January - December, 2017


https://sites.google.com/a/gauhati.ac.in/research/2017/#rm08062018 Flood induced poverty

https://sites.google.com/a/gauhati.ac.in/research/2017/#kb29052018 Broadening of GRB spectra

https://sites.google.com/a/gauhati.ac.in/research/2017/#ph27052018-1 Trace-element geochemistry of minerals

https://sites.google.com/a/gauhati.ac.in/research/2017/#ph27052018 Retrieving age information from rocks

https://sites.google.com/a/gauhati.ac.in/research/2017/#ps23052018 Synthesis of gold nanoparticles

https://sites.google.com/a/gauhati.ac.in/research/2017/#ds18052018 Efficient ammonia gas sensor

https://sites.google.com/a/gauhati.ac.in/research/2017/#us Vibrational energy harvesters

https://sites.google.com/a/gauhati.ac.in/research/2017/#dsarkar Porous silicon MSM device

https://sites.google.com/a/gauhati.ac.in/research/2017/#dm Freestanding polypyrrole films

https://sites.google.com/a/gauhati.ac.in/research/2017/#bdb Relativistic Heavy Ion Collisions

https://sites.google.com/a/gauhati.ac.in/research/2017/#kb Probing the neutrinos at DUNE 

https://sites.google.com/a/gauhati.ac.in/research/2017/#bks Fabrication of Ag/ZnO heterostructure

 C-H functionalization in water
Flood induced vulnerability to poverty - evidence from Brahmaputra Valley

Dr Ratul Mahanta and his coworker provide valuable inputs to the flood induced poverty in this part of the country. This research article is published in International Journal of Disaster Risk Reduction.



Authors

Abstract
This paper attempts to assess household vulnerability to poverty due to flood in Assam. Whether coping measures can reduce vulnerability and what factors affect such coping has also been examined. Applying vulnerability as expected poverty (VEP) approach to data collected through a primary survey of 476 households in 2013, the authors find that almost 83% of these households are vulnerable to poverty due to flood. The results show that incidence of poverty, flood height and use of coping strategies play significant role in determining households’ vulnerability to poverty. The study also suggests that institutional factors, household’s socio-economic conditions and community characteristics determine the use of coping strategies at the household level.


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/2017/#top 
 



Ore genetic implications of refractory sulfides

Dr Pranjit Hazarika and his fellow researchers study trace-element geochemistry of pyrite and arsenopyrite minerals and report about ore genetic implications for late Archean orogenic gold deposits in southern India. This study is published in Mineralogical Magazine.



Authors
Pranjit Hazarika, Biswajit Mishra, and Kamal Lochan Pruseth
Abstract
This study demonstrates coupled behavior of Au and chalcophile elements (Ag, Cu, Te, Sb, Bi and Pb) in the Hutti and Hira-Buddini late Archean orogenic lode gold deposits. The incorporation of Au into pyrite in such deposits is most likely a function of mineral fluid interactions without any effect of arsenic content. Distribution of Au and associated trace elements in pyrite and arsenopyrite from late Archean Hutti and Hira-Buddini orogenic gold deposits, eastern Dharwar Craton, southern India was investigated by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). X-ray element maps acquired by electron probe micro analyzer (EPMA) reveal oscillatory zoning of Co and As indicating the crystallization of pyrite and arsenopyrite in an episodic fluid flow regime in which fluid salinity fluctuated due to fault-valve actions. The absence of any relationship between Au and As in pyrite obviate the role of As in the incorporation of Au into pyrite particularly here and may be generally the case in orogenic gold deposits. On the other hand, positive correlations of Au with Cu, Ag and Te suggest possible influence of these chalcophile elements in the enhanced gold concentration in sulphides. Pb-Bi-Te-Au-Ag bearing micro-particles (< 2 micron) are exclusively observed in micro-fractures and pores in arsenopyrite. The absence of replacement features and element gradient suggests direct precipitation of Pb, Bi, Te, Au and Ag from a fluid that was unreactive towards arsenopyrite. Intermittent fall in fluid pressure caused by the fault-valve action would have resulted in the sporadic precipitation of Au, Pb, Ag, Bi and Te.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/2017/#top 
 



Retrieving age information from rocks

Dr Pranjit Hazarika and his fellow researchers report about a new and low-cost method to retrieve age information from detrital, diagenetic and low to high-T metamorphic, as well as magmatic rocks. This study is published in the journal Chemie der Erde.



Authors
Pranjit Hazarika, Biswajit Mishra, Manoj Kumar Ozha, and Kamal Lochan Pruseth
Abstract
EPMA U-Th-Pbtotal dating in U- and Th bearing minerals (e.g., monazite, zircon, and xenotime) is a low-cost and reliable technique used for retrieving age information from detrital, diagenetic and low to high-T metamorphic, as well as magmatic rocks. Although, the accuracy on measured ages obtained using EPMA is considered to be poor compared to isotopic ages, the superior spatial resolution, ability to integrate textural and age information by in-situ measurement, lack of sample damage and easier and cheaper data generation in EPMA makes chemical dating a very valuable tool to decipher diverse petrological processes. This contribution presents an improved analytical protocol to obtain precise estimates of U, Th and Pb concentrations in xenotime. Results were tested on monazite standard (Moacyr pegmatite, Brazil; TIMS age: 486 to 488 Ma) as the reference material. The proposed analytical protocol has been successfully applied to achieve an analytical uncertainty of less than 10% in U, Th and Pb measurements in xenotime. The protocol was further used to resolve polygenetic xenotime ages (ca. 1.82, 1.28 and 0.93 Ga) in metapelite samples from the Mangalwar Complex, Northwestern India. Monazites in the same samples were also analyzed and found to preserve the two younger ages (i.e., ca. 1.28 and 1.0 Ga). The obtained ages from the xenotime and monazite very well corroborate with the earlier published ages from the area validating the proposed analytical protocol. This improved analytical protocol underscores the application of xenotime chemical dating in metamorphic rocks using readily available electron micro-probes.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/2017/#top 
 



Surfactant free synthesis of gold nanoparticles

Dr Pranjal Saikia and his coworkers have developed methods to immobilise sub-3 nm gold nanoparticles within the mesoporous SBA-15 channels for catalytic applications. The work has been published in the journal Powder Technology.



Authors
Abu Taleb Miah, Saitanya K Bharadwaj, and Pranjal Saikia

Abstract
This work reports surfactant free synthesis of monodisperse gold (~ 2.3 nm) particles confined within the pore channels of ordered hexagonal mesoporous silica SBA-15 (Au/SBA-15) by a modified wetness impregnation method. The synthesized Au/SBA-15 composite showed excellent catalytic activity towards the reduction of different wastewater organic pollutants as well as their mixtures under ambient conditions. The composite was also investigated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). XRD, UV-DR visible spectroscopy, N2 adsorption-desorption analysis, ICP-AES, FT-IR spectroscopy, and TEM were employed to characterize the catalyst samples. The wetness impregnation method followed by a washing step with dilute aqueous NH3 was found to be an effective route to synthesise stable and highly dispersed small gold nanoparticles (Au NPs) within the mesopore channels of SBA-15. All the catalytic reactions followed pseudo-first-order kinetics and catalytic efficiency of the composite was found almost constant up to five cycles.
https://sites.google.com/a/gauhati.ac.in/research/2017/#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/2017/#top 
 



Vibrational energy harvesters

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



Authors
Utpal Sarma and Babk Montazer

Abstract
Modelling and analysis of a MEMS piezoelectric (PZT-Lead Zirconate Titanate) unimorph cantilever with different substrates are presented in this work. Stainless steel and Silicon h110i are considered as substrate. The design is intended for energy harvesting from ambient vibrations. The cantilever model is based on Euler–Bernoulli beam theory. The generated voltage and power, the current density, resonance frequencies and tip displacement for different geometry (single layer and array structure) have been analysed. Variation of output power and resonant frequency for array structure with array elements connected in parallel have been studied. Strain distribution is studied for external vibrations with different frequencies. The geometry of the piezoelectric layer as well as the substrate has been optimised for maximum power output. The variation of generated power output with frequency and load has also been presented. Finally, several models are introduced and compared with traditional array MEMS energy harvester.
https://sites.google.com/a/gauhati.ac.in/research/2017/#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/2017/#top 




One-step preparation of freestanding polypyrrole films at air-water Interface

Dr Debajyoti Mahanta and Sibani Majumdar describe this one-step preparation method, which is published in Chemistry Select, may be an effective pollutant removal!



Authors
Sibani Majumdar and Debajyoti Mahanta

Abstract
A simple one-step method of preparing freestanding polypyrrole (PPy) and p-toluenesulfonic acid doped PPy (PTSA-PPy) films has been developed. This novel method provides a simple and general route for preparing rough surfaced hydrophobic PPy films having many potential applications. It has been shown the effective removal of pollutant by these films from aqueous medium.
https://sites.google.com/a/gauhati.ac.in/research/2017/#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/2017/#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/2017/#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/2017/#top 




C
-H functionalization in water in presence of only molecular oxygen

Dr Pranjal K Baruah and his collaborators demonstrate what is believed to be the first example of C-H functionalization in water in presence of only molecular oxygen without any catalyst. The related article is published in journal Green Chemistry.




Authors
Mohit L Deb, Choitanya D Pegu, Paran J Borpatra, Prakash J Saikia, and Pranjal K Baruah
Department of Applied Sciences (Chemical Science Division), GUIST, GU


Abstract
Recently, C-H functionalization has been in the centre of attraction for being atom and step economical, directive, and environment-friendly than cross-coupling reactions which require prefunctionalization of substrates. Multi-component C-H functionalization gained much interest in synthetic chemistry due to their atom economy, easy mode of operation, and energy savings. We have reported catalyst-free 3-component reaction of naphthols, aldehydes and tetrahydroisoquinolines to synthesize 1,3-oxazines. It is one-pot multi-component C-H functionalization reaction carried out in water using only molecular oxygen as the sole oxidant. No catalyst or chemically synthesized oxidant is required for the reaction. We believe, this is the first example of C-H functionalization taking place in water in presence of only molecular oxygen. 


Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/2017/#top