Local current distribution at large quantum dots (QDs): a self-consistent screening model

We report the implementation of the self-consistent Thomas-Fermi screening theory, together with the local Ohm's law to a quantum dot system in order to obtain local current distribution within the dot and at the leads. We consider a large dot (size $>700$ nm) defined by split gates, and coupled to the leads. Numerical calculations show that the non-dissipative current is confined to the incompressible strips. Due to the non-linear screening properties of the 2DES at low temperatures, this distribution is highly sensitive to external magnetic field. Our findings support the phenomenological models provided by the experimental studies so far, where the formation of the (direct) edge channels dominate the transport.Comment: 6 Pages, 2 Figure

Simultaneous use of Individual and Joint Regularization Terms in Compressive Sensing: Joint Reconstruction of Multi-Channel Multi-Contrast MRI Acquisitions

Purpose: A time-efficient strategy to acquire high-quality multi-contrast images is to reconstruct undersampled data with joint regularization terms that leverage common information across contrasts. However, these terms can cause leakage of uncommon features among contrasts, compromising diagnostic utility. The goal of this study is to develop a compressive sensing method for multi-channel multi-contrast magnetic resonance imaging (MRI) that optimally utilizes shared information while preventing feature leakage. Theory: Joint regularization terms group sparsity and colour total variation are used to exploit common features across images while individual sparsity and total variation are also used to prevent leakage of distinct features across contrasts. The multi-channel multi-contrast reconstruction problem is solved via a fast algorithm based on Alternating Direction Method of Multipliers. Methods: The proposed method is compared against using only individual and only joint regularization terms in reconstruction. Comparisons were performed on single-channel simulated and multi-channel in-vivo datasets in terms of reconstruction quality and neuroradiologist reader scores. Results: The proposed method demonstrates rapid convergence and improved image quality for both simulated and in-vivo datasets. Furthermore, while reconstructions that solely use joint regularization terms are prone to leakage-of-features, the proposed method reliably avoids leakage via simultaneous use of joint and individual terms. Conclusion: The proposed compressive sensing method performs fast reconstruction of multi-channel multi-contrast MRI data with improved image quality. It offers reliability against feature leakage in joint reconstructions, thereby holding great promise for clinical use.Comment: 13 pages, 13 figures. Submitted for possible publicatio

Adaptive pairs trading strategy performance in Turkish derivatives exchange with the companies listed on Istanbul stock exchange

Due to copyright restrictions, the access to the full text of this article is only available via subscription.We implemented model-driven statistical arbitrage strategies in Turkish equities market. Trading signals are generated by optimized parameters of distance method. When the trade in signal is triggered by the model, market-neutral portfolio is created by long in the synthetic ETF, which is based on constrained least squares regression of selected Istanbul Stock Exchange stocks and short in Turkish Derivatives Exchange (Turkdex) index futures contract. We performed pairs trading strategy based on a comparative mean reversion of asset prices with daily data over the period February 2005 through July 2011 in Istanbul Stock Exchange (ISE) and Turkdex. We constructed a hypothetical ISE30 ETF Index on a daily basis in order to originate pairs trading strategy with Turkdex. Because of the leverage rule of (1–10) index futures contracts, we had to evaluate spot stock pairs formation with futures contracts pairs strategy. The results indicate that applied pairs strategy produced overall returns of 901 per cent during the investment period, whereas naive strategy (buy and hold ISE-30 index) return for the same period was 111 per cent. Similar outperformance was observed in the Sharpe and Sortino ratios

Higher-dimensional resolution of dilatonic black hole singularities

We show that the four-dimensional extreme dilaton black hole with dilaton coupling constant $a= \sqrt{p/(p+2)}$ can be interpreted as a {\it completely non-singular}, non-dilatonic, black $p$-brane in $(4+p)$ dimensions provided that $p$ is {\it odd}. Similar results are obtained for multi-black holes and dilatonic extended objects in higher spacetime dimensions. The non-singular black $p$-brane solutions include the self-dual three brane of ten-dimensional N=2B supergravity and a multi-fivebrane solution of eleven-dimensional supergravity. In the case of a supersymmetric non-dilatonic $p$-brane solution of a supergravity theory, we show that it saturates a bound on the energy per unit $p$-volume.Comment: 27 pages, R/94/28, UCSBTH-94-35 (Comments added to the discussion section

Brane-Intersection Dynamics from Branes in Brane Backgrounds

We derive the dynamics of M-brane intersections from the worldvolume action of one brane in the background supergravity solution of another one. In this way we obtain an effective action for the self-dual string boundary of an M2-brane in an M5-brane, and show that the dynamics of the 3-brane intersection of two M5-branes is described by a Dirac-Born-Infeld action.Comment: 12 pages,latex. Typos corrected, reference adde

On the nature of compact stars determined by gravitational waves, radio-astronomy, x-ray emission and nuclear physics

We investigate the question of the nature of compact stars, considering they may be neutron stars or hybrid stars containing a quark core, within the present constraints given by gravitational waves, radio-astronomy, X-ray emissions from millisecond pulsars and nuclear physics. A Bayesian framework is used to combine together all these constraints and to predict tidal deformabilities and radii for a 1.4~M$_\odot$ compact star. We find that present gravitation wave and radio-astronomy data favors asy-stiff EoS compatible with nuclear physics and that GW170817 waveform is best described for binary hybrid stars. In addition, this data favors stiff quark matter, independently of the nuclear EoS. Combining this result with constraints from X-ray observation supports the existence of canonical $1.4$~M$_\odot$ mass hybrid star, with a radius predicted to be $R_{1.4}=12.02(8)$~km.Comment: 5 pages, 3 figure

Using an analytical process to contextualise architectural prototypes for metro stations

In order to meet the pressures of a growing population and employment base, a developing city in the Middle East is planning a new public transport system to allow its sustainable growth. Introducing a new mode of public transport to a city that has a complex urban structure and a dependency on car use necessitates specific design responses to inform the station design process. This paper focuses on a study at the micro scale level that addresses the impact of evidence-based design on contextualised architectural station prototypes. Furthermore, it addresses the processes of working with an architectural design office in creating dynamic design iterations. The research here is presented from a perspective of the process of iterative analytical study to real time projects, reflecting on the balance between academia and practice. In order to construct a set of design principles to station locations, three layers of potential movement patterns are analysed using agents based modelling: movement from station exits; movement towards station entrances and background movement generated through the spatial accessibility values of the surrounding context. In that respect, each prototype station has been contextualised to its unique site. Design proposals developed by architectural teams are informed through fine grain analysis of urban features such as pavement widths and signage locations. The analyses also inform the landscape design process through the positioning of street furniture in relation to potential movement patterns as well as the effect of shading and public realm quality through option testing. To integrate stations within their contexts they must have simple entrances and clear orientation from the points of exit. Overall, the dynamic nature of agent based modelling allows for rapid design feedback to occur permitting an iterative process of design development and optimisation

Simplified calculations of band-gap renormalization in quantum-wells

Non-linear optical properties of photoexcited semiconductor quantum-wells are of interest because of their opto-electronic device application possibilities. Many-body interactions of the optically created electrons and holes lead to the band-gap renormalization which in turn determines the absorption spectra of such systems. We employ a simplified approach to calculate the band-gap renormalization in quantum-well systems by considering the interaction of a single electron-hole pair with the collective excitations (plasmons). This method neglects the exchange-correlation effects but fully accounts for the Coulomb-hole term in the single-particle self-energy. We demonstrate that the density, temperature, and well-width dependence of the band-gap renormalization for GaAs quantum-wells within our model is in good agreement with the experimental results. © 1996 Academic Press Limited

Coupled plasmon-phonon mode effects on the Coulomb drag in double-quantum-well systems

We study the Coulomb drag rate for electrons in a double-quantum-well structure taking into account the electron-optical phonon interactions. The full wave vector and frequency dependent random-phase approximation (RPA) at finite temperature is employed to describe the effective interlayer Coulomb interaction. The electron-electron and electron-optical phonon couplings are treated on an equal footing. The electron-phonon mediated interaction contribution is investigated for different layer separations and layer densities. We find that the drag rate at high temperatures (i.e., T≥0.2EF) is dominated by the coupled plasmon-phonon modes of the system. The peak position of the drag rate is shifted to the low temperatures with a slight increase in magnitude, compared to the uncoupled system results in RPA. This behavior is in qualitative agreement with the recent measurements. Including the local-field effects in an approximate way we also estimate the contribution of intralayer correlations

Variational approach for phonon renormalization effects in photoexcited quantum wires and quantum wells

We investigate the effects of screening on polaronic corrections to the effective band edge in photoexcited quasi-one-dimensional GaAs quantum wires and two-dimensional quantum wells. We develop a variational method to calculate the polaron energy of a two-component plasma (electrons and holes) coupled to LO-phonons. Screening effects are incorporated within a dynamical scheme. We find that the screening effects and finite well width considerably reduce the polaron energy as the plasma density increases. Many-body corrections beyond the random-phase approximation are also considered