X-ray Absorption Spectroscopic Studies of Pulsed-Laser-Deposited Thin Films of Fe3O4 on Si(111) Substrate

P. Thakur,W. K. Choi,K. H. Chae,J.-Y. Kim,R. J. Choudhary,Shailja Tiwari,Ram Prakash,D. M. Phase,Ravi Kumar 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6

We report on the growth and the characterization of magnetite thin films grown on Si(111) substrates by using pulsed laser deposition at different substrate temperatures (TS = 350, 450 and 550 ℃) by performing X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) experiments. The O K− and Fe L3,2−edge XAS spectra reveal that the couplings of the O 2p with Fe 3d orbitals highly rely on the growth processes. The XMCD data of well-characterized thin films exhibit characteristic contributions from Fe3+ A ions in tetrahedral sites and Fe2+ B and Fe3+ B ions in octahedral sites and have spectral features similar to those of the Fe3O4 single crystal. The temperature dependence of the XMCD line shape features remain unchanged below and above the Verwey transition. These investigations demonstrate the experimental conditions for controlled growth of Fe3O4 thin films on Si(111) substrates and suggest that the Fe3O4/Si(111) might a promising spintronic materials for future technology.

Plant responses to nano and micro structured carbon allotropes: Water imbibition by maize seeds upon exposure to multiwalled carbon nanotubes and activated carbon

Dasgupta-Schubert, N.,Tiwari, D.K.,Francis, E. Reyes,Martinez Torres, P.,Villasenor Cendejas, L.M.,Lara Romero, J.,Villasenor Mora, C. Techno-Press 2017 Advances in nano research Vol.5 No.3

Multiwalled carbon-nanotubes (MWCNT) and micro-structured carbon, such as biochar or activated carbon (AC), have been seen to significantly increase the growth indices of certain plant species such as maize (Zea mays L.). Seed imbibition is the stage where environmental factors that affect water transport across the seed coat barrier, make a large impact. This work explores the effect on water imbibition by maize seeds when the aqueous environment surrounding the seed is diluted by small concentrations (10 and 20 mg/l) of pristine MWCNT (p-MWCNT), carboxylate functionalized MWCNT (COO-MWCNT) and AC. The degree of sensitivity of the process to (i) large structural changes is seen by utilizing the nano (the MWCNT) and the micro (the AC) allotropic forms of carbon; (ii) to small changes in the purity and morphology of the p-MWCNT by utilizing 95% pure and 99% pure p-MWCNTs of slightly differing morphologies; and (iii) to MWCNT functionalization by using highly pure (97%) COO-MWCNT. Water imbibition was monitored over a 15 hour period by Near Infrared Thermography (NIRT) and also by seed weighing. Seed surface topography was seen by SEM imaging. Analysis of the NIRT images suggests rapid seed surface topological changes with the quantity of water imbibed. While further work is necessary to arrive at a conclusive answer, this work shows that the imbibition phase of the maize seed is sensitive to the presence of MWCNT even to small differences in the purity of the p-MWCNT and to small differences in the physicochemical properties of the medium caused by the hydrophilic COO-MWCNT.

Prediction of a research vessel manoeuvring using numerical PMM and free running tests

Tiwari, Kunal,Hariharan, K.,Rameesha, T.V.,Krishnankutty, P. Techno-Press 2020 Ocean systems engineering Vol.10 No.3

International Maritime Organisation (IMO) regulations insist on reduced emission of CO₂, noxious and other environmentally dangerous gases from ship, which are usually let out while burning fossil fuel for running its propulsive machinery. Contrallability of ship during sailing has a direct implication on its course keeping and changing ability, and tries to have an optimised routing. Bad coursekeeping ability of a ship may lead to frequent use of rudder and resulting changes in the ship's drift angle. Consequently, it increases vessels resistance and also may lead to longer path for its journey due to zigzag movements. These adverse effects on the ship journey obviously lead to the increase in fuel consumption and higher emission. Hence, IMO has made it mandatory to evaluate the manoeuvring qualities of a ship at the designed stage itself. In this paper a numerical horizontal planar motion mechanism is simulated in CFD environment and from the force history, the hydrodynamic derivatives appearing in the manoeuvring equation of motion of a ship are estimated. These derivatives along with propeller thrust and rudder effects are used to simulate different standard manoeuvres of the vessel and check its parameters against the IMO requirements. The present study also simulates these manoeuvres by using numerical free running model for the same ship. The results obtained from both these studies are presented and discussed here.

Diagnosis of Benzimidazole Resistance in Haemonchus contortus of Sheep by Allele Specific PCR

Tiwari, J.,Kolte, A.P.,Kumar, S.,Swarnkar, C.P.,Singh, D.,Pathak, K.M.L. Asian Australasian Association of Animal Productio 2007 Animal Bioscience Vol.20 No.1

The study was conducted on 162 adult male Haemonchus contortus of sheep collected from Avikanagar, Jaipur and Bikaner regions to diagnose the benzimidazole (BZ) resistance in H. contortus. The BZ resistance is primarily linked with the mutation in ${\beta}$-tubulin isotype 1 gene which substitute phenylalanine (Phe) into tyrosine (Tyr) at the 200 codon of the gene. An allele specific polymerase chain reaction (AS-PCR) technique was used for diagnosis of BZ resistance in H. contortus. In AS-PCR, one reverse primer (TGG 312) was used in two separate reactions with each of 2 forward primers (resistant TGG 331 and susceptible CAW 106 primer) that differed only at 3' nucleotide position. Therefore, the amplified products from resistant and susceptible parasites were produced 267 and 266 bp, respectively. A total of 162 parasites were genotyped, of which 130 parasites found homozygous resistant 'rr', 22 heterozygous 'rS' and 10 homozygous susceptible 'SS' type. The prevalence of 'rr' individuals was higher in Jaipur (98%) followed by Avikanagar (93%) and Bikaner (50%) regions. Overall, the prevalence of BZ resistant allele (r) was higher (87%) as compared to 13% of BZ susceptible allele (S).

Solar Science with the Atacama Large Millimeter/Submillimeter Array-A New View of Our Sun

Wedemeyer, S.,Bastian, T.,Brajš,a, R.,Hudson, H.,Fleishman, G.,Loukitcheva, M.,Fleck, B.,Kontar, E. P.,De Pontieu, B.,Yagoubov, P.,Tiwari, S. K.,Soler, R.,Black, J. H.,Antolin, P.,Scullion, E.,Gu Springer-Verlag 2016 Space science reviews Vol.200 No.1

<P>The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere-a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases.</P>

Engineering a novel bilayer membrane for bone defects regeneration

Tiwari, A.P.,Joshi, M.K.,Maharjan, B.,Ko, S.W.,Kim, J.I.,Park, C.H.,Kim, C.S. North-Holland 2016 Materials letters Vol.180 No.-

We report the fabrication of a novel bilayer scaffold as a barrier membrane via modified-solvent casting and evaporation technique for the regeneration of bone defects. The blended solution of polycaprolactone (PCL) and calcium carbonate (CaCO<SUB>3</SUB>) was treated with hydrochloric acid (HCL), which resulted in the in situ formation of carbon dioxide (CO<SUB>2</SUB>) and water. This led to the phase separation between the PCL and calcium-based compounds and subsequently to the formation of a bilayer membrane. Surface morphology, surface wettability, and energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the formation of a bilayered construct with a PCL-rich thin layer on the upper surface and a calcium-rich porous layer on the lower surface. From the FE-SEM images, the PC30 membrane showed a smooth upper layer with pores less than 10@?m diameter, whereas the lower layer contained many interconnected larger pores up to 1000@?m diameter in addition to the visibly identified macrovoids. The cell adhesion assay showed that both surfaces of the membrane responded well to the cells. In addition, the upper surface prevented the down-growth of the fibroblasts. The initial results suggest a new strategy for the fabrication of the bilayer membrane for regenerative medicine.

Bimodal fibrous structures for tissue engineering: Fabrication, characterization and in vitro biocompatibility

Tiwari, A.P.,Joshi, M.K.,Kim, J.I.,Unnithan, A.R.,Lee, J.,Park, C.H.,Kim, C.S. Academic Press 2016 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.476 No.-

We report for the first time a polycaprolactone-human serum albumin (PCL-HSA) membrane with bimodal structures comprised of spider-web-like nano-nets and conventional fibers via facile electro-spinning/netting (ESN) technique. Such unique controllable morphology was developed by electrospinning the blend solution of PCL (8wt% in HFIP 1,1,1,3,3,3,-Hexafluoro-2-propanol) and HSA (10wt% deionized water). The phase separation during electrospinning caused the formation of bimodal structure. Various processing factors such as applied voltage, feeding rate, and distance between nozzle tip and collector were found responsible for the formation and distribution of the nano-nets throughout the nanofibrous mesh. Field emission electron microscopy (FE-SEM) confirmed that the nano-nets were composed of interlinked nanowires with an ultrathin diameter (10-30nm). When compared with a pure PCL membrane, the membrane containing nano-nets was shown to have better support for cellular activities as determined by cell viability and attachment assays. These results revealed that the blending of albumin, a hydrophilic biomolecule, with PCL, a hydrophobic polymer, proves to be an outstanding approach to developing membranes with controlled spider-web-like nano-nets for tissue engineering.

Electrospun bioactive poly (@?-caprolactone)-cellulose acetate-dextran antibacterial composite mats for wound dressing applications

Liao, N.,Unnithan, A.R.,Joshi, M.K.,Tiwari, A.P.,Hong, S.T.,Park, C.H.,Kim, C.S. Elsevier 2015 Colloids and surfaces. A, Physicochemical and engi Vol.469 No.-

<P>Electrospun nanofibrous mat for wound dressing application was successfully prepared from poly (6caprolactone) (PCL), cellulose acetate (CA) and dextran blend solution. Incorporation of small amount of tetracycline hydrochloride (TCH), an antibacterial drug, improved the cell proliferation, enhanced blood clotting ability and cell attachment as well as antimicrobial activity of the composite mat. The composite mats were characterized by SEM, FTIR and TGA analysis. In order to evaluate the cytocompatibility and cell behavior of the composite scaffolds, fibroblast cells were seeded on the matrix. Results demonstrated that the incorporation of dextran and drug strongly enhanced the adhesion and proliferation of the cells on the composite nanofibers. The antimicrobial activity of the composite was studied by zone inhibition against Gram-positive and Gram-negative bacteria and the result indicates high antibacterial activity. Therefore, as synthesized composite fiber have decent characteristics for wound dressing and skin engineering applications. (C) 2015 Elsevier B.V. All rights reserved.</P>

A Comparison of Pulsed and Continuous Atom Transfer between Two Magneto-optical Traps

S. P. Ram,S. K. Tiwari,S. R. Mishra 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.5

We present the experimental results for a comparison between pulsed and continuous transfer of cold 87Rb atoms between a vapor chamber magneto-optical trap (VC-MOT) and an ultra-highvacuum magneto-optical trap (UHV-MOT) when using a resonant push beam. We find that employing repetitive cycles of a pulsed and unfocused push beam on an unsaturated VC-MOT cloud results in a significantly higher number of atoms transferred to the UHV-MOT than the number obtained with a continuous push beam focused on a continuous VC-MOT. In pulsed transfer, we find that both the VC-MOT loading duration and the push beam duration play important roles in the transfer process and govern the number of atoms transferred to the UHV-MOT. The parameters and processes affecting the transfer have been investigated and are discussed.

Temperature and Phase-space Density of a Cold Atom Cloud in a Quadrupole Magnetic Trap

S. P. Ram,S. R. Mishra,S. K. Tiwari,H. S. Rawat 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.4

We present studies on modifications in the temperature, number density and phase-space densitywhen a laser-cooled atom cloud from optical molasses is trapped in a quadrupole magnetic trap. Theoretically, for a given temperature and size of the cloud from the molasses, the phase-spacedensity in the magnetic trap is shown first to increase with increasing magnetic field gradient andthen to decrease with it after attaining a maximum value at an optimum value of the magneticfieldgradient. The experimentally-measured variation in the phase-space density in the magnetictrap with changing magnetic field gradient is shown to exhibit a similar trend. However, theexperimentally-measured values of the number density and the phase-space density are much lowerthan the theoretically-predicted values. This is attributed to the experimentally-observed temperaturein the magnetic trap being higher than the theoretically-predicted temperature. Nevertheless,these studies can be useful for setting a higher phase-space density in the trap by establishing anoptimal value of the field gradient for a quadrupole magnetic trap.