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The earliest examples of quenched steel may come from ancient Mesopotamia, with a relatively secure example of a fourth-century BC quench-hardened chisel from Al Mina in Turkey. [6] Book 9, lines 389-94 of Homer's Odyssey is widely cited as an early, possibly the first, written reference to quenching: [ 3 ] [ 7 ]
Typically quinine fluoresces blue, which is visible in the right sample. The left sample contains chloride ions which quench quinine's fluorescence, so the left sample does not fluoresce visibly (the violet light is just scattered laser light). In chemistry, quenching refers to any process which decreases the fluorescent intensity of a given ...
For diffusion-limited quenching (i.e., quenching in which the time for quencher particles to diffuse toward and collide with excited particles is the limiting factor, and almost all such collisions are effective), the quenching rate coefficient is given by = /, where is the ideal gas constant, is temperature in kelvins and is the viscosity of ...
Non-photochemical quenching (NPQ) is a mechanism employed by plants and algae to protect themselves from the adverse effects of high light intensity.It involves the quenching of singlet excited state chlorophylls (Chl) via enhanced internal conversion to the ground state (non-radiative decay), thus harmlessly dissipating excess excitation energy as heat through molecular vibrations.
Quench polish quench (QPQ) is a specialized type of nitrocarburizing case hardening that increases corrosion resistance. It is sometimes known by the brand name of Tufftride, Tenifer or Melonite. [1] Three steps are involved: nitrocarburize ("quench"), polish, and post-oxidize ("quench"). [2]
The Dexter energy transfer rate, , is indicated by the formula: = ′ [] where is the separation of the donor from the acceptor, is the sum of the Van der Waals radii of the donor and the acceptor, and ′ is the normalized spectral overlap integral, where normalized means that both emission intensity and extinction coefficient have been adjusted to unit area.
The quencher then returns to the ground state through emissive decay (fluorescence) or nonradiatively (dark quenching). In nonradiative or dark decay, energy is given off via molecular vibrations (heat). With the typical μM or less concentration of sample, the heat from radiationless decay is too small to affect the temperature of the solution.
Here, I and I 0 denote the emission intensity with and without quenching agent present, k q the rate constant of the quenching process, τ 0 the excited-state lifetime in the absence of quenching agent and [Q] the concentration of quenching agent. Thus, if the excited-state lifetime of the photoredox catalyst is known from other experiments ...