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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Antisymmetry of the amino acid code table in terms of codon degeneracy is pointed out, and it is related to a physico-chemical problem of codon-anticodon interaction energy. A strong negative correlation between molecular weight of an amino acid and its codon degeneracy is pointed out, and its implication to the origin of the amino acid code table is discussed. Finally, an earlier form of the amino acid code table is proposed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Cellulose 6 (1999), S. 221-231 
    ISSN: 1572-882X
    Keywords: benzene/cyclohexane mixture ; benzene‐permselectivity ; degree of tosylation ; mechanism of separation ; tosylcellulose membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Tosylcelluloses (TosCells) with different degrees of tosylation were synthesized as membrane materials for the separation of benzene/cyclohexane (Bz/Chx) mixtures. TosCell membranes showed a high benzene‐permselectivity for the Bz/Chx mixtures in pervaporation (PV). An increase in the benzene concentration in the feed mixtures increased permeation rate but decreased the benzene‐permselectivity of the TosCell membranes. The increase in the permeation rate was attributed to the increase of the degree of swelling of the TosCell membranes by the feed mixtures and the decrease in the benzene‐permselectivity was mainly caused by the decrease of sorption selectivity. With low benzene concentrations in the Bz/Chx mixtures, the permeation rate of a TosCell membrane with a higher degree of tosylation was greater than that with a lower degree of tosylation, but was vice versa with a high benzene concentration. The benzene‐permselectivity of the former TosCell membrane was higher than that of the latter membrane. Differences of the permeation rate and benzene‐permselectivity with changes in the benzene concentration in the feed mixture and degree of tosylation of the TosCell membrane were significantly influenced by the degree of swelling of the TosCell membrane and the benzene concentration sorbed into the TosCell membrane. Mechanism of separation for the Bz/Chx mixtures through the TosCell membranes is discussed by the solution–diffusion model.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 193 (1992), S. 983-990 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hydrogels containing phosphate groups were prepared by copolymerization of 2-methacryloyl-oxyethyl dihydrogen phosphate (phosmer) and various hydrophilic monomers [N,N-dimethyl-acrylamide (DMAAm), acrylic acid (AAc) and 2-hydroxyethyl methacrylate (HEMA)], and the swelling behavior was investigated. These hydrogels are thermo-sensitive. Phosmer-DMAAm and phosmer-HEMA hydrogel deswell with increasing temperature, but for the phosmer-AAc hydrogel the swelling ratio increases with temperature. Interestingly, the swelling ratio decreases with an increase in phosphate group content. This unusual behavior may arise from the phosphate group acting both as the functional group and the crosslinking agent.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 194 (1993), S. 927-939 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The permeation and separation characteristics of poly(vinyl chloride) (PVC) and poly[(vinyl chloride)-co-(vinyl acetate)] (poly(VC-co-VAc)) membranes were investigated for aqueous organic acid solutions by pervaporation and evapomeation. The PVC membrane preferentially incorporates organic acids and predominantly permeates water from aqueous organic acid solutions. Water permselectivities of these aqueous solutions through the PVC membrane are significantly dependent on high diffusivity of water across the membrane. It was found that the permeation rate increases and the separation factor for the water permselectivity decreases with increasing vinyl acetate (VAc) content in the poly(VC-co-VAc) membrane. Preferential solubility of acetic acid into the poly(VC-co-VAc) membrane increases with the VAc content. This result was explained by a strong affinity between acetic acid and the VAc unit in the poly(VC-co-VAc) membrane.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 193 (1992), S. 2737-2749 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An ethylene/vinyl alcohol copolymer (EVA)-copper complex membrane was prepared by casting an EVA-CuCl2 mixture (solvent: water-propanol (1:1 v/v) mixture) on a polyethylene substrate and then immersing it in 0,1 M KOH aqueous solution. In the membrane, Cu was distributed asymmetrically in the direction of the membrane cross section. The distribution of Cu could be controlled by the temperature during preparation. The oxidation of hydroquinone during permeation through the complex membrane was performed using membranes with different Cu distribution. This distribution influences the permeation reaction. These results are well reproduced by a relation composed of Fick's law and Michaelis-Menten type reaction kinetics. Therefore, a good reactor can be developed by controlling the catalyst distribution.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Basel : Wiley-Blackwell
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 39 (1997), S. 733-740 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. When a benzene/cyclohexane mixture was permeated through poly(dimethyl acrylamide-random-methyl methacrylate) (DMAA-r-MMA) and poly(dimethyl acrylamide)-graft-poly(methyl methacrylate) (DMAA-g-MMA) membranes by pervaporation, the benzene-permselectivity of the DMAA-r-MMA membrane changed from the diffusivity selectivity to the solubility selectivity with increasing DMAA content but DMAA-g-MMA membranes with a high DMAA content had the higher apparent diffusivity selectivity than the apparent solubility selectivity. Furthermore, the apparent solubility selectivity for a benzene/cyclohexane mixture between the DMAA-r-MMA membrane and the DMAA-g-MMA membrane with a high DMAA content was remarkably different. These results were attributed to the difference of structure between the copolymers.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 12 (1979), S. 219-236 
    ISSN: 1432-1432
    Keywords: Amino acid substitution ; Physico-chemical difference ; Conservative ; Low-constraint ; Protein evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The frequency of amino acid substitutions, relative to the frequency expected by chance, decreases linearly with the increase in physico-chemical differences between amino acid pairs involved in a substitution. This correlation does not apply to abnormal human hemoglobins. Since abnormal hemoglobins mostly reflect the process of mutation rather than selection, the correlation manifest during protein evolution between substitution frequency and physico-chemical difference in amino acids can be attributed to natural selection. Outside of ‘abnormal’ proteins, the correlation also does not apply to certain regions of proteins characterized by rapid rates of substitution. In these cases again, except for the largest physico-chemical differences between amino acid pairs, the substitution frequencies seem to be independent of the physico-chemical parameters. The limination of the substituents involving the largest physicochemical differences can once more be attributed to natural selection. For smaller physico-chemical differences, natural selection, if it is operating in the polypeptide regions, must be based on parameters other than those examined.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 31 (1990), S. 151-160 
    ISSN: 1432-1432
    Keywords: Evolutionary tree ; Amino acid sequence ; Insertion/deletion ; Bootstrap probability ; psbA ; Prochlorothrix
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A maximum likelihood method for inferring protein phylogeny was developed. It is based on a Markov model that takes into account the unequal transition probabilities among pairs of amino acids and does not assume constancy of rate among different lineages. Therefore, this method is expected to be powerful in inferring phylogeny among distantly related proteins, either orthologous or parallogous, where the evolutionary rate may deviate from constancy. Not only amino acid substitutions but also insertion/deletion events during evolution were incorporated into the Markov model. A simple method for estimating a bootstrap probability for the maximum likelihood tree among alternatives without performing a maximum likelihood estimation for each resampled data set was developed. These methods were applied to amino acid sequence data of a photosynthetic membrane protein,psbA, from photosystem II, and the phylogeny of this protein was discussed in relation to the origin of chloroplasts.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 31 (1990), S. 205-210 
    ISSN: 1432-1432
    Keywords: Isozyme ; Intron ; Phylogenetic tree ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Both the mouse cytosolic malate dehydrogenase gene and its mitochondrial counterpart contain eight introns, of which two are present at identical positions between the isozyme genes. The probability that the two intron positions coincide by chance between the two genes has been shown to be significantly small (=1.3×10−3), suggesting that the conservation of the intron positions has a biological significance. On the basis of a rooted phylogenetic tree inferred from a comparison of these isozymes and lactate dehydrogenases, we have shown that the origins of the conserved introns are very old, possibly going back to a date before the divergence of eubacteria, archaebacteria, and eukaryotes. In the aspartate aminotransferase isozyme genes, five of the introns are at identical places. The origins of the five conserved introns, however, are not obvious at present. It remains possible that some or all of the conserved introns have evolved after the divergence of eubacteria and eukaryotes.
    Type of Medium: Electronic Resource
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