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Self-Supervised Visual Representation Learning for Medical Image Analysis: A Comprehensive Survey
No full textDeep learning has developed as a great tool for many computer vision or natural language processing tasks. However, supervised deep learning algorithms require a large amount of labelled data to achieve satisfactory performance. Self-supervised learning, a subcategory of unsupervised learning, circumvents the issue of the requirement of a large amount of data by learning representations from the data without labelled examples. Over the past few years, Self-supervised learning has been applied to various tasks to achieve performance at par with or surpassing the supervised counterparts in several tasks. However, the progress has been so rapid, that a comprehensive account of these developments is lacking. In this study, we attempt to present a review of those methods and show how the self-supervised learning paradigm evolved over the years. Additionally, we also present an exhaustive review of the self-supervised methods applied to medical image analysis. Furthermore, we also present an extensive compilation of the details of the datasets used in the different works and provide performance metrics of some notable works on image and video datasets
Sphere fibrations over highly connected manifolds
No full textWe construct sphere fibrations over (Formula presented.) -connected (Formula presented.) -manifolds such that the total space is a connected sum of sphere products. More precisely, for (Formula presented.) even, we construct fibrations (Formula presented.), where (Formula presented.) is a (Formula presented.) -connected (Formula presented.) -dimensional Poincaré duality complex that satisfies (Formula presented.), in a localised category of spaces. The construction of the fibration is proved for (Formula presented.), where the prime 2, and the primes that occur as torsion in (Formula presented.) are inverted. In specific cases, by either assuming (Formula presented.) is small, or assuming (Formula presented.) is large we can reduce the number of primes that need to be inverted. Integral results are obtained for (Formula presented.) or 4, and if (Formula presented.) is bigger than the number of cyclic summands in the stable stem (Formula presented.), we obtain results after inverting 2. Finally, we prove some applications for fibrations over (Formula presented.), and for looped configuration spaces
Symmetry harmonization: exploring deformed oscillators and dissipative dynamics through the glass of Newton–Hooke algebra
No full textMotivated by the symmetry in the non-relativistic limit of anti-de Sitter geometry, we employ planar dynamical models featuring exotic (deformed) harmonic oscillators, presented through direct and indirect Lagrangian representations. The latter introduces Bateman dissipative oscillator system. Analyzing these dynamic systems with a first-order Lagrangian scheme, our phase-space-based approach utilizes the moment map components to reveal the underlying symmetry algebra. This obtained algebra, interpreted as an extended version of Newton–Hooke (NH) cosmological symmetry algebras, has the potential to cast an augmented non-relativistic shadow over the expanding universe, offering an insightful perspective on extended NH spacetime in 2+1 dimensions through our dynamical realizations
Synchronization in adaptive higher-order networks
No full textMany natural and human-made complex systems feature group interactions that adapt over time in response to their dynamic states. However, most of the existing adaptive network models fall short of capturing these group dynamics, as they focus solely on pairwise interactions. In this study, we employ adaptive higher-order networks to describe these systems by proposing a general framework by incorporating both adaptivity and group interactions. We demonstrate that global synchronization can exist in those complex structures and we provide the necessary conditions for the emergence of a stable synchronous state. We first study the setting in which both pairwise and higher-order interactions are allowed, but only the former adapt in time. We then extend this framework by including higher-order adaptive interactions. In both analyzed settings, we show that the necessary condition is strongly related to the master stability equation, allowing to separate the dynamical and structural properties. We illustrate our theoretical findings through the relevant examples involving adaptive higher-order networks of coupled generalized Kuramoto oscillators with phase lag, coupled with an all-to-all and a nonlocal ring-like structure. We also show that the interplay of group interactions and adaptive connectivity results in the formation of stability regions that can induce transitions between synchronization and desynchronization. Our findings also reveal that the introduction of higher-order adaptation significantly alters the synchronization stability compared to the case with constant higher-order interactions
The distribution of invasive alien plant species in peri-urban areas: a case study from the city of Kolkata
No full textUrbanization results in rapid land transformations impacting bio-diversity and ecosystem services. With urban expansions population transition will predominantly occur in the peri-urban areas of the world’s metropolitan cities like India, China, and Nigeria, which are often located in naturally species-rich regions and highly vulnerable to plant invasions. Thus it is increasingly important to monitor the changes occurring in the floral composition in such areas. The present study was therefore conducted across peri-urban habitats of Greater Kolkata, in order to establish a baseline data on plant species richness, invasive species co-occurrence, invader dominance and understand the bio-diversity pattern. Results showed a total of 62 plant species, mostly annual herbs, belonging to 29 families constituting the species richness in the study area. Both native (53%) and alien (47%) species were almost equally distributed and invasive species (32%) represented the majority among alien species. The findings also indicate that the species pool was dominated by sparsely distributed species. The number of invasive species varied from 2 to 9 per site, with 80% of sites supporting 3 or more species. Alternanthera philoxeroides and Mikania micrantha were the most frequently occurring invasive species. Overall, M. micrantha appeared to be the dominant species with 62% of sites with a high cover (\u3e 70%) and was found to be evenly distributed in areas. However, they pose serious threat to local bio-diversity which shows that species-specific management is needed even in the peri-urban habitats
The eco-evolutionary dynamics of two strategic species: From the predator-prey to the innocent-spreader rumor model
No full textSpecies frequently engage in both competitive and cooperative interactions, delicately balancing these dynamics to optimize their chances of survival and reproduction. While competition drives individuals to compete for limited resources, cooperation can emerge as a strategic response, mitigating risk and enhancing collective payoff. To bridge theoretical game approaches such as payoff, cooperation, and defections in ecological systems, we propose a two-species predator–prey model inspired by the principles and variations of the prisoner\u27s dilemma game. We comprehensively address and analytically verify all stable strategic states, exploring the role of payoff parameters both individually and collectively. Additionally, we investigate the effect of free space. Beyond ecological contexts, we present a model of rumor propagation within a social system to establish connections with the prisoner\u27s dilemma game. In both systems, our primary focus is to discuss strategies and enhance the cooperative factor within the system, given its crucial importance across diverse environments
The p-Bohr radius for vector-valued holomorphic and pluriharmonic functions
No full textWe study a “p-powered” version Knp(F(R)) of the well-known Bohr radius problem for the family F(R) of holomorphic functions f : R → X satisfying ||f|| \u3c ∞, where || . || is a norm in the function space F(R), R ⊂ Cn is a complete Reinhardt domain, and X is a complex Banach space. For all p \u3e 0, we describe in full detail the asymptotic behavior of Knp(F(R)), where F(R) is: (a) the Hardy space of X-valued holomorphic functions defined in the open unit polydisk Dn; and (b) the space of bounded X-valued holomorphic or complex-valued pluriharmonic functions defined in the open unit ball B(lnt ) of the Minkowski space lnt . We give an alternative definition of the optimal cotype for a complex Banach space X in the light of these results. In addition, the best possible versions of two theorems from [C. Bénéteau, A. Dahlner and D. Khavinson, Remarks on the Bohr phenomenon, Comput. Methods Funct. Theory 4 (2004), no. 1, 1–19] and [S. Chen and H. Hamada, Some sharp Schwarz–Pick type estimates and their applications of harmonic and pluriharmonic functions, J. Funct. Anal. 282 (2022), no. 1, Paper No. 109254] have been obtained as specific instances of our results
The spatial dynamics and phase transitions in non-identical swarmalators
No full textSwarmalators, which combine the swarming phenomenon with synchronization, have drawn a lot of attention from researchers in recent years. Nevertheless, the majority of earlier research contends with identical swarmalators, thus neglecting dynamics that might emerge with parameter heterogeneity. In this paper, we therefore study the internal dynamics of non-identical swarmalators with natural frequencies sampled from six distributions: uniform, Gaussian, Lorentz, and its three generalizations. We show how these different distributions relate to the spatial dynamics and how they affect the phase transitions between different dynamical states. We find that, in comparison to the other five distributions, the phase transition curve for the uniform frequency distribution exhibits a more explosive character. Moreover, by changing the phase coupling strength, we find three distinct spatial patterns: drifting periodic, irregular, and static. With these results, we improve our understanding of the complex interplay between synchronization and swarming in non-identical swarmalators, and we also hope to inspire further research along the same lines
Turbulence with associated kinetic energy budget in the region of wave-blocking formed over an obstacle
No full textTurbulence characteristics in the region of wave-blocking over a submerged forward-facing obstacle is explored, and the results are compared with those of base-flow over the obstacle. Wave-blocking over obstacle is setup, adjusting the strong incoming flow with counter-propagating waves, and confirmed by linear dispersion relation. A variation in the flow is detected in three distinct segments: flow from the upstream, wave-blocking over the obstacle and the waves propagating from the downstream. The instantaneous velocity is recorded using a three-dimensional micro-acoustic Doppler velocimeter along the flow. Turbulence properties such as the mean velocity, Reynolds stress, turbulent kinetic energy, and associated coherent structures around the wave-blocking are discussed. Moreover, power spectral density, kinetic energy budget, and turbulence length- and time-scales are examined. The stress fractions to the total shear stress contribute higher for only flow than those of wave-blocking over obstacle. The power-spectral peaks at a fixed frequency for wave-blocking along lee side are greater than those of base-flow over obstacle. Kinetic energy budget for only flow over the obstacle is much higher than that of wave-blocking, indicating loss of energy due to wave-blocking. In the near-bed region, length-scale increases indicating the higher momentum and energy transfer. Increase in anisotropy plays significant role in the production. Results are valuable to ship sailing, design of coastal structures, and sediment transport
Understanding Frailty: Perspectives and Experiences of Rural Older Adults in India
No full textObjectives: In India, frailty has been predominantly studied as a physiological aspect, overlooking the subjective perceptions of community-dwelling older adults, which holds global significance. This study aims to explore frailty perceptions among community-dwelling older adults, comparing those enrolled in a geriatric welfare program facility to those not-enrolled. Methods: A cross-sectional design with a qualitative descriptive framework was employed, using focus group methodology. The study took place in rural West Bengal, located in eastern India, with a sample of 27 participants aged 60–87 years. Data collection occurred between October 2018 and January 2020, conducted through a face-to-face, semistructured discussion guide. Thematic analysis was performed to ensure data saturation and reliability. Results: Three key themes emerged from the analysis: (a) Perceptions of frailty were associated with aging, functional dependence, and psychosocial health, (b) Exposure to a scientific definition led to an ideological dilemma influenced by personal experiences, (c) Walking speed and grip strength were prominent components of frailty. The findings revealed that there was no difference in perception between program-enrolled and nonenrolled older adults, likely due to the concept of frailty being new to all participants. However, it was noteworthy that participants enrolled in the welfare program exhibited a resilient mindset toward the definition and demonstrated a proactive interest in preserving their overall health. Discussion: This novel study underscores the necessity of enhancing community awareness and integrating frailty management into the Indian health care system, which is yet to be fully integrated, aiming to promote the well-being of older adults