LSST optical beam simulator

We describe a camera beam simulator for the LSST which is capable of illuminating a 60mm field at f/1.2 with realistic astronomical scenes, enabling studies of CCD astrometric and photometric performance. The goal is to fully simulate LSST observing, in order to characterize charge transport and other features in the thick fully depleted CCDs and to probe low level systematics under realistic conditions. The automated system simulates the centrally obscured LSST beam and sky scenes, including the spectral shape of the night sky. The doubly telecentric design uses a nearly unit magnification design consisting of a spherical mirror, three BK7 lenses, and one beam-splitter window. To achieve the relatively large field the beam-splitter window is used twice. The motivation for this LSST beam test facility was driven by the need to fully characterize a new generation of thick fully-depleted CCDs, and assess their suitability for the broad range of science which is planned for LSST. Due to the fast beam illumination and the thick silicon design [each pixel is 10 microns wide and over 100 microns deep] at long wavelengths there can be effects of photon transport and charge transport in the high purity silicon. The focal surface covers a field more than sufficient for a 40x40 mm LSST CCD. Delivered optical quality meets design goals, with 50% energy within a 5 micron circle. The tests of CCD performance are briefly described.Comment: 9 pages, 9 figure

Shapes of Normal and Reverse Flow Injection Signals: On-Line Formation of Iodine from Iodate, Iodide, and Hydrogen Ion

Signal shapes for the on-line formation of iodine from iodate, iodide and hydrogen ion in a single-channel manifold using large-volume slug and large-volume time-based injections have been determined using visible spectrophotometry. These large injection volume studies were made first as a means of understanding the shapes of normal and reverse flow injection signals obtained at more conventional injection volumes (10--100 µI). The signal shapes at large injection volumes were determined for the six possible combinations of the reagents in the two solutions serving as carrier stream and injectate so that one solution contained two reagents and the other solution one or two reagents. Each combination of reagents represents two complementary systems in which the roles of each solution as carrier stream and injectate are reversed. At these large injection volumes each signal consisted of two independent peaks caused by dispersion at the front and rear boundaries of the injected bolus. The signals obtained for the time-based injections for complementary systems were identical in shape and height except that the front peak of one system was identical with the rear peak of its complementary system and vice versa. Clearly, at such large injection volumes the terms normal flow injection (nFI) and reverse flow injection (rFI) have no real meaning, the shape of each independent peak being determined by the composition and relative positions of the two solutions forming the boundary at which the peak is formed. For slug injections, similar shapes were observed but the peak heights were affected markedly by the greater dispersion at the rear boundary which travels further than the front boundary. This comparison of the signals obtained with slug and time-based injections, despite different flow-rates being used for the two modes of injection, clearly shows the effect of the unequal dispersion at the two boundaries in the slug injection method. Examination of the signals obtained with time-based injection, however, clearly indicates that the solution compositions, and their relative positions in the flow stream, also affect the shapes and relative heights of the front and rear peaks. The shapes of all these signals are illustrated. The effect of reducing the slug injection volume stepwise from 2 ml to 100 µI was studied for the 103-J- \u3c H+ and H+ \u3c 103-1- systems(\u3c denotes the direction of the boundary shape). This indicated that the shapes and heights of the single peaks observed in the rFI and nFI formation of iodine carried out at the more conventional lower injection volumes are determined by dispersion at the rear and front boundaries of the bolus, respectively. Hence, as the two peaks observed in a large-volume injection merged as the injection volume was decreased, the major peak predominated and became the observed signal. The use of a much smaller injection volume was necessary in rFI than in nFI in order to obtain a single peak

The design of Flow Injection manifolds to give the best detection limits for methods involving on-line chemical derivatisation Part 2. The spectrophotometric determination of chloride

The optimisation of a flow injection manifold for the spectrophotometric determination of chloride is described. Factors contributing to the baseline noise due to refractive index and reagent absorption effects are removed by a combination of design features. Firstly, a double-line manifold is used; secondly, pulse-dampers and a packed bed reactor are incorporated into the flow lines and thirdly a delay coil is introduced to resolve the valve switching peaks from the determinand peaks. The appropriate conditions for obtaining the maximum sensitivity are found from an off-line experiment and the guidelines established on the basis of the well-stirred tank model for dispersion applied to the design of the operating parameters of flow rate ratio and volume injected. Good agreement between the predicted and experimentally determined values were obtained. The resulting manifold gave a linear calibration from the detection limit (4.5-8.0 ppb) to 2.00 ppm

Elimination of Double Peaks in the Iodimetric Flow Injection Visible Spectrophotometric Determination of Sulphite Using a Single-Channel Manifold

A flow injection method of determining sulphite with amperometric monitoring of iodine using a single-channel manifold in which iodine is formed in the reverse flow injection (rFI) manner and reacts with sulphite dispersing in the normal flow injection (nFI) manner has been adapted for use with visible spectrophotometry. The carrier stream consists of an alkaline solution containing iodate and an excess of iodide: injections of acid and then of acidified sulphite are made. The decrease in the iodine signal (measured at 352 nm) in the presence of sulphite is proportional to the sulphite concentration in the injectate. The alkalinity of the carrier stream was adjusted to reduce the signal widths and to prevent the appearance of double peaks. A rectilinear decrease in signal size (down to ca. 10% of the signal size in the absence of sulphite) was obtained in the range 1 x 10-s_7 x 10-4 M sulphite using a single-channel manifold consisting of 3 m of 0.8 mm bore transmission tubing with a flow-rate of 5 ml min-1 and an injection volume of 15 rd, when the carrier stream was 6.7 x 1 Q-6 Min iodate, 6.7 x 10-2 Min iodide and 3.5 x 1 Q-3 Min sodium hydroxide, and the sample solution was 0.1 M in hydrochloric acid

Operator-Schmidt decompositions and the Fourier transform, with applications to the operator-Schmidt numbers of unitaries

The operator-Schmidt decomposition is useful in quantum information theory for quantifying the nonlocality of bipartite unitary operations. We construct a family of unitary operators on C^n tensor C^n whose operator-Schmidt decompositions are computed using the discrete Fourier transform. As a corollary, we produce unitaries on C^3 tensor C^3 with operator-Schmidt number S for every S in {1,...,9}. This corollary was unexpected, since it contradicted reasonable conjectures of Nielsen et al [Phys. Rev. A 67 (2003) 052301] based on intuition from a striking result in the two-qubit case. By the results of Dur, Vidal, and Cirac [Phys. Rev. Lett. 89 (2002) 057901 quant-ph/0112124], who also considered the two-qubit case, our result implies that there are nine equivalence classes of unitaries on C^3 tensor C^3 which are probabilistically interconvertible by (stochastic) local operations and classical communication. As another corollary, a prescription is produced for constructing maximally-entangled operators from biunimodular functions. Reversing tact, we state a generalized operator-Schmidt decomposition of the quantum Fourier transform considered as an operator C^M_1 tensor C^M_2 --> C^N_1 tensor C^N_2, with M_1 x M_2 = N_1 x N_2. This decomposition shows (by Nielsen's bound) that the communication cost of the QFT remains maximal when a net transfer of qudits is permitted. In an appendix, a canonical procedure is given for removing basis-dependence for results and proofs depending on the "magic basis" introduced in [S. Hill and W. Wootters, "Entanglement of a pair of quantum bits," Phys Rev. Lett 78 (1997) 5022-5025, quant-ph/9703041 (and quant-ph/9709029)].Comment: More formal version of my talk at the Simons Conference on Quantum and Reversible Computation at Stony Brook May 31, 2003. The talk slides and audio are available at http://www.physics.sunysb.edu/itp/conf/simons-qcomputation.html. Fixed typos and minor cosmetic

SCANDEX: Service centric networking for challenged decentralised networks

Do-It-Yourself (DIY) networks are decentralised networks built by an (often) amateur community. As DIY networks do not rely on the need for backhaul Internet connectivity, these networks are mostly a mix of both offine and online networks. Although DIY networks have their own home- grown services, the current Internet-based cloud services are often useful, and access to some services could be beneficial to the community. Considering that most DIY networks have challenged Internet connectivity, migrating current ser- vice virtualisation instances could face great challenges. Ser- vice Centric Networking (SCN) has been recently proposed as a potential solution to managing services more efficiently using Information Centric Networking (ICN) principles. In this position paper, we present our arguments for the need for a resilient SCN architecture, propose a strawman SCN architecture that combines multiple transmission technolo- gies for providing resilient SCN in challenged DIY networks and, finally, identify key challenges that need to be explored further to realise the full potential of our architecture.The work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 645124.This is the accepted manuscript of a paper published in the Proceedings of the 2015 Workshop on Do-it-yourself Networking (Sathiaseelan A, Wang L, Aucinas A, Tyson G, Crowcroft J, Proceedings of the 2015 Workshop on Do-it-yourself Networking: an Interdisciplinary Approach, 2015, 15-20, doi:10.1145/2753488.2753490). The final version is available at http://dx.doi.org/10.1145/2753488.275349

Facebook (A)Live? Are Live Social Broadcasts Really Broadcasts?

The era of live-broadcast is back but with two major changes. First, unlike traditional TV broadcasts, content is now streamed over the Internet enabling it to reach a wider audience. Second, due to various user-generated content platforms it has become possible for anyone to get involved, streaming their own content to the world. This emerging trend of going live usually happens via social platforms, where users perform live social broadcasts predominantly from their mobile devices, allowing their friends (and the general public) to engage with the stream in real-time. With the growing popularity of such platforms, the burden on the current Internet infrastructure is therefore expected to multiply. With this in mind, we explore one such prominent platform - Facebook Live. We gather 3TB of data, representing one month of global activity and explore the characteristics of live social broadcast. From this, we derive simple yet effective principles which can decrease the network burden. We then dissect global and hyper-local properties of the video while on-air, by capturing the geography of the broadcasters or the users who produce the video and the viewers or the users who interact with it. Finally, we study the social engagement while the video is live and distinguish the key aspects when the same video goes on-demand. A common theme throughout the paper is that, despite its name, many attributes of Facebook Live deviate from both the concepts of live and broadcast.Comment: Published at The Web Conference 2018 (WWW 2018). Please cite the WWW versio

Guiding chemical pulses through geometry: Y-junctions

We study computationally and experimentally the propagation of chemical pulses in complex geometries.The reaction of interest, CO oxidation, takes place on single crystal Pt(110) surfaces that are microlithographically patterned; they are also addressable through a focused laser beam, manipulated through galvanometer mirrors, capable of locally altering the crystal temperature and thus affecting pulse propagation. We focus on sudden changes in the domain shape (corners in a Y-junction geometry) that can affect the pulse dynamics; we also show how brief, localized temperature perturbations can be used to control reactive pulse propagation.The computational results are corroborated through experimental studies in which the pulses are visualized using Reflection Anisotropy Microscopy.Comment: submitted to Phys. Rev.