Controllable Goos-Hänchen shift in graphene triangular double barrier

We study the Goos-Hänchen (GH) shifts for Dirac fermions in graphene scattered by a triangular double barrier potential. The massless Dirac-like equation was used to describe the scattered fermions by such potential configuration. Our results show that the GH shifts is affected by the geometrical structure of the double barrier. In particular the GH shifts change sign at the transmission zero energies and exhibit enhanced peaks at each bound state associated with the double barrier when the incident angle is less than the critical angle associated with total reflection.     

The lion and man problem revisited

A pursuerP, whose speed is bounded by 1, wants to get closer to an evaderE, whose speed is bounded by >1.P wants to reduce his distancePE fromE below the capture radius . Both players are confined to a circular arena. This problem is equivalent to a problem discussed by Flynn, who characterized and gave numerical bounds to the least upper boundd* on the values ofPE thatE can maintain. He used direct methods and did not use Isaacs' theory.We solve our problem relying on the theory of singular surfaces in differential games. We construct and investigate barriers of the game of kind, and we replace Flynn's bounds ond* by analytical (exact) values for various speeds .The support of the TW Department of THT, Enschede, Holland, is gratefully acknowledged.     

Ab initio study of the ground state and conformational stability of peroxyacetyl nitrate in internal rotation about the peroxide bond

The molecular and electronic structure of the ground state of peroxyacetyl nitrate (PAN) was calculated by the unrestricted Hartree-Fock-Roothaan method with the use of the standard 3–21G and 6–31G basis set. The potential curve of the internal rotation about the peroxide bond of PAN was calculated with the 6–31G basis set. The curve contains two maxima. The ground state of PAN is characterized by a structure in which groups of atoms adjacent to the peroxide bond lie in planes that are perpendicular to each other (the dihedral angle ϱ(COON) is 89.9°). The calculated barriers to rotation are 19.6 and 66.8 kJ mol⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 600–604, April, 1998.     

Barriers to Internal Rotation and Conformational Behaviour of the MESO and D,L Isomers of Pt(II) Complexes with Antitumour Activity

Abstract

The conformational behaviour of a series of ring substituted (ortho-Cl, F and meta or para OH) Pt(II) complexes of general formula [(1,2-hydroxyphenyl)ethylenediamine]PtL₂ [L ? Cl, 1] has been studied by molecular mechanics (MM) methods. Preferred orientations of the phenyl rings, which are important for the complexes′ biological activity, were obtained by calculations of rotational energies about C_sp3?C_ar bonds for all theoretically possible isomers and conformers, meso-λ (R,S/S,R-λ), meso-δ (R,S/S,R-δ), d,l-δ (S,S/R,R-λ) and d,l-λ (S,S/R, R-δ). The influence of the ring substituents and the conformation type on the positions of the energy minima and barriers to rotations about C_sp3?C_ar and C_ar-O(H) bonds were investigated in detail. Theoretical predictions were compared with the experimental results where appropriate.     

Further studies on the rotational barriers of Carbamates. An NMR and DFT analysis of the solvent effect for Cyclohexyl N,N-dimethylcarbamate

The solvent effect on the Gibbs energy of activation for rotation around the (C=O)–N bond in cyclohexyl N,N-dimethylcarbamate was investigated by dynamic NMR spectroscopy and density-functional theory at the B3LYP/6-311+G^** level. The experimental barriers were about 15 kcal mol⁻¹ with no appreciable variation when the solvent polarity was changed. A reaction field model was applied to theoretically mediate the solvent effect and the results were comparable to the experimental data. An analysis, based on the Onsager solvation theory, showed that the solvent effect on rotational barriers can be understood employing the total molecular dipole moment, the difference between the dipole moments of the ground and the transition state structures, or both, as appropriate.     

Comfortable, flexible upholstery fire barriers on base of bast, wool and thermostable fibres

The paper presents elastic barrier materials developed at the INF which play a role of filling and fire barrier material at the same time in upholstery furniture, reducing the development and spread of fire on flammable materials. The presented results of flammability and biophysical tests confirm the comfort of products.The developed barrier materials use natural fibres (wool, flax FR) characterized by good air permeability, hygroscopicity, moisture transport, elimination of electrostatic charges and have effect on climate of interiors also when blended with thermostable fibres such as Polyacrylate. These flexible structures based on blend of natural fibres and thermostable fibres with at least two barrier effects i.e. durable resistance to fire, thermal insulation, control of electrostatic phenomena.     

Conformations and rotational barriers of 2,2′‐bithiazole and 4,4′‐dimethyl‐2,2′‐bithiazole semiemperical,ab initio,and density functional theory calculations

Conformational properties of 2,2′‐bithiazole and 4,4′‐dimethyl‐2,2′‐ bithiazole have been studied by using AM1 and PM3 semiemperical methods and ab initio HF/6‐311+G* and B3LYP/6‐311+G* calculations. All methods agree that the planar s‐trans conformation is the global minimum and the perpendicular conformation is the transition state. Additional local minima were found using the Hartree–Fock (HF) and B3LYP levels for 2,2′‐bithiazole while for 4,4′‐dimethyl derivative the minima was located only at the MP2//B3LYP level. The barrier heights for rotation are 1.72, 7.69, and 7.88 kcal/mol at the PM3, HF, and B3LYP levels, respectively, and methyl substitution did not affect appreciably this value. Fourier expansion terms and bond orders were used to explain the origins of the rotational barrier in terms of π conjugation, electrostatic interaction, and steric effects, which represent the main factors in the shape of the rotational barrier. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 367–377, 2000     

Effects of Halogen Substitution on Naphthazarin Tautomerism in the Ground and Excited States

5,8-Hihydroxyl-1,4-naphthazarin was taken as a model compound to explore the effect of halogen substitution on intramolecular proton transfer process. Calculations indicate that the substitution in the R2- and R4-positions far away from the active region has much weaker influence on the IPT process than that in the R1-and R3-positions. IPT barriers for substitution in the R1-position are higher than that of parent molecule. However, it is quite reverse for substitution in the R3-position. The IPT process is a proton transfer process coupled with charge separation and coulombic interaction would be dominant during this process. As for naphthazarin, halogen substitution would decrease the quantum yields of O2 but increase those of 1O2.