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171.
Conductivity and thermopower measurements of polyacetylene doped with FeCl4 are reported. The conductivity changes over 10 orders of magnitude and reaches the maximum value of 200 Ω-1 cm-1 at y = 0.07. The thermopower reveals the semiconductor to metal transition at y ? 0.002, with high and temperature independent Seebeck coefficient in the dilute limit and a metallic dependence in the heavily doped samples. 相似文献
172.
We discuss several concepts of continuity, weaker than lower semicontinuity, but still implying the existence of a continuous selection for a closed convex valued multifunction from a paracompact Hausdorff topological space into a Banach space. In this way, an extension of Michael's celebrated selection theorem is given. The behavior of -envelop approximations, as well as the localization of continuous selections, is also discussed. 相似文献
173.
J. Pluta K. Wosińska Z. Basrak G. Bizard B. Benoit P. Désesquelles O. Dorvaux D. Durand B. Erazmus F. Hanappe B. Jakobsson C. Lebrun F.R. Lecolley R. Lednicky P. Leszczyński K. Mikhailov K. Miller B. Noren T. Pawlak M. Przewłocki Ö. Skeppstedt A. Staranowicz A. Stavinskiy L. Stuttgé B. Tamain 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):63-68
174.
M. Maliński J. Zakrzewski F. Firszt 《The European physical journal. Special topics》2008,153(1):251-254
This paper presents both theoretical and experimental issues connected with measurements and numerical analysis of the microphone
amplitude and phase photoacoustic spectra of semiconductor samples exhibiting surface absorption connected with defects states
located on their surfaces. The analytical model of surface absorption in semiconductors is described and the results of computations
are compared with experimental amplitude and phase spectra for Zn0.965Be0.035Se crystal samples. This paper shows the importance of the phase spectra for the proper interpretation of the PA (photoacoustic)
results. 相似文献
175.
176.
Katarzyna Paradowska Micha Wolniak Maciej Pisklak Jan A. Gliski Matthew H. Davey Iwona Wawer 《Solid state nuclear magnetic resonance》2008,34(4):202-209
Oxindole alkaloids, isolated from the bark of Uncaria tomentosa [Willd. ex Schult.] Rubiaceae, are considered to be responsible for the biological activity of this herb. Five pentacyclic and two tetracyclic alkaloids were studied by solid-state NMR and theoretical GIAO DFT methods. The 13C and 15N CPMAS NMR spectra were recorded for mitraphylline, isomitraphylline, pteropodine (uncarine C), isopteropodine (uncarine E), speciophylline (uncarine D), rhynchophylline and isorhynchophylline. Theoretical GIAO DFT calculations of shielding constants provide arguments for identification of asymmetric centers and proper assignment of NMR spectra. These alkaloids are 7R/7S and 20R/20S stereoisomeric pairs. Based on the 13C CP MAS chemical shifts the 7S alkaloids (δ C3 70–71 ppm) can be easily and conveniently distinguished from 7R (δC3 74.5–74.9 ppm), also 20R (δC20 41.3–41.7 ppm) from the 20S (δC20 36.3–38.3 ppm). The epiallo-type isomer (3R, 20S) of speciophylline is characterized by a larger 15N MAS chemical shift of N4 (64.6 ppm) than the allo-type (3S, 20S) of isopteropodine (δN4 53.3 ppm). 15N MAS chemical shifts of N1–H in pentacyclic alkaloids are within 131.9–140.4 ppm. 相似文献
177.
A. M. Gagarski I. S. Guseva V. E. Sokolov G. V. Val’ski G. A. Petrov D. O. Krinitsin D. V. Nikolaev T. A. Zavarukhina V. I. Petrova 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(6):773-777
An experiment has been carried out to study neutron-neutron angular correlations in spontaneous fission of 252Cf. Angular dependences of the number of neutron-neutron coincidences obtained in the experiment were compared with the results of the Monte Carlo calculations for various neutron detection thresholds in the range 425–1600 keV. It was inferred that 10–11% of the total number of prompt neutrons from 252Cf (s.f.) in the laboratory system were emitted isotropically and may probably be interpreted as neutrons directly associated with the instant of scission of the nucleus. The analysis allowed their energy distribution to be determined as well. A similar method was also used to describe the angular correlation of prompt neutrons that accompanied the reaction 235U(n th ,f). 相似文献
178.
Weglarz WP Tanasiewicz M Kupka T Skórka T Sułek Z Jasiński A 《Solid state nuclear magnetic resonance》2004,25(1-3):84-87
A 3D spin-echo (3D SE) pulse sequence was used on a 4.7 T research MRI system to produce images of extracted human first molar tooth placed in CuSO4 water solution. The maximal resolution achieved was 35 x 63 x 300 microm3 in read and two phase directions, respectively. The high-intensity signal from water in solution together with the lack of signal from mineralized tooth tissue produce very good contrast allowing to visualize topography of outer and inner surfaces of the tooth. The 3D MR data were median filtered, binarized and then divided into separate segments corresponding to the inner tooth cavities and the hard tooth tissue. The topography of the root canals was visualized and the canals volume was calculated. The presented technique may be used for quantitative analysis of the root canal cavities shape and volume. The results of such an analysis may be applied for estimation of the quality of the impressional mapping methods in restorative dentistry or as an alternative non-impressional 3D mapping method. 相似文献
179.
Katarzyna Siwińska-Stefańska 《Applied Surface Science》2008,254(11):3591-3600
Attempts at modification of silica surface with a polymer (natural latex) directly in the course of the precipitation process have been made. The effects of temperature, non-ionic surfactants and silane coupling agent in preparation of poly[cis-isoprene]-coated silica on the precipitation of polymer/silica composites initiated by ammonium salts (NH4Cl, (NH4)2SO4, NH4HCO3), have been studied. The influence of the process parameters on the quality of the silicas obtained and the character of the polymer adsorption on the silica surface has been determined along with the effect of the surface impregnation with natural latex on physicochemical parameters of the silicas (bulk density, capacities to absorb water, dibutyl phthalate and paraffin oil) and their surface structure. 相似文献
180.
Inelastic incoherent neutron scattering (IINS) and neutron powder diffraction (NPD) studies have been performed for two dimethyl 1-butanols and two dimethyl 2-butanols with CH3 side molecular groups. Low-temperature vibrational density of states confirmed solid-state polymorphism detected by calorimetric methods, i.e., existence of crystalline and ODIC phases for all isomers, orientationally disordered glass for 2,2-DM 1-B and 3,3-DM 2-B, and glass of isotropic phase for 3,3-DM 1-B. Difference in vibrational density of states between glass and the ordered crystal has shown the so-called Boson peak. Influence of the OH group position in the molecules on their vibrational dynamics up to 50 meV is discussed. 相似文献