METU - MEMS Center

Ankara, Turkey

METU - MEMS Center

Ankara, Turkey
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Bacinoglu B.T.,METU - MEMS Center
IEEE Transactions on Wireless Communications | Year: 2017

In this paper, energy-efficient transmission schemes achieving maximal throughput over a finite time interval are studied in a problem setting including energy harvests, data arrivals and channel variation. The goal is to express the offline optimal policy in a way that facilitates a good online solution. We express any throughput maximizing energy efficient offline schedule (EE-TM-OFF) explicitly in terms of water levels. This allows per-slot real-time evaluation of transmit power and rate decisions, using estimates of the associated offline water levels. To compute the online power level, we construct a stochastic dynamic program that incorporates the offline optimal solution as a stochastic process. We introduce the Immediate Fill (IF) metric which provides a lower bound on the efficiency of any online policy with respect to the corresponding optimal offline solution. The online algorithms obtained this way exhibit performance close to the offline optimal, not only in the long run but also in short problem horizons, deeming them suitable for practical implementations. IEEE

Bayraktar O.,Middle East Technical University | Civi O.A.,Middle East Technical University | Akin T.,Middle East Technical University | Akin T.,METU - MEMS Center
IEEE Transactions on Antennas and Propagation | Year: 2012

A reflectarray antennamonolithically integrated with 90 RF MEMS switches has been designed and fabricated to achieve switching of the main beam. Aperture coupled microstrip patch antenna (ACMPA) elements are used to form a 10 × 10 element reconfigurable reflectarray antenna operating at 26.5 GHz. The change in the progressive phase shift between the elements is obtained by adjusting the length of the open ended transmission lines in the elements with the RF MEMS switches. The reconfigurable reflectarray is monolithically fabricated with the RF MEMS switches in an area of 42.46 cm 2 using an in-house surface micromachining and wafer bonding process. The measurement results show that the main beam can be switched between broadside and 40° in the H-plane at 26.5 GHz. © 2011 IEEE.

Onat Y.,University of Hawaii at Manoa | Yalciner A.C.,METU - MEMS Center
Ocean Engineering | Year: 2013

The highly active seismic potential of Eastern Mediterranean raises a question about risk mitigation when a possible tsunami hits the coastline. A proper risk mitigation plan and tsunami assessment can be achieved by creating a fully detailed database. In this study, 38 scenarios created using this database on bathymetric and topographic data in sufficient resolution using valid and verified numerical tool called NAMI DANCE, helps us to understand the tsunami generation, propagation, coastal inundation aided by visualization. The uncertainties in defining seismic source parameters and the effect of dip and rake (slip) angle are discussed. The performance and efficiency of the numerical code, the accuracy of the results in the application to Eastern Mediterranean Tsunamis and the comparisons of simulation results in nested domains for the towns of Iskenderun and Kas are given as case studies. According to this study, north-west and south-west of Turkey may have tsunami risks more than the other regions. The maximum wave amplitudes that hit the coasts are more than 4 m and about 6 m at some localities. The arrival time of the first wave to hit the coast varies between 15 min to 60 min depending on the proximity to the source location. © 2013 Elsevier Ltd.

Baran M.,Kirikkale University | Tankut T.,METU - MEMS Center
ACI Structural Journal | Year: 2011

The purpose of this study is to investigate the behavior of reinforced concrete (RC) frames under cyclic loads strengthened by using precast concrete (PC) panels. The idea is to transform the existing hollow brick infills into strong and rigid infills by bonding relatively highstrength PC panels with a thin layer of epoxy mortar. By this method, the seismic behavior of the frame is improved For this purpose-one being reference-a total of 11 one-third scale, one-bay, two-story deficient RC frames were tested under reversed cyclic lateral loads. Six different panel types were used for strengthening purposes. It was observed that the strength, lateral stiffness, and energy dissipation capacity of strengthened frames were significantly improved Copyright © 2011, American Concrete Institute. All rights reserved.

Ustunkar G.,METU - MEMS Center
Journal of integrative bioinformatics | Year: 2011

Recently, there has been increasing research to discover genomic biomarkers, haplotypes, and potentially other variables that together contribute to the development of diseases. Single Nucleotide Polymorphisms (SNPs) are the most common form of genomic variations and they can represent an individual’s genetic variability in greatest detail. Genome-wide association studies (GWAS) of SNPs, high-dimensional case-control studies, are among the most promising approaches for identifying disease causing variants. METU-SNP software is a Java based integrated desktop application specifically designed for the prioritization of SNP biomarkers and the discovery of genes and pathways related to diseases via analysis of the GWAS case-control data. Outputs of METU-SNP can easily be utilized for the downstream biomarkers research to allow the prediction and the diagnosis of diseases and other personalized medical approaches. Here, we introduce and describe the system functionality and architecture of the METU-SNP. We believe that the METU-SNP will help researchers with the reliable identification of SNPs that are involved in the etiology of complex diseases, ultimately supporting the development of personalized medicine approaches and targeted drug discoveries.

Tosun U.,METU - MEMS Center | Dokeroglu T.,METU - MEMS Center | Cosar A.,METU - MEMS Center
International Journal of Production Research | Year: 2013

The Quadratic Assignment Problem (QAP) is a difficult and important problem studied in the domain of combinatorial optimisation. It is possible to solve QAP instances with 10 - 20 facilities using exhaustive parallel algorithms within a few days on a cluster machine. However, large QAP instances with more than 100 facilities are not solvable using exhaustive techniques. We have explored a variety of Genetic Algorithm crossover operators for this problem and verified its performance experimentally using well-known instances from the QAPLIB library. By increasing the number of processors, generations and population sizes we have been able to find solutions that are the same as (or very close to) the best reported solutions for large QAP instances in QAPLIB. In order to parallelise the Genetic Algorithm we generate and evolve separate solution pools on each cluster processor, using an island model. This model exchanges 10% of each processors solutions at the initial stages of optimisation. We show experimentally that both execution times and solution qualities are improved for large QAP instances by using our Island Parallel Genetic Algorithm. © 2013 Copyright Taylor and Francis Group, LLC.

Yucel D.,METU - MEMS Center | Kose G.T.,Yeditepe University | Hasirci V.,METU - MEMS Center
Biomaterials | Year: 2010

Nerve conduits containing highly aligned architecture that mimics native tissues are essential for efficient regeneration of nerve injuries. In this study, a biodegradable nerve conduit was constructed by converting a porous micropatterned film (PHBV-P(L-D,L)LA-PLGA) into a tube wrapping aligned electrospun fibers (PHBV-PLGA). The polymers were chosen so that the protective tube would erode slower than the fibrous core to achieve complete healing before the tube eroded. The pattern dimensions and the porosity (58.95 (%) with a maximum pore size of 4-5 μm) demonstrated that the micropatterned film would enable the migration, alignment and survival of native cells for proper regeneration. This film had sufficiently high mechanical properties (ultimate tensile strength: 3.13 MPa, Young's Modulus: 0.08 MPa) to serve as a nerve guide. Electrospun fibers, the inner part of the tubular construct, were well aligned with a fiber diameter of ca. 1.5 μm. Fiber properties were especially influenced by polymer concentration. SEM showed that the fibers were aligned parallel to the groove axis of the micropatterned film within the tube as planned considering the nerve tissue architecture. This two component nerve conduit appears to have the right organization for testing in vitro and in vivo nerve tissue engineering studies. © 2009 Elsevier Ltd. All rights reserved.

Koz A.,Technical University of Delft | Cigla C.,METU - MEMS Center | Alatan A.A.,METU - MEMS Center
IEEE Transactions on Image Processing | Year: 2010

With the advances in image based rendering (IBR) in recent years, generation of a realistic arbitrary view of a scene from a number of original views has become cheaper and faster. One of the main applications of this progress has emerged as free-view TV(FTV), where TV-viewers select freely the viewing position and angle via IBR on the transmitted multiview video. Noting that the TV-viewer might record a personal video for this arbitrarily selected view and misuse this content, it is apparent that copyright and copy protection problems also exist and should be solved for FTV. In this paper, we focus on this newly emerged problem by proposing a watermarking method for free-view video. The watermark is embedded into every frame of multiple views by exploiting the spatial masking properties of the human visual system. Assuming that the position and rotation of the virtual camera is known, the proposed method extracts the watermark successfully from an arbitrarily generated virtual image. In order to extend the method for the case of an unknown virtual camera position and rotation, the transformations on the watermark pattern due to image based rendering operations are analyzed. Based upon this analysis, camera position and homography estimation methods are proposed for the virtual camera. The encouraging simulation results promise not only a novel method, but also a new direction for watermarking research. © 2006 IEEE.

Bilgin H.F.,TUBITAK - Marmara Research Center | Ermis M.,METU - MEMS Center
Electric Power Systems Research | Year: 2011

This paper describes the operating principles, design and field performance of two-level, three-leg device commutated current source converter (CSC) topology based Static Synchronous Compensator (STATCOM), which is developed for medium voltage industry applications. In the paper, the relationship between the reactive power and the control variables is obtained, harmonic minimization techniques applicable to CSC are investigated, and then Selective Harmonic Elimination Technique is applied for the elimination of the 5th, 7th, 11th and 13th harmonics in CSC line current. The design principles of the input filter are also set out. Considerations for optimum sizing of STATCOM in common industry applications are described with the design objective of maximum utilization of power semiconductors. Two CSC based STATCOMs, which are rated at ±500 kVAr and 0-1500 kVAr capacitive are implemented and applied to industry. Field results are also given in the paper in order to validate the operating principles and design criteria. © 2010 Elsevier B.V. All rights reserved.

Karabulut S.,METU - MEMS Center
Proceedings of Meetings on Acoustics | Year: 2013

Material selection for acoustically comfortable environments is a very important issue especially for rooms for speech and music as well as for large volumes like shopping centers and foyers. Energy efficient and sustainable materials are devised in construction industry for healthy environments; hence, ecological sound absorbing materials for acoustically sensitive environments are being preferred to get credits for international certification procedures like LEED and BREAM. Nevertheless, most of the acoustic materials in construction industry are perforated with mineral wool based absorption materials behind and have great effects on design of the building environments. Architects usually prefer seamless imperforated materials to avoid changes in the appearance of design environments for acoustical requirements. This article is about development of an ecological imperforated acoustical material which is made of reed and pumice stone. Different layers of pumice stone and reed glued with an ecological binder are evaluated according to frequency range they are effective and an optimization is done to create an acoustic material that is effective especially in medium frequencies. Acoustical performance of the material is justified with measurements of sound absorption coefficient in Kundt Tube. © 2013 Acoustical Society of America.

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