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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational response of calf thymus DNA to solvent conditions altered by varying amounts of ethanol and NaCl has been monitored by circular dichroism (CD). These measurements, which extend over a much greater range of conditions than previously examined, reveal (above critical concentrations of ethanol and salt) a condensed form of the macro-molecule with unusually large positive ellipticity in the 250-300-nm region [the Ψ(+) state]. Mere increase in NaCl concentration at constant 35% (v/v) concentration of ethanol suffices to convert such Ψ(+) samples - via a series of intermediate forms with CD spectra resembling those of A-DNA, then B-DNA - into Ψ(-) states having anomalously large negative ellipticity similar to the well-known Ψ(-) forms produced by above-critical concentrations of poly-(ethylene oxide) and salt. These ethanol/salt-induced transitions are all completely reversible and can occur without formation of any visible precipitates. We suggest that they represent predominantly tertiary structural changes of B-form DNA molecules analogous to the changes which occur in several other systems where Ψ(+) ⇌ Ψ(-) interconversion has been reported. A “skein-of-yarn” model for the condensed tertiary (and quaternary, i.e., aggregated) state of the DNA affords one possible explanation for the inversions of ellipticity in all these cases. Such a model accords well with the accepted description of cholesteric liquid crystals.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Circular dichroism spectroscopy has been used to investigate the influence of DNA molecular size, base composition, and the presence of intercalating agents upon the Ψ transition of DNA brought about by high concentrations of poly(ethylene oxide) and salt (Lerman (1971) Proc. Natl. Acad. Sci. (U.S.) 68, 1886-1890). A molecular weight of 0.15-3.0 × 106 daltons yields maximum formation of Ψ-DNA. Both the amplitude of the large negative CD band at 265 nm - a chief characteristic of the Ψ state - and the thermal stability of Ψ-DNA increase linearly with increasing mole fraction of guanine plus cytosine in the DNA sample. Either ethidium or proflavine, at concentrations where approximately one dye is bound per 5-10 nucleotide residues, can prevent the transition completely. Striking similarities between the Ψ-DNA produced by poly(ethylene oxide) + salt and the complexes formed between DNA and lysine-rich histone f1 suggest the presence of similar nucleic acid-nucleic acid interactions in both types of condensed phase.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 26 (1984), S. 537-543 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A simple and low-cost poultry waste digester (PWD) was constructed to treat the waste from 4000 caged laying hens on University Research Unit No. 2 at North Carolina State University. The system was built basically of a plastic lining with insulation, a heating system, a hot-water tank, and other metering equipment. It was operated at 50°C and pH 7.5-8.0. The initiation of methane production was achieved using the indigenous microflora in the poultry waste. At an optimal loading rate (7.5 kg volatile solids/m3 day), the PWD produced biogas (55% methane) at a rate of 4.0 m3/m3 day. The PWD was biologically stable and able to tolerate temporary overloads and shutdowns. A higher loading rate failed to maintain a high gas production rate and caused drops in methane content and pH value. Under optimal conditions, a positive energy balance was demonstrated with a net surplus of 50.6% of the gross energy. For methane production, the PWD system was proved to be technically feasible. The simple design and inexpensive materials used for this model could significantly reduce the cost of digestion compared to more conventional systems. More studies are needed to determine the durability, the required maintenance of the system, and the most economical method of biogas and solid residue utilization.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 21 (1975), S. 872-878 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The von Karman analogy between heat transfer and momentum transfer in turbulent fluids is shown to apply to heat transfer through wavy liquid films in horizontal, stratified, gas-liquid flow. Nusselt numbers predicted from the analogy are shown to be in good agreement with experimental data for air-water flows involving three-dimensional wavy films and large-amplitude roll waves. The Nusselt numbers encountered with these turbulent water films are found to be in the same range as those associated with condensation of organics in horizontal tubes under stratified flow conditions.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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