List of colloquium

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.

Date : 08-05-2019
Time : 16:00:00
Speaker : Prof. Ramesh P Singh
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

Natural hazards occur at any location on land, ocean and atmosphere, effects of these natural hazards have been observed in the source region and also far from the source. In recent years, efforts have been made to enhance observing systems on land, ocean and atmosphere to study characteristics of changes associated with the natural hazards using ground, borehole and satellite observations. An overview of the observing systems throughout the globe will be presented that have provided information about characteristics of land, ocean and atmosphere associated with prior, during and after occurrence of natural hazards. The dense network of observing systems in monitoring and forecast of an impending natural hazard have helped scientists to minimize loss and forecast of natural hazards. The need of dense network in India especially in the Himalayan and Indo-Gangetic plains is required to monitor and forecast of impending natural hazards. The impact of natural hazards occurring on land, ocean and atmosphere affecting all elements of earth systems have clearly shown the existence of land-ocean-atmosphere coupling.

Date : 10-04-2019
Time : 16:00:00
Speaker : Prof. K. P. Subramanian
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

Mass spectrometry is widely regarded as the most sensitive and specific general purpose analytical technique. Among a variety of techniques used in mass spectrometry, Quadrupole mass analyzer (QMA) has emerged as a common and handy gadget in many laboratories world over. While the principle behind conventional mass analyzers is dispersion, in QMAs mass filtering is based on stable Vs unstable oscillations of ions in a quadrupole RF field. For a given values of parameters defining the AC and DC fields inside a quadrupole, it can be seen that oscillations of ions within a certain mass range are sustained, whereas oscillations of all other ions outside this band are divergent and are removed from the beam. Therefore, QMA is regarded as a mass filter, than a spectrometer. In this colloquium, the history of QMA will be briefly discussed. The basic mathematical steps for analyzing the ion trajectory in a quadrupole field will be presented. The 'filtering property' will be explained in the context of properties of Mathiue Function, which is the governing equation for the function of QMA. From here, the steps towards consolidating these mathematical ideas into a working instrument will be illustrated with an example. Finally, COMSOL simulation of the instrument also will be presented.

Date : 27-03-2019
Time : 16:00:00
Speaker : Prof. Debasis Sengupta
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

The Asian monsoon has two quasi-periodic "modes" of sub-seasonal variability - a northward moving mode in the 30-50 day period band, and a westward moving 10-20 day mode (or the "quasi-biweekly" oscillation). These two modes have been known to tropical meteorologists for over four decades, but the discovery of sub-seasonal modes in the ocean is relatively recent. I shall discuss some remarkable 10-20 day oscillations seen in mooring, satellite and other observations from the equatorial Indian Ocean and north Bay of Bengal.

Date : 20-03-2019
Time : 16:00:00
Speaker : Dr. G. D. Reeves
Area : DEAN'S OFFICE
Venue : K.R. Ramanathan Auditorium, PRL

Abstract

This talk will be centered around some of the space science activities at Los Alamos National Laboratory (LANL) with a particular emphasis on personal involvement in some of those projects. LANL has been involved in space science for over 60 years. The origin of LANL’s Space Science program was the Vela satellite program which started in 1959 to monitor compliance with the test ban treaty. Los Alamos continues that mission to this day with systems such as the Global Position System (GPS) based nuclear detonation detection instruments and research into fundamental physics problem in collaboration with NASA and the international space sciences community. The fundamental space sciences research at LANL has greatly expanded to include solar-terrestrial interactions, studies of the heliopause and interstellar medium with energetic neutral atoms, planetary exploration, magnetospheric physics, radiation belt physics and many other areas. This talk will bring out some of that history and personal recollections of the history and of space sciences at LANL.

Date : 03-10-2018
Time : 16:00:00
Speaker : Prof. Debabrata Goswami
Area : DEAN'S OFFICE
Venue : Nanosims Lecture Hall, PRL

Abstract

Femtosecond laser pulses have been shaped in a programable manner for coherent control at molecular level and for several coherent optical processes that have resulted in applications to fast switching, data compression, ultrasensitive detection, computing, etc. Optical and quantum interaction and their detection remain at the forefront of all such efforts. Typically, however, it is not common for ultrashort time to be connected to ultra-small dimension. Use of femtosecond optical tweezers (FOTs) makes this connection possible. We have developed a novel on-the-fly calibration method of FOT that enables in situ control and contactless measure of absolute temperature and viscosity at nanoscale dimensions. Such measurements and control at the nanoscale have been challenging since the present techniques can only provide relative off-line measurements that are of low spatial resolution. Such spatiotemporal control with ultrashort pulses provides the possibility of manipulation at nanoscale that can yield several interesting results that include visualization of colloidal aggregation in real time, computational logical operation in localized zone that is then reset with the subsequent pulse train. We simultaneously apply the high temporal sensitivity of position autocorrelation and equipartition theorem to precisely measure and control in situ temperature and the corresponding microrheological property around the focal volume of the trap at high spatial resolution. The FOTs use a single-beam high repetition rate laser for optical trapping to result in finer temperature gradients in comparison to the continuous-wave laser tweezers. Thermal effects are often treated delirious and most spectroscopy efforts remain in removing them. We have, on the other hand, used highly repetitive femtosecond laser heating to develop time-resolved photothermal lens spectroscopy that provide molecule level sensitivity.