Quantal Andreev billiards: Semiclassical approach to mesoscale oscillations in the density of states

Andreev billiards are finite, arbitrarily-shaped, normal-state regions, surrounded by superconductor. At energies below the superconducting gap, single-quasiparticle excitations are confined to the normal region and its vicinity, the essential mechanism for this confinement being Andreev reflection. This Paper develops and implements a theoretical framework for the investigation of the short-wave quantal properties of these single-quasiparticle excitations. The focus is primarily on the relationship between the quasiparticle energy eigenvalue spectrum and the geometrical shape of the normal-state region, i.e., the question of spectral geometry in the novel setting of excitations confined by a superconducting pair-potential. Among the central results of this investigation are two semiclassical trace formulas for the density of states. The first, a lower-resolution formula, corresponds to the well-known quasiclassical approximation, conventionally invoked in settings involving superconductivity. The second, a higher-resolution formula, allows the density of states to be expressed in terms of: (i) An explicit formula for the level density, valid in the short-wave limit, for billiards of arbitrary shape and dimensionality. This level density depends on the billiard shape only through the set of stationary-length chords of the billiard and the curvature of the boundary at the endpoints of these chords; and (ii) Higher-resolution corrections to the level density, expressed as a sum over periodic orbits that creep around the billiard boundary. Owing to the fact that these creeping orbits are much longer than the stationary chords, one can, inter alia, hear the stationary chords of Andreev billiards.Comment: 52 pages, 15 figures, 1 table, RevTe

Forest Conservation Knowledge-Community Perception Within Protected Areas: The Case of Karagöl-Sahara National Park

Commitment of local communities to protected areas is essential for conserving forest and biodiversity. However, in many developing countries like Turkey, former management strategies kept human from protected areas using coercion. Fortunately, more recent regimes attempt to give local populations more control on the management but little is known about local residents\u27 perceptions, beliefs and attitudes toward the management of these areas. This study, carried out around the Karagöl Sahara National Park, determined factors which support local communities\u27 positive perceptions towards forest conservation in the park, analysed their assessment of current park management activities compared to former management approaches and draw the implications for effective participatory management of protected areas. We collected socio-demographic data from 100 residents on their awareness of conservation methods. The findings indicated that the positive behavior of local communities towards conservation of forest within Karagöl Sahara National Park was highly correlated with the current management strategy that involved more effectively local communities, the educational level of participants. Participants\u27 perceptions of forest conservation were strongly related to locally perceived benefits. Although 91 % of participants were favorable to the concept of forest and biodiversity conservation within the park. Our results suggested that understanding local residents\u27 perceptions and using them as a starting point to improve the park–people relationship could help park management staff to involve more effectively local communities and improve their awareness about biodiversity conservation within the park

Reentrant topological phase transitions in a disordered spinless superconducting wire

In a one-dimensional spinless p-wave superconductor with coherence length \xi, disorder induces a phase transition between a topologically nontrivial phase and a trivial insulating phase at the critical mean free path l=\xi/2. Here, we show that a multichannel spinless p-wave superconductor goes through an alternation of topologically trivial and nontrivial phases upon increasing the disorder strength, the number of phase transitions being equal to the channel number N. The last phase transition, from a nontrivial phase into the trivial phase, takes place at a mean free path l = \xi/(N+1), parametrically smaller than the critical mean free path in one dimension. Our result is valid in the limit that the wire width W is much smaller than the superconducting coherence length \xi

Şehiriçi fiyat farklılaşması: İstanbul örneği

The existence of price dispersion is one of the most well known principles of economic theory. Earlier studies concentrated on international purchasing power parity (PPP) deviations. In recent years several studies have examined price dispersion within a nation’s borders. In this article the price dispersion among the districts of Istanbul is analyzed by utilizing a data set containing microeconomic price levels from bazaars, convenience stores, and supermarkets. According to results of the study, the prices of homogenous products, except fruit and vegetables, vary less than the prices of differentiated goods as one might expect. Results also indicate that, type of the seller of the product effects price dispersion among the counties of Istanbul.Fiyat farklılaşmasının varlığı iktisat teorisinin en iyi bilinen kaidelerinden biridir. Daha önceki çalışmalar uluslararası satın alma gücü paritesinden sapmaları incelemişlerdir. Son yıllarda birçok çalışmada ise, bir ülkenin sınırları içinde görülen fiyat farklılaşması analiz edilmiştir. Bu çalışmada İstanbul ilçeleri arasındaki fiyat farklılaşması bakkallar, marketler ve pazarlardan toplanan ürün bazında fiyatlar kullanılarak incelenmektedir. Çalışmanın sonuçlarına göre, beklentilere uygun olarak, meyve ve sebze grubu dışındaki homojen malların fiyatları farklılaşmış ürünlerin fiyatlarına göre daha az farklılaşma göstermektedir. Sonuçlar ayrıca satıcılar arasındaki farklılıkların da İstanbul ilçeleri arasındaki fiyat farklılaşmasını etkileyen faktörlerden olduğunu göstermektedir.Publisher's Versio

Interfaces within graphene nanoribbons

We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, in contrast to the behavior of the much studied electron gas waveguides. In the curved nanoribbons, the conductance is very sensitive to details such as whether regions of a semiconducting armchair nanoribbon are included in the curved structure -- such regions strongly suppress the conductance. Surprisingly, this suppression is not due to the band gap of the semiconducting nanoribbon, but is linked to the valley degree of freedom. Though we study these effects in the simplest contexts, they can be expected to occur for more complicated structures, and we show results for rings as well. We conclude that experience from electron gas waveguides does not carry over to graphene nanostructures. The interior interfaces causing extra scattering result from the extra effective degrees of freedom of the graphene structure, namely the valley and sublattice pseudospins