46,148 research outputs found
Numerical Results for the System Noise Temperature of an Aperture Array Tile and Comparison with Measurements
The purpose of this report is to document the noise performance of a complex
beamforming array antenna system and to characterize the recently developed
noise measurement facility called THACO, which was developed at ASTRON. The
receiver system includes the array antenna of strongly coupled 144 TSA
elements, 144 Low Noise Amplifiers (LNAs) (Tmin =35-40K) and the data
recording/storing facilities of the initial test station that allow for
off-line digital beamforming. The primary goal of this study is to compare the
measured receiver noise temperatures with the simulated values for several
practical beamformers, and to predict the associated receiver noise coupling
contribution, antenna thermal noise and ground noise pick-up (due to the back
radiation).Comment: ASTRON repor
PIONIER: a visitor instrument for the VLTI
PIONIER is a 4-telescope visitor instrument for the VLTI, planned to see its
first fringes in 2010. It combines four ATs or four UTs using a pairwise ABCD
integrated optics combiner that can also be used in scanning mode. It provides
low spectral resolution in H and K band. PIONIER is designed for imaging with a
specific emphasis on fast fringe recording to allow closure-phases and
visibilities to be precisely measured. In this work we provide the detailed
description of the instrument and present its updated status.Comment: Proceedings of SPIE conference Optical and Infrared Interferometry II
(Conference 7734) San Diego 201
Coordination Chemistry of Perhalogenated Cyclopentadienes and Alkynes. 17. Reaction of Dichloroethyne With Platinum(0) Phosphine Complexes: Formation of a .pi.-Complex, Isomerization to .beta.-Chloroethynyl Complexes, and Syntheses of Diplatinioethyne Derivatives. Molecular Structures of (Ph3P)2Pt(.eta.2-ClC.tplbond.CCl) and Cl(Ph3P)2PtC.tplbond.CPt(PPh3)2Cl
Dichloroethyne ClCECCl reacts with Pt(PPh3)2(C2H4) or Pt(PPh& to give the a-complex
Pt(PPh3)2(+21C=CC1) (l),w hich can be isomerized by prolonged refluxing in toluene to trans-
(Ph3P)zC1Pt-C==CC1 (2). 2 easily undergoes exchange reactions with alkylphosphines and
with halide anions to yield trans-(R3P)2ClPt-C=CCl (R = Et (3)) Bu (4)) and trans-(Ph3P)z-
(X)Pt-C=CCl (X = F (5a), Br (5b), I (5c)), respectively. The alkylphosphine complexes 3
and 4 can also be obtained by reaction of Pt(PR3)4 (R = Et, “Bu) with ClCECCl or from 1 and
the corresponding phosphine. When Pt(PPh&(CzH4) is added to a solution of 3, a dinuclear
complex 6 is formed, in which the C=C-Cl group acts as a a,a-bridging ligand. Upon standing,
oxidative addition of the remaining C-C1 bond occurs and the p-ethynediyl complex trans-
C1(R3P)2Pt-C=C-Pt(PPh3)2C1-Cis (R = Et (7a)) can be obtained. The corresponding
p-ethynediyl complex 7b (R = Ph) is formed directly from 2 and Pt(PPh&(CzH4). 7b isomerizes
upon heating in toluene to the symmetrical all-trans isomer 8. The molecular structures of 1
and 8 were determined by X-ray diffraction (1: C ~ ~ H ~ ~ C ~ Z P ~ Pa ~=C 10H.3Z11C(3~) AZ,, b =
10.392(4) A, c = 33.675(16) A, P = 90.17(3)’, monoclinic, P21/n, 2 = 4. 8: C74H&1zP4Ptz9 a =
12.938(2) A, b = 19.964(3) A, c = 24.844(3) A, P = 96.14(1)’, monoclinic, C2/c, 2 = 4)
Observing the Sun with Atacama Large Millimeter/submillimeter Array (ALMA): High Resolution Interferometric Imaging
Observations of the Sun at millimeter and submillimeter wavelengths offer a
unique probe into the structure, dynamics, and heating of the chromosphere; the
structure of sunspots; the formation and eruption of prominences and filaments;
and energetic phenomena such as jets and flares. High-resolution observations
of the Sun at millimeter and submillimeter wavelengths are challenging due to
the intense, extended, low- contrast, and dynamic nature of emission from the
quiet Sun, and the extremely intense and variable nature of emissions
associated with energetic phenomena. The Atacama Large Millimeter/submillimeter
Array (ALMA) was designed with solar observations in mind. The requirements for
solar observations are significantly different from observations of sidereal
sources and special measures are necessary to successfully carry out this type
of observations. We describe the commissioning efforts that enable the use of
two frequency bands, the 3 mm band (Band 3) and the 1.25 mm band (Band 6), for
continuum interferometric-imaging observations of the Sun with ALMA. Examples
of high-resolution synthesized images obtained using the newly commissioned
modes during the solar commissioning campaign held in December 2015 are
presented. Although only 30 of the eventual 66 ALMA antennas were used for the
campaign, the solar images synthesized from the ALMA commissioning data reveal
new features of the solar atmosphere that demonstrate the potential power of
ALMA solar observations. The ongoing expansion of ALMA and solar-commissioning
efforts will continue to enable new and unique solar observing capabilities.Comment: 22 pages, 12 figures, accepted for publication in Solar Physic
The Global Magneto-Ionic Medium Survey: Polarimetry of the Southern Sky from 300 to 480 MHz
Much data on the Galactic polarized radio emission has been gathered in the
last five decades. All-sky surveys have been made, but only in narrow, widely
spaced frequency bands, and the data are inadequate for the characterization of
Faraday rotation, the main determinant of the appearance of the polarized radio
sky at decimetre wavelengths. We describe a survey of the polarized radio
emission from the Southern sky, aiming to characterize the magneto-ionic
medium, particularly the strength and configuration of the magnetic field. This
work is part of the Global Magneto-Ionic Medium Survey (GMIMS). We have
designed and built a feed and receiver covering the band 300 to 900 MHz for the
CSIRO Parkes 64-m Telescope. We have surveyed the entire sky between
declinations -90 and +20 degrees. We present data covering 300 to 480 MHz with
angular resolution 81' to 45'. The survey intensity scale is absolutely
calibrated, based on measurements of resistors at known temperatures and on an
assumed flux density and spectral index for Taurus A. Data are presented as
brightness temperatures. We have applied Rotation Measure Synthesis to the data
to obtain a Faraday depth cube of resolution 5.9 radians per metre squared,
sensitivity of 60 mK of polarized intensity, and angular resolution 1.35
degrees. The data presented in this paper are available at the Canadian
Astronomy Data Centre.Comment: Accepted for publication in the Astronomical Journal Modified 29th
June 2019 to replace outdated doi: for access to dat
KAPow: A System Identification Approach to Online Per-Module Power Estimation in FPGA Designs
In a modern FPGA system-on-chip design, it is often insufficient to simply assess the total power consumption of the entire circuit by design-time estimation or runtime power rail measurement. Instead, to make better runtime decisions, it is desirable to understand the power consumed by each individual module in the system. In this work, we combine boardlevel power measurements with register-level activity counting to build an online model that produces a breakdown of power consumption within the design. Online model refinement avoids the need for a time-consuming characterisation stage and also allows the model to track long-term changes to operating conditions. Our flow is named KAPow, a (loose) acronym for ‘K’ounting Activity for Power estimation, which we show to be accurate, with per-module power estimates as close to ±5mW of true measurements, and to have low overheads. We also demonstrate an application example in which a permodule power breakdown can be used to determine an efficient mapping of tasks to modules and reduce system-wide power consumption by over 8%
Temperature induced structural changes in even-odd nylons with long polymethylene segments
Structural transitions of nylons 8 9 and 12 9 heating and cooling processes were investigated using calorimetric, spectroscopic during and real time X-ray diffraction data. These even-odd nylons had three polymorphic forms related to structures where hydrogen bonds were established in two planar directions. Heating processes showed a first structural transition at low temperature where the two strong reflections related to the packing mode of the low temperature structure (form I) disappeared instead of moving together and merging into a single reflection, as observed for conventional even-even nylons. The high temperature structure corresponded to a typical pseudohexagonal packing (form III) attained after the named Brill transition temperature. Structural transitions were not completely reversible since an intermediate structure (form II) became clearly predominant at room temperature in subsequent cooling processes. A single spherulitic morphology with negative birefringence and a flat-on edge-on lamellar disposition was obtained when the two studied polyamides crystallized from the melt state. Kinetic analyses indicated that both nylons crystallized according to a single regime and a thermal nucleation. Results also pointed out a secondary nucleation constant for nylon 12 9 higher than that for nylon 8 9, suggesting greater difficulty in crystallizing when the amide content decreased. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2494–2506Peer ReviewedPostprint (author's final draft
- …