ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1432-0878
    Keywords: Rat ; Oocyte maturation ; in vitro studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary After cultivation in a modified Trowell-system (organ ciilture) oocytes of 12- to 40-day-old rats were studied under the light and electron microscope. The cultivation period was 72 hrs. Egg cells from primary and early secondary follicles which are characterized by the lack of a zona pellucida and by one or at most two very large Golgi's complexes located near the nucleus do not show any alterations. The other egg cells are characterized by membrane packages which can otherwise only be observed in mature egg cells right before or after the ovulation. Meiotic processes or the formation of polar bodies are only seldom to be seen. These egg cells are surrounded by a thick zona pellucida. From these findings the following conclusions can be drawn: 1. In organ cultures meiotic processes are prevented by the inhibitory influence of follicle cells (Foote and Thibault, 1969). 2. A cytoplasmic maturation proceeds independently. 3. In-vivo an inhibitory factor influences the cytoplasmic maturation. This inhibition is not observed in the organ culture. Thus we can be sure that it develops outside the ovary. 4. The synthesis of the zona pellucida continues in-vitro.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 263 (1991), S. 483-493 
    ISSN: 1432-0878
    Keywords: Mineralization in vitro ; Organoid culture ; Calvarial cells ; Matrix vesicles ; Cell necrosis ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Various patterns of mineralization are found in the organism during fetal and postnatal development. Different findings and theories have been published in the literature with regard to the mechanisms of mineralization, many of which are controversely discussed. In the present study the different patterns of mineralization observed in the organoid culture system of fetal rat calvarial cells were investigated by electron microscopy. In organoid culture, calvarial cells grow and differentiate at high density, and deposition of osteoid and mineralization of the matrix occur to a very high extent. Different types of mineralization could be observed more or less simultaneously. It was found that hydroxyapatite crystals were formed at collagen fibrils as well as in the interfibrillar space. Mineralization was frequently seen in necrotic cells and cellular remnants as well as in extra-and intracellular vesicles. Addition of bone or dentin matrices or the artificial hydroxyapatite Interpore 200 to the cells caused an increased mineralization in the vicinity and on the surface of the matrices with and without participation of collagen. On previously formed mineralized nodules, an apposition of mineralizing material appeared due to matrix secretion by osteoblasts. It is concluded that initiation of mineralization occurs-at least in vitro-at every nucleation point under appropriate conditions. These mineralization foci enlarge by further apposition as well as by cellular secretion of a mineralizing matrix. Furthermore, cell necroses may liberate mineralizable vesicles. All these patterns of mineralization are the result of different activities of one cell type.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 264 (1991), S. 563-576 
    ISSN: 1432-0878
    Keywords: Organoid culture ; High density culture ; Human tumors ; Histiotypic reorganization ; Morphological study
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In the present study we describe a new method to cultivate human tumors, which allows organoid differentiation under in vitro conditions. Diverse tumors of different origin and various histopathology which had been heterotransplanted to athymic mice were dissociated into single cells and seeded at high cell density onto a membrane filter consisting of cellulose nitrate at the gas-medium interface. Within a few days, the tumor cells reorganized and differentiated into organoid structures which exhibited the typical histological characteristics of the original tissues. Due to the formation of organoid aggregates, which was also previously seen with normal fetal cells, this type of culture has been described as ‘organoid culture’. In the case of adenocarcinomas of the lung and the colon including the rectum, glandular structures with central lumina, adjacent microvilli, and junctional complexes were formed. Numerous specific intercellular contacts such as desmosomes and tight junctions occurred as well as interdigitations of adjacent cell membranes. In a tumor of the rectum, a typical brush border differentiated at the surface of the reorganized tumor-tissue aggregate. Epidermoid carcinomas of the head and neck developed structures resembling the spinous layer of the epidermis, exhibiting numerous desmosomes and intracytoplasmic bundles of tonofilaments radiating into the desmosomes. Most tumors produced a fragmentary monolayered or multilayered basal lamina of similar morphological appearance as under in vivo conditions. These results illustrate the organoid reorganization and differentiation of human tumor cells under the experimentally rather simple conditions of the organoid culture systems and clearly demonstrate that this in vitro system comes close to the in vivo situation as far as certain differentiation phenomena are concerned.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-0878
    Keywords: Vacuolar ATPase ; Proton pump ; Electrogenic potassium transport ; Marpighian tubules ; Immunocytochemistry ; Formica polyctena (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The presence of a vacuolar-type ATPase in Malpighian tubules of the ant Formica polyctena was investigated immunocytochemically, using antibodies to vacuolar ATPases of Manduca sexta midgut and bovine kidney. Specific labelling was observed at the brush border of the epithelium extending along the entire length of the tubules. These findings agree with the current view that a vacuolar ATPase is situated at the apical membrane of Malpighian tubule cells and other insect epithelial cells, being the energizing element of an electrogenic potassium pump. When antibodies were tested on tubules in different secretion conditions prior to fixation, no differences were observed in the distribution of the vacuolar ATPase.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1436-5057
    Keywords: 65L60 ; Numerical analysis ; nonlinear differential equations ; finite elements ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Das Problem der Berechnung des elektrostatischen Potentials in eindimensionalen Mehrschichtstrukturen mit quantifizierter Elektronenladung wird unter Zuhilfenahme der Theorie monotoner Operatoren und von Störungstheorie untersucht. Eine Fehlerabschätzung wird gegeben für den Fall einer Diskretisierung mit Lagrange-finiten Elementen erster Ordnung. Eine praktische Implementierung dieser Methode bei Verwendung eines quasi-Newton Algorithmus sowie numerische Resultate werden gezeigt.
    Notes: Abstract The problem of computing the electrostatic potential in a one dimensional multilayer semiconductor device with quantized electrons density is analysed using results of monotone operator theory and perturbation calculus. An error estimate is proved for the discretization with Lagrange finite elements of degree one. A practical implementation of the method, using a quasi-Newton algorithm is presented together with some numerical results.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 1435-604X
    Keywords: Laser vascular welding ; Tissue fusion ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract The central problem in microsurgery is the reconstruction of small vessels. The long operating time, foreign body granuloma formation around the suture material as well as aneurysmal alterations of the vessel wall after conventional suture technique make the search for alternatives indispensable. Some of these disadvantages can be avoided as demonstrated by our animal experiments and histological examinations in laser-assisted anastomosing. The aim of this study is to show these aspects in connection with laser application and compare them with conventional suture techniques.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Monatshefte für Mathematik 110 (1990), S. 321-327 
    ISSN: 1436-5081
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We explicitly compute the outer automorphism group Out π1 M of the fundamental group of the Hantzsche — Wendt manifoldM. It is an extension 1→(ℤ2)3→Outπ1 M→S 3⊕ℤ2→1, but not the semidirect product (ℤ2)3⋉(S 3⊕ℤ2) as claimed in [3] (see also [4]). As a consequence, we get a quick algebraic computation of the symmetry groups of the Borromean rings and the figure-8-knot.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Monatshefte für Mathematik 117 (1994), S. 139-143 
    ISSN: 1436-5081
    Keywords: 57M99
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We describe a method for constructing an arbitrary number of closed hyperbolic 3-manifolds of the same volume. In fact we prove that many hyperbolic 3-manifolds of finite volume have an arbitrary number of non-homeomorphic finite convering spaces of the same degree and hence the same volume. This applies, for example, to all hyperbolic 3-manifolds whose universal covering group is a subgroup of finite index in a Coxeter group generated by the reflections in the faces of a hyperbolic Coxeter polyhedron. It also applies to all hyperbolic 3-manifolds of finite volume with at least one cusp.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present calculations and measurements of current as a function of voltage I(V), and conductivity at low voltage as a function of temperature, G(T), for n+ -GaAs/i- Alx Ga1−x As/n+ -GaAs single-barrier tunneling structures. The current is modeled by its tunneling and thermionic emission components. The shape of the conduction-band edge is obtained by solving Poisson's equation self-consistently, together with two different models for the charge density. In the first model, the electron density is evaluated semiclassically, and in the second, the electron density is calculated from the electronic wave functions. Good agreement is obtained with both models between the experimental and the calculated I(V) and G(T) characteristics over the 4.2–200 K temperature range. The fits obtained are very sensitive to small variations (1%) in barrier width and effective barrier height, which allows one to determine these parameters within a narrower uncertainty range.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...