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  • Springer  (48)
  • 1995-1999  (44)
  • 1970-1974  (3)
  • 1935-1939  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Surveys in geophysics 18 (1997), S. 341-361 
    ISSN: 1573-0956
    Keywords: Kuiper-Edgeworth Belt ; Trans-Neptunian Object ; resonance ; solar system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Since the periodicity of comets was first established by Halley, the question of their origin has fascinated astronomers. It is clear that they have to be stored somewhere, since their life time in the inner Solar System is short. Around 1950 the idea emerged that cometary nuclei could be stored in a belt beyond Neptune, and this belt became known as the Kuiper Belt or perhaps more fairly the Kuiper-Edgeworth Belt. In the late 80's optical searches for the belt became numerous and in 1992, the first detection (of 1992 QB1) was made. At the time of writing 39 objects have been discovered and the current state of knowledge regarding these "Kuiper-Edgeworth Belt", or Trans-Neptunian, Objects is reviewed here.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-041X
    Keywords: Key words Deformed ; Drosophila ; Embryogenesis ; Tribolium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We have analyzed the Tribolium castaneum ortholog of the Drosophila homeotic gene Deformed (Dfd) and determined its expression pattern during embryogenesis in this beetle. Tc Deformed (Tc Dfd) is expressed in the blastoderm and the condensing germ rudiment in a region that gives rise to gnathal segments. During germ band extension Tc Dfd is expressed in the mandibular and maxillary segments, their appendages, and the dorsal ridge. Comparison of insect Dfd protein sequences reveals several highly conserved regions. To determine whether common molecular features reflect conserved regulatory functions we used the Gal4 system to express the Tribolium protein in Drosophila embryos. When Tc Dfd is expressed throughout embryonic ectoderm under the control of P69B, the beetle protein autoregulates the endogenous Dfd gene. In addition, the Drosophila proboscipedia gene (a normal target of Dfd) is ectopically activated in the antennal and thoracic segments. We also compared the ability of the beetle and fly proteins to rescue defects in Dfd – mutants by expressing each throughout the embryonic during embryogenesis. Both proteins rescued Dfd – defects to the same extent in that they each restore the development of mouth hooks and cirri, as well as cause gain-of-function abnormalities of posterior mouth parts. As before, pb was ectopically activated in the antennal segment. This is the first demonstration of the ability of a heterologous homeotic selector protein to directly regulate a target gene independent of an endogenous Drosophila autoregulatory loop.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-203X
    Keywords: Wheat ; transformation ; glyphosate ; CP4/GOX ; embryos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The lack of alternative selectable markers in crop transformation has been a substantial barrier for commercial application of agricultural biotechnology. We have developed an efficient selection system for wheat transformation using glyphosate-tolerant CP4 and GOX genes as a selectable marker. Immature embryos of the wheat cultivar Bobwhite were bombarded with two separate plasmids harboring the CP4/GOX and GUS genes. After a 1 week delay, the bombarded embryos were transferred to a selection medium containing 2 mM glyphosate. Embryo-derived calli were subcultured onto the same selection medium every 3 weeks consecutively for 9–12 weeks, and were then regenerated and rooted on selection media with lower glyphosate concentrations. Transgenic plants tolerant to glyphosate were recovered. ELISA assay confirmed expression of the CP4 and GOX genes in R0 plants. Southern blot analysis demonstrated that the transgenes were integrated into the wheat genomes and transmitted to the following generation. The use of CP4 and GOX genes as a selectable marker provides an efficient, effective, and alternative transformation selection system for wheat.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2145
    Keywords: Key words Sex chromosomes ; Sex-differentiating chromocentres ; Heterochromatin ; In situ hybridization ; Phoenix dactylifera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In the date palm, a dioecious mode (separate male and female individuals) and the late initial reproductive age (5–10 years) are major practical constraints for genetic improvement. Early selection on young seedlings could enhance breeding programmes and generate experimental male and female genetic stocks, but no cytogenetic protocol exists for sex determination in an immature date palm. Here we describe a cytological method based on chromomycin staining which demonstrates the occurrence of sexual chromosomes carrying distinctive nucleolar heterochromatin and thus offers, for the first time, the possibility of identifying male and female individuals by simple analysis of root meristems. This observation has been extended by in situ rDNA hybridization, confocal microscopy and dual-label flow cytometry of nuclei.
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  • 5
    ISSN: 1432-2145
    Keywords: Sex chromosomes ; Sex-differentiating chromocentres ; Heterochromatin ; In situ hybridization ; Phoenix dactylifera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the date palm, a dioecious mode (separate male and female individuals) and the late initial reproductive age (5–10 years) are major practical constraints for genetic improvement. Early selection on young seedlings could enhance breeding programmes and generate experimental male and female genetic stocks, but no cytogenetic protocol exists for sex determination in an immature date palm. Here we describe a cytological method based on chromomycin staining which demonstrates the occurrence of sexual chromosomes carrying distinctive nucleolar heterochromatin and thus offers, for the first time, the possibility of identifying male and female individuals by simple analysis of root meristems. This observation has been extended by in situ rDNA hybridization, confocal microscopy and dual-label flow cytometry of nuclei.
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  • 6
    ISSN: 1432-203X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Monocerin is a benzopyran fungal toxin with broad activity on plants, fungi and insects. Its effect upon cell cycle progression has been analyzed in maize roots. Meristematic cells were synchronized by treatment with aphidicolin. Flow cytometric DNA analysis and mitotic indices indicated durations of 1.5 h, 5 h, 2 h and 1 h for respectively G1, S, G2 and M phases of the normal cell cycle at 25°C. Treatment of these synchronized meristems with 0.5 mM monocerin during release after an aphidicolin block produced a short delay in S phase and then a more important delay (about 2.5 h) in entry into mitosis. Treatments for similar durations (3 h) during progression through the cycle revealed two periods of action of monocerin. The first appears to be mid to late S and the second one G2, before the transition point between G2 and M. Action on either one of these target periods could lead to a delay in the G2/M transition, but these two responses did not appear to be additive.
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  • 7
    ISSN: 1432-203X
    Keywords: Key wordsCasuarina glauca ; Gymnostoma deplancheana ; Allocasuarina verticillata ; Actinorhizal plants ; Frankia symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genome size and base composition of diploid plant species from three genera of the Casuarinaceae family were determined by flow cytometry. Casuarina glauca Sieb. ex Spring. and Gymnostoma deplancheana (Miq.) L. Johnson showed a small genome with 2C = 0.70 pg, 58.6% AT, 40.5% GC for the first species and 2C = 0.75 pg, 58.7% AT, 40.5% GC for the second. Allocasuarina verticillata (Lam.) L. Johnson had a larger genome: 2C = 1.90 pg, 59.3% AT, 41.1% GC. One haploid genome of C. glauca is therefore about 340×106 base pairs. In leaves, roots or bark of these three species, polysomaty was virtually absent: a maximum frequency of 4C nuclei of only 0.08 was found in bark of C. glauca. The genome sizes of C. glauca and G. deplancheana are among the smallest described for higher plants. Small genome size, diploidy and the absence of polysomaty are advantageous traits for facilitating molecular approaches to improvement of these actinorhizal plants and developing the study of their symbiotic interactions with Frankia.
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  • 8
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Thermal wave interferometry is a non-destructive inspection technique that has been used successfully for the assessment of coating thickness. The purpose of this paper is to present an evaluation of the suitability of the technique for the measurement and characterization of hydroxyapatite coatings on commercially available prosthetic hip stems. The results indicate a good correlation between the coating thickness values obtained using the interferometry technique and measurements made using optical microscopy of sectioned stems. In addition the results confirm that thermal wave interferometry can be used to accurately assess the changes in coating thickness on samples with a complex geometry.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Environmental monitoring and assessment 38 (1995), S. 157-168 
    ISSN: 1573-2959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract One of the most important databases needed for estimating emissions of carbon dioxide resulting from changes in the cover, use, and management of tropical forests is the total quantity of biomass per unit area, referred to as biomass density. Forest inventories have been shown to be valuable sources of data for estimating biomass density, but inventories for the tropics are few in number and their quality is poor. This lack of reliable data has been overcome by use of a promising approach that produces geographically referenced estimates by modeling in a geographic information system (GIS). This approach has been used to produce geographically referenced, spatial distributions of potential and actual (circa 1980) aboveground biomass density of all forests types in tropical Africa. Potential and actual biomass density estimates ranged from 33 to 412 Mg ha−1 (106g ha−1) and 20 to 299 Mg ha−1, respectively, for very dry lowland to moist lowland forests and from 78 to 197 Mg ha−1 and 37 to 105 Mg ha−1, respectively, for montane-seasonal to montane-moist forests. Of the 37 countries included in this study, more than half (51%) contained forests that had less than 60% of their potential biomass. Actual biomass density for forest vegetation was lowest in Botswana, Niger, Somalia, and Zimbabwe (about 10 to 15 Mg ha−1). Highest estimates for actual biomass density were found in Congo, Equatorial Guinea, Gabon, and Liberia (305 to 344 Mg ha−1). Results from this research effort can contribute to reducing uncertainty in the inventory of country-level emission by providing consistent estimates of biomass density at subnational scales that can be used with other similarly scaled databases on change in land cover and use.
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  • 10
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Concurrent with an investigation of quaternary cast and forged L12 modified Al3Ti's containing 9 at% Cr, Fe and/or Mn, a similar series of four alloys was produced via XDTM technology, whereby 20 vol% of ∼ 0.5 μm TiB2 particles was incorporated as a reinforcement. Following densification by hot pressing and slow isothermal forging, small diameter compression test samples were machined from each compact and tested. The 0.2% yield strength measurements revealed a strength advantage for the particulate reinforced materials over the unreinforced ingot metallurgy matrices to about 1175 K. Furthermore, 900 and 1100 K constant velocity testing indicated that the TiB2 containing materials were stronger than the ingot metallurgy matrices down to strain rates of ∼ 10−7s−1. None of the quaternary L12 alloys + 20 TiB2 consistently displayed a strength advantage over others. However, extrapolation of the present mechanical property data into slower strain regimes indicated that the composites will not possess any strength advantage overthe unreinforced versions. Such losses in strength appeared to be caused by small grains in the particulate reinforced alloys, which promoted grain boundary weakening mechanisms.
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