Galactic cosmic rays (GCRs) are affected by solar modulation while they propagate through the heliosphere. The study of the time variation of GCR spectra observed at Earth can shed light on the ...underlying physical processes, specifically diffusion and particle drifts. Recently, the AMS-02 experiment measured with very high accuracy the time variation of the cosmic-ray proton and helium flux between 2011 May and 2017 May in the rigidity range from 1 to 60 GV. In this work, a comprehensive three-dimensional steady-state numerical model is used to solve Parker's transport equation and reproduce the monthly proton fluxes observed by AMS-02. We find that the rigidity slope of the perpendicular mean free path above 4 GV remains constant, while below 4 GV, it increases during solar maximum. Assuming the same mean free paths for helium and protons, the models are able to reproduce the time behavior of the p/He ratio observed by AMS-02. The dependence of the diffusion tensor on the particle mass-to-charge ratio, A/Z, is found to be the main cause of the time dependence of p/He below 3 GV.
Interplanetary coronal mass ejections (ICMEs) are eruptions of plasma that propagate outward through the heliosphere. ICMEs, and the shocks they drive, cause a sudden decrease in the cosmic-ray flux ...in their local area of the heliosphere, called a Forbush decrease (FD). A method of defining FDs is established, and an automated process for identifying FDs in neutron monitor (NM) data is created. The correlation between ICME properties and FD magnitude in 12 different NMs is examined for 91 ICME-associated FD events occurring from 2001 through 2019 August. A number of ICME properties show positive correlation with FD magnitude, with decreasing correlation strength as NM cutoff rigidity increases.
We study the predictions for the p/He ratio in galactic cosmic rays according to the force-field approximation. The dependence of the time variation of p/He on the local interstellar spectrum (LIS) ...shape and on the mass-to-charge ratio, A/Z, is analyzed in detail. We find that, depending on the rigidity range and the sign of the spectral index of the p/He LIS ratio, the p/He time variation can be correlated or anti-correlated with the phase of the solar cycle. We show that the A/Z dependence is the most probable cause for the p/He decrease recently observed by AMS-02 after 2015 between 2 and 3 GV.
Galactic cosmic rays (GCRs) entering the heliosphere are disturbed by the magnetic field of the Sun, which varies the shape and intensity of their local interstellar spectrum. The force-field ...approximation is a popular way of dealing with solar modulation, especially for studies focused on galactic transport of cosmic rays. The validity of this approach to reproduce the modulated GCR fluxes at Earth is tested using monthly proton fluxes measured by PAMELA between July 2006 and January 2014 and monthly proton and helium fluxes measured by AMS-02 between May 2011 and May 2017. We show that the precision of the new AMS-02 data requires a rigidity-dependent modification of the force-field approximation.
Law, Territory and Conflict Resolution examines the role of law in territorial disputes and legal realities in territorial conflicts by critically reflecting on the well-established assumption that ...law is 'part of the solution' rather than 'part of the problem'.
Galactic cosmic rays (GCRs) are affected by solar modulation while they propagate through the heliosphere. The study of the time variation of GCR spectra observed at Earth can shed light on the ...underlying physical processes, specifically diffusion and particle drifts. Recently, the AMS-02 experiment measured with very high accuracy the time variation of the cosmic ray proton and helium flux between May 2011 and May 2017 in the rigidity range from 1 to 60 GV. In this work, a comprehensive three-dimensional (3D) steady-state numerical model is used to solve Parker's transport equation and is used to reproduce the monthly proton fluxes observed by AMS-02. We find that the rigidity slope of the perpendicular mean free path above 4 GV remains constant, while below 4 GV it increases during solar maximum. Assuming the same mean free paths for helium and protons, the models are able to reproduce the time behavior of the p/He ratio observed by AMS-02. The dependence of the diffusion tensor on the particle mass-to-charge ratio, A/Z, is found to be the main cause of the time dependence of p/He below 3 GV.
A detailed study of alpha interactions on the passivation layer on the end-plate of a true-coaxial high-purity germanium detector is presented. The observation of alpha events on such a surface ...indicates an unexpectedly thin so-called "dead layer" of less than 20 {\mu}m thickness. In addition, the influence of the metalisation close to the end-plate on the time evolution of the output pulses is discussed. The results indicate that alpha contamination can result in events which could be mistaken as signals for neutrinoless double beta decay and provide some guidance on how to prevent this.
Neutron production in lead by cosmic muons has been studied with a Gadolinium doped liquid scintillator detector. The detector was installed next to the Muon-Induced Neutron Indirect Detection ...EXperiment (MINIDEX), permanently located in the T\"ubingen shallow underground laboratory where the mean muon energy is approximately 7 GeV. The MINIDEX plastic scintillators were used to tag muons; the neutrons were detected through neutron capture and neutron-induced nuclear recoil signals in the liquid scintillator detector. Results on the rates of observed neutron captures and nuclear recoils are presented and compared to predictions from GEANT4-9.6 and GEANT4-10.3. The predicted rates are significantly too low for both versions of GEANT4. For neutron capture events, the observation exceeds the predictions by factors of \( 1.65\,\pm\,0.02\,\textrm{(stat.)}\,\pm\,0.07\,\textrm{(syst.)} \) and \( 2.58\,\pm\,0.03\,\textrm{(stat.)}\,\pm\,0.11\,\textrm{(syst.)} \) for GEANT4-9.6 and GEANT4-10.3, respectively. For neutron nuclear recoil events, which require neutron energies above approximately 5 MeV, the factors are even larger, \( 2.22\,\pm\,0.05\,\textrm{(stat.)}\,\pm\,0.25\,\textrm{(syst.)} \) and \( 3.76\,\pm\,0.09\,\textrm{(stat.)}\,\pm\,0.41\,\textrm{(syst.)} \), respectively. Also presented is the first statistically significant measurement of the spectrum of neutrons induced by cosmic muons in lead between 5 and 40 MeV. It was obtained by unfolding the nuclear recoil spectrum. The observed neutron spectrum is harder than predicted by GEANT4. An investigation of the distribution of the time difference between muon tags and nuclear recoil signals confirms the validity of the unfolding procedure and shows that GEANT4 cannot properly describe the time distribution of nuclear recoil events. In general, the description of the data is worse for GEANT4-10.3 than for GEANT4-9.6.
Recapitulation of lung development from human pluripotent stem cells (hPSCs) in three dimensions (3D) would allow deeper insight into human development, as well as the development of innovative ...strategies for disease modelling, drug discovery and regenerative medicine. We report here the generation from hPSCs of lung bud organoids (LBOs) that contain mesoderm and pulmonary endoderm and develop into branching airway and early alveolar structures after xenotransplantation and in Matrigel 3D culture. Expression analysis and structural features indicated that the branching structures reached the second trimester of human gestation. Infection in vitro with respiratory syncytial virus, which causes small airway obstruction and bronchiolitis in infants, led to swelling, detachment and shedding of infected cells into the organoid lumens, similar to what has been observed in human lungs. Introduction of mutation in HPS1, which causes an early-onset form of intractable pulmonary fibrosis, led to accumulation of extracellular matrix and mesenchymal cells, suggesting the potential use of this model to recapitulate fibrotic lung disease in vitro. LBOs therefore recapitulate lung development and may provide a useful tool to model lung disease.
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