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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 45 (1995), S. 219-228 
    ISSN: 0006-3592
    Keywords: formate conversion ; mass spectrometer ; anaerobic conversion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The dynamics of the anaerobic conversion of formate in a microbial mixed culture taken from an anaerobic fluidized bed reactor was studied using a new stirred micro reactor equipped with a membrane mass spectrometer. The microreactor with a toroidally shaped bottom and pitched blade turbine and a cylindrical flow guide was thermostated and additionally equipped with a pH electrode and pH control. During fed-batch experiments using formate, the dissolved gases (methane, hydrogen, and carbon dioxide), as well as the acid consumption rates for pH control were monitored continuously. Initially and at the end of each experiment, organic acids were analyzed using ion chromatography (IC). It was found that about 50% of the formate was converted to methane via hydrogen and carbon dioxide, 40% gave methane either directly or via acetate. This was calculated from experiments using H13CO3- pulses and measurement of 12CH4 and 13CH4 production rates. About 10% of the formate was converted to lactate, acetate, and propionate, thereby increasing the measured CO2/CH4 production ratio. The nondissociated formic acid was shown to be rate determining. From the relatively high Ks value of 2.5 mmol m-3, it was concluded that formate cannot play an important role in electron transfer. During dynamic feeding of formate, hydrogen concentration always increased to a maximum before decreasing again. This peak was found to be very discriminative during modeling. From the various models set up, only those with two-stage degradation and double Monod kinetics, both for CO2 and hydrogen, were able to describe the experimental data adequately. Additional discrimination was possible with the IC measurement of organic acids. © 1995 John Wiley & Sons, Inc.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 127-135 
    ISSN: 0006-3592
    Keywords: membrane mass spectrometer ; kinetic measurements ; anaerobic biofilm ; acetate ; inhibition ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A small, stirred, 14.4-mL tank reactor was designed to serve as a measurement cell for short-term investigation of microbial kinetics. A mass spectrometer membrane probe allowed the measurement of the dissolved gases of hydrogen, methane, oxygen, and carbon dioxide. pH was measured by an electrode and controlled by addition of acid or alkali. The highly sensitive measurement of gases with low solubility allowed rapid measurements at very low conversion. In kinetic experiments, a stepwise increase of substrate concentration (method A) and continuous feed of substrate (method B) were used, allowing quick estimation of substrate kinetics. Acetate conversion in mixed culture biofilms from a fluidized bed reactor was investigated. Substrate inhibition was found to be negligible in the concentration range studied. Experiments at various pH values showed that the undissociated acid form was the kinetic determinant. Kinetic parameters for Haldane kinetics of protons were KSH = 1.3 × 10-5 mol m-3 and KIH = 8.1 × 10-3 mol m-3. With free acid (HAc) as the rate determining species, the kinetic parameters for method A were KSHAc = 0.005 mol m-3 and KIHAc = 100 mol m-3 and for method B were KSHAc = 0.2 mol m-3 and KIHAc = 50 mol m-3. The maximum biomass activity occurred at around pH 6.5. Acetate was exclusively converted to methane and CO2 at pH 〉 6. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 127-135, 1998.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 16 (1972), S. 2079-2089 
    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: Commercial triblock polymers (Kratons) consisting of polystyrene and a polydiene were characterized via gel permeation chromatography and small-angle x-ray scattering in order to determine the amount of free polystyrene and diblock material and to clarify the effect of these polymeric impurities on the morphology of solvent-cast samples. Gel permeation chromatography measurements revealed the Kratons to consist of 80-85% triblock, 15-20% diblock, and trace amounts of free polystyrene. Pure triblocks, impurity-doped pure triblocks, the Kratons, and a postpolymerically degraded Kraton were examined with regard to the effect of polymeric impurities on morphology. Small amounts (〈5%) of free polystyrene induce a regularization of the glassy domains, while increased amounts of this homopolymer apparently lead to diffuse phase boundaries. The presence of diblock polymer results in a loss of macrolattice details, indicating the presence of less ordered and more diffuse glassy domains.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 478 (1981), S. 239-239 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 223-232 
    ISSN: 1057-9257
    Keywords: CdTe ; ZnTe ; Impurities ; Spin resonance ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We present results of electron paramagnetic resonance (EPR) and optical spectroscopy on different charge states of the transition metal impurity iron in ZnTe and CdTe. We identify the energy level position of the Fe+ acceptor in ZnTe at Ev + 1.7eV and estimate its position in CdTe. Ionisation transitions from Fe+to the conduction and valence bands ar found in both absorption spectroscopy and photo-EPR. Optical intra-defect tracsitions from Fe+ to crystalfield-split excited states ar resolved for the first time. This assignment to Fe2+ is based on optically detected EPR. Application of both far-infrared Fourier transform and EPR spectroscopy allows the determination of the total iron concentration in all charge states.
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  • 6
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XX. Metastable Oxidation of a Series of Solid Solutions  -  an Access to W-rich Block Structures in the System Nb2O5/WO3The characteristical region of existence of block structures with building elements that are limited in size in two directions ends in the system Nb2O5/WO3, as was shown by previous investigations, under conditions of equilibrium at a maximum value of 2.654 O/ΣM. For the occurring phases with the ratios Nb2O5: WO3 = 6:1, = 7:3, = 8:5 and = 9:8 as well we now were successful in substituting W for Nb. The original block structure and the corresponding ratio O/ΣM were preserved. The “9:8”-phase W4/4[Nb18W7O69], for example, forms solid solutions W4/4[Nb11W14O69] leaving the size of the building elements ([5 times; 5] blocks) unchanged. Hereby the ratio W/Nb is drastically enhanced from 0.444 to 1.364. By metastable oxidation of these solid solutions at temperatures of about 500°C, for instance in air, one comes back to the system Nb2O5/WO3. In this way the region of existence of block structures could be expanded far beyond the limit at 2.654 O/ΣM to higher W/Nb values.
    Notes: Das charakteristische Existenzgebiet der Blockstrukturen mit zweidimensional begrenzten Bauelementen endet im System Nb2O5/WO3, wie bereits frühere Untersuchungen gezeigt haben, unter Gleichgewichtsbedingungen bei einem Maximalwert von 2,654 O/O/ΣM (M = Nb, W). Es gelang nun, in den mit den Verhältnissen Nb2O5: WO3 = 6:1, 7:3, 8:5 sowie 9:8 auftretenden Phasen im weiten Umfang Nb durch W zu substituieren, wobei ihre ursprüngliche Blockstruktur und das jeweilige Verhältnis O/ΣM erhalten blieben. So bildet z. B. die «9:8»-Phase W4/4[Nb18W7O69] bei unveränderter Größe der Bauelemente ([5 × 5]-Blöcke) einen Mischkristall W4/4[Nb11W14O69]; das Verhältnis W/Nb wird damit drastisch von 0,444 auf 1,364 erhöht. Durch metastabile Oxydation der so erhaltenen Mischkristalle bei Temperaturen um 500°C, z. B. an der Luft, gelangt man in das System Nb2O5/WO3 zurück. Das Existenzgebiet der Blockstrukturen konnte in dieser Weise bis weit über die Grenze bei 2,654 O/ΣM hinaus zu höheren W/Nb-Werten erweitert werden.
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  • 7
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die Reduktion der metastabilen Oxydationsprodukte der NbOx-Phasen (2,4 〈 x 〈 2,5) mit H2O/H2-Mischungen wurde untersucht. Bei niedrigerer Temperatur (≈300°C) ist die Reduktionswirkung noch gering, sie nimmt mit steigender Temperatur beträchtlich zu. Dabei zeigen die Oxydationsprodukte der Zusammensetzung Nb2O5 ein gewisses „Erinnerungsvermögen“; in allen Fällen läft die Reduktion bis zu den ursprünglichen NbOx-Phasen zurück. Man gelangt bei um so niedrigerer Reduktionstemperatur zur Zusammensetzung x des jeweiligen Ausgangsprodukts NbOx zurück, je kleiner die Differenz 2,50-x ist. Bemerkenswert ist, daß die Rückreduktion zum monoklinen Nb12O29 über eine Zwischenstufe der Zusammensetzung 2,439-2,447 O/Nb verläuft. An dieser Stelle liegt eine neue, metastabile NbOx-Phase mit einem charakteristischen Guinierdiagramm vor.Contributions on the Investigation of Inorganic Non-stoichiometric Compounds. XII. Reduction of Metastable Nb2O5 Modifications, Oxidation Products of NbOx Phases (2.4 〈 x 〈 2.5)The reduction of metastable oxidation products of the NbOx phases (2.4 〈 x 〈 2.5) by H2O/H2 mixtures was investigated. At lower temperatures (ca 300°C) the effect of the reduction was slight. It increased considerably with rising temperature. Samples oxidized to the composition Nb2O5 showed a certain “memory of structure”. The original NbOx phases can be obtained in all cases from the oxidized products. The smaller the difference 2.50-x the lower the reaction temperature at which the composition x of the corresponding starting material NbOx is regained. It is remarkable that the re-reduction to the monoclinic Nb12O29 proceeds by way of the intermediate composition 2.439-2.447 O/Nb. At this ratio O/Nb a new metastable NbOx phase with a characteristic x-ray diagram exists.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 484 (1982), S. 98-123 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XV. Some Further Metastable Nb2O5-Modifications, Products of the Slow Oxidation of the NbOx PhasesIf in contrast to previous investigations the blue-black NbOx phases (2.4 〈 x 〈 2.5) are not oxidized in air, but in a rarefied oxygen atmosphere or with steam, five further metastable Nb2O5 forms can be obtained in addition to the numerous already known Nb2O5 modifications. Nb12O29 (mon. and orh.) and Nb47O116 lead to one new Nb2O5 form each. Nb22O54 yields two new Nb2O5 modifications. It can be deduced from the thermal behaviour that in addition to unexspected transitions between the known and the new metastable modifications in all cases H-Nb2O5 appears as final product at high temperature. The electron optical investigation of the new oxidation products of Nb12O29 (mon. and orh.) shows that their structures are determined by R-type tunnels as the characteristic structure element. By this they clearly differ from the already known oxidation products. With this for the first time sodium free niobium oxide structures occur whose structural concept is substantially shaped by R-type tunnels which are known from NaNb13O33.
    Notes: Oxydiert man die blauschwarzen NbOx-Phasen (2,4 〈 x 〈 2,5) im Unterschied zu früheren Untersuchungen nicht an der Luft, sondern in verdünnter Sauerstoffatmosphäre oder mit Wasserdampf, so werden zusätzlich zu den zahlreichen bisher bekannten Nb2O5-Modifikationen fünf weitere metastabile Formen von Nb2O5 erhalten. Nb12O29 (mon. und orh.) geht in je eine, Nb22O54 in zwei und Nb47O116 in eine neue Nb2O5-Form Über. Wie das thermische Verhalten zeigt, tritt außer unerwarteten Übergängen zwischen den bekannten und den neuen metastabilen Modifikationen in allen Fällen als Endstufe bei hoher Temperatur H-Nb2O5 auf.Aus der elektronenoptischen Untersuchung der neuen Oxydationsprodukte von Nb12O29 (mon. und orh.) geht hervor, daß ihr Aufbau durch R-Typ-Lücken als charakteristisches Strukturelement bestimmt ist, so daß sie sich von den bisher bekannten Oxydationsprodukten strukturell klar unterscheiden. Damit liegen erstmals Na-freie Nioboxidstrukturen vor, an deren Aufbau die von NaNb13O33 bekannten R-Typ-Lücken maßgeblich beteiligt sind.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 484 (1982), S. 77-97 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XIV. Oxidation Products of Orthorhombic Nb12O29, Electron Optical InvestigationAn electron optical investigation shows that the orthorhombic starting material Nb12O29(BII) is well ordered. The oxidation products Nb2O5(Ox1BII) and Nb2O5(Ox2BII) are different from each other in structures as well as in their reactions. Nb2O5(Ox1BII) is unstable in the electron beam and differs from BII by characteristic point-defects. The radiation load can lead to the reduction to BII or to a transition into a defect structure with R-type-tunnels. The not well ordered structure of Nb2O5(Ox2BII) is stable in the electron beam. Characteristic is the sequence of [2×5] and [3×4] blocks, the latter in two different orientations. The observed composition O/Nb = 2.500 can be described by the present structural modell assuming vacant niobium tetrahedral sites. The large structural differences between the oxidation products of the orthorhombic and the monoclinic Nb12O29 are remarkable.
    Notes: Wie die elektronenoptische Untersuchung zeigt, ist das orthorhombische Ausgangsprodukt Nb12O29(BII) gut geordnet. Die Oxydationsprodukte Nb2O5(Ox1BII) und Nb2O5(Ox2BII) sind strukturell sowie in ihrem Verhalten verschieden. Das im Elektronenstrahl instabile Nb2O5(Ox1BII) unterscheidet sich von BII durch charakteristische Punktdefekte. Die Strahlbelastung kann zu einer Reduktion zu BII oder zum Übergang in eine Defektstruktur mit R-Typ-Lücken führen. Die wenig geordnete Struktur von Nb2O5(Ox2BII) ist im Elektronenstrahl beständig; charakteristisch ist die Abfolge von [2×5]- und [3×4]-Blöcken, letztere in zwei verschiedenen Orientierungen. Die beobachtete Zusammensetzung O/Nb = 2,500 läßt sich im vorliegenden Strukturmodell mit einer Unterbesetzung der Nb-Tetraederpositionen beschreiben. Bemerkenswert sind die erheblichen strukturellen Unterschiede zwischen den Oxydationsprodukten von orthorhombischem und monoklinem Nb12O29.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 484 (1982), S. 53-76 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XIII. Oxidation Products of Monoclinic Nb12O29, Electron Optical InvestigationThe electron optical investigation shows that the starting material Nb12O29(mon.) is well ordered and that the oxidation products Nb2O5(Ox1BI) and Nb2O5(Ox2BI) have different structures. Nb2O5(Ox1BI) has a similar structure as Nb12O29(mon.), however differs from the latter by characteristic point defects, which in the electron microscope easily disappear by reduction. Nb2O5(Ox2BI) has not a well ordered structure; characteristic are rows of [2×n]-blocks which on the average are separated by five [3×n]-blocks. The average block length is n = 4 octahedra. The observed composition O/Nb = 2.500 can be explained by a structure model with unoccupied tetrahedral sites of Nb.
    Notes: Die elektronenoptische Untersuchung zeigt, daß das monokline Ausgangsprodukt Nb12O29(BI) gut geordnet ist und daß die bei der Oxydation entstehenden Produkte Nb2O5(Ox1BI) und Nb2O5(Ox2BI) unterschiedliche Strukturen besitzen. Nb2O5(Ox1BI) ist sehr ähnlich aufgebaut wie BI, unterscheidet sich hiervon jedoch durch charakteristische Punktdefekte, die durch Reduktion im Elektronenmikroskop leicht wieder verschwinden. Nb2O5(Ox2BI) besitzt eine wenig geordnete Struktur; charakteristisch sind Reihen von [2×n]-Blöcken, die im Mittel durch fünf [3×ln]-Blöcke voneinander getrennt sind; im Durchschnitt ist die Blocklänge n = 4. Die beobachtete Zusammensetzung O/Nb = 2,500 läßt sich im vorliegenden Strukturmodell durch eine Unterbesetzung der Nb-Tetraederpositionen erklären.
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