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11

Digitale Medien

Analysis of a swallow homologue from Drosophila pseudoobscura (2000)

Huang, Z. ; Pokrywka, N. J. ; Yoder, J. H. ; [weitere]

Springer

Development genes and evolution 210 (2000), S. 157-161

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ISSN: 1432-041X

Schlagwort(e): Key words Swallow ; bicoid ; Drosophila ; mRNA localization ; Oogenesis ; Embryogenesis

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract We analyzed a functional homologue of the swallow gene from Drosophila pseudoobscura. The swallow gene of D. melanogaster plays an essential role in localizing bicoid mRNA in oocytes, and swallow mutant embryos show anterior pattern defects that result from the lack of localization of the bicoid morphogen. The pseudoobscura homologue rescues the function of swallow mutants when introduced into the genome of D. melanogaster, and its expression is similar to that of the melanogaster gene. The predicted pseudoobscura and melanogaster proteins are 49% identical and 69% conserved. The coiled-coil domain previously identified in the melanogaster swallow protein is strongly conserved in the pseudoobscura homologue, but the weak similarity of the melanogaster swallow protein to the RNP class of RNA-binding proteins is not conserved in the pseudoobscura homologue. These and other observations suggest a structural role for swallow in localizing bicoid mRNA, perhaps as part of the egg cytoskeleton.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s004270050023

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12

Digitale Medien

Isolation and some properties of a mammalian ribosomal DNA (1976)

Blin, Nikolaus ; Stephenson, Edwin C. ; Stafford, Darrel W.

Springer

Chromosoma 58 (1976), S. 41-50

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ISSN: 1432-0886

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Medizin

Notizen: Abstract The DNA coding for 28 S and 18 S ribosomal RNA, including the spacer regions, has been isolated from calf (Bos taurus) thymus gland. The method used included shearing of the total DNA to a highly homogeneous size population, selective heat denaturation and S 1 nuclease treatment to remove single stranded DNA. Repeated centrifugation on density gradients yields a 140-fold purified rDNA fraction with a GC content of 61.2%. Eco RI nuclease cleaves this DNA into two fragments of 16.4 and 4.9×106 daltons. Hybridization of these fragments with 28 S and 18 S rRNA shows that the 28 S coding sequence is located mostly on the 4.9×106 dalton fragment, while both the 16.4 and 4.9×106 dalton fragments contain the 18 S sequence. The data indicate that the ribosomal RNA gene has a repeat unit of 21.3×106 daltons which includes a nontranscribed spacer of about 12.5×106 daltons.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00293439

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13

Digitale Medien

The porosity dependence of flexural modulus and strength for capsule-free hot isostatically pressed porous alumina (2000)

Kwan, Y. B. P. ; Stephenson, D. J. ; Alcock, J. R.

Springer

Journal of materials science 35 (2000), S. 1205-1211

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ISSN: 1573-4803

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau

Notizen: Abstract Structural properties such as flexural moduli and strength have been measured for a range of porous alumina specimens of different initial powder sizes and final porosities, sintered using the capsule-free hot isostatic pressing method. This processing method produces a porous body in which the closed porosity is negligible. The relationship of these structural properties to total porosity has been investigated. The results indicate that both a power and an exponential function could adequately describe the porosity dependence of flexural strength. The strength values obtained were test method dependent, and were significantly lower for specimens with sintering aids. A power law model based on a critical porosity, as proposed by Phani, gave the best fit for the modulus measurement data. No dependence of mechanical properties on particle size was observed. The strength measurement results did not appear to support suggestions that better strength could be obtained by the capsule-free hot isostatic pressing method than conventional sintering, as reported elsewhere.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1004792605528

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14

Digitale Medien

Characterization of replication-defective transforming RNA tumor viruses by in vitro translation (1979)

Deobagkar, D. N. ; Ven, W. J. M. ; Khan, A. S. ; [weitere]

Springer

Molecular biology reports 5 (1979), S. 115-120

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ISSN: 1573-4978

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00777497

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15

Digitale Medien

A mathematical model of proximal tubule absorption (1979)

Huss, Ronald E. ; Stephenson, John L.

Springer

The journal of membrane biology 47 (1979), S. 377-399

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ISSN: 1432-1424

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Chemie und Pharmazie

Notizen: Summary A previous model of the mechanisms of flow through epithelia was modified and extended to include hydrostatic and osmotic pressures in the cells and in the peritubular capillaries. The differential equations for flow and concentration in each region of the proximal tubule were derived. The equations were solved numerically by a finite difference method. The principal conclusions are: (i) Cell NaCl concentration remains essentially isotonic over the pressure variations considered; (ii) channel NaCl concentration varies only a few mosmol from isotonicity, and the hydrostatic and osmotic pressure differences across the cell wall are of the same order of magnitude; (iii) both reabsorbate osmolality and pressure-induced flow are relatively insensitive to the geometry of the system; (iv) a strong equilibrating mechanism exists in the sensitivity of the reabsorbate osmolality to luminal osmolality; this mechanism is far more significant than any other parameter change.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01869745

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16

Digitale Medien

The effect of irrigation on damage to potato tubers by slugs (1965)

Stephenson, J. W.

Springer

Potato research 8 (1965), S. 145-149

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ISSN: 1871-4528

Quelle: Springer Online Journal Archives 1860-2000

Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Beschreibung / Inhaltsverzeichnis: Zusammenfassung Zwei Kartoffelsorten,Redskin undMajestic, wurden unter vier verschiedenen Bewässerungsverfahren kultiviert: 1. Keine Bewässerung. 2. Bewässerung vor der Knollenbildung; 3. Bewässerung nach der Knollenbildung; 4. Bewässerung während der Wachstumsperiode der Pflanzen. Beide Sorten erlitten den gr\:ossten Schaden durch die NacktschneekenMilax budapestensis(Hazay) undArion hortensis F\'er, wenn die Pflanzen bew\:assert wurden (Tabelle 1). Die Knollen der SorteRedskin waren st\:arker besch\:adigt als jene der SorteMajestic (Tabelle 2). Eine gr\:ossere Anzahl vonRedskin-Knollen wiesen mehr als zwei L\:ocher auf. Die Zeit der Anpflanzung beeinflusste das Ausmass des Schadens bei keiner Sorte in grossem Masse (Tabelle 3). Es wird auf m\:ogliche Erkl\:arungen f\:ur diese Unterschiede hingewiesen. Der Ertrag an unbesch\:adigten Knollen wurde durch die Bew\:asserung erh\:oht, obwohl der Schaden durch die Nacktschnecken ebenfalls zunahm (Tabelle 4). In dieser Hinsicht hatteMajestic mehr Nutzen von der Bew\:asserung alsRedskin.

Kurzfassung: Résumé On a fait pousser deux variétés de Pomme de terre,Redskin etMajestic, dans quatre régimes différents d'alimentation en eau: 1. pas d'irrigation; 2. irrigation avant la formation des tubercules; 3. irrigation après la formation des tubercules; 4. irrigation pendant la période de croissance des plantes. Les limacesMilax budapestensis (Hazay) etArion hortensis Fér. causaient les plus grands dommages aux deux variétés quand les plantes étaient irriguées (Tableau 1). La variétéRedskin était plus sévèrement endommagée queMajestic (Tableau 2). Les tuberculesRedskin avaient la plus grande proportion de tubercules avec plus de deux cavités. Le moment de la plantation était sans importance pour les deux variétés (Tableau 3). L'auteur avance des explications à ropos dep ces différences. L'irrigation augmente la production de tubercules non endommagés même quand elle augmente les dégâts de limaces (Tableau 4). Sousce rapport la variétéMajestic plus que la variétéRedskin profitait de l'irrigation.

Notizen: Summary Two varieties of potato,Redskin andMajestic, were grown with four water regimes;-unirrigated, irrigated before tuber formation, irrigated after tuber formation, and irrigated throughout the growing season. The damage done by slugs and the yields were measured. Both varieties suffered most damage from slugs when irrigated after the tubers started to form. MoreRedskin tubers were damaged thanMajestic and a greater proportion had more than two holes. Possible explanation for these differences are suggested. Yields of undamaged tubers were increased by irrigation even though damage by slugs increased. In this respectMajestic benefitted more thanRedskin from irrigation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF02390584

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17

Digitale Medien

Intracellular calcium during fatigue of cane toad skeletal muscle in the absence of glucose (2000)

Kabbara, A. A. ; Nguyen, L. T. ; Stephenson, G. M. M. ; [weitere]

Springer

Journal of muscle research and cell motility 21 (2000), S. 481-489

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ISSN: 1573-2657

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Medizin

Notizen: Abstract Mechanisms of fatigue were studied in single muscle fibres of the cane toad (Bufo marinus) in which force, intracellular calcium ([Ca2+]i), [Mg2+]i, glycogen and the rapidly releasable Ca2+ from the sarcoplasmic reticulum (SR) were measured. Fatigue was produced by repeated tetani continued until force had fallen to 50%. Two patterns of fatigue in the absence of glucose were studied. In the first fatigue run force fell to 50% in 8–10 min. Fatigue runs were then repeated until force fell to 50% in 〈3 min in the final fatigue run. Addition of extracellular glucose after the final fatigue run prolonged a subsequent fatigue run. In the first fatigue run peak tetanic [Ca2+]i initially increased and then declined and at the time when force had fallen to 50% tetanic [Ca2+]i was 54 ± 5% of initial value. In the final fatigue run force and peak tetanic [Ca2+]i declined more rapidly but to the same level as in first fatigue runs. At the end of the first fatigue run, the rapidly releasable SR Ca2+ store fell to 46 ± 6% of the pre-fatigue value. At the end of the final fatigue run the rapidly releasable SR Ca2+ store was 109 ± 16% of the pre-fatigue value. In unstimulated fibres the nonwashable glycogen content was 176 ± 30 mmol glycosyl units/l fibre. After one fatigue run the glycogen content was 117 ± 17 mmol glycosyl units/l fibre; at the end of the final fatigue run the glycogen content was reduced to 85 ± 9 mmol glycosyl units/l fibre. [Mg2+]i did not change significantly at the end of fatigue in either the first or the final fatigue run suggesting that globally-averaged ATP does not decline substantially in either pattern of fatigue. These results suggest that different mechanisms are involved in the decline of tetanic [Ca2+]i in first compared to final fatigue runs. The SR Ca2+ store is reduced in first fatigue runs; this is not the case for the final fatigue run which is associated with a decline in glycogen and possibly related to either a non-metabolic effect of glycogen or a spatially-localised metabolic decline.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1005650425513

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18

Digitale Medien

Glycogen stability and glycogen phosphorylase activities in isolated skeletal muscles from rat and toad (2000)

Goodman, Craig A. ; Stephenson, Gabriela M. M.

Springer

Journal of muscle research and cell motility 21 (2000), S. 655-662

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ISSN: 1573-2657

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Medizin

Notizen: Abstract There is increasing evidence that endogenous glycogen depletion may affect excitation–contraction (E–C) coupling events in vertebrate skeletal muscle. One approach employed in physiological investigations of E–C coupling involves the use of mechanically skinned, single fibre preparations obtained from tissues stored under paraffin oil, at room temperature (RT: 20–24°C) and 4°C for several hours. In the present study, we examined the effect of these storage conditions on the glycogen content in three muscles frequently used in research on E–C coupling: rat extensor digitorum longus (EDL) and soleus (SOL) and toad iliofibularis (IF). Glycogen content was determined fluorometrically in homogenates prepared from whole muscles, stored under paraffin oil for up to 6 h at RT or 4°C. Control muscles and muscles stored for 0.5 and 6 h were also analysed for total phosphorylase (Phostotal) and phosphorylase a (Phos a) activities. No significant change was observed in the glycogen content of EDL and SOL muscles stored at RT for 0.5 h. In rat muscles stored at RT for longer than 0.5 h, the glycogen content decreased to 67.6% (EDL) and 78.7% (SOL) of controls after 3 h and 25.3% (EDL) and 37.4% (SOL) after 6 h. Rat muscles stored at 4°C retained 79.0% (EDL) and 92.5% (SOL) of glycogen after 3 h and 75.2% (EDL) and 61.1% (SOL) after 6 h. The glycogen content of IF muscles stored at RT or 4°C for 6 h was not significantly different from controls. Phostotal was unchanged in all muscles over the 6 h period, at both temperatures. Phos a was also unchanged in the toad IF muscles, but in rat muscles it decreased rapidly, particularly in EDL (4.1-fold after 0.5 h at RT). Taken together these results indicate that storage under paraffin oil for up to 6 h at RT or 4°C is accompanied by minimal glycogen loss in toad IF muscles and by a time- and temperature-dependent glycogen loss in EDL and SOL muscles of the rat.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1005628500892

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19

Digitale Medien

The spike-strain test for polymeric liquids and its relevance for irreversible destruction of network connectivity by deformation (1979)

Wagner, M. H. ; Stephenson, S. E.

Springer

Rheologica acta 18 (1979), S. 463-468

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ISSN: 1435-1528

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Physik

Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die Grundannahmen derLodgeschen Theorie der gummiartigen Flüssigkeit werden zusammengefaßt. Zwei weitere Annahmen sind notwendig, wenn man das Scher- und Dehnverhalten von Polymerschmelzen und konzentrierten Polymerlösungen bei finiten Deformationen beschreiben will: (1) die Annahme der Zerstörung des temporären Netzwerkes polymerer Flüssigkeiten mit zunehmender Deformation und (2) die Annahme, daß diese Zerstörung ein irreversibler Vorgang ist. Hier wird ein neuer Versuch, der sogenannte „Spike-Strain-Test“, vorgeschlagen. Damit ist es möglich, die Annahme einer irreversiblen Zerstörung des temporären Netzwerkes polymerer Flüssigkeiten mit zunehmender Deformation zu überprüfen. Die Bedeutung dieses Experimentes für eine größere Klasse von rheologischen Zustandsgleichungen wird diskutiert.

Notizen: Summary The basic assumptions ofLodge's rubberlike-liquid constitutive equation for polymer melts and concentrated solutions are summarized. By two additional assumptions — (i) the network disentanglement assumption and (ii) the irreversibility assumption — a modified rubberlike-liquid constitutive equation is obtained, which has been shown to be a valid description of material behaviour in shear and elongational flow. In this paper a novel test — the spikestrain test — is proposed. On the basis of this experiment the assumption of irreversible destruction of network connectivity by deformation can be examined. The significance of the spike-strain test for a larger class of constitutive equations is discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01736952

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20

Digitale Medien

A dynamical model for gravitation (1976)

Stephenson, L. M.

Springer

Foundations of physics 6 (1976), S. 143-155

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ISSN: 1572-9516

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract A gravitational model is proposed that relates the terrestrially measured value of the gravitational constantG directly to the density and angular velocity of the galaxy. The model indicates a constant scalar value forG within most regions of our galaxy, but predicts thatG will be different in other galaxies and zero in intergalactic space. The model offers explanations for galactic cluster stability, discrepancies in terrestrial measurements ofG, and atomic particle stability. The model also provides a causal relationship between strong, electromagnetic, weak, and gravitational interactions. The two postulates required for the proposed model reduce to two assumptions made in GRT in regions whereG is constant; these postulates are consistent with the existence of a 2.7 K blackbody background radiation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00708956

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