Current-Induced Entanglement of Nuclear Spins in Quantum Dots

We propose an entanglement mechanism of nuclear spins in quantum dots driven by the electric current accompanied by the spin flip. This situation is relevant to a leakage current in spin-blocked regions where electrons cannot be transported unless their spins are flipped. The current gradually increases the components of larger total spin of nuclei. This correlation among the nuclear spins markedly enhances the spin-flip rate of electrons and hence the leakage current. The enhancement of the current is observable when the residence time of electrons in the quantum dots is shorter than the dephasing time T*_2 of nuclear spins.Comment: 4 pages, 4 figure

Anisotropic Radial Layout for Visualizing Centrality and Structure in Graphs

This paper presents a novel method for layout of undirected graphs, where nodes (vertices) are constrained to lie on a set of nested, simple, closed curves. Such a layout is useful to simultaneously display the structural centrality and vertex distance information for graphs in many domains, including social networks. Closed curves are a more general constraint than the previously proposed circles, and afford our method more flexibility to preserve vertex relationships compared to existing radial layout methods. The proposed approach modifies the multidimensional scaling (MDS) stress to include the estimation of a vertex depth or centrality field as well as a term that penalizes discord between structural centrality of vertices and their alignment with this carefully estimated field. We also propose a visualization strategy for the proposed layout and demonstrate its effectiveness using three social network datasets.Comment: Appears in the Proceedings of the 25th International Symposium on Graph Drawing and Network Visualization (GD 2017

Conductance Increase by Electron-Phonon Interaction in Quantum Wires

We investigate the influence of electron-phonon interactions on the DC-conductance $\Gamma$ of a quantum wire in the limit of one occupied subband. At zero temperature, a Tomonaga-Luttinger-like renormalization of $\Gamma$ to a value slightly larger than $2e^{2}/h$ is calculated for a realistic quantum wire model.Comment: 12 pages RevTeX, no figure. Appears in Phys. Rev.

Systematic Perturbation Theory for Dynamical Coarse-Graining

We demonstrate how the dynamical coarse-graining approach can be systematically extended to higher orders in the coupling between system and reservoir. Up to second order in the coupling constant we explicitly show that dynamical coarse-graining unconditionally preserves positivity of the density matrix -- even for bath density matrices that are not in equilibrium and also for time-dependent system Hamiltonians. By construction, the approach correctly captures the short-time dynamics, i.e., it is suitable to analyze non-Markovian effects. We compare the dynamics with the exact solution for highly non-Markovian systems and find a remarkable quality of the coarse-graining approach. The extension to higher orders is straightforward but rather tedious. The approach is especially useful for bath correlation functions of simple structure and for small system dimensions.Comment: 17 pages, 5 figures, version accepted for publication in PR

Load distribution in weighted complex networks

We study the load distribution in weighted networks by measuring the effective number of optimal paths passing through a given vertex. The optimal path, along which the total cost is minimum, crucially depend on the cost distribution function $p_c(c)$. In the strong disorder limit, where $p_c(c)\sim c^{-1}$, the load distribution follows a power law both in the Erd\H{o}s-R\'enyi (ER) random graphs and in the scale-free (SF) networks, and its characteristics are determined by the structure of the minimum spanning tree. The distribution of loads at vertices with a given vertex degree also follows the SF nature similar to the whole load distribution, implying that the global transport property is not correlated to the local structural information. Finally, we measure the effect of disorder by the correlation coefficient between vertex degree and load, finding that it is larger for ER networks than for SF networks.Comment: 4 pages, 4 figures, final version published in PR

A comparison of salivary testosterone measurement using immunoassays and tandem mass spectrometry

Enzyme immunoassays (EIAs) are widely used to measure salivary testosterone. However, little is known about how accurately different EIAs assess testosterone, partially because estimates across various EIAs differ considerably. We compared testosterone concentrations across EIAs of three commonly used manufacturers (DRG International, Salimetrics, and IBL International) to liquid chromatography tandem mass spectrometry (LC–MS/MS). Relative to EIAs from Salimetrics and IBL International, EIAs supplied by DRG International provided the closest approximation to LC–MS/MS testosterone concentrations, followed closely by EIAs from Salimetrics, and then IBL. Additionally, EIAs tended to inflate estimates of lower testosterone concentrations in women. Examining our results and comparing them to existing data revealed that testosterone EIAs had decreased linear correspondence with LC–MS/MS in comparison to cortisol EIAs. Overall, this paper provides researchers with information to better measure testosterone in their research and more accurately compare testosterone measurements across different methods

Lombardi Drawings of Graphs

We introduce the notion of Lombardi graph drawings, named after the American abstract artist Mark Lombardi. In these drawings, edges are represented as circular arcs rather than as line segments or polylines, and the vertices have perfect angular resolution: the edges are equally spaced around each vertex. We describe algorithms for finding Lombardi drawings of regular graphs, graphs of bounded degeneracy, and certain families of planar graphs.Comment: Expanded version of paper appearing in the 18th International Symposium on Graph Drawing (GD 2010). 13 pages, 7 figure