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  • Chemistry  (566)
  • 2015-2019  (48)
  • 1955-1959  (518)
  • 1
    Digitale Medien
    Digitale Medien
    Gas-solid contacting with ozone decomposition reaction (1958)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 4 (1958), S. 403-408 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690040405
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  • 2
    Digitale Medien
    Digitale Medien
    Viscosity of dilute solutions of linear and branched polyvinyl acetateA preliminary account of this work was presented at the Ann Arbor High Polymer Research Conference, July 25, 1955. (1956)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 22 (1956), S. 123-135 
    Details
    ISSN: 0022-3832
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The dilute solution viscosity properties of fractions of two linear and one branched sample of polyvinyl acetate in benzene and of two linear and one branched fraction in several solvents were measured at 35°C. Values of total slope, b (from plots of ηsp/c vs. c), and intrinsic viscosities were obtained under the requirement that k′ + β = 0.500 ± 0.002. Empirical plots of log b vs. log [η] gave lines which were straight within the limits of accuracy of the data. For the linear fractions in benzene, Huggins' k′ was constant and the slope of the log b vs. log [η] line was 2; for the branched fractions in benzene, k′ increased with [η] and the slope of the log b vs. log [η] line was greater than 2. The log b vs. log [η] plots form the basis for a “one-point” method for determining [η]. Consideration of these data along with results reported in the literature indicates that k′ is measurably sensitive to branching only for fractions possessing a certain minimum combination of size and complexity. However, in some cases where the variations of k′ are inconclusive, use of the slope of the log b vs. log [η] line may provide a reliable indication of branching. It was found that a comparison between the branched and linear series could also be made at constant values of [η] or b. Two linear fractions in different solvents obeyed a type of Huggins relationship in which k′ did not vary with solvent and the slope of the log b vs. log [η] line was 2. For a higher molecular weight branched fraction, however, k′ varied from solvent to solvent and the slope of the log-log plot was about 1.7. These data do not support a reference point concept of “true” intrinsic viscosity based on a simple linear relationship between b and [η]. Preliminary results dealing with the effects of the shear rate indicated that the measured viscosity properties of branched fractions may be more seriously affected by changes in shear rate than those of linear fractions.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1956.1202210014
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  • 3
    Digitale Medien
    Digitale Medien
    A further interpretation of resonance and electrical factors affecting copolymerization (1959)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 40 (1959), S. 457-468 
    Details
    ISSN: 0022-3832
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: New equations for evaluation of resonance (q) and electrical (∊) factors affecting copolymerization have been derived: \documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{*{20}c} {r_1 } \hfill & { = \exp \left\{ { - {{\left( {q_1 - q_2 } \right)} \mathord{\left/ {\vphantom {{\left( {q_1 - q_2 } \right)} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right\}\exp \left\{ { - 7.23 \times 10^{20} \varepsilon _1 {{\left( {\varepsilon _1 - \varepsilon _2 } \right)} \mathord{\left/ {\vphantom {{\left( {\varepsilon _1 - \varepsilon _2 } \right)} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right\}} \hfill \\ {r_2 } \hfill & { = \exp \left\{ { - {{\left( {q_2 - q_1 } \right)} \mathord{\left/ {\vphantom {{\left( {q_2 - q_1 } \right)} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right\}\exp \left\{ { - 7.23 \times 10^{20} \varepsilon _2 {{\left( {\varepsilon _2 - \varepsilon _1 } \right)} \mathord{\left/ {\vphantom {{\left( {\varepsilon _2 - \varepsilon _1 } \right)} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right\}} \hfill \\ {r_1 r_2 } \hfill & { = \exp \left\{ { - 7.23 \times 10^{20} {{\left( {\varepsilon _1 - \varepsilon _2 } \right)^2 } \mathord{\left/ {\vphantom {{\left( {\varepsilon _1 - \varepsilon _2 } \right)^2 } {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right\}} \hfill \\ \end{array} $\end{document} The new equations will apply over any temperature range, and will express ∊ in terms of e.s.u. and q in kcal./mole. These factors were determined for an extensive list of monomers and were tabulated. Agreement with Hammett σ values and other kinetic and theoretical considerations were found.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1959.1204013715
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  • 4
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    Unlocking P(V): Reagents for chiral phosphorothioate synthesis (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publikationsdatum: 2018-09-21
    Beschreibung: Phosphorothioate nucleotides have emerged as powerful pharmacological substitutes of their native phosphodiester analogs with important translational applications in antisense oligonucleotide (ASO) therapeutics and cyclic dinucleotide (CDN) synthesis. Stereocontrolled installation of this chiral motif has long been hampered by the systemic use of phosphorus(III) [P(III)]–based reagent systems as the sole practical means of oligonucleotide assembly. A fundamentally different approach is described herein: the invention of a P(V)-based reagent platform for programmable, traceless, diastereoselective phosphorus-sulfur incorporation. The power of this reagent system is demonstrated through the robust and stereocontrolled synthesis of various nucleotidic architectures, including ASOs and CDNs, via an efficient, inexpensive, and operationally simple protocol.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 5
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    Response to Comment on "Synthesis and characterization of the pentazolate anion cyclo-N5- in (N5)6(H3O)3(NH4)4Cl" (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publikationsdatum: 2018-03-16
    Beschreibung: Huang and Xu argue that the cyclo -N 5 – ion in (N 5 ) 6 (H 3 O) 3 (NH 4 ) 4 Cl we described in our report is theoretically unfavorable and is instead protonated. Their conclusion is invalid, as they use an improper method to assess the proton transfer in a solid crystal structure. We present an in-depth experimental and theoretical analysis of (N 5 ) 6 (H 3 O) 3 (NH 4 ) 4 Cl that supports the results in the original paper.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 6
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    Encoding of vinylidene isomerization in its anion photoelectron spectrum (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publikationsdatum: 2017-10-20
    Beschreibung: Vinylidene-acetylene isomerization is the prototypical example of a 1,2-hydrogen shift, one of the most important classes of isomerization reactions in organic chemistry. This reaction was investigated with quantum state specificity by high-resolution photoelectron spectroscopy of the vinylidene anions H 2 CC and D 2 CC and quantum dynamics calculations. Peaks in the photoelectron spectra are considerably narrower than in previous work and reveal subtleties in the isomerization dynamics of neutral vinylidene, as well as vibronic coupling with an excited state of vinylidene. Comparison with theory permits assignment of most spectral features to eigenstates dominated by vinylidene character. However, excitation of the 6 in-plane rocking mode in H 2 CC results in appreciable tunneling-facilitated mixing with highly vibrationally excited states of acetylene, leading to broadening and/or spectral fine structure that is largely suppressed for analogous vibrational levels of D 2 CC.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 7
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    CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publikationsdatum: 2018-05-18
    Beschreibung: Carbon dioxide (CO 2 ) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO 2 to ethylene with 70% faradaic efficiency at a potential of –0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO 2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at –0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 8
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    A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publikationsdatum: 2016-09-02
    Beschreibung: Oxygen electrochemistry plays a key role in renewable energy technologies such as fuel cells and electrolyzers, but the slow kinetics of the oxygen evolution reaction (OER) limit the performance and commercialization of such devices. Here we report an iridium oxide/strontium iridium oxide (IrO x /SrIrO 3 ) catalyst formed during electrochemical testing by strontium leaching from surface layers of thin films of SrIrO 3 . This catalyst has demonstrated specific activity at 10 milliamps per square centimeter of oxide catalyst (OER current normalized to catalyst surface area), with only 270 to 290 millivolts of overpotential for 30 hours of continuous testing in acidic electrolyte. Density functional theory calculations suggest the formation of highly active surface layers during strontium leaching with IrO 3 or anatase IrO 2 motifs. The IrO x /SrIrO 3 catalyst outperforms known IrO x and ruthenium oxide (RuO x ) systems, the only other OER catalysts that have reasonable activity in acidic electrolyte.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 9
    Digitale Medien
    Digitale Medien
    Correlation of bubble-cap fractionating-column plate efficiencies (1956)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 2 (1956), S. 18-25 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A method of estimating the true conditions of operation of a bubble-cap tray is presented. Intermediate between the Murphree and the Lewis methods, which represent the extremes of actual operation, this method involves the use of a correlation to determine the degree of liquid mixing on the tray and the use of new relations between the Murphree vapor efficiency, the Lewis case I efficiency, and the true local efficiency. For the last, partial liquid mixing is taken into account.Data were obtained on an 18-in. O.D. three-tray bubble-cap tower containing ten 3-in. bubble caps a tray. Partial liquid mixing was correlated for changes in vapor and liquid rates, pressure, temperature, and weir height for the system ethylene dichloride-toluene.Efficiency data on acetone-water, ethanol-water, and ethylene dichloride-toluene showed the following effects: (1) low concentration of lwo boiler usually, but not always, resulted in low true local efficiencies, always with high Murphree efficiencies; (2) vapor velocity effects are more intimately connected with slot velocity than superficial velocity (and hence entrainment); (3) raising the pressure gives higher efficiencies; (4) an increase in liquid depth increases the true local efficiency but may have no effect on the Murphree efficiency.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690020105
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  • 10
    Digitale Medien
    Digitale Medien
    The mechanics of vertical moving liquid-liquid fluidized systems: I. Interphase contacting of droplets passing through a second quiescent fluid (1959)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 5 (1959), S. 533-539 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Previous publications have shown that for solid spheres fluidized in water a unique relationship exists between the slip velocity and the system holdup. With this work as a model a method is now presented for estimating the behavior of the liquid-in-liquid spray column in which droplets of one phase move through a second quiescent phase.Combining the solids fluidization results with information on the single droplet terminal velocity one can obtain a design estimate of the holdup or interphase contact area for the liquid-liquid spray column. This design estimate includes the particular nature of the liquid droplet of being susceptible to internal circulation, oscillation, and distortion.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690050423
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