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  • Life Sciences (General)  (121)
  • General Chemistry  (99)
  • 2010-2014
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  • 1995-1999  (220)
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  • 2010-2014
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  • 1
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    A model for the kinetics of homotypic cellular aggregation under static conditions (1997)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: We present the formulation and testing of a mathematical model for the kinetics of homotypic cellular aggregation. The model considers cellular aggregation under no-flow conditions as a two-step process. Individual cells and cell aggregates 1) move on the tissue culture surface and 2) collide with other cells (or aggregates). These collisions lead to the formation of intercellular bonds. The aggregation kinetics are described by a system of coupled, nonlinear ordinary differential equations, and the collision frequency kernel is derived by extending Smoluchowski's colloidal flocculation theory to cell migration and aggregation on a two-dimensional surface. Our results indicate that aggregation rates strongly depend upon the motility of cells and cell aggregates, the frequency of cell-cell collisions, and the strength of intercellular bonds. Model predictions agree well with data from homotypic lymphocyte aggregation experiments using Jurkat cells activated by 33B6, an antibody to the beta 1 integrin. Since cell migration speeds and all the other model parameters can be independently measured, the aggregation model provides a quantitative methodology by which we can accurately evaluate the adhesivity and aggregation behavior of cells.
    Schlagwort(e): Life Sciences (General)
    Materialart: Biophysical journal (ISSN 0006-3495); Volume 72; 1; 51-64
    Format: text
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  • 2
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    Biomaterials for tissue engineering: summary (1997)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: This article summarizes presentations and discussion at the workshop "Enabling Biomaterial Technology for Tissue Engineering," which was held during the Fifth World Biomaterials Congress in May 1996. Presentations covered the areas of material substrate architecture, barrier effects, and cellular response, including analysis of biomaterials challenges involved in producing specific tissue-engineered products.
    Schlagwort(e): Life Sciences (General)
    Materialart: Tissue engineering (ISSN 1076-3279); Volume 3; 1; 71-3; discussion 73-6
    Format: text
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  • 3
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    Mitochondrial gene arrangement of the horseshoe crab Limulus polyphemus L.: conservation of major features among arthropod classes (1997)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: Numerous complete mitochondrial DNA sequences have been determined for species within two arthropod groups, insects and crustaceans, but there are none for a third, the chelicerates. Most mitochondrial gene arrangements reported for crustaceans and insect species are identical or nearly identical to that of Drosophila yakuba. Sequences across 36 of the gene boundaries in the mitochondrial DNA (mtDNA) of a representative chelicerate. Limulus polyphemus L., also reveal an arrangement like that of Drosophila yakuba. Only the position of the tRNA(LEU)(UUR) gene differs; in Limulus it is between the genes for tRNA(LEU)(CUN) and ND1. This positioning is also found in onychophorans, mollusks, and annelids, but not in insects and crustaceans, and indicates that tRNA(LEU)(CUN)-tRNA(LEU)(UUR)-ND1 was the ancestral gene arrangement for these groups, as suggested earlier. There are no differences in the relative arrangements of protein-coding and ribosomal RNA genes between Limulus and Drosophila, and none have been observed within arthropods. The high degree of similarity of mitochondrial gene arrangements within arthropods is striking, since some taxa last shared a common ancestor before the Cambrian, and contrasts with the extensive mtDNA rearrangements occasionally observed within some other metazoan phyla (e.g., mollusks and nematodes).
    Schlagwort(e): Life Sciences (General)
    Materialart: Molecular biology and evolution (ISSN 0737-4038); Volume 14; 8; 867-74
    Format: text
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  • 4
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    Effect of 17 days of bed rest on peak isometric force and unloaded shortening velocity of human soleus fibers (1997)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The purpose of this study was to examine the effect of prolonged bed rest (BR) on the peak isometric force (P0) and unloaded shortening velocity (V0) of single Ca(2+)-activated muscle fibers. Soleus muscle biopsies were obtained from eight adult males before and after 17 days of 6 degrees head-down BR. Chemically permeabilized single fiber segments were mounted between a force transducer and position motor, activated with saturating levels of Ca2+, and subjected to slack length steps. V0 was determined by plotting the time for force redevelopment vs. the slack step distance. Gel electrophoresis revealed that 96% of the pre- and 87% of the post-BR fibers studied expressed only the slow type I myosin heavy chain isoform. Fibers with diameter 〉 100 microns made up only 14% of this post-BR type I population compared with 33% of the pre-BR type I population. Consequently, the post-BR type I fibers (n = 147) were, on average, 5% smaller in diameter than the pre-BR type I fibers (n = 218) and produced 13% less absolute P0. BR had no overall effect on P0 per fiber cross-sectional area (P0/CSA), even though half of the subjects displayed a decline of 9-12% in P0/CSA after BR. Type I fiber V0 increased by an average of 34% with BR. Although the ratio of myosin light chain 3 to myosin light chain 2 also rose with BR, there was no correlation between this ratio and V0 for either the pre- or post-BR fibers. In separate fibers obtained from the original biopsies, quantitative electron microscopy revealed a 20-24% decrease in thin filament density, with no change in thick filament density. These results raise the possibility that alterations in the geometric relationships between thin and thick filaments may be at least partially responsible for the elevated V0 of the post-BR type I fibers.
    Schlagwort(e): Life Sciences (General)
    Materialart: The American journal of physiology (ISSN 0002-9513); Volume 273; 5 Pt 1; C1690-9
    Format: text
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  • 5
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    Modulation of Radiation-Induced Apoptosis by Thiolamines (1997)
    In:  Other Sources
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    Publikationsdatum: 2019-08-15
    Beschreibung: Exposure to the thiolamine radioprotector N-(2-mercaptoethyl)-1,3-propanediamine (WR-1065) induced apoptosis in the mouse TB8-3 hybridoma after 60-minute (LD(sub50) = 4.5mM) or during a 20-hour (LD(sub50) = 0.15 mM) exposure. In contrast, a 20-hour exposure to 17 mM L-cysteine or 10 mM cysteamine was required to induce 50 percent apoptosis within 20 hours. Apoptosis was not induced by either a 60-minute or 20-hour exposure to 10 mM of the thiazolidime prodrugs ribose-cysteine (RibCys) or ribose-cysteamine (RibCyst). Thiolamine-induced apoptosis appeared to be a p53-independent process since it was induced by WR-1065 exposure in human HL60 cells. Exposure to WR-1065 (4mM for 15 minutes) or cysteine (10mM for 60 minutes) before and during irradiation protected cells against the induction of both DNA double-strand breaks and apoptosis, while exposure to RibCys (10 mM for 3 hours) did not. Treatment with either WR-1065, cysteine, RibCys or RibCyst for 60 minutes beginning 60 minutes after irradiation did not affect the level of radiation-induced apoptosis. In contrast, treatment with either cysteine, cysteamine or RibCys for 20 hours beginning 60 minutes after irradiation enhanced radiation-induced apoptosis. Similar experiments could not be conducted with WR-1065 because of its extreme toxicity. Our results indicate that thiolamine enhancement of radiation-induced apoptosis is not involved in their previously reported capacity to reduce radiation-induced mutations.
    Schlagwort(e): Life Sciences (General)
    Materialart: International Journal of Radiation Biology (ISSN 0955-3002); 72; 4; 439-448
    Format: text
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  • 6
    Digitale Medien
    Digitale Medien
    [(TptBu, Me)CrR]: A New Class of Mononuclear, Coordinatively Unsaturated Chromium(II) Alkyls with cis-Divacant Octahedral Structure (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1668-1674 
    Details
    ISSN: 0947-6539
    Schlagwort(e): alkenes ; chromium ; cis-divacant octahedral geometry ; polymerizations ; tris(pyrazolyl)borate complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reaction of CrCl2 with TptBu, MeK yielded [TptBu, MeCr(3-tBu, 5-MepzH)Cl] (1) and [TptBu, MeCrCl] (2), while the same reaction in the presence of pyridine gave 1 and [TptBu, MeCr(py)Cl] (3). Alkylation of 3 with Grignard reagents produced the chromium(II) alkyls [TptBu, MeCrR] (4, R = Et; 5, R = Ph; 6, R = CH2SiMe3), which reversibly added to pyridine to form the five-coordinate adducts [TptBu, MeCr(py)R] (7, R = Et; 8, R = Ph; 9, R = CH2SiMe3). 1, 2, 4, and 5 were structurally characterized by X-ray diffraction. The four-coordinate molecules 2, 4, and 5 adopt a highly unusual cis-divacant octahedral coordination geometry, while 1 is the first five-coordinate TptBu, Me-complex of a first-row transition metal. Despite their coordinative unsaturation, chromium alkyls 4-6 do not polymerize ethylene, or even react with it. This observation is inconsistent with the catalytic activity commonly ascribed to divalent chromium in heterogeneous polymerization catalysts. Attempts to oxidize 4-6 (e.g., with [Cp2Fe]BPh4) to cationic chromium(II) alkyls failed, yielding [TptBu, MeCr(thf)][BPh4] (10) instead.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031016
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  • 7
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    Gramicidin S production by Bacillus brevis in simulated microgravity (1997)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: In a continuing study of microbial secondary metabolism in simulated microgravity, we have examined gramicidin S (GS) production by Bacillus brevis strain Nagano in NASA High Aspect Rotating Vessels (HARVs), which are designed to simulate some aspects of microgravity. Growth and GS production were found to occur under simulated microgravity. When performance under simulated microgravity was compared with that under normal gravity conditions in the bioreactors, GS production was found to be unaffected by simulated microgravity. The repressive effect of glycerol in flask fermentations was not observed in the HARV. Thus the negative effect of glycerol on specific GS formation is dependent on shear and/or vessel geometry, not gravity.
    Schlagwort(e): Life Sciences (General)
    Materialart: Current microbiology (ISSN 0343-8651); Volume 34; 4; 199-204
    Format: text
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  • 8
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    Evaluation of cardiac rhythm disturbances during extravehicular activity (1997)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: This study represents the first systematic evaluation of dysrhythmias before, during, and after spaceflight including extravehicular activity (EVA). The data, based on 7 Shuttle crew members, revealed a nonsignificant decrease in ventricular and supraventricular ectopy during EVA, suggesting that the incidence of dysrhythmias is no greater during EVA than with any other phase of a mission or preflight.
    Schlagwort(e): Life Sciences (General)
    Materialart: The American journal of cardiology (ISSN 0002-9149); Volume 79; 8; 1153-5
    Format: text
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  • 9
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    NMR of laser-polarized 129Xe in blood foam (1997)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: Laser-polarized 129Xe dissolved in a foam preparation of fresh human blood was investigated. The NMR signal of 129Xe dissolved in blood was enhanced by creating a foam in which the dissolved 129Xe exchanged with a large reservoir of gaseous laser-polarized 129Xe. The dissolved 129Xe T1 in this system was found to be significantly shorter in oxygenated blood than in deoxygenated blood. The T1 of 129Xe dissolved in oxygenated blood foam was found to be approximately 21 (+/-5) s, and in deoxygenated blood foam to be greater than 40 s. To understand the oxygenation trend, T1 measurements were also made on plasma and hemoglobin foam preparations. The measurement technique using a foam gas-liquid exchange interface may also be useful for studying foam coarsening and other liquid physical properties.
    Schlagwort(e): Life Sciences (General)
    Materialart: Journal of magnetic resonance (San Diego, Calif. : 1997) (ISSN 1090-7807); Volume 126; 1; 79-86
    Format: text
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  • 10
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    Cellular effects of individual high-linear energy transfer particles and implications for tissue response at low doses (1997)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The energy deposition patterns produced by the radiation environment in space can be quite different from those in conventional radiation environments. Furthermore, conventional radiation biological experiments, using randomly distributed particle tracks, cannot access some variables which may be important in determining the health effects of irradiation. Controlled microbeam irradiation provides the means to investigate the effects and unique energy deposition patterns and cell environment for a variety of end points.
    Schlagwort(e): Life Sciences (General)
    Materialart: Radiation research (ISSN 0033-7587); Volume 148; 5 Suppl; S108-14
    Format: text
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