8 research outputs found
Elastic thickness structure of the Andaman subduction zone: implications for convergence of the Ninetyeast Ridge
No full textAbstract not availableR.T. Ratheesh Kumar, B.F. Windley, V.J. Rajesh, M. Santos
Archean tectonics and crustal evolution of the Biligiri Rangan Block, southern India
No full textAbstract not availableR.T. Ratheesh-Kumar, M. Santosh, Qiong-Yan Yang, C. Ishwar-Kumar ,Neng-Song Chen, K. Sajee
Spatial variations of effective elastic thickness over the Ninetyeast Ridge and implications for its structure and tectonic evolution
No full textWe present new data on the strength of oceanic lithosphere along the Ninetyeast Ridge (NER) from two independent methods: spectral analysis (Bouguer coherence) using the fan wavelet transform technique, and spatial analysis (flexure inversion) with the convolution method. The two methods provide effective elastic thickness (T-e) patterns that broadly complement each other, and correlate well with known surface structures and regional-scale features. Furthermore, our study presents a new high resolution database on the Moho configuration, which obeys flexural isostasy, and exhibit regional correlations with the T-e variations. A continuous ridge structure with a much lower T-e value than that of normal oceanic lithosphere provides strong support for the hotspot theory. The derived T-e values vary over the northern (higher T-e similar to 10-20 km), central (anomalously low T-e similar to 0-5 km), and southern (low T-e similar to 5 km) segments of the NER. The lack of correlation of the T-e value with the progressive aging of the lithosphere implies differences in thermo-mechanical setting of the crust and underlying mantle in different parts of the NER, again indicating diversity in their evolution. The anomalously low T-e and deeper Moho (similar to 22 km) estimates of the central NER (between 0.5 degrees N and 17 degrees S) are attributed to the interaction of a hotspot with the Wharton spreading ridge that caused significant thermal rejuvenation and hence weakening of the lithosphere. The higher mechanical strength values in the northern NER (north of 0.5 degrees N) may support the idea of off-ridge emplacement and a relatively large plate motion at the time of volcanism. The low T-e and deeper Moho (similar to 22 km) estimates in the southern part (south of 17 degrees S) suggest that the lithosphere was weak and therefore younger at the time of volcanism, and this supports the idea that the southern NER was emplaced on the edge of the Indian plate. (C) 2013 Elsevier B.V. All rights reserved
Tectonic inheritance of the Indian Shield: New insights from its elastic thickness structure
No full textA new evaluation of the elastic thickness (Te) structure of the Indian Shield, derived from isotropic fan wavelet methodology, documents spatial variations of lithospheric deformation in different tectonic provinces correlated with episodic tectono-thermal events. The Te variations corroborated by shear velocity, crustal thickness, and seismogenic thickness reveal the heterogeneous rheology of the Indian lithosphere. The thinned, attenuated lithosphere beneath Peninsular India is considered to be the reason for its mechanically weak strength (<30 km), where a decoupled crust-mantle rheology under different surface/subsurface loading structures may explain the prominent low Te patterns. The arcuate Te structure of the Western Dharwar province and a NNE-trending band of low Te anomaly in the Southern Granulite Terrane are intriguing patterns. The average Te values (40-50 km) of the Central Indian Tectonic Zone, the Bastar Craton, and the northern Eastern Ghats Mobile Belt are suggestive of old, stable, Indian lithosphere, which was not affected by any major tectono-thermal events after cratonic stabilization. We propose that the anomalously high Te (60-85 km) and high S-wave velocity zone to the north of the Narmada-Son Lineament, mainly in NW Himalaya, and the northern Aravalli and Bundelkhand Cratons, suggest that Archean lithosphere characterized by a high velocity mantle keel supports the orogenic topographic loads in/near the Himalaya. The Te map clearly segments the volcanic provinces of the Indian Shield, where the signatures of the Reunion, Marion, and Kerguelen hotspots are indicated by significantly low Te patterns that correlate with plume- and rift-related thermal and mechanical rejuvenation, magmatic underplating, and crustal necking. The correlations between Te variations and the occurrence of seismicity over seismically active zones reveal different causal relationships, which led to the current seismogenic zonation of the Indian Shield. (C) 2013 Elsevier B.V. All rights reserved
India-Madagascar paleo-fit based on flexural isostasy of their rifted margins
No full textThe present study contributes new constraints on, and definitions of, the reconstructed plate margins of India and Madagascar based on flexural isostasy along the Western Continental Margin of India (WCMI) and the Eastern Continental Margin of Madagascar (ECMM). We have estimated the nature of isostasy and crustal geometry along the two margins, and have examined their possible conjugate structure. Here we utilize elastic thickness (Te) and Moho depth data as the primary basis for the correlation of these passive margins. We employ the flexure inversion technique that operates in spatial domain in order to estimate the spatial variation of effective elastic thickness. Gravity inversion and flexure inversion techniques are used to estimate the configuration of the Moho/Crust-Mantle Interface that reveals regional correlations with the elastic thickness variations. These results correlate well with the continental and oceanic segments of the Indian and African plates. The present study has found a linear zone of anomalously low-Te (1-5 km) along the WCMI (similar to 1680 km), which correlates well with the low-Te patterns obtained all along the ECMM. We suggest that the low-Te zones along the WCMI and ECMM represent paleo-rift inception points of lithosphere thermally and mechanically weakened by the combined effects of the Marion hotspot and lithospheric extension due to rifting. We have produced an India-Madagascar paleo-fit representing the initial phase of separation based on the Te estimates of the rifted conjugate margins, which is confirmed by a close-fit correlation of Moho geometry and bathymetry of the shelf margins. The matching of tectonic lineaments, lithologies and geochronological belts between India and Madagascar provide an additional support for the present plate reconstruction. (C) 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved
Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications
No full textThe occurrence of high-pressure mafic-ultramafic bodies within major shear zones is one of the indicators of paleo-subduction. In mafic granulites of the Andriamena complex (north-eastern Madagascar) we document unusual textures including garnet-clinopyroxene-quartz coronas that formed after the breakdown of orthopyroxene-plagioclase-ilmenite. Textural evidence and isochemical phase diagram calculations in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicate a pressure-temperature (P-T) evolution from an isothermal (780 degrees C) pressure up to c. 24 kbar to decompression and cooling. Such a P-T trajectory is typically attained in a subduction zone setting where a gabbroic/ultramafic complex is subducted and later exhumed to the present crustal level during oceanic closure and final continental collision. The present results suggest that the presence of such deeply subducted rocks of the Andriamena complex is related to formation of the Betsimisaraka suture. LA-ICPMS U-Pb zircon dating of pelitic gneisses from the Betsimisaraka suture yields low Th/U ratios and protolith ages ranging from 2535 to 2625 Ma. A granitic gneiss from the Alaotra complex yields a zircon crystallization age of ca. 818 Ma and Th/U ratios vary from 1.08 to 2.09. K-Ar dating of muscovite and biotite from biotite-kyanite-sillimanite gneiss and garnet-biotite gneiss yields age of 486 +/- 9 Ma and 459 +/- 9 Ma respectively. We have estimated regional crustal thicknesses in NE Madagascar using a flexural inversion technique, which indicates the presence of an anomalously thick crust (c. 43 km) beneath the Antananarivo block. This result is consistent with the present concept that subduction beneath the Antananarivo block resulted in a more competent and thicker crust. The textural data, thermodynamic model, and geophysical evidence together provide a new insight to the subduction history, crustal thickening and evolution of the high-pressure Andriamena complex and its link to the terminal formation of the Betsimisaraka suture in north-eastern Madagascar. (C) 2015 Elsevier B.V. All rights reserved
Effectiveness of Ayurvedic intervention in Primary Open Angle Glaucoma (Kaphaja Adhimantha) - A Case Study
No full textGlaucoma is a diverse group of disorders affecting the eye with a common characteristic potentially progressive optic neuropathy that is determined by both structural changes and functional deficit in which IOP is a key modifiable factor. In Primary Open Angle Glaucoma (POAG), IOP independent mechanisms of glaucomatous nerve damage and visual field loss with unobstructed angle of anterior chamber is observed. The patient has reported gradual diminution of peripheral aspect of visual field (Rt. eye - 6/12 and Lt. eye - 6/12 on Snellen’s distant vision chart) in both eyes for 2 years. There was marked peripheral field defect on both confrontation test and perimetry visual field analysis test. The disease shows clinical similarity with Kaphaja Adhimantha, a disease affecting the whole eye mentioned in Susruta Samhita and Ashtanga Hrudaya. It is a chronic disease comes under life style related disorder. Dukhena Roopam Pasyathi (distorted image or constricted visual field), Sirodukha (headache), Srava (watering), Kandu (itching), Pamsupoornatha (foreign body sensation), Aviladarsana (diminished vision) and Gourava (heaviness of eye and head) are the clinical findings explained in the context of Kaphaja Adhimantha. These clinical findings mentioned in classical literature show resemblance with POAG. The meticulous deployment of kaphaja AbhisyandhaAdhimantha treatment protocol can be used to prevent the progression of ganglionic damage and preservation of eye sight. The logical interpretation on the basis of both subjective and objective clinical findings concluded the diagnosis as Kaphaja Adhimantha and treatment principle adopted was Apatharpana, Kaphahara, Abhisyandhahara and Srothovisodhana. After treatment his vision has improved as 6/6 in both eyes and remarkable change in visual field analysis. The study discusses about the effectiveness of Ayurvedic management in POAG
Construcción de representaciones regularizadas y dimensionalmente reducidas para cuantificar automáticamente similitudes conceptuales entre imágenes: una aplicación a la descripción del cáncer
No full textilustraciones, diagramas, tablasLos espacios de representación alternativos (ARS por sus siglas en ingles) se han convertido en un tema crucial en la inteligencia artificial (IA), ya que los avances recientes en el análisis de características mediante aprendizaje profundo han demostrado que pequeños cambios dentro de dichos espacios de características afectan en gran medida los resultados del modelo. Estos ARS se basan comúnmente en características extraídas de muestras, principalmente para reducir la dimensión del espacio muestral original y mejorar la discriminabilidad de patrones. Sin embargo, la mayor parte de la investigación actual de IA se centra en el rendimiento del modelo, pero hay muy poco progreso en la interpretabilidad del modelo. Particularmente en el campo del análisis de imágenes, la dimensionalidad de la muestra se ha vuelto más importante que la interpretabilidad, debido al tamaño de estas fuentes de información y las limitaciones del poder computacional. A pesar de esto, la transparencia. La interpretabilidad del modelo se vuelve importante en las aplicaciones médicas, donde los médicos no solo buscan predicciones precisas, sino que también esperan explicaciones sobre cómo un modelo calcula dichos resultados. En la práctica clínica, se requieren explicaciones de los resultados para crear esquemas de gestión personalizados de pacientes. Por lo tanto, la opacidad del modelo aparece como uno de los problemas que limita el uso de la IA en la práctica clínica. Además, las técnicas de interpretabilidad de IA se han dedicado al uso de mapas de calor espaciales, que se basan en mapas de activación de capas de red profundas y explicaciones post-hoc basadas en características de ingeniería asociadas supervisadas, que no son suficientes para proporcionar predicciones precisas y ARS comprensibles. Las principales limitaciones de estos proveedores de interpretabilidad radican en la dificultad de ajustar abstracciones de alto nivel que utilizan los especialistas para explicar los resultados de los pacientes en términos de semántica especializada. Estas abstracciones semánticas se denominan comúnmente conceptos y tienen como objetivo mejorar la interpretabilidad o al menos mejorar la comprensión basada en imágenes. Estos conceptos pueden variar desde características de imagen simples basadas en la heterogeneidad de intensidad en imágenes de ultrasonido, hasta dispositivos celulares tipo empalizada en imágenes de histopatología, que requieren enormes niveles de abstracción, interpretación y conciencia semántica, que son características que los modelos de IA actuales no pueden proporcionar. La tesis presentada en este artículo aborda la construcción de ARS y la interpretabilidad basada en conceptos, en diferentes aplicaciones de imágenes de cáncer que van desde imágenes a escala celular hasta espacios de integración de radiología/citología. Este trabajo explora diferentes métodos de construcción de ARS y explota los límites de cada enfoque para determinar sus ventajas y desventajas y evaluar cómo se adaptan a desafíos particulares de la obtención de imágenes de cáncer. En particular, esta disertación demuestra avances en tres temas principales: la construcción de espacios de características diseñados para determinar la relación entre conceptos en diferentes escalas biológicas mientras se logra un rendimiento de clasificación de vanguardia, la construcción de incrustaciones de características profundas que capturan relaciones conceptuales en ARS de baja dimensión y la combinación de características profundas y diseñadas a mano para mejorar el rendimiento y la interpretabilidad del modelo (Texto tomado de la fuente).Alternative representation spaces (ARS) have become a crucial topic in Artificial intelligence (AI), since recent advances on deep feature characterization have evidenced that small changes within such embeddings largely affect model outcomes. These ARS are commonly build upon features extracted from samples, mainly to reduce original sample space dimension, and to enhance pattern discriminability. However, most of the current AI research is focused on model performance, but very few advances on model interpretability. Particularly, in image analysis, sample dimensionality have become more important than interpretability, due to the size of these information sources and the limitations of computational power. However, within this image domain, model transparency becomes crucial in medical applications, where physicians not only look for accurate predictions but also expect to obtain explanations on how a model is computing such outcomes. In clinical practice, explanations of the results are required in order to create personalized patient management schemes. Therefore, model opacity appears as one of the problems that limits the translation of AI to clinical practice. In addition, AI interpretability approaches have been devoted to spatial heatmaps, build upon layer activation maps of Deep networks, and pos-hoc explanations based on supervisely associated engineered features, which are not enough to provide both accurate predictions and understandable ARS. Main limitations of these interpretability providers relies in the difficulty to fit high-level abstractions that specialists use to explain patient outcomes in terms of specialized semantics. Such semantic abstractions are commonly known as concepts, and aim to improve interpretability or at least to enhance image-based understanding. These concepts may go from simple image characteristics based on intensity heterogeneity for ultrasound images, to palisade-like cell arrangements in histopathology images, all requiring huge levels of abstraction, interpretation and semantic awareness, which are not provided by nowadays AI models. Herein presented dissertation addresses ARS construction and concept-based interpretability, throughout different cancer image applications that range from cell scale images, to radiology/cytology integration spaces. This work explores different ARS construction methods, and exploits the limits of each approach to determine their advantages and disadvantages, and to evaluate how they fit particular cancer image challenges. Particularly, this work demonstrates advances on three main topics, building engineered feature spaces to determine relation between concepts at different biological scales while achieving state-of-the-art classification performance, constructing deep feature embeddings that capture conceptual relations in dimensionaly reduced ARS, and mixing handcrafted and deep features to improve model performance an interpretabilityDoctoradoDoctorado en Ingeniería - Ingeniería EléctricaApplied computin
