ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Springer  (190)
  • American Geophysical Union  (21)
  • 1990-1994  (183)
  • 1970-1974  (28)
Collection
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Optical and quantum electronics 26 (1994), S. S273 
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstact A model for the erbium-doped fibre amplifier (EDFA) is presented and discussed. The model is used in a detailed analysis of the waveguide design of 980-nm pumped EDFAs operated in the small-signal gain region. A comparison of results for signals at wavelengths 1532 and 1552 nm is given. The influence of the amplified spontaneous emission on the optimum cut-off wavelength for the LP11-mode of step index fibres is shown to be significant for gains exceeding ∼40 dB. For lower gain levels, the optimum cut-off wavelength is 800 nm. An analysis of EDFAs used as preamplifiers indicates that significant improvements of the noise figures may be obtained by cut-back of the fibre to lengths that are ∼50% of that for maximum gain. Very low noise figures of ∼3.1 dB are only obtainable if a reduction of ∼ 10 dB in the gain is acceptable.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structure and absolute configuration of naturally occurring Carnosol have been investigated by X-ray analyses. Crystal data are: orthorhombic P21212;a=15.762(1),b=13.755(1),c=7.7747(7) Å,Z=4,V=1688.2 Å3, andR=0.031 (2569 reflections). The absolute configuration is established at a significance level better than 0.995 according to HamiltonsR-factor test and is in accordance with that predicted experimentally by chemically means. Correlation of the solid-state IR pattern of the regions sensitive to hydrogen bonding (CO and OH stretching bands) with the X-ray crystal structure is excellent and shows, that even weak inter- and intramolecular hydrogen bonds may be unambiguously identified by IR spectroscopy. The variable-temperature nuclear magnetic resonance studies (NMR) show that the twinning of the signals from the isopropyl methyl protons cannot be due to hindered rotation but can be ascribed magnetic nonequivalence induced by the chiral centers.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1434-4475
    Keywords: Michael type addition ; L-Nucleosides ; 2′,3′,6′-Trideoxy-L-hexofuranose nucleosides ; 3′-(1,2,4-Triazol-1-yl) nucleosides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die quecksilberkatalysierte Hydrolyse von acetyliertemL-Rhamnal1 ergab die α,β-ungesättigten Aldehyde2. 1,2,3-Triazol wurde in Gegenwart von 1,8-Diazabicyclo[5.4.0]-7-undecen mittels einer Addition vom Michael-Typ an C-3 von2 gekoppelt und ergab dann nach Acetylierung am anomeren Zentrum eine anomere Mischung von 1,5-Di-O-acetyl-3-(1,2,4-triazol-1-yl)-2,3,6-trideoxy-L-arabino-hexofuranose (3). Die Reaktion von3 mit silyliertem 2,4-Di-hydroxypyrimidinen4 in Gegenwart von Trimethylsilyltriflat in absolutem Ethanol ergab die entsprechenden Nucleoside7 und8.
    Notes: Summary Mercuric catalyzed hydrolysis of acetylatedL-rhamnal1 gave the α,β-unsaturated aldehyde2. 1,2,4-Triazole was coupled, in a Michael type addition reaction, to2 at C-3 in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to give, after acetylation at the anomeric center, an anomeric mixture of 1,5-di-O-acetyl-3-(1,2,4-triazol-1-yl)-2,3,6-trideoxy-L-arabino-hexofuranose (3). Reaction of3 with silylated 2,4-dihydroxypyrimidines4 in the presence of trimethylsilyl triflate as catalyst followed by deprotection with 33% methylamine in absolute ethanol afforded the corresponding nucleosides7 and8.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1434-4475
    Keywords: 3′-Azido-2′,3′-dideoxy-2-thiouridines ; 5-Alkoxy-2-thiouracils ; Nucleoside synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Reaktion von 3-Azido-5-O-tert-butyldiphenylsilyl-2,3-dideoxy-D-erythro-pentofuranosid (5) mit silyliertem 2-Thiouracil und 5-Alkoxy-2-thiouracil in Gegenwart von Trimethylsilyltrifluormethansulfonat ergab eine anomere Mischung der entsprechenden 3′-Azido-2′,3′-dideoxy-2-thiouridin-Derivate, wobei das α-Anomer das Hauptprodukt darstellte. Die ungeschützten Nucleoside wurden mittels Behandlung mit Tetrabutylammoniumfluorid erhalten.
    Notes: Summary Reaction of 3-azido-5-O-tert-butyldiphenylsilyl-2,3-dideoxy-D-erythro-pentofuranoside (5) with silylated 2-thiouracil and 5-alkoxy-2-thiouracils in the presence of trimethylsilyl trifluoromethanesulfonate afforded an anomeric mixture of the corresponding 3′-azido-2′,3′-dideoxy-2-thiouridine derivatives with the α-anomer as the main product. Deprotected nucleosides were obtained by treatment with tetrabutylammonium fluoride.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1434-4475
    Keywords: Nucleosides, convergent synthesis of ; Uridines, 3′-azido-2′,3′-dideoxy ; Uridines, 3′-fluoro-2′,3′-dideoxy ; AZT analogues ; Human immunodeficiency virus ; Herpes simplex virus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Aus Uracil (8) wurden in einer Mannich-Reaktion in 65–85% Ausbeute die 5-substituierten Dialkylaminomethyluracile11a–f hergestellt. Verbindungen11a–f wurden mit Hexamethyldisilazan silyliert und mit 2,3-Didesoxy-3-fluor-D-erythro-pentofuranosid (4) und 3-Azido-2,3-didesoxy-D-erythro-pentofuranosid (7) unter Verwendung von Trimethylsilyl-trifluormethansulfonat als Katalysator zu den entsprechenden 3′-Fluor-2′,3′-didesoxynucleosiden13a–f und 3′-Azido-2′,3′-didesoxynucleosiden16d, f umgesetzt. Deprotektion der 5-O-(4-Phenylbenzoyl)- geschützten Nucleoside13a–f und16d, f mit gesättigtem methanolischem Ammoniak und Trennung mittels Chromatographie ergab die neuen 2′,3′-Didesoxy-3′-fluoruridine14a–f und15a–f, sowie die 2′,3′-Didesoxy-3′-azidouridine17d, f und18d, f.
    Notes: Summary Uracil (8) was substituted in a Mannich reaction to give the 5-substituted dialkylamino-methyluracils11a–f in 65–85% yield. Compounds11a–f were silylated with hexamethyldisilazane and coupled with 2,3-dideoxy-3-fluoro-D-erythro-pentofuranoside4 and 3-azido-2,3-dideoxy-D-erythro-pentofuranoside7 to give the corresponding 3′-fluoro-2′,3′-dideoxynucleosides13a–f and 3′-azido-2′,3′-dideoxy nucleosides16d, f, respectively, by using trimethylsilyl trifluoromethanesulfonate as a catalyst. Deprotection of the 5-O-(4-phenylbenzoyl) protected nucleosides13a–f and16d, f with saturated methanolic ammonia and separation by chromatography yielded the new derivatives of 2′,3′-dideoxy-3′-fluorouridines14a–f and15a–f and 2′,3′-dideoxy-3′-azidouridines17d, f and18d, f.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 1434-4475
    Keywords: Nucleosides, 2′,3′-dideoxy-3′-mercapto ; Nucleosides, 2′,3′-dideoxy-3′-methylthio ; Nucleosides 2′,3′-didehydro-2′,3′-dideoxy ; Disulfide, bis(2′,3′-dideoxy-nucleosid-3′-yl)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die in drei Stufen aus 2-Desoxy-D-ribose hergestellten Jodide4(α) bzw. 7 wurden einer Reihe von nucleophilen Substitutionsreaktionen unterzogen, wobei die 3-Benzoylthio-, 3-Methylthio-und 3-Thiocyanato-2,3-didesoxy-D-erythro-pentofuranoside8,13 und15 zusätzlich zum Disulfid17 ihrer 3-Mercapto-Analogen entstanden. Bei der Friedel-Crafts-katalysierten Silyl-Hilbert-Johnson Reaktion des Thiobenzoats8 in Verbindung mit den silylierten Nucleobasen Uracil, Thymin und N4-Isobutyrylcytosin9a–c entstanden nach der Schutzgruppenentfernung die 2′,3′-Didesoxy-3′-mercapto-Nucleoside11 und ihre Disulfide12. Unter ähnlichen Bedingungen ergaben die 2′,3′-Didesoxy-3′-methylthiopentofuranoside13 beide Anomere der 2′,3′-Didesoxy-3′-methylthionucleoside19 und20. Es wird das erste Beispiel einer direkten Kopplung 2,3-Didehydro-2,3-didesoxyfuranose vorgestellt. 2′,3′-Didesoxy-3′-mercaptocytidin zeigte Schutzwirkung gegenüber HIV-1 in MT-4 Zellen mit ED50=20 µM.
    Notes: Summary The iodide4(α) or7 synthesized in three steps from 2-deoxy-D-ribose1, has been subjected to a number of nucleophilic substitution reactions producing the 3-benzoylthio-, 3-methylthio- and the 3-thiocyanato-2,3-dideoxy-D-erythro-pentofuranosides8,13 and15, respectively, in addition to the disulfide17 of their 3-mercapto analogue. Subjecting the thiobenzoate8 to the Friedel-Crafts catalyzed silyl Hilbert Johnson reaction in conjunction with the silylated nucleobases of uracil, thymine and N4-isobutyrylcytosine9a–c resulted in the isolation of the 2′,3′-dideoxy-3′-mercapto nucleosides11 and their disulfides12 subsequent to deprotection. The 2,3-dideoxy-3-methylthio-pentofuranoside13 afforded both anomers of the 2′,3′-dideoxy-3′-methylthio nucleosides19 and20 under similar conditions. The first known example of a coupling directly on a 2,3-didehydro-2,3-dideoxyfuranose is presented. 2′,3′-Dideoxy-3′-mercaptocytidine showed protection against HIV-1 in MT-4 cells with ED50=20 µM.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 62 (1992), S. 61-66 
    ISSN: 1570-7458
    Keywords: Ceutorhynchus assimilis ; host finding ; phototaxis ; anemotaxis ; flight activity ; field cage experiments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of host odour, windspeed, position of the sun, and temperature on flight behaviour of the cabbage seedpod weevil (Ceutorhynchus assimilis Paykull) were studied. This weevil showed a positive anemotaxis (upwind flight) inside the odour plume of a host crop (Brassica napus L.). Outside the odour plume the weevil showed a pronounced phototaxis at windspeeds below 1.5 m/s. At higher windspeeds, the seedpod weevils flew downwind. The cabbage seedpod weevil flies most readily at low windspeeds (less than 0.5 m/s) and at temperatures above 22 °C.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Springer
    International journal of biometeorology 16 (1972), S. 85-91 
    ISSN: 1432-1254
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Description / Table of Contents: Zusammenfassung Eine statistische Untersuchung der Beziehung zwischen Luftdruck und der Häufigkeit von perforierten Duodenal- und Präpylorusulcera (1953–1968) ergab, dass die Geschwindigkeit des Luftdruckwechsels der einzig wirklich wichtige biotrope Faktor zu sein scheint. Alte Patienten scheinen empfindlicher zu sein als junge. Je schneller die Luftdruckwechsel sind, desto grösser ist die biologische Wirkung.
    Abstract: Resume On a recherché s'il existait une relation statistique entre la pression barométrique d'une part et la perforation d'ulcères duodénaux et prépyloriques d'autre part. L'étude couvre la période comprise entre 1953 et 1968. Elle a montré que seule la rapidité d'un changement de pression semble avoir un effet biotropique réellement important. Les patient âgés semblent en outre être plus sensibles au phénomène que les plus jeunes. Plus les changements de pression barométriques sont rapides et plus grand est leur effet biologique.
    Notes: Abstract A statistical examination of the relationship between barometric pressure and the incidence of perforated duodenal- and prepyloric ulcer (1953–1968) shows that the velocity of the changes in barometric pressure seems to be the only really important biotropic factor, and that old patients seem more "sensitive" to these changes than young ones, i.e. the faster the changes in barometric pressure the greater the biological effect.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Mathematische Annalen 298 (1994), S. 275-326 
    ISSN: 1432-1807
    Keywords: 17B35 ; 22E27
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 42 (1972), S. 26-41 
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Übersicht Es wird die Erregung der gleich- und gegen-läufigen Präzessionen von Rotoren untersucht. Es wird gezeigt, daß bei Rotoren in rotationssymmetrischen Lagern eine Unsymmetrie der Welle keine gegenläufigen Präzessionea verursachen kann. Bei der geringsten Anisotropie der Lagerung werden jedoch synchrone gegenläufige Präzessionen in derselben Weise wie die gleichläufigen Präzessionen erregt. Allerdings werden die gegenläufigen Präzessionen durch innere Dämpfungskräfte stärker reduziert. Es wird weiterhin eine unwuchtige Welle mit nicht-konstantem Kreisquerschnitt untersucht, die in anisotropen, nachgiebigen Lagern gelagert ist. Die Bewegungsgleichungen werden für diesen Fall unter Berücksichtigung der Querkräfte, der Kreiselmomente und der inneren und äußeren Dämpfung abgeleitet.
    Notes: Summary A study of the excitation of backward and forward precessional motion of rotors is presented. It is shown that if the rotor is supported in bearings with rotational symmetry, a rotating unbalance of the shaft cannot excite backward precessions, but if the bearings have even the slightest anisotropy, backward synchronous precessions are excited just as in the case of forward precessional motions. However, internal damping forces have a marked effect in reducing the amplitudes of the backward precessions. A rotating unbalanced non-uniform continuous circular shaft supported by anisotropic flexible bearings is studied. The governing equations of motion are derived taking into account the effects of transverse shear, gyroscopic moments, and internal and external damping.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...