The Kelvin measurement is a sensitive and label-free method based on work function measurements. Work function, the minimum energy required to extract an electron from a metallic material, can be shifted by ionic charges and dipoles present on the surface. The scanning Kelvin nanoprobe (SKN), a probe-based microscopic imaging device, was used in the detection of work function changes induced by surface-immobilized oligonucleotide / DNA microarrays. The scanning Kelvin nanoprobe was able to study DNA microarrays smaller than 100 µm in size, produced with solution concentrations lower than 10 µmol/L. The limit of detection was estimated to be 15 ng DNA. Better than ± 10% relative variation was achieved for replicate spots. It was observed that higher surface densities of immobilized DNA molecules produced greater work function changes than lower surface densities. Surface saturation with increasing solution concentrations was observed as well. Also, longer strands of DNA produced greater work function changes than shorter strands. Statistical analysis of the results confirmed that non-complementary DNA strands could be differentiated from complementary strands by the Kelvin measurement. Single base mismatches on the complementary DNA strands were also detected by the Kelvin measurement. Different substrate materials were tested in the search for reliable and inexpensive sample slides with satisfactory DNA immobilization efficiency. Materials such as silicon wafers, gold-coated glass slides, gold-coated stainless steel slides, and gold compact discs (CD) were tested. A surface property comparison of gold-coated glass slides and compact discs was made by atomic force microscopy (AFM), and revealed very different microscopic features. The effect of cleaning on gold-coated glass slides was examined by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Technical improvements were made to the SKN equipment progressively. Several revisions to the tip holder design have been employed for better electromagnetic shielding, enhanced robustness and easier tip change. An older signal generator was replaced with a professional PC audio card to provide more stable signal and more convenient on-screen fine tuning, also at a reduced cost. The Labview-based controlling program has also been improved through multiple iterations.

The Rosetta spacecraft is on route to rendezvous with the comet 67P/ Churyomov-Gerasimenko. One of the instruments onboard is the Langmuir probe instrument (LAP) developed by the Swedish Institute of Space Physics. The LAP includes two spherical probes used to measure a number of properties of the surrounding plasma. One measured property is the plasma density for which the spacecraft potential is a good proxy. By the determining the potential between spacecraft and Langmuir probe, the spacecraft potential can be measured. But such measurements are sometimes disturbed by the potential from the spacecraft itself, the influence from photoemitted electrons and the solar wind wake behind Rosetta. In order to correct for the errors caused by spacecraft-plasma interaction in the solar wind a model depending on the spacecraft (and Langmuir probe) orientation is developed. The data is obtained from three-dimensional simulations of Rosetta, with varying plasma parameters, using the software SPIS (Spacecraft Plasma Interaction System). Least squares fitting with a set of basis functions then provide the input for a parametric modelling. The developed model makes it possible to estimate the influence of each of the disturbing effects. The developed model gives good fits to data obtained in SPIS simulations. The two angular dependent factors, modelling perturbation on potential measurements caused by photoelectrons and wake effects, show errors below the 100 mV level in all cases. The model describing the influence from spacecraft potential is slightly less accurate, with errors at or below the 400 mV level in all relevant cases.

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In recent years, nanowires have become increasingly important due to their unique properties and applications. Thus, processes in the fabrication to nanostructures has come a focal point in research. In this research, a new method to fabricate nanowires has been developed. The new technique is called the Scanning Probe Alloying Nanolithography (SPAN). The SPAN was processed using an Atomic Force Microscope (AFM) in ambient environment. Firstly, an AFM probe was coated with gold (Au), and then slid on a silicon (Si) substrate. The contact-sliding motion generated a nanostructure on the substrate, instead of wear. Subsequently, careful examination was carried out at the scale relevant to an AFM probe, in terms of physical dimension and electrical conductivity. The measured conductivity value of the generated microstructures was found to be between the conductivity values of pure silicon and gold. Simple analysis indicated that the microstructures were formed due to frictional energy dispersed in the interface forming a bond to sustain mechanical wear. This research proves the feasibilities of tip-based nanomanufacturing. The SPAN process was developed to increase efficiency of the technique. This study also explored the possibility of the applications as a biosensor and a flexible device. This dissertation contains nine sections. The first section introduces backgrounds necessary to understand the subject matter. It reviews current status of the nanofabrication technologies. The basic concepts of AFM are also provided. The second section discusses the motivation and goals in detail. The third section covers the new technology, scanning probe alloying nanolithography (SPAN) to fabricate nanostructures. The fourth talks about characterization of nanostructures. Subsequently, the characterized nanostructures and their mechanical, chemical, and electrical properties are discussed in the fifth section. In the sixth section, the new process to form a nanostructure is evaluated and its mechanism is discussed. The seventh section discusses the feasibility of the nanostructures to be used in biosensors and flexible devices. The conclusion of the research is summarized in the seventh section.

Das Verhalten einer 3-Punkt-Biegeprobe mit Anriss unter Belastung kann mittels eines Finite-Element-Modells nachgebildet werden. Das Modell ermöglicht die Berücksichtigung von elastisch-plastischem Materialverhalten entsprechend der jeweiligen materialspezifischen Spannungs-Dehnungs-Kurve, welche mit dem Ansatz der multilinearen kinematischen Verfestigung (MKIN) umgesetzt wird. Weiterhin gestattet das Modell die Einbeziehung der realen Rollenkinematik beim Biegevorgang. Für die Beschreibung des Bruchkriteriums wird ein spezielles Damage-Modell verwendet, mit dem man in der Lage ist, das Risswachstums in geeigneter Weise wiederzugeben. Mit diesem Modell lässt sich auch das Teilentlastungs-Compliance-Verfahren nachbilden. Diese Simulation ermöglicht die Einschätzung von Korrekturansätzen zur experimentellen Risslängenbestimmung über die Compliance-Methode.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Over the last few years the World Health Organization (WHO) has endorsed several tests for the rapid detection of multidrug-resistant tuberculosis (MDR-TB) in resource-poor settings. The objective of this study was to compare the cost-effectiveness of a line probe assay test (less than one week for results) to conventional (bacterial culture) drug susceptibility testing (one month for results) for the detection of MDR-TB in an HIV-positive South African population by estimating the incremental cost-effectiveness ratio (ICER) per disability-adjusted life-year (DALY) averted. Costs of testing, drug treatment, hospitalization, as well as estimates for mortality, treatment success, and failure rates were obtained from literature sources, the South African Department of Health, the WHO, the Foundation of Innovative Diagnostics (FIND), and expert opinion. The willingness-to-pay threshold for a DALY averted was pre-set at 3 times the 2009 GDP per capita (about $17,400) for South Africa. In the base-case scenario for a prevalence of 30% of MDR-TB among HIV-positive patients, the average cost per person for the line probe assay testing strategy was $3,539/0.458 DALY averted and the conventional testing approach was $3,011/0.430 DALY averted. The base-line ICER was about $18,800 per DALY averted – about $1,400 above the pre-set threshold. In sensitivity analyses, the model was robust to changes in prevalence (+ 50%); costs (+ 10%), and probabilities of death, success and failure (+ 20%). However, when the treatment success rate for the line probe assay test was increased to 60% (one of the targets set by WHO in TB treatment) the ICER was below the willingness-to-pay level (i.e., cost-effective). The probabilistic sensitivity analysis showed there is a 70% chance that the additional cost of the line probe assay, compared with conventional testing, was less than $30,000 per DALY averted. However, the model may have underestimated the benefits of the line probe assay because it did not account for a decrease in the transmission of the disease due to earlier treatment nor did it measure any benefits more than a year after testing. / text

Heartwater is a tick borne disease that affects ruminants and wild animals in Africa south of the Sahara. It is caused by Ehrlichia ruminantium and transmitted by the tick Amblyomma hebraeum. The protocols currently used to detect heartwater take several days to complete. Here, we describe the development of a pCS20 quantitative real-time PCRTaqMan probe assay to detect E. ruminantium in livestock blood and ticks from the field. The assay is based on the conserved pCS20 gene region of E. ruminantium that contains two overlapping genes, rnc and ctaG [Collins, N.E., Liebenberg, J., De Villiers, E.P., Brayton, K.A., Louw, E., Pretorius, A., Faber, F.E., Van Heerden, H., Josemans, A., Van Kleef, M., Steyn, H.C., Van Strijp, M.F., Zweygarth, E., Jongejan, F., Maillard, J.C., Berthier, D., Botha, M., Joubert, F., Corton, C.H., Thomson, N.R., Allsopp, M.T., Allsopp, B.A., 2005. The genome of the heartwater agent Ehrlichia ruminantium contains multiple tandem repeats of actively variable copy number. PNAS 102, 838–843]. The pCS20 quantitative real-time PCRTaqMan probe was compared to the currently used pCS20 PCR and PCR/32P-probe test with regards to sensitivity, specificity and the ability to detect DNA in field samples and in blood from experimentally infected sheep. This investigation showed that the pCS20 quantitative real-time PCRTaqMan probe was the most sensitive assay detecting seven copies of DNA/ml of cell culture. All three assays, however, cross react with Ehrlichia canis and Ehrlichia chaffeensis. The pCS20 real-time PCR detected significantly more positive field samples. Both the PCR and pCS20 real-time PCR could only detect E. ruminantium parasites in the blood of experimentally infected sheep during the febrile reaction. The PCR/32P-probe assay, however, detected the parasite DNA 1 day before and during the febrile reaction. Thus, because this new quantitative pCS20 real-time PCRTaqMan probe assay was the most sensitive and can be performed within 2 h it is an effective assay for epidemiological surveillance and monitoring of infected animals.

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By modelling and simulating the ESA spacecraft Rosetta in a plasma with solar wind parameters, and simultaneously simulating a particle detection experiment of Langmuir probe voltage sweep type using the ESA open source software SPIS Science, we investigate the features of Rosetta’s envi- ronment in the solar wind and the e↵ect of photoemission from the space- craft on the measurements made by the Langmuir Probe instrument on board Rosetta. For a 10 V positively charged spacecraft and Maxwellian distributed photoelectron emission with photoelectron temperature, Tf = 2 eV in a plasma of typical 1 AU solar wind parameters: ne = 5 ⇥ 106 m3, vSW = 4 ⇥ 105 m/s, Te = 12 eV, Tion = 5 eV, we detect a floating potential of 6.4 (± 0.2) V at Langmuir probe 1. Two models used in literature on photoemission was used and compared and we report a clear preference to the Maxwellian energy distribution of photoelectrons from a point source model with our simulation result.