Experimental investigation of a new steel friction device with link element for seismic strengthening of structures

Papadopoulos, Panikos K.,Salonikios, Thomas N.,Dimitrakis, Stergios A.,Papadopoulos, Alkis P. Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.4

In the present work a new friction device, with a set of single or double rotational friction flanges and a link element, is described and tested. The mechanism may be applied for the strengthening of existing r/c or steel buildings as well as in new constructed buildings. The device has selectable variable behavior in different levels of displacement and an interlock mechanism that is provided by the link element. The link element may be designed to lock at preselected level of displacement, offering in this way an extra safety reserve against strong earthquakes. A summary of the existing literature about other similar mechanisms is initially presented in this paper. The proposed mechanism is presented and described in details. Laboratory experiments are presented in detail and the resulted response that proves the efficiency of the mechanism at selectable levels of strength capacity is discussed. Drawings of the mechanism attached to a r/c frame with connection details are also included. Finally a dynamic analysis of two r/c frames, with and without the proposed mechanism attached, is performed and the resulted response is given. The main conclusion is that the proposed mechanism is a cheap and efficient devise for the improvement of the performance of new or existing framed buildings to seismic loads.

A Fast Steady-State Loss Model of a Modular Multilevel Converter for Optimization Purposes

A. Papadopoulos,S. Rodrigues,E. Kontos,T. Todorcevic,P. Bauer 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

Lesnicar and Marquardt introduced a Modular Multilevel Converter (MMC) topology back in 2003. Although this topology has received a great deal of attention in recent years by both the research community and industry, hitherto no steadystate model has been developed which accurately captured all the relevant power losses while being computationally light. Hence, the aim of this paper is to introduce a fast MMC loss model which captures the key sources of power losses in steady-state operation. The model only requires information which is known a priori, e.g. datasheet information of the components. The proposed model was compared to a loss model developed by Marquardt. Both models presented similar results under the same assumptions. However, the proposed model captures the switching losses more realistically and considers the temperature of operation of the electronics, as well as the losses of the inductors and cooling system in the overall efficiency of the MMC. To validate these new additions, the proposed steady-state model was compared to a dynamic model. Once again the proposed model was able to capture the different sources of power losses. Nonetheless, results demonstrated that the balancing strategy greatly influences the efficiency of the MMC. Therefore, information regarding the envisioned control strategy is necessary to accurately calculate the efficiency curve of the MMC.

Experimental investigation of a new steel friction device with link element for seismic strengthening of structures

Panikos K. Papadopoulos,Thomas N. Salonikios,Stergios A. Dimitrakis,Alkis P. Papadopoulos 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.4

In the present work a new friction device, with a set of single or double rotational friction flanges and a link element, is described and tested. The mechanism may be applied for the strengthening of existing r/c or steel buildings as well as in new constructed buildings. The device has selectable variable behavior in different levels of displacement and an interlock meαchanism that is provided by the link element. The link element may be designed to lock at preselected level of displacement, offering in this way an extra safety reserve against strong earthquakes. A summary of the existing literature about other similar mechanisms is initially presented in this paper. The proposed mechanism is presented and described in details. Laboratory experiments are presented in detail and the resulted response that proves the efficiency of the mechanism at selectable levels of strength capacity is discussed. Drawings of the mechanism attached to a r/c frame with connection details are also included. Finally a dynamic analysis of two r/c frames, with and without the proposed mechanism attached, is performed and the resulted response is given. The main conclusion is that the proposed mechanism is a cheap and efficient devise for the improvement of the performance of new or existing framed buildings to seismic loads.

Benchmark Results on the Linearized Equations of Motion of an Uncontrolled Bicycle

A.L. Schwab,J.P. Meijaard,J.M. Papadopoulos 대한기계학회 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.1S

In this paper we present the lineanzed equations of motion for a bicycle as a benchmark The results obtained by pencil-and-paper and two programs are compared The bicycle model we consider here consists of four rigid bodies, viz a rear frame, a front frame being the front fork and handlebar assembly, a rear wheel and a front wheel, which are connected by revolute Joints<br/> The contact between the knife-edge wheels and the flat level surface is modelled by holonomic constraints In the normal direction and by non-holonomic constraints In the longitudinal and lateral direction The rider is rigidly attached to the rear frame With hands free from the hand-lebat This system has these degrees of freedom, the roll, the steer, and the forward speed For the benchmark we consider the linear Ized equations for small perturbations of the upright steady forward motion The entries of the matrices of these equations form the basis for comparison Three diffrent kinds of methods to obtain the results are compared pencil-and-paper, the numeric multibody dynamics program SPACAR, and the symbolic software system Autosim Because the results of the three methods are the same within the machine round-off error, we assume that the results are correct and can be used as a bicycle dynamics benchmark<br/>

An algorithm for fast 3D inversion of surface electrical resistivity tomography data: application on imaging buried antiquities

Papadopoulos, N.G.,Tsourlos, P.,Papazachos, C.,Tsokas, G.N.,Sarris, A.,Kim, J.H. Blackwell Publishing Ltd 2011 Geophysical prospecting Vol.59 No.3

<P><B>ABSTRACT</B></P><P>In this work a new algorithm for the fast and efficient 3D inversion of conventional 2D surface electrical resistivity tomography lines is presented. The proposed approach lies on the assumption that for every surface measurement there is a large number of 3D parameters with very small absolute Jacobian matrix values, which can be excluded in advance from the Jacobian matrix calculation, as they do not contribute significant information in the inversion procedure. A sensitivity analysis for both homogeneous and inhomogeneous earth models showed that each measurement has a specific region of influence, which can be limited to parameters in a critical rectangular prism volume. Application of the proposed algorithm accelerated almost three times the Jacobian (sensitivity) matrix calculation for the data sets tested in this work. Moreover, application of the least squares regression iterative inversion technique, resulted in a new 3D resistivity inversion algorithm more than 2.7 times faster and with computer memory requirements less than half compared to the original algorithm. The efficiency and accuracy of the algorithm was verified using synthetic models representing typical archaeological structures, as well as field data collected from two archaeological sites in Greece, employing different electrode configurations. The applicability of the presented approach is demonstrated for archaeological investigations and the basic idea of the proposed algorithm can be easily extended for the inversion of other geophysical data.</P>

Cooperative Object Manipulation with Contact Impact Using Multiple Impedance Control

S. Ali A. Moosavian,Evangelos Papadopoulos 제어·로봇·시스템학회 2010 International Journal of Control, Automation, and Vol.8 No.2

Impedance Control imposes a desired behavior on a single manipulator interacting with its environment. The Multiple Impedance Control (MIC) enforces a designated impedance on both a ma-nipulated object, and all cooperating manipulators. Similar to the standard impedance control, one of the benefits of this algorithm is the ability to perform both free motions and contact tasks without switching control modes. At the same time, the potentially large object inertia and other forces are taken into account. In this paper, the general formulation for the MIC algorithm is developed for dis-tinct cooperating manipulators, and important issues are detailed. Using a benchmark system, the re-sponse of the MIC algorithm is compared to that of the Object Impedance Control (OIC). It is shown that in the presence of flexibility, the MIC algorithm results in an improved performance. Next, a sys-tem of two cooperating two-link manipulators is simulated, in which a Remote Centre Compliance is attached to the second end-effector. As simulation results show, the response of the MIC algorithm is smooth, even in the presence of an impact due to collision with an obstacle. It is revealed by both error analysis and simulation that under the MIC law, all participating manipulators, and the manipulated object exhibit the same designated impedance behavior. This guarantees good tracking of manipulators and the object based on the chosen impedance laws which describe desired error dynamics, in performing a manipulation task.

Gallstone Obstructive Ileus 3 Years Post-cholecystectomy to a Patient with an Old Ileoileal Anastomosis

TS Papavramidis,S Potsi,D Paramythiotis,A Michalopoulos,VN Papadopoulos,V Douros,A Pantoleon,A Foutzila-Kalogera,I Ekonomou,N Harlaftis 대한의학회 2009 Journal of Korean medical science Vol.24 No.6

The present case is one of gallstone obstructive ileus due to gallstones 3 yr after laparoscopic cholecystectomy. It is interesting because of the sex of the patient, the fact that ileus occurred 3 yr after cholecystectomy and that the localization of the obstruction was an old side-to-side ileoileal anastomosis due to a diverticulectomy following intussusception of Meckels’ diverticulum at the age of 3.

IL-4 increases type 2, but not type 1, cytokine production in CD8 ⁺ T cells from mild atopic asthmatics

Stanciu, Luminita A,Roberts, Kevan,Papadopoulos, Nikolaos G,Cho, Sang-Heon,Holgate, Stephen T,Coyle, Anthony J,Johnston, Sebastian L BioMed Central 2005 Respiratory research Vol.6 No.-

<P><B>Background</B></P><P>Virus infections are the major cause of asthma exacerbations. CD8<SUP>+ </SUP>T cells have an important role in antiviral immune responses and animal studies suggest a role for CD8<SUP>+ </SUP>T cells in the pathogenesis of virus-induced asthma exacerbations. We have previously shown that the presence of IL-4 during stimulation increases the frequency of IL-5-positive cells and CD30 surface staining in CD8<SUP>+ </SUP>T cells from healthy, normal subjects. In this study, we investigated whether excess IL-4 during repeated TCR/CD3 stimulation of CD8<SUP>+ </SUP>T cells from atopic asthmatic subjects alters the balance of type 1/type 2 cytokine production in favour of the latter.</P><P><B>Methods</B></P><P>Peripheral blood CD8<SUP>+ </SUP>T cells from mild atopic asthmatic subjects were stimulated <I>in vitro </I>with anti-CD3 and IL-2 ± excess IL-4 and the expression of activation and adhesion molecules and type 1 and type 2 cytokine production were assessed.</P><P><B>Results</B></P><P>Surface expression of very late antigen-4 [VLA-4] and LFA-1 was decreased and the production of the type 2 cytokines IL-5 and IL-13 was augmented by the presence of IL-4 during stimulation of CD8<SUP>+ </SUP>T cells from mild atopic asthmatics.</P><P><B>Conclusion</B></P><P>These data suggest that during a respiratory virus infection activated CD8<SUP>+ </SUP>T cells from asthmatic subjects may produce excess type 2 cytokines and may contribute to asthma exacerbation by augmenting allergic inflammation.</P>

Complications reported with the use of orthodontic miniscrews

Antonino Lo Giudice,Lorenzo Rustico,Miriam Longo,Giacomo Oteri,Moschos A,Papadopoulos,Riccardo Nucera 대한치과교정학회 2021 대한치과교정학회지 Vol.51 No.3

Objective: The aim of this systematic review was to evaluate the complications and side effects associated with the clinical use of orthodontic miniscrews by systematically reviewing the best available evidence. Methods: A survey of articles published up to March 2020 investigating the complications associated with miniscrew insertion, in both the maxilla and mandible, was performed using 7 electronic databases. Clinical studies, case reports, and case series reporting complications associated with the use of orthodontic miniscrew implants were included. Two authors independently performed study selection, data extraction, and risk-of-bias assessment. Results: The database survey yielded 24 articles. The risk-of-bias assessment revealed low methodological quality for the included studies. The most frequent adverse event reported was root injury with an associated periradicular lesion, vitality loss, pink discoloration of the tooth, and transitory loss of pulp sensitivity. Chronic inflammation of the soft tissue surrounding the miniscrew with mucosal overgrowth was also reported. The other adverse events reported were lesion of the buccal mucosa at the insertion site, soft-tissue necrosis, and perforation of the floor of the nasal cavity and maxillary sinus. Adverse events were also reported after miniscrew removal and included secondary bleeding, miniscrew fracture, scars, and exostosis. Conclusions: These findings highlight the need for clinicians to preliminarily assess generic and specific insertion site complications and side effects.