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Byline: Abhijit. Chandra, Prabhu. Singh, Saket. Kumar, Nikhil. Chopra, Vishal. Gupta, Pradeep. Joshi, Vivek. Gupta Introduction: Laparoscopic ventral mesh rectopexy (LVMR) has gained widespread acceptance for the management of complete [...]

Byline: Nikhil. Chopra, Vivek. Gupta, Rahul, Saket. Kumar, Pradeep. Joshi, Vishal. Gupta, Abhijit. Chandra Introduction: Most centres offer laparoscopic treatment for liver hydatid cyst (LHC). There have been concerns about [...]

In this technical note we study the problem of exponential synchronization for one of the most popular models of coupled phase oscillators, the Kuramoto model. We consider the special case of finite oscillators with distinct, bounded natural frequencies. Our first result derives a lower bound on the coupling gain which is necessary for the onset of synchronization. This bound improves the one derived by Jadbabaie et al. [8]. We then calculate a lower bound on the coupling gain that is sufficient to guarantee oscillator synchronization and derive further sufficient conditions to ensure exponential synchronization of the angular frequencies of all oscillators to the mean natural frequency of the group. We also characterize the coupling gain that is sufficient for the oscillator phase differences to approach any desired compact set in finite time. Index Terms--Cooperative control, exponential stabilization, Kuramoto oscillators, multi-agent systems, synchronization.

This paper addresses the problem of steady-state position and force tracking in bilateral teleoperation. Passivity-based control schemes for bilateral teleoperation provide robust stability against network delays in the feedback loop and velocity tracking, but do not guarantee steady-state position and force tracking in general. Position drift due to data loss and offset of initial conditions is a well-known problem in such systems. In this paper, we introduce a new architecture, which builds upon the traditional passivity-based configuration by using additional position control on both the master and slave robots, to solve the steady-state position and force-tracking problem. Lyapunov stability methods are used to establish the range of the position control gains on the master and slave sides. Experimental results using a single-degree-of-freedom master/slave system are presented, showing the performance of the resulting system. Index Terms--Bilateral teleoperation, force tracking, position tracking, time delay.

My first ever "painting" was a copy of my grandfather's painting of Kashmir. Charcoal and pastel on rice paper 11 × 8 in. Courtesy of the artist and Chatterjee & Lal PHOTO (COLOR): Nikhil Chopra (b. 1974) Lands, Waters & Skies: Sundersar, 2018. Could you describe the paintings of your grandfather and your memories of Kashmir? It's quite a dark song, and I sing it in the Sackler wing, with the projections of archival footage of America, museums, and institutional Met museum people, in Egypt in the early part of the twentieth century, digging graves in Egypt, excavating priceless pieces from burial sites. [Extracted from the article]

Images courtesy Chatterjee & Lal and the artist PHOTO (COLOR): Performance Lands, Waters and Skies by Nikhil Chopra, Metropolitan Museum of Art, New York. Images courtesy Chatterjee & Lal, Galleria Continua and the artist PHOTO (COLOR): Performance Drawing a Line through Landscape by Nikhil Chopra, documenta 14, 2017. Images courtesy Chatterjee & Lal, Galleria Continua and the artist PHOTO (COLOR): Performance Drawing a Line through Landscape by Nikhil Chopra, documenta 14, 2017. Images courtesy Chatterjee & Lal, Galleria Continua and the artist PHOTO (COLOR): Performance Lands, Waters and Skies by Nikhil Chopra, Metropolitan Museum of Art, New York. [Extracted from the article]

In this brief, false data injection attacks in bilateral teleoperation systems (BTOSs) are studied, where the attacker can inject false data into the states being exchanged between the master and slave robots. To demonstrate the vulnerability of BTOS, a destabilizing false data injection attack (DFDIA) is designed and experimentally implemented. To detect any general false data injection attack, including DFDIA as a special case, a physics-based detection scheme with an encoding–decoding structure is proposed. The efficacy of the proposed attack detection scheme is demonstrated in experiments. [ABSTRACT FROM AUTHOR]

In this paper, vulnerability of a distributed consensus seeking multi-agent system (MAS) with double-integrator dynamics against edge-bound content modification cyber attacks is studied. In particular, we define a specific edge-bound content modification cyber attack called malignant content modification attack (MCoMA), which results in unbounded growth of an appropriately defined group disagreement vector. Properties of MCoMA are utilized to design detection and mitigation algorithms so as to impart resilience in the considered MAS against MCoMA. Additionally, the proposed detection mechanism is extended to detect the general edge-bound content modification attacks (not just MCoMA). Finally, the efficacies of the proposed results are illustrated through numerical simulations. [ABSTRACT FROM AUTHOR]

In order to accomplish cooperative tasks, decentralized systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. Connectivity maintenance has been extensively studied in the last few years, but generally considering undirected communication graphs. In this paper, we introduce a decentralized control and estimation strategy to maintain the strong connectivity property of directed communication graphs. In particular, we introduce a hierarchical estimation procedure that implements power iteration in a decentralized manner, exploiting an algorithm for balancing strongly connected directed graphs. The output of the estimation system is then utilized for guaranteeing preservation of the strong connectivity property. The control strategy is validated by means of analytical proofs and simulation results. [ABSTRACT FROM PUBLISHER]

In order to accomplish cooperative tasks, multi-robot systems are required to communicate among each other. This inter-robot communication can be modeled as a graph. Thus, maintaining the connectivity of the communication graph is a fundamental issue in cooperative robotic systems. Connectivity maintenance has been extensively studied in the last few years, but generally considering only kinematic agents. In this paper we introduce a control strategy which, by exploiting a decentralized procedure for the estimation of the algebraic connectivity of the graph, ensures connectivity maintenance for groups of Lagrangian systems. Collision avoidance control actions are also integrated with the connectivity maintenance algorithm. The control strategy is validated by means of analytical proofs and simulation results. [ABSTRACT FROM AUTHOR]

Input/output (I/O) delays in a closed-loop robotic system can significantly deteriorate both its stability and performance. In this paper, we study the position control problem for robotic manipulators under I/O delays, where the delays manifest as a result of communication with a non-collocated controller. Previous research on this topic has assumed the gravitational torque to be pre-compensated in a collocated manner. This paper studies the stability and regulation performance of the closed-loop system when the compensation for the gravitational torque is provided by a non-collocated controller. We demonstrate that simply utilizing scattering transformation for robotic systems under I/O communication delays results in position drift due to gravity compensation. Hence, a new control algorithm incorporating delayed position feedback and scattering variables is studied subsequently. Stability and performance margins dependent on the round-trip delays and the gravitational model are proposed to guarantee stable position regulation. Since the control architecture with scattering transformation does not address the stability problem due to sensing-actuation delays, a new controller is developed to cope with robotic control systems under time-varying sensing-actuation delays. The proposed control algorithms are studied in this paper via experiments on a manipulator with three degrees of freedom. [ABSTRACT FROM AUTHOR]

To accomplish cooperative tasks, robotic systems are often required to communicate with each other. Thus, maintaining connectivity of the communication graph is a fundamental issue in the field of multi-robot systems. In this paper we present a completely decentralized control strategy for global connectivity maintenance of the communication graph. Considering the disk communication model, we describe a gradient-based control strategy that exploits decentralized estimation of the algebraic connectivity. Unlike previous approaches available in the literature, the proposed control algorithm solves the global connectivity problem in a decentralized manner providing theoretical guarantees, without requiring maintenance of the local connectivity between robotic systems. Moreover, results obtained with simulations and experiments on real robots are described for demonstrating the efficacy of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This study introduces a control algorithm that, exploiting a completely decentralized estimation strategy for the algebraic connectivity of the graph, ensures the connectivity maintenance property for multi robot systems, in the presence of a generic (bounded) additional control term. This result is obtained by driving the robots along the negative gradient of an appropriately defined function of the algebraic connectivity. The proposed strategy is then enhanced with the introduction of the concept of critical robots, that is robots for which the loss of a single communication link might cause the disconnection of the communication graph. Limiting the control action to critical robots will be shown to reduce the control effort that is introduced by the proposed connectivity maintenance control law and to mitigate its effect on the additional (desired) control term. [ABSTRACT FROM PUBLISHER]

The problem of controlling a group of networked mechanical systems to synchronize and follow a common trajectory is studied in this paper. We first address the results for net worked mechanical systems to achieve synchronization when the interagent communication graph is balanced and strongly connected with communication delays. Subsequently, a control law is developed to guarantee synchronization and trajectory tracking for net worked mechanical systems communicating on regular graphs when there are constant time delays in communication and the interconnection topology is time-varying. The case when a human operator input is introduced in the closed-loop system is also considered. It is demonstrated that a bounded human operator input results in bounded tracking and synchronization errors, even when there are constant time delays in communication. The simulation and experimental results are presented by utilizing the kinematic and dynamic models of PHANToM Omni derived in this paper. [ABSTRACT FROM AUTHOR]

Input/output delays in a control system can pose significant impediments to the stabilization problem and potentially degrade the performance of the closed-loop system. In this paper, we study the classical set-point control problem for rigid robots with input–output communication delays in the closed-loop system. We demonstrate that if there are transmission delays between the robotic system and the controller, then the use of the scattering variables can stabilize an otherwise unstable system for arbitrary unknown constant delays. It is also demonstrated that the proposed algorithm results in guaranteed set-point tracking. In the case of time-varying delays, scattering variables together with additional gains can be utilized to stabilize the closed-loop system that is composed of the robotic manipulator and the controller. Furthermore, a scattering representation-based design with position feedback is proposed to improve closed-loop performance under time-varying delays. The proposed algorithms are validated via experiments in this paper. [ABSTRACT FROM AUTHOR]

Passivity-based control has emerged as an important paradigm for synchronization of networked robotic systems. Despite the practical utility of task-space algorithms, the previous results focused on joint-space synchronization and were primarily derived for kinematically identical manipulators. Hence, in this paper, the problem of task-space synchronization of (possibly redundant) heterogeneous robotic systems is studied. By exploiting passivity-based synchronization results that are developed previously, an adaptive control algorithm is proposed to guarantee task-space synchronization of networked robotic manipulators in the presence of dynamic uncertainties and time-varying communication delays. To demonstrate the efficacy of the proposed framework, numerical simulations and experiments are conducted with redundant and nonredundant manipulators, respectively. [ABSTRACT FROM PUBLISHER]

In this brief, we propose a passivity-based framework for control of bilateral teleoperators under time-varying delays and data loss. The usual scattering formalism which guarantees passivity for any constant time delay is extended in several important ways to handle adverse network dynamics. Communication management modules (CMM) are proposed to reconstruct the scattering variables while guaranteeing passivity of the bilateral teleoperator and asymptotic stability of the master/slave velocities under time-varying delays and data losses. The results are also extended to the discrete domain, in particular to the case where communication between the master and slave robots occurs over a packet-switched network. We show that passivity can be maintained in the face of varying delay and packet loss but that it depends fundamentally on the mechanism used to handle missing packets. Our framework unifies several existing results in the continuous and discrete time domain. We develop novel algorithms for the CMM which not only preserve passivity and stability, but have been shown through experiments to improve tracking performance in a single-degree-of-freedom teleoperator system. [ABSTRACT FROM AUTHOR]

Tissue engineering and stem-cell technologies are now at the forefront of scientific advances and offer novel methods for regenerating and recreating tissue. There is cautious optimism that tissue engineering will play an increasing role in the management of a spectrum of urological disease in the future. Copyright © 2013 John Wiley & Sons [ABSTRACT FROM AUTHOR]

Hydatid disease is a parasitic zoonosis caused by the larval form of the Echinococcus worm. Hepatic hydatidosis is the most common form of disease in humans. Centrally located, large hydatid cysts have the tendency to rupture into the adjoining bile duct and form a fistulous communication. Suture closure of the cystobiliary communication detected during surgery is recommended to avoid postoperative complications related to bile leak. In the era of minimally invasive surgery, laparoscopic management of the cystobiliary communication can be challenging, and laparoscopic suturing may not always be feasible. Postoperative endoscopic biliary decompression is necessary in such situations, but it has its own set of potential risk and complications. In this case report, we present a simple and easy technique for laparoscopic closure of the cystobiliary communication when suture ligation is technically not possible.

Objective: To determine if the prevalence of 2 prothrombotic genetic factors, factor V Leiden and prothrombin gene mutation, is increased in patients with antiphospholipid (aPL) antibodies with a history of venous/arterial thrombosis compared to patients with aPL antibodies with no history of thrombosis., Methods: One hundred fifty-seven patients with aPL antibodies were studied. The occurrence of venous and arterial thrombotic events since the time of antibody detection was determined retrospectively, using appropriate clinical and diagnostic criteria. Clinical risk factors for thrombosis were documented and included hypertension, hyperlipidemia, cigarette smoking, diabetes, positive family history, use of oral contraceptive, pregnancy, trauma, hospitalization, varicose veins, and malignancy. Genomic DNA was extracted from blood cells for determination of factor V Leiden mutation G1691 --> A and prothrombin mutation G20210 --> A by polymerase chain reaction and restriction fragment length polymorphism analysis., Results: Of 157 patients, 69 had a history of thrombosis (venous 37, arterial 32); 147 (94%) patients had anticardiolipin (aCL) antibodies; 69 (45%) had lupus anticoagulant (LAC). The prevalence of factor V Leiden in patients with thrombosis was 13% compared to 4.6% in patients without thrombosis (OR 3.11, CI 0.92-10.6). In patients with aCL antibodies, 15% of patients with arterial thrombosis had factor V mutation compared to 3.5% of patients without thrombosis (OR 4.9, CI 1.2-19.3). The prothrombin gene mutation was identified in 5 patients, none of whom had thrombosis. Stepwise logistic regression analysis indicated that LAC (p = 0.005), male sex (p = 0.04), and hypertension (p = 0.03) were the strongest risk factors for developing thrombosis and that no additional risk was conferred by factor V Leiden (p = 0.13) and prothrombin gene mutation., Conclusion: Although the prevalence of factor V Leiden is modestly increased in patients with autoimmune aPL antibodies and thrombosis, these results suggest that its detection does not significantly increase the risk of a thrombotic event, once other clinical risk factors have been considered. Prothrombin gene mutation is not associated with thrombosis in patients with aPL antibodies.