24 research outputs found
Maximum antichains in posets of quiver representations
We study maximum antichains in two posets related to quiver representations. Firstly, we consider the set of isomorphism classes of indecomposable representations ordered by inclusion. For various orientations of the Dynkin diagram of type A we construct a maximum antichain in the poset. Secondly, we consider the set of subrepresentations of a given quiver representation, again ordered by inclusion. It is a finite set if we restrict to linear representations over finite fields or to representations with values in the category of pointed sets. For particular situations we prove that this poset is Sperner
Sequential structures in cluster algebras and representation theory
Gellert F. Sequential structures in cluster algebras and representation theory. Bielefeld: UniversitÀt Bielefeld; 2017.The thesis deals with a range of questions in cluster algebras and the representation theory of quivers. In particular, we provide solutions to the following problems:
1. Does a cluster algebra admit a quantisation and if it does, how unique is it?
2. What is the smallest simply-laced quiver without loops and 2-cycles whose principal extension does not admit a maximal green sequence?
3. Considering the poset of quiver representations of certain orientations of type A diagrams induced by inclusion, what is the width of such a poset?
In particular, for a given cluster algebra we construct a basis of those matrices which provide a quantisation. Leading to the smallest simply-laced quiver as proposed above, we prove several combinatorial lemmas for particular quivers with up to four mutable vertices. Furthermore, we introduce a new kind of periodicity in the oriented exchange graph of principally extended cluster algebras. This periodicity we study in more detail for a particularextended Dynkin quiver of exceptional type A and show that it yields an infinite sequence of cluster tilting objects inside the preinjective component of the associated cluster category
Quantisation Spaces of Cluster Algebras
The article concerns the existence and uniqueness of quantisations of cluster algebras. We prove that cluster algebras with an initial exchange matrix of full rank admit a quanti- sation in the sense of Berenstein-Zelevinsky and give an explicit generating set to construct all quantisations
Advanced electron cyclotron heating and current drive experiments on the stellarator Wendelstein 7-X
During the first operational phase (OP 1.1) of Wendelstein 7-X (W7-X) electron cyclotron resonance heating (ECRH) was the exclusive heating method and provided plasma start-up, wall conditioning, heating and current drive. Six gyrotrons were commissioned for OP1.1 and used in parallel for plasma operation with a power of up to 4.3 MW. During standard X2-heating the spatially localized power deposition with high power density allowed controlling the radial profiles of the electron temperature and the rotational transform. Even though W7-X was not fully equipped with first wall tiles and operated with a graphite limiter instead of a divertor, electron densities of n e > 3·1019 m-3 could be achieved at electron temperatures of several keV and ion temperatures above 2 keV. These plasma parameters allowed the first demonstration of a multipath O2-heating scenario, which is envisaged for safe operation near the X-cutoff-density of 1.2·1020 m-3 after full commissioning of the ECRH system in the next operation phase OP1.2
Thermodynamic and optical investigations of transport phenomena in lipid monolayers
In this thesis, I was able to provide answers to transport processes in lipid monolayers, which are ultimately, all of biological relevance. In particular, I was interested in lipid oxidation and dynamic compression/expansion processes of surfactant monolayers at the air-water interface:
Lipid oxidation was shown to be a consequence of the formation of a high concentration of reactive oxygen species (ROS) during cell respiration, which finally can lead to severe cell damage. It is not yet understood clearly, which part of the lipid molecules is especially prone to a ROS attack. I was particularly interested in the role of the double bonds of the acyl chains of the lipid molecules during oxidation. Further, I wanted to know the time scales of lipid interaction with the ROS.
Compared to lipid vesicles, lipid monolayers have the advantage that many parameters of the system can be adjusted easily. In our system, I made use of this by setting the lateral pressure to low values during H2O2 treatment, which facilitated the ROS to reach the double bonds in the acyl chains.
A prime example of biological systems out of thermal equilibrium was given in the alveolus surface, which is covered with a surfactant monolayer. During breathing, these monolayers undergo such a highly dynamic compression and expansion. Arising flows from breathing could disrupt a film and consequently, it would lose its protective role. One of my goals was to understand flows and their influence on domain shape. Dependent on the strength of the flows, I expected different growth regimes, with differing prevailing transport processes. Once understanding the underlying mechanisms in domain shaping would allow me to draw conclusions on biological systems.
In order to address these questions, I established two systems, both based on the compression of lipid monolayers. I used isotherms to study the phase behavior of the lipids:9 During compression, the lipids can undergo phase transitions from the gaseous phase to the liquid expanded phase (LE-phase) and further from the LE-phase to the liquid condensed phase (LC-phase). A coexistence regime is observed in between the LE-phase and the LC-phase, characterized by a flat increase of lateral pressure with decreasing molecular area. Some lipids exhibited LC-phase domains. These were further investigated with Brewster angle microscopy (BAM). The used BAM was equipped with an integrated Scheimpflug optics, enabling an overall focused image plane. Furthermore, time-resolved observation of the growth of the domains was possible by recording videos (20 frames per seconds).
The first system enabled the investigation of lipid peroxidation, when the lipids were exposed to ROS. I chose DMPC, POPC, DOPC and PLPC, since these are phospholipids differing in the number and position of double bonds in acyl chains, but not in the head group. I used a H2O2 enriched phosphate buffered saline (PBS) solution, which served as a precursor for more reactive ROS, like hydroxyls (.OH). PBS was chosen, since it resembles the cell environment best. During defined waiting times of H2O2 treatment, the ROS diffused vertically from the subphase towards the monolayer. The lipid molecules were in the LE-phase, which facilitated the ROS molecules to reach also the double bonds of the acyl chains. The oxidized monolayers were then compressed at constant compression speed. Since the corresponding isotherms could be measured with high precision, the relative area increase ÎŽA/A between oxidized and non-oxidized monolayer along the isotherm proved to be a good measure for lipid peroxidation. The area increase ÎŽA in the molecular area of the oxidized molecules was explained by the eventually added, more hydrophilic âOOH group at the position of a carbon atom adjacent to a double bond in the unsaturated acyl chain. The âOOH group is drawn to the hydrophilic head group of the lipid. This leads to a kink in the acyl chain, which increases the molecular area A by ÎŽA. A model, which explained this peroxidation process in lipid vesicles, could be adopted to monolayers.
I compared the oxidation of phospholipids, differing in the number and position of the double bonds of their acyl chains. I found that ÎŽA/A increased with the growing number of double bonds in one acyl chain. However, a comparison of DOPC with POPC also showed the importance of the position of the acyl chain. I determined a slow reaction kinetic. It could be estimated by a ât dependence of the number density N_surface, which denominates the ROS sticking on the monolayer. The transport of ROS towards the monolayer was found to be diffusive, because it was the slowest process in the reaction. This interpretation was reinforced by a comparison of the temperature dependence of the relative area increase ÎŽA/A with the Stokes-Einstein diffusion coefficient of water molecules. The initial ROS concentration c_0 in the trough could be traced back (c_0~ 50 nM), which is indeed a realistic value found in human cells.
Concluding, our results can be understood as a feasibility study. The complexity of the monolayer can be arbitrarily increased, for example by the addition of proteins, allowing the investigation of other oxidative processes occurring in the cell membrane.
The second system allowed the investigation of growth of LC domains during fast compression processes of monolayers. I chose erucic acid monolayers, due to its low line tension and a continuous nucleation phase, enabling the formation of fractal domains. The monolayers were investigated with isotherms and BAM videos. Since v_C (compression speed of the monolayer) was continuous over the whole compression time, I had a system with well-defined hydrodynamic conditions. This allowed me a complete analysis of the system, starting with descriptive features of the observed domains to a classification of the observed growth regimes by means of hydrodynamic theory, through to the distinction and quantification of different kind of flows and supersaturations, involving Ivantsov theory:
Dependent on the compression speed v_C, I observed seaweed or dendritic domains. The LE/LC phase transition pressure pi_t was slightly increased compared to pi_inf of the equilibrium isotherm. A high compression speed v_C induced a supersaturation Îc. I introduced the excess lateral pressure Îpi=pi-pi_inf as an appropriate quantity to describe the supersaturation Îc. I showed a linear behavior of Îc on Îpi. Îc is a macroscopic quantity since it is averaged over the whole monolayer area. I characterized the domains of the seaweed and dendritic regime with respect to tip radii, branch lengths, side branch separations and fractal dimensions. I calculated the growth speed of the main branches. A roughly doubling of the growth speed of dendritic domains, compared to seaweed domains was observed. This was an evidence of adjunctive (Marangoni) flow in the subphase.
For each monolayer, I observed drifts during domain growth, which I explained by an anisotropy in the LE-phase, caused by the continuous nucleation of the domains. These kind of surface flows were superimposed to bulk flows in the subphase. Since I had a well established system, I could analyze the influence of these surface flows on domain shape, in terms of magnitude, direction and duration of the surface flows. I therefore used FFT spectra and directionality histograms. At low flows, the FFT showed six-fold symmetry. Higher drifts exhibited incisions in the FFT, eventually leading to dumbbell shaped FFTs at very high drifts. The domains grew preferentially in the direction parallel to the incision.
I used directionality histograms to analyze the angular distribution of the growing domains. They showed that the drift direction always correlated with a minimum in the histogram. In order to analyze drift duration, I split the domain in downstream and upstream side. I could show that for small drift durations, downstream growth was preferred. However, for longer drift durations, the flows got more isotropic and consequently growth was more balanced then.
I could observe only a weak correlation between drift velocity v_D and compression speed v_C. However, dendrites were formed when the compression speed v_C was high, while seaweed domains were formed when v_C was small. Domain distortion occurred in the same way, independent if seaweed or dendritic domains were considered. I further showed that hydrodynamic flows in the subphase and surface flows are superimposed and scale differently. Consequently, they have different impact on domain shape: hydrodynamic flows act on ÎŒm scale and influence the domain morphology (distance between side branches, and tip radius) and the growth speed of the main branches. Surface flows act on the mm to cm scale, cause an anisotropic flow in the LE phase surrounding the domain, and thus affect the overall domain shape.
The anisotropy in the LE-phase led to a locally different degree of supersaturation. To take this into account, I introduced a local normalized supersaturation Î, based on the Ivantsov solution. Therefore, I calculated PĂ©clet numbers p of measured quantities of the system. I obtained values of 0.88 â€Îâ€0.90 for the seaweed regime (p6). Since the Ivantsov solution can only be applied for purely diffusive processes, I applied a modified Ivantsov solution Î_mod, which calculates Î at a distance ahead of the dendrite tip. I was able to determine the progression of the diffusive layer , however a quantitative determination failed.
Applying hydrodynamic theory allowed me to classify the two growth regimes with respect to the Boussinesq number Bq. Since for both growth regimes, I achieved values of Bq<1, bulk viscous losses dominated over surface viscous losses. Further, a cross-over length was calculated, from which one can distinguish, whether advective transport dominates over diffusion.
I further connected the two defined supersaturations Î and Îc via the excess lateral pressure Îpi. From this, I saw differences in the seaweed and dendritic growth regimes: The local normalized supersaturation Î of seaweed growth seemed to be quite stable for a further increase of the lateral excess pressure Îpi, whereas it reacted quite sensitive in the dendritic regime. This was found to be an indication of a non-equilibrium regime, caused by the strong coupling of the monolayer to the subphase. It reinforces therefore the theory of Marangoni-flow.
The findings of this thesis emphasize the importance of understanding highly dynamic compression/expansion processes arising in surfactant monolayers. Using the example of the compression of the alveolus surface, it can be seen that a more realistic model of the pulmonary alveolus is not only enabled by increasing the complexity of the surfactant monolayer (e.g. by adding specific proteins or lipid mixtures to the monolayer). Equally important is the understanding in transport processes and the consequences for the monolayer structure. By the analysis of domain shapes, I presented a method, which is suitable for such a study.In dieser Arbeit konnte ich Antworten auf Transportprozesse in Lipidmonoschichten geben, die letztlich alle von biologischer Relevanz sind. Insbesondere interessierte ich mich fĂŒr Lipidoxidation und dynamische Kompressions-/Expansionsprozesse von Lipid-Monoschichten an der Luft-Wasser-GrenzflĂ€che: Es ist bekannt, dass die Lipidoxidation eine Folge einer hohen Konzentration reaktiver Sauerstoffspezies (ROS) wĂ€hrend der Zellatmung ist, die letztendlich zu schweren ZellschĂ€den fĂŒhren kann. Es ist noch nicht klar, welcher Teil der LipidmolekĂŒle besonders anfĂ€llig fĂŒr einen ROS-Angriff ist. Besonders interessierte mich die Rolle der Doppelbindungen der Alkylketten der LipidmolekĂŒle bei der Oxidation. DarĂŒber hinaus wollte ich die Zeitskalen der Lipidinteraktion mit den ROS bestimmen. Im Vergleich zu Lipidvesikeln haben Lipidmonoschichten den Vorteil, dass viele Parameter des Systems einfach angepasst werden können. In unserem System machte ich mir dies zunutze, indem ich den Laterarldruck wĂ€hrend der H2O2-Behandlung auf niedrige Werte einstellte, was es den ROS erleichterte, die Doppelbindungen in den Alkylketten zu erreichen.
Ein Paradebeispiel fĂŒr biologische Systeme auĂerhalb des thermischen Gleichgewichts ist die AlveolenoberflĂ€che, die mit einer Surfaktant-Monoschicht bedeckt ist. Beim Atmen erfahren diese Monoschichten eine hohe, dynamische Kompression und Expansion. Durch die Atmung entstehende Strömungen könnten den Surfaktantfilm zerstören und so zum Verlust der schĂŒtzenden Funktion fĂŒhren. Eines meiner Ziele war es, FlĂŒsse und ihren Einfluss auf die DomĂ€nenform zu verstehen. AbhĂ€ngig von der StĂ€rke der Strömungen erwartete ich unterschiedliche Wachstumsregime mit unterschiedlich vorherrschenden Transportprozessen. Sobald ich die zugrundeliegenden Mechanismen der DomĂ€nenbildung verstanden hĂ€tte, könnte ich RĂŒckschlĂŒsse auf biologische Systeme ziehen. Um diese Fragen zu beantworten, habe ich zwei Systeme etabliert, die beide auf der Kompression von Lipidmonoschichten basieren. Ich habe Isothermen verwendet, um das Phasenverhalten der Lipide zu untersuchen: WĂ€hrend der Kompression können die Lipide PhasenĂŒbergĂ€nge von der gasförmigen Phase zur flĂŒssigen expandierten Phase (LE-Phase) und weiter von der LE-Phase zur flĂŒssigen kondensierten Phase (LC-Phase) durchlaufen. Zwischen der LE-Phase und der LC-Phase wird ein Koexistenzregime beobachtet, das durch einen flachen Anstieg des Lateraldrucks mit abnehmender MolekĂŒlflĂ€che gekennzeichnet ist. Einige Lipide wiesen LC-PhasendomĂ€nen auf. Diese wurden mit Brewster-Winkelmikroskopie (BAM) weiter untersucht. Das verwendete BAM war mit einer integrierten Scheimpflug-Optik ausgestattet, die eine komplett fokussierte Bildebene ermöglichte. DarĂŒber hinaus war eine zeitaufgelöste Beobachtung des Wachstums der DomĂ€nen durch die Aufnahme von Videos (20 Bilder pro Sekunde) möglich. Das erste System ermöglichte die Untersuchung der Lipidperoxidation, als die Lipide ROS ausgesetzt waren. Ich habe mich fĂŒr DMPC, POPC, DOPC und PLPC entschieden: Phospholipide, die sich in der Anzahl und Position der Doppelbindungen in den Alkylketten unterschieden, nicht jedoch in der Kopfgruppe. Ich habe eine mit H2O2 angereicherte phosphatgepufferte Salzlösung (PBS) verwendet, die als Vorstufe fĂŒr reaktivere ROS wie Hydroxylionen diente. Die Wahl fiel auf PBS, da es die Zellumgebung am besten wiedergab. WĂ€hrend definierter Einwirkzeiten diffundierten die ROS vertikal von der Subphase in Richtung der Monoschicht. Die LipidmolekĂŒle befanden sich in der LE-Phase, was es den ROS-MolekĂŒlen erleichterte, auch die Doppelbindungen der Alkylketten zu erreichen. Die oxidierten Monoschichten wurden dann mit konstanter Kompressionsgeschwindigkeit komprimiert. Da die entsprechenden Isothermen mit hoher PrĂ€zision gemessen werden konnten, erwies sich die relative FlĂ€chenzunahme ÎŽA/A zwischen oxidierter und nichtoxidierter Monoschicht entlang der Isotherme als gutes MaĂ fĂŒr die Lipidperoxidation. Die FlĂ€chenzunahme ÎŽA in der MolekĂŒlflĂ€che der oxidierten MolekĂŒle konnte durch HinzufĂŒgen der hydrophilen âOOH-Gruppe an der Position eines Kohlenstoffatoms neben einer Doppelbindung in der ungesĂ€ttigten Alkylkette erklĂ€rt werden. Die âOOH-Gruppe wird so zur Kopfgruppe des Lipids gezogen. Dies fĂŒhrt zu einem Knick in der Alkylkette, wodurch die MolekĂŒlflĂ€che A um ÎŽA vergröĂert wird. Ein Modell, das diesen Peroxidationsprozess in Lipidvesikeln erklĂ€rt, konnte auf Monoschichten ĂŒbertragen werden.
Ich habe die Oxidation von Phospholipiden verglichen, die sich in der Anzahl und Position der Doppelbindungen ihrer Alkylketten unterscheiden. Ich fand heraus, dass ÎŽA/A mit der wachsenden Anzahl von Doppelbindungen in einer Alkylkette zunahm. Ein Vergleich von DOPC mit POPC zeigte jedoch auch die Bedeutung der Position der Alkylkette. Ich habe eine langsame Reaktionskinetik festgestellt. Diese konnte durch eine ât-AbhĂ€ngigkeit der Belegungsdichte N_surface abgeschĂ€tzt werden, die die an der Monoschicht haftenden ROS angibt. Der Transport von ROS zur Monoschicht erwies sich als diffusiv, da dies der langsamste Prozess in der Reaktion war. Diese Interpretation wurde durch einen Vergleich der TemperaturabhĂ€ngigkeit der relativen FlĂ€chenzunahme ÎŽA/A mit dem Stokes-Einstein-Diffusionskoeffizienten von WassermolekĂŒlen untermauert. Die anfĂ€ngliche ROS-Konzentration c_0 im Trog konnte zurĂŒckverfolgt werden (c_0~ 50 nM), was tatsĂ€chlich ein realistischer Wert ist, der in menschlichen Zellen gefunden wird. Zusammenfassend können unsere Ergebnisse als Machbarkeitsstudie verstanden werden. Die KomplexitĂ€t der Monoschicht kann beispielsweise durch die Zugabe von Proteinen beliebig erhöht werden, wodurch auch andere oxidative Prozesse in der Zellmembran untersucht werden können.
Das zweite System ermöglichte die Untersuchung des Wachstums von LC-DomĂ€nen wĂ€hrend schneller Kompressionsprozesse von Monoschichten. Ich habe mich fĂŒr ErukasĂ€ure-Monoschichten entschieden, da diese eine geringe Linienspannung und eine kontinuierliche Keimbildungsphase aufweisen und die Bildung fraktaler DomĂ€nen ermöglichen. Die Monoschichten wurden mit Isothermen und BAM-Videos untersucht. Da v_C (Kompressionsgeschwindigkeit der Monoschicht) ĂŒber die gesamte Kompressionszeit kontinuierlich war, hatte ich ein System mit wohldefinierten hydrodynamischen Bedingungen. Dies ermöglichte mir eine vollstĂ€ndige Analyse des Systems, beginnend mit beschreibenden Merkmalen der beobachteten DomĂ€nen ĂŒber eine Klassifizierung der beobachteten Wachstumsregime mittels hydrodynamischer Theorie bis hin zur Unterscheidung und Quantifizierung verschiedener Arten von Strömungen und ĂbersĂ€ttigungen unter Einbeziehung der Ivantsov-Theorie: AbhĂ€ngig von der Kompressionsgeschwindigkeit v_C beobachtete ich Seegras oder dendritische DomĂ€nen. Der LE/LC-PhasenĂŒbergangsdruck pi_t war im Vergleich zu pi_inf der Gleichgewichtsisotherme leicht erhöht. Eine hohe Kompressionsgeschwindigkeit v_C induzierte eine ĂbersĂ€ttigung Îc. Ich habe den Ăberschussdruck Îpi=pi-pi_inf als geeignete GröĂe zur Beschreibung der ĂbersĂ€ttigung Îc eingefĂŒhrt. Ich habe ein lineares Verhalten von Îc mit Îpi zeigen können. Îc ist eine makroskopische GröĂe, da sie ĂŒber die gesamte MonoschichtflĂ€che gemittelt wird. Ich habe die DomĂ€nen des Seegras- und Dendritenregimes bezĂŒglich Spitzenradien, AstlĂ€ngen, SeitenarmabstĂ€nden und fraktaler Dimension charakterisiert. Ich habe die Wachstumsgeschwindigkeit der Hauptarme berechnet. Es wurde eine Verdoppelung der Wachstumsgeschwindigkeit dendritischer DomĂ€nen im Vergleich zu SeegrasdomĂ€nen beobachtet. Dies war ein Hinweis fĂŒr einen Zusatzfluss (Marangoni) in der Subphase.
FĂŒr jede Monoschicht beobachtete ich Drifts wĂ€hrend des DomĂ€nenwachstums, die ich durch eine Anisotropie in der LE-Phase erklĂ€rte, die durch die kontinuierliche Keimbildung der DomĂ€nen verursacht wurde. Diese Art von OberflĂ€chenströmungen wurden den Volumenströmungen in der Subphase ĂŒberlagert. Da ich ĂŒber ein gut etabliertes System verfĂŒgte, konnte ich den Einfluss dieser OberflĂ€chenströmungen auf die DomĂ€nenform hinsichtlich GröĂe, Richtung und Dauer der OberflĂ€chenströmungen analysieren. Ich habe dafĂŒr FFT-Spektren und Richtungshistogramme verwendet. Bei niedrigen FlĂŒssen zeigte die FFT eine sechszĂ€hlige Symmetrie. Höhere Drifts zeigten Einschnitte in der FFT, die schlieĂlich bei sehr hohen Drifts zu hantelförmigen FFTs fĂŒhrten. Die DomĂ€nen wuchsen bevorzugt parallel zum Einschnitt. Ich habe Richtungshistogramme verwendet, um die Winkelverteilung der wachsenden DomĂ€nen zu analysieren. Sie zeigten, dass die Driftrichtung immer mit einem Minimum im Histogramm korrelierte. Um die Driftdauer zu analysieren, habe ich die DomĂ€ne in Downstream- und Upstream-Seite aufgeteilt. Ich konnte zeigen, dass fĂŒr kurze Driftdauern das stromabwĂ€rts gerichtete Wachstum bevorzugt wurde. Bei lĂ€ngerer Driftdauer wurden die Strömungen jedoch isotroper und das Wachstum war dann ausgeglichener. Ich konnte nur eine schwache Korrelation zwischen Driftgeschwindigkeit v_D und Kompressionsgeschwindigkeit v_C beobachten. Allerdings bildeten sich Dendriten, wenn die Kompressionsgeschwindigkeit v_C hoch war, wĂ€hrend sich SeegrasdomĂ€nen bildeten, wenn v_C klein war. Die DomĂ€nenverzerrung trat auf die gleiche Weise auf, unabhĂ€ngig davon, ob Seegras- oder dendritische DomĂ€nen berĂŒcksichtigt wurden. Ich habe auĂerdem gezeigt, dass hydrodynamische Strömungen in der Subphase und OberflĂ€chenströmungen sich ĂŒberlagern und unterschiedlich skalieren. Folglich haben sie unterschiedliche Auswirkungen auf die DomĂ€nenform: Hydrodynamische Strömungen wirken im ÎŒm-MaĂstab und beeinflussen die DomĂ€nenmorphologie (Abstand zwischen Seitenarmen und Spitzenradius) und die Wachstumsgeschwindigkeit der Hauptarme. OberflĂ€chenströmungen wirken auf der Skala von mm bis cm, verursachen eine anisotrope Strömung in der die DomĂ€ne umgebenden LE-Phase und beeinflussen somit die gesamte DomĂ€nenform. Die Anisotropie in der LE-Phase fĂŒhrte zu einem lokal unterschiedlichen Grad der ĂbersĂ€ttigung. Um dies zu berĂŒcksichtigen, habe ich eine lokal normalisierte ĂbersĂ€ttigung Î eingefĂŒhrt, die auf der Ivantsov-Lösung basiert. Daher habe ich die PĂ©clet-Zahlen p aus gemessenen GröĂen des Systems berechnet. Ich habe Werte von 0,88 †Πâ€0,90 fĂŒr das Seegrasregime (p6) erhalten. Da die Ivantsov-Lösung nur auf rein diffusive Prozesse angewendet werden kann, habe ich eine modifizierte Ivantsov-Lösung Î_mod bestimmt, die Î in einem Abstand vor der Dendritenspitze berechnet. Den Verlauf der Diffusionsschicht konnte ich zwar bestimmen, eine quantitative Bestimmung war
Seaweed and Dendritic Growth in Unsaturated Fatty Acid Monolayers
The lateral movement in lipid membranes depends on their diffusion constant within the membrane. However, when the flux of the subphase is high, the convective flow beneath the membrane also influences lipid movement. Lipid monolayers of an unsaturated fatty acid at the waterâair interface serve as model membranes. The formation of domains in the liquid/condensed coexistence region is investigated. The dimension of the domains is fractal, and they grow with a constant growth velocity. Increasing the compression speed of the monolayer induces a transition from seaweed growth to dendritic growth. Seaweed domains have broad tips and wide and variable side branch spacing. In contrast, dendritic domains have a higher fractal dimension, narrower tips, and small, well-defined side branch spacing. Additionally, the growth velocity is markedly larger for dendritic than seaweed growth. The domainsâ growth velocity increases and the tip radius decreases with increasing supersaturation in the liquid/condensed coexistence region. Implications for membranes are discussed
Antibiotic use, knowledge and health literacy among the general population in Berlin, Germany and its surrounding rural areas.
Knowledge concerning antibiotic use in the general population is insufficient. The way health literacy is related to antibiotic use aside from knowledge needs further investigation. Our aim was to compare the levels of knowledge of antibiotics and health literacy in individuals who had taken antibiotics in recent years compared with those who not had taken antibiotics.A population-based cross-sectional survey of 2,000 individuals aged 35 and older from Berlin, Germany and its surrounding rural and suburban areas (response rate 59%) with strata urban/rural, sex, age, and education. Computer-assisted personal interviews were conducted by external, trained interviewers during home visits. Knowledge, health literacy, and antibiotic use were assessed using standardized questionnaires.In all, 33.3% (666/2,000) of the participants indicated having had an antimicrobial therapy during the previous 12 months. Adjusting for sex, age, educational level and health literacy, individuals with four correct answers regarding antibiotics were 1.70 times and those with three correct answers 1.94 more likely to have had a history of recent antibiotic use than those who did not have any correct answers. Individuals with sufficient health literacy were 0.57 times less likely to have had a recent history of antibiotic use than individuals with insufficient health literacy.Patients who have used antibiotics might have more knowledge as a result of their recent involvement with the topic of antibiotic use; health literacy may be a preventive mechanism to use antibiotics more critically. Besides improving the health knowledge of the general population and of vulnerable groups such as patients with low levels of health literacy, intervention strategies should focus on providers as well
Experimental investigation of the ECRH stray radiation during the start-up phase in Wendelstein 7-X
Electron cyclotron resonance heating (ECRH) is the main heating mechanism in the Wendelstein 7-X stellarator (W7-X). W7-X is equipped with five absolutely calibrated sniffer probes that are installed in each of the five modules of the device. The sniffer probes monitor energy flux of unabsorbed ECRH radiation in the device and interlocks are fed with the sniffer probe signals. The stray radiation level in the device changes significantly during the start-up phase: plasma is a strong microwave absorber and during its formation the stray radiation level in sniffer probes reduces by more than 95%.
In this paper, we discuss the influence of neutral gas pressure and gyrotron power on plasma breakdown processes
Main reasons for having antimicrobial therapy.
<p>Cross-sectional survey of a population-based sample of 2,000 individuals from Berlin and its surrounding rural and suburban areas. Note. UTI, urinary tract infection; SSI, surgical site infection. 12.8% noted for other reasons and 7.9% I donÂŽt know.</p
Multivariate associations with history of antibiotics.
<p>A cross-sectional survey of a population-based sample of 2,000 individuals from Berlin and its surrounding rural and suburban areas.</p