Frequency multiplexed superconducting quantum interference device readout of large bolometer arrays for cosmic microwave background measurements

A technological milestone for experiments employing transition edge sensor bolometers operating at sub-Kelvin temperature is the deployment of detector arrays with 100s-1000s of bolometers. One key technology for such arrays is readout multiplexing: the ability to read out many sensors simultaneously on the same set of wires. This paper describes a frequency-domain multiplexed readout system which has been developed for and deployed on the APEX-SZ and South Pole Telescope millimeter wavelength receivers. In this system, the detector array is divided into modules of seven detectors, and each bolometer within the module is biased with a unique ～MHz sinusoidal carrier such that the individual bolometer signals are well separated in frequency space. The currents from all bolometers in a module are summed together and pre-amplified with superconducting quantum interference devices operating at 4 K. Room temperature electronics demodulate the carriers to recover the bolometer signals, which are digitized separately and stored to disk. This readout system contributes little noise relative to the detectors themselves, is remarkably insensitive to unwanted microphonic excitations, and provides a technology pathway to multiplexing larger numbers of sensors.     

Double‐Inverse‐Opal Photonic Crystals: The Route to Photonic Bandgap Switching

Photonic crystals with a complete bandgap can stop the propagation of light of a certain frequency in all directions. We introduce double‐inverse‐opal photonic crystals (DIOPCs) as a new kind of optical switch. In the DIOPC, a movable, weakly scattering sphere is embedded within each pore of the inverse‐opal photonic crystal lattice. Switching between a diffusive reflector and a photonic crystal environment is experimentally demonstrated. Theory shows that a complete bandgap can be realized that can be opened or closed by moving the spheres. This functionality opens up new possibilities for the control of light emission and propagation. The close link and interaction between the chemical synthesis and the computational design and analysis underlines the interdisciplinary focus of this report.     

Impact of coagulation and adsorption on DOC fractions of secondary effluent and resulting fouling behaviour in ultrafiltration

Membrane fouling by macromolecular dissolved organic compounds is still a fundamental drawback in low-pressure membrane filtration of secondary effluent. In this study, pre-treatment of secondary effluent by coagulation and/or adsorption was investigated in terms of removal of different dissolved organic carbon (DOC) fractions, especially macromolecular substances. DOC fractionation has been characterised by size exclusion chromatography. Adsorption tests using four commercially available activated carbons yielded a removal of small as well as larger organic compounds, revealing differences in the affinity towards macromolecules depending on the type of applied activated carbon. By contrast, coagulation removed predominantly larger molecules, i.e., biopolymers and humic substances. In terms of DOC reduction, the coagulant ferric chloride was superior to aluminium chloride. A combination of coagulation and adsorption resulted in the addition of individual removal efficiencies, suggesting that different fractions of organic compounds were involved in each of the processes. After removal of macromolecular organic compounds either by coagulation or by adsorption, a significant reduction of membrane fouling was observed in tests using two different types of ultrafiltration flat-sheet membranes in 20-h cross-flow filtration tests.     

Ultrahigh birefringent optical fibers

The modes of weakly guiding fibers, constructed from anisotropic material which exhibits ultrahigh birefringence, are investigated. These modes are plane polarized unless the fiber is virtually uniaxial, withn_{x} = n_{y} neq n_{z}. The modal intensity patterns are, in general, noncircular, even for fibers of circular cross section.     

Figures of merit for doped fibre amplifiers in 1300 nm and 1550 nm windows

Simple and accurate 'figures of merit' for doped fibre amplifiers in the 1550 nm and 1300 nm optical communications windows are presented. These provide an effective comparison of different amplifier systems and configurations. The effects of rare-earth ion, host glass, waveguide structure and pump wavelength are all included.<>     

Yttrium doping of Ba0.5Sr0.5Co0.8Fe0.2O3-δ part II: Influence on oxygen transport and phase stability

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) in its cubic perovskite phase has attracted much interest for potential use as oxygen transport membrane (OTM) due to its very high oxygen permeability at high temperatures. However, performance degradation due to a sluggish phase decomposition occurs when BSCF is operated below 840?°C. Partial B-site substitution of the transition metal cations in BSCF by larger and redox-stable cations has emerged as a potential strategy to improve the structural stability of cubic BSCF. In this study, the influence of yttrium doping (0…10?mol-%) on oxygen transport properties and stability of the cubic BSCF phase is assessed by in situ electrical conductivity relaxation (ECR) and electrical conductivity measurements during long-term thermal annealing both at 700?°C and 800?°C. Detailed phase analysis is performed by scanning electron microscopy (SEM) after long-term annealing of the samples in air at different temperatures.     

Region-based fractal image compression

A fractal coder partitions an image into blocks that are coded via self-references to other parts of the image itself. We present a fractal coder that derives highly image-adaptive partitions and corresponding fractal codes in a time-efficient manner using a region-merging approach. The proposed merging strategy leads to improved rate-distortion performance compared to previously reported pure fractal coders, and it is faster than other state-of-the-art fractal coding methods.     

Properties of atomic-vapor and atomic-layer deposited Sr, Ti, and Nb doped Ta2O5 Metal-Insulator-Metal capacitors

Atomic Vapor Deposition and Atomic Layer Deposition techniques were applied for the depositions of Ta₂O₅, Ti-Ta-O, Sr-Ta-O and Nb-Ta-O oxide films for Metal-Insulator-Metal (MIM) capacitors used in back-end of line for Radio Frequency applications. Structural and electrical properties were studied. Films, deposited on the TiN bottom electrodes, in the temperature range of 225-400 °C, were amorphous, whereas the post deposition annealing at 600 °C resulted in the crystallization of Nb-Ta-O films. Electrical properties of MIM structures, investigated after sputtering Au top electrodes, revealed that the main characteristics were different for each oxide. On one hand, Ti-Ta-O based MIM capacitors possessed the highest dielectric constant (50), but the leakages currents were also the highest (~ 10^− 5 A/cm² at − 2 V). On the other hand, Sr-Ta-O showed the lowest leakage current densities (~ 10^− 9 A/cm² at − 2 V) as well as the smallest capacitance-voltage nonlinearity coefficients (40 ppm/V²), but the dielectric constant was the smallest (20). The highest nonlinearity coefficients (290 ppm/V²) were observed for Nb-Ta-O based MIM capacitors, although relatively high dielectric constant (40) and low leakage currents (~ 10^− 7 A/cm² at − 2 V) were measured. Temperature dependent leakage-voltage measurements revealed that only Sr-Ta-O showed no dependence of leakage current as a function of the measurement temperature.     

Interactive Visualization of Implicit Surfaces with Singularities

This paper presents work on two methods for interactive visualization of implicit surfaces: physically-based sampling using particle systems and polygonization followed by physically-based mesh improvement which explicitly makes use of the surface-defining equation. While most previous work applied to bounded manifolds without singularities and without boundary (topological spheres) we broaden the scope of the methods to include surfaces with such features, in particular cusp points and surface self-intersections. These aspects are not (yet) essential for computer graphics modelling with implicit surfaces but they naturally occur in simulations of interest in mathematical visualization. In this paper we use the Kummer family of algebraic surfaces as an example.