The Lintong–Chang’an Fault Zone (LCFZ) is an important active structure in the Weihe Graben (central China). The study on the activity of the LCFZ is not only of great significance to explore the ...regional tectonic mechanism, but also has practical value in urban seismic mitigation and disaster relief. In this study, based on high-resolution remotely sensed imagery, shallow seismic reflection survey, borehole data and excavation of a foundation pit, we determined the distribution and activity of the Wangjiabian–Houjiawan fault (a branch fault of the LCFZ) in the Shaoling Loess Tableland. Combined with previous studies, we further inferred that the vertical displacements were 0–6 m along the LCFZ, but most displacements were around 1 m. Furthermore, there are eight locations where no displacements have been found in the Late Pleistocene strata. The offsets on the fault zone since the Late Pleistocene display a wave-like pattern, which is unrelated to the regional topographic expression. Compared to other faults in the Weihe Graben, the activity of the LCFZ in vertical component is relatively weak, implying a possible strike–slip motion. In addition, a major active fault may exist on the northwest side of this fault zone, bearing part of the fault motion in this region.
Electroless nickel composite coatings have the potential for high-temperature tribological applications, and a combination of high wear resistance and low friction factor is one of the desirable ...solutions but still a tricky problem. The addition of self-lubricating WSsub.2 and hard Sisub.3Nsub.4 nanoparticles to the Ni-P coatings is expected to obtain good high-temperature tribological performance. In this work, Ni-P-Sisub.3Nsub.4-WSsub.2 composite coatings with various contents of WSsub.2 nanoparticles were prepared using electroless plating and subsequently annealed at 400 °C in an inert atmosphere. The tribological properties of the coatings were evaluated using a ball-on-disc wear instrument at operating temperatures from 25 to 600 °C. The microstructure, chemical composition, and surface morphology of the coatings were characterized by X-ray diffractometry (XRD), energy disperse spectroscopy (EDS), and scanning electron microscopy (SEM). Upon increasing the WSsub.2 dosage in the bath, the WSsub.2 content in the coating increased and the micro-hardness of the as-plated coating increased from 539 to 717 HV. After heat treatment, the coating underwent a crystallization process, and the hardness increased from 878 to 1094 HV. The main wear mechanism of the coating changed from adhesive wear in the as-plated state to abrasive wear in the annealed state. The annealed Ni-P-Sisub.3Nsub.4-WSsub.2 coating with a WSsub.2 dosage of 2.5 g/L in the bath exhibited excellent mechanical properties, with a hardness of 10.9 GPa, a friction coefficient of ~0.51, and a wear rate of 8.4 × 10sup.−15 msup.3Nsup.−1⋅msup.−1 at room temperature, and maintained optimal performance at high temperatures. At operating temperatures of 200, 400, and 600 °C, the form of wear was adhesive wear for coatings with a WSsub.2 dosage <1.5 g/L and abrasive wear for coatings with a WSsub.2 dosage ≥1.5 g/L. The synergism of WSsub.2 and Sisub.3Nsub.4 particles refined the grains of the Ni-P matrix in as-plated coatings and obviously reduced the friction coefficient of friction pairs in annealed coatings at all operating temperatures.
Electroless nickel composite coatings have the potential for high-temperature tribological applications, and a combination of high wear resistance and low friction factor is one of the desirable ...solutions but still a tricky problem. The addition of self-lubricating WS2 and hard Si3N4 nanoparticles to the Ni-P coatings is expected to obtain good high-temperature tribological performance. In this work, Ni-P-Si3N4-WS2 composite coatings with various contents of WS2 nanoparticles were prepared using electroless plating and subsequently annealed at 400 °C in an inert atmosphere. The tribological properties of the coatings were evaluated using a ball-on-disc wear instrument at operating temperatures from 25 to 600 °C. The microstructure, chemical composition, and surface morphology of the coatings were characterized by X-ray diffractometry (XRD), energy disperse spectroscopy (EDS), and scanning electron microscopy (SEM). Upon increasing the WS2 dosage in the bath, the WS2 content in the coating increased and the micro-hardness of the as-plated coating increased from 539 to 717 HV. After heat treatment, the coating underwent a crystallization process, and the hardness increased from 878 to 1094 HV. The main wear mechanism of the coating changed from adhesive wear in the as-plated state to abrasive wear in the annealed state. The annealed Ni-P-Si3N4-WS2 coating with a WS2 dosage of 2.5 g/L in the bath exhibited excellent mechanical properties, with a hardness of 10.9 GPa, a friction coefficient of ~0.51, and a wear rate of 8.4 × 10−15 m3N−1⋅m−1 at room temperature, and maintained optimal performance at high temperatures. At operating temperatures of 200, 400, and 600 °C, the form of wear was adhesive wear for coatings with a WS2 dosage <1.5 g/L and abrasive wear for coatings with a WS2 dosage ≥1.5 g/L. The synergism of WS2 and Si3N4 particles refined the grains of the Ni-P matrix in as-plated coatings and obviously reduced the friction coefficient of friction pairs in annealed coatings at all operating temperatures.
Topoisomerase III （topo III）, a type IA topoisomerase, is widespread in hyperthermophilic archaea. In order to interrogate the in vivo role of archaeal topo III, we constructed and characterized a ...topo III gene deletion mutant of Sulfolobus islandicus. The mutant was ,viable but grew more slowly than the wild-type strain, especially in a nutrient-poor medium. Flow cytometry analysis revealed changes of the mutant in growth cycle characteristics including an increase in proportion of cells containing either more than two genome equivalents or less than one genome equivalent in exponentially-growing cultures. As shown by fluorescence microscopy, a fraction of mutant cells in the cultures were drastically enlarged, and at least some of the enlarged cells were apparently capable of resuming cell division. The mutant also shows a different tran- scriptional profile from that of the wild-type strain. Our results suggest that the enzyme may serve roles in chromosomal segregation and control of the level of supercoiling in the cell.
The topology model of Nanjing public transport network is established. Combined with the thought of complex network, the bus stations are looked as the nodes, and the connection between sites are as ...the sides. On the basis of a large number of statistical data, the characteristics of complex network in Nanjing are researched through Space L and Space P methods. The results show that the degree distribution of the public transport network is in line with the rate of distribution of power and has scale-free properties. And it has a smaller average distance and high clustering coefficient, which is the typical property of small-world.
Zero-forcing (ZF) precoding plays an important role for massive MIMO downlink due to its near optimal performance. However, the high computation cost of the involved matrix inversion hinders its ...application. In this paper, we adopt the first order Neumann series (NS) for a low-complexity approximation. By introducing a relaxation parameter jointly with the channel non-orthogonality between one selected user and others into the precondition matrix, we propose the identity-plus-column NS (ICNS) method. By further choosing the user with the least channel orthogonality with others, the ordered ICNS method is also proposed. Moreover, the sum-rate approximations of the proposed ICNS method and the competitive existing identity matrix based NS (INS) method are derived in closed-form, based on which the performance loss of ICNS due to inversion approximation compared with ideal ZF and its performance gain over INS are explicitly analyzed for three typical massive MIMO scenarios. Finally, simulations verify our analytical results and also show that the proposed two designs achieve better performance-complexity tradeoff than ideal ZF and existing low-complexity ZF precodings for practical large antenna number, correlated channels, and not-so-small loading factor.
Statistical beamforming is an important technique for multi-user massive MIMO downlink, since it depends on the downlink channel covariance only. In this paper, we first derive an explicit analytical ...sum-rate expression for generic channel covariance-based beamforming scheme. Then, a low-complexity joint statistical beamforming and user scheduling algorithm via greedy search is proposed, where the beamforming is based on the signal-to-leakage-and-noise-ratio (SLNR) for closed-form design and tractable analysis, while the user scheduling is based on the derived sum-rate expression. Further, with the help of large-scale asymptotic simplifications and the introduction of the interference user number parameter, a simple analytical sum-rate expression of the joint algorithm is derived for channels with flat power beam spectrum. The expression explicitly exhibits the sum-rate behavior with respect to different network parameters and captures the effect of sum-rate-based user scheduling. Finally, simulation results are provided to verify our analytical results and to show the advantage of the proposed joint design compared with existing schemes.
NOMA, as the newest member of the multiple access family, is envisioned to be an essential component of 5G mobile networks. The combination of NOMA and multi-antenna MIMO technologies exhibits ...significant potential in improving spectral efficiency and providing better wireless services to more users. In this article, we introduce the basic concepts of MIMO-NOMA and summarize the key technical problems in MIMO-NOMA systems. Then we explore the problem formulation, beamforming, user clustering, and power allocation of single/multi-cluster MIMO-NOMA in the literature along with their limitations. Furthermore, we point out an important issue of the stability of successive interference cancellation that arises using achievable rates as performance metrics in practical NOMA/MIMO-NOMA systems. Finally, we discuss incorporating NOMA with massive/millimeter- wave MIMO, and identify the main challenges and possible future research directions in this area.
In frequency division duplexing (FDD) cell-free massive MIMO, the acquisition of the channel state information (CSI) is very challenging because of the large overhead required for the training and ...feedback of the downlink channels of multiple cooperating base stations (BSs). In this paper, for systems with partial uplink-downlink channel reciprocity, and a general spatial domain channel model with variations in the average port power and correlation among port coefficients, we propose a joint-port-selection-based CSI acquisition and feedback scheme for the downlink transmission with zero-forcing precoding. The scheme uses an eigenvalue-decomposition-based transformation to reduce the feedback overhead by exploring the port correlation. We derive the sum-rate of the system for any port selection. Based on the sum-rate result, we propose a low-complexity greedy-search-based joint port selection (GS-JPS) algorithm. Moreover, to adapt to fast time-varying scenarios, a supervised deep learning-enhanced joint port selection (DL-JPS) algorithm is proposed. Simulations verify the effectiveness of our proposed schemes and their advantage over existing port-selection channel acquisition schemes.
PDF
