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71.
Fracture propagation mechanisms in coalbed methane (CBM) reservoirs are very complex due to the development of the internal cleat system. In this paper, the characteristics of initiation and propagation of hydraulic fractures in coal specimens at different angles between the face cleat and the maximum horizontal principal stress were investigated with hydraulic fracturing tests. The results indicate that the interactions between the hydraulic fractures and the cleat system have a major effect on fracture networks. “Step-like” fractures were formed in most experiments due to the existence of discontinuous butt cleats. The hydraulic fractures were more likely to divert or propagate along the butt cleat with an increase in the angles and a decrease in the horizontal principal stress difference. An increase in the injection rate and a decrease in the fracturing fluid viscosity were more conducive to fracture networks. In addition, the influence on fracture propagation of the residual coal fines in the wellbore was also studied. The existence of coal fines was an obstacle in fracturing, and no effective connection can be formed between fractures. The experimental investigation revealed the fracture propagation mechanisms and can provide guidance for hydraulic fracturing design of CBM reservoirs. 相似文献
72.
Chi Wan Sung Wing Shing Wong 《Vehicular Technology, IEEE Transactions on》1997,46(3):676-686
Generally, the channel-assignment problem (CAP) for mobile cellular systems is solved by graph-coloring algorithms. These algorithms, though sometimes can yield an optimal solution, do not supply any information on whether an optimal solution has been found or bow far away it is from the optimum. In view of these undesirable features, two relevant results are presented. First, a lower bound for the minimum number of channels required to satisfy a given call-traffic demand is derived. This lower bound is tighter than the existing ones under certain conditions and can be used as a supplement for other approximate algorithms. Second, we propose an efficient heuristic algorithm to solve this problem. Although the CAP is nondeterministic polynomial (NP) complete in general, our algorithm provides an optimal solution for a special class of network topologies. For the general case, promising results are obtained, and numerical examples show that our algorithm has a better performance than many existing algorithms 相似文献
73.
A. Edwards Mulpuri V. Rao B. Molnar A. E. Wickenden W. Holland P. H. Chi 《Journal of Electronic Materials》1997,26(3):334-339
Doping by ion implantation using Si, O, Mg, and Ca has been studied in single crystal semi-insulating and n-type GaN grown
on a-sapphire substrates. The n-and p-type dopants used in this study are Si and O; Mg and Ca, respectively. Room temperature
activation of Si and O donors has been achieved after 1150°C annealing for 120 s. The activation of Mg and Ca acceptors is
too low to measure at both room temperature and 300°C. Using higher doses to achieve a measurable p-type conduction increases
the amount of damage created by the implantation. Rutherford back scattering measurements on this material indicate that the
damage is still present even after the maximum possible heat treatment. Secondary ion mass spectrometry measurements have
indicated a redistribution in the measured profiles of Mg due to annealing. 相似文献
74.
为提高原油采收率,利用芽孢杆菌L-510对原油进行生物降解,经室内特性分析实验表明,经芽孢杆菌L-510处理后,原油中轻组分范围变宽,非烃组分含量平均增加2.09%,沥青质含量平均下降1.29%;原油含蜡量平均降幅为17.6%,胶质含量平均降幅为26.5%;原油的流动性得到改善,粘温曲线初始表观粘度与处理前相比降幅达50%。用该菌在葡北油田进行微生物吞吐现场试验,生产井经该菌处理4个月后,有效井达到80%,产液量增幅43.8%,产油量增幅51.4%。该菌株可广泛应用于采油工程领域,特别是微生物强化采油领域。 相似文献
75.
76.
Chi‐Jen Wu De‐Kai Liu Ren‐Hung Hwang 《International Journal of Communication Systems》2007,20(1):83-102
This work describes a novel location‐aware, self‐organizing, fault‐tolerant peer‐to‐peer (P2P) overlay network, referred to as Laptop. Network locality‐aware considerations are a very important metric for designing a P2P overlay network. Several network proximity schemes have been proposed to enhance the routing efficiency of existing DHT‐based overlay networks. However, these schemes have some drawbacks such as high overlay network and routing table maintenance overhead, or not being completely self‐organizing. As a result, they may result in poor scalability as the number of nodes in the system grows. Laptop constructs a location‐aware overlay network without pre‐determined landmarks and adopts a routing cache scheme to avoid maintaining the routing table periodically. In addition, Laptop significantly reduces the overlay maintenance overhead by making each node maintain only the connectivity between parent and itself. Mathematical analysis and simulations are conducted to evaluate the efficiency, scalability, and robustness of Laptop. Our mathematical analysis shows that the routing path length is bounded by logd N, and the joining and leaving overhead is bounded by d logd N, where N is the number of nodes in the system, and d is the maximum degree of each node on the overlay tree. Our simulation results show that the average latency stretch is 1.6 and the average routing path length is only about three in 10 000 Laptop nodes, and the maximum degree of a node is bounded by 32. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
77.
Functionalization of Graphene Oxide Films with Au and MoOx Nanoparticles as Efficient p‐Contact Electrodes for Inverted Planar Perovskite Solar Cells 下载免费PDF全文
Sumit S. Bhosale Efat Jokar Amir Fathi Cheng‐Min Tsai Chi‐Yung Wang Eric Wei‐Guang Diau 《Advanced functional materials》2018,28(37)
A graphene oxide (GO) film is functionalized with metal (Au) and metal‐oxide (MoOx) nanoparticles (NPs) as a hole‐extraction layer for high‐performance inverted planar‐heterojunction perovskite solar cells (PSCs). These NPs can increase the work function of GO, which is confirmed with X‐ray photoelectron spectra, Kelvin probe force microscopy, and ultraviolet photoelectron spectra measurements. The down‐shifts of work functions lead to a decreased level of potential energy and hence increased Voc of the PSC devices. Although the GO‐AuNP film shows rapid hole extraction and increased Voc, a Jsc improvement is not observed because of localization of the extracted holes inside the AuNP that leads to rapid charge recombination, which is confirmed with transient photoelectric measurements. The power conversion efficiency (PCE) of the GO‐AuNP device attains 14.6%, which is comparable with that of the GO‐based device (14.4%). In contrast, the rapid hole extraction from perovskite to the GO‐MoOx layer does not cause trapping of holes and delocalization of holes in the GO film accelerates rapid charge transfer to the indium tin oxide substrate; charge recombination in the perovskite/GO‐MoOx interface is hence significantly retarded. The GO‐MoOx device consequently shows significantly enhanced Voc and Jsc, for which its device performance attains PCE of 16.7% with great reproducibility and enduring stability. 相似文献
78.
Jun Ye Kai Wang Zhan Chen Fei-Fei An Yi Yuan Chi Zhang Xiao-Hong Zhang Chun-Sing Lee 《Organic Electronics》2014,15(12):3514-3520
A novel device concept was realized for simple single-layer small-molecule white organic light emitting devices. The single organic active layer here is simply comprised of a newly synthesized sky-blue fluorescent bipolar host (TPASO) and a common orange phosphorescent dopant. Suppressed singlet Föster energy transfer induced by a low-concentration doping and spontaneous high- to low-lying triplet energy transfer, respectively, lead to sky-blue fluorescence from TPASO and orange phosphorescence from the dopant. The resulting two-organic-component device exhibits a low turn-on voltage of 2.4 V, maximum current/power efficiencies up to 11.27 ± 0.02 cd A−1 and 14.15 ± 0.03 lm W−1, and a warm-white CIE coordinate of (0.42, 0.45) at 1000 cd m−2. 相似文献
79.
Xiaoyang Chen Xuejun Qian Kwok‐Ho Lam Chi Tat Chiu Ruimin Chen Zeyu Chen K. Kirk Shung Ping Yu Qifa Zhou 《Advanced functional materials》2019,29(32)
The developments of personalized medicine, ultrasound imaging, and contactless “microscopic handle” techniques are pushing ultrasonic transducers toward features of high frequency, device miniaturization, and even novel function. However, the conventional ultrasonic transducer has severely limited the development of novel ideas for applications due to its ordinary ultrasonic field. Although transducer arrays and monolithic acoustic holograms are capable of producing the complicated ultrasonic field, it is still difficult to achieve high frequency, device miniaturization, and novel function simultaneously. Here, a simple but effective approach is introduced that aims at reconstructing the complicated and high‐frequency ultrasonic field via a compact single‐element ultrasonic transducer. The 3D ultrathin piezoelectric element with a complex configuration is demonstrated theoretically and experimentally to produce the desired complicated ultrasonic field. With helical‐like configuration, the single‐element ultrasonic transducer offers efficient noncontact trapping and manipulation of suspended microparticles and biological cells. Moreover, its strong trapping capability leads to the 3D stacking of microparticles, which is a novel and interesting phenomenon achieved by a single‐element ultrasonic transducer. This work brings the possibility of a complicated ultrasonic field for achieving novel high‐frequency ultrasound applications through the design of smart structure ultrathin piezoelectric materials. 相似文献