Out-of-plane focusing grating couplers for silicon photonics integration with optical MRAM technology

We present the design methodology and experimental characterization of compact out-of-plane focusing grating couplers for integration with magnetoresistive random access memory technology. Focusing grating couplers have recently found attention as layer-couplers for photonic-electronic integration. The components we demonstrate are designed for a wavelength of 1550 nm, fabricated in a standard 220 nm SOI photonic platform and optimized given the fabrication restrictions for standard 193-nm UV lithography. For the first time, we extend the design based on the phase matching condition to a two-dimensional (2-D) grating design with two optical input ports. We further present the experimental characterization of the focusing behaviour by spatially probing the emitted beam with a tapered-and-lensed fiber and demonstrate the polarization controlling capabilities of the 2-D FGCs

Statistical Topological Insulators

We define a class of insulators with gapless surface states protected from localization due to the statistical properties of a disordered ensemble, namely due to the ensemble's invariance under a certain symmetry. We show that these insulators are topological, and are protected by a $\mathbb{Z}_2$ invariant. Finally, we prove that every topological insulator gives rise to an infinite number of classes of statistical topological insulators in higher dimensions. Our conclusions are confirmed by numerical simulations.Comment: 6 pages, 1 table, 5 figures, this is the final, published versio

Evanescently-coupled hybrid III-V/silicon laser based on DVS-BCB bonding

© 2014 IEEE. Controllable electrical breakdown of multiwall nanotubes (MWNTs) is studied utilizing the atomic force microscopy (AFM). Electrical breakdown has been known as the way to fundamentally understand the electrical properties of nanotubes and an approach to develop MWNT based transistors and sensors. Normally, electrical breakdown was known to be happened in the center of MWNT because of the thermal accumulation. However, considering the effect of thermal dissipation, the electrical breakdown could be mechanically controlled by an additional heat sink, which could be the substrate of MWNT device. Therefore, the electrical breakdown process is controllable through controlling Joule heating and thermal dissipation. In this research, we study the crucial factors that affect the electrical breakdown. The AFM based nano robot is used to measure the conductance distribution, and manipulate the three dimensional structure of MWNT in order to change the position of heat sink to control the location where electrical breakdown happened. The controllable electrical breakdown is an alternative approach for conducting bandgap engineering in nanodevice and fabricating high performance nano sensors and transistors.Link_to_subscribed_fulltex

Impact of Uncertainties in Hadron Production on Air-Shower Predictions

At high energy, cosmic rays can only be studied by measuring the extensive air showers they produce in the atmosphere of the Earth. Although the main features of air showers can be understood within a simple model of successive interactions, detailed simulations and a realistic description of particle production are needed to calculate observables relevant to air shower experiments. Currently hadronic interaction models are the main source of uncertainty of such simulations. We will study the effect of using different hadronic models available in CORSIKA and CONEX on extensive air shower predictions.Comment: 12 pages, 6 figures, to appear in the proceedings of International Conference on Interconnection between High Energy Physics and Astroparticle Physics: From Colliders to Cosmic Rays, Prague, Czech Republic, 7-13 Sep 200

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

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.