List of colloquium

Date : 11-03-2020
Time : 16:00:00
Speaker : Prof. Dawn Sumner
Area : DEAN'S OFFICE
Venue : K R Ramanathan Auditorium, PRL main campus

Abstract

Prof. Dawn Sumner's research focuses on reconstructing ancient environments on early Earth and Mars and the early evolution of bacteria, including the origin of oxygenic photosynthesis. Her group studies everything from the environmental settings, geochemistry, and morphology of Archean microbialites to the morphology, climate response, and genomics of modern microbial communities growing in ice-covered Antarctic lakes to the stratigraphy and geochemistry of sedimentary rocks on Mars. Prof. Sumner is a member of NASA's Mars Science Laboratory (MSL), helping the rover Curiosity explore ancient environments in Gale Crater on Mars. She regularly shares her research and adventures with the public. Sumner is dedicated to helping students of all backgrounds prepare for careers in science as well as to creating educational and work environments that are inclusive and supportive, including through the use of feminist research and theory. Prof. Sumner was awarded the Career Award for Outstanding Contributions in Geosciences, Geobiology, and Microbiology from the Geological Society of America in 2016. She is an elected Fellow of the Geological Society of America (in 2014). She was also selected to deliver the honorary Carl Sagan Lecture at the American Geophysical Union (AGU). She had been the Chair of the UC Davis Department of Earth & Planetary Sciences from 2014-2016. She had also been the Chancellor's Fellow, UC Davis, during 2003-2004.

Date : 11-12-2019
Time : 16:00:00
Speaker : Prof. Jyotiranjan S. Ray
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

The most celebrated river of Indian mythology, the Saraswati, has often been hypothesized to be the river of the Bronze Age Harappan civilization in north-western India. The suspected modern counterpart of the glacier-fed Saraswati is the river Ghaggar, which unlike the former is a seasonal stream that originates in the Himalayan foot-hills. Despite the discovery of a large number of settlements along the Ghaggar, many believed that the Harappans depended solely on monsoonal rains, because no proof existed for the river’s uninterrupted flow during the peak of the civilization. This had led many to reject the very idea of the river Saraswati and its hypothesized relationship with the Harappan culture. To resolve the issues related to the existence of the river Saraswati and its drainage area, we investigated the nature of the ancient Ghaggar during the last several thousand years by studying the changes in the sources of the sediments deposited by it. Results of our study, using sophisticated geochemical and isotopic proxies, conclusively establish that the ancient Ghaggar was a round-the-year flowing, glacier-fed river during 9,000 to 4,500 years ago, when the Pre and Early Harappan settlements had flourished along its banks. This river matches with all the descriptions of the river Saraswati, thus reaffirming its existence during the Harappan period.

Date : 04-12-2019
Time : 16:00:00
Speaker : Dr. Haranath Ghosh
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

Superconductors are miracle Materials --- many surprising phenomena they exhibit, from zero resistance to quantum levitation. The race is on to make the first room temperature superconductor, several examples that room temperature superconductivity is a reality will be presented. Available high temperature superconductors may be classified into two categories; conventional (BCS) and unconventional (non-BCS) superconductors. Discovery of Fe-based superconductors is ground breaking and hints for a new path way to high temperature superconductors. The new materials feature FeAs layers instead of Cu-O layers of the famous cuprate high temperature superconductors. Antiferromagnetism in both systems appear from d- electrons, however, in FeAs systems they are much more mobile than cuprates. Unconventional superconducting pairing mechanism (yet to be settled), orbital physics, rich Fermiology, phase diagram and several distinctly different physical properties make them overall a fundamentally different class --- superconductors with not only high Tc but also with technological applications. A pedagogical introduction to the field will open the talk. Structural aspects and its intimate relation to electronic structure, orbital selective nature of various aspects like electron correlation, doping, Lifshitz transition and superconductivity will be emphasized. The latest developments in the field will be discussed along with various challenges in these classes of materials.

Date : 27-11-2019
Time : 16:00:00
Speaker : Dr. Megha Upendra Bhatt
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

The quantitative estimation of elemental concentrations of the lunar surface is an important tool for understanding the processes relevant for the origin and evolution of the Moon. India’s Chandrayaan-1 mission equipped with three spectrometers provided unprecedented observations of the Moon surface with nearly global coverage in the near infrared (NIR) wavelength range at a spatial resolution in the range of hundreds of meters. The NIR observations can be used efficiently for indirect estimation of refractory elements e.g. Fe, Ti, Ca and Mg for obtaining high resolution global elemental maps. This is in contrast to the direct observations, gamma-ray (GRS) and X-ray spectrometers, where the spatial resolution is at least two orders of magnitude lower. The estimation of refractory elements in the NIR range either relies on empirical relationships between the derived spectral parameters of remote observations and in situ chemical analyses of returned lunar samples or on a global elemental estimation derived using remotely sensed GRS data as a reference. The successful estimation of refectory elements depends on the choice of spectral parameters that can decouple maturity from lunar soil composition. In this talk, I will present a new approach of estimating lunar refractory elements using machine learning technique of support vector regression between spectral parameters derived from the Moon Mineralogy Mapper and global elemental maps derived from the GRS measurements. The results obtained from this new approach are consistent in distribution and range with the GRS elemental maps and do not show artifacts in immature areas due to its robustness to space-weathering effects. I will discuss a couple of site specific cases and illustrate how the concept can be applied to the Chandrayaan-2 data-sets.

Date : 31-10-2019
Time : 00:00:00
Speaker : Dr. Alberto Sainz Dalda
Area : DEAN'S OFFICE
Venue : USO Seminar Hall

Abstract

The thermodynamics of the solar chromosphere and the transition region (TR) is critical for understanding how the solar corona is energized from the photosphere. The most common method to recover the stratified information in the solar atmosphere is through 'inversion codes' which employ an iterative algorithm to solve the radiative transfer equation for a given model atmosphere by minimizing the difference between the observed and synthetic spectra. Since 2013, NASA's Interface Region Imaging Spectrograph (IRIS) has been providing unprecedented observations of the solar atmosphere from the upper photosphere to the corona, with special attention to the chromosphere and the TR. IRIS is equipped with both spectral and imaging capabilities in several wavelengths spanning the far- and the near-UV domain. In this talk, I will present inversions of the Mg II h&k lines observed by IRIS using the STiC inversion code which considers non-LTE, partial redistribution, and plane-parallel geometry. The results from this code, while being comprehensive of the thermodynamic conditions in the chromosphere, are unfortunately, computationally intensive and expensive. An alternative approach is using the concept of the Representative Model Atmosphere with the STiC inversion code, called IRIS2. The foundation of this novel code is based on easy-to understand, easy-to-use, representative elements obtained with a basic machine learning technique, such as k-mean clustering. This allows us to obtain a depth-stratified model atmosphere from the upper photosphere to the chromosphere in a few CPU-minutes for any IRIS Mg II h&k data set. I will illustrate how the concepts behind this code can be applied to any spectro(polarimetric) data.

Date : 19-09-2019
Time : 10:15:00
Speaker : Prof. Dipankar Banerjee
Area : DEAN'S OFFICE
Venue : USO Seminar Hall

Abstract

At the Kodaikanal (KKL) observatory we have four sets of data which consist of While light photoheliograms since 1904, the Ca-K line spectroheliograms since 1906, H-alpha spectroheliograms from 1912 to 1998, and Ca-K spectroheliograms of prominences from 1912 to 1998. All these data are collected with the same instruments with no change in their optics in the last 100 years. Thus, these uniform and contiguous images areextremely valuable to study the long term variations of the Sun over a century. We have recently digitized all these datasets and made them open to the global community through the portal https://kso.iiap.res.in. In this talk I will present a summary of recent science results from this digitized archive.

Date : 18-09-2019
Time : 16:00:00
Speaker : Dr Umesh Kadhane
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

Polycyclic aromatic hydrocarbons (PAH) have emerged as strong candidates to explain the origin of infrared emission bands and diffused interstellar bands in astronomical spectra. A large amount of work is being done to understand the survival of these molecules in the harsh interstellar environment. A major channel of excitation namely collective excitation, which is common to all PAHs, has largely remained unexplored till recently. With the help of a series of multi-dimensional investigations spread over nearly 10 years, we have been able to identify the exact role of collective excitation and its after-effects in PAHs exposed to harsh electromagnetic as well as charged particle radiation. This talk presents a comprehensive sketch of this research, including the in-house instrumentation development.

Date : 21-08-2019
Time : 16:00:00
Speaker : Prof. Mahan Mj
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

Instances of hyperbolic geometry come up in nature whenever a system starts developing fast interconnections. Examples include trees, the human brain, and the internet. A tell-tale signature is the existence of a fractal in one dimension less, e.g. the surfaces of trees and brains in the above examples. After dealing with the above examples, we shall discuss a special case where the fractals emerge in the complex plane as a result of symmetries of hyperbolic 3-space. These symmetries act on the complex plane as well; however the dynamics being chaotic, it is hard to get a hold on them directly. Instead, we go to hyperbolic geometry in 3 dimensions, set up a dictionary between the two and finally get a hold on the fractals in the complex plane through our study of hyperbolic geometry in 3 dimensions.

Date : 24-07-2019
Time : 00:00:00
Speaker : Dr. Sachin Gunthe
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

Atmospheric aerosols form because of various emissions from industry, human activities and natural processes. They interact with incoming solar radiation directly by scattering and absorption and indirectly by changing cloud properties. Also, the changes in cloud properties lead to change in precipitation and Hydrological cycle on the Earth. Overall, aerosols are expected to counteract global warming by greenhouse gases but aerosol-cloud interaction and many biosphere-geosphere processes involving aerosols are poorly understood and therefore, they are cause for the largest uncertainty in understanding current and future climate changes. Aerosols of biological origin (bacteria, fungal spore, pollen grains, plant and animal fragments, etc.) are one of the least understood component of the climate system. An overview of changing aerosol properties including bioaerosols over India and their role in cloud and precipitation formation processes on regional and local scale will be given.

Date : 15-05-2019
Time : 16:00:00
Speaker : Dr. Dipankar Saha
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

Food and drinking water security in India is critically dependent on the underlying aquifers. Presently 85% of rural drinking need, 64% of irrigation demand and more than 50% of urban water need is met from groundwater sources. About 8% of India’s GDP is directly linked to groundwater. India is the world’s largest groundwater extractor, with an estimated consumption exceeding a quarter of the global total. Relentless and unplanned extraction of groundwater, often exceeding the annual recharge, has resulted in multipronged un-desirable consequences. The most important of them is desaturation of aquifers, being manifested through declining water levels, drying up of wells and diminishing well yield. The other adverse effect is deteriorating water quality, both in terms of increasing salinity and elevated concentrations of harmful contaminants.