The Changing Face of α Centauri B: Probing plage and stellar activity in K-dwarfs

A detailed knowledge of stellar activity is crucial for understanding stellar dynamos, as well as pushing exoplanet radial-velocity detection limits towards Earth analogue confirmation. We directly compare archival HARPS spectra taken at the minimum in $\alpha$ Cen B's activity cycle to a high-activity state when clear rotational modulation of $\log{R'_{HK}}$ is visible. Relative to the inactive spectra, we find a large number of narrow pseudo-emission features in the active spectra with strengths that are rotationally modulated. These features most likely originate from plage, spots, or a combination of both. They also display radial velocity variations of $\sim$300 m s$^{-1}$ - consistent with an active region rotating across the stellar surface. Furthermore, we see evidence that some of the lines originating from the `active immaculate' photosphere appear broader relative to the `inactive immaculate' case. This may be due to enhanced contributions of e.g. magnetic bright points to these lines, which then causes additional line broadening. More detailed analysis may enable measurements of plage and spot coverage using single spectra in the future.Comment: 6 pages, 4 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS) Letter

Survey propagation at finite temperature: application to a Sourlas code as a toy model

In this paper we investigate a finite temperature generalization of survey propagation, by applying it to the problem of finite temperature decoding of a biased finite connectivity Sourlas code for temperatures lower than the Nishimori temperature. We observe that the result is a shift of the location of the dynamical critical channel noise to larger values than the corresponding dynamical transition for belief propagation, as suggested recently by Migliorini and Saad for LDPC codes. We show how the finite temperature 1-RSB SP gives accurate results in the regime where competing approaches fail to converge or fail to recover the retrieval state

Corporate image: a service recovery perspective

This article explores direct and indirect antecedents that contribute to corporate image formation in a service recovery context. Two studies were carried out in Egypt. Study 1 comprises 29 semistructured interviews with complainants of mobile phone network service providers in Egypt. Study 2 encompasses a mail survey of another 437 complainants. Findings reveal the importance of perceived justice, namely, interactional justice, in corporate image formation, as well as the mediating role of satisfaction with service recovery in the perceived justice-corporate image relationship. Results also reveal two empirical relationships: problem solving as a determinant of distributive justice and follow-up as a driver of procedural justice. Accordingly, this study contributes to the service field by providing the first empirical evaluation of new direct and indirect antecedents of corporate image formation in a service recovery context. Managerial recommendations are provided that encourage service practitioners to emphasize perceived justice and satisfaction with a service recovery process to enhance the company’s image. Additionally, companies should invest in implementing problem solving and follow-up as service recovery strategies since both significantly enhance perceived justice

Dephasing of coupled spin qubit system during gate operations due to background charge fluctuations

It has been proposed that a quantum computer can be constructed based on electron spins in quantum dots or based on a superconducting nanocircuit. During two-qubit operations, the fluctuation of the coupling parameters is a critical factor. One source of such fluctuation is the stirring of the background charges. We focused on the influence of this fluctuation on a coupled spin qubit system. The induced fluctuation in exchange coupling changes the amount of entanglement, fidelity, and purity. In our previous study, the background charge fluctuations were found to be an important channel of dephasing for a single Josephson qubit.Comment: 10 pages, 7 figure. to be publishe

Enhanced Cooperation in an Asymmetric Model of Tax Competition

This paper analyzes enhanced cooperation agreements in corporate taxation in a three country tax competition model where countries differ in size. We characterize equilibrium tax rates and the optimal tax responses due to the formation of an enhanced cooperation agreement. Conditions for strategic complementarity or strategic substitutability of tax rates are crucial for the welfare effects of enhanced cooperation. Simulations show that enhanced cooperation is unlikely to be feasible for small countries. When enhanced cooperation is feasible, it may hamper global harmonization. Only when countries are of similar size is global harmonization a feasible outcome

Phase-slip induced dissipation in an atomic Bose-Hubbard system

Phase slips play a primary role in dissipation across a wide spectrum of bosonic systems, from determining the critical velocity of superfluid helium to generating resistance in thin superconducting wires. This subject has also inspired much technological interest, largely motivated by applications involving nanoscale superconducting circuit elements, e.g., standards based on quantum phase-slip junctions. While phase slips caused by thermal fluctuations at high temperatures are well understood, controversy remains over the role of phase slips in small-scale superconductors. In solids, problems such as uncontrolled noise sources and disorder complicate the study and application of phase slips. Here we show that phase slips can lead to dissipation for a clean and well-characterized Bose-Hubbard (BH) system by experimentally studying transport using ultra-cold atoms trapped in an optical lattice. In contrast to previous work, we explore a low velocity regime described by the 3D BH model which is not affected by instabilities, and we measure the effect of temperature on the dissipation strength. We show that the damping rate of atomic motion-the analogue of electrical resistance in a solid-in the confining parabolic potential fits well to a model that includes finite damping at zero temperature. The low-temperature behaviour is consistent with the theory of quantum tunnelling of phase slips, while at higher temperatures a cross-over consistent with the transition to thermal activation of phase slips is evident. Motion-induced features reminiscent of vortices and vortex rings associated with phase slips are also observed in time-of-flight imaging.Comment: published in Nature 453, 76 (2008

Possible realization of Josephson charge qubits in two coupled Bose-Einstein condensates

We demonstrate that two coupled Bose-Einstein condensates (BEC) at zero temperature can be used to realize a qubit which is the counterpart of Josephson charge qubits. The two BEC are weakly coupled and confined in an asymmetric double-well trap. When the "charging energy" of the system is much larger than the Josephson energy and the system is biased near a degeneracy point, the two BEC represent a qubit with two states differing only by one atom. The realization of the BEC qubits in realistic BEC experiments is briefly discussed.Comment: 4 pages; comments are welcome / Corrected typos in Eq. (16); a note adde

Superconductor-ferromagnet junction phase qubit

We propose a scheme for a phase qubit in an SIFIS junction, consisting of bulk superconductors (S), a proximity-induced ferromagnet (F), and insulating barriers (I). The qubit state is constituted by 0 and $\pi$ phase states of the junction, in which the charging energy of the junction leads to the superposition of the two states. The qubit is operated by the gate voltage applied to the ferromagnet, and insensitive to the decoherence sources existing in other superconducting qubits. We discuss a scalable scheme for qubit measurement and tunable two-qubit coupling.Comment: 3 pages, 3 figure