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  • 11
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract  This study concerns the detection of natural steroid hormones in hair of cattle. Estradiol (E2) and testosterone (T) were chosen as representatives of estrogens and androgens. In particular, the influence of age, sex and hair pigmentation on the steroid concentrations was investigated. Samples were obtained from numerous steers, cows, bulls, and female and male calves. The extraction procedure for E2 and T from hair comprised liquid-liquid and solid-phase extraction and was followed by an essential high-performance liquid chromatography (HPLC) step for further purification of the extracts. Final quantification was performed with specific enzyme immunoassays (EIA). Lower E2-concentrations were detected in the hair of some steers, cows, and bulls (approximately 1 ng/g), in several of these hair samples the concentrations of E2 were below the limit of detection. Testosterone was measured in the hair of steers (approximately 3 ng/g), cows (approximately 6 ng/g), and bulls (in average 15 ng/g). There was a significant difference in the testosterone concentrations of white (approximately 8 ng/g) and of black hair (approximately 33 ng/g) of bulls. In hair from all male and female calves, E2 and T were measured. The concentrations amounted approximately to 9 ng E2/g and 3 ng T/g for female calves and to 5 ng E2/g and 7 ng T/g for male calves. There was no significant influence of sex or hair colour on the steroid concentrations in hair of calves. The results suggest that the method is a powerful means to detect natural steroid hormones in hair of animal origin.
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 1432-0630
    Keywords: 79.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract An electron gun system with post-acceleration is described suitable to operation with a carbon fibre field-emission tip. The system was tested in an electron optical bench with a vacuum pressure of about 10−6 torr. The electron current was most stable if the current to the extraction electrode was minimized. The half width of the energy distribution of the electrons accelerated up to 30 keV was 215 meV for small currents (≈10−9A). The half width of the distribution increases with growing emission current. This increase may be attributed to instabilities in the surface structure due to ion bombardment and to the circumstance that more than one emission centre contributes to the electron current.
    Type of Medium: Electronic Resource
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  • 13
    Publication Date: 2018-11-27
    Description: The neodymium isotope proxy has become a valuable tool for the reconstruction of past ocean water mass provenance and mixing. For its accurate application, knowledge about the origin and preservation of Nd in sedimentary archives is crucial. Recently, concerns have emerged regarding the applicability of neodymium isotopes as a conservative palaeo water mass tracer, given potential Nd fluxes from sediments into bottom waters (Abbott et al., 2015a) and inferred relabelling of ocean waters by settling detrital material (Roberts and Piotrowski, 2015). Consequently, a decoupling of water mass provenance and proxy variations may arise. We investigate the mobility of Nd around extreme detrital sedimentation events such as glacial ice rafting pulses and turbidite deposition in the Northeast Atlantic. The constructed records from sediment leachates span extreme Nd isotope variations including volcanic (εNd ∼ 0) and Laurentian (εNd ∼ −27) sources. We find that Nd was released into pore waters from reactive detritus inside some detrital layers during early diagenesis, thereby overprinting any archived bottom water Nd signature and precluding the reconstruction of past water mass provenance during the affected time intervals. However, we do not observe any definite indication of diffusive vertical migration of Nd into adjacent layers. Furthermore, bottom water Nd isotope signatures were not modified to a measurable degree by any potential benthic flux of Nd during the deposition of these detrital sediment layers. Consequently, the Nd isotope composition of the pelagic glacial Northeast Atlantic water masses were resilient to such episodic large detrital fluxes. Apart from extreme local sedimentation events, we confirm the presence of detritally overprinted deep waters north of 47°N during the peak glacial from comparison of Northeast Atlantic depth transects. We furthermore suggest that the sensitivity of deep waters to this overprinting effect increased during periods of reduced Atlantic Meridional Overturning Circulation and elevated ice rafting. Overall, our study demonstrates that a thorough evaluation of the proportion of Nd originating from physical water mass advection versus in situ chemical inputs is crucial for the reliable application of Nd isotopes as a water mass tracer.
    Type: Article , PeerReviewed
    Format: text
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  • 14
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. We describe two psychophysical experiments testing predictions of the square difference mechanism we have previously proposed for intensity–based stereo. Experiment 1 assesses the relative contributions of disparity and contrast to intensity–based stereo by measuring detection thresholds. The product of disparity and contrast at threshold is shown to be constant. In experiment 2, we measure quantitatively the global depth position perceived in stereograms of curved, smoothly shaded surfaces. The results show that disparity averaging over the surface involves a contrast-dependent weighting function. The results from both experiments are consistent with predictions derived from the square difference mechanism. The relation of this mechanism to feature correspondence stereopsis and shape–from–shading is discussed and a general framework for assessing the modularity of stereopsis is presented.
    Type of Medium: Electronic Resource
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  • 15
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. In homing tasks, the goal is often not marked by visible objects but must be inferred from the spatial relation to the visual cues in the surrounding scene. The exact computation of the goal direction would require knowledge about the distances to visible landmarks, information, which is not directly available to passive vision systems. However, if prior assumptions about typical distance distributions are used, a snapshot taken at the goal suffices to compute the goal direction from the current view. We show that most existing approaches to scene-based homing implicitly assume an isotropic landmark distribution. As an alternative, we propose a homing scheme that uses parameterized displacement fields. These are obtained from an approximation that incorporates prior knowledge about perspective distortions of the visual environment. A mathematical analysis proves that both approximations do not prevent the schemes from approaching the goal with arbitrary accuracy, but lead to different errors in the computed goal direction. Mobile robot experiments are used to test the theoretical predictions and to demonstrate the practical feasibility of the new approach.
    Type of Medium: Electronic Resource
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  • 16
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Doping superlattices of PbTe are prepared by a modified Hot-Wall technique. At 80 K, some of these structures exhibit a photoconductive detectivity close to the theoretical limit ofD *≈1011 cmHz1/2W−1 at 6 μm wavelength. We show from time resolved electron-beam-induced-current investigations that the excellent photoresponse is caused by a lifetime enhancement by nearly two orders of magnitude. The latter value is in good agreement with theoretical estimates.The influence of contact barriers is discussed.
    Type of Medium: Electronic Resource
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  • 17
    ISSN: 1420-9071
    Keywords: Hexacyanoferrate(II) ; 134Cs ; cesium absorption ; biological half-life ; piglet
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The efficacy of different hexacyanoferrates(II) in preventing the enteral absorption of134Cs was studied in piglets. As compared to the controls, oral application of134Cs together with KFe[Fe(CN)6], NH4Fe[Fe(CN)6], or Fe4[Fe(CN)6]3 resulted in a strong reduction of the134Cs-uptake by more than 97%. The decrease in enteral absorption depends on the dose of administered hexacyanoferrate(II), whereas differences between the compounds under study were small. The biological half-life of134Cs in non-hexacyanoferrate(II) treated piglets was 21.6±3.3 days (mean±SD).
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Archiv der Mathematik 38 (1982), S. 448-452 
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 19
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 20
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung Erstmalig wurde radiochemisch reines59Fe (〉 99,9999%) eingesetztg, um die radioaktive Halbwertzeit des59Fe mit 44,52±0,016 (¯m a ±SE) Tagen entsprechend einer Umwandlungskonstantenλ=0.015568±0.000 0056 [d−1] zu bestimmen. Radiochemisch reines59Fe wird im menschlichen Körper bei Männern mit einer Umsatzrate von 0,032%/Tag (=1,2 mg Fe/Tag) und bei menstruierenden Frauen mit 0,052%/Tag (=1,4 mg Fe/Tag) ausgeschieden. Diese Gesamtkörper-59Fe-Eliminationsrate entspricht dem Eisenbedarf des Menschen.
    Type of Medium: Electronic Resource
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