Department of Physics

Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

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IIT Palakkad

We demonstrate the use of graphene oxide (GO) in making p-n junctions. Two variants of p-n junctions made using GO are reported. In one of the variant, we deposit a layer of GO on aluminium zinc oxide (AZO) and study the junction properties using current-voltage (I-V) characteristics. In the other variant, we reduce the GO deposited on a glass substrate to obtain reduced graphene oxide (rGO) and make a GO-rGO bilayer p-n junction. The photovoltaic response of this GO-rGO bilayer is reported. These two approaches provide an inexpensive route to make p-n junctions for realizing GO based electronic devices. © 2019 Elsevier Ltd. All rights reserved.

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Materials Today: Proceedings

Graphene Oxide based p-n junctions

A systematic study of the photoluminescence quenching efficiencies in P3HT: PCBM blends showed a non-linear dependence on the PCBM concentration. We find a faster decrease in PL emission initially which later flattens out around 1:1 composition which tallies well with sample compositions known to give the best power conversion efficiencies. This implies that the exciton dissociation rates dominate the photocurrent generation in these films. We obtained a maximum of 91% photoluminescence quenching for films with a 1:1 blend ratio. A mean field based phenomenological model is presented, which very well describes our experimental results. The generation of free carriers due to various proposed mechanisms like dissociation and delocalization are collectively considered in the model. The model helps us understand the underlying physics and dependence of the quenching efficiency on parameters like excitation intensities. The proposed model will be useful in predicting the behaviour of exciton dissociation in new organic blends. © 2019 IOP Publishing Ltd.

Materials Research Express

Investigation of non-linear dependence of exciton recombination efficiency on PCBM concentration in P3HT:PCBM blends

The microtubule-bound motors kinesin and dynein differ in many respects, a striking difference being that while kinesin is known to function mostly alone, dynein operates in large groups, much like myosinV in actin. Optical tweezer experiments in vitro have shown that the mean detachment time of a bead attached to kinesins under stall conditions is a slowly decreasing function of , while for dyneins, the time increases almost linearly with . This makes dynein a team worker, capable of producing and sustaining a large collective force without detaching. We characterize this phenomenon as 'temporal cooperativity' under load. In general, it is unclear which biophysical properties of a single motor determine whether it behaves cooperatively or not in a group. Our theoretical analysis shows that this is determined by two dimensionless parameters: (i) the ratio of single molecule, load-independent detachment and attachment rates and (ii) the ratio of the applied force per motor to the detachment force of a single motor. We show that the attachment-detachment dynamics of a motor assembly may be mapped to the motion of a hypothetical, overdamped Brownian particle in an effective potential, the form of which depends on the load-dependence of binding and unbinding rate of the motor. In this picture, the total number of motors is proportional to the inverse temperature and cooperative behaviour arises from the trapping of the particle in the minima of the potential, when present. In the latter case, application of results from Kramers' theory predicts that the mean time of escape of the particle, equivalent to the mean detachment time of the bead under stall, increases exponentially with the number of motors, indicating cooperative behaviour. If the potential does not have minima, the detachment time depends only weakly on , which suggests non-cooperative behaviour. In the large limit, the emergence of cooperative behaviour is shown to be similar to a continuous phase transition. © 2018 IOP Publishing Ltd.

Physical Biology

Temporal cooperativity of motor proteins under constant force: Insights from Kramers' escape problem

We present a suite of seven 3D supernova simulations of non-rotating low-mass progenitors using multigroup neutrino transport. Our simulations cover single star progenitors with zero-age main-sequence masses between 9.6 and 12.5 M and (ultra)stripped-envelope progenitors with initial helium core masses between 2.8 and 3.5 M. We find explosion energies between 0.1 and 0.4 Bethe, which are still rising by the end of the simulations. Although less energetic than typical events, our models are compatible with observations of less energetic explosions of low-mass progenitors. In six of our models, the mass outflow rate already exceeds the accretion rate on to the proto-neutron star, and the mass and angular momentum of the compact remnant have closely approached their final value, barring the possibility of later fallback. While the proto-neutron star is still accelerated by the gravitational tug of the asymmetric ejecta, the acceleration can be extrapolated to obtain estimates for the final kick velocity. We obtain gravitational neutron star masses between 1.22 and 1.44 M, kick velocities between 11 and 695 km s−1, and spin periods from 20 ms to 2.7 s, which suggest that typical neutron star birth properties can be naturally obtained in the neutrino-driven paradigm. We find a loose correlation between the explosion energy and the kick velocity. There is no indication of spin-kick alignment, but a correlation between the kick velocity and the neutron star angular momentum, which needs to be investigated further as a potential point of tension between models and observations. © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.

Monthly Notices of the Royal Astronomical Society

Three-dimensional simulations of neutrino-driven core-collapse supernovae from low-mass single and binary star progenitors

We present high-resolution (1024 3) simulations of super-/hypersonic isothermal hydrodynamic turbulence inside an interstellar molecular cloud (resolving scales of typically 20-100 au), including a multidisperse population of dust grains, i.e. a range of grain sizes is considered. Due to inertia, large grains (typical radius a ≳ 1.0μm) will decouple from the gas flow, while small grains (al∼ 0.1μm) will tend to better trace the motions of the gas. We note that simulations with purely solenoidal forcing show somewhat more pronounced decoupling and less clustering compared to simulations with purely compressive forcing. Overall, small and large grains tend to cluster, while intermediate-size grains show essentially a random isotropic distribution. As a consequence of increased clustering, the grain-grain interaction rate is locally elevated; but since small and large grains are often not spatially correlated, it is unclear what effect this clustering would have on the coagulation rate. Due to spatial separation of dust and gas, a diffuse upper limit to the grain sizes obtained by condensational growth is also expected, since large (decoupled) grains are not necessarily located where the growth species in the molecular gas is. © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.

Fulltext

Clustering and dynamic decoupling of dust grains in turbulent molecular clouds

APS March Meeting Abstracts 2019, F59.

States of self stress in disordered solids: memory, heterogeneity and yielding

We present an experimental study of the superconducting properties of NiBi 3 as a function of pressure by means of resistivity and magnetization measurements and combine our results with density functional theory calculations of the band structure under pressure. We find a moderate suppression of the critical temperature from K to K by pressures up to 2 GPa. By taking into account the change of the band structure as a function of pressure, we argue that the decrease in is consistent with conventional, electron-phonon-mediated BCS-type superconductivity. © 2018 IOP Publishing Ltd.

Journal of Physics Condensed Matter

Effect of pressure on the physical properties of the superconductor NiBi 3

Effect of Fe doping on the structure, optical and thermoelectric properties of SrTi 0.8 Sn 0.2 O 3 sample has been investigated. The SrTi 0.8−x Sn 0.2 Fe x O 3 (x = 0, 0.1, 0.3) samples are fabricated using solid-state synthesis route. It is observed that Fe doping helps in reducing the densification temperature of SrTi 0.8 Sn 0.2 O 3 during spark plasma sintering. Precipitation of Sn has been observed in SrTi 0.8−x Sn 0.2 Fe x O 3 (x = 0, 0.1) samples while the SrTi 0.8−x Sn 0.2 Fe x O 3 (x = 0.3) sample is of purely single cubic perovskite phase. All the samples consist of nanocrystalline grains and the grain size varies between 150 to 200 nm. Fourier transform infrared spectroscopy (FTIR) analysis reveals the distortion of TiO 6 octahedra due to the increase in Fe content. Raman spectroscopy analysis has shown that perovskite cubic structure is stable from room temperature to 873 K. From thermophysical measurements, it is shown that the Fermi band gap reduces from 2.87 to 0.66 eV with increase in Fe in the investigated samples. The Seebeck co-efficient is found to change the sign from n–type to p-type with the increase of Fe concentration in SrTi 0.8 Sn 0.2 O 3 which is an interesting observation to obtain p-type SrTiO 3 based thermoelectric materials. The optical and thermoelectric properties show that Fe doping improves the thermoelectric properties of SrTi 0.8 Sn 0.2 O 3 ceramics by altering the Seebeck coefficient and thermal conductivity. © 2019 IOP Publishing Ltd.

Tuning the optical and thermoelectric properties of SrTi 0.8− x Sn 0.2 Fe x O 3

We discuss SL(N, ℂ) Chern-Simons higher spin gauge theories in Euclidean AdS3. With appropriate boundary term, we derive the higher spin generalization of Schwarzian on-shell action. We investigate gravitationally dressed bi-locals, and we study the soft higher spin mode expansion to obtain soft mode eigenfunctions. We also derive the spin-s eigenfunction from Ward identity of W-algebra and a recursion relation. Using the on-shell action, we evaluate the contributions of the soft higher spin modes to the out-of-time-order correlators, and the corresponding Lyapunov exponent of SL(N) higher spin gravity is found to be 2πβ(N−1). © 2019, The Author(s).

Journal of High Energy Physics

Chaos in three-dimensional higher spin gravity

Sesame (Sesamum indicum L.) is one of the major oil yielding plant in India, but the production of sesame seed is very low. Now it is necessary to establish the selection criteria that directly or indirectly increase the seed yield per sesame plant. In this study, freshly harvested seeds of 21 stable advance lines of sesame and their 8 parents such as R-9, B-14, B-9, B-67, T-12, IDP-51, IET-2, HT-1 were taken to evaluate the selection criteria for higher seed yield. The results indicated that number of branches/plant, number of capsule/plant, number of seeds/capsule and 100 seed weight were strongly related with sesame yield. Thus, selection of advance lines of sesame, that have higher seed yield, can be done on the basis of number of branches/plant, number of seeds/capsule, 100 seed weight and harvest index. Moreover, these traits may be employed as the selection criteria for the betterment of sesame seed yield in future agricultural system.