Abstract

Persistent sadness, emotion dysregulation, and loss of pleasure are the key characteristics of depression. It is one of the most commonly reported mental disorders and is a significant contributor to the global burden of disease. However, examining depression is still challenging, especially for individuals at risk for depression. The current thesis attempts to contribute to this area by examining the impact of depression risk on specific aspects of affective experience and perceptual level processing, focusing at global/local biases in individuals vulnerable to depression. More specifically we are interested in understanding whether vulnerability to depression alters the global/local perceptual processing when experience mood congruent versus incongruent music. It was hypothesized that individuals with high compared to low risk of depression would favour local processing and show reduced global precedence effect as depression is associated with the narrow scope of attentional processing. The effect was expected to be more pronounced in negative versus positive affective states because of the mood congruency, further strengthening the narrower scope of attention processing. We address this question by performing 2 studies. We created Navon’s compound stimuli to analyse global/local perceptual processing, and Kessler-10 (in Study 1) and PHQ-9(Study-2) and GAD-7(Study2) to examine depression risks. In Study 1, we used Vastfj ¨ all’s paper, which had a small dataset of ¨ music pieces and the corresponding mood they intend to induce, and in study 2, we used the soundtrack dataset to select music tracks of varying valence and arousal for stimulating particular affective state while performing the perceptual level judgment task. In the first study, which was conducted online, participants’ task was to identify the letter “H” or “O” presented either at the global or local (G/L) perceptual level, using Navon’s method. These stimuli were presented with background music eliciting either pleasant, unpleasant or neutral mood. Each of these categories had 3 music tracks assigned to them, which were randomly assigned to a given participant. Participants were randomly assigned 1 of the 9 tracks (of lyrical music), which belonged to one of the categories, i.e., pleasant, unpleasant, and neutral. Participants were asked to play the assigned track in the background while performing the G/L task. After completing the perceptual level judgment task, participants were asked to fill out the Kessler 10 and Brief Mood Introspection Scale (BMIS) to assess their predisposed and current emotional states respectively. In the second study, which was conducted in a controlled lab setting, participants perform the same perceptual level judgment task but with a four non-lyrical music pieces varying at the valence and arousal levels. In this study, participants were also asked to report their mood after every audio-condition, i.e., high and low arousing and valence conditions, by employing BMIS. Participants were also asked to report their feeling towards the music piece after every audio. Study 1 failed to demonstrate the impact of music on immediate mood manipulation. However, study 2 showed a significant impact of background music on immediate mood, indicating successful mood manipulation. The difference in mood manipulation could be a result of consistency in the music pieces presented to every participant and or enabling the control constant, in which the music was played as soon as the instruction was over and task started. Unlike the first experiment, the music play was automated in the second experiment. Despite reporting a change in immediate mood, individuals with high risks of depression reported consistently lower mood levels than individuals with low risk of depression. The experience of lower mood levels aligns with previous findings, suggesting a negative impact of depression on immediate mood experience. The overarching effect of predisposed mood, encompassing depression or anxiety, on individuals’ transient mood experience and perceptual task performance indicates the pervasive nature of depression. Unlike previous studies, individuals with depression showed faster reaction time for both global and local stimuli in both studies, 1 2, but with reduced accuracy in the second experiment, indicating a speed-accuracy trade-off. Despite faster reaction time, individuals with a high risk of depression showed reduced global precedence than their counterparts with a low risk of depression. The findings are discussed in light of theoretical models of depression.

Abstract

High-power lasers are essential for various commercial, industrial, and military applications. In recent years, there has been a notable trend towards up-scaling laser systems for long-distance propagation. Fiber lasers have revolutionized the laser industry due to their impressive efficiency, durability, and capacity to generate highpower beams in the kilowatt range. Nevertheless, the output power of a single fiber laser is constrained by factors like non-linear effects and excessive heating. Thus, beam combination is a viable solution to generate a high-power beam by combining several low-power lasers. Various methods for combining beams can be employed, including incoherent, coherent, and spectral beam combination techniques. In incoherent beam combinations, lasers are adjusted and combined individually, without consideration of their phase. On the other hand, coherent beam combination requires precise phase matching of the beams and involves sophisticated optical and electronic circuits. Spectral beam combination combines lasers of different wavelengths using diffractive optical elements. Coherent and spectral beam combination methods often lead to increased complexity and cost of the beam combination system. Therefore, incoherent beam combinations are frequently used, especially in directed energy applications, where high intensities at longer distances are essential. Through this technique, high-power laser beams can be generated without requiring precise phase control, making them more practical and cost-effective. This thesis outlines the design and analysis of a multi-channel incoherent beam combination (IBC) system, investigating the behavior of laser beams propagating in atmospheric turbulence. It presents various initial architectures for the IBC system and devises a fiber-actuator-based optical channel design to steer high-power laser beams effectively. To improve system efficiency, this thesis optimizes the initial beam waist and power of each laser beam across different atmospheric conditions. Furthermore, to enhance the combined intensity of the IBC system, it introduces collimated, inclined, and focused-inclined directing mechanisms. Additionally, this thesis delves into the modeling and analysis of alignment errors in fiber lasers and collimating lens arrays, addressing challenges and optimizing system performance. The proposed system optimizes beam-directing channel length and minimizes heat generation, ensuring improved efficiency and suitability for scenarios with moving target locations. This thesis also introduces the incorporation of higher-order Gaussian beams into a high-power incoherent beam combination system. Various higher-order Gaussian beams like Hermite Gaussian (HG) and Laguerre Gaussian (LG) beams can be used for beam combination to generate high intensity at various distances with limited hardware requirements. It provides optimal combination efficiency with minimal hardware requirements. Theoretical modeling and detailed analysis of Hermite and Laguerre Gaussian beams in atmospheric turbulence are conducted, investigating the influence of atmospheric parameters like jitter, turbulence, wind speed, and thermal blooming on beam spreading. This thesis further investigates the impact of steadystate thermal blooming on Laguerre Gaussian beams as they propagate through the atmosphere, considering various modes of LG beams. Additionally, it analyzes how atmospheric turbulence, beam wander, residual mechanical jitter, beam quality, thermal blooming, and bore-sight error collectively influence the intensity and spot size of the beams. Our findings presented in this thesis hold significance for the design of various beam combination systems and have implications for applications in industrial, military, communication, and information transmission within atmospheric propagation scenarios.

Abstract

In the past, curriculum generation has been an elaborate process requiring a team of experts. The resulting curriculum is suitable for all the students in a discipline and is usually limited to a single discipline. The first part of the thesis explores using natural language processing (NLP) techniques for text generation and their application in academic curriculum generation from a user-given set of documents. Specifically, we investigate the use of Wikipedia as an additional external knowledge source for generating informative, and concise academic curricula. We present a detailed analysis of our custom NLP technique and its applicability in curriculum generation. We evaluate the effectiveness of our approach by conducting experiments on a large dataset of academic curriculum content, especially content (NCERT textbook) that is widely used in India in most academic settings. Our results show that our approach significantly outperforms existing unsupervised approaches in generating informative and relevant curriculum content. In the second part of this thesis, we address the critical challenge of organizing the modules and topics generated through natural language processing into a coherent and logical sequence. While the initial phase of our research has successfully demonstrated the capability of NLP techniques, the effectiveness of such content heavily relies on the arrangement and flow of these components. The problem of ordering these modules and topics to create a structured and meaningful academic curriculum is a complex and essential task. In this part of our study, we delve into the realm of document arrangement using a new sequence generation model. In today’s information-rich environment, effective structuring and accessing of digital documents is of utmost importance. The system examines semantic and graph patterns within documents to create well-organized and contextually relevant sequences. By conducting a thorough assessment of current methods and introducing a new sequence generation model, this research aims to improve information retrieval, reduce the cognitive burden, and modernize knowledge management.

Abstract

Early detection and effective management of medical conditions significantly enhance patient outcomes, yet challenges persist due to limited resources, particularly in achieving widespread medical expertise. While supervised deep learning excels in medical image segmentation, the scarcity of labeled data poses significant hurdles for clinical applications. In response, self-supervised learning (SSL) systems have gained traction, leveraging unlabeled medical images to extract essential properties. Among SSL methods, contrastive learning stands out, aiming to minimize the distance between similar images while maximizing it between dissimilar ones, thereby enhancing segmentation accuracy. Current SSL methods exhibit limitations, prompting the advancement of unsupervised learning techniques that leverage data’s inherent structure to learn representations without the need for labeled data. A considerable challenge with unsupervised pre-training is domain shift, which occurs when the distribution of data used for pre-training differs from that used for fine-tuning. Addressing a crucial challenge in thoracic disease diagnosis using X-ray imaging, our work in the second chapter explores the need for anatomically accurate findings and why they shouldn’t be overlooked in interpretability assessments. We propose an innovative self-supervised and weakly supervised pre-training pipeline paired with an auxiliary loss followed by supervised fine-tuning to tackle these limitations effectively. Leveraging the Chest X-ray14 dataset for pre-training and the CheXpert dataset for fine-tuning ensures model stability and generalizability across diverse data sources. Specifically, our approach demonstrates a remarkable 31% improvement in Intersection over Union on the NIH CXR dataset, enabling precise classification across 14 chest X-ray categories. While our focus lies on chest X-rays, our proposed approach extends its applicability to various imaging modalities and clinical workflows, showcasing its broad impact in medical imaging and diagnostics. In our third chapter, we expand the Swin Transformer architecture to learn from multiple medical imaging modalities, enhancing downstream performance. Our novel Swin-FUSE (Swin Multi-Modal Fusion for UnSupervised Enhancement) framework offers several advantages: utilizing CTs and MRIs for pre-training to create complementary feature representations, incorporating a domain-invariance module (DIM) to enhance domain adaptability, and demonstrating high generalizability beyond pretrained tasks. Empirical results on publicly available 3D segmentation datasets showcase a marginal 1-2% performance trade-off compared to single-modality models while achieving a remarkable 27% improvement on out-of-distribution modalities. In our fourth chapter, we introduce an attention-based model for the 2023 ISBI X-ray Projectomic Reconstruction Challenge, aimed at fostering exploration into XNH imaging challenges, particularly focusing on the white matter region of the rodent brain. Our proposed AGU-Net model demonstrates enhanced performance in merging segmented regions and producing accurate segmentations with reduced error rates, as evidenced by its higher scores in the Normalized ERL and Rand merge metrics. Our model achieved an outstanding XPRESS score of 0.8159 on the test set, securing 3 rd place. In summary, this thesis presents innovative solutions leveraging self-supervised pre-training and contrastive learning to enhance representation learning in medical imaging. These advancements extend to domain adaptation tasks, ultimately enhancing the interpretability of conventional black-box machine learning models, thus paving the way for more reliable and clinically relevant diagnostic tools

Abstract

This thesis explores the development, implementation, and evaluation of a BLE-based, mobilecentric access control system that aims to enhance the user experience and reduce dependencies on traditional access hardware. By employing a comprehensive methodology that includes prototype development and user satisfaction analysis, this study demonstrates significant improvements in system efficiency and user engagement. Observations during the research revealed significant improvements in both user experience and system performance compared with mobile access solutions in the market. More than 2000 readers have been installed at various customer sites across India, and around 100,000 users have used mobile access daily for their access to their office space or tech parks. The introduction of asymmetric and symmetric encryption algorithms to provide advanced hands-free mobile access resulted in a reduction in access time from an average of 1200ms to 300ms. The customer study suggests that the system not only adheres to stringent security standards, but also excels in scalability and user satisfaction, achieving a CSAT of over 92%. These results underscore the potential of mobile-centric solutions to revolutionize access control systems by marrying security with convenience

Abstract

Systems of linear equations are fundamental to numerous scientific and engineering domains, often arising from the discretization of partial differential equations (PDEs) used to model real-world phenomena. These systems can be computationally expensive to solve, especially for large-scale problems. Therefore, developing efficient solvers for linear systems is crucial for advancing scientific computing. This thesis examines the use of recursive partitioning for solving linear systems, focusing on systems derived from 3-dimensional structured grids. The research emphasizes the development of a preconditioner based on this partitioning strategy to enhance the efficiency of iterative solvers, notably the Preconditioned Conjugate Gradient (PCG) method. By decomposing the original problem into smaller, more manageable sub-problems, this approach aims to reduce the overall computational time. This strategy aligns with the principles of parallel computing, where tasks are divided and processed concurrently across multiple processors to achieve faster solutions. The effectiveness of the proposed preconditioner is assessed using Skyscraper problems with checkerboard variable jumps as test cases. These problems, known for their intricate coefficient structures, serve as relevant benchmarks for evaluating the performance gains offered by the partitioning approach.

Abstract

Road Networks are the most preferred and important mode of transportation due to its accessibility and connectivity thereby influencing the social and economic activity patterns. Therefore, understanding road network behaviour is crucial for the economic and social development of the country. Geographical Information System(GIS) is designed to store, analyse and manipulate geographical data. Since road network data forms a major part of geographical data, GIS can be employed in understanding and utilizing road network behaviour for a variety of applications. Due to the rapidly increasing road network information and its complexity, road network data management for GIS applications is becoming increasingly difficult. In order to understand the road network behaviour and achieve better road network data management, the study proposes Skeleton Network of a road network extracted using map generalization techniques by exploiting the inherent node/edge characteristics. The Skeleton Network is the most significant and representative network subset capturing the overall connectivity and structure of the road network. Cartographic/Map generalization and Wayfinding/transportation planning are two very important GIS applications. In this work a Model generalization methodology has been proposed which comprises of quadtree based node indexing, density-based node selection, betweenness calculation and network skeleton generation for different scales. The results demonstrate that the proposed methodology has been able to reduce the level of details in the road network by choosing relevant road segments and has also maintained the main characteristics and structure as well as the essential topological, geometrical and semantic properties of the provided road network. In the study we also explore effectiveness of skeleton networks in wayfinding. We propose a method that combines network skeletons and disconnected zones. The methods effectiveness is tested on real-world OpenStreetMap (OSM) road networks, evaluating the balance between computational efficiency and path accuracy. Furthermore we also explore portability of such path computation algorithm into mobile devices. The portability of the skeleton model to mobile devices proves to be quite effective. Less memory footprint, lower CPU and power consumption, efficient and significantly accurate path computation further solidify the feasibility and applicability of the approach.

Abstract

Trajectory planning plays a critical role in autonomous navigation, where the emphasis lies on planning smooth, collision-free trajectories that comply with the robot’s kinematic constraints. It finds itself in various applications, such as autonomous driving, search and rescue, construction, and forestry. In the case of autonomous driving, the idea is to mimic human driving, which involves complex decisions like merging and overtaking, along with lower-level commands. However, standard approaches fail to capture the multi-modal characteristic of human driving. Although autonomous driving finds itself in structured, smooth, planar roads, applications like search and rescue and construction involve uneven terrains. Thus, there should be a distinction in the way trajectory optimization is approached in these scenarios, away from 2D approaches. The first study introduces two methods, which accomplish the task of accomplishing a given high-level driving task. The first method achieves the task of generating trajectories for multiple goals, by parallelizing existing state-of-the-art solvers using multiple CPU threads. The second method introduces a Multi-Convex MPC is based on reformulating the collision avoidance and kinematic constraints and is solved using the Alternating Minimization(AM) technique. The second study introduces an approach to planning trajectories on uneven terrains. It leverages the digital terrain information, represented as a point cloud. The pose of the robot is represented in 6dof. The wheel terrain interaction and pose are expressed as a non-linear problem. The resulting pose prediction, along with Sampling based Model Predictive Control(SMPC), are used to sample smooth and stable trajectories. These studies collectively help advance the understanding of trajectory planning and its implementation in different scenarios.

Abstract

Solar UV radiation challenges the integrity of the genome, causing severe mutations and potentially leading to cancer. Regulatory regions of DNA are particularly important for transcription, and hence preventing damage formation in those regions is essential. When UV damage occurs, it triggers various response systems in the body, the most common being nucleotide excision repair (NER). Global genome nucleotide excision repair (GGNER) takes a broad approach to the repair process, with proteins like Xeroderma Pigmentosum C (XPC) scanning the entire genome for lesions. The mechanism by which XPC identify damage sites from a long, perfectly matched DNA duplex is still not completely resolved. In this thesis, we examine three stages of handling DNA damage: (A) prevention, (B) recognition, and (C) binding to repair protein XPC. Experimentally, it has been found that histone methyltransferase ASH1L prevents the formation of cyclobutane pyrimidine dimers (CPD) in enhancer regions of DNA. Our simulations show that ASH1L binding distorts the geometry of adjacent base pairs, disfavoring the induction of CPD lesions. Subsequently, we studied how the induction of mismatch damage affects the dynamics of DNA fluctuations. FRET lifetime and efficiency analysis has shown that mismatches well recognized by XPC exhibit different intrinsic fluctuations compared to poorly recognized mismatches. We computationally calculated the FRET efficiency for different mismatches from MD simulations. Further, umbrella sampling simulations showed that the fluctuations in the CCC mismatch (a wellrepaired mismatch) can be mapped to a metastable state not accessible to matched DNA or poorly recognized lesions. This suggests a conformational selection mechanism of repair by XPC. Lastly, we investigated the mechanism by which XPC binds to sites of damage. For this study, we used the crystal structure of RAD4 (the yeast ortholog of XPC) bound to pyrimidine (6-4) pyrimidone photoproducts (64pp) to determine the mechanism of RAD4 binding. Using the nudged elastic band method, we determined the minimum energy pathway between the unbound and productively bound states of RAD4. The obtained pathway reveals that the β hairpins of RAD4 cause the DNA to sample multiple twist states, finally reaching a stable twist angle that is favorable for binding. Furthermore, using enhanced sampling in conjunction with our minimum energy path, we determined the energetic cost of some of the key binding events.

Abstract

Inverse Rendering is a core Computer Vision problem as it involves complete decomposition of an image into its constituting atomic components. These components can be stand-alone analyzed or suitably modified and recombined to solve the required image analysis task or achieve the required generative content. Rather than aiming for full decomposition, many applications only require decomposition into only a few factors which themselves are simple combinations of the underlying atomic components. This makes image factorization a critical first step in several computer vision and image processing applications. This factorization could either be optically motivated like reflectance-shading decomposition, white-balancing, illumination spectra-separation etc. or semantically motivated like style-content disentanglement, foreground-background matting etc. In this thesis, we focus on the former and present several image factorization solutions with an aim to use it for a downstream image based rendering application. Initially, we assume Lambertian reflection only under the classical image formation model inspired from the Retinex theory. Our first solution in this category requires multiple images of the scene as input, which we then relax for our second solution which works on the single image input. Afterwards, we propose a novel image formation model based on the specularity of the image content and provide two solutions using the low light enhancement problem as the vehicle for empirical validation. Towards the end, a novel prior induction technique is also presented based on learnable concepts and its utility is shown by improving results of pre-existing state-of-the-art image decomposition networks. We conclude with a summary, limitations, future research directions and possible additional applications. The thesis is organized into four units respectively discussing the problem definition and significance; Lambertian reflection based Intrinsic Image Decomposition problem, specularity respecting novel illumination factorization methods and finally concept based model analysis and conclusion. We hope that with the problems and solutions discussed in this thesis we will be able to define and highlight the importance of image factorization step in multiple vision tasks and pique reader’s interest in this research problem for image generation and beyond.