The formation mechanism for the stopping vortex ring (SVR) and its effects on the development of starting jets have been systematically investigated. The radial inward flow near the nozzle exit, arising from the pressure difference caused by the deceleration of starting jets, is considered to be the main contributing factor to the formation of the SVR. The formation process can generally be divided into (i) the rapid accumulation stage ($t_d^*\leq 1$) and (ii) the development stage ($t_d^*>1$), where $t_d^*$ is the formation time defined by the duration of the deceleration stage. For starting jets with different $(L/D)_d$, the final circulation value and circulation growth rate of the SVR can be scaled by $[(L/D)_d]^{-0.5}$ and $[(L/D)_d]^{-1.5}$, respectively. Here $(L/D)_d$ represents the stroke ratio during the deceleration stage. Analysing the temporal evolution of fluid parcels in the vicinity of the nozzle exit reveals that SVR entrains fluid from both inside and outside of the nozzle. Additionally, the influence of the SVR on the leading vortex ring and the trailing jet has been examined, with particular attention to its effects on the propulsive performance of the starting jet. The SVR affects the profiles of axial velocity and gauge pressure at the nozzle exit, thereby enhancing the generation of total thrust during the deceleration stage. Analysis has shown that depending on the deceleration rate, SVR can enhance the average velocity thrust by at least $10\,\%$ and compensate for up to a $60\,\%$ reduction in pressure thrust due to deceleration.

To evaluate the variations in COVID-19 case fatality rates (CFRs) across different regions and waves, and the impact of public health interventions, social and economic characteristics, and demographic factors on COVID-19 CFRs, we collected data from 30 countries with the highest incidence rate in three waves. We summarized the CFRs of different countries and continents in each wave through meta-analysis. Spearman’s correlation and multiple linear regression were employed to estimate the correlation between influencing factors and reduction rates of CFRs. Significant differences in CFRs were observed among different regions during the three waves (P < 0.001). An association was found between the changes in fully vaccinated rates (rs = 0.41), population density (rs = 0.43), the proportion of individuals over 65 years old (rs = 0.43), and the reduction rates of case fatality rate. Compared to Wave 1, the reduction rates in Wave 2 were associated with population density (β = 0.19, 95%CI: 0.05–0.33) and smoking rates (β = −4.66, 95%CI: −8.98 – −0.33), while in Wave 3 it was associated with booster vaccine rates (β = 0.60, 95%CI: 0.11–1.09) and hospital beds per thousand people (β = 4.15, 95%CI: 1.41–6.89). These findings suggest that the COVID-19 CFRs varied across different countries and waves, and promoting booster vaccinations, increasing hospital bed capacity, and implementing tobacco control measures can help reduce CFRs.

The X-ray emissions in the interaction of 3–6 MeV Xe23+ ions into thick solid In target are measured. The projectile-to-target and target Lα/Lβ X-ray production intensity ratios are observed to strongly depend on the projectile energy. The dependence deviates from Coulomb ionization predictions, which implies the important roles of coupling between subshells and the activation of 4fσ rotational couplings for projectile energy larger than 5 MeV.

Uranium-series dating of oxygen and carbon isotope records for stalagmite SJ3 collected in Songjia Cave, central China, shows significant variation in past climate and environment during the period 20–10 ka. Stalagmite SJ3 is located more than 1000 km inland of the coastal Hulu Cave in East China and more than 700 km north of the Dongge Cave in Southwest China and despite minor differences, displays a clear first-order similarity with the Hulu and Dongge records. The coldest climatic phase since the Last Glacial Maximum, which is associated with the Heinrich Event 1 in the North Atlantic region, was clearly recorded in SJ3 between 17.6 and 14.5 ka, in good agreement in timing, duration and extent with the records from Hulu and Dongge caves and the Greenland ice core. The results indicate that there have been synchronous and significant climatic changes across monsoonal China and strong teleconnections between the North Atlantic and East Asia regions during the period 20–10 ka. This is much different from the Holocene Optimum which shows a time shift of more than several thousands years from southeast coastal to inland China. It is likely that temperature change at northern high latitudes during glacial periods exerts stronger influence on the Asian summer monsoon relative to insolation and appears to be capable of perturbing large-scale atmospheric/oceanic circulation patterns in the Northern Hemisphere and thus monsoonal rainfall and paleovegetation in East Asia. Climatic signals in the North Atlantic region propagate rapidly to East Asia during glacial periods by influencing the winter land–sea temperature contrast in the East Asian monsoon region.

Exposure age dating using in situ10Be and 26Al is a very useful technique for dating fluvial terraces. This is especially true in semiarid regions where other methods suffer from a paucity of suitable dating materials. This article describes sample preparation procedures and analytical benchmarks established at the Xi’an Accelerator Mass Spectrometry (AMS) Center for the study of in situ10Be and 26Al. Four intercomparison samples were analyzed in the study, using an improved sample preparation method. The exposure age results are shown to be in good agreement with published data, and demonstrate the reliability of the dating method. This article also presents new 10Be and 26Al results from quartz samples collected from a series of fluvial terraces from Guanshan River, along the Qilian Shan, northeastern Tibetan Plateau. The ages of three fluvial terraces from the Jinfosi site are shown to be (56.4±5.3) ka for T3, (10.7±1.0) ka for T2, and (7.2±1.0) ka for T1. The dating results are consistent with published data from the same region (10Be, 14C, and optically stimulated luminescence dating methods). A comparison of high-resolution climate records with age constraints for the terrace formation shows a close relationship between terrace formation and climate change.

Recent research activities relevant to high energy density physics (HEDP) driven by the heavy ion beam at the Institute of Modern Physics, Chinese Academy of Sciences are presented. Radiography of static objects with the fast extracted high energy carbon ion beam from the Cooling Storage Ring is discussed. Investigation of the low energy heavy ion beam and plasma interaction is reported. With HEDP research as one of the main goals, the project HIAF (High Intensity heavy-ion Accelerator Facility), proposed by the Institute of Modern Physics as the 12th five-year-plan of China, is introduced.

In order to identify the density and material type, high energy protons, electrons, and heavy ions are used to radiograph dense objects. The particles pass through the object, undergo multiple coulomb scattering, and are focused onto an image plane by a magnetic lens system. A modified beam line at the Institute of Modern Physics of the Chinese Academy of Sciences has been developed for heavy-ion radiography. It can radiograph a static object with a spatial resolution of about 65 µm (1 σ). This paper presents the heavy-ion radiography facility at the Institute of Modern Physics, including the beam optics, the simulation of radiography by Monte Carlo code and the experimental result with 600 MeV/u carbon ions. In addition, dedicated beam lines for proton radiography which are planned are also introduced.

The electron emission yield γ induced by Ne2+ and O2+ impacting on a clean tungsten surface has been measured. The range of projectile energy is from 3 keV/u to 14 keV/u. The total electron yield gradually increases with the projectile velocity. It is found simultaneously that the total electron yield for O2+ is larger than the total electron yield for Ne2+, which is opposite to the results for higher projectile velocity. After considering the contribution from recoiling atoms to the energy distribution and electron emission yield, we find that recoiling atoms are of crucial importance in electron emission in our energy range. Thus, the unexpected results in our experiment can be explained successfully.

X-ray emission from Kr13+ ions in the energy range 1.2–3.6 MeV in steps of 0.6 MeV impacting on an Au target was investigated on electron cyclotron resonance ion source at the Heavy Ion Research Facility in Lanzhou. It was found that a shift of the X-ray lines to the higher energy side occurred. We measured the relationship between the characteristic of X-ray yield of Au M X-rays and Kr L X-rays as a function of incident energy. Furthermore, M-shell X-ray production cross-section of Au induced by Kr13+ was measured. The measured cross-section of target is compared to the classical binary-encounter approximation and plane-wave-born approximation theoretical model, which is a significant different between experimental and theoretical model.

In this work, we review current trends in China to investigate beam plasma interaction phenomena. Recent progresses in China on low energy heavy ions and plasma interaction, ion beam-plasma interactions under the influences of magnetic fields, high energy heavy ion radiography through marginal range method, energy deposition of highly charged ions on surfaces and Raman spectroscopy of surfaces after irradiation of highly charged ions are presented.

Total electron emission yield for impact of slow Neq+(q = 2, 4, 6, 8) ions with various kinetic energy under normal incidence on n-type Si has been measured. It is shown that for the same charge state, the total electron yield γ increases linearly as the kinetic energy of projectile at impact increases, up to velocities corresponding to the “classical” threshold. Separation of kinetic electron yield γKE and potential electron yield γPE shows that γPE is proportional to the ion charge state and γKE increases linearly with projectile velocity. Finally, based on “single hole without hopping” hypothesis, the expression of the “CRF” F(q) is given, and the relation between γKE and q is obtained successfully for the first time, which is also a basis for judging whether the “trampoline effect” exists.

Paleoenvironmental and paleogeomagnetic tracing studies from Chinese loess 10Be have progressed in recent years (Zhou et al. 2007a,b, 2010). In this approach, 10Be flux determined from sediment concentration and accumulation rate may be used to recover information about paleomonsoon rainfall rates as well as past variations in the geomagnetic field strength. However, these methods require that a correction be made for residual undecayed 10Be in remobilized dust. To better understand the feature of the 10Be signals related to the remobilized dust, we report the first observational study on 10Be concentration of modern falling dust using the 3MV multi-element accelerator mass spectrometer (AMS) in the Xi'an AMS Center. Ten samples collected at Ansai observation station (109°19′E, 36°51′N) in northern China from May 2008 to June 2009 are measured along with 3 chemical blanks. The results clearly show that the 10Be content of modern falling dust is relatively uniform, with a mean value of 1.21 x 108 atoms/g, a measurement similar to that of Chinese loess (Zhou et al. 2007a) and to the value found in the study by Shen et al. (2009) on dust 10Be falling near Dingbian, China (1.25 ± 0.06 x 108 atoms/g). Despite the fact that modern dust flux is much higher in spring relative to summer in northern China, 10Be concentration in falling dust remains fairly constant. In addition, we find that dust 10Be concentration is roughly independent of the local precipitation changes. This feature might be considered as an analogue to improve our understanding on the fundamental information of the source component contained in loess 10Be records and its spatial/temporal distribution features.

X-ray emission from Xe30+ ions at 350–600 keV impacting on an Au target was investigated at the Heavy Ion Research Facility at Lanzhou. Characteristic X-rays of Xe ions at energy of about 1.65 keV were observed. This X-ray emission is induced by the decay of very high Rydberg states of Xe ions. It was also found that the yield of such characteristic X-rays is decreasing with increasing the projectile kinetic energy. Simultaneously, the yield of the characteristic Au X-rays from the M shell increases also. These phenomena are qualitatively analyzed with the classical Coulomb over the Barrier Mode (COBM) for highly charged ions interacting with solid state surfaces.

Sn-doped BaO–TiO2–ZnO (BTZ) microwave ceramic materials were investigated as a function of SnO2 content. Addition of a small amount of SnO2 (0.01–0.06 wt%) lowered the sintering temperature of the system to 1160 °C and also greatly reduced the dielectric loss (tan δ), which is closely related to the insulation resistivity. The Sn-doped BTZ materials were found to have excellent dielectric properties at 1 GHz with dielectric constant Ε ≈tangent tan δ ≤ 1 × 10−4, temperature coefficient of dielectric constant, αΕ = 0 ± 30 ppm/°C, and volume resistivity ρv ≥ 1013 ω cm.