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  • 1
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract 5-Methylcytosine has been detected in the DNA of the polytene chromosomes ofSciara coprophila, Drosophila melanogaster andD. persimilis, using specifically purified antibodies to 5-methylcytidine. The 5-methylcytosine is present in GC-rich sequences in the bands. Virtually no 5-methylcytosine is detectable in mitotic metaphase chromosomes ofS. coprophila. Thus, methylation is associated with polytenization in these diptera. Restriction enzyme studies using HpaII, MspI, HhaI and AluI indicate that unmethylated 5′-CCGG-3′, 5′-GCGC-3′ and 5′-AGCT-3′ sequences are abundant in polytene chromosome DNA. These sequences are probably not major sites of methylation. Since the DNA in the bands of polytene chromosomes is generally transcriptionally inactive, as well as extensively methylated, these results are consistent with the hypothesis that genes in the bands have been inactivated by a process involving DNA methylation.
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  • 2
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The organization of DNA in the mitotic metaphase and polytene chromosomes of the fungus gnat, Sciara coprophila, has been studied using base-specific DNA ligands, including anti-nucleoside antibodies. The DNA of metaphase and polytene chromosomes reacts with AT-specific probes (quinacrine, DAPI, Hoechst 33258 and anti-adenosine) and to a somewhat lesser extent with GC-specific probes (mithramycin, chromomycin A3 and anticytidine). In virtually every band of the polytene chromosomes chromomycin A3 fluorescence is almost totally quenched by counterstaining with the AT-specific ligand methyl green. This indicates that GC base pairs in most bands are closely interspersed with AT base pairs. The only exceptions are band IV-8A3 and the nucleolus organizer on the X. In contrast, quinacrine and DAPI fluorescence in every band is only slightly quenched by counterstaining with the GC-specific ligand actinomycin D. Thus, each band contains a moderate proportion of AT-rich DNA sequences with few interspersed GC base pairs. — The C-bands in mitotic and polytene chromosomes can be visualized by Giemsa staining after differential extraction of DNA and those in polytene chromosomes by the use of base-specific fluorochromes or antibodies without prior extraction of DNA. C-bands are located in the centromeric region of every chromosome, and the telomeric region of some. The C-bands in the polytene chromosomes contain AT-rich DNA sequences without closely interspered GC base pairs and lack relatively GC-rich sequences. However, one C-band in the centromeric region of chromosome IV contains relatively GC-rich sequences with closely interspersed AT base pairs. — C-bands make up less than 1% of polytene chromosomes compared to nearly 20% of mitotic metaphase chromosomes. The C-bands in polytene chromosomes are detectable with AT-specific or GC-specific probes while those in metaphase chromosomes are not. Thus, during polytenization there is selective replication of highly AT-rich and relatively GC-rich sequences and underreplication of the remainder of the DNA sequences in the constitutive heterochromatin.
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  • 3
    ISSN: 1573-7527
    Keywords: olfactory plume tracking ; autonomous robot ; resistive polymer sensors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A simple reactive robot is described which is capable of tracking a water vapor plume to its source. The robot acts completely within the plume and is endowed with no deliberate information about wind direction or speed, yet accurately tracks the plume upstream. The robot's behavior, results from the behavior of simple resistive polymer sensors and their strategic placement on the robot's body.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Computing 15 (1975), S. 263-273 
    ISSN: 1436-5057
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Abstract LetA 1 andA 2 be floating point numbers represented in arbitrary base β and randomly chosen from a logarithmic distribution. Letr denote the round-off error $$r = fl(A_1 * A_2 ) - (A_1 * A_2 )$$ where * is floating point multiplication and wherefl(A 1*A 2) denotes the normalizedN digit computer result of forming (A 1*A 2). This paper analyzes the mean and variance of both the actual round-off error and the fraction round-off error. This analysis relies upon sharp order estimates for the digit by digit deviation of logarithmically distributed numbers from uniformly distributed numbers. This completely resolves open questions of Kaneko and Liu and of Tsao. Also included is a generalization to arbitrary base (from binary) of an important round-off theorem of Henrici.
    Notes: Zusammenfassung SeienA 1 undA 2 zufällige Gleitkommazahlen zu einer beliebigen Basis β mit einer logarithmischen Verteilung. Seir der Rundungsfehler $$r = fl(A_1 * A_2 ) - (A_1 * A_2 )$$ , wo * die Gleitkommamultiplikation bedeutet undfl(A 1*A 2) das normalisierteN-stellige Computerresultat für (A 1*A 2). Die Arbeit analysiert Mittelwert und Varianz des Rundungsfehlers sowohl des Ergebnisses wie auch dessen Mantisse. Die Analyse beruht auf scharfen Ordnungsabschätzungen der Abweichung pro Mantissenstelle zwischen logarithmisch verteilten Zahlen und gleichverteilten Zahlen. Offene Probleme von Kaneko und Liu und von Tsao werden vollständig gelöst. Ferner wird ein wichtiger Rundungsfehler-Satz von Henrici auf beliebige Basis (von der Basis 2) verallgemeinert.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Computing 27 (1981), S. 227-236 
    ISSN: 1436-5057
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Es werden einige neue Resultate bezüglich des Fehlers bei der Gleitkomma-Multiplikation mitgeteilt. In Abhängigkeit vom Maß für den Fehler wird festgestellt, für welche Basen der mittlere Multiplikationsfehler minimal wird; dabei sind gegenüber früheren Untersuchungen neue Fehlermaße einbezogen worden. Ein Teil der Ergebnisse hat Nutzanwendungen auf den Computerentwurf.
    Notes: Abstract New results are given on error in floating point multiplication. Certain choices of the base minimize the mean multiplicative error. These choices depend on which measure of error is selected. Some measures are included which were not in earlier studies. Some of the results have application to computer design.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Computing 35 (1985), S. 127-139 
    ISSN: 1436-5057
    Keywords: 65G05 ; 65G10 ; Relative error ; computer arithmetic ; floating point multiplication ; normalization options ; guard digits ; floating point numbers ; floating point precision and significance ; round-off error ; fraction error ; mean and standard deviation of errors ; logarithmically distributed numbers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Es wird ein Modell für den relativen Fehler bei der Gleitkomma-Multiplikation entwickelt unf für verschiedene Kombinationen der Arithmetikparameter stochastisch analysiert. Die Parameter sind die Basis, die Rundungsart, die Anzahl der Schutzstellen, und ob die Normalisierung vor oder nach dem Runden erfolgt. Bei einer angenommenen logarithmischen Verteilung für die Mantisse kommt man zu folgenden Schlüssen: 1. Der durchschnittliche relative Fehler bei der Multiplikation wächst mit der Basis. 2. Dieser Fehler wird minimal für die Basis 2 (am besten mit verborgenem ersten Bit) und recht groß für die Basis 16. 3. Die klassischen Schranken für den relativen Fehler sind pessimistisch. Ihre durchschnittliche Überschätzung wächst mit der Basis.
    Notes: Abstract A model of the relative error in floating point multiplication is developed and is analyzed stochastically for various choices of computer design parameters. These parameters include the base, the type of rounding rule, the number of guard digits, and whether the post-arithmetic normalization shift (if needed) is done before or after rounding. Under the assumption of logarithmic distribution for the fraction (mantissa), the major stochastic conclusions are: 1. The average relative error in multiplication increases as the base increases. 2. This error is minimized by selecting the machine base to be binary (better yet, binary with a hidden bit) and is rather large for machines with base 16. 3. The classical relative error bounds are pessimistic. The average overestimation by those bounds increases as the base increases.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Computing 18 (1977), S. 93-106 
    ISSN: 1436-5057
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Es wird der Einfluß von zwei technischen Kenngrößen einer Rechenanlage auf die Gleitkommamultiplikation untersucht. Die Kenngrößen sind die Anzahl der Schutzstellen und die Ausführung der Normalisierung vor bzw. nach der Rundung. Unsere Ergebnisse über die Genauigkeit der Gleitkommamultiplikation beruhen auf einem stochastischen Modell für Maschinenzahlen. Es gibt einen interessanten Zusammenhang zwischen der Anzahl der Schutzstellen und dem Zeitpunkt der Normalisierung. Zum Beispiel war unser erster Eindruck, daß Normalisierung vor der Rundung der Normalisierung nach der Rundung immer vorzuziehen sei. In der Arbeit wird gezeigt, daß dies für Maschinen mit nur einer Schutzstelle nicht gilt. Auch erhalten wir eine vollständige Erklärung für folgende Beobachtung: Auf einer Maschine mit gerader Basis und Normalisierung vor der Rundung sollte man nicht nur symmetrische Rundung verlangen (im Gegensatz zur Rundung durch Abschneiden), sondern sogar symmetrische Rundungund zwei Schutzstellen.
    Notes: Abstract The effect of two important computer design parameters on floating point multiplication is studied. The parameters are the number of guard digits, and the decision whether the post-arithmetic normalization shift is done before or after rounding. Our results on the accurary of floating point multiplication depend on a stochastic model for computer numbers. There is an interesting interplay between guard digit possibilities and the normalization option. For example, our own first impression was that normalization before rounding would always be preferable to normalization after rounding. Our results show that this is not the case when there is only one guard digit. In a related vein, our results also give comprehensive justification of the following observation: On an even base machine whose architecture provides for normalization before rounding, one should not merely ask for symmetric rounding (rather than rounding by chopping). Instead one should ask for symmetric roundingplus two guard digits.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of network and systems management 3 (1995), S. 371-380 
    ISSN: 1573-7705
    Keywords: Telephone traffic ; network management ; control theory ; dynamic flows ; stability ; routing algorithms ; broadband networks ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract The control of telephony traffic is the task of network management and routing algorithms. In this paper, a study of two trunk groups carrying telephony traffic is used to show that instabilities can arise if there is a delay in getting feedback information for a network controller. The network controller seeks to balance the traffic in the two trunk groups, which may represent two paths from a source to a destination. An analysis shows how factors such as holding time, controller gain and feedback delay influence stability. Simulation of a two service case is also carried out to show that the same instabilities can arise.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Rock mechanics and rock engineering 15 (1982), S. 167-180 
    ISSN: 1434-453X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Summary The Influence of Rock Anisotropy on Stress Measurements by Overcoring Techniques A medium is anisotropic if its properties vary with direction. This is the general characteristic of many rocks, for example, schists, slates, gneisses, phyllites and other metamorphic rocks. Bedded and regularly jointed rocks also display anisotropic behavior. This paper is concerned with the influence of rock anisotropy on in-situ stress measurements. It is limited, to stress measurements by overcoring techniques for which strains and displacements are recorded either on the walls of a pilot hole at the end of one or several boreholes or within instrumented solid or hollow inclusions perfectly bonded to the surface of the pilot hole. The rock is described as homogeneous, continuous, anisotropic and linearly elastic. The following questions are answered with special emphasis on rocks that can be classed as transversely isotropic or orthotropic: the number of independent measurements obtainable in a single borehole; the number of boreholes required to determine the in-situ stress field; the influence of rock anisotropy on these numbers; the influence of the anisotropy type and the error involved by neglecting rock anisotropy.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Rock mechanics and rock engineering 4 (1972), S. 203-223 
    ISSN: 1434-453X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Description / Table of Contents: Zusammenfassung Finite Elemente Analysis der Riβeinleitung in einem Block-Modellversuch Eine biaxial belastete Sand-Gips-Platte mit zwei vertikalen Kluftscharen wurde von Rosenblad untersucht. Durch die Anwendung von zwei Iterationsstufen wurde eine Simulation des Problems mit der Methode der finiten Elemente erreicht. Iterationen mit variierten Klufteigenschaften konvergierten und führten zu Spannungszuständen, welche den Gesetzen der nicht-linearen Kluftdeformation und den Festigheitsgesetzen entsprachen. Da diese Lösung von der biaxialen Belastung des Modells abhängt, ist die äußere Belastung, welche zur Rißeinleitung jedes Blocks führt, daher selbst Gegenstand von Iterationen. Man fand gute Übereinstimmung zwischen dem physikalischen und numerischen Modell, auch im Detail.
    Abstract: Résumé Etude par éléments finis du début de la fracturation, dans un assemblage de blocs en contrainte biaxiale Une plaque d'un mélange sable—plâtre, avec deux systèmes de discontinuités orthogonales, a été etudiée en contrainte biaxiale par Rosenblad. On a etudié le problème avec un modèle d'éléments finis qui itère à deux niveaux. Une série d'itérations sur les propriétés des discontinuités produit une solution, en termes de contraintes, qui respecte les lois non-linéaires de déformabilité et de résistance. Cependant, cette solution dépend du chargement du modèle; donc, la charge nécessaire au commencement de la fracturation fait elle-même l'objet d'itérations. On a obtenu un très bon accord entre les résultats des modèles plysiques et ceux du calcul par éléments finis.
    Notes: Summary Finite Element Analysis of Crack Initiation in a Block Model Experiment A Sand-plaster plate with two perpendicular joint sets loaded biaxially was studied by Rosenblad. A finite element simulation was achieved using two levels of iteration. Iteration with varying joint properties produced a convergent stress state (a “solution”) everywhere respecting the non-linear joint deformability and strength laws. But since this “solution” depends upon the biaxial loading of the model, the external load to initiate cracking of any block is itself the object of iterations. Close agreement was achieved between the physical and numerical models in many details.
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