508 research outputs found
Supercurrent Spectroscopy of Andreev States
We measure the excitation spectrum of a superconducting atomic contact. In
addition to the usual continuum above the superconducting gap, the single
particle excitation spectrum contains discrete, spin-degenerate Andreev levels
inside the gap. Quasiparticle excitations are induced by a broadband on-chip
microwave source and detected by measuring changes in the supercurrent flowing
through the atomic contact. Since microwave photons excite quasiparticles in
pairs, two types of transitions are observed: Andreev transitions, which
consists of putting two quasiparticles in an Andreev level, and transitions to
odd states with a single quasiparticle in an Andreev level and the other one in
the continuum. In contrast to absorption spectroscopy, supercurrent
spectroscopy allows detection of long-lived odd states.Comment: typos correcte
Matematik öğretmen adaylarının örüntü genellemesi bilgilerini kullanarak yaptıkları etkinlik değişiklikleri
The purpose of the study is to evaluate how prospective mathematics teachers (PMTs) modify tasks to facilitate students’ learning of pattern generalization through the use of their mathematical knowledge for teaching. Case study, which is a type of qualitative research method, was used to determine the mathematical characteristics that PMTs use when modifying a mathematical task. The knowledge from which PMTs draw to modify the task has also been outlined. Accordingly, data were collected from PMTs’ task modifications and reflection reports. When PMTs worked on two or more forms of modification, as compared to just using one type of modification, they modified tasks more effectively and comprehensively. The PMTs who make condition modifications need to utilize specialized content knowledge through the use of models or tables. They aimed to help middle school students understand using these modifications, and thus they also utilized their knowledge of content and students. They also used their knowledge of content and teaching, especially while making modifications to questions and context. Task modification activities can be used to help prospective teachers notice the mathematical and pedagogical affordances and limitations offered by tasks.Bu çalışmanın amacı, öğrencilerin örüntü genellemelerine yardımcı olmak için matematik öğretmen adaylarının matematik öğretimi bilgilerini kullanarak yaptıkları etkinlik değişikliklerini değerlendirmektir. Öğretmen adaylarının matematiksel bir etkinliği değiştirirken kullandıkları matematiksel özellikleri belirlemek için nitel araştırma yöntemlerinden durum çalışması kullanılmıştır. Ayrıca öğretmen adaylarının etkinliği değiştirirken kullandıkları bilgileri belirlenmiştir. Veriler, öğretmen adaylarının değiştirdiği etkinliklerden ve yansıtma raporlarından toplanmıştır. Öğretmen adayları, etkinlik üzerinde yalnızca bir tür değişiklik yapmaya kıyasla iki veya daha fazla değişiklik türünü birlikte yaptıklarında, etkinliklerini daha anlamlı ve kapsamlı bir şekilde değiştirmişlerdir. Koşul değişiklikleri yapanlar, model veya tablo ekleyerek uzmanlık alan bilgilerini kullanmıştır. Bu değişiklikleri öğrencilerin anlamasına yardımcı olmak amacıyla da yapmışlar ve böylece öğrenci ve alan bilgilerini de kullanmışlardır. Ayrıca öğretmen adayları, alan ve öğretme bilgilerinden özellikle soru ve bağlam değişikliği yaparken yararlanmıştır. Etkinlik değiştirme çalışmaları, öğretmen adaylarının etkinliklerin sunduğu matematiksel ve pedagojik olanakları ve sınırlılıkları fark etmelerine yardımcı olmak için kullanılabilir
Theory of microwave spectroscopy of Andreev bound states with a Josephson junction
We present a microscopic theory for the current through a tunnel Josephson
junction coupled to a non-linear environment, which consists of an Andreev
two-level system coupled to a harmonic oscillator. It models a recent
experiment [Bretheau, Girit, Pothier, Esteve, and Urbina, Nature (London) 499,
312 (2013)] on photon spectroscopy of Andreev bound states in a superconducting
atomic-size contact. We find the eigenenergies and eigenstates of the
environment and derive the current through the junction due to inelastic Cooper
pair tunneling. The current-voltage characteristic reveals the transitions
between the Andreev bound states, the excitation of the harmonic mode that
hybridizes with the Andreev bound states, as well as multi-photon processes.
The calculated spectra are in fair agreement with the experimental data.Comment: 8 pages, 6 figure
Exciting Andreev pairs in a superconducting atomic contact
The Josephson effect describes the flow of supercurrent in a weak link, such
as a tunnel junction, nanowire, or molecule, between two superconductors. It is
the basis for a variety of circuits and devices, with applications ranging from
medicine to quantum information. Currently, experiments using Josephson
circuits that behave like artificial atoms are revolutionizing the way we probe
and exploit the laws of quantum physics. Microscopically, the supercurrent is
carried by Andreev pair states, which are localized at the weak link. These
states come in doublets and have energies inside the superconducting gap.
Existing Josephson circuits are based on properties of just the ground state of
each doublet and so far the excited states have not been directly detected.
Here we establish their existence through spectroscopic measurements of
superconducting atomic contacts. The spectra, which depend on the atomic
configuration and on the phase difference between the superconductors, are in
complete agreement with theory. Andreev doublets could be exploited to encode
information in novel types of superconducting qubits.Comment: Submitted to Natur
Tunable Superconducting Phase Transition in Metal-Decorated Graphene Sheets
Using typical experimental techniques it is difficult to separate the effects
of carrier density and disorder on the superconducting transition in two
dimensions. Using a simple fabrication procedure based on metal layer
dewetting, we have produced graphene sheets decorated with a non-percolating
network of nanoscale tin clusters. These metal clusters both efficiently dope
the graphene substrate and induce long-range superconducting correlations. This
allows us to study the superconducting transition at fixed disorder and
variable carrier concentration. We find that despite structural inhomogeneity
on mesoscopic length scales (10-100 nm), this material behaves electronically
as a homogenous dirty superconductor. Our simple self-assembly method
establishes graphene as an ideal tunable substrate for studying induced
two-dimensional electronic systems at fixed disorder and our technique can
readily be extended to other order parameters such as magnetism
Superconducting atomic contacts inductively coupled to a microwave resonator
We describe and characterize a microwave setup to probe the Andreev levels of
a superconducting atomic contact. The contact is part of a superconducting loop
inductively coupled to a superconducting coplanar resonator. By monitoring the
resonator reflection coefficient close to its resonance frequency as a function
of both flux through the loop and frequency of a second tone we perform
spectroscopy of the transition between two Andreev levels of highly
transmitting channels of the contact. The results indicate how to perform
coherent manipulation of these states.Comment: 14 pages, 10 figures, to appear in special issue on break-junctions
in JOPC
Dynamics of quasiparticle trapping in Andreev levels
We present a theory describing the trapping and untrapping of quasiparticles
in the Andreev bound level of a single-channel weak link between two
superconductors. We calculate the rates of the transitions between even and odd
occupations of the Andreev level induced by absorption and emission of both
photons and phonons. We apply the theory to a recent experiment [Phys. Rev.
Lett. 106, 257003 (2011)] in which the dynamics of the trapping of
quasiparticles in the Andreev levels of superconducting atomic contacts coupled
to a Josephson junction was measured. We show that the plasma energy
of the Josephson junction defines a rather abrupt transition between a fast
relaxation regime dominated by coupling to photons and a slow relaxation regime
dominated by coupling to phonons. With realistic parameters the theory provides
a semi-quantitative description of the experimental results.Comment: 11 pages, 9 figures. Accepted for publication in Physical Review
On the Precision of Search Engines: Results from a Controlled Experiment
Handling the growing amount of digital information is one of the major challenges when dealing with the World Wide Web (WWW). In particular, users crave for an effective and efficient retrieval of needed information. In this context, search engines adopt a key role. Besides conventional search engines such as Google, semantic search engines have emerged as an alternative approach in recent years. The quality of search results delivered by search engines is in
influenced by many criteria. This paper picks up one specific issue, the precision, and investigates and compares the precision of current both conventional (i.e., non-semantic) and semantic search engines based on a controlled experiment with 77 participants. Specifically, Google, AltaVista, MetaGer, Hakia, Kngine, and WolframAlpha are investigated and compared
Male nudity in ancient Mesopotamian art
Ankara : The Department of Archaeology, İhsan Doğramacı Bilkent University, 2012.Thesis (Master's) -- Bilkent University, 2012.Includes biblioraphical references 83-89.This thesis attempts to study nude male representations in Mesopotamian art. It
analyzes examples of male nudity in art and textual material from the Protoliterate to
the Neo-Assyrian period in Northern and Southern Iraq. It aims to investigate the
implications that the male nudity in Mesopotamian art carries and both the social and
conceptual aspects that are attributed to male nudity in Mesopotamian society. It argues
how nude male representations are embedded within cultural, religious and political
aspects of the society. The thesis also shows the context dependent state of male nudity
and how it is used as a marker in ancient Mesopotamian art pointing to various
identities, physicalities, and political and religious configurations.Girit, AyşenM.S
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