Search results

In the Earth’s upper atmosphere, damage to satellite electronics is caused by exposure to extreme ultraviolet (EUV) radiation. One particular region where this type of radiation occurs is the South Atlantic Magnetic Anomaly region. As a result, there is a need to design and develop a sensor which could be used to investigate the flux and energy levels of radiation in this region. To do so, the aim of this study is to characterise the sensor and its electric response to typical EUV radiation levels based on the photoelectric effect principle.

For this purpose, a copper plate planar sensor prototype with dimensions that fit on the sides of a one-unit (1U) CubeSat was constructed. The sensor prototype was placed in a vacuum chamber and was subjected to continuous radiation from a vacuum ultraviolet deuterium light source at test facilities available in the Western Cape region (South Africa). Subsequently, the terminal voltage of the sensor was measured and compared with theory.

The measured time-averaged terminal voltages indicate the generation of photocurrents of the order of 1 μA, which is consistent with theory.

Conclusively, these results validate the measurement approach and operation of the sensor, which can be used to design a 1U CubeSat sensor that measures EUV radiation in low Earth orbit.

In recent decades, the use of capital punishment has declined, but in its place, a ‘new death penalty’ has arisen: life without parole (LWOP), which is being used far more frequently and for more crimes than capital punishment ever was. Yet, LWOP has received far less scholarly attention than the death penalty. Because of its greater scale, assessing the effects of LWOP on crime has important policy implications and is a better test of extreme penalties. Existing studies of LWOP focus on humanitarian issues and ignore its potentially reciprocal relationship with crime. Therefore, we use available LWOP data to fill these gaps in the literature, using models specifically designed to control for potential reciprocal effects. The results indicate there is no reciprocal causation between LWOP and violent crime and, at best, LWOP’s impact on crime is small, temporary, and, most importantly, no greater than the impact of life with parole.

Incorporating electromagnetic compatibility (EMC) in the design life of traditional satellites is entrenched in the satellite industry. However, EMC treatment of CubeSats has not been widely pursued, for various possible reasons. CubeSats are a young technology platform initially intended for students and researchers at universities to create awareness and excitement amongst them for space technology. This and other factors limited the need for stringent EMC planning. As CubeSats mature in complexity, the success of future missions will rely on incorporating proper EMC designs in their development. This paper aims to address the experimental investigation of known EMC culprits within a CubeSat’s context.

Electromagnetic interference suppression effectiveness of cable trays in CubeSats, as well as crosstalk in high-speed/frequency data links, is investigated, using the PC/104 connector stack. Some recommendations for improving the EMC and, therefore, enhancing satellite mission success are provided.

It was found that, if physically feasible in the CubeSat, cable trays are significant radiation suppressors. A further investigation into crosstalk between pins of the PC/104 connector stack showed that grounding a pin in between two signal pins leads to a significant reduction in the coupled signal.

This paper addresses EMC within the context of a CubeSat and outlines experiments done resulting in cost-effective methods of reducing interference by using already available material (such as unused signal pins available in the PC/104 connector).

This chapter reconstructs and critically examines the recent history of strip searches in Belgium. About 10 years ago the Belgian parliament adopted its first law on prisoners’ rights. A major part of the Prison Act of 12 January 2005 deals with disciplinary and control measures. Article 108, in particular, has provoked quite some controversy. It introduced a clear distinction between the (more superficial) search of an inmates’ clothes on the one hand, and the (substantially more intrusive) measure of strip searching on the other hand. The main difference between these two measures is that the latter involves forcing prisoners to strip naked. Because of their intrinsic intrusiveness, such strip searches were meant to be exceptional measures: they should only take place following an individual assessment and decision by the prison governor. In practice, however, the prison administration tended to interpret Article 108 somewhat differently and the line between searching an inmate’s clothes on the one hand and strip searching on the other became blurred.

I first discuss the problem of order in prisons and explore how strip searches have been regulated in Europe. I then reconstruct the recent history of the regulation of strip searches in Belgium. In order to make sense of this history, I mobilize some of the ideas of Stanley Cohen’s sociology of denial, in particular, his distinction between literal, implicatory and interpretive denial, and apply these to the history of strip searches in Belgium.

A consistent finding from this chapter is that the Belgian prison administration has – through creative manoeuvres of interpretive denial – been able to circumvent the new barriers that were erected by the Prison Act of 12 January 2005 and, in doing so, it has been able to continue stripping detainees naked without an individualized decision from the prison governor. The approach that I develop throughout this chapter helps us better appreciate the limits of legal reform and top-down (European) regulation of strip searches.

The chapter demonstrates that Stanley Cohen’s work on denial is not only useful for scholars who do research on gross human rights violations but also for interpreting more down-to-earth aspects of criminal justice systems across the globe.

This paper aims to report the modelling and simulation work that predicts the behaviours of both a Josephson junction (JJ) and a dc superconducting quantum interference device (SQUID). It is pertinent to predict the SQUID magnetometers’ behaviours via simulations, before subjecting them to real experiments because they are quite expensive to acquire, and can be easily damaged during test analysis.

To achieve this, power simulation (PSIM) was used to model and simulate a JJ, using the basic equation that describes the effective current through it. A dc SQUID magnetometer, which is composed of two JJs, was then modelled and simulated using the modelled JJ. Thermal noise simulation is also included, to observe its effects on the magnetometer’s output. A directly coupled flux-locked loop circuit was later included in the simulation to amplify and linearise the SQUID’s output, which is usually sinusoidal.

When steady bias currents were applied to the JJ, the resulting voltage across it was seen to oscillate. The JJ’s and SQUID’s voltage–current characteristics, and voltage–flux characteristics were also observed in the simulations, and the results respectively agree with the behaviours of a typical JJ and dc SQUID magnetometer.

A way of simulating SQUIDs, without a superconducting simulation tool, is presented. The work provides a much simpler way of studying the behaviour of dc SQUID magnetometers, due to the easy accessibility and fast simulation capability of the software used, with an added advantage of being able to simulate the thermal noise effects, without having to import this facility from secondary software.

The purpose of this paper is to design, build and test a low power high frequency (HF) transmitter that can be received by the Super Dual Auroral Radar Network (SuperDARN) radar installed at SANAE IV, the 4th South African National Antarctic Expedition Station. It is proposed that it may be possible to do propagation studies using the radar and the fixed frequency, ground-based HF transmitter beacon. Interpretation of the measurements can be used to study the ionosphere, especially Travelling Ionospheric Disturbances, which are signatures of atmospheric gravity waves.

In the absence of the actual deployment of the HF transmitter beacon in Antarctica, extensive simulations have been done to evaluate the expected performance of the transmitter in relation to the SuperDARN. A field trial has been executed between Hermanus (34.4241° S, 19.2247° E) and Pretoria (34.0558° S, 18.4589° E) in South Africa. In future, the beacon will be placed at the South Pole with its antenna radiating towards SANAE IV.

The HF transmitter conforms to the power and frequency stability requirements both during propagation tests conducted between Hermanus and Pretoria, as well as when the device was exposed to temperatures that ranged from +40°C to −45°C in a thermal chamber. Propagation in Antarctica is expected to differ from the field tests conducted due to the differences in density and dynamics of the polar ionosphere, compared to the mid-latitude ionosphere.

Space weather research, including forecasting atmospheric gravity waves and determining the expected electron density profile of the ionosphere, is of great scientific interest. The data received from the HF beacon can be used to study and characterize the ionosphere of the region between the South Pole and SANAE IV. Parameters of the ionosphere, such as electron density, geomagnetic storm effects, ionospheric motions and sky wave propagation paths will be better understood from analysing the signal received from this transmitter after it has been reflected and refracted by the ionosphere.

Proceeding from the van Rensburg and Priilaid (“An econometric model for identifying value in South African red wine”, International Journal of Wine Marketing, Vol. 16 No. 1, 2004, pp. 37‐53) econometric valuation methodology mapping out the relationship between wine price and value, this paper seeks to explore the relationship between wine value and value‐for‐money.

A series of regression models are developed from a database of some 537 South African red wines available during the 2004 period. Five cultivars are included here: cabernet, merlot pinotage, pinot noir, and shiraz.

This research finds that successive increments in wine quality ratings are not equally priced. As a result, the relationship between value and price can be better modelled when increments in wine quality (as measured in stars) are proxied by dummy variables.

Allowing for the possibility of the non‐linear hedonic pricing of wine avoids the bias of value‐for‐money misleadingly being identified excessively at the bottom end of the quality spectrum and neglected at the top end.

Distributed wireless sensor networks (DWSNs) are applied in a variety of applications that can enhance the quality of human life. Batteries are the predominant source of energy in DWSNs. One of the key obstacles in the adoption of DWSNs technology is the limited lifetime of batteries in microsensors. Recharging or replacing depleted batteries can significantly increase costs in DWSNs. The purpose of this paper is to address, through a thorough review, this power challenge in DWSNs and to evaluate a 16‐element equiangular spiral rectenna to harvest ambient microwave energy in real‐life scenarios to supply indoor DWSNs.

The paper focuses on the practical implementation of a rectenna that can be used in electromagnetic energy harvesting. The design and measurement of the rectenna follows a broad overview of rectenna designs reported in the literature.

The paper concludes that the 16‐element equiangular spiral rectenna has the potential to generate power that enables long periods of operation of the DWSNs without human intervention in the power management process, thus reducing maintenance and administration costs.

Research into electromagnetic power harvesting is very limited in the South African context. The paper presents a concise overview of existing power harvesting techniques that will benefit novice researchers in the field of electromagnetic energy harvesting. It concludes with the performance characterisation of a spiral array rectenna.

The purpose of this work is to assess the influence of ambient noise on the performance of wireless sensor networks (WSNs) empirically and, based on these findings, develop a mathematical tool to assist technicians to determine the maximum inter-node separation before deploying a new WSN.

A WSN test platform is set up in an electromagnetically shielded environment (RF chamber) to accurately control and quantify the ambient noise level. The test platform is subsequently placed in an operational laboratory to record network performance in typical unshielded spaces. Results from the RF chamber and the real-life environments are analysed.

A minimum signal-to-noise ratio (SNR) at which the network still functions was found to be of the order 30 dB. In the real-life scenarios (machines, telecommunications and computer laboratories), the measured SNR exceeded this minimum value by more than 20 dB. This is due to the low ambient industrial noise levels observed in the 2.4 GHz ISM band for typical environments found at academic institutions. It, therefore, suggests that WSNs are less prone to industrial interferences than anticipated.

A predictive mathematical tool is developed that can be used by technicians to determine the maximum inter-node separation before the WSN is deployed. The tool yields reliable results and promises to save installation time.