Field Emission to control nanometer tip-medium distances in probe storage

In this work, we present a novel concept for high resolution proximity sending based on field emission and provide more insight in the vacuum conditions and electronics needed for stable operation

Field Emission for resonance sensing in MEMS/NEMS

In the past decades, there is a considerable interest in the sensor community to move from micron to nano-devices, typically scaling of resonators such as cantilever beams

Modelling of slotted bolted friction connections as seismic energy dissipaters in braced steel frames

Thesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: The Slotted Bolted Connection provides additional energy dissipation during seismic loading, which leads to a reduction in structural damage. The effects of past earthquakes have shown that braced steel frames are susceptible to structural damage, particularly in the braces and connections. Although steel structures did not collapse during previous earthquakes, such as the 1994 Northridge earthquake, the numerous brittle failures motivated the development of seismic provisions for enhanced ductility. The improved provisions however still result in significant damage following an earthquake, which was seen after the 2011 Christchurch earthquake. One approach to minimise earthquake damage is by using energy dissipation devices. In contrast to other devices, the Slotted Bolted Connection is simple and economic while energy dissipation is provided by the relative sliding between plates in a friction connection. Slotted Bolted Connections were proposed as brace connections in Concentrically Braced Frames, but the lack of a published design procedure has restricted their use. The absence of a design procedure for Slotted Bolted Connection-braces is attributed to insufficient research conducted on the subject. Previous research concentrated mainly on testing of friction materials for the connection. Literature indicated that there is insufficient understanding of the effect that the configuration of the Slotted Bolted Connection has on its performance. To address this, a Finite Element Analysis study was undertaken. Firstly, a Finite Element model of the Slotted Bolted Connection was calibrated using existing experimental results. The Finite Element model was used to investigate; the effect of bolt-impact with the slot-ends, the differences between Symmetric and Asymmetric Slotted Bolted Connections and the influence of the connection on a braced bay. In addition, a modelling technique was developed to perform a non-linear dynamic analysis of a multi-storey building with Slotted Bolted Connection-braces. The bolt-impact investigation demonstrated that the connection requires suitable detailing to ensure ductility. The analyses indicated that the performance of the Symmetric connection was preferable to that of the Asymmetric connection. Contact between the bolt-shanks and the slot-sides during sliding of the connection in a braced bay affected the hysteresis behaviour, but not detrimentally. Dynamic analysis indicated that the Slotted Bolted Connections successfully decreased brace-damage by providing enhanced lateral drift capacity. The findings have clarified important aspects with regard to the configuration of the connections and have demonstrated the benefits of their introduction to Concentrically Braced Frames. The enhanced understanding contributes to the development of a design procedure for Slotted Bolted Connection-braces.AFRIKAANSE OPSOMMING: Die Geboute Gleufverbinding lei tot verminderde strukturele skade deur addisionele energie dissipering tydens seismiese belasting te verskaf. Die nagevolge van vorige aardbewings het die vatbaarheid van verspande staalrame vir strukturele skade bewys, veral in die verspanning en verbindings. Al het staalstrukture tydens vorige aardbewings, soos die 1994 Northridge-aardbewing, nie ineengestort nie, het die talle bros falings tot die ontwikkeling van seismiese voorskrifte vir verbeterde duktiliteit gelei. Die verbeterde voorskrifte lei egter steeds tot beduidende skade, soos gesien ná die aardbewing in Christchurch in 2011. ’n Benadering om aardbewing-skade te verminder, is om van energie dissiperings toestelle gebruik te maak. In teenstelling met ander toestelle, is die Geboute Gleufverbinding eenvoudig en ekonomies. Deur die gly van plate relatief tot mekaar word energie gedissipeer in die verbinding. Die voorstel is om Geboute Gleufverbindings as verspannings-verbindings in Konsentries Verspande Rame te gebruik, maar die gebrek aan ’n gepubliseerde ontwerp-prosedure het die gebruik tot dusver beperk. Die gebrek aan ’n gepubliseerde ontwerp-prosedure vir Geboute Gleufverbinding-verspanning kan aan ’n navorsingstekort op die gebied toegeskryf word. Vorige navorsing het meestal op die toets van wrywing-materiale vir die verbinding, gefokus. Literatuur het ’n onvoldoende begrip oor die uitwerking, wat die opset van die Geboute Gleufverbinding op die gedrag van die verbinding het, aangedui. Om hierdie aan te spreek, is ’n Eindige Element Analise-studie onderneem. Eerstens is ’n Eindige Element-model van die Geboute Gleufverbinding met bestaande eksperimentele resultate gekalibreer. Die Eindige Element-model is gebruik om die volgende te bestudeer: die uitwerking wat bout-impak met die gleuf-ente het; die verskille tussen die Simmetries en Asimmetriese Geboute Gleufverbindings en ook die invloed van die verbinding op ’n verspande vak. ’n Modelleringstegniek om ’n nie-lineêre dinamiese analise van ’n multi-verdieping gebou met Geboute Gleufverbinding-verspanning uit te voer, is ontwikkel. Die bout-impak-ondersoek het gewys dat die verbinding geskikte detaillering verlang om duktiliteit te verseker. Die analises het aangedui dat die gedrag van die Simmetriese verbinding, bó die van die Asimmetriese verbinding, verkies word. Kontak tussen die boutskagte en die gleufkante tydens gly in ’n verspande vak, het ’n verandering in die histerese-gedrag veroorsaak, maar dit was nie nadelig nie. Die dinamiese analise het aangedui dat die Geboute Gleufverbindings tot ’n vermindering in verspanning-skade gelei het deur die sywaartse verplasing-kapasiteit te vermeerder. Die bevindinge het die belangrike aspekte van die opset van die verbindings verklaar en het ook die voordele van die gebruik van die verbindings in Konsentries Verspande Rame aangetoon. Die verbeterde begrip dra by tot die ontwikkeling van ’n ontwerp-prosedure vir Geboute Gleufverbinding-verspanning.National Research Foundation (NRF

High-silica zeolites and their use as catalyst in organic chemistry

Applied Science

Displacement sensing by field emission with nanometer resolution

Field emission is used as a displacement sensing method, exploiting the exponential relation\ud between field emission current and electrode gap. Atomic force microscopy (AFM) probes have been\ud used as field emission source to measure I/V characteristics which were found to correspond well to\ud theory. The field emission sensor was operated in a more linear regime by using feedback on the position\ud of the probe in order to maintain a constant current. The sensitivity of the sensor for displacement was\ud found to be 0.26 V/nm at a range of ~100 nm. From the experimental data, typical parameters for the\ud Fowler-Nordheim equation were deduced and used to model the sensor performance. The measurements\ud confirm that field emission can be applied to sense the distance between a probe tip and sample with\ud <20 nm resolution