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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.
21

Automatisk Summering av Cybersäkerhetsdiskussioner på Onlineforum : En prototyp för abstraktiv textsummering med en Zero-shot modell

Ununger, Andreas January 2022 (has links)
Antalet cyberattacker ökar ständigt och därav också antalet angreppssätt och försvarstekniker. Detta innebär att personer verksamma inom cybersäkerhet behöver spendera mer och mer tid på att hålla sig uppdaterade om de senaste utvecklingarna i branschen. Det är därför av intresse att hitta sätt som kan påskynda denna inhämtning av information. I denna studie utvecklas en prototyp med målet att på ett nytt sätt automatiskt summera en av de många sorters nyhetskällor som finns inom cybersäkerhetsdiskussioner på onlineforum. Prototypen använder sig av abstraktiv textsummering med zero-shot modellen GPT-3. Prototypen som utvecklades utvärderades genom att mäta de summeringar som skapades med SUPERT. Resultatet från mätningen gav ett värde av 0,269 vid mätning mot de originella texterna och 0,358 vid mätning mot ett dataset som städats från text som inte rör cybersäkerhet. Från dessa värdet dras slutsatsen att utvecklingen av prototypen lyckades.
22

Image-Guided Zero-Shot Object Detection in Video Games : Using Images as Prompts for Detection of Unseen 2D Icons / Bildstyrd Zero-Shot Objektdetektering i Datorspel : Användning av Bilder för att Diktera Detektion av Osedda 2D-ikoner

Larsson, Axel January 2023 (has links)
Object detection deals with localization and classification of objects in images, where the task is to propose bounding boxes and predict their respective classes. Challenges in object detection include large-scale annotated datasets and re-training of models for specific tasks. Motivated by these problems, we propose a zero-shot object detection (ZSD) model in the setting of user interface icons in video games. Allowing to quickly and accurately analyze the state of a game, with potentially millions of people watching, would greatly benefit the large and fast-growing video game sector. Our resulting model is a modification of YOLOv8, which, at inference time, is prompted with the specific object to detect in an image. Many existing ZSD models exploit semantic embeddings and high-dimensional word vectors to generalize to novel classes. We hypothesize that using only visual representations is sufficient for the detection of unseen classes. To train and evaluate our model, we create synthetic data to reflect the nature of video game icons and in-game frames. Our method achieves similar performance as YOLOv8 on bounding box prediction and detection of seen classes while retaining the same average precision and recall for unseen classes, where the number of unseen classes is in the order of thousands. / Objektdetektering handlar om lokalisering och klassificering av objekt i bilder, där uppgiften är att föreslå omskrivande rektanglar och prediktera de respektive klasserna. Utmaningar i objektdetektering inkluderar storskaliga annoterade datamängder och omträning av modeller för specifika uppgifter. Motiverade av dessa problem föreslår vi en zero-shot-modell för objektdetektering riktat mot användargränssnittsikoner i datorspel. Att snabbt och precist kunna analysera tillståndet i ett spel, med potentiellt miljontals människor som tittar, skulle vara till stor nytta för den snabbväxande datorspelssektorn. Vår slutliga modell är en modifiering av YOLOv8, som vid inferens förses med det specifika objektet som ska upptäckas i en given bild. Många befintliga zero-shot-modeller inom objektdetektering utnyttjar semantiska inbäddningar och högdimensionella ordvektorer för att generalisera till nya klasser. Vi hypotiserar att det är tillräckligt att använda visuella representationer för att upptäcka osedda klasser. För att träna och utvärdera vår modell skapar vi syntetisk data för att återspegla spelbilder och ikoner från datorspel. Vår metod uppnår liknande prestanda som YOLOv8 på prediktion av omskrivande rektanglar och på sedda klasser där antalet klasser är lågt. Samtidigt upprätthåller vi samma positiva prediktionsvärde och sensitivitet för osedda klasser där antalet klasser uppgår till tusentals.
23

Apprentissage automatique en ligne pour un dialogue homme-machine situé / Online learning for situated human-machine dialogue

Ferreira, Emmanuel 14 December 2015 (has links)
Un système de dialogue permet de doter la Machine de la capacité d'interagir de façon naturelle et efficace avec l'Homme. Dans cette thèse nous nous intéressons au développement d'un système de dialogue reposant sur des approches statistiques, et en particulier du cadre formel des Processus Décisionnel de Markov Partiellement Observable, en anglais Partially Observable Markov Decision Process (POMDP), qui à ce jour fait office de référence dans la littérature en ce qui concerne la gestion statistique du dialogue. Ce modèle permet à la fois une prise en compte améliorée de l'incertitude inhérente au traitement des données en provenance de l'utilisateur (notamment la parole) et aussi l'optimisation automatique de la politique d'interaction à partir de données grâce à l'apprentissage par renforcement, en anglais Reinforcement Learning (RL). Cependant, une des problématiques liées aux approches statistiques est qu'elles nécessitent le recours à une grande quantité de données d'apprentissage pour atteindre des niveaux de performances acceptables. Or, la collecte de telles données est un processus long et coûteux qui nécessite généralement, pour le cas du dialogue, la réalisation de prototypes fonctionnels avec l'intervention d'experts et/ou le développement de solution alternative comme le recours à la simulation d'utilisateurs. En effet, très peu de travaux considèrent à ce jour la possibilité d'un apprentissage de la stratégie de la Machine de part sa mise en situation de zéro (sans apprentissage préalable) face à de vrais utilisateurs. Pourtant cette solution présente un grand intérêt, elle permet par exemple d'inscrire le processus d'apprentissage comme une partie intégrante du cycle de vie d'un système lui offrant la capacité de s'adapter à de nouvelles conditions de façon dynamique et continue. Dans cette thèse, nous nous attacherons donc à apporter des solutions visant à rendre possible ce démarrage à froid du système mais aussi, à améliorer sa capacité à s'adapter à de nouvelles conditions (extension de domaine, changement d'utilisateur,...). Pour ce faire, nous envisagerons dans un premier temps l'utilisation de l'expertise du domaine (règles expertes) pour guider l'apprentissage initial de la politique d'interaction du système. De même, nous étudierons l'impact de la prise en compte de jugements subjectifs émis par l'utilisateur au fil de l'interaction dans l'apprentissage, notamment dans un contexte de changement de profil d'utilisateur où la politique préalablement apprise doit alors pouvoir s'adapter à de nouvelles conditions. Les résultats obtenus sur une tâche de référence montrent la possibilité d'apprendre une politique (quasi-)optimale en quelques centaines d'interactions, mais aussi que les informations supplémentaires considérées dans nos propositions sont à même d'accélérer significativement l'apprentissage et d'améliorer la tolérance aux bruits dans la chaîne de traitement. Dans un second temps nous nous intéresserons à réduire les coûts de développement d'un module de compréhension de la parole utilisé dans l'étiquetage sémantique d'un tour de dialogue. Pour cela, nous exploiterons les récentes avancées dans les techniques de projection des mots dans des espaces vectoriels continus conservant les propriétés syntactiques et sémantiques, pour généraliser à partir des connaissances initiales limitées de la tâche pour comprendre l'utilisateur. Nous nous attacherons aussi à proposer des solutions afin d'enrichir dynamiquement cette connaissance et étudier le rapport de cette technique avec les méthodes statistiques état de l'art. Là encore nos résultats expérimentaux montrent qu'il est possible d'atteindre des performances état de l'art avec très peu de données et de raffiner ces modèles ensuite avec des retours utilisateurs dont le coût peut lui-même être optimisé. / A dialogue system should give the machine the ability to interactnaturally and efficiently with humans. In this thesis, we focus on theissue of the development of stochastic dialogue systems. Thus, we especiallyconsider the Partially Observable Markov Decision Process (POMDP)framework which yields state-of-the-art performance on goal-oriented dialoguemanagement tasks. This model enables the system to cope with thecommunication ambiguities due to noisy channel and also to optimize itsdialogue management strategy directly from data with Reinforcement Learning (RL)methods.Considering statistical approaches often requires the availability of alarge amount of training data to reach good performance. However, corpora of interest are seldom readily available and collectingsuch data is both time consuming and expensive. For instance, it mayrequire a working prototype to initiate preliminary experiments with thesupport of expert users or to consider other alternatives such as usersimulation techniques.Very few studies to date have considered learning a dialogue strategyfrom scratch by interacting with real users, yet this solution is ofgreat interest. Indeed, considering the learning process as part of thelife cycle of a system offers a principle framework to dynamically adaptthe system to new conditions in an online and seamless fashion.In this thesis, we endeavour to provide solutions to make possible thisdialogue system cold start (nearly from scratch) but also to improve its ability to adapt to new conditions in operation (domain extension, new user profile, etc.).First, we investigate the conditions under which initial expertknowledge (such as expert rules) can be used to accelerate the policyoptimization of a learning agent. Similarly, we study how polarized userappraisals gathered throughout the course of the interaction can beintegrated into a reinforcement learning-based dialogue manager. Morespecifically, we discuss how this information can be cast intosocially-inspired rewards to speed up the policy optimisation for bothefficient task completion and user adaptation in an online learning setting.The results obtained on a reference task demonstrate that a(quasi-)optimal policy can be learnt in just a few hundred dialogues,but also that the considered additional information is able tosignificantly accelerate the learning as well as improving the noise tolerance.Second, we focus on reducing the development cost of the spoken language understanding module. For this, we exploit recent word embedding models(projection of words in a continuous vector space representing syntacticand semantic properties) to generalize from a limited initial knowledgeabout the dialogue task to enable the machine to instantly understandthe user utterances. We also propose to dynamically enrich thisknowledge with both active learning techniques and state-of-the-artstatistical methods. Our experimental results show that state-of-the-artperformance can be obtained with a very limited amount of in-domain andin-context data. We also show that we are able to refine the proposedmodel by exploiting user returns about the system outputs as well as tooptimize our adaptive learning with an adversarial bandit algorithm tosuccessfully balance the trade-off between user effort and moduleperformance.Finally, we study how the physical embodiment of a dialogue system in a humanoid robot can help the interaction in a dedicated Human-Robotapplication where dialogue system learning and testing are carried outwith real users. Indeed, in this thesis we propose an extension of thepreviously considered decision-making techniques to be able to take intoaccount the robot's awareness of the users' belief (perspective taking)in a RL-based situated dialogue management optimisation procedure.
24

FAZT: FEW AND ZERO-SHOT FRAMEWORK TO LEARN TEMPO-VISUAL EVENTS FROM LITTLE OR NO DATA

Naveen Madapana (11613925) 20 December 2021 (has links)
<div>Supervised classification methods based on deep learning have achieved great success in many domains and tasks that are previously unimaginable. Such approaches build on learning paradigms that require hundreds of examples in order to learn to classify objects or events. Thus, their immediate application to the domains with few or no observations is limited. This is because of the lack of ability to rapidly generalize to new categories from a few examples or from high-level descriptions of categories. This can be attributed to the significant gap between the way machines represent knowledge and the way humans represent categories in their minds and learn to recognize them. In this context, this research represents categories as semantic trees in a high-level attribute space and proposes an approach to utilize these representations to conduct N-Shot, Few-Shot, One-Shot, and Zero-Shot Learning (ZSL). This work refers to this paradigm as the problem of general classification (GCP) and proposes a unified framework for GCP referred to as the Few and Zero-Shot Technique (FAZT). FAZT framework is an end-to-end approach that uses trainable 3D convolutional neural networks and recurrent neural networks to simultaneously optimize for both the semantic and the classification tasks. Lastly, the problem of systematically obtaining semantic attributes by utilizing domain-specific ontologies is presented. The proposed framework is validated in the domains of hand gesture and action/activity recognition, however, this research can be applied to other domains such as video understanding, the study of human behavior, emotion recognition, etc. First, an attribute-based dataset for gestures is developed in a systematic manner by relying on literature in gestures and semantics, and crowdsourced platforms such as Amazon Mechanical Turk. To the best of our knowledge, this is the first ZSL dataset for hand gestures (ZSGL dataset). Next, our framework is evaluated in two experimental conditions: 1. Within-category (to test the attribute recognition power) and 2. Across-category (to test the ability to recognize an unknown category). In addition, we conducted experiments in zero-shot, one-shot, few-shot and continuous learning conditions in both open-set and closed-set scenarios. Results showed that our framework performs favorably on the ZSGL, Kinetics, UIUC Action, UCF101 and HMDB51 action datasets in all the experimental conditions.<br></div><div><br></div>
25

Multilingual Zero-Shot and Few-Shot Causality Detection

Reimann, Sebastian Michael January 2021 (has links)
Relations that hold between causes and their effects are fundamental for a wide range of different sectors. Automatically finding sentences that express such relations may for example be of great interest for the economy or political institutions. However, for many languages other than English, a lack of training resources for this task needs to be dealt with. In recent years, large, pretrained transformer-based model architectures have proven to be very effective for tasks involving cross-lingual transfer such as cross-lingual language inference, as well as multilingual named entity recognition, POS-tagging and dependency parsing, which may hint at similar potentials for causality detection. In this thesis, we define causality detection as a binary labelling problem and use cross-lingual transfer to alleviate data scarcity for German and Swedish by using three different classifiers that make either use of multilingual sentence embeddings obtained from a pretrained encoder or pretrained multilingual language models. The source languages in most of our experiments will be English, for Swedish we however also use a small German training set and a combination of English and German training data.  We try out zero-shot transfer as well as making use of limited amounts of target language data either as a development set or as additional training data in a few-shot setting. In the latter scenario, we explore the impact of varying sizes of training data. Moreover, the problem of data scarcity in our situation also makes it necessary to work with data from different annotation projects. We also explore how much this would impact our result. For German as a target language, our results in a zero-shot scenario expectedly fall short in comparison with monolingual experiments, but F1-macro scores between 60 and 65 in cases where annotation did not differ drastically still signal that it was possible to transfer at least some knowledge. When introducing only small amounts of target language data, already notable improvements were observed and with the full German training data of about 3,000 sentences combined with the most suitable English data set, the performance for German in some scenarios even almost matches the state of the art for monolingual experiments on English. The best zero-shot performance on the Swedish data was even outperforming the scores achieved for German. However, due to problems with the additional Swedish training data, we were not able to improve upon the zero-shot performance in a few-shot setting in a similar manner as it was the case for German.
26

Monolingual and Cross-Lingual Survey Response Annotation

Zhao, Yahui January 2023 (has links)
Multilingual natural language processing (NLP) is increasingly recognized for its potential in processing diverse text-type data, including those from social media, reviews, and technical reports. Multilingual language models like mBERT and XLM-RoBERTa (XLM-R) play a pivotal role in multilingual NLP. Notwithstanding their capabilities, the performance of these models largely relies on the availability of annotated training data. This thesis employs the multilingual pre-trained model XLM-R to examine its efficacy in sequence labelling to open-ended questions on democracy across multilingual surveys. Traditional annotation practices have been labour-intensive and time-consuming, with limited automation attempts. Previous studies often translated multilingual data into English, bypassing the challenges and nuances of native languages. Our study explores automatic multilingual annotation at the token level for democracy survey responses in five languages: Hungarian, Italian, Polish, Russian, and Spanish. The results reveal promising F1 scores, indicating the feasibility of using multilingual models for such tasks. However, the performance of these models is closely tied to the quality and nature of the training set. This research paves the way for future experiments and model adjustments, underscoring the importance of refining training data and optimizing model techniques for enhanced classification accuracy.
27

Zero/Few-Shot Text Classification : A Study of Practical Aspects and Applications / Textklassificering med Zero/Few-Shot Learning : En Studie om Praktiska Aspekter och Applikationer

Åslund, Jacob January 2021 (has links)
SOTA language models have demonstrated remarkable capabilities in tackling NLP tasks they have not been explicitly trained on – given a few demonstrations of the task (few-shot learning), or even none at all (zero-shot learning). The purpose of this Master’s thesis has been to investigate practical aspects and potential applications of zero/few-shot learning in the context of text classification. This includes topics such as combined usage with active learning, automated data labeling, and interpretability. Two different methods for zero/few-shot learning have been investigated, and the results indicate that:  • Active learning can be used to marginally improve few-shot performance, but it seems to be mostly beneficial in settings with very few samples (e.g. less than 10). • Zero-shot learning can be used produce reasonable candidate labels for classes in a dataset, given knowledge of the classification task at hand.  • It is difficult to trust the predictions of zero-shot text classification without access to a validation dataset, but IML methods such as saliency maps could find usage in debugging zero-shot models. / Ledande språkmodeller har uppvisat anmärkningsvärda förmågor i att lösa NLP-problem de inte blivit explicit tränade på – givet några exempel av problemet (few-shot learning), eller till och med inga alls (zero-shot learning). Syftet med det här examensarbetet har varit att undersöka praktiska aspekter och potentiella tillämpningar av zero/few-shot learning inom kontext av textklassificering. Detta inkluderar kombinerad användning med aktiv inlärning, automatiserad datamärkning, och tolkningsbarhet. Två olika metoder för zero/few-shot learning har undersökts, och resultaten indikerar att: • Aktiv inlärning kan användas för att marginellt förbättra textklassificering med few-shot learning, men detta verkar vara mest fördelaktigt i situationer med väldigt få datapunkter (t.ex. mindre än 10). • Zero-shot learning kan användas för att hitta lämpliga etiketter för klasser i ett dataset, givet kunskap om klassifikationsuppgiften av intresse. • Det är svårt att lita på robustheten i textklassificering med zero-shot learning utan tillgång till valideringsdata, men metoder inom tolkningsbar maskininlärning såsom saliency maps skulle kunna användas för att felsöka zero-shot modeller.
28

Topological regularization and relative latent representations / Topologisk regularisering och relativa latenta representationer

García Castellanos, Alejandro January 2023 (has links)
This Master's Thesis delves into the application of topological regularization techniques and relative latent representations within the realm of zero-shot model stitching. Building upon the prior work of Moschella et al. (2022) that introduces relative latent representations to enhance the similarities between latent spaces of different models, we incorporate the approach of Hofer et al. (2021), which combines Topological Data Analysis (TDA) and Machine Learning techniques for topological densification of class distributions in the latent space. The main research objective is to investigate the impact of topological regularization on zero-shot stitching performance when employing relative latent representations. Theoretical foundations for the relative transformation are established based on the intertwiner groups of activation functions. Empirical analyses are conducted to validate the assumptions underlying the construction of the relative transformation in the latent space. Moreover, experiments are performed on a Large Language Model trained on multilingual Amazon Reviews datasets to evaluate the effectiveness of zero-shot stitching while using the topological densification technique and the relative transformation. The findings indicate that the proposed methodologies can enhance the performance of multilingual model stitching. Specifically, enforcing the relative transformation to preserve the H0 homology death times distributions proves beneficial. Additionally, the presence of similar topological features plays a crucial role in achieving higher model compatibility. However, a more in-depth exploration of the geometric properties of the post-relative transformation latent space is necessary to further improve the topological densification technique. Overall, this work contributes to the emerging field of Topological Machine Learning and provides valuable insights for researchers in transfer learning and representation learning domains. / Denna masteruppsats undersöker tillämpningen av topologiska regleringstekniker och relativa latenta representationer inom området för zero-shot model stitching. Genom att bygga vidare på tidigare arbete av Moschella et al. (2022), som introducerade relativa latenta representationer för att förbättra likheterna mellan latenta rummet hos olika modeller, inkorporerar vi tillvägagångssättet av Hofer et al. (2021), som kombinerar topologisk dataanalys (TDA) och maskininlärningstekniker för topologisk ``förtätning'' av klassfördelningar i det latenta utrymmet. Den huvudsakliga forskningsuppgiften är att undersöka effekten av topologisk reglering på zero-shot model stitching-prestanda när man använder relativa latenta representationer. Teoretiska grunder för den relativa transformationen etableras baserat på intertwinergrupperna för aktiveringsfunktioner. Empiriska analyser genomförs för att validera antagandena som ligger till grund för konstruktionen av den relativa transformationen i det latenta rummen. Dessutom utförs experiment på en stor språkmodell tränad på multilinguella Amazon Reviews-dataset för att utvärdera effektiviteten hos zero-shot model stitching med Hofer's topologiska reglering och relativa transformation. Resultaten visar att de föreslagna metoderna kan förbättra prestationen hos zero-shot model stitching för flerspråkiga modeller. Specifikt är det fördelaktigt att tvinga den relativa transformationen att bevara H0 homologins dödstidsfördelningar. Dessutom spelar närvaron av liknande topologiska egenskaper en avgörande roll för att uppnå högre modellkompatibilitet. Dock krävs en mer ingående utforskning av de geometriska egenskaperna hos det latenta utrymmet efter den relativa transformationen för att ytterligare förbättra Hofer's topologiska reglering. Sammanfattningsvis bidrar detta arbete till det framväxande området Topologisk Maskininlärning och ger värdefulla insikter för forskare inom ``transfer-inlärning'' och representationsinlärningsdomäner.
29

AI Pinpoints Sustainability Priorities where Surveys Can’t : Towards Sustainable Public Procurement with Unsupervised Text Classification / AI hittar hållbarhetsprioriteringar där enkäter går bet : Mot hållbara offentliga upphandlingar med oövervakad textklassificering

Nordstrand, Mattias January 2024 (has links)
There are many sustainability issues related to products, services, and business processes. For example, the production, usage, and disposal of IT equipment all impact sustainability. Therefore, buying more sustainable IT equipment can make a difference. More sustainable IT equipment can be acquired by selecting IT equipment with sustainability certification, such as TCO Certified. TCO Certified makes sustainable purchasing easier, which is useful in public procurement. Public procurement is complex to guarantee objectivity and transparency. Transparency in public procurement also means many public procurement documents are available, which can be analyzed. We hypothesized that the sustainability focuses in these public procurement documents (what the text is about) reflect the sustainability priorities of professional buyers (in their minds, which is indirectly observable). With this link, we investigated differences in sustainability priorities by using a machine learning model for predicting sustainability focuses in public procurement documents. By using a large language model, we automatically extracted sustainability focuses in procurement documents from the e-procurement platform TED. Thereby, we measured the sustainability focus of countries all over the globe. Through interviews with experts, we saw several indications that the used method is a good way of pinpointing sustainability priorities. We provide maps of sustainability focuses around the world (in section 4.12). Moreover, we analyze the results in-depth. One interesting finding includes indications that countries generally do not prioritize an issue more if the issue is of a larger concern. Counterintuitively, countries prioritize an issue more if the issue is of lesser concern. One example of this is circularity focus, which we note is generally less in countries with worse waste management. To our knowledge, analyzing sustainability focuses in procurement documents has not been done on this scale before. We believe these novel results can lead the way for a better understanding of sustainability priorities around the world. / Det finns många hållbarhetsproblem relaterade till produkter, tjänster och affärsprocesser. Till exempel finns det en hållbarhetspåverkan i produktion, användning och avfallshantering av IT-utrustning. Inköp av hållbarare IT-utrustning kan därför göra skillnad. Mer hållbar IT-utrustning kan erhållas genom att välja hållbarhetscertifierad IT-utrustning som exempelvis TCO Certified. TCO Certified gör hållbara inköp enklare och är särskilt användbart inom offentlig upphandling. Offentlig upphandling är komplext i objektivitet- och transparenssyfte. Transparens inom offentlig upphandling innebär också att många offentliga upphandlingsdokument finns tillgängliga och kan analyseras. Vi antog att hållbarhetsfokusen inuti dessa offentliga upphandlings-dokument (vad texten handlar om) hänger ihop med de professionella inköparnas hållbarhetsprioriteringar (deras tankar/känslor/intressen). Med denna länk undersökte vi skillnader i hållbarhetsprioriteringar genom att använda en maskininlärningsmodell för att uppskatta hållbarhetsfokus i offentliga upphandlingsdokument. Med en storskalig språkmodell extraherade vi automatiskt hållbarhetsfokus i dokument från Tenders Electronics Daily. Därigenom mätte vi hållbarhetsfokus för länder över hela världen. Genom intervjuer med experter såg vi flera indikationer på att den använda metoden är ett bra sätt att uppskatta hållbarhetsprioriteringar på. Vi presenterar kartor över hållbarhetsfokus runt om i världen (i avsnitt 4.12). Dessutom analyserar vi resultaten på djupet. En intressant upptäckt är att länder generellt inte prioriterar ett problem mer om problemet är allvarligare i det landet utan snarare tvärtom. Länder prioriterar ett problem mer om problemet är av lägre allvarlighetsgrad i det landet. Till exempel ser vi att cirkularitetsfokuset i offentliga upphandlingar är mindre i länder med sämre avfallshantering. Att analysera hållbarhetsfokus i upphandlingsdokument har inte tidigare gjorts på denna skala såvitt vi känner till. Vi tror våra resultat kan bidra till en bättre förståelse av hållbarhetsprioriteringar runt om i världen.
30

Contributions à l'apprentissage grande échelle pour la classification d'images

Akata, Zeynep 06 January 2014 (has links) (PDF)
La construction d'algorithmes classifiant des images à grande échelle est devenue une tache essentielle du fait de la difficulté d'effectuer des recherches dans les immenses collections de données visuelles inetiquetées présentes sur Internet. Nous visons à classifier des images en fonction de leur contenu pour simplifier la gestion de telles bases de données. La classification d'images à grande échelle est un problème complèxe, de par l'importance de la taille des ensembles de données, tant en nombre d'images qu'en nombre de classes. Certaines de ces classes sont dites "fine-grained" (sémantiquement proches les unes des autres) et peuvent même ne contenir aucun représentant étiqueté. Dans cette thèse, nous utilisons des représentations état de l'art d'images et nous concentrons sur des méthodes d'apprentissage efficaces. Nos contributions sont (1) un banc d'essai d'algorithmes d'apprentissage pour la classification à grande échelle et (2) un nouvel algorithme basé sur l'incorporation d'étiquettes pour apprendre sur des données peu abondantes. En premier lieu, nous introduisons un banc d'essai d'algorithmes d'apprentissage pour la classification à grande échelle, dans le cadre entièrement supervisé. Il compare plusieurs fonctions objectifs pour apprendre des classifieurs linéaires, tels que "un contre tous", "multiclasse", "ranking", "ranking pondéré moyen" par descente de gradient stochastique. Ce banc d'essai se conclut en un ensemble de recommandations pour la classification à grande échelle. Avec une simple repondération des données, la stratégie "un contre tous" donne des performances meilleures que toutes les autres. Par ailleurs, en apprentissage en ligne, un pas d'apprentissage assez petit s'avère suffisant pour obtenir des résultats au niveau de l'état de l'art. Enfin, l'arrêt anticipé de la descente de gradient stochastique introduit une régularisation qui améliore la vitesse d'entraînement ainsi que la capacité de régularisation. Deuxièmement, face à des milliers de classes, il est parfois difficile de rassembler suffisamment de données d'entraînement pour chacune des classes. En particulier, certaines classes peuvent être entièrement dénuées d'exemples. En conséquence, nous proposons un nouvel algorithme adapté à ce scénario d'apprentissage dit "zero-shot". notre algorithme utilise des données parallèles, comme les attributs, pour incorporer les classes dans un espace euclidien. Nous introduisons par ailleurs une fonction pour mesurer la compatibilité entre image et étiquette. Les paramètres de cette fonction sont appris en utilisant un objectif de type "ranking". Notre algorithme dépasse l'état de l'art pour l'apprentissage "zero-shot", et fait preuve d'une grande flexibilité en permettant d'incorporer d'autres sources d'information parallèle, comme des hiérarchies. Il permet en outre une transition sans heurt du cas "zero-shot" au cas où peu d'exemples sont disponibles.

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