Papers by Sourav Karmakar
2006 CSBE/SCGAB, Edmonton, AB Canada, July 16-19, 2006, 2006
For centuries, livestock manure has been utilized as an invaluable soil amendment and fertilizer ... more For centuries, livestock manure has been utilized as an invaluable soil amendment and fertilizer for crops. The continuing growth of the livestock industry in both developed and developing countries coupled with the implementation of more rigorous environmental regulations and protocols are increasing the importance of appropriate manure management systems and practices. A systematic approach to manure management must involve the identification and evaluation of criteria that are necessary for the design and selection of optimal manure management systems. The purpose of such a decision-making process is to analyze the system parameters and to recommend site specific and need-based parameters that result into an optimized manure management strategy. In this article, efforts have been made to identify decision-making criteria related to manure management practices. Decision-support tools for manure management systems have also been reviewed. Not surprisingly, environmental considerations have been found to top the list of the most important manure management criteria. Most of the existing decision-support tools are based on very specific aspects, such as nutrient management. The need to develop whole-farm decision-support tools that address all the major components of manure management systems, such as collection, storage, treatment, and land application, has been identified. Integrated decision support systems (DSS) should be an important part of management approach to identify the suitable system (liquid, semi-solid or solid manure management, composting, bio-energy production) of manure management. Papers presented before CSBE/SCGAB meetings are considered the property of the Society. In general, the Society reserves the right of first publication of such papers, in complete form; however, CSBE/SCGAB has no objections to publication, in condensed form, with credit to the Society and the author, in other publications prior to use in Society publications. Permission to publish a paper in full may be requested from the CSBE/SCGAB Secretary,
Biosystems Engineering, 2007
Soil pressure on tillage tools and its distribution over the tool surface are important factors f... more Soil pressure on tillage tools and its distribution over the tool surface are important factors for tool design with respect to tool wear. Soil stresses due to the tool motion are also very important in identifying the soil mechanical behaviour. The pressure distribution over the surface of a flat tillage tool and the soil stress pattern due to forward motion of the tool were investigated using computational fluid dynamics (CFD) simulations for high-speed tillage. The soil was characterized for its rheological behaviour as a Bingham material. Three-dimensional analyses were carried out by the control volume method with structured mesh using CFX4.4, a commercial CFD code. The results indicated that soil stress due to the tool motion was distributed as a set of pressure bulbs with maximum stress near the tool face that was decreasing along the longitudinal direction. Higher tool speed was accompanied by an increase in soil stress in front of the tool. Soil stress close to the tool tip increased from 220 to 1060 kPa, while the maximum pressure on the tool surface increased from 250 to 1240 kPa when the tool speed was increased from 1 to 10 m s À1. A critical speed range of 4-6 m s À1 was found after which increase in tool speed was accompanied by a decreasing trend of the longitudinal distance of soil failure zone from the tool face. Soil pressure on the tool surface and the resulting draught predicted by CFD modelling were very close when compared to published data based on finite element analysis on similar studies.
Physics Letters A, 2015
Conformation dependent circular current is investigated in a single handed helical geometry in pr... more Conformation dependent circular current is investigated in a single handed helical geometry in presence of magnetic flux φ within a Hartree-Fock mean field approach. The helical model is described by a set of non-planar rings connected by some vertical bonds where each ring is formed by introducing a non-zero hopping between the atoms a and b as shown in Fig. 1. By stretching and compressing the geometry, circular current can be regulated significantly and thus the system can be exploited to design current controlled device at the nano-scale level. The proximity effect between the atomic sites a and b is also discussed in detail which exhibits interesting results.
Physica E: Low-dimensional Systems and Nanostructures, 2014
We put forward a new approach based on Green's function formalism to evaluate precisely persisten... more We put forward a new approach based on Green's function formalism to evaluate precisely persistent charge and spin currents in an Aharonov-Bohm ring subjected to Rashba and Dresselhaus spin-orbit interactions. Unlike conventional methods our present scheme circumvents direct evaluation of eigenvalues and eigenstates of the system Hamiltonian to determine persistent currents which essentially reduces possible numerical errors, especially for larger rings. The interplay of Aharonov-Bohm flux and spin-orbit interactions in persistent charge and spin currents of quantum rings is analyzed in detail and our results lead to a possibility of estimating the strength of any one of the spin-orbit fields provided the other one is known. All these features are exactly invariant even in presence of impurities, and therefore, can be substantiated experimentally.
International Journal of Modern Physics B, 2009
We explore electron transport properties in molecular wires made of heterocyclic molecules (pyrro... more We explore electron transport properties in molecular wires made of heterocyclic molecules (pyrrole, furan and thiophene) by using the Green's function technique. Parametric calculations are given based on the tight-binding model to describe the electron transport in these wires. It is observed that the transport properties are significantly influenced by (a) the heteroatoms in the heterocyclic molecules and (b) the molecule-to-electrodes coupling strength. Conductance (g) shows sharp resonance peaks associated with the molecular energy levels in the limit of weak molecular coupling, while they get broadened in the strong molecular coupling limit. These resonances get shifted with the change of the heteroatoms in these heterocyclic molecules. All the essential features of the electron transfer through these molecular wires become much more clearly visible from the study of our current-voltage (I-V) characteristics, and they provide several key information in the study of molecul...
AIP Advances, 2014
Electric field induced localization properties of a tight-binding ladder network in presence of b... more Electric field induced localization properties of a tight-binding ladder network in presence of backbone sites are investigated. Based on Green's function formalism we numerically calculate two-terminal transport together with density of states for different arrangements of atomic sites in the ladder and its backbone. Our results lead to a possibility of getting multiple mobility edges which essentially plays a switching action between a completely opaque to fully or partly conducting region upon the variation of system Fermi energy, and thus, support in fabricating mesoscopic or DNA-based switching devices.
Physics Letters A, 2012
We investigate the phenomenon of integer quantum Hall effect in a square lattice, subjected to a ... more We investigate the phenomenon of integer quantum Hall effect in a square lattice, subjected to a perpendicular magnetic field, through Landauer-Büttiker formalism within the tight-binding framework. The oscillating nature of longitudinal resistance and near complete suppression of momentum relaxation processes are examined by studying the flow of charge current using Landauer-Keldysh prescription. Our analysis for the lattice model corroborates the finding obtained in the continuum model and provides a simple physical understanding.
Solid State Communications, 2005
To understand the role of electron correlation and disorder on persistent currents in isolated 1D... more To understand the role of electron correlation and disorder on persistent currents in isolated 1D rings threaded by magnetic flux φ, we study the behavior of persistent currents in aperiodic and ordered binary alloy rings. These systems may be regarded as disordered systems with well-defined long-range order so that we do not have to perform any configuration averaging of the physical quantities. We see that in the absence of interaction, disorder suppresses persistent currents by orders of magnitude and also removes its discontinuity as a function of φ. As we introduce electron correlation, we get enhancement of the currents in certain disordered rings. Quite interestingly we observe that in some cases, electron correlation produces kink-like structures in the persistent current as a function of φ. This may be considered as anomalous Aharonov-Bohm oscillations of the persistent current and recent experimental observations support such oscillations. We find that the persistent current converges with the size of the rings.
Physics Letters A, 2010
We propose that a magnetic quantum wire composed of magnetic and non-magnetic atomic sites can be... more We propose that a magnetic quantum wire composed of magnetic and non-magnetic atomic sites can be used as a spin filter for a wide range of applied bias voltage. We adopt a simple tightbinding Hamiltonian to describe the model where the quantum wire is attached to two semi-infinite one-dimensional non-magnetic electrodes. Based on single particle Green's function formalism all the calculations are performed numerically which describe two-terminal conductance and current through the wire. Our exact results may be helpful in fabricating mesoscopic or nano-scale spin filter.
Physics Letters A, 2012
Magneto-transport properties are investigated in a binary alloy ring subjected to an Aharonov-Boh... more Magneto-transport properties are investigated in a binary alloy ring subjected to an Aharonov-Bohm (AB) flux φ within a single-band non-interacting tight-binding framework. In the first part, we expose analytically the behavior of persistent current in an isolated ordere binary alloy ring as functions of electron concentration Ne and AB flux φ. While, in the second part of the article, we discuss electron transport properties through a binary alloy ring attached to two semi-infinite one-dimensional metallic electrodes. The effect of impurities is also analyzed. From our study we propose that under suitable choices of the parameter values the system can act as a p-type or an n-type semiconductor.
Organic Electronics, 2010
We do parametric calculations to elucidate multi-terminal electron transport properties through a... more We do parametric calculations to elucidate multi-terminal electron transport properties through a molecular system where a single phenalenyl molecule is attached to semi-infinite one-dimensional metallic leads. A formalism based on the Green's function technique is used for the calculations while the model is described by tight-binding Hamiltonian. We explore the transport properties in terms of conductance, reflection probability as well as current-voltage characteristic. The most significant feature we articulate is that all these characteristics are very sensitive to the locations where the leads are connected and also the molecule-to-lead coupling strengths. The presence of other leads also has a remarkable effect on these transport properties. We study these phenomena for two-, three-and four-terminal molecular systems. Our numerical study may be utilized in designing tailor-made molecular electronic devices.
Journal of Physics: Condensed Matter, 2008
We have studied the ground state of the one dimensional Hubbard superlattice structures with diff... more We have studied the ground state of the one dimensional Hubbard superlattice structures with different unit cell sizes in the presence of electric field. Self consistent Hartree-Fock approximation calculation is done in the weak to intermediate interaction regime. Studying the charge gap at the Fermi level and the charge density structure factor, we get an idea how the charge modulation on the superlattice is governed by the competition between the electronic correlation and the external electric field.
Journal of Computational and Theoretical Nanoscience, 2011
We explore spin dependent transport through a magnetic quantum wire which is attached to two non-... more We explore spin dependent transport through a magnetic quantum wire which is attached to two non-magnetic metallic electrodes. We adopt a simple tight-binding Hamiltonian to describe the model where the quantum wire is attached to two semi-infinite one-dimensional non-magnetic electrodes. Based on single particle Green's function formalism all the calculations are performed numerically which describe two-terminal conductance and current-voltage characteristics through the wire. Quite interestingly we see that, beyond a critical system size probability of spin flipping enhances significantly that can be used to design a spin flip device. Our numerical study may be helpful in fabricating mesoscopic or nano-scale spin devices.
Journal of Applied Physics, 2012
Using four-terminal Landauer-Büttiker formalism and Green’s function technique, in this present p... more Using four-terminal Landauer-Büttiker formalism and Green’s function technique, in this present paper, we calculate numerically spin Hall conductance (SHC) and longitudinal conductance of a finite size kagome lattice with Rashba spin-orbit (SO) interaction both in the presence and absence of external magnetic flux in clean limit. In the absence of magnetic flux, we observe that depending on the Fermi surface topology of the system SHC changes its sign at certain values of Fermi energy. Unlike the infinite system (where SHC is a universal constant ±e8π), here SHC depends on the external parameters like SO coupling strength, Fermi energy, etc. We show that in the presence of any arbitrary magnetic flux, periodicity of the system is lost and the features of SHC tend to get reduced because of elastic scattering. But again at some typical values of flux (ϕ=12, 14, 34…, etc.) the system retains its periodicity depending on its size and the features of spin Hall effect (SHE) reappears. Our...
EPL (Europhysics Letters), 2011
Electronic transport in a one-dimensional mesoscopic ring threaded by a magnetic flux is studied ... more Electronic transport in a one-dimensional mesoscopic ring threaded by a magnetic flux is studied in presence of Rashba and Dresselhaus spin-orbit interactions. A completely analytical technique within a tight-binding formalism unveils the spin-split bands in presence of the spin-orbit interactions and leads to a method of determining the strength of the Dresselhaus interaction. In addition to this, the persistent currents for ordered and disordered rings have been investigated numerically. It is observed that, the presence of the spin-orbit interaction, in general, leads to an enhanced amplitude of the persistent current. Numerical results corroborate the respective analytical findings.
The European Physical Journal B, 2012
Magnetic response of interacting electrons in a zigzag carbon nanotube threaded by a magnetic flu... more Magnetic response of interacting electrons in a zigzag carbon nanotube threaded by a magnetic flux is investigated within a Hartree-Fock mean field approach. Following the description of energy spectra for both non-interacting and interacting cases we analyze the behavior of persistent current in individual branches of a nanotube. Our present investigation leads to a possibility of getting a filling-dependent metal-insulator transition in a zigzag carbon nanotube.
The European Physical Journal B, 2012
We investigate magneto-transport properties of a θ shaped three-arm mesoscopic ring where the upp... more We investigate magneto-transport properties of a θ shaped three-arm mesoscopic ring where the upper and lower sub-rings are threaded by Aharonov-Bohm fluxes φ1 and φ2, respectively, within a non-interacting electron picture. A discrete lattice model is used to describe the quantum network in which two outer arms are subjected to binary alloy lattices while the middle arm contains identical atomic sites. It is observed that the presence of the middle arm provides localized states within the band of extended regions and lead to the possibility of switching action from a high conducting state to a low conducting one and vice versa. This behavior is justified by studying persistent current in the network. Both the total current and individual currents in three separate branches are computed by using second-quantized formalism and our idea can be utilized to study magnetic response in any complicated quantum network. The nature of localized eigenstates are also investigated from probability amplitudes at different sites of the quantum device.
The European Physical Journal B, 2011
We examine spin dependent transport in a quantum interferometer composed of magnetic atomic sites... more We examine spin dependent transport in a quantum interferometer composed of magnetic atomic sites based on transfer matrix formalism. The interferometer, threaded by a magnetic flux φ, is symmetrically attached to two semi-infinite one-dimensional (1D) non-magnetic electrodes, namely, source and drain. A simple tight-binding model is used to describe the bridge system, and, here we address numerically the conductance-energy and current-voltage characteristics as functions of the interferometer-to-electrode coupling strength, magnetic flux and the orientation of local the magnetic moments associated with each atomic site. Quite interestingly it is observed that, for φ = φ0/2 (φ0 = ch/e, the elementary flux-quantum) a logical XOR gate like response is observed, depending on the orientation of the local magnetic moments associated with the magnetic atoms in the upper and lower arms of the interferometer, and it can be changed by an externally applied gate magnetic field. This aspect may be utilized in designing a spin based electronic logic gate.
The European Physical Journal B, 2010
We have presented the role of the Coulomb interaction (U) and the magnetic field (B) on the groun... more We have presented the role of the Coulomb interaction (U) and the magnetic field (B) on the ground state properties of the quasi-one dimensional graphite ribbon structures at half-filling. Mean field Hartree-Fock Approximation is used to study the systems. To understand the boundary effects in graphite structures, we have compared the results of these systems with those of the square lattice ribbon structures. Studying the density of states, the Drude weight and the charge gap, we have drawn the U − B phase diagrams for the zigzag and the armchair graphite ribbons.
Physics Letters A, 2004
We show exactly that small Hubbard rings exhibit unusual kink-like structures giving anomalous os... more We show exactly that small Hubbard rings exhibit unusual kink-like structures giving anomalous oscillations in persistent current. Singular behavior of persistent current disappears in some cases. In half-filled systems mobility gradually drops to zero with interaction, while it converges to some finite value in nonhalf-filled cases.
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Papers by Sourav Karmakar