Structure and polarity of 8CB films evaporated onto solid substrates

Brewster-angle reflection ellipsometry and surface optical second harmonic generation were used to study the growth of 4'-n-octyl-4-cyanobiphenyl (8CB) films evaporated in air onto polymeric and quartz glass substrates. The layer-by-layer growth of the films terminates after formation of two distinctive interfacial layers. Both of these two layers are polar and tilted. In the first layer the molecules lie nearly flat on the surface, while in the second layer they point on average about 50° toward the surface normal. The dipole moment of the second layer has a lower magnitude and an opposite direction with respect to the dipole moment of the first layer.     

Square roots of semihyponormal operators have scalar extensions

In this paper, we study some properties of , i.e., square roots of semihyponormal operators. In particular we show that an operator has a scalar extension, i.e., is similar to the restriction to an invariant subspace of a (generalized) scalar operator (in the sense of Colojoar?-Foia?). As a corollary, we obtain that an operator has a nontrivial invariant subspace if its spectrum has interior in the plane.     

Ultrahigh-resolution optical coherence tomography using continuum generation in an air-silica microstructure optical fiber

We demonstrate ultrahigh-resolution optical coherence tomography (OCT) using continuum generation in an air-silica microstructure fiber as a low-coherence light source. A broadband OCT system was developed and imaging was performed with a bandwidth of 370 nm at a 1.3-mu;m center wavelength. Longitudinal resolutions of 2.5 microm in air and ~2 microm in tissue were achieved. Ultrahigh-resolution imaging in biological tissue in vivo was demonstrated.     

On odd points and the volume of lattice polyhedra

Denote by _n ³ ,n 2, the lattice consisting of all pointsx in ³ such thatnx belongs to the fundamental lattice ³ of points with integer coordinates. Letl _n be the subset of _n ³ consisting of all points whose coordinates are odd multiples of 1/n. The purpose of this paper is to give several new Pick-type formulae for the volume of three-dimensional lattice polyhedra, that is, polyhedra with vertices in ³. Our formulae are in terms of numbers of only thel _n-points belonging to a lattice polyhedronP in contrast to already known formulae which employ numbers of all the _n ³ -points inP. On our way to establishing the formulae we show that the number of points froml _n belonging to a three-dimensional lattice polyhedronP has some polynomiality properties similar to those of the well-known Ehrhart polynomial expressing the number of points of _n ³ inP. The paper contains also some comments on a problem of finding a volume formula which would employ only the setsl _n and which would be applicable to lattice polyhedra in arbitrary dimensions.Research partially supported by KBN Grant 2 P03A 008 10.     

Aluthge transforms of operators

Associated with every operatorT on Hilbert space is its Aluthge transform (defined below). In this note we study various connections betweenT and , including relations between various spectra, numerical ranges, and lattices of invariant subspaces. In particular, we show that if has a nontrivial invariant subspace, then so doesT, and we give various applications of our results.     

Evidence for changing of cosmic ray composition between 10(17) and 10(18) eV from multicomponent measurements

The average mass composition of cosmic rays with primary energies between 10(17) and 10(18) eV has been studied using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum and the muon density as a function of energy. The results show that the composition is changing from a heavy to lighter mix as the energy increases.     

Tunable stimulated-Brillouin-scattering resonator started by feedback provided by Bragg scattering from the dynamic grating within an active medium

We report a tunable stimulated-Brillouin-scattering resonator that does not require a starting mirror or a wavelength selector. The resonator is based on the Bragg scattering from the dynamic grating within the active medium itself. The laser dye (Rhodamine 6G dissolved in ethanol) was utilized as the active medium and was pumped by a frequency-doubled Nd:YAG laser. The quality factor (M(2)) of the output beam was 2.2. A single short pulse (<1 ns) with a pumping efficiency of ~4% was observed.     

Controlled growth of nanocrystalline silicon on permalloy micro-patterns

Lithographically prepared micrometer-sized permalloy ellipses were used to control the growth of nanocrystalline Si in otherwise amorphous Si film prepared by plasma enhanced chemical vapor deposition. Atomic force microscopy and micro-Raman spectroscopy were employed to study the surface structures before and after the deposition of the Si film. The possible applications of the controlled growth of nanocrystalline Si micro-patterns are discussed as well as the mechanisms leading to the growth of these patterns. PACS 68.55.Ac; 81.15.Gh     

Surface status and size influences of nickel nanoparticles on sulfur compound adsorption

Metallic nickel nanoparticles were incorporated on mesoporous silica to remove sulfur compounds in diesel selectively. In the first method, nickel nanoparticles were formed on mesoporous silica SBA-15 by impregnation and subsequent reduction of nickel nitrate. The sulfur adsorption capacity was strongly dependent on the nickel loading and the average nickel particle size. In the second method, nickel nanoparticles were synthesized in solution in the presence of a capping agent and then incorporated in mesoporous silica MCF by sonication. Although these particles maintain their sizes on the MCF surface after heat treatment, capping agent remaining on the Ni particle surface might interfere the adsorption of sulfur compounds.     

Optical absorption of 1-phenyl-3-methyl-1H-pyrazolo[3,4-b]quinoline derivatives: Molecular dynamics modeling

Paper deals with quantum chemical modeling of the optical absorption spectra of 6-fluoro, 7-trifluoromethyl, 6-cyano, 6-carboethoxy and 6-tert-butyl derivatives of 1-phenyl-3-methyl-1H-pyrazolo[3,4-b]quinoline. The calculations are performed by means of the semiempirical quantum chemical methods (AM1 or PM3) applied to the equilibrium molecular conformation in vacuo (T = 0 K) or molecular dynamic (MD) trajectories as obtained within fragmental or total MD simulations at T = 300 K. The results of these calculations are compared with the measured spectra of optical absorption. The quantum chemical analysis show that the dynamics of the methyl, trifluoromethyl, carboethoxy and tert-butyl groups practically does not influence the absorption spectra whereas the strongest their modifications are found to be related with dynamics of the aromatic group. The semiempirical method AM1 in combination with MD simulations gives for all dyes the best agreement between the calculated and measured spectral positions of absorption bands. In most cases the quantum chemical calculations describe properly the trends of their changes depending on the lateral substituent.