Stable operation of a cw optical parametric oscillator near the signal-idler degeneracy

The frequency stability of a cw optical parametric oscillator (cw OPO) near the signal-idler degeneracy has been studied. The strong tendency of a near-degenerate OPO to mode hop has been suppressed by using a bulk Bragg grating as a spectral filter in the OPO cavity. An experimental demonstration of stable parametric oscillation in a single longitudinal mode of the OPO cavity is reported, together with the capability of tuning the signal-idler difference frequency from 1 to 4 THz. The OPO has potential use in cw terahertz generation.     

Copolymerization of vinylcyclohexane with ethene and propene using zirconocene catalysts

Vinylcyclohexane (VCH) was copolymerized with ethene and propene using methylaluminoxane‐activated metallocene catalysts. The catalyst precursor for the ethene copolymerization was rac‐ethylenebis(indenyl)ZrCl₂ ( 1 ). Propene copolymerizations were further studied with C_s‐symmetric isopropylidene(cyclopentadienyl)(fluorenyl)ZrCl₂ ( 2 ), C₁‐symmetric ethylene(1‐indenyl‐2‐phenyl‐2‐fluorenyl)ZrCl₂ ( 3 ), and “meso”‐dimethylsilyl[3‐benzylindenyl)(2‐methylbenz[e]indenyl)]ZrCl₂ ( 4 ). Catalyst 1 produced a random ethene–VCH copolymer with very high activity and moderate VCH incorporation. The highest comonomer content in the copolymer was 3.5 mol %. Catalysts 1 and 4 produced poly(propene‐co‐vinylcyclohexane) with moderate to good activities [up to 4900 and 15,400 kg of polymer/(mol of catalyst × h) for 1 and 4 , respectively] under similar reaction conditions but with fairly low comonomer contents (up to 1.0 and 2.0% for 1 and 4 , respectively). Catalysts 2 and 3 , both bearing a fluorenyl moiety, gave propene–VCH copolymers with only negligible amounts of the comonomer. The homopolymerization of VCH was performed with 1 as a reference, and low‐molar‐mass isotactic polyvinylcyclohexane with a low activity was obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6569–6574, 2006     

On the summands of near-rings with ATM

We say that a near-ring (N,+,·) has an almost trivial multiplication (ATM) if the product of two elements belongs to the intersection of the additive cyclic groups generated by these two elements. We show that every finite near-ring with ATM can be decomposed to a direct sum where the summands are either near-rings defined on cyclic groups or near-rings whose minimal ideals are zero near-rings. Finally, we show how to construct these summands on cyclic groups.     

Formation of HArF in solid Ar revisited: are mobile vacancies involved in the matrix-site conversion at 30 K?

The HArF molecule can occupy in solid Ar thermally unstable and stable configurations, and their microscopic structure is not understood at the moment. We present additional experimental results on the formation of two HArF configurations and analyze them with emphasis on possible reactions of the unstable configuration with matrix vacancies to form the stable configuration. We conclude that the existing computational scenarios do not describe fully the present experimental data. In order to explain qualitatively the experimental results, two tentative models are discussed. The first model is based on local mobility of matrix vacancies produced during photolysis and the second model considers isomerization of the HArF at Arn supermolecule. More importantly, the present results constitute the experimental basis for future theoretical studies.     

Rewritable Broad-Band Color Filters for Spectral Image Analysis

We propose an optical system to implement rewritable transparent broad-band color filters. The filter consists of a linear variable filter and a liquid crystal spatial light modulator in which an expected filter function is written. A time-integrated intensity image was taken while the filter was passing the lens aperture of a CCD camera. The averaged norm error between the implemented and the expected filter functions was about 5.4#x0025;. The system was applied to spectral estimation in a two-dimensional color image.     

Inhibition of a palladium(II) catalyst upon formation of a di‐μ‐chloro complex: di‐μ‐chloro‐bis­[1,2‐bis­(di­phenyl­phosphino)­ethane‐P,P′]dipalladium(II) bis­(tetra­fluoro­borate) bis­(deutero­chloro­form) solvate

The title compound was formed upon slow evaporation of a solution of the solvated dicationic complex bis­(aceto­nitrile)­bis­[1,2‐bis­(di­phenyl‐phosphino)­ethane]­palladium(II) bis(tetra­fluoro­borate) in deuterated chloro­form. The dinucleur palladium complex forms triclinic crystals and there is an inversion center between the Pd atoms. Compared to the corresponding monomeric compound, the Cl—Pd—Cl angles decrease upon briding from 94.19 (7) to 86.96 (4)°.     

FiD: a software for ab initio structural identification of product ions from tandem mass spectrometric data

We present FiD (Fragment iDentificator), a software tool for the structural identification of product ions produced with tandem mass spectrometric measurement of low molecular weight organic compounds. Tandem mass spectrometry (MS/MS) has proven to be an indispensable tool in modern, cell-wide metabolomics and fluxomics studies. In such studies, the structural information of the MS(n) product ions is usually needed in the downstream analysis of the measurement data. The manual identification of the structures of MS(n) product ions is, however, a nontrivial task requiring expertise, and calls for computer assistance. Commercial software tools, such as Mass Frontier and ACD/MS Fragmenter, rely on fragmentation rule databases for the identification of MS(n) product ions. FiD, on the other hand, conducts a combinatorial search over all possible fragmentation paths and outputs a ranked list of alternative structures. This gives the user an advantage in situations where the MS/MS data of compounds with less well-known fragmentation mechanisms are processed. FiD software implements two fragmentation models, the single-step model that ignores intermediate fragmentation states and the multi-step model, which allows for complex fragmentation pathways. The software works for MS/MS data produced both in positive- and negative-ion modes. The software has an easy-to-use graphical interface with built-in visualization capabilities for structures of product ions and fragmentation pathways. In our experiments involving amino acids and sugar-phosphates, often found, e.g., in the central carbon metabolism of yeasts, FiD software correctly predicted the structures of product ions on average in 85% of the cases. The FiD software is free for academic use and is available for download from www.cs.helsinki.fi/group/sysfys/software/fragid. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Internal rotation in propionic acid: near-infrared-induced isomerization in solid argon

The conformational system of propionic acid (CH3CH2COOH) is studied in solid argon. It is predicted by the ab initio calculations that this molecule has four stable conformers. These four structures are denoted Tt, Tg+/-, Ct, and Cg+/-, and they differ by the arrangement around the C-O and Calpha-C bonds. The ground-state Tt conformer is the only form present at 8 K after deposition of an argon matrix containing propionic acid. For the CH3CH2COOH and CH3CH2COOD isotopologues, narrow-band excitation of the first hydroxyl stretching overtone of the conformational ground state promotes the Calpha-C and C-O internal rotations producing the Tg+/- and Ct conformers, respectively. A subsequent vibrational excitation of the produced Tg+/- form induces its conversion to the Cg+/- conformer by rotation around the C-O bond. In the dark, all of the produced conformers decay to the conformational ground state at different rates. The decay kinetics and its temperature dependence allow the identification of the conformers by IR absorption spectroscopy, which is supported by ab initio calculations of their vibrational spectra. For the CH3CH2COOD isotopologue, the excitation of molecules isolated in different matrix sites results in site-dependent photoisomerization rates for the Calpha-C and C-O internal rotations, which also confirm the identification of the photoproducts.     

Fabrication of blazed gratings by area-coded effective medium structures

Area-coded effective medium structures (ACES) are a recently presented novel type of diffractive structure. Because of their higher stability compared to 2D binary blazed gratings, they have the potential of a broader use in micro-optics applications. The first fabrication with electron-beam lithography validate the theoretical model of blazed ACES. The measured diffraction efficiencies are in very good agreement with the values obtained from rigorous electromagnetic analysis.     

Synthesis of a novel carboxy functionalized PyOX-ligand

A short and convenient synthesis of a carboxy functionalized PyOX-core is presented. The carboxy functionality offers a wide variety of possibilities for further modification. In this paper, the core is functionalized with a mercapto tail.