The covalent triazine framework CTF-1 as a member of the two-dimensional covalent organic frameworks(COFs) is a category of novel metal-free photocatalysts for water splitting. The large band gap severely restricts its energy conversion efficiency. By means of the first-principles calculations, we proposed the decoration of CTF-1 by anchoring halogen atoms onto benzene moieties for improving the solar-to-hydrogen(STH) efficiency. The electronic structures reveal that the halogen substitution successfully decreases the band gap of CTF-1. Meanwhile, the calculated free energy changes along the reaction pathway indicate that all these COFs can spontaneously drive overall water splitting under light irradiation in a specific acid-base environment. The time-dependent ab initio non-adiabatic molecular dynamics simulations suggest that the electron-hole recombination periods of these COFs fall in a few to tens of nanoseconds. Excitingly, CTF-1 modified by linking six iodine atoms onto the benzene ring in the para-position(CTF-1-6I) shows a quite low band gap of 2.81 eV, indicating that it is a visible-light driven COF for overall photocatalytic water splitting. Correspondingly, CTF-1-6I also exhibits an extraordinarily promising STH efficiency of 3.70%, which is an order magnitude higher than that of the pristine CTF-1. 相似文献
In this study, a novel quad-stable energy harvester (QEH) is developed, in which its coordinates of equilibrium points can be user-defined like programming. This programmable feature distinguishes the proposed QEH from all reported magnet-type or buckling-type vibration energy harvesters. It has the advantage that it is easy to develop a high-performance QEH by appropriately programming these coordinate points and customizing a personalized QEH for different vibration environments. The dynamic model is established by the Ritz method and the Lagrange equation. The analytical steady periodic response is obtained by the average method. When the excitation acceleration is 2 m/s2, the peak power is 575 μW at 8.5 Hz. Also, the influence of the coordinate arrangement of the equilibrium points on the energy harvesting performance is studied. A formula that can quickly determine the equilibrium point coordinates is given, and the QEH designed according to this formula has superior performance. At last, the performance of the designed QEH is compared with other reported vibration energy harvesters. It shows that the QEH has a high average output power (287 μW), high normalized power density (59.8 μW/cm3/g2), and wide operating frequency range (8.4 Hz) among these harvesters.
In rock grouting, idealized 2D-radial laminar flow of yield stress fluids (YSF) is a fundamental flow configuration that is used for cement grout spread estimation. A limited amount of works have presented analytical and numerical solutions on the radial velocity profiles between parallel disks. However, to the best of our knowledge, there has been no experimental work that has presented measured velocity profiles for this geometry. In this paper, we present velocity profiles of Carbopol (a simple YSF), measured by pulsed ultrasound velocimetry within a radial flow model. We describe the design of the physical model and then present the measured velocity profiles while highlighting the plug-flow region and slip effects observed for three different apertures and volumetric flow rates. Although the measured velocity profiles exhibited wall slip, there was a reasonably good agreement with the analytical solution. We then discuss the major implications of our work on radial flow.
The quantum thermalization of the Jaynes–Cummings (JC) model in both equilibrium and non-equilibrium open-system cases is studied, in which the two subsystems, a two-level system and a single-mode bosonic field, are in contact with either two individual heat baths or a common heat bath. It is found that in the individual heat-bath case, the JC model can only be thermalized when either the two heat baths have the same temperature or the coupling of the JC system to one of the two baths is turned off. In the common heat-bath case, the JC system can be thermalized irrespective of the bath temperature and the system–bath coupling strengths. The thermal entanglement in this system is also studied. A counterintuitive phenomenon of vanishing thermal entanglement in the JC system is found and proved. 相似文献
SO2 and NO2 are the most important pollution in atmosphere.An optimized long path(LP)differential optical absorption spectroscopy(DOAS)system of high light intensity at an ultraviolet(UV)wavelength is proposed and used to measure the concentration of SO2 and NO2 simultaneously.In contrast to the traditional DOAS,the system adopted a Y-type optical fiber structure instead of a combination of mirrors in the telescope.The UV light intensity test shows that the light intensity of UV can arrive to above 80% of the max measuring range when the light path reaches 135 m,and the integral time of the spectrograph is only 15 ms.The system is proved to be efficacious through laboratory calibration.The maximum error of SO2 calibration is 4.19%,and is 5.22% for NO2.The error of the SO2 and NO2 mixture calibration is within 10%.Field measurement is implemented in a wastewater treatment plant in winter.The measurement light path is 738 m.The concentration of SO2 varies from 6μg/m^3(2.26 ppb)to 20μg/m^3(7.52 ppb),and the concentration of NO2varies from 100μg/m^3(53.2 ppb)to 200μg/m^3(106.4 ppb)approximately.The results are in accordance with the data from a monitoring station nearby in magnitude order and variation tendency mostly. 相似文献
In order to explore the processing and application potential of Chinese yam starch, nine kinds of Chinese yam starch (GY11, GY5, GY2, GXPY, LCY, SFY, MPY, SYPY, ASY) from South China were collected and characterized. The chemical composition, rheological properties, thermal properties, and in vitro starch digestion were compared, and the correlation between the structure and processing properties of these yam starches was analyzed using Pearson correlation. The results show that GY2 had the highest amylose content of 28.70%. All the yam starches were similarly elliptical, and all the yam starch gels showed pseudoplastic behavior. Yam starches showed similar pasting temperatures and resistant starch content, but SYPY showed the largest particle size (28.4 μm), SFY showed the highest setback (2712.33 cp), and LCY showed the highest peak viscosity (6145.67 cp) and breakdown (2672.33 cp). In addition, these yam starches also showed different crystal types (A-type, B-type, C-type), relative crystallinity (26.54–31.48%), the ratios of 1045/1022 cm−1 (0.836–1.213), pasting properties, and rheological properties, so the yam starches have different application potentials. The rheological and pasting properties were related to the structural properties of starch, such as DI, Mw, and particle size, and were also closely related to the thermodynamic properties. The appropriate processing methods and purposes of the processed products of these yam starches can be selected according to their characteristics. 相似文献