Quenched approximation

Fluorescence quenching studies carried out on the first series of porphyrin dimer 53a, trimer 53b, and tetramer 53c show that fluorescence of the porphyrin arrays is quenched approximately 100 times compared to arrays not bearing fullerenes. Due to the properties of the arrays, namely strong excitonic coupling and red shifted, split Soret bands, no conclusions are drawn about the mechanism (ET or eT) of the quenching. 

The quenched approximation is one that neglects creation and annihilation of quark-antiquark pairs. Use of this approximation cannot be right, since at large distances it becomes energetically favourable to produce such pairs. Therefore, the potential concept breaks down. If quark-antiquark pairs are included, the time required to do a lattice calculation is very long with present techniques, and so far the calculation has been done only on lattices which are too small to give a reliable result. 

Phenomenologically, it appears as if the static potential is flavour independent to a good approximation. The static potential determined from QCD in lowest-order perturbation theory is also independent of quark flavour. The situation is more complicated for the non-perturbative part of the potential. In the quenched approximation the strength of the linear potential also appears to be independent of flavour, at least for sufiiciently heavy quarks. A flavour-independent potential means that the same static... 

The economics of the arc-coal process is sensitive to the electric power consumed to produce a kilogram of acetylene. Early plant economic assessments indicated that the arc power consumption (SER = kwh/kgC2H2) must be below 13.2. The coal feedcoal quench experiments yielded a 9.0 SER with data that indicated a further reduction to below 6.0 with certain process improvements. In the propane quench experiment, ethylene as well as acetylene is produced. The combined process SER was 6.2 with a C2H2/C2H4 production ratio of 3 to 2. Economic analysis was completed uti1i2ing the achieved acetylene yields, and an acetylene price approximately 35% lower than the price of ethylene was projected. 

The dye is excited by light suppHed through the optical fiber (see Fiber optics), and its fluorescence monitored, also via the optical fiber. Because molecular oxygen, O2, quenches the fluorescence of the dyes employed, the iatensity of the fluorescence is related to the concentration of O2 at the surface of the optical fiber. Any glucose present ia the test solution reduces the local O2 concentration because of the immobilized enzyme resulting ia an iacrease ia fluorescence iatensity. This biosensor has a detection limit for glucose of approximately 100 ]lM , response times are on the order of a miaute. 

The preceding equation assumes the reaction is completely quenched immediately after the relief point is reached. This behavior is closely approximated if the reaction stops in the quench pool and the reactor empties quickly and thoroughly. If the reaction continues in the quench pool, the temperature Tr should be increased to the maximum adiabatic exotherm temperature. An equation is presented by CCPS (AIChE-CCPS, 1997) that includes the heat of reaction. In some cases, an experiment is necessary to confirm that the reaction indeed stops in the quench pool. 

Poly(ethylene terephthalate) film is produced by quenching extruded film to the amorphous state and then reheating and stretching the sheet approximately three-fold in each direction at 80-100°C. In a two-stage process machine direction stretching induces 10-14% crystallinity and this is raised to 20-25% by... 

Utilization of resonance effects can facilitate unenhanced Raman measurement of surfaces and make the technique more versatile. For instance, a fluorescein derivative and another dye were used as resonantly Raman scattering labels for hydroxyl and carbonyl groups on glassy carbon surfaces. The labels were covalently bonded to the surface, their fluorescence was quenched by the carbon surface, and their resonance Raman spectra could be observed at surface coverages of approximately 1%. These labels enabled assess to changes in surface coverage by C-OH and C=0 with acidic or alkaline pretreatment [4.293]. 

The correlation functions of the partly quenched system satisfy a set of replica Ornstein-Zernike equations (21)-(23). Each of them is a 2 x 2 matrix equation for the model in question. As in previous studies of ionic systems (see, e.g.. Refs. 69, 70), we denote the long-range terms of the pair correlation functions in ROZ equations by qij. Here we apply a linearized theory and assume that the long-range terms of the direct correlation functions are equal to the Coulomb potentials which are given by Eqs. (53)-(55). This assumption represents the mean spherical approximation for the model in question. Most importantly, (r) = 0 as mentioned before, the particles from different replicas do not interact. However, q]f r) 7 0 these functions describe screening effects of the ion-ion interactions between ions from different replicas mediated by the presence of charged obstacles, i.e., via the matrix. The functions q j (r) need to be obtained to apply them for proper renormalization of the ROZ equations for systems made of nonpoint ions. 

Fig. 5 illustrates a peculiar kinetic phenomenon which occurs when an initially disordered alloy is first annealed at temperature T corresponding to area b in Fig. 1 and then quenched to the final temperature T into the spinodal instability area d antiphase boundaries "replicate , generating approximately periodic patterns. This phenomenon reflects the presence of critical, fastest growing concentration waves under the spinodal instability (the Calm waves ). Lowering of the temperature to T < T results in lowering of the minority concentration minimum ("c-well ) within APB, while the expelled solute atoms build the c-bank adjacent to the well . Due to the... 

Heavy-wall drillpipe has approximately twice the usual wall thickness and is usually made from AISI 4140-4I45H. The steel is quenched and tempered to the Rockwell C hardness of various grades from 20 to 28 for grade E, 27 to 30 for grade X-95, 30 to 34 for grade G-105 and 34 to 37 for S 135. 

The reaction is quenched by the addition of 1.28 g (2.94 mmol) of molybdenum pentoxidc/pyridinc/UMPA, and the yellow slurry is stirred initially at OX (30 min), then for 45 min at 25 X. The mixture is added to 1 N sodium hydroxide and extracted with diethyl ether. The ethereal solution is washed with brine, dried over Na,S04 and concentrated in vacuo to give 0.705 g (100%) of an oily, light-yellow solid. Analysis of the crude aldol adduct by 1 C NMR and analytical HPLO (Waters, Radial Pak, 8 mm x 10 cm, silica gel, ethyl acetate/hexane, 15 85) indicates only one. un-diastereomer (2X3S ) accompanied by approximately 10% of the two ethyl acetate/hexane affords fine white needles yield 0.359 g (57%) mp 155.5 156.5X (a]u -92.5 (c = 0.0294, CHCfi). 

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