Recent Research Highlights


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

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

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

https://sites.google.com/a/gauhati.ac.in/research/#rm08062018 Properties of doped monolayer graphene

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

https://sites.google.com/a/gauhati.ac.in/research/#bkg24052018 Quantitative climate reconstruction

https://sites.google.com/a/gauhati.ac.in/research/#us Vibrational energy harvesters

https://sites.google.com/a/gauhati.ac.in/research/#us2 Predicting moisture loss in tea leaves

https://sites.google.com/a/gauhati.ac.in/research/#sk2 Photoluminescent quantum dots

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

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

https://sites.google.com/a/gauhati.ac.in/research/#rt1 Synthesis of Olanzapine salts

https://sites.google.com/a/gauhati.ac.in/research/#rg Solitary waves in dusty plasmas

 Drug-drug, drug-nutraceutical cocrystal
Graphene 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/#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/#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/#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/#top 
 



Quantitative climate reconstruction across Paleocene-Eocene from low latitude

Dr Bikash Gogoi and his collaborators present a multi-proxy study of an upper Paleocene - Lower Eocene succession from the paleo-equatorial region. The study is carried out on a coal-bearing, shallow-marine succession exposed at Jathang, East Khasi hills of Meghalaya. This research article is published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.



Authors
V Prasad, T Utescher, A Sharma, I B Singh, R Garga, B Gogoi, J Srivastava, P R Uddandam, and M M Joachimski
Abstract
The authors present a multi-proxy study of an upper Paleocene-lower Eocene succession from the paleo-equatorial region. The study is carried out on a coal-bearing, shallow-marine succession exposed at Jathang, East Khasi Hills, Meghalaya, northeastern India. The succession was deposited in a low-energy, coastal marsh-bay complex. Dinoflagellate cyst biostratigraphy yields a late Paleocene to early Eocene age for the section. The deposits of the lower part of the succession represent a transgressive systems tract (TST) defined by seven parasequences, each starting with bay sediments deposited during transgression, followed by a shallowing-upward bay fill-marsh deposit.

The main highlights of the work are 
(a) Quantitative climate reconstruction across Paleocene-Eocene from low latitude
(b) Distinct vegetation turnover in tropical region across Paleocene Eocene transition
(c) Lower plant diversity during Paleocene and significantly high during early Eocene
(d) Duration of rainfall pattern mainly determines the climate of tropical rain forest.
Vibrational energy harvesters

Dr Utpal Sarma and Babak Montazer report about works on Piezoelectric MEMS Energy Harvester Systems, which are published in IEEE Transactions on Instrumentation and Measurement and Journal of Circuits, Systems and Computers.



Authors
Utpal Sarma and Babk Montazer

Abstract
This work addresses an efficient way of conversion of ambient vibrational energy to electrical by structure optimisation of piezoelectric film. Polyvinylidene fluoride has been used for this study. The effects of shape variations of cantilever beam with multilayer configuration based on Euler–Bernoulli theorem without considering the proof mass attached at the free end has been investigated. Most of piezoelectric vibrational energy harvesters are designed considering the presence of proof mass and in this paper it has been tried to convey the idea, that with the new optimised shape, the cantilever itself can behave as a flexible proof mass for energy enhancement. The possibility of harvesting energy from three different geometries - (1) near edge width quadratic (NEWQ), (2) half quadratic (HQ), and (3) Trapezoidal have been presented. Scanning electron microscopy is used to measure the thickness of the various layers. The NEWQ design shows the best performance in terms of power and resonance frequency (fr < 200 Hz) compared with the others. Here, the study of the piezo-film models using finite element method simulation software (COMSOL Multiphysics optimization module) and experimental validation are also presented. Using the models, the generation of voltage/power has been analyzed under various excitation frequency and load resistance. Moreover, stress/strain distribution and the displacement have also been highlighted in this paper.
https://sites.google.com/a/gauhati.ac.in/research/#top 
 



Predicting the moisture loss in tea leaves

Dr Utpal Sarma and his co-researchers report about 
a novel in-situ instrumentation technique for prediction of moisture loss from tea leaves during the withering process, which is crucial in determining the tea quality. This work has been published in IEEE Transactions on Instrumentation and Measurement.



Authors
Nipan Das, Kunjalata Kalita, P K Baruah, and Utpal Sarma

Abstract
The first and foremost process in tea manufacturing, withering, is the foundation for producing good quality. Moisture plays an important role in the manufacturing process of tea to get the desired quality. In this work, a novel in-situ instrumentation technique is proposed and validated experimentally for prediction of moisture loss (ML) in the withering process. In the proposed technique, ML is predicted based on the inlet and the outlet relative humidity (RH) and temperature during the process of withering. Network capable smart sensor nodes are developed for the measurement of RH and temperature at the inlet and outlet of the withering trough. Architecture of the nodes and network is described. A scaled-down prototype of an enclosed trough is developed to perform withering of tea leaves. Based on the data measured by the system, ML is predicted by using artificial neural network. Nonlinear autoregressive model with exogenous inputs is used for predicting the ML. The predicted ML is compared with the actual amount of ML measured by weight loss. A total of nine experiments are conducted for nine batches of tea leaves. The data collection, their analysis and results are reported in this paper. The observed result shows a good agreement between the predicted and actual ML. The maximum mean error in prediction is −3.6%.
https://sites.google.com/a/gauhati.ac.in/research/#top 
 



Facile synthesis of photoluminescent quantum dots

Dr Sonit Kumar Gogoi and his fellow researcher report about synthesis of photoluminescent graphitic carbon nitride quantum dots for Hg2+ detection, which is published in the American Chemical Society's journal, ACS Sustainable Chemical Engineering. The works is expected to enhance our knowledge on highly efficient optoelectronic devices.



Authors
Khemnath Patir and Sonit Kumar Gogoi

Abstract
Carbon nitride materials have become highly explored carbon based nanomaterials since their rediscovery in the 1990s due to their semiconductor like behaviour. In this research work, the authors report a facile one pot synthesis of sulfur and oxygen doped carbon nitride quantum dots (SCNQDs) from thiourea and ethylenediaminetetraacetic acid disodium salt by a thermal method. The SCNQDs prepared are characterized by UV− visible, FT-IR, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction, and transmission electron microscopy (TEM) imaging. The authors have demonstrated the Hg2+ sensing ability of SCNQDs in solution as well as in the solid phase, i.e. SCNQDs loaded onto filter paper. The Hg2+ sensing capability of the SCNQDs in the solution phase is the same for Hg2+ ion in double distilled water as well as in tap water, which gives the method a practical applicability in real conditions. The sensitivity of SCNQDs with Hg2+ follows a linear relationship in the range from 10 nM to 1 μM. The minimum detection limit is found to be 0.01 nM, which is lower than previous reports. Similarly the SCNQDs loaded onto filter paper also showed same sensing capability with Hg2+ spiked tap water as Hg2+ in double distilled water solutions. Through this work, the authors have devised a ready to use system for Hg2+ detection with SCNQDs loaded filter paper to be used in biological fluids as well as in environmental samples, which is not available now. Besides, the authors have also made a composite of SCNQDs with poly(vinyl alcohol) (PVA) to observe room temperature phosphorescence (RTP) in SCNQDs.
https://sites.google.com/a/gauhati.ac.in/research/#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 investigate. 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/#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/#top 




Mechanochemical synthesis of Olanzapine salts and their hydration stability

Dr Ranjit Thakuria and his collaborators study mechanochemical properties of Olanzapine salts using X-ray diffraction. This work is published in Crystal Growth & Design.



Authors
Kashyap Kumar Sarmah, Pranamika Sarma, Dharmaraj R Rao, Poonam Gupta, Naba K Nath, Mihails Arhangelskis, and Ranjit Thakuria

Abstract
A series of olanzapine (OLN) dicarboxylic acid salts including earlier reports on olanzapinium malonate (1:1) and maleate (1:1 and 1:2) were prepared mechanochemically using liquid assisted grinding (LAG) in order to study their hydration stability. Powder X-ray diffraction was used as a characterization tool during the investigation. On the basis of the single crystal structures of respective OLN salts, a negative correlation between the dicarboxylic acid chain length and the hydration stability of the corresponding OLN salt was found. Our observations suggest that the overall crystal packing, beyond the stronger hydrogen bond synthon (N+–H···O– in OLN salts compared to O–H···N in OLN hydrates) plays an important role in designing OLN salts with better hydration stability. In addition, melting point analysis showed that OLN dicarboxylic acid salts follow melting point alteration behavior similar to the pure diacids.

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




A
 review on drug-drug and drug-nutraceutical cocrystal/salt

Dr Ranjit Thakuria and his collaborator write about drug-drug and drug-nutraceutical cocrystal/salt in a review article published in the journal Crystals.



Authors
Ranjit Thakuria and Bipul Sarma

Abstract
The pre-formulation of pharmaceutical cocrystals and salts is a concept of crystal engineering that has emerged as a promising technique for drug development in pharmaceutical industry. Recent introduction of pharmaceutical cocrystals in regulatory guidelines of US Food and Drug Administration (FDA) made them one of the potential alternatives when salt preparation is not feasible. Apart from generally regarded as safe (GRAS) coformers, drug‑drug and drug‑nutraceutical cocrystals are recent additions to pharmaceutical cocrystal family that have additional health benefits. Indeed, preparation of salt forms is a routine practice to deal with inadequacies associated with the active pharmaceutical ingredient (API) and happens to be a potentially reliable method. Amongst them, drug-drug and drug-nutraceutical cocrystals have drawn significant importance in the recent past as they reduce drug load and cost effects during multiple disease diagnosis. However, one has to be prudent in the selection of drug molecules, the presence of complementary hydrogen bond synthon, disease management during multiple disease therapy, etc. that play important roles in their preparation. That is the reason why drug–drug cocrystals are scarce in the literature compared to pharmaceutical cocrystals containing GRAS coformers and salt forms. Herein, we discuss case studies preferably the reported drug‑drug, drug‑nutraceutical cocrystals, and a few salts with an emphasis on their role in physicochemical property modulation.

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