Browsing by Subject "Modeling"

Now showing 1 - 20 of 23

Open Access
A practical cell density stabilization technique through drug infusions: a simple pathfinding approach
(IEEE - Institute of Electrical and Electronics Engineers, 2023-07-17) Djema, W.; Bonnet, C.; Özbay, Hitay; Mazenc, F.
We consider a nonlinear system with distributed delays modeling cell population dynamics, where the parameters depend on growth-factor concentrations. A change in one of the growth factor concentrations may lead to a switch in the corresponding model parameter. Our first objective is to achieve a network representation of the switching system involving nodes and edges. Each node stands for a full-fledged nonlinear system with distributed delays where the parameters are constant. For each node, a stable positive steady state may exist. In the network framework, a change in the growth-factor concentration is interpreted as a transition from one node to another. The objective is then to determine the best switching signal steering the biological parameters over time, making the overall dynamic system moving from one operating mode to another, until reaching a desired stable state. Our method provides a (sub)optimal therapeutic strategy, guiding the density of cells from an abnormal state towards a healthy one, through multiple drug infusions. The drug sequence is deduced from the optimal switching signal provided by a classical pathfinding algorithm, associated with the network representation.
Open Access
Analysis of blood cell production under growth factors switching
(Elsevier B.V., 2017) Djema, W.; Özbay, Hitay; Bonnet, C.; Fridman, E.; Mazenc, F.; Clairambault, J.
Hematopoiesis is a highly complicated biological phenomenon. Improving its mathematical modeling and analysis are essential steps towards consolidating the common knowledge about mechanisms behind blood cells production. On the other hand, trying to deepen the mathematical modeling of this process has a cost and may be highly demanding in terms of mathematical analysis. In this paper, we propose to describe hematopoiesis under growth factor-dependent parameters as a switching system. Thus, we consider that different biological functions involved in hematopoiesis, including aging velocities, are controlled through multiple growth factors. Then we attempt a new approach in the framework of time-delay switching systems, in order to interpret the behavior of the system around its possible positive steady states. We start here with the study of a specific case in which switching is assumed to result from drug infusions. In a broader context, we expect that interpreting cell dynamics using switching systems leads to a good compromise between complexity of realistic models and their mathematical analysis. © 2017
Open Access
An analysis of manipulated information and respective alternative costs in information systems and in decision making structures
(International Institute of Informatics and Systemics, IIIS, 2006) Güvenen O.; Öztürk, M.H.
Today Information Technologies create base for the most important decision support systems for the practices in academia, business and politics. The effectiveness and success of operations that are supported by information systems are directly correlated with the quantity, accuracy, timing, credibility and the quality of the information that prevails in the system. Rapid development of these technologies in recent decades allows high level of information transaction and communication through the whole world. The quantity of information that flows through information systems has increased tremendously. New researches and technological applications in this area aim to improve the systems quantitatively. However, despite a huge and continuous increase in information flow, the quality and reliability of the information in the systems are doubtful from many perspectives. We believe that quality and reliability considerations in information technologies are not handled by researchers and users adequately. So in this research we decided to discuss about quality and reliability aspects of the information flow. To be able to evaluate the information from qualitative perspectives, we believe that it is crucial to handle the problem in science and especially in social sciences by endogenising socio-economic phenomena and science methodology approaches. We hope this work will create a stimulus for researchers of Information Technologies and Systems to give importance to the reliability and quality of information issues.
Open Access
Asymptotic wave-like modeling of dielectric lenses
(IEEE, 2007) Yurchenko, V. B.; Altıntaş, Ayhan
We propose asymptotic wave-like approximations for the accurate modeling of dielectric lenses used in quasi-optical systems of millimeter, submillimeter, and infrared wave applications. For the comparison, we obtain an exact full-wave solution of two-dimensional focusing lens problem and use it as a benchmark for testing and validation of asymptotic models being proposed.
Open Access
The development of an inquiry-based teaching unit for Turkish high school mathematics teachers on integral calculus: the case of definite integral
(2017-09) Özdemir, Çiğdem
The 2013 official national curriculum published by the Turkish Ministry of Education formally required high school mathematics teachers to actively incorporate computer software in their teaching. The primary purpose of this study was to demonstrate the development of an inquiry-based teaching unit especially geared for high school mathematics students and teachers for the general concept of integral calculus. The main theme chosen as a case for this proposed inquiry unit was on definite integral and volumes of solids of revolution of real life daily objects. As a result, the primary purpose was to provide the process of developing a practical example of using pedagogically driven dynamic mathematics software (GeoGebra), a 3D digital model coupled with hands-on real life examples, all embedded in a constructivist learning environment. Also, within this study, the perceived effectiveness of the developed teaching unit by in-service high school mathematics teachers based on their experiences was reported.
Open Access
Distinct representations in occipito-temporal, parietal, and premotor cortex during action perception revealed by fMRI and computational modeling
(Elsevier, 2019) Ürgen, Burcu A.; Pehlivan, S.; Saygın, A.
Visual processing of actions is supported by a network consisting of occipito-temporal, parietal, and premotor regions in the human brain, known as the Action Observation Network (AON). In the present study, we investigate what aspects of visually perceived actions are represented in this network using fMRI and computational modeling. Human subjects performed an action perception task during scanning. We characterized the different aspects of the stimuli starting from purely visual properties such as form and motion to higher-aspects such as intention using computer vision and categorical modeling. We then linked the models of the stimuli to the three nodes of the AON with representational similarity analysis. Our results show that different nodes of the network represent different aspects of actions. While occipito-temporal cortex performs visual analysis of actions by means of integrating form and motion information, parietal cortex builds on these visual representations and transforms them into more abstract and semantic representations coding target of the action, action type and intention. Taken together, these results shed light on the neuro-computational mechanisms that support visual perception of actions and provide support that AON is a hierarchical system in which increasing levels of the cortex code increasingly complex features.
Open Access
Effects of compliance on path-tracking performance of a miniature robot
(IEEE - Institute of Electrical and Electronics Engineers, 2023-05-15) Uğur, Mustafa; Arslan, Burak; Özzeybek, Alperen; Özcan, Onur
Path-tracking is often challenging in miniature robots because their feet or wheels tend to slip due to the low robot weight. In this work, we investigate the effect of c-leg compliance on path-tracking performance and the obstacle-climbing capabilities of our foldable and miniature robot with soft, c-shaped legs. With its 82 mm x 60 mm x 29 mm size and 29.25 grams weight, a single module of our robot is one of the smallest untethered miniature robots. Our results show that utilizing soft c-shaped legs provides smooth path-tracking performance, similar to a wheeled differential drive robot. However, modules with rigid c-shaped legs are affected significantly by the impact and slip between the leg and the ground, and they perform rather unpredictably. Additionally, modules with wheels cannot climb obstacles 1 mm or larger. We show that using soft legs enhances the obstacle climbing skills of modules by climbing a 9 mm obstacle, while the module with rigid legs can only climb a 7 mm obstacle. These path-tracking abilities and obstacle-climbing capacity support our vision to build a reconfigurable robot using these modules.
Open Access
Hybrid and model based approaches for new BCI spellers
(2019-07) Memon, Suleman Aijaz
Electroencephalography (EEG) based brain-computer interfaces (BCIs), due to their non-invasive, portable and temporal resolution properties, are widely used in the field of neural engineering. In order to make BCI paradigms more practical and feasible for real life applications, new approaches are being tested such as hybrid BCIs and model based BCIs. In the first phase of this study, a novel hybrid speller BCI is proposed, incorporating P300 and code-modulated visual evoked potential (c-VEP) paradigms, with the objective of improving the spelling accuracy and information transfer rate (ITR), compared to individual P300 and c-VEP paradigms. Moreover, fusion techniques have been applied in order to effectively combine the information of P300 and c-VEP at the score level. We have implemented and compared two different approaches, linear discriminant analysis (LDA) and maximum probability estimation (MPE), in order to identify which one works best for this hybrid BCI. The proposed BCI consists of 36 targets presented as 6x6 matrix on screen with a refresh rate of 120 Hz. Seven healthy subjects participated in experiments where each subject performed a training session followed by five test sessions. The P300 and c-VEP signals are obtained by using bandpass filters of 0.5-6 Hz and 6-41 Hz respectively, on the raw hybrid data. For P300, stepwise linear discriminant analysis (SWLDA) is performed on training data from all the 10 EEG channels to obtain the feature vector. For c-VEP, canonical correlation analysis (CCA) is performed on training data to obtain the reference templates for all 36 symbols. In comparison with the accuracy and ITR values of c-VEP alone, that is without simultaneously making use of the P300 data obtained during the hybrid experiments, MPE-based hybrid improved only by 1.1% and 2.1 bits/min, on average, respectively, whereas the values worsened by 12.3% and 19.8 bits/min in the case of LDA-based hybrid. Moreover, the statistical tests on the mean accuracy and ITR values of all the subjects showed that the results of MPE-based hybrid and of c-VEP alone are not statistically different (p=0.293). Although the MPE-based hybrid is not statistically better than the c-VEP alone, it can be highly effective if the primary goal is to only increase the accuracy, using a range of improvements in P300 methods as discussed in conclusion. However, it would not be useful if the purpose is to increase the speed of the speller since the individual c-VEP paradigm, when optimized for timing, has the capability of giving an average ITR of 114.9bits/min or higher, on its own. In the second phase of this study, model based c-VEP BCI is implemented, aimed at improving the training time compared to the case where all the targets are assigned arbitrary pseudorandom binary sequences and training is required for all the symbols separately. For this purpose, moving average model has been implemented to simulate the responses for c-VEP visual stimulation patterns, for 60Hz and 120Hz monitor refresh rate respectively. The average of the correlation between measured response and modeled response for 60Hz and 120Hz is 0.357 and 0.396 respectively. The average accuracy and ITR obtained for model based c-VEP BCI is 87.1% and 76.4 bits/min for 60Hz respectively and 82.1% and 72.4 bits/min for 120Hz respectively. Modeling results suggest that it is possible to perform a training on a single visual stimulus pattern and achieve a good fit model.
Open Access
Hydrogenation of naphthalene and methylnaphthalene: modeling and spectroscopy
(Elsevier BV, 2002) Sayan, Ş.; Paul, J.
In situ infrared spectra of 1-methylnaphthalene (1-MeNapht)hydrogenation, over sulfided NiMo/Al2O3-TiO2 catalysts, were compared with theoretically derived properties of methylnaphthalene and its bicyclic products: MeDilin, MeTetralin, MeOctalin and MeDecalin, and with conversion data from literature. Comparisons were also made between the un-substituted and methyl-substituted two-rings, and between the 1- and 5-methyl isomers of 1,4-dihydronaphthalene (dilin) and 1,2,3,4-tetrahydronaphthalene (tetralin). IR spectra of MeNapht adsorption, on the sulfided catalyst, were matched with data for adsorption on the catalyst without sulfidation and the empty support. Surface bound MeNapht is observed below 250°C on all catalysts. MeNapht adsorption suppresses OH groups nondiscriminatory on the empty support and the metal loaded catalyst. We relate the results to previous data on the interaction between the supported metal sulfides and titanium modified aluminas. Calculated total energies, and experimentally derived heats of formation, pointed at decahydronaphthalene (decalin) as the dominant product of naphthalene hydrogenation, with tetralin as an abundant intermediate, and dilin and 1,2,3,4,5,6,7,8-octahydronaphthalene (octalin) as short lived transient stages. The spectroscopic modeling showed that the orbital fingerprints of the five bicyclic compounds were not distinctly different, nor more than marginally modified by methyl substitution or isomerization. The only significant difference came at the highest occupied orbital, where a high naphthalene density of states (DoS) overlapped with the valence bands of metal or metal sulfide catalysts. The vibrational bands for naphthalene, dilin, tetralin and octalin were well separated. Octalin and decalin, alone, have similar vibrational spectra. Upheaval of ring degeneracy for methyl-substituted two-ring structures broadened all infrared bands in a characteristic way.
Open Access
Improving the dimensional accuracy of micro parts 3D printed with projection-based continuous vat photopolymerization using a model-based grayscale optimization method
(Elsevier, 2022-09) Guven, Ege; Karpat, Yigit; Cakmakci, Melih
Micro-scale additive manufacturing has seen significant growth over the past years, where improving the accuracy of complex micro-scale geometries is seen as an important challenge. Using grayscale images rather than black and white images during production is an effective method to improve the fabrication quality. This paper presents a model-based optimization method for improving the dimensional accuracy of parts using voxel-based grayscale dynamic optimization during continuous 3D printing. A detailed solidification model has been developed and used to estimate the curing dynamics of the resin used in 3D printing. The irradiance of the light beam projected for each pixel influences a larger volume on the resin than the targeted voxel. The proposed model-based method optimizes the images considering the light distribution from all closely related pixels to maintain the accuracy of the micro part. The results of this method have been applied to the printing of a complex 3D part to show that optimized grayscale images improve the areas with overcuring significantly. It is shown that the number of overcured voxels was reduced by 24.7% compared to the original images. Actual printing results from our experimental setup confirm the improvements in the accuracy and precision of the printing method.
Open Access
Informed feature regularization in voxelwise modeling for naturalistic fMRI experiments
(Wiley, 2020-04-21) Yılmaz, Özgür; Çelik, Emin; Çukur, Tolga
Voxelwise modeling is a powerful framework to predict single‐voxel functional selectivity for the stimulus features that exist in complex natural stimuli. Yet, because VM disregards potential correlations across stimulus features or neighboring voxels, it may yield suboptimal sensitivity in measuring functional selectivity in the presence of high levels of measurement noise. Here, we introduce a novel voxelwise modeling approach that simultaneously utilizes stimulus correlations in model features and response correlations among voxel neighborhoods. The proposed method performs feature and spatial regularization while still generating single‐voxel response predictions. We demonstrated the performance of our approach on a functional magnetic resonance imaging dataset from a natural vision experiment. Compared to VM, the proposed method yields clear improvements in prediction performance, together with increased feature coherence and spatial coherence of voxelwise models. Overall, the proposed method can offer improved sensitivity in modeling of single voxels in naturalistic functional magnetic resonance imaging experiments.
Open Access
An interface model for improving the use of space simulation software in architectural design
(1998) Şenyapılı, Burcu
There is an ongoing debate on the success of architectural software in meeting the designers' wishes and in being familiar with the way designers design. One dominant belief is that as architectural software introduces a work environment closer to that of the paper-based techniques, the efficiency of the use of such software in the profession will increase. We argue that the use will increase by designing interfaces through which the users will be able to customize the digital environment according to their wishes. This thesis introduces a context-specific interface model to transform a state in the user+need space to a digital aid in the virtual design space. This model incorporates the Customization Scale Menu (CSM) to act with the menu options of the architectural space simulation software. The menu options are customized through the selections made on the CSM by the user. These selections will determine the required level of interaction between the software and the user, thus customizing the digital environment according to the user's needs.
Open Access
Introduction
(Academic Press, 2018) Acar, S.; Voyvoda, E.; Yeldan, Alp Erinç
This chapter serves as an introduction to the main research questions, background, and objectives of the study. It describes the context (i.e., conceptualization of duality) and the modeling tools for decarbonized sustainable growth pathways as a way of pursuing a regionally-equitable development strategy.
Open Access
Land cover classification with multi-sensor fusion of partly missing data
(American Society for Photogrammetry and Remote Sensing, 2009-05) Aksoy, S.; Koperski, K.; Tusk, C.; Marchisio, G.
We describe a system that uses decision tree-based tools for seamless acquisition of knowledge for classification of remotely sensed imagery. We concentrate on three important problems in this process: information fusion, model understandability, and handling of missing data. Importance of multi-sensor information fusion and the use of decision tree classifiers for such problems have been well-studied in the literature. However, these studies have been limited to the cases where all data sources have a full coverage for the scene under consideration. Our contribution in this paper is to show how decision tree classifiers can be learned with alternative (surrogate) decision nodes and result in models that are capable of dealing with missing data during both training and classification to handle cases where one or more measurements do not exist for some locations. We present detailed performance evaluation regarding the effectiveness of these classifiers for information fusion and feature selection, and study three different methods for handling missing data in comparative experiments. The results show that surrogate decisions incorporated into decision tree classifiers provide powerful models for fusing information from different data layers while being robust to missing data. © 2009 American Society for Photogrammetry and Remote Sensing.
Open Access
The latest arrival hub location problem for cargo delivery systems with stopovers
(Elsevier, 2007) Yaman, H.; Kara, B. Y.; Tansel, B. C.
In this paper, we concentrate on the service structure of ground-transportation based cargo delivery companies. The transient times that arise from nonsimultaneous arrivals at hubs (typically spent for unloading, loading, and sorting operations) can constitute a significant portion of the total delivery time for cargo delivery systems. The latest arrival hub location problem is a new minimax model that focuses on the minimization of the arrival time of the last item to arrive, taking into account journey times as well as the transient times at hubs. We first focus on a typical cargo delivery firm operating in Turkey and observe that stopovers are essential components of a ground-based cargo delivery system. The existing formulations of the hub location problem in the literature do not allow stopovers since they assume direct connections between demand centers and hubs. In this paper, we propose a generic mathematical model, which allows stopovers for the latest arrival hub location problem. We improve the model using valid inequalities and lifting. We present computational results using data from the US and Turkey.
Open Access
The minimal conditions for a financial crisis: a multiregional intertemporal CGE model of the Asian crisis
(Pergamon Press, 2000) Adelman, I.; Yeldan, E.
The globalization of world capitalism constrains the ability of the developmental state to pursue an independent industrialization and foreign trade strategy. We use an intertemporal, multiregion CGE model, to study the fundamental reasons for a financial crisis. We find that we can create a realistic crisis in the Asia region when capital markets are open and there is an unexpected rise in the risk premium of the Asia region. When capital markets are closed and the state retains all its policy instruments, the Asia region not only avoids a crisis but increases its rate of growth. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.
Open Access
Model-based optimization of microscale parts printed with projection-based continuous vat photopolymerization
(2022-08) Güven, Ege
Micro-scale additive manufacturing has seen significant growth over the past years, where improving the accuracy of complex micro-scale geometries is seen as an important challenge. Using grayscale images rather than black and white images during production is an effective method to improve the fabrication quality. This thesis presents a model-based optimization method for improving the dimensional accuracy of parts using voxel-based grayscale dynamic optimization during continuous 3D printing. A detailed solidification model has been developed and used to estimate the curing dynamics of the resin used in 3D printing. The irradiance of the light beam projected for each pixel influences a larger volume on the resin than the targeted voxel. The proposed model-based method optimizes the images considering the light distribution from all closely related pixels to maintain the accuracy of the micro part. The results of this method have been applied to the printing of complex 3D parts to show that optimized grayscale images improve the areas with overcuring significantly. It is shown that the number of overcured voxels was reduced by 24.7% compared to the original images. Actual printing results from the experimental setup confirm the improve-ments in the accuracy and precision of the printing method. The optimization method has been further improved by allowing variable printing speed during pro-duction and optimizing the speed profile of the print alongside grayscaling. This approach allows for printing of certain geometries that would otherwise be challenging to produce accurately. Computational limitations of performing speed and grayscale optimization simultaneously has been overcome by utilizing the symmetry of certain special cases to reduce optimization variables.
Open Access
Modeling and analysis of issues in hub location problem
(1999) Kara, Bahar Yetiş
The hub location problem has been around for more than 10 years. The first mathematical model was formulated by O’Kelly (1986) which is a quadratic integer program. Since then, nearly all of the researchers in this area have concentrated on developing ’good’ linearizations. However, there are many aspects of the problem that need to be analyzed. In this dissertation, we investigate some of these issues. We first study the application areas of the hub location problem and clarify the underlying assumptions of the real world problems which lead to the customarily defined hub location problem. We identify a certain problem characteristic of cargo delivery systems, which is one of the major application areas of the hub location problem, which is not satisfactorily modeled by means of the customarily defined hub location models. We propose a new hub location model that captures the specific requirements that are particular to cargo delivery systems. Another issue that we concentrate on is the identification, modeling and analysis of the hub location problem under different performance measures, namely minimax and covering criteria. We propose new integer programming models for the hub location problem under minimax and covering objectives. Both of the new models are the result of a different way of approaching the problem and their computational performance is far more superior than the performance of the various linearizations of the basic models proposed for these problems in the literature.
Open Access
Modeling the rheological properties of highly nano-filled polymers
(SAGE Publications Ltd, 2017) Kourki, Hajir; Mortezaei, Mehrzad; Famili, Mohammad Hossein Navid; Malekipirbazari, Milad
Organic and inorganic materials are usually added to polymers in order to achieve some benefits such as reducing the product cost, as well as achieving higher modulus and strength. Addition of these materials would change polymers’ behavior. Adding nano-materials to polymers on the other hand is a new challenge in the field of polymer composites where previous studies were unable to achieve good correlation with nano-composites at higher particle volume fractions. In this research, Yamamoto network theory is developed to investigate the behavior of highly nano-filled systems. For this purpose, five different types of sub-chain and two types of junctions are considered and the effect of particle size, concentration, and the model parameters in association with the behavior of the junctions are studied. Moreover, some experiments are performed on polystyrene filled with nano-silica at different particle size and concentration values in frequency mod in the linear region. At last, we compared the results of our final model with the experiments in order to evaluate its accuracy, which confirmed a very good agreement. © 2016, © The Author(s) 2016.
Open Access
Physics-informed disturbance estimation and nonlinear controller design for a multi-axis gimbal system
(Elsevier, 2022-11-22) Leblebicioglu, Damla; Atesoglu, Ozgur; Cakmakci, Melih
The increasing demand for target tracking, environmental surveys, surveillance and mapping requires multi-axis gimbal systems with high tracking and stabilization performance. In this study, a new torque estimation structure is proposed to compute the complex disturbances negatively affecting the performance of the system. Two different control strategies based on Active Disturbance Rejection Control (ADRC) and Estimated Torque Model are implemented on a two-axis gimbal system. In the first strategy, the purpose is to improve the robustness, environmental adaptability and tracking accuracy of the system. The tuning effort of the ADRC is reduced by integrating a Neural Network (NN) based disturbance compensator (NN assisted ADRC). In the second strategy, NN is replaced with an Estimated Torque Model (ETM assisted ADRC), whose inputs come from plant outputs. The simulation results show that, both NN and ETM assisted control structures decrease the tracking errors. However, the improvements achieved by the physics-informed neural network-based estimator are more significant.