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• 1990-1994  (20)
• 1965-1969  (3)
• 1930-1934  (1)
• 1
Electronic Resource
Springer
Monatshefte für Chemie 123 (1992), S. 823-836
ISSN: 1434-4475
Keywords: Dihetero[2.2]orthometacyclophane ; Dynamic NMR spectroscopy ; Conformational analysis ; Ring interconversion of 9-membered ring
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Description / Table of Contents: Zusammenfassung Die N,N′-Ditosyl-diaza[2.2]orthometacyclophane5a, b wurden aus N,N-Ditosylmetaphenylendiamin durch Umsetzung mit (Z)-1,4-Dichlorbuten bzw. 1,2-Bisbrommethylbenzol gewonnen. Tieftemperatur-NMR-Untersuchungen ergaben, daß5b als 1:1 Mischung einer Sessel- und einer Bootkonformation des gespanntenE,Z-Diazanonadienringes vorliegt. Bei Raumtemperatur ist die zugehörige Ringinversion schnell in der NMR-Zeitskala, die entsprechenden Protonen in beiden Konformeren, auch die aller CH2-Brückenprotonen, ergeben gemittelte Signale. Bei tiefen Temperaturen wird zunächst die Inversion der Methylenbrücken eingefroren (Signale für zweiexo- und zweiendo-CH2-Protonen werden erhalten, ΔG ≠ ca. 52 kJ mol−1). Bei weiterer Temperatursenkung können nach Einfrieren eines zweiten dynamischen Prozesses Sessel- und Bootkonformer anhand von getrennten Signalsätzen identifiziert werden (die freie Aktivierungsenthalpie für den zugehörigen Sessel-Boot-Flip beträgt ΔG ≠ ca. 43.5 kJ mol−1). Die Zuordnung der1H- und13C-NMR-Resonanzen wurde mit Hilfe von zweidimensionalen NMR-Experimenten gesichert.
Notes: Summary The N,N′-ditosyl-diaza[2.2]orthometacyclophanes5a, b were synthesized from N,N-ditosyl-metaphenylenediamine by reaction with (Z)-1,4-dichlorobutene and 1,2-bis-bromomethylbenzene, respectively. Low temperature NMR studies showed that the compound5b exists as a 1:1 mixture of chair and boat form of the strained (E,Z)-diazanonadiene ring. At room temperature all corresponding resonances are averaged on the NMR time scale (including all four ethylene bridge protons). Going to lower temperatures, in a first step the methylene bridge inversion is frozen (giving twoexo H and twoendo H, ΔG ≠ ca. 52kJmol−1). In a second step the chair and boat form can be observed separately (ΔG ≠ ca. 43.5 kJ mol−1 for the chair/boat flip). The assignments were confirmed by 2D NMR experiments.
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• 2
Electronic Resource
Springer
The European physical journal 47 (1990), S. 499-504
ISSN: 1434-6052
Source: Springer Online Journal Archives 1860-2000
Topics: Physics
Notes: Abstract Production of charmed mesons in γγ-interactions at PETRA energies has been observed in the TASSO detector. Cross sections for inclusiveD *± and $$D^0 \bar D^0$$ production have been measured. Neutral and charged meson pairs are estimated to be produced with comparable cross sections, and their sum seems to account for a sizeable fraction of σtot(γγ→hadrons) near the $$c\bar c$$ threshold.
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• 3
Electronic Resource
Springer
The European physical journal 48 (1990), S. 433-444
ISSN: 1434-6052
Source: Springer Online Journal Archives 1860-2000
Topics: Physics
Notes: Abstract The forward-backward asymmetry in the reaction e+e-→bb has been determined at centre of mass energies near 35 GeV using the TASSO detector. We report results from three different methods. The combined result of the measurements is $$\overline A _b = - 0.21 \pm 0.08$$ ignoring $$B^0 \bar B^0$$ mixing. Taking mixing into account leads to a corrected asymmetry of $$\overline {A_b^{cor} } = - 0.28 \pm 0.11$$ . The axial vector coupling constant of theb quark as calculated from the corrected asymmetry isa b=−1.2±0.5 to be compared with the valuea b SM =−1 from the standard model.
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• 4
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College Park, Md. : American Institute of Physics (AIP)
The Journal of Chemical Physics 98 (1993), S. 3747-3753
ISSN: 1089-7690
Source: AIP Digital Archive
Topics: Physics , Chemistry and Pharmacology
Notes: Direct connection between spectroscopic relaxation cross sections and appropriate state-to-state rotational cross sections in vibrational modes enables one to introduce convenient energy corrections to the sudden approximation. Since the angular momentum coupling photon–rotation–vibration is properly taken into account, this approach applies to stretching as well as bending bands. Diode laser experiments have been made for pure 12C16O2 in the infrared Q branch of the (11 10)I←(00 00) band in order to investigate the effect of collisional line mixing on the spectral profile. The energy corrected sudden scaling law is used within the present theoretical approach for both the inversion of j→0 basis cross sections from broadening data and the calculation of line-coupling coefficients. Resulting absorption profiles are in good agreement with measured values without the need for the introduction of any ad hoc decoupling factor for the considered bending band.
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• 5
Electronic Resource
Oxford, UK : Blackwell Publishing Ltd
Journal of fish biology 43 (1993), S. 0
ISSN: 1095-8649
Source: Blackwell Publishing Journal Backfiles 1879-2005
Topics: Biology
Notes: About 20 ovaries of the whitefish ‘Blaufelchen’ (Coregonus lavaretus L.) of Lake Constance (Bodensee) were collected annually from 1964-1991. Absolute and relative fecundity peaked in the early 1980s, lagging about 2 years behind the maximum of total-P in the water (during the circulation period). Out of the biological time-series of Lake Constance, whitefish fecundity is the only one known to follow the phosphorus curve, and this may be the first time-series documented case of parallel trend reversal in the trophic state of a lake and fish biology. It is concluded that fish fecundity serves, at best, as an unspecific monitor of the overall well-being of the fish.
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• 6
Electronic Resource
Springer
Cell & tissue research 65 (1965), S. 409-419
ISSN: 1432-0878
Source: Springer Online Journal Archives 1860-2000
Topics: Biology , Medicine
Notes: Summary Localization of melanin synthesis within the pigment cells of the Cloudman S-91 mouse melanoma was determined by means of a combination of high resolution autoradiography and topographic planimetry. Initial melanin biosynthesis occurred predominantly in the endoplasmic reticulum and associated ribonucleoprotein particles of the melanocytes. By measuring a number of cell organelles and employing the index of “relative specific localization” it could be shown that the nucleus and mitochondria are of little or no importance in the process of melanogenesis.
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• 7
Electronic Resource
Springer
Bioscience reports 11 (1991), S. 213-221
ISSN: 1573-4935
Keywords: erythrocytes ; cell shape transformation ; transmembrane potential ; chlorpromazine
Source: Springer Online Journal Archives 1860-2000
Topics: Biology , Chemistry and Pharmacology
Notes: Abstract The effect of chlorpromazine (CPZ) on the shape of human erythrocytes with different values of transmembrane potential (TMP) was investigated. The shape of red blood cells with negative values of the TMP remained unchanged after the formation of stomatocytes by chlorpromazine, while cells with positive TMP showed a characteristic time course of shape change during the incubation with CPZ. Experiments with vanadate show that this might be due to a difference in the activity of the phospholipid-translocase at different values of TMP.
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• 8
Electronic Resource
Springer
Boundary layer meteorology 53 (1990), S. 223-265
ISSN: 1573-1472
Source: Springer Online Journal Archives 1860-2000
Topics: Geosciences , Physics
Notes: Abstract In the summer of 1988/89 flights were carried out in the Coorong coastal area of South Australia to investigate sea-breeze fronts. The flights yielded data sets of the structure of the fronts in the cross-frontal direction with a spatial resolution of approximately 3 m. The study is focused on the budgets of sensible and latent heat in the vicinity of the front and on frontogenesis/frontolysis processes which are closely related to budget considerations. The frontogenesis relationships and the budgets were established on a 2 km length scale by low-pass filtering of the space series. As the wind components were measured with high accuracy, all processes which determine frontogenesis could be evaluated and are displayed in x,z-cross-sections: these are the confluence, shear and diabatic effects, all of which play a role in ∂q/∂x-, ∂q/∂z-, ∂θ/∂x- as well as ∂θ/∂z-frontogenesis. A detailed analysis is given for two different states of frontal development. The presented results shed much light on the governing physical processes in the frontal region with strong emphasis on the effects of confluence-generated updrafts, on shear instabilities causing bulges and clefts in the frontal surface as well as producing the elevated frontal head, and on processes related to differential heating and moistening.
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• 9
Electronic Resource
New York, NY [u.a.] : Wiley-Blackwell
American Journal of Anatomy 122 (1968), S. 209-236
ISSN: 0002-9106
Keywords: Life and Medical Sciences ; Cell & Developmental Biology
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Medicine
Notes: The ultrastructural characteristics of elasmobranch central nervous system have not been previously reported. This study presents a general assessment of aldehyde perfused brain and spinal cord in three species of shark: tiger, hammerhead and Atlantic nurse. The same distinct cell types are present in the shark that exist in mammals and similar criteria may be used for their differentiation. Neurons have frequently round nuclei with a prominent nucleoli; cytoplasm is abundant and filled with formed elements; somatic synapses and subsurface cisterns are rare. Astrocytes are smaller, and have less cytoplasm and slightly fewer organelles. Glial fibrils occur, but are not invariably present. Separating astrocytes from neurons is the most difficult identification problem. Oligodendrogliocytes are smaller, and have denser cytoplasm and a dark nucleus. The striking feature of capillary morphology is the presence of an appreciable perivascular space containing collagen; many tortuous evanginations of this space occur into surrounding glial processes which completely invest the capillaries. Astrocyte cell bodies frequently lie immediately next to vessels, and capillaries are occasionally totally surrounded by a single astrocyte process, thus being endocellular. Smaller pericapillary processes may be either astrocytic or ependymal. Dendrites, synapses, axons, and myelin have no obvious special characteristics. Sodium, visualized by precipitation techniques, is prominent in the astroglia and neurons.
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• 10
Electronic Resource
Weinheim : Wiley-Blackwell
Acta Polymerica 42 (1991), S. 680-680
ISSN: 0323-7648
Keywords: Chemistry ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Physics
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