			Home About us Contact

Same Energy (same + energy)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignment of dimethylsilylisocyanate

JOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2010
Gamil A. Guirgis
Abstract The Raman (3200-30 cm,1) and/or infrared spectra (3500 to 400 cm,1) of gaseous, liquid and solid dimethylsilylisocyanate, (CH3)2 Si(H)NCO, have been recorded. The MP2(full) calculations, employing a variety of basis sets with and without diffusion functions, have been used to predict the structural parameters, conformational stability, vibrational fundamental wavenumbers, Raman activities, depolarization values and infrared intensities to support the vibrational assignment. The low wavenumber Raman spectrum of the gas with a significant number of Q-branches for the SiNC(O) bend is consistent with an essentially linear SiNCO moiety. The ab initio calculations supported this conclusion as all possible orientations of the NCO moiety lead to nearly the same energy. This result is at variance with the conclusion from the electron diffraction study that the heavy atom skeleton was bent with an angle of 152(5)° with one stable cis conformer. It is believed that this reported angle difference from 180° is due to the shrinkage effect. The SiH distance of 1.486 Å has been obtained from the isolated SiH stretching wavenumber. From the adjustment of the ab initio MP2(full)/6-311+G(d,p) predicted structural parameters, a proposed structure is reported, which is expected to give rotational constants within a few megahertz of the actual ones. These experimental and theoretical results are compared with the corresponding quantities of similar molecules. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Chemical Speciation of Trace Zinc in Ordinary Portland Cement Using X-ray Absorption Fine Structure Analysis

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2004
Isao Tsuyumoto
Chemical change of trace zinc in ordinary portland cement (205.1 ppm) was investigated in hydration process using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Intensities of the peaks appearing at the same energy of ZnO in XANES spectra were decreased with cement hydration. The interatomic distances and the coordination numbers of the first and the second shells calculated from EXAFS spectra indicated that ZnO hydrolyzed to zincate ion [Zn(OH)4]2, with cement hydration keeping their fundamental structure of ZnO4 tetrahedra. [source]

Review of electronic and optical properties of semiconducting ,-conjugated polymers: applications in optoelectronics

POLYMER INTERNATIONAL, Issue 10 2004
André Moliton
Abstract A general overview of the optoelectronic properties of ,-conjugated polymers is presented. Two types of polymer are discerned: interchangeable structures of the same energy (degenerate), such as polyacetylene; and non-degenerate polymers, such as poly(para -phenylene). The band structures of degenerate and non-degenerate polymers are related to their conductivities in doped and non-doped states. In both cases, disorder and impurities play an important role in conductivity. Polarons, bipolarons and excitons are detailed with respect to doping and charge transfers. Given the fibrillic nature of these materials, the variable range hopping (VRH) law for semiconducting polymers is modified to account for metallic behaviours. Optoelectronic properties,electroluminescence and photovoltaic activity,are explained in terms of HOMO and LUMO bands, polaron-exciton and charge movement over one or more molecules. The properties of H- or J-type aggregates and their effects on transitions are related to target applications. Device structures of polymer light-emitting diodes are explicitly linked to optimising polaron recombinations and overall quantum efficiencies. The particularly promising use of ,-conjugated polymers in photovoltaic devices is discussed. Copyright © 2004 Society of Chemical Industry [source]

3236: Corneal grafting assisted by wavelength-optimised ultrashort pulser lasers

ACTA OPHTHALMOLOGICA, Issue 2010
TAL MARCIANO
Purpose We realized an innovative device for ocular surgery by ultrafast pulse laser optimised for corneal grafting. Methods We constructed a demonstrator device that reproduces surgical conditions of corneal transplant. It is thus possible to realize with the help of an easy handling automatised interface all the kinds of already existing corneal transplants. Also, in order to maximize the spatial quality of the beam, a wavefront correction system using a deformable mirror module has been added. The Demonstrator contains an erbium fiber laser emitting at 1,6 microns. This laser delivers a beam of a few Joule with pulse duration of 700 femtoseconds and a repetition rate of 100-200 KHz. It includes deformable mirrors permitting horizontal displacements and a wavefront sensor. It also contains the administration system of the laser beam. Results The experiments carried out with a surgical tunable source confirmed the initial assumptions: the penetration depth is limited to wavelengths close to 1 microns. When increasing the wavelength, the drop of the scattering compensates the absorption and therefore the penetration depth is slowly varying when increasing the wavelength. The laser does not penetrate near the maximum of the water absorption band located at 1,45 microns. However, the use of a wavelength of 1,6 micros enables an important increasing of penetration depth (factor 3) while conserving the same energy of current technologies. Conclusion The use of a laser source with a wavelength corresponding to the window of transparency of the cornea (1,65 microns) permits to increase both the penetration depth of an ultrafast laser source and the cut quality. [source]