August-2018 Seminar

Title : TBA

Date : 20-08-2018
Time : 16:00:00
Speaker : Mr. Vishnudath, Physical Research Laboratory
Senior Research Fellow
Area : Theoretical Physics
Venue : Room No. 469

Abstract

TBA

Title : Photon correlation properties of twisted single photons

Date : 17-08-2018
Time : 00:11:00
Speaker : Mr. Nijil Lal C K
SRF
Area : Atomic, Molecular and Optical Physics
Venue : Room No; 113, PRL Thaltej

Abstract

The demand for secure communication and high precision measurements have led to the emergence of single photon sources (SPS). Heralded single photon sources are considered as one of the most preferred SPS candidates. Incorporating the orbital angular momentum (OAM) as a degree of freedom, these single photon sources become more useful in many quantum information applications. The quantum nature of these sources is measured and characterized in terms of second order correlation function. During the talk, I will discuss the non-classical behaviour of single photons carrying orbital angular momentum. I will also discuss the analogous nature of photon OAM and number states in terms of second order correlation function.

Date : 16-08-2018
Time : 16:00:00
Speaker : Ms. Aarthy E. (PRL, Ahmedabad)
Area : Astronomy & Astrophysics Division
Venue : Seminar Room # 113/114 (Thaltej Campus)

Abstract

NICSPol is a near infrared imaging polarimeter developed for the Near Infrared Camera and Spectrograph (NICS), one of the back end instruments of the 1.2 m Cassegrain telescope at the Mount Abu Infrared Observatory (MIRO), India. The polarimeter consists of a rotating wire grid polarizer which is mounted between the telescope optics and NICS. NICSPol is a general purpose instrument which could be used to study various astrophysical sources like star forming regions, AGNs, Pulsars, XRBs, GRBs, Supernovae et cetera. The observations are carried out for sources by rotating the polarimeter at multiple angles to determine the Stokes parameters, which are then converted into the polarization fraction and polarization angle. In this talk I would brief about the instrument, data acquiring and analysis procedure. The performance of NICSPol is verified with polarimetric standards along with which a preliminary science result will also be discussed.

Title : Understanding elementary processes in surface chemistry using state resolved molecular beam surface scattering experiments

Date : 16-08-2018
Time : 00:14:30
Speaker : Dr. Pranav R. Shirhatti
Area : Atomic, Molecular and Optical Physics
Venue : Room No. 113, PRL Thaltej

Abstract

Chemical reactions occurring on metal surfaces is a subject of wide interest, primarily because of its direct connections to heterogeneous catalyst technology. These processes are often complex and are composed of several elementary steps such as adsorption, diffusion, bond breaking/making and desorption. Moreover, each of these steps are accompanied by energy exchange with the underlying catalyst surface (often a metal) via different pathways and spanning different time scales. Understanding the energetics and dynamics of these elementary steps can have profound implications on our understanding of surface chemistry. In this talk, I will give an overview of some recent efforts in this direction especially focusing on studies involving quantum state resolved molecular beam surface scattering– experiments. Here, the incident molecules (on the target surface) are prepared in a precise quantum state distribution using a combination of molecular beam/laser pumping methods and the scattered molecules are detected using laser spectroscopy based techniques. In particular, I will discuss the case of unusually slow vibrational relaxation rate of CO on Au(111) surface,as suggested by the state resolved scattering experiments and its possible implications for reaction mechanisms in surface chemistry.

Title : TBA

Date : 16-08-2018
Time : 16:00:00
Speaker : Mr. Soumik Bandhopadhyay
Senior Research Fellow
Area : Theoretical Physics
Venue : Room No. 469

Abstract

TBA

Date : 13-08-2018
Time : 16:00:00
Speaker : Mr. Subir Mandal
Area : Space and Atmospheric Sciences Division
Venue : Ground Floor Lecture Hall

Abstract

Gravity waves (GWs) play an important role in the energy budget of the upper atmosphere. As they propagate though the atmosphere they modulate the atmospheric parameters like temperature, pressure, density of atmospheric species. Conventionally, GWs in upper atmosphere are measured using optical airglow emissions which are centered at some particular altitudes and hence carry information corresponding to those altitudes.The information on vertical propagation features of GWs in thermosphere are limited due to the fact that optical airglow emissions are integrated over a range of altitudes. We present results obtained using Digisonde measurement wherein analysis of height variation of iso-electron densities corresponding to different transmission frequencies are carried out. As vertical propagation of waves perturbs the electron density at different altitudes, we obtain GW scale sizes in the vertical direction in addition to other parameters. As Digisonde measurements are not limited to sky conditions, this approach enables investigations of GW behavior in the upper atmosphere in all seasons and all times. Using Hines dispersion relation we derive horizontal scale sizes. In this background, I will present the results obtained and describe the details of the method of obtaining the propagation characteristics of GWs. The results from the radio measurements compare well with those obtained from the established optical measurements, both in day and nighttime.

Date : 13-08-2018
Time : 11:00:00
Speaker : Shivangi Gupta
Area : Astronomy & Astrophysics Division
Venue : Seminar Room # 113/114 (Thaltej Campus)

Abstract

Be/X-ray binaries are among the brightest transient X-ray sources in our Galaxy. The compact object in these systems (which is a mostly a neutron star), revolves in a wide eccentric orbit around massive Be spectral type optical companion. These sources show periodic or Type-I X-ray outbursts, usually associated with periastron passage of binary. It is believed that neutron star accretes matter from a circumstellar disk around the Be star and powers such a strong outbursts. Another kind of X-ray enhancements, Type-II outbursts are also displayed by these systems, which are quite rare and independent of the orbital phase of the binary system. These rare events provide a unique opportunity to probe the emission geometry of these binary system. In this talk I will present results obtained from the spectral and timing studies of such a source, 2S 1417-624 during a Type-II outburst in 2009, using RXTE observations.

Title : Venus Cloud Dynamics and Meteorology Experiment for Venus Balloon

Date : 10-08-2018
Time : 16:00:00
Speaker : Chandan Kumar
Area : Planetary Sciences Division
Venue : Room no 113, Thaltej Campus

Date : 10-08-2018
Time : 16:00:00
Speaker : Ms. Akanksha Bhardwaj (PRL)
Senior Research Fellow
Area : Theoretical Physics
Venue : Room No. 469

Abstract

The Inert Higgs doublet model (IDM) is a theoretically well-motivated model among the Minimal Consistent Dark Matter (MCDM) models and provides many interesting signatures at the LHC. For hierarchical IDM scalar spectrum, the usual searches at the LHC are not efficient enough. In this ongoing work, we propose a new signature (2 Fat-jet + MET) to search for this interesting parameter space of this model. We choose the benchmark points by performing the parameter scan which satisfies all the theoretical and experimental constraints. We perform our analysis for light DM scenarios with the mass of 50-70 GeV, where we probe both the charged and the CP-odd Higgs in 300-700 GeV mass range. We exploit the characteristics of the jet substructure techniques which can lead to the discovery of the 2 fatjet + MET signal with the integrated luminosity of 3000 $fb^{-1}$ at the 13 TeV LHC.

Date : 09-08-2018
Time : 16:00:00
Speaker : Ms. Archita Rai (PRL, Ahmedabad)
Area : Astronomy & Astrophysics Division
Venue :

Abstract

Lynds dark nebulae (LDN) are dark patches seen against the background stars of the Milky Way. They are thought to be the birth places for stars. A catalog of these dark nebulae was made in 1960 by Beverly Turner Lynds, who visually inspected large areas of the Milky Way on the Palomar-Schmidt Survey Plates (POSS). As these regions have large opacity (range ~ 1 to 6) & extinction caused by high density and interstellar dust, the stars embedded in the dark clouds may not be visible in the optical band. To study them, infrared wavelength are expected to provide us with more penetration depth to study the core of the clouds. Hence more stars can be detected and the phenomena like polarisation and extinction which depend upon the distribution of the interstellar dust and the interstellar magnetic field can be studied in detail. In my talk, I will give a brief introduction to one of the Lynds clouds (LDN1340) and discuss its behaviour and properties. I will be discussing the observational aspects of using NICSPOL at the Mt. Abu Infrared Observatory along with other archival photometric data for this study.

Title : Evolution of Coronal Cavity from Quiescent to Eruptive Phase in Association with Coronal Mass Ejection

Date : 07-08-2018
Time : 16:00:00
Speaker : Mr. Ranadeep Sarkar
Senior Research Fellow
Area : Udaipur Solar Observatory (USO)
Venue : USO Seminar Hall

Abstract

The initiation mechanism of coronal mass ejections (CMEs) remains among the most elusive topics in solar physics. The initiation and triggering of CMEs can be studied by observing the coronal cavities in the lower coronal regions. These cavities appear as dark features and are believed to be the density depleted cross-sections of the magnetic flux ropes, where the magnetic field strength attains a much higher value compared to the background corona. Cavities may last for days or even weeks and evolve as the dark core part of the CME during the eruptive phase. In order to understand the pre-eruptive stability conditions for quiescent cavities and the triggering mechanisms for those structures to erupt, it is important to study the morphological evolution of the coronal cavities. In this work, we study the evolution of a cavity in lower corona using the observations from STEREO SECCHI/EUVI and PROBA2/SWAP EUV imager. In the quiescent phase, the cavity centroid height slowly rises from 1.10 to 1.23 RS during its passage on the visible solar disc from May 30 to June 13, 2010 and its initial circular shaped morphology gradually expanded and evolved into elliptical shape prior to the eruption from the western solar limb. The extended field-of-view of SWAP fills the observational gap between 1 to 2 RS. It enables us to capture the complete evolution of the erupting cavity starting from its EUV counterpart in the lower corona up to the white light cavity morphology seen in LASCO C2/C3 field-of-view. During the eruptive phase, we have observed a significant non-radial motion of the cavity at a very low coronal height of 1.3 RS. Furthermore, the geometrical fitting to the cavity morphology in different time-steps during its eruptive phase reveals that it exhibits non self similar expansion in the lower corona. We also discuss the role of the background magnetic field and the possible instabilities which may lead to the non-radial motion and initiation of the cavity eruption respectively.

Title : Sterile Neutrino Search

Date : 06-08-2018
Time : 14:30:00
Speaker : Mr. Kaustav Chakraborty (PRL)
Senior Research Fellow
Area : Theoretical Physics
Venue : Room No. 469

Abstract

The recent MiniBooNE data is consistent in energy and magnitude with the excess of events reported by the Liquid Scintillator Neutrino Detector (LSND). This excess corresponds to a ∆m2 ∼ 0.04eV which hints towards the presence of a light sterile neutrino. I will talk on the evidence of sterile neutrino and the future prospects of sterile neutrino search. I will also talk on ‘partial µ-τ ’ reflection symmetry in the context of sterile neutrino. The predictions of this symmetry is compared with the allowed area in the sin2θ23 − δCP plane as obtained from the global analysis of neutrino oscillation data.

Title : Noble gases and HED meteorites

Date : 03-08-2018
Time : 16:00:00
Speaker : Ramakant R Mahajan
Area : Planetary Sciences Division
Venue : Room no 113, Thaltej Campus

Title : A ROBUST SIGNATURE OF ELECTRON HYDRODYNAMICS IN 2D MATERIALS

Date : 02-08-2018
Time : 11:30:00
Speaker : Prof. Deshdeep Sahdev, Quazar Tech, (New Delhi)
Area : Theoretical Physics
Venue : Room No. 469

Abstract

Electron transport can transition from Ohmic to hydrodynamic when electron-electron scattering dominates, as shown in several recent experiments in systems such as Graphene. We show that microwave-frequency AC sources can excite hydrodynamic behavior involving vigorous vortex generation and reconnection, far more easily than the DC sources used so far. We identify the change of sign in a nonlocal current-voltage phase as a robust probe of the transition to the electronic hydrodynamic regime.

Title : Analysis of atmospheric effects on satellite-based quantum communication: A comparative study

Date : 02-08-2018
Time : 00:14:30
Speaker : Mr. Vishal Sharma
Area : Atomic, Molecular and Optical Physics
Venue : Room 113, PRL Thaltej

Abstract

Quantum Key Distribution (QKD) is a key exchange protocol which is implemented over free space optical links or optical fiber cable. When direct communication is not possible, QKD is performed over fiber cables, but the imperfections in detectors used at the receiver side and also the material properties of fiber cables limit the long-distance communication. Free-space based QKD is free from such limitations and can pave the way for satellite-based quantum com-munication to set up a global network for sharing secret messages. To implement free space optical (FSO) links, it is essential to study the effect of atmospheric turbulence. Here, an analysis is made for satellite-based quantum communication using QKD protocols. The results obtained indicate that SARG04 protocol is an effective approach for satellite-based quantum communication.