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  • Articles  (97)
  • 36.40  (59)
  • tissue culture  (38)
  • Springer  (97)
  • American Institute of Physics
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  • 1990-1994  (97)
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  • 1991  (97)
  • 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
    Primary cultures of shark rectal gland epithelial cells: A model for hormone-sensitive chloride transport (1991)
    Springer
    Methods in cell science 13 (1991), S. 149-161 
    Details
    ISSN: 1573-0603
    Keywords: tissue culture ; sharks ; epithelia ; chloride transport ; kidney tubules ; cell regulation ; cystic fibrosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Methods are described for establishing primary monolayer cultures from chloride-secreting epithelial cells of the dogfish shark (Squalus acanthias) rectal gland (SRG). After stimulation, cultures display exceptionally high rates (150 to 250μA/cm2) of transepithelial chloride secretion. Hormones and neurotransmitters which increase cytoplasmic cyclic AMP, cyclic GMP, calcium or phospholipid-derived second messengers are potent secretagogues. Cultures can be analyzed using a variety of morphologic, biochemical, and electrophysiologic methods. These characteristics make SRG cultures a powerful model for delineating the molecular basis of the transmembrane and intracellular signaling networks that stimulate or inhibit secondary active chloride transport in epithelia. Secondary active chloride transport occurs in a variety of epithelia, including those comprising both the proximal and distal segments of vertebrate nephrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02388119
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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
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    Histology of, and physical factors affecting, transient GUS expression in pearl millet (Pennisetum glaucum (L.) R. Br.) embryos following microprojectile bombardment (1991)
    Springer
    Plant cell reports 10 (1991), S. 120-125 
    Details
    ISSN: 1432-203X
    Keywords: Gramineae ; GUS ; microprojectile bombardment ; pearl millet ; tissue culture ; transient gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transient GUS (β-glucuronidase) expression was visualized in whole and sectioned embryos of Pennisetum glaucum (L.) R. Br. (pearl millet) after microprojectile bombardment with pMON 8678 DNA. Strongest GUS expression occurred in cells located in the center of GUS positive spots with decreasing intensity in surrounding cells. GUS positive cells could be seen up to 12 cell layers beneath the epidermis. Needle-like crystals of the GUS assay product were found throughout the cytoplasm of GUS positive cells. The number of GUS positive spots was correlated to the microprojectile spread pattern on the medium surface. Shorter bombardment distances (6.6 and 9.8 cm) and the standard accelerator speed gave the best results for transient expression but also caused maximum tissue damage. The speed and distance, however, had little influence on the ability of bombarded embryos to form compact callus. The developmental stage of the bombarded immature embryos was the determining factor in the formation of compact callus, from which plants were regenerated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232041
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  • 7
    Electronic Resource
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    A segment of rye chromosome 1 enhances growth and embryogenesis of calli derived from immature embryos of wheat (1991)
    Springer
    Plant cell reports 10 (1991), S. 148-151 
    Details
    ISSN: 1432-203X
    Keywords: wheat ; rye ; embryogenesis ; growth ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The influence of the short arm of rye chromosome 1 (1RS) from Secale cereale var. Imperial on the growth and differentiation of callus cultures from wheat Triticum aestivum var. Chinese Spring immature embryos was analysed. This chromosome arm was found to stimulate both embryogenesis and the rate of growth of calli. Recombinant lines carrying segments of 1RS were used to delineate the regions of 1RS responsible for the tissue culture effects. The enhancement of embryogenesis and the stimulation of growth were shown to be associated with two distinct genetic regions of the chromosome arm; the former is located between the centromere and the Sec 1 locus, while the latter is situated in the immediate vicinity of the Sec 1 locus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232047
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  • 8
    Electronic Resource
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    Efficient shoot regeneration of Brassica campestris using cotyledon explants cultured in vitro (1991)
    Springer
    Plant cell reports 9 (1991), S. 549-554 
    Details
    ISSN: 1432-203X
    Keywords: Brassica campestris ; cotyledon culture ; histology ; organogenesis ; regeneration ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A system has been developed for efficient regeneration of shoots from Brassica campestris in vitro. Using 4-day old cotyledons with petioles as expiants and a combination of BA and NAA in the regeneration media, up to 70% of expiants produced shoots after 2 weeks in culture. The optimal conditions for regeneration were found to include a BA concentration of 2mgL−1 and NAA concentration of 1mgL−1. Light intensity had a profound effect on regeneration potential. The use of silver ions as an inhibitor of ethylene action reduced regeneration rates in this system. Rooting occured simultaneously with shoot formation on these media and the resultant shoots could be rooted readily on minimal medium. The genotype dependency was investigated and indicated that this method would be widely applicable to B. campestris cultivars. Regeneration of one cultivar, a high erucic acid type (R-500), was inefficient in the system described here. Histological studies indicated the development of multiple shoot primordia from the petiolar cut ends of the expiants after the initiation of meristematic activity in the cells about 100μm from the cut site within 2 days of culture initiation. The system described is compatible with previously reported Agrobacterium — mediated transformation protocols involving cotyledonary petioles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232329
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  • 9
    Electronic Resource
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    Differential allelochemical detoxification mechanism in tissue cultures ofAntennaria microphylla andEuphorbia esula (1991)
    Springer
    Journal of chemical ecology 17 (1991), S. 167-174 
    Details
    ISSN: 1573-1561
    Keywords: Allelopathy ; Antennaria microphylla ; small everlasting ; Euphorbia esula ; leafy spurge ; tissue culture ; hydroquinone ; arbutin ; glucosyltransferase ; biotransformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Callus and suspension cultures ofAntennaria microphylla (small everlasting) and the noxious weedEuphorbia esula (leafy spurge) can glucosylate benzene-1,4-diol (hydroquinone) to the corresponding monoglucoside, arbutin. HPLC analysis of extracts from callus tissue corroborates the presence of hydroquinone in the cells of small everlasting. Constitutive levels of a UDPG-dependent glucosyltransferase were detected in cell-free extracts of this tissue. Although this detoxification enzyme was induced in leafy spurge suspension culture cells grown in the presence of hydroquinone, the activity was six-fold lower than that measured in small everlasting. Differential ability to detoxify hydroquinone provides a basis for the observed allelopathic interaction between small everlasting and leafy spurge.
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    URL: http://dx.doi.org/10.1007/BF00994430
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  • 10
    Electronic Resource
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    Alfalfa heat shock genes are differentially expressed during somatic embryogenesis (1991)
    Springer
    Plant molecular biology 16 (1991), S. 999-1007 
    Details
    ISSN: 1573-5028
    Keywords: Medicago sativa L. ; stress response ; tissue culture ; somatic embryogenesis ; heat shock protein (HSP)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have isolated two cDNA clones (Mshsp18-1; Mshsp18-2) from alfalfa (Medicago sativa L.) which encode for small heat shock proteins (HSPs) belonging to the hsp17 subfamily. The predicted amino acid sequences of the two alfalfa proteins are 92% identical and a similar degree of homology (90%) can be detected between Mshsp 18-2 and the pea hsp 17. In comparison to various members of small HSPs from soybean amino acid sequence similarities of 80–86% were identified. The alfalfa HSPs share a homologous stretch of amino acids in the carboxy terminal region with hsp22, 23, 26 from Drosophila. This region contains the GVLTV motif which is characteristic of several members of small HSPs. At room temperature alfalfa hsp 18 mRNAs were not detectable in root and leaf tissues but northern analysis showed a low level of expression in microcallus suspension (MCS). The transcription of Mshsp 18 genes is induced by elevated temperature, CdCl2 treatment and osmotic shock in cultured cells. In alfalfa somatic embryos derived from MCS a considerable amount of hsp 18 mRNA can be detected during the early embryogenic stages under normal culture conditions. The differential expression of these genes during embryo development suggests a specific functional role for HSPs in plant cells at the time of the developmental switch in vitro.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00016072
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  • 11
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    Studies on the kinetics of Na+/H+ exchange in OK cells: Introduction of a new device for the analysis of polarized transport in cultured epithelia (1991)
    Springer
    The journal of membrane biology 120 (1991), S. 173-183 
    Details
    ISSN: 1432-1424
    Keywords: brush border membrane ; amiloride ; tissue culture ; intracellular pH ; fluorescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The present study describes a new perfusion technique—based on the use of a routine spectrofluorometer—which enables fluorometric evaluation of polarity, regulation and kinetics of Na+/H+ exchange at the level of an intact monolayer. Na+/ H+ exchange was evaluated in bicarbonate-free solutions in OK (opossum kidney) cells, a renal epithelial cell line. Na+/H+ exchange activity was measured by monitoring changes in intracellular pH (pH i ) after an acid load, using the pH-sensitive dye 2′7′-bis (carboxyethyl) 5–6-carboxy-fluorescein (BCECF). Initial experiments indicated that OK cells grown on a permeable support had access to apical and basolateral perfusion media. They also demonstrate that OK cells express an apical pH i , recovery mechanism, which is Na+ dependent, ethylisopropylamiloride (EIPA) sensitive and regulated by PTH. Compared to resting conditions (pH i =7.68; pH o =7.4) where Na+/H+ exchange is not detectable, transport rate increased as pH i decreased. A positive cooperativity characterized the interaction of internal H+ with the exchanger, and suggests multiple H+ binding sites. In contrast, extracellular [Na+] increased transport with simple Michaelis-Menten kinetics. The apparent affinity of the exchanger for Na+ was 19mM at an intracellular pH of 7.1 and 60mM at an intracellular pH of 6.6. Inhibition of Na+/H+ exchange activity by EIPA was competitive with respect to extracellular [Na+] and theK i was 3.4 μM. In conclusion, the technique used in the present study is well suited for determination of mechanisms involved in control of epithelial cell pH i and processes associated with their polarized expression and regulation.
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    URL: http://dx.doi.org/10.1007/BF01872400
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  • 12
    Electronic Resource
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    Cold storage of in vitro cultures of hybrid poplar shoots (Populus alba L. x P. grandidentata Michx.) (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 161-168 
    Details
    ISSN: 1573-5044
    Keywords: aspen ; growth suspension ; phenotypic variation ; ultra-structure ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Shoot cultures of P. alba x P. grandidentata ‘Crandon’ were maintained for more than 5 years at 4°C with minimal growth. The highest survival after 2 years and 5 years of cold storage were 70% and 25% respectively using 1-month of pre-storage culture on MS medium containing 1.33 μM BA. When 5-year-old cold-stored shoot cultures were transferred to the greenhouse, color variations were observed. The frequencies of albino and red pigmented plants were 0.25% and 12.8%, respectively. A rosette type growth pattern was also observed on 0.3% of the long-term cold-stored plants. During long-term cold storage there were local disruption of cambium connections and the accumulations of chemicals in some cells, as observed by light microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00041285
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  • 13
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    Callus induction and plant regeneration from anther and inflorescence culture of Sorghum (1991)
    Springer
    Euphytica 52 (1991), S. 177-181 
    Details
    ISSN: 1573-5060
    Keywords: Sorghum bicolor L. Moench ; tissue culture ; callus ; haploid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Twenty-five inbred lines, including grain and forage types from the USA and China, two hybrids, one Sorghum almum, and one Parasorghum (S. versicolor) were tested for their response to anther culture. Three nutrient media were effective in inducing anther calli from six cultivars (Xin White, TX 403-TSB, DDY Sommer Milo, TX 2779, Brawley, and Spur Federal) and one was effective for plant regeneration for one cultivar, Xin White. Averaged over media, callus induction frequency (number of calli per 100 anthers) was highest in cultivars Xin White and TX 403-TSB (6.7 and 3.9%, respectively). The means of cultivars for media C17-2 and Ms-t-z-2, 4.3 and 3.2%, respectively, were superior to that for medium 85D3-2 (0.1%). Expressed as an average of the six cultivars and three media the mean calli induction frequency was 2.6%; however, differential responses of genotype and medium were noted. Among the 10 regeneration media tested, medium MS-d-4 containing Murashige and Skoog basal components plus 2.0 mg/l indole-3-acetic acid (IAA) and 2.5 mg/l kinetin was the most effective for plant regeneration. Numbers of albino plants and calli developing only roots increased directly with callus-induction time, whereas the frequency of plant regeneration decreased. Regenerated plants had varied numbers of chromosomes in root tip cells: 10, 15, 20, 40, and 60. The 29 regenerated plants that reached maturity, however, were highly fertile and contained only 10 bivalents in pollen mother cells. Normal chromosome number and behavior for the regenerated plants suggest that induced calli originated from cells other than microspores. However, spontaneous chromosome doubling in microspore-derived haploids may occur. The appearance of albinos also implies that haploids may have been produced from anther culture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029394
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  • 14
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    Field resistance to late blight (Phytophthora infestans (Mont.) De Bary) in potato (Solanum tuberosum L.) somaclones associated with instability and pleiotropic effects (1991)
    Springer
    Euphytica 56 (1991), S. 75-80 
    Details
    ISSN: 1573-5060
    Keywords: Solanum tuberosum ; potato ; Phytophthora infestans ; late blight ; adventitious regeneration ; somaclonal variation ; tissue culture ; mutation ; maturity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Adventitious regenerants (‘somaclones’) of ‘Bintje’ and their vegetative progeny were screened for field resistance to Phytophthora infestans as follows: the area under the disease progress curve was computed and correlated with resistance rating in ‘Bintje’ and reference varieties. The resistance rating of the somaclones was determined from this relationship. Clones with stable improved field resistance in successive years' trials were detected, however, most of such clones were also maturation mutants. Variation in resistance rating in clone replicates and between years was detected in most clones. The possible basis of the field resistance and reasons for its instability are discussed.
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    URL: http://dx.doi.org/10.1007/BF00041746
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  • 15
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    Application of cell and tissue culture and in vitro selection for disease resistance breeding — a review (1991)
    Springer
    Euphytica 56 (1991), S. 269-285 
    Details
    ISSN: 1573-5060
    Keywords: disease resistance ; in vitro selection ; somaclonal variation ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Somaclonal variation, i.e. the variation induced by cell and tissue culture, offers an opportunity to broaden the genetic variation of crops. As a result of somaclonal variation a wide range of plant characteristics can be altered. However, the selection of agronomically important traits, e.g. disease resistance, has many limitations. The efficiency of selection can be increased by the application of in vitro selection procedures. Selection strategies that may be applied to obtain disease resistant somaclonal variants are described. Their merits and limitations, in relation to the efficiency of the procedures, the frequency of disease resistant variants and the genetics of the resistance obtained, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00042373
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  • 16
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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.
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    URL: http://dx.doi.org/10.1007/BF00028374
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  • 17
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    Food ingestion by planarian intestinal phagocytic cells — a study by scanning electron microscopy (1991)
    Springer
    Hydrobiologia 227 (1991), S. 179-185 
    Details
    ISSN: 1573-5117
    Keywords: planarian ; intestine ; endocytosis ; phagocytosis ; tissue culture ; SEM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tissue-cultured fragments of the intestine of Dugesia japonica were examined by SEM for formation of pseudopodia in the phagocytic cells. For comparison, parallel experiments in vivo were performed using intact animals under starved and fed conditions. When cultures were incubated with fetal calf serum, individual phagocytic cells formed one or two large cup-like pseudopodia. Cultures incubated with latex beads showed pseudopodia that varied in shape according to the size of the beads and that had multiple folds or funnels. Pseudopodia and the modes of their endocytosis in this planarian, however, are morphologically like those of other phagocytes such as digestive cells of Hydra, rat macrophages, and human neutrophils. Culture in vitro of digestive tissue should be an important tool for studying the digestive physiology of planarians at the cellular level.
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    URL: http://dx.doi.org/10.1007/BF00027600
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  • 18
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    A comparison of BA, zeatin and thidiazuron for adventitious bud formation from Picea glauca embryos and epicotyl explants (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 281-287 
    Details
    ISSN: 1573-5044
    Keywords: conifer ; cytokinin ; organogenesis ; Picea glauca ; tissue culture ; white spruce
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Picea glauca (white spruce) zygotic embryos and one-week-old-seedling epicotyl explants were placed on either Woody Plant Medium (WPM) or half-strength Schenk & Hildebrandt (1/2S&H) medium supplemented with varying levels of benzyladenine (BA) (0.1, 1.0, 10, 50, 100 μM), zeatin (10, 50, 100 μM) or thidiazuron (TDZ) (0.01, 0.1 μM). In addition to differences in the number of buds induced at three months on the two media, buds induced on WPM were visually more uniform, less vitrified and elongated faster. On 1/2S&H supplemented with BA, maximum bud induction from embryos occurred on 1.0 μM BA with 0.01 μM TDZ with higher BA concentrations inhibitory to bud induction. In contrast, on WPM there was little difference in the number of buds induced from embryos placed on 10, 50 and 100 μM BA with or without TDZ. One-week-old-seedling epicotyl explants required higher BA levels on 1/2S&H, as bud induction at three months was greatest at 10 μM BA. On WPM, as with the embryos, there were only minor differences in the number of buds induced from epicotyl explants on the various BA levels. Zeatin was more effective at inducing buds than BA with both media. From embryos, bud induction was greatest on 50 or 100 μM zeatin without TDZ and 50 or 100 μM zeatin with or without TDZ on 1/2S&H and WPM respectively. From epicotyl explants on 1/2S&H, there was little difference in the number of buds induced with the zeatin concentrations used, while with WPM, 50 and 100 μM zeatin induced the greatest number of buds. Interestingly, with BA, the epicotyl explants needed a higher level than the embryos for maximal response, while with zeatin, the level was the same for both embryos and epicotyl explants. Long-term (six month) survival was higher on WPM than with 1/2S&H. Additionally, embryos had a higher percentage of genotypes surviving at six-months when compared with epicotyl explants. For overall survival and development of the buds, 50 μM zeatin with 0.01 μM TDZ was the best treatment tested.
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    URL: http://dx.doi.org/10.1007/BF00157592
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  • 19
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    Micropropagation of juvenile and adult Sorbus domestica L. (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 341-348 
    Details
    ISSN: 1573-5044
    Keywords: rooting ; shoot proliferation ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Successful propagation of seedlings and mature trees of Sorbus domestica L. has been achieved by in vitro methods. Multiple shoot formation was obtained by placing shoot apices or nodal segments on a modified Schenck and Hildebrandt medium containing benzyladenine. Regenerated shoots were excised and induced to root on media with auxin. In the best treatments 75–85% of shoots from juvenile material rooted. Rooting capacity of shoots from mature explants was lower (30%) and was not improved by dipping the base of shoots in concentration solutions of indolebutyric or naphthaleneacetic acids. Plantlets were ultimately established in soil.
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    URL: http://dx.doi.org/10.1007/BF00157600
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  • 20
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    Regeneration and transformation of Ribes (1991)
    Springer
    Plant cell, tissue and organ culture 24 (1991), S. 91-95 
    Details
    ISSN: 1573-5044
    Keywords: Agrobacterium ; regeneration ; Ribes nigrum ; tissue culture ; transformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transformation of the black currant cv. Ben More was achieved by utilising the binary vector system of Agrobacterium tumefaciens. This system involved the inoculation of peeled internodal stem segments with A. tumefaciens strain LBA4404 containing the binary vector PBI121.X with the marker genes Betaglucuronidase (GUS) and neomycin phosphotransferase II (NPTII). Shoot regeneration occurred on nutrient media based on M&S salts. Transformation was confirmed by the fluorogenic assay procedure which determined that the GUS gene had been transferred into the plant material and was being expressed. Concurrent transfer of the NPTII gene into the plant material was also confirmed with a ‘dot blot’ assay on selected GUS positive plantlets.
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    Degradation of exogenous indole-3-butyric acid and riboflavin and their influence on rooting response of papaya in vitro (1991)
    Springer
    Plant cell, tissue and organ culture 26 (1991), S. 29-34 
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    ISSN: 1573-5044
    Keywords: Carica papaya ; IBA ; papaw ; papaya ; riboflavin ; root initiation ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Varying concentrations of riboflavin were added to a De Fossard et al. (1974) basal medium containing 10 µM IBA and the effect on adventitious root initiation on shoots of Carica papaya L. was studied. Ninety percent root initiation occurred in 11 days when 1 µM riboflavin was added to the culture medium. Smaller rooting percentages were observed and roots emerged more slowly with riboflavin concentrations greater and less than 1 µM. Tissue culture media were maintained at 27°±1°C in either darkness or 12-h photoperiods for 28 days, and concentrations of riboflavin and IBA were measured at regular intervals using HPLC analysis. In a De Fossard et al. (1974) basal medium, riboflavin concentrations (0.1, 1.0, 10.0 µM) decreased rapidly in light and were independent of the presence of IBA. IBA concentration steadily decreased when media was placed in light, and increasing riboflavin concentrations accelerated the reduction of IBA levels. Concentrations of IBA and riboflavin were stable with dark incubation.
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    Precocious gladiolus corm formation in liquid shake cultures (1991)
    Springer
    Plant cell, tissue and organ culture 26 (1991), S. 63-70 
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    ISSN: 1573-5044
    Keywords: corm ; cytokinin ; Gladiolus ; paclobutrazol ; sucrose ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Conditions were defined for precocious differentiation and improved growth of corms at the base of gladiolus shoots. Shoots were derived from explants cultured on agar solidified media, and corm regeneration was obtained in subsequent liquid shake cultures. Benzyladenine (BA), at 10-7 M, was found to have a stimulating effect mainly when provided to the shoots prior to manifestation of corm growth. Paclobutrazol and sucrose promoted corm formation when supplemented to the liquid media. Paclobutrazol, at 10 mg l-1, shifted assimilate allocation towards the growing corm. A differential promotion of corm development by sucrose was not observed, and the concentration of sucrose at which the sugar demand for maximal shoot and corm growth is satisfied (60 g l-1) was unaltered by the presence of paclobutrazol. The rate of corm growth on shoots cultured in a liquid medium supplemented with paclobutrazol and a saturating sucrose concentration, was a function of the length of the shoot's leaf blades, and was similar in light and in dark.
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    Plant regeneration from somatic tissue of Rhododendron laetum x aurigeranum (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 37-43 
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    ISSN: 1573-5044
    Keywords: organogenesis ; plant growth regulators ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of the source of plant material (greenhouse-grown plants or in vitro shoot cultures), the type of tissue explant (shoot-tip, single-node stem segment, whole leaf, leaf strip or half-leaf section) and growth regulator concentration on shoot regeneration from somatic tissue of Rhododendron laetum × aurigeranum was evaluated. No regeneration response was obtained on explants from greenhouse-grown plants. Adventitious shoots were obtained from callus produced at the basal end of shoot-tip and single-node stem segment explants derived from in vitro-grown shoots cultured on Anderson's medium supplemented with 22.8 μM IAA and 73.8 μM 2iP. The greatest percentage of adventitious shoot regeneration (77%) was induced on leaf sections cultured in the presence of 22.8 μM IAA and 147.6 μM 2iP. Plant regeneration was accomplished with minimal callus formation. This technique represents a further step toward gene manipulation of Rhododendron.
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    The role of cotyledonary tissue in the differentiation of shoots and roots from cotyledon explants of Brassica juncea (L.) Czern. (1991)
    Springer
    Plant cell, tissue and organ culture 24 (1991), S. 55-59 
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    ISSN: 1573-5044
    Keywords: auxin-like factor ; Brassica juncea ; brown mustard ; organogenesis ; regeneration ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In cotyledon cultures of Brassica juncea, shoots and roots invariable differentiate at the cut end of the petiole. Organogenesis occurred only if the proximal cut end of the petiole was in contact with the medium. In the absence of the petiole, differentiation from the lamina was rare. Hence investigations were carried out to study the influence of the cotyledonary lamina on regeneration of shoots and roots from the petiolar cut end. The lamina tissue was surgically removed from the cotyledon explants at different durations (0–10 days) after culturing them on either root-forming (basal medium) or shoot-forming (basal medium containing 5.0 μM N6-benzyladenine) media. The differentiation of roots or shoots from the petioles was dependent on the presence of the lamina for at least 7 days of culture. Quantitative removal of the laminar tissue had a corresponding negative effect on shoot bud differentiation from the petiole. The nature of the ‘lamina factor’ was found to be auxin-like.
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    High frequency of plant regeneration from hypocotyl explants of Brassica carinata A. Br. (1991)
    Springer
    Plant cell, tissue and organ culture 24 (1991), S. 79-82 
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    ISSN: 1573-5044
    Keywords: Brassica carinata ; Ethiopia mustard ; hypocotyl ; plant regeneration ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An efficient tissue culture system for high frequency of plant regeneration from hypocotyl explants of Brassica carinata was developed via manipulation of culture medium and selection of explants. Explants grown on medium containing combinations of 2 mg l-1 BA and 0.01 mg l-1 NAA or 4 mg l-1 kinetin and 0.01 mg l-1 2,4-D regenerated shoots at 100% frequency. High frequency shoot regeneration occurred only from explants originating from 6 to 7-day-old but not younger or older seedlings. Explants showed higher regeneration capacity at the distal end than the proximal end, and the upper segment was more regenerative than the lower segment of hypocotyl. Regenerants were rooted on half-strength growth regulator-free medium, acclimatized and developed into normal, fertile plants.
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    Somatic embryogenesis from immature embryos in meadowfoam (Limnanthes alba) (1991)
    Springer
    Plant cell, tissue and organ culture 24 (1991), S. 193-198 
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    ISSN: 1573-5044
    Keywords: Limnanthes alba ; meadowfoam ; somatic embryogenesis ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Developing embryos from immature seeds were excised and cultured. Optimal proliferation of differentiated secondary embryos occurred on Murashige-Skoog media containing 7% sucrose, 0.1 μM 2,4-D, and 0.1–1.0 μM zeatin. Higher levels of auxins inhibited embryo proliferation. Secondary embryos were subcultured to produce more embryos. The results indicate the feasibility of clonal propagation of meadowfoam.
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    Morphogenesis in leaf, hypocotyl and root explants of Digitalis thapsi L. cultured in vitro (1991)
    Springer
    Plant cell, tissue and organ culture 25 (1991), S. 117-123 
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    ISSN: 1573-5044
    Keywords: Digitalis thapsi ; plant regeneration ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of the auxins 2,4-D, NAA and IAA either alone or in combination with kinetin or BA were investigated to assess the morphogenetic potential of leaf, root and hypocotyl explants of Digitalis thapsi. Calluses were obtained from the three explants in basal medium without the addition of growth regulators and in leaves, the calluses formed roots. Application of 2,4-D, NAA or BA increased callus formation. The presence of NAA induced root formation and that of BA induced shoot formation via callus interphase. Indole-3-acetic acid alone only induced the generation of roots in the hypocotyl callus. Kinetin was ineffective in all the explants tested. Combinations of NAA with kinetin or BA were more effective in inducing organogenesis in leaf explants. Optimum responses were obtained in hypocotyl and root explants by using IAA in combination with BA, the highest rate of shoot regeneration being observed in hypocotyl explants. Rooting of the differentiated shoots was readily achieved in media without growth regulators. Regenerated plantlets were transferred to soil and grew with a survival rate of 70%.
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    Adherence of Agrobacterium tumefaciens to the cells of immature wheat embryos (1991)
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    Plant cell, tissue and organ culture 25 (1991), S. 199-208 
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    ISSN: 1573-5044
    Keywords: Agrobacterium tumefaciens ; cocultivation ; enzymatic digestion ; tissue culture ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Agrobacterium attached to wheat embryos in vitro. This attachment was plasmid independent, and occurred on both wounded and unwounded cell surfaces. The pattern of attachment clearly demonstrated that bacterial attachment to cereal cells follows the same trends observed for dicotyledonous plants. During the inoculation period the bacterial cells attach to the plant cell walls either with lateral or polar orientation. Wounding (mechanical or enzymatic) preferentially promoted adherence of the bacteria at the wound site, however, attachment was not wound dependent.
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    Agrobacterium tumefaciens-gene transfer into wheat tissues (1991)
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    Plant cell, tissue and organ culture 25 (1991), S. 209-218 
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    ISSN: 1573-5044
    Keywords: Agrobacterium tumefaciens ; cocultivation ; tissue culture ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract DNA can be transferred by Agrobacterium tumefaciens to wheat, albeit at very low frequencies. Transfer of agrobacterial DNA occurred in cultures where the embryos had been subjected to partial enzymatic digestion prior to cocultivation with the bacteria. It is unclear whether this is by the normal process mediated by the Ti virulence genes and the border repeats of the T-DNA. The Southern hybridization patterns indicate that in one cell line the T-DNA had undergone extensive rearrangements, and might indicate that the process of T-DNA transfer and integration might differ in the case of cereals. This could suggest the method of transfer and ultimately the expression of these genes in cereal cells may be different to that observed in other monocotyledonous and dicotyledonous species.
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    Effect of temperature, gel concentration and cytokinins on vitrification of Olearia microdisca (J.M. Black) in vitro shoot cultures (1991)
    Springer
    Plant cell, tissue and organ culture 26 (1991), S. 1-6 
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    ISSN: 1573-5044
    Keywords: chilling ; lignin synthesis ; shoot multiplication ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The interaction between gel concentration, cytokinin levels and temperature in vitrification of Olearia microdisca in vitro has been investigated. Vitrified plants displayed tissue hypertrophy and reduced lignification. Cytokinin in the medium was essential for vitrification. Increasing gel concentration or reducing temperature reduced the vitrification in the presence of 20 µM BA. The observed responses were consistent with indirect effects on BA uptake. Alternatively an indirect effect of BA on shoot multiplication rate and hence on lignification of cell walls may be involved.
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    A method for in vitro cell culture of superficial bovine uterine endometrial epithelium (1991)
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    Methods in cell science 13 (1991), S. 247-251 
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    ISSN: 1573-0603
    Keywords: tissue culture ; uterine epithelial cells ; bovine ; monolayer culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Bovine epithelial cells were obtained for culture from the uterine endometrium of adult, cyclic cattle. Using the procedures described herein, cell-specific monolayers of uterine epithelial cells developed rapidly in culture and maintained a good level of viability for seven to eight subcultures. In addition, frozen-thawed uterine epithelial cells also maintained a respectable level of viability during postthaw subculture. Patterns of cell growth for uterine epithelial cells were determined by a growth curve. A growth curve of fresh epithelial cells over an 8-day interval revealed a short lag phase (24 h) followed by a log growth phase for 5 days and then a stationary phase starting on Days 6 or 7 of incubation. This method for isolation and culture of uterine epithelial cells provides a potential model for evaluating uterine epithelial cell secretory capacity during the estrous cycle. This culture system may offer benefits for in vitro culture of bovine embryos.
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    Application of the principles of good manufacturing practices (GMP) to the design and operation of a tissue culture laboratory (1991)
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    Methods in cell science 13 (1991), S. 265-273 
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    ISSN: 1573-0603
    Keywords: tissue culture ; GMP ; laboratory design ; laboratory operation ; contamination control ; environmental control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Recommendations are presented for the design and operation of a tissue culture laboratory to reduce microbial contamination of cultures. These recommendations are based on practices currently used in the manufacturing of sterile drug products, certain medical devices, and in vitro diagnostic products. The recommendations depend on qualification and validation of equipment, systems, and procedures and on the control and monitoring of the laboratory environment and procedures.
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    In vitro propagation of the nitrogen-fixing tree-legume Acacia mangium Willd. (1991)
    Springer
    Plant and soil 135 (1991), S. 151-159 
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    ISSN: 1573-5036
    Keywords: micropropagation ; Acacia mangium ; tissue culture ; Bradyrhizobium spp. ; nodulation ; nitrogen-fixing tree
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In vitro propagation was initiated from 2-week-old and 7-month-old explants of Acacia mangium. Juvenile explants (2 week-old) of 5- to 10-mm lengths composed of two leaves were cultured on Murashige and Skoog (MS) medium containing 1.0 or 2.0 mg L-1 6-benzyladenine (BAP). After 6 weeks, most explants had formed a large cluster of 14–18 axillary shoots produced by prolific branching of the primary axillary shoot after elongation. The maximum multiplication rate (40) was obtained in the first subculture; the rate decreased to 10–20 in the second one. The mean length of shoots was not significantly affected by BAP concentrations during the subsequent cultures. Rooting ability of juvenile explants was greatly affected by BAP concentrations used in the multiplication medium. When both types of explants were multiplied on a MS medium containing 1.0 mg L-1 BAP and transferred to a half-strength MS medium containing 0.05 mg L-1 IBA, only 10% of the juvenile explants were rooted versus 70% of the 7-month-old explants. Rooted plants transferred onto artificial substrate were all nodulated, when inoculated with a specific Bradyrhizobium sp. strain.
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    A programmable micropropagation apparatus using cycled liquid medium (1991)
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    Plant cell, tissue and organ culture 27 (1991), S. 211-218 
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    ISSN: 1573-5044
    Keywords: endogenous microorganisms ; semi-automated micropropagation ; Spathiphyllum ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An apparatus was developed that featured programmable application of liquid medium to plant cultures for micropropagation. Computer control capabilities included liquid medium introduction and medium depth within four culture vessels, medium application and removal on an assigned schedule, schedule adjustment during a culture period and medium replacement. The medium level was controlled using an accurate custom level-sensing technique consisting of thermistors and float switches. Seven-liter polycarbonate containers were modified and used as the culture vessels. Maintaining sterility was a key constraint in the development of the plant tissue culture apparatus.
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    Adventitious shoot regeneration from leaf explants of tissue cultured and greenhouse-grown raspberry (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 249-255 
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    ISSN: 1573-5044
    Keywords: organogenesis ; Rubus idaeus L ; R. × neglectus Peck ; thidiazuron ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Adventitious shoot regeneration was observed using leaf-petiole explants from shoot-proliferating cultures of ‘Comet’ red raspberry (Rubus idaeus L.). A maximum regeneration rate of 70% (3.7 shoots/explant) was obtained using 4.5–9.1 μM (1–2 mg l−1) N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (thidiazuron or TDZ) with 2.5–4.9 μM (0.5–1 mg l−1) 1H-indole-3-butanoic acid (IBA) or 2.3 μM (0.5 mg l−1) TDZ with 4.9 μM (1 mg l−1) IBA in modified Murashige-Skoog medium. TDZ was more effective than N-(phenylmethyl)-1H-purin-6-amine (BA) at promoting regeneration in combinations tested with IBA (maximum 50% regeneration rate; 1.8 shoots/explant). Variation in the agar concentration or incubation temperature, orientation or scoring of the leaf-petiole explants and use of separate leaf or petiole explants had no effect on shoot regeneration. Incubation in the dark for 1, 2 or 3 weeks prior to growth in the light did not influence the percent regeneration rate but depressed the number of adventitious shoots. Explant source, from micropropagated shoots or greenhouse-grown plants, had an effect on shoot regeneration that was genotype dependent. Only 8 of 22 (36%) raspberry cultivars were capable of regeneration from leaf explants derived from greenhouse-grown plants.
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    In vitro micropropagation and plant establishment of muscadine grape cultivars (Vitis rotundifolia) (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 7-14 
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    ISSN: 1573-5044
    Keywords: plant regeneration ; propagation ; tissue culture ; viticulture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Shoot apical meristems were used to establish regenerative axillary bud cultures of 9 muscadine grape cultivars. Meristems taken from 10 cm long shoots had less contamination (3%) and a higher survival rate (94%) than those from shorter or longer shoots. Of media tested, MS, 1/2 MS, and C2D resulted in equivalent shoot proliferation rates, whereas, WPM produced stunted shoots. When pooling results for 3 cultivars, 5, 10 and 20 μM BA and 5 μM TDZ produced the highest average number of shoots per cultured apex (3.4–3.8). However, shoots produced with TDZ were stunted and did not root well. For rooting of shoots directly in potting mix, a rooting powder pretreatment significantly increased the number of roots per shoot but did not affect percent rooting or root length. For rooting in vitro, 1 μM NAA significantly increased all parameters measured. Although more shoots rooted in vitro than in vivo (77% vs. 46%), the latter was judged preferable since acclimatized plants were produced in less time and a major culture step was eliminated. Significant differences among cultivars were noted for measured responses in all experiments.
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    Freeze-preservation of buds from Scots pine trees (1991)
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    Plant cell, tissue and organ culture 27 (1991), S. 89-93 
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    ISSN: 1573-5044
    Keywords: cryopreservation ; Pinus sylvestris L. ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A procedure has been developed for freeze-preservation of buds of the Scots pine (Pinus sylvestris L.). Instead of liquid nitrogen, cold storage in −80°C was used. The partly dormant material used in the experiments was obtained directly from a natural stand in Northern Finland and no prefreezing or cryoprotectants for preconditioning were used. Cooling velocity was 1°C/min up to a terminal freezing temperature of −39°C, after which the buds were immersed in liquid nitrogen at −196°C for 10 minutes. The material was then transferred to a deepfreezer at −80°C and stored up to 6 months. After rapid thawing, the buds were sterilized and their viability was tested by FDA staining and by culturing meristems on 1/2 MS medium for at least two weeks. All the freezing experiments were performed during March and April. The best survival of buds (90–100%) was achieved at the beginning of April, after which a pronounced decline in survival occurred obviously due to a rise in the water content of the buds.
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    In vitro regeneration from excised leaves of Flaveria trinervia (Sprengel) C. Mohr (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 297-302 
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    ISSN: 1573-5044
    Keywords: Flaveria trinervia ; growth regulators ; leaf explant ; tissue culture ; plant regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Flaveria trinervia (Compositae) leaves are used for the treatment of jaundice and fever. From the leaf callus cultures regeneration of plantlets has been achieved. The results showed that BAP greatly stimulated the bud formation in concentrations ranging from 2–5 mg l−1 than at very low concentrations (0.2–1.0 mg l−1). Roots developed on the regenerated shoots, over a range of treatments, but were most prolific in the medium containing 1 mg l−1 IAA. Histological observations revealed that cultured spongy cells of the mesophyll were greatly enlarged and underwent repeated cell divisions leading to the formation of hard nodular callus from which shoot buds differentiated. The shoots obtained were readily rooted and transplanted into glass houses. Cytological studies of the callus showed abnormalities such as bridges, endomitosis and multinucleolate conditions. Root tip squashes of the regenerated plants showed no variations and were diploid in chromosome number.
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    Relationship between growth rate of Helminthosporium oryzae isolates on calluses of rice cultivars and their disease reaction on rice plants (1991)
    Springer
    Plant cell, tissue and organ culture 24 (1991), S. 237-241 
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    ISSN: 1573-5044
    Keywords: disease resistance ; Helminthosporium oryzae ; rice ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rice cultivars showed differential reaction to various isolates of Helminthosporium oryzae, the brown spot pathogen. The calluses obtained from those cultivars behaved in a similar manner to the mycelial growth of pathogenic isolates on them. However, amount of inoculum, size of the callus and period of incubation influenced the reaction of the callus to the fungal isolates.
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    Uptake and metabolism of 6-benzyladenine in shoot cultures of Musa and Rhododendron (1991)
    Springer
    Plant cell, tissue and organ culture 25 (1991), S. 69-74 
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    ISSN: 1573-5044
    Keywords: BA uptake ; cytokinin metabolism ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Shoots of Musa and Rhododendron were cultured in vitro on a medium containing 0.5 mg l-1 BA. Shoots growing in the presence of [14C]BA were harvested at intervals during the culture period. Uptake of BA was linear throughout this culture period in Musa but slowed considerably in Rhododendron shoots after day 10. Rhododendron shoots absorbed 40% of the BA present in the medium and Musa shoots absorbed 52%. In each species the principal metabolite formed was [9G]BA. Benzyladenine was present in significant levels only in the pseudostem of Musa.
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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)
    Springer
    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
    Source: Springer Online Journal Archives 1860-2000
    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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    ISSN: 1434-6079
    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
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    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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    Keywords: 36.40
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    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
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    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
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    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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    Keywords: 36.40
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    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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    Keywords: 36.40
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    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
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    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)
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    The European physical journal 18 (1991), S. 257-265 
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    Keywords: 33.20 ; 35.20 ; 36.40
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    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)
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    The European physical journal 18 (1991), S. 267-280 
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    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)
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    The European physical journal 19 (1991), S. 31-36 
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    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)
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    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)
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    The European physical journal 19 (1991), S. 55-58 
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    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)
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    The European physical journal 19 (1991), S. 77-79 
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    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)
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    The European physical journal 19 (1991), S. 85-87 
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    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)
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    The European physical journal 19 (1991), S. 93-96 
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    Keywords: 36.40 ; 71.45.G
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    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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    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)
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    The European physical journal 19 (1991), S. 129-131 
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    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)
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    The European physical journal 19 (1991), S. 181-184 
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    Keywords: 05.70 ; 07.75 ; 36.40
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    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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    Keywords: 36.40 ; 35.20X ; 79.20X
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    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)
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    The European physical journal 19 (1991), S. 427-429 
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    Keywords: 36.40
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    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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    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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    Keywords: 36.40
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    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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    Keywords: 36.40 ; 34.80 ; 71.35
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    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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    Keywords: 36.40 ; 71.90 ; 78.40
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    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)
    Springer
    The European physical journal 20 (1991), S. 53-55 
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    ISSN: 1434-6079
    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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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80 ; 82.30
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    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)
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    The European physical journal 20 (1991), S. 153-155 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80 ; 33.20
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    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)
    Springer
    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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    ISSN: 1434-6079
    Keywords: 36.40
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    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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    ISSN: 1434-6079
    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)
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    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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    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)
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    The European physical journal 20 (1991), S. 201-203 
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    Keywords: 36.40
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    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)
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    The European physical journal 20 (1991), S. 89-91 
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    Keywords: 36.40 ; 34.80 ; 33.80
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    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)
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    The European physical journal 20 (1991), S. 157-159 
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    ISSN: 1434-6079
    Keywords: 36.40
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    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)
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    The European physical journal 20 (1991), S. 235-238 
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    Keywords: 36.40
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    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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    Keywords: 36.40
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    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
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    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
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    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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    Keywords: 36.40
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    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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    Keywords: 33.20.K ; 36.40 ; 42.20 ; 78.40 ; 82.70
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    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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    Keywords: 36.40 ; 33.60 ; 33.80.E
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    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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    Keywords: 79.60 ; 71.20 ; 36.40
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    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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    Keywords: 79.20 ; 73.20 ; 36.40
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    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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    Keywords: 79.60 ; 36.40
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    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
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    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544028
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  • 93
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    An electron diffraction apparatus for small particle beams (1991)
    Springer
    The European physical journal 20 (1991), S. 457-459 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544036
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  • 94
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    Concluding remarks (1991)
    Springer
    The European physical journal 20 (1991), S. 465-467 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544038
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  • 95
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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 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425596
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  • 96
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    Methods for improving tissue culture of human tracheo-bronchial epithelium obtained at autopsy (1991)
    Springer
    Cytotechnology 5 (1991), S. 155-163 
    Details
    ISSN: 1573-0778
    Keywords: tissue culture ; trypan blue ; cilia ; cell injury ; organ culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Human tracheo-bronchial epithelium obtained from autopsy, surgery, and organ donation will have areas of both viable and non-viable cells. It is important in the initial establishment of epithelial explant and cell cultures that injured, non-viable mucosal epithelium not be used for the cultures. Autopsy cases selected for culture should initially be chosen on the basis of a shorter post mortem interval and cause of death in order to increase the rate of successful culture. Staining the epithelium with the vital dye, trypan blue, in combination with phase contrast microscopy of the bronchial tissues will further identify those areas of the mucosa that are enriched for viable cells. The dead, non-viable areas are trypan blue positive, while the viable areas are clear and have foci of beating, motile cilia. Treatment of the mucosal tissue with mucolytic agents to remove cell debris, dead cells, and microbes trapped in the mucus material will further improve the chances for successful culture. Human tracheo-bronchial epithelium, although non-sterile and often injured at time zero for numerous reasons, can effectively be used in in vitro pathophysiology studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00365432
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  • 97
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    Exfoliative cytologic evaluation of primary cultured lung carcinomas (1991)
    Springer
    Cytotechnology 6 (1991), S. 143-152 
    Details
    ISSN: 1573-0778
    Keywords: tissue culture ; lung cancer ; cytogenetics ; cytotechnology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This paper describes a tissue culture and exfoliative cell culture system that enables one to (1) evaluate the adequacy of primary lung carcinoma cultures for cytogenetic analysis, and (2) predict the likelihood of viable cells and type of differentiation present in the primary lung tumor cultures used for cytogenetics. Primary lung carcinomas were established from explant outgrowths and maintained in serum supplemented or serum free media on plastic or basement membrane associated protein coated dishes in order to obtain cells for karyotypic analysis (Miura et al., 1990). The media from these cultures that would ordinarily have been discarded was aspirated at each media change and used to prepare cytocentrifuge cytology preparations. Papanicolaou stained cells from the preparations were evaluated by cytotechnologists in order to assess (1) the cellularity and presence of cancer cells in the sample, (2) differentiation of the malignant cells, and (3) adequacy for chromosomal studies. We determined that cytology preparations of cell and explant outgrowth cultures from primary lung tumors are a reliable method for screening and evaluating the suitability of primary lung carcinoma cultures for cytogenetic analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00373032
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