Bilkent University, Faculty of Science

Faculty Seminars

Faculty Seminars are scheduled for the first Wednesday of every month and aim to bring together researchers and students  from all walks of science to discuss recent and distinguished advances in science. 

Seminars of the 2008-2009 academic year are as follows:
 

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Speaker:  Prof. Dr. Salim ÇIRACI

Affiliation: Department of Physics, Bilkent University
and
UNAM-Institute of Material Sciences and Nanotechnology

Title: Graphene: A wonder structure of carbon
Date: October 8, 2008, 15:40 at SBZ14.

Abstract: Three-dimensional diamond and graphite, quasi-one dimensional carbon nanotubes and carbon chains, zero dimensional fullerenes; these structures of carbon have dominated science in different periods of time. The dimensionality of these structures has played a prime role in determining their mechanical and electronic properties. For a long time, the missing two-dimensional structure of carbon has been considered to be unstable. Recently, the synthesis of graphene, a two-dimensional honeycomb lattice of carbon disproved the earlier theories conjecturing the instability in two-dimension. Not only the unexpected stability and very high strength, but also its exceptional electronic and magnetic properties have made graphene a wonder-structure. Unique properties arising from its honeycomb lattice can allow physicists to observe strange and interesting relativistic effects at a speed much slower than the speed of light. Because of linear electron and hole bands crossing at the Fermi level the electrons in graphene have very high mobility and behave as if a massless Dirac Fermion. This behavior makes us to expect that the Klein paradox, the most unusual quantum behavior, can be observed. Other features, such as ambipolar electric field effect, chiral quantum Hall effect, jittery motion, Berry phase, sub-micrometer ballistic transport at room temperature have been subjects of active study and future novel technological applications. Graphene pieces may serve as a framework for functionalized structures, such as high capacity hydrogen storage medium. Quasi-one dimensional graphene nanoribbons, which can be produced down to sub nanometer width exhibit exceptional physical properties. Depending on their chirality, graphene nanoribbons can be nonmagnetic or antiferromagnetic semiconductor. However, an antiferromagnetic semiconductor by itself can be modified to be ferrimagnetic metal through periodic vacancies or to be half-metal through applied electric field. If one modulates their width in direct space, confined states are generated even with a local spin direction. Quantum structures made by nanoribbons of different widths or compositions exhibit a wide range of electrical and magnetic properties to be exploited in nanoelectronics and spintronics. Because of its unusual behavior not only graphene, but also BN, Si, SiC, GaAs, ZnO, MX2 honeycomb structures have been now the focus of attention.

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Speaker: Dr. Julius JELLINEK

Affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory,
Argonne, Illinois 60439, USA

Title: Nanoalloys: Tuning Properties Through Size and Composition
Date: November 5, 2008, 15:40 at SBZ14.

Abstract:  I will present a sketch of the history of metals and alloys and an overview of the current status of the field of nanoalloys (alloy nanoparticles). These will be followed by a discussion of our own results on structural, dynamical (thermal), and electronic properties of Ni-Al bimetallic clusters.
 

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Speaker: Prof. Dr. Levent GÜREL

Affiliation: Department of Electrical and Electronics Engineering,
and
BILCEM, Computational Electromagnetics Research Center at Bilkent University.

Title: Computational Electromagnetics: Solving the World’s Largest Integral-Equation Problems with Hundreds of Millions of Unknowns
Date: December 3, 2008, 15:40 at SBZ14.

Abstract:

Since 2006, the world’s largest integral-equation problems in computational electromagnetics have been solved at Bilkent University Computational Electromagnetics Research Center (BiLCEM).  Most recently, breaking the latest world record actually required the solution of 205,000,000x205,000,000 dense matrix equations!  This achievement is an outcome of a multidisciplinary study involving physical understanding of electromagnetics problems, novel parallelization strategies (computer science), constructing parallel clusters (computer architecture), advanced mathematical methods for integral equations, fast solvers, iterative methods, preconditioners, and linear algebra. 

In this seminar, following a general introduction to our work in computational electromagnetics, I will continue to present fast and accurate solutions of large-scale electromagnetic modeling problems involving three-dimensional geometries with arbitrary shapes using the multilevel fast multipole algorithm (MLFMA). Accurate solutions of real-life problems require discretizations with tens or hundreds of millions of unknowns.  To achieve the solution of such extremely large problems, maximizing the computational resources by parallelizing MLFMA on distributed memory architectures is needed.  However, due to its complicated structure, parallelization of MLFMA is not trivial. Recently, we proposed a hierarchical parallelization strategy to increase the efficiency of parallelization.  For more information, please visit www.cem.bilkent.edu.tr.

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Speaker: Prof. Dr. Cihan SAÇLIOĞLU

Affiliation: Sabancı University, Faculty of Engineering and Natural Sciences
 
Title: Much Ado About Nothing: The current picture of the vacuum

Date: December 17, 2008, 15:40 at SBZ14.

Abstract:  We will review at a non-tecnical level aspects of our current understanding of "Nothing"- better known as the vacuum- in physics. This is a vast subject, and we will focus on a few selected topics: the existence of infinitely many inequivalent vacua, the Nambu-Goldstone mechanism of spontaneous symmetry breaking (Physics Nobel prize 2008), the Higgs phenomenon and its origins in the BCS theory of superconductivity, the search for the Higgs boson at the CERN LHC, false and real vacua, the topology of the vacuum, the vacuum in quantum field theory and its observable effects, the landscape of vacua in string theory, the evidence for the Cosmological constant and the composition of the universe in terms of familiar matter, dark matter and the cosmological constant.

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Speaker:  Assoc. Prof. Hakkı Turgay Kaptanoğlu

Affiliation: Bilkent University, Department of Mathematics
 
Title: The Brothers Bohr: A Tale of Two Radii


Date: March 4, 2009, 15:40 at SBZ14.

Abstract: Despite the literary parallels in its title, this talk has nothing to do with Dostoyevsky or Dickens. In the second decade of the 20th century in Denmark, two brothers named Bohr made important breakthroughs in science, Niels in physics, Harald in mathematics. For the older brother Niels, fame came early with the radius of the hydrogen atom put forward by him in 1913 and a Nobel prize in 1922. A different kind of radius in mathematics was named after the younger brother Harald long after his death in the last decade of the 20th century inspired by a paper of his published also in 1913. The latter radius continues to attract attention to this day. This talk is about the story of the latter radius and my modest contributions to it.

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Speaker:  Asst. Prof. Hüseyin BOYACI

Affiliation: Bilkent University, Department of Psychology
 
Title:  Cognitive neuroscience, and the human visual system

Date: April 1, 2009, 15:40 at SBZ14.

Abstract:  Cognitive neuroscience, whose development is propelled with recent advances in brain imaging technologies, studies the biological mechanisms underpinning cognitive functions. I will start my talk with a brief introduction to the methods and technologies commonly used in cognitive neuroscience research. Next I will shift the focus to human visual system by discussing two important organizational principles discovered in the second half of the last century: retinotopic mapping (mapping of a point in the visual field to a specific region in the visual cortex) and the mostly feed-forward hierarchical functional organization.

In the rest of my talk I will discuss the results of some recent brain imaging studies conducted by our group. In those studies, using "visual illusions" (where the perceived magnitude of a stimulus is different than its actual physical magnitude, such as size or lightness) and functional magnetic resonance imaging (fMRI), we have found that the responses of early visual cortical areas, as early as in the primary visual cortex (V1), correlate with the perceived rather than physical magnitude of the visual stimuli. I will explain how and why these findings stand in contradiction to the classical models of the visual system, and argue that they will potentially contribute to important changes in the field of vision in the near future. 

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Speaker:  Asst. Prof. Uygar TAZEBAY

Affiliation: Bilkent University, Department of Molecular Biology and Genetics
 
Title:  Fluorescing Science

Date: May 6, 2009, 15:40 at SBZ14.

Abstract:  The remarkable brightly glowing green fluorescent protein, GFP, was first observed in the jellyfish, Aequorea victoria in 1962. Since then, this protein has become one of the most important tools used in contemporary bioscience. It enables scientists to follow several different biological processes at the same time. 2008 Nobel Prize in Chemistry rewards the initial discovery of GFP and a series of important developments which have led to its use as a tagging tool in bioscience. The story behind the discovery of GFP is one with the three Nobel Prize Laureates in the leading roles: Osamu Shimomura first isolated GFP from the jellyfish Aequorea victoria, Martin Chalfie demonstrated the value of GFP as a luminous genetic tag for various biological phenomena, and Roger Y. Tsien contributed to our general understanding of how GFP fluoresces. He also extended the colour palette beyond green allowing researchers to give various proteins and cells different colours.

Contact person: Ali Sinan Sertöz