Work is focused on computer modeling of PN junction and MOSFET transistor in the program COMSOL Multiphysics and in program TiberCAD. The text is discussed on the drift and diffusion in semiconductors. Also shown is a method of modeling the PN junction and MOSFET transistor in the programs and compare models.

This master's thesis deals with knowledge discovery and is focused on data stream classification. Three ensemble classification methods are described here. These methods are implemented in practical part of this thesis and are included in the classification system. Extensive measurements and experimentation were used for method analysis and comparison. Implemented methods were then integrated into Malware analysis system. At the conclusion are presented obtained results.

L’homme est un animal social. La majorité des décisions que nous prenons se font dans un contexte social et dépendent d’autrui, ce qui implique des calculs cérébraux complexes qui incluent tous les facteurs contextuels et environnementaux. La majorité des études ultérieures de la prise en compte d’autrui dans la décision ont utilisé des tâches de partage de récompenses entre soi et autrui. Les choix possibles amènent le décideur à considérer autrui, mais dans le but de gagner soi-même une récompense ; donc dans un contexte où les récompenses liées à soi et les récompenses liées à autrui sont confondues. Le travail présenté dans cette thèse avait pour but une meilleure compréhension des mécanismes cérébraux soutenant l’intégration d’autrui dans la prise de décision, sans que la récompense pour autrui n’interfère directement avec soi. Nous nous sommes appuyés sur le cadre théorique de la décision perceptuelle et des modèles de diffusion pour l'étude i) des modifications du processus décisionnel induites par une récompense monétaire allant à autrui et ii) de l’impact de l’effet d’audience (le fait de se sentir observé) sur la décision. Nos résultats computationnels montrent qu'une récompense pour autrui, par rapport à une récompense pour soi, et une audience, par rapport au secret, modifient le taux de dérive de la variable de décision. En magnétoencéphalographie, nos résultats indiquent que les décisions pour soi et pour autrui diffèrent pendant, mais aussi après, la prise de décision dans des zones cérébrales associées avec la transformation sensori-motrice, l'ajustement du compromis entre rapidité et justesse et avec la cognition sociale. Ainsi, le cortex temporal montre des différences de -1170 millisecondes (ms) à -1023 ms, de -993 ms à -915 ms et de -343 ms à -188 ms en amont de la réponse. Ce qui suppose une influence sur l’intégration des preuves sensorielles. Après la décision, les régions frontales ont également montré des différences entre soi et autrui, de 153 ms à 303 ms post-réponse, suggérant une différence entre soi et autrui dans l’ajustement du compris entre justesse et rapidité. Le bénéficiaire de la récompense associée à la décision modifie les paramètres décisionnels et les corrélats cérébraux de la décision perceptuelle, démontrant l’importance du contexte social dans l’implémentation de la prise de décision chez l’Homme. Ce travail appuie également l’utilité des modèles mathématiques tels que les modèles de diffusion dans la compréhension des processus décisionnels, même de ceux découlant de la cognition sociale / Humans are inherently social: most of human’s decisions are within a social context and depend on others. For more than a century, researchers explore aspects of social cognition. Aiming to understand human behavior in social contexts, neuro-economic researches showed that taking others into account involve complex brain computations that include all environmental and contextual factors. However, most of the work was made using money allocation tasks; mixing self-affecting and other-affecting rewards into the decision making process. The present work intended the understanding of the brain mechanisms underpinning the integration of others into the decision making process for decisions that include others and do not interfere with self-rewards.Taking advantage of mathematical models from the drift diffusion models framework, we conducted experiments investigating how others influence the mechanistic of perceptual decisions and their correlates in the human brain. We showed that taking rewards for others into account and being observed by others influence the drift rate of the decision variable. The drift rate is higher in audience than in secret and higher for self-rewards than for other-rewards. These results indicate that others are integrated into the accumulation process together with the evidence available for making a decision. At the brain level, we found difference between self and other decisions over the anterior temporal and centro-frontal cortices during decision making. This suggests that the beneficiary of a decision modifies sensory-motor transformation processes. In addition, self- and other-affecting difference showed difference over the medial frontal sensors after the decision making process, indicating a variation in the speed-accuracy tradeoff adjustment process

This thesis describes development of the new selected ion flow-drift tube mass spectrometry technique, SIFDT-MS, for online quantification of volatile organic compounds, VOCs, based on gas phase ion-molecule reactions. SIFDT-MS represents a new generation of the successfully used selected ion flow tube, SIFT- MS, analytical method. The essential extension of SIFDT-MS is the uniform electric field E applied across the flow tube reactor, thus converting it to the flow-drift tube where the ion processes can be governed by strength of field E. Newly introduces Hadamard modulation of the gate lens before the flow-drift tube enables direct ion residence, and correspondently ion-molecule reaction, time measurement that is necessary for the precise concentration calculations under variable conditions. The detailed experimental study of these processes results was carried out to form a basis of the analytical method. In order to overcome a well-known issue of SIFT-MS, when mass spectral peaks of isobaric ions overlap, the pseudoinverse matrix multiplication for isobaric mixtures was demonstrated. Finally two data mining approaches were successfully tested on the data of the fragmentation signals of seven monoterpene isomers obtained in SIFT-MS.

Streamed data classification problems (SDCPs) require classifiers with the ability to learn and to adjust to the underlying relationships in data streams, in real-time. This requirement poses a challenge to classifiers, because the learning task is no longer just to find the optimal decision boundaries, but also to track changes in the decision boundaries as new training data is received. The challenge is due to concept drift, i.e. the changing of decision boundaries over time. Changes include disappearing, appearing, or shifting decision boundaries. This thesis proposes an online learning approach for feed forward neural networks (FFNNs) that meets the requirements of SDCPs. The approach uses regularisation to optimise the architecture via the weights, and quantum particle swarm optimisation (QPSO) to dynamically adjust the weights. The learning approach is applied to a FFNN, which uses rectified linear activation functions, to form a novel SDCP classifier. The classifier is empirically investigated on several SDCPs. Both weight decay (WD) and weight elimination (WE) are investigated as regularisers. Empirical results show that using QPSO with no regularisation, causes the classifier to completely saturate. However, using QPSO with regularisation enables the classifier to dynamically adapt both its implicit architecture and weights as decision boundaries change. Furthermore, the results favour WE over WD as a regulariser for QPSO. / Dissertation (MSc)--University of Pretoria, 2020. / National Research Foundation (NRF) / Computer Science / MSc / Unrestricted

Chemical sensor based systems that are used for detection, identification, or quantification of various gases are very complex in nature. Sensor response data collected as a multivariate time series signals encounters gradual change of the sensor characteristics(known as sensor drift) due to several reasons. In this thesis, drift component of a silicon carbide Field-Effect Transistor (SiC-FET) sensor data was analyzed using time series. The data was collected from an experiment measuring output response of the sensor with respect to gases emitted by certain experimental object at different temperatures. Augmented Dickey Fuller Test (ADF) was carried out to analyze the sensor drift which revealed that stochastic trend along with deterministic trend characterized the drift components of the sensor. The drift started to rise in daily measurements which contributed to the total drift. / Traditional Autoregressive Integrated Moving Average (ARIMA) and deep learning based Long Short-Term Memory (LSTM) algorithm were carried out to forecast the sensor drift in reduced set of data. However, reduction of the data size degraded the forecasting accuracy and imposed loss of information. Therefore, careful selection of data using only one temperature from the temperature cycle was chosen instead of all time points. This chosen data from sensor array outperformed forecasting of sensor drift than reduced dataset using both traditional and deep learning methods.

Wireless personal area networks have emerged as an important communication infrastructure in areas such as at-home healthcare and home automation, independent living and assistive technology, as well as sports and wellness. Wireless personal area networks, including body sensor networks, are becoming more mature and are considered to be a realistic alternative as communication infrastructure for demanding services. However, to transmit data from e.g., an ECG in wireless networks is also a challenge, especially if multiple sensors compete for access. Contention-based networks offer simplicity and utilization advantages, but the drawback is lack of predictable performance. Recipients of data sent in wireless sensor networks need to know whether they can trust the information or not. Performance measurements, monitoring and control is of crucial importance for medical and healthcare applications in wireless sensor networks. This thesis focuses on development, prototype implementation and evaluation of a performance management system with performance and admission control for wireless sensor networks. Furthermore, an implementation of a new method to compensate for clock drift between multiple wireless sensor nodes is also shown. Errors in time synchronization between nodes in Bluetooth networks, resulting in inadequate data fusion, are also analysed. / <p>QC 20120529</p>

In a technologically advanced society, the average person manages dozens of accounts for e-mail, social networks, e-banking, and other electronic services. As the number of these accounts increases, the need for automatic user identification becomes more essential. Biometrics have long been used to identify people and are the most common (if not the only) method to achieve this task. Over the past few years, smartphones have become frequently used gadgets.  These devices have built-in microphones and are commonly used by a single user or a small set of users, such as a couple or a family. This thesis uses a smartphone’s microphone to capture user’s speech and identify him/her. Existing speaker recognition systems typically prompt the user to provide long voice samples in order to provide accurate results. This results in a poor user experience and discourages users who do not have the patience to go through such a process.  The main idea behind the speaker recognition approach presented in this thesis is to provide a seamless user experience where the recording of the user’s voice takes place in the background. An Android application is developed which silently collects voices samples and performs speaker recognition without requiring extensive user interaction.  Two variants of the proposed tool have been developed and are described in depth in this thesis. The open source framework Recognito is used to perform the speaker recognition task. The analysis of Recognito showed that it is not capable of achieving high accuracy especially when the voice samples contain background noise. Finally, the comparison between the two architectures showed that they do not differ significantly in terms of performance. / I ett teknologiskt avancerat samhälle så hanterar den genomsnittliga personen dussintals konton för e-post, sociala nätverk, internetbanker, och andra elektroniska tjänster. Allt eftersom antalet konton ökar, blir behovet av automatisk identifiering av användaren mer väsentlig. Biometri har länge använts för att identifiera personer och är den vanligaste (om inte den enda) metoden för att utföra denna uppgift. Smartphones har under de senaste åren blivit allt mer vanligt förekommande, de ger användaren tillgång till de flesta av sina konton och, i viss mån, även personifiering av enheterna baserat på deras profiler på sociala nätverk. Dessa enheter har inbyggda mikrofoner och används ofta av en enskild användare eller en liten grupp av användare, till exempel ett par eller en familj. Denna avhandling använder mikrofonen i en smartphone för att spela in användarens tal och identifiera honom/henne. Befintliga lösningar för talarigenkänning ber vanligtvis användaren om att ge långa röstprover för att kunna ge korrekta resultat.  Detta resulterar i en dålig användarupplevelse och avskräcker användare som inte har tålamod att gå igenom en sådan process. Huvudtanken bakom den strategi för talarigenkänningen som presenteras i denna avhandling är att ge en sömlös användarupplevelse där inspelningen av användarens röst sker i bakgrunden. En Android-applikation har utvecklats som, utan att märkas, samlar in röstprover och utför talarigenkänning på dessa utan att kräva omfattande interaktion av användaren. Två varianter av verktyget har utvecklats och dessa beskrivs ingående i denna avhandling. Öpen source-ramverket Recognito används för att utföra talarigenkänningen. Analysen av Recognito visade att det inte klarar av att uppnå tillräckligt hög noggrannhet, speciellt när röstproverna innehåller bakgrundsbrus. Dessutom visade jämförelsen mellan de två arkitekturerna att de inte skiljer sig nämnvärt i fråga om prestanda.

Revisorer har i uppdrag att granska huruvida företagsledningens antagande om fortsatt drift stämmer eller inte. Bedömningen leder till en anmärkning i revisionsberättelsen vid tvivel om fortsatt drift, alternativt en utebliven anmärkning om tvivel inte uppstår vid granskningen. Svenska revisorer har dock problem att upptäcka de risker som indikerar konkurs. Träffsäkerheten vid anmärkningar och uteblivna anmärkningar är generellt sett låg vilket lämnar ett stort utrymme för förekomsten av s.k. typ I- och typ II-fel. Felbedömningarna och den låga träffsäkerheten medför problem för intressenter, såsom investerare och kreditgivare. Intressenterna varnas då inte om företagets fortlevnadsproblem och får därmed ingen möjlighet att vidta åtgärder för att undkomma negativa ekonomiska konsekvenser. Tidigare empiriska studier visar att revisorers bedömningar influeras av känslor såsom komfort och diskomfort. Studier visar även att erfarenhet och kompetens, struktur och bedömning samt granskningstid inverkar på fortsatt driftbedömningar samt i vilken grad revisorer upplever komfort och diskomfort i bedömningen. Revisorer uppvisar ibland en oproportionerlig tillit till företagsledningarna vilket åskådliggör en partiskhet och oberoendeproblematik i fortsatt driftbedömningarna. Tidigare studier har dock mestadels tillämpat generaliserbara tillvägagångssätt. Hur revisorer själva beskriver fortsatt driftbedömningarna och dess problematik är, så vitt vi vet, oklart. Syftet med denna studie är att beskriva och analysera de tillvägagångssätt och de förklaringar som några svenska auktoriserade revisorer anger ligger till grund för svårigheter i fortsatt driftbedömningar. Studien genomfördes hösten 2020 med en abduktiv forskningsansats och sex semistrukturerade digitala videointervjuer. Vidare användes en tematisk analysmetod för att sammanställa de transkriberade intervjuerna. Trots att de till synes är erfarna och kompetenta anger de tillfrågade revisorerna att fortsatt driftbedömningarna är svåra och medför diskomfort. Revisorerna beskriver att deras syn på och användning av standarden ISA 570 varierar med anledning av bland annat tolkningssvårigheter. De önskar ändå inte mer riktlinjer i standarden med anledning av att utrymmet för den professionella bedömningen då minskar. Revisorerna beskriver att de upplever tidsbrist i granskningen och de anger dokumentationskrav som en tidstjuv. Fortsatt driftbedömningarna influeras även av individuella känslor enligt revisorerna och en upplevd diskomfort måste reduceras genom dialog med kollegor, företagsledningen och interna experter för att övergå i komfort. Revisorerna anser inte att typ I- och typ II-fel är felaktiga bedömningar såsom teorin beskriver och vi kan därmed konstatera att skillnader mellan teori och praktik föreligger. Revisorerna beskriver att typ II-fel beror på plötsliga händelser som i princip är omöjliga att förutspå eftersom bedömningen innefattar framtiden. Argumentet om att framtiden är inte går att förutspå håller däremot inte då investerare ofta åskådliggör att detta faktiskt är möjligt. Revisorernas beskrivningar av fortsatt driftbedömningen genomsyras genomgående av ett företagsfokus framför ett intressentfokus vilket indikerar en oberoendeproblematik. / Auditors are tasked with examining whether the management´s assumption of going concern is correct or not. The assessment leads to a remark in the auditor´s report in case of doubt about going concern, or alternatively a lack of remark if doubt does not arise during the audit. However, Swedish auditors have problems discovering the risk that indicate bankruptcy. The accuracy of remarks in the field of going concern is generally low, which leaves a lot of room for the occurrence of so-called type I and type II errors. The misjudgements and the low accuracy cause problems for stakeholders, such as investors and lenders. Stakeholders are then not warned about the company´s survival problems and thus were not given the opportunity to take measures to escape negative financial consequences. Previous empirical studies show that auditors´ assessments are influenced by emotions such as comfort and discomfort. Studies show that experience and competence, structure and judgement such as audit time influence going concern assessments and the extent to which auditors experience comfort and discomfort in the assessment. Auditors sometimes show a disproportionate trust in the management skills of companies, which illustrates a bias and an independence problem in going concern assessments. Previous studies, however, mostly apply generalizable approaches. How the auditors themselves describe the going concern assessments is, as far as we know, unclear. The purpose of this study is to describe and analyse the approaches and explanations given by some Swedish certified public auditors as a basis for difficulties in going concern assessments. The study was conducted in the autumn of 2020 with an abductive research approach and six semi-structured digital video interviews. Furthermore, a thematic analysis method was used to compile the transcribed interviews. Despite the fact that they seem to be experienced and competent, the auditors consulted state that going concern assessments are difficult and lead to discomfort. The auditors describe that their views on and use of the standard ISA 570 vary due to, among other things, difficulties of interpretation. However, they do not want more guidelines in the standard due to the fact that the scope for the professional judgement then decreases. The auditors describe that they experience a lack of time in the audit and they state documentation requirements as a time thief. Going concern assessments are also influenced by individual feelings according to the auditors and a perceived discomfort must be reduced through dialogue with colleagues, company management and internal experts in order to achieve comfort. The auditors do not consider that type I and type II errors are incorrect assessments as the theory describes and we can thus state that there are differences between theory and practice. The auditors describe that type II errors are due to sudden events that are impossible to predict because the assessment includes the future. The argument that the future is unpredictable can be questioned because investors often illustrate that this actually is possible. The auditors´ descriptions of the going concern assessment are permeated throughout by a company focus rather than a stakeholder focus, which indicates bias and independence issues.

I slutet av år 2019 bröt viruset covid-19 ut som under senare tid ledde till en global pandemi som har påverkat både folkhälsan och ekonomin. Revisorernas arbete står inför en förändringsfas på grund av pandemin, där specifika delar i revisionen påverkats. Syftet med denna studie är att undersöka hur revisorns åtgärder och bedömningar har påverkats till följd av Covid-19 under revisionsprocessens gång för att revisorn ska känna sig komfortabel med sitt genomförda arbete. Genom att studera komfort teorin och revisionsprocessen tre huvuddelar vilka är planeringsfasen, granskningsfasen och rapporteringsfasen möjliggörs en koppling till studiens insamlade empiri som resulterar i en analys av studiens resultat som vidare resulterar i välgrundade slutsatser och förslag på vidare forskning. Trots de rådande omständigheterna med covid-19 valdes ett genomförande av en kvalitativ studie. Detta gjordes med anledning av att få en mer djupgående förståelse kring vårt ämne. Empirin samlades in genom semistrukturerade intervjuer som utfördes via digitala möten med revisorer från två olika revisionsbyråer från Big-4. Studiens slutsats är att pandemin både haft positiv och negativ påverkan på revisionsprocessen och att revisorerna behöver vidta och genomföra fler åtgärder än tidigare för att uppnå komfort. / Towards the end of 2019 the COVID-19 virus started spreading all over the world, which led to the global pandemic that has had an affect on both the public health and the economy. Because of the pandemic, specific parts of auditing have been affected, which has led to a change in the workload for auditors. The purpose of this study is to examine and analyse how the auditor's measures and assessments have been affected as a result of the COVID-19 outbreak, and how auditors can feel comfortable while they perform their audit process. By examining and exploring the comfort theory and the three main parts of the audit process; the planning phase, the review phase, and the reporting phase, a connection to the study's collected empirical data is enabled and an analysis of the results will result in legitimate conclusions and suggestions for further research. Despite the current circumstances with COVID-19, a qualitative study was chosen. This was chosen in order to get a more in-depth understanding of the subject. The empirics were collected through semi-structured interviews conducted through digital meetings with auditors from two different Big-4 auditing firms. The study concludes that the global pandemic has had both a positive and a negative impact on the audit process, and that auditors need to take and implement further measures than before COVID-19 to achieve comfort.