Search

Hot cracking is a frequent and severe defect that occurs during laser additive manufacturing of superalloys. In this work, a pulsed-wave (PW) laser modulation process was employed to control the solidification microstructure and reduce the hot cracking susceptibility of laser additive manufactured cobalt-based superalloy. The effects of continuous-wave (CW) and PW laser processing modes on the dendrite morphology, element segregation, eutectic phase, and hot cracking of fabricated Co-based superalloys were investigated. Optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to characterize the microstructural characteristics of samples. A two-color pyrometer was used to measure the molten pool temperature variation under different laser processing modes. The results show that coarse columnar dendrites, chain-like eutectic carbides, and hot cracks were observed in the CW sample. In contrast, the fine equiaxed crystals, discrete eutectic carbides, and low-level residual stresses were obtained to avoid hot cracks, owing to the high cooling rate and the periodic melting and solidification of the molten pool under the PW laser processing mode. This work provides a new method for controlling solidification structure and hot cracking of laser additive manufactured Co-based superalloy. [ABSTRACT FROM AUTHOR]

A sustainable and efficient strategy for the synthesis of 3-pyridyl-3,3-disubstituted oxindole derivatives has been achieved via PyBroP (bromotripyrrolidinophosphonium hexafluorophosphate) promoted nucleophilic addition reaction of oxindoles with pyridine N-oxides. The approach worked well under relatively mild conditions. The protocol features a broad substrate scope and good functional group tolerance and gives products in moderate to excellent (52–95%) yields. [ABSTRACT FROM AUTHOR]

Semiconductor thin films for electronic devices are usually produced through processes such as chemical vapor deposition, which requires careful control of the gas flow, heat distribution, and concentration distribution over the substrate to ensure a uniform deposition rate and thickness. Herein, a systematic method is proposed for the theoretical adjustment of metalorganic chemical vapor deposition (MOCVD) process parameters. To this end, a GaN-MOCVD reactor with a vertical injection structure was simulated based on computational fluid dynamics to analyze the stable flow under a fixed flow rate. The orthogonal experimental design was used to analyze the influence of process conditions on film quality. A neural network and genetic algorithm were used to optimize the inlet flow under the stable flow state to render the coefficient of variation <3%. Under these conditions, the flow field in the reactor was stabilized to ensure a uniform thickness for the deposited film. This study provides not only an effective solution for high-quality epitaxial growth but also a theoretical basis for subsequent experiments and equipment improvement. [ABSTRACT FROM AUTHOR]

The dendritic structure, element segregation and Laves phase morphology of laser additive manufactured Inconel 718 were controlled by regulating laser processing parameters. Two typical specimens with different as-fabricated microstructure were obtained. The responses of microstructure and mechanical property of the specimens to direct aging treatment were investigated. The high molten-pool cooling rate from the high laser power (P) of 1200 W and scanning speed (V) of 12 mm/s (P1200/V12) was found to refine the dendrite structure and reduce the Laves phase. The specimen with reduced Nb segregation and discrete Laves phase showed a good aging response with high hardness and tensile strength due to the high-density precipitation of Nb-rich hardening phase. The present work contributes to the control of the microstructure and mechanical properties of Inconel 718. [ABSTRACT FROM AUTHOR]

Background: The duration of antibodies against SARS-CoV-2 in Covid-19 patients remains uncertain. Longitudinal serological studies are needed to prevent disease and transmission of the virus.Methods: In 2020, 414 blood samples were tested, obtained from 157 confirmed Covid-19 patients, in a prospective cohort study in Shanghai.Results: The seropositive rate of IgM peaked at 40.5% (17/42) within 1 month after illness onset and then declined. The seropositive rate of IgG was 90.6% (58/64) after 2 months, remained above 85% from 2 to 9 months and was 90.9% (40/44) after 9 months. Generalized estimating equations models suggested that IgM (P < 0.001) but not IgG significantly decreased over time. Age ≥ 40 years (adjusted odds ratio [aOR] 4.531; 95% confidence interval [CI] 1.879-10.932), and cigarette smoking (aOR 0.344; 95% CI 0.124-0.951) were associated with IgG, and age ≥ 40 years (aOR 2.820; 95% CI 1.579-5.036) was associated with IgM. After seroconversion, over 90% and 75.1% of subjects were estimated to remain IgG-positive 220 and 254 days, respectively. Of 1420 self-reported symptoms questionnaires, only 5% reported symptoms 9 months after onset.Conclusions: In patients with a history of natural infection, anti-SARS-CoV-2 IgG is long-lived, being present for at least 9 months after illness onset. The long duration of natural immunity can mitigate and eliminate Covid-19 and the ongoing pandemic. [ABSTRACT FROM AUTHOR]

Salmonella is the primary cause of community-acquired foodborne infections, so its resistance to antimicrobials, such as aminoglycosides, is a public health issue. Of concern, aminoglycoside resistance in Salmonella is increasing rapidly. Here, we performed a retrospective study evaluating the prevalence of Salmonella harboring armA -mediated aminoglycoside resistance in community-acquired infections and in food or environmental sources. The prevalence rates of armA -harboring Salmonella strains were 1.1/1,000 (13/12,095) and 8.7/1,000 (32/3,687) in outpatient and food/environmental isolates, respectively. All the armA -harboring Salmonella strains were resistant to multiple drugs, including fluoroquinolone and/or extended-spectrum cephalosporins, and most (34/45) belonged to serovar Indiana. The armA gene of these strains were all carried on plasmids, which spanned five replicon types with IncHI2 being the dominant plasmid type. All the armA -carrying plasmids were transferable into Escherichia coli and Acinetobacter baumannii recipients. The conjugation experiment results revealed that the armA -harboring S. Indiana strains had a relatively higher ability to acquire armA -carrying plasmids. The low similarity of their pulsed field gel electrophoresis patterns indicates that the armA -harboring Salmonella strains were unlikely to have originated from a single epidemic clone, suggesting broad armA spread. Furthermore, the genetic backgrounds of armA -harboring Salmonella strains isolated from outpatients exhibited higher similarity to those isolated from poultry than to those isolated from swine, suggesting that poultry consumption maybe an infection source. These findings highlight an urgent need to monitor the prevalence and transmission of armA -harboring Salmonella , especially S. Indiana, to better understand the potential public health threat and prevent the further spread of these strains. [ABSTRACT FROM AUTHOR]

International travel may facilitate the spread of the novel coronavirus disease (COVID‐19). The study describes clusters of COVID‐19 cases within Chinese tour groups travelling in Europe January 16–28. We compared characteristics of cases and non‐cases to determine transmission dynamics. The index case travelled from Wuhan, China, to Europe on 16 January 2020, and to Shanghai, China, on 27 January 2020, within a tour group (group A). Tour groups with the same outbound flight (group B) or the same tourism venue (group D) and all Chinese passengers on the inbound flight (group C) were investigated. The outbreak involved 11 confirmed cases, 10 suspected cases and six tourists who remained healthy. Group A, involving seven confirmed cases and six suspected cases, consisted of familial transmission followed by propagative transmission. There was less pathogenicity with propagative transmission than with familial transmission. Disease was transmitted in shared outbound flights, shopping venues within Europe and inbound flight back to China. The novel coronavirus caused clustered cases of COVID‐19 in tour groups. When tourism and travel opens up, governments will need to improve screening at airports and consider increased surveillance of tour groups—particularly those with older tour members. [ABSTRACT FROM AUTHOR]

We used contact tracing to document how COVID‐19 was transmitted across 5 generations involving 10 cases, starting with an individual who became ill on January 27. We calculated the incubation period of the cases as the interval between infection and development of symptoms. The median incubation period was 6.0 days (interquartile range, 3.5‐9.5 days). The last two generations were infected in public places, 3 and 4 days prior to the onset of illness in their infectors. Both had certain underlying conditions and comorbidity. Further identification of how individuals transmit prior to being symptomatic will have important consequences. [ABSTRACT FROM AUTHOR]

Background: In December 2019, the outbreak of coronavirus disease 2019 (COVID-19) began in Wuhan, China, and rapidly spread to other regions. We aimed to further describe the epidemiological and clinical characteristics of discharged COVID-19 cases and evaluate the public health interventions.Methods: We collected epidemiological and clinical data of all discharged COVID-19 cases as of 17 February 2020 in Shanghai. The key epidemiological distributions were estimated and outcomes were also compared between patients whose illness were before 24 January and those whose illness were after 24 January.Results: Of 161 discharged COVID-19 cases, the median age was 45 years, and 80 (49.7%) cases were male. All of the cases were categorized as clinical moderate type. The most common initial symptoms were fever (85.7%), cough (41.0%), fatigue (19.3%), muscle ache (17.4%), sputum production (14.9%), and there were six asymptomatic cases. 39 (24.2%) cases got infected in Shanghai, and three of them were second-generation cases of Shanghai native cases. The estimated median of the time from onset to first medical visit, admission, disease confirmation, and discharge for 161 cases was 1.0 day (95% CI, 0.6-1.2), 2.0 days (95% CI, 1.5-2.6), 5.2 days (95% CI, 4.6-5.7), 18.1 days (95% CI, 17.4-18.8), respectively. The estimated median of the time from admission to discharge was 14.0 days (95% CI, 13.3-14.6). The time from onset to first medical visit, admission and disease confirmation were all shortened after the Shanghai's first-level public health emergency response. In Cox regression model, the significant independent covariates for the duration of hospitalization were age, the time from onset to admission and the first-level public health emergency response.Conclusions: Local transmission had occurred in Shanghai in late January 2020. The estimated median of the time from onset to discharge of moderate COVID-19 was 18.1 days in Shanghai. Time intervals from onset to first medical visit, admission and disease confirmation were all shortened after the Shanghai's first-level public health emergency response. Age, the first-level public health emergency response and the time from onset to admission were the impact factors for the duration of hospitalization. [ABSTRACT FROM AUTHOR]

Coronavirus disease 2019 (COVID‐19) is an emerging infectious disease first identified in Wuhan City, Hubei Province, China. As of 19 February 2020, there had been 333 confirmed cases reported in Shanghai, China. This study elaborates on the epidemiological and clinical characteristics of COVID‐19 based on a descriptive study of the 333 patients infected with COVID‐19 in Shanghai for the purpose of probing into this new disease and providing reference. Among the 333 confirmed cases in Shanghai, 172 (51.7%) were males and 161 (48.3%) were females, with a median age of 50 years. 299 (89.8%) cases presented mild symptoms. 139 (41.7%) and 111 (33.3%) cases were infected in Wuhan and Shanghai, respectively. 148 (44.4%) cases once had contact with confirmed cases before onset, while 103 (30.9%) cases had never contacted confirmed cases but they had a sojourn history in Wuhan. The onset date of the first case in Shanghai was 28 December, with the peak appearing on 27 January. The median incubation period of COVID‐19 was estimated to be 7.2 days. 207 (62.2%) cases had fever symptoms at the onset, whereas 273 (82.0%) cases experienced fever before hospitalization. 56 (18.6%) adults experienced a decrease in white blood cell and 84 (42.9%) had increased C‐reactive protein after onset. Elderly, male and heart disease history were risk factors for severe or critical pneumonia. These findings suggest that most cases experienced fever symptoms and had mild pneumonia. Strengthening the health management of elderly men, especially those with underlying diseases, may help reduce the incidence of severe and critical pneumonia. Time intervals from onset to visit, hospitalization and diagnosis confirmed were all shortened after Shanghai's first‐level public health emergency response. Shanghai's experience proves that COVID‐19 can be controlled well in megacities. [ABSTRACT FROM AUTHOR]

Polymerization dynamics of single actin filaments coupled with adenosine triphosphate (ATP) hydrolysis is investigated via both theoretical analysis and Brownian dynamics simulations. Brownian dynamics simulations have been applied recently to study the growth behaviors of long filaments as a function of the free actin monomer concentrations, CT, which is found to be in agreement with the associated experiments. In the present study, both ATP cap length and length diffusivity are studied as a function of the free ATP-actin monomer concentrations, CT. The exact analytical expressions are found to be in perfect consistency with Brownian dynamics simulations. Likewise, we find that the length diffusion coefficient is peaked near the critical concentration, CT, cr. It is, therefore, expected that the dependence of length diffusivity on ATP-actin monomer concentrations is utilized to analyze the surprising experiments on the length fluctuations of individual actin filaments. [ABSTRACT FROM AUTHOR]

We present an optofluidic system based on electromagnetic manipulation of a ferrofluid to tune a liquid lens. Both studies of the dynamics of fluid transport and of the optical properties of the liquid lens have been carried out. Thermal and magnetic field simulations of the microcoil actuators are presented. Proof-of-principle experiments demonstrating the adaption of the focal length of the lens have been carried out. It is shown that the lens adaption proceeds in a reversible and reproducible manner, given that the ferrofluid plug moves with a speed below a specific threshold value. Furthermore, the time delay between the actuation and the deflection of the lens surface is studied. [ABSTRACT FROM AUTHOR]

By means of experiment and simulation, we investigated the coupling between the accumulator and the loop in the Tracker Thermal Control System (TTCS) system, which is a typical mechanically pumped carbon dioxide two-phase loop, by studying the system behaviors under the disturbance of the temperature boundary of the condensers, and the step change of the evaporator heat load. We found that the disturbance of the loop affects the accumulator, and in turns, affects the loop itself. If the heat compensation of the accumulator is large enough, e.g., by using the accumulator heater with enough heating power and with a thermal conductance good enough between the heater and the two-phase CO2 inside the accumulator, the loop is controllable over the disturbance. The coupling is a fundamentally important factor to be considered for the design of a stable and controllable two-phase system, such as a mechanically pumped two-phase loop. [ABSTRACT FROM AUTHOR]

Control of solidification structure and crystallographic texture during metal additive manufacturing is a challenging work which attracts the increasing interest of researchers. In the present work, two kinds of scanning strategies (i.e., single-directional scanning (SDS) and cross-directional scanning (CDS) were used to control the solidification structure and crystallographic texture during quasi-continuous-wave laser additive manufacturing (QCW-LAM) of Inconel 718. The results show that the solidification structure and texture are strongly dependent on scanning strategies. The SDS develops a typical fiber texture with unidirectional columnar grains, whereas the CDS develops a more random texture with a mixture of unidirectional and multidirectional grains. In addition, the SDS promotes the continuously epitaxial growth of columnar dendrites and results in the linearly distributed Laves phase particles, while the CDS leads to the alternately distributed Laves phase particles with chain-like morphology and discrete morphology. The changed stacking features of molten-pool boundary and the switched heat flow direction caused by different scanning strategies plays a crucial role on the epitaxial growth of dendrites and the final solidification structure of the fabricated parts. [ABSTRACT FROM AUTHOR]

It is well known that surface roughness always enhances wetting for hydrophilic, but drying for hydrophobic surfaces. In this letter, the authors found that La0.7Sr0.3MnO3 coatings display distinct wettability from superhydrophilicity to superhydrophobictiy, which is tuned by their hierarchical microstructures obtained by annealing the coatings composed of nanopowder at different temperatures. This offers a strong support to Herminghaus’s model [Europhys. Lett. 52, 165 (2000)] which predicts that the material hierarchical structure determines its wettability and widens the range of raw materials for superhydrophobic surfaces. [ABSTRACT FROM AUTHOR]