The predictions of hadronic interaction models for cosmic-ray induced air showers contain inherent uncertainties due to limitations of available accelerator data and theoretical understanding in the ...required energy and rapidity regime. Differences between models are typically evaluated in the range appropriate for cosmic-ray air shower arrays (1015–1020 eV). However, accurate modeling of charged cosmic-ray measurements with ground based gamma-ray observatories is becoming more and more important. We assess the model predictions on the gross behavior of measurable air shower parameters in the energy (0.1–100 TeV) and altitude ranges most appropriate for detection by ground-based gamma-ray observatories. We go on to investigate the particle distributions just after the first interaction point, to examine how differences in the microphysics of the models may compound into differences in the gross air shower behavior. Differences between the models above 1 TeV are typically less than 10%. However, we find the largest variation in particle densities at ground at the lowest energy tested (100 GeV), resulting from striking differences in the early stages of shower development.
In the sub-TeV regime, the most widely used hadronic interaction models disagree significantly in their predictions for post-first interaction and ground-level particle spectra from cosmic ray ...induced air showers. These differences generate an important source of systematic uncertainty in their experimental use. We investigate the nature and impact of model uncertainties through a simultaneous analysis of ground level particles and first interaction scenarios. We focus on air shower primaries with energies close to the transition between high and low energy hadronic interaction models, where the dissimilarities have been shown to be the largest and well within the range of accelerator measurements. Interaction models are shown to diverge as several shower scenarios are compared, reflecting intrinsic differences in the model theoretical frameworks. Finally, we discuss the importance of interactions in the energy regime where the switching between models occurs (
<
1
TeV) and the effect of the choice of model on the number of hadronic interactions within cosmic ray induced air showers of higher energies.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report on four radio-detected cosmic-ray (CR) or CR-like events observed with the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload. Two of the four ...were previously identified as stratospheric CR air showers during the ANITA-I flight. A third stratospheric CR was detected during the ANITA-II flight. Here, we report on characteristics of these three unusual CR events, which develop nearly horizontally, 20-30 km above the surface of Earth. In addition, we report on a fourth steeply upward-pointing ANITA-I CR-like radio event which has characteristics consistent with a primary that emerged from the surface of the ice. This suggests a possible τ-lepton decay as the origin of this event, but such an interpretation would require significant suppression of the standard model τ-neutrino cross section.
The first flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment recorded 16 radio signals that were emitted by cosmic-ray induced air showers. The dominant contribution to the ...radiation comes from the deflection of positrons and electrons in the geomagnetic field, which is beamed in the direction of motion of the air shower. For 14 of these events, this radiation is reflected from the ice and subsequently detected by the ANITA experiment at a flight altitude of ∼36 km. In this paper, we estimate the energy of the 14 individual events and find that the mean energy of the cosmic-ray sample is 2.9 × 1018 eV, which is significantly lower than the previous estimate. By simulating the ANITA flight, we calculate its exposure for ultra-high energy cosmic rays. We estimate for the first time the cosmic-ray flux derived only from radio observations and find agreement with measurements performed at other observatories. In addition, we find that the ANITA data set is consistent with Monte Carlo simulations for the total number of observed events and with the properties of those events.
Spontaneously hypertensive rats (SHR), like patients with sleep apnea, have hypertension, increased sympathetic activity, and increased chemoreceptor drive. We investigated the role of carotid ...chemoreceptors in cardiovascular responses induced by obstructive apnea in awake SHR. A tracheal balloon and vascular cannulas were implanted, and a week later, apneas of 15 s each were induced. The effects of apnea were more pronounced in SHR than in control rats (Wistar Kyoto; WKY). Blood pressure increased by 57±3 mmHg during apnea in SHR and by 28±3 mmHg in WKY (p<0.05, n = 14/13). The respiratory effort increased by 53±6 mmHg in SHR and by 34±5 mmHg in WKY. The heart rate fell by 209±19 bpm in SHR and by 155±16 bpm in WKY. The carotid chemoreceptors were then inactivated by the ligation of the carotid body artery, and apneas were induced two days later. The inactivation of chemoreceptors reduced the responses to apnea and abolished the difference between SHR and controls. The apnea-induced hypertension was 11±4 mmHg in SHR and 8±4 mmHg in WKY. The respiratory effort was 15±2 mmHg in SHR and 15±2 mmHg in WKY. The heart rate fell 63±18 bpm in SHR and 52±14 bpm in WKY. Similarly, when the chemoreceptors were unloaded by the administration of 100% oxygen, the responses to apnea were reduced. In conclusion, arterial chemoreceptors contribute to the responses induced by apnea in both strains, but they are more important in SHR and account for the exaggerated responses of this strain to apnea.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ANITA's fourth long-duration balloon flight in 2016 detected 29 cosmic-ray (CR)-like events on a background of 0.37_{-0.17}^{+0.27} anthropogenic events. CRs are mainly seen in reflection off the ...Antarctic ice sheets, creating a phase-inverted waveform polarity. However, four of the below-horizon CR-like events show anomalous noninverted polarity, a p=5.3×10^{-4} chance if due to background. All anomalous events are from locations near the horizon; ANITA-IV observed no steeply upcoming anomalous events similar to the two such events seen in prior flights.
For 50 years, cosmic-ray air showers have been detected by their radio emission. We present the first laboratory measurements that validate electrodynamics simulations used in air shower modeling. An ...experiment at SLAC provides a beam test of radio-frequency (rf) radiation from charged particle cascades in the presence of a magnetic field, a model system of a cosmic-ray air shower. This experiment provides a suite of controlled laboratory measurements to compare to particle-level simulations of rf emission, which are relied upon in ultrahigh-energy cosmic-ray air shower detection. We compare simulations to data for intensity, linearity with magnetic field, angular distribution, polarization, and spectral content. In particular, we confirm modern predictions that the magnetically induced emission in a dielectric forms a cone that peaks at the Cherenkov angle and show that the simulations reproduce the data within systematic uncertainties.
Obstructive sleep apnea (OSA) is often associated with sympathetic overactivity and hypertension. These associations are mainly attributed to hypoxia acting on arterial chemoreceptors. However, the ...contribution of arousal from sleep is unclear. We measured the effect of OSA and sleep fragmentation on cardiovascular and sympathetic function and gene expression in the brain in rats. Male Wistar rats were fitted with a tracheal balloon and EEG and electromyogram electrodes and assigned to control (
= 6), OSA (
= 9), or arousal (
= 8) treatments. The OSA group was subjected to obstructive apnea, each time the rat entered sleep, for 8 h/day for 15 days. The arousal group was similarly exposed to vibration, which was produced with a miniature vibration motor mounted on the rat's head. Vibration intensity slowly increased until the rat awoke. One day after the last apnea or arousal, rats were anesthetized and arterial blood pressure and splanchnic sympathetic nerve activity (SSNA) were recorded. Baseline mean and diastolic pressure were increased after OSA. Resting SSNA was similar in the three groups, but both OSA and sleep fragmentation increased sympathetic activation in response to airway obstruction and chemoreflex activation by cyanide. OSA increased superoxide dismutases 1 and 2 in the brainstem, whereas sleep fragmentation did not. Our results suggest that sympathetic overactivity to chemoreceptor stimulation was a consequence of arousal from sleep. Our study suggests that sleep disruption may have an important role in the development of apnea-related sympathetic activation.
Obstructive sleep apnea causes a hyperactive chemoreflex, with increased sympathetic activation. However, it is not clear whether this pathophysiologic mechanism is due to repeated hypoxia or to sleep disruption. The present study suggests that sleep fragmentation contributes importantly to increased sympathetic activation after chemoreceptor stimulation. This suggests that sleep fragmentation has an important role in the sympathetic activation seen in sleep apnea patients.
Abstract
The ANtarctic Impulsive Transient Antenna (ANITA) long-duration balloon
experiment is sensitive to interactions of ultrahigh-energy (E>10
18
eV)
neutrinos in the Antarctic ice sheet. The ...third flight of ANITA, lasting 22
days, began in December 2014. We develop a methodology to search for
energetic neutrinos spatially and temporally coincident with potential source
classes in ANITA data. This methodology is applied to several source classes:
the potential IceCube-identified neutrino sources TXS 0506+056 and NGC 1068, flaring high-energy blazars reported by the Fermi All-Sky Variability Analysis, gamma-ray bursts, and supernovae. Among
searches within the five source classes, one candidate was identified as associated
with SN 2015D, although not at a statistically significant level. We proceed to place upper limits on the source classes. We further
comment on potential application of this methodology to more
sensitive future instruments.
At the Pierre Auger Observatory, the radio emission from cosmic-ray-induced air showers is measured. We will discuss the physics results from a setup consisting of three antennas triggered by an ...auxiliary particle detector. With this setup, a total of 494 events were registered in coincidence with the surface detector of the Pierre Auger Observatory. This data allows us to study the dependence of the radio signal on air shower parameters. From an analysis of the measured polarization of the radio signals, we conclude that the emission is dominated by the geomagnetic mechanism. However, the polarization study indicates that the pure geomagnetic description by itself is not sufficient to describe all features of the data set.
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