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  • Chemistry  (10)
  • 14.60.Cd  (1)
  • 1995-1999  (2)
  • 1985-1989  (9)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 328 (1987), S. 129-145 
    ISSN: 1434-601X
    Keywords: 14.60.Cd ; 25.70.Cd ; 25.70.Ef
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Positron lines were observed in heavy ion-atom collisions at bombarding energies close to the Coulomb barrier in subcritical systems with the sum of the atomic numbers of the colliding nucleiZ u =Z 1+Z 2 being smaller thanZ u =172. Each collision system, studied,208Pb +208Pb(Zu=164),238U+181Ta(Zu=165), and238Au(Zu=171), exhibits the emission of two positron lines withZ u -independent c.m. energies of ∼ 258 keV and ∼ 340 keV, and with widths of about 30 keV, superimposed on continuous positron spectra from nuclear pair decay and pair emission induced by the time changing Coulomb field of the collision. The production cross section of thee +-lines rises with a high power ofZ u (ocZ u 22), which is comparable to theZ u 20-dependence for the collision induced positrons.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dinucleoside monophosphates bearing usual protecting groups at the exocyclic amino functions of the heterocyclic bases, the 5′-hydroxy group, the phosphate moiety and the O-6-position of the guanine ring have been analysed by FAB mass specrometry in the negative ion mode. These non-charged key intermediates for oligodeoxynucleotide synthesis exhibit very simple spectra in the mass range of m/z 400-1500 using tetra-ethylene glycol as matrix. Most of the observed ions could easily be assigned. Apart from deprotonated molecular ions sequence specific ions arising from C-O-P bond cleavage and ions derived from loss of protecting groups were observed. The simplicity of spectra interpretation makes FAB mass spectrometry to a rapid and valuable tool for unambiguous identification of dimeric synthons for oligonucleotide synthesis.
    Additional Material: 3 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 525-536 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Temperature of cutting tools by thin filmsDuring the cutting process, cutting tools are exposed to complex mechanical, thermal, dynamic and tribological loads. Especially in the case of dry machining the demands on cutting tools are very high. Dry machining becomes more and more interesting because of tightened up ecolaws and increased costs for the handling of coolants. Due to a renunciation on coolants the cutting tools need to be modified to the process of dry machining. Thereby modern plasma and ion based surface technologies can be used to deposit a thin film adopting the functions of coolants, e.g. cooling and lubricating.In this research project several coating types, e.g. titanium and chromium based coatings, where developed and characterized regarding their mechanical, tribological and thermal properties. For the research, four partners collaborated permuting all steps of surface and coatings design. Materials Science Institute (WW), Aachen University of Technology, performed the development of PVD coatings and the thermophysical characterization by thermal wave analysis. Surface modifications of uncoated and coated tools by ion beam assisted deposition were carried out at Stiftung Institut für Werkstofftechnik (IWT), Bremen. To determine the cutting properties of coated tools, practical tests were performed at Laboratory for Machine Tools and Production Engineering (WZL), Aachen University of Technology.
    Notes: Zerspanwerkzeuge sind während ihres Einsatzes einem komplexen und schwer zu erfassenden Beanspruchungskollektiv ausgesetzt. Dieses wird besonders durch die aus ökonomischen und ökologischen Gründen angestrebte Trockenzerspanung beeinflußt. Der vollständige Verzicht auf Kühlschmierstoffe bedeutet aus technologischer Sicht, daß Werkzeuge, Schneidstoffe und Zerspanoperationen auf die Bedingungen der Trockenzerspanung umgestellt werden müssen. Dabei bieten moderne ionen-und plasmagestütze Oberflächentechnologien insofern einen Lösungsansatz, daß durch Beschichtungen bzw. Oberflächenmodifikationen wichtige Aufgaben der Kühlschmiermittel durch den beschichteten Schneidstoff selbst übernommen werden können. Dies sind vor allem der Ersatz von Schmierung und Kühlung.Für den Bereich der Trockenzerspanung wurden im Rahmen eines Verbundvorhabens u.a Titanbasisschichten sowie Chrombasisschichten entwickelt und hinsichtlich der physikalischen Eigenschaften untersucht. Durch die enge Zusammenarbeit der beteiligten Forschungsstellen konnte das jeweils vorhandene Erfahrungspotential vollständig in die Schichtsystementwicklung einfließen. Diese umfaßte alle iterativen Schritte des Schichtmodifikation, begleitende Schichtanalytik bis hin zum Praxistest. So war beispielsweise das Lehr- und Forschungsgebiet Werkstoffwissenschaften der RWTH Aachen für die Schichtentwicklung sowie fü die thermophysikalische Charakterisierung der Schichten zuständig. Die Stiftung Institut für Werkstofftechnik, Bremen, führte eine Optimierung der Interfaces und der Hartstoffschichten mittels ionenstrahlgestützter Beschichtungsverfahren durch. So konnte das Substrat vor bzw. die Hartstoffschicht nach der Beschichtung an den Anwendungsfall angepaßt werden. Die Untersuchung hinsichtlich der Praxistauglichkeit der beschichteten Schneidstoffe erfolgte am Werkzeugmaschinenlabor der RWTH Aachen durch entsprechende Zerspanversuche.
    Additional Material: 15 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 11 (1988), S. 506-509 
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; Cyclodextrin ; Chiral pharmaceuticals ; Amines ; β-Amino acids ; Cycloalkane-trans-diols ; Inclusion phenomena ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heptakis (3-O-acetyl-2,6-di-O-pentyl)-ß-cyclodextrin is used as a chiral stationary phase in capillary gas chromatography. High enantioselectivity towards trifluoro-acetylated α and β-chiral amines, amino alcohols, α- and β-amino acid esters, and cyclic trans-diols is observed. In contrast to chiral polysiloxane phases, where hydrogen bonding interaction is essential for enantiomer separation, in cyclodextrins inclusion properties contribute to enantioselectivity. This can be concluded from the separation of N-alkylated amino compounds. The new chiral stationary phase exhibits a wide operating temperature range and is stable above 200°C.
    Additional Material: 6 Ill.
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  • 5
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; Cyclodextrin ; Alcohols ; Hydroxy acids ; Carbohydrates ; Cyanohydrins ; Olefins ; Alkyl halides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: O-Perpentylated β-cyclodextrin has been evaluated as chiral stationary phase in capillary gas chromatography. Enantioselectivity is observed towards many chiral hydroxy compounds, including cyanohydrins and carbohydrates. Most importantly, the enantiomers of many olefins and alkyl halides can be resolved on this chiral phase. The thermal stability of the cyclodextrin derivative exceeds 200°C.
    Additional Material: 10 Ill.
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  • 6
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; α-Cyclodextrin ; Lactones ; O-Alkylglycerols ; Chiral pharmaceuticals ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The properties of hexakis(3-O-acetyl-2,6-di-O-pentyl)-α-cyclodextrin as a chiral stationary phase for capillary gas chromatography are described. For the first time the enantiomers of a series of different lactones are separated and their order of elution is assigned. Moreover, the enantiomers of trifluoroacetylated aldols and amino alcohols, the cyclic carbonates of 1,2-diols, 1,3-diols, O-alkylated glycerols, and some chiral pharmaceuticals are also separated on the new chiral phase. The modified α-cyclodextrin is stable above 200°C.
    Additional Material: 7 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 12 (1989), S. 641-644 
    ISSN: 0935-6304
    Keywords: Enantioselective capillary gas chromatography ; Modified cyclodextrins ; Host-guest interactions ; Inclusion phenomena ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of per-O-alkylated as well as partially alkylated/acylated derivatives of α-, β-, and γ-cyclodextrins as chiral stationary phases has opened many new applications to enantioselective gas chromatography. Chiral recognition is now independent of hydrogen bonding interactions and enantiomer separations are achieved for a large variety of compounds which could not be separated before, including lactones, spiroacetals, alkyl halides, olefins, and even compounds with axial asymmetry.
    Additional Material: 8 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 12 (1989), S. 732-738 
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; Cyclodextrin ; Amino acids ; Hydroxy acids ; Terpene alcohols ; Terpene ketones ; Lactones ; Cyclopropane derivatives ; Cyclic ethers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: γ-Cyclodextrin with 3-O-butyryl and 2,6-di-O-pentyl residues is a very versatile chiral stationary phase for enantiomer separation. Most of the common and many uncommon amino acids can be separated as well as α- and β-hydroxy acids, chiral alcohols, diols, triols, ketones, bicyclic, and tricyclic acetals, amines, alkyl halides, lactones, and functionalized cyclopropane derivatives.
    Additional Material: 13 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 12 (1989), S. 790-792 
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; Cyclodextrin ; β-Chiral olefins ; Fe-Carbonyl complexes of alkenes ; Tetramethyl-trans-cyclooctene ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Perpentylated γ-cyclodextrin is a very hydrophobic liquid which exhibits enantioselectivity toward a number of non-polar chiral substrates including the saturated hydrocarbons cis- and trans-pinane, β-chiral olefins, iron(O) tricarbonyl complexes of prochiral olefins and 3,3,8,8-tetramethyl-trans-cyclooctene, a compound with planar chirality.
    Additional Material: 4 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 20 (1985), S. 674-676 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The behaviour of substituted cyclopropenes under electron impact is to a large extent determined by the presence of the unsaturated three-membered ring which is capable of efficient delocalization of the positive charge. The loss of one of the substituents at the C(3) position of the small ring is characteristic for the fragmentation of cyclopropenes; the loss of the substituent which is less electron donating occurs preferentially. The presence of substituents with heteroatoms on the three-membered ring may lead to changes in the fragmentation scheme characteristic for the specific set of substituents.
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