A novel global navigation satellite system-reflectometry (GNSS-R) software receiver and its preliminary experimental results are presented in this study. The antenna systems, the multi-channel radio-frequency front end, and the digital signal processing unit of this receiver are described in detail. With this developed software receiver, the signals in the Global Positioning System L1 band (GPS L1), BeiDou-2 B1, GLObal NAvigation Satellite System L1, and Galileo E1 bands can be tracked and used as the transmissions of GNSS-R to obtain more information about the scattering properties of ground objects. The preliminary experimental results show that various GNSS signals can be successfully acquired and tracked by this receiver. Furthermore, when it was applied to the soil moisture estimation with the ground-based GNSS-R technique, a relative measure error of 5.79 and 1.39% can be obtained with GPS L1 and BeiDou-2 B1 signals, respectively, by comparing the retrieval results with the measuring results provided by a moisture metre.
A power line is particularly vulnerable to wildfires in its vicinity, and various damage including line tripping can be caused by wildfires. Using remote sensing techniques, a novel model developed to assess the risk of line tripping caused by the wildfire occurrence in high-voltage power line corridors is presented. This model mainly contains the wildfire risk assessment for power line corridors and the estimation of the probability of line tripping when a wildfire occurs in power line corridors. For the wildfire risk assessment, high-resolution satellite data, Moderate Resolution Imaging Spectroradiometer (MODIS) data, meteorological data, and digital elevation model (DEM) data were employed to infer the natural factors. Human factors were also included to achieve good reliability. In the estimation of the probability of line tripping, vegetation characteristics, meteorological status, topographic conditions, and transmission line parameters were chosen as influencing factors. According to the above input variables and observed historical datasets, the risk levels for wildfire occurrence and line tripping were obtained with a logic regression approach. The experimental results demonstrate that the developed model can provide good results in predicting wildfire occurrence and line tripping for high-voltage power line corridors.
Unlike nucleobase modifications in canonical restriction-modification systems, DNA phosphorothioate (PT) epigenetic modification occurs in the DNA sugar-phosphate backbone when the nonbridging oxygen is replaced by sulfur in a double-stranded (ds) or single-stranded (ss) manner governed by DndABCDE or SspABCD, respectively. SspABCD coupled with SspE constitutes a defense barrier in which SspE depends on sequence-specific PT modifications to exert its antiphage activity. Here, we identified a new type of ssDNA PT-based SspABCD-SspFGH defense system capable of providing protection against phages through a mode of action different from that of SspABCD-SspE. We provide further evidence that SspFGH damages non-PT-modified DNA and exerts antiphage activity by suppressing phage DNA replication. Despite their different defense mechanisms, SspFGH and SspE are compatible and pair simultaneously with one SspABCD module, greatly enhancing the protection against phages. Together with the observation that the sspBCD-sspFGH cassette is widely distributed in bacterial genomes, this study highlights the diversity of PT-based defense barriers and expands our knowledge of the arsenal of phage defense mechanisms.IMPORTANCE We recently found that SspABCD, catalyzing single-stranded (ss) DNA phosphorothioate (PT) modification, coupled with SspE provides protection against phage infection. SspE performs both PT-simulated NTPase and DNA-nicking nuclease activities to damage phage DNA, rendering SspA-E a PT-sensing defense system. To our surprise, ssDNA PT modification can also pair with a newly identified 3-gene sspFGH cassette to fend off phage infection with a different mode of action from that of SspE. Interestingly, both SspFGH and SspE can pair with the same SspABCD module for antiphage defense, and their combination provides Escherichia coli JM109 with additive phage resistance up to 105-fold compared to that for either barrier alone. This agrees with our observation that SspFGH and SspE coexist in 36 bacterial genomes, highlighting the diversity of the gene contents and molecular mechanisms of PT-based defense systems.
Vulnerability to sudden service disruption due to deliberate sabotage and terrorist attacks is one of the major threats for network system.Much attention focuses on the need to identify critical facilities for hardening facilities against attacks.In order to identify critical facility that affected the system most after their disruptions,R-interdiction model based on P-median problem is presented.Three heuristics: greedy search,neighborhood search and Tabu search are proposed for this model.Then these heuristics are compared by three test examples: Galvao、Europe 150 and USA 263.Computational results indicate that Tabu search consistently have the best performance.Finally we include that R-interdiction problem can increase the robustness of network by comparing the solutions of P-median problem and R-interdiction problem.
The Shaxi porphyry-type Cu-Au deposit is located in the northwestern outer margin of the Luzong volcanic basin, which is situated in the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB), Eastern China. It is a large porphyry-type Cu-Au deposit with confirmed copper resources exceeding 1 Mt and gold resources exceeding 40 tons. Previous studies have extensively investigated the genesis, controlling structures, geochemical characteristics, fluid evolution, alteration zone, and ages of mineralization and host rocks in this deposit. However, research on the influence of the physical and chemical properties of the host rocks on the mineralizing processes has not been explored in detail. This study employs the finite element method to apply numerical modeling of multiple physical and chemical fields, interlinking heat transfer, fluid flow, material migration, mineralization reaction, and their coupling with porosity and permeability of rock, to investigation of the influence of different porosities, permeabilities, and chemical properties of the host rocks on the mineralizing processes in the Shaxi deposit. The results show that the porosity and permeability of the host rocks play a significant role in the mineralization of porphyry-type systems. The different porosity and permeability of the intrusions and strata control the depth, the mineralization intensity, the morphology of the ore bodies, and the spatial location of the mineralization center. The chemical properties of the strata significantly restrict the mineralization intensity and horizontal spatial rather than affecting the depth of mineralization. Furthermore, the formation of skarn-type deposits may require a longer period of time than that of porphyry-type deposits under the same mineralization conditions and ore grade. This paper also indicates that the numerical modeling method employed in this study can be used to predict the mineralization depth and spatial location of deep concealed porphyry-type deposits, aiding research in deep-seated mineral exploration.
Abstract Based on the very low frequency (VLF) signals observed on the ground in mid‐latitude areas of China from February 2016 to February 2019, atmospheric noise in the 3–30 kHz band is investigated in detail. The statistical analysis indicates that the seasonal variations of the atmospheric noise of different bands are similar in the general trend but different in magnitude, the largest of which can reach 10 dB. According to the accuracy analysis of the atmospheric noise model by the Consultative Committee of International Radio (CCIR), despite the valid long‐term variation of the atmospheric noise provided by the CCIR at the observation station, it overestimates the atmospheric noise level and thus, is unable to show the detailed characteristics of the short‐term variation of the atmospheric noise. Combined with the global lightning observation, the correlation between atmospheric noise and global lightning activities is analyzed to find that the lightning within a range of 3,500 km can dominate the atmospheric noise at the observation site, along with distant lightning playing a minor role. Not only do the results deepen our understanding of the distribution of atmospheric noise in mid‐latitudes in China, but they also reveal the correlation between atmospheric noise and global lightning, thereby benefiting the study of VLF signal propagation and its communication application.
Many spaceborne synthetic aperture radars (SARs), which operate separately in the X, C, and L bands, have been employed to monitor ultra-high-voltage (UHV) and extra-high-voltage (EHV) power lines. However, a full interpretation of the scattering characteristics of these power lines in spaceborne SAR images remains a challenging task. A numerical simulation of the radar cross-section (RCS) of UHV/EHV power lines in the X, C, L, and P bands over a wide range of incidence angles is presented in this paper. A physical model of the UHV/EHV power line is first built. Here, two practical shapes of the UHV/EHV power line are considered, which include the symmetrical catenary when two suspension points have the same height and the inclined catenary when the heights of two suspension points are different. Then, the multilevel fast multipole algorithm (MLFMA) is used for the analysis of the backscatter behavior of UHV/EHV power lines in the X, C, L, and P bands. The effects of several parameters of practical importance on the backscatter RCS of UHV/EHV power lines are also studied, which include the carrier frequency, polarization type, aspect angle of illumination, span length, height difference between two suspension points, conductor sag, and cable diameter. In addition, several comparisons made between simulated and practical observation results demonstrate that the obtained theoretical results can be used to interpret the scattering characteristics of UHV/EHV power lines in spaceborne SAR images and can provide some useful suggestions for monitoring UHV/EHV power lines using spaceborne SAR images.
This paper summarizes the advantage and disadvantage of chemical fertilizer in crop production,the function of organic fertilizer in crop production and the pressure of inorganic fertilizer on ecological environment,and the current status and developmental prospects of mixed application of organic fertilizer and inorganic fertilizer in crop production.
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