December-2018 Seminar

Date : 11-12-2018
Time : 16:00:00
Speaker : Mr. Himanshu Saxena
Junior Research Fellow
Area : Geosciences Division
Venue : Ground Floor Lecture Hall

Abstract

The fixed nitrogen is the most important nutrient fuelling phytoplankton growth in the ocean. Thanks to the N2-fixers, a special group of marine plankton that are able to convert dissolved nitrogen gas into bioavailable nitrogen such as ammonium. Marine nitrogen-fixing cyanobacteria play a central role in the open-ocean microbial community. Once thought ocean to be dominated by cyanobacteria in the warm oceans, it is now clear that marine N2-fixing organisms in the ocean are more diverse, and are geographically more widespread than expected. In this talk, I will be discussing the types of N2 fixers and how they contribute to the nitrogen budget of the ocean. In addition, lack of knowledge about nitrogen fixation in the Indian Ocean will also be discussed.

Title : Parametric source: Trends and applications

Date : 10-12-2018
Time : 00:16:00
Speaker : Dr. S. Chaitanya Kumar
Area : Atomic, Molecular and Optical Physics
Venue : Room No. 113/114, Thaltej

Abstract

Practical solid-state sources of tunable coherent radiation extending from the ultraviolet to mid-infrared can have an immense impact not only on the research and industry, but also on our daily life. In particular, mid-infrared wavelength range covering the molecular finger-print region is of great interest for variety of applications including spectroscopy and biomedicine. Nonlinear frequency conversion sources such as optical parametric oscillators have emerged as powerful tools, enabling access to these different spectral regions and are capable of providing broad and continuous wavelength coverage, operating in all time-scales from continuous-wave to ultrafast femtosecond regime. In this talk, I will present some of the recent advances in the development of parametric sources together with some interesting applications.

Title : Complex Evolution of Magnetic Helicity in Active Regions

Date : 06-12-2018
Time : 16:00:00
Speaker : Dr. B. Ravindra
Associate Professor
Area : Udaipur Solar Observatory (USO)
Venue : USO Seminar Hall

Abstract

Active regions on the Sun emerge on different scales, latitudes and time of the solar activity. These active region magnetic fields are believed to be generated through dynamo action at the shear layer located beneath the convection zone. These magnetic fields are concentrated into flux tubes which rise through the convection zone and form bipolar sunspots at the photosphere. The simulations show that magnetic fields emerge from the photosphere with a twist. Some of the active regions show more twist than the others. The twists in the active regions are measured through a quantity called magnetic helicity. With the available long time sequence of magnetograms, several studies have been reported in the literature about the measure of helicity flux density in active region coronae. In this talk, I will discuss the components of helicity flux measured through the partitioning of the magnetograms into a set of unipolar regions; the methodology adapted for the magnetograms partitioning; the magnitude of the helicity flux components and its application to rotating and emerging sunspot regions.

Date : 04-12-2018
Time : 16:00:00
Speaker : Mr. Mohammad Atif Khan
Junior Research Fellow
Area : Geosciences Division
Venue : Ground Floor Lecture Hall

Abstract

Nitrous oxide is an undervalued but an important long-lived greenhouse gas and ozone-depleting entity, which has increased by almost 20 percent compared to the pre-industrial era, thus becoming a global concern. In this talk, the concepts of global warming, the greenhouse effect, and global emission rates of N2O from various reservoirs will be discussed. N2O production by different microbial pathways and factors influencing its emission in the terrestrial ecosystem will also be discussed. At last, the importance of the stable isotopic composition of N2O in identifying the processes responsible for its production and major sources will be introduced.

Date : 03-12-2018
Time : 16:00:00
Speaker : K. Renuka
Area : Space and Atmospheric Sciences Division
Venue : Ground Floor Lecture Hall

Abstract

Black carbon is an atmospheric pollutant that comes from incomplete combustion of fossil and biomass fuels. It affects human health by causing cancer, respiratory diseases and cardiovascular dysfunctions. It also affects the earth’s climate by interacting with radiation either directly or indirectly. There exist large uncertainties in estimates of radiative forcing of BC due to uncertainty in emission fluxes and variations in optical properties for BC emitted from biomass burning. Using an emission inventory based on MODIS fire counts and a Lagrangian particle dispersion model we have quantified the contribution of biomass burning emissions to the observed BC concentrations at Ahmedabad. The results will be discussed in the seminar.