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  • 1
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    The potential role of spectral properties in detecting thresholds in the Earth system: application to the thermohaline circulation (2003)
    Springer
    Details
    Publication Date: 2003-06-01
    Print ISSN: 1616-7341
    Electronic ISSN: 1616-7228
    Topics: Geosciences , Physics
    Published by Springer
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    PAPER CURRENT
  • 2
    Electronic Resource
    Electronic Resource
    Genetic mosaic analysis of decapentaplegic and wingless gene function in the Drosophila leg (1996)
    Springer
    Development genes and evolution 206 (1996), S. 180-194 
    Details
    ISSN: 1432-041X
    Keywords: Key words Positional information ; Pattern formation ; decapentaplegic ; wingless ; Leg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Genetically mosaic flies were constructed which lack a functional decapentaplegic (dpp) or wingless (wg) gene in portions of their leg epidermis, and the leg cuticle was examined for defects. Although dpp has previously been shown to be transcribed both ventrally and dorsally, virtually the only dpp-null clones that affect leg anatomy are those which reside dorsally. Conversely, wg-null clones only cause leg defects when they reside ventrally – a result that was expected, given that wg is only expressed ventrally. Both findings are consistent with models of leg development in which the future tip of the leg is specified by an interaction between dpp and wg at the center of the leg disc. Null clones can cause mirror-image cuticular duplications confined to individual leg segments. Double-ventral, mirror-image patterns are observed with dpp-null clones, and double-dorsal patterns with wg-null clones. Clones that are doubly mutant (null for both dpp and wg) manifest reduced frequencies for both types of duplications. Duplications can include cells from surrounding non-mutant territory. Such nonautonomy implies that both dpp and wg are involved in positional signaling, not merely in the maintenance of cellular identities. However, neither gene product appears to function as a morphogen for the entire leg disc, since the effects of each gene’s null clones are restricted to a discrete part of the circumference. Interestingly, the circumferential domains where dpp and wg are needed are complementary to one another.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004270050044
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  • 3
    Electronic Resource
    Electronic Resource
    Interactions of decapentaplegic, wingless, and Distal-less in the Drosophila leg (1994)
    Springer
    Development genes and evolution 203 (1994), S. 310-319 
    Details
    ISSN: 1432-041X
    Keywords: Positional information ; Pattern formation ; Developmental genetics ; Polar Coordinate Model ; Janus mutants ; bristles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genes decapentaplegic, wingless, and Distalless appear to be instrumental in constructing the anatomy of the adult Drosophila leg. In order to investigate how these genes function and whether they act coordinately, we analyzed the leg phenotypes of the single mutants and their inter se double mutant compounds. In decapentaplegic the tarsi frequently exhibit dorsal deficiencies which suggest that the focus of gene action may reside dorsally rather than distally. In wingless the tarsal hinges are typically duplicated along with other dorsal structures, confirming that the hinges arise dorsally. The plane of symmetry in double-ventral duplications caused by decapentaplegic is virtually the same as the plane in double-dorsal duplications caused by wingless. It divides the fate map into two parts, each bisected by the dorsoventral axis. In the double mutant decapentaplegic wingless the most ventral and dorsal tarsal structures are missing, consistent with the notion that both gene products function as morphogens. In wingless Distal-less compounds the legs are severely truncated, indicating an important interaction between these genes. Distal-less and decapentaplegic manifest a relatively mild synergism when combined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00457802
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  • 4
    Electronic Resource
    Electronic Resource
    Pattern as a function of cell number and cell size on the second-leg basitarsus ofDrosophila (1979)
    Springer
    Development genes and evolution 187 (1979), S. 105-127 
    Details
    ISSN: 1432-041X
    Keywords: Drosophila ; Pattern formation ; Leg ; Bristle ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The bristle pattern of the second-leg basitarsus inDrosophila melanogaster was studied as a function of the number and size of the cells on this segment in well-fed and starved wild-type flies, in triploid flies, and in two mutants (dachs andfour-jointed) that have abnormally short basitarsi. The second-leg basitarsi of well-fed, wild-type flies from 22 otherDrosophila species were studied in a similar manner. There are typically 8 longitudinal rows of evenly-spaced bristles on the second-leg basitarsus, and in each row the number of bristles was consistently found to vary in proportion to the estimated number of cells along the segment, and the interval between bristles was found to vary in proportion to the average cell diameter on the segment. These correlations are interpreted to mean that the spacing of the bristles within each row is controlled developmentally, whereas the number of bristles is not. The interval between bristles is evidently measured either as a fixed number of cells or as a distance which indirectly depends upon cell diameter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00848266
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  • 5
    Electronic Resource
    Electronic Resource
    A high-resolution morphogenetic map of the second-leg basitarsus inDrosophila melanogaster (1979)
    Springer
    Development genes and evolution 187 (1979), S. 129-150 
    Details
    ISSN: 1432-041X
    Keywords: Drosophila ; Pattern formation ; Leg ; Bristle ; Cell lineage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The lineages of cells on the second-leg basitarsus ofDrosophila melanogaster were analyzed by examining gynandromorphs andMinute mosaics. Bracts lie proximal to bristles on the adult basitarsus, yet bract precursor cells were found to originate lateral to bristle precursor cells. In 6 of the 8 longitudinal rows of bristles on this segment, the bract cells arise ventral to the bristle cells; in the others they arise dorsally. The lateral cell origins are interpreted as reflecting a pattern of lateral cell movements associated with evagination of the leg disc. An unusual discrepancy was observed in the relative frequencies of male vs. female bracts and bristles in gynandromorphs. The discrepancy suggests that there is a cell-autonomous sexual difference in either the time at which cells begin moving during evagination or the speed with which they move. On the basis of the results, it is reasoned that the bristle pattern of the basitarsus does not originate in its final form. Prior to evagination, the bristle cells of each row are apparently closer together than in the final pattern, and the rows are farther apart. Evidence is presented which suggests that the bristle cells of each row may originally be arranged in a jagged line which is later straightened by cell movements. The two locations where the anterior/posterior compartment boundary of the second leg passes through the basitarsus were found to vary relative to the bristle pattern. If this boundary is assumed to be a fixed line of positional values, then the extent of the observed variability — which is estimated to be ± 1 or 2 cell diameters — provides a measure of the precision of patterning around the circumference.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00848267
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  • 6
    Electronic Resource
    Electronic Resource
    Extra tarsal joints and abnormal cuticular polarities in various mutants ofDrosophila melanogaster (1986)
    Springer
    Development genes and evolution 195 (1986), S. 145-157 
    Details
    ISSN: 1432-041X
    Keywords: Drosophila ; Cell polarity ; Limb development ; Pattern formation ; Bristle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The legs of flies from 16 different mutant strains ofDrosophila melanogaster were examined for abnormal cuticular polarities and extra joints. The strains were chosen for study because they manifest abnormal cuticular polarities in some parts of the body (10 strains) or because they have missing or defective tarsal joints (6 strains). All but three of the stocks were found to exhibit misorientations of either the bristles, hairs, or “bract-socket vectors” on the legs. The latter term denotes an imaginary vector pointing from a hairlike structure called a “bract” to the bristle socket with which it is associated. On the legs of wild-type flies nearly all such vectors point distally, as do the bristles and hairs. In the mutant flies, the most common vector misorientation is a 180° reversal. When the bract-socket vectors of adjacent bristle sites in the same bristle row point toward one another, the distance between the sites is frequently abnormally large, whereas when the vectors point in opposite directions, the interval is frequently abnormally small. This correlation is interpreted to mean that bristle cells actively repel one another via cytoplasmic extensions that are longer in the direction of the bract-socket vector than in the opposite direction. Repulsive forces of this kind may be responsible for “fine-tuning” the regularity of bristle spacing in wild-type flies. Extra tarsal joints were found in eight of the 16 strains. A ninth strain completely lacking tarsal joints appears in some cases to have an extra tibia-basitarsus joint in its tibia. Whereas the tarsi of wild-type flies contain four joints, the tarsi ofspiny legs mutant flies contain as many as eight joints. In this extreme extra-joint phenotype, four of the joints correspond to the normal wild-type joints, and there is an extra joint in every tarsal segment except the distal-most (fifth) segment. Nearly all such ectopic extra joints have inverted polarity. In other strains the extra tarsal joints are located mainly at the wild-type joint sites, and joints of this sort have wild-type polarity. The alternation of normal and inverted (extra) joints inspiny legs resembles the alternation of normal and inverted (extra) body segment boundaries in the embryonic-lethal mutantpatch, suggesting that tarsal and body segmentation may share a common patterning mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02439432
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  • 7
    Electronic Resource
    Electronic Resource
    Sensitive periods for abnormal patterning on a leg segment inDrosophila melanogaster (1990)
    Springer
    Development genes and evolution 199 (1990), S. 31-47 
    Details
    ISSN: 1432-041X
    Keywords: Bristle ; Pattern formation ; Drosophila ; Gamma rays ; Mitomycin C ; Heat shock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The development of a leg segment of the fruitflyDrosophila melanogaster was analyzed in order to determine whether the orderliness of the segment's bristle pattern originates via waves of cellular interactions, such as those that organize the retina. Fly development was perturbed at specific times by either teratogenic agents (gamma rays, heat shock, or the drug mitomycin C) or temperature-sensitive mutations (l(1)63, l(1) Notchts1, orl(1) shibire ts1 ), and the resulting abnormalities (e.g., missing or extra structures) were mapped within the pattern area. If bristles develop in a linear sequence across the pattern, then they should show sensitivity to perturbations in the same order, and wavefronts of cuticular defects should result. Contrary to this prediction, the maps reveal no evidence for any directional waves of sensitivity. Nevertheless, other clues were uncovered as to the nature and timing of patterning events. Chemosensory bristles show earlier sensitivities than mechanosensory bristles, and longer bristles precede shorter ones. The types and sequence of cuticular abnormalities imply the following stages of bristle pattern development: (1) scattered inception of bristle mother cells, each surrounded by an inhibitory field, (2) alignment of the mother cells into rows, (3) differential mitoses, (4) assignment of cuticular fates to the mitotic progeny, (5) polytenization of the bristle cells, (6) fine-tuning adjustments in bristle spacing, and (7) signalling from bristle cells to adjacent epidermal cells, inducing them to form “bracts”.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01681531
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  • 8
    Electronic Resource
    Electronic Resource
    Arrangement of bristles as a function of bristle number on a leg segment inDrosophila melanogaster (1990)
    Springer
    Development genes and evolution 199 (1990), S. 48-62 
    Details
    ISSN: 1432-041X
    Keywords: Bristle ; Sensilla ; Pattern formation ; Drosophila ; achaete-scute complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The arrangement of bristles on a leg segment of the fruitflyDrosophila melanogaster was studied in various mutants that have abnormal numbers of bristles on this segment. Eighteen mutations at six different genetic loci were analyzed, plus five double or triple mutant combinations. Recessive mutations at theachaete-scute locus were found to affect distinct groups of bristles:achaete mutations remove mechanosensory bristles, whereasscute mutations remove mainly chemosensory bristles. Mechanosensory bristles remain uniformly spaced along the longitudinal axis unless their number decreases below a certain threshold, suggesting that spacing is controlled by cell interactions that cannot function when bristle cells are too far apart. Above a certain threshold, bristle spacing and alignment both become irregular, perhaps due to excessive force from these same interactions. Chemosensory bristles occupy definite positions that are virtually unaffected by removal of individual bristles from the array. Extra chemosensory bristles develop only near the six normal sites. At two of the six sites the multiple bristles tend to exhibit uniform longitudinal spacing — a property confined to mechanosensory bristles in wild-type flies. To explain the various mutant phenotypes the following scheme is proposed, with different mutations directly or indirectly affecting each step: (1) spots and stripes are demarcated within the pattern area, (2) one bristle cell normally arises within each spot, multiple bristle cells within each stripe, (3) incipient bristle cells inhibit neighboring cells from becoming bristle cells, and (4) the bristle cells within each stripe become aligned to form rows and then repel one another to generate uniform spacing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01681532
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  • 9
    Electronic Resource
    Electronic Resource
    Hail frequency in the Pretoria — Witwatersrand area during 1962 to 1972 (1974)
    Springer
    Pure and applied geophysics 112 (1974), S. 765-776 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary Hail observations were made in the Transvaal, South Africa, during the decade 1962 to 1972. The hail-reporting network covered an area of 2800 km2 with Pretoria in the northeast and the also densely-populated Witwatersrand in the south. A panel of about 800 voluntary observers contributed 10 560 hail reports during this period. Isopleths of hail frequency within the network were plotted. The pattern was strikingly similar to the isohyetal map. More rain and hail occurred in the urban areas than elsewhere and there was a relationship to topography. Pretoria received less hail than the Witwatersrand, a ridge about 300 m higher than Pretoria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876951
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  • 10
    Electronic Resource
    Electronic Resource
    Die Stromverdrängung in Rohren und Koaxialleitern (1959)
    Springer
    Electrical engineering 44 (1959), S. 306-317 
    Details
    ISSN: 1432-0487
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Übersicht Im folgenden wird in bekannter Weise mit Hilfe derMaxwellschen Gleichungen die Stromverdrängung für Rohre und besonders für Koaxialleiter für beliebige Frequenzen zahlenmäßig berechnet. Der WirkwiderstandsbelagR und der induktive Widerstand ωL im Leiterinnern werden getrennt als Funktionen des Radienverhältnisses und der Frequenz in Kurven angegeben. Diese Arbeit ist eine Ergänzung zu den bisher veröffentlichten Arbeiten, insbesondere zu den von mehreren Autoren angegebenen einfachen Näherungslösungen für sehr kleine und sehr große Frequenzen. Es ist damit für den gesamten Frequenzbereich eine schnelle zahlenmäßige Ermittlung der Wechselstromwiderstände und der Eindringtiefe möglich.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580531
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