Nonperturbative analysis of coupled quantum dots in a phonon bath

Transport through coupled quantum dots in a phonon bath is studied using the recently developed real-time renormalization-group method. Thereby, the problem can be treated beyond perturbation theory regarding the complete interaction. A reliable solution for the stationary tunnel current is obtained for the case of moderately strong couplings of the dots to the leads and to the phonon bath. Any other parameter is arbitrary, and the complete electron-phonon interaction is taken into account. Experimental results are quantitatively reproduced by taking into account a finite extension of the wavefunctions within the dots. Its dependence on the energy difference between the dots is derived.Comment: 8 pages, 6 figure

Calculation Approaches for Determining the Sliding Friction Coefficient – Analytical Consideration and FE-Modelling

Microstructures on polymer surfaces are known to reduce friction and thevisibility of scratches. Due to the complex interaction of multiple surface areas in contactwith each other the prediction of coefficient of friction (COF) or wear is difficult and dependson an empirical solution. This article deals with possibilities of calculating the deformingpart of friction via an analytical solution and a FE-model. In a first step the modelling ofsingle contacts is demonstrated. The analytical calculation based on the Hertzian contactequations is extended regarding viscoelastic material parameters. The basic approach ofFE-modelling is explained including calibration of the material model using the softwareMCalibration®. The article introduces the different procedures of simulating and modellingCOF and wear taking into account the area of contact and resulting stress distribution

Electron Neutrino Pair Annihilation: A New Source for Muon and Tau Neutrinos in Supernovae

We show that in a supernova core the annihilation process nu_e nu_e-bar -> nu_{mu,tau} nu_{mu,tau}-bar is always more important than the traditional reaction e^+ e^- -> nu_{mu,tau} nu_{mu,tau}-bar as a source for muon and tau neutrino pairs. We study the impact of the new process by means of a Monte Carlo transport code with a static stellar background model and by means of a self-consistent hydrodynamical simulation with Boltzmann neutrino transport. Nucleon bremsstrahlung NN -> NN nu_{mu,tau} nu_{mu,tau}-bar is also included as another important source term. Taking into account nu_e nu_e-bar -> nu_{mu,tau} nu_{mu,tau}-bar increases the nu_mu and nu_tau luminosities by as much as 20% while the spectra remain almost unaffected. In our hydrodynamical simulation the shock was somewhat weakened. Elastic nu_{mu,tau} nu_e and nu_{mu,tau} nu_e scattering is not negligible but less important than nu_{mu,tau} e^+ or e^- scattering. Its influence on the nu_{mu,tau} fluxes and spectra is small after all other processes have been included.Comment: 11 pages, 9 eps-figs, submitted to Ap

Quantum walks of correlated photon pairs in two-dimensional waveguide arrays

We demonstrate quantum walks of correlated photons in a 2D network of directly laser written waveguides coupled in a 'swiss cross' arrangement. The correlated detection events show high-visibility quantum interference and unique composite behaviour: strong correlation and independence of the quantum walkers, between and within the planes of the cross. Violations of a classically defined inequality, for photons injected in the same plane and in orthogonal planes, reveal non-classical behaviour in a non-planar structure.Comment: 5 pages, 5 figure

Low Mach preconditioning for turbomachinery flow simulations with cavities and variable gas compositions

The optimization of turbomachines increasingly relies on highly accurate numerical performance predictions. Loss predictions require the cavities of the machine to be included in numerical simulations. Commonly, in cavities, the velocity of the simulated fluid is small. For density-based solvers, this results in slow convergence and inaccurate computations. Further, the fluid in cavities is often composed of several gases. This paper presents the low Mach preconditioning method for multi-component thermally perfect gas of DLR’s inhouse solver TRACE. Two low Mach academic test cases, a lid driven cavity and an air and exhaust gas mixing layer, are computed to validate the preconditioner. Both test cases show an accelarated convergence and an improved accuracy, when preconditioning is used. A 1.5 stage low-pressure turbine rig with a labyrinth seal is computed with thermally perfect air. The result shows a good agreement with the experimental reference. The fluid is then changed to exhaust gas, and two air inflows are added in the labyrinth seal, to analyze the effect of low Mach preconditioning on the mixing of the two gases. The preconditioned computation shows an improved convergence in the cavity. Moreover, the wall temperature and the gas distribution in the cavity differ, when preconditioning is applied

Real-Time-RG Analysis of the Dynamics of the Spin-Boson Model

Using a real-time renormalization group method we determine the complete dynamics of the spin-boson model with ohmic dissipation for coupling strengths $\alpha\lesssim 0.1-0.2$. We calculate the relaxation and dephasing time, the static susceptibility and correlation functions. Our results are consistent with quantum Monte Carlo simulations and the Shiba relation. We present for the first time reliable results for finite cutoff and finite bias in a regime where perturbation theory in $\alpha$ or in tunneling breaks down. Furthermore, an unambigious comparism to results from the Kondo model is achieved.Comment: 4 pages, 5 figures, 1 tabl

Common Sense Beliefs About The Central Self, Moral Character, And The Brain

To assess lay beliefs about self and brain, we probed people\u27s opinions about the central self, in relation to morality, willful control, and brain relevance. In study 1, 172 participants compared the central self to the peripheral self. The central self, construed at this abstract level, was seen as more brain-based than the peripheral self, less changeable through willful control, and yet more indicative of moral character. In study 2, 210 participants described 18 specific personality traits on 6 dimensions: centrality to self, moral relevance, willful control, brain dependence, temporal stability, and desirability. Consistent with Study 1, centrality to the self, construed at this more concrete level, was positively correlated to brain dependence. Centrality to the self was also correlated to desirability and temporal stability, but not to morality or willful control. We discuss differences and similarities between abstract (Study 1) and concrete (Study 2) levels of construal of the central self, and conclude that in contemporary American society people readily embrace the brain as the underlying substrate of who they truly are