HIAF (High Intensity heavy ion Accelerator Facility), a new facility planned in China for heavy ion related researches, consists of two ion sources, a high intensity Heavy Ion Superconducting Linac ...(HISCL), a 45 Tm Accumulation and Booster Ring (ABR-45) and a multifunction storage ring system. The key features of HIAF are unprecedented high pulse beam intensity and versatile operation mode. The HIAF project aims to expand nuclear and related researches into presently unreachable region and give scientists possibilities to conduct cutting-edge researches in these fields. The general description of the facility is given in this article with a focus on the accelerator design.
We perform a comprehensive study of Milky Way (MW) satellite galaxies to constrain the fundamental properties of dark matter (DM). This analysis fully incorporates inhomogeneities in the spatial ...distribution and detectability of MW satellites and marginalizes over uncertainties in the mapping between galaxies and DM halos, the properties of the MW system, and the disruption of subhalos by the MW disk. Our results are consistent with the cold, collisionless DM paradigm and yield the strongest cosmological constraints to date on particle models of warm, interacting, and fuzzy dark matter. At 95% confidence, we report limits on (i) the mass of thermal relic warm DM, m_{WDM}>6.5 keV (free-streaming length, λ_{fs}≲10h^{-1} kpc), (ii) the velocity-independent DM-proton scattering cross section, σ_{0}<8.8×10^{-29} cm^{2} for a 100 MeV DM particle mass DM-proton coupling, c_{p}≲(0.3 GeV)^{-2}, and (iii) the mass of fuzzy DM, m_{ϕ}>2.9×10^{-21} eV (de Broglie wavelength, λ_{dB}≲0.5 kpc). These constraints are complementary to other observational and laboratory constraints on DM properties.
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Mixed organolead halide perovskites (MOHPs), CH3NH3Pb(BrxI1−x)3, have been shown to undergo phase segregation into iodide‐rich domains under illumination, which presents a major challenge to their ...development for photovoltaic and light‐emitting devices. Recent work suggested that phase‐segregated domains are localized at crystal boundaries, driving investigations into the role of edge structure and the growth of larger crystals with reduced surface area. Herein, a method for growing large (30×30×1 μm3) monocrystalline MAPb(BrxI1−x)3 single crystals is presented. The direct visualization of the growth of nanocluster‐like I‐rich domains throughout the entire crystal revealed that grain boundaries are not required for this transformation. Narrowband fluorescence imaging and time‐resolved spectroscopy provided new insight into the nature of the phase‐segregated domains and the collective impact on the optoelectronic properties.
Iodide‐rich clusters form and grow in the MAPb(BrxI1−x)3 single crystal under continuous light illumination. A combination of widefield microscopy and confocal microscopy provides detailed insight into phase segregation in individual MAPb(BrxI1−x)3 microplatelets.
Droplets provide a well-known transmission media in the COVID-19 epidemic, and the particle size is closely related to the classification of the transmission route. However, the term “aerosol” covers ...most particle sizes of suspended particulates because of information asymmetry in different disciplines, which may lead to misunderstandings in the selection of epidemic prevention and control strategies for the public. In this review, the time when these droplets are exhaled by a patient was taken as the initial time. Then, all available viral loads and numerical distribution of the exhaled droplets was analyzed, and the evaporation model of droplets in the air was combined with the deposition model of droplet nuclei in the respiratory tract. Lastly, the perspective that physical spread affects the transmission risk of different size droplets at different times was summarized for the first time. The results showed that although the distribution of exhaled droplets was dominated by small droplets, droplet volume was proportional to the third power of particle diameter, meaning that the viral load of a 100 μm droplet was approximately 106 times that of a 1 μm droplet at the initial time. Furthermore, the exhaled droplets are affected by heat and mass transfer of evaporation, water fraction, salt concentration, and acid-base balance (the water fraction > 98%), which lead them to change rapidly, and the viral survival condition also deteriorates dramatically. The time required for the initial diameter (do) of a droplet to shrink to the equilibrium diameter (de, about 30% of do) is approximately proportional to the second power of the particle diameter, taking only a few milliseconds for a 1 μm droplet but hundreds of milliseconds for a 10 μm droplet; in other words, the viruses carried by the large droplets can be preserved as much as possible. Finally, the infectious droplet nuclei maybe inhaled by the susceptible population through different and random contact routes, and the droplet nuclei with larger de decompose more easily into tiny particles on account of the accelerated collision in a complex airway, which can be deposited in the higher risk alveolar region. During disease transmission, the infectious droplet particle size varies widely, and the transmission risk varies significantly at different time nodes; therefore, the fuzzy term “aerosol” is not conducive to analyzing disease exposure risk. Recommendations for epidemic prevention and control strategies are: 1) Large droplets are the main conflict in disease transmission; thus, even if they are blocked by a homemade mask initially, it significantly contains the epidemic. 2) The early phase of contact, such as close-contact and short-range transmission, has the highest infection risk; therefore, social distancing can effectively keep the susceptible population from inhaling active viruses. 3) The risk of the fomite route depends on the time in contact with infectious viruses; thus, it is important to promote good health habits (including frequent hand washing, no-eye rubbing, coughing etiquette, normalization of surface cleaning), although blind and excessive disinfection measures are not advisable. 4) Compared with the large droplets, the small droplets have larger numbers but carry fewer viruses and are more prone to die through evaporation.
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•The transmission risk of infectious droplets under varying environments and times.•How the viral load, diameter, evaporation, and deposition are linked to infection risk.•The large droplets dominate initially.•The risk of small droplet nuclei (originally from large droplets) must also be taken seriously.
Air pollution in the Arctic caused by local emission sources is a challenge that is important but often overlooked. Local Arctic air pollution can be severe and significantly exceed air quality ...standards, impairing public health and affecting ecosystems. Specifically in the wintertime, pollution can accumulate under inversion layers. However, neither the contributing emission sources are well identified and quantified nor the relevant atmospheric mechanisms forming pollution are well understood. In the summer, boreal forest fires cause high levels of atmospheric pollution. Despite the often high exposure to air pollution, there are neither specific epidemiological nor toxicological health impact studies in the Arctic. Hence, effects on the local population are difficult to estimate at present. Socioeconomic development of the Arctic is already occurring and expected to be significant in the future. Arctic destination shipping is likely to increase with the development of natural resource extraction, and tourism might expand. Such development will not only lead to growth in the population living in the Arctic but will likely increase emission types and magnitudes. Present‐day inventories show a large spread in the amount and location of emissions representing a significant source of uncertainty in model predictions that often deviate significantly from observations. This is a challenge for modeling studies that aim to assess the impacts of within Arctic air pollution. Prognoses for the future are hence even more difficult, given the additional uncertainty of estimating emissions based on future Arctic economic development scenarios.
Key Points
Local Arctic air pollution is among the most severe world wide
Arctic meteorological conditions exacerbate air pollution and create unique pollution formation mechanisms
Future economic activities in the Arctic are expected to increase local air pollution
The Massachusetts Institute of Technology's iLab project has developed a distributed software toolkit and middleware service infrastructure to support Internet-accessible laboratories and promote ...their sharing among schools and universities on a worldwide scale. The project starts with the assumption that the faculty teaching with online labs and the faculty or academic departments that provide those labs are acting in two roles with different goals and concerns. The iLab architecture focuses on fast platform-independent lab development, scalable access for students, and efficient management for lab providers while preserving the autonomy of the faculty actually teaching the students. Over the past two years, the iLab architecture has been adopted by an increasing number of partner universities in Europe, Australia, Africa, Asia, and the United States. The iLab project has demonstrated that online laboratory use can scale to thousands of students dispersed on several continents.
We use observations from the April 2008 NASA ARCTAS aircraft campaign to the North American Arctic, interpreted with a global 3-D chemical transport model (GEOS-Chem), to better understand the ...sources and cycling of hydrogen oxide radicals (HOx≡H+OH+peroxy radicals) and their reservoirs (HOy≡HOx+peroxides) in the springtime Arctic atmosphere. We find that a standard gas-phase chemical mechanism overestimates the observed HO2 and H2O2 concentrations. Computation of HOx and HOy gas-phase chemical budgets on the basis of the aircraft observations also indicates a large missing sink for both. We hypothesize that this could reflect HO2 uptake by aerosols, favored by low temperatures and relatively high aerosol loadings, through a mechanism that does not produce H2O2. We implemented such an uptake of HO2 by aerosol in the model using a standard reactive uptake coefficient parameterization with γ(HO2) values ranging from 0.02 at 275 K to 0.5 at 220 K. This successfully reproduces the concentrations and vertical distributions of the different HOx species and HOy reservoirs. HO2 uptake by aerosol is then a major HOx and HOy sink, decreasing mean OH and HO2 concentrations in the Arctic troposphere by 32% and 31% respectively. Better rate and product data for HO2 uptake by aerosol are needed to understand this role of aerosols in limiting the oxidizing power of the Arctic atmosphere.
A model intercomparison activity was inspired by the large suite of observations of atmospheric composition made during the International Polar Year (2008) in the Arctic. Nine global and two regional ...chemical transport models participated in this intercomparison and performed simulations for 2008 using a common emissions inventory to assess the differences in model chemistry and transport schemes. This paper summarizes the models and compares their simulations of ozone and its precursors and presents an evaluation of the simulations using a variety of surface, balloon, aircraft and satellite observations. Each type of measurement has some limitations in spatial or temporal coverage or in composition, but together they assist in quantifying the limitations of the models in the Arctic and surrounding regions. Despite using the same emissions, large differences are seen among the models. The cloud fields and photolysis rates are shown to vary greatly among the models, indicating one source of the differences in the simulated chemical species. The largest differences among models, and between models and observations, are in NOy partitioning (PAN vs. HNO3) and in oxygenated volatile organic compounds (VOCs) such as acetaldehyde and acetone. Comparisons to surface site measurements of ethane and propane indicate that the emissions of these species are significantly underestimated. Satellite observations of NO2 from the OMI (Ozone Monitoring Instrument) have been used to evaluate the models over source regions, indicating anthropogenic emissions are underestimated in East Asia, but fire emissions are generally overestimated. The emission factors for wildfires in Canada are evaluated using the correlations of VOCs to CO in the model output in comparison to enhancement factors derived from aircraft observations, showing reasonable agreement for methanol and acetaldehyde but underestimate ethanol, propane and acetone, while overestimating ethane emission factors.
Abstract
We use a recent census of the Milky Way (MW) satellite galaxy population to constrain the lifetime of particle dark matter (DM). We consider two-body decaying dark matter (DDM) in which a ...heavy DM particle decays with lifetime
τ
comparable to the age of the universe to a lighter DM particle (with mass splitting
ϵ
) and to a dark radiation species. These decays impart a characteristic “kick velocity,”
V
kick
=
ϵ
c
, on the DM daughter particles, significantly depleting the DM content of low-mass subhalos and making them more susceptible to tidal disruption. We fit the suppression of the present-day DDM subhalo mass function (SHMF) as a function of
τ
and
V
kick
using a suite of high-resolution zoom-in simulations of MW-mass halos, and we validate this model on new DDM simulations of systems specifically chosen to resemble the MW. We implement our DDM SHMF predictions in a forward model that incorporates inhomogeneities in the spatial distribution and detectability of MW satellites and uncertainties in the mapping between galaxies and DM halos, the properties of the MW system, and the disruption of subhalos by the MW disk using an empirical model for the galaxy–halo connection. By comparing to the observed MW satellite population, we conservatively exclude DDM models with
τ
< 18 Gyr (29 Gyr) for
V
kick
= 20 kms
−1
(40 kms
−1
) at 95% confidence. These constraints are among the most stringent and robust small-scale structure limits on the DM particle lifetime and strongly disfavor DDM models that have been proposed to alleviate the Hubble and
S
8
tensions.
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