3000 km transmission of densely-spaced, 2.5 Gbit s-1 directly-modulated channels demultiplexed with a concave grating demultiplexer

WDM transmission and demultiplexing of four directly-modulated DFB lasers at 2.5 Gbit s-1, with very narrow channel spacing (50 GHz) over 3000 km of dispersion-shifted fibre has been performed with a single-span recirculating loop test-bed. A high-performance free-space concave grating demultiplexer is used for the first time in a dense WDM transmission experiment.     

UNSCHEDULED DNA SYNTHESIS: A QUANTITATIVE INDICATOR OF RESIDUAL IMMUNODETECTABLE PYRIMIDINE DIMERS IN HUMAN FIBROBLASTS AFTER ULTRAVIOLET-B IRRADIATION

We have addressed the question whether the level of UV-B induced DNA damage can be accurately assessed by the measurement of the rate of unscheduled DNA synthesis (UDS). Cultured human fibroblasts were irradiated with UV radiation at 290, 313 or 365 nm. The LD50 was 85 J/m2 at 290 nm, 4500 J/m2 at 313 nm, and 70 kJ/m2 at 365 nm. The analysis of UDS measurements indicate complete arrest of repair processes within 24 h after irradiation, irrespective of the dose (in the range 10-60 J/m2 at 290 nm, and 250-1000 J/m2 at 313 nm). Irradiation at 365 nm failed to yield detectable evidence of UDS. Incubation of irradiated cells with an antiserum directed against both 6-4 type and cyclobutane-type pyrimidine dimers shows a clear parallelism between the disappearance of the antibody-binding determinants and the variation of the rate of UDS vs time after the end of the irradiation. Thus it is concluded that in UV-B irradiated normal cultured human fibroblasts, the lack of UDS reflects the absence of immunodetectable pyrimidine dimers.     

Theoretical determination of the magnetic properties of 2-pyrone and 4-pyrone,and o-benzoquinone and p-benzoquinone

A series of theoretical procedures, relying on the conventional common-origin and distributed-origin approaches, and adopting extended gaugeless as well as London basis sets, have been applied at the Hartree-Fock level of accuracy to predict magnetic susceptibilities and nuclear magnetic shieldings of four molecular systems that aroused particular interest and discussion concerning their aromatic character. The theoretical results are of near Hartree-Fock quality. Comparison with experimental values for magnetic susceptibilities seems to indicate that the latter need to be revised. Analysis of calculated properties and of plots of current density induced by the magnetic field in the π-electrons provides simple and effective tools for the classification of 2- and 4-pyrones, and o- and p-benzoquinone as non-aromatic.     

Improved calculation of spin-dependent properties for internally contracted multireference configuration interaction wavefunctions

A general approach to evaluate spin-dependent properties for internally contracted multireference configuration interaction wavefunctions is presented. The spin-orbit atomic integral program as implemented within MOLPRO is extended to treat arbitrary basis sets, and the spin-spin atomic integrals are added. The increased accuracy of the code is demonstrated by means of calculations of the fine structures of the lowest levels of O and O⁺.     

MULTIFUNCTIONAL HYDROPHILIC POLYMERS

ABSTRACT

Different types of multifunctional hydrophilic polymers were synthesized and characterized in view of their possible biomedical application. Several poly(amide)s and poly(ester-amide)s containing oligo(oxyethylene) segments and tartaric or succinic acid residues were prepared by activated polycondensation methods. New functional derivatives of β-cyclodextrin were obtained by reaction with glycidyl ether of protected polyols. The mechanism of β-cyclodextrin polymerization with epichlorohydrine was investigated by ¹³C-NMR spectroscopy.     

Spin-orbit matrix elements for internally contracted multireference configuration interaction wavefunctions

An efficient method for the calculation of Breit-Pauli spin-orbit matrix elements for internally contracted multireference configuration interaction wavefunctions is presented. Instead of taking all two-electron contributions of the wavefunction explicitly into account, the most important two-electron contributions of the spin-orbit operator are incorporated by means of an effective one-electron Fock operator. As a further refinement, explicit two-electron contributions can be reinstated for the dominant all-internal parts of the wavefunctions.     

The anharmonic force field of cis-1-chloro-2-fluoroethylene

A comprehensive anharmonic vibrational analysis of cis-1-chloro-2-fluoroethylene and its isotopomers has been performed on the basis of a complete ab initio quartic force field constructed by means of second-order Møller-Plesset perturbation theory (MP2) and the coupled-cluster singles and doubles approach, augmented for structural optimization and harmonic force field by a contribution of connected triple excitations (CCSD(T)). The theoretical force field was scaled by global least-squares fitting to all spectroscopic data and parameters experimentally determined for this molecule. This final force field, employing standard perturbation theory, yields a complete set of spectroscopic molecular constants providing a critical assessment of experimental rotational and centrifugal distortion constants, fundamentals, overtones, and combination bands determined over many years. Effects of Fermi and Darling-Dennison resonances were included by matrix diagonalization.     

A graphical scheme for addressing determinants in large configuration interaction treatments

A graphical technique is proposed for generating and addressing all required α and β strings of spin-orbitals for configuration interaction treatments based on determinants. Compared with other treatments, this scheme, as well as reducing to a minimum the number of logical operations, avoids entirely the storage of the massive tables and vectors usually required for addressing the determinants. The generation is proposed of all required addresses to locate the determinants in the CI vectors, before and after application of the Hamiltonian, at run time using graphs and one intermediate table of acceptable dimensions. The scheme, which has been tested on a small personal computer, appears ideal when limited computational resources are available for the CI treatment. It is believed also to be useful for larger applications.     

Rotational spectrum,dynamics and bond energy of 2,5-dihydrofuran—krypton van der Waals complex

The equilibrium conformation, dynamics and dissociation energy of the weakly bonded 2,5-dihydrofuran-Kr complex have been deduced from its free jet millimetre-wave spectrum. The equilibrium distance of Kr with respect to the centre of mass of the molecule is 3.61 Å, with Kr tilted 12.8° from the perpendicular to the centre of mass of the ring towards the oxygen atom. The dissociation energy is estimated from the centrifugal distortion constant D_J to be about 3.5kJ mol^?1.     

Ab initio dynamics of the He + H+ 2 → HeH+ +H reaction: a new potential energy surface and quantum mechanical cross-sections

The reaction He + H⁺ ₂(v,j = 0) → HeH⁺(v′ = 0, j′) for v = 0, 1,2 and 3 and for scattering energies near the threshold (0.95–1.15 eV) has been studied by calculating ab initio points at MRCI level and ‘exact’ integral quantum reactive cross-sections. More than 1400 nuclear geometries have been chosen to cover the most important regions for the dynamics, an extended set of points being taken directly on a hyperspherical coordinate grid. A many-body expansion with a large number of terms permits an accurate analytical representation of the potential energy surface with a root-mean-square deviation <12meV. The hyperquantization algorithm has been extended to obtain quantum mechanical integral cross-sections which are compared with previous calculations and with experimental results.