•We examine the effect of government responses of G7 countries to COVID-19.•We focus on reaction of G7 stock market returns.•We show the importance of lockdowns, travel bans, and economic ...stimulus.•Lockdowns resulted in cushioning the effects of COVID-19 most.
This paper examines the effect of government responses of G7 countries to the coronavirus pandemic (COVID-19) on stock market returns. Using time-series data, we show that lockdowns, travel bans, and economic stimulus packages all had a positive effect on the G7 stock markets. However, lockdowns were most effective in cushioning the effects of COVID-19. Our results are robust to different measures of returns and controls for other factors of returns.
It has been proven that the use of colloidal templates is a facile, flexible strategy to create the periodic micro/nanostructured arrays in comparison with photolithography, electron beam lithography
...etc
. Utilizing colloidal monolayers as templates or masks, different periodic micro/nanostructured arrays including nanoparticle arrays, pore arrays, nanoring arrays and nanorod/nanotube arrays can be fabricated by chemical and physical processes. Chemical routes, including direct solution/sol dipping strategy, wet chemical etching, electrodeposition, electrophoretic deposition
etc.
have advantages of simple operation and low costs. However, they have some disadvantages of impurities on surface of arrays due to incomplete decomposition of precursors, residue of surfactants in self-assembling or electrochemical deposition. More importantly, it is quite difficult to achieve very uniform morphology of micro/nanostructure arrays on a large-area by the above routes. Whereas another method, a physical route (for instance: reactive ion etching, pulsed laser deposition, thermal evaporation deposition, atomic layer deposition, sputtering deposition), combining with colloidal monolayer template can well resolve these problems. In this review, we focus on introducing the recent progress in creating micro/nanostructured arrays based on colloidal templates with physical routes. The parameters of the microstructure or nanostructure can be tuned by colloidal templates with different periodicity and experimental conditions of the physical processes. The applications of micro/nanostructured arrays with controllable morphology and arrangement parameters in self-cleaning surfaces, enhanced catalytic properties, field emitters
etc.
are also presented in the following sections.
The recent progress in the creation and application of micro/nanostructured arrays based on colloidal templates assisted by physical processes is introduced. It is helpful to design, fabricate novel periodic arrays according to need by selecting suitable routes for different applications.
An effective and inexpensive method is developed to fabricate periodic arrays by sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. By a colloidal ...template induced precursor solution dipping strategy, different periodic arrays of semi‐hollow sphere array, inverse opal with monolayer pore arrays and hole arrays are obtained under different conditions. After magnetron sputtering deposition, their morphologies are changed to novel micro/nanostructured arrays of honeycomb‐shaped arrays, hollow cavity arrays, and regular network arrays due to multiple direction deposition of sputtering deposition and shadow effect. After coating a gold thin layer, these periodic micro/nanostructured arrays are used as SERS active substrates and demonstrate a very stable SERS performance compared with periodic arrays achieved by direct colloidal template‐induced chemical deposition. Additionally, a honeycomb‐shaped array displays better SERS enhancement than that of a hollow cavity array or a regular network array. After optimization of honeycomb‐shaped arrays with different periodicities, an array with periodicity of 350 nm demonstrates much stronger SERS enhancement and possesses a low detection limit of 10−11 M R6G. Such stable SERS performance is useful for practical application in portable Raman detecting devices to detect organic molecules.
Via a colloidal template‐induced precursor solution dipping strategy, a semi‐hollow sphere array is formed, and its morphology changed to a novel ordered honeycomb‐shaped micro/nanostructured array after magnetron sputtering deposition. After coating a gold thin layer, the periodic array is used as SERS active substrate and demonstrates very stable SERS performance.
The dynamic characteristics of supersonic double-parameter jets and their interaction with the molten pool were experimentally studied. The effects of jet inclination angles and gas flow ratios on ...gas intensity, coalescence characteristics, and dynamic parameter distributions were discussed. The characteristics of the cavity formed by the interaction of the jet and molten pool were revealed. The results show that the jet inclination angle has more influence on the jet coalescence compared with the gas flow rate. However, the gas flow ratio plays a decisive role in the velocity distribution along the jet centerline compared with the jet inclination angle. The velocity peaks of the double-parameter jets were obviously different at fixed axial distances. Compared with other variables, the small-nozzle inclination has a greater impact on the cavity diameter, while the large-nozzle flow ratio has a greater impact on the cavity depth. The depth and width of the cavity formed by the double-parameter jets are more advantageous than that formed by the single-parameter jets. Furthermore, the double-parameter jets were applied to the actual smelting of a 260t converter.
The jet behavior of interlaced multiple nozzles and the impingement of multiple jets onto the surface of the molten metal bath in a steelmaking converter are numerically studied. The interlaced jet ...hydrodynamic behaviors such as jet profile, coalescence characteristics, and dynamic parameter distributions penetration depth and impact area, as well as time-dependent evolution of liquid bath are discussed. The results are compared with traditional nozzles. It is found that the single nozzle characteristics of staggered jet are similar to those of traditional jet. However, two sets of staggered nozzles with different flow rate and inclination angle having a less disturbance flows, cause weaker coalescence of the jets and larger area surrounded by isovelocity in the molten pool. In the initial stage of the interaction between the interlaced nozzles and the molten pool, the “low stirring zone” is more likely to concentrate in the outer side near the furnace wall than in the center of the molten pool. Two cavities, one deep and one shallow, are formed on the bath surface. The average depth of the two cavities is similar to traditional nozzles, and the diameter of the cavity is increased by about 11% compared to traditional nozzles.
The heat transfer mechanism and water-cooling effect during oxygen lance blowing changes by slag sticking at the nozzle. In order to effectively overcome this problem, in this study, the equivalent ...heat transfer method was applied to modify the heat transfer coefficient of the oxygen lance nozzle under different slag thicknesses and steel slag thermal conductivities. In addition, the gas–liquid two-phase heat transfer model was established by computational fluid dynamics numerical simulation, and the cooling effects for different types of oxygen lance nozzles were calculated by the improved model. The results show that the error rate between the calculated value of the modified model and the field measured value was reduced to 3.3%–4.6%. The nozzle with double angle and double flow design was found to be conducive to the improvement of the cooling system. In this study, the best cooling effect was obtained when the flow ratio of large nozzles and small nozzles is 60%/40% and the angle is 12°/17°.
A facile and general strategy is presented for homogenous and ultrathin metal sulfide wrapping on plasmonic metal (PM) nanoparticles (NPs) based on a thiourea-induced isotropic shell growth. This ...strategy is typically implemented just via adding the thiourea into pre-formed PM colloidal solutions containing target metal ions. The validity of this strategy is demonstrated by taking the wrapped NPs with Au core and CuS shell or Au@CuS NPs as an example. They are successfully fabricated via adding the thiourea and Cu2+ solutions into pre-formed Au NP colloidal solution. The CuS shell layer is highly homogenous (<10% in relative standard deviation of shell thickness), regardless of the NPs’ shape or curvature. The shell thickness can be controlled from tens down to 0.5 nm just by the addition of different amounts of shell precursors. The formation of the shell layer on the Au NPs can be attributed to the alternative deposition of Cu2+ and S2– ions on the thiourea-modified surface of Au NPs in the solution, which induces the isotropic shell growth. Further, this strategy is of good universality. Many other sulfide-wrapped PM NPs, such as Ag@CuS, Au@PtS2, Au@HgS, Ag@Ag2S NPs, and Ag@CuS nanorods, have been successfully obtained with homogeneous and ultrathin shells. Importantly, such ultrathin sulfide-wrapped PM NPs can be used for surface enhanced Raman scattering (SERS)-based detection of trace heavy-metal ions with strong anti-interference via the ion exchange process between the metal sulfide shell and heavy-metal ions. This study provides a simple and controllable route for wrapping the homogenous and ultrathin sulfide layers on the PM NPs, and such wrapped NPs have good practical applications in the SERS-based detection of trace heavy-metal ions.
In oxygen steelmaking, one important aspect is to depict the splashing induced by the impingement of multiple jets quantitatively. In this paper, experiments were conducted to investigate the splash ...sheets. The results demonstrated that with the decrease of lance height, the sheet area increased, while the sheet height decreased. The sheet diameter was much less affected by the gas flow rate compared to the sheet height. The cavity width-to-depth ratio is a critical parameter affecting the sheet shape. The sheet area produced by the 5-nozzle jet was larger than that produced by the 6-nozzle jet. Taking the sheet area reduction as the critical condition where the cavity mode changes from splashing to penetrating, the critical lance height was investigated under various ejecting conditions. This was further represented by the blowing number as a normalized formula. At last, curve fitting illustrating the conditions that lead to the penetrating mode was conducted.
A facile and low-cost method to prepare periodic Au@metal-organic framework （MOF） （MIL-100（Fe）） nanoparticle arrays was developed. The arrays were fabricated in situ using monolayer colloidal ...crystals as templates, followed by Au deposition on substrates, and annealing. MIL-100（Fe） coatings were applied on the nanospheres using a simple solvent thermal process. The prepared periodic Au@MIL-100（Fe） nanoparticle （NP） arrays were characterized by two peaks in the visible spectra. The first peak represented the surface plasmon resonance （SPR） of the Au nanospheres, and the other peak, or the diffraction peak originated from the periodic structure in the NP array. After modification with 3-aminophenylboronic acid hemisulfate （PBA）, the Au@MIL-100（Fe） NP arrays exhibited sensitive responses to different glucose concentrations with good selectivity. These responses could be due to the strong interaction between PBA and glucose molecules. The diffraction peak was sensitive at low glucose concentrations （less than 12 mM）, whereas the SPR peak rapidly responded at high concentrations. The peaks thus demonstrated satisfactory complementary sensitivity for glucose detection in different concentration regions. These results can be used to develop a dual-channel biosensor. We also created a standard diagram, which can be used to efficiently monitor blood glucose levels. The proposed strategy can be extended to develop different dual-channel sensors using Au@MIL-100（Fe） NP arrays agents. functionalized with different recognition
Surface-enhanced Raman spectroscopy (SERS) can boost the pristine Raman signal significantly which could be exploited for producing innovative sensing devices with advanced properties. However, the ...inherent complexity of SERS systems restricts their further applications in rapid detection, especially in situ detection in narrow areas. Here, we construct an efficient and flexible SERS-based Lab-on-Fiber (LOF) sensor by integrating Ag/Au nanocap arrays obtained by Ag/Au coating polystyrene nanospheres on the optical fiber face. We obtain rich “hot spots” at the nanogaps between neighboring nanocaps, and further achieve SERS performance with the assistance of laser-induced thermophoresis on the metal film that can achieve efficiency aggregation of detected molecules. We achieve a high Raman enhancement with a low detection limitation of 10−7 mol/L for the most efficient samples based on the above sensor. This sensor also exhibits good repeatability and stability under multiple detections, revealing the potential application for in situ detection based on the reflexivity of the optical fiber.
PDF
