Hyperconjugation versus back bonding in AH3−nXn species (A = Si and Ge; X = F,Cl and Br; and n = 1, 2 and 3)

In this research two competing phenomena, back bonding and hyperconjugation, have been investigated based on Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analyses for radical AH_3?nX_n species, where A = Si and Ge, and n = 1, 2 and 3. It is demonstrated in this article that both above phenomena will be occurred significantly, while back bonding is the only event in analogous compounds with carbon and hyperconjugation is rather negligible. It was also found that only one back bonding with the help of keyword $CHOOSE in NBO analysis can be found in this type of compounds with reasonable structure, while it can be sometimes detected in AH_3?nX_n without using keyword $CHOOSE. It is also shown that there is always an increase in bond length in comparison with reference molecules in mentioned species due to existing hyperconjugation, while if the central atom is carbon, we have always a decrease of bond length due to only having back bonding. Additionally, from AIM point of view, the delocalization indices for α-spin (majority spin) is more than β-spin (minority spin) in radical species for molecules without back bonding, while the situation in our compounds is quite reverse, which can be attributed to the π back bonding in the β-spin electrons.     

Electron Density Analysis of Hyperconjugation

Hyperconjugation is analyzed through the electron density of orbitals responsible for hyperconjugative interactions, which cannot be detected by means of conventional electron‐density‐based calculations. This interaction is detected through the π electron density topology, by excluding σ electron density from the total. As the presence of the hyperconjugation phenomenon in carbocation systems is well understood, several carbocations are benchmarked, and the results show that the positive carbon atom establishes a hyperconjugative critical point with the adjacent methyl group(s). Also, π localization and delocalization indices are employed to support the conclusions made by the topological analysis.     

Decomposition of deformation density into orbital components

In this research, deformation density matrix has been introduced as matrix representation of the density difference between the complex and fragments. The deformation density matrix is then diagonalized to obtain the magnitude of displaced charges as eigenvalues. Correspondingly, the eigenvectors reveal the spaces responsible for reorganization of the electrons because of the complex formation. The formalism has been applied on some CO₂ planar clusters, and the results showed that how the deformation density can be successfully separated into in‐plane and out‐of‐plane contributions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Block deformation analysis: Density matrix blocks as intramolecular deformation density

Block deformation analysis as deformation density of atomic orbitals is introduced to analyze intramolecular interactions. In this respect, density matrix blocks in terms of natural atomic orbitals are employed to find interacting and noninteracting multicenter subsystem and extract the corresponding deformation density. Eigenanalysis of this deformation density is performed to result eigenvalues and eigenorbitals as displaced charge due to the intramolecular interaction and orbital space responsible for charge reorganization, respectively, that possesses advantages of other methods, simultaneously. It is applied to several small molecules, different types of carbon allotropes including zero-, one-, and two-dimensional nanostructures, and challenging systems such as ortho-hydrogen atoms in planar biphenyl. Results highly correlate with delocalization and Wiberg bond indices and show that eigenvalues of block deformation analysis deserved to be considered as bonding index.     

Molecular Modeling of Human CCR2 Receptor within POPC Lipid Bilayer

Structural Chemistry - Chemokine receptor 2 (CCR2), a G-protein coupled receptor (GPCR), is a critical target for several inflammatory and autoimmune diseases. The main restriction on designing...     

The Eigenvalues of a Class of Elliptic Differential Operators

Consider $\left(M,g\right)$ as an $n$-dimensional compact Riemannian manifold. In this paper we are going to study a class of elliptic differential operators which appears naturally in the study of hypersurfaces with constant mean curvature and also the study of variation theory for $1$-area functional.     

A Tunable Er3+-Doped Fiber Laser by Use of an Integrated Optics Mach-Zehnder Interferometer

Wavelength tunability of an Er³⁺-doped fiber laser is reported by the use of an integrated optics Mach-Zehnder interferometer driven electro-optically. A pump laser threshold of 5 mW and a continuous tunable band from 1530 nm to 1554 nm are achieved with a drive voltage varying between 0 to +7 volts. An evaluation of the design and improvements are given based on the experimental and theoretical analysis.     

Micrometer-sized graphitic balls produced together with single-wall carbon nanohorns

We present in this report a new type of particles with micrometer-order sizes, which we called giant graphitic balls (GG balls). The GG balls are produced by CO2 laser ablation of graphite together with single-wall carbon nanohorns. They have graphitic structures whose layers tend to align parallel with the GG-ball surfaces, resulting in polygonal-like arrangements. Comparing the GG-ball structure with that of the previously reported polygonal graphite-particles, the growth mechanism of the GG ball is discussed briefly.     

A model of driver's lane-changing behaviour at an urban signalised intersection

The aim of this research is to study and develop models for driver's lane-changing behaviour in an urban area using the logistic regression method. A pilot study was conducted using a videotape recording technique to film an approach road leading to a signalised intersection in an urban road during the morning off-peak period. Inter-related coding methods were designed to describe and verify the driver's lane-changing manoeuvre. A questionnaires study to analyse the driver's background, experience, attitudes, lane-changing practices and their driving behaviour on the road was carried out in order to develop lane-changing behaviour models using the logistic regression method. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Maximum temperature analysis in a Li-ion battery pack cooled by different fluids

Journal of Thermal Analysis and Calorimetry - The use of Li-ion battery in electric vehicles is becoming extensive in the modern-day world owing to their high energy density and longer life. But...