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  • Chemistry  (112)
  • Holocene
  • Interspecific hybridization
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  • 1
    Electronic Resource
    Electronic Resource
    Interspecific hybridization between common and tepary beans: increased hybrid embryo growth, fertility, and efficiency of hybridization through recurrent and congruity backcrossing (1994)
    Springer
    Theoretical and applied genetics 88 (1994), S. 324-331 
    Details
    ISSN: 1432-2242
    Keywords: Phaseolus acutifolius ; Phaseolus vulgaris ; Common and tepary beans ; Interspecific hybridization ; Congruity and recurrent backcrosses ; In-vitro embryo culture ; Gene introgression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cultivated common bean (Phaseolus vulgaris L.) and tepary bean (Phaseolus acutifolius A. Gray) genotypes possessing desirable agronomic traits were hybridized. The F1 hybrids were backcrossed twice with the common bean (i.e., recurrent backcrossing). Also, alternate backcrosses with common and tepary beans (i.e., congruity backcrossing) were carried out. Embryo culture was necessary for all initial interspecific crosses, and its requirement was proportionally lower when the common bean was used as the recurrent parent and as the last parent of congruity backcrosses. Modification of the embryo culture technique was necessary to produce congruity hybrids. Effects of both tepary and common bean genotypes on the success rate of hybridization were observed. Tepary accession G 40001 and common bean cultivar ICA Pijao facilitated interspecies hybridization. Growth of hybrid embryos before rescue, recovery of mature hybrid plants, and the vigor and fertility of F1 hybrids all increased with increased recurrent and congruity backcrosses and intermatings between male-sterile F1 and selected fertile F2 plants of the third and fifth congruity backcrosses. Introgression of tepary genes was verified by means of seed protein electrophoretic analysis and morphological markers. The results suggest that congruity backcrossing can help to gradually reduce or overcome P. vulgaris x P. acutifolius hybridization barriers such as genotype incompatibility, early embryo abortion, hybrid sterility, and lower frequencies of hybridization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223640
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  • 2
    Electronic Resource
    Electronic Resource
    In vitro attempts to overcome the cross-incompatibility between Vaccinium corymbosum L. and V. elliottii Chapm. (1985)
    Springer
    Theoretical and applied genetics 69 (1985), S. 591-596 
    Details
    ISSN: 1432-2242
    Keywords: Interspecific hybridization ; Embryo rescue ; Ovule culture ; Ovary culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Seed was readily obtained from V. corymbosum zygotes using embryo rescue techniques, even when embryos were cultured at proembryonic stages. Best in vitro seed development was obtained when ovules were cultured attached to placental tissues. Successful fruit and seed development in culture occurred only when the fruit was cut longitudinally or when the basal portion of the fruit was removed previous to plating. Addition of various vitamins, amino acids, and growth regulators to the nutrient medium did not increase seed production. Attempts to rescue hybrid embryos from V. croymbosum (tetraploid) x V. elliottii (diploid) crosses by in ovulo and in ovary culture gave a few presumably hybrid seed, but at a rate no greater than when normal crossing procedures are used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00251109
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  • 3
    Electronic Resource
    Electronic Resource
    Upland vegetation in the north-west Iberian peninsula after the last glaciation: Forest history and deforestation dynamics (1997)
    Springer
    Vegetation history and archaeobotany 6 (1997), S. 215-233 
    Details
    ISSN: 1617-6278
    Keywords: Pollen analysis ; Late-glacial ; Holocene ; Iberian peninsula
    Source: Springer Online Journal Archives 1860-2000
    Topics: Archaeology , Biology
    Notes: Abstract This paper presents the results of pollen analyses from organic sediments of seven cores (299 spectra) in a mountainous area of the north-west Iberian peninsula. The pollen diagrams, supported by seven14C dates, are used to construct a regional pollen sequence covering the main stages of vegetation dynamics, from the last phases of the Late-glacial until the present. During the Late-glacial Interstadial an important development of cryophilous forests (Betula andPinus) was recorded, although various mesophilous and thermophilous tree elements were also present. The Younger Dryas, palynologically clearly defined, is characterized by an important reduction in tree pollen percentages and the expansion of steppe formations (Poaceae andArtemisia). At the beginning of the Holocene, there was an expansion ofQuercus and a spread of other trees, which combined to give a vegetation cover of varied composition but dominated by mixed deciduous forests. Such forest formations prevailed in these mountains until 3000 years ago, when successive deforestation phases are recorded at various times as a result of increased farming activity. The results are compared with data from other mountainous areas in the northern Iberian peninsula and southern France.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01370443
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis and structural data of nylon 1,4 (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1445-1448 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080250520
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  • 5
    Electronic Resource
    Electronic Resource
    Degradation and stabilization of high molecular weight polyethylene in solution (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 2469-2477 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The changes in the molar mass of high molecular weight polyethylene, in o-dichlorobenzene, with time are examined using viscometry. The results show that the molar mass decreases with time and that the observed decay can be satisfactorily explained by a simple degradation model. Commercial antioxidants can inhibit the degradation process if the appropriate concentration is chosen. Thus, at very low concentrations a polynuclear phenol shows good antioxidant behavior but this decreases with an increase in concentration due to direct oxidation of the inhibitor. Conversely, zinc dimethyldithiocarbamate shows the best stabilizing activity which increases with concentration. The results are explained on the basis of the established mechanistic action of these compounds and show that viscometry is not an accurate method for measuring the molar mass of high molecular weight polyethylene samples unless the appropriate conditions are chosen. Even with the best inhibitor, some degradation is still observed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080250912
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  • 6
    Electronic Resource
    Electronic Resource
    The interaction of poly(methacrylate) radicals with diphenyldiacetylenes (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 3147-3151 
    Details
    ISSN: 0887-624X
    Keywords: polymerization of methyl methacrylate ; diphenylbutadiynes ; ESR spectra ; radical stabilization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The free radical polymerization of methyl methacrylate (MMA) in the presence of p,p′- disubstituted diphenylbutadiynes was studied. Both the rate and degree of polymerization are somewhat lowered by the presence of the diynes, but the propagating radicals were stabilized giving clear ESR signals of the interacted polyMMA radicals at the polymerization temperature of 70°C. The magnitude of the interaction depended on the electron density of the diynes; in the cases of diphenylbutadiyne and dimethoxycarbonyldiphenylbutadiyne, the intoraction was more enhanced showing ESR signals with smaller spectra widths and increasing the number of radicals with the polymerization time, while in the cases of electron donor-substituted diynes the interaction was weaker and the radical concentration remained constant during the polymerization. These systems are considered to be examples of the stabilization of transient radicals by the direct interaction of radicals with additives without formation or breaking of chemical bonds. No diacetylenic group was found in the polyMMA obtained. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321615
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  • 7
    Electronic Resource
    Electronic Resource
    Stereoregular polyamides derived from methylene-L-tartaric acid and aliphatic diamines (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 713-721 
    Details
    ISSN: 0887-624X
    Keywords: stereorgular polyamides ; stereoregular nylons ; chiral polyamides ; chiral nylons ; polytartaramides ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoregular polyamides containing two chiral backbone carbons in the repeating unit were prepared by polycondensation of bis(pentachlorophenyl) 2,3-O-methylene-L-tartrate with 1,9 and 1,12-alcanediamines activated as N,N′-bis(trimethylsilyl) derivatives. The polymers were characterized by elemental analysis, IR, and 1H-NMR spectroscopy, and differential scanning calorimetry. Both viscosimetry and GPC were used to estimate the molecular weights which ranged between 6000 and 44000. These polytartaramides were readily soluble in chloroform, displayed moderate optical activity in solution, and formed highly crystalline films.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300503
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis of stereoregular polygluconamides from D-glucose and D-glucosamine (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 299-305 
    Details
    ISSN: 0887-624X
    Keywords: polygluconamides ; stereoregular polyamides ; stereoregular nylons ; chiral polyamides ; chiral nylons ; aminoaldonic acids ; sugar polyamides ; carbohydrate monomers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two stereoregular polygluconamides, one (3) of polypeptide-type and the other (16) being a polycaproamide containing four stereocenters in the main chain of the repeating unit, have been prepared from D-glucosamine and D-glucose, respectively. The new polyamides were characterized by elemental analysis, and IR, 1H- and 13C-NMR spectroscopies. The molecular weights for 3 and 16 were estimated as 25,000 and 67,000, respectively, on the basis of viscosimetric measurements. Both polyamides display high optical activity; they are highly hydrophilic and readily soluble in water as well as in a variety of organic solvents including chloroform. Polyamide 16 is highly crystalline and yields resistant films with spherulitic texture. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1995.080330211
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  • 9
    Electronic Resource
    Electronic Resource
    Poly(α-isobutyl-β-D,L-aspartate)s: Polymerization effects on configuration and crystal structure of the stereocopolymers (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 1959-1968 
    Details
    ISSN: 0887-624X
    Keywords: optically active polyamides ; helical nylons ; nylon-3 ; poly(β-amide)s ; poly(β-aspartate)s ; poly(α-isobutyl-β-L-aspartate) ; stereoselective polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different polymerization methods were used for the preparation of poly(α-isobutyl-β-D,L-aspartate)s containing variable ratios of D- to L-aspartic units and the microstructure of the resulting stereocopolymers was examined by NMR spectroscopy. Anionic ring-opening polymerization in solution of enantiomeric mixtures of α-isobutyl-β-D- and L-aspartalactams was found to proceed stereoselectively rendering block copolymers composed of right- and left-handed helical sequences. Configurationally statistical copolymers were obtained instead when the enantiomeric lactam mixtures were polymerized in the bulk. Random stereocopolymers could be prepared also by polycondensation in solution of mixtures of pentachlorophenyl α-isobutyl-β-D and -L-aspartates. The conformation in solution and the crystal structure of the resulting copolymers were investigated in connection with their stereochemical configuration and these features compared with those displayed by optically pure poly(α-isobutyl-β-L-aspartate). © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    A theoretical study of the comonomer effect in the ethylene polymerization with zirconocene catalytic systems (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1157-1167 
    Details
    ISSN: 0887-624X
    Keywords: zirconocene catalysts ; ethylene ; 1-hexene ; copolymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The PM3(tm) semiempirical method has been used to optimize the structures for the reactants and transition states of the first and second ethylene insertion processes into zirconocene catalytic systems. The results obtained for these reactions are compared with calculations published in the literature performed at different ab-initio theoretical levels. The agreement between our calculations and those reported in the literature is satisfactory. Taking advantage of the reduced computational effort required in semiempirical calculations two additional processes related with the so-called comonomer effect were also studied: ethylene/1-hexene copolymerization, and chain termination reaction, both in the homopolymerization and in copolymerization of ethylene with 1-hexene comonomer. The calculated activation energies support some experimental findings such as the higher polymerization activities in the presence of comonomers and also the molecular weight reduction of the copolymers due to the more favorable β-elimination reactions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1157-1167, 1998
    Additional Material: 3 Ill.
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