The Advanced Small Analyzer for Neutrals (ASAN) is an international payload onboard the Chinese Chang’E-4 rover. It performed for the first time measurements of energetic neutral atoms (ENAs) on the ...lunar surface. We show a typical mass separated ENA energy spectrum measured by the ASAN. After normalizing to the impinging solar wind proton energy, good agreement to previous measurements from Chandrayaan-1 and IBEX is found. The hydrogen ENA albedo is estimated to be 32% for energy above 30 eV, comparable to the estimates obtained from Chandrayaan-1 and IBEX. Particle fluxes at lower energies are generally higher than those observed by Chandrayaan-1 and IBEX, and possible reasons are discussed.
•First energetic neutral atom measurements directly on the lunar surface.•Good agreement with remote observations at higher energies.•Different from remote observations at lower energies.
Cosmic‐ray neutron probes are widely used to monitor environmental water content near the surface. The method averages over tens of hectares and is unrivaled in serving representative data for ...agriculture and hydrological models at the hectometer scale. Recent experiments, however, indicate that the sensor response to environmental heterogeneity is not fully understood. Knowledge of the support volume is a prerequisite for the proper interpretation and validation of hydrogeophysical data. In a previous study, several physical simplifications have been introduced into a neutron transport model in order to derive the characteristics of the cosmic‐ray probe's footprint. We utilize a refined source and energy spectrum for cosmic‐ray neutrons and simulate their response to a variety of environmental conditions. Results indicate that the method is particularly sensitive to soil moisture in the first tens of meters around the probe, whereas the radial weights are changing dynamically with ambient water. The footprint radius ranges from 130 to 240 m depending on air humidity, soil moisture, and vegetation. The moisture‐dependent penetration depth of 15 to 83 cm decreases exponentially with distance to the sensor. However, the footprint circle remains almost isotropic in complex terrain with nearby rivers, roads or hill slopes. Our findings suggest that a dynamically weighted average of point measurements is essential for accurate calibration and validation. The new insights will have important impact on signal interpretation, sensor installation, data interpolation from mobile surveys, and the choice of appropriate resolutions for data assimilation into hydrological models.
Key Points:
Neutron transport modeling revised with a near‐ground cosmic‐ray spectrum
Footprint radius is 130–240 m depending on humidity, soil moisture, and vegetation
Detector is extraordinarily sensitive to the first few meters
•The wavelet packet energy spectrum is utilized in structural health monitoring and assessment.•Multi-threshold wavelet packet denoising method is used to reduce impacts of noise in ...signals.•Structural damage indicators are extracted from the wavelet packet energy to qualify damages.•Baseline thresholds are set by the convergence analysis of defined structural damage indicators.•It is able to detect and alarm possible structural damages under uncertainty in a dynamic manner.
A novel methodology about structural health monitoring and assessment using the wavelet packet energy spectrum is developed by analyzing the acceleration response signal, aiming to identify the structural damage in real time and perform early structural damage alarming. The structural damage warning will be made according to baseline thresholds, which are obtained from a convergence analysis based on the mean and variance value of two structural damage indicators, namely energy ratio deviation (ED) and energy ratio variance (EV). To illustrate the effectiveness of the method, the operational stage of the Wangzong tunnel in the Wuhan Metro Line 3 in China is taken as a case study. The results demonstrate that (1) The multi-threshold wavelet packet denoising method is effective in removing noise and reserving information within 0.1 Hz; (2) The damage indicators ED and EV from the wavelet packet energy spectrum are sensitive to structural damage, whose mean and variance value will converge well along with the growth of wavelet packet component number; and (3) By the threshold value based on the one-side 98% upper confidence limit, the potential structural damage can be detected and alarmed dynamically in the underground filling with complexity and uncertainty. In conclusion, this research contributes to developing new metrics for structural health evaluation with consideration of time dimension and vibration properties of the structure, which is helpful in detecting and alarming the possible structural damage prior to structural failures. Its inherent limitations lie in the relatively complicated computing process and strict requirements in sensor location.
Cosmic rays around the so-called knee in the spectrum at around PeV primary energy are generally galactic in origin. Observations on the form of their energy spectrum and their mass composition are ...fundamental tools to understand the origin, acceleration and propagation mechanism of high-energy cosmic rays. In addition, it is required to find signatures to clarify the transition from galactic to extragalactic sources, which are believed to be responsible for the highest-energy cosmic rays above EeV. This brief review focuses on recent experimental results around the knee of the all-particle energy spectrum and composition in the energy range of the knee up to EeV energies.
Purpose
Proton pencil beam energy spectrum is an essential parameter for calculations of dose and linear energy transfer. We extract the energy spectrum from measured integral depth dose (IDD).
...Methods
A measured IDD (measIDD) in water is decomposed into many IDDs of mono‐energetic pencil beams (monoIDDs) in water. A simultaneous iterative technique is used to do the decomposition that extracts the energy spectrum of protons from the measIDD. The monoIDDs are generated by our analytic random walk model‐based proton dose calculation algorithm. The linear independence of the monoIDDs is considered and high spatial resolution monoIDDs are used to improve their linear independence. To validate the extraction, first we use synthesized IDDs (synIDD) with Gaussian energy spectrum and compare the extracted energy spectrum with the Gaussian; second, for the energy spectrum extracted from measIDDs, the accuracy of the extraction is validated by comparing the calculated IDD from the energy spectrum with the measIDD. The measIDDs are derived from commissioning of a cyclotron proton pencil beam system with a Bragg peak ionization chamber. The nominal energy of the pencil beams is from 70 to 245 MeV. The monoIDDs are generated for energies from 0.05 to 275 MeV in steps of 0.05 MeV with a spatial resolution of 1 mm.
Results
The difference of the extracted and original Gaussian energy spectrum peaked at 75 and 80 MeV was <1%. As the energy decreased, the difference increased but was reduced by using 0.1‐mm monoIDDs. The difference was not sensitive to the energy interval of monoIDDs when the interval increased from 0.05 to 1 MeV. For the energy spectrum extraction from measIDDs, there was a main peak near the nominal energy but the spectrum was not in Gaussian distribution. In three example cases (70, 160, and 245 MeV), the relative differences of the measIDDs and calculated IDDs were within 3.4%, 2.9%, and 4.7% of the Bragg peak value, respectively. Fitting the spectrum by Gaussian distribution, we had σ = 0.87, 1.51, and 0.86 MeV, respectively, for these three examples, and the relative differences of the resultant calculated IDDs from the measIDDs were within 4.7%, 7.4%, and 4.5%, respectively.
Conclusions
Our algorithm accurately extracted the energy spectrum from the synIDDs and measIDDs. High‐resolution monoIDDs are necessary to extract low‐energy spectrum. Energy spectrum extraction from measIDD reveals important information for beam modeling.
The anomalous cosmic rays have been studied for about fifty years. Through theoretical and numerical models, we can learn how and where they are originating. When Voyager 1 and 2 spacecraft observed ...the solar wind termination shock, the main efforts were focused on try to explain the source spectrum and the acceleration mechanism. Nevertheless, there is another feature of the spectrum that need a better understanding, and it is related with the peak intensity in the energy spectrum, that occurred at different energies in consecutive solar minima. Qualitatively, it can be explained in terms of drifts and its relation with the acceleration process. In the past some works have been partially successful to explain the observations. In this paper we do another effort to explain the shift in the peak intensity of anomalous cosmic ray energy spectrum. We use a numerical model which includes diffusive shock acceleration, and the effects of the heliosheath. The present work analyzes the role played by different factors in the energy shift of the peak intensity between two successive minima, in particular the location of the region of observations with respect to the shock, the heliospheric distance, the effects of turbulence on the reduction of weak scattering drifts, as well as a possible latitudinal dependence in the ion injection on the shock.
To examine the species dependence of the sustained energy spectrum gaps, in this letter, we analyzed the magnetic local time distribution of sustained proton and oxygen gaps and find that there is a ...clear difference between proton and oxygen ions: proton sustained gaps are predominantly distributed near the prenoon sector, while oxygen sustained gaps are mostly in the afternoon sector with lower occurrence rate than that for protons. This is primarily due to the different charge exchange loss rates of protons and oxygen ions. This scenario is supported by particle‐tracing simulations, which reproduce most of the observed characteristics. Through model‐data comparison, we found that the spectral gaps at different local times are formed by two different types of mechanisms: (a) the gap is formed due to the extended drift time which is responsible for the gap appearing on the dayside for both proton and oxygen ions; (b) the gap is formed inside the Alfven layer, which accounts for the observed sustained gaps in proton energy spectrums but not in oxygen ions due to the different charge exchange losses at various energies on the preexisting ion populations that lie on closed drift paths. These findings may provide insight into our understanding of ion composition and possible wave generation in the inner magnetosphere.
Plain Language Summary
The dynamic evolution of the Earth's magnetosphere is complicated, and the temporal and spatial variations of the ion populations provide unique insights into the underlying physics. In this study, we have investigated a peculiar signature in the energy spectrum of ions, in which their fluxes show a sustained gap within a very narrow energy range throughout a full orbit of Van Allen Probes. Through a statistical survey, we find that proton sustained gaps are predominantly distributed near the prenoon sector, while oxygen sustained gaps are mostly in the afternoon sector with the total occurrence rate much lower than that for protons. By using particle‐tracing simulations that reproduce most of the observed characteristics, we reveal that the difference in the magnetic local time distribution of proton and oxygen sustained gaps is primarily due to the different charge exchange loss rates between proton and oxygen ions of various energies.
Key Points
The sustained spectral gaps show clear species dependence with higher occurrence rate for protons than for oxygen ions
Proton sustained gaps are predominantly distributed near the prenoon sector while oxygen gaps are in the afternoon sector
The different magnetic local time (MLT) distributions between proton and oxygen spectral gaps are primarily caused by the different charge exchange loss rates
Objective: To investigate the value of energy spectrum CT multi-parameter quantitative analysis in the differential diagnosis of lung squamous cell carcinoma and adenocarcinoma. Methods: Seventy-five ...patients with lung cancer who were confirmed by pathology and underwent energy spectrum CT scanning were collected, including 40 cases of squamous cell carcinoma and 35 cases of adenocarcinoma. We measured and compared the energy spectrum parameters of arterial phase and venous phase between the two groups. Results: The spectrum curve of adenocarcinoma (λ40～65 keV) in arterial and venous phase, effective atomic number, concentration of iodine (water) and standardized iodine concentration were greater than that of squamous carcinoma, the difference was statistically significant, the difference of water (iodine) concentration between the two groups of arterial phase held no statistical significance, the water (iodine) concentration of adenocarcinoma was lower than that of squamous cell carcinomas, the difference was statistically significant. The results of ROC curve analysis showed that the energy spectrum (λ40～65 keV) in the venous phase was of great value in the differentiation of squamous cell carcinoma and adenocarcinoma, with the AUC of 0.839, the sensitivity of 88.6% and the specificity of 72.5%. Conclusion: Adenocarcinoma and squamous cell carcinoma of lung show different energy spectrum CT parameters. It holds certain value to distinguish them, which can provide a new method for preoperative diagnosis.
A submesoscale‐permitting global ocean simulation is used to study the upper ocean turbulence in high kinetic energy (KE) regions. Submesoscale processes peak in winter so that the geostrophic KE ...spectra tend to be relatively shallow in winter (∼k−2) with steeper spectra in summer (∼k−3). This transition in KE spectral scaling has two phases. In the first phase (late autumn), KE spectra show the presence of two spectral regimes: ∼k−3 power‐law in mesoscales and ∼k−2 power‐law in submesoscales. The first phase appears with the onset of mixed‐layer instabilities, which convert available potential energy into KE, and this process results in a flattening of KE spectra at submesoscales. However, KE spectra at longer wavelengths follow ∼k−3 scaling associated with a forward enstrophy transfer. In the second phase (late winter), KE produced through mixed‐layer instabilities is transferred to larger scales, and k−2 power‐law also develops in mesoscales.
Plain Language Summary
Mesoscale and submesoscale motions are important for heat and material transport in the oceans. In the upper ocean, submesoscale turbulence shows seasonal variability and is pronounced in winter. The same distinction is reflected in horizontal wavenumber spectra of kinetic energy (KE) and spectral energy fluxes. In this study, geostrophic KE spectra are analyzed in a submesoscale‐permitting global ocean model to study the seasonal variability in the upper ocean turbulence. We interpret the results in terms of different physical mechanisms and their effects on the evolution of KE spectra over an annual cycle. We find that both mesoscale and submesoscale processes contribute to their characterization.
Key Points
Seasonality in the upper ocean turbulence is interpreted in terms of interior baroclinic instabilities and mixed‐layer instabilities
Temporal variability in the geostrophic kinetic energy spectrum can be subdivided into distinct seasonal phases
Both a forward enstrophy transfer and an inverse kinetic energy transfer control the spectral slope in the kinetic energy spectrum
In this article, we have investigated an electron energy spectrum, optical absorption coefficients (OACs) and polarizability under the effect of the co-directed electric and magnetic fields in the ...multilayer spherical quantum antidot (MSQAD) Al
0.3
Ga
0.7
As/GaAs/Al
0.3
Ga
0.7
As with off-center impurity. The calculations were done for different dot sizes within the effective mass approximation using the matrix method. The dependence of the total, linear, and nonlinear OACs on the incident photon energy is calculated considering the intraband electron quantum transitions. The donor polarizability and impurity binding energy as function of electric field intensity are obtained at different values of the magnetic field induction.
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