Akhilesh Arora

Delhi Technological University

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T. R. Ravindran

Indira Gandhi Centre for Atomic Research

B. B. Arora

Delhi Technological University

R. Kesavamoorthy

Vellore Institute of Technology University

B. V. R. Tata

University of Hyderabad

Satyaprakash Sahoo

Institute of Physics, Bhubaneshwar

V. Sivasubramanian

Indira Gandhi Centre for Atomic Research

T. Sakuntala

Bhabha Atomic Research Centre

M. Rajalakshmi

R.V. College of Engineering

S.C. Kaushik

Indian Institute of Technology Delhi

Takehiko Yagi

The University of Tokyo

Cooperative Institutions

Indira Gandhi Centre for Atomic Research

Homi Bhabha National Institute

Delhi Technological University

Bhabha Atomic Research Centre

Indian Institute of Technology Delhi

Indian Institute of Science Bangalore

Indian Institute of Technology Bombay

Vellore Institute of Technology University

National Taiwan University

University of Madras

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Reentrant Phase Transition in Charged Colloidal Suspensions

Physical Review Letters (1988)

Akhilesh Arora B. V. R. Tata A. K. Sood R. Kesavamoorthy

We report the observation of a novel phase transition in dilute aqueous suspensions of polystyrene particles as a function of ionic impurity concentration $C$. The suspension phase separates into dense and rare phases only for a restricted range of $C$ which depends on particle concentration $n$. The dense phase has liquidlike or crystalline order depending on $n$ and $C$. Free energies of the homogeneous and the phase-separated states are calculated with an effective interparticle potential. The calculated phase diagram is in qualitative agreement with the present experimental results.

Suspension

Reentrancy

Polystyrene

Aqueous suspension

Particle (ecology)

Colloidal particle

10.1103/physrevlett.60.2438

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Citations (63)

Raman spectroscopic study of pressure induced amorphization in Cavansite

Journal of Physics Conference Series (2012)

T. R. Ravindran Akhilesh Arora G. Parthasarathy

High pressure phase transformations in calcium aluminum silicate (cavansite), a rare mineral, are reported up to a pressure of 15 GPa using Raman spectroscopy. Structural transformations are indicated at 1, 4, 6 and 8 GPa followed by amorphization above 15 GPa. The amorphous phase is quenchable to ambient pressure.

Ambient pressure

Calcium silicate

10.1088/1742-6596/377/1/012004

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Citations (1)

Instrumental Distortions of Raman Lines

Applied Spectroscopy (1982)

Akhilesh Arora V. Umadevi

The effect of spectrometer resolution on the peak intensity and the full width at half maximum (FWHM) of a Lorentzian spectrum is obtained by evaluating the convoluted line shapes. Spectrometer resolution functions (SRF) having Gaussian and triangular profiles are considered separately. Empirical relations to estimate the true peak intensity and the FWHM from the observed parameters are suggested. These relations are valid over an extended range of parameters with an accuracy better than that of other methods suggested earlier. As an application, the true FWHM's and peak intensities of the main component of the Raman active A g mode of sulphate ion in potash alum at low temperatures are evaluated.

Line width

10.1366/0003702824639682

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Citations (41)

Vibrational spectroscopy and phonon dispersion of GaSb

Indian Journal of Pure & Applied Physics (2008)

Bipul Rakshit Vipul Srivastava Sankar P. Sanyal Prafulla K. Jha T. R. Ravindran

Formalism (music)

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High-pressure Raman spectroscopic study of zirconium tungstate

Journal of Physics Condensed Matter (2001)

T. R. Ravindran Akhilesh Arora T. A. Mary

Raman spectroscopic measurements on negative-thermal-expansion (NTE) material zirconium tungstate Zr(WO4)2 at 20 K over the complete range of phonon frequencies yield 39 out of the predicted 54 optical phonons. The modes are assigned as lattice modes, and translational, librational and internal modes of the WO4 ion. High-pressure measurements in a diamond anvil cell (DAC) have revealed that in addition to the low-frequency rigid-unit modes (RUMs) several other phonons, including the bending modes of the WO4 ion, also exhibit negative Grüneisen parameter in the cubic phase. In the high-pressure orthorhombic phase above 0.3 GPa splitting of phonon modes is found to be consistent with the lowering of symmetry. Pressure-induced amorphization in this system at 2.2±0.3 GPa is argued to arise because a pressure-induced decomposition of the compound into a mixture of ZrO2 and WO3 is kinetically constrained. The temperature dependence of specific heat and thermal expansion coefficient are calculated and compared with reported results. In contrast to earlier models and calculations, which considered only the phonons below 8 meV (64 cm-1) to explain the NTE, it is shown that modes much higher than 8 meV also contribute significantly to NTE in this material.

Negative Thermal Expansion

Orthorhombic crystal system

Lattice (music)

Diamond anvil cell

Tungstate

10.1088/0953-8984/13/50/316

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Citations (71)

Thermodynamic Performance Enhancement of an Air Conditioner With Dew Point Evaporative Cooler

ASME Journal of Engineering for Sustainable Buildings and Cities (2023)

Sunil Kumar Gupta B. B. Arora Akhilesh Arora

Abstract The vapor-compression-based conventional split air conditioners (CACs) consume a large portion of total electrical power and pose an alarming threat to global environment. The present work aims to reduce cooling load and power consumption of CAC by employing a dew point evaporative cooler (DPEC). DPEC consists of a counter flow type heat and mass exchanger with alternate layers of dry and wet channels. The intake air is sensibly cooled before entering the cooling room through the evaporator coil of the air conditioner. Also, the working air (a part of outlet air in dry channel), after absorbing sensible heat of intake air and water vapors from the wet channel surface, is allowed to pass across the condenser coils. The intake dry-bulb temperature (T0 = 29–44 °C) and specific humidity (ω0 = 6–22 g/kg) are taken as input parameters. While the cooled air entering the evaporator decreases the cooling load on the conditioned space, the compression work is also reduced due to increased heat transfer in the condenser. The maximum reductions in cooling load and monthly energy consumption at T0 = 44 °C and ω0 = 6 g/kg are found as 59.54% and 340 kW h, respectively. The water consumption for different months of the cooling season varies from 1037.8 L to 2905.95 L. The average energy savings with the DPEC system for hot-dry climate (from April to June) and hot-humid climate (from July to September) of New Delhi, India, are observed to be 479.6 kW h and 79.1 kW h, respectively. The proposed system is found to payback in about 3.37 years.

Evaporative cooler

Condenser (optics)

Dry-bulb temperature

Dew point

Cooling capacity

Vapor-compression refrigeration

Wet-bulb temperature

Chiller

Cooling load

10.1115/1.4063498

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Citations (3)

Confined Acoustic Phonon in CdS_1−xSe_x Nanoparticles in Borosilicate Glass

Journal of Nanoscience and Nanotechnology (2009)

Sanjeev K. Gupta Prafulla K. Jha Satyaprakash Sahoo Akhilesh Arora Yu. M. Azhniuk

We calculate low-frequency Raman scattering from the confined acoustic phonon modes of CdS1-xSex nanoparticles embedded in borosilicate glass. The calculation of the Raman scattering by acoustic phonons in nanoparticles has been performed by using third-order perturbation theory. The deformation potential approximation is used to describe the electronphonon interaction. The Raman-Brillouin electronic density and the electron-phonon interaction are found to increases with decreasing size of nanoparticle. A good agreement between the calculated and reported low-frequency Raman spectra is found.

Borosilicate glass

Brillouin zone

10.1166/jnn.2009.1168

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Citations (1)

Optimum Performance Analysis of a Hybrid Cascade Refrigeration System Using Alternative Refrigerants

Materials Today Proceedings (2018)

Naushad Ahmad Ansari Akhilesh Arora Samsher Gautam K. Manjunath

Coefficient of performance

Vapor-compression refrigeration

Exergy efficiency

10.1016/j.matpr.2018.10.122

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Citations (7)

Identification of chemical compounds under the surface film during a surface treatment process using laser Raman spectroscopy

Deleted Journal (2003)

R. V. Subba Rao N. Parvathavarthini R.K. Dayal Akhilesh Arora Baldev Raj

Laser Raman Spectroscopy was employed to analyse the surfaces of rusted 9Cr-1Mo (modified) steel specimens that were pickled, pickled and passivated for different durations in a specific process optimization study. It wasobserved that the surface oxide scales were completely removed by the surface treatment of acid pickling for 600 s. The study demonstrated the ability of the technique as a potential monitoring tool in surface chemical processing of metallic components for both laboratory studies and in-service application.

Pickling

Surface-Enhanced Raman Spectroscopy

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Vibrational, magnetic, and dielectric behavior of La-substituted BiFeO3-PbTiO3

Journal of Applied Physics (2011)

K. K. Mishra A. T. Satya A. Bharathi V. Sivasubramanian V. R. K. Murthy

Phonons and magnetic and ferroelectric ordering in La-substituted (Bi1−xLax)0.5Pb0.5Fe0.5Ti0.5O3 for samples with 0.0 ≤ x ≤ 0.5 are investigated using Raman, magnetization, and polarization measurements as a function of temperature. The system is tetragonal for pure Bi0.5Pb0.5Fe0.5Ti0.5O3 with a large c/a ratio. The anisotropy is reduced when Bi is partially replaced by La (0 ≤ x ≤ 0.5), and it turns cubic for x ≥ 0.4. All the properties are found to change significantly with changes in the c/a ratio. Evidence of spin-glass-like magnetic ordering at low temperature is found in the case of x = 0.2. A mechanism for the systematic change of magnetic ordering temperature as a function of doping is also discussed. The phonon frequencies and line widths exhibit discontinuous changes across the tetragonal-cubic transition. Large polarization and forbidden Raman scattering in the cubic phase are explained on the basis of symmetry breaking due to the formation of a polar nano region, which leads to relaxor behavior.

Tetragonal crystal system

10.1063/1.3673240

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Citations (76)