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  • Springer  (48)
  • Wiley-Blackwell  (5)
  • Nature Publishing Group  (3)
  • 1995-1999  (45)
  • 1980-1984  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Microchimica acta 131 (1999), S. 57-64 
    ISSN: 1436-5073
    Keywords: Key words: dye-encapsulating liposomes; pH sensing; oxygen sensing; optochemical nanosensors.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract  This paper describes the optochemical pH and oxygen sensing properties of dye-encapsulating and fluorescently labeled nano-sized unilamellar liposomes. To prepare the oxygen sensitive liposomes a lipid mixture consisting of dimyristoylphospatidylcholine, cholesterol, and dihexadecyl phosphate (molar ratio 5:4:1) all dissolved in dry isopropyl alcohol is injected into a sensing dye solution. The mixture is then sonicated with a liposome maker to form dye-encapsulating liposomes. A lipid mixture consisting of dimyristoylphospatidylcholine, N-(fluorescein-5-thiocarbamoyl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine triethylammonium salt (fluorescein DHPE), cholesterol, and dihexadecyl phosphate (molar ratio 20:1:16:4) is used to prepare the pH sensitive liposomes by the same sonication technique. Fluorescein labeled DHPE phospholipids are combined with DMPC phospholipids in a 1:20 ratio to incorporate the sensing dye directly into the bilayer membrane, virtually eliminating any instability due to dye leakage. Oxygen sensing liposomes are created by encapsulating the oxygen sensitive ruthenium tris(1,10)-phenanthroline complex [Ru(phen)3]. The dye is believed to exist both in free solution within the liposome, and as an adherent on the inner membrane of the liposome. High uniformity of the liposomes is realized by extruding them back and forth through a 100 nm pore-size polycarbonate membrane. TEM images of the liposomes, stained with uranyl acetate, show that the liposomes are unilamellar, spherical in shape, maintain high structural integrity, and average 70 nm in diameter. The liposomes show high stability with respect to dye leaking at room temperature for 8 days, and high photostability when exposed to the excitation light. Individual liposomes are used to monitor the pH and oxygen level in their vicinity during the enzymatic oxidation of glucose by the enzyme glucose oxidase. The newly prepared environmentally sensitive liposomes can be applied for non-invasive pH and oxygen determination in tissues and single biological cells.
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  • 2
    Publication Date: 1999-06-24
    Print ISSN: 0026-3672
    Electronic ISSN: 1436-5073
    Topics: Chemistry and Pharmacology
    Published by Springer
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  • 3
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] We previously described a method for isolating murine hematopoietic stem cells capable of reconstituting lethally irradiated recipients, which depends solely on dual-wavelength flow cytometric analysis of murine bone marrow cells stained with the fluorescent DNA-binding dye Hoechst 33342. This ...
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 309 (1984), S. 150-151 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We worked in the sandy and rocky habitats of the Israeli arid zone. Sampling locations were chosen along a precipitation gradient. Rodents were sampled in four plots per location. Sampling was repeated for two seasons in the rocky habitat and four seasons in the sandy habitat. The desert locations ...
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A site-specifically modified, double-stranded deoxyoligo-nucleotide with the sequence d(CCTCTG*G*TCTCC)-d(GGA-GACCAGAGG), where G*G* represents the cw-[Pt(NH3)2-{d(GpG)-N7(G6),-N7(G7)}] intrastrand crosslink, was prepared and crystallized. The structure was solved by conventional multiple ...
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 14 (1982), S. 179-186 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The presence of thresholds for finite quark masses alters the behavior of the QCD coupling constant. While the alterations are small they can have significant influence on the determination of the scale parameter Λ. Part of the discrepancy between recent highQ 2 determinations of Λ and older lowQ 2 determinations can be attributed to charm and bottom thresholds. We present simple, analytic expressions for the mass dependence of α(Q 2) and exploit these to discuss Λ determinations, scale breaking and the phenomenon of temporary freedom when more than 17 quark flavors exist.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 47 (1980), S. 323-327 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Seed distribution (clump size) selection has been proposed as a possible mechanism of resource subdivision for competing heteromyid rodent species. To test this hypothesis, field experiments were conducted over two years during both richer and sparser seasons of the year. None of the predictions derived from the hypothesis were supported by our results. Though some selectivity was displayed by both Dipodomys spectabilis and D. merriami, the patterns of selectivity did not match the expected patterns. Our results further indicate that clump selection may be influenced by variables other than the density of seeds within a clump. These results have led us to conclude that clump size selection is unlikely to play a role in the coexistence of different species of the genus Dipodomys.
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  • 8
    ISSN: 1420-9098
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Resume Chez les Guêpes et les Frelons, les cellules sont hexagonales lorsqu'elles sont situées dans les zones centrales du rayon. Les cellules périphériques, comme toutes les cellules au début de leur construction, ont des parois arrondies plutôt que angulaires. La transformation d'une cellule en forme de gobelet, à parois arrondies, en une cellule hexagonale avec un angle de 120° entre les parois est partiellement due à des processus de transformation des parois cellulaires existantes au moment où de nouvelles parois leur sont attachées depuis le côté extérieur. Le développement de la construction des cellules initiales aboutit à 6 parois dans les rayons construits autour d'une seule cellule centrale ou à 5,5 parois lorsqui'il y a 2 cellules centrales contiguës. Cependant, dans les constructions ultérieures, ce type d'évolution des parois diminue graduellement à mesure que de nouveaux anneaux de cellules sont ajoutés, pour atteindre une valeur moyenne de 3 nouvelles parois par cellule, indépendamment du fait que le rayon s'est construit autour d'une ou de deux cellules centrales. Les résultats présentés dans cet article sur l'utilisation plus efficiente des parois dans les rayons plus grands apportent une confirmation du caractère économique de l'utilisation des matériaux dans la construction du rayon par les Vespinæ.
    Notes: Summary The individual cell in the hornet or wasp comb is hexagonal in cross-section when it is one of the inner “ring” of cells. On the other hand, peripheral cells, like all cells built initially, have rounded rather than angled walls. This transformation from a goblet-shaped cell with rounded walls to an hexagonally-walled cell with an angle of 120° between each two walls is partly acheived by additional processing of the existing cell walls as new walls (between old and new cells) are accreted onto them from the outside. The comb cells are essentially hexagonal so that the “expenditure” in the building of the initial cell(s) is either 6 walls (in combs built around a single central cell) or 5.5 walls (where there are two abutting, central cells). With subsequent building, however, this “wall expenditure” diminishes gradually as more rings of cells are laid down, approaching an average value of 3 new walls per cell regardless of whether the comb is built around one or rather two central cells. Presented data on more efficient wall utilization in the larger combs offer further confirmation of the frugality of comb construction by Vespinæ.
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  • 9
    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: 2 concentration and associated climate change on crop yields. Such model predictions are largely untested in the field, for lack of experimental data. We tested the CERES-Wheat model, modified to include leaf-level photosynthesis response to elevated CO2 using field data from 2 yr of Free-Air Carbon Dioxide Enrichment (FACE) experiments with spring wheat (Triticum aestivum L. cv. Yecora Rojo) in Maricopa, AZ. Two irrigation treatments (well-watered, WW; water-deficit stressed, WS) and two atmospheric CO2 concentrations (ambient, 350 μmol mol-1, elevated, 550 μmol mol-1) were simulated. The model was evaluated using measurements of crop phenology, aboveground dry matter (DM) production, grain yield, and evapotranspiration (ET). Model calculations of crop phenology were within 2 to 3 d of observed values under WW, ambient CO2 conditions in both years. The model did not simulate the accelerated crop phenology (5-8 d at physiological maturity) observed in the WW and elevated CO2 treatments, indicating the need to include effects of increased stomatal resistance on canopy temperature. Simulations of DM and grain yield were within 10% of measured values, except for a tendency to overcalculate DM response to CO2 by 10 to 15% in Year 1 for WS treatments. The model undercalculated cumulative ET under WW conditions by 15%; model sensitivity analyses suggest that simulation of potential evapotranspiration (PET) was too low for this arid site. The model reproduced measured dynamics of CO2-water interactions. Simulated reductions in water loss due to elevated CO2 were about 4%, in agreement with measurements. The model simulated larger increases in DM production and yield due to elevated CO2 under WS than under WW conditions. In Year 1, simulated crop response to CO2 was 2% larger (measured:3%) under WS than under WW conditions; in Year 2, it was 11% larger (measured: to be further evaluated with additional experimental datasets, is an important attribute of models used to project crop yields under elevated CO2 and climate change.
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  • 10
    ISSN: 1432-1041
    Keywords: Diltiazem ; sustained-release formulation ; pharmacokinetics ; bioavailability ; bioequivalence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract The usual dosage regimen of diltiazem (Tildiem) is 60 mg 3–4 times a day. A sustained-release formulation has been developed (Mono-Tildiem LP 300 mg) in order to allow a single daily administration. Two repeated dosing studies were performed in healthy volunteers. The absolute bioavailability of sustained-release diltiazem LP 300 mg was investigated using concomitant i.v. administration of 13C-labelled drug: absolute bioavailability of the “once a day” formulation was 35%. The second study compared sustained-release diltiazem LP 300 mg with the standard formulation of diltiazem. The results showed that the diltiazem plasma concentrations obtained after the LP formulation remained stable between 2 and 14 h after administration and were compatible with a once a day administration. Relative bioavailability of sustained-release diltiazem LP 300 mg was 79.3% compared with diltiazem. Therefore, a unitary dose of sustained-release diltiazem LP 300 mg was chosen as the dose equivalent to the daily dose administered with the standard diltiazem formulation.
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