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11

Digitale Medien

In-situ scanning tunnelling microscopy of hydrogenated amorphous silicon and microcrystalline silicon (1998)

Flewitt, A.J. ; Froggatt, M.W.D. ; Milne, W.I. ; [weitere]

Springer

Applied physics 66 (1998), S. 1101-1105

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ISSN: 1432-0630

Schlagwort(e): PACS: 68.55; 72.20; 81.10

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s003390051305

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12

Digitale Medien

Investigation of groundwater flow in karst areas using component separation of natural potential measurements (1999)

Wanfang, Z. ; Beck, Barry F. ; Stephenson, J. Brad

Springer

Environmental geology 37 (1999), S. 19-25

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ISSN: 1432-0495

Schlagwort(e): Key words Natural potential technique ; Topographic effect ; Karst terrane ; Groundwater recharge

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie

Notizen: Abstract The natural (electrical) potential (NP) method – also known as self-potential, spontaneous potential and streaming potential (SP) – has been used to locate areas of groundwater flow in karst terrane. NP is the naturally occurring voltage at the ground surface resulting from ambient electrical currents within the earth. The measurement of NP can be used to characterize groundwater flow in karst terrane because electrical potential gradients are generated by the horizontal flow of water along fractures or conduits and the vertical infiltration of water into fractures or shafts. NP data from a site on the Mitchell Plain of southern Indiana, USA, revealed that NP data can be decomposed into three components: topographic effect, residual NP and noise. At this site, NP was inversely proportional to elevation, but the correlation varied with time. The topographic correction factor varied from –2.5 to –1.2 mV/m (NP change per unit elevation increase), with an average linear correlation coefficient (R) of 0.95. Because the site slopes toward an adjacent creek that is the local groundwater discharge zone, one possible explanation for this effect is a streaming-potential mechanism generated by groundwater movement toward the creek. The residual NP data revealed three negative anomalies at the survey area. Two of them coincide with sinkholes. A part of the third anomaly is coincident with a small valley, and concentrated infiltration does occur at this elevation in other valleys at the site, as evidenced by the existence of sinkholes. However, the dispersed, low-magnitude nature of the third anomaly does not prove the existence of concentrated groundwater recharge activity.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s002540050355

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13

Digitale Medien

Simultaneous auroral observations described in the historical records of China, Japan and Korea from ancient times to AD 1700 (1999)

Willis, D. M. ; Stephenson, F. R.

Springer

Annales geophysicae 18 (1999), S. 1-10

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ISSN: 0992-7689

Schlagwort(e): Magnetospheric physics (auroral phenomena; storms and substorms)

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract Early auroral observations recorded in various oriental histories are examined in order to search for examples of strictly simultaneous and indisputably independent observations of the aurora borealis from spatially separated sites in East Asia. In the period up to AD 1700, only five examples have been found of two or more oriental auroral observations from separate sites on the same night. These occurred during the nights of AD 1101 January 31, AD 1138 October 6, AD 1363 July 30, AD 1582 March 8 and AD 1653 March 2. The independent historical evidence describing observations of mid-latitude auroral displays at more than one site in East Asia on the same night provides virtually incontrovertible proof that auroral displays actually occurred on these five special occasions. This conclusion is corroborated by the good level of agreement between the detailed auroral descriptions recorded in the different oriental histories, which furnish essentially compatible information on both the colour (or colours) of each auroral display and its approximate position in the sky. In addition, the occurrence of auroral displays in Europe within two days of auroral displays in East Asia, on two (possibly three) out of these five special occasions, suggests that a substantial number of the mid-latitude auroral displays recorded in the oriental histories are associated with intense geomagnetic storms.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s00585-000-0001-6

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14

Digitale Medien

GCM simulation of the Southern Oscillation from 1979–88 (1995)

Stephenson, David B ; Royer, J -F

Springer

Climate dynamics 11 (1995), S. 115-128

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ISSN: 1432-0894

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract The Southern Oscillation (SO) is examined in three 10 year AMIP-type integrations of a 30-level GCM having prescribed monthly mean observed sea surface temperatures for the period January 1979 to December 1988. Three horizontal spectral resolutions of T21, T42 and T79 are investigated and the results are compared with the low-frequency variability, having periods longer than 8 months, in the observed Darwin and Tahiti sea level pressures (SLP) and in the T106 ECMWF analyses from May 1985 to April 1991. Both the ECMWF analyses and the GCM results give unrealistic SLP variability at Tahiti resulting in low Darwin-Tahiti SLP correlations and low S/N ratios for the Tahiti-Darwin SO index. The ECMWF analyses are in particularly poor agreement with the observations during 1987 with anomalously high SLP at Tahiti. Examination of the ECMWF assimilated SSTs, reveals that this may be related to the assimilated SSTs being too cold in the central and eastern equatorial Pacific during mid-1987. The GCM results show the familiar SLP dipole in the tropical Pacific albeit displaced eastwards compared to previous observational studies especially at T42 resolution, thus accounting for the problems at Tahiti which lies near strong gradients in the correlation pattern. Time-longitude diagrams of low-level convergence and correlation maps of upper-level streamfunction suggest that the model is reproducing the SO divergence anomalies although too weakly at T21 resolution and at different longitudinal locations at T42 and T79 resolutions. The time-mean low-level convergences in the GCM simulations give ITCZs and SPCZs in qualitative agreement with the observations with a tendency for increased convergence in the eastern Pacific ITCZ at higher resolution. Longitudinal shifts are not apparent in the time-mean convergence when comparing the GCM results at different resolutions.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00211677

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15

Digitale Medien

GCM simulation of the Southern Oscillation from 1979–88 (1995)

Stephenson, David B ; Royer J-F

Springer

Climate dynamics 11 (1995), S. 115-128

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ISSN: 1432-0894

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract. The Southern Oscillation (SO) is examined in three 10 year AMIP-type integrations of a 30-level GCM having prescribed monthly mean observed sea surface temperatures for the period January 1979 to December 1988. Three horizontal spectral resolutions of T21, T42 and T79 are investigated and the results are compared with the low-frequency variability, having periods longer than 8 months, in the observed Darwin and Tahiti sea level pressures (SLP) and in the T106 ECMWF analyses from May 1985 to April 1991. Both the ECMWF analyses and the GCM results give unrealistic SLP variability at Tahiti resulting in low Darwin-Tahiti SLP correlations and low S/N ratios for the Tahiti-Darwin SO index. The ECMWF analyses are in particularly poor agreement with the observations during 1987 with anomalously high SLP at Tahiti. Examination of the ECMWF assimilated SSTs, reveals that this may be related to the assimilated SSTs being too cold in the central and eastern equatorial Pacific during mid-1987. The GCM results show the familiar SLP dipole in the tropical Pacific albeit displaced eastwards compared to previous observational studies especially at T42 resolution, thus accounting for the problems at Tahiti which lies near strong gradients in the correlation pattern. Time-longitude diagrams of low-level convergence and correlation maps of upper-level streamfunction suggest that the model is reproducing the SO divergence anomalies although too weakly at T21 resolution and at different longitudinal locations at T42 and T79 resolutions. The time-mean low-level convergences in the GCM simulations give ITCZs and SPCZs in qualitative agreement with the observations with a tendency for increased convergence in the eastern Pacific ITCZ at higher resolution. Longitudinal shifts are not apparent in the time-mean convergence when comparing the GCM results at different resolutions.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s003820050064

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16

Digitale Medien

A comparison of global tropospheric teleconnections using observed satellite and general circulation model total ozone column data for 1979–91 (1998)

Ambrizzi, T. ; Kayano, M. T. ; Stephenson, D. B.

Springer

Climate dynamics 14 (1998), S. 133-150

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ISSN: 1432-0894

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract The total ozone column is well correlated with tropospheric fields such as the heights of the upper tropospheric geopotential surfaces and thus it can provide useful information on temporal variability in the troposphere. The global availability of long period satellite measurements of the total ozone column, taken by the TOMS instruments since 1978, provides a valuable and independent data set for use in studies of seasonal and interannual climate variability. In this study, the global low-frequency seasonal teleconnections in the observed TOMS data from 1979–91 have been investigated using seasonal teleconnectivity maps and empirical orthogonal function analysis. They have also been compared with the results from a simulation made with the atmospheric GCM at Météo-France, having prescribed observed sea surface temperatures for the same period. In the observed total ozone, strong ENSO-related wave number one longitudinal dipole patterns are seen in both the tropics and in the Southern Hemisphere extratropics. The model shows much weaker variability in total ozone yet appears to be able to capture similar teleconnection patterns in the tropics related to ENSO. In the SH extratropics, the model total ozone shows a strong wave number 3 response rather than the wave number one dipole seen in the observations. A wave number 3 response is also evident in the 200 hPa geopotential height simulated by the model and in the NCEP analysis, and is consistent with the response in a linearised barotropic model forced in the Indonesian region. The different responses in the modelled and observed total ozone, suggest that tropopause effect is not the major factor in the SH extratropics, and it is likely that horizontal ozone transport also plays a role in this region. Despite a generally poor simulation of the zonal mean total ozone, the model was able to capture the anomalous strengthening of the SH stationary waves during austral spring of 1988, related to an intense stratosphere sudden warming.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s003820050214

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17

Digitale Medien

Effects of pollination intensity on the vigor of the sporophytic and gametophytic generation of Cucurbita texana (1997)

Jóhannsson, Magnús H. ; Stephenson, A. G.

Springer

Sexual plant reproduction 10 (1997), S. 236-240

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ISSN: 1432-2145

Schlagwort(e): Key words Cucurbita texana ; Pollen ; Pollen performance ; Pollen competition

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract We examined the effects of pollen competition (pollen load size) on sporophytic vigor and gametophytic performance in Cucurbita texana, a wild gourd, while controlling for alternative interpretations of the data. Under field conditions we compared the vigor of progeny produced from large and small pollen loads and examined the in vitro performance of the pollen produced by the progeny. We found that the progeny from large pollen loads germinated faster and had a greater reproductive output (male flowers and fruits) than progeny produced from small pollen loads. In addition, we found that the pollen produced on plants derived from large pollen loads grew faster in vitro than the pollen produced on plants derived from small pollen loads. These findings indicate that pollen competition affects the performance of the resulting sporophytic generation and the microgametophytes they produce.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s004970050092

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18

Digitale Medien

Variation in sporophytic and gametophytic vigor in wild and cultivated varieties of Cucurbita pepo and their F1 and F2 generations (1998)

Jóhannsson, M. H. ; Stephenson, A. G.

Springer

Sexual plant reproduction 11 (1998), S. 265-271

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ISSN: 1432-2145

Schlagwort(e): Key words Cucurbita ; Pollen tube growth ; Pollen performance ; Hybridization ; Variation

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract This study examines sporophytic and gametophytic vigor in wild and cultivated varieties of Cucurbita pepo L. and their hybrids in order to determine whether hybrid vigor extends to the microgametophyte generation. It also examines the variation in sporophytic and gametophytic vigor to discern the non-genetic influences of pollen provisioning by the sporophyte on pollen performance from the genetic influences of the microgametophyte’s own genotype on pollen performance. A cultivated and a wild C. pepo and their F1 and the F2 generations were grown under field conditions and flower and fruit production were monitored over one summer. We found that the four types of plants differed significantly in the number of male and female flowers and the number of fruits they produced. The F1 plants produced significantly more male flowers and marginally more female flowers and fruits than the parental lines. To estimate gametophytic vigor pollen was germinated in vitro and pollen tube length measured after 30 min. We found that pollen tubes from the F1 plants had significantly greater growth than tubes from the parental lines or the F2 generation, indicating that hybrid vigor extends to the microgametophytic generation. By partitioning the variance of pollen tube growth into ’within’ and ’among’ plant components of variation, we were able to show that the genotype of the microgametophyte influences pollen performance in vitro, but that expression of hybrid vigor in the microgametophyte is likely to be due to an environmental effect related to provisioning of the pollen grains during development.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s004970050152

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19

Digitale Medien

Cloning and characterisation of glutamine synthetase from Colletotrichum gloeosporioides and demonstration of elevated expression during pathogenesis on Stylosanthes guianensis (1997)

Stephenson, Sally-Anne ; Green, Jonathan R. ; Manners, J. M. ; [weitere]

Springer

Current genetics 31 (1997), S. 447-454

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ISSN: 1432-0983

Schlagwort(e): Key words Expression quantification ; Glutamine synthetase ; Pathogenesis ; Nitrogen metabolism

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract Experiments were designed to clone and identify genes of the fungal phytopathogen Colletotrichum gloeosporioides expressed at high levels during growth on the compatible host Stylosanthes guianensis when compared with expression in axenic culture. A cDNA clone (pCgGS) that hybridised preferentially to a cDNA probe prepared from infected leaves was isolated by the differential screening of a cDNA library from a nitrogen-starved axenic culture of C. gloeosporioides. The DNA sequence of pCgGS is highly homologous to genes for glutamine synthetase (GS) in other organisms. pCgGS contained all of the conserved regions assigned as catalytic domains in GS enzymes. Comparison with genomic sequences indicated that in C. gloeosporioides the GS gene is present as a single copy with three introns. To our knowledge this is the first report of the cloning of a GS from a filamentous fungus. A second clone (pCgRL1) was also isolated and represented a partial cDNA of the 25s rRNA of C. gloeosporioides. Because pCgRL1 did not hybridise to plant rRNA under high-stringency hybridisation conditions, it was used as a reference to quantify the expression of fungal GS mRNA during pathogenesis in S. guianensis compared to fungal growth in axenic culture. The results indicated that elevated expression of GS occurred during pathogenesis of C. gloeosporioides on S. guianensis, particularly at early stages of infection where expression was about six-times higher than during growth in rich culture media. This work also demonstrates that fungal-specific 25s rRNA fragments, such as pCgRL1, have considerable utility as a reference for quantifying pathogen gene expression in infected plants.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s002940050228

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20

Digitale Medien

UV spectroscopy of metal volatilization during thermal plasma processing of waste glass melts (1996)

Wood, Jeffrey W. ; Cortez, Rebecca ; Cahill, David G. ; [weitere]

Springer

Plasma chemistry and plasma processing 16 (1996), S. 449-460

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ISSN: 1572-8986

Schlagwort(e): Spectroscopy ; volatilization ; iron ; nickel ; chromium ; waste vitrification

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein

Notizen: Abstract Atomic emission spectroscopy (AES) is used to monitor volatilization during waste vitrification with thermal plasmas. Model baste specimens consist of am alumino-silicate clay spiked with 10 wt. % Fe, Ni, or Cr. Specimens are vitrified in processing atmospheres with 0, 8.5, and 17 vol. % oxygen/argon concentrations. Particulate generated from condensation of the volatilized materials is collected following each specimen run and analyzed by energy dispersive X-ray analysis to determine composition. Spectra are collected from the ultraviolet range 240–380 nm in where the presence of metal vapor is readily detected. Correlation between line emission intensities and volatilization rates allows the establishment of provisional detection limits for the volatilization of Ni, Cr, Si, and Fe, of 1 × 103 g/s, 4 × 104 g/s, 2 × 104 g/s, and 5 × 105 g/s, respectively. The results of this investigation support the concept of using AES as an in-situ process monitor for feedback to optimize plasma processing of hazardous metal-containing waste.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01447155

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