Photocatalysis is a promising solar energy conversion technique. Here we report a simple but efficient way to fabricate black Ni-doped TiO2 photoanodes for photoelectrochemical water-splitting. The ...black Ni-doped TiO2 photoanodes were fabricated through anodization for nanotube growth and one-step tin metal reduction in argon atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectra were used to characterize the black Ni-doped TiO2 photoanodes. The black Ni-doped TiO2 photoanodes presented large amounts of Ti3+ and oxygen vacancy, which ensured high capability of absorbing visible and infrared light. The black Ni-doped TiO2 photoanodes exhibited an excellent and stable photocatalytic activity compared to undoped TiO2 photoanode. The maximum photoconversion efficiency of the black Ni-doped TiO2 photoanodes was 2.95% at −0.56 V vs Ag/AgCl, which was almost ten times as high as that of the undoped TiO2 photoanode.
•Black Ni-doped TiO2 photoanodes were fabricated through one-step Sn-reduction.•Maximum photoconversion efficiency was ten times that of undoped TiO2 photoanode.•Ti3+ and oxygen vacancies contribute to the excellent photocatalytic activity.•Black Ni-doped TiO2 demonstrate a good chemical stability.
Reversible emulsion drilling fluids can concentrate the advantages of water-based drilling fluids and oil-based drilling fluids. Most of the existing reversible emulsion drilling fluid systems are ...surfactant-based emulsifier systems, which have the disadvantage of poor stability. However, the use of modified nanoparticles as emulsifiers can significantly enhance the stability of reversible emulsion drilling fluids, but ordinary nanoparticles have the disadvantages of high cost and easily causing environmental pollution. In order to solve the shortcomings of the existing reversible emulsion drilling fluid system, the modified nanocrystalline cellulose was considered to be used as an emulsifier to prepare reversible emulsion drilling fluid. After research, the modified nanocrystalline cellulose NWX-3 can be used to prepare reversible emulsions, and on this basis, reversible emulsion drilling fluids can be constructed. Compared with the reversible emulsion drilling fluid stabilized by HRW-DMOB (1.3 vol.% emulsifier), the reversible emulsion drilling fluid stabilized by the emulsifier NWX-3 maintained a good reversible phase performance, filter cake removal, and oily drill cuttings treatment performance with less reuse of emulsifier (0.8 vol.%). In terms of temperature resistance (150 °C) and stability (1000 V < W/O emulsion demulsification voltage), it is significantly better than that of the surfactant system (temperature resistance 120 °C, 600 V < W/O emulsion demulsification voltage < 650 V). The damage of reservoir permeability of different types of drilling fluids was compared by physical simulation, and the damage order of core gas permeability was clarified: water-based drilling fluid > reversible emulsion drilling fluid > oil-based drilling fluid. Furthermore, the NMR states of different types of drilling fluids were compared as working fluids, and the main cause of core permeability damage was the retention of intrusive fluids in the core.
The reversible emulsion drilling fluid system combines the advantages of both oil-based and water-based drilling fluids, which can achieve ideal results in different stages of drilling and ...completion, and the system can be reused to effectively reduce costs. However, the research on reversible emulsions mainly focuses on the development of new reversible emulsifiers, while the specific phase transformation mechanism of reversible emulsion systems is still unclear. In this paper, a stable reversible emulsion was prepared using the reversible emulsifier DMOB as a raw material, and the reversible emulsion performance of the alkali response from the O/W emulsion phase to the W/O emulsion was studied. The microstructure of reversible emulsions was studied by a microscope, a cryogenic transmission electron microscopy, and a laser particle size analyzer. The changes in macroscopic properties of reversible emulsions in the process of alkali conversion were studied by pH, conductivity, demulsification voltage, static stability, viscosity, rheology, and other indicators, and the conversion mechanism of reversible emulsions from O/W emulsion ⟶ bicontinuous structure ⟶ O/W/O emulsion ⟶ W/O emulsion was clarified. The details are as follows: in the first stage, when the amount of NaOH ≤ 0.43 vol.%, the overall particle size of the emulsion decreases first and then increases with the increase in NaOH dosage. In the second stage, when the amount of NaOH was 0.45 vol.%, a double continuous structure was formed inside the emulsion. In the third stage, when the amount of NaOH is 0.48 vol.%, the O/W/O emulsion is formed, and with the increase in stirring time, the internal oil droplets gradually accumulate and are discharged from the water droplets, and finally, the W/O emulsion is formed. In the fourth stage, when the dosage of 0.50 vol.% ≤ NaOH ≤ 5.00 vol.%, the W/O emulsion was formed, and with the increase of NaOH dosage, the structure and compactness between water droplets increased first and then decreased. In the whole process, with the increase in the amount of NaOH solution, the total particle size of the emulsion first decreased and then increased.
Reversible emulsification drilling fluids can achieve conversion between oil-based drilling fluids and water-based drilling fluids at different stages of drilling and completion, combining the ...advantages of both to achieve the desired drilling and completion effects. The foundation of reversible emulsion drilling fluids lies in reversible emulsions, and the core of a reversible emulsion is the reversible emulsifier. In this study, we prepared a reversible emulsifier, DMOB(N,N-dimethyl-N′-oleic acid-1,4-butanediamine), and investigated the reversible phase inversion process of reversible emulsions, including the changes in the reversible emulsifier (HLB) and its distribution at the oil–water interface (zeta potential). From the perspective of the acid–alkali response mechanism of reversible emulsifiers, we explored the reversible phase inversion mechanism of reversible emulsions and reversible emulsification drilling fluids. It was revealed that the reversible phase inversion of emulsions could be achieved by adjusting the pH of the emulsion system. Then the proportion of ionic surfactants changed in the oil–water interface and subsequently raised/lowered the HLB value of the composite emulsifier at the oil–water interface, leading to reversible phase inversion of the emulsion. The introduction of organic clays into reversible emulsification drilling fluid can affect the reversible conversion performance of the drilling fluids at the oil–water interface. Thus, we also investigated the influence of organic clays on reversible emulsions. It was demonstrated that a dosage of organic clay of ≤2.50 g/100 mL could maintain the reversible phase inversion performance of reversible emulsions. By analyzing the microstructure of the emulsion and the complex oil–water interface, we revealed the mechanism of the influence of organic clay on the reversible emulsion. Organic clay distributed at the oil–water interface not only formed a complex emulsifier with surfactants, but also affected the microstructure of the emulsion, resulting in a difficult acid-induced phase transition, an easy alkali-induced phase transition, and improved overall stability.
Using a new and direct measure of investor attention generated from the SEC's EDGAR log files, we revisit the stock return predictability of call-put implied volatility spread through the lens of ...investor attention. We find that as investor attention heightens, the volatility spread return predictability becomes more pronounced, providing favorable evidence for the informed trading hypothesis as opposed to the mispricing hypothesis. More importantly, we document the construction and profitability of spread-and-high-attention portfolios. A portfolio that goes long on stocks with the highest investor attention and the highest volatility spread and short on stocks with the highest attention and the lowest volatility spread generates a Fama-French 5-factor monthly alpha of 2.43%.
We suggest that the distortion of the positive risk–return relation in the ICAPM is a consequence of trading by informed investors to exploit mispricing. We hypothesize and demonstrate that a ...non‐positive (strongly positive) risk–return relation following positive (negative) market returns is attributed to short‐selling (purchasing) of overpriced (underpriced) stocks along with optimistic (pessimistic) expectations conditional on good (bad) market news. We verify this asymmetry in the risk–return relation through the indirect risk–return relation conditional on good (bad) market news. We also find that the attenuation (reinforcement) of the positive risk–return relation is more profound in high‐ (low‐) sentiment periods.
Stocks can be mispriced for at least two reasons: value-relevant information is not timely incorporated or investor sentiment can induce mispricing. Using the mispricing measure proposed by ...Stambaugh, Yu, and Yuan (2015), we show that informed trading in the options market, proxied by the implied volatility spread, can substantially alleviate stock mispricing. Higher implied volatility spread reliably predicts subsequently lower stock mispricing after controlling for an array of economic variables including firm size, illiquidity, idiosyncratic volatility, institutional ownership, and investor's divergence of opinions. In addition, this effect is more pronounced when the options trading volume is higher, consistent with the notion that higher options trading volume provides better camouflage for informed trading in the spirit of Kyle (1985). Our findings highlight the importance of information incorporation to reduce asset mispricing. We further show that a self-financing monthly portfolio that goes long on most underpriced stocks and short on most overpriced stocks when the implied volatility spread is the lowest yields statistically and economically significant abnormal returns.
Investor Attention Strategy Wang, Xuewu (Wesley)
The journal of behavioral finance,
10/2017, Volume:
18, Issue:
4
Journal Article
Peer reviewed
This article documents the motivation, the construction, and the profitability of an investment strategy based on investor attention in the options market. Using the option volume after a 1-week ...dormant period as a proxy for investor attention, the author shows that heightened investor attention after the dormant period has rich investment implications. A portfolio constructed on the basis of volume spike events immediately after the dormant period generates an abnormal return of 68 basis points on a monthly basis (8.16% on an annualized basis). This abnormal return is robust to risk adjustment using standard asset pricing models. The author's findings constitute strong evidence that it is profitable for outside investors to mimic attentive investors in the options market and reap economically and statistically significant profits.
•This study indicates that the companies in emerging markets may have partially different mechanisms to select flotation methods from the ones in developed markets.•Companies with high levels of ...information asymmetry tend to choose private placements and avoid either public offerings or rights issues.•The ownership structure does not play a key role in a company’s choice of flotation method.•The removal of profitability requirements boosts the popularity of private placements and allows companies to raise capital while limiting the adverse selection cost.
Using a comprehensive sample of Chinese seasoned equity offerings, we compare three major equity flotation methods employed by listed firms in China: rights issues, public offerings, and private placements. The dominant flotation method changed significantly around 2005. We examine the valuation effects of the three methods before and after 2005 and identify the determinants affecting the choice of flotation method. Our results support the information asymmetry hypothesis in that firms with high levels of information asymmetry tend to choose private placements and avoid either public offerings or rights issues. Ownership structure does not seem to be a key factor in determining the selection of flotation method. Profitability requirements of refinancing prevent many listed firms from raising additional capital externally. The removal of profitability requirements for private placements in 2006 boosts the popularity of private placements and explains the shift from rights issues to private placements to some extent.
Relative permeability modifier (RPMs) is a water control technique that is implemented for enhancing gas recovery rates and prolonging well productive life during fracturing the tight gas reservoir. ...RPMs filtrate into formation for a certain depth along with the fracturing fluid to control water output by a “drag” effect on water phase only. To optimize RPM treatment, both experimental investigation and numerical simulation are used in this paper. In laboratory, transient core-flooding tests were conducted to investigate the water control performance of newly formulated polymer (RPM). The relative permeability of gas was corrected due to gas volume changes during displacement. The results showed that the selective water control effect of RPM by reducing water relative permeability dramatically with little impact on gas relative permeability. The RPM concentration was optimized as 0.01 %XSJ-14(A)+0.05 %XSJ-14(B) while injection volume as 5PV by comparison of relative permeability curves. A 2D fracture model of a tight gas model was built to compare the production before and after RPM treatment. The results of numerical simulation confirmed the different flow control effect of RPM on water and gas. A sensitivity analysis was conducted for the effect of fracture length, fracture conductivity, RPM filtration and RR value. The results indicate that there are limits of all the factor on RPM’s water control performance.
