The Scale of Public Space: Taksim Square in Istanbul

This article aims at following the traces of the transformation of public sphere in Turkey through its manifestations on urban public spaces with the case study of Taksim Square. In this attempt, the article illustrates how Taksim square, as a public space, has been shaped by struggles between different ideologies, discourses, political decisions and daily activities taking place at personal, interpersonal, local, national, supranational and global scales. Through this way this article also aims at understanding how these contestations at different scales are affecting people, individually and collectively, from daily life practices to political integration. The article also discusses that our daily life practices and preferences are political decisions and our participation in public sphere occurs through those daily actions of the personal spheres. Therefore, the article suggests that a paradigm shift is needed in the design and production of the built environments that will facilitate the coexistence of multiple counter publics

Oeuvre Vs. Abstract Space: Appropriation of Gezi Park in Istanbul

The Gezi Park incidents of summer 2013 in Istanbul have marked a turning point in the political life and democracy in Turkey. The peaceful environmentalist protestations in central Gezi Park have turned into a countrywide upheaval against the neo-liberal and conservative policies of the government, pouring millions of people into streets in different cities. It was a time that Turkey witnessed the formation of a new type of public sphere that encompasses a variety of counter publics, and its spatial incarnation –the Gezi Commune-, reclaimed, created, shaped and inhabited by the free will of people. This was the instant creation of oeuvre through appropriation of the urban space, and a spatial manifestation of reclaiming the right to the city. This article is a reflection on possibility of creation of oeuvre in contemporary society, and a new way of architectural thinking and practice that can pave the way for it

Pacifying the Fermi-liquid: battling the devious fermion signs

The fermion sign problem is studied in the path integral formalism. The standard picture of Fermi liquids is first critically analyzed, pointing out some of its rather peculiar properties. The insightful work of Ceperley in constructing fermionic path integrals in terms of constrained world-lines is then reviewed. In this representation, the minus signs associated with Fermi-Dirac statistics are self consistently translated into a geometrical constraint structure (the {\em nodal hypersurface}) acting on an effective bosonic dynamics. As an illustrative example we use this formalism to study 1+1-dimensional systems, where statistics are irrelevant, and hence the sign problem can be circumvented. In this low-dimensional example, the structure of the nodal constraints leads to a lucid picture of the entropic interaction essential to one-dimensional physics. Working with the path integral in momentum space, we then show that the Fermi gas can be understood by analogy to a Mott insulator in a harmonic trap. Going back to real space, we discuss the topological properties of the nodal cells, and suggest a new holographic conjecture relating Fermi liquids in higher dimensions to soft-core bosons in one dimension. We also discuss some possible connections between mixed Bose/Fermi systems and supersymmetry.Comment: 28 pages, 5 figure

A Simple Method for Finding Optimal Paths of Hot and Cold Streams inside Shell and Tube Heat Exchangers to Reduce Pumping Cost in Heat Exchanger Network Problems

In this paper, a simple method is presented for the synthesis and retrofit of heat exchanger networks (HENs) by considering pressure drop as well as finding proper path of streams inside heat exchangers (HEs) to reduce the pumping cost of network. Generally, HEN problems lead to MINLP models which have convergence difficulties due to the existence of both continuous and integer variables. In this study, instead of solving these variables simultaneously, a combination of Genetic Algorithm (GA) with Quasi Linear Programming (QLP) and Integer Linear Programming (ILP) was used for solving the problem. GA was used to find optimal HENs structure and streams paths, whereas continuous variables were solved by QLP. For the retrofit of HENs, a modified ILP model was used. Results show that the proposed method has the ability to reduce the cost of annual pumping due to considering optimal paths for streams in the HEs compared to the literature. This work is licensed under a Creative Commons Attribution 4.0 International License

On cognitive readiness in construction decision making

Cognitive readiness (CR) in construction is the mental, emotional and interpersonal skills that relate to the way project teams perceive, remember, think, speak and solve problems. CR compliments the necessary technical and contextual competences, and is necessary for making appropriate decisions in real-world problems. The investigation of cognitive enablers and barriers as well as their prioritization, adaptation and implementation in construction projects is the subject ofthe work described here

The Berry phase of dislocations in graphene and valley conserving decoherence

We demonstrate that dislocations in the graphene lattice give rise to electron Berry phases equivalent to quantized values {0,1/3,-1/3} in units of the flux quantum, but with an opposite sign for the two valleys. An elementary scale consideration of a graphene Aharonov-Bohm ring equipped with valley filters on both terminals, encircling a dislocation, says that in the regime where the intervalley mean free path is large compared to the intravalley phase coherence length, such that the valley quantum numbers can be regarded as conserved on the relevant scale, the coherent valley-polarized currents sensitive to the topological phases have to traverse the device many times before both valleys contribute, and this is not possible at intermediate temperatures where the latter length becomes of order of the device size, thus leading to an apparent violation of the basic law of linear transport that magnetoconductance is even in the applied flux. We discuss this discrepancy in the Feynman path picture of dephasing, when addressing the transition from quantum to classical dissipative transport. We also investigate this device in the scattering matrix formalism, accounting for the effects of decoherence by the Buttiker dephasing voltage probe type model which conserves the valleys, where the magnetoconductance remains even in the flux, also when different decoherence times are allowed for the individual, time reversal connected, valleys.Comment: 14 pages, 7 figures; revised text, added figure, accepted for publication by PR

Electronic States of Graphene Grain Boundaries

We introduce a model for amorphous grain boundaries in graphene, and find that stable structures can exist along the boundary that are responsible for local density of states enhancements both at zero and finite (~0.5 eV) energies. Such zero energy peaks in particular were identified in STS measurements [J. \v{C}ervenka, M. I. Katsnelson, and C. F. J. Flipse, Nature Physics 5, 840 (2009)], but are not present in the simplest pentagon-heptagon dislocation array model [O. V. Yazyev and S. G. Louie, Physical Review B 81, 195420 (2010)]. We consider the low energy continuum theory of arrays of dislocations in graphene and show that it predicts localized zero energy states. Since the continuum theory is based on an idealized lattice scale physics it is a priori not literally applicable. However, we identify stable dislocation cores, different from the pentagon-heptagon pairs, that do carry zero energy states. These might be responsible for the enhanced magnetism seen experimentally at graphite grain boundaries.Comment: 10 pages, 4 figures, submitted to Physical Review