naveen kumar - Academia.edu (original) (raw)
Papers by naveen kumar
Journal of Earth System Science, 2009
Analytical solutions are obtained for one-dimensional advection-diffusion equation with variable ... more Analytical solutions are obtained for one-dimensional advection-diffusion equation with variable coefficients in a longitudinal finite initially solute free domain, for two dispersion problems. In the first one, temporally dependent solute dispersion along uniform flow in homogeneous domain is studied. In the second problem the velocity is considered spatially dependent due to the inhomogeneity of the domain and the dispersion is considered proportional to the square of the velocity. The velocity is linearly interpolated to represent small increase in it along the finite domain. This analytical solution is compared with the numerical solution in case the dispersion is proportional to the same linearly interpolated velocity. The input condition is considered continuous of uniform and of increasing nature both. The analytical solutions are obtained by using Laplace transformation technique. In that process new independent space and time variables have been introduced. The effects of the dependency of dispersion with time and the inhomogeneity of the domain on the solute transport are studied separately with the help of graphs. Aris moment method, perturbation approach, method using Green's function, superposition method have also been used to get the analytical
Langmuir : the ACS journal of surfaces and colloids, Jan 30, 2013
We use contact angle goniometry, imaging ellipsometry, and atomic force microscopy to study the s... more We use contact angle goniometry, imaging ellipsometry, and atomic force microscopy to study the stability and wettability of Langmuir−Blodgett (LB) monolayers of stearic acid on silica substrates, upon drying and exposure to aqueous solutions of varying salinity. The influences of Ca 2+ and Na + ions are compared by varying their concentrations, both in the subphase before the LB transfer, and in the droplets to which the dried LB layers are exposed. Ca 2+ ions in the subphase are found to enhance the stability, leading to contact angles up to 100°, as compared to less than 5°for Na + . Consistent with the macroscopic wettability, AFM images show almost intact films with few holes exposing bare substrate when prepared in the presence of Ca 2+ , while subphases containing Na + result in large areas of bare substrate after exposure to aqueous drops. The observations on varying the composition of the droplets corroborate the stabilizing effect of Ca 2+ . We attribute these findings to the cation-bridging ability of Ca 2+ ions, which can bind the negatively charged stearate groups to the negatively charged substrates. We discuss the relevance of our findings in the context of enhanced oil recovery.
This work is dedicated to the study of radiation reaction signatures in the framework of classica... more This work is dedicated to the study of radiation reaction signatures in the framework of classical and quantum electrodynamics. Since there has been no distinct experimental validation of radiation reaction and its underlying equations so far and its impact is expected to be substantial for the construction of new experimental devices, e.g., quantum x-free electron lasers, a profound understanding of radiation reaction effects is of special interest. Here, we describe how the inclusion of quantum radiation reaction effects changes the dynamics of ultra-relativistic electron beams colliding with intense laser pulses significantly. Thereafter, the angular distribution of emitted radiation is demonstrated to be strongly altered in the quantum framework, if in addition to single photon emission also higher order photon emissions are considered. Furthermore, stimulated Raman scattering of an ultra-intense laser pulse in plasmas is examined and forward Raman scattering is found to be significantly increased by the inclusion of radiation reaction effects in the classical regime. The numerical simulations in this work show the feasibility of an experimental verification of the predicted effects with presently available lasers and electron accelerators.
The dynamics of intense laser pulses in plasmas are investigated both theoretically and numerical... more The dynamics of intense laser pulses in plasmas are investigated both theoretically and numerically. The linear growth and nonlinear saturation of relativistic stimulated Raman scattering of plasmons are investigated by means of a nonlinear dispersion relation and via direct Vlasov simulations. We observe acceleration of electrons up to ultra-relativistic energies by a positive electrostatic potential that is created by intense
Energy flux transport of a finite high current relativistic electron beam with the Gaussian profi... more Energy flux transport of a finite high current relativistic electron beam with the Gaussian profile in both the transverse and axial directions in a dense collisional background plasma is studied by means of three-dimensional particle-in-cell simulations. Simulation results reveal the development of a needle-like super-filament formation in both homogeneous as well as inhomogeneous collisional background plasmas. However, in the case of an inhomogeneous background plasma, the beam suffers severe filamentation due to the lower plasma density encountered in the early stage, and only the head of the super-filament survives and travels further inside the plasma. This may not be desirable for the fast ignition fusion scheme.
The influence of surface plasma waves on high-order harmonic generation from the interaction of i... more The influence of surface plasma waves on high-order harmonic generation from the interaction of intense lasers with overdense plasma is analyzed. It is shown that the surface waves lead to the emission of harmonics away from the optical axis, whereas the high-order on-axis harmonics are lowered in intensity. Our simulation results indicate that surface plasma wave generation plays a crucial role in surface high-order harmonic generation experiments. Furthermore, a novel surface plasma wave generation process different from the well-known two-surface wave decay is observed in the highly relativistic regime.
ABSTRACT It’s shown that the imposition of sub-laser wavelength relief structures on the surface ... more ABSTRACT It’s shown that the imposition of sub-laser wavelength relief structures on the surface of mass-limited-targets results into several folds higher short-pulse laser absorption, and consequently the efficient generation of fast ions. The optimum relief parameters for enhanced short-pulse laser absorption and higher ion acceleration are estimated numerically by particle-in-cell simulations and then corroborated by analytical scalings. The stability of the pre-imposed surface modulation during the laser pulse foil interaction is also examined.
We study transverse and longitudinal electron heating effects on the target stability and the ion... more We study transverse and longitudinal electron heating effects on the target stability and the ion spectra in the radiation pressure dominated regime of ion acceleration by means of multi dimensional particle-in-cell (PIC) simulations. Efficient ion acceleration occurs when the longitudinal electron temperature is kept as low as possible. However, tailoring of the transverse electron temperature is required in view of suppressing the transverse instability, which can keep the target structure intact for longer duration during the acceleration stage. We suggest using the surface erosion of the target to increase the transverse temperature, which improves both the final peak energy and the spectral quality of the ions in comparison with a normal flat target. PACS numbers: 41.75.Jv, 52.38.Kd
A systematic study on the Weibel instability induced filamentation of a relativistic electron bea... more A systematic study on the Weibel instability induced filamentation of a relativistic electron beam is made by including the effects of collisions and temperature. The stabilization and de-stabilization of the beam filamentation due to beam temperature and plasma collisions, respectively, is explored through an analytical model and PIC simulations. The de-stabilization of the beam filamentation is attributed to the collision driven negative energy wave generation in the beam plasma system. PACS. 52.57.-z Laser inertial confinement -52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams -52.65.Rr Particle-in-cell method
MIMO-OFDM system has been currently recognized as one of the most competitive technology for 4G m... more MIMO-OFDM system has been currently recognized as one of the most competitive technology for 4G mobile wireless systems. Techniques such as use of multiple antennas can be utilized in order to obtain a multiplexing gain, a diversity gain, or an antenna gain, thus enhancing the throughput (in terms of capacity) or bit rate, the error performance, or the signal-to-noise ratio of wireless systems, respectively. In this paper various receive combing techniques such as MRC, EGC and SC for enhancement of diversity have been discussed. Receive combining techniques with LDPC codes enhance the performance of overall system by providing coding gain. Overview of Alamouti’s STBC along with maximum likelihood (ML) decoding algorithms also discussed.
Journal of Case Reports, 2014
Indian heart journal
Objective: The objective of this study was to determine the clinical and angiographic profile of ... more Objective: The objective of this study was to determine the clinical and angiographic profile of patients with extremely high coronary artery calcium scores (CACS; z1000) by electron beam computed tomography (EBCT). Methods: All patients at Rush University Medical Center who had a calcium score z1000 and a coronary angiogram performed from 1997 to 2002 were identified using a prospectively collected database. The baseline demographics, symptom status, and degree of coronary stenosis by angiography and subsequent rate of coronary intervention were compared with that of patients with calcium scores b1000. Results: The clinical and angiographic profile of patients with severe coronary calcification, detected by EBCT, revealed that patients with scores z1000 had a significantly higher prevalence of coronary stenosis z50% compared with patients with scores b1000 (97% vs. 57%, P b.001). The group with CACS z1000 was more likely to be male (90% vs. 75%, P = .027) and was older (64F8 vs. 59F10, P = .001) compared with the group with less severe calcification. Although there was a significantly higher rate of luminal stenosis detected by coronary angiography in the cohort with CACS z1000, there was no difference in subsequent percutaneous coronary intervention (PCI) and utilization of intracoronary stents between the two groups. Conclusions: A markedly elevated coronary calcium score ( z1000) is correlated with increasing age and is associated with an increased likelihood of coronary stenosis z50%. However, the decision to perform coronary angiography in patients with severe coronary calcification should not be based solely on these findings, but should remain primarily dependent on the degree of ischemia detected by clinical and functional assessment. D 2004 Elsevier Inc. All rights reserved.
The Journal of heart valve disease, 2013
Infective endocarditis (IE) is a worldwide problem, and at least one-third of cases are culture-n... more Infective endocarditis (IE) is a worldwide problem, and at least one-third of cases are culture-negative despite the use of appropriate laboratory techniques. A broad-range polymerase chain reaction (PCR) amplification was performed of the 16S rRNA gene, followed by single-strand sequencing for 26 surgically removed heart valves from patients with culture-negative endocarditis who had undergone valve repair or replacement. Two of the 26 patients were PCR-positive, and sequencing of the amplicon identified the etiological agent. Gram-stained smears of the heart valves were positive in both cases. Three of the remaining 24 cases which were negative by PCR also showed the presence of micro-organisms in Gram-stained smears. The study results emphasize that, in suspected IE cases when there is no growth in culture, a combination of microscopy and 16S rRNA sequencing can be used to identify the pathogen in excised valvular tissue.
... Communication Engineering Department for their encouragement and cooperation. I would also li... more ... Communication Engineering Department for their encouragement and cooperation. I would also like to thank Ms. Sakshi Grover Bajaj (Assistant Professor), Mohit Bhasin , Anil Rawat and Simran Kaur who were always there at the need of the hour and provided me all ...
Journal of Earth System Science, 2009
Analytical solutions are obtained for one-dimensional advection-diffusion equation with variable ... more Analytical solutions are obtained for one-dimensional advection-diffusion equation with variable coefficients in a longitudinal finite initially solute free domain, for two dispersion problems. In the first one, temporally dependent solute dispersion along uniform flow in homogeneous domain is studied. In the second problem the velocity is considered spatially dependent due to the inhomogeneity of the domain and the dispersion is considered proportional to the square of the velocity. The velocity is linearly interpolated to represent small increase in it along the finite domain. This analytical solution is compared with the numerical solution in case the dispersion is proportional to the same linearly interpolated velocity. The input condition is considered continuous of uniform and of increasing nature both. The analytical solutions are obtained by using Laplace transformation technique. In that process new independent space and time variables have been introduced. The effects of the dependency of dispersion with time and the inhomogeneity of the domain on the solute transport are studied separately with the help of graphs. Aris moment method, perturbation approach, method using Green's function, superposition method have also been used to get the analytical
Langmuir : the ACS journal of surfaces and colloids, Jan 30, 2013
We use contact angle goniometry, imaging ellipsometry, and atomic force microscopy to study the s... more We use contact angle goniometry, imaging ellipsometry, and atomic force microscopy to study the stability and wettability of Langmuir−Blodgett (LB) monolayers of stearic acid on silica substrates, upon drying and exposure to aqueous solutions of varying salinity. The influences of Ca 2+ and Na + ions are compared by varying their concentrations, both in the subphase before the LB transfer, and in the droplets to which the dried LB layers are exposed. Ca 2+ ions in the subphase are found to enhance the stability, leading to contact angles up to 100°, as compared to less than 5°for Na + . Consistent with the macroscopic wettability, AFM images show almost intact films with few holes exposing bare substrate when prepared in the presence of Ca 2+ , while subphases containing Na + result in large areas of bare substrate after exposure to aqueous drops. The observations on varying the composition of the droplets corroborate the stabilizing effect of Ca 2+ . We attribute these findings to the cation-bridging ability of Ca 2+ ions, which can bind the negatively charged stearate groups to the negatively charged substrates. We discuss the relevance of our findings in the context of enhanced oil recovery.
This work is dedicated to the study of radiation reaction signatures in the framework of classica... more This work is dedicated to the study of radiation reaction signatures in the framework of classical and quantum electrodynamics. Since there has been no distinct experimental validation of radiation reaction and its underlying equations so far and its impact is expected to be substantial for the construction of new experimental devices, e.g., quantum x-free electron lasers, a profound understanding of radiation reaction effects is of special interest. Here, we describe how the inclusion of quantum radiation reaction effects changes the dynamics of ultra-relativistic electron beams colliding with intense laser pulses significantly. Thereafter, the angular distribution of emitted radiation is demonstrated to be strongly altered in the quantum framework, if in addition to single photon emission also higher order photon emissions are considered. Furthermore, stimulated Raman scattering of an ultra-intense laser pulse in plasmas is examined and forward Raman scattering is found to be significantly increased by the inclusion of radiation reaction effects in the classical regime. The numerical simulations in this work show the feasibility of an experimental verification of the predicted effects with presently available lasers and electron accelerators.
The dynamics of intense laser pulses in plasmas are investigated both theoretically and numerical... more The dynamics of intense laser pulses in plasmas are investigated both theoretically and numerically. The linear growth and nonlinear saturation of relativistic stimulated Raman scattering of plasmons are investigated by means of a nonlinear dispersion relation and via direct Vlasov simulations. We observe acceleration of electrons up to ultra-relativistic energies by a positive electrostatic potential that is created by intense
Energy flux transport of a finite high current relativistic electron beam with the Gaussian profi... more Energy flux transport of a finite high current relativistic electron beam with the Gaussian profile in both the transverse and axial directions in a dense collisional background plasma is studied by means of three-dimensional particle-in-cell simulations. Simulation results reveal the development of a needle-like super-filament formation in both homogeneous as well as inhomogeneous collisional background plasmas. However, in the case of an inhomogeneous background plasma, the beam suffers severe filamentation due to the lower plasma density encountered in the early stage, and only the head of the super-filament survives and travels further inside the plasma. This may not be desirable for the fast ignition fusion scheme.
The influence of surface plasma waves on high-order harmonic generation from the interaction of i... more The influence of surface plasma waves on high-order harmonic generation from the interaction of intense lasers with overdense plasma is analyzed. It is shown that the surface waves lead to the emission of harmonics away from the optical axis, whereas the high-order on-axis harmonics are lowered in intensity. Our simulation results indicate that surface plasma wave generation plays a crucial role in surface high-order harmonic generation experiments. Furthermore, a novel surface plasma wave generation process different from the well-known two-surface wave decay is observed in the highly relativistic regime.
ABSTRACT It’s shown that the imposition of sub-laser wavelength relief structures on the surface ... more ABSTRACT It’s shown that the imposition of sub-laser wavelength relief structures on the surface of mass-limited-targets results into several folds higher short-pulse laser absorption, and consequently the efficient generation of fast ions. The optimum relief parameters for enhanced short-pulse laser absorption and higher ion acceleration are estimated numerically by particle-in-cell simulations and then corroborated by analytical scalings. The stability of the pre-imposed surface modulation during the laser pulse foil interaction is also examined.
We study transverse and longitudinal electron heating effects on the target stability and the ion... more We study transverse and longitudinal electron heating effects on the target stability and the ion spectra in the radiation pressure dominated regime of ion acceleration by means of multi dimensional particle-in-cell (PIC) simulations. Efficient ion acceleration occurs when the longitudinal electron temperature is kept as low as possible. However, tailoring of the transverse electron temperature is required in view of suppressing the transverse instability, which can keep the target structure intact for longer duration during the acceleration stage. We suggest using the surface erosion of the target to increase the transverse temperature, which improves both the final peak energy and the spectral quality of the ions in comparison with a normal flat target. PACS numbers: 41.75.Jv, 52.38.Kd
A systematic study on the Weibel instability induced filamentation of a relativistic electron bea... more A systematic study on the Weibel instability induced filamentation of a relativistic electron beam is made by including the effects of collisions and temperature. The stabilization and de-stabilization of the beam filamentation due to beam temperature and plasma collisions, respectively, is explored through an analytical model and PIC simulations. The de-stabilization of the beam filamentation is attributed to the collision driven negative energy wave generation in the beam plasma system. PACS. 52.57.-z Laser inertial confinement -52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams -52.65.Rr Particle-in-cell method
MIMO-OFDM system has been currently recognized as one of the most competitive technology for 4G m... more MIMO-OFDM system has been currently recognized as one of the most competitive technology for 4G mobile wireless systems. Techniques such as use of multiple antennas can be utilized in order to obtain a multiplexing gain, a diversity gain, or an antenna gain, thus enhancing the throughput (in terms of capacity) or bit rate, the error performance, or the signal-to-noise ratio of wireless systems, respectively. In this paper various receive combing techniques such as MRC, EGC and SC for enhancement of diversity have been discussed. Receive combining techniques with LDPC codes enhance the performance of overall system by providing coding gain. Overview of Alamouti’s STBC along with maximum likelihood (ML) decoding algorithms also discussed.
Journal of Case Reports, 2014
Indian heart journal
Objective: The objective of this study was to determine the clinical and angiographic profile of ... more Objective: The objective of this study was to determine the clinical and angiographic profile of patients with extremely high coronary artery calcium scores (CACS; z1000) by electron beam computed tomography (EBCT). Methods: All patients at Rush University Medical Center who had a calcium score z1000 and a coronary angiogram performed from 1997 to 2002 were identified using a prospectively collected database. The baseline demographics, symptom status, and degree of coronary stenosis by angiography and subsequent rate of coronary intervention were compared with that of patients with calcium scores b1000. Results: The clinical and angiographic profile of patients with severe coronary calcification, detected by EBCT, revealed that patients with scores z1000 had a significantly higher prevalence of coronary stenosis z50% compared with patients with scores b1000 (97% vs. 57%, P b.001). The group with CACS z1000 was more likely to be male (90% vs. 75%, P = .027) and was older (64F8 vs. 59F10, P = .001) compared with the group with less severe calcification. Although there was a significantly higher rate of luminal stenosis detected by coronary angiography in the cohort with CACS z1000, there was no difference in subsequent percutaneous coronary intervention (PCI) and utilization of intracoronary stents between the two groups. Conclusions: A markedly elevated coronary calcium score ( z1000) is correlated with increasing age and is associated with an increased likelihood of coronary stenosis z50%. However, the decision to perform coronary angiography in patients with severe coronary calcification should not be based solely on these findings, but should remain primarily dependent on the degree of ischemia detected by clinical and functional assessment. D 2004 Elsevier Inc. All rights reserved.
The Journal of heart valve disease, 2013
Infective endocarditis (IE) is a worldwide problem, and at least one-third of cases are culture-n... more Infective endocarditis (IE) is a worldwide problem, and at least one-third of cases are culture-negative despite the use of appropriate laboratory techniques. A broad-range polymerase chain reaction (PCR) amplification was performed of the 16S rRNA gene, followed by single-strand sequencing for 26 surgically removed heart valves from patients with culture-negative endocarditis who had undergone valve repair or replacement. Two of the 26 patients were PCR-positive, and sequencing of the amplicon identified the etiological agent. Gram-stained smears of the heart valves were positive in both cases. Three of the remaining 24 cases which were negative by PCR also showed the presence of micro-organisms in Gram-stained smears. The study results emphasize that, in suspected IE cases when there is no growth in culture, a combination of microscopy and 16S rRNA sequencing can be used to identify the pathogen in excised valvular tissue.
... Communication Engineering Department for their encouragement and cooperation. I would also li... more ... Communication Engineering Department for their encouragement and cooperation. I would also like to thank Ms. Sakshi Grover Bajaj (Assistant Professor), Mohit Bhasin , Anil Rawat and Simran Kaur who were always there at the need of the hour and provided me all ...