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1

Digitale Medien

Effects of ammonium ions on the depolarization-induced and direct activation of the contractile apparatus in mechanically skinned fast-twitch skeletal muscle fibres of the rat (1996)

Stephenson, Gabriela M. M. ; Stephenson, D. George

Springer

Journal of muscle research and cell motility 17 (1996), S. 611-616

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ISSN: 1573-2657

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Medizin

Notizen: Summary Mechanically skinned fibre preparations from the extensor digitorum longus muscle of the rat were used to test whether a rise in myoplasmic [NH4 +] in the range 2–10 mm interferes with the mechanism of excitation-contraction coupling in fast-twitch mammalian muscle. Under our conditions (pH 7.10, Mg2+ 1 mm, temperature 23° C), [NH4 +] up to 10 mm had little effect on the Ca+-activated force and on the peak of the t-system depolarization-induced force response. However, the duration of the depolarization-induced force response was decreased significantly at [NH4 +] ≥2 mm. From these data we conclude that the intracellular accumulation of NH4 + is not likely to play a major role in fatigue. Nevertheless, the build up of NH4 + during fatigue, may have a significant inhibitory effect on the force output by decreasing the duration of the t-system depolarization-induced activation of the contractile apparatus.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00154055

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2

Digitale Medien

Microfluorometric analyses of glycogen in freshly dissected, single skeletal muscle fibres of the cane toad using a mechanically skinned fibre preparation (1998)

Nguyen, Long Thanh ; Stephenson, D. George ; Stephenson, Gabriela M. M.

Springer

Journal of muscle research and cell motility 19 (1998), S. 631-638

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ISSN: 1573-2657

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Medizin

Notizen: Abstract The main objective of this study was to analyse glycogen in single muscle fibres, using a recently developed microfluorometric method which detects subpicomol amounts of NADPH, glucose and glycogen (as glucosyl units) (detection limit 0.16–0.17pmol in a 25nl sample) without fluorochrome amplification. The fibres were freshly dissected from the twitch region of the iliofibularis muscle of the cane toad (Bufo marinus), and were mechanically skinned under paraffin oil to gain access to the intracellular compartments. The results show that: (1) glycogen concentrations in toad skeletal muscle fibres range between 25.8 and 369mmol glucosyl units/litre fibre volume; (2) there is a large variation in glycogen content between individual fibres from the iliofibularis muscle of one animal; (3) there are seasonal differences in the glycogen content of toad single muscle fibres; (4) the total amount of glycogen in single muscle fibres of the toad does not decrease significantly when storing the tissue, under paraffin oil, at 20–25°C for up to 6h or at 4°C for up to 24h; and (5) 15–26% of fibre glycogen can be washed in an aqueous solution at pH 5–7, within 5min, while 74–85% of fibre glycogen remains associated with the washed skinned fibre, even after 40min exposure of the skinned fibre preparation to the aqueous environment. The retention of most glycogen in the fibre preparation after mechanical removal of the plasma membrane and extensive washing indicates that in toad skeletal muscle fibres the largest proportion of glycogen is tightly bound to intracellular structures. The results also show that the skinned muscle fibre preparation is well suited for microfluorometric glycogen determination, since low molecular weight non-glycogen contributors to the fluorescence signal can be removed from the myoplasmic space prior to the glycogen hydrolysis step.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1005377030193

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3

Digitale Medien

Coring artifacts and contaminant inventories in lake sediment (1996)

Stephenson, M. ; Klaverkamp, J. ; Motycka, M. ; [weitere]

Springer

Journal of paleolimnology 15 (1996), S. 99-106

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ISSN: 1573-0417

Schlagwort(e): lake sediments ; gravity core ; freeze core ; coring artifacts ; contaminant concentration ; contaminant inventory

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Geologie und Paläontologie

Notizen: Abstract Sediments of Lake 382, Experimental Lakes Area, Canada, were sampled at six sites using a 5-cm Wildco KB core sampler (KB), a similar device incorporating a ball check valve (BC), and a 0.2 m by 1.2 m flat-faced aluminum freeze core sampler (FC). Cores were sectioned at 1-cm intervals to a depth of 15 cm. Contaminant (210Pb and 137Cs) concentrations (Bq g-1) were measured by gamma spectroscopy, and inventories (Bq cm-2) were calculated following standard methods. Sediments collected using FC, BC and KB had similar contaminant concentrations, however, cores collected by FC and BC had lower estimated inventories than KB cores. Differences between estimates appear to be caused by differences in the water content (WC) of core material. Laboratory studies confirm that FC sediments have higher WC than tube-cored sediment. We hypothesize that ice crystal formation increases the WC of freeze cores, resulting in lower contaminant inventories. Loss of surficial sediment caused by a ‘bow wave’ may have a similar effect on BC samples. We conclude that KB core gear is appropriate for sampling sediments to measure contaminant concentrations and inventories in recently deposited sediments.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00176992

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4

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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5

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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6

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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7

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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8

Digitale Medien

Metal co-injection moulding (1996)

Alcock, J. R. ; Logan, P. M. ; Stephenson, D. J.

Springer

Journal of materials science 15 (1996), S. 2033-2035

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ISSN: 1573-4811

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00278613

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9

Digitale Medien

Effects of pollen selection on progeny vigor in a Cucurbita pepo × C. texana hybrid (1996)

Quesada, M. ; Winsor, J. A. ; Stephenson, A. G.

Springer

Theoretical and applied genetics 92 (1996), S. 885-890

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ISSN: 1432-2242

Schlagwort(e): Key words Microgametophyte selection ; Pollen selection ; Pollen competition ; Cucurbita texana ; Cucurbita pepo

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract We examined the effects of pollen selection for rapid pollen-tube growth on progeny vigor. First, we crossed a wild gourd (Cucurbita texana) to a cultivated zucchini (Cucurbita pepo cv `Black Beauty') to produce an F1 and then an F2 generation. Half of the F1 seeds were produced by depositing small loads of C. texana pollen onto the stigmas of C. pepo. These small pollen loads were insufficient to produce a full complement of seeds and, consequently, both the fast- and the slow-growing pollen tubes were permitted to achieve fertilization. An F2 generation was then produced by depositing small loads of F1 pollen onto stigmas of F1 plants. The F2 seeds resulting from two generations of small pollen loads are termed 'the non-selected line' because there was little or no selection for pollen-tube growth rate on these plants. The other half of the F1 and F2 seeds were produced by depositing large pollen loads (〉10000 pollen grains) onto stigmas and then allowing only the first 1% or so of the pollen tubes that entered the ovary to fertilize the ovules. We did this by excising the styles at the ovary at 12–15 h after pollination. The resulting F2 seeds are termed `the selected line' because they were produced by two generations of selection for only the fastest growing pollen tubes. Small pollen loads from the F2 plants, both the selected and the non-selected lines, were then deposited onto stigmas of different C. pepo flowers, and the vigor of the resulting seeds was compared under greenhouse and field conditions. The results showed that the seeds fertilized by pollen from the selected line had greater vegetative vigor as seedlings and greater flower and fruit production as mature plants than the seeds fertilized by pollen from the non-selected line. This study demonstrates that selection for fast pollen-tube growth (selection on the microgametophyte) leads to a correlated increase in sporophyte (progeny) vigor.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s001220050207

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10

Digitale Medien

Effects of pollen selection on progeny vigor in a Cucurbita pepo x C. texana hybrid (1996)

Quesada, M. ; Winsor, J. A. ; Stephenson, A. G.

Springer

Theoretical and applied genetics 92 (1996), S. 885-890

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ISSN: 1432-2242

Schlagwort(e): Microgametophyte selection ; Pollen selection ; Pollen competition ; Cucurbita texana ; Cucurbita pepo

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract We examined the effects of pollen selection for rapid pollen-tube growth on progeny vigor. First, we crossed a wild gourd (Cucurbita texana) to a cultivated zucchini (Cucurbita pepo cv ‘Black Beauty’) to produce an F1 and then an F2 generation. Half of the F1 seeds were produced by depositing small loads of C. texana pollen onto the stigmas of C. pepo. These small pollen loads were insufficient to produce a full complement of seeds and, consequently, both the fast- and the slow-growing pollen tubes were permitted to achieve fertilization. An F2 generation was then produced by depositing small loads of F1 pollen onto stigmas of F1 plants. The F2 seeds resulting from two generations of small pollen loads are termed the non-selected line because there was little or no selection for pollen-tube growth rate on these plants. The other half of the F1 and F2 seeds were produced by depositing large pollen loads (〉10 000 pollen grains) onto stigmas and then allowing only the first 1% or so of the pollen tubes that entered the ovary to fertilize the ovules. We did this by excising the styles at the ovary at 12–15 h after pollination. The resulting F2 seeds are termed ‘the selected line’ because they were produced by two generations of selection for only the fastest growing pollen tubes. Small pollen loads from the F2plants, both the selected and the non-selected lines, were then deposited onto stigmas of different C. pepo flowers, and the vigor of the resulting seeds was compared under greenhouse and field conditions. The results showed that the seeds fertilized by pollen from the selected line had greater vegetative vigor as seedlings and greater flower and fruit production as mature plants than the seeds fertilized by pollen from the non-selected line. This study demonstrates that selection for fast pollen-tube growth (selection on the microgametophyte) leads to a correlated increase in sporophyte (progeny) vigor.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00221902

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