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  • 1
    ISSN: 1572-879X
    Keywords: microwave absorption ; electrical conductivity ; single crystal particles ; doped Si powders ; ZnO powder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A microwave absorption technique based on cavity perturbation theory is shown to be applicable for electrical conductivity measurements of both a small, single-crystal particle and finely divided powder samples whenσ values fall in either the low (σ〈0.1 Ω−1 cm−1) or the intermediate (0.1 ≤σ≤ 100 Ω−1 cm−1) conductivity region. The results here pertain to semiconductors in the latter region. If the skin depth of the material becomes significantly smaller than the sample dimension parallel to theE-field, an appreciable error can be introduced into the calculated conductivity values; however, this discrepancy is eliminated by correcting for the field attenuation associated with the penetration depth of the microwaves. A modification of this approach utilizing the skin depth allows a first-order correction to be applied to powder samples which results in the accurate measurement of absoluteσ values, and results with doped Si powders are compared toσ values obtained from one small single particle using this microwave technique as well as reported DCσ values determined with single crystals. The use of this microwave absorption technique with small particles having high surface/volume ratios, such as catalyst supports and oxide catalysts, under controlled environments can provide fundamental information about adsorption and catalytic processes on such semiconductor surfaces. An application to a ZnO powder demonstrates this capability.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 243 (1994), S. 225-233 
    ISSN: 1617-4623
    Keywords: Protein synthesis ; Translation ; Accuracy ; Macrolide antibiotics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Inaccurate protein synthesis produces unstable β-galactosidase, whose activity is rapidly lost at high temperature. Erythromycin, lincomycin, clindamycin, and celesticetin were shown to counteract the error-inducing effects of streptomycin on β-galactosidase synthesized in the antibiotic-hypersensitive Escherichia coli strain DB-11 Met −. Newly synthesized β-galactosidase was more easily inactivated by high temperatures when synthesized by bacteria partially starved for arginine, threonine, or methionine. Simultaneous treatment with erythromycin or linocomycin yielded β-galactosidase that was inactivated by high temperatures less easily than during starvation alone, an effect attributed to stimulation of ribosome editing. When synthesized in the presence of canavanine, β-galactosidase was inactivated by high temperature more easily but this effect could not be reversed by erythromycin. The first arginine in β-galactosidase occurs at residue 13, so the effect of erythromycin during arginine starvation is probably to stimulate dissociation of erroneous peptidyl-tRNAs of at least that length. Correction of errors induced by methionine starvation is probably due to stimulation of dissociation of erroneous peptidyl-tRNAs bearing peptides at least 92 residues in length. All the effects of erythromycin or the tested lincosamides on protein synthesis are probably the result of stimulating the dissociation from ribosomes of peptidyl-tRNAs that are erroneous or short.
    Type of Medium: Electronic Resource
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