A bi-directional fixed-latency clock distribution system Yang, Y.; Ó Murchadha, A.; Meures, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2013, Letnik:
732
Journal Article
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The Askar'yan Radio Array (ARA) Collaboration is constructing a giant array of radio-frequency antennas deployed in the ice near the geographic South Pole. This experiment aims at detecting the ...extremely weak signal of neutrinos with energies in excess of 100PeV from ultrahigh-energy cosmic ray interactions with the cosmic microwave background radiation. The antennas are located in shallow holes drilled to depths of 200m and need high fidelity RF signal transmission over extended lengths to the data acquisition logic at the surface. We report on a transmission scheme whereby signals are digitized in the ice and the waveforms are digitally sent via high-speed serial links. Reconstruction algorithms require distribution of a low-jitter clock from the surface down to the digitization boards in the holes with knowledge of the overall time delay between the two clock domains. Previously, we designed a clock synchronization system using electrical signaling over CAT5. This year we have updated our solution to optical fibers using high speed transceiver blocks in Spartan-6 FPGAs. This note describes our improvements on the latter solution: technical details as well as methods of maintaining a fixed phase between two clocks after power cycles and resets.
We report on a search for ultra-high-energy (UHE) neutrinos from gamma-ray bursts (GRBs) in the data set collected by the Testbed station of the Askaryan Radio Array (ARA) in 2011 and 2012. From 57 ...selected GRBs, we observed no events that survive our cuts, which is consistent with 0.12 expected background events. Using NeuCosmA as a numerical GRB reference emission model, we estimate upper limits on the prompt UHE GRB neutrino fluence and quasi-diffuse flux from 107 to 1010 GeV. This is the first limit on the prompt UHE GRB neutrino quasi-diffuse flux above 107 GeV.
Owing to their small interaction cross-section, neutrinos are unparalleled astronomical tracers. Ultra-high energy (UHE; E > 10 PeV) neutrinos probe the most distant, most explosive sources in the ...Universe, often obscured to optical telescopes. Radio-frequency (RF) detection of Askaryan radiation in cold polar ice is currently regarded as the best experimental measurement technique for UHE neutrinos, provided the RF properties of the ice target can be well-understood. To that end, the Askaryan Radio Array (ARA) experiment at the South Pole has used long-baseline RF propagation to extract information on the index-of-refraction (n=ϵr) in South Polar ice. Owing to the increasing ice density over the upper 150–200 m, rays are measured along two, nearly parallel paths, one of which refracts through an inflection point, with differences in both arrival time and arrival angle that can be used to constrain the neutrino properties. We also observe (first) indications for RF ice birefringence for signals propagating along predominantly horizontal trajectories, corresponding to an asymmetry of order 0.1% between the ordinary and extra-ordinary birefringent axes, numerically compatible with previous measurements of birefringent asymmetries for vertically-propagating radio-frequency signals at South Pole. Qualitatively, these effects offer the possibility of redundantly measuring the range from receiver to a neutrino interaction in Antarctic ice, if receiver antennas are deployed at shallow (z ∼ −25 m) depths. Such range information is essential in determining both the neutrino energy, as well as the incident neutrino direction.
The Askaryan Radio Array (ARA) is a new detector deployed at the South Pole designed to detect ultrahigh-energy neutrinos using radio frequency signals emitted by neutrino-induced cascades in the ...glacial ice. The whole array will contain 37 stations which cover O(100) km 2 surface area. Each station consists of four two-hundred-meter-deep holes spaced 20 meters apart with 4 antennas in each hole at depths ranging from 180 - 200 m. A custom-designed ASIC nominally located in close proximity to the antennas is used for high-speed digitization of the induced RF signals. In order to perform the complex particle reconstructions, each antenna signal must be recorded with a time precision of 50 ps relative to other antennas in the same station. In addition the digital data stream from the digitizer must be transmitted from the hole bottom to logic on the surface. This note describes our group's solution to both challenges that uses commercially available high-speed transceivers and the clock data recovery functions built into these ICs. This includes both a CAT5E twisted pair version and an optical fiber version. While this application is discussed in particular, the technology has potential applications in many fields: any system that requires ultra-high precision synchronization of two or more remote clocks could benefit from the system described herein.
Eschatology is central to Christian theology: the significance of the death and resurrection of Christ is the promise of the “kingdom of God”. This paper takes up this idea in discussion with ...contemporary Christian theologians and discusses it phenomenologically by recourse to Husserl’s account of “horizon”. The horizon is both finite and infinite: always limited in its actualization but with an infinity of potential actualizations. This is explored with respect to time and its relation to the eternal, as well as the dispositions of hope and fear with respect to the eschaton. The final section draws these insights together in a discussion of the eschaton to understand the eschatological destiny of nature in a “new heaven and a new earth” (Revelations, 21: 1) and conceiving of eschatological justice as a harmony of horizonal perspectives.
Target varieties for language learning are contentious in applied linguistics and sociolinguistics. Debates centre on the nature and utility of alternative norms. Approximation to 'native speaker' ...practices is the hallmark of language education. Thus, policy and pedagogy frequently orient toward achieving nativelike production. While many language learning stakeholders are committed to this model, it is also contested. Opponents point to the ideological assumptions about 'native' and 'nonnative' speech inherent in the model, and to the unrealistic aims it presents to teachers and learners. While much research focuses on learner preferences, little work exists on teacher attitudes. This article aims to address this dearth in the target variety debate. By focusing on Irish as a minority language, the article supplements the literature on classroom targets for English and other major languages. A thematic analysis of interviews with Irish language pedagogues is presented and reveals their engagement with target varieties for the language.
We analytically construct an infinite number of trapped toroids in spherically symmetric Cauchy hypersurfaces of the Einstein equations. We focus on initial data which represent “constant density ...stars” momentarily at rest. There exists an infinite number of constant mean curvature tori, but we also deal with more general configurations. The marginally trapped toroids have been found analytically and numerically; they are unstable. The topologically toroidal trapped surfaces appear in a finite region surrounded by the Schwarzschild horizon.
Significant advances in numerical simulations of black-hole binaries have recently been achieved using the puncture method. We examine how and why this method works by evolving a single black hole. ...The coordinate singularity and hence the geometry at the puncture are found to change during evolution, from representing an asymptotically flat end to being a cylinder. We construct an analytic solution for the stationary state of a black hole in spherical symmetry that matches the numerical result and demonstrates that the evolution is not dominated by artefacts at the puncture but indeed finds the analytical result.
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