259 research outputs found
Generative models for natural images
Nous traitons de modeĢles geĢneĢratifs construits avec des reĢseaux de neurones dans le contexte de la modeĢlisation dāimages. De nos jours, trois types de modeĢles sont particulieĢrement preĢdominants: les modeĢles aĢ variables latentes, tel que lāauto-encodeur variationnel (VAE), les modeĢles autoreĢgressifs, tel que le reĢseau de neurones reĢcurrent pixel (PixelRNN), et les modeĢles geĢneĢratifs antagonistes (GANs), qui sont des modeĢles aĢ transformation de bruit entraineĢs aĢ lāaide dāun adversaire. Cette theĢse traite de chacun de ces modeĢles.
Le premier chapitre couvre la base des modeĢles geĢneĢratifs, ainsi que les reĢseaux de neurones pro- fonds, qui constituent la technologie principalement utiliseĢe aĢ lāheure actuelle pour lāimpleĢmentation de modeĢles statistiques puissants.
Dans le deuxieĢme chapitre, nous impleĢmentons un auto-encodeur variationnel avec un deĢcodeur auto-reĢgressif. Cela permet de se libeĢrer de lāhypotheĢse dāindeĢpendance des dimensions de sortie du deĢcodeur variationnel, en modeĢlisant une distribution jointe tracĢ§able aĢ la place, et de doter le modeĢle auto-reĢgressif dāun code latent. De plus, notre impleĢmentation a un couĢt computationnel significativement reĢduit, si on le compare aĢ un modeĢle purement auto-reĢgressif ayant les meĢmes hypotheĢses de modeĢlisation et la meĢme performance. Nous deĢcrivons lāespace latent de facĢ§on hieĢrarchique, et montrons de manieĢre qualitative la deĢcomposition seĢmantique des causes latente induites par ce design. Finalement, nous preĢsentons des reĢsultats obtenus avec des jeux de donneĢes standards et deĢmontrant que la performance de notre impleĢmentation est fortement compeĢtitive.
Dans le troisieĢme chapitre, nous preĢsentons une proceĢdure dāentrainement ameĢlioreĢe pour une variante reĢcente de modeĢles geĢneĢratifs antagoniste. Le Ā«Wasserstein GANĀ» minimise la distance, mesureĢe avec la meĢtrique de Wasserstein, entre la distribution reĢelle et celle geĢneĢreĢe par le modeĢle, ce qui le rend plus facile aĢ entrainer quāun GAN avec un objectif minimax. Cependant, en fonction des parameĢtres, il preĢsente toujours des cas dāeĢchecs avec certain modes dāentrainement. Nous avons deĢcouvert que le coupable est le coupage des poids, et nous le remplacĢ§ons par une peĢnaliteĢ sur la norme des gradients. Ceci ameĢliore et stabilise lāentrainement, et ce sur diffeĢrents types du parameĢtres (incluant des modeĢles de langue sur des donneĢes discreĢtes), et permet de geĢneĢrer des eĢchantillons de haute qualiteĢs sur CIFAR-10 et LSUN bedrooms.
Finalement, dans le quatrieĢme chapitre, nous consideĢrons lāusage de modeĢles geĢneĢratifs modernes comme modeĢles de normaliteĢ dans un cadre de deĢtection hors-distribution Ā«zero-shotĀ». Nous avons eĢvalueĢ certains des modeĢles preĢceĢdemment preĢsenteĢs dans la theĢse, et avons trouveĢ que les VAEs sont les plus prometteurs, bien que leurs performances laissent encore un large place aĢ lāameĢlioration. Cette partie de la theĢse constitue un travail en cours.
Nous concluons en reĢpeĢtant lāimportance des modeĢles geĢneĢratifs dans le deĢveloppement de lāintelligence artificielle et mentionnons quelques deĢfis futurs.We discuss modern generative modelling of natural images based on neural networks. Three varieties of such models are particularly predominant at the time of writing: latent variable models such as variational autoencoders (VAE), autoregressive models such as pixel recurrent neural networks (PixelRNN), and generative adversarial networks (GAN), which are noise-transformation models trained with an adversary. This thesis touches on all three kinds.
The first chapter covers background on generative models, along with relevant discussions about deep neural networks, which are currently the dominant technology for implementing powerful statistical models.
In the second chapter, we implement variational autoencoders with autoregressive decoders. This removes the strong assumption of output dimensions being conditionally independent in variational autoencoders, instead tractably modelling a joint distribution, while also endowing autoregressive models with a latent code. Additionally, this model has significantly reduced computational cost compared to that of a purely autoregressive model with similar modelling assumptions and performance. We express the latent space as a hierarchy, and qualitatively demonstrate the semantic decomposition of latent causes induced by this design. Finally, we present results on standard datasets that demonstrate strongly competitive performance.
In the third chapter, we present an improved training procedure for a recent variant on generative adversarial networks. Wasserstein GANs minimize the Earth-Moverās distance between the real and generated distributions and have been shown to be much easier to train than with the standard minimax objective of GANs. However, they still exhibit some failure modes in training for some settings. We identify weight clipping as a culprit and replace it with a penalty on the gradient norm. This improves training further, and we demonstrate stability on a wide variety of settings (including language models over discrete data), and samples of high quality on the CIFAR-10 and LSUN bedrooms datasets.
Finally, in the fourth chapter, we present work in development, where we consider the use of modern generative models as normality models in a zero-shot out-of-distribution detection setting. We evaluate some of the models we have discussed previously in the thesis, and find that VAEs are the most promising, although their overall performance leaves a lot of room for improvement.
We conclude by reiterating the significance of generative modelling in the development of artificial intelligence, and mention some of the challenges ahead
Ambient awareness on a sidewalk for visually impaired
Safe navigation by avoiding obstacles is vital for visually impaired while walking on a sidewalk. There are both static and dynamic obstacles to avoid. Detection, monitoring, and estimating the threat posed by obstacles remain challenging. Also, it is imperative that the design of the system must be energy efficient and low cost. An additional challenge in designing an interactive system capable of providing useful feedback is to minimize users\u27 cognitive load. We started the development of the prototype system through classifying obstacles and providing feedback. To overcome the limitations of the classification-based system, we adopted the image annotation framework in describing the scene, which may or may not include the obstacles. Both solutions partially solved the safe navigation but were found to be ineffective in providing meaningful feedback and issues with the diurnal cycle. To address such limitations, we introduce the notion of free-path and threat level imposed by the static or dynamic obstacles. This solution reduced the overhead of obstacle detection and helped in designing meaningful feedback. Affording users a natural conversation through an interactive dialog enabled interface was found to promote safer navigation. In this dissertation, we modeled the free-path and threat level using a reinforcement learning (RL) framework.We built the RL model in the Gazebo robot simulation environment and implanted that in a handheld device. A natural conversation model was created using data collected through a Wizard of OZ approach. The RL model and conversational agent model together resulted in the handheld assistive device called Augmented Guiding Torch (AGT). The AGT provides improved mobility over white cane by providing ambient awareness through natural conversation. It can inform the visually impaired about the obstacles which are helpful to be warned about ahead of time, e.g., construction site, scooter, crowd, car, bike, or big hole. Using the RL framework, the robot avoided over 95% obstacles. The visually impaired avoided over 85% obstacles with the help of AGT on a 500 feet U-shape sidewalk. Findings of this dissertation support the effectiveness of augmented guiding through RL for navigation and obstacle avoidance of visually impaired users
A Doubly-Fed Induction Generator (DFIG)-Based Wind-Power System with Integrated Energy Storage for Remote Electrification
Electrification of off-grid remote communities is commonly accomplished through diesel generators. The method may even be employed in cases where there exists an unĀ reliable connection to the power grid. Regardless, the method is environmentally-hostile, typically costly, and likely risky. Therefore, to mitigate the reliance on diesel fuel, utiĀ lization of renewable energy resources has been considered in recent years. This thesis investigates the feasibility of and technical considerations involved in the employment of a specific class of variable-speed wind-power systems, integrated with battery energy storĀ age, for remote electrification applications.
The wind-power system under consideration is based on the doubly-fed induction genĀ erator (DFIG) technology, which features a number of characteristics that render it atĀ tractive for the incorporation of battery energy storage. This thesis identifies the control strategy, different control sub-functions, and the controllers structures/parametes required to accommodate the battery energy storage. The developed control strategy enables the operation of the wind-power/storage system in the off-grid (islanded) mode of operation, as well as the grid-connected mode of operation. Under the developed control strategy, the wind-power/storage system can operate in parallel with constant-speed wind-power units, passive loads, and induction motor loads. The effectiveness of the proposed control strategy has been demonstrated through comprehensive simulation studies enabled by the commercial software package PSCAD/EMTDC.
In addition to the control aspects, this thesis studies the reliability aspects of the proĀ posed wind-power/storage system, for an example remote electrification system. Thus, a new reliability assessment method has been developed in this thesis, which combines the existing analytical and simulation-based probabilistic approaches. The reliability analysis conducted indicates that the battery energy storage capacity, the wind magnitude and proĀ file, and the load profile impose remarkable impacts on the reliability of the electrification system. It also indicates that a connection to the power grid, however unreliable, signifiĀ cantly mitigates the need for a large battery to achieve a given degree of reliability
Factors associated with stress among first-year undergraduate students attending an Australian university
Objective: The aim of this study was to examine the relationship between stress and various socio-demographic, health and behavioural factors among undergraduate students studying in an Australian university.
Methods: A cross-sectional survey was carried out among firstyear undergraduate students studying at Griffith University. Participants were recruited from four different academic groups (N=728). The questionnaire used in this study comprised of three sections: socio-demographic information, stress scale and a food frequency questionnaire. K-means Cluster analysis was performed to identify the major dietary patterns and multinomial logistic regression analysis was used to examine the factors associated with stress.
Results: Nearly 53% of the students had some degree of stress with 37.4% experiencing moderate to severe levels of stress. The factors most strongly associated with having mild or moderate/ severe stress levels included being in a relationship [OR =1.71, 95% CI (1.02-2.87) and OR=1.61, 95% CI (1.06-2.44)], studying a non-health related degree [OR=1.68, 95% CI (1.03-2.73) and OR=1.51, 95% CI (1.04-2.19)], working ā„ 21 hours per week [OR=2.12, 95% CI (1.02-4.40) and OR=2.21, 95% CI (1.32-3.67)], and engaging in an unhealthy dietary pattern [OR=2.67, 95% CI (1.25-5.72) and OR=2.76, 95% CI (1.47-5.16)]. Being a female [OR=1.84, 95% CI (1.25-2.72)], living in a shared accommodation [OR=0.52, 95% CI (0.27-0.98)], rarely exercising [OR=2.64, 95% CI (1.59-4.39)], having a body mass index (BMI) of 25 or over [OR=2.03, 95% CI (1.36-3.04)], and engaging in a dietary pattern that was low in protein, fruit and vegetables [OR=1.72, 95% CI (1.06-2.77)] were also associated with having moderate/severe stress levels.
Conclusion: This study found that more than half of the undergraduate students had some levels of stress. Both mild and moderate/severe levels of stress were associated with sociodemographic characteristics, risky health behaviours and poor dietary patterns. Our findings reinforce the need to promote healthy behaviours among undergraduate university students in order to maintain good mental health.</p
Detecting semantic anomalies
We critically appraise the recent interest in out-of-distribution (OOD)
detection and question the practical relevance of existing benchmarks. While
the currently prevalent trend is to consider different datasets as OOD, we
argue that out-distributions of practical interest are ones where the
distinction is semantic in nature for a specified context, and that evaluative
tasks should reflect this more closely. Assuming a context of object
recognition, we recommend a set of benchmarks, motivated by practical
applications. We make progress on these benchmarks by exploring a multi-task
learning based approach, showing that auxiliary objectives for improved
semantic awareness result in improved semantic anomaly detection, with
accompanying generalization benefits.Comment: Preprint for AAAI '20 publicatio
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