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Kumar, S.

Publications and source records attributed to Kumar, S..

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Electro-optical and dielectric properties of CdSe quantum dots and 6CHBT liquid crystals composites

We have prepared the composites of a room temperature nematic liquid crystal namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and Cadmium Selenide Quantum Dots (CdSe-QDs) and investigated their electro-optical and dielectric properties. Effect of dispersion of CdSe-QDs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters, such as switching threshold voltage and splay elastic constant have been altered drastically for composites. Dispersion of QDs in a liquid crystals medium destabilizes nematic ordering of the host and decreases the nematic-to-isotropic transition temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Systematic study of iodine nuclei in A∼125 mass region

Excited states of {sup 127}I were populated via {sup 124}Sn({sup 7}Li,{sup 4}nγ){sup 127}I fusion-evaporation reaction at beam energy of 33 MeV. Multipolarities of several transitions were determined and spins of corresponding states have been confirmed. The band-head spin and parity of an already reported band at 2901.2 keV has been confirmed. Based on the observed characteristic features and by comparing with the systematics of odd mass iodine nuclei, a πg{sub 7/2}⊗νh{sub 11/2}{sup 2} configuration has been proposed for this band. The experimental B(M1)/B(E2) values for πg{sub 7/2} band were compared with the theoretical results of semi classical model of Frauendorf and Donau and found in well agreement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Shape evolution at high spin states in Kr and Br isotopes

The high spin states in A = 75, Kr and Br isotopes have been populated via fusion-evaporation reaction at an incident beam energy of 90 MeV. The de-exciting γ-rays were detected utilizing the Indian National Gamma Array (INGA). Lifetime of these excited high spin states were determined by Doppler-shift attenuation method. Experimental results obtained from lifetime measurement are interpreted in the frame work of projected shell-model to get better insight into the evolution of collectivity. Comparison of the calculations of the model with transitional quadrupole moments Q{sub t} of the positive and negative parity bands firmly established their configurations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Dipole bands in high spin states of {sub 57}{sup 135}La{sub 78}

High spin states of {sup 135}La have been investigated using the reaction {sup 128}Te({sup 11}B,4n){sup 135}La at a beam energy of 50.5 MeV. Two negative parity dipole bands (ΔI = 1) have been established. Crossover E2 transitions have been observed for the first time in one of the dipole bands. For the Tilted Axis Cranking (TAC) calculations, a three-quasiparticle (3qp) configuration π(h{sub 11/2}){sup 1}⊗ν(h{sub 11/2}){sup −2} and a five-quasiparticle (5qp) configuration π(h{sub 11/2}){sup 1}(g{sub 7/2}/d{sub 5/2}){sup 2}⊗ν(h{sub 11/2}){sup −2} have been taken for the two negative parity dipole bands. The comparison of experimental observables with TAC calculations supports the configuration assignments for both the dipole bands.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Nuclear structure studies close to N = Z = 50

The level structures in {sup 98,99}Rh, and {sup 99}Pd nuclei have been investigated through in beam γ-ray spectroscopic techniques following the {sup 75}As({sup 28}Si, xpyn) fusion-evaporation reaction at E{sub lab} = 120 MeV. These investigations were carried out using Indian-National-Gamma-Array (INGA) consisting of Compton-suppressed clover detectors at the Inter-University Accelerator Centre, New Delhi. The level structures observed in {sup 99}Pd, and {sup 98,99}Rh have been established up to ∼ 11 MeV, 10 MeV and 16 MeV excitation energy and spin ∼ 23ħ, 23ħ, and 28ħ respectively. In the doubly-odd {sup 98}Rh nucleus, new band structures and isomeric states have been identified at lower spins and new states below the previously identified 2{sup +} ground state (T{sub 1/2} = 8.5 m) are identified. In the present work {sup 99}Rh structure have been observed similar to {sup 101}Rh which is based on p{sub 1/2} and g{sub 9/2} orbitals. Various positive and negative parity states in these nuclei are observed to be energetically more favored with respect to the neighboring ones, and are likely to be the maximally aligned states obtained by angular momentum coupling of the valence particles (holes). The level structures observed in {sup 99}Pd have been interpreted in the framework of a microscopic theory based on the deformed Hartree-Fock (HF) and angular momentum projection techniques. Band structures at low excitation energy are based on the low-Ω νg{sub 7/2} and νd{sub 5/2} orbitals, have been observed in {sup 99}Pd. Band structure at higher spins are reproduced with the ν(g{sub 7/2}){sup 2}⊗ν(g{sub 9/2}){sup −1}⊗ν(h{sub 11/2}){sup 2}⊗π(g{sub 9/2}){sup 6} configurations. Observation of new E1 transitions linking the opposite parity νh{sub 11/2} and νd{sub 5/2} bands provide fingerprints of possible octupole correlations in {sup 99}Pd. The extracted values of the B(E1)/B(E2) ratios for the lower levels in the νh{sub 11/2} band are ∼ 10{sup −7} [fm]{sup −2}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Effect of cadmium selenide quantum dots on the dielectric and physical parameters of ferroelectric liquid crystal

The effect of cadmium selenide quantum dots (CdSe QDs) on the dielectric relaxation and material constants of a ferroelectric liquid crystal (FLC) has been investigated. Along with the characteristic Goldstone mode, a new relaxation mode has been induced in the FLC material due to the presence of CdSe QDs. This new relaxation mode is strongly dependent on the concentration of CdSe QDs but is found to be independent of the external bias voltage and temperature. The material constants have also been modified remarkably due to the presence of CdSe QDs. The appearance of this new relaxation phenomenon has been attributed to the concentration dependent interaction between CdSe QDs and FLC molecules.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Orientational order parameter measurements of discotic liquid crystal

The IR dichroism technique is a convenient method which can be used to measure the molecular order parameter corresponding to the IR bands exclusively present in the disc –like molecules in discotic liquid crystal (DLC). To measure orientational order parameter, homeotropic alignment of discotic liquid crystal was attained by slow cooling of sample from isotropic phase on untreated flat CaF{sub 2} substrate. The homeotropic alignment thus achieved was found to be thermodynamically stable in the discotic mesophase. IR spectra were recorded at different temperatures for the DLC. The order parameter was calculated by comparing the spectra of discotic phase with that of the isotropic phase. Order parameter has been presented as function of temperature for different significant IR bands present in the DLC.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Fast Multiresolution Reads of Massive Simulation Datasets

Today’s massively parallel simulation codes can produce output ranging up to many terabytes of data. Utilizing this data to support scientific inquiry requires analysis and visualization, yet the sheer size of the data makes it cumbersome or impossible to read without computational resources similar to the original simulation. We identify two broad classes of problems for reading data and present effective solutions for both. The first class of data reads depends on user requirements and available resources. Tasks such as visualization and user-guided analysis may be accomplished using only a subset of variables with a restricted spatial extent at a reduced resolution. The other class of reads requires full resolution multivariate data to be loaded, for example to restart a simulation. We show that utilizing the hierarchical multiresolution IDX data format enables scalable and efficient serial and parallel read access on a variety of hardware from supercomputers down to portable devices. Here, we demonstrate interactive view-dependent visualization and analysis of massive scientific datasets using low-power commodity hardware, and we compare read performance with other parallel file formats for both full and partial resolution data.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2013

Nuclear Data Sheets for A = 215

The evaluated spectroscopic data are presented for 12 known nuclides of mass 215 (Hg, Tl, Pb, Bi, Po, At, Rn, Fr, Ra, Ac, Th, Pa). For {sup 215}Hg, {sup 215}Tl, {sup 215}Pb, and {sup 215}Pa nuclei, no excited states are known. The decay characteristics of {sup 215}Hg and {sup 215}Tl are unknown. The decay scheme of {sup 215}Pb is considered as incomplete. Ordering of γ cascades in the decay of 36.9–s isomer of {sup 215}Bi and for high–spin states above 2251 keV in {sup 215}Fr are not established. High–spin excitations, including several isomeric states, are well known in {sup 215}Bi, {sup 215}Po, {sup 215}Rn, {sup 215}Fr, {sup 215}Ra, and {sup 215}Ac. No particle–transfer reaction data are available for any of the A=215 nuclei. The rms charge radii for {sup 215}Pb, {sup 215}Bi, {sup 215}Po, {sup 215}Rn, {sup 215}Fr and {sup 215}Ra have been evaluated by Daniel Abriola, from extrapolation or interpolation of available evaluated data in 2013An02 for radii of respective Z chains using formula 9 in 2004An14. This evaluation was carried out as part of ENSDD–workshop at VECC, Kolkata for Nuclear Structure and Decay Data, organized and hosted by VECC and Board of Research in Nuclear Sciences (BRNS) in Kolkata, India, November 26–29, 2012. This work supersedes the previous A = 215 evaluation (2001Br31) published by E. Browne which covered literature prior to May 2001.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

DISCOVERY OF A NEW TeV GAMMA-RAY SOURCE: VER J0521+211

We report the detection of a new TeV gamma-ray source, VER J0521+211, based on observations made with the VERITAS imaging atmospheric Cherenkov Telescope Array. These observations were motivated by the discovery of a cluster of >30 GeV photons in the first year of Fermi Large Area Telescope observations. VER J0521+211 is relatively bright at TeV energies, with a mean photon flux of (1.93 ± 0.13{sub stat} ± 0.78{sub sys}) × 10{sup –11} cm{sup –2} s{sup –1} above 0.2 TeV during the period of the VERITAS observations. The source is strongly variable on a daily timescale across all wavebands, from optical to TeV, with a peak flux corresponding to ∼0.3 times the steady Crab Nebula flux at TeV energies. Follow-up observations in the optical and X-ray bands classify the newly discovered TeV source as a BL Lac-type blazar with uncertain redshift, although recent measurements suggest z = 0.108. VER J0521+211 exhibits all the defining properties of blazars in radio, optical, X-ray, and gamma-ray wavelengths.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

From spin induced ferroelectricity to spin and dipolar glass in a triangular lattice: The CuCr{sub 1−x}V{sub x}O{sub 2} (0≤x≤0.5) delafossite

The change from antiferromagnetism induced ferroelectricity to spin glass ferroelectric relaxor has been studied along the CuCr{sub 1−x}V{sub x}O{sub 2} (0≤x≤0.5) solid solution of polycrystalline samples. As x increases from CuCrO{sub 2} (x=0) to CuCr{sub 0.82}V{sub 0.18}O{sub 2}, it is found that the Néel temperature decreases from ∼24 K down to ∼13 K. This progressive weakening of the antiferromagnetism of CuCrO{sub 2} induces a rapid decrease of the spin induced ferroelectricity with polarization values going from ∼44 μC/m{sup 2} down to ∼1.5 μC/m{sup 2} for x=0.04 and x=0.08, respectively. Beyond x=0.18 (0.20≤x≤0.50), ac-magnetic susceptibility and magnetization measurements evidence a spin glass state while dielectric permittivity and polarization measurements point towards a relaxor behaviour. This shows that competing magnetic interactions in delafossites are an efficient way to transform a spin induced magnetoelectric into a multiglass (spin and dipolar) state. - Graphical abstract: The P(T) curves evidencing the aging effect on polarization in CuCr{sub 0.5}V{sub 0.5}O{sub 2}: E=135 kV/m is applied during cooling at different temperatures. The P values and the inflection point of the transition depend on the poling temperature suggesting a relaxor behaviour. This effect related to the spin glass state is not observed for the lowest vanadium content. - Highlights: • Samples of the CuCr{sub 1−x}V{sub x}O{sub 2} series have been studied. • The V content increase induces a change from antiferromagnetism to spin glass. • A behavior characterisitic of a spin and dipole glass is demonstrated. • The ferroelectricity is shown to go from spin induced to relaxor. • Competing magnetic interactions are efficient way to generate multiglass state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2013

Combining Satellite Data and Models to Assess the Impacts of Urbanization on the Continental US Surface Climate

Urbanization is one of the most important and long lasting forms of land transformation. Urbanization affects the surface climate in different ways: (1) by reduction of the vegetation fraction causing subsequent reduction in photosynthesis and plant s water transpiration, (2) by alternation of surface runoff and infiltration and their impacts on soil moisture and the water table, (3) by change in the surface albedo and surface energy partitioning, and (4) by transformation of the surface roughness length and modification of surface fluxes. Land cover and land use change maps including urban areas have been developed and will be used in a suite of land surface models of different complexity to assess the impacts of urbanization on the continental US surface climate. These maps and datasets based on a full range of available satellite data and ground observations will be used to characterize distant-past (pre-urban), recent-past (2001), present (2010), and near future (2020) land cover and land use changes. The main objective of the project is to assess the impacts of these land transformation on past, current and near-future climate and the potential feedbacks from these changes on the atmospheric, hydrologic, biological, and socio-economic properties beyond the immediate metropolitan regions of cities and their near suburbs. The WRF modeling system will be used to explore the nature and the magnitude of the two-way interactions between urban lands and the atmosphere and assess the overall regional dynamic effect of urban expansion on the northeastern US weather and climate

Bounoua, L.↗