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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Machine Learning for Improving Detection of Cooling Complications : A case study / Maskininlärning för att förbättra detektering av kylproblem

Bruksås Nybjörk, William January 2022 (has links)
The growing market for cold chain pharmaceuticals requires reliable and flexible logistics solutions that ensure the quality of the drugs. These pharmaceuticals must maintain cool to retain the function and effect. Therefore, it is of greatest concern to keep these drugs within the specified temperature interval. Temperature controllable containers are a common logistic solution for cold chain pharmaceuticals freight. One of the leading manufacturers of these containers provides lease and shipment services while also regularly assessing the cooling function. A method is applied for detecting cooling issues and preventing impaired containers to be sent to customers. However, the method tends to miss-classify containers, missing some faulty containers while also classifying functional containers as faulty. This thesis aims to investigate and identify the dependent variables associated with the cooling performance, then Machine Learning will be performed for evaluating if recall and precision could be improved. An improvement could lead to faster response, less waste and even more reliable freight which could be vital for both companies and patients. The labeled dataset has a binary outcome (no cooling issues, cooling issues) and is heavily imbalanced since the containers have high quality and undergo frequent testing and maintenance. Therefore, just a small amount has cooling issues. After analyzing the data, extensive deviations were identified which suggested that the labeled data was misclassified. The believed misclassification was corrected and compared to the original data. A Random Forest classifier in combination with random oversampling and threshold tuning resulted in the best performance for the corrected class labels. Recall reached 86% and precision 87% which is a very promising result. A Random Forest classifier in combination with random oversampling resulted in the best score for the original class labels. Recall reached 77% and precision 44% which is much lower than the adjusted class labels but still displayed a valid result in context of the believed extent of misclassification. Power output variables, compressor error variables and standard deviation of inside temperature were found clear connection toward cooling complications. Clear links could also be found to the critical cases where set temperature could not be met. These cases could therefore be easily detected but harder to prevent since they often appeared without warning. / Den växande marknaden för läkemedel beroende av kylkedja kräver pålitliga och agila logistiska lösningar som försäkrar kvaliteten hos läkemedlen. Dessa läkemedel måste förbli kylda för att behålla funktion och effekt. Därför är det av största vikt att hålla läkemedlen inom det angivna temperaturintervallet. Temperaturkontrollerade containrar är en vanlig logistisk lösning vid kylkedjefrakt av läkemedel. En av de ledande tillverkarna av dessa containrar tillhandahåller uthyrning och frakttjänster av dessa medan de också regelbundet bedömer containrarnas kylfunktion. En metod används för att detektera kylproblem och förhindra skadade containrar från att nå kund. Dock så tenderar denna metod att missklassificera containrar genom att missa vissa containrar med kylproblem och genom att klassificera fungerande containrar som skadade. Den här uppsatsen har som syfte att identifiera beroende variabler kopplade mot kylprestandan och därefter undersöka om maskininlärning kan användas för att förbättra återkallelse och precisionsbetyg gällande containrar med kylproblem. En förbättring kan leda till snabbare respons, mindre resursslöseri och ännu pålitligare frakt vilket kan vara vitalt för både företag som patienter. Ett märkt dataset tillhandahålls och detta har ett binärt utfall (inga kylproblem, kylproblem). Datasetet är kraftigt obalanserat då containrar har en hög kvalité och genomgår frekvent testning och underhåll. Därför har enbart en liten del av containrarna kylproblem. Efter att ha analyserat datan så kunde omfattande avvikelser upptäckas vilket antydde på grov miss-klassificering. Den trodda missklassificeringen korrigerades och jämfördes med den originella datan. En Random Forest klassificerare i kombination med slumpmässig översampling och tröskeljustering gav det bästa resultatet för det korrigerade datasetet. En återkallelse på 86% och en precision på 87% nåddes, vilket var ett lovande resultat. En Random Forest klassificerare i kombination med slumpmässig översampling gav det bästa resultatet för det originella datasetet. En återkallelse på 77% och en precision på 44% nåddes. Detta var mycket lägre än det justerade datasetet men det presenterade fortfarande godkända resultat med åtanke på den trodda missklassificeringen. Variabler baserade på uteffekt, kompressorfel och standardavvikelse av innetemperatur hade tydliga kopplingar mot kylproblem. Tydliga kopplingar kunde även identifieras bland de kritiska fallen där temperaturen ej kunde bibehållas. Dessa fall kunde därmed lätt detekteras men var svårare att förhindra då dessa ofta uppkom utan förvarning.
2

Wildfire Spread Prediction Using Attention Mechanisms In U-Net

Shah, Kamen Haresh, Shah, Kamen Haresh 01 December 2022 (has links) (PDF)
An investigation into using attention mechanisms for better feature extraction in wildfire spread prediction models. This research examines the U-net architecture to achieve image segmentation, a process that partitions images by classifying pixels into one of two classes. The deep learning models explored in this research integrate modern deep learning architectures, and techniques used to optimize them. The models are trained on 12 distinct observational variables derived from the Google Earth Engine catalog. Evaluation is conducted with accuracy, Dice coefficient score, ROC-AUC, and F1-score. This research concludes that when augmenting U-net with attention mechanisms, the attention component improves feature suppression and recognition, improving overall performance. Furthermore, employing ensemble modeling reduces bias and variation, leading to more consistent and accurate predictions. When inferencing on wildfire propagation at 30-minute intervals, the architecture presented in this research achieved a ROC-AUC score of 86.2% and an accuracy of 82.1%.
3

Resource Allocation for Sequential Decision Making Under Uncertainaty : Studies in Vehicular Traffic Control, Service Systems, Sensor Networks and Mechanism Design

Prashanth, L A January 2013 (has links) (PDF)
A fundamental question in a sequential decision making setting under uncertainty is “how to allocate resources amongst competing entities so as to maximize the rewards accumulated in the long run?”. The resources allocated may be either abstract quantities such as time or concrete quantities such as manpower. The sequential decision making setting involves one or more agents interacting with an environment to procure rewards at every time instant and the goal is to find an optimal policy for choosing actions. Most of these problems involve multiple (infinite) stages and the objective function is usually a long-run performance objective. The problem is further complicated by the uncertainties in the sys-tem, for instance, the stochastic noise and partial observability in a single-agent setting or private information of the agents in a multi-agent setting. The dimensionality of the problem also plays an important role in the solution methodology adopted. Most of the real-world problems involve high-dimensional state and action spaces and an important design aspect of the solution is the choice of knowledge representation. The aim of this thesis is to answer important resource allocation related questions in different real-world application contexts and in the process contribute novel algorithms to the theory as well. The resource allocation algorithms considered include those from stochastic optimization, stochastic control and reinforcement learning. A number of new algorithms are developed as well. The application contexts selected encompass both single and multi-agent systems, abstract and concrete resources and contain high-dimensional state and control spaces. The empirical results from the various studies performed indicate that the algorithms presented here perform significantly better than those previously proposed in the literature. Further, the algorithms presented here are also shown to theoretically converge, hence guaranteeing optimal performance. We now briefly describe the various studies conducted here to investigate problems of resource allocation under uncertainties of different kinds: Vehicular Traffic Control The aim here is to optimize the ‘green time’ resource of the individual lanes in road networks that maximizes a certain long-term performance objective. We develop several reinforcement learning based algorithms for solving this problem. In the infinite horizon discounted Markov decision process setting, a Q-learning based traffic light control (TLC) algorithm that incorporates feature based representations and function approximation to handle large road networks is proposed, see Prashanth and Bhatnagar [2011b]. This TLC algorithm works with coarse information, obtained via graded thresholds, about the congestion level on the lanes of the road network. However, the graded threshold values used in the above Q-learning based TLC algorithm as well as several other graded threshold-based TLC algorithms that we propose, may not be optimal for all traffic conditions. We therefore also develop a new algorithm based on SPSA to tune the associated thresholds to the ‘optimal’ values (Prashanth and Bhatnagar [2012]). Our thresh-old tuning algorithm is online, incremental with proven convergence to the optimal values of thresholds. Further, we also study average cost traffic signal control and develop two novel reinforcement learning based TLC algorithms with function approximation (Prashanth and Bhatnagar [2011c]). Lastly, we also develop a feature adaptation method for ‘optimal’ feature selection (Bhatnagar et al. [2012a]). This algorithm adapts the features in a way as to converge to an optimal set of features, which can then be used in the algorithm. Service Systems The aim here is to optimize the ‘workforce’, the critical resource of any service system. However, adapting the staffing levels to the workloads in such systems is nontrivial as the queue stability and aggregate service level agreement (SLA) constraints have to be complied with. We formulate this problem as a constrained hidden Markov process with a (discrete) worker parameter and propose simultaneous perturbation based simulation optimization algorithms for this purpose. The algorithms include both first order as well as second order methods and incorporate SPSA based gradient estimates in the primal, with dual ascent for the Lagrange multipliers. All the algorithms that we propose are online, incremental and are easy to implement. Further, they involve a certain generalized smooth projection operator, which is essential to project the continuous-valued worker parameter updates obtained from the SASOC algorithms onto the discrete set. We validate our algorithms on five real-life service systems and compare their performance with a state-of-the-art optimization tool-kit OptQuest. Being ��times faster than OptQuest, our scheme is particularly suitable for adaptive labor staffing. Also, we observe that it guarantees convergence and finds better solutions than OptQuest in many cases. Wireless Sensor Networks The aim here is to allocate the ‘sleep time’ (resource) of the individual sensors in an intrusion detection application such that the energy consumption from the sensors is reduced, while keeping the tracking error to a minimum. We model this sleep–wake scheduling problem as a partially-observed Markov decision process (POMDP) and propose novel RL-based algorithms -with both long-run discounted and average cost objectives -for solving this problem. All our algorithms incorporate function approximation and feature-based representations to handle the curse of dimensionality. Further, the feature selection scheme used in each of the proposed algorithms intelligently manages the energy cost and tracking cost factors, which in turn, assists the search for the optimal sleeping policy. The results from the simulation experiments suggest that our proposed algorithms perform better than a recently proposed algorithm from Fuemmeler and Veeravalli [2008], Fuemmeler et al. [2011]. Mechanism Design The setting here is of multiple self-interested agents with limited capacities, attempting to maximize their individual utilities, which often comes at the expense of the group’s utility. The aim of the resource allocator here then is to efficiently allocate the resource (which is being contended for, by the agents) and also maximize the social welfare via the ‘right’ transfer of payments. In other words, the problem is to find an incentive compatible transfer scheme following a socially efficient allocation. We present two novel mechanisms with progressively realistic assumptions about agent types aimed at economic scenarios where agents have limited capacities. For the simplest case where agent types consist of a unit cost of production and a capacity that does not change with time, we provide an enhancement to the static mechanism of Dash et al. [2007] that effectively deters misreport of the capacity type element by an agent to receive an allocation beyond its capacity, which thereby damages other agents. Our model incorporates an agent’s preference to harm other agents through a additive factor in the utility function of an agent and the mechanism we propose achieves strategy proofness by means of a novel penalty scheme. Next, we consider a dynamic setting where agent types evolve and the individual agents here again have a preference to harm others via capacity misreports. We show via a counterexample that the dynamic pivot mechanism of Bergemann and Valimaki [2010] cannot be directly applied in our setting with capacity-limited alim¨agents. We propose an enhancement to the mechanism of Bergemann and V¨alim¨aki [2010] that ensures truth telling w.r.t. capacity type element through a variable penalty scheme (in the spirit of the static mechanism). We show that each of our mechanisms is ex-post incentive compatible, ex-post individually rational, and socially efficient

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