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  • 1
    Electronic Resource
    Electronic Resource
    Developing an appropriate strategy to assess genetic variability in plant germplasm collections (1999)
    Springer
    Theoretical and applied genetics 98 (1999), S. 1125-1131 
    Details
    ISSN: 1432-2242
    Keywords: Key words Lupin ; Lupinus albus ; Germplasm collection ; ISSR-PCR ; Microsatellite ; Genebank
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The value of molecular biology for monitoring the genetic status of germplasm collections is subject to practical limitations. The large number and variability of accessions held usually dictates the approach that can be employed. A quick, simple but reliable molecular protocol must be combined with an appropriate strategy for handling large sample sizes. In this study, ISSR-PCR was used to reveal genetic variability within and between accessions held in a collection of lupin germplasm. Pooling of DNA from individuals within accessions was found to be the most appropriate strategy for assessing large quantities of plant material. Band profiles generated from pools containing five individuals were fully representative of all constituent individuals used in the mix. Pools comprising 10 or 20 individuals, however, sometimes failed to contain minor bands that had been present only in the profile of one individual. Variation was observed between pools containing five different genotypes from the same accession. Routine large-scale screens are required to assess the genetic diversity and homogeneity of the lupin germplasm collection held in Reading. It is concluded that 2–3 pools of five genotypes may be sufficient to represent the genetic variability within and between accessions in the lupin and similar collections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220051176
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  • 2
    Electronic Resource
    Electronic Resource
    Quantitative comparison of food niches in some freshwater zooplankton (1987)
    Springer
    Oecologia 72 (1987), S. 331-340 
    Details
    ISSN: 1432-1939
    Keywords: Food niche ; Rotifers ; Cladocerans ; Copepods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The abilities of some zooplankton (rotifers, cladocerans, copepods) to ingest different sizes and kinds of food cells were quantified by determining the relative efficiencies with which they ingested nine tracer-cell types, ranging from a coccoid bacterium (0.45 μm3) to the alga Cryptomonas erosa (800–920 μm3). These efficiencies were obtained by dividing the clearance rate of each zooplankton group (species population, developmental stage or size class of a species population) on each 32P-labeled cell type by that of a simultaneously-offered, 33P-labeled, standard cell type — Chlamydomonas reinhardtii. Similarities of efficiency patterns on these cell types (food niches) between all possible pairs of the 17 zooplankton groups from 4 ecosystems were determined by calculating correlation coefficients. Although the utilization of the tested cell types may vary greatly within a species, three feeding guilds could be distinguished — based primarily on the efficiencies with which the smallest cell types were ingested. Guild I (Poyarthra vulgaris, Keratella crassa, Diaptomus minutus nauplii) ate the smallest cells (〈4 μm diameter) (bacterium, Synechococcus, Nannochloris) and Ankistrodesmus very ineffifently but the three Cryptomonas species very efficiently. Guild II (Bosmina longirostris, D. minutus copepodites and Adults) had higher efficiencies on Synechococcus, Nannochloris, Ankistrodesmus, Stichococcus, and Stephanodiscus than guild I but similarly low ones on the bacterium and high ones on the Cryptomonas species. Guild III (Conochilus inicornis, Keratella cochlearis, Ceriodaphnia quadrangula, Diaphanosoma leuchtembergianum) differed from guilds I and II in having uniformly high efficiencies on all the small cells as well ad the larger ones. Principal component analysis of the matrix of correlation coefficients provided objective confirmation of the three guilds and provided a visual representation of the food niches of the 17 zooplankton groups in 3-dimensional space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377560
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  • 3
    Electronic Resource
    Electronic Resource
    Electric potential gradient changes during explosive activity at Sakurajima volcano, Japan (1992)
    Springer
    Bulletin of volcanology 54 (1992), S. 590-594 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract We report electric potential gradient measurements carried out at Sakurajima volcano in Japan during: (1) explosions which generated ash plumes, (2) steam explosions which produced plumes of condensing gases, and (3) periods of ashfall and plume-induced acid rainfall. Sequential positive and negative deviations occurred during explosions which generated ash plumes. However, no deflections from background were found during steam explosions. During periods of ashfall negative electric potential gradients were observed, while positive potential gradients occurred during fallout of plume-induced acid rain from the same eruption. These results suggest that a dipole arrangement of charge develops within plumes such that positive charges dominate in the volcanic gas-rich top and negative charges in the following ash-rich part of the plume. The charge polarity may be reversed for other volcanoes (Hatakeyama and Uchikawa 1952). We suggest that charge is generated by fracto-emission (Donaldson et al. 1988) processes probably during magma fragmentation within the vent, rather than by frictional effects within the plume.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00569942
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  • 4
    Electronic Resource
    Electronic Resource
    The aerodynamic behaviour of volcanic aggregates (1993)
    Springer
    Bulletin of volcanology 55 (1993), S. 481-488 
    Details
    ISSN: 1432-0819
    Keywords: aggregates ; fall velocity ; volcanic plumes ; porosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A large proportion of solid material transported within the atmosphere during volcanic eruptions consists of particles less than 500 μm in diameter. The majority of these particles become incorporated into a wide range of aggregate types, the aerodynamic behaviour of which has not been determined by either direct observation or in the laboratory. In the absence of such data, theoretical models of fallout from volcanic plumes make necessarily crude assumptions about aggregate densities and fall velocities. Larger volcanic ejecta often consists of pumice of lower than bulk density. Experimental data are presented for the fall velocities of porous aggregates and single particles, determined in systems analogous to that of ejecta falling from a volcanic plume. It is demonstrated that the fall of aggregates may be modelled in identical fashion to single particles by using a reduced aggregate density dependent on the porosity, and a size corresponding to an enclosing sphere. Particles incorporated into aggregates attain a substantially higher fall velocity than single particles. This is due to the larger physical dimensions of the aggregate, which overcomes the effect of lower aggregate density. Additionally, the internal porosity of the aggregate allows some flow of fluid through the aggregate and this results in a small increase in fall velocity. The increase in fall velocity of particles incorporated into aggregates, rather than falling individually, results in the enhanced removal of fine material from volcanic plumes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00304591
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  • 5
    Electronic Resource
    Electronic Resource
    Sedimentation of tephra by volcanic plumes: I. Theory and its comparison with a study of the Fogo A plinian deposit, Sao Miguel (Azores) (1992)
    Springer
    Bulletin of volcanology 54 (1992), S. 329-344 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Sedimentation of ejecta from volcanic plumes has been studied as a function of distance from the source in the Fogo A plinian deposit, Sao Miguel, Azores. The Fogo A trachytic pumice deposit is reversely graded and can be divided into two parts on the basis of pumice colour, abundance of syenite accessory lithic clasts and distribution. The lower syenite-poor part was dispersed to the south and was clearly influenced by wind. The upper syenite-rich part is coarsegrained and has a nearly symmetrical distribution around the vent. Elongation of isopachs to the east indicate a weak wind influence. The grain-size variations of lithic and crystal components in the upper coarse part were studied. Total accumulation and accumulation per unit area (expressed in kg/m2) show good fits to a gaussian function at distances greater than ∼7 km for grain diameters less than 2 cm. These results agree with a theoretical model for a radially spreading turbulent current moving over a quiescent fluid. The gaussian coefficient is shown to be a function of grain size and the flow rate of material into the umbrella region of the eruption column. The coefficient is therefore also a function of column height. The column height deduced from these data is 21 km, which is in broad agrrement with the column height of 27 km deduced from maximum clast dispersal using the method of Carey and Sparks (1986). The accumulation of clasts larger than 2 cm agrees with a theory for the fallout of clasts from the margins of the ascending eruption column, which treats the plume as a succession of large eddies that decrease their mass of particles as an exponential function of time. Calculations are also presented for the influence of the radial inflow of surrounding air into the column on the deposition of clasts. These calculations constrain the wind speed during the later part of the Fogo A eruption to be at most a few metres per second. The study has allowed four different dynamic categories of clast behaviour to be recognised in eruption columns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301486
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  • 6
    Electronic Resource
    Electronic Resource
    Non-explosive, constructional evolution of the ice-filled caldera at Volcán Sollipulli, Chile (1996)
    Springer
    Bulletin of volcanology 58 (1996), S. 67-83 
    Details
    ISSN: 1432-0819
    Keywords: Key words Caldera ; Radar ; Gravity ; Ice ; Subglacial eruptions ; Sollipulli ; Chile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  A radar and gravity survey of the ice-filled caldera at Volcán Sollipulli, Chile, indicates that the intra-caldera ice has a thickness of up to 650 m in its central part and that the caldera harbours a minimum of 6 km3 of ice. Reconnaissance geological observations show that the volcano has erupted compositions ranging from olivine basalt to dacite and have identified five distinct volcanic units in the caldera walls. Pre- or syn-caldera collapse deposits (the Sharkfin pyroclastic unit) comprise a sequence which evolved from subglacial to subaerial facies. Post-caldera collapse products, which crop out along 17 of the 20 km length of the caldera wall, were erupted almost exclusively along the caldera margins in the presence of a large body of intra-caldera ice. The Alpehué crater, formed by an explosive eruption between 2960 and 2780 a. BP, in the southwest part of the caldera is shown to post date formation of the caldera. Sollipulli lacks voluminous silicic pyroclastic rocks associated with caldera formation and the collapse structure does not appear to be a consequence of a large-magnitude explosive eruption. Instead, lateral magma movement at depth resulting in emptying of the magma chamber may have generated the caldera. The radar and gravity data show that the central part of the caldera floor is flat but, within a few hundred metres of the caldera walls, the floor has a stepped topography with relatively low-density rock bodies beneath the ice in this region. This, coupled with the fact that most of the post-caldera eruptions have taken place along the caldera walls, implies that the caldera has been substantially modified by subglacial marginal eruptions. Sollipulli caldera has evolved from a collapse to a constructional feature with intra-caldera ice playing a major role. The post-caldera eruptions have resulted in an increase in height of the walls and concomitant deepening of the caldera with time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450050127
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  • 7
    Electronic Resource
    Electronic Resource
    Separators in Graphs with Negative and Multiple Vertex Weights (1999)
    Springer
    Algorithmica 23 (1999), S. 57-71 
    Details
    ISSN: 1432-0541
    Keywords: Key words. Graph separator, Cutset, Divide-and-conquer algorithm, Separator theorem, Graph algorithms.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. A separator theorem for a class of graphs asserts that every graph in the class can be divided approximately in half by removing a set of vertices of specified size. Nontrivial separator theorems hold for several classes of graphs, including graphs of bounded genus and chordal graphs. We show that any separator theorem implies various weighted separator theorems. In particular, we show that if the vertices of the graph have real-valued weights, which may be positive or negative, then the graph can be divided exactly in half according to weight. If k unrelated sets of weights are given, the graph can be divided simultaneously by all k sets of weights. These results considerably strengthen earlier results of Gilbert, Lipton, and Tarjan: (1) for k=1 with the weights restricted to being nonnegative, and (2) for k〉1 , nonnegative weights, and simultaneous division within a factor of (1+ε ) of exactly in half.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009250
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  • 8
    Electronic Resource
    Electronic Resource
    The origin of accretionary lapilli (1994)
    Springer
    Bulletin of volcanology 56 (1994), S. 398-411 
    Details
    ISSN: 1432-0819
    Keywords: accretionary lapilli ; aggregation volcanic ash ; volcanic plume ; wind tunnel collision and coalescence ; fallout
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Experimental investigations in a recirculating wind tunnel of the mechanisms of formation of accretionary lapilli have demonstrated that growth is controlled by collision of liquid-coated particles, due to differences in fall velocities, and binding as a result of surface tension forces and secondary mineral growth. The liquids present on particle surfaces in eruption plumes are acid solutions stable at ≪ 100% relative humidity, from which secondary minerals, e.g. calcium sulphate and sodium chloride, precipitate prior to impact of accretionary lapilli with the ground. Concentric grain-size zones within accretionary lapilli build up due to differences in the supply of particular particle sizes during aggregate growth. Accretionary lapilli do not evolve by scavenging of particles by liquid drops followed by evaporation — a process which, in wind tunnel experiments, generates horizontally layered hemispherical aggregates. Size analysis of particles in the wind tunnel air stream and particles adhering to growing aggregates demonstrate that the aggregation coefficient is highly grain-size dependent. Theoretical simulation of accretionary lapilli growth in eruption plumes predicts maximum sizes in the range 0.7–20 mm for ash cloud thicknesses of 0.5–10 km respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326465
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  • 9
    Electronic Resource
    Electronic Resource
    Ice-melt collapse pits and associated features in the 1991 lahar deposits of Volcán Hudson, Chile: criteria to distinguish eruption-induced glacier melt (1995)
    Springer
    Bulletin of volcanology 57 (1995), S. 293-302 
    Details
    ISSN: 1432-0819
    Keywords: Lahars ; Jökulhlaup ; Geohazards ; Glacier melt ; Ice-rafting ; Subsidence ; Ring fractures ; Current crescent ; Kettle-hole ; Sandur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract In subaerial volcaniclastic sequences structures formed by ice blocks can provide information about a volcano's history of lahar generation by glacier melt. At Volcán Hudson in Chile, catastrophic lahars were initiated by eruption-induced melting of glacier ice in August and October 1991. They transported large ice blocks 50 km down the Rio de los Huemules valley to the sea. Large current crescents with lee-side lenses were formed where ice blocks were deposited during waning stages of the flood. When stranded blocks of ice melted, they left cone-shaped and ring-shaped heaps of ice-rafted debris on the sediment surface. Several hundred ice blocks were completely buried within the aggrading lahar sediment, and when these melted circular collapse pits formed in the sediment. Collapse types included subsided coherent blocks of sediment bounded by an outward-dipping ring-fracture, trapdoor structures with horseshoe-shaped fractures, downsag pits with centroclinal dips locally up to 60°, pits with peripheral graben and crevasses, piecemeal (highly fragmented) collapse structures and funnel-shaped pits containing disaggregated sediment. A sequence of progressive collapse is inferred in which initial downsag and subsidence on an outward-dipping ring fracture produces a small diameter pit. This is followed by widening of the pit by progressive development of concentric ring fractures and downsag outside the early formed pit, and by collapse of overhanging pit walls to produce vertical to inward-dipping walls and aprons of collapse debris on the pit floor. The various structures have potential for preservation even in regions prone to high rainfall and flooding, and they can be used to indicate that former lahars contained abundant blocks of ice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301289
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  • 10
    Electronic Resource
    Electronic Resource
    The origin of accretionary lapilli (1994)
    Springer
    Bulletin of volcanology 56 (1994), S. 398-411 
    Details
    ISSN: 1432-0819
    Keywords: Key words accretionary lapilli ; aggregation ; volcanic ash ; volcanic plume ; wind tunnel ; collision and coalescence ; fallout
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Experimental investigations in a recirculating wind tunnel of the mechanisms of formation of accretionary lapilli have demonstrated that growth is controlled by collision of liquid–coated particles, due to differences in fall velocities, and binding as a result of surface tension forces and secondary mineral growth. The liquids present on particle surfaces in eruption plumes are acid solutions stable at 〈100% relative humidity, from which secondary minerals, e.g. calcium sulphate and sodium chloride, precipitate prior to impact of accretionary lapilli with the ground. Concentric grain–size zones within accretionary lapilli build up due to differences in the supply of particular particle sizes during aggregate growth. Accretionary lapilli do not evolve by scavenging of particles by liquid drops followed by evaporation – a process which, in wind tunnel experiments, generates horizontally layered hemispherical aggregates. Size analysis of particles in the wind tunnel air stream and particles adhering to growing aggregates demonstrate that the aggregation coefficient is highly grain–size dependent. Theoretical simulation of accretionary lapilli growth in eruption plumes predicts maximum sizes in the range 0.7–20 mm for ash cloud thicknesses of 0.5–10 km respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326465
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