Effects on the motion of a body attracted by a rotating source, part 2 Progress report

Iterative method determining variation of any order of planned circular orbit about rotating gravitational sourc

Frequency correlations in reflection from random media

We present a theoretical study of frequency correlations of light backscattered from a random scattering medium. This statistical quantity provides insight into the dynamics of multiple scattering processes accessible both, in theoretical and experimental investigations. For frequency correlations between field amplitudes, we derive a simple expression in terms of the path length distribution of the underlying backscattering processes. In a second step, we apply this relation to describe frequency correlations between intensities in the regime of weak disorder. Since, with increasing disorder strength, an unexplained breakdown of the angular structure of the frequency correlation function has recently been reported in experimental studies, we explore extensions of our model to the regime of stronger disorder. In particular, we show that closed scattering trajectories tend to suppress the angular dependence of the frequency correlation function.Comment: 10 pages, 8 figure

Phase diagram of a graphene bilayer in the zero-energy Landau level

Bilayer graphene under a magnetic field has an octet of quasidegenerate levels due to spin, valley, and orbital degeneracies. This zero-energy Landau level is resolved into several incompressible states whose nature is still elusive. We use a Hartree-Fock treatment of a realistic tight-binding four-band model to understand the quantum ferromagnetism phenomena expected for integer fillings of the octet levels. We include the exchange interaction with filled Landau levels below the octet states. This Lamb-shift-like effect contributes to the orbital splitting of the octet. We give phase diagrams as a function of applied bias and magnetic field. Some of our findings are in agreement with experiments. We discuss the possible appearance of phases with orbital coherence

Edge structure of graphene monolayers in the {\nu} = 0 quantum Hall state

Monolayer graphene at neutrality in the quantum Hall regime has many competing ground states with various types of ordering. The outcome of this competition is modified by the presence of the sample boundaries. In this paper we use a Hartree-Fock treatment of the electronic correlations allowing for space-dependent ordering. The edge influence is modeled by a simple perturbative effective magnetic field in valley space. We find that all phases found in the bulk of the sample, ferromagnetic, canted antiferromagnetic, charge-density wave and Kekul$\'e$ distortion are smoothly connected to a Kekul$\'e$-distorted edge. The single-particle excitations are computed taking into account the spatial variation of the order parameters. An eventual metal-insulator transition as a function of the Zeeman energy is not simply related to the type of bulk order.Comment: 18 pages, 11 figures, corresponds to published versio

Semimetallic features in quantum transport through a gate-defined point contact in bilayer graphene

We demonstrate that, at the onset of conduction, an electrostatically defined quantum wire in bilayer graphene (BLG) with an interlayer asymmetry gap may act as a 1D semimetal, due to the multiple minivalley dispersion of its lowest subband. Formation of a non-monotonic subband coincides with a near-degeneracy between the bottom edges of the lowest two subbands in the wire spectrum, suggesting an $8e^2/h$ step at the conduction threshold, and the semimetallic behaviour of the lowest subband in the wire would be manifest as resonance transmission peaks on an $8e^2/h$ conductance plateau.Comment: 9 pages, 8 figures (including appendices

[Book Review:] Contact mechanics and friction: physical principles and applications

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively

A global-to-local model for the representation of human faces

In the context of face modeling and face recognition, statistical models are widely used for the representation and modeling of surfaces. Most of these models are obtained by computing Principal Components Analysis (PCA) on a set of representative examples. These models represent novel faces poorly due to their holistic nature (i.e.\ each component has global support), and they suffer from overfitting when used for generalization from partial information. In this work, we present a novel analysis method that breaks the objects up into modes based on spatial frequency. The high-frequency modes are segmented into regions with respect to specific features of the object. After computing PCA on these segments individually, a hierarchy of global and local components gradually decreasing in size of their support is combined into a linear statistical model, hence the name, Global-to-Local model (G2L). We apply our methodology to build a novel G2L model of 3D shapes of human heads. Both the representation and the generalization capabilities of the models are evaluated and compared in a standardized test, and it is demonstrated that the G2L model performs better compared to traditional holistic PCA models. Furthermore, both models are used to reconstruct the 3D shape of faces from a single photograph. A novel adaptive fitting method is presented that estimates the model parameters using a multi-resolution approach. The model is first fitted to contours extracted from the image. In a second stage, the contours are kept fixed and the remaining flexibility of the model is fitted to the input image. This makes the method fast (30 sec on a standard PC), efficient, and accurate

A novel ex vivo model for investigation of fluid displacements in bone after endoprosthesis implantation

Tissue perfusion and mass transport in the vicinity of implant surfaces prior to integration or bonding may play a crucial role in modulating cellular activities associated with bone remodeling, in particular, at early stages of the integration process. Furthermore, fluid displacements have been postulated to transduct mechanical stress signals to bone cells via loading-dependent flow of interstitial fluid through the lacunocanalicular network of bone. Thus, an understanding and new possibilities for influencing these processes may be of great importance for implant success. An ex vivo model was developed and validated for investigation of fluid displacements in bone after endoprosthesis implantation. This model serves to explicate the effects of surgical intervention as well as mechanical loading of the implant-bone construct on load-induced fluid flow in the vicinity of the implant. Using this model, we intend to quantify perfusion and extravascular flow dynamics in the vicinity of implants and define optimal conditions for enhancing molecular transport of osteotropic agents from the implant surface to apposing bone as well as from the blood supply to the implant surface. Furthermore, the elucidation of main transport pathways may help in understanding the distribution of wear particles in bone surrounding implant, a process which has been postulated to cause osteolysis and implant loosenin

Flux conservation in coherent backscattering and weak localisation of light

The standard theoretical description of coherent backscattering, accord- ing to which maximally crossed diagrams accounting for interference between counter- propagating path amplitudes are added on top of the incoherent background, violates the fundamental condition of flux conservation. In contrast to predictions of previous theories, we show that including maximally crossed diagrams with one additional scat- tering event does not restore flux conservation. Instead, we propose that the latter is recovered when treating the effects of coherent backscattering and weak localisation in a unified framework. On the basis of this framework, we demonstrate explicitly flux conservation in leading order of the weak disorder parameter 1/(kl).Comment: 18 page