34 research outputs found
Parametric Analysis of Viscoelastic Hyperboloidal Helical Rod
No full textErmis, Merve/0000-0003-0201-6586; Kutlu, Akif/0000-0001-6865-3022; Eratlı, Nihal/0000-0003-3788-9870; OMURTAG, Mehmet Hakki/0000-0003-2669-6459The objective of this study is to perform a pioneering research about a viscoelastic hyperboloidal helical rod having a standard type of distortional behavior and a Kelvin type of bulk compressibility. Field equations are based on the Timoshenko beam theory, and the exact curvatures of the hyperboloidal geometry are considered through the formulation. The numerical analysis is carried out by the mixed finite element method, considering the rotary inertia, in the Laplace space, and the results are transformed back to time space numerically using the modified Durbin's algorithm. A cantilevered hyperboloidal helical rod having solid circular, hollow circular, and thin-walled hollow circular cross sections is handled, and the rod is loaded by rectangular and triangular impulsive types of point load at the tip. Through the analysis, different values of retardation time, three different relaxation functions associated with shear modulus, and three different creep functions associated with bulk modulus are handled. Finally, a benchmark example is presented, and the influence of the loading and the material parameters on the helix geometry is discussed.Scientific and Technological Research Council of Turkey [111M308]; Research Foundation of ITU [38078]The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research is supported by the Scientific and Technological Research Council of Turkey under project no. 111M308 and Research Foundation of ITU under project no. 38078
Multi-agent Planning and Coordination for Automated Aircraft Ground Handling
No full textInspired by the vision of fully autonomous airside operations at Schiphol airport, this study aims to contribute to the short-term goal of automated aircraft ground handling. In this research, we design and evaluate a multi-agent system for planning of automated ground handling. There are two main components in the system, task allocation optimization, and multi-agent path planning. To allocate tasks to ground support equipment (GSE) vehicles, an auction mechanism inspired by temporal sequential single item (TeSSI) auction is proposed. Ground handling tasks scheduling for GSE vehicles is modeled as several single-vehicle pickup and delivery optimization problems (SPDP), and the values of the objective functions are applied to generate bids for GSE vehicle agents in the auction. Moreover, Prioritized Safe Interval Path Planning for large agents (LA-SIPP) is used to plan collision-free paths for GSE vehicle agents in the model to execute tasks. Experimental studies have shown that the system is able to perform task allocation and path planning of ground handling tasks for flights in 3 aircraft stands within a 4-hour time in a reasonable computational time. Moreover, the model is capable to replan the tasks for agents when disruption happens. Applying the lowest possible numbers of vehicles used in the current operation, the model can always reach success allocation and path planning rates higher than 81% and 98%, respectively.Aerospace Engineerin
Inflammatory markers of contrast-induced nephropathy in patients with acute coronary syndrome
No full textMulti-agent planning and coordination for automated aircraft ground handling
No full textInspired by the vision of fully autonomous airside operations at Schiphol airport, this study aims to contribute to the short-term goal of automated aircraft ground handling. In this research, we design and evaluate a multi-agent system for planning of automated ground handling. There are two main components in the system: task allocation optimization and multi-agent path planning. To allocate tasks to ground support equipment (GSE) vehicles, an auction mechanism inspired by temporal sequential single item (TeSSI) auction is proposed. Ground handling tasks scheduling for GSE vehicles is modeled as several single-vehicle pickup and delivery optimization problems (SPDP), and the values of the objective functions are used to generate bids for GSE vehicle agents in the auction. Prioritized safe interval path planning for large agents (LA-SIPP) is used to plan collision-free paths for GSE vehicle agents in the model to execute tasks. The aim is to increase the success rates of allocating tasks and finding collision free paths without causing flight delays, given the limited resources such as a small number of available GSE vehicles, time windows constraints and conflicting interests of different agents. Due to the results, even for the instances with frequent flights and the most limited resources, the success rates of allocation and path planning were higher than 81% and 98%, respectively. Furthermore, periodic task allocation and path planning of the ground handling tasks for flights in three aircraft stands during a planning time window of the day, as well as replanning in case of disruptions were performed in a short CPU time. There is a lack of research dealing with the complete process of ground handling, since existing studies concerning the automation of ground handling operations involve fleet assignment or task scheduling models without an integration of detailed path planning. Our main contribution is to present a framework that combines task allocation and path planning for automation of ground handling operations and provides solutions using a multi-agent perspective.Air Transport & Operation
The Calculation of Mass Attenuation Coefficients of Well-Known Thermoluminescent Dosimetric Compounds at Wide Energy Range
No full text32nd International Physics Congress of Turkish-Physical-Society (TPS) -- SEP 06-09, 2016 -- Bodrum, TURKEYThe photon mass attenuation coefficients of LC BaSO3, CaCO3 and CaSOzi thermoluminescent dosimetric compounds at 100; 300; 500; 600; 800; 1,000; 1,500; 2,000; 3,000 and 5,000 keV gamma-ray energies were calculated. For this purpose, FLUKA Monte Carlo (MC) program which is one of the well-known MC codes was used in this study. Furthermore, obtained results were analyzed by means of ROOT program. National Institute of Standards and Technology (NIST) values were also used to compare the obtained theoretical values because the mass attenuation values of the used compounds could not found in the literature. Calculated mass attenuation coefficients were highly in accordance with the NIST values. As a consequence, FLUKA was successful in calculating the mass attenuation coefficients of the most used thennoluminescent compound.Turkish Phys SocEge UniversityEge University [2014 FEN 026]The Author thanks to Dr. E. Pilicer for his help in the calculation procedure and to Dr. C. Celiktas for his precious contribution to the study. This work was supported by Scientific Research Project of Ege University under Project No. 2014 FEN 026
Assessment of right ventricular systolic and diastolic parameters in pulmonary sarcoidosis
No full text#nofulltext# --- Yolcu, Mustafa (Arel Author)The clinical manifestations of cardiac involvement are seen in about 5% of patients with sarcoidosis; however, the incidence of cardiac involvement is higher in the autopsy series. About 14% of patients with pulmonary sarcoidosis (PS) without known cardiac involvement had diastolic dysfunction. We aimed to determine the role of parameters of right ventricular (RV) systolic and diastolic function in patients with PS without evidence of cardiac symptoms. Our study population consisted of 28 patients with grades 1–4 PS and 24 healthy subjects. This study was a clinical prospective cohort study. RV end-diastolic area was found to be significantly higher in the PS group (p=0.032). RV fractional area change (RVFAC) and tricuspid annular plane systolic excursion (TAPSE) were shown to be statistically lower in the PS group as compared to the control group (p<0.001). However, pulmonary arterial systolic pressure was significantly higher in the PS group (p=0.003). The tricuspid E velocity and E/A ratio were found to be significantly lower in the PS group (p=0.025 and 0.009, respectively), while the tricuspid A velocity and myocardial performance index (MPI) were found to be significantly lower in the control group (p=0.034 and 0.007, respectively). Early detection of cardiac involvement in PS is crucial because of the increased morbidity and risk of sudden cardiac death. RV diastolic Doppler parameters, tissue Doppler MPI, RVFAC and TAPSE are practical and cheap techniques in the diagnosis of cardiac involvement in patients with PS. A thorough transthorasic echocardiographic examination including RV systolic and diastolic functions and tissue Doppler MPI should constitute the mainstay of initial management and follow-up in PS
A Sequential Approach to the Management of Ostial Coronary Lesions via the Modified Flower Petal Technique
No full textThere is still no consensus on the optimal technique for performing percutaneous coronary intervention (PCI) in ostial coronary lesions, due to potential complications. The modified flower petal technique is one of the techniques to management of ostial lesions. It seems suitable technique in terms of covering the coronary ostium well. In this report, we discuss a patient who underwent PCI with sequential modified flower petal technique, first to the left anterior descending artery ostial lesion, and then to the circumflex artery (CXA) upon the ostium of CXA was affected after the procedure following coronary angiography
A case of stent thrombosis presenting as acute myocardial infarction related to right coronary artery originating from the left coronary system
No full textRight coronary artery (RCA) originating f min the left coronary system is a subtype of single coronary artery (SCA) anomaly, and the origin of RCA as a branch from the left anterior descending artery (LAD) is a very rare variant. A 55-year-old male who had a percutaneous coronary intervention (PCI) history was hospitalized due to acute coronary syndrome. Coronary angiography revealed an aberrant RCA originating from the mid-LAD as well as stent thrombosis. A successful PCI was performed and he was discharged from the hospital three days after the PCI. It is known that there is an increased incidence of atherosclerosis and stent thrombosis in coronary anomaly patients. Therefore, interventional cardiologists should consider the most suitable PCI strategy before stenting and avoid complex techniques
Long term results of free flaps in facial contour restoration
No full textFacial defects can be reconstructed by utilization of free tissue transfers. This can be the result of a congenital, post-traumatic, post-radiotherapy or post-surgical condition. Microsurgical reconstruction techniques enable one stage correction. We have utilized various free flaps (omentum 4, serratus anterior muscle Rap 3, scapular flap 4 and groin flap 1) for facial contour restoration in 12 patients who had tissue deficits because of Romberg's disease, hemifacial microsomia, hypoplasia due to radiotherapy, tumor resection and post trauma. All vessel anastomosis were performed by the second author. No flap was lost. In conclusion, late descent of omentum, muscle and dermal fat tissue could not be prevented, whereas there was relatively minimal sagging of scapular tissue, therefore multiple flap revisions were performed in all patients in the long term
Eigenstrain reconstruction of residual stresses induced by selective laser melting
No full textSelective laser melting (SLM) is an additive manufacturing (AM) technique that is used for metallic products. These products are built in a layer by layer manner by means of selectively melting and hence fusing a layer of metal powder with a laser scanning along a predefined path. The SLM process is able to create products with complex geometries, high accuracy, and within a single manufacturing step. Although SLM presents a number of advantages, the thermal loading causing residual stresses and distortions is an important issue in SLM products. Residual stresses may lead to a limited load resistance and cracks leading to impaired toughness. Distortions may cause the SLM product to be manufactured outside of design tolerances. Therefore, for an SLM product it is essential to accurately predict residual stresses and distortion in the design phase. In literature a great variety of modelling techniques are proposed to capture the physics of the process. Two most widely used approaches to model the process are the melting pool scale and the layer by layer modelling approach. The latter is a computationally efficient way of modelling but does not contain complex process history whereas the former is computationally expensive but can capture the effects of scanning strategy and other process parameters. In this thesis a novel modelling approach is presented which combines the advantages of modelling at the layer scale and the melting pool scale. The general idea is that, the source of strain, giving rise to residual stresses during the SLM process for a given scanning strategy is reconstructed from a detailed simulation and mapped onto a layer. In order to do this the eigenstrain reconstruction method (ERM) is utilised. In this method an equivalent strain source is reconstructed for a residual stress field. The reconstructed equivalent strain source or eigenstrain can be used as a building block to describe the strain source for an entire layer or product. By defining the strain source for an entire product, the residual stresses in the product can be predicted directly. The novelty of the work presented in this thesis lies in the way the residual stress field is predicted. In literature the residual stress field caused by the SLM process is directly mapped to a layer or product. In this approach it is not the stress field that is mapped to the layer or product but the strain source. The advantage of this idea is that the resulting residual stress fields fromthe strain source are continuous in the SLMproduct. Although the ERM is widely used to model 1D and 2D residual stress fields for welding and peening processes, so far no fully 3D ERM has been implemented. In real SLM products the residual stress fields are always multi-axial. Therefore, it is necessary to extend ERMto 3D which is capable of dealing with the multidimensionality of the residual stress fields. One of the requirements of ERMis the input of a reference residual stress field. Therefore an expensive numerical reference model is developed which includes the effect of scanning strategy on the residual stress and warpage of a SLMproduct. The ERM model developed in this thesis is validated by reconstructing the residual stress fields for three geometries; a line, layer and ten layer geometry. The residual stress distributions calculated by the eigenstrain are compared with the results of the expensive numerical reference model. In this model the scanning strategy is incorporated by a point by point modelling approach. The performance of ERM is evaluated by calculating the corresponding residual stress field error between reference and ERM results, which lies within 0.5-4%. It is concluded that the ERMis a suitablemethod to reconstruct equivalent strain sources or eigenstrains for predicting 3D residual stress fields caused by the SLMprocess. The contribution to the field consists of an expansion of ERMto three dimensions and a hybrid model for the SLMprocess which combines the computational efficiency of the global approach with the detail of the local approach.Mechanical, Maritime and Materials EngineeringProcess and Energ
