Nanolayers of selected porphyrin and phthalocyanine dyes on solid substrates studied by electronic absorption and IR reflection–absorption spectroscopy

Electronic absorption and IR reflection–absorption spectra in non-polarized and in polarized light for lead porphyrin as well as magnesium and lead phthalocyanine dyes when deposited in the form of Langmuir–Blodgett (LB) nanolayers on solid inorganic surfaces (quartz, semiconductor and metal) were measured. Some IR bands of the Langmuir–Blodgett dye layers’ spectra show frequency shifts and changes in the relative intensities as well as in half widths when compared with the vibrational features of powdered dyes dispersed in KBr pellets, which were used as references. The FT-IR spectroscopic examination of the Langmuir–Blodgett layers allowed to estimate electron redistribution at the interface between dye layer and solid substrates. The Langmuir–Blodgett films of different thicknesses (3, 5, 10 layers) were studied at various angles of IR beam incidence and different light polarizations. The most spectacular results were obtained for the grazing incidence (80°) and films of 5 layers for dyes on the Au substrate. The IR spectroscopy was supported with electronic absorption studies (UV–vis) to follow interaction at interface between the dye layers and the substrates as well as to evaluate linear dichroism and to determine arrangement of molecules in the Langmuir–Blodgett films. Molecular arrangement in the Langmuir–Blodgett layers was discussed. It was shown that the dye molecular planes are rather randomly oriented in the Langmuir–Blodgett films with a tendency that the Q_y and Q_x transition moments in the phthalocyanine macroring are slightly directed along the y-axis (Langmuir–Blodgett dipping direction) and the x-axis direction, respectively.     

Non-vanishing of the twisted cohomology on the complement of hypersurfaces

Generically, the cohomology with coefficients in a local system of rank one on the complement in of the union of a finite number of hypersurfaces vanishes except in the highest dimension. We study the non-generic case, in which the cohomology in other dimensions does not vanish. When the hypersurfaces are hyperplanes, many examples of this kind are known. In this paper, we consider the case in which the hypersurfaces need not be hyperplanes. We prove that the hypersurfaces given by some particular linear systems have non-vanishing local system cohomologies.

     

Stabilization of hexagonal close-packed metallic nickel for alumina-supported systems prepared from Ni(II) glycinate

The decomposition in flowing argon of the neutral complex [Ni^II(glycinate)₂(H₂O)₂] leads to a mixture of face-centered cubic (fcc) and hexagonal close-packed (hcp) metallic nickel. The latter is the main phase when the Ni(II) complex is supported on alumina. Unlike most hexagonal Ni phases described earlier, and similar to hexagonal Ni₃C, the unit cell parameters (a=0.2493 and ) lead to Ni-Ni distances equal to those encountered in fcc Ni. TEM shows that the nanoparticles are protected by graphite layers, whose elimination by heating in hydrogen results in transformation to the fcc phase and crystal growth. Magnetic measurements provide evidence of the coexistence of superparamagnetic and ferromagnetic nanoparticles. This result is in line with the broad size distribution observed by TEM and is interpreted on the basis of the metallic character of hcp Ni particles.     

Crystal structure of an ammonium thiocyanate complex of 18–crown–6

The title compound (C₁₃H₃₀N₂O₇S) has been determined from three‐dimensional X‐ray diffraction data. The crystals are monoclinic, a = 22.654(8) Å, b = 8.652(4) Å, c = 23.925(9) Å, β = 123.880(9)°, V = 3893(3) ų, Z = 8, D_calc = 1.192 g/cm³, space group C2/c. The structure was solved by direct methods and refined by full‐matrix least squares method (R = 0.051). The ammonium cation is displaced by 1.08 Å from the mean plane of the ligand causing hydrogen bonding with the macrocyclic O atoms in a perching arrangement. The thiocyanate anion forms an extended hydrogen bonded chain with the cation via the occluded water molecule. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Distance-Regular Graphs of Valency Four

Let W be a Coxeter group acting as a matrix group by way of the dual of the geometric representation. Let L be the lattice of intersections of all reflecting hyperplanes associated with the reflections in this representation. We show that L is isomorphic to the lattice consisting of all parabolic subgroups of W. We use this correspondence to find all W for which L is supersolvable. In particular, we show that the only infinite Coxeter group for which L is supersolvable is the infinite dihedral group. Also, we show how this isomorphism gives an embedding of L into the partition lattice whenever W is of type An, Bn or Dn. In addition, we give several results concerning non-broken circuit bases (NBC bases) when W is finite. We show that L is supersolvable if and only if all NBC bases are obtainable by a certain specific combinatorial procedure, and we use the lattice of parabolic subgroups to identify a natural subcollection of the collection of all NBC bases.     

An improved technique for solving two‐dimensional shallow water problems

A numerical model for solving the 2D shallow water equations is proposed herewith. This model is based on a finite volume technique in a generalized co‐ordinate system, coupled with a semi‐implicit splitting algorithm in which a Helmholtz equation is used for the surface elevation. Several benchmark problems have proven the good accuracy of this method in complex geometries. Nevertheless, several numerical perturbations were noted in the surface elevation. After finding the origin, a new numerical technique is suggested, to avoid these perturbations. Several severe tests are proposed to validate this technique. Copyright © 1999 John Wiley & Sons, Ltd.     

Effect of cylinder electrode arrangement on the ionic wind properties of needle–cylinder electrodes

Needle–cylinder electrodes designed to generate ionic wind have been explored experimentally. The increase of the gap distance between needle and cylinder from 4 mm to 16 mm cause an increase of the ionic wind velocity from 1.1 m/s to 2.46 m/s. The opposite behavior was observed when this distance lengthened from 18 to 28 mm. At the same time, a step voltage was used to increase the ionic wind velocity up to 3.6 m/s. These results indicate that electrode arrangement is very important to maximize the ionic wind velocity.     

Thermal optics distortion of face pump slab lasers with two pump arrangements

Two pump arrangements, which are the slow axis and the fast axis of LD stacks parallel to the length direction of the slab, are simulated. From the results the optical intensity along the width of the slab is Gaussian and super-Gaussian distribution, respectively. Then based on heat conduction equation and conductively cooling boundary condition, the calculation of the distribution of absorbed pump power, temperature and thermal stress with the tool of finite element analyses is performed. From these results we numerically calculate the thermal focusing in zigzag and perpendicular zigzag planes using the ray tracing method running at low and high repetition rates. It is found that the temperature distribution along width has a significant impact on the thermal stress and thermal optics distortion, especially running at high repetition rate or high average power. Finally, the conclusion was that the pump arrangement with the fast axis of LD stacks parallel to the length direction of the slab is superior to the slow axis of LD stacks parallel to the length direction of the slab in decreasing thermal lens effect and obtaining high beam quality.     

Synthesis and characterization of boronates derived from non-symmetric amino-bis-phenols

The condensation of 2-[[(2-hydroxyphenyl)amino]methyl]-phenols (1a-1e) with different arylboronic acids led to 12 new monomeric boronates of the type 2-aryl-dibenzo[d,h]-6-aza-1,3-dioxa-2-boracyclononene (2a-2l). The boronates were characterized by ¹H-, ¹³C-, ¹¹B- and 2D-NMR experiments, FT infrared, mass spectra and elemental analyses. The stereochemistry of the H-N → B-Ph fusion is always cis, as established through the NMR spectra, as well as the X-ray structures of four boronates (2a, 2e, 2f and 2l). Hydrogen bonds between the amine proton and the oxygen ester of the five- membered ring are present in three X-ray structures (2a, 2e and 2f), while the supramolecular structure in the derivative possessing a primary amine (2l) is built up through the protons present in this moiety instead of the proton from the H-N → B-Ph fragment.