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11.
A.V. Idesman K. Subramanian J.R. Foley R.L. Sierakowski 《Journal of sound and vibration》2010,329(14):2851-2872
An accurate solution for high-frequency pulse propagation in an axisymmetric elastic bar is obtained using a new finite element technique that yields accurate non-oscillatory solutions for wave propagation problems in solids. The solution of the problem is very important for the understanding of dynamics experiments in the split Hopkinson pressure bar (SHPB). In contrast to known approaches, no additional assumptions are necessary for the accurate solution of the considered problem. The new solution helps to elucidate the complicated distribution of parameters during high-frequency pulse propagation down the bar as well as to estimate the applicability of the traditional dispersion correction used in the literature for the analysis of wave propagation in a finite bar. Due to the dimensionless formulation of the problem, the numerical results obtained depend on Poisson's ratio, the length of the bar and the pulse frequency, and are independent of Young's modulus, the density and the radius of the bar. 相似文献
12.
We construct a map from the classifying space of a discrete Kac–Moody group over the algebraic closure of the field with p elements to the classifying space of a complex topological Kac–Moody group and prove that it is a homology equivalence at primes q different from p. This generalizes a classical result of Quillen, Friedlander and Mislin for Lie groups. As an application, we construct unstable Adams operations for general Kac–Moody groups compatible with the Frobenius homomorphism. Our results rely on new integral homology decompositions for certain infinite dimensional unipotent subgroups of discrete Kac–Moody groups. 相似文献
13.
Vesicle electrokinetic chromatography (VEKC) using vesicles synthesized from the oppositely charged surfactants cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) and from the double-chained anionic surfactant bis(2-ethylhexyl)sodium sulfosuccinate (AOT) was applied to the indirect measurement of octanol-water partition coefficients (log Po/w). A variety of small organic molecules with varying functional groups, pesticides, and organic acids were evaluated by correlating log Po/w and the logarithm of the retention factor (log k') and comparing the calibrations. A linear solvation energy relationship (LSER) analysis was conducted to describe the retention behavior of the vesicle systems and compared to that of octanol-water partitioning. The solute hydrogen bond donating behavior is slightly different with the vesicle interactions using CTAB-SOS vesicles as compared to the octanol-water partitioning model. The AOT vesicle and octanol-water partitioning systems showed similar partitioning characteristics. VEKC provides rapid separations for determinations of log Po/w in the range of 0.5 to 5 using CTAB-SOS vesicles and 0 to 5.5 using AOT vesicles. 相似文献
14.
Counterion and organic modifier are two parameters in EKC that can be varied in order to obtain improved solubility, selectivity, and efficiency. The effect of changing surfactant counterion and/or organic modifier on the chromatographic and electrophoretic properties of cetyltrimethylammonium bromide (CTAB)/sodium octyl sulfate (SOS) vesicles is examined in EKC. The vesicles are prepared in a 1:3.66 cationic/ anionic mole ratio for a total surfactant concentration of 69 mM. The cationic CTAB is replaced by cetyltrimethylammonium chloride (CTAC) and the first use of CTAC/SOS vesicles is reported. The mean diameter of the CTAC/SOS vesicles is 96 nm while that of the CTAB/SOS vesicles is 85 nm. A class I modifier (2-amino-1-butanol) and a class II modifier (acetonitrile) have similar effects on the EOF, elution range, methylene selectivity, and the efficiency of the CTAB/SOS vesicles and the CTAC/SOS vesicles. Upon addition of 10% ACN, there is roughly a 10-fold increase in the efficiency of heptanophenone, a model hydrophobic compound, compared to the efficiency using unmodified vesicles. Linear free energy relationship (LFER) analysis using the Abraham solvation model is employed to characterize solute-vesicle interactions. The results suggest that organic modifier-vesicle interactions depend somewhat on the counterion. 相似文献
15.
Electric dipole radiation consists of traveling and evanescent plane waves. When radiation is detected in the far field, only the traveling waves will contribute to the intensity distribution, as the evanescent waves decay exponentially. We propose a method to spatially separate the traveling and evanescent waves before detection. It is shown that when the radiation passes through an interface, evanescent waves can be converted into traveling waves and can subsequently be observed in the far field. Let the radiation be observed under angle theta(t) with the normal. Then there exists an angle theta(ac) such that for 0 < or = theta(t) < theta(ac) all intensity originates in traveling waves, whereas for theta(ac) < theta(t) < pi/2 only evanescent waves contribute. It is shown that with this technique and under the appropriate conditions almost all far-field power can be provided by evanescent waves. 相似文献
16.
F B?hm R Edge S Foley L Lange T G Truscott 《Journal of photochemistry and photobiology. B, Biology》2001,65(2-3):177-183
Porphyrins such as protoporphyrin IX (PP IX) and uroporphyrin I (UP I) can be phototoxic to human cells. To study the protective ability of antioxidants (beta-carotene, lycopene, ascorbic acid and alpha-tocopherol), against such porphyrin phototoxicity, membrane destruction experiments (Jurkat cells) and human cell cultures (fibroblasts) were performed. Both beta-carotene and lycopene and also the combination of beta-carotene, ascorbic acid and alpha-tocopherol offered cell protection against PP IX phototoxicity. Investigations of both cell membrane protection and of cell growth showed differences in terms of the protection afforded by the anti-oxidants. Thus, for PP IX, carotenoids alone, and in combination with ascorbic acid and alpha-tocopherol, showed higher protection factors in general than UP I. However, for membrane protection there was significant protection against UP I by the combination of beta-carotene, ascorbic acid and alpha-tocopherol but not by any of these anti-oxidants alone. The membrane protection against PP IX by beta-carotene, and especially lycopene, is significant presumably because of the high lipophilicity of all these molecules. However, the hydrophilic UP I will cause phototoxicity mainly via H(2)O(2), radical or singlet oxygen production in the aqueous phase, and these reactive species may be generated some distance from the cell membrane. This may lead to the little or no protection observed for UP I by the individual antioxidants. Nevertheless, a combination of beta-carotene, ascorbic acid and alpha-tocopherol offers membrane protection against the phototoxicity of both porphyrins. This is believed to occur as a result of synergistic processes. Our results suggest that the treatment of porphyria cutanea tarda and erythropoietic protoporphyria may be improved by the use of a combination of the antioxidants studied. 相似文献
17.
18.
M. Terrones P.M. Ajayan F. Banhart X. Blase D.L. Carroll J.C. Charlier R. Czerw B. Foley N. Grobert R. Kamalakaran P. Kohler-Redlich M. Rühle T. Seeger H. Terrones 《Applied Physics A: Materials Science & Processing》2002,74(3):355-361
Self-assembly pyrolytic routes to large arrays (<2.5 cm2) of aligned CNx nanotubes (15–80 nm OD and <100 μm in length) are presented. The method involves the thermolysis of ferrocene/melamine mixtures
(5:95) at 900–1000 °C in the presence of Ar. Electron energy loss spectroscopy (EELS) reveals that the N content varies from
2–10%, and can be bonded to C in two different fashions (double-bonded and triple-bonded nitrogen). The electronic densities
of states (DOS) of these CNx nanotubes, using scanning tunneling spectroscopy (STS), are presented. The doped nanotubes exhibit strong features in the
conduction band close to the Fermi level (0.18 eV). Using tight-binding and ab initio calculations, we confirm that pyridine-like
(double-bonded) N is responsible for introducing donor states close to the Fermi Level. These electron-rich structures are
the first example of n-type nanotubes. Finally, it will be shown that moderate electron irradiation at 700–800 °C is capable
of coalescing single-walled nanotubes (SWNTs). The process has also been studied using tight-binding molecular dynamics (TBMD).
Vacancies induce the coalescence via a zipper-like mechanism, which has also been observed experimentally. These vacancies
trigger the organization of atoms on the tube lattices within adjacent tubes. These results pave the way to the fabrication
of nanotube heterojunctions, robust composites, contacts, nanocircuits and strong 3D composites using N-doped tubes as well
as SWNTs.
Received: 10 October 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002 相似文献
19.
In lattice QCD, the maximum entropy method can be used to reconstruct spectral functions from Euclidean correlators obtained in numerical simulations. We show that at finite temperature the most commonly used algorithm, employing Bryan's method, is inherently unstable at small energies and gives a modification that avoids this. We demonstrate this approach using the vector current-current correlator obtained in quenched QCD at finite temperature. Our first results indicate a small electrical conductivity above the deconfinement transition. 相似文献
20.
Reversible Modulation of Surface Plasmons in Gold Nanoparticles Enabled by Surface Redox Chemistry
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Dr. Zheng Li Dr. Jonathan J. Foley IV Dr. Sheng Peng Dr. Cheng‐Jun Sun Dr. Yang Ren Dr. Gary P. Wiederrecht Dr. Stephen K. Gray Dr. Yugang Sun 《Angewandte Chemie (International ed. in English)》2015,54(31):8948-8951
Switchable surface redox chemistry is demonstrated in gold@iron/iron oxide core–shell nanoparticles with ambient oxidation and plasmon‐mediated reduction to modulate the oxidation state of shell layers. The iron shell can be oxidized to iron oxide through ambient oxidation, leading to an enhancement and red‐shift of the gold surface plasmon resonance (SPR). This enhanced gold SPR can drive reduction of the iron oxide shell under broadband illumination to reversibly blue‐shift and significantly dampen gold SPR absorption. The observed phenomena provide a unique mechanism for controlling the plasmonic properties and surface chemistry of small metal nanoparticles. 相似文献