April-2017 Seminar

Date : 28-04-2017
Time : 14:30:00
Speaker : Dr. Surender Pratap
Area : Theoretical Physics
Venue : Room No. 469

Abstract

We report and adduced band structure in the confined region of potential well. LDOS, transmission, charge distribution have been calculated in the confined region of well. Transmission curves show oscillations with the increase of layers of unit cell. While in other part, we study level spacing distributions of finite sized 1-dimensional disordered systems. As the systems evolves from quasi ballistic to strongly localized regime, systems crosses over from strongly non-Wigner-Dyson type level spacing distribution to a universal Poisson distribution in the thermodynamic limit.

Date : 28-04-2017
Time : 00:16:00
Speaker : Mr. Rahul Kumar Kushwaha
JRF
Area : Atomic, Molecular and Optical Physics
Venue : Room No: 006, PRL Thaltej

Date : 27-04-2017
Time : 17:00:00
Speaker : Dr. Avijeet Prasad
Post Doctoral Fellow (PDF)
Area : Udaipur Solar Observatory (USO)
Venue : USO Seminar Hall

Date : 27-04-2017
Time : 16:00:00
Speaker : Dr. Navinder Singh
Area : Theoretical Physics
Venue : Room No. 469

Abstract

In this first work under PRL's TDP project (No. TDP-ESR-623) we generalize the magneto-resistance phenomenon where the resistivity of materials change under a transverse magnetic field to a regime where in addition to magnetic field there is also a transverse ac field of resonant frequency with the Zeeman splitting. Our theoretical calculations predict this effect and the experiment to test it is under development (under TDP project). The idea is the following. In a magnetic field, electron spin levels are Zeeman split. If a resonant ac field is applied there is a new channel of momentum relaxation. An additional resistivity is predicted. The whole work is based upon a generalization of the Einstein's derivation of Planck's black-body radiation formula to non-equilibrium systems. This talk will summarize the theory work.

Date : 27-04-2017
Time : 16:00:00
Speaker : Dr. S. Rathna Kumar
Area : Astronomy & Astrophysics Division
Venue : Seminar Room # 113/114 (Thaltej Campus)

Abstract

Measurement of time delays between the images of gravitationally lensed quasars has been demonstrated to be a competitive method to constrain cosmological parameters. During the next decade, the Large Synoptic Survey Telescope (LSST) is expected to discover and monitor on the order of thousand lensed quasars. Hence it is of interest to develop time delay measurement algorithms that are not only fast, but also accurate and precise. In this talk, I shall describe a recent effort to rigorously test the difference-smoothing algorithm on a large sample of simulated light curves from the first edition of Strong Lens Time Delay Challenge (TDC1) and the refinements that were required to make it competitive with the best performing algorithms of TDC1. I shall also briefly touch on the upcoming TDC2, which is expected to address the problem of reliably measuring time delay from a combination of multi-filter light curves as expected from LSST.

Date : 24-04-2017
Time : 16:00:00
Speaker : Subir Mandal
Area : Space and Atmospheric Sciences Division
Venue : Ground Floor Lecture Hall

Abstract

Various kinds of waves and oscillations are present in the Earth’s atmosphere. Atmospheric waves are of different spatial and temporal scales, and are in general, generated in lower atmosphere. They carry energy and momentum from their source regions as they propagate to upper atmospheric altitudes. The breaking of waves is associated with release of energy in the background atmosphere, and hence the waves in Earth’s atmosphere play a crucial role in the coupling processes of different atmospheric regions. A broad introduction of different types of waves and their characteristic properties will be given. Observations of such wave features (mainly gravity waves) on different atmospheric parameters (e.g., temperature, wind, neutral and plasma densities, etc.) will be presented.

Date : 21-04-2017
Time : 14:30:00
Speaker : Mr. Selvaganapathy J
Area : Theoretical Physics
Venue : Room No. 469

Abstract

The existence of the principles of Quantum Mechanics and of Classical General Relativity points some difficulties at the small scale: the space-time uncertainty emerges from the Heisenberg principle, thereby suggesting that space-time has a quantum structure at small length scale: the space-time becomes fuzzy i.e. noncommutative(NC) at this scale. One of the property of the NC theory is that it is nonlocality inherent, which includes the gravity with standard model naturally. There is no theoretical prediction for energy scale at which noncommutative effects arise. So the energy scale can ranges from TeV scale to Planck scale. In this talk I would like to give a brief description about the non-commutative standard model (NCSM) and a phenomenological survey of this model. In particularly, I would like to discuss about neutral triple gauge boson interaction at LHC.At the end, I would like to discuss about the Drell-Yan process in the NCSM.

Date : 20-04-2017
Time : 16:00:00
Speaker : Dr. Aritra Biswas
Area : Theoretical Physics
Venue : Room No. 469

Abstract

We show that for a heavy vector-like quark model with a down type isosinglet, branching ratio for c--> u gamma decay is enhanced by more than O(10^2) as compared to that in the Standard model when QCD corrections to next-to-leading order are incorporated. In a left-right symmetric model (LRSM) along with a heavy vector-like fermion, enhancement of this order can be achieved at the bare (QCD uncorrected) level itself. We propose that a measurement of the photon polarization could be used to signal the presence of such new physics inspite of the large long distance effects. We find that there is a large region within the allowed parameter space of the LRSM, as well as in the model with vector-like quark with additional left-right symmetry, where the photon polarization can be dominantly right-handed.

Date : 20-04-2017
Time : 16:00:00
Speaker : Dr. Main Pal
Area : Astronomy & Astrophysics Division
Venue : Seminar Room # 113/114 (Thaltej Campus)

Abstract

Active galactic nuclei (AGN) are the most luminous, long-lived and highly variable sources in the Universe. These objects emit almost over entire electromagnetic spectrum. In case of Seyfert type 1 AGN, the UV/optical to X-ray spectrum consists of complex spectral components such as powerlaw, soft X-ray excess below ~2 keV, iron- K lines near 6 keV, Compton hump in 10-50 keV and big blue bump (BBB) in the UV/optical bands. These components can be used to probe the unresolved central engine and various physical processes in the vicinity of the supermassive blackhole. The variability nature of these features in the X-ray to UV/optical bands are less well understood. I will discuss these components and their relationship through spectral and timing variability study in detail in Seyfert 1 galaxies such as 1H 0419-577, II Zw 177 and Fairall 9.

Date : 18-04-2017
Time : 16:00:00
Speaker : Mr. Satish R V.
Senior Research Fellow
Area : Geosciences Division
Venue : Ground Floor Lecture Hall

Abstract

Atmospheric carbonaceous aerosols consisting of black carbon (BC) and organic carbon (OC) influence Earth’s radiative balance by interacting with the solar radiation. The role of BC in the atmosphere is reasonably well understood and incorporated into climate model studies. On the other hand, OC considered as “white” for many years because they efficiently scatter visible radiation. Recent findings suggest that a significant part of organic aerosols absorbs light at near UV and visible region and termed as Brown Carbon (BrC). To assess the role of BrC on regional/global level, it is inevitable to understand their sources and characteristics on temporal and spatial scale. However, such studies are very limited in literature. This study presents the BrC spectral characteristics and chemical composition of PM2.5 samples collected before, during and after a large scale paddy-residue burning over Patiala (30.2oN, 76.3oE), located in the northwestern IGP during October-November, 2014. Results from this study will be discussed.

Date : 17-04-2017
Time : 16:00:00
Speaker : Nidhi Tripathi
Area : Space and Atmospheric Sciences Division
Venue : Ground Floor Lecture Hall

Abstract

Volatile organic compounds (VOCs) are ubiquitous trace gases in the global troposphere. VOCs are emitted from a variety of natural and anthropogenic sources. VOCs are precursors of ozone and secondary organic aerosols (SOA) and hence are important species from climate change perspective. VOCs control the oxidizing capacity of the troposphere mainly due to fast reactions with hydroxyl (OH) and other radicals. Measurements of VOCs are technically challenging due to fast reactivity and low concentrations in the atmosphere. In recent years, Proton Transfer Reaction-Mass Spectrometry (PTR-MS) has emerged as a robust technique for accurate and fast measurements of many VOCs present in air. In my presentation, I will discuss the important aspects of the Proton Transfer Reaction-Time of Flight-Mass Spectrometer (PTR-TOF-MS) which is an innovative technology for high time- and mass- resolution measurements of VOCs.

Date : 13-04-2017
Time : 00:16:00
Speaker : G. Joshva Raj
Post Doctoral Fellow
Area : Atomic, Molecular and Optical Physics
Venue : Room No: 113, PRL Thaltej Campus

Abstract

The talk will be started with the presentation of my Ph.D thesis which is entitled as “A Theoretical Study on the Effect of Temperature on Supercontinuum Generation and Modulational Instability in Liquid-core Photonic Crystal Fiber”. The generation of supercontinuum light and modulational instability in photonic crystal fiber will be explained. The investigation of the effect of temperature on such highly nonlinear phenomena will be detailed. The possibility of using temperature as a control parameter in order to tune the bandwidth of broadband spectrum will be discussed. Following the thesis presentation, a research proposal on the studies on entangled photon pair generation using spontaneous four-wave mixing in erbium doped photonic crystal fiber will be discussed. An useful application of optical fibers is the production of entangled photon pairs using FWM. Various types of fiber have been investigated in the context of FWM assisted entangled photon pairs. In this line, the necessity of investigating erbium doped photonic crystal fiber as a medium to generate entangled photon pairs will be discussed. The methodology and the techniques that are required to carry out the investigation of four-wave mixing in erbium doped photonic crystal fiber in the quantum realm will be explained.

Date : 10-04-2017
Time : 00:14:30
Speaker : Prof. Anders Kastberg
Area : Atomic, Molecular and Optical Physics
Venue : Room 469, fourth floor, PRL Main building

Abstract

In this seminar, I will review the physical processes leading to ”sub-Doppler” temperatures in laser cooled atom. These processes are generally accepted to be well described by sop called ”Sisyphus cooling”. However, recent experimental and theoretical findings show that the Sisyphus model is at best a partial explanation for the relevant light-atom interaction. Aside from the purely academic question about the nature of the cooling process, there are indications, partially controversial, that the ensuing momentum distribution in the atomic cloud follows a power law. This could in turn makes such samples good candidate for fundamental studies of anomalous diffusion and non-ergodicity. Moreover, the acute sensitivity of the cooling process on the exact atomic structure may also provide a tool for precession spectroscopy.

Date : 06-04-2017
Time : 17:00:00
Speaker : Prof.S.P. Rajaguru
Area : Udaipur Solar Observatory (USO)
Venue : USO Seminar Hall

Date : 04-04-2017
Time : 14:30:00
Speaker : Newton Nath
Area : Theoretical Physics
Venue : Room No. 469

Abstract

In this talk, we will discuss about the minimal extended type-I seesaw (MES) model which can give rise to eV scale sterile neutrino. In this model, three right handed neutrinos and one extra singlet S are added to generate a light sterile neutrino. We study the zero textures of the Yukawa matrices for the MES model. Remarkably we obtain only two allowed one-zero textures namely, m_{e\tau} = 0 and m_{\tau\tau}=0 having inverted hierarchical mass spectrum. We also discuss the importance of next-to-leading order correction terms in this model.

Date : 04-04-2017
Time : 16:00:00
Speaker : Dr. M. G. Yadava
Scientist SG
Area : Geosciences Division
Venue : Ground Floor Lecture Hall

Abstract

Cyclicity in time series of climate proxies, belived to be of solar origin, is documented in the high resolution archives such as ice cores or tree rings in the present and the geological past. The smallest cycle with 11 yrs periodicity is attributed to the sunspot activity and has a measurable effect on the Earth’s climate as shown by the Maunder minimum. Indian rainfall also shows 11yr periodicity, in the modern rainfall and the proxy data from climate archives. It seems that 11 yr solar cycle has been affecting the Earth’s climate over hundreds of million years by holding its stable periodicity over time. Some of the proxy based evidences will be presented to discuss a debatable topic, which needs continued investigation for better understanding.