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  • 1
    ISSN: 1573-904X
    Keywords: cervical intraepithelial neoplasia ; bioadhesive ; 5-fluorouracil ; liquid scintillation spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The potential use of bioadhesive technology for the treatment of cervical intraepithelial neoplasia was investigated. A cervical patch was designed containing 5-fluorouracil in a bioadhesive matrix and polyvinyl chloride as the backing layer. The concentration of 5-fluorouracil at specified tissue depths from the cervical surface was determined in vitro in relation to the ability of the drug to reach precancerous foci in cervical crypts up to 4 mm below the tissue surface. Thus, tissue was exposed to drug-loaded patches spiked with 5-fluorouracil-6-3H and subsequently sectioned to obtain tissue slices at different depths. The concentration of 5-fluorouracil was determined by liquid scintillation spectrometry. Drug penetration into cervical tissue exceeded a depth of 5.5 mm. Furthermore, the concentration in the tissue depended on the drug loading in the patch. Patches containing 10 and 20 mg of 5-fluorouracil produced a linear drug gradient that was established after a 4 hour application of the patch and persisted over 24 hours. However, patches containing 3.5 mg of 5-fluorouracil displayed signs of drug exhaustion after 24 hours. The penetration characteristics of 5-fluorouracil through cervical tissue using the cervical patch delivery system were sufficiently favourable to warrant further clinical investigations.
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  • 2
    ISSN: 1573-904X
    Keywords: autoradiography ; bioadhesive ; cervical intraepithelial neoplasia ; 5-fluorouracil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The distribution of 5-fluorouracil through cervical tissue has been assessed following the in vitro application of a bioadhesive patch to excised human cervix. The bioadhesive matrix contained a total of 20 mg of 5-fluorouracil spiked with 5-fluorouracil-6-3H and was applied for fixed periods of either 4 or 24 hours. Tissue slices were sectioned perpendicular to the plane of the applied patch and the autoradiographic image developed by placing a frozen tissue slice on Hyperfilm with subsequent instant thawing and refreezing, the resulting bilayer being maintained at −18°C for 24 hours. The developed image was analysed by scanning densitometry and raster scans were visualised with three-dimensional contouring software. The autoradiograms showed darker areas surrounding tissue ducts, suggesting that 5-FU was spilling from the lumen into the surrounding stroma. Transport of 5FU via aqueous channels may thus make an important contribution to the rapid penetration of the drug through the cervical stroma. Three-dimensional autoradiographic images showed that, for a 4-hour patch application, there were areas of relatively low drug concentration within the upper 5 mm of tissue, where CIN lesions can exist in the glandular tissue or cervical crypts. However, extending the application time to 24 hours produced areas of high drug concentration extending throughout this region.
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  • 3
    ISSN: 1573-904X
    Keywords: a.c. impedance spectroscopy ; percutaneous local anesthesia ; tetracaine ; lidocaine-prilocaine eutectic mixture ; reservoir effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-7160
    Keywords: Trade policy ; conjectural variations ; markovian strategies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract The authors study strategic trade policy in the framework of an explicit dynamic game in which home and foreign duopolists compete in a third-country market for non-competitive rents. Dynamics are introduced on the demand side by assuming demand for the product depends on past consumption of that good. The analysis demonstrates that the perfect equilibrium of the dynamic game can be replicated by a conjectural variations equilibrium, and that optimal policy requires a tax on exports.
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  • 5
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Benthic macroinvertebrate assemblages were surveyed from similar erosional biotopes of four pristine streams in the remote Huron Mountain region of the upper peninsula of Michigan during the summers of 1992 and 1993. Semi-quantitative samples from five sites, each in a 1.5 km stretch of Mountain Stream, Pine River, Salmon-Trout River and Huron River, were the basis for structural and functional comparisons between streams. Ancillary water chemistry data reflect the relative pollution free nature of these streams. Both water chemistry and macroinvertebrate data served as the first baseline data for Huron Mountain streams. No new or rare species were found among the 194 species sampled. Temporal differences in taxonomic makeup within streams were due to differences among insect species life cycles. Taxonomic makeup between streams was generally similar, but certain differences are shown to be possibly related to factors such as lake sources, interspecific interactions, and stream size. Based on relative abundance of each functional feeding group, assemblages in all streams were functionally similar and collector-dominated. ANOVA results indicated significant differences in functional feeding group abundance and biomass between streams in every case. The functional variations reflected by specific differences in taxonomic composition between stream assemblages are discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 288 (1994), S. 65-78 
    ISSN: 1573-5117
    Keywords: Anthopotamus verticis ; burrowing mayflies ; Ephemeroptera ; microhabitat ; substrate particle size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A field and laboratory study was designed to elucidate the microhabitat of the North American riverine mayfly Anthopotamus verticis (Say). Previous reports have suggested that these mayflies are surface sprawlers or clingers; but despite a flattened body shape that is often associated with sprawling or clinging benthos, our investigation showed that larvae of A. verticis burrow and inhabit the hyporheic biotope. Substrate particle size was found to be a primary limiting factor in the microdistribution of the larvae. When homogeneous substrates (either fine, medium, or coarse gravel, or small or large pebbles) were provided, small, mid-sized, and large larvae significantly preferred coarse gravel or small pebbles. Small larvae were better represented in coarse gravel, and large larvae were better represented in small pebbles. Vertical distribution was deeper in coarse gravel than in medium gravel, and smaller larvae were generally found deeper than large larvae. In the field, larvae occur in gravel or pebbles (excluding coarse sand or smaller particles) or mixed substrates, often at the interface of large rocks and finer substrates. Videomacroscopic examination also indicated larvae to be interstitial dwellers. Although relatively crude burrowers, larvae do use their tusks to excavate substrate, and their gills to generate interstitial current. We distinguish the fossorial behavior of Anthopotamus from most other ephemeroid mayflies because tube burrows are not formed. Minimum-sized interstices may be required for filter feeding and/or adequate ventilation, and may explain a deeper penetration of smaller larvae in finer substrates.
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  • 7
    ISSN: 1573-5117
    Keywords: Chironomus tentans ; zinc ; cadmium ; chromium ; emergence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This experiment tested the effects of heavy metal contaminated sediment on emergence of chironomids. The number of adults emerging from test chambers containing an uncontaminated sediment and ones with sediment containing 1030 ppm cadmium (Cd), 17,300 ppm zinc (Zn), and 1640 ppm chromium (Cr) were observed for 14 days. It was found that emergence was reduced by over three times and delayed for two days in the heavy metal contaminated sediment.
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  • 8
    ISSN: 1573-5117
    Keywords: Chironomus tentans ; zinc ; cadmium ; avoidance reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Avoidance reactions of chironomid larvae to contaminated sediment taken from a heavy metal impacted lake were studied. Heavy metal levels in the test sediment ranged from background of 0.6 parts per million (ppm) cadmium, 77 ppm zinc and 17 ppm chromium to a maximum of 1,029 ppm cadmium, 17,262 ppm zinc and 2,106 ppm chromium. A linear relationship was established between cadmium and zinc levels in the sediment and avoidance by chironomids. An approximate threshold avoidance of metals in the sediment was determined to be between 213–422 ppm cadmium, 4385–8330 ppm zinc and 799–1513 ppm chromium.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1572-9605
    Keywords: YBCO ; optical constants ; attenuated total reflection ; ellipsometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Otto configuration attenuated total reflection (ATR) measurements of the excitation of surface plasmons in the infrared have been carried out on YBCO films deposited on MgO (100) substrates. The dielectric constants for YBCO at 3.392μm are determined to be −10+15i forc-axis material. The anisotropic nature of the cuprate is seen from films with other orientations: nearlya-axis material has constants of 4.0+7.0i. It is thus not metallic in its optical response along thec-axis which lies parallel to the substrate plane. Ellipsometric measurements in the visible onc-axis material point to a maximum surface plasmon energy of 1 eV.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1572-8889
    Keywords: feeding behavior ; morphology ; Ephemerellidae ; videomacroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The feeding behavior and functional morphology associated with feeding in Ephemerella needhamiMcDunnough larvae were studied using videomacroscopic techniques, gut content analysis, and scanning electron microscopy. Two stereotypic feeding cycles were employed by the larvae. In the maxillary brushing cycle, the maxillae are the primary food-gathering organs, with the main food being detritus deposited on the filamentous alga Cladophora.In the mandibular biting cycle, the mandibles are the primary food-gathering organs used to bite Cladophora filaments.Epiphytic diatoms on Cladophorawere another important part of the diet. Behavioral similarities are apparent in the choreography and synchronization of mouthpart movements among mayflies from several families. Functional morphological comparisons are drawn with hypognathous E. needhami, Cloeon dipterum, Baetis rhodani,and Siphlonurus aestivalis, aswell as the prognathous Heptageniidae. Differences in mouthpart usage and structure are related to the relative development of setal fields and combs and the feeding microhabitat.
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