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The South African national calibration facility is currently not equipped for mammography, dose-measuring equipment. A therapy X-ray machine was used as a calibration unit at the national secondary standards dosimetry laboratory (SSDL) for medium and low energy X-ray, therapy calibrations. It is not necessarily intuitive that the latter calibrations are applicable to diagnostic X-ray beams generated by high frequency generators. The response of measuring equipment calibrated in a therapy X-ray beam, compared to its response in a diagnostic or clinical mammography unit, is unknown. The aim of the research was to investigate whether there was a measurable difference between the X-ray beam qualities available for low energy diagnostic radiology and radiation therapy, i.e. up to 100 kV. The beam qualities studied included both mammography and conventional diagnostic radiography, i.e. nominally 20 kV to 100 kV. The diagnostic and therapy X-ray tubes under investigation had different target-filter combinations, inherent filtration and theoretically, different X-ray spectra. Practically, spectrometry of X-ray beams is not possible because of the sophistication of the instrumentation, comprehensive analyses being very time consuming and not practically applicable to the clinical environment (Kharatti and Zarrad, 2003). Furthermore, not all SSDL’s or Hospitals have access to spectral analysers. Clinical beam quality is instead specified in terms of both the tube peak voltage and the half-value layer (HVL), the thickness of material that will reduce the maximum output of the X-ray beam to 50%. The goal was to compare measured HVLl’s to the ones recommended by the International Electro technical Commission (IEC-61267, 2005) for available mammography beam qualities. The method was validated using attenuation curves. The attenuation curves were then used to derive the suitability of the X-ray spectra for calibration of mammography ionisation chambers (Waggener and Blough, 1999). One of the low energy therapy units was found to be suitable for introducing a regional calibration service for mammography.

Maintenance has traditionally been viewed as an unavoidable part of the manufacturing function. It is often identified as an opportunity to wantonly reduce costs, whenever the need to reduce manufacturing cost arises. Its potential to contribute to an organisation’s competitive advantage and business sustainability, has not received significant attention, and consequently formulation and execution of maintenance strategies have been poor, inconsistent or unfocused. Alignment of business strategy and maintenance strategy should help an organization to achieve or improve upon its business performance. Likewise, maintenance performance measures should be linked to an organization’s strategy, in order to provide useful information for making effective decisions. This fit or alignment, can only be achieved when maintenance is viewed as a critical business function, integrated with other business functions in support of business strategy. The impact of alignment between maintenance strategy and business strategy - on business strategy - is studied empirically in this thesis. The results confirm that alignment between maintenance and business strategy is strongly positively correlated with business performance. Copyright / Dissertation (MBA)--University of Pretoria, 2010. / Gordon Institute of Business Science (GIBS) / unrestricted

In this thesis we have focussed on two types of axially symmetric ion trap mass analysers viz., the quadrupole ion trap mass analyser and the toroidal ion trap mass analyser. We have undertaken three numerical studies in this thesis, one study is on the quadrupole ion trap mass analysers and two studies are on the toroidal ion trap mass analysers. The first study is related to improvement of the sensitivity of quadrupole ion trap mass analysers operated in the resonance ejection mode. In the second study we have discussed methods to determine the multipole coefficients in the toroidal ion trap mass analysers. The third study investigates the stability of ions in the toroidal ion trap mass analysers. The first study presents a technique to cause unidirectional ion ejection in a quadrupole ion trap mass spectrometer operated in the resonance ejection mode. In this technique a modified auxiliary dipolar excitation signal is applied to the endcap electrodes. This modified signal is a linear combination of two signals. The first signal is the nominal dipolar excitation signal which is applied across the endcap electrodes and the second signal is the second harmonic of the first signal, the amplitude of the second harmonic being larger than that of the fundamental. We have investigated the effect of the following parameters on achieving unidirectional ion ejection: primary signal amplitude, ratio of amplitude of second harmonic to that of primary signal amplitude, different operating points, different scan rates, different mass to charge ratios and different damping constants. In all these simulations unidirectional ejection of destabilized ions has been successfully achieved. The second study presents methods to determine multipole coefficients for describing the potential in toroidal ion trap mass analysers. Three different methods have been presented to compute the toroidal multipole coefficients. The first method uses a least square fit and is useful when we have ability to compute potential at a set of points in the trapping region. In the second method we use the Discrete Fourier Transform of potentials on a circle in the trapping region. The third method uses surface charge distribution obtained from the Boundary Element Method to compute these coefficients. Using these multipole coefficients we have presented (1) equations of ion motion in toroidal ion traps (2) the Mathieu parameters in terms of multipole coefficients and (3) the secular frequency of ion motion in these traps. It has been shown that the secular frequency obtained from our method has a good match with that obtained from numerical trajectory simulation. The third study presents stability of ions in practical toroidal ion trap mass analysers. Here we have taken up for investigation four geometries with apertures and truncation of electrodes. The stability is obtained in UDC-VRF plane and later this is converted into A-Q plane on the Mathieu stability plot. Though the plots in terms of Mathieu parameters for these structures are qualitatively similar to the corresponding plot of linear ion trap mass analysers, there is a significant difference. The stability plots of these have regions of nonlinear resonances where ion motion is unstable. These resonances have been briefly investigated and it is proposed that they occur on account of hexapole and octopole contributions to the field in these toroidal ion traps.

The Magnetospheric Multiscale mission led by NASA has been designed to study the micro-physics of Magnetic Reconnection in Earth's magnetosphere by using four identical spacecrafts with instruments with high temporal and spatial resolutions. Among these instruments are the Dual Ion Spectrometers (DIS) engineered to measure the 3D distribution of ion flux in space. The detector assembly of the DIS consists of Micro-Channel Plates (MCP) mounted in Chevron configuration. Centre d'Etude Spatiale des Rayonnements (CESR), Toulouse is responsible for the provision and testing of all fifty MCP pairs for this mission. The goal of the work was to participate in the testing and characterization of the first prototype of the MCPs. It was achieved by understanding the working and characteristics of the MCPs in general and getting familiar with the detector assembly of the DIS i.e. the MCP pair and the detector circuit board in particular. To perform the testing, it was necessary to understand the testing system as well. These topics are described in this report along with the testing procedure and the data analysis. The testing procedure was developed eventually after facing several problems during the testing. MCP pair characteristics like pulse height distributions, gain, resistance and the MCP operating voltages for the mission were determined on analyzing the data. Crosstalk was found in the circuit board of the detector assembly and has also been discussed. / Validerat; 20101217 (root)

This thesis presents results of investigations on fields and multipole expansion coefficients in axially symmetric (referred to as 3D)and two dimensional (2D)ion trapmass analysers. 3D mass analysers have a three-electrode geometry with two (electrically shorted) endcap electrodes and one central ring electrode. rf-only or rf/dc potential applied across the electrodes creates a linear trapping field in the central cavity of the mass analyser.2Dmass analysers have four longitudinal electrodes in which the opposite pairs of electrodes are electrically shorted. Here, rf-only or rf/dc potential applied across the pair of electrodes creates a linear trapping field and fragment ions of the analyte gas are trapped along the central axis of the mass analyser. Both these mass analysers have apertures machined on the electrodes (holes in case of 3D traps and slits in case of 2D traps) to permit entry of electrons for ionizing the analyte gas and for collection of destabilized fragment ions. This thesis is concerned with how these apertures influence the fields and multipole expansion coefficients within the traps. This thesis is divided into five chapters. Chapter 1 provides the background information which is required for the thesis. It begins with a description of the geometry of the 3D and the 2D mass analysers used in the present work.These include the quadrupole ion trap (QIT) and cylindrical ion trap (CIT) for 3D structures and the linear ion trap (LIT) and the rectilinear ion trap (RIT) for 2D structures. This is followed by a brief description of the numerical method, the boundary element method (BEM), used in the thesis. Also presented here are the Green’s function for 3D and 2D geometries. In the final section, the scope of the thesis is presented. Chapter 2 presents two approximate analytical expressions for nonlinear electric fields in the principal direction in axially symmetric (3D) and two dimensional (2D) ion trap mass analysers with apertures on the electrodes. Considered together (3D and 2D), we present composite approximations for the principal unidirectional nonlinear electric fields in these ion traps. The composite electric field E has the form E= EnoAperture + EdueToAperture where EnoAperture is the field within an imagined trap which is identical to the practical trap except that the apertures are missing; and where EdueToAperture is the field contribution due to apertures on the two trap electrodes. The field along the principal axis of the trap can in this way be well approximated for any aperture that is not too large. To derive EdueToAperture, classical results of electrostatics have been extended to electrodes with finite thickness and different aperture shapes. EnoAperture is a modified truncated multipole expansion for the imagined trap with no aperture. The first several terms in the multipole expansion are in principle exact (though numerically determined using the BEM), while the last term is chosen to match the field at the electrode. This expansion, once computed, works with any aperture in the practical trap. The composite field approximation for axially symmetric (3D) traps is checked for three geometries: the quadrupole ion trap (QIT), the cylindrical ion trap (CIT) and an arbitrary other trap. The approximation for 2D traps is verified using two geometries: the linear ion trap (LIT)and the rectilinear ion trap (RIT). In each case, for two aperture sizes (10% and 50% of the trap dimension), highly satisfactory fits are obtained. These composite approximations may be used in more detailed nonlinear ion dynamics studies than have been hitherto attempted. In Chapter 3we complement and complete the work presented in Chapter 2 by considering off-axis fields in the axially symmetric (3D) and the two dimensional (2D) ion traps whose electrodes have apertures. Our approximation has two parts. The first, EnoAperture, is the field obtained numerically for the trap under study with no apertures. We have used the boundary element method (BEM) for obtaining this field. The second part, EdueToAperture, is an analytical expression for the field contribution of the aperture. In EdueToAperture, aperture size is a free parameter. A key element in our approximation is the electrostatic field near an infinite thin plate with an aperture, and with different constant valued far field intensities on either side. Compact expressions for this field can be found using separation of variables, wherein the choice of coordinate system is crucial. This field is, in turn, used four times within our trap specific approximation. The off-axis field expressions for the 3D geometries were tested on the quadrupole ion trap (QIT) and the cylindrical ion trap (CIT), and the corresponding expressions for the 2D geometries were tested on the linear ion trap (LIT) and rectilinear ion trap (RIT). For each geometry, we have considered apertures which are 10%, 30% and 50% of the trap dimension. We have found that our analytical correction term EdueToAperture, though based on a classical small-aperture approximation, gives good results even for relatively large apertures. Chapter 4 presents approximate analytical expressions for estimating the variation in multipole expansion coefficients with the size of apertures in axially symmetric (3D) and two dimensional (2D) ion trap mass analysers. Following the approach adopted in Chapter 2 and Chapter 3 which focused on the role of apertures to fields within traps, here too, the analytical expression is a sum of two terms, An,noAperture, the multipole expansion coefficient for a trap with no apertures and An,dueToAperture, the multipole expansion coefficient contributed by the aperture. An,noAperture has been obtained numerically and An,dueToAperture is obtained from the nth derivative of the potential within the trap. The expressions derived have been tested on two 3D geometries and two 2D geometries. These include the quadrupole ion trap (QIT) and the cylindrical ion trap (CIT) for 3D geometries and the linear ion trap (LIT) and the rectilinear ion trap (RIT) for the 2D geometries. Multipole expansion coefficients A2 to A24, estimated by our analytical expressions were compared with the values obtained numerically (using the boundary element method) for aperture sizes varying up to 50% of the trap size. In all the plots presented, it is observed that our analytical expression for the variation of multipole expansion coefficients versus aperture size closely follows the trend of the numerical evaluations for the range of aperture sizes considered. The maximum relative percentage errors, which provide an estimate of the deviation of our values from those obtained numerically for each multipole expansion coefficient, are seen to be in the range of 10% to 15%. The leading multipole expansion coefficient, A2, however, is seen to be estimated very well by our expressions, with most values being within 1% of the numerically determined values, with larger deviations seen for the QIT and LIT only at larger aperture sizes. Chapter 5 presents a few concluding remarks.

This diploma work is aimed at the use of infrared spectrometry by Fire Brigade Units of the Czech Republic. A new portable instrument True Defender FT produced by Ahura was used for this purpose. It was lent by the Institute of Citizens´Protection in Lázně Bohdaneč. The goal of this work is to get acquainted with this instrument and to evaluate its ability to identify unknown substances. Experimental part was aimed at the testing of this spectrometer with the help of model sample set, containing samples from real situations solved by members of Fire Brigade Units of the Czech Republic. Possibilities of mobile infrared spectometer True Defender FT and mobile Raman spectometer First Defender are finally compared.