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Hofmann T.,Helmholtz Center Berlin | Kumar P.,National Institute of Technology Delhi | Enderle M.,Laue Langevin Institute | Wallacher D.,Helmholtz Center Berlin
Physical Review Letters | Year: 2013

The structure of solid deuterium confined in 9 nm wide tubular silicon nanochannels has been studied by means of elastic neutron scattering techniques. As a result we report the formation of fcc D2 as the stable solid phase in confinement in contrast to the hcp bulk structure. Further, a preferred alignment of D2 nanocrystals with respect to the surrounding crystalline silicon matrix is discussed in terms of heteroepitaxial growth of solid D2 on crystalline pore walls. © 2013 American Physical Society. Source


Yoon P.H.,University of Maryland University College | Yoon P.H.,Kyung Hee University | Pandey V.S.,Kyung Hee University | Pandey V.S.,National Institute of Technology Delhi | Lee D.-H.,Kyung Hee University
Journal of Geophysical Research: Space Physics | Year: 2014

Motivated by satellite observation of large-amplitude whistler waves propagating in oblique directions with respect to the ambient magnetic field, a recent letter discusses the physics of large-amplitude whistler waves and relativistic electron acceleration. One of the conclusions of that letter is that oblique whistler waves will eventually undergo nonlinear steepening regardless of the amplitude. The present paper reexamines this claim and finds that the steepening associated with the density perturbation almost never occurs, unless whistler waves have sufficiently high amplitude and propagate sufficiently close to the resonance cone angle. Key Points Nonlinear steepening of oblique whistlers is studied Only high-amplitude whistlers or those near resonance cone undergo steepening Model sinusoidal oblique whistlers employed in the simulations are justifiable ©2014. American Geophysical Union. All Rights Reserved. Source


Sharma A.K.,National Institute of Technology Delhi
Sensing and Imaging | Year: 2014

Phase interrogation based surface plasmon resonance (SPR) biosensor is proposed for the determination of Hb concentration. Previous experimental results describing variation of refractive index of human blood with Hb concentration at different wavelengths are considered for design simulations. The biosensor design with silica substrate and gold layer is considered. The sensor’s performance is closely analyzed in terms of phase sensitivity and resolution. The influence of operating wavelength on biosensor’s performance for Hb measurement is critically investigated, which points to carry out the Hb measurement at a shorter wavelength as phase sensitivity and resolution increase significantly with decrease in wavelength. The results are explained in terms of suitable physical concepts such as radiation damping. Use of contamination-preventing biochemical layer ascertains the stability of measurement with the intended SPR biosensor probe. The simulation results also highlight that the resolution of Hb measurement achievable with the proposed biosensor is much higher compared with several existing methods. © 2015, Springer Science+Business Media New York. Source


Tripathi D.,National Institute of Technology Delhi | Anwar Beg O.,Sheffield Hallam University
Mathematical Biosciences | Year: 2013

Magnetic fields are increasingly being utilized in endoscopy and gastric transport control. In this regard, the present study investigates the influence of a transverse magnetic field in the transient peristaltic rheological transport. An electrically-conducting couple stress non-Newtonian model is employed to accurately simulate physiological fluids in peristaltic flow through a sinusoidally contracting channel of finite length. This model is designed for computing the intra-bolus oesophageal and intestinal pressures during the movement of food bolus in the digestive system under magneto-hydro-dynamic effects. Long wavelength and low Reynolds number approximations have been employed to reduce the governing equations from nonlinear to linear form, this being a valid approach for creeping flows which characterizes physiological dynamics. Analytical approximate solutions for axial velocity, transverse velocity, pressure gradient, local wall shear stress and volumetric flow rate are obtained for the non-dimensional conservation equations subject to appropriate boundary conditions. The effects of couple stress parameter and transverse magnetic field on the velocity profile, pressure distribution, local wall shear stress and the averaged flow rate are discussed with the aid of computational results. The comparative study of non-integral and integral number of waves propagating along the finite length channel is also presented. Magnetic field and non-Newtonian properties are found to strongly influence peristaltic transport. © 2013 Elsevier Inc. Source


Tripathi D.,National Institute of Technology Delhi | Pandey S.K.,Indian Institute of Technology BHU Varanasi | Beg O.A.,Gort Engovation Research Propulsion and Biomechanics
International Journal of Thermal Sciences | Year: 2013

The present paper describes a mathematical study on peristaltic flow of viscoelastic fluids (with the robust Jeffrey model) through a finite length channel under the influence of heat transfer. The study is motivated by the need to further elucidate the mechanisms inherent in swallowing of diverse food bolus types (bread, fruit jam and almost all edible semi-solids) through the oesophagus, by taking account of the viscous and elastic effects. The expressions for temperature field, axial velocity, transverse velocity, volume flow rate, pressure gradient, local wall shear stress, mechanical efficiency, stream function, and reflux limit are obtained, when the Reynolds number is small and the wavelength is large, by using appropriate analytical and numerical methods. The computational results are presented in graphical form. The influence of thermophysical (heat transfer), relaxation time and retardation time parameters on pressure distribution, local wall shear stress profiles, temperature profiles and velocity profiles are studied in detail. Furthermore we investigate the effects of these parameters on two inherent phenomena (reflux and trapping) characterizing peristaltic flow using streamline plots. The present study emphasizes an important observation, namely that pressure along the entire length of the channel reduces when the magnitude of relaxation time (retardation time is fixed) or Grashof number or indeed thermal conductivity increase, whereas pressure is enhanced by increasing the magnitude of retardation time (relaxation time is fixed). © 2013 Elsevier Masson SAS. All rights reserved. Source

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