List of colloquium

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.

Date : 29-08-2018
Time : 16:00:00
Speaker : Dr. Navinder Singh
Area : DEAN'S OFFICE
Venue : Nanosims Lecture Hall, PRL

Abstract

Air travel has become one of the most common means of transportation. One wonders about the lifting capacity of uniquely designed wings of Boeing airliners. You might have peeped through the window of an airliner and have noticed the moment of ailerons and flaps when plane takes off or lands, and that might have excited your curiosity. The physics behind these mechanisms is both interesting and challenging. The common question which is generally asked is: How does an airplane gain lift? And the most common answer is via the Bernoulli principle. It turns out that it is wrongly applied in common explanations, and there are certain misconceptions in this field. In an alternative explanation the push of air from below the wing is argued to be the lift generating force via Newton's law. There are problems with this explanation too. In this presentation we will try to clear these misconceptions, and the correct explanation, using the Lancaster-Prandtl circulation theory, will be discussed. The physical meaning of the Kutta-Joukowski condition will be illustrated. At the end, a brief discussion of a new viewpoint advanced in PRL will also be presented which goes beyond the Lancaster-Prandtl theory. This talk will discuss the physics of paragliders and powered paragliders.

Date : 01-08-2018
Time : 16:00:00
Speaker : Prof. Deshdeep Sahdev
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

It is an interesting and remarkable fact that every Nobel-prize winning piece of work in Experimental Physics was carried out on apparatus designed and developed by the physicist in question, be it Rutherford, Raman, Mossbauer or Binnig. I will start by taking the audience through a fascinating journey which saw my team developing Scanning Probe Microscopes, Physical Properties Measurement Systems and hi-end CVDs all the way out to internationally competitive standards. I will then describe how we have gone about enhancing the base so developed for research in material science, condensed matter physics and nano-technology, with packages for scientific computation, many designed and developed (like our instruments) essentially from scratch. By the end of the talk, I hope to have convinced the audience that the complete & seamless, indigenous integration of theory, computation, experiment and instrumentation, which we are beginning to achieve at QuazarTech holds out the promise (not only for us but for centers all over India) of tackling some really interesting physics problems, a few of which I will describe.

Date : 30-05-2018
Time : 16:00:00
Speaker : Dr. Navinder Singh
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

Every child has at one time or another played with a magnet and been fascinated by its mysterious ways. It is an uncanny feeling to experience the repulsion between the like poles of two magnets. The "magical" properties of magnets have fascinated mankind over the centuries. Questions like why only iron, cobalt, nickel, or their alloys show ferromagnetic behaviour whereas other elements do not, comes to every curious mind? This presentation is devoted to the historical development of the key ideas in the vast field of magnetism. The presentation follows a chronological order (which is also the logical one from the conceptual point of view). We start from the Greeks, to medieval times to and the 20th century, and highlight the key contributions of people line William Gilbert; Coulomb; Poisson; Oersted; Ampere; Faraday; Maxwell; Pierre Curie; Langevin; Weiss; van Vleck; Heisenberg; Pauli; Slater; Stoner; Anderson; Moriya, Hubbard and others. It will be shown how the advent of quantum mechanics resolved some baffling problems in the field. The current problems in the magnetic properties of strongly correlated electronic systems will be presented, and finally we will summarize the current status of the field of magnetism.

Date : 23-05-2018
Time : 16:00:00
Speaker : Dr. Shanti Pappu
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

In the history of scientific thought, the story of our origins, has been one of the endless fascination and heated debates. The study of human evolution has been approached in recent years through interdisciplinary research including archaeology, palaeoanthropology and genetics, situated within a geochronological and palaeoenvironmental framework. Much of the early fossil and archaeological evidence for the story of human evolution arises from discoveries in Africa. Debates range around the timing and nature of dispersals of differing species out of Africa, with alternate theories being periodically proposed. In this context, the geographical position of South Asia, and its rich and diverse prehistoric archaeological record, critically informs our understanding of cultural aspects of human evolution, behavioral changes and adaptation of populations to past environmental variability. Here, we first situate the South Asian prehistoric record in a global context. We then move to our specific research project comprising excavations at the site of Attirampakkam, Tamil Nadu and other sites along the SE coast of India. Archaeological, geomorphological and geochronological studies here have led to paradigm shifts in our understanding of the prehistoric record of India, reframing current concepts of the age and nature of the early Palaeolithic (Stone Age) occupation of India. In particular age estimates for different cultural phases at Attirampakkam ranging from around 1.7 million years ago to around 172,000 years ago have stimulated global debates on existing theories of the timing and nature of population dispersals out of Africa and across Asia. Implications of these studies in terms of paradigm shifts in viewing trajectories of cultural evolution and population dispersals across Eurasia are discussed here. We conclude by emphasising the crucial importance of Indian archaeology and associated sciences in contributing towards a global perspective of human origins.