October-2017 Seminar

Date : 18-10-2017
Time : 16:00:00
Speaker : Dr. Arindam Mazumdar (Physical research laboratory, Ahmedabad)
Area : Theoretical Physics
Venue : Room No. 469

Abstract

Primordial perturbations generated at the time of Inflation is expected to produce the fluctuations in CMB as well as the large scale structures(LSS) of the universe.Standard LambdaCDM theory is expected to describe these CMB observations and LSS observations under a single theoretical framework. However,some recent observations have pointed out some tensions between these two types of observations under LambdaCDM theory. In this talk I will cover some earlier attempts to resolve these tensions.Then I will describe our attempt with viscous cold dark matter to resolve the problem.

Date : 12-10-2017
Time : 16:00:00
Speaker : Dr. Siddhartha Chattopadhyay (Max Planck Institute for Nuclear Physics, Heidelberg, Germany)
Area : Theoretical Physics
Venue : Room No. 469

Abstract

In this talk, I will present recent results on the correlation effects in strong field ionization of diatomic molecules. In this work, we have studied $\mathrm{H}_2$, $\mathrm{LiH}$, and $\mathrm{HF}$ molecules, aligned collinearly with the linear polarization of the external field.To elucidate the possible role of electron correlation in the enhanced-ionization (EI) phenomena we consider different levels of approximation with the time-dependent generalized-active-space configuration-interaction (TD-GASCI) method. The results of our studies show that correlation is important and they also demonstrate significant deviations between the results of the single-active-electron approximation and more accurate configuration-interaction methods.We will further investigate the role of low-lying excited states in the EI phenomena. With the inclusion of correlation we show strong carrier-envelope-phase effects in the EI of the asymmetric heteronuclear $\mathrm{LiH}$ molecule. The correlated calculation shows an intriguing feature of cross-over in enhanced ionization with two carrier-envelope-phases at criticalinter-nuclear separation.

Date : 12-10-2017
Time : 16:00:00
Speaker : Mr. Vaibhav Dixit
Scientist/Engineer C
Area : Astronomy & Astrophysics Division
Venue : Seminar Room # 113/114 (Thaltej Campus)

Abstract

Artificial Intelligence (AI) is the capability of the machines to perform a task intelligently like humans. Deep learning is a subset of AI which takes inspiration from model of human brain. It is based on neural networks with several layers of nodes. Deep learning encourages computational models that are built on multiple layers to learn representations of data with multiple levels of abstraction. It has surpassed the human performance in several trivial tasks like image recognition and segmentation as well as found applications in various commercial activities like self-driving cars, stock market prediction, cancerous tissue identification and production line performance etc. Given the sheer magnitude of projects undertaken by various organizations, we would end up having Petabytes of data, and no manpower to go through all of them manually. Under such a scenario, we would need intelligent systems which can devour large data. Higher dimensionality of the data, no prior knowledge of the data generation process, low signal to noise ratio and missing information are some other limiting factors in analysis done by humans. However deep learning overcomes these challenges and can open new avenues for scientific research. Deep learning is going to change the way we do science. The talk will focus on some areas of applications of deep learning in astronomy.

Date : 09-10-2017
Time : 16:00:00
Speaker : Dr. Victor Mukherjee ( Weizmann Institute of Science, Rehovot, Israel)
Area : Theoretical Physics
Venue : Room No:469

Abstract

Control in open quantum systems out of equilibrium is necessary to achieve various tasks, ranging from efficient cooling or heating of the systems, controlling decoherence in open quantum systems, to engineering quantum technologies, such as quantum heat engines and quantum probes. I will talk about control in quantum systems out of equilibrium in presence of Markovian and non-Markovian baths, as well as use of control in quantum technologies.

Date : 09-10-2017
Time : 16:00:00
Speaker : R. P. Singh
Area : Space and Atmospheric Sciences Division
Venue : Ground Floor Lecture Hall

Abstract

The Earth's upper atmosphere is influenced by the incoming solar radiation from above and upward propagating atmospheric waves that originate in the lower atmosphere. Mesosphere Lower Thermosphere (MLT) region is that part of the upper atmosphere where most of the atmospheric waves deposit their energy and momentum affecting the overall structure and composition of the region. For this study of MLT wave dynamics, data from the in-house built passive remote sensing techniques are made use of. These optical remote sensing techniques are in a continuous mode of operation from Gurushikhar, Mt. Abu since 2013. New insights have been obtained by the analyses of these long-term observations of mesospheric nightglow emission intensities (O2 and OH) and temperatures. Some of the recent results, which deal with the solar and atmospheric influences in the MLT region, and vertical coupling of atmospheres during tropical cyclone will be discussed.

Date : 03-10-2017
Time : 14:30:00
Speaker : Prahlad Epili
Graduate Student (4th year)
Area : Astronomy & Astrophysics Division
Venue : Seminar Room # 113/114 (Thaltej Campus)

Abstract

In X­-ray astronomy, the study of X­-ray binaries shows interesting features of the stellar X­-ray sources. Among these the spectacular variability seen in High mass X­-ray binaries (HMXBs) at different time scales can be studied to understand the nature of the two stellar components, the physics of matter at extreme physical conditions, the ‘accretion’ process governing the mass transfer to the compact object etc. Majority of these HMXBs are bright and transient in nature. One such class of bright X­-ray transients are Be/X­-ray binaries. In theses sources, an abrupt accretion of huge amount of matter from the normal star onto the neutron star is seen with X­-ray outbursts, i.e an enhancement in the X­-ray emission. Study of these X­-ray outbursts (some are periodic and some are aperiodic) forms an important basis to further our understanding of these sources. EXO 2030+375 is a transient Be/X­-ray binary system. It has been caught in X­-ray outbursts numerous times during 1996­2011 in the RXTE era. We have studied the decade long X­ ray observations of this binary to understand its long term X­-ray variability. The details of the study will be presented.