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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Ultramicroscopy 11 (1983), S. 75-79 
    ISSN: 0304-3991
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-072X
    Keywords: Bradyrhizobium ; Electron microscopy ; Mutants ; Nitrogen fixation ; Nodulation ; Soybean ; Symbiosis ; Transposon Tn5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genome of the slow-growing Bradyrhizobium japonicum (strain 110) was mutagenized with transposon Tn5. A total of 1623 kanamycin/streptomycin resistant derivatives were screened in soybean infection tests for nodulation (Nod) and symbiotic nitrogen fixation (Fix). In this report we describe 14 strains possessing a stable, reproducible Nod+Fix- phenotype. These strains were also grown under microaerobic culture conditions to test them for free-living nitrogen fixation activity (Nif). In addition to strains having reduced Fix and Nif activities, there were also strains that had reduced symbiotic Fix activity but were Nif+ ex planta. Analysis of the genomic structure revealed that the majority of the strains had a single Tn5 insertion without any further apparent physical alteration. A few strains had additional insertions (by Tn5 or IS50), or a deletion, or had cointegrated part of the vector used for Tn5 mutagenesis. One of the insertions was found in a known nif gene (nifD) whereas all other mutations seem to affect different, hitherto unknown genes or operons. Several mutant strains had an altered nodulation phenotype, inducing numerous, small, widely distributed nodules. Light and electron microscopy revealed that most of these mutants were defective in different stages of bacteroid development and/or bacteroid persistence. The protein patterns of the mutants were inspected by two-dimensional gel electrophoresis after labelling microaerobic cultures with l-(35S)methionine. Of particular interest were mutants lacking a group of proteins the synthesis of which was known to be under oxygen control. Such strains can be regarded as potential regulatory mutants.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The quality of cryosections prepared from high pressure frozen bovine articular cartilage has been recently evaluated by systematic electron diffraction analysis, and vitrification found to be zone-dependent. The lower radial layer was optimally frozen throughout the entire section thickness (150 μm), whereas in the upper radial, transitional and superficial layers this was achieved down to a depth of only approximately 5–50 μm. These differences were found to correlate proportionally with proteoglycan concentration and inversely with water content. In the current investigation, extracellular matrix ultrastructure was examined in high pressure frozen material (derived from the lower radial zone of young adult bovine articular cartilage), by both cryoelectron microscopy of cryosections and by conventional transmission electron microscopy of freeze-substituted and embedded samples. Several novel features were revealed, in particular, the existence of a fine filamentous network; this consisted of elements 10–15 nm in diameter and with a regular cross-banded structure similar to that characterising collagen fibrils. These filaments were encountered throughout the entire extracellular space, even within the pericellular region, which is generally believed to be free of filamentous or fibrillar components. The proteoglycan-rich interfibrillar/filamentous space manifested a fine granular appearance, there being no evidence of the reticular network previously seen in suboptimally frozen material.
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  • 4
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The quality of cryosections prepared from high pressure frozen bovine articular cartilage has been recently evaluated by systematic electron diffraction analysis, and vitrification found to be zone-dependent. The lower radial layer was optimally frozen throughout the entire section thickness (150 μm), whereas in the upper radial, transitional and superficial layers this was achieved down to a depth of only approximately 5–50 μm. These differences were found to correlate proportionally with proteoglycan concentration and inversely with water content. In the current investigation, extracellular matrix ultrastructure was examined in high pressure frozen material (derived from the lower radial zone of young adult bovine articular cartilage), by both cryoelectron microscopy of cryosections and by conventional transmission electron microscopy of freeze-substituted and embedded samples. Several novel features were revealed, in particular, the existence of a fine filamentous network; this consisted of elements 10–15 nm in diameter and with a regular cross-banded structure similar to that characterising collagen fibrils. These filaments were encountered throughout the entire extracellular space, even within the pericellular region, which is generally believed to be free of filamentous or fibrillar components. The proteoglycan-rich interfibrillar/filamentous space manifested a fine granular appearance, there being no evidence of the reticular network previously seen in suboptimally frozen material.
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  • 5
    Publication Date: 2017-10-02
    Description: Are small (less than approx. 1 km diameter) craters on Mars and the Moon dominated by primary impacts, by secondary impacts of much larger primary craters, or are both primaries and secondaries significant? This question is critical to age constraints for young terrains and for older terrains covering small areas, where only small craters are superimposed on the unit. If the martian rayed crater Zunil is representative of large impact events on Mars, then the density of secondaries should exceed the density of primaries at diameters a factor of ~1000 smaller than that of the largest contributing primary crater. On the basis of morphology and depth/diameter measurements, most small craters on Mars could be secondaries. Two additional observations (discussed below) suggest that the production functions of Hartmann and Neukum predict too many primary craters smaller than a few hundred meters in diameter. Fewer small, high-velocity impacts may explain why there appears to be little impact regolith over Amazonian terrains. Martian terrains dated by small craters could be older than reported in recent publications.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXVI, Part 13; LPI-Contrib-1234-Pt-13
    Format: application/pdf
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  • 6
    ISSN: 1573-0972
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Description / Table of Contents: Résumé La principale caractéristique deBacillus thuringiensis est de produire, au cours de la sporulation, un métabolite insecticide. Celui-ci se dépose habituellement dans le sporange sous forme cristalline. Ces cristaux, lorsqu'ils sont ingérés par des insectes sensibles, se dissolvent dans l'intestin, et les polypeptides ainsi libérés sont activés par protéolyse. Les molécules toxiques qui en résultent tuent les insectes par destruction de l'épithélium intestinal. Parmi les 30 sous-espèces décrites, celle appeléeisraelensis ou BT H-14 est active à l'égard de quelques familles deDiptera parmi lesquelles on trouve des espèces appartenant aux GenresCulex, Aedes, Anopheles etSimulium, qui sont des vecteurs de maladies infectieuses tropicales. La sous-espèceisraelensis, découverte il ya seulement 10 ans, a déjà été utilisée par plusieurs firmes comme base de puissants insecticides pour la lutte contre les stades larvaires de ces vecteurs. La toxine produite par la sous-espèceisraelensis est contenue dans une enveloppe et une partie seulement de l'inclusion présente un arrangement cristallin. La solubilisation de l'inclusion en milieu réducteur donne une bande prédominante, correspondant à un poids moléculaire de 25 à 30.000 daltons. Des bandes accessoires sont situées autour de 130.000 et 65.000 daltons. Le mode d'action au niveau moléculaire n'est pas encore connu en détail. Cependant, il semble que la toxine soit cytolytique et agisse par destruction des systèmes de perméabilité membranaire. L'efficacité sur le terrain deB. thuringiensis subsp.israelensis a été démontrée dans de nombreux pays. Les résultats les plus impressionants ont été obtenus en Afrique Orientale, où BT H-14 a été employé dans une large opération sur le terrain de lutte contre les larves deSimulium damnosum, vectrices de la cécité des rivières. Il existe plusieurs possibilitiés pour accroître l'efficacité des préparations commerciales. La modification de la toxine par manipulation génétique et l'amélioration de la persistance des formules sont deux perspectives prometteuses, actuellement à l'étude dans plusieurs laboratoires.
    Abstract: Resumen La característica mas importante deBacillus thuringiensis es la producción de un metabolito con propiedades insecticidas durante el proceso de esporulación. Este se deposita normalmente en forma cristalina dentro del esporangio. Dichos cristales al ser ingeridos por larvas de insectos susceptibles se disuelven en el intestino y los polipéptidos liberados son activados mediante proteolisis. Las moléculas tóxicas resultantes matan a los insectos por destrucción del epitelio intestinal. Entre 30 subespecies, la denominadaisraelensis o BT H-14 es activa contra algunas familias de Diptera entre las cuales encontramos especies pertenecientes a los génerosCulex, Aedes, Anopheles ySimulium que son vectores de enfermedades tropicales infecciosas. La subespecieisraelensis, descubierta hace tan solo 10 años, ha sido ya utilizada por varias compañias como la base de potentes insecticidas para el control de los estadios larvales de dichos vectores. La toxina producida por la especieisraelensis esta incluida en una envuelta y tan solo una parte de la inclusión tiene extructura cristalina. La solubilización de la inclusión bajo condiciones reductoras produce una banda prominente en un rango de pesos moleculares entre 25000 y 30000 daltons. Se encuentran ademas bandas adicionales alrededor de 130000 y 65000 daltons. El modo de acción a nivel molecular no esta totalmente dilucidado. Sin embargo, parece ser que la toxina es citolítica y actua alterando los sistemas de permeabilidad de membrana. La eficacia en el campo deBacillus thuringiensis subsp.israelensis ha sido demostrada en muchos paises. Los resultados mas notables se han obtenido en la región oeste de Africa donde la cepa BT H-14 fue empleada en una gran operación de campo para controlar las larvas deSimulium damnosum, vectores de la cegera de rio. Como resultado se redujo la incidencia de la enfermedad. Se conocen distintos procedimientos para incrementar la eficacia de preparaciones comerciales. La modificación de las toxinas mediante ingeniería genética y la mejora de las formulaciones para conseguir una mayor persistencia son ejemplos de dos áreas prometedoras en la cuales se esta investigando en varios laboratorios.
    Notes: Summary Bacillus thuringiensis subsp.israelensis produces a δ-endotoxin which is insecticidal against larvae of mosquitoes and blackflies. The toxin particles introduced into the water at concentrations of a few ng/ml kill rapidly after uptake by target larvae. Breakdown of the function of the gut epithelium is the primary cause for the lethal action of the toxin. The molecular mode of action is not yet understood in its details. However, it appears that the toxin is cytolytic and acts by disruption of membrane permeability systems. Field efficacy ofB. thuringiensis subsp.israelensis has been demonstrated in many countries. Most impressive results were obtained in West Africa where this microbial larvicide has been included in a large field programme to control blackflies, the vector of river blindness.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Plant/Operations Progress 7 (1988), S. 127-135 
    ISSN: 0278-4513
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The modeling of evaporation and dispersion from chemical spills has been an active area. The available models span the range of very simple calculational methods, for quick response at the time of accidents, to more complex transient models that predict the results of hypothesized events. Conservative assumptions are often used in all of these models in place of more accurate and more complicated computational techniques.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0005-2736
    Keywords: Cryofixation ; Electron microscopy ; Lipidic particle ; Membrane fusion ; Phospholipid bilayer
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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