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Gradient-based optimization and control frameworks have been utilized in several applications. The learning rate parameter is typically chosen following a schedule or using methods such as line search to enhance the convergence rate. Recently, the machine learning community has developed methodologies for automated tuning of the learning rate, known as adaptive gradient methods. This paper develops a control theory-inspired framework for modeling adaptive gradient methods that solve non-convex optimization problems. We first model the adaptive gradient methods in a state–space framework, which allows us to present simpler convergence proofs of prominent adaptive optimizers, such as AdaGrad, Adam, and AdaBelief. The proposed framework is constructive because it allows synthesizing new adaptive optimizers. To illustrate this fact, we then utilize the transfer function paradigm from classical control to propose a new variant of Adam, coined AdamSSM, and prove its convergence. We add an appropriate pole-zero pair in the transfer function from squared gradients to the second moment estimate. Applications on benchmark machine learning tasks of image classification using CNN architectures and language modeling using LSTM architecture demonstrate that the AdamSSM algorithm improves the gap between generalization accuracy and faster convergence than the recent adaptive gradient methods. [ABSTRACT FROM AUTHOR]

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]

Introduction: Most centres offer laparoscopic treatment for liver hydatid cyst (LHC). There have been concerns about the management of intra-peritoneal spillage, bleeding, and cystobiliary communication (CBC) during laparoscopic surgery for LHC. CBC can exist in 13%-37% of cases of LHC. No randomised studies have compared open versus laparoscopic approach for the treatment of LHC. We specifically analysed the outcomes of laparoscopic treatment of LHC with special reference to associated biliary complications. Patients and Methods: We analysed our prospectively collected data of patients undergoing laparoscopic treatment of LHC from 2009 to 2016. Patients undergoing open surgery or interventional radiology procedures were not included. Data analysed included demographic profile, investigational parameters, intra-operative findings and postoperative results with special reference to biliary complications and presence/management of CBC. Results: A total of 41 patients underwent laparoscopic treatment of LHC. History of jaundice was present in 5 (12.2%) patients. CBC was documented in 16 (39.02%) patients. In 11 patients, CBC was detected intra-operatively as visible communication, which was suture ligated or clipped. Five patients had occult CBC, detected as bile leak in the post-operative period. The leak resolved spontaneously in 7 patients and with biliary stenting in 2 patients. Only one patient had a persistent biliary leak. Postoperative bile leak was more common in patients with raised alkaline phosphatase. No statistically significant association was seen with size or location of the cyst, number of cysts and World Health Organisation classification. Conclusion: Laparoscopic treatment of LHC with associated CBC provides acceptable results. [ABSTRACT FROM AUTHOR]

Design of a physical system and its controller has significant ramifications on the overall system performance. The traditional approach of first optimizing the physical design and then the controller may lead to sub-optimal solutions. This is due to the interdependence between the physical design and control parameters through the dynamic equations. Recognition of this fact paved the way for investigation into the “Co-Design” research theme wherein the overall system’s physical design and control are simultaneously optimized. In this paper, a novel approach to address the co-design problem for a class of Linear Time Invariant (LTI) dynamic systems controlled by a Linear Quadratic Regulator (LQR) feedback is presented. The considered co-design problem is formulated as a non-convex optimization problem with Algebraic Riccati Equation (ARE) constraint and convex design objective function. Using Semi-Definite Programming (SDP) duality, the ARE constraint is reduced into equivalent Bilinear Matrix Inequality (BMI) constraints. This reformulated co-design problem is solved using an iterative algorithm based on the Generalized Benders Decomposition (GBD) and Gradient Projection Method. The proposed algorithm converges to a solution which is within a specified tolerance from the nearest local minimum (in special cases global minimum) in a finite number of iterations. Necessary and sufficient conditions are developed to test minimality. Three examples are presented to show efficacy of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Abstract: Networked control of robotic systems is widely recognized as a potentially transformative technological enabler for several applications. However, the issues of time delays in communication and recovery from data losses have emerged as the pivotal issues that have stymied practical deployment. The study for control of robotic system with input/output communication delays has attracted many researchers’ attention, but the existing results have been primarily developed for rigid-joint robots. Since joint flexibility is largely unavoidable in practical manipulators, in this paper the set-point control problem for flexible-joint robots with input/output communication delays is studied. It is demonstrated that the scattering variables address the stability problem for unknown constant delays, however, in contrast to the rigid-robot case, they cannot guarantee set-point regulation. In addition, we compute the explicit dependence of the regulation errors on the communication delays, control gains, and the desired set-point configuration. Without exact knowledge of time delays, a scattering variable based controller with position feedback is subsequently studied in this paper to guarantee stability with improved regulation performance. The control architecture is further extended to the case with time-varying delays. Simulation results are presented to validate the efficacy of the proposed control algorithms. [Copyright &y& Elsevier]

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]

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]

Abstract: In teleoperation systems operating in complex environments, due to the cognitive limitations of the human operator and lack of complete information about the remote environment, safety and performance of such systems can potentially be comprised. In order to ensure the safety and enhance the efficiency of complex teleoperation systems operating in cluttered environments, in this paper we investigate a semi-autonomous control framework for bilateral teleoperation. The semi-autonomous teleoperation system is composed of heterogeneous master and slave robots, where the slave robot is assumed to be a redundant manipulator. Considering robots with different configurations, and in the presence of dynamic uncertainties and asymmetric communication delays, we first develop a control algorithm to ensure position and velocity tracking in the task space. Additionally in the absence of dynamic uncertainty, and in the presence of human operator and environmental forces, all signals of the proposed teleoperation system are proven to be ultimately bounded. The redundancy of the slave robot is then utilized for achieving autonomous sub-task control, such as singularity avoidance, joint limits, and collision avoidance. The control algorithms for the proposed semi-autonomous teleoperation system are validated through numerical simulations on a non-redundant master and a redundant slave robot. [Copyright &y& Elsevier]

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]

Abstract: Bilateral teleoperators, designed within the passivity framework using concepts of scattering and two-port network theory, provide robust stability against constant delay in the network and velocity tracking, but cannot guarantee position tracking in general. In this paper we fundamentally extend the passivity-based architecture to guarantee state synchronization of master/slave robots in free motion independent of the constant delay and without using the scattering transformation. We propose a novel adaptive coordination architecture which uses state feedback to define a new passive output for the master and slave robots containing both position and velocity information. A passive coordination control is then developed which uses the new outputs to state synchronize the master and slave robots in free motion. The proposed algorithm also guarantees ultimate boundedness of the master/slave trajectories on contact with a passive environment. Experimental results are also presented to verify the efficacy of the proposed algorithms. [Copyright &y& Elsevier]

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. [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]

Multisubsystem co-design refers to the simultaneous optimization of physical plant and controller of a system decomposed into multiple interconnected subsystems. In this paper, two decentralized (multilevel and bilevel) approaches are formulated to solve multisubsystem co-design problems, which are based on the direct collocation and decomposition-based optimization methods. In the multilevel approach, the problem is decomposed into two bilevel optimization problems, one for the physical plant and the other for the control part. In the bilevel approach, the problem is decomposed into subsystem optimization subproblems, with each subproblem having the optimization model for physical plant and control parts together. In both cases, the entire time horizon is discretized to convert the continuous optimal control problem into a finite-dimensional nonlinear program. The optimality condition decomposition method is employed to solve the converted problem in a decentralized manner. Using the proposed approaches, it is possible to obtain an optimal solution for more generalized multisubsystem co-design problems than was previously possible, including those with nonlinear dynamic constraints. The proposed approaches are applied to a numerical and engineering example. For both examples, the solutions obtained by the decentralized approaches are compared with a centralized (all-at-once) approach. Finally, a scalable version of the engineering example is solved to demonstrate that using a simulated parallelization with and without communication delays, the computational time of the proposed decentralized approaches can outperform a centralized approach as the size of the problem increases. [ABSTRACT FROM AUTHOR]

Multisubsystem co-design refers to the simultaneous optimization of physical plant and controller of a system decomposed into multiple interconnected subsystems. In this paper, two decentralized (multilevel and bilevel) approaches are formulated to solve multisubsystem co-design problems, which are based on the direct collocation and decomposition-based optimization methods. In the multilevel approach, the problem is decomposed into two bilevel optimization problems, one for the physical plant and the other for the control part. In the bilevel approach, the problem is decomposed into subsystem optimization subproblems, with each subproblem having the optimization model for physical plant and control parts together. In both cases, the entire time horizon is discretized to convert the continuous optimal control problem into a finite-dimensional nonlinear program. The optimality condition decomposition method is employed to solve the converted problem in a decentralized manner. Using the proposed approaches, it is possible to obtain an optimal solution for more generalized multisubsystem co-design problems than was previously possible, including those with nonlinear dynamic constraints. The proposed approaches are applied to a numerical and engineering example. For both examples, the solutions obtained by the decentralized approaches are compared with a centralized (all-at-once) approach. Finally, a scalable version of the engineering example is solved to demonstrate that using a simulated parallelization with and without communication delays, the computational time of the proposed decentralized approaches can outperform a centralized approach as the size of the problem increases. [ABSTRACT FROM AUTHOR]

Codesign refers to the process of integrating the optimization of the physical plant design and control of a system. In this paper, a new class of codesign problems with a multisubsystem architecture in both design and control is formulated and solved. Our work here extends earlier research on models and solution approaches from single system to multisubsystem codesign. In this class, the optimization model for the physical design part in each subsystem is assumed to have a convex objective function with convex inequality and linear equality constraints. The optimization model for the control part of each subsystem belongs to a class of finite time-horizon linear quadratic regulator (LQR) feedback control. A new multilevel decentralized method is proposed that can obtain optimal or near-optimal solutions for this class of codesign problems. Details of the model and approach are presented and demonstrated by a numerical as well as a more complex spring-mass-damper system example. The proposed decentralized approach has been compared with a centralized approach. Using a scalable test problem, it is shown that as the size of the problem is increased, the computation effort for the decentralized approach increases linearly while that of the centralized approach increases nonlinearly. [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]

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]

This paper considers the multi-agent linear least-squares problem in a server–agent network architecture. The system comprises multiple agents, each with a set of local data points. The agents are connected to a server, and there is no inter-agent communication. The agents' goal is to compute a linear model that optimally fits the collective data. The agents, however, cannot share their data points. In principle, the agents can solve this problem by collaborating with the server using the server–agent network variant of the classical gradient-descent method. However, when the data points are ill-conditioned , the gradient-descent method requires a large number of iterations to converge. We propose an iterative pre-conditioning technique to mitigate the deleterious impact of the data points' conditioning on the convergence rate of the gradient-descent method. Unlike the conventional pre-conditioning techniques, the pre-conditioner matrix used in our proposed technique evolves iteratively. We show that our proposed algorithm converges linearly with an improved rate of convergence in comparison to both the classical and the accelerated gradient-descent methods. For the special case, when the solution of the least-squares problem is unique, our algorithm converges to the solution superlinearly. Through numerical experiments on benchmark least-squares problems, we validate our theoretical findings, and also demonstrate our algorithm's improved robustness against process noise. [ABSTRACT FROM AUTHOR]

Introduction: Vasculobiliary and vascular injuries following cholecystectomy are the most serious complications requiring complex surgical management resulting in greater patient morbidity and mortality.Methodology: The study was performed at a tertiary teaching hospital of North India. Records of patients referred for biliary or vascular injury sustained during cholecystectomy were reviewed retrospectively to identify patients with vascular injury between January 2009 and March 2018. Clinical profile, hospital course and outcome of these patients were analysed.Results: Over nine years, 117 patients were referred for cholecystectomy related complications. Total incidence of vascular injury was 5.1% (6/117). Combined vasculobiliary injury (VBI) occurred in 3.4% (4/117) while isolated vascular injury was present in 1.7% patients (2/117). Most (5/6) patients were operated for uncomplicated gall stone disease. Incidences of portal vein (PV) and right hepatic artery (RHA) injuries were equal (3/6). PV injuries were repaired either during cholecystectomy (1/3) or during re-exploration after damage control packing (2/3). RHA injuries presented as pseudoaneurysm and were managed surgically (2/3) or by coil embolization (1/3). All VBI referrals (4/117) were following open cholecystectomy. In VBI patients, vascular injury was diagnosed intra-operatively in two while it was diagnosed several weeks after cholecystectomy in two others. Biliary injury manifested as bile leak post-operatively in all four of them. Nature of biliary injury could be characterized in only 50% (2/4) patients. Definitive repair of biliary injury was performed in one patient only. There was one mortality in our series.Conclusion: Vascular injury is an uncommon complication of cholecystectomy with catastrophic outcome if not managed timely and properly. Adequate surgeon training, keeping the possibility of aberrant vasculobiliary anatomy in all cases, and proper surgical technique is crucial for prevention of such injuries. However in such an event, proper documentation and referral to tertiary centre will help in decreasing morbidity and further litigation. [ABSTRACT FROM AUTHOR]

Introduction: Laparoscopic ventral mesh rectopexy (LVMR) has gained widespread acceptance for the management of complete rectal prolapse (CRP). However, there have been concerns considering its use in patients with a redundant sigmoid colon. This study was conducted to evaluate the anatomical and functional results following LVMR, particularly in cases of CRP with a redundant sigmoid colon. Materials and Methods: Retrospective analysis of 25 patients who underwent LVMR from January 2011 to September 2016 was performed. Patients were divided into two groups according to the duration of follow-up. Group A (long-term) with follow-up >3 years and Group B (mid-term) <3 years. Results: The study included 25 patients (M:F = 1.5:1) with a median age of 38 years. Eighty-eight percent of the patients had a redundant sigmoid colon. Significant improvement in post-operative Wexner score as compared to pre-operative values was seen in patients with pre-existing constipation (P < 0.0001). In patients presenting with faecal incontinence (FI), significant improvement in post-operative St. Mark's incontinence score was observed. Functional outcomes remain consistent in long-term follow-up (>3 years). Conclusions: LVMR seems to be a feasible surgical procedure with minimum morbidity and good long-term functional outcomes. It provides satisfactory results in patients with redundant sigmoid colon and improves pre-existing constipation and FI. [ABSTRACT FROM AUTHOR]

Control technology is one of the fundamental disciplines of robotics. This special issue presents the recent theory and practice of control technology applied to networked and distributed robotics. [Extracted from the article]

Objective: To estimate performance of a single-nucleotide polymorphism-based noninvasive prenatal screen for fetal aneuploidy in high-risk and low-risk populations on single venopuncture.Methods: One thousand sixty-four maternal blood samples from 7 weeks of gestation and beyond were included; 1,051 were within specifications and 518 (49.3%) were low risk. Cell-free DNA was amplified, sequenced, and analyzed using the Next-generation Aneuploidy Test Using SNPs algorithm. Samples were called as trisomies 21, 18, 13, or monosomy X, or euploid, and male or female.Results: Nine hundred sixty-six samples (91.9%) successfully generated a cell-free DNA result. Among these, sensitivity was 100% for trisomy 21 (58/58, confidence interval [CI] 93.8-100%), trisomy 13 (12/12, CI 73.5-100%), and fetal sex (358/358 female, CI 99.0-100%; 418/418 male, CI 99.1-100%), 96.0% for trisomy 18 (24/25, CI 79.7-99.9%), and 90% for monosomy X (9/10, CI 55.5-99.8%). Specificity for trisomies 21 and 13 was 100% (905/905, CI 99.6-100%; and 953/953, CI 99.6-100%, respectively) and for trisomy 18 and monosomy X was 99.9% (938/939, CI 99.4-100%; and 953/954, CI 99.4-100%, respectively). However, 16% (20/125) of aneuploid samples did not return a result; 50% (10/20) had a fetal fraction below the 1.5th percentile of euploid pregnancies. Aneuploidy rate was significantly higher in these samples (P<.001, odds ratio 9.2, CI 4.4-19.0). Sensitivity and specificity did not differ in low-risk and high-risk populations.Conclusions: This noninvasive prenatal screen performed with high sensitivity and specificity in high-risk and low-risk cohorts. Aneuploid samples were significantly more likely to not return a result; the number of aneuploidy samples was especially increased among samples with low fetal fraction. This underscores the importance of redraws or, in rare cases, invasive procedures based on low fetal fraction.Level Of Evidence: II. [ABSTRACT FROM AUTHOR]

OBJECTIVE: To estimate performance of a single-nucleotide polymorphism-based noninvasive prenatal screen for fetal aneuploidy in high-risk and low-risk populations on single venopuncture. METHODS: One thousand sixty-four maternal blood samples from 7 weeks of gestation and beyond were included; 1,051 were within specifications and 518 (49.3%) were low risk. Cell-free DNA was amplified, sequenced, and analyzed using the Next-generation Aneuploidy Test Using SNPs algorithm. Samples were called as trisomies 21, 18, 13, or monosomy X, or euploid, and male or female. RESULTS: Nine hundred sixty-six samples (91.9%) successfully generated a cell-free DNA result. Among these, sensitivity was 100% for trisomy 21 (58/58, confidence interval [CI] 93.8-100%), trisomy 13 (12/12, CI 73.5-100%), and fetal sex (358/358 female, CI 99.0-100%; 418/418 male, CI 99.1-100%), 96.0% for trisomy 18 (24/25, CI 79.7-99.9%), and 90% for monosomy X (9/10, CI 55.5-99.8%). Specificity for trisomies 21 and 13 was 100% (905/905, CI 99.6-100%; and 953/953, CI 99.6-100%, respectively) and for trisomy 18 and monosomy X was 99.9% (938/939, CI 99.4-100%; and 953/954, CI 99.4-100%, respectively). However, 16% (20/125) of aneuploid samples did not return a result; 50% (10/20) had a fetal fraction below the 1.5th percentile of euploid pregnancies. Aneuploidy rate was significantly higher in these samples (P<.001, odds ratio 9.2, CI 4.4-19.0). Sensitivity and specificity did not differ in low-risk and high-risk populations. CONCLUSIONS: This noninvasive prenatal screen performed with high sensitivity and specificity in high-risk and low-risk cohorts. Aneuploid samples were significantly more likely to not return a result; the number of aneuploidy samples was especially increased among samples with low fetal fraction. This underscores the importance of redraws or, in rare cases, invasive procedures based on low fetal fraction. [ABSTRACT FROM AUTHOR]