Ground states in the Many Interacting Worlds approach

Recently the Many-Interacting-Worlds (MIW) approach to a quantum theory without wave functions was proposed. This approach leads quite naturally to numerical integrators of the Schr\"odinger equation. It has been suggested that such integrators may feature advantages over fixed-grid methods for higher numbers of degrees of freedom. However, as yet, little is known about concrete MIW models for more than one spatial dimension and/or more than one particle. In this work we develop the MIW approach further to treat arbitrary degrees of freedom, and provide a systematic study of a corresponding numerical implementation for computing one-particle ground and excited states in one dimension, and ground states in two spatial dimensions. With this step towards the treatment of higher degrees of freedom we hope to stimulate their further study.Comment: 16 pages, 8 figure

Riemann solvers and undercompressive shocks of convex FPU chains

We consider FPU-type atomic chains with general convex potentials. The naive continuum limit in the hyperbolic space-time scaling is the p-system of mass and momentum conservation. We systematically compare Riemann solutions to the p-system with numerical solutions to discrete Riemann problems in FPU chains, and argue that the latter can be described by modified p-system Riemann solvers. We allow the flux to have a turning point, and observe a third type of elementary wave (conservative shocks) in the atomistic simulations. These waves are heteroclinic travelling waves and correspond to non-classical, undercompressive shocks of the p-system. We analyse such shocks for fluxes with one or more turning points. Depending on the convexity properties of the flux we propose FPU-Riemann solvers. Our numerical simulations confirm that Lax-shocks are replaced by so called dispersive shocks. For convex-concave flux we provide numerical evidence that convex FPU chains follow the p-system in generating conservative shocks that are supersonic. For concave-convex flux, however, the conservative shocks of the p-system are subsonic and do not appear in FPU-Riemann solutions

Wave trains, solitons and modulation theory in FPU chains

We present an overview of recent results concerning wave trains, solitons and their modulation in FPU chains. We take a thermodynamic perspective and use hyperbolic scaling of particle index and time in order to pass to a macroscopic continuum limit. While strong convergence yields the well-known p-system of mass and momentum conservation, we generally obtain a weak form of it in terms of Young measures. The modulation approach accounts for microscopic oscillations, which we interpret as temperature, causing convergence only in a weak, average sense. We present the arising Whitham modulation equations in a thermodynamic form, as well as analytic and numerical tools for the resolution of the modulated wave trains. As a prototype for the occurrence of temperature from oscillation-free initial data, we discuss various Riemann problems, and the arising dispersive shock fans, which replace Lax-shocks. We predict scaling and jump conditions assuming a generic soliton at the shock front

Control of protein synthesis in yeast mitochondria: The concept of translational activators

AbstractMitochondria contain their own genome which codes for a small number of proteins. Most mitochondrial translation products are part of the membrane-embedded reaction centers of the respiratory chain complexes. In the yeast Saccharomyces cerevisiae, the expression of these proteins is regulated by translational activators that bind mitochondrial mRNAs, in most cases to their 5′-untranslated regions, and each mitochondrial mRNA appears to have its own translational activator(s). Recent studies showed that these translational activators can be part of feedback control loops which only permit translation if the downstream assembly of nascent translation products can occur. In several cases, the accumulation of a non-assembled protein prevents further synthesis of this protein but not translation in general. These control loops prevent the synthesis of potentially harmful assembly intermediates of the reaction centers of mitochondrial enzymes. Since such regulatory feedback loops only work if translation occurs in the compartment in which the complexes of the respiratory chain are assembled, these control mechanisms require the presence of a translation machinery in mitochondria. This might explain why eukaryotic cells maintained DNA in mitochondria during the last two billion years of evolution. This review gives an overview of the mitochondrial translation system and summarizes the current knowledge on translational activators and their role in the regulation of mitochondrial protein synthesis. This article is part of a Special Issue entitled: Protein import and quality control in mitochondria and plastids

Limits on isotropic Lorentz violation in QED from collider physics

We consider the possibility that Lorentz violation can generate differences between the limiting velocities of light and charged matter. Such effects would lead to efficient vacuum Cherenkov radiation or rapid photon decay. The absence of such effects for 104.5 GeV electrons at the Large Electron Positron collider and for 300 GeV photons at the Tevatron therefore constrains this type of Lorentz breakdown. Within the context of the standard-model extension, these ideas imply an experimental bound at the level of -5.8 x 10^{-12} <= \tilde{\kappa}_{tr}-(4/3)c_e^{00} <= 1.2 x 10^{-11} tightening existing laboratory measurements by 3-4 orders of magnitude. Prospects for further improvements with terrestrial and astrophysical methods are discussed.Comment: Replaced with final version published in PR

How lipid flippases can modulate membrane structure

AbstractPhospholipid flippases, are proteins able to translocate phospholipids from one side of a membrane to the other even against a gradient of concentration and thereby able to establish, or annihilate, a transmembrane asymmetrical lipid distribution. This lipid shuttling forms new membrane structures, in particular vesicles, which are associated with diverse physiological functions in eukaryotic cells such as lipid and protein traffic via vesicles between organelles or towards the plasma membrane, and the stimulation of fluid phase endocytosis. The transfer of lipids is also responsible for the triggering of membrane associated events such as blood coagulation, the recognition and elimination of apoptotic or aged cells, and the regulation of phosphatidylserine dependent enzymes. Exposure of new lipid-head groups on a membrane leaflet by rapid flip-flop can serve as a specific signal and, upon recognition, can be the cause of physiological modifications. Membrane bending is one of the mechanisms by which such activities can be triggered. We show that the lateral membrane tension is an important physical factor for the regulation of the size of the membrane invaginations. Finally, we suggest in this review that this diversity of functions benefits from the diversity of the lipids existing in a cell and the ability of proteins to recognize specific messenger molecules

Action minimizing fronts in general FPU-type chains

We study atomic chains with nonlinear nearest neighbour interactions and prove the existence of fronts (heteroclinic travelling waves with constant asymptotic states). Generalizing recent results of Herrmann and Rademacher we allow for non-convex interaction potentials and find fronts with non-monotone profile. These fronts minimize an action integral and can only exists if the asymptotic states fulfil the macroscopic constraints and if the interaction potential satisfies a geometric graph condition. Finally, we illustrate our findings by numerical simulations.Comment: 19 pages, several figure

The Disulfide Relay of the Intermembrane Space Oxidizes the Ribosomal Subunit Mrp10 on Its Transit into the Mitochondrial Matrix

SummaryMost mitochondrial proteins are synthesized in the cytosol and directed into the organelle; matrix proteins contain presequences that guide them through translocases in contact sites of the outer and inner membrane. In contrast, the import of many intermembrane space proteins depends on cysteine residues and the oxidoreductase Mia40. Here, we show that both import machineries can cooperate in the biogenesis of matrix proteins. Mrp10, a conserved protein of the mitochondrial ribosome, interacts with Mia40 during passage into the matrix. Mrp10 contains an unconventional proline-rich matrix-targeting sequence that renders import intermediates accessible to Mia40. Although oxidation of Mrp10 is not essential for its function in mitochondrial translation, the disulfide bonds prevent proteolytic degradation of Mrp10 and thereby counteract instability of the mitochondrial genome. The unconventional import pathway of Mrp10 is presumably part of a quality-control circle that connects mitochondrial ribosome biogenesis to the functionality of the mitochondrial disulfide relay