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1
Content available remote

Effect of Temperature on Non-Destructive Wave Propagation in Uranium Monopnictides

100%
Singh R., Singh R., Singh M., Chaurasia S.
Acta Physica Polonica A
|
2009
|
vol. 115
|
issue 3
664-670
EN
Acoustic attenuation due to phonon-phonon interaction, thermoelastic mechanism and dislocation damping were evaluated in uranium monopnictides (viz. UN, UAs and USb) in the temperature range 50-500 K, along the three crystallographic directions of propagation, viz. [100], [110] and [111] for longitudinal and shear modes of propagation. Due to antiferromagnetic property of these compounds ultrasonic attenuation due to magnon-phonon interaction was also obtained. The second- and third-order elastic moduli of B1-type uranium monopnictides were obtained using electrostatic and the Born repulsive potentials. Gruneisen numbers and acoustic coupling constants were evaluated for longitudinal and shear waves along different directions of propagation and polarization. Results were discussed and compared with available data. It was found that the temperature dependence of attenuation due to phonon-phonon interaction and thermoelastic loss mechanisms follow the third and fourth order polynomial fit laws, respectively, and acoustic attenuation is mainly governed by phonon-phonon interaction in this temperature range.
2
Content available remote

Ultrasonic Attenuation in Alloys

89%
Kor S., Singh R.
Acta Physica Polonica A
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1993
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vol. 83
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issue 6
751-758
EN
Ultrasonic attenuation was evaluated in metallic alloys, Ni_{x}Cu_{1-x} (x = 1.00, 0.70, 0.60, 0.45 and 0) due to phonon-phonon (p-p) interaction and thermoelastic loss in a wide temperature region along ⟨110⟩ crystallographic direction for longitudinal and shear waves. Ultrasonic Grüneisen parameters, nonlinearity constants and ultrasonic attenuation due to p-p interaction and thermoelastic loss were determined from 50 K to 500 K using the Born-Mayer and electrostatic potentials. The results were compared with available experimental results.
3
Content available remote

Ultrasonic Attenuation in Dielectric Crystals

89%
Kor S., Singh R.
Acta Physica Polonica A
|
1991
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vol. 80
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issue 6
805-810
EN
Ultrasonic attenuation and non-linearity parameters have been evaluated for dielectric crystals RbCl, RbBr and RbI in a wide temperature range. Basic physical parameters, nearest neighbour distance and hardness parameters of the substance and Coulomb and Born-Mayer potentials have been used to obtain ultrasonic attenuation due to phonon-viscosity mechanism along (100) direction of propagation for longitudinal and shear waves. Results are as expected and it has been concluded that ultrasonic attenuation is a fundamental property of the substance.
4
Content available remote

Dielectric and Ac Conductivity Studies of Mn-Doped Na_{1.86}Li_{0.10}K_{0.04}Ti_3O_7 Ceramics

89%
Singh R., Shripal
|
|
vol. 125
|
issue 1
67-72
EN
Dielectric-spectroscopic and ac conductivity studies on 0.01 and 1.0 molar percentage manganese doped layered Na_{1.86}Li_{0.10}K_{0.04}Ti_3O_7 ceramics have been reported. The dependence of loss tangent (tan δ) and relative permittivity (ε_{r}) on temperature in the range 350-775 K and on frequency in the range 10 kHz-1 MHz have been undertaken. The losses are the characteristics of dipole mechanism, electrical conduction and space charge polarization. The obtained conductivity plots between log(σ_{ac}T) versus 1000/T have been divided into four regions namely region I, II, III, and IV. The mechanism of conduction in region I is acknowledged to electronic hopping conduction. The less frequency and more temperature dependent region II is ascribed as a mixed mechanism "associated interlayer ionic conduction, electron hopping, and alkali ion hopping conduction". The unassociated interlayer ionic conduction along with alkali ion hopping conduction mechanisms are contributing to the transport process in the mid temperature region III. The mechanism of conduction in the highest temperature region IV may be recognized as the modified interlayer ionic conduction. The conductivity versus frequency curves lead to conclude that the electronic hopping conduction diminishes with the rise of temperature.
5
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Content available

Sound Attenuation at High Temperatures in Pt

89%
Singh R., Pandey K.
Acta Physica Polonica A
|
2006
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vol. 109
|
issue 2
219-228
EN
Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss was evaluated in VIII group transition metal Pt in a wide temperature range (100 K to 1500 K) for longitudinal and shear waves along〈100〉, 〈110〉 and〈111〉 directions and for shear waves polarised along different directions. Electrostatic and Born-Mayer potentials were used to obtain second and third order elastic constants, taking nearest-neighbour distance and hardness parameter as input data. Second and third order elastic constants data obtained at different temperatures were used to obtain Gruneisen parameters and non-linearity or anisotropy parameters which in turn were used to evaluate (α/f^2)_l and (α/f^2)_s in Akhiezer regime. The results were discussed and it was found that at lower temperatures (α/f^2) increases rapidly with temperature and then rate of increase becomes very small. Contribution to the total attenuation due to thermoelastic loss is negligible so that due to phonon-phonon interaction establishing that major part of energy from sound wave is removed due to interaction with thermal phonons (lattice vibrations).
6

Marker-assisted selection for leaf rust resistance genes Lr19 and Lr24 in wheat (Triticum aestivum L.)

72%
Singh R., Datta D., Singh P. S., Tiwari R.
Journal of Applied Genetics
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2004
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vol. 45
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issue 4
399-403
EN
Leaf rust caused by Puccinia recondita f.sp. tritici is a wheat disease of worldwide importance. Wheat genotypes known to carry specific rust resistance genes and segregating lines that originated from various cross combinations and derived from distinct F2 lineage, so as to represent a diverse genetic background, were included in the present study for validation of molecular markers for Lr19 and Lr24. STS markers detected the presence of the leaf rust resistance gene Lr19 in a Thatcher NIL (Tc*Lr19) and Inia66//CMH81A575 and of the gene Lr24 in the genotypes Arkan, Blue Boy II, Agent and CI17907. Validation of molecular markers for Lr19 and Lr24 in parental lines, followed by successful detection of these genes in F3 lines from various cross combinations, was carried out. The molecular test corresponded well with the host-pathogen interaction test response of these lines.
7
Content available remote

Phase transition in CeSe, EuSe and LaSe under high pressure

72%
Singh S., Singh R., Gour A.
Open Physics
|
2007
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vol. 5
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issue 4
576-585
EN
The high pressure phase transition and elastic behavior of rare earth monoselenides (CeSe, EuSe and LaSe) which crystallize in a NaCl-structure have been investigated using the three body interaction potential (TBIP) approach. These interactions arise due to the electronshell deformation of the overlapping ions in crystals. The TBP model consists of a long range Coulomb, three body interactions and the short range overlap repulsive forces operative up to the second neighboring ions. The authors of this paper estimated the values of the phase transition pressure and the associated volume collapse to be closer than other calculations. Thus, the TBIP approach also promises to predict the phase transition pressure and pressure variations of elastic constants of lanthanide compounds.
8
Content available remote

First Principle Investigations on Electronic, Magnetic, Thermodynamic, and Transport Properties of TlGdX₂ (X = S, Se, Te)

72%
Gautam R., Kumar A., Singh R.
Acta Physica Polonica A
|
2017
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vol. 132
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issue 4
1371-1378
EN
In the present research paper, we investigated spin polarized electronic, magnetic, thermodynamic, and transport properties of thallium gadolinium dichalcogenides TlGdX₂ (X = S, Se, Te) using density functional theory. Electronic structure reveals that all the three compounds are wide band gap semiconductors which are beneficial for good thermoelectric performance. Calculated magnetic moment of TlGdX₂ is found to be in good agreement with available experimental values and mainly dominant by Gd³⁺ ions. Semiclassical Boltzmann transport theory has been used to calculate the Seebeck coefficient and electrical conductivity for the proposed dichalcogenides. Calculated values of the Seebeck coefficient and electrical conductivity are found to be consistent with available experimental values in literature. Thermodynamic properties of TlGdX₂ have also been estimated for the first time and explained on the basic facts.
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