Physics


https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Wind profiling results from GU ST-Radar

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Al-doped ZnO transparent conductors

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Big Bang nucleosynthesis at LHC (CERN)

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Graphene quantum dots moisture sensor

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Looking for a fifth force

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Dust dynamics over lunar surface

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Graphene oxide filter paper

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Binary stars in King 1 open cluster

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Antibacterial properties of ZnO

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 DFT study of fullerene

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Sensitive detection of biomimetic apatite

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Analysing indoor power lines

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Fractal nature of ZnO nanoparticles

https://sites.google.com/a/gauhati.ac.in/research/#ds11092019 Powerline communication

https://sites.google.com/a/gauhati.ac.in/research/physics/#kb14092019 Re-awakening of an X-Ray binary

https://sites.google.com/a/gauhati.ac.in/research/physics/#ds13062019 CDs-porous silicon photo sensor

https://sites.google.com/a/gauhati.ac.in/research/physics/#mpb12042019 Driving the electrons unstable

https://sites.google.com/a/gauhati.ac.in/research/physics/#bb05032019 Probing protons at LHC

https://sites.google.com/a/gauhati.ac.in/research/physics/#bks23022019 AZO transparent conductors

https://sites.google.com/a/gauhati.ac.in/research/physics/#kk20022019 Targets for nuclear reaction experiments

https://sites.google.com/a/gauhati.ac.in/research/physics/#ds19022019 Properties of PANI-SA composites

https://sites.google.com/a/gauhati.ac.in/research/physics/#kb11022019 One more neutrino

https://sites.google.com/a/gauhati.ac.in/research/physics/#mpb18012019 Modeling magnetospheric oscillations

https://sites.google.com/a/gauhati.ac.in/research/physics/#sh30112018 Detection of arsenic in water

https://sites.google.com/a/gauhati.ac.in/research/physics#mpb27102018 Dust levitation in an inverse sheath

https://sites.google.com/a/gauhati.ac.in/research/physics#hkk12082018 Graphene based soil moisture sensor

https://sites.google.com/a/gauhati.ac.in/research/physics/#sd28062018 Annealing effect on silver nanocomposite

https://sites.google.com/a/gauhati.ac.in/research/physics/#ds26062018 Room temperature ethanol sensor

https://sites.google.com/a/gauhati.ac.in/research/physics/#sb14062018 Properties of monolayer graphene

https://sites.google.com/a/gauhati.ac.in/research/physics/#bks30052018 ZnO based transparent conductor

https://sites.google.com/a/gauhati.ac.in/research/physics/#kb29052018 Broadening of GRB spectra

https://sites.google.com/a/gauhati.ac.in/research/physics/#agb Efficient ammonia gas sensor

https://sites.google.com/a/gauhati.ac.in/research/physics/#agb Porous silicon MSM device

https://sites.google.com/a/gauhati.ac.in/research/physics/#agb Relativistic Heavy Ion Collisions

https://sites.google.com/a/gauhati.ac.in/research/physics/#agb Coherence in firefly emission

https://sites.google.com/a/gauhati.ac.in/research/physics/#kb Probing the neutrinos at DUNE

https://sites.google.com/a/gauhati.ac.in/research/physics/#bks Gravitational theories at galactic centre

https://sites.google.com/a/gauhati.ac.in/research/physics/#bks Fabrication of Ag/ZnO heterostructure

https://sites.google.com/a/gauhati.ac.in/research/physics/#rg Solitary waves in dusty plasmas
First observation by the GU ST-Radar : Wind profiling to understand thunderstorm dynamics
Manoj Saikia and collaborators report the first observation by the Stratospheric-Tropospheric Radar (ST-Radar) at Gauhati University related to wind profiling in the event of a thunderstorm. The GU ST-Radar is a newly established National facility for atmospheric research. This work is published in the journal Natural Hazards.


Authors
M Devi1,2, S Patgiri1,2, A Medhi1, S Das1, M Saikia1, A K Barbara2, S S Kakatkar3, and K P Ray3
from other organisations

Abstract
The wind profiling features received from recently installed stratospheric-tropospheric (ST) radar of Gauhati University (GU) (26.2 N, 91.75 E) are presented in the paper along with the validation process of the data by using radiosonde-derived wind parameters. The final focus of the paper is directed onto the thunderstorm-related changes in wind fields covering both vertical and composite components. Starting with the seasonal thunderstorm occurrence character over Guwahati through eight years of observations, the importance of the work on this meteorologically sensitive subtropical zone is highlighted. For identifying the process of growth of thunderstorm, the magnitudes of updrafts and downdrafts are extracted from the ST Radar-derived storm-time wind profilings. For evaluation of atmospheric system dynamics, the structure constant 𝐶n2 is calculated through radar Bragg-scattered signals and the resultant modifications induced by the thunderstorm on this parameter are presented and brought into ambit of discussions. The paper finally identifies the storm-induced effects in the wind field-derived variabilities, for possible adaptation as inputs for a thunderstorm predictive model.

Journal Reference


Botany    https://sites.google.com/a/gauhati.ac.in/research/#top 
 



Photo sensing zinc oxide porous silicon and ammonia sensing cadmium sulphide
Deepali Sarkar and her collaborators report about two works - one involving UV-visible photo sensing property of zinc oxide porous silicon and the other involving cadmium sulphide nanoparticle which can sense ammonia at room temperature. These works are published in the journals Materials Science in Semiconductor Processing and Sensors and Actuators A: Physical.



Authors
M Das, S Sarmah, D Barman, B K Sarma, and D Sarkar &
Ali Akbar, Mausumi Das, and D Sarkar

Abstract #1
Present article deals with fabrication of UV–Visible radiation sensing photodetector (PD) by architecting planar and sandwiched (PD1 and PD2) electrode configurations on ZnO-PS:p-Si heterostructure. PS:p-Si structure is prepared by electrochemical anodisation method. Thin ZnO layer of ~162 nm is deposited on PS:p-Si substrate using pulsed DC magnetron sputtering technique. Gold (Au) is combined with Aluminium (Al) to provide rectifying Schottky contacts to the devices. Prior to device testing, it is tested for various conventional characterisations. FESEM studies confirm uniform deposition of nanocrystalline ZnO thin film with mean particle size of ~ 35 nm, whereas its cross section shows uniform interface between ZnO and PS with combined thickness of ~700 nm. Cross sectional EDX analysis confirms diffusion of ZnO particles into PS layer. UV–visible absorption spectrum gives band gap of ZnO as ~3.3 eV. Reflectance measurement of the heterostructure shows decrease in reflectivity compared to bulk c-Si with ZnO-PS:p-Si showing multiple interference pattern compared to bare ZnO coated on glass within the spectral range 200 nm-800 nm. The pattern is remarkably increased compared to that of PS:p-Si. Photoluminescence study reveals various luminescence bands peaked at ~378 nm, 388 nm, 398 nm, 410 nm, 420 nm, 433 nm, 450 nm, 467 nm, 482 nm 492 nm and 597 nm. Current- Voltage (I–V) measurement for dark current (Id) gives low leakage current of the devices PD1 and PD2 respectively as 6.6 x 10−8 A and 7.5 x 10−7A at -5 V, which is however an order of magnitude more than the ZnO coated one on glass. Both the devices PD1 and PD2 show UV–Visible photoresponse, whereas the ZnO device on glass shows response to UV (375 nm) only. Both the devices show response time ~1 s in visible range which is nearly half the value in UV range.

Abstract #2
In this work, a chemical co-dispersion technique is employed to develop CdS decorated polyaniline (PANI) nanocomposite. The composite film is used to develop into room temperature ammonia (NH3) sensor. Prior to sensing study, the composite films are characterized to elucidate the structural, morphological and thermal properties. Structural and morphological studies reveal attachment of CdS nanoparticles on polyaniline nanorods. Gas sensing properties of PANI-CdS composite sensor is studied thoroughly and compared with bare PANI sensor. The room temperature gas response towards acetone, ammonia, methanol, formaldehyde and ethanol is investigated and found the sensor to be selective towards ammonia. The maximum gas response of 250% is achieved with 74% stability for the composite sensors upon exposure of 100 ppm of NH3 at room temperature. Response and recovery times show a decreasing trend with increasing concentration of NH3 gas.

Transparent conductors with aluminium-doped zinc oxide layers
Bimal Kumar Sarma and his graduate students prepare transparent conductors with Al-doped ZnO layers. Some of these conductors may find their places as potential candidates for next generation optoelectronic devices. These research works are published in the journals Materials Today Communications and Vacuum.


Authors
Bimal K Sarma and Pradhyut Rajkumar &
Dipak Barman and Bimal K Sarma

Abstract #1
The objective of this work is to provide high quality indium free transparent and conducting oxide film in which ZnO is the primary component and Al is the only dopant. A range of Al-doped ZnO (AZO) transparent conductors has been realised from the developed AZO sputtering targets with varying dopant concentrations with content of the dopant material Al2O3 added in the range 0.5–5.0 wt.%. X-ray diffraction, Raman spectroscopy, AFM measurements, and elemental analyses reveal promising material properties. The sheet resistance of 2.3 Ω/sq, visible light transmittance over 90%, and figure of merit of 75.9 mΩ–1 are the optimal electro-optical characteristics of AZO thin films. The resistivity of AZO films is dependent on the dopant concentrations with the lowest value estimated to be 1.66 × 10–4 Ω cm. A comparison of the figure of merit of AZO films with that of ITO suggests application potential of AZO as transparent conducting oxide. High transparency effect of AZO films in the near-UV spectral region is limited by the strong fundamental absorption. The hypsochromic shift of this onset of band-to-band absorption accentuates beyond 1.0 wt.% of Al2O3, which is primarily ascribed to the Moss-Burstein effect in this degenerate semiconductor. The bulk plasmon frequencies fall in the near infrared region where transmittance curves of AZO films completely differ from that of ZnO. A significantly high free carrier absorption in the near infrared suggests formation of free electron gas upon doping. With abundance of free electrons and low dielectric loss, AZO may serve as a promising infrared plasmonic material.

Abstract #2
In this work, an attempt has been made to develop thin and flexible transparent conductors based on the interfaces of Ag nanoparticles (AgNP) and Al:ZnO (AZO) deposited by sequential magnetron sputtering. The entire deposition process is completed within 20–28 min without breaking vacuum thereby preventing post-deposition oxidation of Ag NPs. The co-existence of high transmittance and low sheet resistance along with stability under mechanical bending is a bit difficult to achieve in bare AZO thin film having thickness below 200 nm. The resistivity of the optimised AZO/AgNP/AZO composite structure is significantly low at 3.3 × 10−5 Ω cm, which is two orders lower than that of AZO thin film of similar thickness. The figure of merit of the optimised composite structure peaks at 39.0 mΩ−1 corresponding to Ag NPs growth period of 5 min. The novel fabrication of AZO/AgNP interface in a dry and vacuum environment facilitates superior bending stability required for a flexible transparent conductor. The findings suggest that a system of two thin layers of AZO with embedded Ag NPs can be a potential candidate as an indium free transparent conductor for the next generation optoelectronic device.

Big Bang nucleosynthesis at LHC (CERN)
Buddhadeb Bhattacharjee and collaborators (through ALICE collaboration) study the collisions of Pb-Pb nuclei in the ALICE detector at LHC, CERN. The ALICE experiment creates an environment similar to the one created just after the Big Bang. This work is published in journal Physical Review C


Authors
S Acharya1 and 1097 other authors1 (B Bhattacharjee, N Hussain, G Volpe1, Y C Morales1, N Jacazio1, A O Velasquez1, I Ravasenga1, and  O V Rueda1)
from other institutions

Abstract
Midrapidity production of  π±, K± , and (p bar)p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at √sNN = 5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum (pT) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0 – 90% . The comparison of the pT -integrated particle ratios, i.e., proton-to-pion (p/π) and kaon-to-pion (K/π) ratios, with similar measurements in Pb-Pb collisions at √sNN = 2.76 TeV show no significant energy dependence. Blast-wave fits of the pT spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios (p/π, K/π) as a function of pT show pronounced maxima at pT ≈ 3 GeV/c in central Pb-Pb collisions. At high pT, particle ratios at 5.02 TeV are similar to those measured in pp collisions at the same energy and in Pb-Pb collisions at √sNN = 2.76 TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high pT and compatible with measurements at √sNN = 2.76 TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.

Journal Reference

https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Graphene quantum dots to sense moisture

Hemen Kalita and collaborators prepare graphene quantum dots which can be used as sensor for measurement of soil moisture. This work is published in the journal Carbon.


Authors
Hemen Kalita, Vinay S Palaparthy1, Maryam Shojaei Baghini1, and M Aslam1
from other institutions

Abstract
Graphene quantum dots (GQDs) the quantum dot variety of graphene represent a new group of quantum dots with exciting properties. Herein we report the electrochemical synthesis of GQDs with size ranging from 3 to 5 nm in diameter from graphene oxide (GO) at room temperature with LiClO4 in propylene carbonate as the electrolyte. The size of the GQDs can be tuned by playing with different parameters such as the applied potential, oxidation and reduction time, concentration of the supporting electrolyte. GQDs are promising candidate for humidity sensors, chemical sensors, nanoelectronic devices and biomarkers. In this paper, the potential use of the GQD as soil moisture sensors is also explored. We fabricated the micro-sensor where GQDs is used as the sensing material to perform the soil moisture measurements on two different soils. In our study, we observed that when soil water content varies from 0% to 32%, then sensor resistance changes by 99% and 97% for the red soil (silt loam) and black soil (clayey), respectively. We found that sensor response time was around 180 s for the both silt loam and clayey soils.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Probing the galactic centre looking for a fifth force

Sanjeev Kalita explores the possibility of new gravitational physics with the Scalaron fifth force at the centre of our home galaxy - the Milky Way. This research work is published in the Astrophysical Journal.


Author
Abstract
The Galactic Centre black hole (Sgr A*) provides an ideal laboratory for astronomical tests of new gravitational physics. This work reports that curvature correction [f(R)] to quantum vacuum fluctuations naturally yields a Yukawa-type scalar fifth force with potential exp(-Mψr)/r, where Mψ is the mass of the f(R) scalarons. Estimating the UV and IR cutoff scales of vacuum fluctuations, the Yukawa coupling strength is connected to the scalaron field amplitude. Whereas recently constrained Yukawa coupling and range correspond to light scalarons with Mψ = 1.37 x 10−21 – 5.49 x 10−20 eV, vacuum fluctuations yield a massive scalaron with Mψ = 10−16 eV. Scalaron-induced periastron shift of stellar orbits near Sgr A* has been studied with respect to the semi-major axis in the range a = 10–1000 au. It is found that the scalarons resulting from quantum fluctuations affect the precession of orbits with a = 128–256 Rs . The possibility of future constraints on massive scalarons in observations near Sgr A* is discussed. This is a new and independent effort to express a prototype quantum gravity effect in terms of astronomically accessible quantities.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Dust dynamics over lunar surface

Madhurjya P Bora and graduate student Rinku Deka investigate dust dynamics above the lunar surface and show that dust clouds with striations may form within a few metres of the surface. This work is published in the journal Physics of Plasmas.


Authors
Abstract
The authors have presented a basic model for a one dimensional collisionless space charge limited (SCL) plasma sheath consisting of electrons, ions, and two kinds of dust populations - a nano-dust population and a micrometer sized dust population. They have assumed that the nano-dust particles, plasma electrons, photoelectrons, and ions are the constituents of the plasma fluid and the micrometer sized dust particles behave as suspended impurities in the plasma without affecting the plasma dynamics. They have assumed that the charges of the micrometer-dusts are determined from the current balance on them and the charges on the nano-dusts are fixed. Due to photoemission, like the lunar surface charges to a positive potential, so the nano-dust and micrometer-dust particles charge to a positive potential. The electron densities have been derived by assuming both the electrons and photoelectrons to be Maxwellian, whereas the ion and nano-dust densities are derived from energy conservation of the ions and nano-dust particles and the continuity equations. Being a constituent of plasma, the nano-dusts do affect the sheath dynamics through the Poisson equation, which determines the plasma potential in the sheath region. The typical conditions for the levitation of dust particles in an SCL sheath including the maximum height and maximum size of the particles are calculated.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Filtering dye pollutants with a graphene paper

Hemen Kumar Kalita and collaborators demonstrate how to remove dye pollutants from aqueous solution with the help of a surface tailored graphene paper. This work is published in the journal EnvironmentalScience: Water Research & Technology.


Authors
Hemen Kalita, Himanshu Tyagi1 and M Aslam1
from other institution

Abstract
The potential application of graphene as a filter paper for selectively removing cationic and anionic dyes from aqueous solutions is demonstrated herein. A surface-tailored graphene paper was fabricated by the vacuum filtration technique on a microporous substrate to remove two different classes of dyes. A negatively charged graphene paper was fabricated from graphene oxide (GO) solution, and a positively charged graphene paper was fabricated from polyallylamine-functionalised GO solution. The solutions of methylene blue (MB) and methyl orange (MO) were filtered through the negatively charged graphene paper (GO−) and positively charged graphene paper (GO+). The stacking structure of the GO− and GO+ paper successfully removed the MB and MO mixtures from the solution. The GO− and GO+ paper demonstrated a high retention rate of 99.8% for MB dye and 99.5% for MO dye. The pore size of the paper was found to be less than 7 nm, providing more insights into the rejection mechanism. The rejection mechanism involves the adsorption and electrostatic interaction (i.e. cationic–anionic interaction) between the dye and graphene sheets, which result in the fast and efficient removal of the dye. The GO paper displayed adsorption capacities as high as 311 and 340 mg g−1 for MB and MO dyes, respectively. The results indicate that the surface-tailored graphene paper is a great alternative for the next generation cost-effective filters in practical water purification applications.

Detection of binary stars in King 1 open cluster

Eeshankur Saikia and collaborators report the detection of binary stars in the open cluster field King 1. This work is published in the journal Research in Astronomy and Astrophysics.


Authors
Parvej Reja Saleh, Debasish Hazarika, Ajaz Ahmad Dar1, Padmakar Singh Parihar1, and Eeshankur Saikia
from other institutions

Abstract
A rarely studied open cluster, King 1 is observed using the 1.3-m telescope equipped with a 2k x 4k CCD at Vainu Bappu Observatory, India. We analyze the photometric data obtained from CCD observations in both B and V bands. Out of 132 detected stars in the open cluster King 1 field, we have identified four stellar variables, and two among them are reported as newly detected binary systems. The parallax values from Gaia DR2 suggest that the open cluster King 1 is in the background of these two detected binary systems, falling along the same line of sight, giving rise to different parallax values. Periodogram analysis was carried out using Phase Dispersion Minimization (PDM) and the Lomb-Scargle (LS) method for all the detected variables. PHysics Of Eclipsing BinariEs (PHOEBE) is extensively employed to model various stellar parameters of both the detected binary systems. Based on the modeling results obtained from this work, one of the binary systems is reported for the first time as an Eclipsing Detached (ED) and the other as an Eclipsing Contact (EC) binary of W-type W UMa.

https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Antibacterial properties of flower-shaped ZnO (FZnO) microstructures

Eeshankur Saikia and collaborators study antibacterial properties of flower-shaped ZnO microstructures using nonlinear dynamics tools. This research work is reported in Scientific Reports.


Authors
Abstract
The present study reports the antibacterial properties of flower-shaped ZnO (FZnO) microstructures and its comparison with that of hexagon-shaped bulk ZnO (BZnO) nanostructures. The samples are prepared successfully by wet chemical method and the surface morphologies, structures and size of the ZnO samples are characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), BET adsorption isotherm, and Photoluminescence (PL) Spectroscopy. The SEM and TEM images of the sample have confirmed flower-shaped structure of the ZnO. The materials are also analyzed by using an innovative tool called Lacunarity, a nonlinear dynamical (NLD) tool for proper understanding of the inherent surface properties of the particles formed, comparing the results estimated with the BET results obtained, thereby confirming our proposition to use it as an important parameter in predictive models. In this new approach, geometry of the surface structure is being associated with biological properties, in order to come up with easier ways to identify materials for any such applications where rich surface structure is desired. The photocatalytic activity of the flower-shaped material is carried out to find out its optical properties as another marker for confirming the antimicrobial activities. It has been reported for the first time that the prominent antibacterial activities are favoured by the FZnO microstructure having lesser Lacunarity, significantly better than its bulk counterpart, for inhibiting gram negative - Escherichia coli microorganism.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Electrical and optical properties of fullerene

Sankar M Borah and his colleagues study electrical and nonlinear optical properties of fullerene through density functional theory (DFT). Fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. This work is published in the journal Applied Physics A.


Authors
Samir Thakur, Sankar M Borah, Ashok Singh1, and Nirab C Adhikary1
from other institutions

Abstract
The authors used density functional theory (DFT) to investigate the structural, electronic and nonlinear optical properties of N, P, As and Sb doped fullerene. The average polarizability and hyperpolarizability is significantly improved when these impurities are substituted individually in the (C60) lattice structure. The maximum hyperpolarizability is calculated for N-doped fullerene (3541.27 au) followed by P-doped fullerene (259.71 au), As-doped fullerene (102.52 au) and Sb-doped fullerene (32.06 au). A similar trend is observed and the polarizability is found to decrease monotonically. Both the polarizability and hyperpolarizability values are found to decrease with an increasing energy gap of the doped fullerene. N-Doped fullerene has the lowest energy gap (1.28 eV) followed by P-doped fullerene (1.94 eV), As-doped fullerene (2.02 eV) and Sb-doped fullerene (2.10 eV). The lowest energy gap minimizes the excitation energy and thus improves the nonlinear optical response. From the calculation of time-dependent-DFT (TD-DFT), it is observed that the maximum absorption wavelength of N-doped fullerene, which is about 830 nm, is shifted towards the longer wavelength at the infrared region in the case of P, As, and Sb-doped fullerenes. The results obtained through this study will help encourage the potential utilization of the metal-free doped-fullerene systems as a form of unique optical devices, thermal radiation detector, etc.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Sensitive detection of biomimetic apatite

Bimal Kumar Sarma and his collaborator report about sensitive detection of biomimetic apatite. Biomimetics is process of the imitation of the models, systems, and elements of nature for the purpose of solving complex human problems. This research work is published in the journal Applied Surface Science.



Authors
Abstract
Versatile surface-enhanced Raman spectroscopy (SERS) active Ag/ZnO heterostructures grown on glass and conducting Al-doped ZnO (AZO) have been developed to enable detection of analytes having very low molar concentration. The SERS substrate is composed of Ag nanoparticles decorated on ZnO microrods arranged mostly in flower-like patterns. ZnO microrods are synthesized by a hydrothermal method followed by the photo-de- position of Ag nanoparticles to fabricate Ag/ZnO heterostructure. The demonstration of the SERS activity is first accomplished by probing methyl orange and rhodamine 6G with a band specific SERS substrate enhancement factor (SSEF) as high as 5.4 x 107 and analytical enhancement factor (AEF) of 1.3 x 1010, exceptionally high enhancement achieved through use of the metal-semiconductor heterostructure where charge transfer at the interface plays an important role during SERS. The nanocrystalline hydroxyapatite prepared by a biomimetic process is detectable using the SERS active substrate with considerable enhancement of the characteristic Raman signals. This work is a novel attempt to probe biomimetic hydroxyapatite using SERS which would pave the way to understand early stages of bone mineralization. The use of AZO, an indium free transparent conductor is crucial to facilitate enhanced charge transfer at the interface which accentuates Raman active modes at low concentration of biomimetic apatite.

Journal References
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Analysing indoor power lines

Banty Tiru and her collaborators analyse the aspects of indoor power lines. This is an emerging technology which looks at using the power lines (the electrical wirings which supplies electricity to our houses) as a means of communication which will effectively remove the need for other media for communication. This work is published in the journal Arabian Journal for Science and Engineering (Springer).


Authors
Abstract
One of the challenges faced by indoor power line communication systems is the frequency-selective channels that are time varying and dependent on a large number of variabilities. A probable solution is to extract as much determinism as possible through prediction and statistical analysis of the frequency-selective notches. However, such deterministic tools are available only for simple open- and short-circuit branches and not for complex loads and topologies. This paper proposes an alternate method to predict and analyze notches using a minimum of four parameters without evaluating the transfer function. Termed as the load frequency mapping, the method is applicable for any frequency-dependent time-invariant loads and topologies and also capable of performing statistical analysis of random channels. A high decrease in prediction error (99.46–93.63%) is found for all the channels analyzed. Statistical analysis of 26 power line cables using random loads shows that some cables and loads offer more variations in frequency selectivity than others. For capacitive loads, the variation is more for the low-frequency notches and for those modeled as parallel resonant circuits at the frequencies near the resonance. Maximum variation is found for cables with high characteristic impedance with loads having high resonant frequencies and low quality factor and least for inductive loads. The power line therefore has considerable amount of determinism, and this can be incorporated to complement for fading channels or analysis of variability optimized for dual purpose of power delivery and data transfer.

Journal References
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Fractal nature of nanoparticles

Eeshankur Saikia and co-workers have reported multifractal nature in ZnO nanoparticles. This work is published in the journal Material Science and Engineering C.


Authors
Rajat K Saha, Mrinal K Debanath, and Eeshankur Saikia

Abstract
ZnO nanoparticles (NPs) have variety of applications in different fields due to its size, structure, as well as physical and chemical properties. One of its prominent characteristics is its antibacterial behaviour. Nonlinear Dynamical Theory (NLD) has a vast scope in the field of material science, especially when subtle correlations are searched for to extract hidden information. Since nano-ZnO materials may be used in inhibiting pathogens, its nonlinear features can be quantified and calibrated with the help of NLD tools. Multi-fractal Analysis (MFA) is an important diagnostic tool of NLD for not only analysing nonlinear signal or images, but also predicting any spurious events likely to occur in the system under study. Thus, the analysis of the surface texture of the ZnO nano particles formed, using the TEM images and relate it with the variations of the XRD signal using NLD tools, is our first attempt reported here. Further, tools of MFA are used, for the first time, to see if there exists any correlation between the texture of the nano particles formed and the Zone of Inhibition (ZoI) we obtain as an output after allowing certain pathogens inhibit in the presence of the same nano particles. Analysis of TEM images guide us to predict the texture and structure of crystallites of ZnO:Cu samples which are responsible for overall behaviour of inhibiting pathogens. In this paper, MFA of ZoI images, TEM images, and signal of four different Cu-doped ZnO nanoparticles are carried out and their outcomes are calibrated for estimating the size and pattern of unknown NPs synthesised under similar physical and chemical condition. Moreover, that MFA can be used reliably to predict spurious or abnormal surface structure or bacterial inhibition is also established.

https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Powerline communication

Banty Tiru, her graduate student, and collaborator explores if the powerlines (supplying electricity to our homes) can be used as a medium of communication. This research work is published in the Journal of Circuits, Systems and Computers.


Authors
Abstract
This paper deals with the development of a realistic power line channel simulator wherein power line communication devices can be tested before implementation to meet the massive need of data transfer. The statistics of the noise follow the experimentally observed in different sites, namely the time-varying non-white power spectral densities (PSDs) of the background noise and a target non Gaussian amplitude distribution. The procedure based on the inverse cumulative distribution function method of generation of random numbers and iteratively updating a target spectrum necessitates knowledge of a maximum of 17 parameters for successful implementation and has been validated for three sites in the low-frequency (< 500kHz) and high-frequency (1–30MHz) bands. The average percentage errors in prediction of the mean of the channel capacity (CC) are 12.68% and 10.66% in the two bands, respectively. The minimum correlations of the distribution of BER of OFDM in a channel corrupted by the simulated and observed noises are is 0.883 and 0.801 in the two bands which are high compared to 0.422 and 0.355, respectively, when the requirement of a target amplitude distribution is neglected. With low-frequency noise emulated by a data acquisition card, an average percentage error of 11.82% in the CC and a correlation of 0.867 (against 0.498) in BER are obtained. The noise thus generated can be used as a testbed for system testing, instead of the conventional static models (additive white Gaussian noise or with time-invariant coloured PSD), leading to better optimisation of the implemented devices.

Journal References
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Re-awakening of an X-Ray binary

Kalyanee Boruah and collaborators report about a surprise outburst from the low-mass X-Ray binary GRS 1716-249. The last time an outburst was observed was 23 years ago! This work and another related works are published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).


Authors
Priya Bharali, Sunil Chandra1, Jaiverdhan Chauhan1, Javier A García1, Jayashree Roy1, Markus Boettcher1, and Kalyanee Boruah
from other institutions

Abstract
In this work, the author present a spectral and temporal analysis of Swift/XRT and NuSTAR observations of GRS 1716–249 during its recent 2016–2017 outburst. This low-mass X-ray binary underwent an extraordinary outburst after a long quiescence of 23 years, since its last major outburst in 1993. The source was observed over two different epochs during 2017 April 7 and 10. The best-fitting joint spectral fitting in the energy range 0.5–79.0 keV indicates that the spectrum is best described by relatively cold, weak disc blackbody emission, dominant thermal Comptonisation emission, and a relativistically broadened fluorescent iron Kα emission line. The authors observed a clear indication of a Compton hump around 30 keV. They also detected an excess feature of 1.3 keV. Assuming a lamp-post geometry of the corona, we constrained the inner disc radius for both observations to 11.92+8.62−11.92 RISCO (i.e. an upper limit) and 10.39+9.51−3.02 RISCO (where RISCO is the radius of the innermost stable circular orbit) for the first epoch (E1) and second epoch (E2), respectively. A significant (5σ) type C quasi-periodic oscillation (QPO) at 1.20 ± 0.04 Hz is detected for the first time for GRS 1716–249, which drifts to 1.55 ± 0.04 Hz (6σ) at the end of the second observation. The derived spectral and temporal properties show a positive correlation between the QPO frequency and the photon index.

In a subsequent report, the authors also report about the observation of a newly discovered X-Ray transient.

CDs-porous silicon nanostructured photo sensor

Deepali Sarkar and her coworkers are studying the photo sensing properties of CDs-proous silicon based metal-semiconductor-metal (MSM) hetero-structure. This work is published in Journal of Materials Science: Materials in Electronics.


Authors
Abstract
Present work reports light sensing property of metal–semiconductor–metal device based on nanostructured CdS-PS:p-Si hetero-structure. PS with thickness of ~ 1500 nm is prepared on p-Si (100) oriented wafer using electrochemical anodization method. Thin nanostructured n-CdS layer of ~ 170 nm is deposited on PS:p-Si substrate by vacuum evaporation. FESEM observation confirms growth of hierarchical flower like CdS nanostructure on PS:p-Si substrate. UV–Vis absorption spectrum gives bandgap of CdS nanostructure to be 2.6 eV. Reflectance measurement of CdS-PS:p-Si hetero-structure shows multiple interference pattern within the spectral range of 200–800 nm, with remarkable blue shift of the pattern compared to that of PS:p-Si structure. Photoluminescence study of the hetero-structure reveals presence of various luminescence bands peaked at ~ 450, 460, 468, 482, 560, and 590 nm. Dark current (Id) analysis shows low leakage current ~ 32 nA at − 2 V with ideality factor (n) and reverse saturation current (Is) values of 1.57 and 0.2 nA respectively. Spectral response of the hetero-structure at a bias voltage of − 2 V and irradiation wavelength of 400 nm shows maximum responsivity (Rλ) value of ~ 0.6 AW−1 and external quantum efficiency of ~ 180%. Response and recovery times of the device are ~ 160 and ~ 350 ms respectively. The prepared hetero-structure has been compared with other silicon based optoelectronic switching devices to find suitability of an alternate choice.

Driving the electrons unstable - a numerical simulation

Madhurjya P Bora and graduate student Suniti Changmai show how the photoemission in a plasma can drive the electron two-stream instability (ETSI) and can modify a plasma sheath. This research work is published in the journal Physics of Plasmas.



Authors

Abstract
Analysis related to the onset and evolution of the electron two-stream instability (ETSI) near a surface with a continuous photoemission flux is presented. With the help of a particle-in-cell simulation code, it is shown that when a surface emits photoelectrons due to exposure to ultraviolet photons (or due to similar mechanisms), it may lead to the onset of the ETSI due to the relative bulk velocity difference between the photoelectrons and the plasma electrons. It is shown that the ETSI thus developed is sustained through the lifetime of the plasma and prevents thermalisation of the electrons, which leads to a distortion in the electron velocity distribution function (EVDF) resulting a high energy tail, at least near the surface. We have shown that the resultant EVDF can be highly Lorentzian with a spectral index of ~1.5. The simulation results are supported with the corresponding theory, which are found to be in good agreement.

https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Probing the protons at Large Hadron Collider (LHC)

Buddhadeb Bhattacharjee and graduate student Pranjal Sarma explore a possible mechanism of intermittency during p-p collisions at Large Hadron Collider (LHC) in CERN. This work is published in Physical Review C.


Authors

Abstract
Nonstatistical fluctuation in pseudorapidity (η), azimuthal (φ), and pseudorapidity-azimuthal (η – φ) distribution spectra of primary particles of PYTHIA Monash (default) generated pp events at √s = 2.76, 7, and 13 TeV have been studied using the scaled factorial moment technique. A weak intermittent type of emission could be realised for minimum-bias (MB) pp events in χ(η – φ) space and a much stronger intermittency could be observed in high-multiplicity (HM) pp events in all χ(η), χ(φ), and χ(η – φ) spaces at all the studied energies. For HM pp events, at a particular energy, the intermittency index αq is found to be largest in two-dimensional χ(η – φ) space and least in χ(η) space, and no centre of mass energy dependence of αq could be observed. The anomalous dimensions dq are observed to be increased with the order of the moment q, suggesting a multifractal nature of the emission spectra of various studied events. While, the coefficient λq is found to decrease monotonically with the order of the moment q for two-dimensional analysis of MB pp events as well as for one-dimensional analysis of HM pp events, a clear minimum in λq values could be observed from the two-dimensional HM pp data analysis. For PYTHIA Monash generated sets of data, the strength of the intermittency is found to vary significantly with the variation of the strength of the colour reconnection (CR) parameter, i.e. reconnection range RR, for RR = 0.0, 1.8 and 3.0, thereby, establishing a strong connection between the CR mechanism and the observed intermittent type of emission of primary charged particles of the studied high-multiplicity pp events.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



The physics of transparent conductors

Bimal Kumar Sarma and his graduate students come up with an AZO transparent conductor with high figure of merit for possible optoelectronic applications. This research is published in the journal Applied Surface Science.


Authors
Bikash Sarma, Dipak Barman, and Bimal K Sarma

Abstract
This work presents a broad study of transparent and conducting Al-doped ZnO (AZO) thin films that could replace indium tin oxide (ITO) as transparent electrode in optoelectronic devices. AZO thin films are deposited by pulsed DC magnetron sputtering at a sputtering power of 80 W with different pulse frequencies in the range 50-100 kHz. Diffraction data confirm formation of doped ZnO and AZO thin films exhibit preferred orientation in the c-direction. The crystallite sizes of Al:ZnO are in the range 16–21 nm. The field emission scanning electron microscopy and atomic force microscopy of AZO thin films reveal nucleation and growth of uniform and dense films with better quality films deposited at a pulse frequency 75 kHz. A simple and non-destructive optical method is adopted to determine thickness and dispersion parameters such as dispersion energy, carrier concentration to effective mass ratio, and plasma frequency. AZO thin films offer excellent visible light transparency and limited transparency in the near-infrared region due to free carrier absorption. The sheet resistance of AZO thin films is recorded in the range 9-45 Ω/sq making these transparent conducting oxides (TCOs) suitable for optoelectronic applications. The figure of merit as high as 1.99 × 10−2 Ω−1 is achieved for AZO thin film deposited at a pulse frequency of 75 kHz. AZO thin film sputtered with a pulse frequency of 75 kHz is quite stable in ambient oxidising environment and surface adsorption sites might govern the initial oxidation of films when exposed to atmosphere. Excellent figure of merit and good stability of sputtered AZO thin films as TCO fulfil the requirements of a transparent electrode in photovoltaics.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Fabricating targets for nuclear reaction experiments

Kushal Kalita, graduate student Nabendu Kumar Deb, and their collaborators report about fabrication of thin nickel targets for present and future nuclear reaction experiments. This research work is published in the journal Vacuum.


Authors
Nabendu Kumar Deb, Kushal Kalita, S R Abhilash1, Pankaj K Giri1, Rohan Biswas1, G R Umapathy1, D Kabiraj1, and S Chopra1
1from other institutions

Abstract
To perform nuclear reaction experiments at HIRA, IUAC, New Delhi, thin (100–150 ) and pure 61,62Ni targets of uniform thickness are required. Self supporting targets are preferable for such case but, instead, carbon-backed isotopic targets are fabricated by adapting physical vapour deposition technique as it was comparatively more stable and consistent. Around 25 thin targets of both 61,62Ni isotopes are prepared using the limited amount of available enriched target material (less than 100 mg). The carbon-backed slides along with the parting agents are prepared using a diffusion pump based coating unit and the target material is deposited over the carbon-backed slides in the turbo pump based coating unit. To obtain consistent and intact targets, some trials were done with deposited slides and was found that the material degrades in any of the slides when kept idle for few days. The thicknesses of the targets are verified using profilometer, α energy loss technique, and RBS technique. They were found to be in good agreement with each other using the three techniques. The purity and the uniformity of the fabricated targets are further confirmed after verification using the RBS, the EDS and the XRD techniques.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Studying dielectric properties of PANI-SA composites

Deepali Sarkar and her graduate students study the dielectric properties of polyaniline (PANI) sulphonic acid (SA) composites. This work is published in the journal Synthetic Metals.


Authors
Mausumi Das, Ali Akbar, and D Sarkar

Abstract
Present work is primarily emphasised on the study of dielectric properties of sulphonic acids (SA) incorporated polyaniline (PANI). SA's function as dopants as well as surfactants for PANI. The PANI and PANI-SA samples are prepared by interfacial technique. The three composites prepared with three SA's [camphor sulphonic acid (CSA), dodecylbenzene sulphonic acid (DBSA) and polystyrene sulfonic acid (PSSA)] are characterised by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field effect scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA) and differential thermogram (DTG) prior to dielectric studies. The results of PANI not incorporated with SA are also shown for comparison. XRD shows enhancement of crystallinity on SA doping. FTIR confirms the molecular structure with enhanced oxidation states on SA doping. FESEM shows fibrillar morphology with reduced fibre diameter from 86 nm in pure PANI to minimum of 50 nm in one of the composites. TGA and DTG results show better thermal stability on SA doping. The dielectric and AC conductivity measurements of the undoped and dopedPANI are studied in the frequency range of 42 kHz - 2 MHz and in the temperature range of 300 K–330 K. The dielectric constant for all the PANI composites increases with increase in temperature which indicates increase in mobility of the electric dipoles in the polymers. The dielectric constant for DBSA doped PANI is nearly 5000 which is much higher in context to interfacially polymerised nanofibres compared to that of undoped PANI where this value is about 800. Electric modulus studies show relaxation peaks in imaginary modulus spectra which ascertains about the type of relaxation process. The AC conductivity of the composites is found to be much higher than that of undoped PANI. The electrical conductivity increases with increase of temperature. This is suggested to be caused due to the activated trapped charge carriers.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



One more neutrino!

Kalpana Bora and her collaborators ask whether the sterile neutrino can fit into the existing neutrino hierarchy. Sterile neutrino is a possible dark matter candidate. This research is published in The European Physical Journal C.


Authors
Neelakshi Sarma, Kalpana Bora, and Debasish Borah1
1from other institution

Abstract
Motivated by the recent resurrection of the evidence for an eV scale sterile neutrino from the MiniBooNE experiment, the authors revisit one of the most minimal seesaw model known as the minimal extended seesaw that gives rise to a 3 + 1 light neutrino mass matrix. The authors consider the presence of A4 flavour symmetry which plays a nontrivial role in generating the structure of the neutrino mass matrix. Considering a diagonal charged lepton mass matrix and generic vacuum alignments of A4 triplet flavons, we classify the resulting mass matrices based on their textures. Keeping aside the disallowed texture zeros based on earlier studies of 3 + 1 neutrino textures, we categorise the remaining ones based on texture zeros, μ-τ symmetry in the 3 × 3 block and hybrid textures. After pointing out the origin of such 3 + 1 neutrino textures to A4 vacuum alignments, the authors use the latest 3 + 1 neutrino oscillation data and numerically analyse the texture zeros and μ–τ symmetric cases. The authors find that a few of them are allowed from each category predicting interesting cor- relations between neutrino parameters. They also find that all of these allowed cases prefer normal hierarchical pattern of light neutrino masses over inverted hierarchy.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Modeling aperiodic magnetospheric oscillations

Graduate Student Murchana Khusroo and Madhurjya P Bora explain why the magnetic oscillations in earth's magnetosphere are always almost aperiodic. This research work is published in Physical Review E


(Featured in the Kaleidoscope of Phys Rev E for the Month of Jan 2019)

Authors

Abstract
The authors present an analysis of a Hall-magnetohydrodynamics model of the magnetospheric plasma with finite Larmor radius effect. Through a bifurcation analysis of the resultant nonlinear system, they show that this nonlinear model does not possess a limit cycle, which rules out regular periodic oscillations with constant amplitude. However, it does result in a train of magnetosonic solitons, localised in space, with amplitudes increasing in time, which are largely in agreement with what is usually observed in the magnetopause region. We call these oscillations aperiodic magnetospheric oscillations. The authors emphasise that most of the train of solitary oscillations observed by the Cluster fleet and other spacecrafts do not have constant amplitudes: they either continuously increase or decrease. These train of solitons with non-constant amplitudes is a primary solution of their mathematical model.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Detection of arsenic in water

Simanta Hazarika and graduate student Chiranjib Rajkonwar describe a method which has the potential for being an in-situ method for detection of groundwater arsenic. This research is published in the journal Laser Physics.





Authors

Abstract
Ingestion of arsenic by the human body through drinking water induces numerous diseases. Therefore, detection and estimation of arsenic concentration in water, especially in groundwater, is important to protect the human world from its toxicity. In this work we demonstrate a laser induced fluorescence resonance energy transfer (LIFRET) method for the determination of the arsenic concentration in water. The fluorescence resonance energy transfer (FRET) is observed in an aqueous solution of 1, 8-naphthalimide and rhodamine-B by exciting it with a laser radiation of wavelength 405 nm. It is observed that if arsenic contaminated water is added to the pure solution of 1, 8-naphthalimide and rhodamine-B the wavelength of the peak in its FRET spectrum shifts from its pure value at 632.45 nm (peak position of the FRET spectrum of a pure solution of 1, 8-naphthalimide and rhodamine-B). These shifts of wavelengths are towards the lower wavelength side, corresponding to an increase in the concentration of arsenic added to the solution. In the present work, based on the shifting of the peak wavelength value of the FRET spectra corresponding to different concentrations of arsenic, we have described a method for the estimation of arsenic in water up to a lowest limit of 0.00001 gm l−1 (the maximum permissible limit of arsenic in water according to the World Health Organisation). The LIFRET method described in this work is portable, relatively cost effective, more convenient and has the potential for any in situ measurement of arsenic in the ground water of arsenic contaminated areas.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Dust levitation in an inverse sheath

Rinku Deka and Madhurjya P Bora put forward a theory which could probably explain appearances of dust streaks above lunar surface. This research is published in the journal Physics of Plasmas.



Authors

Abstract
The results of an analysis of the physics of levitation of negatively charged dust particles over a surface (wall) in an inverse sheath are reported in this research work. It is shown that in a suitable parameter regime, the ion-drag force may balance the combined electrostatic and gravitational forces on the dust particles owing to its hollow profile as one moves away from the surface. The authors' analysis shows that the parameter regimes in which such a situation may result are realisable in laboratory and space plasma environments, particularly the near-surface dayside lunar plasma. The lunar surface and dust grains are electrostatically charged due to the interaction with the solar wind plasma environment and the photoemission of electrons due to solar UV radiation. This results in a process that charges the surface positively and generates a near-surface photoelectron inverse plasma sheath. The potential structure changes from a monotonic classical sheath to an inverse sheath as the emitted electron density becomes larger than the plasma electron density. In a relatively newer, recently developed charging model, called the Patched Charge Model, it was shown both theoretically and experimentally that even in a photoelectron-rich environment, dust particles lying on a regolith surface can attain large negative potential due to the formation of micro-cavities. This negative potential may reach such values so that dust mobilisation and lofting may become possible. In their work, the authors have assumed the existence of such negatively charged dust particles in a photoelectron-rich environment and argue that once the dust lofting is effected, the levitation can be sustained through the ion-drag force. The conditions of levitation are investigated for these dust particles, and the levitation distances from the lunar surface are calculated.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Garphene based soil moisture microsensor

Dr Hemen Kumar Kalita and his collaborators have developed and an in-situ graphene-based microsensor for agricutural use, which opens up a range of novel future applications. This work is published in the journal Sensors and Actuators B: Chemical.




Authors
Vinay S Palaparthy1, Hemen Kalita, Sandeep G Surya1, Maryam Shojaei Baghini1, and M Aslam1
1 from other institutions

Abstract
In this work, the authors have designed a robust graphene oxide (GO) based capacitive sensor which is highly sensitive to soil moisture. The sensor consists of inter-digitated electrode (IDE) with chemically synthesised GO as the sensing platform. They have used the MEMS fabrication technique to fabricate the IDE and have performed the characterisation such as AFM, RAMAN and XPS on the as-prepared GO to understand the surface properties of the GO. The sensor response changes by 340% and 370% over soil moisture changes from 1% to 55% for red and black soil, respectively. GO sensor array shows a fast response time of 100–120 seconds for the soil moisture measurements. For in-situ soil moisture measurements, the diurnal temperature and salt concentration (soil conductivity) are the variable parameters, which might affect the sensor response. They observe that the sensor output changes by 6% when the ambient temperature varies from 25°C to 65°C, which leads to just 3% discrepancies for the soil moisture measurements. For the salt concentration (soil conductivity) measurements the sensor output changes by 4% when salt concentration in the soil sample varies from 0 mol to 0.35 mol (standard for the field measurement), and discrepancies in the soil moisture measurements is around 2%.

Effect of annealing temperature on  silver-PVA nanocomposite

Dr Sulochana Deb and her collaborator are reporting the effect of annealing temperature on the optical properties of silver nanoparticles embedded in polyvinyl alcohol (PVA) matrix. This work is published in the journal Optik.



Authors

Abstract
The present article reports the effect of annealing temperature on the morphology and optical properties of silver nanoparticles embedded in polyvinyl alcohol (PVA) matrix. The nanocomposite films prior to annealing shows spherical grains. These films are annealed at five different temperatures (373 K, 423 K, 473 K, 523 K and 573 K) in vacuum and the effects on surface morphology and optical properties are investigated. The unannealed and annealed films are characterised by FESEM, XRD, FTIR spectra, TGA, UV–vis absorption spectra and photoluminescence (PL) spectra. Scanning electron microscopy images show the change in shape and size with increase of annealing temperature. Spherical shapes of the grains in pre annealed samples get changed to nanocubes and nanorods at higher annealing temperatures of 523 K and 573 K respectively. UV–vis spectra show a remarkable change of surface plasmon resonance peak with the increase in annealing temperature. XRD shows a characteristic intense peak of silver nano at 2θ = 38ο for (111) crystalline plane with no significant change with annealing temperature. Photoluminescence spectra show a tendency of red shift of emission peak.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Room temperature ethanol sensor

Dr Deepali Sarkar and her collaborators have developed an ethanol sensor from polypyrrole embedded in polyvinyl alcohol matrix. This work is published in Polymer Bulletin.


Authors

Abstract
Polypyrrole (PPy) is embedded in Polyvinyl Alcohol (PVA) matrix to give a homogeneous composite solution by dispersing PPy in PVA solution. Scanning Electron Microscopic (SEM) study on the film prepared from the composite solution shows uniform distribution of nearly spherical shaped PPy grains of average diameter of 20 nm. The X-ray diffraction (XRD), UV-Visible and Fourier Transform Infra-Red (FTIR) spectroscopic characterisations of the composite film are carried out for structural and optical properties. The enhanced thermal stability of the PPy-PVA composite film is confirmed by thermogravimetric analysis (TGA). XRD shows signature of amorphous nature for PVA along with some crystallinity arising for PPy. UV-Visible absorption spectrum shows two absorption peaks for π-π* and polaronic transition; FTIR spectrum suggests cross linking between PPy and PVA. Studies on sensing of the PPy-PVA composite film for Ethanol, Ammonia, Toluene, Chloroform and Acetone vapours at room temperature (300 K) are done for comparison. The composite film shows best response among all these vapours towards Ethanol requiring smallest response time.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Structural, electronic and optical properties of heteroatom doped monolayer graphene

Dr Sankar Moni Borah and his coworkers present a theoretical study of the structural, electronic, and optical properties of doped monolayer graphene with the help of density functional theory (DFT). This research article is published in Optik.


Authors

Abstract
The authors present a theoretical work on the influence of doped and co-doped Al, Al-S, Al-N and Al-P heteroatoms in the mono layer graphene surface. The Density functional study reveals that, Al, P and S co-doping significantly modifies the neighbourhood bonding arrangement of the graphene sheet. The Natural population analysis revels that Al, P and S co-doping makes the graphene surface as electron rich system. From the molecular orbital analysis it is found that HOMO-LUMO energy gap decreases by starting from the pristine graphene in following manner Al doping > Al-S co-doping> Al-N co-doping >Al-P co-doping. On the other hand, the time dependent density functional theory (TD-DFT) calculation shows that the maximum absorbing wavelength of Al-P and Al-N co-doped graphene systems shifted towards the lower wavelength range with respect to Al doped graphene.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



ZnO based multilayer transparent conductor

Dr Bimal Kumar Sarma and his collaborator Bikash Sarma present electro-optical studies of ZnO (Zinc Oxide) based multilayer transparent conductor. This research work is published in Journal of Alloys and Compounds.



Authors

Abstract
A broad study on transparent and conducting ZnO/Ag/ZnO multilayer thin films is presented in this report. Bottom ZnO layer, mid Ag layer, and top ZnO layer are deposited on flexible and glass substrates by Pulsed DC and DC magnetron sputtering technique. X-ray diffraction (XRD) studies of multilayer structures reveal formation of nanocrystalline wurtzite ZnO which exhibit (002) preferable orientation along with the feeble appearance of (111) peak of Ag from the intermediate layer. High transmittance of 81.8% with low sheet resistance 17.0 U/sq are achieved for ZnO/Ag/ZnO thin films deposited on glass and transmittance of 77.3% with sheet resistance 14.7 U/sq are observed for ZnO/Ag/ZnO thin films deposited on PET. XRD studies facilitate to understand the role of texture and residual stress of ZnO on the electro- optical properties of ZnO/Ag/ZnO multilayer thin films. XRD analyses and electro-optical measurements confirm that the tensile residual stress of ZnO above certain level is favourable for lower sheet resistance primarily due to the lattice extension in the transverse direction to the film surface. Due to high Hall mobility, low sheet resistance and reasonably good figure of merit, sputtered ZnO/Ag/ZnO multilayer thin films meet the requirements of transparent conductors in photovoltaics.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Broadening of spectra from gamma ray bursts (GRB)

Dr Kalyanee Boruah and her fellow researchers construct a model to explain the broadening of GRB spectra. GRBs are some of the most powerful emissions of electromagnetic radiation in the Universe. This research work has been published in New Astronomy.



Authors
Priya Bharali, Sunder Sahayanathan, Ranjeev Misra, and Kalyanee Boruah
Abstract
The observations of the prompt emission of gamma ray bursts (GRB) by GLAST Burst Monitor (GBM), on board Fermi Gamma-ray Space Telescope, suggest the presence of a significant thermal spectral component, whose origin is not well understood. Recently, it has been shown that for long duration GRBs, the spectral width as defined as the logarithm of the ratio of the energies at which the spectrum falls to half its peak value, lie in the range of 0.84-1.3 with a median value of 1.07. Thus, while most of the GRB spectra are found to be too narrow to be explained by synchrotron emission from an electron distribution, they are also significantly broader than a blackbody spectrum whose width should be 0.54. Here, the authors consider the possibility that an intrinsic thermal spectrum from a fire-ball like model, may be observed to be broadened if the system undergoes a rapid temperature evolution. A toy-model is being constructed here to show that for bursts with durations in the range 5-70 s, the widths of their 1 second time-averaged spectra can be at the most ≲ 0.557. Thus, while rapid temperature variation can broaden the detected spectral shape, the observed median value of  ~1.07 requires that there must be significant sub-photospheric emission and/or an anisotropic explosion to explain the broadening for most GRB spectra.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



Efficient ammonia gas sensor

Dr Deepali Sarkar and Mausumi Das report about the development of an efficient ammonia (NH3) gas sensor at room temperature from one-pot synthesised zinc oxide (ZnO). This research work is published in Ceramics International.


Authors
Mausumi Das and Deepali Sarkar

Abstract
Development of efficient room temperature ammonia (NH3) gas sensor from one pot synthesised zinc oxide (ZnO) – polyaniline (PANI) nanocomposite is reported in the present article. Prior to gas sensing study, the material is characterised to understand the structural, morphological, compositional, optical and thermal properties. Structural and morphological studies indicate good incorporation of ZnO particles in PANI matrix. The gas sensing efficiency of ZnO-PANI nanocomposite is examined at room temperature for ethanol (C2H5OH), methanol (CH3OH) and NH3 gas. The results confirm that ZnO-PANI nanocomposite to be highly selective for NH3 with fast response time and better stability. The response and recovery times are observed to be significantly dependent on NH3 concentration and the lowest detection limit of the sensor for NH3 is found 10 ppm. ZnO-PANI nanocomposite shows better gas sensing efficiency as compared to the sensors developed from single phase PANI film.
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 
 



UV-Visible optical photodetection from porous silicon MSM device

Dr Deepali Sarkar and her collaborators describe the fabrication process of Metal-Semiconductor-Metal structure of porous silicon, which will be used for photodetection. This research article is published in Superlattices and Microstructures.



Authors
M Das, S Sarmah, and D Sarkar

Abstract
Silicon photodiodes have been in use as UV detectors and some compound semiconductors as visible detectors for a long time. However their implementation to the optoelectronic field is limited due to high fabrication cost as well as sophisticated prerequisites. The present research aims at fabricating porous silicon Metal-Semiconductor-Metal structure and its photodetection property for the UV wavelength range from 250 to 390 nm along with a portion of visible spectrum. Porous silicon thickness attained is ~ 2 mm with uniform distribution of pores. It shows characteristic visible yellow/green luminescence under UV-Visible irradiation. The responsivities, obtained through photoconductivity measurement of the device, are obtained as 1.42 and 2.00 AW-1 for UV and visible ranges respectively, whereas the response times in corresponding ranges as 0.70 and 1.00 s. These results suggest superiority of the device as a UV-Visible detector compared to silicon or other semiconductor detectors. However, the device shows ageing effect due to slow oxidation of the PS layer.
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 




Rapidity and Relativistic Heavy Ion collisions

Dr Buddhadeb Bhattacharjee and his collaborators explore more about rapidity (a parameter which is a measure of relativistic velocity in collisions of sub-atomic particles) in Relativistic Heavy Ion Collisions in two research works published in Nuclear Physics A and Physical Review C.



Authors
Kalyan Dey and Buddhadeb Bhattacharjee &
Nur Hussain and Buddhadeb Bhattacharjee

Abstract #1
Strangeness enhancement factor (E_s) is considered to be one of the traditional signatures of formation of Quark Gluon Plasma (QGP) in relativistic heavy ion collisions (HIC). Generally, strangeness enhancement factor is believed to be maximum at mid-rapidity. However, in this work, it is shown that strangeness enhancement factor could be minimum as well at mid-rapidity depending upon the nature of the quark content of the produced particles of HIC. Rapidity dependent strangeness enhancement factors for the identified particles have been studied with the help of a string based hadronic transport model UrQMD-3.3 (Ultra-relativistic Quantum Molecular Dynamics) at FAIR energies. A strong rapidity dependent strangeness enhancement could be observed with our generated data for Au+Au collisions at the beam energy of 30A GeV. The strangeness enhancement is found to be maximum at mid-rapidity for the particles containing leading quarks while for particles consisting of produced quarks only, the situation is seen to be otherwise. Such rapidity dependent strangeness enhancement could be traced back to the dependence of rapidity width on centrality or otherwise on the distribution of net-baryon density.

Abstract #2
Width of the rapidity distributions of produced particles of heavy ion collisions carry a number of information about the collisions dynamics. NA49, a CERN collaboration, proposed by analysing CERN Super Proton Synchrotron (SPS) data, a universal mass ordering of the rapidity width of the produced charged particles. Such universal mass ordering was contradicted by GU group. In one of our recent works at AGS and low SPS energies [1], from a study on UrQMD-generated Monte Carlo events, as well as from existing experimental results, it has been shown that the universal mass ordering is violated with a jump in the rapidity width of lambda. A separate mass ordering of various mesons and baryons have been proposed. Width of the rapidity distribution of leading particles is shown to have non-trivial net baryon density distribution affect. In this work it has been shown with UrQMD-generated data that the observed jump in the rapidity width of lambda is a universal characteristics of heavy ion collisions data from AGS and SPS to RHIC and LHC energies.

Journal References
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 




Coherence in firefly emission

There may be more than what we see in the light of the firefly in the summer sky! Dr Anurup Gohain Borua and his fellow researchers investigates. Find more about it in the research communication published in Current Science. The findings of this research have also been featured in India Science Wire - Vigyan Prasar on February 16, 2018.



Authors
Upamanyu Sharma, Angana Goswami, and Anurup Gohain Barua

Abstract
The emission spectrum of the Indian species of firefly Luciola Praeusta has been shown to consist of two broad green and red-coloured sectors, with a narrow yellow one in between. In this work, interference patterns of the light of this firefly-species have been shown to contain a laser-like emission. The value of the coherence length (implying the degree of monochromaticity) for the yellow-coloured light has been shown to be an astonishing 23.5 cm, while reasonably good spatial coherence for this radiation has been obtained.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 




Probing the neutrinos

Dr Kalpana Bora and her collaborators explore the physics of Majorana neutrinos with reference to the Deep Underground Neutrino Experiment near Fermilab (DUNE, formerly LBNE). This work is published in Physical Review D.


Authors
Kalpana Bora, Debasish Borah, and Debajyoti Dutta

Abstract
This study probes different texture zero neutrino mass matrices at long baseline neutrino experiment DUNE particularly focusing on its sensitivity to the octant of atmospheric mixing angle θ23 and leptonic Dirac CP phase δcp. Assuming a diagonal charged lepton basis and Majorana nature of light neutrinos, the authors first classify the possible light neutrino mass matrices with one and two texture zeros and then numerically evaluate the parameter space which satisfies the texture zero conditions. Apart from using the latest global fit values of neutrino oscillation parameters, they also use the latest bound on the sum of absolute neutrino masses (Σi|mi|) from the Planck mission data and the updated bound on effective neutrino mass Mee from neutrinoless double beta decay (0νββ) experiment to find the allowed Majorana texture zero mass matrices. For the allowed texture zero mass matrices from all these constraints, they then feed the corresponding light neutrino parameter values satisfying the texture zero conditions into the numerical analysis in order to study the capability of DUNE to allow/exclude them once it starts taking data. The authors also find that the DUNE will be able to exclude some of these texture zero mass matrices which restrict the (θ23 − δcp) to a very specific range of values, depending on the values of the parameters that Nature has chosen.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 




Gravitational theories near the galactic centre

Dr Sanjeev Kalita explores the properties of gravity near the galactic centre, the telltale sign of which may be detected by the Extremely Large Telescope (ELT). This work is published in Astrophysical Journal.

https://en.wikipedia.org/wiki/Extremely_Large_Telescope


Author
Sanjeev Kalita

Abstract
The author has used the Parameterised Post Newtonian (PPN) framework of General Relativity to examine the modification of the law of gravity near the Galactic Centre Black Hole, Sgr A*. Quantum gravity near black hole singularities largely expect such modifications. This is the first astrophysical test of new gravitational physics near the Galactic Centre. Periastron anomaly of the S-stars having compact orbits (within the central milli parsec, r = 50-100 au) near the black hole has been used to see the difference between General Relativity and Brans-Dicke scalar-tensor gravity and f(R) theories which are serious rivals to General Relativity and are capable of addressing several cosmological issues. Mild to strong values of spin and quadrupole of the black hole have been used. Possibility of detection of such deviation through upcoming astrometric observations of the Extremely Large Telescopes (ELTs) are discussed. New observational strategies for measuring the black hole spin and extracting modified gravity signals are also suggested. The work also reports possibility of black hole hair and super Kerr spin (naked singularity) which are otherwise unanticipated in existing black hole physics.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 




Fabrication of Ag/ZnO heterostructure

Dr Bimal Kumar Sarma and his collaborator describe fabrication of Ag/ZnO heterostructure and the role of surface coverage of ZnO microrods by Ag nanoparticles on its photophysical and photocatalytic properties. This work is published in Applied Surface Sceince.



Authors
Bikash Sarma and Bimal K Sarma

Abstract
This report presents findings on microstructural, photophysical, and photocatalytic properties of Ag/ZnO heterostructure grown on flexible and silicon substrates. ZnO microrods are prepared by thermal decomposition method for different solute concentrations and Ag/ZnO heterostructure are fabricated by photo-deposition of Ag nanoparticles on ZnO microrods. X-ray diffraction and electron microscopy studies confirm that ZnO microrods belong to the hexagonal wurtzite structure and grown along [001] direction with random alignment showing that majority microrods are aligned with (100) face parallel to the sample surface. Plasmonic Ag nanoparticles are attached to different faces of ZnO. In the optical reflection spectra of Ag/ZnO heterostructure, the surface plasmon resonance peak due to Ag nanoparticles appears at 445 nm. Due to the oxygen vacancies the band gaps of ZnO microrods turn out to be narrower compared to that of bulk ZnO. The presence of Ag nanoparticles decreases the photoluminescence intensity which might be attributed to the non-radiative energy and direct electron transfer in the plasmon–exciton system. The quenching of photoluminescence in Ag/ZnO heterostructure at different growth conditions depend on the extent of surface coverage of ZnO by plasmonic Ag nanoparticles. Photocatalytic degradation efficiency of Ag/ZnO heterostructure is higher than that of ZnO microrods. The extent of surface coverage of ZnO microrods by Ag nanoparticles is crucial for the observed changes in photophysical and photochemical properties.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top 





Solitary waves in dense dusty plasmas

Rajita Goswami analyses a phenomena which is expected to be seen in dense dusty plasmas. This communication is published in Physics of Plasmas.



Authors
Rajita Goswami and Madhurjya P Bora

Abstract
In this report the authors present an analysis of the effect of polarization force on dust acoustic solitons with self-consistent inclusion of the polarization effect into the dust-charging model. This has been carried out considering the dependence of dust-charge number on dust potential which is affected by the polarization force. Their analysis shows that inclusion of polarization effect into the dust-charging model results solitons of much higher amplitudes.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/physics/#top