Statistical azimuthal structuring of the substorm onset arc: Implications for the onset mechanism

The onset of an auroral substorm is generally thought to occur on a quiet, homogeneous auroral arc. We present a statistical study of independently selected substorm onset arcs and find that over 90% of the arcs studied have resolvable characteristic spatial scales in the form of auroral beads. We find that the vast majority (~88%) of auroral beads have small amplitudes relative to the background, making them invisible without quantitative analysis. This confirms that auroral beads are highly likely to be ubiquitous to all onset arcs, rather than a special case phenomena as previously thought. Moreover, as these auroral beads grow exponentially through onset, we conclude that a magnetospheric plasma instability is fundamental to substorm onset itself

Statistical characterisation of the growth and spatial scales of the substorm onset arc

We present the first multi-event study of the spatial and temporal structuring of the aurora to provide statistical evidence of the near-Earth plasma instability which causes the substorm onset arc. Using data from ground-based auroral imagers, we study repeatable signatures of along-arc auroral beads, which are thought to represent the ionospheric projection of magnetospheric instability in the near-Earth plasma sheet. We show that the growth and spatial scales of these wave-like fluctuations are similar across multiple events, indicating that each sudden auroral brightening has a common explanation. We find statistically that growth rates for auroral beads peak at low wavenumber with the most unstable spatial scales mapping to an azimuthal wavelength λ≈1700 − 2500 km in the equatorial magnetosphere at around 9-12 RE. We compare growth rates and spatial scales with a range of theoretical predictions of magnetotail instabilities, including the cross-field current instability and the shear-flow ballooning instability. We conclude that, although the cross-field current instability can generate similar magnitude of growth rates, the range of unstable wavenumbers indicates that the shear-flow ballooning instability is the most likely explanation for our observations

Effects of Phenanthrene, A Polycyclic Aromatic Hydrocarbon on Zebrafish (Danio Rerio) Early Development

Polycyclic Aromatic Hydrocarbons (P AH) are ubiquitous environmental contaminants released from different sources such as forest fires and ocean oil seeps, as well as land based runoff and creosote. These sources of P AHs are both natural and anthropogenic. Some P AHs have been known to be carcinogenic and mutagenic. In this project, the effects of phenanthrene, a P AH compound. on early embryogenesis involving somitogenesis (development of somites) were studied using zebrafish (Danio rerio) early embryos as an experimental system. The developmental stage relevant to this project was the segmentation stage, during which time somites develop. In early embryos, somite patterning is under the influence of Wnt signaling. Although the process of somitogenesis remains to be fully understood, the "clock and wavefront" model is widely accepted and the process involves a variety of cellular and molecular interactions. This research shows the developmental stage specific effects of phenanthrene on somitogenesis. Other developmental abnormalities due to phenanthrene exposure were also noticed and documented; these abnormalities included pericardiallyolk sac edema and scoliosis. Embryos treated at 2 hours post fertilization (hpt) were most sensitive to phenanthrene exposure and displayed abnormal development of somites and showed a decreased total somite number. Embryos treated at 8 and 12 hpf did not show such abnormalities, suggesting there is a critical time in development when somitogenesis is most affected by phenanthrene. Involvement of the Wnt signaling pathway in somitogenesis with an apparent increase in nuclear ~-catenin was tested through pharmacological and immunological studies. l-Azakenpaullone, an inhibitor of Glycogen Synthase Kinase-3~ (GSK-3~), was used to target a specific step in the pathway. The results from embryos exposed to this inhibitor were similar to embryos exposed to phenanthrene. Immunostaining of embryos exposed to both compounds reveals nuclear accumulation of ~-catenin, suggesting that phenanthrene may be causing abnormalities by disrupting a specific step in the Wnt signaling pathway. Preliminary Western blot analysis using antibodies to phosphorylated forms of GSK-3~ (anti-Ser 9GSK-3~) also supports this notion.Kalmoni, Rana. 2010. Effects of Phenanthrene, A Polycyclic Aromatic Hydrocarbon on Zebrafish (Danio Rerio) Early Development. Department of Biology, Sonoma State University

What effect do substorms have on the content of the radiation belts?

Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently energized through wave-particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1–3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM-H, but decreases in the radiation belt show no apparent link with magnetospheric activity levels

Statistical azimuthal structuring of the substorm onset arc: implications for the onset mechanism

The onset of an auroral substorm is generally thought to occur on a quiet, homogeneous auroral arc. We present a statistical study of independently-selected substorm onset arcs and find that over 90% of the arcs studied have resolvable characteristic spatial scales in the form of auroral beads. We find that the vast majority (~88%) of auroral beads have small amplitudes relative to the background, making them invisible without quantitative analysis. This confirms that auroral beads are highly likely to be ubiquitous to all onset arcs, rather than a special case phenomena as previously thought. Moreover, as these auroral beads grow exponentially through onset, we conclude that a magnetospheric plasma instability is fundamental to substorm onset itself

What effect do substorms have on the content of the radiation belts?

Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently energized through wave-particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1–3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM-H, but decreases in the radiation belt show no apparent link with magnetospheric activity levels

Exploring Liberal Arts Education: Unveiling the African Perspective

This is a dynamic magazine which details the African perspective and context of liberal arts education. This magazine captures different community members\u27 stories and experiences across diverse institutions. It also includes quotes, and research articles under core themes

Semi-autonomous agricultural crop sprayer for medium-scale farms in Ghana

Group Capstone Project submitted to the Department of Engineering, Ashesi University in partial fulfillment of the requirements for the award of Bachelor of Science degree in Mechanical Engineering, May 2022Most small-scale farmers in Ghana that have transitioned into medium-scale farming are currently using lever-operated Knapsacks for fertilizer/pesticide application. For farm sizes above five hectares, it becomes inefficient and labour intensive, resulting in health issues. Efficient methods like drones and tractors are expensive. Hence, the need to design and fabricate a cost-effective, semi-autonomous sprayer with low labour intensity. This project designs and fabricates a mechanical system equipped with a nozzle and navigation control system. The nozzle system turns the nozzles on and off and directs the crop sprayer via Bluetooth. The nozzle control system also has flow sensors that measure the flow rate from each nozzle. Results obtained from testing the system show that the on and off control of one nozzle increases the flow rate in the other nozzle, which can be attributed to an increase in pressure. Also, the cost of automating the system is cost-effective for medium-scale farmers. The system was able to control the nozzles for potential savings for farmers while reducing manual labour.Ashesi Universit

The role of magnetospheric plasma instabilities in auroral and substorm dynamics

The auroral substorm is the manifestation of explosive energy release from the rapid and global reconfiguration of the magnetotail. The auroral substorm is marked by a sudden brightening and poleward expansion of the most equatorward auroral arc in the midnight sector of the ionosphere. The temporal sequence of magnetospheric processes which lead to the dynamic auroral substorm display remain disputed to this day. This thesis contains original research on the development and exploitation of novel data analysis techniques in order to analyse ground-based all sky imager data of the aurora, enabling the study of substorm processes in remarkable detail. Fourier analysis techniques are used to find the spatial scales of wave-like signatures (otherwise known as auroral beads/rays), which form along substorm onset arcs. Growth rates of ∼0.05 s⁻¹ are found from the exponential growth of the power spectral density of individual spatial scales. By analysing the dataset in this way, comparisons are made between observations and theoretical predictions of plasma instabilities at the near-Earth edge of the plasma-sheet which have been proposed to play a critical part in the substorm onset process. Auroral arc tracking techniques are developed to automate and increase the size of the database of events analysed. The vast majority of independently identified substorm onsets are preceded by azimuthal structuring along the onset arc with median wavelengths of ∼80 km. These beads grow and develop into a magnetospheric instability around 2 minutes prior to auroral substorm onset. Showing that beads are a common feature along the substorm onset arc provides unprecedented quantitative evidence that a near-Earth instability is a fundamental component of the substorm onset process. Finally, analysis techniques are extended to state-of-the-art high resolution multi-spectral auroral data to investigate the processes driving auroral beads. Beads can be resolved in the green-, blue- and red-line aurora with spatial scales as small as 30 km, which later develop into larger structures of ∼80 km. These observations are consistent with Alfvén wave accelerated auroral particle precipitation and therefore imply that the substorm onset arc and auroral beads are driven unstable by waves