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from article Absorption
Incident sunlight is absorbed, reflected, and scattered by tree leaves. (Credit: Shutterstock / photolinc)
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from article Bioorganic chemistry
Vancomycin and an analog that is active against vancomycin-resistant bacteria.
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from article Bioorganic chemistry
Foldamers that mimic proteins.
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from article Bioorganic chemistry
The rate of this intramolecular lactonization, relative to that of intermolecular esterification, mimics the rate increase caused by an enzyme's binding and orienting substrates for a bimolecular reaction.
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from article Bioorganic chemistry
Intramolecular models of enzymatic general acid and general base catalysis. (a) Intramolecular general acid catalysis causes this acetal to hydrolyze at pH 7 more than 107 times faster than the corresponding acetal without the carboxylic acid group.…
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from article Bioorganic chemistry
An antibody raised against the phosphonate analog of a tetrahedral intermediate catalyzes the hydrolysis of cocaine to ecgonine methyl ester.
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from article Bioorganic chemistry
A functionalized cyclodextrin mimics the enzyme RNase by catalyzing the regioselective hydrolysis of a model phosphodiester.
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from article Bioorganic chemistry
Enzyme-catalyzed reactions that have been commercialized as industrial processes.
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from article Bioorganic chemistry
Mechanism of DNA scission by calicheamicin. Reductive or nucleophilic cleavage of the trisulfide triggers conjugate (Michael) addition to the enone, rehybridization of the bridgehead carbon, and Bergman cyclization of the enediyne, generating a…
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from article Negative temperature
Populations (n) of states of a thermodynamic system consisting of N magnetically interacting nuclei of spin 2 at absolute temperatures T = +D/k and T = −D/k, where k is Boltzmann's constant and D is the energy spacing between successive states.
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from article Luminescence
Schematic representation of energy levels and electronic transitions in an atomic gas. E1, ground state; E2 and E3, excited states; 1, excitation; 2, emission of resonance luminescence; 3, radiationless transition to lower excited state; 4,…
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from article Luminescence
Configuration coordinate curves for a simple luminescence center. Transition A → B shows absorption, and transition C → D shows emission. Energy EQ is that necessary for the excited state to reach point E, from which a transition to the ground state…
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from article Luminescence
Variation of the brightness of a thallium-activated potassium chloride phosphor with temperature. °F = (K × 1.8) − 459.67.
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from article Luminescence
Variation of the width of the F-center absorption band in potassium chloride at its half-maximum points, FE, as a function of the square root of the temperature. °F = (K × 1.8) − 459.67.
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from article Luminescence
Emission of thallium-activated potassium chloride at 4 K (−452°F). In a plot of this particular form, a gaussian curve would consist of two straight lines which make equal angles with the abscissa.
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from article Luminescence
Graph showing the absorptance (100 minus percent of transmission) and edge emission of cadmium sulfide at 4 K (−452°F).
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from article Luminescence
Excitation spectra for emission of calcium carbonate phosphors, using manganese as an activator, with different impurity sensitizers: 1, no sensitizer; 2, thallium; 3, lead; and 4, cerium.
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from article Luminescence
Energy-band model for luminescence processes in zinc sulfide. Electron energy increases vertically.
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from article Luminescence
Energy-band model for luminescence processes in zinc sulfide which uses copper as the activator and aluminum as the coactivator.
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from article Quantized electronic structure (QUEST)
Geometric configurations of (a) quantum well, (b) quantum wires, and (c) quantum dots.
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from article Quantized electronic structure (QUEST)
Electron energy levels and electron standing waves for n = 1, 2, 3, and 4 quantum states in a quantum well.
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from article Quantized electronic structure (QUEST)
Principles of operation of quantum-well devices. (a) Quantum-well laser. (b) Quantum-well infrared detector. (c) High-electron-mobility transistor (HEMT or MODFET). Electrons in the quantum well that came from donor atoms in the barrier are free to…
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from article Liquid chromatography
Chromatogram showing the separation of various ethoxylates (nonionic surfactants) from an environmental water sample by liquid chromatography. EO = ethoxylate. Cx = alkyl. OP = octylphenol. NP = nonylphenol. (Credit: U.S. EPA)
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from article Flow of granular solids
Bounds on mass flow and funnel flow. (a) Geometry of a transition hopper, showing slope angles θc and θp. (b) Range of kinematic angle of friction (φ′) and θc leading to mass flow and funnel flow. (c) Range of φ′and θp leading to mass flow and…
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from article Flow of granular solids
Flow patterns in a funnel-flow bin, showing segregation of solids. (a) Charge coming in is greater than draw coming out, resulting in draw with a preponderance of fine particles. (b) Draw is greater than charge, resulting in draw with a…
