An active power filter (APF) plays an important role in compensating the harmonic component of a nonlinear load current. In this paper, deadbeat control (DBC), which has high control performance and ...fast dynamic response, is used as a current controller for an APF. An improved DBC (Imp_DBC) is introduced to suppress the adverse effect of the current sampling error and to enhance the interference rejection capability of the control system. The characteristics of the conventional DBC and Imp_DBC are analyzed using transfer functions in the discrete-time domain. The robustness of the system is improved with the inductance variation. Specifically, aiming at the dramatic change of the harmonic component of the nonlinear load current, a current-tracking error compensation method is proposed. The phenomena of the upper co-nvex and lower concave in grid current are eliminated. Finally, the experimental setup of three-phase three-line APF is built, and the effectiveness of this method is verified by experiments.
•Shale artificial fracture core models were developed with rough fracture surfaces.•Mineral hydration impairment on artificial fractures conductivity was revealed.•Mechanism of conductivity ...impairment were investigated from various aspects.•Hydration inhibitor increase fracture conductivity by 3.4 and 2.6 times, respectively.•Other factors impair fracture conductivity and implications were discussed.
The shale gas fields are mainly in mountainous areas in China. Surface water is the major source of hydraulic fracturing fluid to develop shale gas. The clay mineral is generally rich in the shale gas reservoir. When encountered with low salinity surface water, the clay minerals are easy to hydrate in the process of fracturing and well shut-in. The hydration of clay minerals would result in the expansion, dispersion, and migration of mineral particles from the fracture surface, changing the structure and space of fractures, thereby affecting fracture conductivity. In this paper, shale artificial fracture core models were developed with rough fracture surfaces. With proppant-supported and self-supported fracture core models, the impact of hydration time, net pressure, and dislocation distance of fracture surfaces on the artificial conductivity were evaluated systematically. The results show that the conductivity of proppant-supported and self-supported fractures decreases by 85.3–95.1% under hydration. The turning point of conductivity is 8.0 hrs. and 4.3 hrs., respectively. At the initial stage of production, the artificial fracture could be protected better if the net pressure on the fracture is maintained from small to large. At the same time, the initial net pressure on fracture should be less than the proppant crushing pressure. Certain dislocation distances of self-supported fractures would augment the conductivity by 6.4–12.8 times. After hydration, illite and montmorillonite in the rock surface expanded and dispersed when encountered with water. The fracture surface strength decreases by 29.8%, while the surface roughness decreases by 46.1–51.6%, and some proppants were crushed. Then the fracture conductivity space was reduced. By adding KCl into the fracturing fluid, hydration can be effectively inhibited, which can increase the proppant-supported and self-supported fracture conductivity by 2.5–3.4 times, compared with fracturing fluid prepared with surface water. This study provides a theoretical basis for the optimization of shale gas reservoir fracturing technology and production strategy.
A laser-dressed
V
-type atom trapped in a two-mode optical cavity is investigated, which induces a SWAP gate on the two modes of the cavity. Two laser fields are imposed to interact with the atom ...dispersively, which leads to an effective interaction between two atomic excited states. The state of the atom prepared initially in the ground state keeps invariant, but the photon exchange between the two cavity modes occurs. Compared with the schemes (Lin et al. in Phys Rev A 77:064301, 2008 and Yan et al. in Quantum Inf Process 17:71, 2018) that use
∇
-type atoms, the present scheme is more practical, because usually the
∇
-type atom may be hardly obtained due to the dipole transition selection rule. In addition, the robustness of the SWAP gate against the pulse control error is strengthened by using time-dependent shaped pulses. The effect of the atomic spontaneous radiation and the photon loss is discussed by means of the numerical simulations.
The parallel three-phase grid-connected converters sharing dc and ac bus can increase the system power level effectively. However, the circulating current will occur inevitably. The existing studies ...primarily focus on dc, fundamental, and low-frequency circulating current. The high-frequency circulating current (HFCC) caused by asynchronous carriers is studied emphatically in this paper, which is based on the analysis of the change of circulating current in one control cycle. A novel method to suppress HFCC caused by asynchronous carriers of modules is proposed. In this method, the carrier period of slave module is adjustable and the carrier period of the master module is constant. When a large phase shift between modules occurs, an adjusting cycle is inserted to carrier of slave module to realize resynchronizing with master module. It is noted that there is no other commutation between the two modules (expect the dq current reference), such as the carrier information. Finally, the feasibility and effectiveness of the proposed method are verified by experiments.
There is a strong demand for novel native peptide motifs for post-synthetic modifications of peptides without pre-installation and subsequent removal of directing groups. Herein, we report an ...efficient method for peptide late-stage C(sp
3
)-H arylations assisted by the unmodified side chain of asparagine (Asn) without any exogenous directing group. Thereby, site-selective arylations of C(sp
3
)-H bonds at the N-terminus of di-, tri-, and tetrapeptides have been achieved. Likewise, we have constructed a key building block for accessing agouti-related protein (AGRP) active loop analogues in a concise manner.
An efficient method for peptide late-stage C(sp
3
)-H arylations assisted by unmodified side chain of asparagine (Asn) without any exogenous directing group has been reported.
Small water bodies ranging in size from 1 to 50,000 m2, are numerous, widely distributed, and have various functions in water storage, agriculture, and fisheries. Small water bodies used for ...agriculture and fisheries are economically significant in China, hence it is important to properly identify and analyze them. In remote sensing technology, water body identification based on band analysis, image classification, and water indices are often designed for large, homogenous water bodies. Traditional water indices are often less accurate for small water bodies, which often contain submerged or floating plants or easily confused with hill shade. Water quality inversion commonly depends on establishing the relationship between the concentration of water constituents and the observed spectral reflectance. However, individual variation in water quality in small water bodies is enormous and often far beyond the range of existing water quality inversion models. In this study, we propose a method for small water body identification and water quality estimation and test its applicability in Wuhan. The kappa coefficient of small water body identification is over 0.95, and the coefficient of determination of the water quality inversion model is over 0.9. Our results show that the method proposed in this study can be employed to accurately monitor the dynamics of small water bodies. Due to the outbreak of the COVID-19 pandemic, the intensity of human activities decreased. As a response, significant changes in the water quality of small water bodies were observed. The results also suggest that the water quality of small water bodies under different production modes (intensive/casual) respond differently in spatial and temporal dimensions to the decrease in human activities. These results illustrate that effective remote sensing monitoring of small water bodies can provide valuable information on water quality.
Co9S8 is a highly promising electrochemically active material for energy devices; its rational design and manufacture for further enhancing the electrochemical activity and durability are still ...challenging. Herein, Co9S8@CNT compounds are synthesized by one-step pyrolysis, which self-assembled the monomolecular precursor and carbon nanotubes (CNTs). The CNTs effectively improve the electrical conductivity of the materials and availability of the catalytically active sites, which means that the electrochemical ability of Co9S8@CNT is better than that of individual Co9S8 and CNTs. The onset potential of Co9S8@CNT is 132 mV, which has greatly decreased. At the mass current density of 10 mA mg−1, the overpotential is 337 mV, and the Tafel slope is 49.8 mV dec−1. The addition of CNTs makes up for the deficiency of low electrical conductivity of the CoSx. Furthermore, the three-dimensional (3D) structure of the composite improves its electrocatalytically active surface area, and the electrocatalytic ability has been improved efficiently, owing to the increased number of catalytic sites on the surface.
With high clay content in shale gas reservoir, the hydration is easy during hydraulic fracturing, which will affect the fracture conductivity and productivity of gas wells. The illite content of the ...Longmaxi formation shale in Yongchuan District is high (more than 80% of clay mineral content), and gas wells have a high productivity after fracturing and shut-in. However, the hydration effect mechanism of fracturing fluid on illite rich shale is not clear. Therefore, in this paper, core hydration experiments are performed for the illite rich shale reservoir. The water imbibition characteristic of near-fracture shale is obtained, and the micro-morphology and microfracture development characteristics of hydration are studied. Moreover, the hydration mechanism of near-fracture shale is then explored from the aspects of ion diffusion and mineral interlayer spacing variation. It is deduced that the fracturing fluid is spontaneously imbibed into small pores preferentially during well shut-in after fracturing. After the near-fracture shale is touched by water, some clay minerals peel and fall off from the fracture surface after hydration, accompanied by the development of microfractures. The interlayer spacing of clay minerals expands (smectite expands by 8.8% and illite 1.5%) after water immersion, and the ion diffusion occurs. The first 15 h is the rapid diffusion stage (surface effect), while the second 15 h is the stable rising stage (internal effect). This study systematically analyzes the hydration characteristics of near-fracture illite rich shale and reveals its hydration mechanism, which are crucial for the optimization of well shut-in time and exploitation system of shale gas reservoir after fracturing.
•The fracturing fluid preferentially and spontaneously enters the smaller pores.•The hydration of clay minerals occurs and accompanied by mineral shedding.•Primary and secondary microfracture development phenomenon occurs during immersion.•Ion diffusion mainly contain surface action stage and internal matrix action stage.•Illite hydration is main reason for microfracture development of illite-rich shale.
The effects of three pyridine derivative additives, 4-hydroxypyridine, 4-picolinic acid, and 4-cyanopyridine, on Al-Mn coatings were investigated in 1-ethyl-3-methylimidazolium chloride-AlCl3-MnCl2 ...(EMIC-AlCl3-MnCl2) ionic liquids. The smooth mirror-like bright Al-Mn coatings were obtained only in the EMIC-AlCl3-MnCl2 ionic liquids containing 4-cyanopyridine, while the matte Al-Mn coatings were electrodeposited from EMIC-AlCl3-MnCl2 without additives or containing either 4-hydroxypyridine or 4-picolinic acid. The scanning electron microscope and X-ray diffraction showed that the bright Al-Mn coatings consisted of nanocrystals and had a strong (200) preferential orientation, while the particle size of matte Al-Mn coatings were within the micron range. The brightening mechanism of 4-cyanopyridine is due to it being adsorbed onto the cathode to produce the combined effect of (1) generating an overpotential to promote Al-Mn nucleation; (2) inhibiting the growth of the deposited nuclei and enabling them grow preferentially, making the coating composed of nanocrystals and with a smooth surface. The brightening effect of 4-cyanopyridine on the Al-Mn coatings was far better than that of the 4-hydroxypyridine and the 4-picolinic acid. In addition, the bright Al-Mn coating was prepared in a bath with 6 mmol·L−1 4-cyanopyridine and displayed superior corrosion resistance relative to the matte coatings, which could be attributed to its unique nanocrystalline structure that increased the number of grain boundaries and accelerated the formation of the protective layer of the corrosion products.
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