4,602 research outputs found
A feasibility study for the detection of weak electromagnetic signal/bursts with hard-limited arrays
"The objective of this report was to investigate the use of a noncoherent detector based on polarity-coincidence statistic. Two channel, polarity-coincidence and polarity-difference, statistics were analyzed. The signal, common to both channels, consists of sinusoidal bursts where the exact frequency of the signal is nearly known, but other parameters such as amplitude, phase, and pulse starting time are unknown. The noise inputs are dependent, narrow band, Markov processes. It is shown that the performance depends not only on the signal uncertainties, but on the precise shape of the cross-correlation functions between the noise inputs. By using two polarity-difference statistics in addition to the polarity-coincidence statistic, it is shown that the decrease in performance, as well as the cost of hard limiting due to correlated inputs, can be made small." - NIOSHTIC-2NIOSHTIC no. 10003948Contract J031803
The Origin of Sequential Chromospheric Brightenings
Sequential chromospheric brightenings (SCBs) are often observed in the
immediate vicinity of erupting flares and are associated with coronal mass
ejections. Since their initial discovery in 2005, there have been several
subsequent investigations of SCBs. These studies have used differing detection
and analysis techniques, making it difficult to compare results between
studies. This work employs the automated detection algorithm of Kirk et al.
(Solar Phys. 283, 97, 2013) to extract the physical characteristics of SCBs in
11 flares of varying size and intensity. We demonstrate that the magnetic
substructure within the SCB appears to have a significantly smaller area than
the corresponding H-alpha emission. We conclude that SCBs originate in the
lower corona around 0.1 R_sun above the photosphere, propagate away from the
flare center at speeds of 35 - 85 km/s, and have peak photosphere magnetic
intensities of 148 +/- 2.9 G. In light of these measurements, we infer SCBs to
be distinctive chromospheric signatures of erupting coronal mass ejections.Comment: 25 pages, 9 figures, 5 table
The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles
In the G0 experiment, performed at Jefferson Lab, the parity-violating
elastic scattering of electrons from protons and quasi-elastic scattering from
deuterons is measured in order to determine the neutral weak currents of the
nucleon. Asymmetries as small as 1 part per million in the scattering of a
polarized electron beam are determined using a dedicated apparatus. It consists
of specialized beam-monitoring and control systems, a cryogenic hydrogen (or
deuterium) target, and a superconducting, toroidal magnetic spectrometer
equipped with plastic scintillation and aerogel Cerenkov detectors, as well as
fast readout electronics for the measurement of individual events. The overall
design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method
Geomagnetic origin of the radio emission from cosmic ray induced air showers observed by CODALEMA
The new setup of the CODALEMA experiment installed at the Radio Observatory
in Nancay, France, is described. It includes broadband active dipole antennas
and an extended and upgraded particle detector array. The latter gives access
to the air shower energy, allowing us to compute the efficiency of the radio
array as a function of energy. We also observe a large asymmetry in counting
rates between showers coming from the North and the South in spite of the
symmetry of the detector. The observed asymmetry can be interpreted as a
signature of the geomagnetic origin of the air shower radio emission. A simple
linear dependence of the electric field with respect to vxB is used which
reproduces the angular dependencies of the number of radio events and their
electric polarity.Comment: 9 pages, 15 figures, 1 tabl
TETRA Observation of Gamma Rays at Ground Level Associated with Nearby Thunderstorms
Terrestrial Gamma ray Flashes (TGFs) -- very short, intense bursts of
electrons, positrons, and energetic photons originating from terrestrial
thunderstorms -- have been detected with satellite instruments. TETRA, an array
of NaI(Tl) scintillators at Louisiana State University, has now been used to
detect similar bursts of 50 keV to over 2 MeV gamma rays at ground level. After
2.6 years of observation, twenty-four events with durations 0.02- 4.2 msec have
been detected associated with nearby lightning, three of them coincident events
observed by detectors separated by ~1000 m. Nine of the events occurred within
6 msec and 3 miles of negative polarity cloud-to-ground lightning strokes with
measured currents in excess of 20 kA. The events reported here constitute the
first catalog of TGFs observed at ground level in close proximity to the
acceleration site.Comment: To be published in Journal of Geophysical Research: Space Phys. 118,
Quantum Memories. A Review based on the European Integrated Project "Qubit Applications (QAP)"
We perform a review of various approaches to the implementation of quantum
memories, with an emphasis on activities within the quantum memory sub-project
of the EU Integrated Project "Qubit Applications". We begin with a brief
overview over different applications for quantum memories and different types
of quantum memories. We discuss the most important criteria for assessing
quantum memory performance and the most important physical requirements. Then
we review the different approaches represented in "Qubit Applications" in some
detail. They include solid-state atomic ensembles, NV centers, quantum dots,
single atoms, atomic gases and optical phonons in diamond. We compare the
different approaches using the discussed criteria.Comment: 22 pages, 12 figure
High Performance Data Acquisition and Analysis Routines for the Nab Experiment
Probes of the Standard Model of particle physics are pushing further and further into the so-called “precision frontier”. In order to reach the precision goals of these experiments, a combination of elegant experimental design and robust data acquisition and analysis is required. Two experiments that embody this philosophy are the Nab and Calcium-45 experiments. These experiments are probing the understanding of the weak interaction by examining the beta decay of the free neutron and Calcium-45 respectively. They both aim to measure correlation parameters in the neutron beta decay alphabet, a and b. The parameter a, the electron-neutrino correlation coefficient, is sensitive to λ, the ratio of the axial-vector and vector coupling strengths in the decay of the free neutron. This parameter λ, in tandem with a precision measurement of the neutron lifetime τ , provides a measurement of the matrix element Vud from the CKM quark mixing matrix. The CKM matrix, as a rotation matrix, must be unitary. Probes of Vud and Vus in recent years have revealed tension in this unitarity at the 2.2σ level. The measurement of a via decay of free cold neutrons serves as an additional method of extraction for Vud that is sensitive to a different set of systematic effects and as such is an excellent probe into the source of the deviation from unitarity. The parameter b, the Fierz interference term, appears as a distortion in the mea- sured electron energy spectra from beta decay. This parameter, if non-zero, would indicate the existence of Scalar and/or Tensor couplings in the Weak interaction which according to the Standard Model is purely Vector minus Axial-Vector. This is therefore a search for physics beyond the standard model, BSM, physics search. The Nab and Calcium-45 experiments probe these parameters with a combination of elegant experimental design and brute force collection and analysis of large amounts of digitized detector data. These datasets, particularly in the case of the Nab experiment, are anticipated to span multiple petabytes of data and will require high performance online analysis and precision offline analysis routines in order to reach the experimental goals. Of particular note are the requirements for better than 3 keV energy resolution and an understanding of the uncertainty in the mean timing bias for the detected particles within 300 ps. Presented in this dissertation is an overview of the experiments and their design, a description of the data acquisition systems and analysis routines that have been developed to support the experiments, and a discussion of the data analysis performed for the Calcium-45 experiment
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