Search results for "Quenching"
showing 10 items of 275 documents
Pionic effects in deep inelastic scattering off nuclei
1992
The structure functions calculated in the Chiral bag model reproduce quite well, after appropriate perturbative evolution to large energy scales, the experimental data. We use these results to interpret the structure of the $EMC$ data as a quenching of the pion decay constant due to the in medium behavior of the nucleon. This explanation supports recent proposals of this phenomenon whose origin is the scale invariance of the $QCD$ lagrangian.
Charmonium dissociation and heavy quark transport in hot quenched lattice QCD
2012
We study the properties of charmonium states at finite temperature in quenched lattice QCD on large and fine isotropic lattices. We perform a detailed analysis of charmonium correlation and spectral functions both below and above Tc. Our analysis suggests that the S wave states disappear at about 1.5 Tc. The charm diffusion coefficient is estimated and found to be approximately 1/{\pi}T at 1.5Tc {\leq} T {\leq} 3Tc.
Radiation processes in oxygen-deficient silica glasses: Is ODC(I) a precursor of E′-center?
2006
Abstract The accumulation of radiation-induced defects under non-destructive X-ray and destructive cathodoexcitation was studied in pure silica KS-4V glasses possessing an absorption band at 7.6 eV. The correspondence between the existence of this band and the creation of the E′-center by radiation was checked. Detection of induced defects was accomplished by measurement of the luminescence during irradiation, post irradiation afterglow or phosphorescence, induced optical absorption, and thermally stimulated luminescence. In all samples, these observed phenomena associated with charge trapping and recombination on the oxygen-deficient luminescence center. Others centers of luminescence were…
The Medium-Depending Fluorescence of Quadrupolar Donor-Acceptor-Donor Substituted Distyrylbenzenes with High Two-Photon Absorption Cross-Sections
2006
ABSTRACT1,4-Distyrylbenzenes with terminal dialkylamino groups and a central 2,5-disubstitution with electron-accepting groups were prepared via twofold Horner-olefination. These chromophores with a quadrupolar donor-acceptor-donor substitution and C2-symmetry absorb in the violet to green region of the visible spectrum exhibit large two-photon-absorption cross-sections when irrdiated in the NIR. Whereas a variation of the solvent polarity only slightly alters the absorption spectra, the fluorescence appears to be highly responsive. Besides a positive solvatochromism, the emission is very sensitive towards protonation. Quenching or appearance of new emitting species depends on the substitut…
Structure–property relationship of isomeric diphenylethenyl-disubstituted dimethoxycarbazoles
2015
Isomeric 3,6-dimethoxy- and 2,7-dimethoxycarbazoles containing diphenylethenyl moieties were synthesized by condensation of the appropriate dimethoxycarbazoles with diphenylacetaldehyde. The solid-state structures and the molecular order of the compounds were proven by X-ray crystallography. Both compounds were found to be capable of glass formation with comparable glass transition temperatures (70–71 °C). They exhibited high thermal stabilities, with the 5% weight loss temperatures exceeding 375 °C. The isomer having diphenylethenyl groups at C-3 and C-6 positions and methoxy groups at C-2 and C-7 positions (3a) exhibited aggregation-induced emission (AIE), while its counterpart having dip…
Size Reduction of CdSe/ZnS Core−Shell Quantum Dots Photosensitized by Benzophenone: Where Does the Cd(0) Go?
2011
The size of core-shell CdSe/ZnS quantum dots can be decreased by using the combined action of an n,π* aromatic ketone and UVA light. Energy-dispersive X-ray spectroscopy as well as X-ray photoelectron spectroscopy techniques gave information on the photosensitization mechanism and the eventual destiny of Cd(2+) and Se(2-) core ions. Our data support the electron transfer from the BP ketyl radical to Cd(2+), leading to Cd(0) and H(+), as well as to the recovery of benzophenone. Elemental Cd remains on the core and, eventually, can be oxidized to CdO. In addition, Se(2-) counterions disperse inside the solution mainly attached to protonated amine ligands. The Se(2-) combines with H(+), leadin…
Assemblies of semiconductor quantum dots and light-harvesting-complex II
2010
Abstract A novel hybrid system composed of fluorescent core/shell semiconductor quantum dots and the light harvesting complex II (LHCIIb), a membrane protein of higher plants, has been assembled. Experiments with different mutants show that hybrid formation can be mediated by a C-terminal His 6 tag attached to the protein as well as by positive charges of the first N-terminal amino acids of LHCIIb. Quenching of the quantum dot fluorescence upon binding of LHCIIb was partially attributed to energy transfer from the quantum dots to LHCIIb.
The Role of Site-Specific Hydrogen Bonding Interactions in the Solvation Dynamics of N-Acetyltryptophanamide
2012
Measurements of the ultrafast broadband UV fluorescence of N-acetyltryptophanamide (NATA) provide detailed information on its relaxation patterns in three different solvents: methanol (MeOH), water and acetonitrile (ACN). Several processes leading to excited state solvation and cooling are found to occur on different characteristic time scales and are thoroughly analyzed. Comparison between protic MeOH and aprotic ACN allows one to single out a 12 Ps component in the former, which is attributed to the rearrangement of H-bonds existing between the protic solvent and excited NATA. This significantly stabilizes the excited state and provides the molecule with an efficient cooling mechanism. Th…
Kinetic solvent effects on the reaction of an aromatic ketone pi,pi* triplet with phenol. rate-retarding and rate-accelerating effects of hydrogen-bo…
2007
Quenching of the 2-benzoylthiophene π,π* triplet, 3BT*, by phenol yields the corresponding ketyl and phenoxyl radicals. Reaction rates were measured in 10 solvents having a range of hydrogen-bond acceptor strengths (β2H values). There appear to be two mechanisms: (i) a bimolecular reaction of 3BT* with “free” (i.e., not H-bonded) phenol in which the 3BT* accepts both a proton and an electron from the phenol, the rate decreasing as β2H increases; (ii) a trimolecular reaction of 3BT* with phenol that is H-bonded to a solvent molecule, PhO−H···S, in which the proton goes to the S and the electron to the 3BT*, the rate increasing as β2H increases.
Spontaneous lifetimes and relaxation cross-sections of the D1Π state of NaRb
2003
Abstract The time-resolved intensity of dispersed laser induced fluorescence following the Ar + -laser D 1 Π←X 1 Σ + excitation was measured for both 23 Na 85 Rb and 23 Na 87 Rb isotopomers in a thermal cell. Spontaneous radiative lifetime values determined for v ′ ( J ′ ) rovibronic levels of the D 1 Π state in the v ′ range from 0 to 17 and J ′ from 8 to 131 varied from 22.5 to 17.3 ns. Averaged collisional quenching cross-section values of (3–6)×10 −14 cm 2 were obtained for NaRb (D 1 Π, v ′ , J ′ ) + Rb collisions from the Stern–Volmer plots.