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51.
52.
A. Kučírková K. Navrátil L. Pajasová V. Vorlíček 《Applied Physics A: Materials Science & Processing》1996,63(5):495-503
Optical properties of semi-insulating polycrystalline silicon (SIPOS) films were investigated over the wide region of wavelengths. The vibrational modes of Si-O-Si and Si-Si bonds were studied by IR and Raman spectroscopy. A pronounced effect of oxygen content on the measured spectra was observed. Optical constants of SIPOS films have been compared with those of amorphous silicon and glassy silicon dioxide and their values have been successfully interpreted in terms of the theory of effective medium. The results have shown that the amorphous character prevails in the as-deposited SIPOS films. 相似文献
53.
We give a simple proof of ergodicity of eigenfunctions of the Laplacian with Dirichlet boundary conditions on compact Riemannian manifolds with piecewise smooth boundaries and ergodic billiards. Examples include the Bunimovich stadium, the Sinai billiard and the generic polygonal billiard tables of Kerckhoff, Masur and Smillie. 相似文献
54.
55.
Peggy S. Eis Józef Kuśba Michael L. Johnson Joseph R. Lakowicz 《Journal of fluorescence》1993,3(1):23-31
Time-resolved fluorescence resonance energy transfer (FRET) measurements were used to measure distance distributions and intramolecular dynamics (site-to-site diffusion) of a 28-residue single-domain zinc finger peptide in the absence and presence of zinc ion. Energy transfer was measured between TRP14 and a N-terminal DNS group. As expected, the TRP-to-DNS distance distribution for zinc-bound peptide is shorter and narrower (R
av=11.2 Å,hw=2.8 Å) than the metal-free peptide (R
av=20.1 Å,hw=14.5 Å). The degree of mutual donor-to-acceptor diffusion (D) was also determined for these distributions. For zinc-bound peptide there is no detectible diffusion (D0.2 Å2/ns), whereas for metal-free peptide a considerable amount of motion is occurring between the donor and the acceptor (D=12 Å2/ns). These results indicate that the zinc-bound peptide folds into a unique, well-defined conformation, whereas the metal-free conformation is flexible and rapidly changing. The absence of detectible mutual site-to-site diffusion between the donor and the acceptor in the metal-bound zinc finger peptide indicates that intramolecular motion is essentially frozen out, on the FRET time scale, as a consequence of zinc coordination.Dedicated to the memory of Barbara D. Wells. 相似文献
56.
Bogumil Zelent Józef Kuśba Ignacy Gryczynski Michael L. Johnson Joseph R. Lakowicz 《Journal of fluorescence》1993,3(3):199-207
We examined the time-dependent intensity decays ofN-acetyl-l-tryptophanamide (NATA) when collisionally quenched by acrylamide in propylene glycol over a range of temperatures. The intensity decays of NATA became increasingly heterogeneous in the presence of acrylamide. The NATA intensity decays were not consistent with the Collins-Kimball radiation boundary condition (RBC) model for quenching. The steady-state Stern-Volmer plots show significant upward curvature, and quenching of NATA by acrylamide was observed even in vitrified propylene glycol, where translational diffusion cannot occur during the lifetime of the excited state. These frequencydomain and steady-state data indicate a through-space quenching interaction between NATA and acrylamide, and the results are consistent with a rate constant for quenching that depends exponentially on the fluorophore-quencher separation distance. The exponential distance-dependent rate of quenching also explains the upward curvature of the Stern-Volmer plot, and the steady-state data aid in determining the interaction distance between NATA and acrylamide. These results suggest that the distance-dependent quenching rates need to be considered in the interpretation of acrylamide quenching of proteins. 相似文献
57.
The synthesis of 2-phenylsparteine-N16-oxide (7) and its perchlorate salt (7-H+) was carried out. On the basis of spectral data, and by comparison with appropriate sparteine-N-oxides, the mechanism of formation and the structures of the two new compounds were proposed. It was found, the basicity of the new N-oxide is unexpectedly high and comparable to the basicity of quaternary ammonium hydroxides. The structure and the strength of intramolecular H-bond in 7-H+ makes 7 an excellent “catcher” proton or specific ”sponge” proton. 相似文献
58.
J. Kučera J. Kučera A. R. Byrne A. R. Byrne J. Mizera J. Mizera M. Lučaníková M. Lučaníková Z. Řanda Z. Řanda 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):251-257
Summary Radiochemical neutron activation procedures using liquid-liquid extraction with tetraphenylarsonium chloride in chloroform
from 1M HCl and solid extraction with ALIQUAT 336 incorporated in a polyacrylonitrile binding matrix from 0.1M HCl were developed
for accurate determination of rhenium in biological and environmental samples at the sub-ng . g-1 level. Concentrations of Re in the range of 0.1 to 2.4 ng . g-1 were determined in several botanical reference materials (RM), while in a RM of road dust a value of ~10 ng . g-1 was found. Significantly elevated values of Re, up to 90 ng . g-1 were found in seaweed (brown algae). Results for Re in the brown algae Fucus vesiculosus in which elevated 99Tc values had previously been determined suggested possible competition between Re and Tc in the accumulation process. 相似文献
59.
The extraction of Am, Eu, Ce(III), Zr(IV), and Sr from aqueous nitric acid— nitrate media by dibutyl N,N-diethylcarbamylphosphonate
and dibutyl N,N-diethylcar-bamylmethylenephosphonate dissolved in carbon tetrachloride was studied. The trivalent actinide
and lanthanide elements may be separated in certain aqueous phase acidity regions from Fe(III), Zr(IV), and Sr, whereas the
separation of actinide elements from the lanthanide elements is poor. The extractant to metal ratio in the extracted complexes
of Am, Eu, and Ce(III) is 3. The interferences in the extraction due to acidic impurities in the extracting agent are discussed. 相似文献
60.
Krystyna Cieśla H. Rahier Grażyna Zakrzewska-Trznadel 《Journal of Thermal Analysis and Calorimetry》2004,77(1):279-293
One to three endothermal peaks atributted to melting of bulk and interfacial water were observed by DSC in the regenerated
cellulose — water system. The profiles of thermal effects depend on water content, time of conditioning, film pretreatment
and the conditions applied during the preceding freezing-thawing cycles. The occurrence might be deduced of melting-crystallisation
processes. A large amount of non-freezable strongly bounded water was also detected.
Although cellulose absorbs water quickly after immersion, the structural changes consisting on ordering of polymer fraction
occur during further conditioning due to increase in strength of water binding. Using the membranes in the separation module
at 90°C causes weakening of these bonds. Differences between interaction of particular cellulose films with water can be detected
during the first, the second and the third heating.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献