Recent Research Highlights



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https://sites.google.com/a/gauhati.ac.in/research/#bk01072019 Killing the killers

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

https://sites.google.com/a/gauhati.ac.in/research/#udb03062019 A changing coastline

https://sites.google.com/a/gauhati.ac.in/research/#th23052019 Indian Research Articles in PLoS Journals

https://sites.google.com/a/gauhati.ac.in/research/#nn06052019 Pigments from the deep sea

https://sites.google.com/a/gauhati.ac.in/research/#hps08052019 Heavy metals in freshwater wetlands

https://sites.google.com/a/gauhati.ac.in/research/#ac04052019 Bayesian inference for queuing model

https://sites.google.com/a/gauhati.ac.in/research/#ph03052019 Xenotime dating of Meghalayan rocks

https://sites.google.com/a/gauhati.ac.in/research/#nn26042019 How plankton shaped our ecosystem

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

https://sites.google.com/a/gauhati.ac.in/research/#us04042019 Microwave safe!

https://sites.google.com/a/gauhati.ac.in/research/#sb14032019 A new plant species from Assam

https://sites.google.com/a/gauhati.ac.in/research/#rt08032019 Cocrystal dissociation - a case study

https://sites.google.com/a/gauhati.ac.in/research/#sm06032019 Treating oral cancer

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

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

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

https://sites.google.com/a/gauhati.ac.in/research/#us20022019 Measuring soil moisture

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

https://sites.google.com/a/gauhati.ac.in/research/#rt12022019 A perspective on π-π stacking

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

https://sites.google.com/a/gauhati.ac.in/research/#hc01022019 Schistura rebuw - a new species of fish

https://sites.google.com/a/gauhati.ac.in/research/#kt09012019 Modeling magnetospheric oscillations

https://sites.google.com/a/gauhati.ac.in/research/#tkg08122018 Killing cancer cells

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

https://sites.google.com/a/gauhati.ac.in/research/#kt21112018 Funiculosone - an antimicrobial metabolites
A concoction of oils for the killer mosquitoes 

Bulbuli Khanikor and her scholars test a concoction of plant-based oils to target the Aedes aegypti mosquitoes, which is the primary cause of diseases like dengue fever, chikungunya, etc. This research work is published in Nature Scientific Reports.


Authors
Riju Sarma, Kamal Adhikari, Sudarshana Mahanta, and Bulbuli Khanikor

Abstract
Twenty-eight combinations of plant essential oil-based terpene compounds were prepared and tested against larval and adult stages of Aedes aegypti. Initially five plant essential oils (EOs) were assessed for their larvicidal and adulticidal efficacy and two of their major compounds from each EO were identified from GC-MS results. Identified major compounds namely Diallyldisulfide, Diallyltrisulfide, Carvone, Limonene, Eugenol, Methyl Eugenol, Eucalyptol, Eudesmol and α-pinene were purchased and tested individually against Aedes aegypti. Binary combinations of these compounds were then prepared using sub-lethal doses, tested and their synergistic and antagonistic effects were determined. The best larvicidal compositions and the best adulticidal composition of terpene compounds and terpene plus commercial mosquitocidal compounds were highlighted based on small scale and large scale treatments on Aedes aegypti.

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.

How are we changing a coastline?

Ujjal Deka Baruah and his fellow researchers report the long & short time changes of the Puri Coastline due to natural and anthropogenic (human) causes using satellite imagery. This research is published in Environmental Earth Sciences.


Authors
from other institutions

Abstract
The coastal regions of India are densely populated and most biological productive ecosystems which are threatened by erosion, natural disaster, and anthropogenic interferences. These threats have made priority in appraisal of shoreline dynamicity as part of sustainable management of coastal zones. The present study assessed the long- to short-term dynamicity of shoreline positions along the coast of Puri district, Odisha, India, during the past 25 years (1990–2015) using open-source multi-temporal satellite images (Landsat TM, ETM+, and OLI) and statistical-based methods (endpoint rate, linear regression rate and weighted linear regression). The long-term assessment during 1990–2015 shows that shoreline accredited at the rate of 0.3 m a−1 with estimated mean accretion and erosional rate of 1.18 m a−1 and 0.64 m a−1, respectively. A significant trend of coastal erosion is primarily observed on the northern side of Puri district coast. A cyclic pattern of accretion (during 1990–1995 and 2000–2004) and erosion (during 1995–2000 and 2009–2015) was observed during the assessment of short-term shoreline change. It exhibited significant correlation with the landfall of severe cyclones and identified cyclic phases after severe cyclonic storms, i.e., phase of erosion, phase of accretion and phase of stabilisation. Overall, the natural processes specifically the landfall of tropical cyclones and anthropogenic activities such as the construction of coastal structures, encroachment and recent construction in the coastal regulatory zone, and construction of dams in upper catchment areas are the major factors accountable for shoreline changes. The output of the research undertaken is not only crucial for monitoring the dynamism of coastal ecosystem boundaries but to enable long- to short-term coastal zone management planning in response to recently reported high erosion along the Puri coast. Moreover, the usage of open-source satellite imageries and statistical-based method provides an opportunity in developing cost-effective spatial data infrastructure for shoreline monitoring and vulnerability mapping along the coastal region.

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



Influence in the citation growth of Indian Research Articles in PLoS Journals

Tilak Hazarika and his colleagues put forward a study to show how the citation profile of Indian Research Articles in PLoS Journals are affected. This work is published in the journal Journal of Scientometric Research.


Authors
Abstract
The general approach of research impact evaluation is entirely based upon citations. But in the current Web2.0 era, this citation based evaluation process often do not include the generic discussions people make in social media, blogs, online scholarly discussion forums or even the online readership of the article. Altmetrics, often referred as the article level metrics is a tool that have emerged, which crowd source all the non-citation based discussions from various web2.0 platforms and tries to reflect the overhaul attention that an article gets. Since its introduction, altmetrics have been able to gather a good attention from the scientific community, and researchers are trying to evaluate if it does have scholarly value to complement the citation based impact measure process. The current study tries to evaluate altmetrics penetration in Indian research articles and the influence of altmetrics in the citation growth process. The problem was addressed taking the example of Indian research articles published in PLoS journals. Two hypothesis were set for the study and PLoS altmetrics data were taken to run the t-test for paired sample mean to test the hypothesis. Findings from the t-test estimated a low significant p value, hence rejecting the null hypothesis and accepting the alternate hypothesis proving the positive influence of altmetrics in the citation growth process for the Indian research articles in PLoS journals. Also the presence of altmetrics data in the Indian research articles of PLoS journals is evaluated in the study.

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



Scouring the deep sea to find pigments

Nilamoni Nath and coworkers find five new water soluble pigments from the deep sea off the coast of Japan. This work is published in the Journal of Natural Products.



Authors
Klaus Wolkenstein1, Juan Carlos Fuentes-Monteverde1, Nilamoni Nath, Tatsuo Oji1, and Christian Griesinger1
from other institutions

Abstract
Five new water-soluble amido- and aminoanthraquinone pigments, hypalocrinins A–E (1–5), the new amidoanthraquinone biaryls hypalocrinin F (6) and hypalocrinin G (7), and the known compounds 6-bromoemodic acid (8), crinemodin (9), and crinemodin sulfate (10) were isolated from the deep sea crinoid Hypalocrinus naresianus collected off Japan. The structures of the compounds were elucidated by NMR spectroscopy and mass spectrometry. Amido- and aminoquinones are quite unusual among natural products. The hypalocrinins are the first naturally occurring anthraquinones and anthraquinone biaryls conjugated with taurine.

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



Heavy metals in freshwater wetlands

Hari Prasad Sarma and coworkers investigate the heavy metal pollution in freshwater wetlands such as Deepor Beel (near Guwahati, Assam, India, Location : 26.1196, 91.6475). This research work is published in the journal Environmental Pollution.


Authors
Suravi Kalita1, Hari Prasad Sarma, and Arundhuti Devi1
from other institutions

Abstract
The sediment characterisation of wetlands belonging to the Northeastern Region of India particularly regarding the assessment of sediment carbon stock is very scanty. The presently available literature on the wetlands cannot be employed as a common model for managing the wetlands of the Northeastern Region of India as wetlands are a sensitive ecosystem with a different origin or endogenous interventions. Thereby, this research was conducted on Deepor Beel for investigating the spatial and seasonal variation of sediment parameters, the relationship between the parameters and pollution status of the wetland. Results revealed that the study area is of an acidic nature with a sandy clay loam type texture. Organic carbon, total nitrogen and available nitrogen were higher in sediments in the monsoon period. The mean stock of the sediment carbon pool of Deepor Beel is estimated to be 2.5 ± 0.7 kg m−2. The average non-residual fraction percentage (63.2%) of Pb was higher than the residual fraction. Zn content ~490 mg kg−1 exceeding its effect range medium (ERM) was determined to suggest frequent biological adverse effects. Highest metal enrichment factor (EF) values were shown by Zn and Pb, which ranged between 78 and 255. Risk assessment code (RAC) values of Pb between 21 and 29% indicated its high bio-accessibility risk. Pearson's coefficient matrix revealed a low degree of positive correlation between organic carbon content and metal concentration. Principal component analysis revealed that the first component comprising of EC, basic cations and metals accounted for 62.3% of variance while the second component (OM, OC, TN, AN, AP) and the third component (pH) accounted for 21.8% and 7.0% of the variance, respectively. The present study revealed the adverse impact of human inputs on the Deepor Beel quality status.

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



Bayesian inference & prediction for queuing model

Amit Choudhury and his collaborator estimate traffic intensity for single server queuing model using Bayesian inference. Bayesian inference is an important technique in mathematical statistics, which uses Bayes' theorem to update the probability for a hypothesis as more evidence or information becomes available. This research works is published in the journal Communications in Statistics - Simulation and Computation.

Figure used under Creative Commons 
https://en.wikipedia.org/wiki/Creative_Commons 
license


Authors

Abstract
This paper is concerned with the problem of estimating traffic intensity, ρ for single server queuing model in which inter-arrival and service times are exponentially distributed (Markovian) using data on queue size (number of customers present in the queue) observed at any random point of time. Here, it is assumed that ρ is unknown but random quantity. Bayes estimator of ρ are derived under squared error loss function assuming two forms of prior information on ρ. The performance of the proposed Bayes estimators is compared with that of the corresponding classical version estimator based on max- imum likelihood principle. The model comparison criterion based on Bayes factor is used to select a suitable prior for Bayesian analysis.

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



Xenotime chemical dating of Meghalayan metamorphic rocks

Pranjit Hazarika and his collaborators validate xenotime (a rare-earth phosphate mineral) chemical dating for metamorphic rocks in the Meghalaya-region. This research work is published in Journal of Earth System Science.


Authors
Pritom Borah, Pranjit Hazarika, Amulya Chandra Mazumdar, and Mridul Rabha1
1from other institution

Abstract
Monazite and xenotime are the two most useful and commonly used geochronometers for deciphering ages from metamorphic rocks. The low analytical cost involved in electron probe micro-analyser chemical dating, ease of sample preparation and abundance in metamorphic rocks of wide P–T conditions make monazite and xenotime dating most widely used technique for age determination amongst metamorphic petrologists. This contribution presents age comparisons between coexisting monazite and xenotime in the basement metapelitic rocks of the central part of the Shillong–Meghalaya Gneissic Complex (SMGC). Thermobarometric estimates in the studied samples indicate granulite facies conditions of metamorphism with peak P–T conditions of ~ 6.5 kbar and -750 ºC. Results indicate that xenotime in the basement rocks in the central SMGC formed in four discrete geological events while monazite either formed only in the latest Pan-African granulite grade metamorphic event or recrystallised during this event. Monazite in the studied samples yielded a single ubiquitous age of ca. 500 Ma. Xenotime in the study area, although found in only one sample, preserves four distinct ages at 1153±29, 930±36, 823±41,and 490±11 Ma. Preservation of Grenvillian ages in xenotime from central SMGC marks the eastward extension of Rodinia amalgamation front in the Indian Shield. The Neoproterozoic ages in xenotime from central SMGC suggest that the ca. 820 Ma high-grade metamorphism in the Eastern Indian Tectonic Zone had a wider impact in the SMGC than perceived previously.

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



How predatory plankton created modern ecosystems!

Nilamoni Nath and his collaborators shed light on the great zigsaw puzzle involving intricacies how our modern ecosystem has come to this stage. This research work is published in Nature Communications.
This highlight is also featured in GU Homepage.


Authors

Abstract
Eukaryotic algae rose to ecological relevance after the Neoproterozoic Snowball Earth glaciations, but the causes for this consequential evolutionary transition remain enigmatic. Cap carbonates were globally deposited directly after these glaciations, but they are usually organic barren or thermally overprinted. Here we show that uniquely-preserved cap dolos- tones of the Araras Group contain exceptional abundances of a newly identified biomarker: 25,28-bisnorgammacerane. Its secular occurrence, carbon isotope systematics and co- occurrence with other demethylated terpenoids suggest a mechanistic connection to extensive microbial degradation of ciliate-derived biomass in bacterially dominated ecosys- tems. Declining 25,28-bisnorgammacerane concentrations, and a parallel rise of steranes over hopanes, indicate the transition from a bacterial to eukaryotic dominated ecosystem after the Marinoan deglaciation. Nutrient levels already increased during the Cryogenian and were a prerequisite, but not the ultimate driver for the algal rise. Intense predatory pressure by bacterivorous protists may have irrevocably cleared self-sustaining cyanobacterial eco- systems, thereby creating the ecological opportunity that allowed for the persistent rise of eukaryotic algae to global importance.

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



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/#top 
 



Microwave safe!

Your kitchen microwave can probably make you eat better Rajmas! Utpal Sarma and his collaborators report that high power microwave can effectively disinfect the red kidney beans (Indian Rajma) while keeping the nutritional values intact. This research is published in the journal IEEE Access.


Authors
Chitra Gautam1, Sk Masiul Islam1, Shashikant Sadistap1, and Utpal Sarma
1 from other institutions

Abstract
In this work, the effect of microwave heat on the nutritional characteristics of affected red kidney beans, i.e., Rajma is studied. Evaluation of crude protein content in microwave heated red kidney beans are carried out using standard Kjeldahl method and Fourier transform infra-red (FTIR) spectroscopy. Red kidney beans affected by Pulse Beetle (Callosobruchus chinensis) have been analysed throughout the experiments. The heat treatment of the samples is undertaken using a domestic microwave oven at 2.45 GHz. The samples are heated at different microwave powers, such as 90, 270, 450, 750, and 900 W, while the exposure time is varied from 30-90 s. The effective microwave power for maximum disinfestation is found to be 270-450 W at 30-60 s. Most of the red kidney beans are damaged at 900 W for 60 s. Using Kjeldahl method, a constant crude protein level of 22.5% is obtained for untreated and treated samples at 90-450 W. Crude protein level of red kidney beans is changed at 750-900 W. From FTIR analysis, the absorbance spectrum of carbohydrate peaks is found at 900-1250 cm -1 , a moisture peak at 1650 cm -1 , and a protein peaks at 2800-3000 cm -1 . Statistical analysis of the treated and untreated samples represents the lowest error of 0.0016 at 450 W power level for 60 s. Variances are determined to be the lowest with a value of 270 W and 450 W at 90 s and 60 s. These findings indicate the optimum microwave heat treatment for red kidney beans to retain its protein content.

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



Impatiens kamrupana - a new plant species from Assam

Souravjyoti Borah and fellow researchers report about discovery of a new plant species Impatiens kamrupana (Balsaminaceae) from Assam. This is now listed and published in the journal Phytotaxa.


Authors
Souravjyoti Borah, Jatindra Sarma, and Rajib Gogoi

Abstract
Impatiens Kamrupana - a new species is discovered from Kamrup district (rural) of Assam, bordering the adjoining state of Meghalaya. The new species is easily distinguished from its allied taxa by its bicoloured, white and purple flowers and sub-bucciniform lower sepal with straight to slightly curved spur.

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



Cocrystal dissociation under controlled humidity

Ranjit Thakuria and collaborators report a case study of cocrystal dissociation under a controlled environment. Cocrystals can be defined to be consisted of two or more components that form a unique crystalline structures having unique properties. This research work is published in Organic Process Research and Development.


Authors
Ranjit Thakuria1, Mihails Arhangelskis2, Mark D Eddleston2, Ernest H H Chow2, Kashyap Kumar Sarmah, Barry J Aldous2, Joseph F Krzyzaniak2, and William Jones2
1 Department of Chemistry, University of Cambridge
2 from other institutions

Abstract
Caffeine-glutaric acid cocrystal polymorphs, Form I and Form II, are presented as a model system to study cocrystal dissociation under controlled humidity. On the basis of relative humidity (RH) data, it is observed that Form I transforms to Form II at high RH and that the rate of the polymorphic phase transformation increases with increasing RH, with the relative stability of the cocrystal following a trend similar to that of the coformer deliquescence point for other caffeine dicarboxylic acid cocrystals. In addition, reduction in particle size, change in crystal morphology with greater number of crystal faces exposed to surrounding atmosphere, and internal arrangement of molecules in the crystal structure are shown to influence cocrystal instability and favour dissociation under increased humidity.

Treating oral cancer

Subhash Medhi and his collaborators explore the way an oral carcinoma (cancer) can be effectively treated. This research is published in the journal Artificial Cells, Nanomedicine, and Biotechnology.


Authors
Rituraj Bharadwaj, Bhanu P Sahu1, Jayanta Haloi, Damiki Laloo1, Prajjalendra Barooah, Chenole Keppen, Manab Deka, and Subhash Medhi
1 from other institution

Abstract
High recurrence rates are found in patients undergoing the standard treatment, and delay in initiation of treatment is considered as the most prominent cause for no relevant improvement in the survival rate . Moreover, conventional chemotherapy suffers from numerous drawbacks including poor drug specificity , undesired side effects and resistance towards the treatment. SLN have been chosen to be the best mode of anticancer drug delivery since they are generally made up of physiological lipids thus they are well accepted by our physiological system. The present research study includes preparation of PTX, 5- FU and AA entrapped SLN to ensure a sustained release of drug at the desired concentration and at a specific site for the treatment of oral cancer. The study involves evaluation of each of these SLN and their combination for the effective treatment of oral cancer. Entrapment of PTX, 5-FU, and AA d within the SLN by using high-speed homogenisation and ultrasonication method were evaluated both in-vitro and in-vivo to get the best combination for the effective therapeutic efficacy.

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/#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/#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/#top 
 



Measuring soil moisture

Utpal Sarma, Manash Protim Goswami, and graduate student Babak Montazer report a novel method to measure soil moisture. This work is published in the IEEE Transactions on Instrumentation and Measurement.


Authors

Abstract
This paper addresses the optimisation and implementation of a fringing field capacitive soil moisture sensor using the printed circuit board technology. It includes the analysis of a novel configuration of an interdigital sensor for measuring soil moisture with two existing configurations. The optimised designs were simulated by using a 3-D finite-element method and fabricated by using a copper clad board. The performance of the fabricated sensors was evaluated using four soil samples collected from different locations. The observations were compared with the standard gravimetric method to evaluate the soil water content of the samples. The characterisation method and the results of the whole sensing system are discussed in terms of calibration, dynamic test, and repeatability.

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



Stacking - in the chemical way

Ranjit Thakuria and his collaborators elaborate on the nature and applications of π-π interactions. This work is published in the journal Crystal Growth & Design.


Authors
Ranjit Thakuria, Naba K Nath1, and Binoy K Saha1
1from other institutions

Abstract
This research article is a perspective published by the Guest Editors Ranjit Thakuria, Naba K Nath and Binoy K Saha for the Virtual Special Issue of Crystal Growth & Design on π−π Stacking in Crystal Engineering: Fundamentals and Applications. It highlights the nature of π−π interactions and their uses in various fields ranging from crystal engineering to material science to biochemistry and discusses about the articles published in the special issue.

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



Schistura rebuw - a new species of stone loach

Hrishikesh Choudhury and his colleagues have reported the finding of a new fish species from the Kameng River of lower Arunachal Pradesh. This finding is published in the journal Zootaxa


Authors
Hrishikesh Choudhury, Abhinit Dey, Ratul Ch Bharali1, Dandadhar Sarma, and Waikhom Vishwanath1
1 from other institutions

Abstract
Schistura rebuw, new species, is described from the Kameng River, a north-bank tributary of the Brahmaputra, Arunachal Pradesh, India. The new species is easily distinguished from all known congeners in the Brahmaputra basin by its unique sexual dimorphism, specifically a suborbital slit in adult females, and a suborbital flap in adult males; and a colour pattern of 10–11 blackish bars on a greyish-beige body, the pre-dorsal bars mostly broken or incomplete, coalescing dorsally in a more or less alternate fashion.

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



What it takes to take on cancer

Tridib Kumar Goswami and his collaborators synthesise complexes which are found to kill cancer cells through generation of reactive oxygen species (ROS). This research work is published in Journal of Inorganic Biochemistry.


Authors
Atrayee Banaspati, Dhananjay Das, Chandan J Choudhury, Arnab Bhattacharyya1, and Tridib K Goswami
1 from other institution

Abstract
Four ternary copper(II) complexes of N-salicylyl-L-Tryptophan (Sal-TrpH) and phenanthroline bases of general formula [Cu(Sal-Trp)(L)], where L is 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2), dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3) and 2-(anthracen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (aip, 4), are synthesised and fully characterised. The complexes are evaluated for their affinity for biomolecules and photocytotoxic activities. Single crystal X-ray diffraction studies of complex 1 reveals that it has a square pyramidal CuN3O2 core with the phenolate oxygen of salicylaldehyde occupying the axial coordination site in the solid state. Complexes 1–4 display the Cu(II)-Cu(I) redox couples at ~ −0.3 V vs Ag/AgCl reference electrode in DMF-0.1 M [BunN4](ClO4). A Cu(II)-based weak d-d band ~650 nm and a moderately strong ligand to metal charge transfer band at ~430 nm are observed in DMF-Tris-HCl buffer (pH 7.2) (1:4 v/v). The complexes are efficient binders to calf thymus DNA and model proteins such as bovine serum albumin and lysozyme. They cleave supercoiled plasmid DNA efficiently when exposed to 446 and 660 nm laser radiation. They are cytotoxic to HeLa (human cervical cancer) and MCF-7 (human breast cancer) cells showing significant enhancement of cytotoxicity upon photo-excitation with low energy visible light. The complexes are found to kill cancer cells through generation of reactive oxygen species (ROS) as confirmed by DCFDA (2′,7′-dichlorofluorescin diacetate) assay. The apoptotic cell death induced by complex 4 is confirmed by Annexin V-Fluorescein isothiocyanate-Propidium iodide assay. Confocal microscopic images using 4 shows its primary cytosolic localisation in the HeLa and MCF-7 cells.

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



Funiculosone - a new antimicrobial metabolites

Kumanand Tayung and his collaborators have isolated a new antimicrobial metabolites which also shows anticandidal activity against Candida albicans Berkhout. This research is published in the journal Phytochemistry.



Authors
Srichanadan Padhi1, Marco Masi1, Alessio Cimmino1, Angela Tuzi1, Subhrakanta Jena1, Kumananda Tayung, and Antonio Evidente1
1 from other institutions

Abstract
An undescribed substituted dihydroxanthene-1,9-dione, named funiculosone, was isolated together with its two analogues identified as mangrovamide J and ravenelin, from the culture filtrates of Talaromyces funiculosus (Thom) Samson, Yilmaz, Frisvad & Seifert (Trichocomaceae), an endolichenic fungus isolated from lichen thallus of Diorygma hieroglyphicum (Pers.) Staiger & Kalb (Graphidaceae), in India. Funiculosone was characterised, essentially by spectroscopic methods, as 4,8,9a-trihydroxy-3,4a-dimethyl-4a,9a-dihydro-4H-xanthene-1,9-dione. Its relative stereochemistry was deduced by single crystal X-ray analysis while the absolute configuration was assigned as 4S,4aS,9aS by ECD spectra in comparison to that of the closely related mangrovamide J. This latter, to which, not being an amide, an inappropriate common name was given, was only recently isolated, together with undescribed and known prenylatedindole alkaloids and chromone derivatives from an unidentified Penicillium sp. X-ray structural analysis of the isolated mangrovamide J, for which no biological activity was previously reported, revealed polymorphism and a new crystalline phase is described. All the compounds displayed antibacterial activity with an IC50 range 23–104 μg/mL when assayed against Escherichia coli Escherich and Staphylococcus aureus Ogston. Funiculosone also showed anticandidal activity against Candida albicans Berkhout with an IC50 35 μg/mL.

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