Preparation and applications of periodical gold nanoparticle arrays

Diese Arbeit beschäftigt sich mit der Herstellung und Anwendungen von periodischen Goldnanopartikel-Arrays (PPAs), die mit Hilfe von Nanosphären-Lithografie hergestellt wurden. In Abhängigkeit der verwendeten Nanosphären-Größe wurden dabei entweder kleine dreieckige Nanopartikel (NP) (bei Verwendung von Nanosphären mit einem Durchmesser von 330 nm) oder große dreieckige NPD sowie leicht gestreckte NP (bei Verwendung von Nanosphären mit einem Durchmesser von 1390 nm) hergestellt. Die Charakterisierung der PPAs erfolgte mit Hilfe von Rasterkraftmikroskopie, Rasterelektronenmikroskopie und optischer Spektroskopie. Die kleinen NP besitzen ein Achsverhältnis (AV) von 2,47 (Kantenlänge des NPs: (74+/-6) nm, Höhe: (30+/-4) nm. Die großen dreieckigen NP haben ein AV von 3 (Kantenlänge des NPs:(465+/-27) nm, Höhe: (1530+/-10) nm) und die leicht gestreckten NP (die aufgrund der Ausbildung von Doppelschichten ebenfalls auf der gleichen Probe erzeugt wurden) haben eine Länge von (364+/-16)nm, eine Breite von (150+/-20) nm und eine Höhe von (150+/-10)nm. Die optischen Eigenschaften dieser NP werden durch lokalisierte Oberflächenplasmon-Polariton Resonanzen (LPPRs) dominiert, d.h. von einem eingestrahlten elektromagnetischen Feld angeregte kollektive Schwingungen der Leitungsbandelektronen. In dieser Arbeit wurden drei signifikante Herausforderungen für Plasmonik-Anwendungen bearbeitet, welche die einzigartigen optischen Eigenschaften dieser NP ausnutzen. Erstens wurden Ergebnisse der selektiven und präzisen Größenmanipulation und damit einer Kontrolle der interpartikulären Abstände von den dreieckigen Goldnanopartikel mit Hilfe von ns-gepulstem Laserlicht präsentiert. Die verwendete Methode basiert hierbei auf der Größen- und Formabhängigkeit der LPPRs der NP. Zweitens wurde die sensorischen Fähigkeiten von Gold-NP ausgenutzt, um die Bildung von molekularen Drähten auf den PPAs durch schrittweise Zugabe von unterschiedlichen molekularen Spezies zu untersuchen. Hierbei wurde die Verschiebung der LSPPR in den optischen Spektren dazu ausgenutzt, die Bildung der Nanodrähte zu überwachen. Drittens wurden Experimente vorgestellt, die sich die lokale Feldverstärkung von NP zu nutze machen, um eine hochgeordnete Nanostrukturierung von Oberflächen mittels fs-gepulstem Laserlicht zu bewerkstelligen. Dabei zeigt sich, dass neben der verwendeten Fluenz die Polarisationsrichtung des eingestrahlten Laserlichts in Bezug zu der NP-Orientierung sowie die Größe der NP äußerst wichtige Parameter für die Nanostrukturierung darstellen. So konnten z.B. Nanolöcher erzeugt werden, die bei höheren Fluenzen zu Nanogräben und Nanokanälen zusammen wuchsen. Zusammengefasst lässt sich sagen, dass die in dieser Arbeit gewonnen Ergebnisse von enormer Wichtigkeit für weitere Anwendungen sind.

Biological Photonic Crystals: Diatoms

The aim of this work was to produce a variety of fluorescent diatom cell wall material as a basis for spectroscopic investigations of the influence of the photonic structure on the emission of an incorporated laser dye. This goal was achieved by the method of in vivo-fluorochromation, in which the fluorescence dyes are incorporated by the diatom cells during cell wall formation. Several fluorescent dyes (mostly rhodamines) known as strong laser dyes, were tested for a possible application within this method. The results of this work show that half of the tested rhodamines can be applied for an in vivo-fluorochromation of diatom cells. For a successful incorporation into the diatom cell wall, a relatively low toxicity to diatom cells is necessary. Replacement of the carbon acid function at the carboxyphenyl ring of the rhodamine by a methyl or ethylester function showed to convert a rhodamine of relatively low toxicity to a rhodamine leading to severe lethal effects within the cells. In contrast to their carbon acid forms, which posses a net neutral charge of the molecule, rhodamine esters exhibit a net positive charge. The enhanced toxicological effects seem to be due to an increased accumulation of positive charged rhodamines within the mitochondria, an increased hydrophobicity due to the attachment of an alkyl substituent, an increased retention time of the dyes within the mitochondria and a therefore stronger negative effect on the mitochondrial membrane bound energy processes of the diatom cell. Therefore rhodamines with a positive net charge deriving from a methyl or ethylester function at the carboxy phenyl ring instead of a carbon acid substituent showed not to be suitable for long-term investigations/ biomineralization studies of diatoms. Investigations performed on diatom species of different orders showed that rhodamine 19, rhodamine B, and rhodamine 101 can presumably be successfully applied for in vivo-fluorochromation to all diatom species. The results obtained here can help to find further laser dyes for an in vivo-fluorochromation of diatom cells and therefore for the production of fluorescent nanostructural elements for a detailed optical investigation of the diatom cell wall. First optical measurements performed on in vivo-fluorochromated cell walls did not give any hints concerning the photonic structure of the diatom cell. Cell wall parts with different nanostructural elements were investigated and by comparison of the obtained fluorescence emission spectra, no special features that might derive from photonic structural effects could be observed. Results concerning the concentration dependent shifts within the emission spectra, as well as the decrease of fluorescence intensity of the stained cell wall structures with increasing dye concentration, depict that several effects occurring by interaction of the molecules within the cell wall can have an impact on the technical application of fluorescent cell walls. It can be assumed that the investigation of the photonic crystal behaviour and the possibility to achieve laser action within the diatom cell wall can be hampered by molecular interactions. The results give hints to prevent such obstacles. Comparison of the recent findings and state of the art of in vivo-fluorochromation of diatom cell wall material, make clear that the here presented results are of importance and can offer a considerable contribution to the development and establishment of new biosilification markers, for diatoms as well as for other biosilifying organisms.

Development and Integration of Biocontrol Products in Branched Broomrape (Phelipanche ramosa) management in Tomato

Parasitic weeds of the genera Striga, Orobanche, and Phelipanche pose a severe problem for agriculture because they are difficult to control and are highly destructive to several crops. The present work was carried out during the period October, 2009 to February, 2012 to evaluate the potential of arbuscular mycorrhizal fungi (AMF) to suppress P. ramosa on tomatoes and to investigate the effects of air-dried powder and aqueous extracts from Euphorbia hirta on germination and haustorium initiation in Phelipanche ramosa. The work was divided into three parts: a survey of the indigenous mycorrhizal flora in Sudan, second, laboratory and greenhouse experiments (conducted in Germany and Sudan) to construct a base for the third part, which was a field trial in Sudan. A survey was performed in 2009 in the White Nile state, Sudan to assess AMF spore densities and root colonization in nine fields planted with 13 different important agricultural crops. In addition, an attempt was made to study the relationship between soil physico-chemical properties and AMF spore density, colonization rate, species richness and other diversity indices. The mean percentage of AMF colonization was 34%, ranging from 19-50%. The spore densities (expressed as per 100 g dry soil) retrieved from the rhizosphere of different crops were relatively high, varying from 344 to 1222 with a mean of 798. There was no correlation between spore densities in soil and root colonization percentage. A total of 45 morphologically classifiable species representing ten genera of AMF were detected with no correlation between the number of species found in a soil sample and the spore density. The most abundant genus was Glomus (20 species). The AMF diversity expressed by the Shannon–Weaver index was highest in sorghum (H\= 2.27) and Jews mallow (H\= 2.13) and lowest in alfalfa (H\= 1.4). With respect to crop species, the genera Glomus and Entrophospora were encountered in almost all crops, except for Entrophospora in alfalfa. Kuklospora was found only in sugarcane and sorghum. The genus Ambispora was recovered only in mint and okra, while mint and onion were the only species on which no Acaulospora was found. The hierarchical cluster analysis based on the similarity among AMF communities with respect to crop species overall showed that species compositions were relatively similar with the highest dissimilarity of about 25% separating three of the mango samples and the four sorghum samples from all other samples. Laboratory experiments studied the influence of root and stem exudates of three tomato varieties infected by three different Glomus species on germination of P. ramosa. Root exudates were collected 21or 42 days after transplanting (DAT) and stem exudates 42 DAT and tested for their effects on germination of P. ramosa seeds in vitro. The tomato varieties studied did not have an effect on either mycorrhizal colonization or Phelipanche germination. Germination in response to exudates from 42 day old mycorrhizal plants was significantly reduced in comparison to non-mycorrhizal controls. Germination of P. ramosa in response to root exudates from 21 day old plants was consistently higher than for 42 day-old plants (F=121.6; P<.0001). Stem diffusates from non-mycorrhizal plants invariably elicited higher germination than diffusates from the corresponding mycorrhizal ones and differences were mostly statistically significant. A series of laboratory experiments was undertaken to investigate the effects of aqueous extracts from Euphorbia hirta on germination, radicle elongation, and haustorium initiation in P. ramosa. P. ramosa seeds conditioned in water and subsequently treated with diluted E. hirta extract (10-25% v/v) displayed considerable germination (47-62%). Increasing extract concentration to 50% or more reduced germination in response to the synthetic germination stimulants GR24 and Nijmegen-1 in a concentration dependent manner. P. ramosa germlings treated with diluted Euphorbia extract (10-75 % v/v) displayed haustorium initiation comparable to 2, 5-Dimethoxy-p-benzoquinon (DMBQ) at 20 µM. Euphorbia extract applied during conditioning reduced haustorium initiation in a concentration dependent manner. E. hirta extract or air-dried powder, applied to soil, induced considerable P. ramosa germination. Pot experiments were undertaken in a glasshouse at the University of Kassel, Germany, to investigate the effects of P. ramosa seed bank on tomato growth parameters. Different Phelipanche seed banks were established by mixing the parasite seeds (0 - 32 mg) with the potting medium in each pot. P. ramosa reduced all tomato growth parameters measured and the reduction progressively increased with seed bank. Root and total dry matter accumulation per tomato plant were most affected. P. ramosa emergence, number of tubercles, and tubercle dry weight increased with the seed bank and were, invariably, maximal with the highest seed bank. Another objective was to determine if different AM fungi differ in their effects on the colonization of tomatoes with P. ramosa and the performance of P. ramosa after colonization. Three AMF species viz. GIomus intraradices, Glomus mosseae and Glomus Sprint® were used in this study. For the infection, P. ramosa seeds (8 mg) were mixed with the top 5 cm soil in each pot. No mycorrhizal colonization was detected in un-inoculated control plants. P. ramosa infested, mycorrhiza inoculated tomato plants had significantly lower AMF colonization compared to plants not infested with P. ramosa. Inoculation with G. intraradices, G. mosseae and Glomus Sprint® reduced the number of emerged P. ramosa plants by 29.3, 45.3 and 62.7% and the number of tubercles by 22.2, 42 and 56.8%, respectively. Mycorrhizal root colonization was positively correlated with number of branches and total dry matter of tomatoes. Field experiments on tomato undertaken in 2010/12 were only partially successful because of insect infestations which resulted in the complete destruction of the second run of the experiment. The effects of the inoculation with AMF, the addition of 10 t ha-1 filter mud (FM), an organic residues from sugar processing and 36 or 72 kg N ha-1 on the infestation of tomatoes with P. ramosa were assessed. In un-inoculated control plants, AMF colonization ranged between 13.4 to 22.1% with no significant differences among FM and N treatments. Adding AMF or FM resulted in a significant increase of branching in the tomato plants with no additive effects. Dry weights were slightly increased through FM application when no N was applied and significantly at 36 kg N ha-1. There was no effect of FM on the time until the first Phelipanche emerged while AMF and N application interacted. Especially AMF inoculation resulted in a tendency to delayed P. ramosa emergence. The marketable yield was extremely low due to the strong fruit infestation with insects mainly whitefly Bemisia tabaci and tomato leaf miner (Tuta absoluta). Tomatoes inoculated with varied mycorrhiza species displayed different response to the insect infestation, as G. intraradices significantly reduced the infestation, while G. mosseae elicited higher insect infestation. The results of the present thesis indicate that there may be a potential of developing management strategies for P. ramosa targeting the pre-attachment stage namely germination and haustorial initiation using plant extracts. However, ways of practical use need to be developed. If such treatments can be combined with AMF inoculation also needs to be investigated. Overall, it will require a systematic approach to develop management tools that are easily applicable and affordable to Sudanese farmers. It is well-known that proper agronomical practices such as the design of an optimum crop rotation in cropping systems, reduced tillage, promotion of cover crops, the introduction of multi-microbial inoculants, and maintenance of proper phosphorus levels are advantageous if the mycorrhiza protection method is exploited against Phelipanche ramosa infestation. Without the knowledge about the biology of the parasitic weeds by the farmers and basic preventive measures such as hygiene and seed quality control no control strategy will be successful, however.

Folien zur Vorlesung Sortierverfahren

Die hier frei verfügbare Foliensammlung stammt aus der gleichnamigen Master-Veranstaltung im Sommersemester 2014. Das zugehörige Skript (in Englisch) kann als PDF heruntergeladen werden von der Universität Turku (Lutz M. Wegner, Sorting – The Turku Lectures, Lecture Notes in Computing 2014, Univ. of Turku, Finland, http://tucs.fi/publications/attachment.php?fname=bWegner_LutzMx14a.full.pdf). Das überarbeitete Material geht auf eine dort im Jahre 1987 gehaltene Gastvorlesung zurück. Betrachtet werden Varianten von Quicksort und Heapsort, speziell bei Quicksort solche für Multimengen und Vorsortierung, sowohl für verkettete Listen als auch für Datenstrukturen mit Direktzugriff. Neben dem Standardheapsort werden die Floydverbesserung und Dijkstras Smoothsort vorgestellt. Eine Netzwerkvariante und zwei Externspeicherverfahren auf Basis von Quicksort und Heapsort werden untersucht. Der Stand der Technik bei den stabilen, in-situ Verfahren wird skizziert. Der Stoff eignet sich für eine Vorlesung mit angegliederten Projektübungen, in denen Studierende selbstständig Algorithmen, die als Pseudo-Code vorgegeben sind, in effizienten, lauffähigen Java-Code umsetzen und in einer Laufzeitbibliothek mit vorgegebenen Testdaten messen.