Zur Reaktionskinetik der Oxidation von Kohlenstoffmaterialien aus Biomasse

Zur Modellierung von Vergasungs- und Verbrennungsprozessen zur energetischen Nutzung von Biomasse ist die Kenntnis von reaktionskinetischen Daten für die Sauerstoff-Oxidation von Biomassepyrolysaten erforderlich. Eine ausführliche Literaturübersicht zeigt den Stand der Forschung bezüglich der experimentellen Ermittlung von reaktionskinetischen Parametern für die Oxidation von Pyrolysaten aus Lignin, Cellulose und pflanzlicher Biomasse sowie der Suche nach einem plausiblen Reaktionsmechanismus für die Reaktion von Sauerstoff mit festen Kohlenstoffmaterialien. Es wird eine Versuchsanlage mit einem quasistationär betriebenen Differentialreaktor konstruiert, die eine Messung der Reaktionskinetik und der reaktiven inneren Oberfläche (RSA) für die Reaktion eines Pyrolysats aus Maispflanzen mit Sauerstoff ermöglicht. Die getrockneten und zerkleinerten Maispflanzen werden 7 Minuten lang bei 1073 K in einem Drehrohrofen pyrolysiert. Das Pyrolysat zeichnet sich vor allem durch seine hohe Porosität von über 0,9 und seinen hohen Aschegehalt von 0,24 aus. Die RSA wird nach der Methode der Messung von Übergangskinetiken (TK) bestimmt. Die Bestimmung der RSA erfolgt für die Reaktionsprodukte CO und CO2 getrennt, für die entsprechend ermittelten Werte werden die Bezeichnungen CO-RSA und CO2-RSA eingeführt. Die Abhängigkeit dieser Größen von der Sauerstoffkonzentration läßt sich durch eine Langmuir-Isotherme beschreiben, ebenso das leichte Absinken der CO-RSA mit der Kohlendioxidkonzentration. Über dem Abbrand zeigen sich unterschiedliche Verläufe für die CO-RSA, CO2-RSA und die innere Oberfläche nach der BET-Methode. Zur Charakterisierung der Oberflächenzwischenprodukte werden temperaturprogrammierte Desorptionsversuche (TPD) durchgeführt. Die Ergebnisse zeigen, daß eine Unterscheidung in zwei Kohlenstoff-Sauerstoff-Oberflächenkomplexe ausreichend ist. Die experimentellen Untersuchungen zum Oxidationsverlauf werden im kinetisch bestimmten Bereich durchgeführt. Dabei werden die Parameter Temperatur, Sauerstoff-, CO- und CO2-Konzentration variiert. Anhand der Ergebnisse der reaktionskinetischen Untersuchungen wird ein Reaktionsmechanismus für die Kohlenstoff-Sauerstoff-Reaktion entwickelt. Dieser Reaktionsmechanismus umfaßt 7 Elementarreaktionen, für welche die reaktionskinetischen Parameter numerisch ermittelt werden. Darüber hinaus werden reaktionskinetische Parameter für einfachere massenbezogene Reaktionsgeschwindigkeitsansätze berechnet und summarische Reaktionsgeschwindigkeitsansätze für die Bildung von CO und CO2 aus dem Reaktionsmechanismus hergeleitet.

Zur Adsorption und Reaktion von Stickstoffmonoxid an Aktivkohle

Die Verwendung von Aktivkohlen und -koksen stellt eine Alternative zu herkömmlichen Prozessen zur Verminderung der NOx-Emissionen in Rauchgasen dar. An diesen Materialien wird Stickstoffmonoxid adsorbiert und katalytisch zu N2 reduziert. Eine einheitliche Erklärung über die ablaufenden Vorgänge und die Reaktionsmechanismen gibt es noch nicht. Die Ergebnisse der bisher veröffentlichten wissenschaftlichen Arbeiten sind sehr unterschiedlich, wenn nicht sogar widersprüchlich. In dieser Arbeit wird, anhand der Messung von NO-Durchbruchskurven und thermischen Desorptionsspektren, die Adsorption und Reaktion von Stickstoffmonoxid an Aktivkohlen und -koksen in Anwesenheit von Sauerstoff und Wasserdampf untersucht. Zur Durchführung der experimentellen Untersuchungen wird eine Versuchsanlage, bestehend aus einer Vorrichtung zur Gasgemischaufbereitung, einem Festbettreaktor und einer Gasanalytik, konzipiert und aufgebaut. Die Untersuchungen erfolgen bei Temperaturen zwischen 100 und 150 °C. Die NO-, O2- und H2O-Konzentrationen werden anhand der Rauchgaszusammensetzung kohlegefeuerter Kraftwerke gewählt. Die experimentellen Untersuchungen konzentrieren sich auf die Verwendung einer Aktivkohle aus Ölpalmschalen, die in einem Drehrohrreaktor am Institut für Thermische Energietechnik der Universität Kassel hergestellt wurde. Die experimentellen Ergebnisse zeigen, dass während des Prozesses NO-Adsorption, -Reduktion und -Oxidation, NO2-Bildung, -Adsorption und -reduktive Desorption, H2O-Adsorption sowie O2-Vergasung gleichzeitig stattfinden. Bei niedrigen Temperaturen werden die NO2-Bildung und die Adsorption bevorzugt. Die NO-Reduktion läuft über adsorbiertes NO mit CO2- und CO-Bildung. Durch O2-Vergasung werden aktive freie Cf-Plätzen für die NO-Reaktion und -Adsorption gebildet. Wasserdampf wird an der Aktivkohle adsorbiert und belegt aktive Plätze für diese Prozesse. Aus den experimentellen Ergebnissen werden kinetische und Gleichgewichtsparameter der NO-Sorption bestimmt. Ein vereinfachtes mathematisches Modell des Festbettreaktors, das zur Berechnung der NO-Durchbruchskurven bei unterschiedlichen Temperaturen dient, wird aufgestellt.

Der Einfluss eines operanten Therapieverfahrens zur Behandlung frühkindlichen Stotterns bei deutschsprachigen Kindern

Kindliches Stottern ist eine Störung des Sprechablaufs mit unbekannter Ätiologie, die im Verlauf der Sprachentwicklung beginnt und bei ungefähr 5% aller Kinder auftritt. Im deutschsprachigen Raum gibt es zum jetzigen Zeitpunkt kein Therapieverfahren zur Behandlung kindlichen Stotterns, dessen Therapie-Effekte empirisch gesichert sind. Darüber hinaus wurden bisher kaum Forschungsprojekte zum Stottern im Kindesalter durchgeführt. Ziel dieses von Juni 2003 bis Mai 2005 an der Universitätsklinik Frankfurt durchgeführten Projektes war es, die Wirksamkeit eines bisher in Deutschland noch nicht eingeführten Therapieverfahrens zur Behandlung von stotternden Vorschulkindern, das sog. Lidcombe Programm (Onslow, Packman & Harrison, 2003) zu untersuchen. In dem vorliegenden Projekt wurde untersucht, inwieweit die sofortigen Veränderungen der Sprechflüssigkeit während der Behandlung mit dem Lidcombe Programm primär auf diese Methode oder auf den Einfluss von Spontanremission zurückzuführen ist. Die übergeordnete Zielsetzung der Studie war die Schaffung einer Datengrundlage über die Effektivität des Lidcombe-Programms bei der Behandlung deutschsprachiger Vorschulkinder. Es wurden insgesamt 46 Vorschulkinder, welche nachfolgende Kriterien erfüllten, untersucht: (1) Alter zwischen 3,0 und 5,11 Jahren; (2) Deutsch als Muttersprache sowohl für das Kind als auch für die Eltern; (3) Beginn der Stottersymptomatik vor mindestens sechs Monaten; (4) Stottersymptomatik von mindestens 3% gestotterter Silben während einer Unterhaltung mit dem Untersucher und/oder den Eltern in der Klinik im Rahmen der Erstdiagnostik; (5) keine neurologischen Erkrankungen oder regelmäßige Einnahme von Medikamenten. Die Teilnehmer wurden randomisiert in zwei Gruppen eingeteilt. Die Kinder der Gruppe 1 begannen sofort mit der Behandlung mit dem Lidcombe-Programm. Die Kinder der Gruppe 2 warteten sechzehn Wochen und begannen dann mit der Behandlung. Für jedes Kind wurde der mittlere Prozentsatz gestotterter Silben zu Beginn jeder Behandlungsstunde im Gespräch mit der Therapeutin ermittelt, und darüber hinaus vor Beginn der Behandlung und nach sechzehn Therapiestunden auf Grund von jeweils vier zu Hause und in der Klinik aufgenommenen Spontansprachproben. Die Ergebnisse der vorliegenden Studie haben gezeigt, dass das Lidcombe-Programm auch für deutschsprachige Kinder ein effektives Therapiekonzept zur Reduktion einer Stottersymptomatik darstellt. Alle Vorschulkinder, die mit dem Lidcombe-Programm behandelt wurden, zeigten eine Abnahme des Prozentsatzes gestotterter Silben. Die Daten belegen ebenfalls, dass der Kurzzeit-Effekt des Lidcombe-Programms auf frühkindliches Stotterns den einer spontanen Remission überwiegt. Die behandelten Kinder zeigten eine signifikant höhere Abnahme ihrer Stottersymptomatik (M = 6,9%) als dies in der unbehandelten Kontrollgruppe (M = 2,5%) beobachtet werden konnte. Zwar sank auch in der Kontrollgruppe der Prozentsatz gestotterter Silben während des Untersuchungszeitraumes bei einigen Kindern, im Vergleich verringerte sich jedoch der Prozentsatz gestotterter Silben in der Therapiegruppe um mehr als das Doppelte. Diese ersten Daten weisen darauf hin, dass das Lidcombe-Programm für die deutschsprachige Therapie des kindlichen Stotterns eine ausgezeichnete Bereicherung darstellt und zu einer sinnvollen Ergänzung der therapeutischen Handlungskompetenz im Bereich der Redeflussstörungen führt.

Effects of tillage on processes of organic matter sequestration

To increase the organic matter (OM) content in the soil is one main goal in arable soil management. The adoption of tillage systems with reduced tillage depth and/or frequency (reduced tillage) or of no-tillage was found to increase the concentration of soil OM compared to conventional tillage (CT; ploughing to 20-30 cm). However, the underlying processes are not yet clear and are discussed contradictorily. So far, few investigations were conducted on tillage systems with a shallow tillage depth (minimum tillage = MT; maximum tillage depth of 10 cm). A better understanding of the interactions between MT implementation and changes in OM transformation in soils is essential in order to evaluate the possible contribution of MT to a sustainable management of arable soils. The objectives of the present thesis were (i) to compare OM concentrations, microbial biomass, water-stable aggregates, and particulate OM (POM) between CT and MT soils, (ii) to estimate the temporal variability of water-stable aggregate size classes occurring in the field and the dynamics of macroaggregate (>250 µm) formation and disruption under controlled conditions, (iii) to investigate whether a lower disruption or a higher formation rate accounts for a higher occurrence of macroaggregates under MT compared to CT, (iv) to determine which fraction is the major agent for storing the surplus of OM found under MT compared to CT, and (v) to observe the early OM transformation after residue incorporation in different tillage systems simulated. Two experimental sites (Garte-Süd and Hohes Feld) near Göttingen, Germany, were investigated. Soil type of both sites was a Haplic Luvisol. Since about 40 years, both sites receive MT by a rotary harrow (to 5-8 cm depth) and CT by a plough (to 25 cm depth). Surface soils (0-5 cm) and subsoils (10-20 cm) of two sampling dates (after fallow and directly after tillage) were investigated for concentrations of organic C (Corg) and total N (N), different water-stable aggregate size classes, different density fractions (for the sampling date after fallow only), microbial biomass, and for biochemically stabilized Corg and N (by acid hydrolysis; for the sampling date after tillage only). In addition, two laboratory incubations were performed under controlled conditions: Firstly, MT and CT soils were incubated (28 days at 22°C) as bulk soil and with destroyed macroaggregates in order to estimate the importance of macroaggregates for the physical protection of the very labile OM against mineralization. Secondly, in a microcosm experiment simulating MT and CT systems with soil <250 µm and with 15N and 13C labelled maize straw incorporated to different depths, the mineralization, the formation of new macroaggregates, and the partitioning of the recently added C and N were followed (28 days at 15°C). Forty years of MT regime led to higher concentrations of microbial biomass and of Corg and N compared to CT, especially in the surface soil. After fallow and directly after tillage, a higher proportion of water-stable macroaggregates rich in OM was found in the MT (36% and 66%, respectively) than in the CT (19% and 47%, respectively) surface soils of both sites (data shown are of the site Garte-Süd only). The subsoils followed the same trend. For the sampling date after fallow, no differences in the POM fractions were found but there was more OM associated to the mineral fraction detected in the MT soils. A large temporal variability was observed for the abundance of macroaggregates. In the field and in the microcosm simulations, macroaggregates were found to have a higher formation rate after the incorporation of residues under MT than under CT. Thus, the lower occurrence of macroaggregates in CT soils cannot be attributed to a higher disruption but to a lower formation rate. A higher rate of macroaggregate formation in MT soils may be due to (i) the higher concentrated input of residues in the surface soil and/or (ii) a higher abundance of fungal biomass in contrast to CT soils. Overall, as a location of storage of the surplus of OM detected under MT compared to CT, water-stable macroaggregates were found to play a key role. In the incubation experiment, macroaggregates were not found to protect the very labile OM against mineralization. Anyway, the surplus of OM detected after tillage in the MT soil was biochemically degradable. MT simulations in the microcosm experiment showed a lower specific respiration and a less efficient translocation of recently added residues than the CT simulations. Differences in the early processes of OM translocation between CT and MT simulations were attributed to a higher residue to soil ratio and to a higher proportion of fungal biomass in the MT simulations. Overall, MT was found to have several beneficial effects on the soil structure and on the storage of OM, especially in the surface soil. Furthermore, it was concluded that the high concentration of residues in the surface soil of MT may alter the processes of storage and decomposition of OM. In further investigations, especially analysis of the residue-soil-interface and of effects of the depth of residue incorporation should be emphasised. Moreover, further evidence is needed on differences in the microbial community between CT and MT soils.

3D Simultaneous Inversion for Seismic Structure and Local Hypocenters in Germany under Consideration of Seismic Anisotropy in the Upper Mantel

The main task of this work has been to investigate the effects of anisotropy onto the propagation of seismic waves along the Upper Mantle below Germany and adjacent areas. Refraction- and reflexion seismic experiments proved the existence of Upper Mantle anisotropy and its influence onto the propagation of Pn-waves. By the 3D tomographic investigations that have been done here for the crust and the upper mantle, considering the influence of anisotropy, a gap for the investigations in Europe has been closed. These investigations have been done with the SSH-Inversionprogram of Prof. Dr. M. Koch, which is able to compute simultaneously the seismic structure and hypocenters. For the investigation, a dataset has been available with recordings between the years 1975 to 2003 with a total of 60249 P- and 54212 S-phase records of 10028 seismic events. At the beginning, a precise analysis of the residuals (RES, the difference between calculated and observed arrivaltime) has been done which confirmed the existence of anisotropy for Pn-phases. The recognized sinusoidal distribution has been compensated by an extension of the SSH-program by an ellipse with a slow and rectangular fast axis with azimuth to correct the Pn-velocities. The azimuth of the fast axis has been fixed by the application of the simultaneous inversion at 25° - 27° with a variation of the velocities at +- 2.5 about an average value at 8 km/s. This new value differs from the old one at 35°, recognized in the initial residual analysis. This depends on the new computed hypocenters together with the structure. The application of the elliptical correction has resulted in a better fit of the vertical layered 1D-Model, compared to the results of preceding seismological experiments and 1D and 2D investigations. The optimal result of the 1D-inversion has been used as initial starting model for the 3D-inversions to compute the three dimensional picture of the seismic structure of the Crust and Upper Mantle. The simultaneous inversion has showed an optimization of the relocalization of the hypocenters and the reconstruction of the seismic structure in comparison to the geology and tectonic, as described by other investigations. The investigations for the seismic structure and the relocalization have been confirmed by several different tests. First, synthetic traveltime data are computed with an anisotropic variation and inverted with and without anisotropic correction. Further, tests with randomly disturbed hypocenters and traveltime data have been proceeded to verify the influence of the initial values onto the relocalization accuracy and onto the seismic structure and to test for a further improvement by the application of the anisotropic correction. Finally, the results of the work have been applied onto the Waldkirch earthquake in 2004 to compare the isotropic and the anisotropic relocalization with the initial optimal one to verify whether there is some improvement.

Gone with the internet - How the old education was lost

Despite its young history, Computer Science Education has seen a number of "revolutions". Being a veteran in the field, the author reflects on the many changes he has seen in computing and its teaching. The intent of this personal collection is to point out that most revolutions came unforeseen and that many of the new learning initiatives, despite high financial input, ultimately failed. The author then considers the current revolution (MOOC, inverted lectures, peer instruction, game design) and, based on the lessons learned earlier, argues why video recording is so successful. Given the fact that this is the decade we lost print (papers, printed books, book shops, libraries), the author then conjectures that the impact of the Internet will make this revolution different from previous ones in that most of the changes are irreversible. As a consequence he warns against storming ahead blindly and suggests to conserve - while it is still possible - valuable components of what might soon be called the antebellum age of education.

Simultaneous Drying and Separation of Composite Agricultural Material for Hay Processing

In composite agricultural materials such as grass, tee, medicinal plants; leaves and stems have a different drying time. By this behavior, after leaving the dryer, the stems may have greater moisture content than desired, while the leaves one minor, which can cause either the appearance of fungi or the collapse of the over-dried material. Taking into account that a lot of grass is dehydrated in forced air dryers, especially rotary drum dryers, this research was developed in order to establish conditions enabling to make a separation of the components during the drying process in order to provide a homogeneous product at the end. For this, a rotary dryer consisting of three concentric cylinders and a circular sieve aligned with the more internal cylinder was proposed; so that, once material enters into the dryer in the area of the inner cylinder, stems pass through sieve to the middle and then continue towards the external cylinder, while the leaves continue by the inner cylinder. For this project, a mixture of Ryegrass and White Clover was used. The characteristics of the components of a mixture were: Drying Rate in thin layer and in rotation, Bulk density, Projected Area, Terminal velocity, weight/Area Ratio, Flux through Rotary sieve. Three drying temperatures; 40°C, 60° C and 80° C, and three rotation speeds; 10 rpm, 20 rpm and 40 rpm were evaluated. It was found that the differences in drying time are the less at 80 °C when the dryer rotates at 40 rpm. Above this speed, the material adheres to the walls of the dryer or sieve and does not flow. According to the measurements of terminal velocity of stems and leaves of the components of the mixture, the speed of the air should be less than 1.5 m s-1 in the inner drum for the leaves and less than 4.5 m s-1 in middle and outer drums for stems, in such way that only the rotational movement of the dryer moves the material and achieves a greater residence time. In other hand, the best rotary sieve separation efficiencies were achieved when the material is dry, but the results are good in all the moisture contents. The best rotary speed of sieve is within the critical rotational speed, i.e. 20 rpm. However, the rotational speed of the dryer, including the sieve in line with the inner cylinder should be 10 rpm or less in order to achieve the greatest residence times of the material inside the dryer and the best agitation through the use of lifting flights. With a finite element analysis of a dryer prototype, using an air flow allowing speeds of air already stated, I was found that the best performance occurs when, through a cover, air enters the dryer front of the Middle cylinder and when the inner cylinder is formed in its entirety through a sieve. This way, air flows in almost equal amounts by both the middle and external cylinders, while part of the air in the Middle cylinder passes through the sieve towards the inner cylinder. With this, leaves do not adhere to the sieve and flow along drier, thanks to the rotating movement of the drums and the showering caused by the lifting flights. In these conditions, the differences in drying time are reduced to 60 minutes, but the residence time is higher for the stems than for leaves, therefore the components of the mixture of grass run out of the dryer with the same desired moisture content.

Funktion und Biogenese kleiner RNAs in Dictyostelium discoideum

RNA mediated gene silencing pathways are highly conserved among eukaryotes and they have been well investigated in animals and in plants. Longer dsRNA molecules trigger the silencing pathways: RNase III proteins and their dsRNA binding protein (dsRBP) partners recognize those molecules as a substrate and process 21 nucleotide long microRNAs (miRNAs) or small interfering RNAs (siRNAs). Some organisms encode RNA dependent RNA polymerases (RdRPs), which are able to expand the pool of existing siRNAs. Argonaute proteins are able to bind small regulatory RNAs and are subsequently recruited to target mRNAs by base complementary. This leads in turn to transcriptional or posttranscriptional silencing of respective genes. The Dictyostelium discoideum genome encodes two Dicer homologues (DrnA and DrnB), five Argonaute proteins (AgnA to AgnE) and three RdRPs (RrpA to RrpC). In addition, the amoeba is known to express miRNAs and siRNAs, while the latter derive mainly from the DIRS-1 retrotransposon. One part of this work focused on the miRNA biogenesis pathway of D. discoideum. It was shown that the dsRNA binding protein RbdB is a necessary component for miRNA processing in the amoeba. There were no mature miRNAs detectable by Northern blot analysis in rbdB- strains, which is also true for drnB mutants. Moreover, primary miRNA-transcripts (pri-miRNAs) accumulated in rbdB- and drnB- strains. Fluorescence microscopy studies showed a nuclear localization of RbdB. RbdB accumulated in distinct perinucleolar foci. These were reminiscent of plant dicing bodies that contain essential protein components for miRNA processing. It is well known that RNase III enzymes and dsRBPs work together during miRNA processing in higher eukaryotes. This work demonstrated that the same is true for members of the amoebozoa supergroup. In Arabidopsis the nuclear zinc finger protein Serrate (SE) is also necessary for miRNA processing. The D. discoideum homologue SrtA, however, is not relevant which has been shown by the analysis of the respective knockdown strain. MiRNAs are known to be differentially expressed in several RNAi knockout strains. The accumulation of miRNAs in agnA- strains and a strong decrease in rbdB- strains were criteria that could thus be successfully used (among others) to identify and validate new miRNAs candidates by Illumina®-RNA sequencing. In another part of this study, the silencing and amplification of the DIRS-1 retrotransposons was analyzed in more detail. It was already known that DIRS-1 transcripts and extrachromosomal DIRS-1 DNA molecules accumulated in agnA- strains. This phenotype was correlated with the loss of endogenous DIRS-1 siRNAs in the knockout strain. By deep sequencing analysis of small RNAs from the AX2 wild type and the agnA- strain, the strong decrease of endogenous DIRS-1 siRNAs in the mutant strain (accounting for 70 %) could be confirmed. Further analysis of the data revealed an unequal distribution of DIRS-1 derived siRNAs along the retroelement in the wild type strain, since only very few of them matched the inverted terminal repeats (ITRs) and the 5’- half of the first open reading frame (ORF). Besides, sense and antisense siRNAs were asymmetrically distributed, as well. By using different reporter constructs it was shown indirectly that AgnA is necessary for the RrpC mediated production of secondary DIRS-1 siRNAs. These analyses also demonstrated an amplification of siRNAs in 5’- and in 3’-direction. Further analysis of the agnA- strain revealed that not only DIRS-1 sense transcripts but also ORF2 and ORF3 encoded proteins were enriched. In contrast, the ORF1 encoded protein GAG was equally expressed in the mutant and the wild type. This might reflect the unequal distribution of endogenous DIRS-1 siRNAs along the retrotransposon. Southern Blot and PCR-analyses showed that extrachromosomal DIRS-1 DNA molecules are present in the cytoplasm of angA- strains and that they are complementary to sense transcripts of intact DIRS-1 elements. Thus, the extrachromosomal DIRS-1 intermediates are likely incomplete cDNA molecules generated by the DIRS-1 encoded reverse transcriptase. One could hypothesize that virus like particles (VLPs) are the places of DIRS-1 cDNA synthesis. At least, DIRS-1 GAG proteins interact and fluorescence microscopy studies showed that they localize in distinct cytoplasmic foci which accumulate in close proximity to the nuclei.

A simple retroelement based knock-down system in Dictyostelium

Characteristics of DIRS-1 Mediated Knock-Downs __ We have previously shown that the most abundant Dictyostelium discoideum retroelement DIRS-1 is suppressed by RNAi mechanisms. Here we provide evidence that both inverted terminal repeats have strong promoter activity and that bidirectional expression apparently generates a substrate for Dicer. A cassette containing the inverted terminal repeats and a fragment of a gene of interest was sufficient to activate the RNAi response, resulting in the generation of ~21 nt siRNAs, a reduction of mRNA and protein expression of the respective endogene. Surprisingly, no transitivity was observed on the endogene. This was in contrast to previous observations, where endogenous siRNAs caused spreading on an artificial transgene. Knock-down was successful on seven target genes that we examined. In three cases a phenotypic analysis proved the efficiency of the approach. One of the target genes was apparently essential because no knock-out could be obtained; the RNAi mediated knock-down, however, resulted in a very slow growing culture indicating a still viable reduction of gene expression.