50 research outputs found
Energetics of Propellant Options for High-Power Hall Thrusters
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76265/1/AIAA-16376-173.pd
Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger
Observatory and is used to detect the radio emission of cosmic-ray air showers.
These observations are compared to the data of the surface detector stations of
the Observatory, which provide well-calibrated information on the cosmic-ray
energies and arrival directions. The response of the radio stations in the 30
to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of
the incoming electric field. For the latter, the energy deposit per area is
determined from the radio pulses at each observer position and is interpolated
using a two-dimensional function that takes into account signal asymmetries due
to interference between the geomagnetic and charge-excess emission components.
The spatial integral over the signal distribution gives a direct measurement of
the energy transferred from the primary cosmic ray into radio emission in the
AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air
shower arriving perpendicularly to the geomagnetic field. This radiation energy
-- corrected for geometrical effects -- is used as a cosmic-ray energy
estimator. Performing an absolute energy calibration against the
surface-detector information, we observe that this radio-energy estimator
scales quadratically with the cosmic-ray energy as expected for coherent
emission. We find an energy resolution of the radio reconstruction of 22% for
the data set and 17% for a high-quality subset containing only events with at
least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO
Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy
We measure the energy emitted by extensive air showers in the form of radio
emission in the frequency range from 30 to 80 MHz. Exploiting the accurate
energy scale of the Pierre Auger Observatory, we obtain a radiation energy of
15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV
arriving perpendicularly to a geomagnetic field of 0.24 G, scaling
quadratically with the cosmic-ray energy. A comparison with predictions from
state-of-the-art first-principle calculations shows agreement with our
measurement. The radiation energy provides direct access to the calorimetric
energy in the electromagnetic cascade of extensive air showers. Comparison with
our result thus allows the direct calibration of any cosmic-ray radio detector
against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI.
Supplemental material in the ancillary file
Measurement of the cosmic ray spectrum above eV using inclined events detected with the Pierre Auger Observatory
A measurement of the cosmic-ray spectrum for energies exceeding
eV is presented, which is based on the analysis of showers
with zenith angles greater than detected with the Pierre Auger
Observatory between 1 January 2004 and 31 December 2013. The measured spectrum
confirms a flux suppression at the highest energies. Above
eV, the "ankle", the flux can be described by a power law with
index followed by
a smooth suppression region. For the energy () at which the
spectral flux has fallen to one-half of its extrapolated value in the absence
of suppression, we find
eV.Comment: Replaced with published version. Added journal reference and DO
Performance and active thermal control of 2-kW hall thruster with segmented electrodes
The performance and plume characteristics of a 2-k W Hall thruster with segmented anodes for thermal control of the main anode are characterized. Diagnostics performed included thrust, specific impulse, and efficiency, as well as the ion current density in the plume. The apparatus included an inverted-pendulum thrust stand for performance measurements and a shielded Faraday probe for ion current density characterization. Data were taken at several operating points and at several ratios of current to the main anode vs the shim electrodes. The data show a general increase in centerline current density, thrust, specific impulse, and efficiency as discharge current is moved to the shims. Thermal measurements show up to 50°C control authority in the main anode temperature
Performance characterization and ion energy analysis of a 2-kW hall thruster with segmented anodes
The goal of this paper is to describe the change in performance and ion energy distribution in a 2-kW Hall thruster operated with segmented anodes. The effect on the performance and ion energy distribution as discharge current is shifted from the main anode to tlie shim electrodes is examined. Performance was largely unaffected by shifting current from the main anode to the shims. A water cooled ExB probe was utilized to determine the Ion energy distribution. A change in the dominant singly charged ion energy was observed when the shim electrode voltage was varied. Measurable increases in singly charged xenon velocities correlated with slight performance gains. The tliruster geometry examined here has been proposed for control of tlie temperature of a bismuth propellant feed system. No significant change in thrust, Isp, or efficiency indicates that a bismuth thruster could be operated and thermally controlled using segmented anodes without significant impact on the performance
Käytännön kosteikkosuunnittelu
Maatalouden vesiensuojelua edistetään monin tavoin. Ravinteita ja eroosioainesta sisältäviä valumavesiä pyritään puhdistamaan erilaisissa kosteikoissa. Tämä opas on kirjoitettu avuksi pienimuotoisten kosteikkojen perustamiseen. Oppaassa esitetään käytännönläheisesti kosteikon toteuttamisen eri vaiheet paikan valinnasta suunnitteluun ja rakentamiseen. Vuonna 2010 julkaistun painoksen tiedot on saatettu ajantasalle.
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