High-energy cosmic-ray electrons and positrons (CREs), which lose energy quickly during their propagation, provide a probe of Galactic high-energy processes and may enable the observation of ...phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been measured directly up to approximately 2 teraelectronvolts in previous balloon- or space-borne experiments, and indirectly up to approximately 5 teraelectronvolts using ground-based Cherenkov γ-ray telescope arrays. Evidence for a spectral break in the teraelectronvolt energy range has been provided by indirect measurements, although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range 25 gigaelectronvolts to 4.6 teraelectronvolts by the Dark Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The largest part of the spectrum can be well fitted by a 'smoothly broken power-law' model rather than a single power-law model. The direct detection of a spectral break at about 0.9 teraelectronvolts confirms the evidence found by previous indirect measurements, clarifies the behaviour of the CRE spectrum at energies above 1 teraelectronvolt and sheds light on the physical origin of the sub-teraelectronvolt CREs.
First experimental proof of a clear and strong dependence of the standard phase scintillation index (σφ) derived using Global Positioning System measurements on the ionospheric plasma flow around the ...noon sector of polar ionosphere is presented. σφ shows a strong linear dependence on the plasma drift speed measured by the Super Dual Auroral Radar Network radars, whereas the amplitude scintillation index (S4) does not. This observed dependence can be explained as a consequence of Fresnel frequency dependence of the relative drift and the used constant cutoff frequency (0.1 Hz) to detrend the data for obtaining standard σφ. The lack of dependence of S4 on the drift speed possibly eliminates the plasma instability mechanism(s) involved as a cause of the dependence. These observations further confirm that the standard phase scintillation index is much more sensitive to plasma flow; therefore, utmost care must be taken when identifying phase scintillation (diffractive phase variations) from refractive (deterministic) phase variations, especially in the polar region where the ionospheric plasma drift is much larger than in equatorial and midlatitude regions.
Key Points
A clear strong linear dependence of phase scintillation index on the plasma drift speed around noon sector of the polar ionosphere is presented
Observed dependence can be very possibly explained by the dependence of the shifted Fresnel frequency from the relative drift
Amplifies the importance of using dynamic cutoff frequency in detrending the phase of GPS signal in the polar region
Based on in situ and ground‐based observations, a new type of “polar cap hot patch” has been identified that is different from the classical polar cap enhanced density structure (cold patches). ...Comparing with the classical polar cap patches, which are transported from the dayside sunlit region with dense and cold plasma, the polar cap hot patches are associated with particle precipitations (therefore field‐aligned currents), ion upflows, and flow shears. The hot patches may have the same order of density enhancement as classical patches in the topside ionosphere, suggesting that the hot patches may be produced by transported photoionization plasma into flow channels. Within the flow channels, the hot patches have low‐energy particle precipitation and/or ion upflows associated with field‐aligned currents and flow shears. Corresponding Global Navigation Satellite System (GNSS) signal scintillation measurements indicate that hot patches may produce slightly stronger radio signal scintillation in the polar cap region than classical patches. A new type of polar cap patches, “polar cap hot patches,” is identified to differentiate enhanced density structures from classical patches. Hot patches are associated with particle precipitations, ion upflows, field‐aligned currents, and shear flows in the polar cap. Hot patches may lead to slightly stronger ionospheric scintillations of GNSS signals in the polar cap region than classical patches.
Key Points
A new type of polar cap patches, “polar cap hot patches,” is identified to differentiate enhanced density structures from classical patches
Hot patches are associated with particle precipitations, ion upflows, field‐aligned currents, and shear flows in the polar cap
Hot patches may lead to slightly stronger ionospheric scintillations of GNSS signals in the polar cap region than classical patches
The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This ...work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with 2
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years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time that an experiment directly measures the cosmic ray protons up to ~100 TeV with high statistics. The measured spectrum confirms the spectral hardening at ~300 GeV found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee and sheds new light on the origin of Galactic cosmic rays.
A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GWth nuclear power reactors of the Daya Bay and Ling Ao nuclear power ...facilities served as intense sources of ν¯e’s. Comparison of the ν¯e rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors (∼1500–1950 m) relative to detectors near the reactors (∼350–600 m) allowed a precise measurement of ν¯e disappearance. More than 2.5 million ν¯e inverse beta-decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (December, 2011–July, 2012) with a subsequent 1013 days using the complete configuration of eight detectors (October, 2012–July, 2015). The ν¯e rate observed at the far detectors relative to the near detectors showed a significant deficit, R=0.949±0.002(stat)±0.002(syst). The energy dependence of ν¯e disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle sin22θ13=0.0841±0.0027(stat)±0.0019(syst) and the effective neutrino mass-squared difference of |Δmee2|=(2.50±0.06(stat)±0.06(syst))×10−3 eV2. Analysis using the exact three-flavor probability found Δm322=(2.45±0.06(stat)±0.06(syst))×10−3 eV2 assuming the normal neutrino mass hierarchy and Δm322=(−2.56±0.06(stat)±0.06(syst))×10−3 eV2 for the inverted hierarchy.
The dependencies of global positioning system (GPS) scintillation indices on ionospheric plasma flow and the rate of change of total electron content (TEC) around the dawn sector for the first time ...of the polar ionosphere are investigated. The phase scintillation index (σφ) derived from GPS measurements of the Canadian High Arctic Ionospheric Network (CHAIN) shows linear dependencies on both the plasma drift speed measured by the SuperDARN radar and on the rate of change of TEC estimated from the GPS receivers of CHAIN. However, the amplitude scintillation index (S4) does not show any dependence on the plasma flow or the rate of change of TEC. These results further support Wang et al. (2018), https://doi.org/10.1002/2017JA024805 at the noon sector. The dependence of the phase scintillation index on the plasma flow further evidences that the standard phase scintillation index is dominated by refractive variations due to the use of a fixed cut‐off frequency of 0.1 Hz while detrending the phase observable. The dependence of the phase scintillation index on the rate of change of TEC consolidates the dominance of refractive variations inside.
Plain Language Summary
In decades, the standard scintillation indices are widely used to represent the strength of scintillations in the ionosphere, which were usually calculated from the sixth order Butterworth filter with a fixed cut‐off frequency of 0.1 Hz by the ground‐based Global Navigation Satellite System (GNSS) receiver automatically. At middle‐to‐low latitudes, the applications of these indices are working very well. However, over the polar ionosphere, the completely different scintillation phenomenon “Phase without Amplitude” occurred when confronting the hazard conditions. Then, in order to explaining this weird, many researchers have carried out a lot of valuable approaches, fundamentally challenging the direct adopt of standard phase scintillation index. Here, for the first time, we present an experimental evidence on the dawn sector to prove the clear positive dependence of phase scintillation index on the convection flow speed and also the TEC variations. It reminds us to be careful when using the standard phase scintillation index over the polar region, in particular with high‐speed flows.
Key Points
The dependencies of global positioning system scintillation indices on plasma flow and total electron content (TEC) variation were evaluated around the dawn sector of polar ionosphere
The phase scintillation index depends linearly only on the plasma flow speed and the rate of change of TEC
However, the amplitude scintillation index does not rely on the plasma flow and also the rate of change of TEC
Background
The Child–Pugh (CP) score is used widely to assess liver function and predict postoperative outcomes in patients with hepatocellular carcinoma (HCC). Recently, the albumin–bilirubin (ALBI) ...score has been validated as a predictor of overall survival in these patients. This study aimed to compare the ability of the ALBI and CP scores to predict outcomes in patients with HCC after liver resection with curative intent.
Methods
Consecutive patients who underwent liver resection with curative intent for HCC between January 2007 and July 2013 were included in this retrospective study. The performance of the ALBI score in predicting postoperative liver failure (PHLF) and long‐term survival was compared with that of the CP score.
Results
A total of 1242 patients were enrolled. Of these, 166 (13·4 per cent) experienced PHLF. The area under the receiver operating characteristic (ROC) curve of the ALBI score for predicting PHLF was greater than that of the CP score (0·723 versus 0·607; P < 0·001). Similar to findings for CP grade, the incidence and severity of PHLF increased with increasing ALBI grade. The ALBI grade stratified patients into at least two distinct overall survival cohorts (P < 0·001), whereas the CP grade did not. The ALBI grade also classified patients with CP grade A disease into two distinct overall survival cohorts (P < 0·001), and overall survival rates in the group with poorer survival were similar to those in the majority of patients with CP grade B disease. Both CP and ALBI scores had low power in predicting disease‐free survival.
Conclusion
The ALBI grade predicted PHLF and overall survival in patients with HCC undergoing liver resection with curative intent more accurately than the CP grade.
ALBI score may be better
This paper is a statistical survey of polar cap patches in relation to solar and geomagnetic activity. Ten thousand six hundred eighty‐eight patches have been identified from in situ plasma ...observations of the Defense Meteorological Satellite Program F16 satellite for 14 years (2005–2018). These patches are divided into two groups: (a) cold patches, which consist of dense but cold plasma; and (b) hot patches, which consist of dense but hot plasma. The statistical results indicate that (a) the occurrence of cold patches is clearly dependent on solar and geomagnetic activity, but hot patches don not show such dependence; (b) both cold and hot patches preferably appear in the winter season; (c) the spatial size of both cold and hot patches decreases (increases) with solar (geomagnetic) activity; (d) the spatial size of cold patches appears larger than that of hot patches under similar solar and geomagnetic activity.
Plain Language Summary
Polar cap patches are localized regions of enhanced plasma density in the polar ionosphere. They are associated with strong electron density gradients resulting in non‐negligible ionospheric scintillations for satellite communication and navigation systems. To characterize polar cap patches and investigate their statistical dependence on solar and geomagnetic activity, 10,688 patches have been identified from 14 years of in situ Defense Meteorological Satellite Program satellite plasma observations. These patches have been divided into cold and hot patches. We find that cold patches occur more frequently during solar maximum years. The spatial size of cold and hot patches decreases with solar activity (increases with geomagnetic activity). Furthermore, the spatial size of cold patches is larger than that of hot patches under similar solar and geomagnetic activity.
Key Points
The occurrence of cold patches is clearly dependent on solar and geomagnetic activity, while hot patches do not show such dependence
In NH winter, the spatial size of both cold and hot patches decreases (increases) with solar (geomagnetic) activity
In NH winter, the spatial size of cold patches appears larger than that of hot patches under similar solar and geomagnetic activity
A novel fast electron beam emitting along the surface of a target irradiated by intense laser pulses is observed. The beam is found to appear only when the plasma density scale length is small. ...Numerical simulations reveal that the electron beam is formed due to the confinement of the surface quasistatic electromagnetic fields. The results are of interest for potential applications of fast electron beams and deep understanding of the cone-target physics in the fast ignition related experiments.
Biomass burning, the largest global source of elemental carbon (EC) and primary organic carbon (OC), is strongly associated with many subjects of great scientific concern, such as secondary organic ...aerosol and brown carbon which exert important effects on the environment and on climate in particular. This study investigated the relationships between levoglucosan and other biomass burning tracers (i.e., water soluble potassium and mannosan) based on both ambient samples collected in Beijing and source samples. Compared with North America and Europe, Beijing was characterized by high ambient levoglucosan concentrations and low winter to summer ratios of levoglucosan, indicating significant impact of biomass burning activities throughout the year in Beijing. Comparison of levoglucosan and water soluble potassium (K+) levels suggested that it was acceptable to use K+ as a biomass burning tracer during summer in Beijing, while the contribution of fireworks to K+ could be significant during winter. Moreover, the levoglucosan to K+ ratio was found to be lower during the typical summer period (0.21 ± 0.16) compared with the typical winter period (0.51 ± 0.15). Levoglucosan correlated strongly with mannosan (R2 = 0.97) throughout the winter and the levoglucosan to mannosan ratio averaged 9.49 ± 1.63, whereas levoglucosan and mannosan exhibited relatively weak correlation (R2 = 0.73) during the typical summer period when the levoglucosan to mannosan ratio averaged 12.65 ± 3.38. Results from positive matrix factorization (PMF) model analysis showed that about 50% of the OC and EC in Beijing were associated with biomass burning processes. In addition, a new source identification method was developed based on the comparison of the levoglucosan to K+ ratio and the levoglucosan to mannosan ratio among different types of biomass. Using this method, the major source of biomass burning aerosol in Beijing was suggested to be the combustion of crop residuals, while the contribution from softwood burning was also non-negligible, especially in winter.
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