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991.
The problems involved in extrapolating the 12C(α, γ)16O cross section to stellar energies are investigated. In the R-matrix formalism used, the extrapolated cross section is shown to be approximately independent of the interaction radius and the boundary condition number. Simultaneously good fits to recent 12C(α, γ)16O data and the 12C + α elastic scattering p-wave phase shift are shown. 相似文献
992.
We construct field equations and generalised Bloch equations for multiphoton processes involving the coherent interaction of a number of distinct electric fields with an arbitrary number of atomic eigenstates, and apply the equations to some physical examples. Transient stimulated hyper-Raman scattering, in the low-conversion regime and far from saturation, has been studied analytically. Assuming that the pump pulse interacts with the medium byn-photon absorption, we find expression for the intensity of the generated Stokes pulse. 相似文献
993.
High resolution measurements of the (γ, n), (γ, 2n), (γ, p), (γ, np) and (γ, 2p) cross sections of 40Ar over a photon energy range of 10 to 28 MeV are reported. From this data, the total photon absorption cross section integrated to 26 MeV is found to be 434 ± 40 MeV mb. The results of a dynamic collective model (DCM) calculation compare favourably with the photoabsorption cross section, supporting the use of the DCM in this mass region. It is confirmed that isospin plays an important role in the decay of the 40Ar giant dipole resonance. 相似文献
994.
995.
D. P. Barber J. B. Dainton L. C. Y. Lee R. Marshall J. C. Thompson D. T. Williams T. J. Brodbeck G. Frost A. M. Osborne G. N. Patrick G. F. Pearce T. Sloan G. R. Brookes W. J. Haynes P. B. Wilkes LAMP Group 《Zeitschrift fur Physik C Particles and Fields》1979,2(1):1-6
Measurements of the photoproduction processes γρ→ρ+ n and γρ→ρ-Δ++ (1236) are reported in the energy range 2.8 to 4.8 GeV. The data show shrinkage of the differential cross section in this energy region for the process γρ→ρ-Δ++ (1236); no shrinkage is observed for the ρ+ n process. The energy dependences of the ρ+ n and ρ-Δ++ (1236) total cross sections are much steeper than current model prediction. The ρ spin density matrices for each process are also presented. 相似文献
996.
Shaobo Li Madushani Dharmarwardana Raymond P. Welch Yixin Ren Dr. Christina M. Thompson Prof. Ronald A. Smaldone Prof. Jeremiah J. Gassensmith 《Angewandte Chemie (International ed. in English)》2016,55(36):10691-10696
Metal–organic frameworks (MOFs) are promising high surface area coordination polymers with tunable pore structures and functionality; however, a lack of good size and morphological control over the as‐prepared MOFs has persisted as an issue in their application. Herein, we show how a robust protein template, tobacco mosaic virus (TMV), can be used to regulate the size and shape of as‐fabricated MOF materials. We were able to obtain discrete rod‐shaped TMV@MOF core–shell hybrids with good uniformity, and their diameters could be tuned by adjusting the synthetic conditions, which can also significantly impact the stability of the core–shell composite. More interestingly, the virus particle underneath the MOF shell can be chemically modified using a standard bioconjugation reaction, showing mass transportation within the MOF shell. 相似文献
997.
Pyrrolocytosine (PC), is a highly fluorescent analog of the natural nucleobase cytosine. The fluorescence of PC is quenched upon helix formation but the origin of the quenching is not known. We investigated the effects of base stacking in the aqueous phase by following the fluorescence of dinucleotides and trinucleotides containing PC. The quantum yields and lifetimes (ns) (in parenthesis) obtained at 25 degrees C were: PC-T, 0.026 (2.0), PC-C, 0.033 (2.5), PC-A, 0.032 (2.7), PC-G, 0.021 (2.0), T-PC-T, 0.044 (3.0) and G-PC-G, 0.036 (0.65 and 2.6), compared with 0.038 (2.9) for PC and 0.028 (2.1) for the nucleoside triphosphate. The results show that base stacking does not, except in the case of guanine, quench the fluorescence of PC; indeed the increased solvent shielding can enhance the emitted fluorescence. In the case of G-PC-G the guanines do shield the fluorescent base from the solvent but a particular environment of PC between two guanines also appears to allow a rapid nonradiative pathway, suggested to be electron transfer to the excited PC, to depopulate the excited state leading to the shorter fluorescence lifetime. 相似文献
998.
Woo CH Thompson BC Kim BJ Toney MF Fréchet JM 《Journal of the American Chemical Society》2008,130(48):16324-16329
A comparison of three samples of poly(3-hexylthiophene) having regioregularities of 86, 90, and 96% is used to elucidate the effect of regioregularity on polymer-fullerene-composite solar cell performance. It is observed that polymer samples with lower regioregularity are capable of generating fullerene composites that exhibit superior thermal stability. The enhanced thermal stability of the composites is attributed to a lower driving force for polymer crystallization in the less regioregular polymer samples, which is supported with two-dimensional grazing incidence X-ray scattering and differential scanning calorimetry measurements. Furthermore, it is demonstrated that all three polymer samples are capable of generating solar cells with equivalent peak efficiencies of approximately 4% in blends with [6,6]-phenyl-C61-butyric acid methyl ester. While it may be non-intuitive that polymers with lower regioregularity can exhibit higher efficiencies, it is observed that the charge-carrier mobility of the three polymers is on the same order of magnitude (10(-4) cm2 V(-1) s(-1)) when measured from the space-charge-limited current, suggesting that highly regioregular and crystalline polythiophenes are not required in order to effectively transport charges in polymer solar cells. Overall, these results suggest a design principle for semicrystalline conjugated polymers in fullerene-composite solar cells in which crystallization-driven phase separation can be dramatically suppressed via the introduction of a controlled amount of disorder into the polymer backbone. 相似文献
999.
Wampler RD Kissick DJ Dehen CJ Gualtieri EJ Grey JL Wang HF Thompson DH Cheng JX Simpson GJ 《Journal of the American Chemical Society》2008,130(43):14076-14077
The unique symmetry properties of second harmonic generation (SHG) microscopy enabled sensitive and selective imaging of protein microcrystals with negligible contributions from solvated proteins or amorphous protein aggregates. In studies of microcrystallites of green fluorescent protein (GFP) prepared in 500 pL droplets, the SHG intensities rivaled those of fluorescence, but with superb selectivity for crystalline regions. GFP in amorphous aggregates and in solution produced substantial background fluorescence, but no detectable SHG. The ratio of the forward-to-backward detected SHG provides a measure of the particle size, suggesting detection limits down to crystallites 100 nm in diameter under low magnification (10x). In addition to being sensitive and highly selective, second-order nonlinear optical imaging of chiral crystals (SONICC) is directly compatibility with virtually all common protein crystallization platforms. 相似文献
1000.
Chmielewski MJ Zhao L Brown A Curiel D Sambrook MR Thompson AL Santos SM Felix V Davis JJ Beer PD 《Chemical communications (Cambridge, England)》2008,(27):3154-3156
The first example of anion templated pseudorotaxane formation between two neutral components in solution and in surface assembled monolayers is described. 相似文献