Two topics dealing with adhesion are addressed: an investigation of the cling of thin polymeric films and an analysis of the effects of viscoelasticity on adhesive systems involving curvature mismatch. The results of an investigation into the mechanisms of adhesion and debonding energy associated with the cling between polymeric films and various substrates is presented first. The thermodynamic work of adhesion, electrostatic attraction, and substrate roughness apparently play significant roles in the cling of a film to a substrate. Peel tests are conducted and strain energy release rates are determined which show different debonding energies for the various film-substrate systems. In the analysis of adhesive systems involving curvature mismatch, the focus of the work is on modeling the bond behavior using the solution to the beam on a viscoelastic foundation problem. In addition, the behavior of the adhesive is modeled with a recursive technique using a stress distribution obtained from the solution to the beam on an elastic foundation problem. Debond rate tests are described and conducted so that experimental results may be compared with analytical results. For both adhesion topics, the mechanisms and mechanics of adhesion are considered and experimental tests are conducted. / Master of Science

Social media can trigger past traumatic memories in viewers when posters post sensitive content. Strict content moderation and blocking/reporting features do not work when triggers are nuanced and the posts may not violate site guidelines. Viewer-side interventions exist to help filter and hide certain content but these put all the responsibility on the viewer and typically act as 'aftermath interventions'. Trigger and content warnings offer a unique solution giving viewers the agency to scroll past content they may want to avoid. However, there is a lack of education and awareness for posters for how to add a warning and what topics may require one. We conducted this study to determine if poster-side interventions such as a nudge algorithm to add warnings to sensitive posts would increase social media users' knowledge and understanding of how and when to add trigger and content warnings. To investigate the effectiveness of a nudge algorithm, we designed the TWIST (Trigger Warning Includer for Sensitive Topics) app. The TWIST app scans tweet content to determine whether a TW/CW is needed and if so, nudges the social media poster to add one with an example of what it may look like. We then conducted a 4-part mixed methods study with 88 participants. Our key findings from this study include (1) Nudging social media users to add TW/CW educates them on triggering topics and raises their awareness when posting in the future, (2) Social media users can learn how to add a trigger/content warning through using a nudge app, (3) Researchers grew in understanding of how a nudge algorithm like TWIST can change people's behavior and perceptions, and (4) We provide empirical evidence of the effectiveness of such interventions (even in short-time use). / Master of Science / Social media can trigger past traumatic memories in viewers when posters post sensitive content. Strict content moderation and blocking/reporting features do not work when triggers are nuanced and the posts may not violate site guidelines. Viewer-side interventions exist to help filter and hide certain content but these put all the responsibility on the viewer and typically act as 'aftermath interventions'. Trigger and content warnings offer a unique solution giving viewers the agency to scroll past content they may want to avoid. However, there is a lack of education and awareness for posters for how to add a warning and what topics may require one. We conducted this study to determine if poster-side interventions such as a nudge algorithm to add warnings to sensitive posts would increase social media users' knowledge and understanding of how and when to add trigger and content warnings. To investigate the effectiveness of a nudge algorithm, we designed the TWIST (Trigger Warning Includer for Sensitive Topics) app then conducted a 4-part mixed methods study with 88 participants. Our findings from this study show that nudging social media users to add TW/CW educates them on triggering topics and raise their awareness when posting in the future. It also shows social media users can learn how to add a trigger/content warning through using a nudge app.

No / Introduction: Potential-sensitive dyes have primarily been used to optically record action potentials (APs) in whole heart tissue. Using these dyes to record drug-induced changes in AP morphology of isolated cardiac myocytes could provide an opportunity to develop medium throughout assays for the pharmaceutical industry. Ideally, this requires that the dye has a consistent and rapid response to membrane potential, is insensitive to movement, and does not itself affect AP morphology. Materials and methods: We recorded the AP from isolated adult guinea-pig ventricular myocytes optically using di-8-ANEPPS in a single-excitation dual-emission ratiometric system, either separately in electrically field stimulated myocytes, or simultaneously with an electrical AP recorded with a patch electrode in the whole-cell bridge mode. The ratio of di-8-ANEPPS fluorescence signal was calibrated against membrane potential using a switch-clamp to voltage clamp the myocyte. Results: Our data show that the ratio of the optical signals emitted at 560/620 nm is linearly related to voltage over the voltage range of an AP, producing a change in ratio of 7.5% per 100mV, is unaffected by cell movement and is identical to the AP recorded simultaneously with a patch electrode. However, the APD90 recorded optically in myocytes loaded with di-8-ANEPPS was significantly longer than in unloaded myocytes recorded with a patch electrode (355.6 ± 13.5 vs. 296.2 ± 16.2ms; p< 0.01). Despite this effect, the apparent IC50 for cisapride, which prolongs the AP by blocking IKr, was not significantly different whether determined optically or with a patch electrode (91 ± 46 vs. 81 ± 20 nM). Discussion: These data show that the optical AP recorded ratiometrically using di-8- ANEPPS from a single ventricular myocyte accurately follows the action potential morphology. This technique can be used to estimate the AP prolonging effects of a compound, although di-8-ANEPPS itself prolongs APD90. Optical dyes require less technical skills and are less invasive than conventional electrophysiological techniques and, when coupled to ventricular myocytes, decreases animal usage and facilitates higher throughput assays.

We examined the short-term (1 - 4 years postharvest) effects of 7 silvicultural treatments on terrestrial salamander populations at 4 sites in southwest Virginia and West Virginia. The 3 silvicultural treatments with the most canopy removal (4-7 m2 basal area Shelterwood, Leavetree, Clearcut) had significantly fewer salamanders than the control (p < 0.10) postharvest. No differences were found among treatments in age class distribution, the percent of females that were gravid, or average clutch size. We tested the nighttime, surface-count census method for visibility and behavior-induced bias among silviculture treatments and estimated the proportion of a salamander population that is active on the surface in harvested and control habitats. Instantaneous rates of salamander activity ranged from 1.3 to 11.7% of the population for redback (Plethodon cinereus) and slimy salamanders (P. glutinosus). Timber harvest caused up to a 2-fold increase or decrease in activity rates. There was evidence for bias in the night census method, but differences were not consistent enough to suggest general bias corrections. We also tested whether poorly fed salamanders exhibited risk-sensitive foraging in a dry environment in a laboratory experiment. Poorly fed salamanders were observed out of their simulated burrows less than well fed salamanders suggesting salamanders, particularly females and small adults, are risk-averse. / Master of Science

The wireless technology of today provides combat systems with the potential to communicate mission critical data to every asset involved in the operation. In such a dynamic environment, the network must be able maintain communication by adapting to subsystems moving relative to each other. A theoretical and experimental foundation is developed that allows an autonomous ground vehicle to serve as an adaptive communication node in a larger network. The vehicle may perform other functions, but its primary role is to constantly reposition itself to maintain optimal link quality for network communication. Experimentation with existing wireless network hardware and software led to the development, implementation, and analysis of two main concepts that provided a signal optimization solution. The first attracts the communication ground vehicle to the network subsystems with weaker links using a vector summation of the signal-to-noise ratio and network subsystem position. This concept continuously generates a desired waypoint for repositioning the ground vehicle. The second concept uses a-priori GIS data to evaluate the desired vehicle waypoint determined by the vector sum. The GIS data is used primarily for evaluating the viewshed, or line-of-sight, between two network subsystems using elevation data. However, infrastructure and ground cover data are also considered in navigation planning. Both concepts prove to be powerful tools for effective autonomous repositioning for maximizing the communication link quality. / Master of Science

No / In support of the increasing number of elderly population, wearable sensors and portable mobile devices capable of monitoring, recording, reporting and alerting are envisaged to enable them an independent lifestyle without relying on intrusive care programmes. However, the big data readings generated from the sensors are characterized as multidimensional, dynamic and non-linear with weak correlation with observable human behaviors and health conditions which challenges the information transmission, storing and processing. This paper proposes to use Locality Sensitive Bloom Filter to increase the Instance Based Learning efficiency for the front end sensor data pre-processing so that only relevant and meaningful information will be sent out for further processing aiming to relieve the burden of the above big data challenges. The approach is proven to optimize and enhance a popular instance-based learning method benefits from its faster speed, less space requirements and is adequate for the application.

This dissertation addresses critical challenges in forest management and restoration in the Lower Mississippi Alluvial Valley (LMAV) through a series of interconnected studies focused on improving habitat suitability modeling and growth prediction for oak species. The research employs advanced modeling techniques to enhance our understanding of species-habitat relationships and forest dynamics in the context of climate change. Initial studies focused on developing ensemble habitat suitability models for American chestnut (Castanea dentata) and butternut (Juglans cinerea), two historically important but currently threatened tree species. These models predict suitable habitats and potential range shifts under various climate change scenarios, highlighting the species' vulnerabilities and informing conservation strategies. Building on these approaches, the research expands to model habitat suitability for eight key oak species in the LMAV. This multi-species analysis reveals both shared and distinct ecological requirements among the oak species, providing valuable insights for targeted restoration efforts. Niche overlap analysis further elucidates potential species interactions and habitat partitioning within the region. The dissertation culminates in the development of improved climate-sensitive growth and yield models for bottomland oaks. By incorporating habitat suitability predictions as a modifier, these models demonstrate significantly enhanced accuracy compared to traditional approaches. This integrated modeling framework offers a more comprehensive understanding of oak growth dynamics under changing environmental conditions. Throughout the research, the importance of key environmental drivers, such as temperature, precipitation, and soil characteristics, is consistently highlighted. The studies also underscore the potential impacts of climate change on species distributions and forest composition in the LMAV. This research contributes to the advancement of forest modeling techniques and provides practical insights for sustainable forest management, conservation of threatened species, and climate change adaptation strategies. The findings have important implications for decision-making in forestry and conservation, particularly in the LMAV but with potential applications to other regions. Future research directions are suggested, including the use of higher-resolution datasets and validation across diverse ecosystems to further improve model applicability and accuracy.

Silicon photon multipliers, or SiPMs, are single photon detectors that have grown increasing interest in the last decade as an alternative to photomultiplier tubes in many field of physics, engineering and medicine. Compared to PMTs, SiPMs are more compact, rugged and operate at much lower bias voltage, in the order of tens of volts. Moreover they are insensitive to magnetic field and can achieve a very high radiopurity SiPM detectors work on the principle of a diode operated above the breakdown voltage, in Geiger mode. In this condition, the electric field in the depletion region is high enough that the electron-hole pairs, generated by a single photon absorption through photoelectric effect, create secondary charges by impact ionization in a potentially diverging avalanche effect that can be exploited to generate a macroscopical current at the output of the diode. Thanks to this effect, the SiPM is capable of counting the number of impinging photons down to single photon level. Noise sources in the SiPM include dark counts and correlated noise. Dark counts are counts happening when an electron-hole pair is generated in the active volume of the device in absence of photon absorptions. These events are caused either by thermal generation, diffusion from the neutral region or by tunnel effect. Correlated noise events, or counts, on the other hand, are generated when a primary firing cell retriggers after a certain time or cause the triggering of another cell. All these noise sources introduce errors in the photon count by adding fake events to the output signal of the detector.Traditional SiPM application is 511 keV gamma-ray detection in PET machines, using scintillator LYSO crystals to convert a single gamma ray into a flash of visible photons. An application based on the same principle was studied in this thesis by coupling FBK RGB-HD SiPMs with CsI:Tl crystals in order to detect lower energy X and gamma-rays. This setup has proven to be effective in the detection of radiation with energy as low as 5.9 keV with a resolution of 38.3%, which is the minimum value of energy resolution measured with SiPMs coupled to scintillator crystals at such low energy. At the same time it was observed that large area detectors provided a dynamic range wide enough to simultaneously detect radiation ranging from 6.4 keV to 122 keV with minimal saturation. In another activity of this thesis it was developed a simulation software that reproduces the behaviour of a SiPM under different light conditions by taking into account the detector efficiency, the dead time and the recharge behaviour of its cells and theoretical modelizations of the noise parameters that affect the measurement. From a given light profile the simulation generates a waveform that reproduces the one measured during the operation of real SiPMs. This waveform was then analysed using FBK software developed for SiPM characterization and the results showed an excellent agreement between the simulated detector and a reference SiPM. This software will become a useful tool for the design of SiPMs for future experiments because it will allow to tune the properties of the detectors to specific applications and it will reduce the need of layout and process split to find the optimal configuration of the detector parameters.Among all FBK technologies, this work was focused on the position-sensitive LG-SiPM. Unlike standard SiPMs, which have a single output, the LG-SiPM employs a more complex structure that splits the current signal into four output channels with ratios depending on the position of the impinging light on its surface. Center of mass calculations are used to reconstruct the position of the firing cell with precision down to some tens of microns while maintaining the fast time response of SiPMs. An application of the LG-SiPM was studied in the framework of the ARIADNE experiment in collaboration with the university of Liverpool. In this work the LG-SiPM was used to detect scintillation light coming from ionization tracks generated by alpha particles inside a CF4 TPC chamber. The ionized electrons where drifted through the action of a high electric field in the TPC towards a THGEM where they created light with timing depending on the distance of each track segment from the scintillator. The LG detector was able to reconstruct the 3D track particle inside the chamber with an error below 8 mm RMS inside the 40 l chamber and, at the same time, to reconstruct the energy released by the particle as function of time and calculate the total energy of the interacting particle and its linear energy transfer. These results open a novel approach for the TPC position reconstruction that combines the low number of readout channels needed for the LG detector to its time-continuous response which allows to reconstruct the tree-dimensional track of a particle inside the chamber.During the experiment it emerged the presence of an artifact that drifted all the reconstructed tracks towards the centre of the detection area, at the end of the signal. This effect was studied by creating a second simulation software that recreates the electrical behaviour of the LG-SiPM equivalent circuit when one or more cells trigger. It was simulated the output of the circuit with different light conditions and different values of the circuit elements and it was observed that the presence of the artifact was related to low intensity currents flowing through the net of the LG-SiPM metal tracks and quenching resistors. Several simulations were run in order to identify the optimal configuration of parameters for the reduction of this unwanted effect and to implement improvements in future LG-SiPM productions.Another application of the LG-SiPM in the field of radiation detection is the position reconstruction of the scintillation light emitted by gamma-rays in a monolithic crystal. Using a thin CsI:Tl crystal and lowering the detector temperature it was possible to distinguish different positions of interaction on the surface of the detector with an error below 1 mm FWHM. This technology can be effective for the creation of monolithic, position sensitive X and gamma-ray detector with good energy resolution for low energy spectroscopy or medical imaging devices.

This study investigates the awareness and ability of students at the University of North Texas (UNT) in securing their personal and sensitive information on mobile phones. In an era marked by increasing digitization, mobile phones play a pivotal role in our daily lives, making it essential to understand the practices and knowledge of individuals when it comes to safeguarding their personal information. To achieve this, the study adopts a multidimensional approach through the integration of three prominent theoretical frameworks, which are the technology acceptance model (TAM), the theory of planned behavior (TPB), and protection motivation theory (PMT). This integrated framework enables a comprehensive understanding of student perceptions, intentions, and motivations concerning mobile phone security. To gather data, a quantitative research method was employed, using a structured survey in the form of a questionnaire. Respondents were asked to rate their agreement with various statements using a 5-point Likert scale, ranging from 1 = strongly disagree to 5 = strongly agree. The survey included questions designed to assess student awareness, knowledge, attitudes, and behaviors related to securing personal information on their mobile phones. The findings of this study shed light on the existing gaps in the knowledge and practices of students related to mobile phone security. The outcomes can inform educational institutions and policymakers on the necessity of implementing awareness programs and security measures to protect personal information in the digital age. This research contributes to a deeper understanding of mobile phone security practices and paves the way for potential interventions to empower UNT students and users of mobile technology to protect their sensitive data effectively.

Methamphetamine (METH) abuse has become a fast growing drug problem that has developed into a global epidemic. In fact, METH is one of the most commonly abused substances with an estimated 35 million abusers worldwide and is said to be the second most popular illicit drug. The Western Province of South Africa has seen a dramatic increase in drug abuse in recent years where METH is the primary or secondary drug of abuse. Interestingly, more than 50% of these individuals are under the age of 20 years. The longer duration of euphoric effects of METH has attracted many users away from cocaine in favour of METH. In addition to the rapid euphoric effect of METH, the direct short-term effects include arousal, reduced fatigue, an increase in blood pressure, reduced appetite as well as sustained attention. Chronic METH abuse may result in debilitating and long-lasting effects that includes mood disorders such as depression. Studies suggest a strong relationship between exposure to adverse environmental factors early in life and the later development of a neuropsychiatric disorder, such as depression. However, these severe consequences do not seem to invoke cessation of the drug. The euphoric and addictive properties of METH causes users to abuse the drug with an increase in frequency and dose, even though it might not have been their original intention. The primary objective of this study was to investigate the effect of early-life administration of METH to stress-sensitive (Flinders Sensitive Line - FSL) and control (Flinders Resistant Line - FRL) rats on depressive-like behaviour and regional brain monoamine levels later in life. The study implemented a sixteen-day period for administration of METH or a vehicle control from postnatal day 19 (PnD19) to postnatal day 34 (PnD34). The latter developmental stage corresponds to pre-adolescence in the rat when neurological development are similar to that seen in human adolescents, and represents the stage when drug abuse is most common in humans. Chronic dosing of METH and saline was performed twice daily at 09:00 and at 15:00. The animals received a sub-cutaneous (SC) escalating dose regimen of METH during the 16 day period (mimicking binging behaviour in humans), with every dose escalating in increments of 0.2 mg/kg from 0.2 mg/kg to 6.0 mg/kg. The study then investigated whether early-life administration of METH would cause depressive-like behaviours directly after the injection period (immediate drug effects before withdrawal on PnD35) or later in life (after the withdrawal period in early adulthood on PnD60). The behavioural effects were assessed in a battery of tests and thereafter the rats were sacrificed and the frontal cortex removed and snap frozen for later analyses of altered neurochemistry. The study demonstrated that chronic METH treatment during pre-adolescence induces significant behavioural changes related to depression in humans directly after the injection period (PnD35) and later in life (PnD60). The animals displayed antidepressant-like behaviour in the forced swim test (FST) before withdrawal, yet a depressogenic effect was observed 25 days post-withdrawal. This effect also seems to be additive to the congenital depressive-like phenotype of FSL rats, suggesting a role for genetic susceptibility. This observation would be in line with the two-hit hypothesis of depression, suggesting that the manifestation of depression will result when a genetic predisposition is followed by an environmental stressor (i.e. METH) later in life. The data suggests a working hypothesis that individuals that already have a predisposition to depression may be more susceptible to developing depression when abusing METH. The fact that the FSL control rats were more immobile than FRL control rats also confirmed the face validity of the FSL genetic rat model of depression. Locomotor activity assessment indicated that METH treatment decreased locomotor activity in FSL and FRL rats compared to their vehicle controls on PnD35 but not on PnD60. It is important to note that the effects observed in locomotor activity could not have contributed to the immobility observed in the FST, confirming that the immobility in the FST indeed reflects psychomotor and not locomotor effects. The study also demonstrated that METH significantly lowers social interaction behaviour in both FRL and FSL rats, both immediately following drug treatment (PnD35) and after withdrawal (PnD60). It is therefore clear that this effect of METH is long-lasting, putatively related to neurodevelopmental effects. In addition, the rats investigated the familiar object for a greater amount of time in the novel object recognition test (nORT) on PnD35 and PnD60 and may be the result of loss of recognition memory for the familiar object. This data confirms that METH results in cognitive memory deficits probably due to sustained adverse neurodevelopmental effects. Neurochemical analyses of the frontal cortex indicated decreased serotonin (5-HT) and norepinephrine (NE) levels on PnD35. METH is widely recognised for its pro-inflammatory effects, while the reduced 5-HT levels observed may have been the result of an increase in circulating pro-inflammatory cytokines. Neurochemical analyses provided thought-provoking data concerning the role of the permissive hypotheses of depression, indicating that dopamine (DA) is most likely not responsible for the behavioural effects observed, at least under the current study conditions, whereas 5-HT is decidedly more involved than expected. The data also suggest that depletion in NE plays a role in the development of depressive-like behaviours following METH exposure. Based on these findings, we propose that disturbances in 5-HT and NE are a crucial mechanism in how METH abuse may precipitate or worsen depressive-like symptoms in individuals who abuse METH. It should be noted that this study does not discard the role of DA in the development of depression after METH exposure, although under the current study conditions it appears that DA does not play a central role. The current study demonstrated that pre-adolescent exposure to METH can reproduce most of the behavioural changes seen in depressed individuals, and that these behavioural data can be used to identify causal neurochemical factors. Environmental stressors such as METH abuse should be regarded as an additional diagnostic criterion and is relevant to an accumulative risk factor hypothesis. Furthermore, although further study is required, the data suggests that early-life exposure to METH may predispose an individual to mood disorders and behavioural abnormalities later in life. / MSc (Pharmacology), North-West University, Potchefstroom Campus, 2015