Abhijit Das - Academia.edu (original) (raw)
Papers by Abhijit Das
Digital Holography and Three-Dimensional Imaging, 2011
A wavefront sensor is a device that measures the phase profile or wavefront of a beam. Wavefront ... more A wavefront sensor is a device that measures the phase profile or wavefront of a beam. Wavefront sensing is important in a number of areas such as, in computer and semi conductor industry to measure the flatness of surfaces; to analyze the quality of a laser beam; to test the smoothness of optical elements; in astronomy to measure the atmospheric turbulence and so on. One of the most popular wavefront sensors in such applications is the Shack-Hartmann wavefront sensor (SHWS) [1]. Here the beam under observation is incident on a two dimensional array of ...
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Communications and Control Engineering, 2014
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49th IEEE Conference on Decision and Control (CDC), 2010
Abstract This paper studies synchronization using reduced state information based on output infor... more Abstract This paper studies synchronization using reduced state information based on output information passed between neighbor nodes. The node states are estimated using cooperative dynamical observers at each node. It is shown how to design cooperative state variable state feedbacks and observers at each node that are dual to each other, in a sense that extends the classical system theory notion of duality to dynamical systems on graphs. It is shown that unbounded consensus regions that guarantee synchronization on arbitrary ...
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IEEE ICCA 2010, 2010
Abstract Traditional research on cooperative networked systems has focused on analysis of given p... more Abstract Traditional research on cooperative networked systems has focused on analysis of given protocols for simple linear systems, mainly the integrator or double integrator dynamics. Pinning control has been developed for nonlinear systems, generally using either a Jacobian linearization method or a Lipschitz assumption. Work has also progressed on nonlinear coupling protocols. In this paper we present a design method for adaptive controllers for distributed systems having non-identical unknown nonlinear dynamics, and ...
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Challenges and Paradigms in Applied Robust Control, 2011
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2008 IEEE International Conference on Control Applications, 2008
Abstract For a typical quadrotor model, one can identify the two well known inherent rotorcraft c... more Abstract For a typical quadrotor model, one can identify the two well known inherent rotorcraft characteristics; under-actuation and strong coupling in pitch-yaw-roll. To confront these problems and design a station-keeping tracking controller, dynamic inversion is used here. Typical applications of dynamic inversion require the selection of the output control variables to render the internal dynamics stable. This means that in many cases tracking can not be guaranteed for the actual desired outputs. Instead, here, the internal dynamics of ...
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Advanced Microscopy Techniques III, 2013
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Abstract In this paper we describe a point scanning optical microscope where the illumination bea... more Abstract In this paper we describe a point scanning optical microscope where the illumination beam can be programmably controlled in real time using a liquid crystal spatial light modulator (LCSLM). With an appropriate pattern displayed on the LCSLM, the device can be made to act as a binary diffraction hologram. In the proposed microscope the illumination beam is in fact the+ 1 order beam diffracted from the binary hologram. By displaying a sequence of binary holograms it is possible to make a beam scanning, ...
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IEEE Transactions on Automatic Control, 2011
This technical note studies synchronization of identical general linear systems on a digraph cont... more This technical note studies synchronization of identical general linear systems on a digraph containing a spanning tree. A leader node or command generator is considered, which generates the desired tracking trajectory. A framework for cooperative tracking control is proposed, including full state feedback control, observer design and dynamic output feedback control. The classical system theory notion of duality is extended to networked systems. It is shown that unbounded synchronization regions that achieve synchronization on arbitrary digraphs containing a spanning tree can be guaranteed by using linear quadratic regulator based optimal control and observer design methods at each node.
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Automatica, 2010
This paper is concerned with synchronization of distributed node dynamics to a prescribed target ... more This paper is concerned with synchronization of distributed node dynamics to a prescribed target or control node dynamics. A design method is presented for adaptive synchronization controllers for distributed systems having non-identical unknown nonlinear dynamics, and for a target dynamics to be tracked that is also nonlinear and unknown. The development is for strongly connected digraph communication structures. A Lyapunov technique is presented for designing a robust adaptive synchronization control protocol. The proper selection of the Lyapunov function is the key to ensuring that the resulting control laws thus found are implementable in a distributed fashion. Lyapunov functions are defined in terms of a local neighborhood tracking synchronization error and the Frobenius norm. The resulting protocol consists of a linear protocol and a nonlinear control term with adaptive update law at each node. Singular value analysis is used. It is shown that the singular values of certain key matrices are intimately related to structural properties of the graph.
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Journal of Intelligent and Robotic Systems, 2009
The dynamics of a quadrotor are a simplified form of helicopter dynamics that exhibit the same ba... more The dynamics of a quadrotor are a simplified form of helicopter dynamics that exhibit the same basic problems of underactuation, strong coupling, multi-input/multi-output design, and unknown nonlinearities. Control design for the quadrotor is more tractable yet reveals corresponding approaches for helicopter and UAV control design. In this paper, a backstepping approach is used for quadrotor controller design. In contrast to most other approaches, we apply backstepping on the Lagrangian form of the dynamics, not the state space form. This is complicated by the fact that the Lagrangian form for the position dynamics is bilinear in the controls. We confront this problem by using an inverse kinematics solution akin to that used in robotics. In addition, two neural nets are introduced to estimate the aerodynamic components, one for aerodynamic forces and one for aerodynamic moments. The result is a controller of intuitively appealing structure having an outer kinematics loop for position control and an inner dynamics loop for attitude control. The control approach described in this paper is robust since it explicitly deals with unmodeled state-dependent disturbances and forces without needing any prior knowledge of the same. A simulation study validates the results obtained in the paper.
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Review of Scientific Instruments, 2013
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Review of Scientific Instruments, 2014
In this work we describe laser beam scanning using a ferroelectric liquid crystal spatial light m... more In this work we describe laser beam scanning using a ferroelectric liquid crystal spatial light modulator. Commercially available ferroelectric liquid crystal spatial light modulators are capable of displaying 85 colored images in 1 s using a time dithering technique. Each colored image, in fact, comprises 24 single bit (black and white) images displayed sequentially. We have used each single bit image to write a binary phase hologram. For a collimated laser beam incident on the hologram, one of the diffracted beams can be made to travel along a user defined direction. We have constructed a beam scanner employing the above arrangement and demonstrated its use to scan a single laser beam in a laser scanning optical sectioning microscope setup.
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Journal of Optics, 2013
Abstract In this article we investigate the beam deflection by a one-dimensional binary diffracti... more Abstract In this article we investigate the beam deflection by a one-dimensional binary diffraction grating. We propose a simple theoretical expression that can be used to predict the beam deflection angle due to both periodic and aperiodic binary grating profiles. We show that the theoretically calculated beam deflection angles agree well with the experimentally obtained deflection angles for various grating patterns. Thus the expression can be used to precisely position the deflected beam at a predetermined location. Further, ...
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Chemical Physics Letters, 2011
Orientation of water molecules around ionic arsenic has been studied in detail using density func... more Orientation of water molecules around ionic arsenic has been studied in detail using density functional B3LYP method. Both trivalent and pentavalent ionic states of arsenic are considered to investigate the orientations. The structure, stability and energetics of the ionic arsenic–water complexes, As3+–nH2O (n=1–6) and As5+–nH2O (n=3–6) have been investigated with increasing number of water molecules. The change in binding energy
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Automatica, 2010
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American Control Conference ( …, Jun 30, 2010
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International Journal of Robust and Nonlinear Control, Sep 10, 2011
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Digital Holography and Three-Dimensional Imaging, 2011
A wavefront sensor is a device that measures the phase profile or wavefront of a beam. Wavefront ... more A wavefront sensor is a device that measures the phase profile or wavefront of a beam. Wavefront sensing is important in a number of areas such as, in computer and semi conductor industry to measure the flatness of surfaces; to analyze the quality of a laser beam; to test the smoothness of optical elements; in astronomy to measure the atmospheric turbulence and so on. One of the most popular wavefront sensors in such applications is the Shack-Hartmann wavefront sensor (SHWS) [1]. Here the beam under observation is incident on a two dimensional array of ...
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Communications and Control Engineering, 2014
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49th IEEE Conference on Decision and Control (CDC), 2010
Abstract This paper studies synchronization using reduced state information based on output infor... more Abstract This paper studies synchronization using reduced state information based on output information passed between neighbor nodes. The node states are estimated using cooperative dynamical observers at each node. It is shown how to design cooperative state variable state feedbacks and observers at each node that are dual to each other, in a sense that extends the classical system theory notion of duality to dynamical systems on graphs. It is shown that unbounded consensus regions that guarantee synchronization on arbitrary ...
Bookmarks Related papers MentionsView impact
IEEE ICCA 2010, 2010
Abstract Traditional research on cooperative networked systems has focused on analysis of given p... more Abstract Traditional research on cooperative networked systems has focused on analysis of given protocols for simple linear systems, mainly the integrator or double integrator dynamics. Pinning control has been developed for nonlinear systems, generally using either a Jacobian linearization method or a Lipschitz assumption. Work has also progressed on nonlinear coupling protocols. In this paper we present a design method for adaptive controllers for distributed systems having non-identical unknown nonlinear dynamics, and ...
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Challenges and Paradigms in Applied Robust Control, 2011
Bookmarks Related papers MentionsView impact
2008 IEEE International Conference on Control Applications, 2008
Abstract For a typical quadrotor model, one can identify the two well known inherent rotorcraft c... more Abstract For a typical quadrotor model, one can identify the two well known inherent rotorcraft characteristics; under-actuation and strong coupling in pitch-yaw-roll. To confront these problems and design a station-keeping tracking controller, dynamic inversion is used here. Typical applications of dynamic inversion require the selection of the output control variables to render the internal dynamics stable. This means that in many cases tracking can not be guaranteed for the actual desired outputs. Instead, here, the internal dynamics of ...
Bookmarks Related papers MentionsView impact
Advanced Microscopy Techniques III, 2013
Bookmarks Related papers MentionsView impact
Abstract In this paper we describe a point scanning optical microscope where the illumination bea... more Abstract In this paper we describe a point scanning optical microscope where the illumination beam can be programmably controlled in real time using a liquid crystal spatial light modulator (LCSLM). With an appropriate pattern displayed on the LCSLM, the device can be made to act as a binary diffraction hologram. In the proposed microscope the illumination beam is in fact the+ 1 order beam diffracted from the binary hologram. By displaying a sequence of binary holograms it is possible to make a beam scanning, ...
Bookmarks Related papers MentionsView impact
IEEE Transactions on Automatic Control, 2011
This technical note studies synchronization of identical general linear systems on a digraph cont... more This technical note studies synchronization of identical general linear systems on a digraph containing a spanning tree. A leader node or command generator is considered, which generates the desired tracking trajectory. A framework for cooperative tracking control is proposed, including full state feedback control, observer design and dynamic output feedback control. The classical system theory notion of duality is extended to networked systems. It is shown that unbounded synchronization regions that achieve synchronization on arbitrary digraphs containing a spanning tree can be guaranteed by using linear quadratic regulator based optimal control and observer design methods at each node.
Bookmarks Related papers MentionsView impact
Automatica, 2010
This paper is concerned with synchronization of distributed node dynamics to a prescribed target ... more This paper is concerned with synchronization of distributed node dynamics to a prescribed target or control node dynamics. A design method is presented for adaptive synchronization controllers for distributed systems having non-identical unknown nonlinear dynamics, and for a target dynamics to be tracked that is also nonlinear and unknown. The development is for strongly connected digraph communication structures. A Lyapunov technique is presented for designing a robust adaptive synchronization control protocol. The proper selection of the Lyapunov function is the key to ensuring that the resulting control laws thus found are implementable in a distributed fashion. Lyapunov functions are defined in terms of a local neighborhood tracking synchronization error and the Frobenius norm. The resulting protocol consists of a linear protocol and a nonlinear control term with adaptive update law at each node. Singular value analysis is used. It is shown that the singular values of certain key matrices are intimately related to structural properties of the graph.
Bookmarks Related papers MentionsView impact
Journal of Intelligent and Robotic Systems, 2009
The dynamics of a quadrotor are a simplified form of helicopter dynamics that exhibit the same ba... more The dynamics of a quadrotor are a simplified form of helicopter dynamics that exhibit the same basic problems of underactuation, strong coupling, multi-input/multi-output design, and unknown nonlinearities. Control design for the quadrotor is more tractable yet reveals corresponding approaches for helicopter and UAV control design. In this paper, a backstepping approach is used for quadrotor controller design. In contrast to most other approaches, we apply backstepping on the Lagrangian form of the dynamics, not the state space form. This is complicated by the fact that the Lagrangian form for the position dynamics is bilinear in the controls. We confront this problem by using an inverse kinematics solution akin to that used in robotics. In addition, two neural nets are introduced to estimate the aerodynamic components, one for aerodynamic forces and one for aerodynamic moments. The result is a controller of intuitively appealing structure having an outer kinematics loop for position control and an inner dynamics loop for attitude control. The control approach described in this paper is robust since it explicitly deals with unmodeled state-dependent disturbances and forces without needing any prior knowledge of the same. A simulation study validates the results obtained in the paper.
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Review of Scientific Instruments, 2013
Bookmarks Related papers MentionsView impact
Review of Scientific Instruments, 2014
In this work we describe laser beam scanning using a ferroelectric liquid crystal spatial light m... more In this work we describe laser beam scanning using a ferroelectric liquid crystal spatial light modulator. Commercially available ferroelectric liquid crystal spatial light modulators are capable of displaying 85 colored images in 1 s using a time dithering technique. Each colored image, in fact, comprises 24 single bit (black and white) images displayed sequentially. We have used each single bit image to write a binary phase hologram. For a collimated laser beam incident on the hologram, one of the diffracted beams can be made to travel along a user defined direction. We have constructed a beam scanner employing the above arrangement and demonstrated its use to scan a single laser beam in a laser scanning optical sectioning microscope setup.
Bookmarks Related papers MentionsView impact
Journal of Optics, 2013
Abstract In this article we investigate the beam deflection by a one-dimensional binary diffracti... more Abstract In this article we investigate the beam deflection by a one-dimensional binary diffraction grating. We propose a simple theoretical expression that can be used to predict the beam deflection angle due to both periodic and aperiodic binary grating profiles. We show that the theoretically calculated beam deflection angles agree well with the experimentally obtained deflection angles for various grating patterns. Thus the expression can be used to precisely position the deflected beam at a predetermined location. Further, ...
Bookmarks Related papers MentionsView impact
Chemical Physics Letters, 2011
Orientation of water molecules around ionic arsenic has been studied in detail using density func... more Orientation of water molecules around ionic arsenic has been studied in detail using density functional B3LYP method. Both trivalent and pentavalent ionic states of arsenic are considered to investigate the orientations. The structure, stability and energetics of the ionic arsenic–water complexes, As3+–nH2O (n=1–6) and As5+–nH2O (n=3–6) have been investigated with increasing number of water molecules. The change in binding energy
Bookmarks Related papers MentionsView impact
Automatica, 2010
Bookmarks Related papers MentionsView impact
American Control Conference ( …, Jun 30, 2010
Bookmarks Related papers MentionsView impact
International Journal of Robust and Nonlinear Control, Sep 10, 2011
Bookmarks Related papers MentionsView impact