•SARS-CoV-2 RNA was not detected in the air in a designated hospital for COVID-19.•Environmental surface in medical areas was frequently contaminated.•Strict environmental surface disinfection and ...enhanced hand hygiene were recommended.
Coronavirus disease 2019 (COVID-19) is characterized by risk of nosocomial transmission; however, the extent of environmental contamination and its potential contribution of environmental contamination to SARS-CoV-2 transmission are poorly understood. This study aimed to investigate whether environmental contamination may play a role in SARS-CoV-2 transmission.
Air samples were collected by natural precipitation, and environmental surface samples were collected by conventional surface swabbing. SARS-CoV-2 RNA detection was performed using reverse transcription polymerase chain reaction.
Viral RNA was not detected in the 44 air samples. The positive rates in 200 environmental surface samples in medical areas (24.83%) was higher than that in living quarters (3.64%), with a significant difference (P < .05). The positive rates were 25.00% and 37.50% for the general isolation ward and intensive care unit, respectively, and no significant difference was observed between them (P = .238). The top 5 sampling sites with a positive rate in medical areas were beepers (50.00%), water machine buttons (50.00%), elevator buttons (42.86%), computer mouses (40.00%), and telephones (40.00%).
Most of the touchable surfaces in the designated hospital for COVID-19 were heavily contaminated, suggesting that the environment is a potential medium of disease transmission. These results emphasize the need for strict environmental surface hygiene practices and enhanced hand hygiene to prevent the spread of the virus.
•32,277 craters larger than 200 m are mapped in the landing area, near Mons Rümker.•Craters smaller than 1 km are denser in the east and west parts of the area.•The N (D>1 km) of different geologic ...units in the landing area are calculated.•Radioisotope dating of returned samples can calibrate lunar chronology function.
Chang'e-5 (CE-5) is the first sample-return mission of China's lunar exploration and will be launched in 2020. The planned landing area is near Mons Rümker in Oceanus Procellarum. It is important to have a detailed geological analysis of the landing area prior to the lunar sample collection. The crater size-frequency distribution curve, combined with radioisotope dating of components of the returned sample by CE-5, may allow a refinement of the lunar chronology function. Based on a digital orthophoto map with a pixel size of 1.5 m generated from more than 700 Lunar Reconnaissance Orbiter Camera Narrow Angle Camera images of the CE-5 landing area, all impact craters larger than 200 m in diameter were extracted. Using the resultant crater catalogue of 32,277 craters, a systematic analysis of the landing area including the crater distribution, morphology characteristics, and geologic model ages is conducted. The results show that craters smaller than 1,000 m are denser in the east and the west parts of the region, while those larger than 1,000 m tend to be more concentrated in the central part, particularly within the range of 61.5°W–64.5°W. Within nine geologic units divided using the spectral characteristics, the geologic unit of Em1 (Eratosthenian-aged mare, Em) near the Mons Rümker is the youngest with a model age of 2.02−0.16+0.16 Ga. The three Rümker plateau (IR) units are the oldest parts of the landing area with the largest model age of 3.49−0.12+0.073 Ga. The crater catalogue and the surface model age analysis results can contribute to the CE-5 mission as well as further scientific research.
Chang’E-5 is the first lunar sample return mission of China. The spacecraft was landed in the northwest of the Procellarum KREEP Terrane (43.0576°N, 308.0839°E) on 1 December 2020 and returned 1731 g ...samples from a previously unvisited region. The landing area has been proposed as one of the youngest mare basalt units of the Moon and holds important information of lunar thermal evolution and chronology. However, the absolute model ages estimated in previous studies are quite different, ranging from 2.07 Ga to 1.21 Ga. Such significant difference may be caused by (1) different crater counting areas, (2) different crater diameter ranges, (3) effects of secondary craters, and (4) biases in crater identification. Moreover, the accurate landing site was unknown and the ages were estimated over the Eratosthenian-aged mare unit (Em4) instead. In light of the above unsatisfactory conditions, this study seeks to establish a standard crater size-frequency distribution of the CE-5 landing site. We derived the concentrations of FeO and TiO2 to map out the pure basaltic areas where external ejecta deposits are negligible and thus secondary craters are rare. Based on the geochemistry of basaltic ejecta excavated by fresh craters in the mare unit, the FeO concentration threshold for mapping pure basaltic areas is 17.2 wt.%. The morphologically flat subunits in the pure basaltic areas were selected for crater identification and age dating to exclude the contamination of external ejecta to the best as we could. In the Chang’E-5 sampling site subunit, we detected 313 craters with a diameter greater than 100 m and derived the absolute model age as 1.49−0.084+0.084 Ga. The craters identified in all pure basaltic subunits of Em4 gave the model age of 1.41−0.028+0.027 Ga. As least affected by secondary craters, the crater size-frequency distribution of the sample-collected pure basaltic subunit can provide important constraints for lunar cratering chronology function in combination with isotopic age of returned samples.
Late Cenozoic basaltic lavas in eastern and southeastern China commonly display spectacular columnar joints. In four volcanic fields in this region, we have observed and classified five types of ...colonnade (vertical, inclined, horizontal, fanning upwards, and fanning downwards) that provide information on the cooling regime and emplacement mechanism of the lava flows. In total, we analyzed the geometry and morphology of joints across ten different lava flow areas in the Changle volcanic field (CVF), Luhe volcanic field (LVF), eastern Zhejiang volcanic field (EZVF), and Niutoushan-Linjin Island-Nanding Island volcanic field (NLNVF). Field observations show that columnar-jointed alkaline basalts commonly exhibit narrow and irregular shapes indicating fast cooling. Tholeiites with columnar joints, in contrast, show wide and regular polygons, indicating slower cooling. Vertical columnar joints and other types (horizontal and fanning shaped) have different mature patterns, with the implication that lavas flowed on relatively flat land and in paleo-valleys, respectively. This study suggests a simple qualitative description of different types of colonnade can be made based on their alignment patterns, which represents a direct and easy way to derive solidification processes after lava eruption from colonnaded lavas in outcrop.
•Crack propagation behavior under four typical fatigue overloads was obtained.•The crack-tip strain fields under four overloading cases were measured using DIC.•The virtual extensometer based on ...crack-tip DIC measurement was used to determine COD.•The overloading effects on the crack growth behavior were analyzed from three aspects.
In this paper experimental correlations between da/dN and ΔK and between a vs. N of an extra-low-interstitial titanium (Ti-6Al-4V ELI) alloy under four typical overload conditions (OL, UL, OL-UL and UL-OL) in an otherwise constant amplitude loading were obtained. By means of the digital image correlation (DIC) technique, the crack-tip deformation fields as well as the crack opening process corresponding to the four overloading patterns were measured. The results shown that both the crack propagation behaviors and the crack-tip strain distributions of the Ti-alloy were greatly influenced by the overloading conditions applied. The effect of the overloading pattern (sequence) on the fatigue crack propagation behavior of the Ti-alloy was then analyzed by combining the crack-tip deformation measurements with the fatigue crack propagation results from three possible mechanisms, i.e., the crack-tip blunting effect, the crack closure effect and crack-tip plastic zone effect. It was found that for the present investigated Ti-6Al-4V ELI alloy, the above three mechanisms made contributions in different extents to the fatigue crack growth retardation behavior.
The last glaciation during the late Paleozoic ice age commenced at around the Guadalupian–Lopingian (G–L) boundary and is synchronous with the emplacement of the Emeishan large igneous province. ...Using CA-TIMS zircon U–Pb dating, we obtained an age of 259.51 ± 0.21 Ma for the uppermost tuff from the Puan volcanic sequence in the eastern Emeishan large igneous province, constraining the timing of Emeishan volcanism and providing another candidate age for the G–L boundary. In addition, we determined an age of 259.69 ± 0.72 Ma for a basal claystone in the immediately overlying Longtan Formation from a drill core section in southwest South China. These ages, along with source weathering trends of mudstones from the lower Longtan Formation, and compiled paleotemperature records, indicate an earliest Wuchiapingian cooling coinciding with the onset of the last Permian glaciation. This global cooling is associated with positive shifts in both organic and carbonate carbon isotopic records and likely a decrease in atmospheric pCO2. A hypothesised causal linkage is proposed in which the rapid post-eruptive basaltic weathering of the Emeishan province in an equatorial humid belt may accelerate the atmospheric CO2 consumption and lead to climate cooling. Our work supports the long-term climate cooling effects of large igneous provinces.
•Uppermost tuff from the eastern Emeishan large igneous province is dated at 259.51 ± 0.21 Ma.•Basal claystone of the overlying Longtan Formation is determined at 259.69 ± 0.72 Ma.•Source weathering trends of the Longtan mudstones reveal an earliest Wuchiapingian cooling.•Global-scale cooling is associated with positive shifts in δ13C and decrease in atmospheric pCO2.•Emeishan basaltic weathering in an equatorial humid belt may accelerate CO2 consumption.
•Co-combustion of lignite and waste activated sludge (WAS) is conducted.•Mineral transformation and emission behaviors of heavy metals are determined.•Anorthite, quartz, pyroxene, and albite are the ...main components of lignite-WAS ash.•Effects of O2 concentration and temperature on the volatilization of heavy metals.
Co-combustion of dried waste activated sludge (WAS) and lignite was conducted in a horizontal tube furnace system. The mineral transformation and emission behaviors of Cd, Cr, Ni, Pb, and Zn during combustion were examined. The above heavy metals (HMs) were selected because they are more abundant in WAS than in lignite. In the combustion condition of 1000°C–21% O2–30min, the minerals in lignite ash were mainly anorthite (CaAl2Si2O8), quartz (SiO2), pyroxene Ca(Mg,Fe)Si2O6, and albite (NaAlSi3O8). By contrast, the minerals in WAS ash were mainly quartz (SiO2), anorthite (CaAl2Si2O8), and hematite (Fe2O3). When 90% lignite and 10% WAS were co-combusted, hematite was hardly detected in the combustion product because hematite reacted with quartz and calcium oxide, which are abundant in lignite ash, and generated a large amount of pyroxene. Anorthite and pyroxene were generated continuously during the combustion process, but albite was mainly generated during the first 5min of combustion. High temperature promoted the generation of complex components, such as sodian anorthite (Ca, Na)(Si, Al)2Si2O8 or (Ca, Na)(Si, Al)4O8. High O2 concentration promoted the reaction among the three main mineral elements, i.e., silicon, aluminum, and calcium, and generated a large amount of anorthite. During the co-combustion of WAS and lignite, the volatilization percentages of Cd, Pb, and Zn exceeded 30% after a combustion time of 30min, and the order was Cd>Pb>Zn. By contrast, the volatilization percentages of Cr and Ni were lower than 15%. High temperature caused an increase in the volatility of HMs, especially Zn and Ni, although the volatilization percentage of Ni remained low. High O2 concentration also caused an increase in the volatility of HMs, except for Cr and Ni, which showed a slight increase or decrease with increasing O2 concentration in the inlet atmosphere.
On January 3, 2019, Chang'E-4 (CE-4) probe successfully achieved soft landing on the farside of the Moon. A large number of small craters in the landing area can be found in the high-resolution ...remote sensing images. These small craters played a vital role in the evolution of lunar regolith because of the overturning and mixing of lunar surface material through excavating and ejecting during impact processes. However, the research of the gardening process by small craters and the evolution of farside lunar regolith are still insufficient. This research aims to make quantitative analysis to the evolution of the lunar regolith from regional small impacts and apply them in the CE-4 landing area. Firstly, the processes of excavation and ejection of a single small impact on the lunar surface are analyzed, during which the formation and distribution of lunar regolith are numerically modeled. Then, based on the remote sensing observation and the analysis of regional impact flux, a group of impact events with resulting lunar regolith are modeled by Monte Carlo method. Thirdly, the above analysis is applied in the CE-4 landing area, and the thickness, grain size distribution, and overturning times of the lunar regolith are calculated. Finally, the influencing factors are discussed and evolution process of lunar regolith is summarized. The results indicate that the formation of lunar regolith is controlled by larger impact events, while the surficial overturning and mixing of lunar regolith are mainly caused by smaller impact events. In addition, the lunar regolith is mostly formed in the earlier times because of the high impact flux at that time. For example, the absolute model age of the CE-4 landing area is about 3.5 Ga, while the lunar regolith had mostly been formed before 3.0 Ga and changed slowly afterwards. Our model beyond the observational capability of the Yutu-2's lunar penetrating radar (LPR), and the results can contribute to better understanding of the regional lunar regolith formation and evolution.
•Lunar regolith evolution is quantitatively analyzed with the proposed EMSC.•Lunar regolith formation is mostly controlled by larger impact events.•Lunar regolith in CE-4 landing area is mainly formed before 3.0 Ga.
Support recovery of sparse signals via orthogonal matching pursuit (OMP) has been extensively studied in recent years. In this paper, by exploiting the knowledge about orthogonal projection matrix ...and Schur complement, we study the sufficient conditions for exact support recovery of sparse signals with OMP in the framework of restricted isometry property (RIP). In the noisy case, we prove that under some constraints on the minimum magnitude of the nonzero elements of the K-sparse signal, OMP can exactly recover the support of the signal if the restricted isometry constant δ κ+1 satisfies δ κ+1 <; 1/√K + 1. Our constraints on the minimum magnitude of nonzero elements of the signal are weaker than existing ones. In the noiseless case, although it has been proved that δ κ+1 <; 1/√K + 1 is a sharp condition for exactly recovering any K-sparse signal with OMP, our result shows that under some constraints on the signal, OMP can also exactly recover the signal if δ κ+1 satisfies δ κ+1 <; √2/2.
Highly evolved lithology distributes across the Moon sparsely but serves as a critical record of the extensive differentiation processes of lunar magmas. In contrast to the Apollo-returned highly ...evolved rocks that essentially formed before the end of the Nectarian period, silicic lithologies detected by remote sensing within the nearside Procellarum KREEP Terrane (PKT) have cratering model age as young as ∼2.5 Ga (Chevrel et al., 2009). The formation mechanism of the young silicic magmatism remains enigmatic. Here we present a detailed study of lithic clasts with highly evolved compositions from the northwestern PKT returned by Chang’E-5 mission. Two different types of highly evolved lithic clasts were recognized: (a) Type A clasts predominately consist of granophyric intergrowths of K-feldspar and quartz. They are highly depleted in incompatible elements (except for K, Rb, Cs, and Ba) and have a V-shaped REE pattern, which can be explained by silicate liquid immiscibility (SLI) following the fractionation of merrillite from a KREEP-like melt. The microtextural features of quartz in Type A clasts indicate that they could have crystallized through relatively slow cooling at temperature below 870 °C, supporting a shallow intrusive origin. The silicic intrusion exposed in the interior, rim, and ejecta of Aristarchus crater has a cratering model age of ∼2.5–3.7 Ga, which could be the source for Type A clasts; (b) Type B clast has little MgO, high incompatible element concentrations, and an REE pattern inclined to the right. Thermodynamic calculations indicate that Type B clast likely formed through SLI of the ∼25% residual melt of Em3 basalts in the Chang’E-5 landing region. This is consistent with the crystallization age of 2.57 ± 0.26 Ga for the zirconolite in Type B clast. The highly evolved samples from Chang’E-5 regolith provide new evidence that SLI may have played an important role in the young highly evolved intrusive bodies’ formation on the Moon. Furthermore, our thermodynamic modeling results show that compared to KREEP basalt, partial melting of quartz monzodiorite/monzogabbro at ∼930–1000 °C can produce melts with composition close to lunar granites and felsites. Thus, if a series of silicic volcanisms distributed mostly within the PKT was generated through this mechanism, quartz monzodiorite/monzogabbro may also widely distribute within the lunar nearside upper crust.
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