The nature of ultrahigh-energy cosmic rays (UHECRs) at energies >1020 eV remains a mystery. They are likely to be of extragalactic origin, but should be absorbed within ∼50 Mpc through interactions ...with the cosmic microwave background. As there are no sufficiently powerful accelerators within this distance from the Galaxy, explanations for UHECRs range from unusual astrophysical sources to exotic string physics. Also unclear is whether UHECRs consist of protons, heavy nuclei, neutrinos or γ-rays. To resolve these questions, larger detectors with higher duty cycles and which combine multiple detection techniques are needed. Radio emission from UHECRs, on the other hand, is unaffected by attenuation, has a high duty cycle, gives calorimetric measurements and provides high directional accuracy. Here we report the detection of radio flashes from cosmic-ray air showers using low-cost digital radio receivers. We show that the radiation can be understood in terms of the geosynchrotron effect. Our results show that it should be possible to determine the nature and composition of UHECRs with combined radio and particle detectors, and to detect the ultrahigh-energy neutrinos expected from flavour mixing.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report the development of high-performance and low-cost extended short-wavelength infrared (eSWIR) focal-plane arrays (FPAs) fabricated from molecular beam epitaxial (MBE)-grown HgCdTe on Si-based ...substrates. High-quality
n
-type eSWIR HgCdTe (cutoff wavelength ∼2.68
μ
m at 77 K, electron carrier concentration 5.82 × 10
15
cm
−3
) layers were grown on CdTe/Si substrates by MBE. High degrees of uniformity in composition and thickness were demonstrated over three-inch areas, and low surface defect densities (voids 9.56 × 10
1
cm
−2
, micro-defects 1.67 × 10
3
cm
−2
) were measured. This material was used to fabricate 320 × 256 format, 30
μ
m pitch FPAs with a planar device architecture using arsenic implantation to achieve
p
-type doping. The dark current density of test devices showed good uniformity between 190 K and room temperature, and high-quality eSWIR imaging from hybridized FPAs was obtained with a median dark current density of 2.63 × 10
−7
A/cm
2
at 193 K with a standard deviation of 1.67 × 10
−7
A/cm
2
.
We describe the APERture Tile In Focus (Apertif) system, a phased array feed (PAF) upgrade of the Westerbork Synthesis Radio Telescope that transforms this telescope into a high-sensitivity, ...wide-field-of-view
L
-band imaging and transient survey instrument. Using novel PAF technology, up to 40 partially overlapping beams are formed on the sky simultaneously, significantly increasing the survey speed of the telescope. With this upgraded instrument, an imaging survey covering an area of 2300 deg
2
is being performed that will deliver both continuum and spectral line datasets, of which the first data have been publicly released. In addition, a time domain transient and pulsar survey covering 15 000 deg
2
is in progress. An overview of the Apertif science drivers, hardware, and software of the upgraded telescope is presented, along with its key performance characteristics.
One of the main technologies to open up a wider field of view for today’s radio telescopes are phased arrays. This is especially the case for radio astronomy instruments operating below 2
GHz. ...Nowadays, the existing dish-type instruments are being upgraded with phased array feeds (PAF) in the focal plane. This increases the field of view at the expense of needing more analog electronics and digital signal processing. One of the digital signal processing functionalities used to combine the digitized signals from the PAF is a beam-former which creates multiple high sensitivity beams within the field of view of the dish. Before beams can be formed, the signals from the PAF need to be calibrated using a correlator. In this paper, we present a solution where these two operations are combined by using the beam-former also as a correlator. The statistics unit used as part of the beam-former implementation, can be used as well for calculating correlation products. With the proper settings of the beam-former weight of each beamlet, a frequency sub-band with a direction, can be used as a single cross correlation product. By implementing the correlator on the beam-former, the digital resources and development time can be reduced. To validate the idea, two versions of the algorithm are implemented in the Apertif PAF system on the Westerbork Synthesis Radio Telescope (WSRT). Results show that two full-bandwidth correlation matrices per beam, needed to determine the static beam weights for the calibration, and a single column of the correlation matrix, used to compensate for any drift between the receiver chains, can be performed.
We describe the APERture Tile In Focus (Apertif) system, a phased array feed (PAF) upgrade of the Westerbork Synthesis Radio Telescope that transforms this telescope into a high-sensitivity, ...wide-field-of-view L-band imaging and transient survey instrument. Using novel PAF technology, up to 40 partially overlapping beams are formed on the sky simultaneously, significantly increasing the survey speed of the telescope. With this upgraded instrument, an imaging survey covering an area of 2300 deg2 is being performed that will deliver both continuum and spectral line datasets, of which the first data have been publicly released. In addition, a time domain transient and pulsar survey covering 15 000 deg2 is in progress. An overview of the Apertif science drivers, hardware, and software of the upgraded telescope is presented, along with its key performance characteristics.
Astronauts are required to operate within isolated, confined and extreme environments (ICE). Isolated, confined and controlled (ICC) environments, such as the NASA Human Exploration Research Analog ...(HERA) site, provide ways of studying and predicting behavioral changes that occur in response to prolonged exposure to ICE environments. An important aspect of behavior is affordance perception. An affordance refers to a possibility for action. Affordance perception and related behavior may be affected by sleep, emotional health and stress. The inability to accurately perceive changes in affordances may increase the risk adopted during a task, possibly compromising mission success.
Investigate changes in affordance perception during a 30-day exposure to an ICC environment and investigate the relationship between affordance perception and sleep, emotional health and physiological markers of stress.
Sixteen subjects completed five sessions of the perception-action coupling task (PACT), a novel tablet-based affordance perception task, on days 3, 10, 17, 24 and 5-days post-mission. The 15-min PACT presents a series of virtual balls and apertures varying in ball to aperture size ratio (B-AR) from 0.2 to 1.8. Subjects determined whether the ball could fit through the aperture and responded based on their perception of this action possibility. Participants also completed an emotional health questionnaire, the Mental Health Checklist (MHCL) throughout the mission. Actigraphy was used to collect sleep measures. Multiple ANOVA were conducted to assess changes in PACT response time (RT), accuracy (ACC) and lapses across time and to assess the role of individual differences in sleep, MHCL measures and salivary biomarkers of stress on performance.
A significant main effect of time was observed on PACT RT (F4, 60 = 3.631, p = .010, n2p = .195) which was faster on day 24 (0.738 ± 0.088s) than day 17 (0.768 ± 0.092s). No differences were observed between other timepoints. ACC and lapses did not vary during the mission (p > .05). Individual differences in sleep duration, sleep efficiency, MHCL measures and salivary biomarkers related to individual differences in aspects of PACT performance.
Modest changes in PACT performance were observed during a 30-day ICC exposure. Individual differences in performance may relate to individual differences in sleep and emotional health.
•An affordance refers to an action possibility.•Successful movement behaviors require accurate and efficient affordance perception.•Sleep and emotional health may impact adaptability in different environments.•Affordance perception may not be degraded in isolated and confined environments.•Differences in sleep and emotional health may influence affordance-based behaviors.
The origin of high-energy cosmic rays in the energy range from 1014 to 1018 eV is explored with the KASCADE and KASCADE-Grande experiments. Radio signals from air showers are measured with the LOPES ...experiment. An overview on results is given.
LOPES - LOFAR PrototypE Station (LOFAR - LOw Frequency ARray) is an array of dipole antennas used for the detection of radio emission from cosmic ray air showers. It is co-located and triggered by ...the KASCADE (KArlsruhe Shower Core and Array Detector) experiment, which also provides information about air shower properties like electron number Ne, muon number Nµ, azimuth and zenith angle. LOPES-10 (the first phase of LOPES, consisting of 10 antennas) detected a significant number of cosmic ray air showers with a zenith angle larger than 50°, and many of those have very high field strengths. The most inclined event that has been detected with LOPES-10 has a zenith angle of almost 80°. This is important, because cosmic ray air showers with large inclinations, triggered close to the ground, would be a signature of neutrino events. Due to the small baseline of the LOPES-10 detector, it is not yet possible to determine accuratelly the radius of curvature of the showers front, which is related to the distance to the maximum of shower development. However, this should be possible in the future with a large baseline radio telescope like LOFAR.
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