Abstract
Proton-boron (p
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B) fusion is an attractive potential energy source but technically challenging to implement. Developing techniques to realize its potential requires first developing the ...experimental capability to produce p
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B fusion in the magnetically-confined, thermonuclear plasma environment. Here we report clear experimental measurements supported by simulation of p
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B fusion with high-energy neutral beams and boron powder injection in a high-temperature fusion plasma (the Large Helical Device) that have resulted in diagnostically significant levels of alpha particle emission. The injection of boron powder into the plasma edge results in boron accumulation in the core. Three 2 MW, 160 kV hydrogen neutral beam injectors create a large population of well-confined, high -energy protons to react with the boron plasma. The fusion products, MeV alpha particles, are measured with a custom designed particle detector which gives a fusion rate in very good relative agreement with calculations of the global rate. This is the first such realization of p
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B fusion in a magnetically confined plasma.
The purpose of this study is to show that social distancing is a public good under the COVID-19 pandemic.
We apply economic theory to analyse a cross-sectional survey.
Economic theory is complemented ...with empirical evidence. An online survey of those aged 30–49 years in Japan (n = 2177) was conducted between April 28 and May 7. Respondents were selected by quota sampling with regard to age group, gender and prefecture of residence. Our main figure shows the proportion of people who increased/did not change/decreased social distancing, relative to the level of altruism and sensitivity to public shaming. The results of OLS and logit models are shown in Supplementary Materials.
Social distancing is a public good under the COVID-19 pandemic for which the free-rider problem is particularly severe. Altruism and social norms are crucial factors in overcoming this problem. Using an original survey, we show that people with higher altruistic concerns and sensitivity to shaming are more likely to follow social distancing measures.
Altruism and social norms are important for reducing the economic cost of the pandemic.
•Social distancing is a public good under the COVID-19 pandemic.•The free-rider problem is particularly severe in the case of COVID-19.•We explain three mechanisms for mitigating the problem—altruism, shaming and legal sanctions.•People with higher altruistic concerns and sensitivity to shaming are more likely to follow social distancing measures.•An important task for policymakers is to integrate psychological, social and legal measures.
Using the Arase and Van Allen Probes satellite observations, we investigate the nonlinear electromagnetic ion cyclotron (EMIC) rising‐tone (RT) emissions with an increase of the solar wind dynamic ...pressure in the dayside magnetosphere. We find that EMIC RT emissions are accompanied by the extended dayside uniform zone (DUZ) over |MLAT| < 25° due to the dayside magnetospheric compression by an increase in Pdyn. Using the observed plasma and magnetic field data, we modeled the threshold amplitude for the nonlinear EMIC waves and compared it with the observation. The small gradient of the ambient magnetic field strongly contributes to the reduction in the threshold amplitude of nonlinear wave growth compared to other parameters. When the threshold amplitude falls to comparable level of pre‐existing EMIC waves, EMIC RT emissions are immediately triggered, suggesting direct evidence that the DUZ is the preferred condition to cause the nonlinear EMIC RT emission in the dayside magnetosphere.
Plain Language Summary
Electromagnetic ion cyclotron (EMIC) waves play an important role in controlling the dynamics of charged particles in the inner magnetosphere. Especially, nonlinear EMIC rising‐tone (RT) emissions can cause the rapid loss of relativistic electrons and ring current ions. Here, we present direct evidence demonstrating that the distortion of the dayside magnetic field causes nonlinear EMIC RT emission in response to the intensification of the solar wind dynamic pressure. Remarkably, these nonlinear EMIC waves are generated through a reduction in the threshold wave amplitudes by the distortion of the magnetic fields, even in the absence of any significant change in the pre‐existing EMIC wave amplitude. The present result provides new insights into a triggering process of nonlinear plasma waves in the magnetosphere.
Key Points
Electromagnetic ion cyclotron (EMIC) waves with rising‐tone (RT) elements were observed in the dayside magnetosphere during an increase in the solar wind dynamic pressure
Increasing solar wind dynamic pressure extends the dayside uniform zone of the magnetic field to higher magnetic latitudes
The uniform zone leads to the reduction of the nonlinear threshold wave amplitude, which triggers nonlinear EMIC RT emissions
Full geometry optimizations of several inorganic model clusters, CaMn(4)O(4)XYZ(H(2)O)(2) (X, Y, Z = H(2)O, OH(-) or O(2-)), by the use of the B3LYP hybrid density functional theory (DFT) have been ...performed to illuminate plausible molecular structures of the catalytic site for water oxidation in the S(0), S(1), S(2) and S(3) states of the Kok cycle for the oxygen-evolving complex (OEC) of photosystem II (PSII). Optimized geometries obtained by the energy gradient method have revealed the degree of symmetry breaking of the unstable three-center Mn(a)-X-Mn(d) bond in CaMn(4)O(4)XYZ(H(2)O)(2). The right-elongated (R) Mn(a)-X···Mn(d) and left-elongated (L) Mn(a)···X-Mn(d) structures appear to occupy local minima on a double-well potential for several key intermediates in these states. The effects of insertion of one extra water molecule to the vacant coordination site, Mn(d) (Mn(a)), for R (L) structures have also been examined in detail. The greater stability of the L-type structure over the R-type has been concluded for key intermediates in the S(2) and S(3) states. Implications of the present DFT structures are discussed in relation to previous DFT and related results, together with recent X-ray diffraction results for model compounds of cubane-like OEC cluster of PSII.
Particle acceleration by plasma waves and spontaneous wave generation are fundamental energy and momentum exchange processes in collisionless plasmas. Such wave-particle interactions occur ...ubiquitously in space. We present ultrafast measurements in Earth's magnetosphere by the Magnetospheric Multiscale spacecraft that enabled quantitative evaluation of energy transfer in interactions associated with electromagnetic ion cyclotron waves. The observed ion distributions are not symmetric around the magnetic field direction but are in phase with the plasma wave fields. The wave-ion phase relations demonstrate that a cyclotron resonance transferred energy from hot protons to waves, which in turn nonresonantly accelerated cold He
to energies up to ~2 kilo-electron volts. These observations provide direct quantitative evidence for collisionless energy transfer in plasmas between distinct particle populations via wave-particle interactions.
Recent years have seen debate regarding the ability of electromagnetic ion cyclotron (EMIC) waves to drive EEP (energetic electron precipitation) into the Earth's atmosphere. Questions still remain ...regarding the energies and rates at which these waves are able to interact with electrons. Many studies have attempted to characterize these interactions using simulations; however, these are limited by a lack of precise information regarding the spatial scale size of EMIC activity regions. In this study we examine a fortuitous simultaneous observation of EMIC wave activity by the RBSP‐B and Arase satellites in conjunction with ground‐based observations of EEP by a subionospheric VLF network. We describe a simple method for determining the longitudinal extent of the EMIC source region based on these observations, calculating a width of 0.75 hr MLT and a drift rate of 0.67 MLT/hr. We describe how this may be applied to other similar EMIC wave events.
Plain Language Summary
The Earth is surrounded by the Van Allen radiation belts, rings of high‐energy charged particles trapped by the Earth's magnetic field. These particle populations are constantly changing, driven by forces from the Sun, Earth, and from the belts themselves. One of the most important drivers of this dynamism is the interaction between particles and electromagnetic waves. One such wave species, known as Electromagnetic Ion Cyclotron (EMIC) waves, has come under scrutiny recently due to experimental results calling into question the theoretical energy limits of their interactions with radiation belt electrons. Studying these waves and their interactions is hampered by our inability to accurately determine the size of the source region of these waves. In this study, we investigate a single EMIC wave event observed simultaneously by two separate satellites and use a network of ground‐based radio wave receivers to estimate the size of the EMIC region. We also explain how the method used in this study may be generalized to other EMIC wave events. This method will allow us to carry out statistical analysis of the size of EMIC wave regions in general, aiding future research into the impacts of these waves on the radiation belts.
Key Points
The extent of an EEP‐driving EMIC source region is estimated using conjunctions between in situ and ground‐based observations
A single EMIC wave event is observed simultaneously by conjugate RBSP‐B and Arase spacecraft and ground‐based instruments
Conjugate measurements by the AARDDVARK network are used to track the EEP from the event and estimate the extent and drift rate
Equatorial noise (EN) emissions are observed inside and outside the plasmapause. EN emissions are referred to as magnetosonic mode waves. Using data from Van Allen Probes and Arase, we found ...conversion from EN emissions to electromagnetic ion cyclotron (EMIC) waves in the plasmasphere and in the topside ionosphere. A low‐frequency part of EN emissions becomes EMIC waves through branch splitting of EN emissions, and the mode conversion from EN to EMIC waves occurs around the frequency of M/Q = 2 (deuteron and/or alpha particles) cyclotron frequency. These processes result in plasmaspheric EMIC waves. We investigated the ion composition ratio by characteristic frequencies of EN emissions and EMIC waves and obtained ion composition ratios. We found that the maximum composition ratio of M/Q = 2 ions is ~10% below 3,000 km. The quantitative estimation of the ion composition will contribute to improving the plasma model of the deep plasmasphere and the topside ionosphere.
Plain Language Summary
Equatorial noise (EN) emissions are whistler mode waves. Using Van Allen Probe and Arase (ERG) plasma wave data, we found that EN emissions propagate toward the Earth and are converted to electromagnetic ion cyclotron (EMIC) waves in the deep plasmasphere and the topside ionosphere. We suggest that minor ions with a mass per charge (M/Q) = 2, that is, deuteron or alpha particles, play an important role in this process. The processes reported here are a new generation process of plasmaspheric EMIC waves. Moreover, we determined the ion composition ratio using characteristics of wave dispersion. We derived the altitude profile of the ion composition ratio and identified the maximum ratio of M/Q = 2 ions of about 10% in the deep plasmasphere.
Key Points
The first measurements of the conversion from equatorial noise to EMIC waves are presented
Existence of M/Q = 2 ions (deuteron or alpha particle) in the deep plasmasphere is essential to cause the conversion
The ion composition ratio is quantitatively estimated in the deep plasmasphere using characteristics of the wave dispersion
Using magnetic field and electron density data from the Arase satellite for the period from March 2017 to September 2019, we investigate the spatial properties of Pi2 pulsations in relation to the ...plasmapause over a wide latitudinal range (absolute magnetic latitude, |Mlat|, < 45°) in the inner magnetosphere. Magnetic field disturbances that have high coherence (> 0.7) with Pi2 pulsations in the north‐south (H) component at low‐latitude ground stations on the nightside, are dominantly identified from the magnetic fields in the radial (BR) and compressional (BP) components when the satellite is in the pre‐midnight sector. In particular, high‐coherence BP events are distributed over wide L‐values and latitudinal ranges on the nightside in the pre‐midnight sector. We identify the location of the plasmapause using the electron densities measured by Arase, and found that the BP‐H power ratio and the cross phases of the high‐coherence events show a gradual peak and a clear phase change from 0° to 180° in the vicinity of the plasmapause, respectively. These features indicate that mid‐ and low‐latitude Pi2 pulsations on the nightside are excited by the plasmaspheric virtual resonance mode.
Key Points
A statistical study of off‐equatorial Pi2 pulsations was conducted using magnetic field and electron density data from the Arase satellite
Most events that had high coherence with low‐latitude ground Pi2 were dominated by the compressional component
The cross‐phase and power distributions of high‐coherence events were consistent with the plasmaspheric virtual resonance mode
Background and purpose
A nationwide survey was conducted to understand the epidemiology of cerebral amyloid angiopathy‐related intracerebral hemorrhage (CAA‐related ICH) and cerebral amyloid ...angiopathy‐related inflammation/vasculitis (CAA‐ri) in Japan.
Methods
To estimate the total number and clinical features of patients with CAA‐related ICH and CAA‐ri between January 2012 and December 2014 and to analyze their clinical features, questionnaires were sent to randomly selected hospitals in Japan.
Results
In the first survey, 2348 of 4657 departments responded to the questionnaire (response rate 50.4%). The total numbers of reported patients with CAA‐related ICH and CAA‐ri were 1338 and 61, respectively, and their total numbers in Japan were estimated to be 5900 95% confidence interval (CI) 4800–7100 and 170 (95% CI 110–220), respectively. The crude prevalence rates were 4.64 and 0.13 per 100 000 population, respectively. The clinical information of 474 patients with CAA‐related ICH obtained in the second survey was as follows: (i) the average age of onset was 78.4 years; (ii) the prevalence increased with age; (iii) the disease was common in women; and (iv) hematoma most frequently occurred in the frontal lobe. Sixteen patients with CAA‐ri for whom data were collected in the second survey had the following characteristics: (i) median age of onset was 75 years; (ii) cognitive impairment and headache were the most frequent initial manifestations; and (iii) focal neurological signs, such as motor paresis and visual disturbance, were frequently observed during the clinical course.
Conclusions
The numbers of patients with CAA‐related ICH and CAA‐ri in Japan were estimated.
We present the first direct evidence of an in situ excitation of drift‐compressional waves driven by drift resonance with ring current protons in the magnetosphere. Compressional Pc4–5 waves with ...frequencies of 4–12 mHz were observed by the Arase satellite near the magnetic equator at L ∼ 6 in the evening sector on 19 November 2018. Estimated azimuthal wave numbers (m) ranged from −100 to −130. The observed frequency was consistent with that calculated using the drift‐compressional mode theory, whereas the plasma anisotropy was too small to excite the drift‐mirror mode. We discovered that the energy source of the wave was a drift resonance instability, which was generated by the negative radial gradient in a proton phase space density at 20–25 keV. This proton distribution is attributed to a temporal variation of the electric field, which formed the observed multiple‐nose structures of ring current protons.
Plain Language Summary
During magnetic storms and substorms, energetic ions are sporadically injected into the geospace, which distorts the stable population and velocity distributions of ions in space. At these moments, various plasma instabilities lead to ultra‐low frequency (ULF) wave excitations. The lowest‐frequency waves in the ULF range have a wavelength comparable to the size of the Earth and are typically analyzed using magnetohydrodynamic principles. This approach considers the plasma environment using macroscale parameters such as pressure and density. In this paper, we report a spacecraft observation of a broadband compressional ULF wave that cannot be interpreted using magnetohydrodynamics. Such waves have rarely been reported and analyzed; however, their interaction with energetic ions is important to understand magnetospheric energy dynamics. The plasma conditions were described using the kinetic theory, which involves particle velocity distributions. We observed that a drift resonance occurred between the energetic protons and waves, while the gradient instability condition was satisfied for a part of time. Therefore, we concluded that the wave was in a drift‐compressional mode excited through drift resonance and gradient instability. The interpretation of compressional waves via satellite observations of energetic ions has been receiving increasing attention to understand their excitation mechanism.
Key Points
Pc4–5 compressional ultra‐low frequency waves with an azimuthal wave number of −130 were observed in the nose structure on duskside
Theoretically predicted values of drift‐compressional mode frequency match the observed wave frequency
Both radial ion temperature gradient and drift resonance of 20–25 keV protons serve as energy sources of the wave
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