Switching Networked Attitude Control of an Unmanned Quadrotor

George Nikolakopoulos,Kostas Alexis 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.2

In this article, a switching networked attitude controller for an unmanned quadrotor over a wireless sensor network is presented. To deal with the network induced time varying delays, the quadrotor is being modeled as a switching time varying linear system, while the applied switching output feedback control scheme, is calculated based on Linear Matrix Inequalities, and is able to guarantee the stability of the quadrotor under arbitrary changes in the time delays.

Extended-Duration Treatment of Superficial Vein Thrombosis of the Lower Limbs with Tinzaparin

Konstantinos M. Nikolakopoulos,Stavros K. Kakkos,Chrysanthi P. Papageorgopoulou,Ioannis A. Tsolakis 대한혈관외과학회 2018 Vascular Specialist International Vol.34 No.1

Purpose: To identify risk factors for recurrent thromboembolic events (RTEs) and define the optimum duration of treatment with tinzaparin in patients with superficial vein thrombosis (SVT) of the lower limbs. Materials and Methods: A total of 147 consecutive patients with significant SVT were treated with subcutaneously administered tinzaparin. The composite primary endpoint of the study was RTE, deep-vein thrombosis (DVT) and/or pulmonary embolism (PE) at 120 days. Patients were stratified into group A, where patients received a variable dose of tinzaparin for up to 60 days (n=98), and a subsequent group B-ext, where patients received a standardized intermediate dose of tinzaparin (n=49) for 90 days. Results: RTEs occurred in 15/147 patients (10.2%), including recurrent SVT (n=10), DVT (n=4) and fatal PE (n=1). RTEs were less frequent in group B-ext (0% vs. 15.3% for group A, P=0.004), a difference that remained significant at the oneyear follow-up. Clinically extensive SVT was an independent predictor for RTEs (hazard ratio, 5.94; 95% confidence interval, 2.05-17.23; P=0.001, Cox regression). Predictors or DVT or PE in group A included clinically extensive SVT (P=0.004), absence of local pain (P=0.023) and the ultrasound findings of superficial axial vein thrombosis (any, P=0.006 or isolated, P=0.036) and multiple thrombosed superficial venous sites (P<0.001). Conclusion: An extended three-month regimen of tinzaparin in patients with SVT of the lower limbs is more effective than a shorter course and may be desirable in patients with risk factors.

Pharmacological Thromboprophylaxis after Major Abdominal Surgery: Should the Duration be Individualized?

Chrysanthi Papageorgopoulou,Konstantinos Nikolakopoulos,Charalampos Seretis 대한혈관외과학회 2022 Vascular Specialist International Vol.38 No.2

Experimental Constrained Optimal Attitude Control of a Quadrotor Subject to Wind Disturbances

Kostas Alexis,George Nikolakopoulos,Anthony Tzes 제어·로봇·시스템학회 2014 International Journal of Control, Automation, and Vol.12 No.6

The design and experimental verification of a Constrained Finite Time Optimal Controller (CFTOC) for attitude maneuvers of an Unmanned Quadrotor operating under severe wind conditions is the subject of this article. The quadrotor’s nonlinear dynamics are linearized in various operating points resulting in a set of piecewise affine models. The CFTO–controller is designed for set-point maneuvers taking into account the switching between the linear models and the state and actuation constraints. The control scheme is applied on experimental studies on a prototype quadrotor operating both in absence and under presence of forcible atmospheric disturbances. Extended experimental results indicate that the proposed control approach attenuates the effects of induced wind–gusts while performing accurate attitude set–point maneuvers.

Switching Model Predictive Control of a Pneumatic Artificial Muscle

George Andrikopoulos,George Nikolakopoulos,Ioannis Arvanitakis,Stamatis Manesis 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.6

In this article, a switching Model Predictive Controller (sMPC) scheme for the position control of a Pneumatic Artificial Muscle (PAM) is being presented. The control scheme is based on a constrained linear and PieceWise Affine (PWA) system model approximation that is able to capture the high nonlinearities of the PAM and improve the overall model accuracy, and is composed of: a) a feed-forward term regulating control input at specific reference set-points, and b) a switching Model Predic-tive Controller handling any deviations from the system’s equilibrium points. Extended simulation studies were utilized in order to investigate and evaluate the efficacy of the suggested controller in the positioning problem of a PAM.

A Full Error Dynamics Switching Modeling and Control Scheme for an Articulated Vehicle

Thaker Nayl,George Nikolakopoulos,Thomas Gustafsson 제어·로봇·시스템학회 2015 International Journal of Control, Automation, and Vol.13 No.5

In this article, a complete analysis towards the development of a switching modeling and control framework for an articulated vehicle, under the effect of varying slip angles will be presented. The established nonlinear kinematic model, of the nonholonomic articulated vehicle, will be transformed into an error dynamics model, which in the sequel will be linearized around multiple nominal slip angle cases. The proposed control architecture will consist of a switching control scheme, based on multiple model predictive controllers, for the articulated vehicle under varying slip angles. The controllers will be developed in order to improve the performance of the articulated vehicle’s path tracking, while compensating the varying slippage effect. The current measured slip angle is being considered as the switching rule and a corresponding switching control scheme is being defined, being able to apply constraints on the states, the control signal and the output variables. Both the non-slip and slip models will be derived to highlight the significance of accounting for slips in path following control and their significant effect on deteriorating the performance of the overall control scheme when not considered. Multiple simulation results will be presented to prove the efficacy of the overall suggested scheme.

A Comparative Field Study of Global Pose Estimation Algorithms in Subterranean Environments

Nikolaos Stathoulopoulos,Anton Koval,George Nikolakopoulos 제어·로봇·시스템학회 2024 International Journal of Control, Automation, and Vol.22 No.2

In this article, we perform a novel and extended field evaluation of the state-of-the-art algorithmic frameworks’ performance on global pose estimation. More specifically, we focus on relocalizing a mobile robot in a pre-built 3D point cloud map of a large subterranean environment. The evaluation is divided into two parts. The first part consists of multiple simulations performed in two different Gazebo SubT worlds, where one is flat with various types of features, while another has uneven structure and is more textured. The second part is an experimental evaluation and takes place in a real-world underground tunnel. In all evaluation tests, the robot’s pose is selected in such a way that we can test the robustness, as well as the feature extraction capability, of each algorithm. The evaluation is carried out using three ROS packages: a) hdl_global_localization using both BBS and FPFH+RANSAC, b) LIO-SAM_based_relocalization, and c) Fast-LIO-Localization. Our goal is to have a clear view of each algorithm’s efficiency in terms of CPU load, memory allocation and time to relocalize, while we increase the size of the map and transverse the robot in different parts of the map.

A Systematic Review and Meta-Analysis of Randomized Trials Comparing Two-Stage with One-Stage Brachio-Basilic Vein Fistulas

Stavros K. Kakkos,George C. Lampropoulos,Konstantinos M. Nikolakopoulos,Ioannis A. Tsolakis,Spyros I. Papadoulas,Evangelos C. Papachristou,Dimitrios Goumenos,Miltos K. Lazarides 대한혈관외과학회 2018 Vascular Specialist International Vol.34 No.3

Purpose: There is currently debate if brachio-basilic vein fistula (BBVF) should be performed as a one-stage or two-stage procedure. The aim of the present study was to perform a systematic review and meta-analysis on BBVF staging.Materials and Methods: On February 25, 2016, a search for randomized-controlled trials (RCTs) on BBVF procedures was performed in MEDLINE and Scopus data-bases. Meta-analyses were performed with fixed-effect or random-effects models as appropriate with risk ratios (RRs). The primary efficacy and safety outcome measures were BBVF maturation and development of complications, respectively. Specific types of complications, including loss of functional secondary patency and long-term complications were all secondary outcome measures.Results: We identified three RCTs reporting on 126 patients. Maturation failure of two-stage BBVFs (3/47, 6.4%) was less frequent than one-stage BBVFs (16/79, 20.3%; RR, 0.27; P=0.02). Complication rates of two-stage and one-stage BBVFs were similar (RR, 0.80; P=0.54), but on sensitivity analysis these were less likely to occur with two-stage BBVFs (37% vs. 69% for one-stage BBVFs; RR, 0.57; P=0.03). Two-stage BBVFs were less likely to lose their functional secondary patency (21.3% vs. 31.6% for one-stage BBVFs; RR, 0.61; P=0.11). This non-significant trend be-came significant (RR, 0.36; P=0.02) on sensitivity analysis. There was no difference in specific complication rates of the two study groups. Conclusion: Among candidates for BBVF fistula, there is evidence to suggest that two-stage BBVFs achieve higher maturation rates compared to one-stage BBVFs. The evidence for difference in long-term secondary patency is less robust, calling for further research.

Fault Resilient Decentralized Multi-sensorial Fusion Based Pose Estimation for Autonomous Navigation Around Asteroid

Moumita Mukherjee,Avijit Banerjee,Sumeet Gajanan Satpute,George Nikolakopoulos 제어·로봇·시스템학회 2023 International Journal of Control, Automation, and Vol.21 No.6

A decentralized multi-sensor fusion-based resilient pose estimation architecture for autonomous navigation of satellites around an asteroid is presented in this article. Navigation around an asteroid is challenging due to dynamic illumination conditions, which restricts the vision-based localization and is partially ineffective for a longer duration of the operation. Moreover, drift in sensor measurement and temporal sensor failure is often encountered in long-duration sustainable space missions. This is more so around a debris-prone region, where momentary obstruction leads to inaccurate sensor measurement for a temporary period of operation. In order to establish a resilient localization mechanism for satellites around an asteroid, the proposed framework embeds a unique automatic fault detection and isolation approach in a decentralized fusion formalism. Furthermore, a unified framework can operate autonomously during temporary and long-range inoperative periods. In the first stage, innovative fault detection is proposed, which operates based on the residual of a judiciously designed filter assembly. Secondly, a novel fault-resilient isolation fusion called the fault-resilient optimal information filter fusion (FR-OIF) technique is presented, enabling self-resiliency by embedding an inbuilt fault isolation mechanism. The proposed resilient asteroid navigation approach is demonstrated with a simulation study considering a satellite equipped with multiple onboard sensors such as an inertial measurement unit, star tracker, camera and 3D Lidar in the proximity of the asteroid Ryugu. At the same time, its superiority is also demonstrated through a comparison with the centralized multi-sensorial fusion approach.

Endovascular Juxtarenal Aortic Aneurysm Repair Using the ALTO Abdominal Stent Graft System: The First Case Series

Fotios O. Efthymiou,Andreas L. Tsimpoukis,Marianna A. Papatsirou,Natasa K. Kouri,Spyros I. Papadoulas,Konstantinos M. Nikolakopoulos,Stavros K. Kakkos 대한혈관외과학회 2022 Vascular Specialist International Vol.38 No.2

The ALTO abdominal stent graft system (Endologix Inc., Irvine, CA, USA) is a latest-generation polymer-based device used to treat patients with abdominal aortic aneurysms. The present study describes the first case series of patients with abdominal aortic aneurysms, including two patients with juxtarenal aneurysms, treated using the ALTO stent graft system. Six males were treated using the ALTO device at a single public center. All procedures were uneventful, and the dosimetric results recorded in terms of kerma-area product and fluoroscopy time were similar to those reported in previous studies. At the 1-month follow-up, computed tomography angiography showed no evidence of endoleak, device migration, thrombosis, or structural graft failure. This clinical series demonstrates that the use of the ALTO stent graft system is associated with promising patient outcomes. Lifelong postoperative imaging surveillance may highlight possible late failures and suggest potential graft improvements.