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Choudhuri G.,Quality Assurance Division | Mukherjee P.,Variable Energy Cyclotron Center | Gayathri N.,Variable Energy Cyclotron Center | Kain V.,Material Science Division | And 5 more authors.
Journal of Nuclear Materials | Year: 2017

Effect of heavy-ion irradiation on the crystalline phase transformation of oxide of Zr-2.5Nb alloys has been studied. The steam-autoclaved oxide of pressure tube is irradiated with 306 KeV Ar+9 ions at a dose of 3 × 1019 Ar+9/m2. The damage profile has been estimated using “Stopping and Range of Ions in Matter” computer program. The variation of the crystal structure along the depth of the irradiated oxide have been characterized non-destructively by Grazing Incidence X-ray Diffraction technique and compared with unirradiated-oxide. The effect of different base metal microstructures on the characteristic of oxide has also been studied. Base metal microstructure as well as the cross-sectional oxide have been characterized using transmission electron microscope. Heavy ion irradiation can significantly alter the distribution of phases in the oxide of the alloy. The difference in chemical state of alloying element has also been found between unirradiated-oxide with that of irradiated-oxide using X-ray photo electron spectroscopy. Chemical state of Nb in steam autoclaved oxide is also altered when the base metal is α + β heat treated. © 2017 Elsevier B.V.

Hemnani P.,Homi Bhabha National Institute | Rajarajan A.K.,Solid State Physics Division | Joshi G.,Accelerator Control Division | Ravindranath S.V.G.,Bhabha Atomic Research Center
Procedia Computer Science | Year: 2016

A FPGA based radio frequency source and pulse programmer for NQR is described. With the use of direct digital synthesis (DDS), the RF source has the ability to yield RF signal with short switching time and high resolution in frequency and phase. To facilitate the generation of RF pulses, pulse programmer implemented in FPGA, is also used as auxiliary controller of DDS. The pulse programmer controls the DDS to generate RF pulses according to predefined parameters. © 2016 The Authors. Published by Elsevier B.V.

Rose J L.,National Institute of Technology Calicut | Tata B.V.R.,Bhabha Atomic Research Center | Aswal V.K.,Solid State Physics Division | Hassan P.A.,Chemistry Division | And 2 more authors.
European Physical Journal E | Year: 2015

Abstract.: Structural transitions triggered by p H in an aqueous micellar system comprising of a cationic surfactant (cetylpyridinium chloride) and an aromatic dibasic acid (phthalic acid) was investigated. Reversible switching between liquid-like and gel-like states was exhibited by the system on adjusting the solution p H. Self-assembled structures, responsible for the changes in flow properties were identified using rheology, light scattering techniques and cryogenic Transmission Electron Microscopy (cryo-TEM). High-viscosity, shear-thinning behavior and Maxwell-type dynamic rheology shown by the system at certain p H values suggested the growth of spheroidal/short cylindrical micelles into long and entangled structures. Light scattering profiles also supported the notion of p H-induced microstructural transitions in the solution. Cryo-TEM images confirmed the presence of spheroidal/short cylindrical micelles in the low-viscosity sample whereas very long and entangled thread-like micelles in the peak viscosity sample. p H-dependent changes in the micellar binding ability of phthalic acid is proposed as the key factor regulating the morphological transformations and related flow properties of the system.Graphical abstract: [Figure not available: see fulltext.]. © 2015, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

Linet Rose J.,National Institute of Technology Calicut | Tata B.V.R.,Bhabha Atomic Research Center | Talmon Y.,Technion - Israel Institute of Technology | Aswal V.K.,Solid State Physics Division | And 2 more authors.
RSC Advances | Year: 2015

Macroscopic properties of amphiphilic systems can be reversibly controlled by tailoring micellar morphology via appropriate choice of additive and external stimulus. In this work we report an aqueous micellar system showing pH responsive viscoelasticity and optical properties. pH sensitive behaviour of a phenolic acid, namely, ortho-coumaric acid (OCA) is effectively utilized to tune self-assembly in cetyltrimethylammonium bromide (CTAB) solution. Reversible switching between colourless, gel-like state and fluorescent green colour, liquid-like state can be attained by pH adjustment. pH dependent changes in bulk properties and the microstructures responsible for the behaviour were studied by means of rheology, UV-vis and fluorescence spectroscopic techniques, small angle neutron scattering (SANS) and cryogenic transmission electron microscopy (cryo-TEM). Rheological studies suggested transition between viscoelastic fluid and Newtonian liquid or vice versa, with specific changes in pH. Viscoelasticity of the system is attributed to the presence of entangled threadlike micelles. pH sensitive interactions between surfactant micelles and phenolic additive is regarded as the key factor regulating the morphological transitions and related flow behaviour in CTAB-OCA solution. © The Royal Society of Chemistry 2015.

Chakraborty S.,Bhabha Atomic Research Center | Arora A.K.,Bhabha Atomic Research Center | Sivasubramanian V.,Bhabha Atomic Research Center | Krishna P.S.R.,Solid State Physics Division | Venkata Krishnan R.,Bhabha Atomic Research Center
Journal of Physics Condensed Matter | Year: 2012

Processes occurring at macroscopic and microscopic length scales across the glass transition (Tg) in lead-tellurite glass (PbO) x(TeO2)1-x (x = 0.1-0.3) are investigated using Brillouin and Raman spectroscopy, respectively. For all the samples, the temperature dependence of the longitudinal acoustic (LA) mode is found to exhibit a universal scaling below Tg and a rapid softening above Tg. The lower value of elastic modulus at a higher concentration of network modifier PbO, estimated from Brillouin data, arises due to loss of network rigidity. From quantitative analysis of the reduced Raman spectra, several modes are found to exhibit anomalous changes across Tg. Instead of the expected anharmonic behaviour, several modes exhibit hardening, suggesting stiffening of the stretching force constants with temperature, the effect being more pronounced in glasses with higher x. In addition, incorporation of PbO in the glass is also found to narrow down the bond-length distribution, as evident from the sharpening of the Raman bands. The stiffening of the force constants of molecular units at a microscopic length scale and the decrease of elastic constant attributed to loss of network rigidity on a macroscopic length scale appear to be opposite. These different behaviours at two length scales are understood on the basis of a microscopic model involving TeOn and PbO units in the structure. © 2012 IOP Publishing Ltd.

Maheshwari P.,Radiochemistry Division | Mukherjee S.,Radiochemistry Division | Bhattacharya D.,Solid State Physics Division | Sen S.,Technical Physics Division | And 5 more authors.
ACS Applied Materials and Interfaces | Year: 2015

Surface engineering of SiO2 dielectric using different self-assembled monolayer (SAM) has been carried out, and its effect on the molecular packing and growth behavior of copper phthalocyanine (CuPc) has been studied. A correlation between the growth behavior and performance of organic field effect transistors is examined. Depth profiling using positron annihilation and X-ray reflectivity techniques has been employed to characterize the interface between CuPc and the modified and/or unmodified dielectric. We observe the presence of structural defects or disorder due to disorientation of CuPc molecules on the unmodified dielectric and ordered arrangement on the modified dielectrics, consistent with the high charge carrier mobility in organic field effect transistors in the latter. The study also highlights the sensitivity of these techniques to the packing of CuPc molecules on SiO2 modified using different SAMs. Our study also signifies the sensitivity and utility of these two techniques in the characterization of buried interfaces in organic devices. © 2015 American Chemical Society.

Vekariya R.L.,Sardar Patel University | Aswal V.K.,Solid State Physics Division | Hassan P.A.,Bhabha Atomic Research Center | Soni S.S.,Sardar Patel University
Langmuir | Year: 2014

The isotropic micellar state of Pluronic P123 in the presence and absence of N-alkylpyridinium halide ionic liquids (ILs) is investigated using SANS, DLS, and 1H NMR studies. The micellar structural parameters are obtained as a function of variation in alkyl chain length, anions, and concentrations of ILs by fitting the SANS scattering data with a model composed of core-shell form factor and a hard sphere structure factor of interaction. Addition of ILs decreases the micellar core, aggregation number, and hard sphere radius of P123 micelles. From quantitative analysis, we determined the amount of solvent (D2O + IL) present inside the core and the core-shell interface along with cationic head groups. This is further supported by monitoring interaction between ILs and polymer micelle using 1H NMR spectroscopy. The results are discussed and explained as a function of concentration of C8PyCl, alkyl chain length, and anions of N-alkylpyridinium halides. © 2014 American Chemical Society.

News Article | February 22, 2017
Site: www.cemag.us

Mildred “Millie” Dresselhaus, known for her research involving carbon nanotubes, graphene, and other nanocarbon materials, died in Cambridge, Mass. on Feb. 20 at the age of 86. Dr. Dresselhaus was a pioneer in the field of condensed matter and carbon’s atomic properties of carbon, earning her the nickname “Queen of Carbon Science” from a journalist. Her revolutionary studies of carbon included the exploration of each layer of carbon atoms (predecessors to graphene), creating carbon fibers that are stronger than steel, and discovering innovative carbon structures that eventually led to the development of buckyballs and nanotubes. “We lost a giant — an exceptionally creative scientist and engineer who was also a delightful human being,” said MIT president L. Rafael Reif. “Among her many ‘firsts,’ in 1968, Millie became the first woman at MIT to attain the rank of full, tenured professor. She was the first solo recipient of a Kavli Prize and the first woman to win the National Medal of Science in Engineering.” Born in Brooklyn to Polish Jewish immigrants, Dresselhaus earned her B.A. in Physics from Hunter College in 1951, her M.A. in Physics from Radcliffe College/Harvard University in 1953, and her Ph.D. in Physics from the University of Chicago in 1958. Dresselhaus was a National Science Foundation postdoctoral fellow at Cornell University, and then spent seven years as a staff member at MIT’s Lincoln Laboratory in the Solid State Physics Division to begin her study of carbon science. She published a 1963 paper in the IBM Journal for Research and Development on the topic of graphite — these studies still form the backbone for explorations of the electronic structure of fullerenes and carbon nanotubes. Dresselhaus joined the staff at MIT in 1967, eventually becoming an Institute Professor Emerita as well as a professor emerita in the physics and electrical engineering and computer science departments. She became a pioneer for women in STEM, working toward improving women’s living conditions at MIT, at a time when females made up just 4 percent of the undergraduate population. Under her guidance, MIT developed an equal and joint admission process for women and men. Dresselhaus’s work was at the forefront of the development of novel forms of nanostructured carbons including intercalation compounds, carbon nanotubes, and graphene. She is credited for the resurgence of the Thermoelectrics research field because of her early work on low dimensional thermoelectricity in the early ‘90s, and authored four books on carbon science. She was the Director of the Office of Science at the U.S. Department of Energy from 2000 to 2001 and served on the DOE's Energy Research Advisory Board for seven years; she is credited as co-inventor on five U.S. patents; and she received over 20 honorary doctorates from educational institutions around the world. She was also an avid violin and viola player. Her awards include the 2012 Kavli Prize in Nanoscience, the Presidential Medal of Freedom in 2014, the 2008 Buckley Prize, and the National Medal of Science in 1990. Coincidentally, Dresselhaus was the subject of a General Electric Web video just two weeks ago, in a GE campaign calling for 20,000 women to fill STEM roles by the year 2020. In the hypothetical “What if scientists were celebrities?” scenario, Dresselhaus had a doll made in her likeness, baby girls in a hospital nursery were named after her, and people excitedly posed with her for selfies and then mobbed the streets to attend her lectures.

Sahoo A.,Jadavpur University | Nath P.P.,Bengal Institute of Technology | Bhagat V.,Jadavpur University | Krishna P.S.R.,Solid State Physics Division | Joarder R.N.,Jadavpur University
Physics and Chemistry of Liquids | Year: 2010

Hydrogen-bonded cluster analysis of liquid D-methanol data at room and elevated temperatures was carried out and nature of molecular association was extracted. The analysis, based on a choice of suitable centre structure corresponding to an effective pair potential, hardsphere plus a square-well ledge, determines if the H-bonded clusters are broken with the rise in temperature. It is shown that clusters present at room temperature are more or less preserved at elevated temperatures. At low Q (Q being the scattering vector), Ornstein-Zernike behaviour is produced extremely well. The analysis enables the extraction of atom-atom distribution functions, such as gOO(r), gOD(r) and gDD(r), the variation of which with temperature confirm the same observation. © 2010 Taylor & Francis.

Singh L.J.,Manipur University | Singh R.K.H.,Manipur University | Chitra R.,Solid State Physics Division | Choudhury R.R.,Solid State Physics Division
AIP Conference Proceedings | Year: 2011

Four new Cu(II) complexes of 4,4□-diaminodiphenyl sulfone(DDS) with different anions(chloride, sulphate or acetate) were synthesized and characterized by X-ray diffraction studies. It is observed that all the complexes crystallize in monoclinic system unlike the pure DDS which crystallizes in orthorhombic system. Complexes of DDS with CuSO4 in 1:1 and 2:1 stoichiometric ratio crystallize in monoclinic system with much larger volume compared to other DDS complexes. © 2011 American Institute of Physics.

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