Bogazici University

Physics Colloquium

Tarih:  22 Şubat Çarşamba (2016)

Saat: 15:30  (Çay ve kurabıye servısı saat 15:00’da başlıyacak).

Yer: Feza Gursey Semıner Odası (KB 309),

Boğaziçi Üniversitesi, Fizik Bölümü



Dr. Seydi Yavas

Since the invention of the laser in the 60s, the main advances in the pulsed laser technology have been achieved in two directions; shorter pulses and higher powers. In order to achieve this purpose, many laser types are developed and always replaced with simpler, smaller, cheaper alternatives that can deliver the same or better parameters. In the recent 20 years, fiber lasers have become an important alternative that can satisfy and even develop the parameters of current lasers while reducing the complexity, costs, and instability.
Today, more than 50 companies sell short-pulse fiber lasers for applications as diverse as ophthalmology, micromachining, medical imaging and precision metrology. Mainly, fiber- laser-based micromachining is routinely implemented in the fabrication processes for widely used consumer products. However, new applications of fiber lasers are continuously developed, and according to the applications always new requirements emerge. Particularly for the relatively new ultrafast-pulsed laser applications, these requirements usually can not be satisfied by the off- the-shelf products.
In this presentation, I will summarize the ultrashort and short pulsed fiber lasers that are custom-built and utilized for biological and transparent material processing, spectroscopy and imaging during my thesis study. I am going to cover both scientific and commercial aspects of laser development process and applications. I am going to conclude with a discussion of the emerging application fields that we can utilize these lasers for, here in Boğaziçi University.




Tarih: 16 Aralık Cuma (2016)

Saat: 14:00

Yer: Feza Gürsey Seminer Odası (KB 309),

Boğaziçi Üniversitesi Fizik Bölümü


Microfabricated Tools for Quantitative Biology and Medicine



Mechatronics Program, FENS, Sabanci University

Understanding the interactions between tumor cells and immune cells in a quantitative manner will provide valuable information to reveal the mechanism of diseases, immune defense and development of new treatment reagents and strategies for the diseases. Today one of the biggest limitations relies on the traditional methods and tools that we use to investigate the rare cells and specific events in biology particularly in immunology. Since these techniques are not adequate enough to be selective, specific and quantitative, the rare cells such as the metastatic or drug resistant ones or the events such as onset symptoms of tumors and infections are being masked by majority of the cells or events in the population. Therefore, we cannot diagnosis on time or provide successful strategies. As a consequence, our approaches might not target the right cells at the right time in the right place. To overcome these limitations, we might profit from engineering approaches and tools. We can develop quantitative, accurate, reproducible and precise methods and use microfabricated tools to understand the nature and behavior of rare cells and events. The improvements from microfabricated tools in conjunction with microscopy might provide statistics from large numbers of single cells, short assay time, less sample consumption, less waste production, quantitative and reproducible data, single-cell resolution images, high-throughput, spatio-temporal tracking and real-time assays, etc. This talk will present recently developed microfabricated tools to understand the immune cell-tumor cell interactions. I will present our microfluidic applications and their preliminary data from my research group. 


Konuşmacı Hakkında:

Meltem Elitas is a Faculty Member in Mechatronics Program at Sabanci University. Her background is in Electrical and Mechatronics Engineering. She has obtained her Doctorate from Bioengineering and Biotechnology Department at Ecole Polytechnique Federale de Lausanne. She has performed her Postdoctoral studies at Yale University Biomedical Engineering Department. Her research interests are surgical tools for robotic surgery, biomechatronics, cellular heterogeneity, cellular interactions, tumor microenvironment, live cell imaging and development of microfabricated tools for quantitative biology.



Tarih: 23 Kasim, Çarşamba (2016)

Saat: 15:30  (Çay ve kurabiye ikramı 15:00’te başlıyacaktır).

Yer: Feza Gürsey Seminer Odası (KB 309),

Boğaziçi Üniversitesi Fizik Bölümü


New Prospects for Accretion in White Dwarf Binaries

Solen Balman, Ph.D., Middle East Technical University, Physics Department

Cataclysmic Variables (CVs), compact binaries with white dwarf (WD) primaries, constitute laboratories to study accretion flows, gas dynamics, outflows, transient outbursts, and explosive nuclear burning under a variety of astrophysical plasma conditions. CVs, together with related accreting WD binaries, have been studied over decades and are important for population studies of galactic X-ray sources. However, recent space- and ground-based high resolution spectral and timing studies, along with recent surveys indicate that we still have observational and theoretical complexities yet to answer. I will review briefly evolutionary aspects and concentrate on  diversity of dwarf nova outburst, the nova-like systems and the optically thick-thin disk transition conditions, and the the disk wind models. I will point out how accretion phase shapes the thermonuclear eruptions on the surface of WD binaries and Nova evolution. Also, I will discuss how flickering variability studies from optical to X-rays can be probes to determine accretion history and indicate the connection of time and spectral variability of CVs with Low-Mass X-ray Binaries and Active Galactic Nuclei.

Tarih: 16 Kasim, Çarşamba (2016)

Saat: 15:30  (Çay ve kurabiye ikramı 15:00’te başlıyacaktır).

Yer: Feza Gürsey Seminer Odası (KB 309),

Boğaziçi Üniversitesi Fizik Bölümü


Başlık: Supersymmetric Rhapsody: Is this the real life? Is this just fantasy?

Dieter Van den Bleeken, Department of Physics, Bogazici University

Abstract: Supersymmetry is a beautiful idea that unifies forces and matter. In this colloquium I will first review the basics and why it has become a mainstream concept in theoretical physics, afterwards I will discuss the questions in the title based on recent experimental data.


Boğaziçi Üniversitesi

Physics Colloquium

Tarih: 12 Ekım Çarşamba (2016)

Saat: 15:30  (Çay ve kurabiye servisi 15:00’da başlıyacaktır.).

Yer: Feza Gürsey Seminer Odası (KB 309),

Boğaziçi Üniversitesi, Fizik Bölümü



Başlık: Use of Graphene in Femtosecond Pulse Generation 

Alphan Sennaroğlu, Departments of Physics and Electrical-Electronics Engineering, Koc University

Over the last decade, graphene has emerged as an important nano-structured material with unique electrical and optical characteristics In particular, its nonlinear optical characteristics make it suitable as an initiator of femtosecond pulses from lasers. The first part of the talk will provide a general overview of lasers, methods of femtosecond pulse generation, optical characteristics of graphene and application of graphene in femtosecond pulse generation. The second part of the presentation will focus on some of our recent experiments where graphene has been exploited as a fast saturable absorber to generate pulses from tunable solid-state lasers working in the near and middle infrared.


Boğaziçi Üniversitesi

Physics Colloquium

Tarih: 12 Ekım Çarşamba (2016)

Saat: 15:30  (Çay ve kurabiye servisi 15:00’da başlıyacaktır.).

Yer: Feza Gürsey Seminer Odası (KB 309),

Boğaziçi Üniversitesi, Fizik Bölümü


Başlık: Gravitational Waves and the LIGO Gravitational Wave Observatory

Metin Arık, Department of Physics, Bogazici University

Since Einstein’s prediction, It has taken us 100 years to observe a gravitational waves. This talk  will review some basics concerning gravitational waves and give a description of the  Ligo Observatory and its discovery of gravitational waves.

28 Eylül Çarşamba,  15:30

Saat: 15:30  (Çay ve kurabiye ikramı 15:00’te başlayacaktır)

Yer: Feza Gürsey Seminer Odası (KB 309)

Başlık: VHE gamma ray astrophysics and a Polish contribution to the CTA project

Michal Ostrowski, Astronomical Observatory, Jagiellonian University

In the talk I plan to present some basic information about VHE gamma ray astrophysics based on HESS results, to shortly describe the CTA project and a progress with our SST-1M small Cherenkov telescope constructed in collaboration with Switzerland et al.


Boğaziçi Üniversitesi Fizik Bölümü, Feza Gürsey Seminer Odası


21 Eylül Çarşamba (2016)

Saat: 15:30  (15:00’da çay ve kurabiye servisi olacaktır)

How do we know that the climate is changing and what will happen in the future?

Levent Kurnaz, Department of Physics, Bogazici University

How do we know that the climate is changing and what will happen in the future? The climate of the earth has been stable for the past 18.000 years. However with the invention of the steam engine in the 18th century, humanity started to change the structure of the atmosphere. With this change we see that the climatology of our planet is also changing. The important issue now is to assess these changes and figure out what the future holds. Climate modelling holds the clue this assessment. The results of these models show us how we should be preparing for the upcoming changes.

5 Ağustos Cuma (2016)

Saat: 15:30  (15:00’da çay ve kurabiye servisi olacaktır)


Enio Da Silveira, Pontifıcia Universidade Catolica do Rio de Janeiro, Rio De Janeiro, Brazil Radiolysis of amino acids Cintia A. P. da Costa

Valine, (CH3)2 CHCH (NH2) COOH, is a protein amino acid that has been identified in extraterrestrial environments and in the Murchison meteorite [1]. The knowledge of half-lives of small organic molecules under ionizing radiation is important for the setup of models describing the spread out of prebiotics across the Solar System or the Galaxy. We have investigated typical effects of MeV cosmic ray ions on prebiotic molecules in laboratory by impinging ions produced by the PUC-Rio Van de Graaff accelerator. Pure valine films, deposited by evaporation on KBr substrates, were irradiated by H+, He+ and N+ ion beams, from 0.5 to 1.5 MeV and up to a fluence of 1015 projectiles/cm2 . The sample temperature was varied from 10 K to 300 K. The irradiation was interrupted several times for Mid-FTIR analysis of the sample. The main findings are: 1- The column density of the valine decreases exponentially with fluence. 2- In some cases, a second exponential appears in the beginning of irradiation; this feature has been attributed to sample compaction by the ion beam [2]. 3- Destruction cross sections of valine are in the 10−15 cm2 range, while compaction cross sections are in the 10−14 cm2 range. 4- Destruction cross section increases with the stopping power of the beam and also with the sample temperature. 5- Surprisingly, during the radiolysis of valine, just CO2 is seen by as a daughter molecule formed in the bulk. 6- After long beam fluence, also a CO peak appears in the infrared spectrum; this species is however interpreted as a fragment of the formed CO2 molecules. 7- Considering the flux ratio between laboratory experiments and actual galactic cosmic rays, half-life of valine is predicted for ISM conditions [3]. This work on pure valine is the first measurement of a series. New experiments are planned for determining cross sections of valine dissolved in H2O or CO2, inspired by the study performed for glycine [4]. [1]

  1. Ehrenfreund and S. B. Charnley, Annu. Rev. Astron. Astrophys. 2000. 38:427. [2] C. Mej´ıa et al., Icarus 250 (2015) 222. [3] D. P. P. Andrade et al., Mon. Not. R. Astron. Soc. 430 (2013) 787. [4] P. A. Gerakines and R. L. Hudson, Icarus 252 (2015) 466.

Acknowledgments. The agencies CNPq (INEspa¸co) and FAPERJ are acknowledged for partial support to this work.

26 Temmuz Salı (2016)

Saat: 15:30  (15:00’da çay ve kurabiye servisi olacaktır)

Farhang Loran, Department of Physics, Isfahan University of Technology, Isfahan, 84156-83111, Iran

Non-chiral CFT with integer spectrum

The partition function of 2d conformal field theory is a modular invariant function. It is known that the partition function of an extremal CFT can be uniquely determined in terms of the Klein function, and has certain holographic interpretation. In this talk, we study the partition functions of non-chiral CFTs with integer spectrum. We show that every such function can be mapped to a chiral partition function whose structure can be determined quite similar to the extremal CFT partition functions. In this way, we compute the number of low-energy states in the non-chiral theory.

 Farhang Loran is an Associate Professor of Physics in the Department of
 Physics at the Isfahan University of Technology. He completed his
 undergraduate studies in 1999 and his Ph.D. in 2002 in Physics at the same
 university. His research interests lie in the areas of black holes, quantum
 gravity and AdS/CFT correspondence.

Note: Dr. Farhang Loran’s visit to Bogazici University is supported by Turkish Academy of Sciences.

25 Temmuz Pazartesi (2016)

Saat: 15:30  (15:00’da çay ve kurabiye servisi olacaktır)

Ogan Ozsoy, Physics Department, Syracuse University, USA

Alternative Sources of Gravitational Waves 
During inflation, vacuum fluctuations of the metric are stretched to nearly scale invariant super-horizon gravitational waves. These tensor modes later lead to B-type polarization of the Cosmic Microwave Background. A positive detection of B-mode polarization has been heralded not only as a smoking gun for the existence of Inflation but also as a way to establish the scale at which inflation takes place. However, presence of secondary mechanisms of gravitational wave production may invalidate this conclusion. In this talk, I will revisit alternative sources of tensor modes and challenges they face in the light of constraints on the level of non-gaussianity and model building.
17 Nisan Çarşamba, 15:30
Ümit Deniz Göker, Bogazici University

The Reasons of Unexpected Variation in UV Region During the Recent Solar Cycle 23: Observational, Statistical and Theoretical Applications.

A study of variations of solar spectral irradiance (SSI) and international sunspot number (ISSN) in the wavelength ranges 121.5 nm-300.5 nm, and solar surface indices (total solar irradiance (TSI), magnetic field, Ca II K-flux, faculae and plage areas) due to the number and the type of sunspots/sunspot groups (SGs) in solar activity cycles (SACs) 21-23 is given. Satellite observations were used for SSI and ISSN variations and the data were reduced with MATLAB while solar surface indices and SGs were established with ground-based telescopes and their statistical analysis have been done by Phyton Programming Language. In this respect, negative correlations of intensities of UV (289.5 nm-300.5 nm) emission lines with the ISSN index during the unusually prolonged minimum between the SACs 23 and 24 were revealed. Nevertheless, these negative correlations indicate that the UV emissions are in close connection with the classes of sunspots/SGs and variations of solar surface indices. Finally, I applied the time series analysis of spectral lines correspond to the wavelengths 121.5 nm-300.5 nm and found an unexpected increasing in 298.5 nm for the Fe II spectral line. In the theoretical work, how the variation of Fe II element causes an important changes in UV and how this variation relates with the sunspots/SGs and solar surface indices are demonstrated.


Ümit Deniz Göker received the Ph.D. degree in “Plasma Astrophysics/Shock Applications on Solar Physics” from Ege University in 2010 with the supervision of Prof. E. Rennan Pekünlü and with the supervision of Prof. Eric R. Priest from St. Andrews University, Scotland, UK. She also attended a project on “The Design of Turbopumps Using Fuel and Cavitation Optimization” in Istanbul Technical University with the leadership of Prof. Can Fuat Delale from 2005-2006. Now, she is a Postdoctoral Associate with the Boğaziçi University. She continues her studies on different fields of Plasma Physics and Astrophysics: “Shock Wave Structures on the Solar Chromosphere and Corona” with Assoc. Prof. Istvan Ballai in Sheffield University, UK; and “Observational and Theoretical Studies on Supernova Remnants” with Prof. E. Nihal Ercan in Boğaziçi University. Recently, she has been accepted to a project cooperation with Asst. Prof. Punit Kumar “Propagation of Shock Waves in High Density Degenerate Astrophysical Quantum Plasmas” in Indian Space Research Organisation (ISRO).

3 Mayıs Çarşamba, 15:30
Prof. Dr. Dejan Urosevic, Belgrade University, Faculty of Mathematics, Department of Astronomy

On the Continuum Radio Spectra of Supernova Remnants

In this lecture, in the introductory part, will be presented on which way the radio spectra in continuum are formed. After that will be explained particle acceleration mechanisms to ultrarelativstic energies – it is necessary for understanding of different forms of radio spectra. Further will be presented several forms of continuum radio spectra of supernova remnants – firstly based on theoretical predictions, and after that those which were detected by observations. Finally, the most important and updated activities of our group from Department of Astronomy, Faculty of Mathematics, University of Belgrade, related to structure and evolution of emission nebulae (especially related to supernova remnants, their continuum radio spectra, Sigma-D relation and equipartition calculation)) will be mentioned.

 11 Mayıs Çarşamba, 15:30

 Dizem Arifler, Middle East Technical University, Northern Cyprus Campus

Computational Biophotonics and Nanophotonics: Advancing the Prospects of Optical Cancer Diagnostics

Biophotonics is an emerging field that focuses on development of optical technologies for medical imaging, diagnosis, and therapy. Optical techniques enable noninvasive and real-time assessment of tissue structure without the need for biopsy removal and hence hold significant promise as highly sensitive and cost-effective diagnostic tools that can identify curable preinvasive cancer. Further, if optical techniques are used in combination with nanophotonic contrast enhancers, it is possible to sense molecules that might indicate progression of cancer. This molecular specificity is likely to pave the way for dramatic improvements in early cancer diagnosis. In the first part of the talk, I will give an overview of the field of biophotonics and its applications to cancer detection from an applied physics perspective. I will also describe the physical principles that form the basis of medical nanophotonics and optical contrast enhancement for improved cancer detection. In the second part of the talk, I will discuss how we can use computational studies to advance the prospects of optical cancer diagnostics. I will then focus on my research work and elaborate on a series of specific projects that have recently been completed or are currently in progress.


Dizem Arifler received the B.S. degree in Physics, and the M.S. and Ph.D. degrees in Biomedical Engineering from The University of Texas at Austin, USA, in 2000, 2002, and 2005, respectively. After graduation, she returned back to Cyprus and she has been a faculty member since then. She is currently with the Physics Group at Middle East Technical University, Northern Cyprus Campus. In 2013, she received a short-term European Commission fellowship to carry out research as a visiting scholar in Department of Medical Physics and Biomedical Engineering at University College London. Her research interests include diagnostic optical imaging and spectroscopy, computational electromagnetics and its applications to biophotonics and nanophotonics, numerical and statistical approaches to analysis of photon propagation through tissues, and design of optical sensors for medical applications.

23 Mart Çarşamba, 15:30

Tekin Dereli, Koç University

New Improved Massive (3D) Gravity

Abstract:  (2+1)-dimensional gravity has long received attention as a theoretical tool that highlights the topological aspects of gravitation. There is a recent rise of interest with papers on New Massive Gravity (2009) and Minimal Massive (3D) Gravity (2014). I will briefly review these models and give a generic extension using the language of exterior differential forms. (2+1)-space-times with constant curvature and constant torsion will be discussed as background solutions.

Short Bio: T.D. received his B.S. and Ph.D. degrees in physics from METU. He taught for many years at METU, Ankara University and (since 2001) at Koç University. He held long-term research appointments at Yale and Brandeis Universities (USA), Lancaster University (UK), University of Vienna (Austria) and Karlsruhe University (Germany), He was an Associate Member of ICTP (Italy). Among many honours and prizes, T.D. won the TUBITAK Science Prize in 1996. He published more than 120 research papers and is still writing papers on a very wide range of subjects in mathematical physics; covering topics in QFT, gauge theories, spin structures,  differential geometry and topology in physics, gravitation and cosmology.

16 Mart Çarşamba, 15:30

E. Aslı Yetkin, Assistant Professor, İstanbul Bilgi University

Engineering sensorial delay, nonadditivity of critical Casimir forces, and control of active matter systems

Observation of charmonium like new states (X(3872) ,Y(3940),Y(4260)) since 2003, which do not fit into conventional quark model, renewed the interest in exotic states.

Many models like meson molecule, tetraquark, and quark-gluon hybrid are proposed to explain the observed charmonium spectroscopy.

The observation of Y(3940) near the JpsiOmega threshold motivated similar searches near JpsiPhi threshold. In this talk, I will summarise recent developments on the observation of a peaking structure in the JpsiPhi mass spectrum from B to JpsiPhiK decay.

9 Mart Çarşamba, 15:30

Giovanni Volpe, Bilkent Üniversitesi

1) Engineering sensorial delay to control the behaviour of a group of robots. Ensembles of autonomous agents, such as swarms of insects, human crowds and groups of robots,  exhibit collective behaviors independent of each agent’s specific motion. In this work, we have shown that time delays between signal sensing and processing affect the individual and collective long-term behaviors. Sensorial delay can therefore be used as a novel parameter to control these behaviors.
2) Experimental measurement of the nonadditivity of critical Casimir forces. Critical Casimir forces are potentially a powerful tool to control the self-assembly and complex behavior of micro- and nanoparticles. In order to fully exploit their potential, it is crucial to understand whether and to what extent many-body forces are in action. Despite having been predicted theoretically, their experimental demonstration has been lacking. Employing holographic optical tweezers, we provided the first experimental demonstration of the nonadditivity of critical Casimir forces.
3) Controlling active matter in disordered potentials. Many living systems, such as bacterial colonies, exhibit collective and dynamic behaviors that are sensitive to changes in environmental conditions. Our results show that a colloidal active matter system switches between gathering and dispersal of individuals in response to the roughness of an attractive potential generated by extended light fields.


17 Şubat Çarşamba, 15:30

İbrahim Semiz, Boğaziçi Üniversitesi

What do the cosmological supernova data really tell us?

Not much by themselves, apparently.

In the end of last century, analysis of the type Ia supernova (SN) data revealed that the expansion of the universe is accelerating, leading to the concept of dark energy. The most common interpretation of the data assumes that Einstein gravity (GR) is correct and the universe is dominated by matter (some of it dark) plus a cosmological constant-like dark energy.

However, the additions of the concepts of dark matter and dark energy to the paradigm could be pointing to the necessity of replacing GR by a better theory. In this work, we try to determine the expansion history of the universe from the SN data, using only the homogeneity and isotropy of the universe and the assumption that gravitation is due to the geometry of the universe, but not necessarily obeying Einstein’s Equations. This is called a “model-independent,” or “cosmographic” approach. We find that the acceleration history of the universe cannot be reliably determined in this approach due to the irregularity and parametrization-dependence of the results.

However, adding the gamma-ray-burst (GRB) data to the dataset cures most of the irregularities, at the cost of compromising the model-independent nature of the study slightly. Then we can determine the redshift of transition to cosmic acceleration as a function of the spatial curvature of the universe.

If Einstein gravity is assumed, we find a redshift at which the density of the universe predicted from the supernova data is independent of curvature. We use this point to derive an upper limit on matter density today, hence a lower limit on the density of dark energy. While these limits do not improve the generally accepted ones, they are derived only using the SN and GRB data, i.e. without making any assumptions about the properties of dark energy.

11 Şubat Perşembe, 12:00

İlke Ercan, Boğaziçi Üniversitesi,

From Maxwell’s Demon to Nanocircuits: A Physical Information Theoretic Approach to Computing

Heat dissipation is a critical challenge facing the realization of emerging nanocomputing technologies. There are different components of this dissipation, and a part of it comes from the unavoidable cost of implementing logically irreversible operations. This stems from the fact that information is physical and manipulating it irreversibly requires energy. The unavoidable dissipative cost of losing information irreversibly fixes the fundamental limit on the minimum energy cost for computational strategies that utilize ubiquitous irreversible information processing.

A relation between the amount of irreversible information loss in a circuit and the associated energy dissipation was formulated by Landauer’s Principle in a technology-independent form. In a computing circuit, in addition to the information-theoretic dissipation, other physical processes that take place in association with irreversible information loss may also have an unavoidable thermodynamic cost that originates from the structure and operation of the circuit. In conventional CMOS circuits such unavoidable costs constitute only a minute fraction of the total power budget, however, in nanocircuits, it may be of critical significance due to the high density and operation speeds required. The lower bounds on energy, when obtained by considering the irreversible information cost as well as unavoidable costs associated with the operation of the underlying computing paradigm, may provide insight into the fundamental limitations of emerging technologies. This motivates us to study the problem of determining heat dissipation of computation in a way that reveals fundamental lower bounds on the energy cost for circuits realized in new computing paradigms.

In this talk, we introduce a physical-information-theoretic approach to determining minimum energy requirements of computation for concrete circuits realized within specific paradigms and discuss its application to prominent nanacomputing proposals such as Nano Application Specific Integrated Circuits (NASICs) and Quantum-dot Cellular Automata (QCA). We also comment on the role of fundamental lower bounds in technology assessment for determining the trends in nanoelectronic computing.

Short Bio: İlke Ercan earned her doctorate degree in February 2014 from Electrical and Computer Engineering Department at the University of Massachusetts, Amherst, under Professor Neal G. Anderson’s supervision. She has an M.S.E.C.E. with concentration in Electrophysics from the same department, a B.S. in Physics and an undergraduate minor degree in Philosophy and History of Science from Middle East Technical University, Ankara, Turkey. Upon completing her PhD, she worked as a Visiting Faculty at Smith College Picker Engineering Program in Spring and Fall 2014. She pursued her postdoctoral research under supervision of Professor Udo Schwalke, Institute for Semiconductor Technology and Nanoelectronics, and Professor Alfred Nordmann, Institute for Philosophy at TU Darmstadt in Spring and Summer 2015. She joined the Electrical and Electronics Engineering Department at Boğaziçi University in Fall 2015.



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