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931.
M. Abbas F. D’Amico L. Morresi N. Pinto M. Ficcadenti R. Natali L. Ottaviano M. Passacantando M. Cuccioloni M. Angeletti R. Gunnella 《The European physical journal. E, Soft matter》2009,28(3):285-291
We present thick, uniform and rather flat melanin films obtained using spray deposition. The morphology of the films was investigated
using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Temperature-dependent electrical resistance of
melanin thin films evidenced a semiconductor-like character and a hysteretic behavior linked to an irreversible process of
water molecule desorption from the melanin film. X-ray Photoelectron Spectroscopy (XPS) was carried out to analyze the role
of the functional groups in the primary and secondary structure of the macromolecule, showing that the contribution of the
5,6-dihydroxyindole-2-carboxylic acid (DHICA) subunit to the molecule is about 35%. Comparison of the optical absorption of
the thick (800nm) and thin (80nm) films showed a spectral change when the thickness increases. From in vacuum photoconductivity
(PC) measured at controlled temperatures, we suggest that the melanin films exhibit a possible charge transport mechanism
by means of delocalized states along the stacked planar secondary structure. 相似文献
932.
Gauhar Abbas B. Ananthanarayan 《The European Physical Journal A - Hadrons and Nuclei》2009,41(1):7-11
We obtain stringent bounds in the 〈r
2
-c plane where these are the scalar radius and the curvature parameters of the scalar K
form factor, respectively, using analyticity and dispersion relation constraints, the knowledge of the form factor from the
well-known Callan-Treiman point , as well as at , which we call the second Callan-Treiman point. The central values of these parameters from a recent determination are accomodated
in the allowed region provided the higher loop corrections to the value of the form factor at the second Callan-Treiman point
reduce the one-loop result by about 3% with . Such a variation in magnitude at the second Callan-Treiman point yields 0.12 fm2
〈r
2
0.21 fm2and 0.56 GeV-4
c
1.47 GeV-4and a strong correlation between them. A smaller value of shifts both bounds to lower values. 相似文献
933.
Sarah Murrison David Glowacki Dr. Christian Einzinger Dr. James Titchmarsh Stephen Bartlett Dr. Ben McKeever‐Abbas Dr. Stuart Warriner Dr. Adam Nelson Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(9):2185-2189
Look, no ortho substituents! A series of polycycles were prepared by using a three‐component Joullié–Ugi reaction. The rate of rotation about the bond between a highly hindered bridgehead and a phenyl ring with no ortho substituents was measured, and was highly dependent on the substitution. Rotamer half‐lives of up to 21 h at 298 K were observed (see figure). Rotamers resulting from this restricted rotation were isolated for the first time.
934.
A CF3-containing diamine, 2,2′-thiobis-[4-methyl(2-trifluoromethyl)4-aminophenoxy) phenyl ether] (DA), was successfully synthesized from 2-2′-sulfide-bis-(4-methyl phenol) and 2-chloro-5-nitrobenzotrifluoride. The sulfur containing diimide-diacid (DIDA) was prepared by condensation reaction of diamine DA and trimellitic anhydride. A series of novel organic-soluble polyamide-imides (PAIs) bearing flexible ether and sulfide links, electron-withdrawing trifluoromethyl groups and ortho-phenylene units were synthesized from DIDA, by direct polycondensation with various aromatic diamines in N-methyl-2-pyrrolidone using triphenyl phosphite and pyridine as a condensing agent in the presence of dehydrating agent (LiCl). The polyamide-imides were obtained in high yields and possessed inherent viscosities in the range of 0.42-0.95 dL g−1. All of the polymers were amorphous in nature, showed outstanding solubility and could be easily dissolved in amide-type polar aprotic solvents (e.g., N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide) and even dissolved in less polar solvents (e.g., pyridine and tetrahydrofuran). They showed good thermal stability with glass transition temperatures between 195-245 °C, 10% weight loss temperatures in excess of 485 °C, and char yields more than 50% at 700 °C in nitrogen atmosphere. Moreover, these PAIs possessed low refractive indexes (n = 1.57-1.59) and low birefringence (Δ ≈ 0.02) due to the trifluoromethyl pendent groups and thioether bridged ortho-catenated aromatic rings that interrupt chain packing and increase free volume. 相似文献
935.
936.
937.
Abstract
Condensation of 2-acetylpyrrole with 5-methylfuran-2-carboxyaldehyde and 4-chlorobenzaldehyde in 20% NaOH give the corresponding 2-chalconylpyrroles. Some new 2-alkoxy-3-cyano-4,6-diarylpyridines were synthesized by condensation of chalcones with malononitrile, followed by cyclization in sodium alkoxide. The reactivity of chalcones towards nitrogen nucleophiles such as thiourea and hydroxylamine hydrochloride to provide thiopyrimidines and isoxazolines was investigated. 相似文献938.
Common fixed point results for noncommuting mappings without continuity in generalized metric spaces
Using the setting of a generalized metric space, a fixed point theorem is proved for one map, and several fixed point theorems are proved for two maps. These results generalize several well known comparable results in the literature. 相似文献
939.
Ahmed M. El-Khatib Bohaysa A. Salem Mohamed S. Badawi Mona M. Gouda Abouzeid A. Thabet Mahmoud I. Abbas 《Chinese Journal of Physics (Taipei)》2017,55(2):478-489
The coincidence summing effect is considered to be one of the most important problems in γ-ray spectrometry. It has played an important role in the detector calibration process, especially at low source-to-detector distances, which are the typical conditions when the environmental samples have to be measured. In this work, the γ–γ coincidence summing correction factors (CSCF) for a 3″×?3″ NaI(Tl) γ-ray detector have been calculated at different distances from the detector end cap. These factors with NaI(Tl) γ-ray detectors have rarely been discussed in the previous literature, due to the lack of the separation process of the close gamma energy lines in the scintillation detector spectrum. The γ–γ CSCF were calculated for 60Co, 133Ba and 152Eu radioactive point sources, which show the simple and the complex decay scheme of several radionuclides. In order to obtain the CSCF, the following parameters must be estimated by the numerical simulation method (NSM): the total efficiency (εT), the full-energy peak efficiency (εP) and the effective solid angle (Ωeff). These parameters were calculated numerically depending on the direct mathematical method and efficiency transfer method. The obtained CSCF was used to correct the measured efficiency curves, which were measured at different distances, then compared to the ETNA and EFFTRAN programs, as well as the CSCF. The results show a good agreement, especially at large source-to-detector distances. 相似文献
940.
Compressible subsonic turbulent starting jet with a relatively large Reynolds number of significant practical importance is investigated using large eddy simulation (LES), starting from a smooth contraction nozzle. The computational domain of truncated conical shape is determined through the comparison of the time-averaged numerical solution with the particle imaging velocimetry measurements for the steady jet. It is shown that the starting jet consists of a leading vortex ring followed by a quasi-steady jet, and the instantaneous velocity field exhibits contraction and expansion zones, corresponding to the high pressure (HP) and low pressure (LP) regions formed by the convecting vortex rings, and are related to the Kelvin-Helmholtz instability. The thin boundary layer inside the smooth contraction nozzle evolves into a shear layer at the nozzle exit and develops with the downstream penetration of the jet. Using λ 2 criterion, the formation and evolution of the vortical structures are temporally visualized, illustrating distortion of vortex rings into lobed shapes prior to break-down. Rib-shape streamwise vortex filaments exist in the braid region between a pair of consecutive vortex rings due to secondary instabilities. Finally, formation and dynamics of hairpin vortices in the shear layer is identified. 相似文献