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Hubei province in China has had the most confirmed coronavirus disease 2019 (COVID-19) cases and has reported sustained transmission of the disease. Although Lu'an city is adjacent to Hubei province, its community transmission was blocked at the early stage, and the impact of the epidemic was limited. Therefore, we summarised the overall characteristics of the entire epidemic course in Lu'an to help cities with a few imported cases better contain the epidemic. A total of 69 confirmed COVID-19 cases and 11 asymptomatic carriers were identified in Lu'an during the epidemic from 12 January to 21 February 2020. Fifty-two (65.0%) cases were male, and the median age was 40 years. On admission, 56.5% of cases had a fever as the initial symptom, and pneumonia was present in 89.9% of cases. The mean serial interval and the mean duration of hospitalisation were 6.5 days (95% CI: 4.8–8.2) and 18.2 days (95% CI: 16.8–19.5), respectively. A total of 16 clusters involving 60 cases (17 first-generation cases and 43 secondary cases) were reported during the epidemic. We observed that only 18.9% (7/37) index cases resulted in community transmission during the epidemic in Lu'an, indicating that the scale of the epidemic was limited to a low level in Lu'an city. An asymptomatic carrier caused the largest cluster, involving 13 cases. Spread of COVID-19 by asymptomatic carriers represents an enormous challenge for countries responding to the pandemic.
This paper investigates the volatility in regime-switching models formulated based on the geometric Brownian motion with its drift and volatility factors randomized with Markov chains. By developing explicit formulas about occupation time of Markov chains, we analysis the difference between global volatility of this model and the volatility caused by Brownian randomness, in order to measure the volatility caused by regime-switching after justifying its existence. Utilizing this structure of volatility, we optimize the methods of volatility parameters estimation.
As China implements the voluntary vaccination programme of one-dose of varicella vaccine (VarV) for decades, robust estimates of the impact of voluntary vaccination era on epidemiology of varicella are needed. We estimated the vaccination coverage (VC) of VarV by using surveillance data on immunisation. The descriptive epidemiological method was used to describe the changing epidemiology of varicella from 2007 to 2018. The screening method was used to estimate the vaccine effectiveness (VE) of VarV. The overall VC for VarV was 71.7%, ranged from 47.7% to 79.5% among 2008–2017 birth cohorts. In total, 16 660 varicella cases were reported during 2007–2018, the incidence increased from 10.0 cases per 100 000 population in 2007 to 65.2 cases per 100 000 population in 2018. A shift in age group of varicella was observed since 2012, with the age increased from 5–9 years to 10–14 years. The overall VE was 79.9%, and the VE increased from 60.1% in 2008 birth cohort to 96.2% in 2017 birth cohort. We found that the overall VE for VarV is moderate, but appears highly effective within 5 years after vaccination. In addition, a shift varicella infection to older ages has occurred at the long-term moderate level VC of one-dose VarV. Therefore, to contain the incidence of varicella and prevent any potential shift to older ages, the introduction of VarV into routine immunisation programme is likely needed in Lu'an.
To investigate whether implementation of a universal salt iodization (USI) programme has sufficient effects on pregnant women in Chongqing, the present study evaluated the iodine nutritional status of pregnant women living in Chongqing by spot urinary iodine concentration (UIC), to provide scientific suggestions to better meet the specific iodine needs of this vulnerable group.
A random spot urine sample and household table salt sample were provided by each participant.
A total of 2607 pregnant women from twenty-six of thirty-nine districts/counties in Chongqing participated.
The overall median UIC of pregnant women was 171·80 μg/l (interquartile range (IQR) = 113·85–247·00 μg/l) and 40·97 % (n 1057) of participants were iodine insufficient. The median iodine in table salt samples was 25·40 mg/kg (IQR = 23·10–28·30 mg/kg); 93·26 % (n 2406) of samples examined were found to be adequately iodized. Iodine nutritional status was not significantly different according to table salt iodization category. Trimester was identified to be statistically associated with UIC (P < 0·01). Seven districts/counties had median UIC below 150 μg/l and one district had median UIC of 277·40 μg/l.
The USI programme in Chongqing prevents iodine deficiency generally, but does not maintain iodine status within adequate and recommended ranges throughout pregnancy. Usage of non-iodized or unqualified iodized salt and the slight change of dietary habits of iodized salt in Chongqing may present a substantial challenge to fight iodine-deficiency disorders; more efforts are needed to ensure adequate iodine intake during pregnancy besides the USI programme.
Bismuth (Bi)-based photocatalytic materials are widely used in the field of photocatalytic degradation of wastewater. In this study, β-Bi2O3/BiOBr heterojunction photocatalysts were prepared by an in situ chemical transformation method. BiOBr molecules are arrayed to cross each other to form a pore around β-Bi2O3. The prepared photocatalyst had a large specific surface area and excellent adsorption and photocatalytic properties. The β-Bi2O3/BiOBr with a molecular ratio of 11.1% had the highest catalytic activity. The result of a degradation experiment, performed with Rhodamine B (RhB) as the target pollutant, revealed that the degradation rate reached 99.85% after 25 min under visible light irradiation. The pore structure can adsorb contaminants and the heterojunction facilitates the separation of photogenerated electron–hole pairs to enhance the photocatalytic properties. The high adsorption performance and heterojunction achieved higher photocatalytic efficiency. This semiconductor photocatalyst with high adsorption performance provides a new approach to control water pollution.
Geochronological, major and trace element, and Sr–Nd–Hf isotopic data are reported for the monzonitic rocks of the Fushan pluton in the Taihang Mountains, central North China Craton, in order to investigate their sources, petrogenesis and tectonic implications. Zircon U–Pb dating results reveal that the Fushan pluton was emplaced during the Early Cretaceous (∼126–124 Ma). The monzonites and quartz monzonites are mainly characterized by calc-alkaline and magnesian features and display light rare earth element (LREE) enrichment and flat heavy REE (HREE) patterns with slightly positive Eu anomalies. They have similar whole-rock initial 87Sr/86Sr ratios (0.70653–0.70819), εNd(t) values (−13.6 to −18.6) and zircon εHf(t) values (−21.8 to −17.3). The primary magma of the Fushan pluton was derived from the partial melting of a spinel-facies amphibole-bearing ancient enriched lithospheric mantle. The monzonitic rocks also have high Ba–Sr and low Y and Yb contents, with high Sr/Y and La/Yb ratios. These geochemical features of monzonitic rocks are not only inherited from the magma source but also significantly enhanced by crystal fractionation during magmatic evolution; e.g. hornblende fractionation increased the Ba–Sr concentrations and Sr/Y ratios. During the Early Cretaceous, the slab sinking and roll-back of the Palaeo-Pacific Plate could have created an ancient big mantle wedge beneath East Asia and induced a lithospheric extensional process in the central North China Craton within an intracontinental setting.
A series of metal oxides (MnFeOx, MnCrOx, MnTiOx, and MnFeTiOx) supported on attapulgite (ATP) were synthesized by coprecipitation for the low-temperature selective catalytic reduction (SCR) of NOx with NH3. Then, they were subjected to appropriate characterizations for their properties (XRD, TEM, BET, XPS, etc.). The catalytic activity of MnFeTiOx/ATP catalyst was over 95% NOx conversion within a wide temperature window between of 175 and 300 °C, and 88% N2 selectivity. Moreover, MnFeTiOx/ATP presented excellent potassium resistance relative to the traditional V–W–Ti catalyst, and its denitration performance was significantly improved. The NOx conversion rate could be restored to nearly 90% at 210 °C after removing potassium via washing of K–MnFeTiOx/ATP. In addition, the MnFeTiOx/ATP showed better SO2 resistance and stability than the traditional V–W–Ti catalyst. Therefore, the MnFeTiOx/ATP catalyst has been proved to have broad prospects in NH3-SCR.
Considering the nonlocal small-scale effect and surface effect, we perform the size-dependent vibration analysis of carbon nanotube (CNT). The modified governing equations for CNT’s vibration behaviors are derived by using the nonlocal Euler–Bernoulli and Timoshenko beam models, together with the consideration of surface tension and surface elasticity. According to the numerical experiments, both small-scale effect and surface effect make a substantial difference. For flexural vibration, size effect for CNT’s vibration behaviors weakens with the increase of its diameter, but strengthens with the increase of the length–diameter ratio; for shear vibration with constant length–diameter ratio, a nonlinear correlation between size effect and CNT’s diameter exists, suggesting that there is a typical diameter for CNTs, which corresponds to the “strongest” size effect. In addition, the effects of elastic substrate modulus, temperature change, and axial preloading on the vibration behaviors and their size-dependence are analyzed, respectively.
Novel cerium-loaded MnTiOx/attapulgite (Ce/MnTiOx/ATP) and cerium-doped MnTiOx/attapulgite (Ce–MnTiOx/ATP) catalysts for low-temperature selective catalytic reduction of nitrogen oxides (NOx) with ammonia (NH3-SCR) were synthesized by co-precipitation methods. The results of catalytic activity testing for the as-prepared Ce–MnTiOx/ATP and Ce/MnTiOx/ATP indicated that the Ce–MnTiOx/ATP catalyst exhibited better catalytic performance with over 80% NOx conversion within a wide temperature window between 170 and 350°, and the highest NOx conversion attained for the Ce–MnTiOx/ATP catalyst was 97.5%. A series of characterization illustrated that the Ce–MnTiOx/ATP catalyst exhibited a higher specific surface area, oxygen vacancy, redox ability, and acid site as compared to that of the Ce/MnTiOx/ATP catalyst. The performance tests showed that the Ce–MnTiOx/ATP catalyst exhibited not only better SO2 & H2O resistance but also higher N2 selectivity and good stability. Therefore, the Ce–MnTiOx/ATP catalyst was testified to be a promising catalyst for NH3-SCR.
The mass-balance of Muztag Ata No. 15 (MZ15) glacier in the eastern Pamir is reconstructed between 1980 and 2012 using an energy-based mass-balance model. The results show that this glacier has been characterized by obvious interannual mass-balance changes during 1980–2012 with a slightly positive mass balance during 1998–2012. Precipitation in the ablation season is a primary driver of these mass-balance fluctuations. Distinct changes in the mass-balance of MZ15 glacier between 1980–1997 and 1998–2012 are thought to be associated with changes in the regionally averaged meridional wind speed and corresponding precipitation in the ablation season. The negative and positive mass-balance phases during 1980–1997 and 1998–2012, respectively, were associated with northerly and southerly wind anomalies in the eastern Pamir and their corresponding decreasing and increasing precipitation. These changes in circulation appear to be linked to the mid-latitude climate. Finally, contrary to the variation of most glaciers on the Tibetan Plateau, glaciers in the Karakoram-western Kunlun-eastern Pamir appear to have retreated more slowly over the past 10 years than during the 1970s-2000. This contrasting trend may be caused by different changes in snowfall and different topography factors in different regions under warming and increased precipitation.
Three gravity cores (LZK1, ZKA4, and CSJA6) from the incised Yangtze paleo-valley comprise a thick sequence of the post-glacial deposit. Nineteen genera (26 species) of the benthic foraminifers are described from these cores, with detailed down-core foraminiferal variations to investigate their paleoenvironmental implications. Three foraminiferal assemblages are recognized for the lower, middle, and upper parts of the cores respectively. The lower part is dominated by Ammonia beccarii var. and Florilus decorus with lower abundance and diversity. In the middle part, the foraminifers are abundant and diverse, dominated by both Ammonia beccarii var. and Elphidium advenum. Cavarotalia annectens, Pararotalia nipponica, and porcellaneous benthic foraminiferal forms are always present, sometimes abundant. The upper part is characterized by the Ammonia beccarii-Elphidium magellanicum assemblage, except for the Core ZKA4, which is barren of foraminifers in this interval. AMS 14C dates and foraminiferal assemblages both confirm that the transgression-regression sequence in these cores belongs to the “Ammonia transgression” during the Holocene. In addition to documenting the post-glacial sea-level fluctuations, the benthic foraminifers also reflect a warmer climate during the early–middle Holocene. The foraminiferal differences among the three cores can be used to interpret the influence of seawater during the post-glacial sea-level fluctuations. The area in the vicinity of Core ZKA4 was affected by marine water only during the middle Holocene, which was much shorter than the areas of the other cores.
We study the instability mechanisms leading to slug flow formation in an inclined pipe subject to gravity forces. We use a phase-field approach, where the Cahn–Hillard model is used to model the interface. At the inlet, a stratified flow is imposed with a specified velocity profile. We validate our numerical results by comparing against previous theoretical models and by predicting the various flow regimes for horizontal and inclined pipes, including stratified flow, slug flow, dispersed bubble flow and annular flow. Subsequently, we focus on slug formation in an inclined pipe and connect its appearance with specific vortical dynamics. A two-dimensional channel geometry is first considered. When the heavy fluid is injected as the top layer, inverted vortex shedding emerges, which periodically impacts on the bottom wall, as it develops further downstream. The accumulation of heavy fluid in the bottom wall causes a back flow that induces rolling waves and interacts with the upstream jet. When the heavy fluid is placed as the bottom layer, the heavy fluid accumulates and initially forms a massive slug at the bottom region, close to the inlet. Subsequently, the heavy fluid slug starts to break into smaller pieces, some of which translate along the pipe. During the accumulation phase, a back flow forms also generating rolling waves. Occasionally, a rolling wave can reach the top of the pipe and form a new slug. To describe the generation of vorticity from the two-phase interface and pipe walls in the slug formation, we study the circulation dynamics and connect it with the resulting two-phase flow patterns. Finally, we conduct three-dimensional (3-D) simulations in a circular pipe and compare the differences between the 3-D flow patterns and its circulation dynamics against the 2-D simulation results.
In this paper, an alternative lattice Boltzmann (LB)model for incompressible flows is proposed. By modifying directly the moments of the equilibrium distribution function (EDF), the continuous expression of the EDF in tensor Hermite polynomials is derived using the moment expansion and then discretizedwith the discrete velocity vectors of the D2Q9 lattice. The present model as well as its counterpart, the incompressible LB model proposed by Guo, reproduces the incompressible Navier-Stokes (N-S) equations for both steady and unsteady flows. Besides, an alternative pressure formula, which represents the pressure as the diagonal part of the stress tensor, is adopted in the present model. Furthermore, in order to enhance the stability of the present LB model, an additional relaxation time pertaining to the non-hydrodynamic mode is added to the BGK collision operator. The present LB model is validated by two benchmark tests: the cavity flow with different Reynolds number (Re) and the flow past an impulsively started cylinder at Re=40 and 550.
In this paper, we consider the transform magnetic (TM) model of electromagnetic scattering in the cavity. By the Polynomial Preserving Recovery technique, we present superconvergence analysis for the vertex-edge-face type finite element. From the numerical example, we can see that the provided method is efficient and stable.
We experimentally investigate the generation of above-threshold harmonics completely from argon atoms on an excited state using mid-infrared femtosecond laser pulses. The highly nonlinear dependences of the observed signal on the pulse energy and polarization of the probe laser pulses indicate its nonperturbative characteristic.
The dislocation movements under the action of electric pulses (athermal effect) at cryogenic conditions were studied by ex situ transmission electron microscopy (TEM) observations and slip trace analysis innovatively. By applying electric pulses directly through aluminum TEM samples in a liquid nitrogen bath, plenty of non-octahedral-like dislocation glides generally forming at high temperatures (e.g., >453 K for aluminum) were observed at cryogenic temperatures (<130 K). Occurrence of the non-octahedral-like dislocation glides indicates a substantial increase in the degrees of freedom for dislocation glides, offering a new/complementary explanation for the acceleration effect of electric pulses on dislocation movements, especially in the sole athermal effect. In comparison, previous theories relied on extra driving force and/or increased dislocation mobility on the octahedral planes in a face-centered cubic metal. The athermal effects of electric pulse were discussed and the selective heating at the dislocation cores was proposed to account for non-octahedral-like dislocation glides.
Beyond the traditional phase conversion or biphase mixing hybrid, we developed the dilute magnesium-doped wollastonite inks and three-dimensional (3D) printing approaches to fabricate the ultrahigh strength bioceramic porous scaffolds. The mechanical strength (>120 MPa) of the porous bioceramics was an order of magnitude higher than the pure wollastonite and other stoichiometric Ca–Mg silicate porous bioceramics. This abnormal but expected improvement in strength in bioceramic scaffolds is equivalent or even superior to the mechanical requirement in load-bearing bone defects. The breakthrough is totally unexpected, and it quickly opens the door for the 3D printing bioceramics manufacture and large-area segmental bone defect repair applications.