Singh Simutech Pvt. Ltd.

Bharatpur, India

Singh Simutech Pvt. Ltd.

Bharatpur, India
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Singh K.P.,Singh Simutech Pvt. Ltd | Singh K.P.,University of Rochester | Guo C.,University of Rochester
Physical Chemistry Chemical Physics | Year: 2017

The nanochannel diameter and surface charge density have a significant impact on current-voltage characteristics in a nanofluidic transistor. We have simulated the effect of the channel diameter and surface charge density on current-voltage characteristics of a fluidic nanochannel with positive surface charge on its walls and a gate electrode on its surface. Anion depletion/enrichment leads to a decrease/increase in ion current with gate potential. The ion current tends to increase linearly with gate potential for narrow channels at high surface charge densities and narrow channels are more effective to control the ion current at high surface charge densities. The current-voltage characteristics are highly nonlinear for wide channels at low surface charge densities and they show different regions of current change with gate potential. The ion current decreases with gate potential after attaining a peak value for wide channels at low values of surface charge densities. At low surface charge densities, the ion current can be controlled by a narrow range of gate potentials for wide channels. The current change with source drain voltage shows ohmic, limiting and overlimiting regions. © the Owner Societies 2017.


Malik A.K.,Ccs University | Singh K.P.,Singh Simutech Pvt. Ltd. | Sajal V.,Jaypee Institute of Information Technology
Physics of Plasmas | Year: 2014

A mechanism of efficient and highly focused terahertz (THz) radiation generation by photo-mixing of top-hat like lasers with frequencies ω 1, ω 2 and wave numbers k 1, k 2 in pre-formed rippled density (corrugated) plasma is proposed. In this mechanism, intensity variation of lasers offers nonlinear ponderomotive force at frequency ω ′ = ω 1 - ω 2 and wave number k ′ = k 1 - k 2 which couples with density ripples in the plasma and leads to a strong nonlinear oscillatory current that resonantly excites highly focused and intense THz radiation at frequency ω U H = √(ωp2 + ωc2) (where ω c is electron cyclotron frequency). The efficiency of emitted THz radiation of the order of 15% is obtained under optimum conditions. It is observed that focus and intensity of emitted radiation can be controlled by selecting a proper profile index of the lasers, ripple parameters, and tuning of external magnetic field. © 2014 AIP Publishing LLC.


Singha K.P.,Singh Simutech Pvt. Ltd. | Kumar M.,Singh Simutech Pvt. Ltd.
Biomicrofluidics | Year: 2010

We have studied the effect of flap parameters on fluid rectification in a microfluidic diode. We use Navier-Stokes equations and arbitrary Lagrangian-Eulerian formulation to obtain dynamics of fluid flow and motion of the flap. The flap opens during forward flow and seals against a stopper during reverse flow. This allows flow in the forward direction and prevents it in the reverse direction. The rectifier is fluidic analog to a semiconductor diode in function because it rectifies fluid flow. Velocity-pressure (V-P) curves analog to the current-voltage (I-V) curves of the electronic diode has been obtained. The effect of the flap parameters, such as length, thickness, and Young's modulus has been found out. The transient response of the flap and fluid flow under oscillating pressure driven flow has also been obtained. © 2010 American Institute of Physics.


Singh K.P.,University of Sydney | Singh K.P.,Singh Simutech Pvt. Ltd. | Kumar M.,Singh Simutech Pvt. Ltd.
Journal of Physical Chemistry C | Year: 2011

We have simulated ion current rectification (ICR) in a bipolar nanochannel fluidic diode for different nanochannel diameters, electrolyte concentrations, and surface charge densities. The ICR decreases with diameter of the fluidic nanochannel due to decrease in unipolar character of the electrolyte. The ICR decreases with electrolyte concentration due to surface charge screening by counterions. The ICR increases with channel diameter for a given ratio of channel diameter to Debye length. Scaling of forward and reverse current densities with electrolyte concentration has been determined using curve fitting for different values of surface charge densities and channel diameters. The ICR can be increased by increasing surface charge density to enhance unipolar character of the electrolyte. The fluid velocity close to the nanochannel walls is driven by body force and along the center by the fluid pressure, which gives rise to a curly fluid flow. © 2011 American Chemical Society.


Pal Singh K.,University of Sydney | Pal Singh K.,Singh Simutech Pvt. Ltd. | Kumari K.,Singh Simutech Pvt. Ltd. | Kumari K.,Indian Institute of Technology Delhi | Kumar M.,Singh Simutech Pvt. Ltd.
Applied Physics Letters | Year: 2011

We have simulated bipolar nanochannel based fluidic diode for different values of junction sharpness. We can obtain significant ion current rectification even for a smooth junction between oppositely charged zones. The rectification increases with junction sharpness due to increase in unipolar character of electrolyte but a sharp junction is not a necessary condition for rectification. The ion current rectification increases with surface charge density due to increase in unipolar character of electrolyte and decrease in reverse ion current. The fluid enters (exits) the nanochannel through the centre from (to) the opposite directions for reverse (forward) bias due to fluid pressure. © 2011 American Institute of Physics.


Singh K.P.,University of Sydney | Singh K.P.,Singh Simutech Pvt. Ltd. | Kumar M.,Singh Simutech Pvt. Ltd.
Physical Review Special Topics - Accelerators and Beams | Year: 2011

The acceleration of electrons by a radially polarized intense laser pulse has been studied. The axial electric field of the laser is responsible for electron acceleration. The axial electric field increases with decreasing laser spot size; however, the laser pulse gets defocused sooner for smaller values and the electrons do not experience high electric field for long, reducing the energy they can reach. The electron remains confined in the electric field of the laser for longer and the electron energy peaks for the normalized laser spot size nearly equal to the normalized laser intensity parameter. Electron energy peaks for initial laser phase φ0=π due to accelerating laser phase and decreases with transverse initial position of the electrons. The energy and angle of the emittance spectrum of the electrons generated during ionization of krypton and argon at low densities have been obtained and a right choice of laser parameters has been suggested to obtain high energy quasimonoenergetic collimated electron beams. It has been found that argon is more suitable than krypton to obtain high energy electron beams due to higher ionization potential of inner shells for the former. © 2011 American Physical Society.


Pal Singh K.,University of Sydney | Pal Singh K.,Singh Simutech Pvt. Ltd. | Kumar M.,Singh Simutech Pvt. Ltd.
Journal of Applied Physics | Year: 2011

We have simulated bipolar nanopore fluidic diodes for different values of surface charge densities, electrolyte concentrations, and thickness of transition zone. Nanopore enrichment leads to increased nanopore conductivity with the surface charge density at low electrolyte concentrations. Potential drop across the nanopore and electric field inside the nanopore decreases. Forward current and ionic current rectification peaks for a specific value of surface charge density. Even though the electro-osmotic current component remains small as compared to other components, its non-inclusion in the modeling leads to serious errors in the solutions. Significant ion current rectification can be obtained even if transition zone between oppositely charged zones is not narrow. The effect of the surface charge is screened by counterions at higher electrolyte concentrations, which leads to reduced electrolyte polarization and a decrease in the ion current rectification. © 2011 American Institute of Physics.


Singh K.P.,Singh Simutech Pvt. Ltd.
Physical Chemistry Chemical Physics | Year: 2016

The ion current rectification has been obtained as a function of the location of a heterojunction in a bipolar conical nanopore fluidic diode for different parameters to determine the junction location for maximum ion current rectification using numerical simulations. Forward current peaks for a specific location of the junction and reverse current decreases with the junction location due to a change in ion enrichment/depletion in the pore. The optimum location of the heterojunction shifts towards the tip with base/tip diameter and surface charge density, and towards the base with the electrolyte concentration. The optimum location of the heterojunction has been approximated by an equation as a function of pore length, base/tip diameter, surface charge density and electrolyte concentration. The study is useful to design a rectifier with maximum ion current rectification for practical purposes. © 2016 the Owner Societies.


Singh K.P.,University of Sydney | Singh K.P.,Singh Simutech Pvt. Ltd. | Kumar M.,Singh Simutech Pvt. Ltd.
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2012

We have simulated the effect of gate length and dielectric thickness on ion and fluid transport in a fluidic nanochannel with negative surface charge on its walls. A short gate is unable to induce significant cation enrichment in the nanochannel and ion current is controlled mostly by cation depletion at positive gate potentials. The cation enrichment increases with increasing gate length and/or decreasing dielectric thickness due to higher changes induced in the surface charge density and zeta-potential. Thus, long gates and thin dielectric layers are more effective in controlling ion current. The model without Navier-Stokes equations is unable to correctly predict phenomena such as cation enrichment, increase in channel conductivity, and decreasing electric field. Body force and induced fluid velocity decrease slowly and then rapidly with gate potentials. The effectiveness of ion current control by a gate reduces with increasing surface charge density due to reduced fractional change in zeta-potential. © The Royal Society of Chemistry 2012.


Singh K.P.,Singh Simutech Pvt. Ltd.
Sensors and Actuators, B: Chemical | Year: 2016

Ion current rectification (ICR) in a fluidic unipolar nanopore consisting of a charged zone and one or two neutral zones has been investigated. The effect of length and location of surface charge on its walls on ion transport in a fluidic unipolar nanopore have been studied. The ICR can be reversed by keeping a neutral zone towards the tip instead of charged zone in a nanopore. A longer neutral zone towards the base of the nanopore enhances ICR and a longer charged zone towards the base enhances reverse rectification. The effect of asymmetry of the pore on ICR has also been analyzed by comparing results with nanochannel. © 2016 Elsevier B.V. All rights reserved.

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