4,003 research outputs found
Endogenous measures for contextualising large-scale social phenomena: a corpus-based method for mediated public discourse
This work presents an interdisciplinary methodology for developing endogenous measures of group membership through analysis of pervasive linguistic patterns in public discourse. Focusing on political discourse, this work critiques the conventional approach to the study of political participation, which is premised on decontextualised, exogenous measures to characterise groups. Considering the theoretical and empirical weaknesses of decontextualised approaches to large-scale social phenomena, this work suggests that contextualisation using endogenous measures might provide a complementary perspective to mitigate such weaknesses.
This work develops a sociomaterial perspective on political participation in mediated discourse as affiliatory action performed through language. While the affiliatory function of language is often performed consciously (such as statements of identity), this work is concerned with unconscious features (such as patterns in lexis and grammar). This work argues that pervasive patterns in such features that emerge through socialisation are resistant to change and manipulation, and thus might serve as endogenous measures of sociopolitical contexts, and thus of groups.
In terms of method, the work takes a corpus-based approach to the analysis of data from the Twitter messaging service whereby patterns in users’ speech are examined statistically in order to trace potential community membership. The method is applied in the US state of Michigan during the second half of 2018—6 November having been the date of midterm (i.e. non-Presidential) elections in the United States. The corpus is assembled from the original posts of 5,889 users, who are nominally geolocalised to 417 municipalities. These users are clustered according to pervasive language features. Comparing the linguistic clusters according to the municipalities they represent finds that there are regular sociodemographic differentials across clusters. This is understood as an indication of social structure, suggesting that endogenous measures derived from pervasive patterns in language may indeed offer a complementary, contextualised perspective on large-scale social phenomena
Resource Management in Mobile Edge Computing for Compute-intensive Application
With current and future mobile applications (e.g., healthcare, connected vehicles, and smart grids) becoming increasingly compute-intensive for many mission-critical use cases, the energy and computing capacities of embedded mobile devices are proving to be insufficient to handle all in-device computation. To address the energy and computing shortages of mobile devices, mobile edge computing (MEC) has emerged as a major distributed computing paradigm. Compared to traditional cloud-based computing, MEC integrates network control, distributed computing, and storage to customizable, fast, reliable, and secure edge services that are closer to the user and data sites. However, the diversity of applications and a variety of user specified requirements (viz., latency, scalability, availability, and reliability) add additional complications to the system and application optimization problems in terms of resource management. In this thesis dissertation, we aim to develop customized and intelligent placement and provisioning strategies that are needed to handle edge resource management problems for different challenging use cases: i) Firstly, we propose an energy-efficient framework to address the resource allocation problem of generic compute-intensive applications, such as Directed Acyclic Graph (DAG) based applications. We design partial task offloading and server selection strategies with the purpose of minimizing the transmission cost. Our experiment and simulation results indicate that partial task offloading provides considerable energy savings, especially for resource-constrained edge systems. ii) Secondly, to address the dynamism edge environments, we propose solutions that integrate Dynamic Spectrum Access (DSA) and Cooperative Spectrum Sensing (CSS) with fine-grained task offloading schemes. Similarly, we show the high efficiency of the proposed strategy in capturing dynamic channel states and enforcing intelligent channel sensing and task offloading decisions. iii) Finally, application-specific long-term optimization frameworks are proposed for two representative applications: a) multi-view 3D reconstruction and b) Deep Neural Network (DNN) inference. Here, in order to eliminate redundant and unnecessary reconstruction processing, we introduce key-frame and resolution selection incorporated with task assignment, quality prediction, and pipeline parallelization. The proposed framework is able to provide a flexible balance between reconstruction time and quality satisfaction. As for DNN inference, a joint resource allocation and DNN partitioning framework is proposed. The outcomes of this research seek to benefit the future distributed computing, smart applications, and data-intensive science communities to build effective, efficient, and robust MEC environments
Affinity-Based Reinforcement Learning : A New Paradigm for Agent Interpretability
The steady increase in complexity of reinforcement learning (RL) algorithms is accompanied by a corresponding increase in opacity that obfuscates insights into their devised strategies. Methods in explainable artificial intelligence seek to mitigate this opacity by either creating transparent algorithms or extracting explanations post hoc. A third category exists that allows the developer to affect what agents learn: constrained RL has been used in safety-critical applications and prohibits agents from visiting certain states; preference-based RL agents have been used in robotics applications and learn state-action preferences instead of traditional reward functions. We propose a new affinity-based RL paradigm in which agents learn strategies that are partially decoupled from reward functions. Unlike entropy regularisation, we regularise the objective function with a distinct action distribution that represents a desired behaviour; we encourage the agent to act according to a prior while learning to maximise rewards. The result is an inherently interpretable agent that solves problems with an intrinsic affinity for certain actions. We demonstrate the utility of our method in a financial application: we learn continuous time-variant compositions of prototypical policies, each interpretable by its action affinities, that are globally interpretable according to customers’ financial personalities.
Our method combines advantages from both constrained RL and preferencebased RL: it retains the reward function but generalises the policy to match a defined behaviour, thus avoiding problems such as reward shaping and hacking. Unlike Boolean task composition, our method is a fuzzy superposition of different prototypical strategies to arrive at a more complex, yet interpretable, strategy.publishedVersio
OCM 2023 - Optical Characterization of Materials : Conference Proceedings
The state of the art in the optical characterization of materials is advancing rapidly. New insights have been gained into the theoretical foundations of this research and exciting developments have been made in practice, driven by new applications and innovative sensor technologies that are constantly evolving.
The great success of past conferences proves the necessity of a platform for presentation, discussion and evaluation of the latest research results in this interdisciplinary field
On the Principles of Evaluation for Natural Language Generation
Natural language processing is concerned with the ability of computers to understand natural language texts, which is, arguably, one of the major bottlenecks in the course of chasing the holy grail of general Artificial Intelligence. Given the unprecedented success of deep learning technology, the natural language processing community has been almost entirely in favor of practical applications with state-of-the-art systems emerging and competing for human-parity performance at an ever-increasing pace. For that reason, fair and adequate evaluation and comparison, responsible for ensuring trustworthy, reproducible and unbiased results, have fascinated the scientific community for long, not only in natural language but also in other fields. A popular example is the ISO-9126 evaluation standard for software products, which outlines a wide range of evaluation concerns, such as cost, reliability, scalability, security, and so forth. The European project EAGLES-1996, being the acclaimed extension to ISO-9126, depicted the fundamental principles specifically for evaluating natural language technologies, which underpins succeeding methodologies in the evaluation of natural language.
Natural language processing encompasses an enormous range of applications, each with its own evaluation concerns, criteria and measures. This thesis cannot hope to be comprehensive but particularly addresses the evaluation in natural language generation (NLG), which touches on, arguably, one of the most human-like natural language applications. In this context, research on quantifying day-to-day progress with evaluation metrics lays the foundation of the fast-growing NLG community. However, previous works have failed to address high-quality metrics in multiple scenarios such as evaluating long texts and when human references are not available, and, more prominently, these studies are limited in scope, given the lack of a holistic view sketched for principled NLG evaluation.
In this thesis, we aim for a holistic view of NLG evaluation from three complementary perspectives, driven by the evaluation principles in EAGLES-1996: (i) high-quality evaluation metrics, (ii) rigorous comparison of NLG systems for properly tracking the progress, and (iii) understanding evaluation metrics. To this end, we identify the current state of challenges derived from the inherent characteristics of these perspectives, and then present novel metrics, rigorous comparison approaches, and explainability techniques for metrics to address the identified issues.
We hope that our work on evaluation metrics, system comparison and explainability for metrics inspires more research towards principled NLG evaluation, and contributes to the fair and adequate evaluation and comparison in natural language processing
Disentanglement Learning for Text-Free Voice Conversion
Voice conversion (VC) aims to change the perceived speaker identity of a speech signal from one to another, while preserving the linguistic content. Recent state-of-the-art VC systems typically are dependent on automatic speech recognition (ASR) models and they have gained great successes. Results of recent challenges show these VC systems have reached a level of performance close to real human voices. However, they are highly relying on the performance of the ASR models, which might experience degradations in practical applications because of the mismatch between training and test data.
VC systems independent of ASR models are typically regarded as text-free systems. They commonly apply disentanglement learning methods to remove the speaker information of a speech signal, for example, vector quantisation (VQ) or instance normalisation (IN). However, text-free VC systems have not reached the same level of performance as text-dependent systems. This thesis mainly studies disentanglement learning methods for improving the performance of text-free VC systems. Three major contributions are summarised as follows.
Firstly, in order to improve the performance of an auto-encoder based VC model, the information loss issue caused by the VQ of the model is studied. Two disentanglement learning methods are exploited to replace the VQ of the model. Experiments show that these two methods improve the naturalness and intelligibility performance of the model, but hurt the speaker similarity performance of the model. The reason for the degradation of the speaker similarity performance is studied in the further analysis experiments.
Next, the performance and the robustness of Generative Adversarial Networks (GAN) based VC models are studied. In order to improve the performance and the robustness of an GAN based VC model, a new model is proposed. This new model introduces a new speaker adaptation layer for alleviating the information loss issue caused by a speaker adaptation method based on IN. Experiments show that the proposed model outperformed the baseline models on VC performance and robustness.
The third contribution studies whether Self-Supervised Learning (SSL) based VC models can reach the same level of performance of the state-of-the-art text-dependent models. An encoder-decoder framework is established for experiments. In this framework, the performance of a VC systems implemented with a SSL model can be compared to a VC system implemented with an ASR model. Experiment results show that SSL based VC models can reach the same level of naturalness performance of the state-of-the-art text- dependent VC models. Also, SSL based VC models gained advantages on intelligibility performance when tested on out of domain target speakers. But they performed worse on speaker similarity
Medical Image Segmentation: Thresholding and Minimum Spanning Trees
I bildesegmentering deles et bilde i separate objekter eller regioner. Det er et essensielt skritt i bildebehandling for å definere interesseområder for videre behandling eller analyse.
Oppdelingsprosessen reduserer kompleksiteten til et bilde for å forenkle analysen av attributtene oppnådd etter segmentering. Det forandrer representasjonen av informasjonen i det opprinnelige bildet og presenterer pikslene på en måte som er mer meningsfull og lettere å forstå.
Bildesegmentering har forskjellige anvendelser. For medisinske bilder tar segmenteringsprosessen sikte på å trekke ut bildedatasettet for å identifisere områder av anatomien som er relevante for en bestemt studie eller diagnose av pasienten. For eksempel kan man lokalisere berørte eller anormale deler av kroppen. Segmentering av oppfølgingsdata og baseline lesjonssegmentering er også svært viktig for å vurdere behandlingsresponsen.
Det er forskjellige metoder som blir brukt for bildesegmentering. De kan klassifiseres basert på hvordan de er formulert og hvordan segmenteringsprosessen utføres. Metodene inkluderer de som er baserte på terskelverdier, graf-baserte, kant-baserte, klynge-baserte, modell-baserte og hybride metoder, og metoder basert på maskinlæring og dyp læring. Andre metoder er baserte på å utvide, splitte og legge sammen regioner, å finne diskontinuiteter i randen, vannskille segmentering, aktive kontuter og graf-baserte metoder.
I denne avhandlingen har vi utviklet metoder for å segmentere forskjellige typer medisinske bilder. Vi testet metodene på datasett for hvite blodceller (WBCs) og magnetiske resonansbilder (MRI). De utviklede metodene og analysen som er utført på bildedatasettet er presentert i tre artikler.
I artikkel A (Paper A) foreslo vi en metode for segmentering av nukleuser og cytoplasma fra hvite blodceller. Metodene estimerer terskelen for segmentering av nukleuser automatisk basert på lokale minima. Metoden segmenterer WBC-ene før segmentering av cytoplasma avhengig av kompleksiteten til objektene i bildet. For bilder der WBC-ene er godt skilt fra røde blodlegemer (RBC), er WBC-ene segmentert ved å ta gjennomsnittet av bilder som allerede var filtrert med en terskelverdi. For bilder der RBC-er overlapper WBC-ene, er hele WBC-ene segmentert ved hjelp av enkle lineære iterative klynger (SLIC) og vannskillemetoder. Cytoplasmaet oppnås ved å trekke den segmenterte nukleusen fra den segmenterte WBC-en. Metoden testes på to forskjellige offentlig tilgjengelige datasett, og resultatene sammenlignes med toppmoderne metoder.
I artikkel B (Paper B) foreslo vi en metode for segmentering av hjernesvulster basert på minste dekkende tre-konsepter (minimum spanning tree, MST). Metoden utfører interaktiv segmentering basert på MST. I denne artikkelen er bildet lastet inn i et interaktivt vindu for segmentering av svulsten. Fokusregion og bakgrunn skilles ved å klikke for å dele MST i to trær. Ett av disse trærne representerer fokusregionen og det andre representerer bakgrunnen. Den foreslåtte metoden ble testet ved å segmentere to forskjellige 2D-hjerne T1 vektede magnetisk resonans bildedatasett. Metoden er enkel å implementere og resultatene indikerer at den er nøyaktig og effektiv.
I artikkel C (Paper C) foreslår vi en metode som behandler et 3D MRI-volum og deler det i hjernen, ikke-hjernevev og bakgrunnsegmenter. Det er en grafbasert metode som bruker MST til å skille 3D MRI inn i de tre regiontypene. Grafen lages av et forhåndsbehandlet 3D MRI-volum etterfulgt av konstrueringen av MST-en. Segmenteringsprosessen gir tre merkede, sammenkoblende komponenter som omformes tilbake til 3D MRI-form. Etikettene brukes til å segmentere hjernen, ikke-hjernevev og bakgrunn. Metoden ble testet på tre forskjellige offentlig tilgjengelige datasett og resultatene ble sammenlignet med ulike toppmoderne metoder.In image segmentation, an image is divided into separate objects or regions. It is an essential step in image processing to define areas of interest for further processing or analysis.
The segmentation process reduces the complexity of an image to simplify the analysis of the attributes obtained after segmentation. It changes the representation of the information in the original image and presents the pixels in a way that is more meaningful and easier to understand.
Image segmentation has various applications. For medical images, the segmentation process aims to extract the image data set to identify areas of the anatomy relevant to a particular study or diagnosis of the patient. For example, one can locate affected or abnormal parts of the body. Segmentation of follow-up data and baseline lesion segmentation is also very important to assess the treatment response.
There are different methods used for image segmentation. They can be classified based on how they are formulated and how the segmentation process is performed. The methods include those based on threshold values, edge-based, cluster-based, model-based and hybrid methods, and methods based on machine learning and deep learning. Other methods are based on growing, splitting and merging regions, finding discontinuities in the edge, watershed segmentation, active contours and graph-based methods.
In this thesis, we have developed methods for segmenting different types of medical images. We tested the methods on datasets for white blood cells (WBCs) and magnetic resonance images (MRI). The developed methods and the analysis performed on the image data set are presented in three articles.
In Paper A we proposed a method for segmenting nuclei and cytoplasm from white blood cells. The method estimates the threshold for segmentation of nuclei automatically based on local minima. The method segments the WBCs before segmenting the cytoplasm depending on the complexity of the objects in the image. For images where the WBCs are well separated from red blood cells (RBCs), the WBCs are segmented by taking the average of images that were already filtered with a threshold value. For images where RBCs overlap the WBCs, the entire WBCs are segmented using simple linear iterative clustering (SLIC) and watershed methods. The cytoplasm is obtained by subtracting the segmented nucleus from the segmented WBC. The method is tested on two different publicly available datasets, and the results are compared with state of the art methods.
In Paper B, we proposed a method for segmenting brain tumors based on minimum spanning tree (MST) concepts. The method performs interactive segmentation based on the MST. In this paper, the image is loaded in an interactive window for segmenting the tumor. The region of interest and the background are selected by clicking to split the MST into two trees. One of these trees represents the region of interest and the other represents the background. The proposed method was tested by segmenting two different 2D brain T1-weighted magnetic resonance image data sets. The method is simple to implement and the results indicate that it is accurate and efficient.
In Paper C, we propose a method that processes a 3D MRI volume and partitions it into brain, non-brain tissues, and background segments. It is a graph-based method that uses MST to separate the 3D MRI into the brain, non-brain, and background regions. The graph is made from a preprocessed 3D MRI volume followed by constructing the MST. The segmentation process produces three labeled connected components which are reshaped back to the shape of the 3D MRI. The labels are used to segment the brain, non-brain tissues, and the background. The method was tested on three different publicly available data sets and the results were compared to different state of the art methods.Doktorgradsavhandlin
Mathematical Modeling of Biological Systems
Mathematical modeling is a powerful approach supporting the investigation of open problems in natural sciences, in particular physics, biology and medicine. Applied mathematics allows to translate the available information about real-world phenomena into mathematical objects and concepts. Mathematical models are useful descriptive tools that allow to gather the salient aspects of complex biological systems along with their fundamental governing laws, by elucidating the system behavior in time and space, also evidencing symmetry, or symmetry breaking, in geometry and morphology. Additionally, mathematical models are useful predictive tools able to reliably forecast the future system evolution or its response to specific inputs. More importantly, concerning biomedical systems, such models can even become prescriptive tools, allowing effective, sometimes optimal, intervention strategies for the treatment and control of pathological states to be planned. The application of mathematical physics, nonlinear analysis, systems and control theory to the study of biological and medical systems results in the formulation of new challenging problems for the scientific community. This Special Issue includes innovative contributions of experienced researchers in the field of mathematical modelling applied to biology and medicine
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