Development and evaluation of a programmable radio frequency signal

ThesisMost commercially available signal generators make use of a phase-locked loop in combination with analogue frequency synthesis to generate the desired frequency range. Advances in the development of components being used in digital frequency synthesis have made the use of direct digital synthesis (DDS) a viable option in radio frequency (RF) signal generation. The project consists of designing the interfacing between a DDS unit and a microcontroller to provide a versatile frequency generator in the lower high frequency (HF) spectrum. The research was aimed at testing the following hypothesis: A programmable Radio Frequency signal generator can be developed, using a DDS-based system with a microcontroller providing the required intelligence. A continuously variable frequency range in 1 Hz steps over a spectrum of 0- 10 MHz can be achieved. The following features were included in the design of the signal generator: • Setting the generator to a specific frequency; • Displaying the frequency and prompts from the microcontroller on a liquid crystal display; • Interfacing with a keypad; • Interfacing with a personal computer for remote RS232 operation; • Interfacing with a rotary optical encoder for up-and-down frequency control; • Sweeping of a range of frequencies; • Setting the step size of frequency increments; • Frequency shift keying (FSK) capability. The above features allowed ample demonstration of the software control over the associated hardware and enabled easy evaluation of the product. To evaluate the product, it was decided to concentrate on the following measurable aspects of a typical radio frequency (RF) signal generator: • The accuracy of the output frequency; • Evaluating the frequency range limits of the generator; • Making a spectral analysis of the output signal. During the execution of the project, insight was gained with respect to the following: • DDS theory; • DDS hardware interfacing; • C-programming as well as using the versatile DSSOOO microcontroller; • The importance of sound design principles in a hybrid digital and analogue radio frequency project. • Setting the step size of frequency increments; • Frequency shift keying (FSK) capability. The above features allowed ample demonstration of the software control over the associated hardware and enabled easy evaluation of the product. To evaluate the product, it was decided to concentrate on the following measurable aspects of a typical radio frequency (RF) signal generator: • The accuracy of the output frequency; • Evaluating the frequency range limits of the generator; • Making a spectral analysis of the output signal. During the execution of the project, insight was gained with respect to the following: • DDS theory; • DDS hardware interfacing; • C-programming as well as using the versatile DSSOOO microcontroller; • The importance of sound design principles in a hybrid digital and analogue radio frequency project

Confronting the constraints of morphological taxonomy in the Botryosphaeriales

Identification of fungi and the International Code of Nomenclature underpinning this process, rests strongly on the characterisation of morphological structures. Yet, the value of these characters to define species in many groups has become questionable or even superfluous. This has emerged as DNA-based techniques have increasingly revealed cryptic species and species complexes. This problem is vividly illustrated in the present study where 105 isolates of the Botryosphaeriales were recovered from both healthy and diseased woody tissues of native Acacia spp. in Namibia and South Africa. Thirteen phylogenetically distinct groups were identified based on Internal Transcribed Spacer (ITS) rDNA PCR-RFLP and translation elongation factor 1-α (TEF1-α) sequence data, two loci that are known to be reliable markers to distinguish species in the Botryosphaeriales. Four of these groups could be linked reliably to sequence data for formerly described species, including Botryosphaeria dothidea, Dothiorella dulcispinae, Lasiodiplodia pseudotheobromae and Spencermartinsia viticola. Nine groups, however, could not be linked to any other species known from culture and for which sequence data are available. These groups are, therefore, described as Aplosporella africana, A. papillata, Botryosphaeria auasmontanum, Dothiorella capri-amissi, Do. oblonga, Lasiodiplodia pyriformis, Spencermartinsia rosulata, Sphaeropsis variabilis and an undescribed Neofusicoccum sp. The species described here could not be reliably compared with the thousands of taxa described in these genera from other hosts and regions, where only morphological data are available. Such comparison would be possible only if all previously described taxa are epitypified, which is not a viable objective for the two families, Botryosphaeriaceae and Aplosporellaceae, in the Botryosphaeriales identified here. The extent of diversity of the Botryosphaeriales revealed in this and other recent studies is expected to reflect that of other undersampled regions and hosts, and illustrates the urgency to find more effective ways to describe species in this, and indeed other, groups of fungi.THRIP initiative of the Department of Trade and Industry, DST/NRF Centre of Excellence in Tree Health Biotechnology (CTHB), (DST) and National Research Foundation (NRF).http://www.persoonia.orghttp://www.ingentaconnect.com/content/nhn/pimjtm201

A near IR imaging survey of intermediate and high-mass young stellar outflow candidates

We have carried out a near-infrared imaging survey of luminous young stellar outflow candidates using the United Kingdom Infrared Telescope. Observations were obtained in the broad band K (2.2 mu) and through narrow band filters at the wavelengths of H_2 v=1--0 S(1) (2.1218 mu) and Br gamma (2.166 mu) lines. Fifty regions were imaged with a field of view of 2.2 X 2.2 arcmin^2. Several young embedded clusters are unveiled in our near-infrared images. 76% of the objects exhibit H_2 emission and 50% or more of the objects exhibit aligned H_2 emission features suggesting collimated outflows, many of which are new detections. These observations suggest that disk accretion is probably the leading mechanism in the formation of stars, at least up to late O spectral types. The young stellar objects responsible for many of these outflows are positively identified in our images based on their locations with respect to the outflow lobes, 2MASS colours and association with MSX, IRAS, millimetre and radio sources. The close association of molecular outflows detected in CO with the H_2 emission features produced by shock excitation by jets from the young stellar objects suggests that the outflows from these objects are jet-driven. Towards strong radio emitting sources, H_2 jets were either not detected or were weak when detected, implying that most of the accretion happens in the pre-UCHII phase; accretion and outflows are probably weak when the YSO has advanced to its UCHII stage.Comment: 64 pages, 53 figures, Accepted for publication in the MNRA

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

State of the climate in 2018

In 2018, the dominant greenhouse gases released into Earth’s atmosphere—carbon dioxide, methane, and nitrous oxide—continued their increase. The annual global average carbon dioxide concentration at Earth’s surface was 407.4 ± 0.1 ppm, the highest in the modern instrumental record and in ice core records dating back 800 000 years. Combined, greenhouse gases and several halogenated gases contribute just over 3 W m−2 to radiative forcing and represent a nearly 43% increase since 1990. Carbon dioxide is responsible for about 65% of this radiative forcing. With a weak La Niña in early 2018 transitioning to a weak El Niño by the year’s end, the global surface (land and ocean) temperature was the fourth highest on record, with only 2015 through 2017 being warmer. Several European countries reported record high annual temperatures. There were also more high, and fewer low, temperature extremes than in nearly all of the 68-year extremes record. Madagascar recorded a record daily temperature of 40.5°C in Morondava in March, while South Korea set its record high of 41.0°C in August in Hongcheon. Nawabshah, Pakistan, recorded its highest temperature of 50.2°C, which may be a new daily world record for April. Globally, the annual lower troposphere temperature was third to seventh highest, depending on the dataset analyzed. The lower stratospheric temperature was approximately fifth lowest. The 2018 Arctic land surface temperature was 1.2°C above the 1981–2010 average, tying for third highest in the 118-year record, following 2016 and 2017. June’s Arctic snow cover extent was almost half of what it was 35 years ago. Across Greenland, however, regional summer temperatures were generally below or near average. Additionally, a satellite survey of 47 glaciers in Greenland indicated a net increase in area for the first time since records began in 1999. Increasing permafrost temperatures were reported at most observation sites in the Arctic, with the overall increase of 0.1°–0.2°C between 2017 and 2018 being comparable to the highest rate of warming ever observed in the region. On 17 March, Arctic sea ice extent marked the second smallest annual maximum in the 38-year record, larger than only 2017. The minimum extent in 2018 was reached on 19 September and again on 23 September, tying 2008 and 2010 for the sixth lowest extent on record. The 23 September date tied 1997 as the latest sea ice minimum date on record. First-year ice now dominates the ice cover, comprising 77% of the March 2018 ice pack compared to 55% during the 1980s. Because thinner, younger ice is more vulnerable to melting out in summer, this shift in sea ice age has contributed to the decreasing trend in minimum ice extent. Regionally, Bering Sea ice extent was at record lows for almost the entire 2017/18 ice season. For the Antarctic continent as a whole, 2018 was warmer than average. On the highest points of the Antarctic Plateau, the automatic weather station Relay (74°S) broke or tied six monthly temperature records throughout the year, with August breaking its record by nearly 8°C. However, cool conditions in the western Bellingshausen Sea and Amundsen Sea sector contributed to a low melt season overall for 2017/18. High SSTs contributed to low summer sea ice extent in the Ross and Weddell Seas in 2018, underpinning the second lowest Antarctic summer minimum sea ice extent on record. Despite conducive conditions for its formation, the ozone hole at its maximum extent in September was near the 2000–18 mean, likely due to an ongoing slow decline in stratospheric chlorine monoxide concentration. Across the oceans, globally averaged SST decreased slightly since the record El Niño year of 2016 but was still far above the climatological mean. On average, SST is increasing at a rate of 0.10° ± 0.01°C decade−1 since 1950. The warming appeared largest in the tropical Indian Ocean and smallest in the North Pacific. The deeper ocean continues to warm year after year. For the seventh consecutive year, global annual mean sea level became the highest in the 26-year record, rising to 81 mm above the 1993 average. As anticipated in a warming climate, the hydrological cycle over the ocean is accelerating: dry regions are becoming drier and wet regions rainier. Closer to the equator, 95 named tropical storms were observed during 2018, well above the 1981–2010 average of 82. Eleven tropical cyclones reached Saffir–Simpson scale Category 5 intensity. North Atlantic Major Hurricane Michael’s landfall intensity of 140 kt was the fourth strongest for any continental U.S. hurricane landfall in the 168-year record. Michael caused more than 30 fatalities and $25 billion (U.S. dollars) in damages. In the western North Pacific, Super Typhoon Mangkhut led to 160 fatalities and$6 billion (U.S. dollars) in damages across the Philippines, Hong Kong, Macau, mainland China, Guam, and the Northern Mariana Islands. Tropical Storm Son-Tinh was responsible for 170 fatalities in Vietnam and Laos. Nearly all the islands of Micronesia experienced at least moderate impacts from various tropical cyclones. Across land, many areas around the globe received copious precipitation, notable at different time scales. Rodrigues and Réunion Island near southern Africa each reported their third wettest year on record. In Hawaii, 1262 mm precipitation at Waipā Gardens (Kauai) on 14–15 April set a new U.S. record for 24-h precipitation. In Brazil, the city of Belo Horizonte received nearly 75 mm of rain in just 20 minutes, nearly half its monthly average. Globally, fire activity during 2018 was the lowest since the start of the record in 1997, with a combined burned area of about 500 million hectares. This reinforced the long-term downward trend in fire emissions driven by changes in land use in frequently burning savannas. However, wildfires burned 3.5 million hectares across the United States, well above the 2000–10 average of 2.7 million hectares. Combined, U.S. wildfire damages for the 2017 and 2018 wildfire seasons exceeded $40 billion (U.S. dollars)

A heterogeneous Thorium-based fuel design for a PWR aimed at increasing fuel cycle length

MEng (Nuclear Engineering), North-West University, Potchefstroom Campus, 2016A new heterogeneous Thorium based fuel design has been proposed for Pressurised Water Reactors in order to increase fuel cycle lengths. This design incorporates ThO2 pellets which have been included between UO2 fuel pellets to breed fissile U233 through transmutation of Th232. A heterogeneous design was chosen in order to increase the conversion ratio of the fuel beyond what has been achieved with homogeneous Thorium based fuels. The results of this dissertation have shown that it is possible to introduce this design into an infinite reactor simulation, where a high conversion ratio can be achieved in order to increase the fuel lifetime and thereby increase the fuel cycle lengths. The use of different fuel configurations have been explored to develop a concept design which can serve as a proof of concept for further development. This design has undergone preliminary optimisation steps and shows promise as an advanced fuel design. However, the occurrence of energy peaks within the fuel lattice causes some concerns for safety. The concept design studied for this dissertation has provided positive results and due consideration for further development is strongly advised. Some safety concerns have been addressed, but the use of Thorium based fuels is still met with major challenges and concerns which could not be addressed within the given time for this study.Master

The continuous depolymerization of filled polytetrafluoroethylene with a continuous process

A new method for beneficiating unfilled as well as filled polytetrafluoroethylene (PTFE) waste has been developed. This process does not use any carrier gas while forming the depolymerization products. It enables polymer manufacturers and end‐users to reuse and adds value to filled fluorocarbon polymer waste. The filler material was qualified by means of scanning electron microscopy and thermogravimetric analysis and the success of the depolymerization process inside a rotating kiln was proved by visual observation. The PTFE was depolymerized inside a kiln‐type reactor declined at a 5° angle, with a central rotating paddle screw to scrape the inner wall of the reactor, which was able to operate within the temperature range of 600–800°C and pressure range of 10–90 kPa. Different ratios of the useful products tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and octafluorocyclobutane (OFCB) were produced. The optimum conditions for TFE production are 600°C and 10–30 kPa, for HFP production it was 800°C and 10 kPa, and for OFCB production 600°C and 90 kPa. Temperatures of 700°C should be avoided as this leads to considerable amounts of undesirable HFE and OFP as well as the very toxic PFI

Effects of Four Different Meal Types on the Population Pharmacokinetics of Single-Dose Rifapentine in Healthy Male Volunteers▿

Rifapentine and its primary metabolite, 25-desacetyl rifapentine, are active against mycobacterium tuberculosis. The objectives of this study were to describe the population pharmacokinetics of rifapentine and 25-desacetyl rifapentine in fasting and fed states. Thirty-five male healthy volunteers were enrolled in an open-label, randomized, sequential, five-way crossover study. Participants received a single 900-mg dose of rifapentine after meals with high fat (meal A), bulk and low fat (meal B), bulk and high fat (meal C), high fluid and low fat (meal D), or 200 ml of water (meal E). Venous blood samples were collected over 72 h after each rifapentine dose, and plasma was analyzed for rifapentine and 25-desacetyl rifapentine using high-performance liquid chromatography. Pharmacokinetic data were analyzed by nonlinear mixed-effect modeling using NONMEM. Compared with the fasting state, meal A had the greatest effect on rifapentine oral bioavailability, increasing it by 86%. Meals B, C, and D resulted in 33%, 46%, and 49% increases in rifapentine oral bioavailability, respectively. Similar trends were observed for 25-desacetyl rifapentine. As meal behavior has a substantial impact on rifapentine exposure, it should be considered in the evaluation of optimal dosing approaches