Title : Uranium in the ocean: Inferences on bottom water anoxia during the Last Glacial Period

Abstract

The paleo-oceanographic studies suggest that deep ocean was depleted in dissolved oxygen (O2) during the last glacial period (LGP, ~18 kyr BP). Therefore, paleoceanographers have sought a direct tracer for studying the changes in dissolved O2 in the deep ocean during the LGP. Geochemical proxies like redox-sensitive trace elements (Vanadium, Molybdenum, Uranium, Manganese) in bulk sediments have been used to reconstruct the past bottom water environment. Example, in oxic seawater, uranium is present in relatively high concentration as uranyl-carbonate complexes which are highly soluble. Under O2 deficient (anoxic) conditions, uranium can be reduced from U(VI) to a less soluble tetravalent state U(IV), which is particle reactive and gets fixed into the sediments. A geochemical study validating this concept was published in 1993 (‘Geochemical evidence for anoxic deep water in the Arabian Sea during the last glaciation’; Sarkar, Bhattacharya & Sarin; Geochimica et Cosmochimica Acta). The purpose of this seminar is to discuss two recent articles (Geochemical Perspectives Letters 2024 and Marine Geology 2025) using the very same concept/approach published more than three decades ago (PRL study).

Title : Quantum mechanics, decoherence, and quantum-to-classical transition

Abstract

This talk is divided into two parts: First part will be an elementary introduction to the theory of decoherence, quantum mechanics, and quantum-to-classical transition. We will discuss how Niels Bohr's idea of the "cut" and the requirement of a classical apparatus for the interpretation of quantum mechanics can be rationalized in the framework of the modern theory of decoherence by Zurek and others. In the second part, we present our results related to the Ovchinnikov-Erikhman theory of decoherence. We point out the problems with this scenario and revise it to apply it to a realistic case of the motion of conduction electrons. Interesting results are obtained. Our results agree with the alternative master equation approach.

Title : Evolution of the Laxmi Basin, Arabian Sea, during the Deccan volcanism

Abstract

The Laxmi Basin is a prominent geomorphic feature and a marginal depression in the Northwest Indian Ocean (Arabian Sea). This ~300 km wide basin separates the western Indian continental margin from the Laxmi Ridge (LR), which is believed to be continental. The precise nature of the basin's basement remains controversial, with differing views suggesting it could be either a stretched continental crust with magmatic intrusions related to continental rifting (contemporaneous with Deccan volcanism) or a pre-Paleogene oceanic crust. Additionally, a geochemical study of the basin's igneous basement indicates that these rocks formed in a subduction zone setting. Understanding the crust's nature has implications for the geodynamic events of continental breakup and the formation of the Indian Ocean during the Late Cretaceous. To address this controversy, we conducted geochemical and isotopic studies on basaltic lava samples from this basement, recovered during IODP 355. In this talk, I will present the results of our study and our inferences regarding the crustal nature of the Laxmi Basin.

Title : NICER insight into the High-Energy Universe

Abstract

Since its deployment to the International Space Station in June 2017, the Neutron Star Interior Composition Explorer (NICER) has significantly advanced our understanding of compact objects in the X-ray sky. With exceptional timing and spectral capabilities in the 0.2 - 12 keV range, NICER enables detailed studies of accretion-powered and magnetically driven phenomena. A major focus has been on thermonuclear X-ray bursts -brief, intense explosions caused by unstable burning of hydrogen and helium on neutron star surfaces, which offer key insights into the physics of dense matter. This talk will highlight crucial findings from eight years of NICER observations, covering burst behavior, accretion dynamics, X-ray transients, and magnetar activities. It will also discuss efforts to understand the interaction between compact objects and their optical companions through X-ray and optical observations. Finally, I will present recent updates on the long-term calibration of the JEM-X instruments aboard ESA's INTEGRAL mission and ongoing progress toward establishing the INTEGRAL Legacy Archive.

Title : An overview of compact X-ray binaries

Abstract

Compact objects represent some of the most extreme environments in the universe. When these dense remnants are part of a binary system, they can draw in matter from their companion stars through a process known as accretion. This transfer of material releases vast amounts of energy, making these systems strong sources of X-rays. Compact X-ray binaries, in which a neutron star or black hole accretes matter from a companion, offer unique opportunities to study energetic processes like accretion dynamics, outbursts, and thermonuclear bursts on neutron star surfaces. This talk will introduce the fundamental concepts behind accretion, compact binaries, and related phenomena, and will highlight why these systems are key to advancing our knowledge of high-energy astrophysics.

Title : Nitrogen loss processes in aquatic ecosystems

Abstract

Nitrogen, though abundant in the atmosphere, often limits primary productivity in aquatic ecosystems. These ecosystems play a crucial role in regulating the global nitrogen cycle both by converting inert atmospheric nitrogen into bioavailable forms through dinitrogen fixation and by removing excess reactive nitrogen via microbially mediated loss processes, including denitrification, anaerobic ammonium oxidation (anammox), and, to some extent, dissimilatory nitrate reduction to ammonium (DNRA). However, with increasing anthropogenic nitrogen inputs and climate-driven environmental changes, the efficiency and dominance of these pathways are shifting, with significant implications for ecosystem health, biogeochemical feedbacks, and nitrogen budgets. In this seminar, I will discuss the mechanisms, environmental controls, and experimental approaches used to study nitrogen loss processes in aquatic ecosystems.

Title : Probing Compressed Inert Scalars with Forward Muon Tagging at the Muon Collider

Abstract

The compressed mass spectrum of the Inert Doublet Model (IDM) poses a significant challenge for current collider experiments, as the soft visible decay products and suppressed production rates hinder conventional search strategies. In this talk, I will explore the discovery prospects of such a compressed electroweak sector at a future high energy Muon Collider operating at 10 TeV. Focusing on vector boson fusion (VBF) production of inert scalar pairs, I will demonstrate how forward muon tagging provides a powerful handle to isolate signal events in scenarios where traditional missing energy based searches fail. After reviewing the relevant dark matter and experimental constraints on the IDM parameter space, I will present a detailed collider analysis using both cut-based methods and multivariate techniques. The impact of detector energy resolution will be discussed, highlighting the importance of precision instrumentation. Our results show that even in highly compressed and experimentally challenging scenarios, the clean environment and forward coverage of the Muon Collider can significantly enhance discovery potential, making it a compelling probe of dark sectors.

Title : Advancing the Warm Calibration Unit for METIS on ELT: From Design Finalization to MAIT Phase

Abstract

METIS, an advanced mid-infrared imager and spectrograph for the wavelength range 2.9-13.5 microns (astronomical L, M, and N-band), stands as one of the three science instruments at the Extremely Large Telescope (ELT). It will provide diffraction-limited imaging, coronagraphy, high-resolution integral field spectroscopy, and low and medium-resolution slit spectroscopy. Within the collaborative international METIS consortium, the University of Cologne is responsible for the design, manufacturing, and integration of the Warm Calibration Unit (WCU) of the instrument. The main role of WCU is to provide a stable and controllable reference signal to METIS that will allow troubleshooting and calibrating the response of METIS in various observing modes. In this talk, I will present the key requirements from METIS that drive the design of the WCU, followed by an overview of its optical and opto-mechanical design, and functional role within the instrument. The final part of the presentation will focus on the current status of the Manufacturing, Assembly, Integration, and Testing (MAIT) phase, including a brief discussion on the alignment verification plans for the offner relay optics of WCU.

Title : Recent boulder falls on Planetary bodies: Insight into recent activities

Abstract

Rockfalls or boulder falls on Earth are very common and occur almost daily in certain parts of the world. In contrast, rockfalls on Mars are rare, and no rockfalls have been reported on the Moon in the last decade. This difference underscores the value of studying boulder falls on planetary bodies, as they provide important insights into geological processes. On planetary bodies like Mars and the Moon, millions of boulders/rocks are present on the surface, formed through the weathering of the crust, impact breccia’s, and other geological processes. These boulders vary in size, ranging from a few meters to several tens or even hundreds of meters. On the Moon, these boulders are particularly abundant. To date, using the latest high-resolution images from the Chandrayaan-2 Orbiter High-Resolution Camera (OHRC) and Lunar Reconnaissance Orbiter Narrow Angle Camera (LRO-NAC) there is no report of recent movement of even a single boulder over the past decade. This brings an intriguing question: do all the boulders on the Moon have reached equilibrium, or have there been movements in the last few decades to centuries, which is not been detected to date? How does the detection of movement of boulders help in understanding the recent activities? In this presentation, I will provide evidence for recent boulder falls and their hotspot regions on the Moon related to seismic activity/moonquakes, impact-generated surface shaking, and thermal weathering. Aside from very recent impacts, the primary activity observed on the Moon over the past few decades to centuries is the boulder falls. With the newly identified boulder falls, the Moon joins Earth and Mars, with records of recent boulder falls driven by multiple sources suggesting a sporadically active Moon. Such regions could be potential landing sites for future missions to understand the recent surface/subsurface activity on the Moon.