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861.
We present direct experimental observation of exciton-phonon bound states in the photoluminescence excitation spectra of isolated single-walled carbon nanotubes (SWNT) in aqueous suspension. The photoluminescence excitation spectra from several distinct SWNTs show the presence of at least one sideband related to the tangential modes, lying 0.2 eV above the main absorption or emission peak. Both the energy position and line shapes of the sidebands are in excellent agreement with recent calculations [Phys. Rev. Lett. 94, 027402 (2005)] that predict the existence of exciton-phonon bound states, a sizable spectral weight transfer to these exciton-phonon complexes, and that the amount of this transfer depends on the specific nanotube structure and diameter. 相似文献
862.
P. P.?FáveroEmail author J. M.R.?Cruz 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,47(3):363-368
A generalization of the pure site and pure bond percolation problems
in which pairs of nearest neighbor sites (site dimers) and linear
pairs of nearest neighbor bonds (bond dimers) are independently
occupied at random on a square lattice is studied. We called this
model as dimer site-bond percolation. Motivated by considerations of
cluster connectivity, we have used two distinct schemes (denoted as
and
) for dimer site-bond percolation. In
(
), two points are said to be connected if a sequence
of occupied sites and (or) bonds joins them. By using
finite-size scaling theory, data from
and
are
analyzed in order to determine i) the phase boundary between the
percolating and non-percolating regions and ii) the numerical
values of the critical exponents of the phase transition occurring
in the system. The results obtained are discussed in comparison with
the corresponding ones for classical monomer site-bond percolation. 相似文献
863.
864.
Andreu Y Galbán J de Marcos S Castillo JR 《Fresenius' Journal of Analytical Chemistry》2000,368(5):516-521
A method for the determination of direct bilirubin by reaction with bilirubin oxidase (BOx) is reported. The procedure is based on the changes in fluorescence which take place during the enzymatic reaction of BOx with any of the three forms of bilirubin (free, conjugated and with albumin) when the solution is excited at 240 nm and the emission is measured at 440 nm. The change in fluorescence was studied thoroughly. It seems mainly due to the fluorescence of one of the reaction products. A theoretical study was carried out to relate the changes in fluorescence observed to the species taking part in the reaction and to establish some of the enzymatic reaction constants. The optimum reaction conditions were studied for each of the three types of bilirubin together with their analytical characteristics (linear range and precision). Selective determination of direct bilirubin was carried out for various synthetic samples with good results. A linear response up to 7 mg L(-1) of direct bilirubin was obtained. Using optimum conditions, the precision for free and conjugated bilirubin was 3.4% (n = 5) and 3.0% (n = 5), respectively. 相似文献
865.
Jaime-Figueroa S Kurz LJ Liu Y Cruz R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(6):1167-1178
The synthesis and NMR study (1H, 13C, and 19F) of a complete series of 4,5-substituted 1-acetyl-8-fluoronaphthalenes are reported. This data revealed a 6J(H,F) and a 5J(C,F) through space coupling between the fluorine and the methyl on the acetyl group (1H and 13C). The magnitude of this coupling constant changes depending on the nature of the substituent at C-4, the internuclear distance, and the solvent. 相似文献
866.
Evaluation of Crohn's disease using half-fourier RARE and gadolinium-enhanced SGE sequences: initial results 总被引:4,自引:0,他引:4
To assess the bowel changes in Crohn's disease, 11 consecutive patients underwent magnetic resonance imaging (MRI) study using T(2)-weighted half-Fourier rapid acquisition with relaxation enhancement (RARE) and gadolinium-enhanced standard and fat suppressed spoiled gradient echo (SGE) sequences. Comparison was made between MR findings of disease extent, severity, and complications and clinical data, endoscopic findings and/or surgical specimens in all patients. We found that the half-Fourier RARE images showed bowel wall thickening, dilatation of bowel and bowel obstruction well in all patients, however severity of bowel disease could not be determined as the signal intensity of diseased bowel was comparable to normal bowel in 10/11 patients. Gadolinium-enhanced fat suppressed SGE demonstrated variations of mural enhancement that correlated well with extent of disease severity in 10/11 patients. Complications such as intraperitoneal (i. p.) abscess (2 patients), gastric outlet obstruction (1 patient), bowel obstruction (2 patients), and fistula formation (3 patient), were accurately shown. We conclude that T(2)-weighted half-Fourier RARE and gadolinium-enhanced fat suppressed SGE sequences are complementary techniques that possess different imaging features that are of value for assessing bowel changes in Crohn's disease. 相似文献
867.
Nesterenko VO Marinelli JR de Souza Cruz FF Kleinig W Reinhard PG 《Physical review letters》2000,85(15):3141-3144
A remarkable orbital quadrupole magnetic resonance, so-called twist mode, is predicted in alkali metal clusters where it is represented by Ipi = 2(-) low-energy excitations of valence electrons with strong M2 transitions to the ground state. We treat the twist by both macroscopic and microscopic ways. In the latter case, the shell structure of clusters is fully exploited, which is crucial for the considered size region ( 8相似文献
868.
M. G. Olayo J. Morales G. J. Cruz S. R. Barocio R. Olayo 《Journal of Polymer Science.Polymer Physics》2003,41(13):1501-1508
A numerical and experimental study of the plasma variables in the synthesis of polyaniline in radio‐frequency (RF) glow discharges is presented. The plasma variables were measured on the basis of data collected by electrostatic Langmuir probes placed along the reactor. The results showed the distribution of the electric potential and the electronic energy and density during the polymerization reactions. The region with the lowest energy was the zone adjoining the grounded electrode, whereas the maximum energy was located near the RF electrode. In the second zone, the energy was around twice that of the grounded zone, and both were beyond the typical atomic bonding energy found in most organic polymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1501–1508, 2003 相似文献
869.
The magnetic field and temperature dependence of the magnetization of bulk aluminum near the normal-superconductor transition has been measured. Due to the large amount of supercooling in one of the samples it was possible to extend the measurements well below the critical temperature. A comparison of the experimental results with theory is presented. 相似文献
870.
Measurement of the Meissner penetration depth, λ(T) were made in amorphous Zr70Cu30 samples. The results indicate that this amorphous alloy behaves as a BCS superconductor with 2Δ(0)?kTc = 3.8, where Δ(0) is the superconducting energy gap at T=0 and Tc the critical temperature. It is also concluded that the low energy excitation, TLS, characteristics of amorphous material does not contribute to Tc. 相似文献