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  • Articles  (96)
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  • 36.40  (59)
  • cell culture  (37)
  • Springer  (96)
  • Annual Reviews
  • 1990-1994  (96)
  • 1980-1984
  • 1991  (96)
  • 1
    Electronic Resource
    Electronic Resource
    Coherent raman spectroscopy of nitrogen molecules and clusters in supersonic jets (1991)
    Springer
    Applied physics 52 (1991), S. 84-89 
    Details
    ISSN: 1432-0649
    Keywords: 36.40 ; 42.65 ; 47.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Coherent Stokes and anti-Stokes Raman scattering CSRS and CARS have been employed to study the spectroscopy of nitrogen molecules and clusters in the expansion of a supersonic jet. In the vibrational spectrum, at strong stagnation conditions, an intense redshifted peak is observed which can be assigned to the intramolecular vibrations in large N2 clusters having adopted the β-phase structure. Another weak feature is assigned to nitrogen clusters in the α-phase. In the rotational region of the spectrum only monomer features have been observed. The failing to observe librational motions is consistent with the finding that the nitrogen clusters are predominantly in the orientationally unordered β-phase. The low rotational temperature suggests supercooling of the β-phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357660
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  • 2
    Electronic Resource
    Electronic Resource
    Laser-fluorescence diagnostics for condensation in laser-ablated copper plasmas (1991)
    Springer
    Applied physics 53 (1991), S. 353-361 
    Details
    ISSN: 1432-0649
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We are investigating the thermodynamic conditions under which condensation occurs in laser ablated copper plasma plumes. The plasma is created by XeCl excimer laser ablation (308 nm, 300 mJ/pulse) at power densities from 500–1000 MW/cm2 into backing pressures of helium in the range 0–50 torr. We use laser-induced fluorescence (LIF) to probe velocity and relative density of both atomic copper and the copper dimer molecule, Cu2, which is formed during condensation onset. At low pressure (10 mtorr), the atomic Cu velocity peaks at approximately 2×106 cm/s. Copper dimer time-of-flight data suggest that condensation onset occurs after the Cu atoms have slowed very significantly. Excitation scans of the Cu2A-X (0,0) and (1,1) bands yield a rotational and vibrational temperature in the neighborhood of 300 K for all conditions studied. Such low temperatures support the theory that Cu2 is formed under thermally and translationally cold conditions. Direct laser beam absorption is used to determine the number density of atomic copper. Typical densities attained with 5 torr of helium backing gas are 6–8×1013 cm−3. Rayleigh scattering from particulate is easily observable under conditions favorable to particulate production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00331827
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  • 3
    Electronic Resource
    Electronic Resource
    Toxicity of the mycotoxins fumonisins B1 and B2 and Alternaria alternata f. sp. lycopersici toxin (AAL) in cultured mammalian cells (1991)
    Springer
    Mycopathologia 116 (1991), S. 97-104 
    Details
    ISSN: 1573-0832
    Keywords: Fumonisin B1 ; fumonisin B2 ; AAL toxin ; T-2 toxin ; mycotoxin ; Fusarium moniliforme ; bioassay ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Fumonisins B1 and B2 and AAL toxin are a series of structurally related mycotoxins. Fumonisins B1 and B2, produced by Fusarium moniliforme Sheldon induce toxic hepatitis and hepatomas in rats and leukoencephalomalacia in horses. The cancer-promotion assay which has been used to guide their purification is slow and consumes large amounts of sample. We have examined a series of cultured mammalian cell lines in order to develop a more rapid and sensitive bioassay system, which may be useful for examining structure-activity relationships and the mechanism(s) of action of these toxins. Of 9 rat hepatoma cell lines tested, all except the two most de-differentiated lines were sensitive to the three toxins, with a toxic response visible by 48 h. Approximate IC50 values for the most sensitive hepatoma line, H4TG, were 4, 2 and 10 μg/ml for fumonisins B1, B2 and AAL toxin, respectively „in 100 μl cultures. Among 15 cell lines from other sources, only MDCK dog kidney epithelial cells were sensitive (IC50 = 2.5, 2 and 5 μg/ml, respectively). Studies in co-cultures of sensitive and insensitive cell lines and in cultures of a sensitive cell line over a range of cell densities indicated that cytotoxicity of fumonisins B1 and B2 does not involve metabolite activation to a derivative stable enough to diffuse to adjacent cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00436371
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  • 4
    Electronic Resource
    Electronic Resource
    Modified culture method for human corneal epithelial cells (1991)
    Springer
    Methods in cell science 13 (1991), S. 45-48 
    Details
    ISSN: 1573-0603
    Keywords: cell culture ; corneal epithelium ; primary explant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An improved procedure for the primary culture of pure human corneal epithelial cells from corneal explants is described. Confluent monolayers of epithelial cells can be consistently produced from small segments of donor corneas regardless of donor age and without feeder layers. Incubating segments on collagen at the air-liquid interface significantly improves the yield of cells per cornea and shortens cell migration time as compared to culturing on plastic. Fibroblast contamination is eliminated by serum-free medium and confirmed by indirect immunofluorescent staining for keratin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02388203
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  • 5
    Electronic Resource
    Electronic Resource
    Culture of human renal cortex epithelial cells (1991)
    Springer
    Methods in cell science 13 (1991), S. 143-147 
    Details
    ISSN: 1573-0603
    Keywords: kidney ; renal cortex ; proximal tubule ; enzymatic dissociation ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A procedure is described for the establishment and propagation of epithelial cell rich cultures derived from normal human kidney cortex (NHK-C cells). Cells are harvested from tissue fragments of donor human kidney by progressive enzymatic dissociation. NHK-C cultures are morphologically heterogeneous but exhibit, predominantly, the functional characteristics of cells of the kidney proximal tubule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02388118
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  • 6
    Electronic Resource
    Electronic Resource
    Cluster emission under ion bombardment of metallic targets (1991)
    Springer
    Applied physics 52 (1991), S. 213-217 
    Details
    ISSN: 1432-0630
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Mass spectroscopic studies of the neutral particles sputtered by Ar+ ions at 8 keV from polycrystaline samples have been performed, using non-resonant laser ionization and subsequent time-of-flight mass spectroscopy. Besides sputtered atoms, also dimer and trimer contributions in the order of 10−1 to 10−2 and 10−3 to 10−4, respectively, are found in the sputtered flux. The data obtained here together with previously published data by other groups for different bombarding energies provide strong support for the validity of the recombination model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00324422
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  • 7
    Electronic Resource
    Electronic Resource
    Laser-stimulated desorption of potassium atoms (1991)
    Springer
    Applied physics 52 (1991), S. 445-447 
    Details
    ISSN: 1432-0630
    Keywords: 82.65 ; 36.40 ; 73.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Desorption of K atoms by laser-excitation of surface plasmons in small K particles is reported. The desorption rate has been measured for different laser wavelengths and particle sizes. Time-of-flight measurements reveal a kinetic energy of the desorbed atoms of Ekin=0.13(3) eV. From the experimental data it is concluded that the desorption mechanism is non-thermal in nature. Comparison of the results reported here with our earlier work on Na desorption is made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323657
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of low nitrate and high sugar concentrations on anthocyanin content and composition of grape (Vitis vinifera L.) cell suspension (1991)
    Springer
    Plant cell reports 9 (1991), S. 500-504 
    Details
    ISSN: 1432-203X
    Keywords: anthocyanin ; cell culture ; nitrate ; sucrose ; Vitis vinifera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In pigmented cells of Vitis vinifera suspension cultures, best accumulation of anthocyanins was obtained when nitrate concentration was reduced from 25 mM to 6.25 mM and when sucrose concentration was increased from 88 mM to 132 mM. Under such conditions growth was greatly decreased. However, cell viability was maintained. The increases in anthocyanins in pigmented cells were due largely to increases in peonidin — glucoside. The high sucrose and the low nitrate concentrations can be one of the important culture factors in controlling of anthocyanin production by cell cultures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232105
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  • 9
    Electronic Resource
    Electronic Resource
    A mechanism for the loss of cytochrome P-450 in primary mouse hepatocytes (1991)
    Springer
    Molecular and cellular biochemistry 108 (1991), S. 151-156 
    Details
    ISSN: 1573-4919
    Keywords: cytochrome P-450 ; mitochondria ; heme ; hepatocytes ; mitochondrial DNA ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This study examined various biochemical parameters such as mitochondria and mitochondrial DNA (mtDNA), total heme and cyto P450 content in fresh hepatocytes and dedifferentiated hepatocytes. These parameters were chosen in order to understand the dramatic decrease in drug metabolism in cultured hepatocytes. The data in this study shows a temporal decrease in cytochrome P450, total heme and also a decrease in mitochondria. Also, the ratio of mtDNA content to mitochondrial density was found to increase as hepatocytes underwent dedifferentiation. Stereological analysis of cell preparations provided a measure of mitochondrial density per cell area and mtDNA content was assessed by the use of a specific radiolabelled probe. This study demonstrates that a loss of the organelle which is partially responsible for synthesis of heme correlates with a decrease in cytochrome P450.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00233120
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  • 10
    Electronic Resource
    Electronic Resource
    Adrenergic hormones and control of cardiac myocyte growth (1991)
    Springer
    Molecular and cellular biochemistry 104 (1991), S. 35-43 
    Details
    ISSN: 1573-4919
    Keywords: α1-adrenergic receptors ; β-adrenergic receptors ; cardiac muscle ; cell culture ; gene expression ; protein kinase C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The molecular mechanisms of cardiac myocyte growth are relevant to important problems in cardiovascular disease. A cell culture model has been developed to explore the role of adrenergic hormones in cardiac myocyte growth and gene expression. Activation of a cardiac myocyte α1-adrenergic receptor by catecholamines induces hypertrophic growth of neonatal rat cardiac myocytes and initiates selective increases in contractile protein gene transcription. These effects on growth and gene expression do not depend on contractile activity. The cardiac myocytes contain at least two subtypes of α1-adrenergic receptors and at least three isoforms of protein kinase C (PKC). A distinct α1 receptor subtype may mediate hypertrophy and gene transcription. Different isoforms of PKC are translocated to different intracellular sites on activation, and there is evidence that the β-PKC isoform may be an element in the signal transduction pathway from an α1 receptor at the surface to the cardiac myocyte nucleus. Growth regulation through a β-adrenergic receptor can also be demonstrated in the culture model. The growth response mediated through a β-adrenergic receptor differs in several respects from that transduced through an al adrenergic receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229801
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  • 11
    Electronic Resource
    Electronic Resource
    Sequence analysis of a chalcone isomerase cDNA of Phaseolus vulgaris L. (1991)
    Springer
    Plant molecular biology 16 (1991), S. 167-169 
    Details
    ISSN: 1573-5028
    Keywords: Phaseolus vulgaris ; cell culture ; chalcone isomerase ; elicitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00017927
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  • 12
    Electronic Resource
    Electronic Resource
    Molecular cloning of a cDNA from Lupinus polyphyllus cell cultures encoding a ribosomal protein (rps16) (1991)
    Springer
    Plant molecular biology 16 (1991), S. 739-740 
    Details
    ISSN: 1573-5028
    Keywords: Lupinus polyphyllus ; cell culture ; cDNA clone ; ribosomal protein ; rps 16
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00023439
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  • 13
    Electronic Resource
    Electronic Resource
    Expression and stability of amplified genes encoding 5-enolpyruvylshikimate-3-phosphate synthase in glyphosate-tolerant tobacco cells (1991)
    Springer
    Plant molecular biology 17 (1991), S. 1127-1138 
    Details
    ISSN: 1573-5028
    Keywords: tobacco ; 5-enolpyruvylshikimate-3-phosphate synthase ; cDNA clone ; gene expression ; gene amplification ; glyphosate ; cell culture ; tolerance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two distinct cDNAs for 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) were obtained from a glyphosate-tolerant tobacco cell line. The cDNAs were 89% identical and the predicted sequences of the mature proteins were greater than 83% identical with EPSPS proteins from other plants. Tobacco EPSPS proteins were more similar to those from tomato and petunia than Arabidopsis. One cDNA clone, EPSPS-1, represented a gene that was amplified in glyphosate-tolerant cells, while the gene for EPSPS-2 was unaltered in these cells. Consequently, EPSPS-1 mRNA was more abundant in tolerant than unselected cells, whereas EPSPS-2 mRNA was at relatively constant levels in these cell lines. Exposure of unselected cells and tobacco leaves to glyphosate produced a transient increase in EPSPS mRNA. However, glyphosate-tolerant cells containing amplified copies of EPSPS genes did not show a similar response following exposure to glyphosate. A significant proportion of the EPSPS gene amplification was maintained when tolerant cells were grown in the absence of glyphosate for eight months. Plants regenerated from these cells also contained amplified EPSPS genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00028730
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  • 14
    Electronic Resource
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    Studies of serum-free medium for the generation of lymphokine-activated killer cells (1991)
    Springer
    Cytotechnology 6 (1991), S. 39-47 
    Details
    ISSN: 1573-0778
    Keywords: cell culture ; lymphocyte ; lymphokine-activated killer cell ; recombinant interleukin 2 ; serum-free medium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We examined a serum-free medium (designated as TYI 101) for the generation of lymphokine-activated killer (LAK) cells from human lymphocytes, regional lymph node lymphocytes (RLNL) and peripheral blood lymphocytes (PBL). TYI 101 medium consisted of, in addition to nutrient mixture, transferrin, insulin, fetuin, sodium selenite, 2-mercaptoethanol, o-phosphorylethanolamine, chick egg yolk and porcine kidney extract. These hormones were effective for supporting RLNL proliferation as assessed by (3H)-thymidine uptake. When human lymphocytes from two different sources were cultivated with recombinant interleukin 2 (rIL-2) in TYI 101 medium, LAK activity was generated. In cultures of PBL from a healthy donor, LAK cells were generated in TYI 101 medium as efficiently as in RPMI 1640 medium supplemented with 10% human AB-type serum (RPMI-AB). In cultures of RLNL from lung cancer patients, LAK activity obtained in TYI 101 medium was about sixty-five percent of that in RPMI-AB. However, the addition of a small amount of AB-type serum improved the generation of LAK activity, LAK cell expansion, and cell viability in TYI 101 medium. We conclude that TYI 101 medium can be used for the generation of LAK cells from human lymph node lymphocytes with supplementation of none or only a reduced amount of human serum.
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    URL: http://dx.doi.org/10.1007/BF00353701
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  • 15
    Electronic Resource
    Electronic Resource
    Development of a new culture system for human lymphokine-activated killer cells: Comparison with a conventional static culture method (1991)
    Springer
    Cytotechnology 7 (1991), S. 75-83 
    Details
    ISSN: 1573-0778
    Keywords: adoptive immunotherapy ; cell culture ; cell culture apparatus ; Interleukin-2 ; lymphokine-activated killer cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We recently developed a new culture system based on dialysis perfusion (designated JCC-device) for the generation and expansion of human lymphokine-activated killer (LAK) cells (Murata et al., 1990). More recently we have scaled up the volume of the culture vessel of the JCC-device from 100 ml to 400 ml for clinical use. In the present study, using this new 400 ml JCC-device, we cultured human lymph node lymphocytes (LNL) obtained from 8 surgical patients with primary lung cancer, and investigated the cellular characteristics in comparison with a conventional batchwise culture system using tissue culture dishes. With the JCC-device, the cell density reached a maximum 2.7×107 cells/ml with greater than 90% viability by the appropriate exchange of perfusion medium and by making additions at the appropriate intervals for recombinant interleukin-2 (rIL-2). The expansion fold of LNL with the JCC-device, ranging 6.6- to 19.2-fold (mean 13.8-fold), was not significantly different from that in dish cultures. There was no marked difference in cell surface phenotypes between the two culture systems in 7 out of 8 cases. As for LAK activity of LNL, the JCC culture was either superior or equal in 4 out of 8 cases, but inferior in the other 4 cases to the conventional dish cultures. In the latter cases, the usage of serum for the JCC culture was limited, which might have resulted in the low LAK activity. The JCC-device was able to reduce the consumption of basal medium, rIL-2 and serum by 20%, 84% and 96%, respectively compared to the conventional tissue culture systems. The JCC-device improved the routine performance of adoptive immunotherapy with LAK cells and rIL-2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350913
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  • 16
    Electronic Resource
    Electronic Resource
    A new method for the encapsulation of mammalian cells (1991)
    Springer
    Cytotechnology 7 (1991), S. 121-130 
    Details
    ISSN: 1573-0778
    Keywords: cell culture ; cellulose sulphate ; encapsulation ; monoclonal antibodies ; poly-dimethyl-diallyl-ammoniumchloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A new encapsulation method was developed for the cultivation of mammalian cells. The capsules were produced using a solution of sodium cellulose sulphate (CS)(1.5%) and poly-dimethyl-diallyl-ammoniumchloride (PDMDAAC). When CS droplets fell into the precipitation bath consisting of a 2% solution of PDMDAAC, immediately a membrane at the interphase was built up. The influences of varying encapsulation process parameters on capsule characteristics, cell growth, and monoclonal antibody production were tested. This new method showed advantages when compared to other methods mainly due to time simplicity of the whole process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350918
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  • 17
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    Serum-free culture of carcinoma cell lines (1991)
    Springer
    Cytotechnology 5 (1991), S. 31-46 
    Details
    ISSN: 1573-0778
    Keywords: serum-free ; cell culture ; carcinoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00365532
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  • 18
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    Influence of temperature on the proliferative response of rainbow trout gonadal fibroblasts to cortisol and RU 486 (1991)
    Springer
    Fish physiology and biochemistry 9 (1991), S. 261-269 
    Details
    ISSN: 1573-5168
    Keywords: Cortisol ; RU 486 ; temperature ; rainbow trout ; cell culture ; [3H]-Thymidine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The rainbow trout gonadal cell line, RTG-2, which survives temperatures from 0 to 28°C and proliferates at 5 to 26°C, responded to cortisol from 28°C to 0°C by influencing [3H]-thymidine incorporation into DNA. Over the normal temperature range of rainbow trout, 10–22°C, cortisol inhibited [3H]-thymidine incorporation. The antiglucocorticoid RU 486 had no effect on [3H]-thymidine incorporation at these temperatures and blocked the response to cortisol. Another antiglucocorticoid RU 362 also had no effect but was less effective in blocking the cortisol response. During incubation at 28°C this inhibitory response to cortisol was detected inconsistently during the first 24 h but was observed consistently during the second 24 h. At 0°C, cortisol and RU 486 had no effect during short treatments, but a 60 h exposure to either steroid stimulated [3H]-thymidine incorporation over a 48 h labelling period. These results suggest that temperature shifts between 10–22°C, do not change the direction of a response to cortisol and support the use of the upper portion (20–22°C) of the temperature range for studies on salmonid cells in culture.
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    URL: http://dx.doi.org/10.1007/BF02265147
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  • 19
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    Effects of high ammonium concentrations on growth and anthocyanin formation in grape (Vitis vinifera L.) cell suspension cultured in a production medium (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 169-174 
    Details
    ISSN: 1573-5044
    Keywords: ammonium ; anthocyanin ; cell culture ; growth kinetics ; production medium ; Vitis vinifera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cultivating Vitis vinifera cell suspensions in a production medium which is characterized by high sucrose and low nitrate concentrations (132 mM and 6.25 mM respectively) repressed growth but enhanced the intracellular accumulation of anthocyanins, especially peonidin 3-glucoside. Increasing the ammonium concentration of the production medium from 2 to 8–16 mM increased growth and decreased the accumulation of anthocyanins and peonidin 3-glucoside specifically. Instead, peonidin 3-p-coumaroylglucoside accumulated. At 24 mM ammonium concentration, growth was inhibited and accumulation of peonidin 3-p-coumaroylglucoside was significant (p〈0.05) and represented 42% of total anthocyanins after 12 days of culture compared with 19% in the production medium with 2 mM ammonium.
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    URL: http://dx.doi.org/10.1007/BF00041286
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  • 20
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    Ferric chelate reduction by suspension culture cells and roots of soybean: A kinetic comparison (1991)
    Springer
    Plant and soil 130 (1991), S. 75-80 
    Details
    ISSN: 1573-5036
    Keywords: cell culture ; FeHEDTA ; Glycine max ; iron chelate reduction ; iron nutrition ; soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The abilities of suspension cultures and intact roots of soybean (Glycine max L. cv. Hawkeye) to reduce ferric chelate were compared. Ferric chelate was supplied as ferric hydroxyethylethylenediaminetriacetic acid (FeHEDTA) and reduction was measured spectrophotometrically using bathophenan-throlinedisulfonic acid (BPDS) as the ferrous scavenger. Ferric chelate reduction by cell suspension cultures showed typical saturation kinetics; however, no difference was observed between cells that had been continuously grown with Fe (+Fe) and those that had been grown for four days without added Fe (−Fe). Values for Km and Vmax, determined from a Lineweaver-Burk plot, were 57 μM and nmoles mg-1 dry weight for the +Fe cells and 50 μM and 22 nmoles mg-1 dry weight for the -Fe cells, respectively. Ferric chelate reduction by Fe-deficient roots also exhibited saturation kinetics, while roots grown with adequate Fe did not reduce ferric chelate. The Km and Vmax values for Fe-deficient roots were 45 μM and 20 nmoles mg-1 dry weight, respectively, and did not differ from values obtained for cells in culture. This study offers strong evidence that the mechanism responsible for the reduction of ferric chelate is the same for cultured cells and roots and that the process is controlled at the cellular level. We propose that suspension cultures can be used as an alternative to intact roots in the study of ferric chelate reduction.
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    URL: http://dx.doi.org/10.1007/BF00011858
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  • 21
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    Actual, potential and speculative applications of seaweed cellular biotechnology: some specific comments on Gelidium (1991)
    Springer
    Hydrobiologia 221 (1991), S. 181-194 
    Details
    ISSN: 1573-5117
    Keywords: callus ; cell culture ; domestication ; protoplast ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cellular biotechnology is a promising application in the propagation and selection of superior strains of seaweeds. Although axenic cultures, organogenetic tissue cultures, vegetative micro-propagation, callus induction and high yields of agar from calli have been described for several species of Gelidium, a number of basic problems remain to be solved. These include standardized methods for obtaining axenic cultures, identification of requirements for organic nutrients, PGR's, cellular disorganization and reorganization, somaclonal variation and somatic incompatibilities. Future progress in seaweed biotechnology will depend on the resolution of many of these problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00028374
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  • 22
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    Experiments with culture media for planarian cells (1991)
    Springer
    Hydrobiologia 227 (1991), S. 187-192 
    Details
    ISSN: 1573-5117
    Keywords: Turbellaria ; planaria ; cell culture ; leucine uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have tested various conditions for the culture of cells dispersed from planarians. The cells were procurred by digestion of planarian tissue in pronase and filtering through a nylon mesh. Using incorporation of L-[3H]leucine into protein as a gauge of cell growth, we found that the optimum salt concentration was about 50% of that for mammalian cells (about 160 mOsm) and that optimum pH was about 8. Sera from several species and a tetrapeptide (Arg-Gly-Asp-Ser, the cell-attachment sequence in fibronectin) greatly increased leucine uptake and extended cell survival up to a period of about two weeks. Various growth factors and some other substances tested had no effect on uptake of leucine, cell morphology, or survival. A few other compounds tested were cytotoxic. None of the experimental media promoted cell proliferation.
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    URL: http://dx.doi.org/10.1007/BF00027601
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  • 23
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    Study of a factor produced by suspension-cultured Pinus radiata cells which enhances cell growth at low inoculum densities (1991)
    Springer
    Plant cell, tissue and organ culture 26 (1991), S. 53-59 
    Details
    ISSN: 1573-5044
    Keywords: cell culture ; cell wall ; conditioned medium ; inoculum density ; low inoculum growth factor ; Pinus radiata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Pinus radiata cells in suspension culture abruptly lose their growth capacity when diluted below a critical inoculum density. This threshold density can be lowered by adding the supernatant (conditioned medium) from healthy cultures which have been grown separately at high densities. Fresh medium is conditioned rapidly indicating that the factor responsible is either potent or produced rapidly. Activity-response curves increase progressively with concentration indicating that still greater effect may be obtained if the factor can be concentrated following separation from other medium components. The effect is not mimicked by a number of candidate compounds (including auxins, cytokinins, polyamines and vitamins). Partial characterisation studies indicate that the factor is relatively small (〈1 000 dalton) and possibly an oligosaccharide. It is considered that the factor is an essential structural component of the walls of expanding cells where it is reversibly-bound.
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    Two types of asymmetric acetylcholinesterase in chick hindlimb muscle: Developmental profiles,in Vivo and in cell culture, and recovery after inactivation (1991)
    Springer
    Cellular and molecular neurobiology 11 (1991), S. 191-201 
    Details
    ISSN: 1573-6830
    Keywords: acetylcholinesterase ; asymmetric-form types ; chick hindlimb muscle ; development ; cell culture ; diisopropylfluorophosphate inactivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. We have analyzed the behavior of two types of asymmetric molecular forms (A forms) of acetylcholinesterase (AChE) during development of chick hindlimb muscle,in vivo and in cell culture, and upon irreversible inactivation of peroneal muscle AChE with diisopropylfluorophosphate (DFP)in vivo. 2. In agreement with previous developmental studies on chick muscle, globular forms of AChE (G forms) are predominant in chick hindlimb at early embryonic ages, being gradually replaced by A forms as hatching (and, therefore, onset of locomotion) approaches. Of the two A-form types, AI appears and accumulates significantly earlier than AII, so that A/G and II/I ratios higher than 1 are attained only at about hatching time. 3. Cultures prepared from 11-day chick embryo hindlimb myoblasts express both types of A forms, with a combined activity of 27% of total AChE after 12 days in culture. AI forms appear again earlier and are much more abundant than type II asymmetric species through the life span of cultures. 4. All AChE activity in the peroneal muscle is irreversibly inactivated by injection of DFPin vivo. The recovery of A forms follows the same sequence described for normal development, with a delayed and slower recovery of AII forms as compared with AI. 5. Several hypotheses involving tail polypeptides or tissue target molecules, or posttranslational interconversion, are proposed to help explain the earlier appearance and accumulation of AI forms in chick muscle.
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    Accumulation of peonidin 3-glucoside enhanced by osmotic stress in grape (Vitis vinifera L.) cell suspension (1991)
    Springer
    Plant cell, tissue and organ culture 24 (1991), S. 49-54 
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    ISSN: 1573-5044
    Keywords: anthocyanin ; cell culture ; osmotic potential ; reverse-phase HPLC ; Vitis vinifera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cell cultures of grapes, Vitis vinifera L. cv Gamay Fréaux were grown under different conditions of external osmotic potential induced by an increase of sucrose concentration or by the addition of mannitol to the culture medium. Addition of 82 mM mannitol or increasing sucrose concentration to 132 mM had similar effects on repressing growth. Cyanidin 3-glucoside, peonidin 3-glucoside and peonidin 3-p-coumaroylglucoside are three main anthocyanins of Vitis cells. Increasing osmotic potential from −0.43 MPa to −0.8 MPa in the medium resulted in a significant intracellular accumulation of anthocyanin especially peonidin 3-glucoside in the pigmented cells. High osmotic potential appears to stimulate the methylation of anthocyanins. Osmotic potential is an important culture factor and may be useful in the controlling of anthocyanin production and composition.
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    Increased anthraquinone production in Galium vernum cell cultures induced by polymeric adsorbents (1991)
    Springer
    Plant cell, tissue and organ culture 24 (1991), S. 207-210 
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    ISSN: 1573-5044
    Keywords: anthraquinone production ; cell culture ; Galium vernum ; polymeric adsorbents ; secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Anthraquinones produced by suspension cultures of Galium vernum are completely retained intracellularly. Surprisingly, in the presence of some polymeric adsorbents anthraquinones are partially released into the culture medium. The secretion and in situ removal stimulates anthraquinone production in cell cultures of Galium vernum. Best results were obtained with Wofatit ES and Amberlite XAD-2.
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    Isolation and characterization of Daucus carota L. cell lines resistant to 2-deoxy-D-glucose (1991)
    Springer
    Plant cell, tissue and organ culture 25 (1991), S. 147-152 
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    ISSN: 1573-5044
    Keywords: cell culture ; Daucus carota ; 2-deoxy-D-glucose ; invertase ; selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Variant carrot (Daucus carota L.) cell lines resistant to the growth inhibitory effects of the glucose analogue 2-deoxy-D-glucose (dGlc) were isolated utilizing a feeder plate technique. Growth of sensitive cells was less than 7.5% of controls on medium supplemented with 3.0 mM dGlc, whereas resistant variants achieved growth ranging from 15% to 70% of that in controls. Increased levels of acid invertase activity in variant cell lines in response to dGlc in the culture medium, together with decreased sensitivity of the acid invertase enzyme (EC 3.2.1.26) to dGlc, is proposed as one of several potential mechanisms contributing to the observed dGlc resistance.
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    Morphologic identification of epithelial cell types of the human tracheo-bronchus in cell culture (1991)
    Springer
    Methods in cell science 13 (1991), S. 5-11 
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    ISSN: 1573-0603
    Keywords: bronchial epithelium ; cell culture ; intermediate filaments ; carbohydrate cytochemistry ; lectins ; peroxidase-labeled lectins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A protocol is presented for correlating the morphology of human bronchial epithelial cells after Papanicolaou staining with their periodic acid schiff (PAS)/AB-reactivity, intermediate filament type, and the pattern of staining with lectins having specific affinities for glycoconjugates:griffionia simplicifolia (GSA-IB4; terminal alpha-d-galactose),Dolichos biflorus (DBA,N-acetyl-d-galactosamine). The combination of these stains identified differentiation markers in morphologic studies of normal, transformed, and malignant bronchial epithelial cells in culture.
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    Use of the pH-sensitive dye BCECF to study pH regulation in cultured human kidney proximal tubule cells (1991)
    Springer
    Methods in cell science 13 (1991), S. 205-209 
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    ISSN: 1573-0603
    Keywords: pH ; NH 4 + ; BCECF ; human kidney ; proximal tubule ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This protocol describes the use of the pH-sensitive, intracellularly trapped dye 2′,7′-bis (2-carboxyethyl), 5 (and -6) carboxyfluorescein (BCECF), to characterize the pH regulating mechanisms in cultured human kidney proximal tubule cells. This is a reliable method for intracellular pH measurements and is applicable to single cells, cell suspensions, and confluent cultures.
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    A direct fluorimetric DNA assay on cell suspensions (1991)
    Springer
    Methods in cell science 13 (1991), S. 285-288 
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    ISSN: 1573-0603
    Keywords: DNA ; fluorimetry ; fibroblast ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An improved direct fluorimetric assay is described using bisbenzimidazol fluorescence at 356 nm excitation and 458 nm emission wavelengths. The turbidity of the medium was shown to have no effect on fluorescence under an absorbance of 0.2 at the excitation wavelength. The method was evaluated by comparisons with a colorimetric DNA assay and cell counting. The linearity of fluorescence was determined up to 15μg/ml of DNA. The method was very reproducible and sensitive to detect 10 ng/ml of DNA and may be used for cell suspensions containing around 5000 cells/ml or more.
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    Fetal bovine oviduct epithelial cell monolayers: Method of culture and identification (1991)
    Springer
    Methods in cell science 13 (1991), S. 289-294 
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    ISSN: 1573-0603
    Keywords: fetal bovine ; oviduct ; cell culture ; microscopy ; immunocytochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Bovine epithelial cell monolayers were obtained for culture from fetal oviduct after in situ trypsinization. Isolated ciliated and secretory cells obtained in high yield with good viability were suspended in B2-MENEZO'S medium supplemented with 7.5% fetal bovine serum FBS. The plated primary cultures reached confluency 2 days after initial seeding, producing a monolayer of cohesive polygonal cells with viability of 85 to 95%. Associated with this large epithelial cell population, ciliated cells as well as a few elongated spindle cells were observed. After the first subculture the ciliated cells disappeared and the epithelial cells in the monolayer grew more rapidly to confluence than adult-derived cultures. In addition, frozen-thawed oviduct epithelial cells also maintained a level of 75 to 85% viability during postthaw subculture. The epithelial cells maintained their secretory activity in culture as indicated by electron microscopy and immunocytochemistry. The cell culture monolayers contained keratin, a specific cytoskeletal component of epithelial cells. This culture system may offer benefits for in vitro culture of mammalian embryos.
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    A method for estimating oxygen availability of stationary plant cell cultures in liquid media (1991)
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    Plant cell, tissue and organ culture 26 (1991), S. 195-201 
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    ISSN: 1573-5044
    Keywords: Brassica napus ; cell culture ; diffusion ; liquid medium ; oxygen availability ; protoplast culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A method for estimating the oxygen availability in plant cell cultures grown in stationary liquid media (e.g. many protoplast cultures) was developed. The method is based on short-term measurements of respiration rate versus oxygen concentration on a sample of cells, suspended in liquid media. From such data it is possible to estimate the oxygen concentration at the bottom of a stagnant liquid culture, by calculating the amount of oxygen reaching the cells by diffusion. As an example, rape (Brassica napus L. cv. Omega) hypocotyl protoplasts were grown with different oxygen concentrations at the site of the cells, obtained by varying the cell density, the height of the liquid layer and the oxygen content of the gas phase. The number of surviving calli was positively correlated with the estimated oxygen availability in the range between 60 and 350 μM O2, below 60 μM all cells died. This indicates that oxygen availability can be a limiting factor in the range usually encountered in protoplast cultures, and that the method can be useful when designing optimal growth conditions for stationary cultures of plant cells.
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    l-Phenylalanine ammonia-lyase in suspension culture cells of spruce (Picea abies) (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 267-274 
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    ISSN: 1573-5044
    Keywords: cell culture ; enzyme induction ; fungal elicitor ; l-phenylalanine ammonia-lyase ; Picea abies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activity of l-phenylalanine ammonia-lyase (PAL) (EC 4.3.1.5) was determined in seedlings, callus cells, cell suspension cultures and in young needles of spruce (Picea abies) (L.) (Karst). PAL activity increased up to 10 fold in response to transferring suspension cultured cells into new cultivation medium. PAL was also induced about 10 fold when callus cells were transferrd into liquid medium. The increase was transient and it required the presence of a carbohydrate. In cell suspension cultures, grown in the dark (white cells), but not in light-grown cultures (green cells), PAL activity was induced up to 30 fold by UV-light. With a cell wall preparation of Rhizosphaera kalkhoffii, a forest pathogenic fungus, used as elicitor, the activity of PAL could be induced more than 10 fold. The degree of induction depended on the elicitor concentration. Induction was prevented by cycloheximide but not by actinomycin D.
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    Proteoglycan synthesis in cultures of murine retinal neurons and photoreceptors (1991)
    Springer
    Cellular and molecular neurobiology 11 (1991), S. 579-591 
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    ISSN: 1573-6830
    Keywords: proteoglycans ; glycosaminoglycans ; mouse retina ; photoreceptors ; retinal neurons ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. In recent years, a number of histochemical and immunocytochemical studies have suggested that proteoglycans, particularly those in the inter-photoreceptor matrix, exhibit altered distributions in several murine models for retinal degenerations. We are using a cell culture system to characterize the proteoglycans synthesized by neurons and photoreceptors derived from mouse retina, with the long-term goal of analyzing their role in retinal degenerations. 2. In this study we describe initial studies using cells derived from the retinas of normal mice. Cultures of retinal neurons and photoreceptors, which were free of glial, epithelia, or endothelial cells, were labeled with3H-glucosamine and35SO4. Proteoglycans isolated from the medium and cell layer were analyzed on the basis of charge, relative hydrodynamic size, and glycosaminoglycan content. 3. The studies indicate that the cultures actively synthesize proteoglycans. The medium contained predominantly chondroitin sulfate/dermatan sulfate, while the cell layer had a higher proportion of heparan sulfate, indicating a differential distribution between the two compartments.
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    Studies of Sb and Bi cluster produced by laser desorption (1991)
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    The European physical journal 19 (1991), S. 203-206 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 79.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Direct production of cations and anions of metal clusters of Sb and Bi by laser evaporation in a vacuum has been studied. Bulk sample substrates are irradiated by 1064, 532 and 355 nm beams at variable intensity, and the ions produced are accelerated and identified by time-of-flight mass spectrometry. At 1064 nm, the cation distributions show that Sb 3 + and Bi 3 + are the most abundant species, while the monomer and dimer cations are almost non-existent. The anion spectra indicate very low yields of Sb− and Bi− with dominant dimer anion species. These patterns persist with laser power variation within the stable operation domain. With lower incident laser wavelength, the mass distributions are modified, favouring the production of the light cluster ions. In no circumstances were Sb and Bi ions withn〉5 observed. Many of the observed phenomena can be explained if one assumes that for these elements, clusters withn〈6 are formed on the substrate surface. Cluster ions are produced via a prompt desorption process, and are subjected to photon induced reactions due to the same incident laser beam. However, more detailed investigation of the desorption properties will be necessary to confirm such a desorption mechanism.
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    STM observation of Au fine-particles on graphite (1991)
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    The European physical journal 19 (1991), S. 333-335 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.16.D ; 82.65.F
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    Topics: Physics
    Notes: Abstract Gold particles deposited on graphite in vacuum have been studied by STM observation in air. Liquid-like coalescence between small gold-particles has been observed near room temperature. Preparation of small particles in vacuum is discussed. Small particles are formed in nucleation process if the degree of coalescence of particles is reduced. Over 400 Au particles of 5 nm in diameters with a narrow size-distribution with FWHM 2 nm and a high density of 3×1012/cm2 is prepared by evaporating gold in a vacuum of about 2×10−5 Torr and at the substrate (HOPG) temperature of 20°C.
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    Adsorption — desorption kinetics on epitaxially oriented palladium clusters (1991)
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    The European physical journal 19 (1991), S. 347-351 
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    ISSN: 1434-6079
    Keywords: 82.65.Jv ; 36.40
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    Topics: Physics
    Notes: Abstract Palladium clusters with a low size dispersion and a single crystallographic shape have been obtained by epitaxial growth on (100) MgO. The isothermal adsorption — desorption kinetics of CO is obtained by a molecular beam method allowing the direct determination of the global adsorption probability and of the mean life time of CO molecules on the clusters. Three main results are deduced from these measurements: — an increase of the adsorption rate of CO on the clusters by the capture of CO molecules physisorbed on the substrate, — a faster desorption rate from (100) than from (111) facets at high coverage, — an increase of the adsorption energy for clusters smaller than 3 nm.
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    Structural stability and energetics of C, Si, and Ge microclusters: empirical many-body potential energy function calculation (1991)
    Springer
    The European physical journal 19 (1991), S. 423-425 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract The structural stability and energetics of carbon, silicon, and germanium microclusters containing 3−7 atoms have been investigated by using a recently developed empirical many-body potential energy function (PEF), which comprises two- and three-body atomic interactions. The PEF satisfies both bulk cohesive energy per atom and bulk stability exactly. It has been found that the most stable C3−4 microclusters are linear withD ∞h symmetry but C5−7 microclusters are planar withD nh symmetry. Silicon and germanium microclusters show similar structural stability. TheX n (X=Si, Ge;n=3−7) microclusters are found to be most stable in the following forms:X 3 is triangular withD 3h symmetry,X 4 is tetragonal withT d symmetry,X 5 is square pyramidal withD 4h symmetry,X 6 is bipyramidal square withO h symmetry, and finallyX 7 is square pyramidal having two atoms underneath withD 2h symmetry.
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    C n carbon clusters (n=4−6, 60, 70): interesting cases of computation/observation comparisons (1991)
    Springer
    The European physical journal 19 (1991), S. 431-433 
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    ISSN: 1434-6079
    Keywords: 35.20 ; 36.40 ; 82.30Q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent theoretical studies proved some of the small carbon clusters C n (n≈1−10) are represented by several isomeric structures. Evaluation of the isomer relative stabilities is necessary for comparison of theoretical data with observation, this being exemplified by the C4 and C6 cases. For the former cluster a new energy estimation has been suggested based on the isomerism reasoning. Relative-stability evaluation for clusters of different dimensions is discussed on the C60/C70 system, pointing out a strong pressure-dependency of the picture. The scheme is matched to the recent observations of Bethune and Meijer.
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    On the shell structure and geometry of monovalent metal clusters (1991)
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    The European physical journal 21 (1991), S. 271-279 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Hückel model is used to study the electronic structure of monovalent metal clusters. In an fcc cluster the Hückel model gives an estimate to the electronic structure of a free electron cluster. It is shown that the surface faceting of the fcc cluster can destroy the electronic shell structure already when the cluster has about 100 electrons. In the Hückel model the icosahedral structure has smaller total energy than the fcc structures, from which the Wulff construction has the smallest energy already when the cluster has 600 atoms.
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    The structure of deposited metal clusters generated by laser evaporation (1991)
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    The European physical journal 21 (1991), S. 285-288 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Metal clusters have been produced using a laser evaporation source. A Nd-YAG laser beam focused onto a solid silver rod was used to evaporate the material, which was then cooled to form clusters with the help of a pulsed high pressure He beam. TOF mass spectra of these clusters reveal a strong occurrence of small and medium sized clusters (n〈100). Clusters were also deposited onto grid supported thin layers of carbon-films which were investigated by transmission electron microscopy. Very high resolution pictures of these grids were used to analyze the size distribution and the structure of the deposited clusters. The diffraction pattern caused by crystalline structure of the clusters reveals 3-and 5-fold symmetries as well asfcc bulk structure. This can be explained in terms of icosahedron and cuboctahedron type clusters deposited on the surface of the carbon layer. There is strong evidence that part of these cluster geometries had already been formed before the depostion process. The non-linear dependence of the cluster size and the cluster density on the generating conditions is discussed. Therefore the samples were observed in HREM in the stable DEEKO 100 microscope of the Fritz-Haber-Institut operating at 100 KV with the spherical aberrationc S =0.5 mm. The quality of the pictures was improved by using the conditions of minimum phase contrast hollow cone illumination. This procedure led to a minimum of phase contrast artefacts. Among the well-crystallized particles were a great amount of five- and three-fold symmetries, icosahedra and cuboctahedra respectively. The largest clusters with five- and three-fold symmetries have been found with diameters of 7 nm; the smallest particles displaying the same undistorted symmetries were of about 2 mm. Even smaller ones with strong distortions could be observed although their classification is difficult. The quality of the images was improved by applying Fourier filtering techniques.
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    Neutral mass-selected lead cluster beams (1991)
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    The European physical journal 19 (1991), S. 199-201 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Neutral lead cluster beams with ultra-narrow size distribution were produced by neutralization of mass-selected lead cluster ions, Pb n + withn≤12, in sodium vapor under near-resonant conditions. Absolute charge exchange cross sections were measured as a function of cluster size and are on the order of 40 Å2 forn≥4. Possible fragmentation of the clusters associated with charge transfer was examined by translational spectroscopy. No indication of fragmentation was found.
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    Thermionic emission from giant fullerenes (1991)
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    The European physical journal 19 (1991), S. 409-412 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Large even-numbered carbon clusters in the size range from 100 to 600 atoms (giant fullerenes) were generated by laser vaporization and directly injected as positive ions via a supersonic beam into the magnetic trap of an ion cyclotron resonance apparatus. Intense laser excitation of the magnetically levitated fullerenes at 4.0 eV was found to result in production of multiply charged fragments in the trap. Details of the time scale and size dependence of this process suggest it is due to thermionic emission from the superheated gas phase clusters.
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    Electronic transitions in C60 and its ions (1991)
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    The European physical journal 19 (1991), S. 435-438 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electronic spectrum of C60 is calculated using quantum mechanical methods. The first allowed transition in C60 is calculated at an energy of 3.5 eV and with an oscillator strength of 0.09. Several transitions are found at higher energies with comparatively strong oscillator strengths, the strongest one being at 5.78 eV (λ=214 nm). The calculated energy level diagram of C60 is also used to predict wavelengths for transitions in C 60 + and C 60 − . A comparison is made with some recently observed diffuse interstellar bands at 1180 nm and 1320 nm, which have been speculated to originate from C 60 + .
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    Internal excitation effects in the photodissociation of size selected ethylene and methanol dimers (1991)
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    The European physical journal 18 (1991), S. 181-188 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 82.50.F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The infrared photodissociation spectra of C2H4 and CH3OH dimers are measured for different internal excitation energies ΔE. The dimers are size-selected in a scattering process with He and the internal energy is varied by using (1) different collision energies, (2) different scattering angles and (3) by measuring the complete energy loss spectra with and without laser radiation by time-of-flight analysis of the scattered clusters. For (CH3OH)2 the width Γ of the spectrum increases strongly with ΔE, while the cross section at the maximum is constant, a normal behaviour for an inhomogeneously broadened system. For (C2H4)2 Γ is nearly constant after a sort of threshold and the cross section increases with increasing ΔE. These results are explained by hot band excitation and the coupling to the darkv 10-mode.
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    Sub-doppler-spectroscopy of Na3 (1991)
    Springer
    The European physical journal 18 (1991), S. 257-265 
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    ISSN: 1434-6079
    Keywords: 33.20 ; 35.20 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Rotationally cold Na3-molecules are formed during the adiabatic expansion of an argon beam, seeded with 5% sodium vapor. With a single mode tunable dyelaser crossing the molecular beam perpendicularly within the ion source of a mass spectrometer the Na3-molecules are excited into levels of the2 A 2-state which are then ionized by acw argon-laser. Rotational lines of the electronic2 A 2 ←X 2 B 2 transition and their hyperfine structure could be resolved using an OODR-technique. A preliminary analysis of the measured spectra is discussed and a comparison of the experimental results with ab initio calculations is presented.
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    Calculation of photoionization cross sections of Na2–8 and K2–8 clusters (1991)
    Springer
    The European physical journal 18 (1991), S. 267-280 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80E
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    Notes: Abstract Analysis of free metal clusters studied with photoionization mass spectrometry or photoelectron spectroscopy requires theoretical predictions of the photoionization cross sections to gain a deeper physical understanding. Calculated energy-dependent photoionization cross sections of Na2–8 and K2–8 clusters are presented in this study. The ground state electronic structure of the clusters are calculated using the Local Spin Density method (LSD) which is also the starting point for the cross section calculation with the continuum multiple scattering method. A basic analysis of the photoionization process is given within the independent electron picture. Strong resonances are predicted in the UV cross sections (5–10 eV) of K3–8 but not for Na3–8, interpreted as shape resonances, i.e. quasibound states in which electrons are trapped by a potential barrier. Unfortunately experimental data are only known close to the ionization threshold and a comparison between our values and experimental data in a broad energy range is not possible.
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    Computer simulations of small semiconductor and metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 31-36 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract A brief survey is presented of recent simulations of small clusters, made with both ab-initio and classical approaches, with particular emphasis on the application of the Car-Parrinello method. The discussion mainly focusses on the structural properties of a variety of materials and on the effects of temperature.
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    The influence of shells, electron thermodynamics, and evaporation on the abundance spectra of large sodium metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 47-50 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20.Wg ; 03.65.-w
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    Topics: Physics
    Notes: Abstract Measurements of the mass abundance spectra of sodium clusters containing up to 600 atoms are presented. The clusters are produced in a seeded supersonic expansion of Ar or Kr gas, and the spectra are obtained by a time-of-flight technique. The sawtooth features in the spectra are interpreted as evidence of a regular spherical shell structure with magic numbers,N 0, scaling approximately with the cube root of the number of sodium atoms. Altogether twelve shell closings are observed,N 0=2, 8, 20, 40, 58, 92, 138, 196, 260, 344, 440 and 558. There is also a pronounced odd-even staggering all the way up toN=70. The experimentally observed intensity changes for the clusters around the magic numbers are discussed in terms of the electronic free energy,F(N), calculated at finite temperature, and the second differences of the free energy Δ2 F(N)=F(N−1)−2F(N)+F(N+1). The processes behind the non-uniform abundance distributions, and the thermodynamics of finite electron systems with non-uniform level spacings are discussed on this basis.
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    Semiclassical variational study of size effects in neutral and charged jellium droplets (1991)
    Springer
    The European physical journal 19 (1991), S. 55-58 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
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    Topics: Physics
    Notes: Abstract An analytic expression for the total energy of metallic clusters composed ofN identical atoms of valencev and with net chargeQ is obtained by means of a variational solution of the Thomas-Fermi-Weizsäcker energy density functional within the spherical jellium model. The minimum energy is given as an expansion in decreasing powers of the cluster radiusR=r s Z 1/3, withZ=vN andr s the radius per electron of the bulk metal. The coefficients are obtained as functions ofr s . Terms of volume (R 3), surface (R 2), curvature (R), constant (R 0), (1/R) and (1/R 2) are clearly separated in the formula, as well as the different contributions (kinetic, coulombic and exchange-correlation) to each of them. The asymptotic values (R→∞) for the work functions,W(r s ), and surface energies σ(r s ), are compared to analogous semiclassical and Kohn-Sham calculations of jellium-like surfaces and to the experimental values. The size dependent behaviour of chemical potentials, μ(R), electron affinities,AF(R), and ionization potentials,IP(R), are easily obtained for any kind of metallic clusters. In particular we discuss the Coulomb and quantum corrections to the coefficients β, δ in the asymptotic formulae:IP≃W+β/R andAF≃W+δ/R.
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    Absolute cross sections for electron impact ionization of Ag2 (1991)
    Springer
    The European physical journal 19 (1991), S. 77-79 
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    ISSN: 1434-6079
    Keywords: 34.80G ; 36.40 ; 35.20V
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    Topics: Physics
    Notes: Abstract The previously measured relative cross section function for electron impact ionization (EII) of neutral Ag2 has now been calibrated quantitatively by combining the electron impact ionization with in situ non resonant two photon ionization (NR2PI). By comparing the NR2PI saturation intensities measured for Ag 2 + and Ag+ with the corresponding EII intensities, the ratio between the electron impact ionization cross sections (EIICS) of neutral Ag2 and Ag was determined to be σAg2/σAg=1.53 for an electron energy of 46 eV. This result agrees well with the geometricn 2/3-rule $$(\sigma X_n \sim n^{2/3} )$$ commonly proposed for the dependence of the EIICS of clustersX n on the cluster sizen.
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    Thermal broadening of plasmon absorption in potassium cluster ions (1991)
    Springer
    The European physical journal 19 (1991), S. 85-87 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 78.40-q
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    Notes: Abstract The optical absorption spectrum around the surface plasmon peak is presented for K 21 + . Hot, charged potassium clusters are produced by an adapted liquid metal ion source. The plasmon is found to be slightly red shifted from and distinctly broader than the one reported in an experiment on colder clusters by Bréchignac et al. [3]. Mechanisms responsible for the temperature dependence of the width and position of the surface plasmon in small metal clusters are discussed.
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    Response properties of sodium clusters within a jellium-like model with finite surface thickness (1991)
    Springer
    The European physical journal 19 (1991), S. 93-96 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 71.45.G
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    Topics: Physics
    Notes: Abstract The usual spherical jellium model of alkaline clusters is generalized to allow for a finite surface thickness in the positive background distribution. Static (relative stability, ionization potentials) and response properties have been calculated and the results show a better agreement with experiments.
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    The elastic scattering on jellium clusters (1991)
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    The European physical journal 19 (1991), S. 97-99 
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    ISSN: 1434-6079
    Keywords: 34.80.B ; 36.40
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    Topics: Physics
    Notes: Abstract The following calculations are based on the local density approximation potential (LDA) of W. Ekardt for the spherical jellium-background model (SJBM). Taking into account the smooth shape of the potential, the WKB approximation was used to calculate the energy and angular dependence of the electron scattering cross-sections fo rsmall Na clusters. The number of phase shifts needed to describe the scattering in the range of energies 〈4.5 eV increases with the size of cluster. The calculated elastic electron scattering cross-sections for the Na clusters, corresponding to the shell closings (8, 20, 40), are exhibiting a pronounced peak structure, correlated with resonance states. The computed peaks of the angular dependences of the cross-sections on energy are shifted to small angles with increasing the cluster size. The absence of fragmentation at these small electron energies presents a challenge for the experimentalists.
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    Bimetallic cluster cations ejected from a liquid metal ion source: Li-Na and Li-Mg (1991)
    Springer
    The European physical journal 19 (1991), S. 129-131 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 79.70 ; 35.20X
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    Topics: Physics
    Notes: Abstract Cluster ions of alloys (Li-Na, Li-Mg) have been produced by a liquid metal ion source (LMIS), and analyzed by mass spectrometry. For the Li-Na system, bimetallic clusters with various compositions were formed, and dominant bimetallic species were Na2Li+, NaLi+, NaLi 2 + and NaLi 8 + with this sequence of ion intensity. These clusters are systems containing 2 or 8 valence electrons except for NaLi+. For the Li-Mg, observed bimetallic clusters were limited to only three species (MgLi+, MgLi 2 + and Mg2Li+), but unexpectedly small multiply charged homonuclear clusters, Mg 2 2+ and Mg 3 2+ , were observed.
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    Enthalpies of formation of gaseous Zintl-molecules over sodium-tellurium alloys (1991)
    Springer
    The European physical journal 19 (1991), S. 181-184 
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    ISSN: 1434-6079
    Keywords: 05.70 ; 07.75 ; 36.40
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    Topics: Physics
    Notes: Abstract The vapor over sodium-tellurium alloys was investigated using Knudsen effusion mass spectrometry. The stoichiometries of the molecules in the gas phase are compared with the stoichiometries of those appearing in liquid ammonia. Enthalpies of formation for the gaseous molecules are obtained using van't Hoff plots and third law evaluations.
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    Magic numbers in sims of Mn similar to those of charged Ar clusters (1991)
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    The European physical journal 19 (1991), S. 189-190 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20X ; 79.20X
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    Topics: Physics
    Notes: Abstract Manganese cluster ions Mn k + (k≲60) have been produced by 7 keV Xe ion bombardment and analyzed by a double-focusing mass spectrometer. Discontinuous variations of intensity are found atk=5, 14, 16, 29, 34, 45 and 54. Most of these magic numbers coincide with or differ by only one from those observed in Ar k + . The similarity in magic numbers between Mn k + and Ar k + indicates that the bonding nature in the charged Mn clusters is similar to that in the charged Ar clusters; The polarization force between a positive ion in the center of a cluster and surrounding neutral atoms is dominant binding force.
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    Evidence of linear chain forn≧10 carbon negative ion clusters revealed by mass selected photodetachment spectroscopy (1991)
    Springer
    The European physical journal 19 (1991), S. 427-429 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract Photodetachment spectra of negative carbon clusters are reported in the size range from 5 through 20 atoms. The clusters were prepared in a supersonic beam by laser vaporization and 2nd (2.3 eV) and 3rd (3.5 eV) harmonics of Nd-YAG laser were used for photodetachment. The resultant data indicate that carbon negative cluster ions in the 10–20 range take the forms of both linear chain and cyclic ring under a certain condition.
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    Reaction of small carbon clusters with hydrogen during laser vaporization of graphite (1991)
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    The European physical journal 19 (1991), S. 447-449 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract The hydrogen uptake for small carbon clusters C4 to C22 has been studied at high hydrogen pressure. This study indicate that both chain and ring structures exist in parallel.
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    Structural properties of 3-dimensional carbon clusters (1991)
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    The European physical journal 19 (1991), S. 443-446 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract Structural properties of 3d carbon clusters were calculated employing recently developed model potential energy functions for carbon. Primarily, spherical shell structures were included in the present investigation. Configurations corresponding to local energy minima were calculated for various shells of an icosahedron containing different number of C atoms. For C60, the two low-lying isomers, the buckminsterfullerene and truncated dodecahedron, were found to be almost isoenergetic. It was also found that fully relaxed structures of C90 and C120 have energies very comparable to that of C60. Furthermore, a systematic analysis carried out in this study for carbon clusters with varying dimensionalities, revealed an interesting relationship between the bond lengths and the distribution of bond angles. In all cases, shorter bond distances were found to be associated with larger bond angles.
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    Electron energy loss spectroscopy of van-der-Waals clusters (1991)
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    The European physical journal 20 (1991), S. 35-38 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80 ; 71.35
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    Topics: Physics
    Notes: Abstract A method to measure electron energy loss spectra (EELS) of clusters with a high resolution (30 meV) has been developed and has been applied to some van der Waals clusters (Ar n , Kr n ). Structures have been found which relate to the excitation of atoms on the surface and inside the cluster. An influence of the cluster size on the spectra has been observed.
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    On the nature of bulk and surface excitations in Argon clusters (1991)
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    The European physical journal 20 (1991), S. 39-42 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 71.90 ; 78.40
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    Topics: Physics
    Notes: Abstract Absorption spectra of Ar clusters containing between 10 and 106 atoms are dominated by strong transitions into bulk and surface states. The intensity variation of bulk and surface excitations is analyzed within a model, which divides the cluster into a surface layer and into an interior part. The thickness of the surface layer is determined by the intensity ratio of bulk and surface excitations. For then=2, 2′ excitons a reasonable value ranging between the radius of then=2 exciton and the nearest neighbour distance is obtained. In case of then=1 excitons the thickness of the surface layer is much smaller than the nearest-neighbour distance indicating that then=1 surface excitons might be interpreted as excitations of atoms on the cluster surface.
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    Theory for excess electrons in clusters of rare gas atoms (1991)
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    The European physical journal 20 (1991), S. 53-55 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract An exact theory for excess electrons in clusters of rare gas atoms is limited to small sizes,n 〈 20, because of many body polarization interactions which make it necessary to solve a large system of linear equations. We present a simple dielectric screening approximation, which avoids this difficulty and which is in very good agreement with the exact calculation. This approximation can be used to examine the excitation energies of excess electrons and exciton energies in large clusters. A new atomic structure is proposed for a cluster of 12 Xe atoms, resulting in an increased binding energy for the excess electron, which is larger than the electron affinity of a cluster of 13 atoms. This might explain the relatively large abundance of Xe 12 − observed in the experiment.
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    Liquid drop model of multiply charged metal cluster fission (1991)
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    The European physical journal 20 (1991), S. 111-113 
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    Keywords: 36.40 ; 61.25
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    Topics: Physics
    Notes: Abstract Qualitative similarities and differences between metal cluster and nuclear fission are discussed in terms of the liquid drop model. Points covered include the dependence onz 2/n of the relative fission rate, the critical size, and the competition between fission and evaporation.
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    The relation of cluster ion distributions to neutral cluster distributions in cluster beam experiments (1991)
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    The European physical journal 20 (1991), S. 115-118 
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    Keywords: 36.40 ; 33.80 ; 82.30
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    Topics: Physics
    Notes: Abstract One of the major problems in cluster beam experiments with uncharged clusters is to relate the detected distribution of cluster ions to the original distribution of the neutrals. Fragmentation of the clusters, differences in ionization efficiencies, and desorption of ligands for chemically reacted clusters distort the initial distribution. In this contribution the abundances of the neutral and the ionized particles will be related by rate equations in terms of phenomenological rate constants. Two approaches are chosen. In the more simple one the ionization and decay processes are fast and take place during the excitation pulse. In the second approach delayed processes are also allowed. In both cases recursion formulas are derived as analytical solutions of the coupled rate equations for the time evolution of the neutral and ionized cluster intensities. The general solutions contain a considerable number of parameters which have to be reduced by experimental conditions and observations. Applications are discussed.
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    Photofragmentation of cluster ions: the visible photoabsorption spectrum of Ar2N 2 + (1991)
    Springer
    The European physical journal 20 (1991), S. 153-155 
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    Keywords: 36.40 ; 33.80 ; 33.20
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    Topics: Physics
    Notes: Abstract The absolute cross section for photodissociation of Ar2N 2 + was measured as a function of wavelength in the 470–550 nm range. A structureless broad band was observed; the cross section has a maximum of ∼ 210 × 10−18 cm2 at ∼ 500 nm. The measurement of the photofragment time-of-flight spectrum shows that(1) N 2 + , Ar+ and Ar 2 + are produced in the photodissociation of Ar2N 2 + in the wavelength range studied, and that(2) the observed visible absorption band is ascribable to a parallel-type transition of Ar2N 2 + , which possibly retains a linear geometry.
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    On the structure and stability of Ar n and Ar n + clusters at finite temperature (1991)
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    The European physical journal 20 (1991), S. 147-151 
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    Keywords: 36.40 ; 71.10 ; 77.30
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    Notes: Abstract For Ar2–29 and Ar 2–29 + clusters at 20 K in the polarization model presented here the electrodynamical dipole-dipole many-body problem is solved selfconsistently with the Monte-Carlo method (MC) at 20 K, i.e. the instantaneous dipole-dipole interaction is solved to infinite perturbation order and in cluster expansion to the order of the cluster size. The long range many-body dipole-dipole interaction is coupled to exchange interaction by a modified effective dipole polarizability. This model will be compared to the dimer model and classical MC simulation of Ar n . The resulting different magic numbers in the binding energies are discussed in this connection with different experimental techniques of cluster ionization. By the mean square cluster diameter a shape parameter is introduced and it is found that with this parameter structural form transition in cluster growth can be resolved, and surprisingly do not correlate with the magic numbers.
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    Evaporation of Lennard-Jones clusters (1991)
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    The European physical journal 20 (1991), S. 163-166 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract Extensive molecular dynamics simulations have been done to study the evaporation of a 13-atom Lennard-Jones cluster. The survival probability and the evaporative lifetime are calculated as a function of the cluster total energy from a classical trajectory analysis. The results are interpreted in terms of the RRK theory of unimolecular dissociation. The calculation of the binding energy of the evaporated species from the evaporation rate and the average kinetic energy release is discussed.
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    IR-photodissociation of size selected molecular clusters and their structures (1991)
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    The European physical journal 20 (1991), S. 177-180 
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    Keywords: 36.40 ; 82.50.F
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    Notes: Abstract Infrared photodissociation spectra of (CH3NH2) n clusters were measured fromn=2 ton=6 near the monomer absorption of the C-N stretching mode at 1044 cm−1 using a cw-CO2 laser. The clusters were size-selected by scattering from a helium beam. The spectrum of cold dimers shows a red (1038 cm−1) and a blue (1048 cm−1) shifted peak which is attributed to the non-equivalent position of the C-N in the open dimer structure. The larger clusters exhibit only one peak between 1045.4 cm−1 and 1046.0 cm−1 caused by the equivalent position of the C-N in the cyclic structures of the larger clusters. Structure calculations confirm these results. Secondly, the mixed complexes C2H4-CH3COCH3 and C2H4-(CH3COCH3)2 were investigated. The dimer spectrum, measured around the monomer frequency of the out-of-plane bending mode of C2H4 at 949 cm−1, shows two peaks at 946.2 cm−1 and 961.3 cm−1. This splitting is attributed to two different isomers that are found in configuration calculations. A similar behaviour is found for the trimer.
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    Fragmentation by electron impact ionization and intracluster reactions of size selected (N2H4) n and (OCS) n clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 181-183 
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    Keywords: 36.40 ; 34.80.G
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    Notes: Abstract The hydrogen-bonded (N2H4) n clusters and the van der Waals (OCS) n clusters are size selected in a scattering experiment with a He beam up to the cluster sizen=6. By measuring the angular distributions of the scattered clusters the complete fragmentation pattern of electron impact ionization is obtained. For Hydrazine the two main fragment masses are the protonated species (N2H4) n−1H+ and with somewhat weaker intensities also the nominal ion mass (N2H4) n + . The largest intensity is observed for the monomer ion N2H 4 + to which clusters up ton=5 fragment. For carbonylsulfide, completely different results are obtained. Aside from the fragments of the OCS monomer and the van der Waals cluster fragments (OCS) 2 + and (OCS) 3 + signals at mass S 2 + , S 3 + and S2OCS+ are detected. This indicates a fast chemical reaction in the cluster according to: S + OCS → CO + S2 which occurs for clusters of sizen ≥ 2. Peaks at S 3 + and S2OCS+ are seen for the first time forn ≥ 5 according to a further reaction of S2 in the cluster.
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    Energy transfer rates in inhomogeneous van der Waals clusters (1991)
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    The European physical journal 20 (1991), S. 185-187 
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    Keywords: 33.65 ; 33.80E ; 36.40
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    Topics: Physics
    Notes: Abstract The internal energy exchanges inside an inhomogeneous van der Waals cluster are investigated by means of molecular dynamic calculations. The very long time scales for relaxation of the high frequency degrees of freedom are examined within the framework of Nekhoroshev's theorem.
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    Production and stability of oxygen cluster cations and anions, revisited (1991)
    Springer
    The European physical journal 20 (1991), S. 201-203 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Stoichiometric and non-stoichiometric, positive and negative oxygen cluster ions (n up to 70) have been produced in a crossed neutral beam/electron beam ion source. The abundance and stability of the ions formed have been analyzed with a double focussing sector field mass spectrometer in a series of experiments. Positive and negative ion mass spectra observed exhibit distinct abundance anomalies, however, at different cluster sizes. Abundance maxima and minima correlate with correspondingly small and large metastable fractions of (O2) n + and (O2) n − ions, respectively. (O2) n + ions may also lose up top=(n−1) monomers by collision induced dissociation with monotonously decreasing probability with increasingp. Metastable fractions determined for (O2) n − ions produced with appr. zero eV electrons are in general larger than those for ions produced with appr. 7 eV electrons. (O2) n − ions are also observed to decay via autodetachment, with lifetimes increasing with increasing cluster size. Finally, here we were able to prove that an apparent loss of the monomer fragment O (and higher homologues) observed in the metastable time regime is due to ordinary metastable monomer evaporation in the acceleration region. Moreover, we will also present here some new data and interpretation concerning the electron attachment cross section function for O2 clusters.
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    Metal carbide clusters formed by laser ablation of metal oxide-graphite systems (1991)
    Springer
    The European physical journal 20 (1991), S. 89-91 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80 ; 33.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The laser ablation of solid targets made of mixtures of simple components yields cluster ions of various composition. In this paper, positive cluster ions formed by laser ablation of metal oxide and graphite systems are reported. The formation of Me m C n + cluster ions indicate a chemical reaction in the surrounding area hit by the laser beam.
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    Metastable decay of Ar n + involving single monomer evaporation and the loss of peculiar numbers of monomers (1991)
    Springer
    The European physical journal 20 (1991), S. 157-159 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Production and stability of Ar n +* ions (withn up to 420) formed by electron impact ionization of a supersonic Ar cluster beam were investigated with a double focussing sector field mass spectrometer. The present study confirms previous magic number determinations up to the 4th icosahedral shell. A systematic study of metastable dissociations (monomer evaporation, magic number evaporation) for singly charged cluster ions as a function of cluster size, internal excitation energy and time elapsed since ion formation gives new insight into the ionization process and subsequent reactions of the ions formed. At a well-defined threshold energy ofca. 28 eV, the magic number loss mechanism occurs simultaneously with the well known single monomer evaporation process which proceeds at all energies. The new mechanism is the first known example of cluster ion metastability showing an exponential dependence on time, providing further evidence that the precursor parent cluster ion is produced in a specific energy state.
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    Melting of gold microclusters (1991)
    Springer
    The European physical journal 20 (1991), S. 235-238 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The transition from solid-like to liquid-like behavior in Au n ,n=6, 7, 13, clusters is studied using molecular dynamics simulations. A Gupta-type potential with all-neighbour interactions is employed to incorporaten-body effects. The melting-like transition is described in terms of short-time averages of the kinetic energy per particle, root-mean-square bond length fluctuations and mean square displacements. A comparison between melting temperatures of Au n and Ni n clusters is presented.
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    Structural and dynamical properties of transition metal clusters (1991)
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    The European physical journal 20 (1991), S. 239-242 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Results of molecular dynamics simulation studies of structural and dynamical properties of 12-, 13-, and 14-atom transition metal clusters are presented. The calculations are carried out using a Gupta-like potential expressed in reduced units. The transformation to absolute units involves two size-dependent parameters which effectively convert the potential into a size-dependent one. The minimum energy geometries of the clusters are obtained through the technique of simulated thermal quenching. A melting-like transition is observed as the energy of the clusters is increased. A novel element of the transition is that it may involve a premelting state.
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    Size effects in the solid phase transition of SF6 clusters (1991)
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    The European physical journal 20 (1991), S. 251-253 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.14F ; 64.70K
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The structure of SF6 clusters produced in a free jet expansion is studied by electron diffraction methods. A solid phase transition is known to occur when clusters are warmed up by changing several experimental conditions in the expansion of a Ne + SF6 mixture. In the present study, the total stagnation pressure and the SF6 mole fraction are varied in order to understand how these parameters influence the structural state of the clusters and further to observe the phase transition for different cluster sizes. When the stagnation pressurep 0 is larger than about 10 bar, a given mole fraction results in clusters with identical structure and probably identical temperature. Whenp 0 is decreased below 10 bar, identical structures are found for lower and lower mole fractions. This structural behaviour suggests that for small clusters, containing less than about 500 molecules, the transition steps occur at temperatures lower than those observed for larger clusters. The possibility of detecting a temperature variation in the diffraction patterns of small cubic clusters is discussed.
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    Kinetics of phase changes in large molecular clusters (1991)
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    The European physical journal 20 (1991), S. 255-257 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.14.F ; 64.60.Q ; 82.20.M
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A method has been devised to study the kinetics of phase changes in an unfamiliar regime of extreme undercooling and rate of transformation. We show how electron diffraction can monitor the time evolution of phase changes in molecular clusters condensed from the vapor in supersonic flow. Transitions taking place in microseconds are readily followed. Examples include solid state transformations as well as the freezing of liquid clusters. Aspects of the experiment making it possible to observe familiar transitions under highly unusual conditions will be discussed along with some advantages of the new technique.
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    Theory of the structural fluctuation of Au55 clusters (1991)
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    The European physical journal 20 (1991), S. 259-261 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Stabilities and structural fluctuations of both neutral and charged Au55 clusters are examined and discussed in relation to recent experimental observations of small gold particles with an electron microscope. Transition probabilities between the icosahedral and cuboctahedral structures are calculated according to the transition state theory using a model potential consisting of attractive many-body, repulsive pairwise and Coulomb parts. It is shown that for a neutral cluster the cuboctahedral structure has too short life time to be observed around room temperature and that, on the other hand, for more than 6-fold multiply charged clusters, both structures have life times of the order of 0.1 s around room temperature and, therefore, the transition between them can be observed.
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    Optical plasmon losses in stabilized Au55 clusters (1991)
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    The European physical journal 20 (1991), S. 297-300 
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    ISSN: 1434-6079
    Keywords: 33.20.K ; 36.40 ; 42.20 ; 78.40 ; 82.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Au55 cluster compounds are investigated by optical spectroscopy and TEM. The optical spectra appear to be rather structureless, neither showing a collective excitation resonance nor exhibiting distinct absorption bands known from lower nuclearity clusters. We discuss changes of the electronic properties compared to larger Au clusters affecting both, 6sp electrons and5d-6sp interband transitions, the cluster-ligand-interaction being considered as a charge transfer process. We additionally report on a low temperature instability of the cluster compound, which results in changed optical extinction spectra. A characteristic absorption feature at λ=400 nm is attributed to small, ligand-free Au cluster fragments.
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    Negative ion photoelectron spectroscopy of solvated electron cluster anions, (H2O) n − and (NH3) n − (1991)
    Springer
    The European physical journal 20 (1991), S. 9-12 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.60 ; 33.80.E
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The photodetachment spectra of (H2O) n =2−69/− and (NH3) n =41−1100/− have been recorded, and vertical detachment energies (VDEs) were obtained from the spectra. For both systems, the cluster anion VDEs increase smoothly with increasing sizes and most species plot linearly withn −1/3, extrapolating to a VDE (n=∞) value which is very close to the photoelectric threshold energy for the corresponding condensed phase solvated electron system. The linear extrapolation of this data to the analogous condensed phase property suggests that these cluster anions are gas phase counterparts to solvated electrons, i.e. they are embryonic forms of hydrated and ammoniated electrons which mature with increasing cluster size toward condensed phase solvated electrons.
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    Photoemission on gold-55-clusters derived from gold-phosphine AuP(C6H5)3Cl (1991)
    Springer
    The European physical journal 20 (1991), S. 377-379 
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    ISSN: 1434-6079
    Keywords: 79.60 ; 71.20 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We measured XPS and UPS spectra of gold clusters with 55 atoms, embedded in an electrically isolating phosphine matrix, and of gold-phosphine, from which the clusters were chemically derived. Compared to the spectra of bulk gold the valence band spectrum and the core level spectra of the clusters showed shifts of the peaks and the fermi level to higher binding energies. The shift of the peaks could qualitatively be interpreted by a final state effect. We succeeded in a separation of bulk and surface contributions to the core level spectra and in a reasonable quantitative analysis of the valence band spectrum of the clusters. The Au 4f core level spectrum of gold-phosphine showed two peaks at 1.5 eV higher binding energies than the corresponding peaks of the clusters.
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    Electronic structure of Cr clusters on graphite (1991)
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    The European physical journal 20 (1991), S. 387-390 
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    ISSN: 1434-6079
    Keywords: 79.20 ; 73.20 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electronic structure of small chromium clusters deposited by evaporation onto clean polycrystalline graphite has been studied by means of Auger, X-ray Photoemission (XPS) and Electron Energy Loss (EELS) spectroscopies. The XPS results show an increase in the binding energy of both core levels and valence band reducing the cluster size. The EELS measurements show a variation of the intensity ratio of L3-to-L2 ionization core edges. We interpret this change as due to different redistribution, within the clusterd-band, of the empty states above the Fermi level. As a consequence the XPS results may also be attributed to sizeable change of the electronic structure of the small clusters.
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    Synchrotron radiation study of silver and chromium particles supported on graphite (1991)
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    The European physical journal 20 (1991), S. 391-394 
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    ISSN: 1434-6079
    Keywords: 79.60 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Silver and chromium particles in the size range 10 nm to 25 nm formed by deposition in ultra-high vacuum on graphite have been studied using synchrotron radiation. We have determined the island size by measuring the spectral dependence of the reflectivity of each sample using light in the photon energy range 35 eV to 190 eV. Comparing this measurement to a calculation of the reflectivity modified by the size-dependent extinction, determined using Mie theory, gives the average particle radius. Using this sizing technique we find that, for the growth of silver at room temperature, the average radius increases linearly with the cube root of evaporation time. Deposition with the substrate at elevated temperatures produces, for similar coverages, an increase in the average size for temperatures between 200°C and 225°C followed by a rapid decrease above 225°C. Chromium shows size effects in the photoemission spectra from the 3s and 3p core levels and the 3d valence band. With decreasing radius a decrease in the multiplet splitting of the 3s core level and a large change in the relative intensity among the 3p multiplets occurs indicating increased electron correlation as the system becomes smaller. A narrowing of the valence band also occurs which we attribute to a structural change at the surface of the particles.
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    High resolution MW spectroscopy of Rydberg clusters for the studies of small metal cluster ions: a preliminary experiment (1991)
    Springer
    The European physical journal 20 (1991), S. 407-409 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.40. Hp ; 32.30. Bv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Microwave spectroscopy in highly excited Rydberg states is proposed for structure determination of small metal cluster ions. An experimental setup for microwave optical triple resonance is developed and tested for Yb atom. Many microwave transitions are measured with the line width less than 1 MHz (HWHM).
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    Formation of silver clusters in nozzle expansions (1991)
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    The European physical journal 20 (1991), S. 425-428 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.50.C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The first successful experiments to generate continuum silver cluster beams from nozzle expansions are described. A mixture Ar/Ag expands out of a conical nozzle (0.35 mm dia., 10° cone angle, length 17 mm). At 2150 K, total pressure 300 kPa, silver partial pressure 8 kPa the silver intensity measured with a rate meter 479mm away from the source is 1.8 nm/s, or 0.02 g m−2s−1. The data for the onset of clustering confirm the predictions of the scaling laws developed to compare condensation in nozzle expansions of metal vapors with that of rare gases.
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    An electron diffraction apparatus for small particle beams (1991)
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    The European physical journal 20 (1991), S. 457-459 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.14
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An electron diffraction apparatus is described which has been developed for use with small particle beams. The apparatus features a pulsed 100 kV electron beam and on-line parallel measurement of the diffraction pattern using linear charge coupled devices. Preliminary results on a molecular beam of small silver particles are presented.
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    Concluding remarks (1991)
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    The European physical journal 20 (1991), S. 465-467 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Viewing cluster science as the embryology of the full-grown forms of matter we encounter in our surroundings, makes it appear to a relative newcomer as a highly dynamic discipline. Lines of attack showing marked progress or potential promise are briefly reviewed, and a sketch of the vast field of still-open problems is presented.
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    Electron transfer collisions between sulfur dioxide clusters and laser-excited Rydberg atoms (1991)
    Springer
    The European physical journal 21 (1991), S. 177-184 
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    ISSN: 1434-6079
    Keywords: 34.50.g ; 34.70. ; 35.20.W ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electron attachment to SO2 clusters is studied in a pulsed crossed beam apparatus, using laser-excited nf Rydberg atoms as a low energy electron source. The results are interpreted as an attachment to a dimer subcluster followed by a rapid impulsive dissociation of the nascent dimer anion. The remaining cluster anions possess a large amount of internal energy. At low principal quantum numbersn, the influence of the Rydberg ionic core leads to an important evaporation process interpreted with simple model calculations.
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    Nutrient optimization for high density biological production applications (1991)
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    Cytotechnology 5 (1991), S. 15-30 
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    ISSN: 1573-0778
    Keywords: high density ; cell culture ; serum-free medium ; hybridoma ; CHO cells ; virus production ; insect cells ; adoptive immunotherapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Conclusion At the 1989 annual meeting of the U.S. Tissue Culture Associations, Ricahrd am, a leading investigator in the serum-free nutrient requirements of cultured cells, commented on the process of medium development. He noted that a survey of major media manufacturers revealed that, among the top selling mammalian cell culture media formulations, most were nearly thirty years old. This commentary is noteworthy considering the tremendous changes in cell culture understanding and derived applications which have emerged over these three decades. Fastidious cell types relatively unknown to investigators of the 1950s and 1960s are now being cultivated in defined, serum-free environments. Culture environments range from limiting dilution clonal recoveries to maintenance cultures approaching tissue densities. While research applications continue to predominate, applications of cell culture have expanded to the engineered production of biopharmaceuticals, to replacement of animal models for toxicology testing, and to the preservation, activation and expansion of human cells, tissues and organs. It is likely that future nutrient medium development will be predicated upon the design of a minimal number of defined formulations of relatively generic utility to a broad class of cell types. Analytical techniques derived from those described herein will be exploited in the user laboratory and in collaboration with the supplier to optimize the nutrient composition for the desired biological response.
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    Growth and protein production kinetics of a murine myeloma cell line transfected with the human growth hormone gene (1991)
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    Cytotechnology 5 (1991), S. 223-231 
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    ISSN: 1573-0778
    Keywords: cell culture ; kinetics ; Ig promoter/enhancer ; plasmacytoma ; recombinant protein production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A model mammalian cell system for the production of recombinant proteins was investigated. Murine myeloma cells which had lost the ability to produce both heavy and light chain immunoglobulin molecules were transfected with a vector containing the immunoglobulin heavy chain promoter and enhancer elements linked to the human growth hormone gene. The growth kinetics of G32, a clonal isolate, were found to be similar to both the parent myeloma and hybridomas. However, production of hGH by G32 was growth associated, rather than as a secondary metabolite as is the case for hybridomas. In addition, G32 produced hGH at molar levels greater than most hybridomas.
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    Primary cell culture from embryos of the Japanese scallop Mizuchopecten yessoensis (Bivalvia) (1991)
    Springer
    Cytotechnology 6 (1991), S. 49-54 
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    ISSN: 1573-0778
    Keywords: Bivalvia ; cell culture ; embryo ; mitosis ; scallop
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Primary cell cultures obtained from embryos of Mizuchopecten yessoensis (Bivalvia) survived for four months. Although the number of cells progressively decreased during the cultivation, mitotic cells were observed both at the first stages and at the end. A possibility of growing marine invertebrates cells in long term primary culture is discussed.
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    Characterization of endosteal osteoblasts isolated from human maxilla and mandible: An experimental system for biocompatibility tests (1991)
    Springer
    Cytotechnology 7 (1991), S. 39-48 
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    ISSN: 1573-0778
    Keywords: cell culture ; endosteal human osteoblasts ; maxilla ; mandible ; titanium ; biocompatibility ; alkaline phosphatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Fragments of cancellous and cortical bone from human maxilla and mandible were cultured by the explant technique. Cells isolated by trypsinization of primary cultures were characterized as osteoblasts on the basis of intracellular alkaline phosphatase activity, the constituents of the extracellular matrix, and response to human parathormone (PTH). In culture, the osteoblasts often gave rise to superposed clumps of large cells whose cytoplasm contained endoplasmic reticulum, numerous mitochondria, vacuoles, and a dense network of intermediate filaments, often at the level of the plasma membrane. In the presence of vitamin C and 1,25-dihydroxyvitamin D3, the osteoblasts produced an extracellular matrix composed of collagen type I and various non-collagenous proteins, including osteocalcin. Biochemical test results were comparable to those reported for osteoblasts of other origins (rat calvaria, human iliac crest), and namely elevated intracellular alkaline phosphatase activity and cAMP accumulation in response to stimulation by human PTH (1–34). Osteoblasts isolated in this manner were cultured in the presence of pure titanium disks to determine the effects of exposure to this metal. Electron microscopy revealed few significant differences in cell growth and specific enzyme activity compared to control osteoblasts grown on plastic dishes, reflecting the excellent biologic and biochemical relationship between the osteoblasts and pure titanium. This experimental system thus appears suitable for biocompatibility studies, and in particular, evaluation of dental implants.
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    Characterization of the Unstirred Water Layer in Caco-2 Cell Monolayers Using a Novel Diffusion Apparatus (1991)
    Springer
    Pharmaceutical research 8 (1991), S. 222-227 
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    ISSN: 1573-904X
    Keywords: Caco-2 ; unstirred water layer ; intestinal permeability ; steroids ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Caco-2 monolayers grown on Transwell polycarbonate membranes have been characterized as a valuable tool in drug transport studies. Despite the clear advantages of this system, the lack of stirring may create an unstirred water layer (UWL) whose resistance may limit the transcellular transport of lipophilic molecules. The objective of this study was to evaluate a novel diffusion cell where the transport buffer is mixed by gas lift and to determine the mixing flow rate needed to reduce the thickness (h) of the UWL adjacent to cell monolayers. The transport of the leakage marker, mannitol, remained at least 15-fold lower than the flux of testosterone, indicating that the stirring flow rates used did not affect the integrity of the monolayers. The permeability (P) of testosterone (log PC 3.13) across monolayers mounted on this diffusion cell was 4.07, 10.90, and 14.18 × 10−5 cm/sec at flow rates of 0, 15, and 40 ml/min, respectively, and the apparent UWLs were calculated to be 1966, 733, and 564µm. P and h in the stagnant Transwell were 3.08 × 10−5 cm/sec and 2597 µm, respectively. On the other hand, h was significantly smaller in the unstirred, cell-free membranes than in their cell-containing counterparts. P was correlated with lipophilicity and, in the case of the more lipophilic compounds, with the mixing flow rate.
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    The Influence of Peptide Structure on Transport Across Caco-2 Cells (1991)
    Springer
    Pharmaceutical research 8 (1991), S. 1453-1460 
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    ISSN: 1573-904X
    Keywords: peptide ; transport ; permeability ; lipophilicity ; hydrogen bonding ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The relationship between structure and permeability of peptides across epithelial cells was studied. Using confluent monolayers of Caco-2 cells as a model of the intestinal epithelium, permeability coefficients were obtained from the steady-state flux of a series of neutral and zwitterionic peptides prepared from D-phenylalanine and glycine. Although these peptides ranged in lipophilicity (log octanol/water partition coefficient) from −2.2 to +2.8, no correlation was found between the observed flux and the apparent lipophilicity. However, a strong correlation was found for the flux of the neutral series and the total number of hydrogen bonds the peptide could potentially make with water. These results suggest that a major impediment to peptide passive absorption is the energy required to break water–peptide hydrogen bonds in order for the solute to enter the cell membrane. This energy appears not to be offset by the favorable introduction of lipophilic side chains in the amino acid residues.
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    The use of tuftsin in experimental leprosy (1991)
    Springer
    Bulletin of experimental biology and medicine 112 (1991), S. 1152-1156 
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    ISSN: 1573-8221
    Keywords: experimental leprosy ; synthetic tuftsin ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00839564
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