Thermal conductance as a probe of the non-local order parameter for a topological superconductor with gauge fluctuations

We investigate the effect of quantum phase slips on a helical quantum wire coupled to a superconductor by proximity. The effective low-energy description of the wire is that of a Majorana chain minimally coupled to a dynamical $\mathbb{Z}_2$ gauge field. Hence the wire emulates a matter-coupled gauge theory, with fermion parity playing the role of the gauged global symmetry. Quantum phase slips lift the ground state degeneracy associated with unpaired Majorana edge modes at the ends of the chain, a change that can be understood as a transition between the confined and the Higgs-mechanism regimes of the gauge theory. We identify the quantization of thermal conductance at the transition as a robust experimental feature separating the two regimes. We explain this result by establishing a relation between thermal conductance and the Fredenhagen-Marcu string order-parameter for confinement in gauge theories. Our work indicates that thermal transport could serve as a measure of non-local order parameters for emergent or simulated topological quantum order.Comment: 5 pages, 2 figures; v2: different introduction, added references, updated figure 2; published version to appear in PR

Higher-order structural organization of the mitochondrial proteome charted by in situ cross-linking mass spectrometry

Mitochondria are densely packed with proteins, of which most are involved physically or more transiently in protein-protein interactions (PPIs). Mitochondria host among others all enzymes of the Krebs cycle and the oxidative phosphorylation (OXPHOS) pathway and are foremost associated with cellular bioenergetics (1, 2). However, mitochondria are also important contributors to apoptotic cell death (3) and contain their own genome (4) indicating that they play additionally an eminent role in processes beyond bioenergetics (5). Despite intense efforts in identifying and characterizing mitochondrial protein complexes by structural biology and proteomics techniques, many PPIs have remained elusive. Several of these (membrane embedded) PPIs are less stable in-vitro hampering their characterization by most contemporary methods in structural biology. Particularly in these cases, cross-linking mass spectrometry (XL-MS) has proven valuable for the in-depth characterization of mitochondrial protein complexes in situ. Here, we highlight experimental strategies for the analysis of proteome-wide protein-protein interactions in mitochondria using XL-MS. We showcase the ability of in situ XL-MS as a tool to map sub-organelle interactions and topologies, and aid in refining structural models of protein complexes. We describe some of the most recent technological advances in XL-MS that may benefit the in situ characterization of PPIs even further, especially when combined with electron microscopy and structural modelling

Acoustic tests of duct-burning turbofan jet noise simulation

The results of a static acoustic and aerodynamic performance, model-scale test program on coannular unsuppressed and multielement fan suppressed nozzle configurations are summarized. The results of the static acoustic tests show a very beneficial interaction effect. When the measured noise levels were compared with the predicted noise levels of two independent but equivalent conical nozzle flow streams, noise reductions for the unsuppressed coannular nozzles were of the order of 10 PNdB; high levels of suppression (8 PNdB) were still maintained even when only a small amount of core stream flow was used. The multielement fan suppressed coannular nozzle tests showed 15 PNdB noise reductions and up to 18 PNdB noise reductions when a treated ejector was added. The static aerodynamic performance tests showed that the unsuppressed coannular plug nozzles obtained gross thrust coefficients of 0.972, with 1.2 to 1.7 percent lower levels for the multielement fan-suppressed coannular flow nozzles. For the first time anywhere, laser velocimeter velocity profile measurements were made on these types of nozzle configurations and with supersonic heated flow conditions. Measurements showed that a very rapid decay in the mean velocity occurs for the nozzle tested

Acoustic tests of duct-burning turbofan jet noise simulation: Comprehensive data report. Volume 2: Model design and aerodynamic test results

The selection procedure is described which was used to arrive at the configurations tested, and the performance characteristics of the test nozzles are given

SEM-EDS analyses of small craters in stardust aluminium foils: implications for the Wild-2 dust distribution

Implications for the Wild-2 dust distribution of the statistical results obtained by SEM-EDS from nearly 300 impact craters on aluminium foils of the Stardust sample tray assembly

The background from single electromagnetic subcascades for a stereo system of air Cherenkov telescopes

The MAGIC experiment, a very large Imaging Air Cherenkov Telescope (IACT) with sensitivity to low energy (E < 100 GeV) VHE gamma rays, has been operated since 2004. It has been found that the gamma/hadron separation in IACTs becomes much more difficult below 100 GeV [Albert et al 2008] A system of two large telescopes may eventually be triggered by hadronic events containing Cherenkov light from only one electromagnetic subcascade or two gamma subcascades, which are products of the single pi^0 decay. This is a possible reason for the deterioration of the experiment's sensitivity below 100 GeV. In this paper a system of two MAGIC telescopes working in stereoscopic mode is studied using Monte Carlo simulations. The detected images have similar shapes to that of primary gamma-rays and they have small sizes (mainly below 400 photoelectrons (p.e.)) which correspond to an energy of primary gamma-rays below 100 GeV. The background from single or two electromagnetic subcascdes is concentrated at energies below 200 GeV. Finally the number of background events is compared to the number of VHE gamma-ray excess events from the Crab Nebula. The investigated background survives simple cuts for sizes below 250 p.e. and thus the experiment's sensitivity deteriorates at lower energies.Comment: 15 pages, 7 figures, published in Journ.of Phys.

Coulomb-assisted braiding of Majorana fermions in a Josephson junction array

We show how to exchange (braid) Majorana fermions in a network of superconducting nanowires by control over Coulomb interactions rather than tunneling. Even though Majorana fermions are charge-neutral quasiparticles (equal to their own antiparticle), they have an effective long-range interaction through the even-odd electron number dependence of the superconducting ground state. The flux through a split Josephson junction controls this interaction via the ratio of Josephson and charging energies, with exponential sensitivity. By switching the interaction on and off in neighboring segments of a Josephson junction array, the non-Abelian braiding statistics can be realized without the need to control tunnel couplings by gate electrodes. This is a solution to the problem how to operate on topological qubits when gate voltages are screened by the superconductor

Coulomb stability of the 4\pi-periodic Josephson effect of Majorana fermions

The Josephson energy of two superconducting islands containing Majorana fermions is a 4\pi-periodic function of the superconducting phase difference. If the islands have a small capacitance, their ground state energy is governed by the competition of Josephson and charging energies. We calculate this ground state energy in a ring geometry, as a function of the flux -\Phi- enclosed by the ring, and show that the dependence on the Aharonov-Bohm phase 2e\Phi/\hbar remains 4\pi-periodic regardless of the ratio of charging and Josephson energies - provided that the entire ring is in a topologically nontrivial state. If part of the ring is topologically trivial, then the charging energy induces quantum phase slips that restore the usual 2\pi-periodicity.Comment: 4 pages, 4 figures; v2: more references, improved phase-slip formula, and a discussion of the effect of overlapping Majorana'

Charm Production in DPMJET

In this work, charm production in the {\sc dpmjet} hadronic jet simulation is compared to experimental data. Since the major application of {\sc dpmjet} is the simulation of cosmic ray-induced air showers, the version of the code integrated in the CORSIKA simulation package has been used for the comparison. Wherever necessary, adjustments have been made to improve agreement between simulation and data. With the availability of new muon/neutrino detectors that combine a large fiducial volume with large amounts of shielding, investigation of prompt muons and neutrinos from cosmic ray interactions will be feasible for the first time. Furthermore, above $\gtrsim 100$ TeV charmed particle decay becomes the dominant background for diffuse extraterrestrial neutrino flux searches. A reliable method to simulate charm production in high-energy proton-nucleon interactions is therefore required.Comment: 10 pages, to be published in JCA