Planar waveguide lasers and structures created by laser ablation — an overview

The parameters of planar and channel waveguide lasers fabricated by different techniques are reviewed. Materials and properties of thin films used for creation of planar waveguide lasers are summarized. The parameters of active and passive planar waveguides created by the method of pulsed laser deposition and problems of laser deposition are described. The aspects of laser generation of planar waveguide lasers, resonators and channel waveguides are presented. The results of our experiments of laser deposition of thin Ti:sapphire layers and thin layers of Nd:YAG and Nd:YAP are briefly discussed. This work was supported by the grant of Czech Grant Agency No. 102/96/0429.     

Nonconforming P1 elements on distorted triangulations: Lower bounds for the discrete energy norm error

Compared to conforming P1 finite elements, nonconforming P1 finite element discretizations are thought to be less sensitive to the appearance of distorted triangulations. E.g., optimal-order discrete H¹ norm best approximation error estimates for H² functions hold for arbitrary triangulations. However, the constants in similar estimates for the error of the Galerkin projection for second-order elliptic problems show a dependence on the maximum angle of all triangles in the triangulation. We demonstrate on an example of a special family of distorted triangulations that this dependence is essential, and due to the deterioration of the consistency error. We also provide examples of sequences of triangulations such that the nonconforming P1 Galerkin projections for a Poisson problem with polynomial solution do not converge or converge at arbitrarily low speed. The results complement analogous findings for conforming P1 finite elements.     

Simple one-step process for immobilization of biomolecules on polymer substrates based on surface-attached polymer networks

For the miniaturization of biological assays, especially for the fabrication of microarrays, immobilization of biomolecules at the surfaces of the chips is the decisive factor. Accordingly, a variety of binding techniques have been developed over the years to immobilize DNA or proteins onto such substrates. Most of them require rather complex fabrication processes and sophisticated surface chemistry. Here, a comparatively simple immobilization technique is presented, which is based on the local generation of small spots of surface attached polymer networks. Immobilization is achieved in a one-step procedure: probe molecules are mixed with a photoactive copolymer in aqueous buffer, spotted onto a solid support, and cross-linked as well as bound to the substrate during brief flood exposure to UV light. The described procedure permits spatially confined surface functionalization and allows reliable binding of biological species to conventional substrates such as glass microscope slides as well as various types of plastic substrates with comparable performance. The latter also permits immobilization on structured, thermoformed substrates resulting in an all-plastic biochip platform, which is simple and cheap and seems to be promising for a variety of microdiagnostic applications.     

Drug resistance: a periplasmic ménage à trois

The paradigm tripartite efflux transporter AcrA-AcrB-TolC confers multiple drug resistance to Escherichia coli. Tikhonova et?al. (2011) now examine how the three components connect to unity and highlight the critical role of AcrA membrane proximal domain conformation for successful assembly.     

Explicitly correlated coupled cluster calculations for the benzenium ion (C6H7(+)) and its complexes with Ne and Ar

Explicitly correlated coupled cluster theory at the CCSD(T)-F12x (x = a, b) level (Adler, T. B.; Knizia, G.; Werner, H.-J. J. Chem. Phys. 2007, 127, 221106) has been employed in a study of the benzenium ion (C6H7(+)) and its complexes with a neon or an argon atom. The ground-state rotational constants of C6H7(+) are predicted to be A0 = 5445 MHz, B0 = 5313 MHz, and C0 = 2731 MHz. Anharmonic vibrational wavenumbers of this cation were obtained by combination of harmonic CCSD(T*)-F12a values with anharmonic contributions calculated by double-hybrid density functional theory at the B2PLYP-D level. For the complexes of C6H7(+) with Ne or Ar, the lowest energy minimum is of π-bonded structure. The corresponding dissociation energies D0 are estimated to be 160 and 550 cm(-1), respectively. There is no indication of H-bonds to the aromatic or aliphatic hydrogen atoms. Instead, three nonequivalent local energy minima were found for nuclear configurations where the rare-gas atom lies in the ring-plane and approximatly points to the center of one of the six CC bonds.     

XPS investigations of electrolyte/electrode interactions for various Li-ion battery materials

For future Li-ion battery applications the search for both new design concepts and materials is necessary. The electrodes of the batteries are always in contact with electrolytes, which are responsible for the transport of Li ions during the charging and discharging process. A broad range of materials is considered for both electrolytes and electrodes so that very different chemical interactions between them can occur, while good cycling behavior can only be obtained for stable solid-electrolyte interfaces. X-ray photoelectron spectroscopy (XPS) was used to study the most relevant interactions between various electrode materials in contact with different electrolyte solutions. It is shown how XPS can provide useful information on reactivities and thus preselect suitable electrode/electrolyte combinations, prior to electrochemical performance tests.     

On the equilibrium structures of the complexes H2C3H+ · Ar and c-C3H3(+) · Ar: results of explicitly correlated coupled cluster calculations

Explicitly correlated coupled cluster theory at the CCSD(T)-F12x (x = a, b) level [T. B. Adler et al., J. Chem. Phys. 127, 221106 (2007)] has been employed in a study of the potential energy surfaces for the complexes H(2)C(3)H(+) · Ar and c-C(3)H(3)(+) · Ar. For the former complex, a pronounced minimum with C(s) symmetry was found (D(e) ≈ 780 cm(-1)), well below the local "H-bound" minimum with C(2v) symmetry (D(e) ≈ 585 cm(-1)). The absorption at 3238 cm(-1) found in the recent infrared photodissociation spectra [A. M. Ricks et al., J. Chem. Phys. 132, 051101 (2010)] is, thus, interpreted as an essentially free acetylenic CH stretching vibration of the propargyl cation. A global minimum of C(s) symmetry was also obtained for c-C(3)H(3)(+) (D(e) ≈ 580 cm(-1)), but the energy difference with respect to the local C(2v) minimum is only 54 cm(-1).     

Neue Cyclosporine aus Tolypocladium inflatum. Die Cyclosporine K–Z

Novel Cyclosporins from Tolypocladium inflatum. The Cyclosporins K–Z The fungus T. inflatum produces a plethora of oligopeptides, the cyclosporins, which exhibit remarkable biological activities. Cyclosporin A, the main metabolite, represents a potent immunosuppressant which opened new ways in the immunotherapy of bone marrow and organ transplantations. In addition to the already described cyclosporins A–I, we report now the isolation of the cyclosporins K–Z. The structural assignments of these novel congeners are based on chemical degradation, correlation reactions, mass spectra, and extensive analysis of ¹H- and ¹³C-NMR spectra. All cyclosporins are cyclic undecapeptides differing from each other by minor variations in the amino-acid sequence. Comparison of the immunosuppressive and antifungal effects furnished new information concerning structure-activity relationships.     

Growth of active Nd-doped YAP thin-film waveguides by laser ablation

3 (YAP) thin films as a promising material for application in a planar waveguide laser has been studied. The films have been grown on sapphire(0001) and YAP(001) substrates by laser ablation. The influence of the substrate temperature and ambient oxygen pressure on the crystalline structure, concentration of Nd incorporated into films, and consequent luminescence spectra were investigated. The waveguiding properties were observed and refractive index of the films was evaluated. Received: 8 February 1998/Accepted: 9 February 1998