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  • 36.40  (73)
  • wheat  (36)
  • Springer  (109)
  • American Chemical Society
  • Essen : Verl. Glückauf
  • Krefeld : Geologischer Dienst Nordhein-Westfalen
  • 2015-2019
  • 2005-2009
  • 1985-1989  (109)
  • 1980-1984
  • 1989  (109)
Collection
Publisher
  • Springer  (109)
  • American Chemical Society
  • Essen : Verl. Glückauf
  • Krefeld : Geologischer Dienst Nordhein-Westfalen
Years
  • 2015-2019
  • 2005-2009
  • 1985-1989  (109)
  • 1980-1984
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 53 (1989), S. 17-29 
    ISSN: 1570-7458
    Keywords: Mayetiola destructor ; Cecidomyiidae ; oviposition ; host specificity ; wheat ; oats ; insect-plant interactions ; thresholds ; deprivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Résumé Les réactions de femelles préalablement accouplées de Mouches de Hesse ont été examinées en analysant le comportement de femelles isolées sur blé et sur avoine. Le répertoire comportemental de ces femelles comprenait: le vol, l'atterrissage sur feuille, la flexion du corps de sorte que l'extrémité de l'abdomen touchât la surface de la feuille, l'antennation, les mouvements de l'extrémité de l'abdomen sur la feuille à angle droit des nervures, le repos avec la tarière droite et encore dévaginée, le repos avec la tarière télescopée à l'intérieur du corps. Sur blé plus que sur avoine, les femelles après atterrissage ont présenté une fréquence plus élevée de passage de la flexion à l'antennation que de la flexion à l'abdomen droit. Durant les 5 premières minutes d'observation, les individus libérés dans des enceintes avec blé fléchirent et ‘antennèrent’ 2 à 3 fois plus que ceux libérés sur avoine. Les durées des différentes séquences différaient aussi: sur blé, pendant les 5 premières minutes, les femelles passèrent plus de 50% du temps à fléchir, tandis que sur avoine elles passèrent plus de 50% du temps en repos. Les femelles restèrent aussi plus longtemps sur les feuilles de blé et y pondirent 4 fois plus d'oeufs que sur avoine. Les femelles de M. destructor ont montré une plasticité du seuil d'acceptation. Pendant les premières heures de ponte, elles ont été très sélectives et refusèrent, ou ne pondirent que quelques oeufs sur avoine, mais acceptèrent volontiers le blé. La discrimination s'est poursuivie tant que les femelles ont eu accès au blé en même temps qu'à l'avoine. Cependant, quand les femelles ont été privées de blé pendant plusieures heures, l'acceptation de l'avoine a augmenté. Cet accroissement de l'acceptation a eu lieu à peu près au moment où les femelles sur blé pondaient leurs derniers oeufs.
    Notes: Abstract Responses of mated female Hessian flies were investigated by analysing the behaviour of individual flies in wheat and oats. The behavioural repertoire of such females included: flying, alighting on leaves, arching of the body so that the tip of the abdomen touched the leaf surface, antennation, movements of the tip of the abdomen across the leaf at right angles to leaf veins, sitting with the ovipositor straight but still extended, and sitting with the ovipositor telescoped into the body. After alighting, females on wheat showed a higher frequency of transitions from arching to antennation and a lower frequency of transitions from arching to abdomen straight than females on oats. During the first 5 min of observations, individuals released into arenas with wheat arched and antennated 2–3 times more frequently than females released into oats. Time allotted to behaviours also differed; during the first 5 min, females in wheat spent 50 percent more time arching, whereas females in oats spent 50 percent more time sitting. Females in wheat also stayed longer and laid 4 times more eggs than females in oats. Temporal changes in egglaying were monitored by quantifying hourly rates of egglaying in no-choice assays for several hours following mating at 9:00 am. During the first and second hours post-mating, egglaying occurred infrequently. However, during the third hour post-mating (11:00 am to noon) females on wheat laid 5 times more eggs than females on oats. Rates of egglaying decreased on wheat but increased on oats during the fourth hour, and then during the fifth hour, decreased on both wheat and oats. Changes in egglaying responses were also evident when behaviours of individual females were measured 1–3 h vs. 3–7 h post-mating. Females deprived of host plants and released into wheat or oats later in the day showed higher frequencies of arching and antennation and laid more eggs before leaving the arena.
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  • 2
    ISSN: 1570-7458
    Keywords: Coccinella septempunctata ; Coccinellidae ; wheat ; egg laying ; larva ; adult ; vertical distribution ; Coccinella septempunctata ; Coccinellidae ; blé ; ponte ; larve ; adulte ; répartition spatiale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Summary At the beginning of spring, post-hibernating adults of Coccinella septempunctata L. (Col., Coccinellidae), larvae and nymphs are found on the lower part of wheat plants. In June, adults born in the field as well as their progeny are dispersed all over the plant and a significant proportion of them is found on the apical parts of plants. Most of the egg clutches are layed on soil lumps, stones and small wild plants which represent preferential sites. Variations in coccinellid distribution may be influenced by climatic conditions, especially the temperature, by the thermophilic nature of this species and by the repartition of the three main aphid species on the plants. These results are relevant for the selection of a sampling methods.
    Notes: Résumé Au début du printemps les adultes de Coccinella septempunctata L. (Col., Coccinellidae) issus des sites d'hivernation, les larves et les nymphes qui en proviennent, fréquentent le sol et les parties basses du blé. En juin, les adultes nés dans le champ et leur descendance sont dispersés sur toute la hauteur des talles bien qu'une fraction non négligeable de leur population se rencontre à l'extrémité supérieure. La plupart des pontes sont déposées sous les mottes de terre, les pierres et les petites adventices qui constituent des sites privilégiés. Ces variations de la distribution de cette coccinelle peuvent être mises en relation avec le climat, en particulier la température, avec la thermophilie de cette espèce et avec la répartition sur les différentes parties des talles des 3 espèces de puceron qui se succèdent au cours de la saison. Ces observations sont importantes à considérer lors du choix ou de la mise au point d'une méthode d'échantillonnage.
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  • 3
    ISSN: 1573-0867
    Keywords: Phosphorus ; lupin ; chickpea ; wheat ; nodulation ; dry matter production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A glasshouse experiment was conducted to examine the comparative growth and P uptake response following P fertilizer application in lupins (Lupinus angustifolius L. cv. Chittick) and chickpeas (Cicer arietinum cv. Tyson) compared to wheat (Triticum aestivum cv. Sunstar). Measurements of dry matter, phosphorus uptake and nodule numbers were made at 50 and 100 days after sowing. At the 50 day harvest, the two legume crops produced less dry matter and accumulated less plant P than wheat but no such species interactions were present at the 100 day harvest. Chickpeas showed strong positive responses in nodule numbers with increasing rates of P fertilizer while such effects were less and more variable with lupins.
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  • 4
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    Nutrient cycling in agroecosystems 20 (1989), S. 27-32 
    ISSN: 1573-0867
    Keywords: Cropping system ; phosphorus ; rice ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A long term field experiment was conducted on a sandy loam soil from 1983 to 1987 to determine how to best apply phosphorus fertilizer in a rice-wheat cropping system. The treatments included 9 combinations of phosphorus application either to both rice and wheat or to rice or wheat alone. Direct application of phosphorus at 13 kg/ha to both the crops resulted in significantly higher total productivity of the rice-wheat cropping system as compared with 26 kg P/ha applied either to rice or wheat alone. Phosphorus at 13 kg/ha for rice and 26 kg/ha for wheat was as efficient as 13 kg P/ha for rice and 13 kg P/ha for wheat. The higher rate of P (26 kg/ha) applied to both rice and wheat resulted a decline in the total productivity. The residual effects of phosphorus applied to either rice or wheat were significant to the succeeding crop but was inferior to its direct application. Phosphorus increased the leaf area index, chlorophyll content of leaves, and interception of more photosynthetically active radiation (PAR) which resulted in increased grain yield of rice and wheat. Phosphorus status of the surface soil declined markedly, in the absence of P application from 15.4 to 6.4 kg P/ha. Phosphorus applied at 26 kg P/ha to both the crops resulted a build up of the available P status of soil. Phosphorus application at 13 kg/ha to both rice and wheat maintained the phosphorus status of the soil at original level.
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  • 5
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    Nutrient cycling in agroecosystems 20 (1989), S. 59-66 
    ISSN: 1573-0867
    Keywords: Ammonia volatilization ; nitrogen leaching ; denitrification ; time of N application ; wheat ; Triticum aestivum ; Triticale ; irrigation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Grain yield, nitrogen (N) assimilation, ammonia (NH3) volatilization, denitrification and fertilizer N distribution were examined in three commercially grown cereal crops; two were sown into conventionally tilled fields, while the third was direct drilled into an untilled field. The crops were top dressed with urea at establishment, tillering or ear initiation. Crop yield and N assimilation were measured in 16 m by 2.5 m plots receiving 0, 35, 70, 105, 140 or 175 kg N ha−1. A mass balance micrometeorological technique was used to measure NH3 volatilization, and other fertilizer N transformations and transfers were studied using15N labelled urea in microplots. On the conventionally tilled sites application of urea increased the grain yield of wheat from 3.9 to 5.5 t ha−1, when averaged over the five application rates, three application times and two sites. There were no site or application time effects. However, on the direct drilled site, time of application had a significant effect on grain yield. When urea was applied at establishment, grain yield was not significantly increased and the mean yield (2.81 t ha−1) was less than that obtained from treatments fertilized at tillering or ear initiation (4.09 and 4.0 t ha−1, respectively). Much of the variation in grain yield at the no-till site could be ascribed to differences in NH3 volatilization. At the no-till site, NH3 losses were equivalent to 24, 12 and 1% of the N applied at establishment, tillering and ear initiation, respectively. Negligible volatilization of NH3 occurred at the other sites. The surface soil at the no-till site had the highest urease activity and the soil was covered with alkaline ash resulting from stubble burning. Plant recovery of fertilizer N did not vary with application time on conventionally tilled sites (mean 62%). However, plant recovery of15N applied to the no-till site at establishment (35% of the applied N) was significantly less than that from plots where the application was delayed (45% at tillering and 55% at ear initiation, respectively). Leaching of N to below 300 mm depth was minimal (0 to 5% of the applied N). The calculated denitrification losses ranged from 1% to 14% of the applied N. The results show that the relative importance of NH3 volatilization, leaching and denitrification varied with site and fertilization time. The importance of the various N loss mechanisms needs to be taken into account when N fertilization strategies are being developed.
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  • 6
    ISSN: 1573-5028
    Keywords: chloroplast DNA ; cytochrome b-559 ; photosystem II ; psbL ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The N-terminal amino acid sequence of a 3.2 kDa photosystem II polypeptide is shown to be identical to that of a polypeptide encoded by an open reading frame of 38 codons (orf38) in wheat chloroplast DNA. Orf38 is located just downstream of the psbE and psbF genes for the polypeptides of cytochrome b-559. Analysis of the transcription of this region of chloroplast DNA shows that psbE, psbF and orf38 are co-transcribed to give a 1.1 kb polycistronic transcript which also contains another open reading frame of 40 codons. The orf38 and orf40 products are hydrophobic polypeptides which are both predicted to span the thylakoid membrane once. Orf38 and orf40 are highly conserved, and map to similar locations adjacent to psbE and psbF, in all organisms from which this region of DNA has been sequenced. We propose that orf38 is named psbL.
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  • 7
    ISSN: 1573-5028
    Keywords: ADP-glucose pyrophosphorylase ; cDNAs ; gene organisation ; polypeptides ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A cDNA clone (WL : AGA.1) encoding wheat leaf ADP-glucose pyrophosphorylase has been isolated from a λgt11 expression library, by immunological screening with anti-spinach leaf ADP-glucose pyrophosphorylase serum. The WL : AGA.1 cDNA is 948 bp long and contains approximately 55% of the complete wheat leaf ADP-glucose pyrophosphorylase mRNA sequence, estimated from Northern blot experiments. A wheat endosperm cDNA library was subsequently constructed in λgt11 and six clones hybridising to the cDNA insert of clone WL : AGA.1 were isolated. The longest of these wheat endosperm ADP-glucose pyrophosphorylase cDNAs, clone WE : AGA.7, is nearly full-length (1798 bp), indicated by Northern blot analysis of wheat endosperm mRNA and nucleotide sequence analysis. Southern hybridisation analysis and restriction enzyme mapping indicated that the wheat leaf and wheat endosperm ADP-glucose pyrophosphorylase cDNAs and genes are members of two distinct gene families. In addition, restriction enzyme mapping revealed polymorphism in the wheat endosperm ADP-glucose pyrophosphorylase cDNAs, indicating the existence of at least two wheat endosperm ADP-glucose pyrophosphorylase gene sub-families. Subsequent nucleotide sequence analysis indicates that there is approximately 55% identity between wheat leaf and wheat endosperm ADP-glucose pyrophosphorylase cDNAs. In contrast, members of each sub-family of endosperm cDNA, represented by clones WE : AGA.3 and WE : AGA.7, are 96% identical.
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  • 8
    ISSN: 1573-5028
    Keywords: aleurone ; barley ; protoplasts ; transient expression ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methods have been developed for the isolation of aleurone protoplasts from developing caryopses of Hordeum vulgare and Triticum aestivum in order to study transient expression of introduced genes. Chimaeric gene constructs were introduced into aleurone protoplasts by polyethylene glycol (PEG). Transient expression directed by the 35S promoter from cauliflower mosaic virus (CaMV) of the reporter gene encoding chloramphenicol acetyl transferase (CAT) was detected in aleurone protoplasts from developing barley and wheat grains. Using a similar construct, CAT activity increased when the alcohol dehydrogenase intron 1 fragment from maize was ligated between the 35S promoter and the CAT coding region. The demonstration of transient expression in protoplasts from developing aleurone layers indicates that they may be useful for investigating tissue and developmental control of genes coding for cereal seed proteins.
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  • 9
    ISSN: 1573-5028
    Keywords: F1F0 ATPase ; chloroplast coupling factor ; mitochondrial gene ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 10
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    Plant and soil 120 (1989), S. 125-131 
    ISSN: 1573-5036
    Keywords: canola ; fallow ; N mineralization ; N immobilization ; organic matter ; rhizosphere ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A greenhouse experiment was conducted to determine the influence of cropping variables on nitrogen dynamics in a soil amended with green manure. Surface soil from various long-term spring wheat rotations was amended with15N-labelled legume green manure (Lathyrus tingitanus) and subsequently cropped (canola [Brassica napus] and spring wheat [Triticum aestivum]) or incubated without a crop for 56 days in a greenhouse. Nitrogen mineralization from both the indigenous soil N and from green manure was suppressed in cropped soil. Net N mineralization in the uncropped and cropped treatments averaged 73 and 43 mg kg−1, respectively. This difference was attributed, in part, to enhanced biological immobilization in the rhizosphere. Previous cropping practices also had significant effect on N mineralization, largely by their influence on indigenous organic matter quality. These observations suggest that short-term N mineralization is favored by fallowing soil after green manure application whereas N retention in organic matter is favored by immediate cropping.
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  • 11
    ISSN: 1573-5036
    Keywords: characterization ; deleterious rhizobacteria ; inhibitory bacteria ; pseudomonads ; toxin ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A toxin produced by a deleterious rhizobacterial pseudomonad that inhibits both winter wheat (Triticum aestivum L.) root andEscherichia coli growth was characterized. The toxin was rapidly deactivated at pH 2 and 12 and by autoclaving (121°C, 15 minutes). Less toxin was destroyed as the temperature and time of exposure decreased, and at 40°C it was stable for at least 24 hours. The toxin was extremely polar and could not be extracted from culture filtrates with organic solvents. The compound eluted after the void volume from a Sephadex G-10 column indicating a molecular weight of less than 700. The toxin adsorbed to Dowex 50W strong cation exchange resin and eluted with 2M NH4OH. Numerous thin layer chromatography solvent systems were unsuccessful at purifying the toxin. The partially purified toxin inhibited several different microorganisms while the producing strains were resistant. The toxin appears unique to toxins produced by recognized plant pathogenic bacteria.
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  • 12
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    Euphytica 42 (1989), S. 41-44 
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; frost resistance ; locus Fr1 ; recombinant lines ; chromosome 5A
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A gene for frost resistance on chromosome 5A of wheat was located using single chromosome recombinant lines from the cross between the substitution line Hobbit (Triticum spelta 5A) and Hobbit. In this sample of recombinant lines the locus for frost resistance, designated Fr1, is completely linked to the locus Vrn1 controlling vernalisation requirement. The results can be explained by a pleiotropic action of the Vrn1 locus or close genetic linkage between Vrn1 and Fr1. Further detailed study is necessary to resolve these alternative hypotheses.
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  • 13
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; dwarfing genes ; drought stress ; yield ; yield components
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Near-isogenic tall (no dwarfing gene), semidwarf (Rht1 or Rht2) and dwarf (Rht1 + Rht2 or Rht3) spring wheat lines were evaluated for yield and yield components under irrigated and rainfed conditions. Under irrigated conditions, the dwarf and the semidwarf lines exhibited a significant yield advantage over the tall lines. Under rainfed conditions, the semidwarf lines outyielded the tall as well as the dwarf lines. Percent yield reduction in response to drought stress was highest with the dwarfs and lowest with the tall lines. Dry matter production of the tall lines and that of the semidwarf lines did not differ significantly and both produced significantly more dry matter than the dwarf lines under irrigated as well as rainfed conditions. Plant height and kernel weight decreased with increasing degree of dwarfness while number of kernels per spikelet, harvest index and days to heading increased under both moisture regimes. The dwarfing genes did not have any significant influence on number of tillers/m2 and spikelets per spike in either moisture regime.
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  • 14
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; chromosome substitution ; frost resistance ; hardening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The highly frost resistant wheat variety Cheyenne (donor) and the poorly frost resistant variety Chinese Spring (recipient) were frozen at −9° C and −11° C at various stages of hardening, as were a number of substitution lines of these two varieties (CS/Ch 3A, CS/Ch 5A, CS/Ch 7A, CS/Ch 2B, CS/Ch 4B, CS/Ch 5B, CS/Ch 4D, CS/Ch 5D). Chromosomes 5A, 5B, 5D, 4B and 7A of Cheyenne increased the frost resistance of the recipient variety to varying extents. However, the frost resistance changed not only as a function of the different chromosomes, but also as a function of the duration of hardening, indicating that genes responsible for frost resistance are expressed differently during different phases of the hardening process.
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  • 15
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; Puccinia recondita ; leaf rust resistance ; alien gene transfers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Nine transfers of leaf rust (Puccinia recondita Rob. ex Desm.) resistance to wheat (Triticum aestivum L.) from Agropyron elongatum Host. Beauv., Triticum speltoides Tausch and rye (Secale cereale L.) were backcrossed up to 10 times to commercial wheat cultivars. The objective was to study the effect of the transfers on agronomic and quality characters and to make them available in desirable genetic backgrounds. The results varied greatly for different transfers. In four cases no promising material was obtained even after nine backcrosses. However, for the remaining five transfers material with potential as a new cultivar was obtained.
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  • 16
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; Puccinia recondita f. sp. tritici ; wheat leaf rust ; partial resistance ; latency period ; gene action ; oligogenic inheritance ; transgressive segregation ; number of genes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Crosses were made between the highly susceptible Little Club and the partially resistant cultivars Westphal 12A, Akabozu and BH 1146 to obtain F1, F2 and backcross generations. Latency period (LP) was determined in plants inoculated at the young flag leaf stage with a monospore culture of race ‘Flamingo’ of wheat leaf rust. Broad sense heritability of LP in the F2 averaged 0.8. The genes showed partial to almost complete recessive inheritance. Scaling tests indicated that additive gene action was the most important factor in the inheritance of partial resistance. The tests showed that there were no indications for additive x additive, additive x dominance or dominance x dominance interactions. The number of effective factors was estimated as one or two for Akabozu, three or more for Westphal 12A, and two or three for BH 1146. BH 1146 also possessed a (semi-)dominant gene for a lower infection type which was temperature sensitive in its expression. The genes of the various parents had unequal effect on LP.
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  • 17
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; Puccinia recondita f. sp. tritici ; wheat leaf rust ; partial resistance ; latency period ; oligogenic inheritance ; transgressive segregation ; number of genes ; heritability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Three partially resistant spring wheat cultivars, with a long latency period were crossed among each other and with the highly susceptible Little Club, with a very short latency period. Parents, F3 and F5 plants have been inoculated with the leaf rust race Flamingo in the young flag leaf stage to determine the latency period. From the crosses with Little Club, it was concluded that Westphal 12A carries three, Akabozu two and BH 1146 two or three genes for a longer latency period. BH 1146 appears to carry also one hypersensitive resistance gene. Transgressive segregation occurred in crosses between partially resistant cultivars. From crosses between the partially resistant cultivars, it was concluded that the genes in Akabozu and Westphal 12A are different, while those in Akabozu and BH 1146 are at least partly different. The possibilities of accumulation of LP-prolonging genes are discussed.
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  • 18
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; anther culture ; callus initiation ; cytoplasm ; cytoplasmic male sterility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Nuclear and cytoplasmic factors affect tissue culture response in wheat (Triticum aestivum), and cytoplasmic male sterility may enhance callus initiation in anther culture. Three wheat nuclear genotypes, each in normal and two alien cytoplasms conferring cytoplasmic male sterility, were evaluated for callus initiation frequency in anther culture. Nuclear genotype had the greatest effect on callus initiation, but cytoplasm and nucleus X cytoplasm interaction also produced significant effects. The nuclear genotype of ‘Chris’ outperformed ‘Butte’ and ‘Coteau’ in all cytoplasms. Ordinary wheat and Triticum timopheevi cytoplasms outperformed Aegilops speltoides cytoplasm. Cytoplasmic male sterility did not increase callus initiation. This suggests manipulating the nuclear genotype is the best strategy for improving the capacity of wheat to initiate callus in anther culture.
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  • 19
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    Plant and soil 120 (1989), S. 273-282 
    ISSN: 1573-5036
    Keywords: aluminum toxicity ; biological tests ; calcium deficiency ; root growth ; sorghum ; subsurface soils ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two relatively simple procedures based on 4-day seedling growth were developed for identifying soil calcium (Ca) deficiency and/or aluminum (Al) toxicity. Test A uses any large-seeded cultivar that a farmer might consider planting and reveals whether the cultivar will suffer from Ca deficiency by comparing root growth in untreated soil to that in soil receiving a minimal Ca addition (0.1 meq.100mL−1 soil), sufficient to eliminate possible deficiency. Al toxicity is detected by comparing root growth in a sample receiving the minimal Ca treatment with growth in the soil treated with enough lime to neutralize exchangeable Al. In test B, potential Al toxicity problems are detected for any widely-grown standard crop by comparing its growth with that of a different, Al-tolerant variety on soil samples receiving 0.1 meq.100mL−1 Ca. With this test Ca deficiency in the untreated sample is detected by an increase in root growth of the Al-tolerant variety resulting from a small addition of Ca. The tests agreed with diagnoses made by standard chemical methods in about 84% of the cases examined. The proposed tests can be carried out using simple, easily-available materials without the necessity of sending soils to an analytical laboratory.
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  • 20
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    Euphytica 40 (1989), S. 103-109 
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; triticale ; wheat-triticale hybrids ; Secale cereale ; rye ; Gaeumannomyces graminis ; take-all ; resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Fifteen triticale and wheat-triticale hybrid lines were evaluated for resistance to the take-all fungus Gaeumannomyces graminis var. tritici and compared with five wheat and two rye lines in inoculated field and pot trials. The triticale and wheat-triticale hybrid lines varied in rye chromosome number and degree of resistance expressed. One line, Venus with seven pairs of rye chromosomes consistently showed levels of resistance intermediate between wheat and rye. A trend was observed where increasing rye chromosome content led to greater resistance but exceptions showed that variation within triticales could not be ascribed to rye chromosome content alone.
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  • 21
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; gliadins ; electrophoresis ; cultivar identification ; breeding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The process of the separation of gliadin proteins of wheat, using polyacrylamide gel electrophoresis, was studied in detail. It was shown that electrophoresis is a dynamic process during which the pH of the gel changes together with the potassium ion concentration. The most positive effect on the separation of the gliadins was generated by a moving front, which is a boundary between regions with a low concentration of K+ ions and a low pH, and region with a high concentration of K+ ions and a high pH, after optimization of the concentrations of the cations and anions in the electrode solutions. The finding was exploited for the development of an extremely simple electrophoresis system, in which buffers were not needed for obtaining a high resolution. The system was further improved by applying a stacking gel. The advantages of this system are discussed. This new approach may be useful for improving electrophoresis systems for other applications.
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  • 22
    ISSN: 1573-5060
    Keywords: alloplasmic line ; breeding ; chromosome ; eyespot resistance ; substitution line ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The variety Roazon possesses genes for resistance to eyespot including that on the 7D chromosome transferred from Aegilops ventricosa. In order to assess the level of resistance due to the latter, we developed the intervarietal substitution for the 7D chromosome of ‘Roazon’ into ‘Courtot’ which is very susceptible to eyespot. As ‘Roazon’ contains Aegilops ventricosa cytoplasm, the substitution lines were produced both with wheat and Aegilops cytoplasm. Resistance was assessed at the seedling and the adult plant stage. No cytoplasmic effect was observed. The substitution lines were as resistant as ‘Roazon’. This shows that the chromosome 7D genes for resistance introduced from Aegilops ventricosa result in a high level of resistance in wheat.
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  • 23
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    Euphytica 44 (1989), S. 143-150 
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; Triticum durum ; durum ; environmental correlations ; grain yield ; plant height ; tiller number ; grain size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Environmental correlation coefficients were computed among all pairs of five traits, namely grain yield, heading date, number of tillers per m2, plant height and 1000-grain weight (grain size) using 30 Triticum durum and 30 Triticum aestivum varieties grown in 18 environments. Grain yield was significantly correlated with the other four traits in almost all of the varieties. The mean correlation coefficient over all varieties ranged from 0.58 to −0.83 for durum wheat and 0.66 to 0.88 for aestivum wheat. The correlation coefficients between heading date and the other traits were also significant, ranging from −0.45 to −0.79 in durum wheat and −0.61 to −0.85 in aestivum wheat. The correlation coefficient between number of tillers with plant height and 1000-grain weight were the smallest, 0.19−0.32 in durum wheat and 0.39−0.60 in aestivum wheat. It was concluded that agronomic practices favouring early and good stand establishment in the dry regions will favour the yield components and important adaptive traits, which contribute towards larger yields. Significant differences were found among genotypes in the environmental correlation coefficients and the associated changes in one trait as a result of changes in other traits.
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  • 24
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; Puccinia recondita f. sp. tritici ; wheat leaf rust ; partial resistance ; latency period ; infection frequency ; urediosorus size ; growth stage ; component analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Latency period (LP), infection frequency (IF) and urediosorus size (US) of leaf rust were determined on primary leaves and young flag leaves of 18 spring wheat cultivars. A large growth stage effect and a large cultivar effect on all three components were observed. Partial resistance as measured by the three components was generally better expressed in the adult plant stage than in the seedling stage. Associated variation of the components was observed: long LP, low IF and small US tended to go together. The association was not complete, cultivars with clear deviations of this association for one of the components were found suggesting the existence of at least partly different genetic factors controlling the respective components. LP measured on flag leaves gave the most reliable results and, therefore, could best be used as a selection criterion in breeding programs for partial resistance.
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  • 25
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; Puccinia recondita f.sp. tritici ; leaf rust ; temperature sensitivity ; latency period ; infection frequency ; urediosorus size ; growth stage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Three components of partial resistance (PR) were studied at three post-infection temperatures using seven spring wheat genotypes differing in level of PR and two different wheat leaf rust races. The components were latency period (LP), infection frequency (IF) and urediosorus size (US). The expression of LP was more sensitive to temperature than the expression of the other two components. LP-prolonging genes were better expressed at low temperatures than at high temperatures and cultivar differences tended to increase with decreasing temperature in both seedling and adult plant stages. The reaction of IF to temperature differed from that of LP and US, probably because IF is regulated by another mechanism than LP and US. It is recommended to perform PR-screening tests at low rather than at high temperatures. If temperatures are maintained at about 8–13°C (night-day), seedlings can be used to screen for PR instead of the more expensive adult plant tests. The effectiveness of PR in seedling stage at low temperatures suggests that the seedling stage may have epidemiological significance as the low temperatures (8–13°C) are relevant for seedlings in the field.
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  • 26
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    Euphytica 44 (1989), S. 273-282 
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; race-specificity ; Puccinia recondita f.sp. tritici ; wheat leaf rust ; partial resistance ; hypersensitive resistance ; latency period ; disease severity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Partial resistance (PR) in wheat to wheat leaf rust (Puccinia recondita f.sp. tritici) is characterized by a slow epidemic build-up despite a susceptible infection type. Two greenhouse tests and two field tests, in which 11 spring wheat cultivars were exposed to five wheat leaf rust races, revealed some indication for race-specificity of PR. In the greenhouse, the expression of PR was highly dependent on the environment. Significant cultivar-race interactions in the first experiment were lost in the second experiment probably due to cultivar-environment and cultivar-race-environment interactions. In the polycyclic field tests several factors played a role in explaining the inconsistency of the cultivar-race interactions, such as differences in initial inoculum, genotypic differences in earliness, interplot interference or environmental conditions. One cultivar-race combination showed a significant but small interaction towards susceptibility in both field experiments. The interaction was probably too small to detect in the monocyclic greenhouse tests. The results do not conflict with the idea that a gene-for-gene relationship could exist between PR-genes in the host and genes in the pathogen. Some problems with regard to the selection of PR in wheat to wheat leaf rust are discussed.
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  • 27
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    Euphytica 44 (1989), S. 241-245 
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; Puccinia recondita f.sp. tritici ; leaf rust ; partial resistance ; environmental stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Five spring wheat cultivars differing in partial resistance (PR) to wheat leaf rust were tested at Wageningen (the Netherlands) on a sandy and a clay site, El Batan (CIMMYT, Mexico) and Ponta Grossa (Brazil) over two years. The cultivars were Skalavatis 56, Little Club (both very susceptible), Westphal 12A, Akabozu and BH 1146 (all three with high levels of PR). The results showed that PR was expressed at all four locations in both years. The level of expression was influenced by the environment but the cultivar ranking was hardly affected. Selection for PR in the field can therefore be carried out over a wide range of environments.
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  • 28
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    Euphytica 44 (1989), S. 247-258 
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; Puccinia recondita f.sp. tritici ; leaf rust ; epidemiological parameters ; microfield ; race nursery ; partial resistance ; components of resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Eighteen spring wheat cultivars were tested in microfields and race nurseries for their partial resistance PR to wheat leaf rust under low and high disease pressure respectively. Large differences existed between the 18 cultivars, Skalavatis 56 being the most susceptible and Ponta Grossa 1 being the most resistant cultivar. Of the three epidemic parameters, disease severity (DS) at the time that the susceptible check was severely diseased and area under the transformed disease severity curve (AUTC) and the logistic growth rate (r), AUTC and DS were highly correlated. Both seemed to be reliable estimators of PR but DS should be preferred for economical reasons. The logistic growth rate seemed to be unsuitable as an estimator of partial resistance. High and low disease pressure gave similar cultivar ranking. PR can be screened and selected equally well in race nurseries with low space, low time and low cost input as in microfields with high space, time and cost input. Cultivar differences in development rate had a large impact on the cultivar differences for amount of disease and can therefore greatly bias the estimation of cultivar resistance. The resistance of early cultivars tended to be underestimated whereas the resistance of late cultivars tended to be overestimated. The effect of differences in developmental rate was most pronounced in the flag leaf. It is advisable to avoid the assessment of disease levels on the flag leaf only and to incorporate in the tests several susceptible and resistant checks that cover the range of development rates in the material to be selected, because otherwise selection for resistance will tend to select also for lateness. Regression of the epidemiological parameters on three components of partial resistance revealed that latency period (LP) is an important factor in determining the resistance observed in the field explaining on average 67% of the observed variation. Adding infection frequency (IF) and urediosorus size (US) to the linear model increased the proportion of the observed variation in the field explained by the components to 80%. This result supports the idea that the components of PR inherit independently, at least, in part.
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  • 29
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    Plant and soil 114 (1989), S. 269-278 
    ISSN: 1573-5036
    Keywords: deleterious ; inhibitory bacteria ; pseudomonads ; rhizobacteria ; toxin ; wheat
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We studied the production of a toxin inhibitory to both winter wheat (Triticum aestivum L.) root growth andEscherichia coli that was produced by a rhizobacterial pseudomonad. Of several carbon sources tested, the most rapid growth and highest toxin concentrations were obtained with glucose, glycerol, or trehalose. Toxin production was repressed with L-cysteine as the nitrogen source. Toxin was produced during the late exponential and early stationary phase of growth by the bacterium and, contrary to studies with other toxins, was unaffected by Fe and P concentrations in the growth medium. Toxin production by the bacterium was the same at growth temperatures of 25 and 15°C while it produced less at 5°C. If the bacterium was able to grow, it produced toxin. No compound tested induced an increase in toxin production indicating toxin production is constitutive.
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  • 30
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    Plant and soil 115 (1989), S. 83-87 
    ISSN: 1573-5036
    Keywords: karnal funt ; Neovossia indica ; secondary spread ; wheat
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Wheat-spikes inoculated withN. indica at the boot-leaf stage produced secondary sporidia when later incubated (intact/detached) under moist conditions in the laboratory. Sporidia were also released from inoculated spikes in the field where sporidial release exhibited diurnal periodicity. More sporidia were trapped between 5–6 o'clock than during the later parts of the day but no sporidia were trapped between 14–18 o'clock. However, they could be trapped at any time of the day from the detached spikes incubated under moist conditions in the laboratory. Sporidia trapped in different experiments were invariably of the allantoid type and they proved viable and infective. Maximum sporidia developed on the outer glumes of florets, and this observation was supported by scanning electron microcope studies. Sporidia developed at 15 and 20°C but not at 30°C. These findings indicated that repeated cycles of sporidial production in spikes provided more inoculum than expected from soil-borne teliospores ofN. indica.
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    Plant and soil 116 (1989), S. 29-36 
    ISSN: 1573-5036
    Keywords: cytokinins ; potassium ; seaweed concentrate ; wheat
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effects of the seaweed concentrate “Kelpak’ on the growth and yield of wheat grown under conditions of varying K supply were investigated. Kelpak had no significant effect on the yield of wheat receiving an adequate K supply, but significantly increased the yield of K stressed plants. The increase in yield was caused by an increase in both grain number and individual grain weight. Although the beneficial effects of seaweed concentrates have often been attributed to their cytokinin content, several lines of evidence suggested that this group of plant growth regulators may not be solely responsible for the observed effects of Kelpak on wheat. Irrespective of the physiological mechanism of action, Kelpak would appear to have considerable potential for increasing yield in K stressed wheat and may therefore reduce the requirement of wheat for K fertilization.
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  • 32
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    Plant and soil 117 (1989), S. 157-165 
    ISSN: 1573-5036
    Keywords: bacterial metabolites ; gnotobiotics ; growth inhibition ; plant genotypes ; Pseudomonas ; rhizosphere ; Serratia ; symptoms ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract With the aim of elucidating mechanisms behind bacteria-induced deleterious effects and differential cultivar responses to bacterial inoculations, wheat seedlings were subjected to various tests under gnotobiotic conditions. Inoculation with two deleterious Pseudomonas isolates, Å 112 (fluorescent) and Å 313 (nonfluorescent), induced leaf symptoms and shoot and root growth inhibition, while inoculation with growthneutral bacteria (Serratia liquefaciens andEscherichia coli) had no such effects. Deleterious effects were induced at low inoculum densities (〈103 cells per plant), but required addition of nutrient broth in small amounts for consistency. Effects similar to those obtained with living inoculum could be induced by treating plants with sterile culture filtrates from isolate Å 313 or volatile bacterial metabolites from isolate Å 112. Wheat cultivars previously found to differ in their reaction to inoculation under non-sterile conditions, responded differentially to Å 112 and Å 313 also in the gnotobiotic assay. The results agree with the hypothesis that neither cultivar reaction nor the bacterial effects as such are mediated by interactions with an indigenous rhizosphere microflora.
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  • 33
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    Nutrient cycling in agroecosystems 19 (1989), S. 137-142 
    ISSN: 1573-0867
    Keywords: S ; calcite ; dolomite ; soybean ; corn ; wheat ; soil acidity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Liming costs have escalated since the mid 1970's in the United States. Studies of crop response to lime with irrigation are limited as well as those of crop response to soil acidifying agents. This study was conducted to determine yield response of irrigated soybean [Glycine max (L.) Merrill], corn (Zea mays L.), and wheat (Triticum aestivum L.) to lime and S and the change in soil pH, in response to lime and S. Irrigated soybean, corn, and wheat were grown on Dothan and Tifton loamy fine sand (Plinthic Acrisols) with different levels of calcite, dolomite, and S. Soil samples were collected before applying treatments and during each growing season. Soil pH and Mehlich I extractable P, K, Ca, and Mg in addition to grain yield of each crop were determined. Highest soybean yield (4.2 t ha−1) occurred in 1984 at a soil pH of 4.9 (1:1 v/v soil—water suspension) while the yield was zero at a pH of 3.7 on S treated plots. A soil pH of 4.8 in 1985 reduced soybean yield from 3.4 to 2.7 t ha−1 in comparison to untreated plots (pH = 5.6). In 1986, soybean yield was 0.8 t ha−1 at pH 4.0 in comparison to 2.3 t ha−1 at pH 5.1 and 5.9. Corn did not respond to lime with control pH of 5.3 in 1985 or 5.1 in 1986 but S at pH 4.6 reduced yield from 12.3 to 8.7 t ha−1 in 1985 and S reduced yield from 11.0 to 0.9 t ha−1 at pH 4.0 in 1986. Sulfur reduced wheat yield from 4.3 to 1.7 t ha−1 in 1985 and from 2.2 to 0.9 t ha−1 in 1987. Soil pH after cropping with S addition was 4.4 each year. Wheat did not respond to lime when unlimed soil had a pH of 5.2 or above.
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  • 34
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    Plant and soil 113 (1989), S. 213-221 
    ISSN: 1573-5036
    Keywords: microbial biomass ; 32P ; rhizosphere ; soil organic-P ; wheat
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract 32P-labelled monocalcium phosphate solution was supplied by point injection to the root system of wheat plants grown in soil cores in a controlled environment. There was no detectable incorporation of32P into organic P fractions in the soil remaining after roots were removed, confirming field observations. The techniques used to measure organic P (including biomass P) could detect an incorporation of32P into soil microbial biomass equivalent to 0.3 μgP.g−1 soil, compared to a total soil biomass P content estimated to be ca. 6.5 μgP.g−1 soil. The limited incorporation of the added P into microbial biomass in the root-free soil may be due partly to a limited diffusion of32P into the non-rhizosphere soil and partly to the removal of32P-labelled microbial biomass adhering to or in very close association with the root surface. it is proposed that in studies of soil nutrient status, total soil biomass P (roots + soil flora + microfauna) should be measured, rather than attempting an estimate of microbial P. A sequential extraction procedure using a single soil sample, where a biocide is added to the extracting solution, is proposed as an alternative to the conventional procedure for measuring soil biomass P where two soil samples, one treated with a biocide, are extracted simultaneously.
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  • 35
    ISSN: 1573-5036
    Keywords: Fusarium camptoceras ; Fusarium sp. ; Medicago spp. ; neosolaniol monoacetate ; phytotoxicity ; toxicity ; trichothecenes ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The toxicity of 12 South African isolates of an undescribedFusarium sp. from soil and other substrates was tested in plants and animals. TheFusarium sp. resemblesF. camptoceras but differs in several respects. Two reference cultures ofF. camptoceras were therefore included in the toxicity tests. An isolate ofF. graminearum Gr 1, a known pathogen of annualMedicago spp. (medics) and wheat, was also included in the plant tests. Maize cultures of all theFusarium sp. isolates and oneF. camptoceras isolate were toxic to ducklings. Ethyl acetate extracts of cultures of nine of ten isolates of theFusarium sp. were dermotoxic to rabbit skin. In soil infested with sand-bran inoculum of the fungi, allFusarium sp. isolates, oneF. camptoceras isolate andF. graminearum Gr 1 caused significant (P=0.05) mortality of medics, whereas onlyF. graminearum Gr 1 caused mortality of wheat plants. Seven isolates of theFusarium sp. caused stunting of medic and wheat plants as well as discolouration, necrosis and die-back of the tap root of medics and the primary roots of wheat. The fungus could, however, not be isolated from these necrotic roots. In contrast,F. graminearum Gr 1 that caused discolouration of medic roots and typical crown rot symptoms of wheat, was readily isolated from affected roots and crowns. Maize cultures of isolates of theFusarium sp. and ofF. camptoceras were chemically analysed for neosolaniol monoacetate (NMA), diacetoxyscirpenol (DAS) and T-2 toxin. NMA was detected at levels ranging from 310 to 2060 ng g−1 in 10 of theFusarium sp. isolates, but not in theF. camptoceras isolates. The mortality of medic plants and the NMA yields of isolates of theFusarium sp. in maize cultures were significantly correlated (r=0.84,P〈0.05). A solution containing 10 mg litre−1 of pure NMA was only slightly toxic to ducklings. Exposure of seeds to this solution had no effect on medics and wheat, but exposure of seedlings caused marked mortality in medics and reduction of shoot length in wheat. A solution containing 100 mg litre−1 of NMA was acutely toxic to ducklings, but had no effect on medic and wheat plants when added to soil. Phytotoxic effects on medic and wheat plants were obtained with a concentration of 5000 ng NMA g−1 soil. In all tests, the phytotoxic effects were more drastic in medics than in wheat: medics were killed, whereas wheat seedlings were stunted. This is the first report of the phytotoxicity of NMA to medics and wheatin vivo and probably also the first report of the phytotoxic effects of a pure trichothecene added to soil.
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  • 36
    ISSN: 1573-5044
    Keywords: wheat ; Triticum aestivum ; ABA ; ABA analogs ; somatic embryogenesis ; precocious germination
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    Topics: Biology
    Notes: Abstract Zygotic embryos from ten spring wheat (Triticum aestivum L.) genotypes were tested for embryogenic callus induction in the presence or absence of externally supplied (±)-abscisic acid (ABA) and two of its analogs, methyl abscisate and methyl epoxy-beta-ionylideneacetate. (±)-ABA and its analogs suppressed precocious germination of cultured late-stage embryos and promoted embryogenic callus induction. A significantly greater number of plants was regenerated from calli induced in the presence of ABA and ABA analogs. Early-stage embryos when cultured in the presence of (±)-ABA showed a negative response. Possible roles of ABA with respect to the expression of somatic embryogenesis are discussed.
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  • 37
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    The European physical journal 11 (1989), S. 239-248 
    ISSN: 1434-6079
    Keywords: 31.20.T ; 36.40
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    Topics: Physics
    Notes: Abstract Monte-Carlo calculations have been performed for positively charged argon clusters in the temperature range between 10 K and 40 K using two different models (one with a dimer ion core, the other one with a trimer ion). The argon-argon interaction potential stems from empirical data, the ion-neutral atoms potential is determined by ab initio MRD-CI calculations. Special stability is found for clusters sizesn=13, 19, 23 and 25/26 atoms using the ‘trimeric core model’ and for those withn=14,n=17,n=20 using the ‘dimeric core model’. The geometrical structure of the clusters is given and the construction principles are discussed in light of the interactions among neutral argon atoms and the ion-neutral atoms interaction.
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    The European physical journal 12 (1989), S. 85-87 
    ISSN: 1434-6079
    Keywords: 36.40 ; 61.55
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    Topics: Physics
    Notes: Abstract We present a study of the stability of clusters models made of a numberN of atoms in the range 500 to 6000 atoms, freely interacting through the Lennard-Jones potential. The potential energy per atom, calculated for relaxed models, shows that stable models belong to an icosahedral sequence whenN〈1600 and to a decahedral sequence beyond. A coexistence size range of both structures is discussed in connection with experimental results on argon clusters in free jet expansions.
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  • 39
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    The European physical journal 12 (1989), S. 167-171 
    ISSN: 1434-6079
    Keywords: 36.40 ; 64.70
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    Topics: Physics
    Notes: Abstract The evolution of thermodynamic, dynamic and quantum size effects in clusters is expected to contribute towards the merging between microscopic and macroscopic points of view in molecular, surface and bulk phenomena.
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    The European physical journal 12 (1989), S. 241-244 
    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80.E ; 34.80.G
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    Topics: Physics
    Notes: Abstract Photoionization measurements on cluster beams obtained by coexpanding sodium and sodium chloride vapors allow inferences regarding the thermodynamic stability of a number of mixed metal/salt aggregates. We discuss the possibility of observing composition dependent metal/insulator transitions among clusters with a fixed number of monomer units.
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  • 41
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    The European physical journal 12 (1989), S. 551-554 
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.50 ; L
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    Topics: Physics
    Notes: Abstract Low energy ion beam techniques have been used to perform a detailed study of the reactions of Al 25 + and Si 25 + with a range of simple molecules (D2, CH4, O2, C2H4, CO and N2). The reactions were studied over a center of mass collision energy range from 0.2eV up to 7eV. Activation barriers for chemisorption onto the clusters were deduced from the experimental results. The activation barriers for chemisorption on Al 25 + and Si 25 + are generally similar and show a qualitative correlation with the electronic properties of the reactant molecule. However, the products of the chemical reactions of Al 25 + and Si 25 + which result from cluster fragmentation are quite different. Si 25 + shows a tendency to undergo fission as observed in a number of recent studies of the dissociation of the bare clusters.
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  • 42
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    The European physical journal 12 (1989), S. 103-105 
    ISSN: 1434-6079
    Keywords: 36.40 ; 78.70
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    Topics: Physics
    Notes: Abstract The structures of Ag, Fe and Ge microclusters were determined using EXAFS. The measurements were performed over a wide range of clusters sizes. The clusters were prepared using the gas aggregation technique and isolated in solid argon at 4.2 K. The measurements were performed at the National Synchrotron Light Source (NSLS) at beam line X-18B. A strong contraction of the interatomic distances was observed for Ag dimers and multimers. Silver clusters larger than 12 A mean diameter show a small contraction of thenn distance and a structure consistent with an fcc lattice. By contrast clusters smaller than 12 A show the presence of a small expansion and a strong reduction or absence ofnnn in the EXAFS signal. This points towards a different crystallographic structure for Ag microclusters with diameter less than 12 A. In iron clusters we observe a gradual reduction of thenn distance as the cluster size decreases. The interatomic distance for iron dimers was determined to be 1.94 A, in good agreement with earlier measurements. The iron microclusters show a bcc structure down to a mean diameter of 9 A. Iron clusters with 9 A mean diameter show a structure inconsistent with a bcc lattice. The new structure is consistent with an fcc or hcp lattice. The measurements on Ge clusters show the presence of only nearest neighbors. There was clear evidence of temporal annealing as determined by variations in the near edge structure of the K-absorption edge. Absorption edge measurements were also performed for free Ge clusters travelling perpendicular to the direction of the synchrotron radiation beam. The measurements performed on the free clusters were consistent with those obtained for matrix isolated clusters.
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    The European physical journal 12 (1989), S. 253-261 
    ISSN: 1434-6079
    Keywords: 33.65 ; 33.80E ; 36.40
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    Topics: Physics
    Notes: Abstract The ionization process of homogeneous and heterogeneous van-der-Waals clusters has been investigated using various ionization methods (electron bombardment, charge exchange, photoionization methods), and different analyzing techniques. Direct and indirect ionization processes can be distinguished in the experiments from the shape of the ionization curve which depends on the type of cluster. These features appear differently in homogeneous and heterogeneous systems: Homogeneous systems exhibit characteristic ionization efficiency curves where the direct ionization path appears as a sudden increase in the ionization efficiency while the indirect transition gives rise to a long drawn out tail extending to the true ionization threshold. In heterogeneous clusters the indirect ionization path proceeds via excited states of the component with the larger ionization potential and subsequent energy transfer to the other component. These transitions are shifted and broadened depending on the type of internal interaction. Conclusions are drawn concerning the geometry and the interaction potential inside the cluster. The resolution of the TEPICO (Threshold Electron Photo Ion Coincidence) experiments makes it possible to determine the kinetic energy release of the fragments. It is shown that the results are related to the stabilities of the cluster ions involved in the fragmentation chain. Results are presented for pure rare gas clusters (Ar n , Kr n , Xe n ) and for mixed systems (Ar n O2m , Ar n Xe, Kr n Xe, (CH4) n Ne).
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  • 44
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    The European physical journal 12 (1989), S. 285-287 
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    Keywords: 36.40 ; 34.80.G
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    Notes: Abstract N2 cluster ions are produced by electron impact ionization of a supersonic N2 cluster beam and analyzed with a double focussing sector field mass spectrometer. It is found that metastable N2 cluster ions lose more than one N2 molecule in the μs time regime and decay predominantly via sequential series (N2) n + *→(N2) n−1 + *→...→N 2 + , evaporating a single monomer in each of these successive decay steps. The metastable decay rates determined in detail for cluster sizes 2≤n≤6 andn=20 lie between 1 and 106s−1. These rates(i) depend strongly on the time elapsed after ion formation and on the respective parent cluster ion size, and(ii) exhibit a quasiperiodic pattern in magnitude.
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  • 45
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    The European physical journal 12 (1989), S. 293-295 
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    Keywords: 36.40 ; 34.40 ; 34.80.G
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    Notes: Abstract (CO2) n , (NO) n and (NH3) n clusters are generated in a supersonic molecular beam and size selected by scattering from an He beam. By measurements of angular dependent mass spectra, TOF distributions and the angular dependence of the scattered signal quantitative information on the fragmentation probability by electron impact is derived. The van der Waals systems (CO2) n and (NO) n appear only at masses which are simply multiples of the monomer mass. The preferred cluster ion is the monomer ion for all investigated cluster sizes withn=2 to 4. The fragment pattern for the quasi-hydrogen bonded (NH3) n -cluster shows, beside a large number of fragment masses, a preference for protonated ions. The results are explained in terms of simple models based on the structural change from the neutral to the ionized configuration and the fragmentation pattern of the monomer followed by ionmolecule reactions.
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  • 46
    ISSN: 1434-6079
    Keywords: 36.40 ; 32.80.K
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    Topics: Physics
    Notes: Abstract A new technique is presented which allows direct observation of initial kinetic energies in multiphoton ionisation-fragmentation processes of molecules and clusters and provides an unambiguous determination of metastable decay channels. Results are presented for the unimolecular loss of a monomer from clusters (C6H6) 8 + to (C6H6) 12 + and for the reaction C6H 6 + →C4H 4 + +C2H2. We also observe a significant amount of probably collision induced fragmentation processes (C6H6) n + →(C6H6) n−x + + (C6H6) x withx much larger than 1.
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  • 47
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    The European physical journal 12 (1989), S. 319-326 
    ISSN: 1434-6079
    Keywords: 79.60 ; 36.40
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    Topics: Physics
    Notes: Abstract Photoemission spectra of valence electrons in metal clusters, together with threshold ionization potential measurements, provide a coherent picture of the development of the electronic structure from the isolated atom to the large metallic cluster. An insulator-metal transition occurs at an intermediate cluster size, which serves to define the boundary between small and large clusters. Although the outer electrons may be delocalized over the entire cluster, a small cluster remains insulating until the density of states near the Fermi level exceeds 1/kT. In large clusters, with increasing cluster size, the band structure approaches that of the bulk metal. However, the bands remain significantly narrowed even in a 1000-atom cluster, giving an indication of the importance of long-range order. The core-electron binding-energy shifts of supported metal clusters depend on changes in the band structure in the initial state, as well as on various final-state effects, including changes in core hole screening and the coulomb energy of the final-state charge. For cluster supported on amorphous carbon, this macroscopic coulomb shift is often dominant, as evidenced by the parallel shifts of the core-electron binding energy and the Fermi edge. Auger data confirm that final-state effects dominate in cluster of Sn and some other metals. Surface atom core-level shifts provide a valuable guide to the contributions of initial-state changes in band structure to cluster core-electron binding energy shifts, especially for Au and Pt. The available data indicate that the shift observed in supported, metallic clusters arise largely from the charge left on the cluster by photoemission. As the metal-insulator transition is approached from above, metallic screening is suppressed and the shift is determined by the local environment.
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  • 48
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    The European physical journal 12 (1989), S. 533-536 
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    Keywords: 33.20.K ; 35.20.G ; 36.40
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    Topics: Physics
    Notes: Abstract The electronic (UV-visible) spectrum of the molecular cluster Au55(PPh3)12Cl6 shows features corresponding to the 520 nm plasma resonance and the shorter-wavelength interband transition of colloidal gold. These absorptions differ qualitatively from the simpler one-electron transitions of lower-nuclearity cluster molecules. Differential scanning calorimetry has been used to measure the enthalpy of decomposition of Au55(PPh3)12Cl6. The Au-Au bonding appears to be substantially stronger than in bulk gold.
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  • 49
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    The European physical journal 12 (1989), S. 537-541 
    ISSN: 1434-6079
    Keywords: 82.30 ; 36.40
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    Topics: Physics
    Notes: Abstract Recent studies of the reactions of free or isolated transition metal clusters with simple molecules will be reviewed. Cluster chemical reactions are carried out in a laser-vaporization cluster source coupled to a continuous-flow reactor. Reactions can be categorized as chemisorptive (or surface) reactions, and bulk reactions. Chemisorptive reactions can be characterized asfacile, in which most cluster sizes of a given metal are equally reactive towards a particular reagent, oractivated, in which strong dependence of reactivity on cluster size is found. Under the normal operating conditions of the cluster reactor, a reaction may be kinetically controlled or at equilibrium. Following chemisorption, adsorbate decomposition and product desorption may occur. Specific reactions to be discussed include the reactions of iron clusters with ammonia and with water and the reactions of nickel clusters with ammonia.
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    The European physical journal 12 (1989), S. 571-573 
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    Keywords: 82.30 ; 36.40
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    Topics: Physics
    Notes: Abstract Aluminum clusters were generated by a laser vaporization method. Ionization potential of Al2 was found to be lower than that of Al. In the reaction with oxygen at high concentration, the mixed cluster Al9O7 survives predominantly as a stable cluster. Ammonia was found to be adsorbed weakly on the Aln surface.
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    The European physical journal 12 (1989), S. 579-582 
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    Notes: Abstract The effect of chlorine on the properties of Rh particles supported on alumina was studied using the hydroconversion of alkanes as a molecular probe. Chloride ions on the alumina have little influence on the Rh particles. Chlorine adsorbed on the Rh particles decreases the chemisorption capacity and increases the metal-support interaction, which results in modifications of their catalytic properties. Depending on the alkane processed, specific activity can be depressed up to four orders of magnitude.
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  • 52
    ISSN: 1434-6079
    Keywords: 36.40 ; 82.65.Jv ; 82.60.Cx
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    Notes: Abstract The aim of this work is to contribute to an explanation of thelowering of the specific activity of Pd/Al2O3 catalysts, towards hydrogenation of acetylenic molecules,as the dispersion increases. For this purpose, the interaction energy between these catalysts and H2, CO, propylene and propyne was directly measured by adsorption microcalorimetry at 323 K. In the case of propyne, the enthalpy of adsorption was found to be more than 50% higher for the catalysts with 97% dispersion than for the one with 26% dispersion, for coverages ranging from 0.2 to 0.7.This high enthalpy of adsorption (up to 290 kJ.mol−1) is attributed to a different proportion of edges and crystalline planes in the smallest Pd crystallites and is indeed consistent with a “blocking”chemisorption or with a hindered desorption of the products of a catalytic hydrogenation, i.e. with a lowering of the specific activity.
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  • 53
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    The European physical journal 13 (1989), S. 153-159 
    ISSN: 1434-6079
    Keywords: 31.20 ; 36.40 ; 78.70.D
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    Topics: Physics
    Notes: Abstract In this study we present theoretical X-ray absorption near-edge spectra (XANES) evaluated for Fe2, Ni2, and Ni3 using a modified multiple-scattered wave procedure. The calculations were performed for different internuclear distances of the dimers and by varying the geometry from linear to equilateral triangular for Ni3. The calculated absorption spectra for both Fe2 and Ni2 predict a broad resonant structure at the threshold and weak 1s transitions to unoccupied valence orbitals −5→0 eV giving a shoulder at the threshold. The resonance structure at the threshold of Ni3 appeared to be sensitive to the geometry of the clusters.
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  • 54
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80G
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    Notes: Abstract We report the development of an ion source for generating intense, continuous beams of both positive and negative cluster ions. This device is the result of the marriage of the inert gas condensation method with techniques for injecting electrons directly into expanding jets. In the preliminary studies described here, we have observed cluster ion size distributions ranging fromn=1−400 for Pb n + and Pb n − , and fromn=12−5700 for Li n − .
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  • 55
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    The European physical journal 14 (1989), S. 247-261 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract The atomic structure and thermodynamic properties of transition-metal clusters containingN atoms are investigated forN=6 and 7 using the method of molecular dynamics, where Gupta's potential taking into account many-body interaction is employed. The caloric curve (total energy — temperature curve) and the structural fluctuations are studied. The “fluctuating state” is found forN=6 in the region of the temperature near below the melting point, where clusters undergo structural transition from one isomer to others without making any topological change. The fluctuating state differs from the coexistence state in that the former involves no atomic diffusion, and goes to a structural phase transition of the bulk whenN is increased. On the other hand, the motion of atom-permutation is found in the low-temperature region of the liquid state, being induced by the cooperative motion of two atoms. It is discussed that such a motion easily occurs along the surface and may be considered to be one of the characteristics of small clusters. The fluctuating state is discussed in relation to the structural fluctuation of gold clusters observed experimentally.
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  • 56
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    Keywords: 36.40 ; 33.80
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    Notes: Abstract The fluence dependence of lead cluster ion distributions at 222 nm and 308 nm reveal markedly different behavior. Results obtained at 308 nm display a simple uniform increase in intensity with higher laser fluence with little change in relative intensities. At 222 nm, however, a significant transformation is found from a markedly different low fluence distribution to a high fluence pattern, which is essentially indistinguishable from that observed at 308 nm. It is concluded that mass spectra obtained at 308 nm, regardless of fluence, or at 222 nm and high fluence contain appreciable contributions from fragmentation. Hence, under these conditions the mass spectra are found to be dominated by cluster ion stabilities. Magic numbers observed at both high and low fluence correspond well to those obtained using electron-impact ionization, and in many instances parallel the magic numbers characteristic of rare-gas clusters. This suggests the stabilities of both neutral and monovalent cationic lead clusters are largely determined by close-packing considerations, and are not appreciably influenced by electronic structure. Similar preferences for close-packed structures are also found for mixed lead-antimony clusters containing one or two antimony atoms that are ionized using high fluence 308 nm excitation.
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  • 57
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    The European physical journal 11 (1989), S. 323-326 
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    Keywords: 36.40 ; 31.20
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    Notes: Abstract The Density Functional Formalism is used to calculate the minimum number of atoms (N c ) a multiply charged jellium-like spherical cluster must contain to be stable against coulomb explosion into two smaller fragments. In the case of alkaline clusters, which are systems for which the jellium model can be applied, we findN c equal to 31 and 23 for the explosion of Na N 2+ and Cs N 2+ respectively, in good agreement with the experimental value ofN c = 18 for Cs N 2+ . Calculated critical numbers for triply and tetracharged Cs clusters are 108 and 323 respectively. In addition the model predicts that the most favourable fragmentation channel is the ejection of a singly charged monomer.
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    The European physical journal 12 (1989), S. 237-239 
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    Keywords: 31.20 ; 36.40
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    Notes: Abstract A spherical average pseudopotential method (SAPS) is used to investigate some properties of compound alkali clusters. The effect that the substitution of a Sodium atom by a Lithium atom in a Na n cluster has on the stabilities and geometries is studied forn≤21. We have found that substitution is always energetically possible. On the other hand equiatomic Na n Cs n clusters are considered in the size rangen≤16. We find a strong segregation effect of the Cesium atoms towards the cluster surface. This agrees with what happens in liquid Na x Cs1−x alloys.
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    The European physical journal 12 (1989), S. 249-251 
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    Keywords: 36.40 ; 34.80 ; 33.80
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    Topics: Physics
    Notes: Abstract Sodium halide clusters are generated by inert gas condensation and probed by electron and photon induced dissociation. The dependence of fragmentation on electron energy and initial cluster temperature indicates a direct electronic fragmentation process without an intermediate state of vibrationally hot clusters.
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    The European physical journal 12 (1989), S. 269-271 
    ISSN: 1434-6079
    Keywords: 33.80.E ; 36.40
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    Topics: Physics
    Notes: Abstract Intra-cluster ion-molecule reactions in benzene clusters and benzene-water binary clusters were observed in Resonance-Enhanced Multi-Photon Ionization (REMPI) Time-of-Flight (TOF) mass spectra. Condensation reactions of the excited dimer unit or higher cluster unit are found to occur within clusters.
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    The European physical journal 12 (1989), S. 263-267 
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    Keywords: 36.40 ; 34.80.G
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    Notes: Abstract Metastable decay of cluster ions has been discovered only recently. It was noted that one has to take this metastable decay into account when using mass spectrometry to probe neutral clusters, because ion abundance anomalies in mass spectra of rare gas and molecular clusters are caused by delayed metastable evaporation of monomers following ion production. Moreover, it was found that(i) the individual metastable reaction rates k depend strongly on cluster size and cluster ion production pathways and that(ii) there exists experimental evidence (k=k(t)) and a theoretical prediction that a given mass selected cluster ion generated by electron impact ionization of a nozzle expansion beam will comprise a range of metastable decay rates. In addition, it was discovered that metastable Ar cluster ions which lose two monomers in the μs time regime decay via sequential decay series Ar n + *→Ar n−1 + *→Ar n−2 + * with cluster sizes 7≤n≤10 andn=3 (similar results were obtained recently in case of N2 cluster ions). Conversely, the dominant metastable decay channel of Ar 4 + * into Ar 2 + was found to proceed predominantly via a single step fissioning process.
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  • 62
    ISSN: 1434-6079
    Keywords: 36.40 ; 07.75
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    Notes: Abstract Clusters of Ar, Kr, Xe, N2, O2, CO2, SO2 and NH3 formed by supersonic nozzle expansion have been studied by electron impact ionization mass spectrometry (up to 15000 amu). Besides mass spectra of singly charged ions showing the characteristic anomalous distributions, we have in particular investigated the properties of multiply charged cluster ions. Critical appearance sizes of doubly and triply charged cluster ions, n2 and n3 respectively, found in the present study confirm recent theoretical predictions about n3/n2 and their dependence on the properties of the cluster constituents. The appearance energies of multiply charged cluster ions determined are shifted way below the appearance energies of the respective monomer ions. These huge red shifts together with the observed linear threshold laws and large maximum ionization efficiencies indicate that multiply charged cluster ions are produced by sequential single ionization events of one incoming electron at different cluster sites. Furthermore, we have also obtained for the first time clear evidence that (for electron energies above the appearance energy of doubly charged ions) an appreciable amount of singly charged (also fragment) ions is produced via Coulomb explosion of unstable doubly charged ions in the ion source.
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  • 63
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    The European physical journal 12 (1989), S. 291-292 
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    Keywords: 36.40 ; 34.50.H ; 34.80.D
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    Topics: Physics
    Notes: Abstract Van der Waals clusters of various molecules were collisionally ionized by high-Rydberg rare gas atoms and slow electrons. Negative cluster ions thus produced were detected by mass spectroscopy. The ionization mechanism were investigated by measurements of the size- and the energy-dependences of the electron attachment cross sections.
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    The European physical journal 12 (1989), S. 303-305 
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    Keywords: 36.40 ; 34.80.G
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    Topics: Physics
    Notes: Abstract Electron attachment and electron impact ionization of SF6 clusters have been investigated quantitatively in a molecular beam/electron ion source/mass spectrometer system as a function of electron energy E (0≤E≤180 eV) and as a function of cluster size.
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    The European physical journal 12 (1989), S. 189-191 
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    Keywords: 36.40 ; 64.60
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    Notes: Abstract The atomic structure and thermodynamic properties of transition-metal 6- and 7-atom clusters are investigated using the molecular dynamics method, where Gupta's potential taking into account many-body interaction is employed. The caloric and the structural fluctuations are studied. The “fluctuating state” is found forN=6 in the region of the temperature near and below the melting point, where clusters undergo structural transition from one isomer to others without making any topological change. The fluctuating state differs from the “coexistence state” found in Ar clusters [1] i.e. the former involves no liquid state. In the liquid state the motion of atom-permutation occurs besides the breathing motion. On the other hand, the fluctuating state is not found forN=7 but only the motion of atom-permutation in the liquid state. The coexistence state is found in both cases of 6- and 7-atom clusters. We also discuss a possibility of larger clusters displaying the fluctuating state.
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  • 66
    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
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    Notes: Abstract The spherical jellium model and self-consistent Weighted Density Approximation (WDA) to density functional theory have been used to study the stability of X N n (n=−1, 0, +1, +2; X=Ag, Cu;N≤25) clusters. The calculated magic numbers coincide with the observed ones. The first (IP1) and second (IP2) ionization potentials of Ag N and Cu N as a function of size show the typical oscillations induced by the electronic shell-filling effect. IP1 of Cu N is about 0.5 eV higher than IP1 of Ag N in the range studied (N≤25). For both Cu N and Ag N , IP1 appears to converge well towards the respective experimental values of the work function. The use of WDA allows us to obtain bound negative clusters of small size or with a nearly empty external shell, which is not possible using the Local Density Approximation (LDA) [1, 2]. However the electron affinity of X N clusters obtained as the difference of energies of the neutral and the negatively charged clusters, becomes negative forN=2, 3 and 8 (very close to zero forN=8), revealing that WDA needs further refinements.
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    The European physical journal 12 (1989), S. 225-227 
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    Keywords: 36.40 ; 79.70 ; 35.20.X
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    Notes: Abstract Cluster abundance of Li n + (n≤19), Na n + (n≤25), Si n z+ (n≤8 forz=1, 3≤n≤7 forz=2), Ge n z+ (n≤11 forz=1, 3≤n≤9 forz=2,n=4 forz=3), Sn n z+ (n≤7 forz=1, 3≤n≤9 forz=2,n=4 forz=3) and Pb n z+ (n≤6 forz=1, 5≤n≤7 forz=2) ejected from a liquid metal ion source has been investigated by mass spectrometry. The abundance spectra of alkali metal clusters showed distinct maxima and steps atn=3, 7, 9, 13 and 19 for Li, and atn=3, 5, 11, 13 and 19 for Na. Mass spectra of Si, Ge and Sn clusters were very similar each other, showing intensity drops aftern=4 and 6 (and alson=10 for Ge) for singly charged clusters. The magic numbers observed are discussed in terms of stability of charged clusters.
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    The European physical journal 12 (1989), S. 451-452 
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    Keywords: 76.60 ; 36.40
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    Topics: Physics
    Notes: Abstract In this paper we present measurements of nuclear relaxation times of31P in the polynuclear cluster compounds Au55(PPh3)12Cl6 and Ru55(P(t-Bu)3)12Cl20. Above 15 K the data can be described as a Korringa process, while below 15 K the relaxation time appears to be thermally activated.
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    The European physical journal 12 (1989), S. 543-546 
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    Keywords: 31.20 ; 36.40
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    Notes: Abstract Analysis of ab initio wave functions shows that the interaction between halogen atoms (F, Cl, and Br) and Ag clusters is ionic, and that the halogen ionicity is essentially −1. The interaction and the bonding arise, almost entirely, from the Coulomb attraction between the charged halogen and the metal and from polarization of the two subunits. Large shifts in equilibrium bond distances and vibrational energies are caused by an external electric field. These changes arise from a dominant Stark effect.
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    The European physical journal 12 (1989), S. 567-570 
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    Keywords: 36.40 ; 82.30
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    Topics: Physics
    Notes: Abstract The results of a detailed study of the primary and secondary reactions of carbon cluster ions, C n + (3≤n≤20), with HCN are presented and discussed. The experiments were performed in a Fourier transform (ICR) mass spectrometer, using direct laser vaporization of graphite to form the carbon cluster ions. Evidence for two structural forms of then=7, 8 and 9 cluster ions is obtained from their differing reactivity with HCN. The C 7 + ion is anomalous in its behavior in many respects, which is interpreted by an isomerization mechanism. The HCN reactions offer a contrast to the reactions with nonpolar neutrals studied previously. All HCN reactions produced ions of the type CnX+ (primary product) or CnXY+ (secondary product) where X, Y=H, CN or HCN. Fragmentation of the original carbon cluster was not observed, while radiative association is an important reaction channel. Low-energy collision-induced dissociation studies of the product ions support the mechanism of insertion into the H-CN bond and formation of covalent bonds at the carbene site for the primary reactions. In most secondary reactions however, the HCN associates weakly with the ion, rather than binding covalently.
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    The European physical journal 13 (1989), S. 171-178 
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    Keywords: 35.20.V ; 35.20.W ; 36.40
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    Topics: Physics
    Notes: Abstract Distinct temperature effects could be observed in the threshold regions of photoionisation efficiency (PIE) measurements of sodium clusters. Simulations of the PIE thresholds at various temperatures were carried out with a simple, semiclassical model. Fitting the simulations to the experimental data allows to correct ionisation potential assignments for thermal effects and estimate internal temperatures of polyatomic sodium clusters.
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    The European physical journal 14 (1989), S. 339-351 
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    Keywords: 36.40 ; 35.20.V ; 33.80.E
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    Topics: Physics
    Notes: Abstract The photoionisation threshold region of homogeneous Argon and Krypton clusters Ar n and Kr n forn up to 24 formed in a free jet expansion has been studied in detail, using the threshold photoelectron photoion coincidence (TPEPICO) time of flight technique. Measurements performed at a variety of different expansion conditions (nozzle temperature and stagnation pressure) demonstrate that fragmentation of larger clusters contributes substantially to the shape of the TPEPICO spectra even for the smallest clusters and at all photon energies higher than about 200 meV to 400 meV above the ionisation threshold. The determination of ionisation potentials for these cluster ions is discussed and careful estimates are given and compared with recent theoretical values.
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    The European physical journal 11 (1989), S. 87-91 
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    Keywords: 36.40 ; 79.70 ; 35.20.X
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    Notes: Abstract Sodium cluster ions Na+ n withn ranging up to 25 have been observed from a liquid sodium ion source by using a magnetic mass analyzer. Ion intensity as a function of cluster size showed distinct steps and local maxima atn=3, 5, 11, 13 and 19 (magic numbers), and a pronounced odd-even alternation. The features in the ion abundance curve are attributed to the relative stability of cluster ions. The observed magic numbers are only partially explained by the electronic shell model, indicating need to include a consideration of atomic structure in a cluster.
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  • 74
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    Notes: Abstract The core-valence correlation potential has been derived for Na and K employing atomic calculations which make use of the density functional formula worked out by Lee, Yang and Parr based on Colle-Salvetti approach. The numerical potential is fitted with a small number of Gaussians leading to a very simple expression for an one-electron corevalence correlation operatorŴ cv . The core-valence correlation corrections can be computed by applyingŴ cv on a quite general class of wavefunctions. Applications of theŴ cv operator within the framework of valence-electron-only calculations using effective Hamiltonians are presented for Na and K atoms, for Na2, K2, NaK and their cations. Almost all the corrections calculated for the physical properties due to the core-valence correlation lead to results which are in good agreement with those obtained from much more sophisticated treatments and experimental data.
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    ISSN: 1434-6079
    Keywords: 82.50 ; 36.40 ; 35.20.V
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    Notes: Abstract Pulse radiolysis and time-resolved optical spectroscopy were used to observe the earliest steps of silver aggregation in the presence of an electron donor whose electrochemical potential is close to those of usual photographic developers. A critical size has to be reached by the silver aggregate before it is thermodynamically able to accept electrons from the donor, then to grow by an autocatalytic process with alternate adsorption of Ag+ ions and electron scavenging. From a computer simulation the critical aggregation numbern c is found to be 4 and hence the electrochemical potential of the critical aggregate is ≈−0.4 V/NHE. The size-dependence of the electrochemical potential in an aqueous solution is discussed and compared with that of the ionization potential in the gas phase. A tentative extrapolation of the present interpretation to the mechanism of the photographic development is proposed.
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    The European physical journal 12 (1989), S. 199-203 
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    Keywords: 36.40
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    Notes: Abstract A detailed study of the stability of alkali-atom clusters is presented and discussed. Free clusters are produced in an unseeded adiabatic expansion and ionized by a pulsed laser beam. A tandem time-of-flight system provides a size selection of ionized species and mass spectrometry of fragments. We have investigated for sodium and potassium clusters containing up to fifty atoms: the metastable decay following ionization, the photo-induced dissociation, the collisional induced dissociation and the collisional charge exchange. Experimental evidence is shown for dissociative process involving evaporation of monomers and dimers. This is explained by the statistical unimolecular theory and by the energetics of the systems.
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    The European physical journal 12 (1989), S. 205-208 
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    Keywords: 36.40 ; 31.20
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    Notes: Abstract We have studied several decay processes of potassium clusters and found that a dimer-decay mechanism can explain the observed lowest abundance of K10 in the K n mass spectra. Total-energy curves for decay processes are calculated using a jellium-background model for positive-ion cores and the local-spin-density-functional approximation for valence electrons. The energy-barrier height for a dimer decay of K10 from the energy-minimum point is found to be 0.18 eV, which is a reasonable magnitude for the decay to take place thermally in the experiment. The monomer decay of K9 and the dimer decay of K11, which are expected to be the most favorable decays of K9 and K11, are found to have high barriers. Monomer and dimer decays of K8 are also studied and the monomer decay is found to be more favorable, in accord with the high-nozzle-temperature mass spectrum.
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    The European physical journal 12 (1989), S. 221-224 
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    Keywords: 36.40 ; 79.00
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    Notes: Abstract We analyse the role of the fragmentation processes in the liquid metal ion source technique from a theoretical and an experimental point of view. We show that the “double peak” structure of the energy distribution of Sn 7 + ions is due to the fact that there are two kinds of ions. On the one hand, ions which are directly emitted from the tip; on the other hand, ions produced by fragmentation at some distance (100–1000 Å) from the tip. We show that the existence of a peak for the second kind of ions strongly depends on the electric field mapping. We also deduce from the energy separation of the two peaks a life-time of the mother particles. The value obtained is compared to an evaluation made with the RRKM theory. The charge and mass of the mother particles are also discussed.
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    The European physical journal 12 (1989), S. 235-236 
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    Keywords: 36.40 ; 34.80.G
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    Notes: Abstract Compound cluster ions of heavy post-transition atoms (In, Pb, As, Sb, Bi) are enriched by electron induced dissociation if they are analogous to the Zintl polyanions Pb 5 2− and Pb 9 4− with respect to the atom and valence electron number.
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  • 80
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    The European physical journal 14 (1989), S. 237-245 
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    Keywords: 36.40 ; 31.20
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    Notes: Abstract We propose the “triangle contraction” as an important reconstruction mechanism of six-membered-ring silicon clusters on the basis of the force and virial analysis for Si6, Si10, Si14, Si18, Si22, and Si26 clusters. Forces acting on atoms have been calculated using the local-density-functional scheme with linear-combination-of-atomic-orbitals-Xα method. Calculated forces show that most of the (111)-surface equilateral triangles have tendency to contract, indicating the generality of the triangle-contraction mechanism.
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  • 81
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    The European physical journal 12 (1989), S. 11-13 
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    Keywords: 07.75 ; 36.40 ; 34.80.G
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    Notes: Abstract Using the Knudsen cell effusion technique it is possible to generate a molecular beam containing intermetallic molecules. Mass spectrometric studies were carried out with the systems: cesium/antimony, cesium/antimony/bismuth, cesium/antimony/indium, cesium/antimony/tin and cesium/antimony/bismuth/tin. In all these systems intermetallic particles with extraordinary stoichiometries could be detected. A brief discussion of the appearance energies and the bonding principle of these molecules or clusters are given.
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    The European physical journal 12 (1989), S. 53-59 
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    Keywords: 31.20N ; 36.40
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    Notes: Abstract The group theoretical consequences of the Tensor Surface Harmonic Theory have been developed for [ML2] n , [ML4] n and [ML5] n clusters where either thexz andyz orx 2−y 2 andxy components toL d π andL d δ do not contribute equally to the bonding. The closed shell requirements for such clusters are defined and the orbital symmetry constraints pertaining to the interconversion of conformers of these clusters are described.
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  • 83
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    The European physical journal 12 (1989), S. 65-68 
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    Notes: Abstract The importance of quantum mechanics for the thermal behaviour of Argon clusters with special respect to phase transitions is investigated applying a Path-Integral Monte-Carlo (PIMC) method. Results for the small-angle neutron scattering function (SANS) for various cluster sizes and temperatures are presented.
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  • 84
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    The European physical journal 12 (1989), S. 73-75 
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    Notes: Abstract Energy barriers between low-lying configurational states were calculated for several small Al clusters. Calculations were carried out considering a model potential comprising two- and three-body interactions. Parameters used in this potential energy function were evaluated from fits to high level ab initio calculations for Al clusters. Energy barriers separating low-lying configurations were found to be in varying heights. Results indicate that isomeric transformations between several low-lying high-symmetry forms of small Al clusters are quite likely and may take place at relatively low temperatures.
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  • 85
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    The European physical journal 11 (1989), S. 249-255 
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    Keywords: 36.40 ; 61.20
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    Notes: Abstract A theory is proposed for modeling the autoassociation of alcohol molecules either in the neat liquid or in inert (non-complexing) solvents. This autoassociation by hydrogen bonds takes the form of clusters which can be predominantly open or cyclized chains, depending on the concentration. Chain conformation statistics are used for calculating the dipole moment of each type of chain. Cyclization equilibrium theory is employed for obtaining formulae for the fraction of all types of clusters. The total Kirkwood angular correlation factorg is calculated in function of the concentration. For this only two parameters are used; the first one is a common equilibrium constant for H bond dissociation; the second one is closely linked to the stiffness of the chains. A numerical illustration is presented for the case of normal hexanol in various aliphatic solvents, for which several dielectric data exist in the literature.
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  • 86
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    The European physical journal 12 (1989), S. 7-9 
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    Keywords: 36.40 ; 47.55.E ; 61.14.F
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    Topics: Physics
    Notes: Abstract A pulsed nozzle source has been installed in the electron diffraction unit at the University of Michigan. The pulsed mode of operation is found to offer several important advantages in the investigation of clusters generated in nozzle flow. These advantages, including the feasibility of operating without a skimmer, are discussed. Design features and characteristic results are briefly outlined.
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  • 87
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    The European physical journal 12 (1989), S. 37-40 
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    Keywords: 36.40 ; 33.30 ; 33.20.E
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    Notes: Abstract The method of loading sodium clusters in zeolites, consisting of the controlled thermal decomposition of physisorbed sodium azide, is discussed. The influence of the azide loading, the azide decomposition rate and the sintering process on the amount of ionic and metallic sodium clusters in zeolite Y was followed by ESR. The method is compared to other metal deposition techniques.
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  • 88
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    The European physical journal 12 (1989), S. 61-64 
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    Keywords: 31.20 ; 36.40
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    Notes: Abstract Optimized molecular geometries and electronic structures are determined for neutral, positively charged, and negatively charged carbon and silicon clusters containing up to ten atoms. The effects of polarization functions and electron correlation are included in these claculations. Carbon clusters have linear or monocyclic ground state geometries whereas silicon clusters containing five or more atoms have three-dimensional ground state structures. Neutral C4, C6 and C8 all have linear and monocyclic isomers of comparable stability whereas the ionic forms appear to be generally more stable as linear geometrical arrangements. In the case of neutral and positively charged carbon clusters, the odd-numbered clusters are significantly more stable than the adjacent even-numbered clusters whereas the opposite order of stability occurs for the negative ions. This is due to the large values of the electron affinities of the linear forms of even-numbered clusters such as C4 and C6. The relative stabilities of silicon clusters does not change with the charge state of the clusters.
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    The European physical journal 12 (1989), S. 69-71 
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    Keywords: 36.40 ; 61.55
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    Notes: Abstract It is widely believed that the lowest energy configurations for small rare gas clusters have icosahedral symmetry. This contrasts with the bulk crystal structures which have cuboctahedral fcc symmetry. It is of interest to understand the transition between this finite and bulk behavior. To model this transition in rare gas clusters we have undertaken optimization studies within the Lennard-Jones pair potential model. Using a combination of Monte Carlo and Partan Search optimization methods, the lowest energy relaxed structures of Lennard-Jones clusters having icosahedral and cuboctahedral symmetry were found. Studies were performed for complete shell clusters ranging in size from one shell having 13 atoms to 14 shells having 10,179 atoms. It was found that the icosahedral structures are lower in energy than the cuboctahedral structures for cluster sizes having 13 shells or fewer. Additional studies were performed using the more accurate Aziz-Chen [HFD-C] pair potential parameterized for argon. The conclusions appear to be relatively insensitive to the form of the potential.
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    The European physical journal 12 (1989), S. 89-92 
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    Notes: Abstract Compact and tetravalent clusters with icosahedral local or global symmetries are generated by mapping from ideal structures in curved space onto a tangent euclidean 3D space. The observed elastic energy of the clusters can thus be interpreted as an intrinsic curvature associated to a frustrated local order. It is then proposed a kind of classification of the very rich family of possible clusters using a limited set of parameters.
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  • 91
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    The European physical journal 12 (1989), S. 15-18 
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    Keywords: 33.20.N ; 36.40
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    Notes: Abstract A new apparatus for depositing intense beams of neutral, mass selected metal clusters in rare gas matrices or on a solid surface has been constructed. Metal cluster cations, produced by Ar+ sputtering, may be energy analyzed and then mass selected in a quadrupole mass filter. The clusters are neutralized by low energy electrons and then co-deposited with a rare gas on a 4 K sapphire window. Matrix samples were interrogated in situ by UV-optical absorption spectroscopy. Good quality neutral Ag spectra were obtained following a 30 min. Kr deposition of a ca. 2.5 nA cm−2 beam of Ag+. Line strength measurements imply matrices containing about 1013 atoms cm−2, corresponding to a neutralization efficiency of about 50%. Preliminary experiments on Ag 2 + yielded only Ag spectra, but with a lesser yield, perhaps indicative of incomplete fragmentation.
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  • 92
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    The European physical journal 12 (1989), S. 93-96 
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    Keywords: 61.14 ; 36.40
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    Topics: Physics
    Notes: Abstract SF6 clusters are produced during the free jet expansion of a Ne-SF6 mixture and studied by electron diffraction methods. Present experiments have been performed at constant nozzle diameter, stagnation pressure and stagnation temperature, adjustable parameters being the SF6 mole fraction X and the nozzle-to-skimmer distancex s /d. It is possible to warm up SF6 clusters by increasing either X, and thus the cluster size, orx s /d, which makes them collide with background molecules downstream of the Mach disk. In both cases, cold clusters made of several hundreds of molecules experience a structural transition, similar to that observed in bulk material, from the triclinic to the bcc plastic structure. A molecular dynamics simulation accounts correctly for intermediate stages of the transition which are visible in experimental patterns. Contrary to bulk results, cluster results show that the structural transition occurs over some temperature range.
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  • 93
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    The European physical journal 12 (1989), S. 307-314 
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    Keywords: 31.20.D ; 31.30 ; 36.40
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    Topics: Physics
    Notes: Abstract The results of the systematic ab-initio CI investigation of neutral and charged Li n , Na n , BeLi k and MgNa k clusters are summarized and analyzed. The general characteristic features of the electronic structure are pointed out:a) The participation of the atomic orbitals, which are empty in Ia and IIa metal atoms, allows for a higher valency of these atoms in clusters.b) Jahn-Teller and pseudo-Jahn-Teller effects strongly influence the electronic and geometric structure of clusters.c) Deformations of cluster geometry can lead to biradicaloid structures with higher spin multiplicity in their ground states.d) The peculiarities of the electronic structures of clusters can be deduced from the presence of many “surface” atoms. The theoretical results agree with experimental data presently available and they are useful for interpretation of the experimental findings.
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    The European physical journal 12 (1989), S. 341-346 
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    Keywords: 31.20.D ; 36.40
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    Topics: Physics
    Notes: Abstract The crucial importance of correlation effects versus delocalization, and their nature in small Alkali clusters is analysed from an ab-initio point of view through a detailed investigation of the Li2 dimer. The role of the external correlation (provided by extended basis sets and large Configuration Interaction calculations) is shown to lower the energy of ionic configurations and to increase their weight in the electronic wavefunction, increasing simultaneously the importance of delocalization versus internal correlation within thes-band. Effective interactions are determined from accurate diabatic calculations on dimers and transfered to clusters via an effective hamiltonian spanned bys orthogonal orbitals. Although not including explicitely thep-band, this model provides results in good agreement with abinitio calculations on Lithium clusters.
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    The European physical journal 12 (1989), S. 381-386 
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    Keywords: 31.20.N ; 36.40 ; 79.20.N
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    Topics: Physics
    Notes: Abstract Negative cluster ions M p C n − (M normal element,n〈10,p=1−4) produced by various experimental techniques from carbides show in their emission intensities a very strong even-odd effect according to the parity of the carbon atom numbern. This is in particular the case when M=N, F, Cl (p=1), M=H, Al, Si, S (p=1, 2) or M=B (p=1−4). The largest intensities of M p C n − ions always take place for evenn except in the cases of NC n − , B2C n − and Al2C n − , for which the maxima of emission occur for oddn. This oscillating behaviour corresponds to alternations in the stability of the clusters which are mainly due to the fact that, in Pitzer and Clementi model (linear chains in thesp hybridization within the framework of Hückel theory), the HOMO (highest occupied molecular orbital) of the clusters lies in a double degenerateπ level band: a cluster with a complete HOMO is always more stable than a cluster with a nearly empty HOMO. This result involves that the total number ofπ electrons is the main factor governing the parity of the stability alternations. Accordingly, since the knowledge of theπ electron number requires the determination of theσ electron number too, these alternations enable us to infer a very likely electronic structure of the ions.
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    The European physical journal 12 (1989), S. 401-403 
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    Keywords: 36.40 ; 33.35.Ex
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    Topics: Physics
    Notes: Abstract The paramagnetic susceptibility of small divalent clusters (Mg and Zn) trapped in Xe and Adamantane matrices has been studied with EPR spectroscopy. This study represents an observation of the transition between the atomic behaviour and the extended solid. The signal of clusters 〉15 Å as a function of temperatures shows that their susceptibility has a Curie-low behaviour. These results are contrary to the quantum size effects models of Kubo [1] and Mühlschlegel [2].
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    The European physical journal 12 (1989), S. 431-434 
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    Keywords: 35.20.V ; 36.20 ; 36.40
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    Topics: Physics
    Notes: Abstract A newly developed photoion-photoelectron Vacuum-UV coincidence spectrometer has been coupled to a supersonic metal atom cluster beam source and has been used to investigate the electronic structure of isolated mercury clusters in the size range from 1 to 110 at several selected discrete excitation energies between 11.3 and 7.1 eV. Excitation of the van der Waals cluster Hg10 at the center of the strongD 3/2-autoionization line at 10.7 eV yields a photoelectron kinetic energy distribution between 0 and 2.5 eV indicating the population of Hg10 ionic states, which are also accessible by threshold ionization.
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    The European physical journal 12 (1989), S. 443-444 
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    Keywords: 07.75 ; 36.40
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    Notes: Abstract Unusually high ionization energies have been observed for Cs-O clusters having certain sizes and composition, namely for Cs2n+zOn with z=8, 18, 34, 58 and 92. The anomalies are well-defined for clusters containing from 1 to 7 oxygen atoms. The indicated values of z are identical to the number of electrons in closed shells of angular momentum.
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  • 99
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    Keywords: 36.40 ; 75.20
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    Notes: Abstract Metal cluster compounds are composed of large macromolecules, which consist of a metal core (cluster) containing a certain number (n=6–560) of metal atoms, to which core a shell of ligands is coordinated. They provide excellent model systems for an assembly of identical metal clusters, embedded in a dielectric matrix. We discuss a number of physical properties of these materials.
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    The European physical journal 12 (1989), S. 453-455 
    ISSN: 1434-6079
    Keywords: 33.30 ; 36.40
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    Notes: Abstract The magnetic properties of molecular metal cluster compounds resemble those of small metal particles in the metametallic size regime. Even-electron metal carbonyl clusters with 10 or more metal atoms are paramagnetic, because their frontier orbital separations of less than 1 eV lead to high-spin electronic configurations. The rhodium cluster [Rh17S2(CO)32]3− gives EPR below 200 K withg=2.04, the first example of this type of paramagnetism in an even-electron carbonyl cluster of this 4d metal. Its spectral parameters are compared with those of osmium carbonyl clusters and some significant differences highlighted. Attempts have also been made to generate radical cations from lower-nuclearity, diamagnetic molecular clusters such as Rh6(CO)16 by chemical oxidation in sulphuric acid. An EPR active species (g=2.09) believed to be [Rh6(CO)16]+ has been obtained.
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