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  • 1
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    Layered intrusions and traffic jams (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-01-01
    Description: A wide range of explanations has been proposed for the origin of repetitive layering in mafic-ultramafic and in (per)alkaline intrusions. Here we propose that the interaction of mineral grains that sink and float in the crystallizing magma is an alternative mechanism that can explain many of the features of layered intrusions, without the need to invoke extrinsic factors. Similar to traffic jams on a motorway, small perturbations in crystal density develop that impede further ascent or descent of buoyant or heavy minerals, respectively. These "traffic jams" separate layers of magma from the rest of the magma chamber. The magma in the individual layers further evolves as a largely independent subsystem, with gravitational sorting organizing the mineral distribution within each layer. Layering can develop in the intermediate range between full mineral separation in low-viscosity or slowly cooling magma chambers and homogeneous crystallization in high-viscosity or fast-cooling chambers. This self-organization mechanism provides a novel explanation for the formation of rhythmic layering in low-viscosity magmas, for example in the Ilímaussaq igneous complex in southwest Greenland.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 2
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    Nicotine activation of alpha4* receptors: sufficient for reward, tolerance, and sensitization (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-11-06
    Description: The identity of nicotinic receptor subtypes sufficient to elicit both the acute and chronic effects of nicotine dependence is unknown. We engineered mutant mice with a4 nicotinic subunits containing a single point mutation, Leu9' --〉 Ala9' in the pore-forming M2 domain, rendering a4* receptors hypersensitive to nicotine. Selective activation of a4* nicotinic acetylcholine receptors with low doses of agonist recapitulates nicotine effects thought to be important in dependence, including reinforcement in response to acute nicotine administration, as well as tolerance and sensitization elicited by chronic nicotine administration. These data indicate that activation of a4* receptors is sufficient for nicotine-induced reward, tolerance, and sensitization.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tapper, Andrew R -- McKinney, Sheri L -- Nashmi, Raad -- Schwarz, Johannes -- Deshpande, Purnima -- Labarca, Cesar -- Whiteaker, Paul -- Marks, Michael J -- Collins, Allan C -- Lester, Henry A -- DA-15663/DA/NIDA NIH HHS/ -- DA-3194/DA/NIDA NIH HHS/ -- MH-49716/MH/NIMH NIH HHS/ -- NS-11756/NS/NINDS NIH HHS/ -- New York, N.Y. -- Science. 2004 Nov 5;306(5698):1029-32.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15528443" target="_blank"〉PubMed〈/a〉
    Keywords: Alkaloids/metabolism ; Animals ; Azocines/metabolism ; Bicyclo Compounds, Heterocyclic/metabolism ; Brain/drug effects/metabolism ; Calcium/metabolism ; Cells, Cultured ; *Drug Tolerance ; Leucine ; Mice ; Mice, Inbred C57BL ; Motor Activity/drug effects ; Neurons/metabolism ; Nicotine/*pharmacology ; Point Mutation ; Pyridines/metabolism ; Quinolizines/metabolism ; Receptors, Nicotinic/genetics/*physiology ; *Reward ; Serine ; Tobacco Use Disorder/*metabolism ; Up-Regulation
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Habenular alpha5 nicotinic receptor subunit signalling controls nicotine intake (2011)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2011-02-01
    Description: Genetic variation in CHRNA5, the gene encoding the alpha5 nicotinic acetylcholine receptor subunit, increases vulnerability to tobacco addiction and lung cancer, but the underlying mechanisms are unknown. Here we report markedly increased nicotine intake in mice with a null mutation in Chrna5. This effect was 'rescued' in knockout mice by re-expressing alpha5 subunits in the medial habenula (MHb), and recapitulated in rats through alpha5 subunit knockdown in MHb. Remarkably, alpha5 subunit knockdown in MHb did not alter the rewarding effects of nicotine but abolished the inhibitory effects of higher nicotine doses on brain reward systems. The MHb extends projections almost exclusively to the interpeduncular nucleus (IPN). We found diminished IPN activation in response to nicotine in alpha5 knockout mice. Further, disruption of IPN signalling increased nicotine intake in rats. Our findings indicate that nicotine activates the habenulo-interpeduncular pathway through alpha5-containing nAChRs, triggering an inhibitory motivational signal that acts to limit nicotine intake.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3079537/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3079537/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Fowler, Christie D -- Lu, Qun -- Johnson, Paul M -- Marks, Michael J -- Kenny, Paul J -- DA020686/DA/NIDA NIH HHS/ -- DA026693/DA/NIDA NIH HHS/ -- F32 DA026693/DA/NIDA NIH HHS/ -- P30 DA015663/DA/NIDA NIH HHS/ -- P30 DA015663-10/DA/NIDA NIH HHS/ -- P30DA015663/DA/NIDA NIH HHS/ -- R01 DA020686/DA/NIDA NIH HHS/ -- R01 DA020686-05/DA/NIDA NIH HHS/ -- England -- Nature. 2011 Mar 31;471(7340):597-601. doi: 10.1038/nature09797. Epub 2011 Jan 30.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory for Behavioral and Molecular Neuroscience, Department of Molecular Therapeutics, The Scripps Research Institute-Scripps Florida, Jupiter, Florida 33458, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21278726" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Female ; Habenula/drug effects/*metabolism/physiology ; Male ; Mice ; Mice, Knockout ; Nicotine/*metabolism/pharmacokinetics/pharmacology ; Rats ; Receptors, Nicotinic/deficiency/genetics/*metabolism ; Reward ; *Signal Transduction/drug effects ; Tobacco Use Disorder/genetics/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis, Crosslinking, and Properties of Benzocyclobutene-Terminated Bisphenol A Polycarbonates (1994)
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 4106-4113 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00093a012
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  • 5
    Electronic Resource
    Electronic Resource
    Products and Mechanism of the Thermal Crosslinking of Benzocyclobutene-Terminated Bisphenol A Polycarbonates (1994)
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 4114-4126 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00093a013
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of chain end group composition and concentration on the properties of bisphenol A-tetrabromobisphenol A copolycarbonates (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1885-1891 
    Details
    ISSN: 0887-624X
    Keywords: copolycarbonate ; bisphenol A ; tetrabromobisphenol A ; end group ; analysis ; properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The types and concentrations of end groups present in bisphenol A-tetrabromobisphenol A copolycarbonates (BA-TBBA coPCs) have major effects on the copolymer solution washability and thermal stability. Six types of coPC end groups are possible: two by monophenol capping of each comonomer, two phenolics (BA-OH and TBBA-OH), and two carbamates (one from each comonomer). BA-TBBA coPCs were prepared by typical solution and interfacial methods and their phenolic and carbamate end group concentrations were correlated with their solution washability and thermal discoloration. Both phenolic and carbamate end groups proved deleterious to these two copolymer properties. An improved interfacial process that employs 4-N,N-dimethylaminopyridine as the coupling catalyst provides coPCs having low concentrations of phenolic and carbamate end groups and that, therefore, wash without emulsification and are thermally stable. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321009
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis and thermochemistry of phenylmaleimide- and phenylnadimide-terminated bisphenol A polycarbonates (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 385-390 
    Details
    ISSN: 0887-624X
    Keywords: polycarbonate ; maleimide terminated ; synthesis ; crosslinking ; stability ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenylmaleimide (PMI)- and phenylnadimide (PNI)-terminated bisphenol A polycarbonates (PCs) were prepared by solution or interfacial phosgenation processes, and their thermal crosslinking, both with and without a free radical initiator, and the thermal stability of the resultant network polymers were investigated. m-PMI PCs were prepared by interfacial phosgenation of bisphenol A and m-hydroxyphenylmaleimide, but p-hydroxyphenylmaleimide caused rapid phosgene hydrolysis under interfacial conditions and PCs from it could only be made by solution phosgenation. The degree of crosslinking of PMI PCs, as measured by their gel fraction, heated in the absence of a free radical initiator was generally higher at 250°C than at 300°C and increased with the concentration of PMI end groups. m- and p-PMI PCs form thermosets having nearly complete gel fractions by radical initiated curing at 150-200°C. The gel fraction of these thermosets decreases with exposure to higher temperatures (300°C). This behavior is attributed to BA PC chain degradation induced by nitrogen-containing maleimide reaction products. p-PNI PC was prepared by solution phosgenation and the thermal reaction of it in the presence of the initiator produced only a small increase in molecular weight. © 1997 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
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  • 8
    Electronic Resource
    Electronic Resource
    Physical, thermomechanical, and rheological properties of bisphenol A-tetrabromobisphenol a copolycarbonates (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 52 (1994), S. 1809-1814 
    Details
    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 physical, thermomechanical, and rheological properties of bisphenol A-tetrabromobisphenol A copolycarbonates (BA-TBBA coPCs) were studied as a function of copolymer composition. TBBA carbonate segments in the copolymer induce proportionally increased glass transition temperatures, heat distortion temperatures, ignition resistance, tensile and flexural moduli, and density. Properties that do not change proportionately with copolymer composition are coefficient of linear thermal expansion, ambient notched Izod and dart puncture impact strengths, and refractive index. Many properties of BA-TBBA coPCs, including glass transition temperature, heat distortion temperature under load, and modulus, approach those of amorphous high-performance thermoplastics such as polyetherimide and polyethersulfone. However, these copolymers have the possible advantage of melt blending with bisphenol A polycarbonate to form homogeneous alloys with variable and controllable properties. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070521215
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  • 9
    Electronic Resource
    Electronic Resource
    Interfacial synthesis and characterization of random and segmented block bisphenol A-tetrabromobisphenol A copolycarbonates (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 52 (1994), S. 467-481 
    Details
    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 chain sequence architecture of bisphenol A-tetrabromobisphenol A copolycarbonates depends on the process employed to prepare them. An interfacial process involving a single-step phosgenation produces a segmented block copolymer, contrary to previous assumptions. An interfacial two-step phosgenation process allows the preparation of random copolycarbonates. In each process the control of the pH of the acqueous phase of the two phase reaction mixture is required to achieve complete comonomer conversion to copolymer and to obtain the desired sequence architecture. The chain sequence architecture of these copolycarbonates can be estimated by examination of their Fourier transform infrared spectra. The relative bandwidth of the carbonate stretching band is roughly proportional to the copolycarbonate number average sequence length, allowing the facile distinction between block and random copolymers. The number average sequence lengths of these copolycarbonates were quantified by carbon-13 NMR spectroscopy. These analyses showed that the one-step phosgenation process yields segmented block copolycarbonates having number average sequence lengths from about 4 to 9, and the two-step phosgenation process produces random copolycarbonates having sequence lengths from 1.6 to 2. The distribution of the aromatic carbon triads of these random copolymers shows them to have an alternate-segmented block architecture, which is consistent with the synthesis conditions, rather than a statistically random distribution of comonomer segments. Dynamic mechanical analysis of two of these copolycarbonates shows a dependence of their low temperature secondary transitions on the copolymer sequence structure. A segmented block copolycarbonate, having a number average sequence length of about 4, displays two distinct peaks in its tan δ curve at temperatures corresponding to those transitions observed in the respective homopolymers. The tan δ curve of a random copolycarbonate shows a single low temperature secondary transition midway between those of the homopolymer. © 1994 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070520401
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  • 10
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    Products and Mechanism of the Thermal Crosslinking of Benzocyclobutene-Terminated Bisphenol A Polycarbonates (1994)
    American Chemical Society
    Details
    Publication Date: 1994-07-01
    Print ISSN: 0024-9297
    Electronic ISSN: 1520-5835
    Topics: Chemistry and Pharmacology , Physics
    Published by American Chemical Society
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