The Calorimetric Electron Telescope (CALET), in operation on the International Space Station since 2015, collected a large sample of cosmic-ray iron over a wide energy interval. In this paper a ...measurement of the iron spectrum is presented in the range of kinetic energy per nucleon from 10GeV/n to 2.0 TeV/n allowing the inclusion of iron in the list of elements studied with unprecedented precision by space-borne instruments. The measurement is based on observations carried out from January 2016 to May 2020. The CALET instrument can identify individual nuclear species via a measurement of their electric charge with a dynamic range extending far beyond iron (up to atomic number Z = 40). The energy is measured by a homogeneous calorimeter with a total equivalent thickness of 1.2 proton interaction lengths preceded by a thin (3 radiation lengths) imaging section providing tracking and energy sampling. The analysis of the data and the detailed assessment of systematic uncertainties are described and results are compared with the findings of previous experiments. The observed differential spectrum is consistent within the errors with previous experiments. In the region from 50 GeV/n to 2 TeV/ n our present data are compatible with a single power law with spectral index−2.60±0.03.
Hybrid code simulations of the MHD scale Kelvin‐Helmholtz (K‐H) instability have been conducted. In contrast to the homogeneous background case where the large‐scale ion mixing across the shear layer ...occurs inside the vortex obeying the hydrodynamic similarity law, the ion mixing is found to be reduced when the background magnetic field is inhomogeneous. This stabilization effect is twofold: it is an ion kinetic effect which reduces the saturation vortex size and so the mixing length when the shear layer width and the wavelength of the growing mode are small. The reduction effect still works even when the shear layer width/wavelength are large and a well defined vortical motion as in the fluid model is evident. The mixing is suppressed for this case because the ions on the lower magnetic field (magnetosheath) side cannot enter within the vortex island: The rolled‐up magnetopause current sheet block them out electrostatically. The geophysical implication of the present result is that the K‐H mixing alone may not be as efficient as to produce the large‐scale mixing blob of the low‐latitude boundary layer (LLBL) when the magnetic field intensity is highly different across the magnetopause.
A‘torus’‐like velocity distribution of the helium pickup ions has been detected in interplanetary space by GEOTAIL. A statistical survey shows that the observation probability of the ‘torus’ ...distribution amounts to nearly 20% and that the distribution pattern depends on the local magnetic field directions and turbulence levels. These results support the recent finding of a low pitch angle scattering rate and a large mean free path.
Although clinicians commonly use computed tomography or ultrasonography to diagnose acute appendicitis, the accuracy of these imaging tests remains unclear.
To review the diagnostic accuracy of ...computed tomography and ultrasonography in adults and adolescents with suspected acute appendicitis.
The authors used MEDLINE, EMBASE, bibliographies, review articles, textbooks, and expert opinion to retrieve English- and non-English-language articles published from 1966 to December 2003.
The authors included prospective studies evaluating computed tomography or ultrasonography followed by surgical confirmation or clinical follow-up in patients at least 14 years of age with suspected appendicitis.
One assessor (for non-English-language studies) or 2 assessors (for English-language studies) independently reviewed each article to abstract relevant study characteristics and results.
Twelve computed tomography studies and 14 ultrasonography studies met inclusion criteria. Computed tomography had an overall sensitivity of 0.94 (95% CI, 0.91 to 0.95), a specificity of 0.95 (CI, 0.93 to 0.96), a positive likelihood ratio of 13.3 (CI, 9.9 to 17.9), and a negative likelihood ratio of 0.09 (CI, 0.07 to 0.12). Ultrasonography had an overall sensitivity of 0.86 (CI, 0.83 to 0.88), a specificity of 0.81 (CI, 0.78 to 0.84), a positive likelihood ratio of 5.8 (CI, 3.5 to 9.5), and a negative likelihood ratio of 0.19 (CI, 0.13 to 0.27). Verification bias and inappropriate blinding of reference standards were noted in all of the included studies.
The summary assessment of the diagnostic accuracy for both tests was limited by the small number of studies, heterogeneity among study samples, and poor methodologic quality in the original studies.
Computed tomography is probably more accurate than ultrasonography for diagnosing appendicitis in adults and adolescents. Prospective studies that apply gold standard diagnostic testing to all study participants would more reliably estimate the true diagnostic accuracy of these tests.
We present the measurement of the energy dependence of the boron flux in cosmic rays and its ratio to the carbon flux in an energy interval from 8.4 GeV/n to 3.8 TeV/n based on the data collected ...by the Calorimetric Electron Telescope (CALET) during ∼6.4 yr of operation on the International Space Station. An update of the energy spectrum of carbon is also presented with an increase in statistics over our previous measurement. The observed boron flux shows a spectral hardening at the same transition energy E_{0}∼200 GeV/n of the C spectrum, though B and C fluxes have different energy dependences. The spectral index of the B spectrum is found to be γ=-3.047±0.024 in the interval 25<E<200 GeV/n. The B spectrum hardens by Δγ_{B}=0.25±0.12, while the best fit value for the spectral variation of C is Δγ_{C}=0.19±0.03. The B/C flux ratio is compatible with a hardening of 0.09±0.05, though a single power-law energy dependence cannot be ruled out given the current statistical uncertainties. A break in the B/C ratio energy dependence would support the recent AMS-02 observations that secondary cosmic rays exhibit a stronger hardening than primary ones. We also perform a fit to the B/C ratio with a leaky-box model of the cosmic-ray propagation in the Galaxy in order to probe a possible residual value λ_{0} of the mean escape path length λ at high energy. We find that our B/C data are compatible with a nonzero value of λ_{0}, which can be interpreted as the column density of matter that cosmic rays cross within the acceleration region.
Observations of tailward cold O+ beams (COBs) in the distant lobe/mantle shed new light upon plasma supply mechanisms to the magnetotail since their location up to a tailward distance of 210 RE is ...not explicable with a conventional view of magnetospheric dynamics. The COBs exist primarily in the mantlelike regions that correspond to the transport route of magnetic flux tubes reconnected at the dayside magnetopause, and thus it has been suggested that these high‐energy COBs in the distant lobe/mantle have originated from trapped O+ ions in the dayside magnetosphere. In order to examine the validity of this scenario the phase space density (PSD) of the COBs observed by Geotail is compared statistically with that of mirroring O+ ions around the cusp observed by FAST at low altitudes (400–4200 km) utilizing particle trajectory tracings in empirical magnetospheric models. The energy distribution of the averaged peak PSD of COBs is different at energies below and above ∼1 keV and thus suggests that more than one source contributes to the COBs. The mirroring O+ increases in quantity with increasing solar activity and suggest increment of trapped O+ ions in the dayside magnetosphere. A statistical comparison shows that the O+ PSD around the low‐altitude cusp is similar to that of COBs above ∼1 keV, while the COB PSD is typically higher than that of O+ at FAST at energies <∼1 keV. These results suggest that the trapped O+ in the dayside magnetosphere is a potential source of COBs at energies above 1 keV, while for COBs below 1 keV, polar O+ outflows from the cusp/cleft regions are the most probable source, as suggested by a conventional view.
Nonthermal particle acceleration is one of the most important topics in the physics of cosmic plasmas. Owing to rapid advances in in situ and remote-sensing observations of these plasmas, much ...details on acceleration processes are now being accumulated. I will review several topics from these recent observational and theoretical accomplishments and discuss their physical significance.
We present the results of a direct measurement of the cosmic-ray helium spectrum with the CALET instrument in operation on the International Space Station since 2015. The observation period covered ...by this analysis spans from October 13, 2015, to April 30, 2022 (2392 days). The very wide dynamic range of CALET allowed for the collection of helium data over a large energy interval, from ∼40 GeV to ∼250 TeV, for the first time with a single instrument in low Earth orbit. The measured spectrum shows evidence of a deviation of the flux from a single power law by more than 8σ with a progressive spectral hardening from a few hundred GeV to a few tens of TeV. This result is consistent with the data reported by space instruments including PAMELA, AMS-02, and DAMPE and balloon instruments including CREAM. At higher energy we report the onset of a softening of the helium spectrum around 30 TeV (total kinetic energy). Though affected by large uncertainties in the highest energy bins, the observation of a flux reduction turns out to be consistent with the most recent results of DAMPE. A double broken power law is found to fit simultaneously both spectral features: the hardening (at lower energy) and the softening (at higher energy). A measurement of the proton to helium flux ratio in the energy range from 60 GeV/n to about 60 TeV/n is also presented, using the CALET proton flux recently updated with higher statistics.
In August 2015, the CALorimetric Electron Telescope (CALET), designed for long exposure observations of high energy cosmic rays, docked with the International Space Station (ISS) and shortly ...thereafter began to collect data. CALET will measure the cosmic ray electron spectrum over the energy range of 1 GeV to 20 TeV with a very high resolution of 2% above 100 GeV, based on a dedicated instrument incorporating an exceptionally thick 30 radiation-length calorimeter with both total absorption and imaging (TASC and IMC) units. Each TASC readout channel must be carefully calibrated over the extremely wide dynamic range of CALET that spans six orders of magnitude in order to obtain a degree of calibration accuracy matching the resolution of energy measurements. These calibrations consist of calculating the conversion factors between ADC units and energy deposits, ensuring linearity over each gain range, and providing a seamless transition between neighboring gain ranges. This paper describes these calibration methods in detail, along with the resulting data and associated accuracies. The results presented in this paper show that a sufficient accuracy was achieved for the calibrations of each channel in order to obtain a suitable resolution over the entire dynamic range of the electron spectrum measurement.
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