54 research outputs found
Extended Object Tracking of Pedestrians in Automotive Applications
No full textRecent advances in sensor technology have lead to increased resolution of novel sensors, while tracking applications where distance between sensors and objects of interest is very small have gained research interest recently. In these cases, it is possible that multiple sensor detections are generated by each object of interest. Extended Object Tracking (EOT) approaches consist of algorithms which make use of multiple sensor detections per object to jointly estimate their kinematic and shape extent attributes within the Bayesian tracking framework. In the last decade, various EOT algorithms have been proposed for different types of tracking applications. This M.Sc. thesis project addresses the problem of extended tracking of a single pedestrian walking in the area of a stationary vehicle (referred as ego-vehicle in this report) during a real automotive scenario. The objective is to achieve accurate estimation of both the kinematic attributes (2D centroid position/velocity), as well as its shape extent in x-y plane. In more detail, PreScan software is enabled to design a simulation scenario that is very close to a real automotive application, in terms of motion characteristics of objects of interest and sensor data acquisition. In the considered scenario, different sensor modalities are mounted on the ego-vehicle, namely a Lidar sensor and a mono camera sensor. Moreover, OpenPose library is employed to to obtain pose detections of human body parts from obtained camera images. Concerning shape extent representation, the simplest and most popular approach in previous studies, in general and especially for VRUs tracking, is to assume an elliptical shape. In fact, the Random Matrix Model (RMM), proposed originally by Koch, 2008, is a state-of-the-art EOT state modeling approach that allows for joint estimation of centroid kinematics and physical extent for considered elliptical objects of interest. Based on that, a RMM-based filter using Lidar position measurements has been proposed by Feldmann, 2011. In this project, this algorithm is used as a baseline filter for comparison with our proposed algorithm. In addition, an alternative tracking algorithm is proposed in this study, which has the following differences with respect to the baseline filter: State Initialization of the filter: In our proposed version of the tracking algorithm, human pose detections of shoulders and ankles are are associated with obtained Lidar position measurements in order to provide initial values for the kinematic state (2D position/velocity) and shape parameters (ellipse orientation and semi-axes lengths) of the pedestrian.Measurement Update step of the filter: In our proposed version of the tracking algorithm, camera-obtained pose detections of pedestrian shoulders are associated with obtained Lidar position measurements in order to create an extra measurement, for pedestrian heading angle. Subsequently, a nonlinear filtering update step fusing Lidar-obtained point cloud data for pedestrian position and human-pose-obtained measurement for pedestrian heading angle is implemented. Both considered tracking algorithms are evaluated for the designed simulation scenario. In detail, the following performance metrics are used for evaluation of each filter: RMSE for estimated pedestrian 2D position and velocity, respectively.Modified Hausdorff distance for estimated pedestrian shape extent. In more detail, Monte Carlo simulations with multiple runs are designed to evaluate performance of each state initialization approach and each tracking algorithm, where the following parameters change in each run: Additive zero-mean Gaussian measurement noise on obtained Lidar position detections. Initial simulation timestep.Mechanical Engineering | Systems and Contro
Performance Assessment of Various PV Module Types under Desert Conditions through Device Simulations and Outdoor Measurements
No full textThe Middle East region is considered as one the most promising areas for PV deployment due to its vast solar potential. Despite this fact, successful deployment of PV systems in the region is challenging due to local weather conditions. Dust storms are very frequent in these areas, which not only cause heavy soiling on PV module surface but may also significantly affect the form and intensity of the solar spectrum due to airborne dust particles which scatter sunlight. In addition, the combination of high ambient temperatures and increased irradiance levels pose additional challenges in PV module performance and reliability. Therefore, in this work a customized device simulator is proposed aiming to provide accurate calculations of PV module energy yield and performance using local climate data including solar radiation spectrum and temperature measurements. Simulation data are validated with outdoor IV measurements on various types of commercial c-Si based PV modules including polycrystalline Si and bifacial PERC, located at KAUST University at the Western Region of Saudi Arabia.Seasonal performance variations of various solar cell technologies due to local spectrum variations are also investigated.The authors acknowledge the support of the Supercomputing Laboratory at King Abdullah University of Science & Technology (KAUST) in Thuwal, Saudi Arabia; the KAUST Economic development for their technical support and Saudi Aramco R&D Center - Carbon Management Division for their financial support through grant RGC#3893
Seasonal Performance Assessment of Various PV Technologies in a Desert Climate through Device Simulations and Outdoor Measurements
No full textMiddle East is considered as one the most promising areas for PV deployment due to its vast solar potential. Successful deployment of PV systems in the region is challenging, however, due to local weather conditions. Frequent dust storms in these areas cause heavy soiling on PV module surface and significantly affecting the solar panels performance. In addition, the combination of high ambient temperatures and increased UV irradiance levels pose additional challenges in PV module reliability. This work focuses on the influence of local climate effects
on the performance and energy yield of various PV module technologies by processing local weather data over various periods. Simulation data are validated with outdoor IV measurements on various types of commercial c-Si based PV modules, located at KAUST University, Western Region of Saudi Arabia.The authors acknowledge the support of the Supercomputing Laboratory at King Abdullah University of Science & Technology (KAUST) in Thuwal, Saudi Arabia; the KAUST Economic development for their technical support and Saudi Aramco R&D Center -Carbon Management Division for their financial support through grant RGC#3893
Mini-laparoscopic cholecystectomy with the MiniLap® percutaneous surgical system: a series of 32 patients
No full textKonstantinos Sapalidis,1 Christoforos Kosmidis,1 Nikos Michalopoulos,1 Stylianni Laskou,1 Efstathios Pavlidis,1 Stelios Mantalovas,1 Dimitrios Giannakidis,1 Aikaterini Amaniti,1 Charilaos Koulouris,1 Athanasios Katsaounis,1 Alexandru C Munteanu,1 Valeriou Surlin,1 Paul Zarogoulidis,2 Isaak Kesisoglou1 1Third Department of Surgery, AHEPA Hospital, Aristotle University of Thessaloniki, Thessaloniki, Greece; 2Pulmonary-Oncology Department, “Theageneio” Cancer Hospital, Thessaloniki, Greece Background: In recent years, mini-laparoscopic procedures are gaining the preference of most surgeons due to their potentially better surgical outcomes. The Mini Lap Percutaneous Surgical System with MiniGrip® Handle is currently the less invasive instrument and can be applied to a wide range of operations. The current paper presents its application on percutaneous laparoscopic cholecystectomy. Materials and methods: From January 2017 to June 2017, 32 patients underwent percutaneous laparoscopic cholecystectomy with the MiniLap® system. All operations were performed by the same surgical team. Results: No conversions and no overall complications were reported. Drainage were not necessary. Mean surgical time was 35 minutes, while patients were released in <24 hours after the operation. Conclusion: The MiniLap system with the use of the mini grip handle seems to sustain the benefits of performing laparoscopically. However, further trials should be conducted so as to establish its safety on cholecystectomies. Keywords: cholecystectomy, minimally invasive surgery, MiniGrip handle, percutaneous cholecystectomy, mini-laparoscop
Regularized semiclassical limits: Linear flows with infinite Lyapunov exponents
No full textSemiclassical asymptotics for Schrödinger equations with non-smooth potentials give rise to ill-posed formal semiclassical limits. These problems have attracted a lot of attention in the last few years, as a proxy for the treatment of eigenvalue crossings, i.e. general systems. It has recently been shown that the semiclassical limit for conical singularities is in fact well-posed, as long as the Wigner measure (WM) stays away from singular saddle points. In this work we develop a family of refined semiclassical estimates, and use them to derive regularized transport equations for saddle points with infinite Lyapunov exponents, extending the aforementioned recent results. In the process we answer a related question posed by P.L. Lions and T. Paul in 1993. If we consider more singular potentials, our rigorous estimates break down. To investigate whether conical saddle points, such as -|x|, admit a regularized transport asymptotic approximation, we employ a numerical solver based on posteriori error control. Thus rigorous upper bounds for the asymptotic error in concrete problems are generated. In particular, specific phenomena which render invalid any regularized transport for -|x| are identified and quantified. In that sense our rigorous results are sharp. Finally, we use our findings to formulate a precise conjecture for the condition under which conical saddle points admit a regularized transport solution for the WM. © 2016 International Press.Part of this work was completed while Th. Katsaounis was visiting the Dept. of Mathematics of Univ. of Leicester, UK. The author would like to thank prof. E. Georgoulis and the department for their hospitality and support
Localization in Adiabatic Shear Flow Via Geometric Theory of Singular Perturbations
No full textWe study localization occurring during high-speed shear deformations of metals leading to the formation of shear bands. The localization instability results from the competition between Hadamard instability (caused by softening response) and the stabilizing effects of strain rate hardening. We consider a hyperbolic–parabolic system that expresses the above mechanism and construct self-similar solutions of localizing type that arise as the outcome of the above competition. The existence of self-similar solutions is turned, via a series of transformations, into a problem of constructing a heteroclinic orbit for an induced dynamical system. The dynamical system is in four dimensions but has a fast–slow structure with respect to a small parameter capturing the strength of strain rate hardening. Geometric singular perturbation theory is applied to construct the heteroclinic orbit as a transversal intersection of two invariant manifolds in the phase space.The authors thank Prof. Peter Szmolyan for valuable discussions on the use of geometric singular perturbation theory
Design of a predictive score to assess the risk of developing hypocalcemia after total thyroidectomy. A retrospective study
No full textAnastasios Papanastasiou,1 Konstantinos Sapalidis,1 Stylianos Mantalobas,1 Stefanos Atmatzidis,1 Nikolaos Michalopoulos,1 Valeriu Surlin,1 Athanasios Katsaounis,1 Aikaterini Amaniti,1 Paul Zarogoulidis,1 Ioannis Passos,1 Charilaos Koulouris,1 Efstathios Pavlidis,1 Dimitrios Giannakidis,1 Stelian Mogoanta,2 Christoforos Kosmidis,1 Isaak Kesisoglou113rd Department of Surgery, “AHEPA” University Hospital, Aristotle University of Thessaloniki, Medical School, Thessaloniki, Greece; 2Department of Surgery, Faculty of Dentistry, University of Medicine and Pharmacy of Craiova, Craiova, RomaniaBackground: Temporary hypocalcemia is the most common complication in patients after total thyroidectomy. To date, according to the literature, various predictors of the above complication have been proposed, but none of them seems to be effective enough.Objectives: The aim of this study was to develop a reliable predictive tool for biochemical hypocalcemia in the first 48 hrs after total thyroidectomy without central dissection by analyzing several parameters relevant to this operation and to suggest a new score.Methods: A retrospective study was performed on patients who had undergone total thyroidectomy without central neck dissection from October 2017 until January 2018. Data were collected from 36 patients and studied if there was a statistically significant relationship between the risk of hypocalcemia and 10 preselected prognostic factors.Results: The prognostic score was formed, which included the 6 factors that showed a statistically significant relationship. Moreover, an extensive check of the predictive value of the above score was performed. It was found, therefore, that at a value of 3 and above the sensitivity was 100%, the specificity 79.16%, the positive prognostic value (PPV) 70.58% and the negative predictive value (NPV) 100%.Conclusions: High sensitivity of CaReBe’S TiP score makes it feasible to predict patients with postoperative hypocalcemia. High NPV would allow surgeons to exclude patients with a score less than 3 from supplementary calcium medication and achieve a shorter hospitalization for them.Keywords: design, thyroidectomy, hypocalcemia, prognostic factor
Emergence of Coherent Localized Structures in Shear Deformations of Temperature Dependent Fluids
No full textShear localization occurs in various instances of material instability in solid mechanics and is typically associated with Hadamard-instability for an underlying model. While Hadamard instability indicates the catastrophic growth of oscillations around a mean state, it does not by itself explain the formation of coherent structures typically observed in localization. The latter is a nonlinear effect and its analysis is the main objective of this article. We consider a model that captures the main mechanisms observed in high strain-rate deformation of metals, and describes shear motions of temperature dependent non-Newtonian fluids. For a special dependence of the viscosity on the temperature, we carry out a linearized stability analysis around a base state of uniform shearing solutions, and quantitatively assess the effects of the various mechanisms affecting the problem: thermal softening, momentum diffusion and thermal diffusion. Then, we turn to the nonlinear model, and construct localized states -in the form of similarity solutions -that emerge as coherent structures in the localization process. This justifies a scenario for localization that is proposed on the basis of asymptotic analysis in [10]
Axisymmetric Flows with Swirl for Euler and Navier–Stokes Equations
No full textWe consider the incompressible axisymmetric Navier–Stokes equations with swirl as an idealized model for tornado-like flows. Assuming an infinite vortex line which interacts with a boundary surface resembles the tornado core, we look for stationary self-similar solutions of the axisymmetric Euler and axisymmetric Navier–Stokes equations. We are particularly interested in the connection of the two problems in the zero-viscosity limit. First, we construct a class of explicit stationary self-similar solutions for the axisymmetric Euler equations. Second, we consider the possibility of discontinuous solutions and prove that there do not exist self-similar stationary Euler solutions with slip discontinuity. This nonexistence result is extended to a class of flows where there is mass input or mass loss through the vortex core. Third, we consider solutions of the Euler equations as zero-viscosity limits of solutions to Navier–Stokes. Using techniques from the theory of Riemann problems for conservation laws, we prove that, under certain assumptions, stationary self-similar solutions of the axisymmetric Navier–Stokes equations converge to stationary self-similar solutions of the axisymmetric Euler equations as ν→0. This allows to characterize the type of Euler solutions that arise via viscosity limits.Research was partially supported by King Abdullah University of Science and Technology (KAUST) (Grant No. BAS/1/1652-01-01) baseline funds
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