Microstructure of Bentonite in Iron Ore Green Pellets

Sodium-activated calcium bentonite is used as a binder in iron ore pellets and is known to increase strength of both wet and dry iron ore green pellets. In this article, the microstructure of bentonite in magnetite pellets is revealed for the first time using scanning electron microscopy. The microstructure of bentonite in wet and dry iron ore pellets, as well as in distilled water, was imaged by various imaging techniques (e.g., imaging at low voltage with monochromatic and decelerated beam or low loss backscattered electrons) and cryogenic methods (i.e., high pressure freezing and plunge freezing in liquid ethane). In wet iron ore green pellets, clay tactoids (stacks of parallel primary clay platelets) were very well dispersed and formed a voluminous network occupying the space available between mineral particles. When the pellet was dried, bentonite was drawn to the contact points between the particles and formed solid bridges, which impart strength to the solid compac

Transmigration of polymorphnuclear neutrophils and monocytes through the human blood-cerebrospinal fluid barrier after bacterial infection in vitro

Background: Bacterial invasion through the blood-cerebrospinal fluid barrier (BCSFB) during bacterial meningitis causes secretion of proinflammatory cytokines/chemokines followed by the recruitment of leukocytes into the CNS. In this study, we analyzed the cellular and molecular mechanisms of polymorphonuclear neutrophil (PMN) and monocyte transepithelial transmigration (TM) across the BCSFB after bacterial infection. Methods: Using an inverted transwell filter system of human choroid plexus papilloma cells (HIBCPP), we studied leukocyte TM rates, the migration route by immunofluorescence, transmission electron microscopy and focused ion beam/scanning electron microscopy, the secretion of cytokines/chemokines by cytokine bead array and posttranslational modification of the signal regulatory protein (SIRP) α via western blot. Results: PMNs showed a significantly increased TM across HIBCPP after infection with wild-type Neisseria meningitidis (MC58). In contrast, a significantly decreased monocyte transmigration rate after bacterial infection of HIBCPP could be observed. Interestingly, in co-culture experiments with PMNs and monocytes, TM of monocytes was significantly enhanced. Analysis of paracellular permeability and transepithelial electrical resistance confirmed an intact barrier function during leukocyte TM. With the help of the different imaging techniques we could provide evidence for para- as well as for transcellular migrating leukocytes. Further analysis of secreted cytokines/chemokines showed a distinct pattern after stimulation and transmigration of PMNs and monocytes. Moreover, the transmembrane glycoprotein SIRPα was deglycosylated in monocytes, but not in PMNs, after bacterial infection. Conclusions: Our findings demonstrate that PMNs and monoctyes differentially migrate in a human BCSFB model after bacterial infection. Cytokines and chemokines as well as transmembrane proteins such as SIRPα may be involved in this process

Development of an ion optical transfer system for an imaging secondary ion mass spectrometer

In dieser Arbeit wird die Entwicklung einer Transferoptik für ein neuartiges bildgebendes Sekundärionen-Massenspektrometer basierend auf einem Zweistrahlgerät aus fokussiertem Ionenstrahl und Rasterelektronenmikroskop und einem Ionenfallen-Massenspektrometer vorgestellt. Das ionenoptische Transfersystem, welches die beiden konventionellen Ausgangsgeräte verbindet, wird aus einer elektrostatischen Transferlinse und einem hochfrequenten Ionenleitsystem aufgebaut. Zur Entwicklung und Charakterisierung der elektrostatischen Transferlinse werden sowohl Transmissionsberechnungen, als auch Berechnungen der optischen Eigenschaften in paraxialer Näherung durchgeführt. Zur Charakterisierung des Hochfrequenz-Ionenleitsystem wird das Transmissionsverhalten eines einzelnen Hochfrequenz-Oktupols über Simulationen und über die adiabatische Näherung bestimmt. Anschließend wird die Transmission des Hochfrequenz-Ionenleitsystems unter dem Einfluss von stoßbedingter Dämpfung der Ionen an einem Hintergrundgas leichter Masse im Rahmen eines Hartkugelstreumodells simuliert. Konstruktion und Aufbau sowie einige an dem Aufbau erhaltene Ergebnisse werden anhand von exemplarischen Messungen vorgestellt. Mit dem durch die Integration des ionenoptischen Transfersystems erhaltenen neuartigen bildgebenden Sekundärionen-Massenspektrometer werden eine laterale Auflösung von 1µm und eine Tiefenauflösung von 1nm erreicht.In this study, the development of an ion optical transfer system for a novel secondary ion mass spectrometer based on a crossbeam with focused ion beam and scanning electron microscope and an ion trap mass spectrometer is presented. The ion optical transfer system connecting the conventional devices consists of an electrostatic transfer lens and a radio frequency ion guide. Development and characterisation of the electrostatic transfer lens is carried out by calculating the transmission and by calculating the optical properties in paraxial approximation. Characterisation of the radio frequency ion guide is carried out by calculating the transmission properties of a single radio frequency octupole using simulations and an approach based on adiabatic approximation. Subsequent, the transmission characteristics of the radio frequency ion guide is calculated regarding collisional cooling of the ions with a buffer gas by using a hard sphere collision model. Design and construction as well as some experimental results achieved with the obtained set up are presented based on exemplarily measurements. Using the novel dedicated secondary ion mass spectrometer with the incorporated ion optical transfer system, a lateral resolution of 1µm and a depth resolution of 1nm can be achieved