XPS characterization of silver electrodes and catalyst for oxygen reduction

The combined analysis of the silver GDE using an ex-situ surface sensitive technique (XPS) and in-situ electrochemical measurements (EIS, CV) show that the performance of the silver GDE is significantly influenced by the degree of degradation of the electrodes, e. g., the reduction of the active surface due to the decomposition of the PTFE. These findings indicate a different degree of decomposition of the PTFE on the on the GDE

Noise at a Fermi-edge singularity

We present noise measurements of self-assembled InAs quantum dots at high magnetic fields. In comparison to I-V characteristics at zero magnetic field we notice a strong current overshoot which is due to a Fermi-edge singularity. We observe an enhanced suppression in the shot noise power simultaneous to the current overshoot which is attributed to the electron-electron interaction in the Fermi-edge singularity

The Effect of Speech-to-Text Software on Learning a New Writing Strategy

Handwriting and spelling present elementary students with significant sources of load on working memory as the various writing processes compete for cognitive resources (Kellogg, Whiteford, Turner, Cahill & Mertens, 2013). Several studies have shown that speech-to-text (STT) software can improve students\u27 writing on a specific text (Higgins & Raskind, 1997; MacArthur & Cavalier, 2004; Quinlan, 2004); however, the question of whether STT can be used to teach writing strategies has been neglected. This pretest-post-test between groups study experimentally tested the effects of composition modality on learning a persuasive writing strategy. First, all students (N=45) completed a pretest of persuasive writing. They then, received instruction in Dragon NaturallySpeaking (version 11). Next, students were randomly assigned to participate in four lessons that emphasized dialectical elements of persuasive writing, in one of two modalities: STT or handwriting. Finally, all students completed post-tests of persuasive writing in both modalities (STT and handwriting). Writing samples were evaluated for word count, number of types of rhetorical moves, surface errors, and word errors. Students also completed measures of cognitive load for the pretest, each writing activity, and post-test. Both training conditions resulted in large, statistically significant, pre-to-post-test gains on word count, holistic quality and rhetorical moves. Students in the STT condition reported more effort compared to students in the handwriting condition for both post-tests. Students in both instructional conditions showed a high level of transfer from the trained modality to the untrained modality. Students who learned through handwriting, compared to students who learned through STT, showed more surface errors on the STT post-test. The results suggest that STT could be an equally effective alternative for teaching composition strategies

Multicritical scaling in a lattice model of vesicles

10 pages, 3 figure

Causal vs. Noncausal Description of Nonlinear Wave Mixing; Resolving the Damping-Sign Controversy

Frequency-domain nonlinear wave mixing processes may be described either using response functions whereby the signal is generated after all interactions with the incoming fields, or in terms of scattering amplitudes where all fields are treated symetrically with no specific time ordering. Closed Green's function expressions derived for the two types of signals have different analytical properties. The recent controversy regarding the sign of radiative damping in the linear (Kramers Heisenberg) formula is put in a broader context

Hartree-Fock theory of a current-carrying electron gas

State-of-the-art simulation tools for nonequilibrium quantum transport systems typically take the current-carrier occupations to be described in terms of equilibrium distribution functions characterized by two different electrochemical potentials, while for the description of electronic exchange and correlation, the local density approximation (LDA) to density functional theory is generally used. However, this involves an inconsistency because the LDA is based on the homogeneous electron gas in equilibrium, while the system is not in equilibrium and may be far from it. In this paper, we analyze this inconsistency by studying the interplay between nonequilibrium occupancies obtained from a maximum entropy approach and the Hartree-Fock exchange energy, single-particle spectrum and exchange hole, for the case of a two-dimensional homogeneous electron gas. The current dependence of the local exchange potential is also discussed. It is found that the single-particle spectrum and exchange hole have a significant dependence on the current, which has not been taken into account in practical calculations since it is not captured by the commonly used functionals. The exchange energy and the local exchange potential, however, are shown to change very little with respect to their equilibrium counterparts. The weak dependence of these quantities on the current is explained in terms of the symmetries of the exchange hole

Enhanced Shot Noise in Tunneling through a Stack of Coupled Quantum Dots

We have investigated the noise properties of the tunneling current through vertically coupled self-assembled InAs quantum dots. We observe super-Poissonian shot noise at low temperatures. For increased temperature this effect is suppressed. The super-Poissonian noise is explained by capacitive coupling between different stacks of quantum dots

Area-width scaling in generalised Motzkin paths

13 pages, 3 figures19 pages, 3 figure

Critical Property of Geometric Phase in the Dicke Model

We obtain the ground-state energy level and associated geometric phase in the Dicke model analytically by means of the Holstein-Primakoff transformation and the boson expansion approach in the thermodynamic limit. The non-adiabatic geometric phase induced by the photon field is derived with the time-dependent unitary transformation. It is shown that the quantum phase transition characterized by the non-analyticity of the geometric phase is remarkably of the first-order. We also investigate the scaling behavior of the geometric phase at the critical point, which can be measured in a practical experiment to detect the quantum phase transition.Comment: 1 figur

Nonequilibrium fluctuation-dissipation relations for one- and two-particle correlation functions in steady-state quantum transport

We study the non-equilibrium (NE) fluctuation-dissipation (FD) relations in the context of quantum thermoelectric transport through a two-terminal nanodevice in the steady-state. The FD relations for the one- and two-particle correlation functions are derived for a model of the central region consisting of a single electron level. Explicit expressions for the FD relations of the Green's functions (one-particle correlations) are provided. The FD relations for the current-current and charge-charge (two-particle) correlations are calculated numerically. We use self-consistent NE Green's functions calculations to treat the system in the absence and in the presence of interaction (electron-phonon) in the central region. We show that, for this model, there is no single universal FD theorem for the NE steady state. There are different FD relations for each different class of problems. We find that the FD relations for the one-particle correlation function are strongly dependent on both the NE conditions and the interactions, while the FD relations of the current-current correlation function are much less dependent on the interaction. The latter property suggests interesting applications for single-molecule and other nanoscale transport experiments.Comment: This revised version is now accepted for publication in the Journal of Chemical Physics (March 2014). arXiv admin note: text overlap with arXiv:1305.507