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  • 1
    Publication Date: 2014-04-30
    Description: Speciation generally involves a three-step process--range expansion, range fragmentation and the development of reproductive isolation between spatially separated populations. Speciation relies on cycling through these three steps and each may limit the rate at which new species form. We estimate phylogenetic relationships among all Himalayan songbirds to ask whether the development of reproductive isolation and ecological competition, both factors that limit range expansions, set an ultimate limit on speciation. Based on a phylogeny for all 358 species distributed along the eastern elevational gradient, here we show that body size and shape differences evolved early in the radiation, with the elevational band occupied by a species evolving later. These results are consistent with competition for niche space limiting species accumulation. Even the elevation dimension seems to be approaching ecological saturation, because the closest relatives both inside the assemblage and elsewhere in the Himalayas are on average separated by more than five million years, which is longer than it generally takes for reproductive isolation to be completed; also, elevational distributions are well explained by resource availability, notably the abundance of arthropods, and not by differences in diversification rates in different elevational zones. Our results imply that speciation rate is ultimately set by niche filling (that is, ecological competition for resources), rather than by the rate of acquisition of reproductive isolation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Price, Trevor D -- Hooper, Daniel M -- Buchanan, Caitlyn D -- Johansson, Ulf S -- Tietze, D Thomas -- Alstrom, Per -- Olsson, Urban -- Ghosh-Harihar, Mousumi -- Ishtiaq, Farah -- Gupta, Sandeep K -- Martens, Jochen -- Harr, Bettina -- Singh, Pratap -- Mohan, Dhananjai -- England -- Nature. 2014 May 8;509(7499):222-5. doi: 10.1038/nature13272. Epub 2014 Apr 30.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637, USA. ; 1] Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637, USA [2] Department of Zoology, Swedish Museum of Natural History, 10405 Stockholm, Sweden. ; 1] Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637, USA [2] Institute of Pharmacy and Molecular Biotechnology, University of Heidelberg, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany. ; 1] Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang District, Beijing 100101, China [2] Swedish Species Information Centre, Swedish University of Agricultural Sciences, Box 7007, 75007 Uppsala, Sweden. ; Systematics and Biodiversity, Department of Biology and Environmental Sciences, University of Gothenburg, 40530 Gothenburg, Sweden. ; Wildlife Institute of India, PO Box 18, Chandrabani, Dehradun 248001, India. ; Institute of Zoology, Johannes Gutenberg University, Mainz 55099, Germany. ; Max Planck Institute for Evolutionary Biology, August Thienemannstrasse 2, 24306 Plon, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24776798" target="_blank"〉PubMed〈/a〉
    Keywords: *Altitude ; Animals ; Body Size ; China ; *Ecosystem ; *Genetic Speciation ; India ; Phylogeny ; Reproduction ; Songbirds/anatomy & histology/*classification/*physiology ; Tibet
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 27 (1982), S. 4421-4438 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The second stage of batch poly(ethylene terephthalate) (PET) reactor with bis(2-hydroxyethyl) terephthalate (BHET) as the feed has been simulated. In this stage, the overall polymerization is not diffusion limited and is known to be a complex reaction. In this work it has been assumed to consist of polycondensation, reaction with monofunctional compounds (cetyl alcohol), redistribution, and cyclization reactions. The forward and reverse steps of each of these have been modelled in terms of the rate constants involving functional groups and the reacted bonds. The equations for the calculation of the molecular weight distribution (MWD) in batch reactors have been written and solved numerically. The MWD reported in this work is assumed to include the monofunctional products only, and, for the case where ethylene glycol is not removed from the reaction mass, it was found to be unaffected by the choice of the redistribution rate constant (kr). Since the removal of ethylene glycol is not mass transfer controlled, its concentration in the reaction mass is assumed be given by the vapor-liquid equilibrium existing at the pressure applied on the reactor. In this work, the level of ethylene glycol concentration, yg (≡[G]/[P1]0), has been taken as a parameter, and, on application of vacuum, the MWD results were found to vary with kr with the sensitivity increasing with yg. It was then shown that the importance of the redistribution reaction is enhanced when the cyclization reaction also occurs. The effect of vacuum on the performance of the reactor has been studied by varying yg. For yg less than 0.01, the change in the MWD of the polymer becomes very small. The effects of polymerization temperature and initial concentration of monofunctional compounds on MWD were found to be small.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 30 (1985), S. 1095-1112 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Hydroxyl terminated natural rubber (HTNR) was prepared by the depolymerization of masticated natural rubber in the presence of H2O2 in toluene. Probable mechanisms leading to the formation of side reaction products are proposed based on the analytical data. A comparative study of some formulation variables was made for their effect in improving the flow characteristics and mechanical properties of an aluminized polyurethane (PU) propellant system based on HTNR. This PU system has also been compared for its theoretical performance characteristics with some other state-of-the-art systems.
    Additional Material: 6 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 26 (1988), S. 595-599 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copolymers of tributyltin methacrylate (M1) with cyclohexyl methacrylate, ethoxyethyl methacrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate were synthesized in solution at 55°C utilizing azobisisobutyronitrile initiator. Copolymer compositions were determined by tin analysis; monomer reactivity ratios were calculated by Kelen-Tüdös method. Since the reactivity ratios indicate the distribution of different monomer units in the polymer chain, the measured values are compared and discussed. Preliminary results of the biotoxicity studies on some of the copolymers are also reported.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 64 (1977), S. 169-177 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Ungesättigte Polyester aus Bisphenol-A bzw. dimethyl-di-3,5-dichlor-4-hydroxyphenyl-methan und Dimethyl-di-3,5-dibrom-4-hydroxyphenyl-methan wurden einer 18 Mrad Dosis aus einer Co60-Quelle ausgesetze. Untersuchungen des Halogengehalts, der Säurezahl, der Grenzviskosität und des Isomerengehalts vor und nach der Bestrahlung deuten auf eine verhältnismäßig hohe Strahlungsbeständigkeit hin.
    Notes: Unsaturated polyesters made by using bisphenol-A, dimethyl-di-(3,5-dichloro-4-hydroxyphenyl) methane, and dimethyl-di-(3,5-dibromo-4-hydroxyphenyl) methane, respectively, were exposed to a does of 18 Mrad from a Co60 source. On irradiation, there is very little change in the halogen content in the polyesters, determined by Parr Bomb method. This indicates their stability to γ-irradiation. Study of acid value, intrinsic viscosity and isomerisation of these polyesters before and after irradiation corroborates to some extent that incorporation of aromatic rings in the polyester chain stabilises it against radiation. Minor changes in acid values and intrinsic viscosities are discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 6 (1969), S. 161-170 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Temperaturabhängigkeit des dielektrischen Verhaltens von drei vernetzten Polyesterharzen, basierend auf der Kondensation von Chlormethylacetat mit Bisphenol-A (I), 2,2-Di-(4-hydroxy-3,5-dichlorphenyl)-propan (II) und 2,2-Di-(4-hydroxy-3,5-dibromphenyl)-propan (III), wurde im Mikrowellenbereich bei einer Wellenlänge von 3,21 cm untersucht. Die Dielektrizitätskonstanten dieser Polyester sind 2,93 (I), 2,914 (II) und 2,77 (III); sie ändern sich im Temperaturbereich von 30 bis 85°C nicht. Die Erniedrigung der Dielektrizitätskonstante durch Einbau von 2,2-Di-(4-hydroxy-3,5-dichlorphenyl)-propan und 2,2-Di-(4-hydroxy-3,5-dibromphenyl)-propan in die Polyesterkette wird auf die Abnahme an Ester-und Äthergruppen pro Gewichtsanteil an gehärtetem Polyester zurückgeführt. Der Verlustfaktor des Polyesterharzes aus Biphenol-A ist bei 55 °C am größten ; die Relaxationszeit dieses Polyesters beträgt 1 bis 7 · 10-11 sec bei 55°C. Dieses Ergebnis kann der freien Drehbarkeit der Ätherbindung zugeschrieben werden, die durch Abwesenheit von Halogen in den 3,5-Positionen des Bisphenols-A mög-lich ist. Es kann ferner auf der Abwesenheit von sekundären Kräften zwischen den Ketten wegen der voluminösen p-Phenylengruppen in der Polyesterkette und der Vernetzung durch voluminöse Moleküle wie Styrol beruhen. Im Falle der chlorierten und bromierten Polyester sind Bewegungen um die Äther- und Esterbindungen schwierig. Der Verlustfaktor des chlorierten Bisphenol-A-Polyesters variiert weniger mit der Temperatur als der des bromierten Polyesters. Das kann an im Brompolyester vorkommendem Homopolystyrol oder an großen Vernetzungsbrük-ken aus Polystyrol liegen.Diese Ergebnisse werden auch durch Hydrolyseuntersuchungen der Grundharze und durch den “heat distortion point” der vernetzten Polyester gestützt.
    Notes: The variation of dielectric behaviour with temperature of three crosslinked polyester resins based on the condensates of chloro-methyl acetate and bisphenol-A, 2,2-di-(4-hydroxy 3,5-dichloro phenyl) propane and 2,2-di-(4-hydroxy 3,5-dibromo phenyl) propane were studied in the microwave frequency region at wave length 3.21 cm. The dielectric constants of these polyesters are 2.93, 2.91 and 2.77 respectively and do not change with temperature in the 30-85°C region. The decrease in dielectric constant after incorporating 2,2-di-(4-hydroxy 3,5-dichloro phenyl) propane and 2,2-di-(4-hydroxy 3,5-dibromo phenyl) propane in the polyester chain is attributed to the decrease in the number of ester and ether groups in the polyester chain per unit weight of the cured polyesters. It is found that the loss factor for bisphenol-A based polyester resin is maximum at 55°C and the relaxation time of this polyester is 1-7 · 10-11 sec at 55°C. It can be assigned to the free motion of ether linkages due to the absence of halide groups at 3,5 position of bisphenol-A incorporated in the polyester chain. This can also be attributed to the absence of secondary forces between the chains due to the presence of bulky p-phenylene groups in the polyester chain and crosslinking by bulky molecules like styrene. In case of chlorinated and brominated polyesters, the motion about ether and ester linkages is difficult. The chlorinated bisphenol-A polyester has less variation in loss factor as compared to that of bromo polyester. It may be due to the homo polystyrene or large polystyrene segments present in bromo polyester.These results are also supported by the studies on hydrolytic stability of their base resins and by the heat distortion point of the crosslinked polyesters.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 15 (1971), S. 147-156 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Einfluß von γ-Strahlen auf Hexachlorendomethylenhexahydrophthalsäure (HCPS) enthaltende ungesättigte Polyester wurde untersucht. Dazu wurden vier Polyester mit verschiedenem Molverhältnis an Chlorendic-Säure zu Isophthalsäure mit einer Co60-Quelle bestrahlt. Durch die Bestrahlung erniedrigt sich der Chlorgehalt stark mit zunehmendem Gehalt an Isophthalsäure. Mit steigendem Gehalt an HCPS nimmt die durch die Bestrahlung hervorgerufene Änderung der Säurezahl ab. Die Grenzviskosität steigt bei Polyestern, die viel Isophthalat-Gruppen enthalten, und fält bei solchen mit hohem Gehalt an HCPS. Der Einfluß der γ-Be-strachlung auf das Verhätnis von cis- und trans-Form in diesen Polyestern wurde an Infrarotspektren untersucht. Es zeigt sich, daß mit zunehmendem Gehalt an HCPS die durch die Bestrahlung verursachte trans-cis-Umwandlung stark ansteigt.
    Notes: The effect of gamma ray irradiation on chlorendic acid based unsaturated polyesters was studied. Four different types of unsaturated polyesters, made by varying the molar ratios of chlorendic acid to isophthalie acid were irradiated with a Co60 qource. After irradiation, the chlorine content decreases rapidly as the isophthalate content in the polyester chain increases. As the chlorendle acid content increases, the change in acid value after irradiation decreases. The increase in intrinsic viscosity is quite marked in high isophthalate containing polyesters after gamma ray irradiation and there is a noticeable decrease in intrinsic viscosity after gamma irradiation of high chlorendic acid containing polyesters. The effect of gamma irradiation on the percentage of cis and trans forms of these polyesters was studied with the help of infrared spectra. It appears that as the chlorendic acid content increases, on gamma irradiation conversion from trans unsaturation to cis unsaturation increases rapidly.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 44 (1975), S. 47-65 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Sieben Polyester mit verschiedenem Halogengehalt wurden hinsichtlich der Kinetik ihres Abbaus sowie ihrer flammhemmenden Wirkung untersucht. Davon hatten die Polyester Nr. 1,2,3 und 4 ein Molverhältnis von Chlorendischer Säure (Diels-Alder-Addukt aus perchloriertem Cyclopentadien und Maleinsäureanhydrid) zu Isophthalsäure von 0.25, 0.67, 1.5 und 4.0. Die Polyester 5, 6 und 7 basierten auf Dimethyl-di-(p-oxyacetoxymethylphenyl)-methan, Dimethyl-di-(3,5-dichlor-4-oxyacetoxymethylphenyl)-methan und Dimethyl-di-(3,5-dibrom-4-oxyacetoxymethylphenyl)-methan.Die Untersuchungen wurden mittels thermogravimetrischer Analyse (TGA), Differentialthermoanalyse (DTA), IR-Spektroskopie und Glühstab-Analyse ausgeführt. Die thermische Stabilität dieser Polyester nahm in der folgenden Reihenfolge ab: 5 〉 6 〉 7 〉 1 〉 2 〉 3 〉 4, wenn man die Schwellentemperatur als Maß für die thermische Stabilität betrachtet. Die aus TGA-Kurven ermittelte Temperatur bei 50-proz. Gewichtsverlust stützt dies zu einem gewissen Ausmaß. Die Untersuchungen ergaben ferner einen zweistufigen Abbau. Die erste Stufe erstreckte sich von 250-450°C, die zweite von 450-600°C. Bei der ersten Stufe verengt sich der Temperaturbereich für den Abbau mit ansteigendem Halogengehalt. Bromierung ist wirkungsvoller als Chlorierung. Die Aktivierungsenergie für den Abbau dieser Polyester zeigte den selben Trend wie die thermische Stabilität. Aber die Flammhemmung ist etwa umgekehrt zur thermischen Stabilität. Diese Untersuchungen bestätigen auch einen cyclischen Mechanismus für die Flammhemmung.
    Notes: Seven polyesters having different amounts of halogen were studied for kientics of degradation and fire retardant efficiency. Out of them, the polyesters number 1, 2, 3, and 4 had the molar ratios of chlorendic acid to isophthalic acid of 0.25, 0.67, 1.5, and 4.0 respectively. The polyesters number 5, 6, and 7 were based on dimethyl-di-(p-oxyacetoxymethylphenyl)-methane, dimethyl-di-(3,5-dichloro-4-oxyacetoxymethylphenyl) methane and dimethyl-di-(3,5-dibromo-4-oxyacetoxymethylphenyl)-methane respectively. These studies were done with the help of thermogravimetric analysis (TGA), differential thermal analysis (DTA), infra-red spectroscopy and glow rod apparatus. The thermal stability of these polyesters decreased in the following order: 5 〉 6 〉 7 〉 1 〉 2 〉 3 〉 4, taking the threshold temperature as a measure of the thermal stability. The 50% weight loss temperature determined from TGA curves supported this to some extent. These studies further revealed that these polyesters degrade in two stages. The first stage of degradation ranged from 250-450°C. The second stage of degradation is in the range of 450-600°C. In the first stage, the range of temperature for degradation is constricted by increasing the halogen content. Bromination is more effective than chlorination. The activation energy for degradation of these polyesters showed the same trend as the thermal stability. But the flame resistance is somewhat in the reverse order of thermal stability. These studies also confirm a cyclic mechanism for flame retardancy.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 57 (1995), S. 209-218 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An industrial semibatch nylon 6 reactor has been optimized using a one-variable (at a time) search technique. The vapor release rate from the reactor and the final monomer conversion have been constrained to lie very close to the values currently present. The degree of polymerization of the product is , similarly, constrained to lie at a value of 152. The optimal pressure histories for two values of the jacket fluid temperature, Tj, have been evaluated using two objective functions, I1 and I3, namely, the total reaction time (I1 = tf) and the concentration of the cyclic dimer (I3 = [C2]f) in the product. It is observed that as Tj is increased from 270 to 280°C, I1 improves while I3 worsens simultaneously. This suggests that these two optimal points lie on the Pareto set for the two-objective function problem. © 1995 John Wiley & Sons, Inc.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 62 (1996), S. 1395-1405 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The relationship between the microstructure and corresponding mechanical properties developed during injection molding of blends containing a liquid crystalline polymer (LCP) as the minor component and an engineering polymer system has been studied. A wholly aromatic copolyester LCP (Vectra A950) was melt blended at different compositions with a thermoplastic matrix consisting of a commercial compatibilized blend of polyamide-6 and ABS (Triax 1180). These blends were prepared under two different sets of injection molding conditions. In the first case, a higher melt temperature, higher barrel temperature, lower injection pressure, lower mold temperature, and shorter residence time in the mold were used during injection molding, as compared with the second case. The mechanical properties of the blends were superior to those of the base polymer. In the second case, the resulting injection-molded specimens had a distinct skin-core morphology where elongated fibrils of LCP constituted the skin layer. The mechanical properties of the blends processed under the second set of processing conditions were superior to those of the first, though the trends in both cases were the same. To study the effects of process variables the 15% LCP blend and the second set of processing conditions were taken as the base. Samples were injection-molded by varying one parameter at a time. It was seen that the properties of the blend were increased by maintaining a lower barrel temperature, greater injection pressure, lower injection speed, higher mold temperature, and a greater residence time in the heated mold. Thus it was found that the processing conditions played a vital role in determining the mechanical properties and morphology of the polyblends. © 1996 John Wiley & Sons, Inc.
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