A modified plane wave model for calculating UV photo-ionization cross-sections

Photoionization cross-sections are calculated for a number of molecules, using a plane wave method. Agreement with experimental data is considerably improved with respect to common plane wave results if the energy of the photoelectron is assumed to equal the incident photon energy

Non-aqueous retention measurements: ultrafiltration behaviour of polystyrene solutions and colloidal silver particles

The retention behaviour of polyimide ultrafiltration membranes was investigated using dilute solutions of polystyrene in ethyl acetate as test solutions. It is shown that flow-induced deformation of the polystyrene chains highly affects the membrane retention. This coil-stretch transition is not instantaneous, but gradual. The concept of a deformation resistance has been ontroduced to explain this behaviour. This concept can be applied to describe the flux behaviour of the membranes during the tests as well. Solute deformation allows comparison of the pore size distributions of the membranes qualitatively. Retention measurements were also performed with silver sol particles that were prepared in mixtures of ethanol and water; these sols remain stable as long as the ethanol concentration does not exceed 57 vol%. The sols were completely retained by the membranes, which is probably caused by the fact that the effective diameter of the particles is much larger than that observed by transmission electron microscopy

Photoelectron spectra of fluorine substituted diazanaphthalenes: “Even cases”

The high resolution He 584 Å photoelectron spectra of three diazanaphthalenes and some of their fluorine derivatives are presented. The qualitative model that is used frequently in the discussion of lone-pair level splittings is examined

Characterization of new membrane materials by means of fouling experiments Adsorption of bsa on polyetherimide-polyvinylpyrrolidone membranes

The hydrophilicity of polyetherimide-polyvinylpyrrolidone (PEI-PVP) microfiltration membranes can be adjusted by means of a suitable post-treatment. The influence of the nature of the membrane surface on fouling properties was studied using permeation experiments before and after exposure to a protein (BSA) solution and adsorption experiments with 14C labelled BSA. A correlation between the permeation experiments and the radiolabelled BSA adsorption experiments was found. The PVP in the membrane matrix prevents BSA adsorption taking place to a large extent and it appeared that heat-treated PEI-PVP membranes showed the same nonfouling behaviour as, for example, cellulose acetate membranes

Recent advances in the formation of phase inversion membranes made from amorphous or semi-crystalline polymers

Structural characteristics in membranes formed by diffusion induced phase separation processes are discussed. Established theories on membrane formation from ternary systems can be extended to describe the effects of high or low molecular weight additives. A mechanism for the formation of nodular structures in the top layer of ultrafiltration membranes is presented. In the last part structures arising from polymer crystallization during immersion precipitation are discussed

Interaktion von Tumorzellen in der hämatopoetischen Stammzellnische

Die bei Mann und Frau häufigsten Tumorentitäten, das Mamma- sowie Prostatakarzinom, metastasieren im fortgeschrittenen Stadium häufig in den Knochen, was zu erheblichen Komplikationen führt. Vorhergehende Studien stellten die These auf, dass die Tumorzellen ähnliche Bindungsstrukturen wie die hämatopoetischen Stammzellen (HSC) zur Adhäsion in der hämatopoetischen Stammzellnische nutzen. Hierfür spielen sowohl zelluläre Bestandteil der Nische, wie Osteoblasten und mesenchymale Stammzellen (MSC) eine Rolle, als auch Bestandteile der extrazellulären Matrix. Mit Hilfe von in vitro Experimenten wurde die Rolle dieser Faktoren für die Adhäsion der Prostatakarzinomzelllinie PC3, der Mammakarzinomzelllinie MDA-MB-231 sowie der CD34+ Zelllinie KG-1a in der hämatopoetischen Stammzellnische untersucht. Die stärkste Adhäsion bestand hierbei an LM 511, 521 und Kollagen IV, drei typische Bestandteile der extrazellulären Matrix in der Nische. Die Adhäsion an LM 111 und 211, welche nicht in der Nische exprimiert werden, war hingegen gering. Die beobachteten Zell-Matrix-Interaktionen waren signifikant stärker als die analysierten Zell-Zell-Interaktionen. Dies spricht für einen größeren Einfluss der über Integrine vermittelten Zell-Matrix-Adhäsion verglichen mit der Zell-Zell-Adhäsion. Der Vergleich der Adhäsion der CD34+ KG-1a Zelllinie mit aus Nabelschnurblut isolierten HSC zeigte signifikante Unterschiede, weshalb die Verwendung von KG-1a als Surrogatzelllinie für humane HSC zumindest bei der Durchführung von „Single Cell Force Spectroscopy“(SCFS)-Experimenten kritisch hinterfragt werden muss, da hierbei die unterschiedliche Zellgröße von KG-1a und primären HSC eine entscheidende Rolle für die Adhäsionsstärke spielt. Zudem wurde untersucht, ob PC3 und MDA-MB-231 Zellen KG-1a Zellen in ihrer Adhäsion an CAL 72, einer osteoblastischen Zelllinie, beeinflussen. Die Bindung von KG-1a an CAL 72 wurde durch die Koinkubation mit PC3 und MDA-MB-231 nicht beeinflusst. Ebenso ließen sich an CAL 72 gebundene KG-1a Zellen nicht durch die Inkubation mit PC3 oder MDA-MB-231 aus ihrer Bindung verdrängen. Die durchgeführte Studie unterstützt die These, dass Tumorzellen vakante Stellen im Knochenmark besetzen können, hämatopoetische Stammzellen jedoch nicht aktiv aus ihrer Bindung verdrängen

Wenn Bartonellen ihre Anker auswerfen : Bartonella henselae verbindet Infektionsforschung mit Blutgefäßwachstum

Bei gesunden Menschen verläuft die Infektion mit Bartonella henselae als vergleichsweise harmlose "Katzenkratzkrankheit". Erst mit Beginn der AIDS-Pandemie zeigte sich, dass das Bakterium bei immungeschwächten Patienten auch die pathologische Neubildung von Blutgefäßen auslösen kann. Diese Pathogenitätsstrategie unterscheidet die Spezies der Bartonellen von allen anderen bakteriellen Infektionserregern des Menschen. Für Mikrobiologen ist Bartonella henselae deshalb ein interessanter Modellorganismus, weil Blutgefäßwachstum in erster Linie eine Domäne der Tumorforschung ist

Evaluation of the Perceived Persuasiveness Questionnaire:User-Centered Card-Sort Study

Background: eHealth technologies aim to change users’ health-related behavior. Persuasive design and system features can make an eHealth technology more motivating, engaging, or supportive to its users. The Persuasive Systems Design (PSD) model incorporates software features that have the possibility to increase the persuasiveness of technologies. However, the effects of specific PSD software features on the effectiveness of an intervention are still largely unknown. The Perceived Persuasiveness Questionnaire (PPQ) was developed to gain insight into the working mechanisms of persuasive technologies. Although the PPQ seems to be a suitable method for measuring subjective persuasiveness, it needs to be further evaluated to determine how suitable it is for measuring perceived persuasiveness among the public. Objective: This study aims to evaluate the face and construct validity of the PPQ, identify points of improvement, and provide suggestions for further development of the PPQ. Methods: A web-based closed-ended card-sort study was performed wherein participants grouped existing PPQ items under existing PPQ constructs. Participants were invited via a Massive Open Online Course on eHealth. A total of 398 people (average age 44.15 years, SD 15.17; 251/398, 63.1% women) completed the card sort. Face validity was evaluated by determining the item-level agreement of the original PPQ constructs. Construct validity was evaluated by determining the construct in which each item was placed most often, regardless of the original placement and how often 2 items were (regardless of the constructs) paired together and what interitem correlations were according to a cluster analysis. Results: Four PPQ constructs obtained relatively high face validity scores: perceived social support, use continuance, perceived credibility, and perceived effort. Item-level agreement on the other constructs was relatively low. Item-level agreement for almost all constructs, except perceived effort and perceived effectiveness, would increase if items would be grouped differently. Finally, a cluster analysis of the PPQ indicated that the strengths of the newly identified 9 clusters varied strongly. Unchanged strong clusters were only found for perceived credibility support, perceived social support, and use continuance. The placement of the other items was much more spread out over the other constructs, suggesting an overlap between them. Conclusions: The findings of this study provide a solid starting point toward a redesigned PPQ that is a true asset to the field of persuasiveness research. To achieve this, we advocate that the redesigned PPQ should adhere more closely to what persuasiveness is according to the PSD model and to the mental models of potential end users of technology. The revised PPQ should, for example, enquire if the user thinks anything is done to provide task support but not how this is done exactly

Polyimide ultrafiltration membranes for non-aqueous systems

Polymeric ultrafiltration membranes have already been employed in numerous aqueous separation processes. On the other hand, the number of non-aqueous applications is still rather limited. This is mainly due to the often poor chemical resistance of the polymers used for membrane preparation; most membranes have been developed for aqueous applications only. In this thesis the preparation, characterization, and application of polyimide ultrafiltration membranes has been described, which may be applicable in non-aqueous separation processes