properties have been synthesized as precursors to carbene-based CSC pincer ligands. Palladation afforded CSC Pd(II) pincer complexes for bulky and electron rich ligand systems, whereas the least donating ligand led to the formation of a pseudo-pincer complex. All complexes have been fully characterized by multinuclei NMR spectroscopies, ESI mass spectrometry and X-ray diffraction analysis. The catalytic activities of pincer versus pseudo-pincer complexes have been compared in the intermolecular hydroamination of alkynes with anilines as well.     

Straightforward synthesis of 1-alkyl-2-(trifluoromethyl)aziridines starting from 1,1,1-trifluoroacetone

An efficient and straightforward approach towards the synthesis of 1-alkyl-2-(trifluoromethyl)aziridines starting from 1,1,1-trifluoroacetone via imination, α-chlorination, hydride reduction and ring closure was developed. In addition, novel primary β-iodo amines were obtained by regioselective ring opening of these 2-(trifluoromethyl)aziridines using alkyl iodides, and their synthetic potential was demonstrated by converting them into novel α-CF(3)-β-phenylethylamines upon treatment with lithium diphenylcuprate.     

Formation and hydrogen release of hydrazine bisborane: transfer vs. attachment of a borane

The reactivity of hydrazine in the presence of diborane has been investigated using ab initio quantum chemical computations (MP2 and CCSD(T) methods with the aug-cc-pVTZ basis set). Portions of the relevant potential energy surface were constructed to probe the formation mechanism of the hydrazine diborane (BH(3)BH(3)NH(2)NH(2)) and hydrazine bisborane (BH(3)NH(2)NH(2)BH(3)). The differences between both adducts are established. The release of hydrogen molecules from hydrazine bisborane adducts has also been characterized. Our results suggest that the BH(3)NH(2)NH(2)BH(3) adduct, which has been prepared experimentally, is formed from the starting reactants hydrazine + diborane. The observed adduct is produced by a transfer of a BH(3) group from BH(3)BH(3)NH(2)NH(2) rather than by the direct attachment of a separate BH(3) group, generated by predissociation of diborane, to BH(3)NH(2)NH(2).     

The Number of Occurrences of a Fixed Spread among n Directions in Vector Spaces over Finite Fields

We study a finite analog of a problem of Erd?s, Hickerson and Pach on the maximum number of occurrences of a fixed angle among n directions in three-dimensional spaces.