Browsing by Subject "Simulation"

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A coherent coupling between graphene plasmon and molecular vibration in strong coupling regime
(2024-08) Hossain, Md Faysal
Manipulating the energy states of atoms or molecules is of great interest due to its unlimited potential in spectroscopy, analytical chemistry, atomic structural analysis, imaging, chemical and biological sensing, and many other fields of micro-nanotechnology. Various ways of atomic or molecular energy modulation have been employed to date, such as electric or magnetic field excitation, molecular vibrational or rotational excitation, quantum tunneling, and laser excitation. When electromagnetic wave interacts with materials, it may fall into either a weak, i.e., Fano resonance and Purcell effect, or strong coupling regime depending on the coupling strength. The formation of hybridized polaritonic states in the strong coupling regime opens up a new way to modify materials' physical and chemical properties by altering energy levels of the material excitation. While the formation of polaritonic states has been demonstrated for excitonic transitions, the same phenomenon can also take place with molecular vibrations. In general, a Fabry-Pérot (FP) cavity having two parallel metal or dielectric mirrors is used to induce strong coupling as a cavity optical mode interacts with molecular vibrations of a material placed in the cavity. However, a planar optical cavity has a limited spatial resolution for monitoring polaritonic states. Moreover, strong coupling in the FP cavity represents an ensemble-average due to spatially-varied optical fields inside the FP cavity. To address some of the limitations of the FP cavity, I used a deep metal grating as a new optical resonator to demonstrate vibrational strong coupling (VSC). First, I simulated the optical properties of the deep metal grating and found that the hybridization between localized surface plasmon resonances and magnetic polaritons is responsible for generating strong mid-infrared optical resonances. When single-layer graphene was integrated into the grating, the grating resonances showed Fano line shapes as a result of a weak coupling between discrete graphene plasmon modes and continuum grating resonances. In addition, with the addition of a molecular absorber to the deep metal grating, VSC was achieved with tunability in polaritonic energy states by changing the system parameters including the grating height and widths, as well as the chemical potential applied to the graphene. In parallel with simulations, I generated a large area of double-layer graphene by chemical vapor deposition and fabricated deep metal grating structures by electron-beam lithography and inductively-coupled plasma etching.
Open Access
AB- Türkiye ilişkileri sürecinde Türk şeker sektörü simülasyon sonuçları
(Sanayi ve Teknoloji Bakanlığı Sanayi ve Verimlilik Genel Müdürlüğü, 2008) Aytüre, S.; Demir, Nazmi
Bu araştırmada, dokuz bağıntılı bir ekonometrik model yardımı ile alternatif senaryolar altında, Türkiye'nin şeker arz-talep dengeleri simüle edilmektedir. Araştırmanın ortaya çıkardığı en önemli bulgu Türkiye'nin AB'ye 2014' de üye olması halinde önemli bir şeker ithalatçısı konumuna gireceğidir. Şeker sektörü giderek göreceli biçimde küçülecek ve 1.5 milyon ton civarındaki bir üretim eşiğinde dengelenecektir. Fabrikalarının üçte birinin rekabet edemeyerek kapanacağı, pancar ekim alanları ve pancar üretici sayılarının %35'den fazla azalacağı beklenen şeker sektöründe ortaya çıkacak işsizlik, gelir kayıpları, sosyal ve çevresel olumsuzluklara şimdiden çare aranması gerekmektedir. Çoğu sulanmakta olan ve terkedilmesi beklenen pancar ekim alanlarına ekilebilecek alternatif ürünlerin ve/veya tarım dışı gelir kaynaklarının saptanması için çalışmalara başlanması kaçınılmazdır. Şekerpancarı üreticilerinden ve şeker fabrikalarından ayakta kalabilecek olanların AB nin kendi içinde ayakta kalabileceklerle rekabet edebilmeleri için en emin yol tarladan nihai tüketiciye kadar şeker sektörünün tüm üretim aşamalarında verimliliği arttıracak adımları atmaktır. Pancarda polar şeker oranını ve verim düzeyini arttıracak pancar tohumlukları ve bunlara uygun agronomik koşulların sağlanması, ölçeğe getiri için fabrikaların birleşmeleri, kapasitelerini arttırmaları, yabancı sermaye ile teknolojilerini yenilemeleri birçok alternatif arasında sadece birkaç çıkış yolu olarak görülmelidir.
Open Access
Analyses of serial production line systems for interdeparture time variability and WIP inventory systems
(International Journal of Operations and Quantitative Management, 2004) Erel, E.; Sabuncuoglu, I.; Kok, G. A.
This paper investigates the well-known and extensively studied unpaced production line problem for the interdeparture time variability and work-in-process (WIP) inventory. The primary objective is to examine the relationships between the interdeparture time variability and some system design factors such as the number of stations, buffer capacity, and location of a bottleneck station. The performance of the system is also evaluated for average and variance of WIP inventory. Simulation is used as a modeling and analysis tool with the results being tested by appropriate statistical procedures. The analysis of the results reveals several important findings on the interdeparture time variability and WIP inventory. We confirm and strengthen some of the previous findings on throughput. In this paper, we also discuss managerial implications and suggest further research areas.
Open Access
Analysis of a hospital call center
(2012) Budak, Ezel Ezgi
In this thesis, we study the call center operations of a particular hospital located in Ankara, namely Güven Hospital. The hospital call center takes role as a medical consulting and appointment center and also domestic call traffic flows over the call center. These three types of calls are classified as consulting, appointment and domestic calls. The arriving call rate to the call center vary depending on hours and each agent is capable of giving service to each type of calls.( i.e. Agents are multitasking). Different types of calls have different exponential service time distributions. Regardless of call type calls may abandon during their waiting time in the call center. Abandonment rate and arrival rates of the calls are assumed to be exponential. Call center directs some percent of appointment calls to a doctor who gives service in the call center and some percent of consulting calls to hospital units depending on customers’ requests. A domestic call only receives service from the call center. Some percent of these diverted calls to doctor and hospital units return to call center. This diverting and returning process among call center, doctor and hospital units constitutes the call center network of the hospital. The aim of this study is to model this call center network as to reflect the properties of the analyzed system. Accordingly, the system is modeled with queuing network and simulation approaches. Different models are developed with different divert and return rates and different number of agents being multi-tasking or dedicated to give service to a specific call type. These models are compared in terms of systems performance metrics and related numerical analyses are reported.
Open Access
Analysis of order review/release problems in production systems
(Elsevier Science B.V., Amsterdam, Netherlands, 1999) Sabuncuoglu, İhsan; Karapınar, H.Y.
Order Review/Release (ORR) activities have mostly been ignored in past job shop research. In most previous studies, arriving jobs are immediately released to the shop floor without considering any information about the system or job characteristics. In practice however, these jobs are often first collected in a pool and then released to the system according to a specific criterion. Although practitioners often observe the benefits of ORR, researchers have found limited support for the use of these input regulation policies. One objective of this paper is to examine this research paradox in a capacitated system. We also offer a new classification framework for existing research work. Finally, for the first time in this paper, both periodic and continuous ORR methods are compared simultaneously under various experimental conditions against different performance measures. The results of simulation experiments and statistical tests are also presented in the paper.
Open Access
Analysis of scheduling problems in dynamic and stochastic FMS environment : comparison of rescheduling polices
(2001) Kızılışık, Ö Batuhan
In this thesis, we study the reactive scheduling problems in a dynamic and stochastic flexible manufacturing environment. Specifically, we test different scheduling policies (how-to-schedule and when-to-schedule policies) under process time variations and machine breakdowns in a flexible manufacturing system. These policies are then compared with on-line scheduling schemes. The performance of the system is measured for the mean flowtime criterion. In this study, a beam search based algorithm is used. The algorithm allows us to generate partial or full schedules. The results indicate that on-line scheduling schemes are more robust than the off-line algorithm in dynamic and stochastic environments.
Open Access
Analysis of simple inventory control systems with execution errors: Economic impact under correction opportunities
(Elsevier, 2010-06) Gel, E. S.; Erkip, N.; Thulaseedas, A.
Motivated by recent empirical evidence, we study the economic impact of inventory record inaccuracies that arise due to execution errors. We model a set of probable events regarding the erroneous registering of sales at each demand arrival. We define correction opportunities that can be used to (at least partially) correct inventory records. We analyze a simple inventory control model with execution errors and correction opportunities, and demonstrate that decisions that consider the existence of recording errors and the mechanisms with which they are corrected can be quite complicated and exhibit complex tradeoffs. To evaluate the economic impact of inventory record inaccuracies, we use a simulation model of a (Q,r) inventory control system and evaluate suboptimalities in cost and customer service that arise as a result of untimely triggering of orders due to inventory record inaccuracies. We show that the economic impact of inventory record inaccuracies can be significant, particularly in systems with small order sizes and low reorder levels.
Open Access
Analysis of variance reduction techniques in various systems
(2003) Çelik, Sabri
In this thesis, we consider four different Variance Reduction Techniques (VRTs): Antithetic Variates (AV), Latin Hypercube Sampling (LHS), Control Variates (CV), and Poststratified Sampling (PS). These methods individually or in combination are applied to the steady state simulation of three well-studied systems. These systems are M/M/1 Queuing System, a Serial Line Production System, and an (s,S) Inventory Policy. Our results indicate that there is no guarantee of a reduction in variance or an improvement in precision in estimates. The performance of VRTs totally depends on the system characteristics. Nevertheless, CV performs better than PS, AV and LHS on the average. Therefore, instead of altering the input part of the simulation, extracting more information by CV should be more effective. However, if any extra information about the system is not available, AV or LHS can be favored since they do not require additional knowledge about the system. Furthermore, since the analysis of output data through CV or PS requires a negligible time compared to the simulation run time, applying CV and PS at all possible cases and then selecting the best one can be the best strategy in the variance reduction. The use of the combination of methods provides more improvement on the average.
Open Access
Analytical loading models and control strategies in flexible manufacturing systems: a comparative study
(1990) Kırkavak, Nureddin
There are three problem areas in designing and implementing a manufacturing line : the part family selection and grouping, system configuration and toolings and the operational control of manufacturing. The manufacturing process has to be stream-lined by considering resources and products to achieve flow lines operating around product families with acceptable levels of utilization. The stream-lined processes have to be assigned to tandem machines in the manufacturing lines. Then, interactions between production and inventory levels should be controlled at the operational level. Based on this framework, first a system configuration and tooling problem is modeled. The model turns out to be a large mLxed integer linear program, so that some alternative optimal seeking or heuristic techniques are used to solye the model for constructing a flow line structured Flexible Manufacturing System. Push systems of the Material Requirements Planning type or pull systems like the base-stock or Kanban schemes are often seen as alternatives for controlling manufacturing systems. The differentiating features of push, pull and a hybrid strategy are studied by discrete event simulation under different system and environmental characteristics for Flexible Manufacturing Systems. The impact of assignment of operations to machines on the performance of the system is also discussed.
Open Access
Animation of deformable models
(Pergamon Press, 1994) Güdükbay, Uğur; Özgüç, B.
Although kinematic modelling methods are adequate for describing the shapes of static objects, they are insufficient when it comes to producing realistic animation. Physically based modelling remedies this problem by including forces, masses, strain energies and other physical quantities. The paper describes a system for the animation of deformable models. The system uses physically based modelling methods and approaches from elasticity theory for animating the models. Two different formulations, namely the primal formulation and the hybrid formulation, are implemented so that the user can select the one most suitable for an animation depending on the rigidity of the models. Collision of the models with impenetrable obstacles and constraining of the model points to fixed positions in space are implemented for use in the animations. © 1994.
Open Access
Animation of human motion : an interactive tool
(1991) Mahmud, Syed Kamran
The goal of this work is the implementation of an interactive, general purpose, human motion animation tool. The tool uses parametric key-frame animation as the animation technique. DiflPerent abstractions of motion specification in key-frame generation are explored, and a new notion of semi goal-directed animation for generating key-frame orientations of human body is introduced to resolve the tradeoif between animator and machine burden in choosing a level of motion specification.
Open Access
Approximate fourier domain expression for bloch-siegert shift
(John Wiley and Sons Inc., 2015) Turk, E. A.; Ider, Y. Z.; Ergun, A. S.; Atalar, Ergin
Purpose: In this study, a newsimple Fourier domain-based analytical expression for the Bloch-Siegert (BS) shift-based B1 mapping method is proposed to obtain |B1+| more accurately while using short BS pulse durations and small off-resonance frequencies.Theory and Methods: A new simple analytical expression for the BS shift is derived by simplifying the Bloch equations. In this expression, the phase is calculated in terms of the Fourier transform of the radiofrequency pulse envelope, and thus making the off- and on-resonance effects more easily understandable. To verify the accuracy of the proposed expression, Bloch simulations and MR experiments are performed for the hard, Fermi, and Shinner-Le Roux pulse shapes.Results: Analyses of the BS phase shift-based B1 mapping method in terms of radiofrequency pulse shape, pulse duration, and off-resonance frequency show that |B1+| can be obtained more accurately with the aid of this new expression.Conclusions: In this study, a new simple frequency domain analytical expression is proposed for the BS shift. Using this expression, |B1+| values can be predicted from the phase data using the frequency spectrum of the radiofrequency pulse. This method works well even for short pulse durations and small offset frequencies.
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
Atomistic structure simulation of silicon nanocrystals driven with suboxide penalty energies
(American Scientific Publishers, 2008) Yılmaz, Dündar E.; Bulutay, Ceyhun; Çağın, T.
The structural control of silicon nanocrystals embedded in amorphous oxide is currently an important technological problem. In this work, an approach is presented to simulate the structural behavior of silicon nanocrystals embedded in amorphous oxide matrix based on simple valence force fields as described by Keating-type potentials. After generating an amorphous silicon-rich-oxide, its evolution towards an embedded nanocrystal is driven by the oxygen diffusion process implemented in the form of a Metropolis algorithm based on the suboxide penalty energies. However, it is observed that such an approach cannot satisfactorily reproduce the shape of annealed nanocrystals. As a remedy, the asphericity and surface-to-volume minimization constraints are imposed. With the aid of such a multilevel approach, realistic-sized silicon nanocrystals can be simulated. Prediction for the nanocrystal size at a chosen oxygen molar fraction matches reasonably well with the experimental data when the interface region is also accounted. The necessity for additional shape constraints suggests the use of more involved force fields including long-range forces as well as accommodating different chemical environments such as the double bonds.
Open Access
BI-objective optimization of grid-connected decentralized energy systems
(2016-07) Altıntaş, Onur
We present a bi-objective two stage stochastic programming model for optimal sizing of a grid-connected hybrid renewable energy system. In this system, solar and wind are the main electricity generation resources. National grid is assumed to be a carbon-intense alternative to renewables and used as a backup source to ensure reliability. Storage device is included to examine its role in reducing the carbon emission and the intermittency of renewable sources. It is assumed that decision maker is sensitive to both cost and carbon emission, therefore two objectives are considered: total cost and carbon emission caused by electricity purchased from the utility grid. A simulation optimization algorithm has been developed for the problem.
Open Access
Cirosu düşük perakende noktalarına Unilever ürünlerinin dağıtımı için karma sistem tasarımı
(TMMOB Makina Mühendisleri Odası, 2007) Körpeoğlu, Ersin; Nadar, Emre; Bozkaya, Efe Burak; Sever, Derya; Karaşan, Oya Ekin
Unilever’in doğrudan ulaşamadığı düşük potansiyelli ama sayıca fazla perakendecilere Unilever ürünlerini ulaştırmayı amaçlayan bu projede, öncelikle bu noktalara hizmet vermeyi engelleyen etkenler belirlenmiştir. Başta yüksek ulaşım maliyetleri olmak üzere sistemdeki bu etkenleri ortadan kaldırmak amacıyla, firmanın istekleri doğrultusunda bir karma dağıtım sistemi tasarlanmıştır. Sıcak satış, telefonla satış ve depodan satış bölümlerinden oluşan bu sistem; doğrusal olmayan tamsayılı programlama tekniğiyle modellenmiş ve tanımlanan ek kısıtlar ile doğrusal hale getirilmiştir. Problemin boyutunun büyük olması nedeniyle CPLEX ile doğrudan çözülemeyen modelimiz için buluşsal bir algoritma geliştirilmiştir. Buluşsal algoritmanın başarısını ölçmek amacıyla model, kesin olarak çözülebildiği 37 tane koşturum örneği için buluşsal algoritma ile kıyaslanmış; buluşsal algoritmanın en iyi değerinin modelin en iyi değerinden ortalama %14.6 saptığı, 37 koşturumun 14’ünde algoritmanın en iyi hedef değerini verdiği gözlemlenmiştir. Modelleme sürecinde rassal olmadığı kabul edilen parametrelerin benzetim çalışması aracılığıyla rassal olduğu durumun ele alınmasıyla, modelin belirsizlik içeren durumlarda da işlevselliğini koruduğu gösterilmiştir. Veritabanı ve müşteri kartı tasarımı gibi yan uygulamalarla da desteklenen proje, firma yönetimi tarafından pilot uygulamaya alınmıştır. Sonuç olarak firmaya karlı ve esnek bir dağıtım kanalı oluşturulmuş ve düşük potansiyelli perakende noktalarına düşük maliyetle ulaşım sağlanmıştır.
Open Access
Comments on "Ensuring Safety of Implanted Devices Under MRI Using Reversed Polarization"
(Wiley, 2011-10-24) Eryaman, Y.; Hersek, S.; Atalar, Ergin
Open Access
The concept of beauty in art
(Elsevier, 2022-01-01) Turan, Fulya; Vargel, İ.; Özgür, F. F.
Before the invention of the camera, it was only possible to document beauty through art. For centuries, art and beauty were inseparable. Different meanings were attributed to the “beautiful” in history. Sometimes noble simplicity and calm sublimity were accepted as beauty; sometimes moral beauty was at the forefront. Among the beauties, a special place and importance was given to female beauty in the history of art. The untouched, desired, hopelessly loved woman of the Middle Ages later became the main subject of a painting genre. Nudes, which were first made for religious reasons such as to depict a specific scene from the bible, later diversified under the subject of Venus. The female body has become the object of sensual consumption. In addition to female beauty, the beauty of nature has always been among the subjects of art. Art imitated nature for a while because it was beautiful. It was the background to which man was exposed during his natural evolution. The proportions of nature were good for people, they were found beautiful. Nature, which was previously handled only with a style based on imitation, was handled with an abstract expression in time, thanks to the avant-garde artists of the 20th century. It was a period in which different styles of expression were tried. Modernism, where wisdom, beauty, and refinement were sought, was for an elite audience who idealized nature. It left its place to postmodernism in which sensual stimulation was sought rather than an intellectual admiration, which is for mass media and where craftsmanship is idealized. The individual of the 21st century consumer society, who is passionately attracted to the beauty of their own image that is presented to the gaze of others on social media, resembles the nobles of the Renaissance period, when the charm of the wealth obtained through overseas trade was depicted with a similar passion.
Open Access
Contagion of network products in small-world networks
(Springer, 2019-05-20) İkizler, Hüseyin
We formulate a model in which agents embedded in an exogenous social network decide whether to adopt a new network product or not. In the theoretical part of the paper, we characterize the stochastically stable equilibria for complete networks and cycles. For an arbitrary network structure, we develop a novel graph decomposition method to characterize the set of recurrent communication states, which is a superset of stochastically stable equilibria of the adoption game presented in our model. In the simulation part, we study the contagion process of a network product in small-world networks that systematically represent social networks. We simulate a generalization of the Morris (Rev Econ Stud 67(1):57–78, 2000) Contagion model that can explain the chasm between early adopters and early majority. Our numerical analysis shows that the failure of a new network product is less likely in a highly cliquish network. In addition, the contagion process reaches to steady state faster in random networks than in highly cliquish networks. It turns out that marketers should work with mixed marketing strategies, which will result in a full contagion of a network product and faster contagion rates with a higher probability.
Open Access
Continuous time control of make-to-stock production systems
(2010) Bulut, Önder
We consider the problem of production control and stock rationing in a make-tostock production system with multiple servers –parallel production channels--, and several customer classes that generate independent Poisson demands. At decision epochs, in conjunction with the stock allocation decision, the control specifies whether to increase the number of operational servers or not. Previously placed production orders cannot be cancelled. We both study the cases of exponential and Erlangian processing times and model the respective systems as M /M /s and M /Ek /s make-to-stock queues. We characterize properties of the optimal cost function, and of the optimal production and rationing policies. We show that the optimal production policy is a state-dependent base-stock policy, and the optimal rationing policy is of state-dependent threshold type. For the M /M /s model, we also prove that the optimal ordering policy transforms into a bang-bang type policy when we relax the model by allowing order cancellations. Another model with partial ordercancellation flexibility is provided to fill the gap between the no-flexibility and the full-flexibility models. Furthermore, we propose a dynamic rationing policy for the systems with uncapacitated replenishment channels, i.e., exogenous supply systems. Such systems can be modeled by letting s --the number of replenishment channels-- go to infinity. The proposed policy utilizes the information on the status of the outstanding replenishment orders. This work constitutes a significant extension of the literature in the area of control of make-to-stock queues, which considers only a single server. We consider an arbitrary number of servers that makes it possible to cover the spectrum of the cases from the single server to the infinite servers. Hence, our work achieves to analyze both the exogenous and endogenous supply leadtimes.