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For Beyond 5G/6G system, satellite communication systems become an effective component of the space and terrestrial integrated network. Among typical applications, massive Machine Type of Communication (mMTC) is a promising and challenging application. The demands of low power consumption and light signaling make random access methods as the potential solution. Up to now, contention resolution-based ALOHA methods, such as contention resolution diversity slotted ALOHA (CRDSA), improve the throughput significantly. However, its throughput will meet the inflection point soon with the normalized load increasing since collisionless packets are hardly existing. In fact, the diversity of transmitting packets is not utilized totally. In this paper, an improved random access method, named coherent CRDSA method (C-CRDSA), is proposed. It accumulates replicated packets coherently at receiver and further improve the throughput over CRDSA. Detailed derivations and simulations are given. Simulation results corroborate the effectiveness of the proposed method.

In this paper, we proposed a cooperative beamforming ALOHA (CBA) scheme based on linearly constrained minimum variance criterion for low Earth orbit satellite (LEO) IoT networks to solve the problem of ‘deadlock’ in multi-satellite scenario. In multi-satellite overlapping coverage areas, packets can be received by multiple satellite receivers by sending them only once, which forms the concept of spatial diversity. The cooperative beamforming collision resolution technique combined with successive interference cancellation scheme is design to efficiently resolve packet collision by iteration way at the gateway station. The performance of cooperative beamforming ALOHA scheme is evaluated via mathematical analysis and simulations. Simulation results show that the proposed CBA scheme can effectively solve the problem of ‘deadlock’ and improve the performances of random access compared with benchmark problems.

With the development of the array signal processing techniques, more and more robust methods are proposed for non-stationary interference cancellation at the beamforming stage. Among these methods, null widening methods or well-known covariance matrix taper (CMT) methods are the research hotspots. However, the typical CMT-class methods modified the whole covariance matrix with the same taper matrix, which means that all the nulls produced by the covariance matrix will be widened to the same width in cosine angular domain. This will make a waste of degrees of freedom (DOFs) in the scene that different interference sources have a different degree of non-stationarity. In this Letter, also adopting CMT structure, a flexible widening method is discussed, which utilises the relationship between each eigenvector and the steering vector of each interference source. The proposed method can widen different nulls with different width, which can save the consumption of DOFs as many as possible according to the demand. Besides, as a subspace-based method, it can preserve the minimal sample support property. The simulation results show the effectiveness of the proposed method.

Although biodiversity and ecosystem functions are strongly shaped by contemporary environments, such as climate and local biotic and abiotic attributes, relatively little is known about how they depend on long-term geological processes. Here, along a 3000-m elevational gradient with tectonic faults on the Tibetan Plateau (that is, Galongla Mountain in Medog County, China), we study the joint effects of geological and contemporary environments on biological communities, such as the diversity and community composition of plants and soil bacteria, and ecosystem functions. We find that these biological communities and ecosystem functions generally show consistent elevational breakpoints at 2000–2800 m, which coincide with Indus-Yalu suture zone fault and are similar to the elevational breakpoints of soil bacteria on another mountain range 1000 km away. Mean annual temperature, soil pH and moisture are the primary contemporary determinants of biodiversity and ecosystem functions, which support previous findings. However, compared with the models excluding geological processes, inclusion of geological effects, such as parent rock and weathering, increases 67.9 and 35.9% of the explained variations in plant and bacterial communities, respectively. Such inclusion increases 27.6% of the explained variations in ecosystem functions. The geological processes thus provide additional links to ecosystem properties, which are prominent but show divergent effects on biodiversity and ecosystem functions: parent rock and weathering exert considerable direct effects on biodiversity, whereas indirectly influence ecosystem functions via interactions with biodiversity and contemporary environments. Thus, the integration of geological processes with environmental gradients could enhance our understanding of biodiversity and, ultimately, ecosystem functioning across different climatic zones.

In this article, we investigate the spectrum-sharing for a space information network comprised of a geostationary orbit (GEO) satellite and a pair of low earth orbit (LEO) satellites, where one spectrum-sensing LEO (SLEO) is used to sense the status of spectrum occupancy of the GEO, and one data-transmission LEO (DLEO) satellite is allowed to access the shared spectrum of the GEO with the aid of the SLEO. In order to improve the throughput of the DLEO satellite, a spectrum sharing framework has been conceived relying on two stages. Differing from the conventional spectrum-sharing scheme, the data-transmission LEO satellite has the ability to access the shared spectrum both in overlay mode and in underlay mode. In overlay mode, the DLEO can perform transmission at any required transmit power. By contrast, in underlay mode, a spectrum-sensing and power allocation aided spectrum-sharing (SPA-SS) scheme is proposed to guarantee that the maximal amount of interference is imposed on the GEO caused by the DLEO. To be specific, in the first stage, the SLEO is invoked for performing spectrum-sensing, where the time intervals of spectrum-sensing have been specifically optimized to alleviate the interference received at the GEO in the second stage. Moreover, an adaptive power allocation is designed to maximal the throughput of the DLEO in the second stage, whilst maintaining the maximal interference imposed on the GEO is lower than the tolerable interference temperature of the GEO. Numerical results show that the proposed SPA-SS scheme outperforms the traditional spectrum-sharing scheme in terms of not only the average throughput, but also of the time-utilization ratio.

Nonstationary interference, generated by time-varying propagation paths or relative motions between the receiving array and jamming sources, is a serious problem faced with radar and wireless communication systems. To solve this problem, null widening has been proposed and proven to be able to achieve reliable performance. However, most existing methods were proposed for full-array or dimension-reduced beamformer. Little literature discusses its application on sidelobe canceller, a useful technique in real system. In this paper, a computationally efficient null widening method for sidelobe canceller is proposed. This method is a covariance matrix taper-based method which puts fictitious interferences into snapshots to widen the sharp null. The proposed method can achieve satisfactory performance and needs less computation costs than existing methods. Detailed derivations and simulation results show its effectiveness.

A new phosphate Ba3In4(PO4)6 has been discovered in the exploration of novel host materials for color-tunable phosphors in BaO-In2O3-P2O5 system. The crystal-structure determination using powder XRD data reveals it belongs to the cubic langbeinite structure type (S.G. P213), unlike Mg3In4(PO4)6 crystallizing the triclinic system (S.G. P 1 ¯ ). The existence of PO4 has been verified by IR spectra of the title compound. DTA and experimental indicate that this new phosphate has a high melting point of ∼1293 °C. Combined with calculated electronic structure and experimental UV-Vis diffuse reflectance spectrum, it has a wide direct energy band gap which is favorable for host materials. The site symmetry of Eu3+ ions and the cross relaxation of Tb3+ ions in this matrix have been clarified according to their luminescence properties. Red-pink-green tunable emission can be realized adjusting the Eu3+ and Tb3+ contents. The quantum yields of representative phosphors under the excitation of 370–392 nm ultraviolet radiation have been measured and discussed. The PL intensity of Ba3In4(PO4)6: 0.02Eu3+, 0.015 Tb3+ phosphor at 423 K of is about 67% of that at 298 K. Present results indicate that the Ba3In4(PO4)6-based phosphors are valuable for the multicolor and stable thermal performance in the display and lighting fields.

Bromine (Br) is one of the trace elements in halite. Br content and the Br/chlorine (Cl) molar ratio can be used to reveal dry climates, the degree of evaporation, and/or brine concentration. The Br content of basal halite is more useful than that the Br content of halite from later stages when being used to distinguishing marine from nonmarine origins. Evaporite deposits on the Khorat Plateau (KP) have been a primary source of evaporites in southeastern Asia. The origin (i.e., marine, nonmarine, or a combination of the two) of these deposits is still disputed. In this study, we used the Br concentration of basal halite and the Br/Cl molar ratio to explore the origin of these deposits and the environmental changes that took place in the Late Cretaceous. We analyzed a total of 330 halite samples from borehole ZK2893 for cations (K+, Ca2+, Na+, and Mg2+) and anions (Br−, Cl−, and SO42−). The Br content ranged from 24.04 to 277.87 ppm, and the Br/Cl molar ratio ranged from 0.02 to 0.27 ppm. The low Br content (24.04 ppm) and Br × 103/Cl molar ratio (0.02) of the basal halite suggested that no marine water was in the basin when the halite precipitation began. The temporal variations in the Br content and the Br × 103/Cl molar ratio of halite implied that: (1) the climate in this area during the Late Cretaceous was dry, with two dry stages occurring from 92 to 85 Ma and from 80 to 72 Ma; and (2) the drying trend increased from 92 to 85 Ma and from 80 to 72 Ma, with two extremely dry events occurring during the periods 89–85 Ma and 76–73 Ma.

Understanding the mechanisms underlying biodiversity patterns is a central issue in ecology, while how temperature and precipitation jointly control the elevational patterns of microbes is understudied. Here, we studied the effects of temperature, precipitation and their interactions on the alpha and beta diversity of soil archaea and bacteria in alpine grasslands along an elevational gradient of 4,300-5,200 m on the Tibetan Plateau. Alpha diversity was examined on the basis of species richness and evenness, and beta diversity was quantified with the recently developed metric of local contributions to beta diversity (LCBD). Typical alpine steppe and meadow ecosystems were distributed below and above 4,850 m, respectively, which was consistent with the two main constraints of mean annual temperature (MAT) and mean annual precipitation (MAP). Species richness and evenness showed decreasing elevational patterns in archaea and nonsignificant or U-shaped patterns in bacteria. The LCBD of both groups exhibited significant U-shaped elevational patterns, with the lowest values occurring at 4,800 m. For the three diversity metrics, soil pH was the primary explanatory variable in archaea, explaining over 20.1% of the observed variation, whereas vegetation richness, total nitrogen and the K/Al ratio presented the strongest effects on bacteria, with relative importance values of 16.1%, 12.5% and 11.6%, respectively. For the microbial community composition of both archaea and bacteria, the moisture index showed the dominant effect, explaining 17.6% of the observed variation, followed by MAT and MAP. Taken together, temperature and precipitation exerted considerable indirect effects on microbial richness and evenness through local environmental and energy supply-related variables, such as vegetation richness, whereas temperature exerted a larger direct influence on LCBD and the community composition. Our findings highlighted the profound influence of temperature and precipitation interactions on microbial beta diversity in alpine grasslands on the Tibetan Plateau.

International audience; The Tibetan Plateau (TP) and Arctic permafrost constitute two large reservoirs of organic carbon, but processes which control carbon accumulation within the surface soil layer of these areas would differ due to the interplay of climate, soil and vegetation type. Here, we synthesized currently available soil carbon data to show that mean organic carbon density in the topsoil (0–10 cm) in TP grassland (3.12 ± 0.52 kg C m$^{−2}$) is less than half of that in Arctic tundra (6.70 ± 1.94 kg C m$^{−2}$). Such difference is primarily attributed to their difference in radiocarbon-inferred soil carbon turnover times (547 years for TP grassland versus 1609 years for Arctic tundra) rather than to their marginal difference in topsoil carbon inputs. Our findings highlight the importance of improving regional-specific soil carbon turnover and its controlling mechanisms across permafrost affected zones in ecosystem models to fully represent carbon-climate feedback.

Single-phase white-emission phosphors possess a judicious usage potential in phosphor-converted white-light-emitting diodes (WLEDs). Recently, numerous efforts have been made toward the development of new patterns of white-emitting phosphors that achieve excellent quantum yield, superior thermal stability, and applaudable cost effectiveness of WLEDs. Finding suitable single-component white phosphor hosts to provide an ideal local environment for activators remains urgent. Inspired by the original discovery of the promising host MgIn

Based on the frequency division multiplexing principle of the multi-beam antenna, this paper proposes a new method for locating interference sources by only one single satellite. According to the antenna pattern function expression of multi-beam antennas, the positioning equations are derived and established by analyzing the link that interfering signal arrives at the spaceborne multi-beam antenna from the ground. Importantly, the gain error is introduced in the positioning process when we evaluate the performance of this positioning method. Considering the difficulty of solving nonlinear positioning equations, a new algorithm combining the Particle Swarm Optimization (PSO) and grid search is proposed. At the same time, in this paper, in order to analyze the feasibility of this new algorithm, we introduce the Monte Carlo method in the process of this experiment. Finally, this new algorithm is compared with the traditional Particle Swarm Optimization in terms of speed and accuracy, which shows the superiority of this new algorithm.

Most of transmitted signals of satellite Internet of Things (IoT) terminals have the characteristics of low baud rate, short packet length and burstiness. The collision of massive access of IoT terminals can be solved by a random multiple access technology in company with an efficient and reliable collision separation method in the receiver. However, most existing signal separation technologies are proposed for continuous signals, and the receiving structure is designed based on the phase-locked loop. In this paper, a short burst signal separation method based on adaptive minimum mean square error (MMSE) filtering is proposed for the classical contention resolution diversity slotted Aloha (CRDSA). The proposed method estimates the frequency and phase difference between copies by amplitude and phase estimation (APES) firstly and cancels the collision signal based on a MMSE filter. The theoretical analysis and simulation results verify the feasibility of the proposed method.

At present, the research on the single satellite frequency measurement and localization technology mainly focuses on the use of multiple satellite observation positions in a single flight orbit to forward the ground target source signals, but there are many limitations in locating the interference source with limited field of view. In this paper, based on the single-orbit single-satellite time-division frequency-measuring localization technology, a localization technology of single-satellite time-division Doppler frequency measurement in different orbits is proposed, which is based on the optimal observation satellite position. Firstly, the positioning model and the positioning equation of the single-satellite time-division Doppler frequency measurement and localization technology in different orbits are constructed. Secondly, a calculation formula for Geometric Dilution of Precision (GDOP) is derived and the optimal model of the observation satellite position is constructed. Finally, based on the positioning process, the minimum positioning error is targeted. Computer simulation results show that the availability and accuracy of the technique are improved significantly in the scene with limited field of view.

The design and optimization of fade mitigation techniques in Q/V bands satellite communications require rain attenuation time series. Methods for synthesizing short-term and long-term rain attenuation time series at Q/V bands are integrated in this paper. Firstly, based on the ‘Event-on-Demand’ model, the rain attenuation process is transformed into a first-order stationary Markov process after nonlinear transformation. The generation steps of short-term rain attenuation time series are analyzed. Then, the principle of Dirac-lognormal distribution model is analyzed, and the steps of generating long-term rainfall attenuation time series are given. Finally, the short-term and long-term rain attenuation time series at Q/V bands are obtained through simulation. The power spectrum estimation of the series shows the validity of the rain attenuation time series.

Recently beam hopping technique is considered as a potential key technology in the next generation of high throughput satellite (HTS) systems for its flexible resource allocation. This paper is focused on the downlink resource allocation of beam hopping in the HTS System. Firstly, the user traffic model which varies in geography and time is built. Then with the proposed uneven traffic distribution model, the beam hopping time slot optimization algorithm is provided based on fairness objective function. Finally, the beam hopping pattern is designed to be combined with precoding to suppress co-channel interference. The simulation results show that compared with the traditional methods, the proposed algorithm can dynamically adjust the resource allocation with the change of the traffic requirements, and eliminate the co-channel interference of the beam as much as possible to meet the traffic requirements of each beam, thus improving the capacity of the satellite network.

In this paper, we investigate the spectrum sensing of a weak signal based on multiple low earth orbit (LEO) satellites in the presence of a spectrum-sharing node, which can generate the interference imposed on the sensing LEO satellites. In order to improve the sensing ability of the weak signal, a cooperative spectrum sensing method relying on satellite formation is proposed. Specifically, firstly, some satellites will be chosen from multiple LEO satellites for formation purposes, where the specific number of satellites chosen can be adjusted by evaluating the probability of detection weak signal, as detailed later. Then, considering the object that both restraining the interference and magnifying the weak signal, the weighted value of each satellite for beamforming may be optimized with the aid of genetic algorithm, and the receive gains of the weak signal and the interference can be achieved. Finally, the probability of detecting the weak signal can be evaluated by calculating the signal to interference plus noise ratio (SINR), and the number of the chosen satellites can be decided accordingly. Simulation results show that the proposed method not only can suppress the interference imposed on the sensing satellites, but also can increase SINR of sensing satellites for the weak signal, resulting in improving the probability of detection.

In a satellite system, the ability to generate future spectrum occupancy can play an important role in increasing spectrum efficiency, and spectrum prediction is emerging as an efficient approach for increasing spectrum efficiency. In order to predict spectrum occupancy more accurately, we propose a bidirectional long short-term memory network (BiLSTM)-based spectrum prediction (SP) scheme, which can be performed in two stages. Specifically, in the first stage, the historical spectrum data may be pre-processed, and in the second stage, the pre-processed data should be sent to BiLSTM model, which will perform training and generate the optimized hyperparameters firstly. Then, BiLSTM will be activated to perform prediction via the optimized hyperparameters. Performance evaluations show that the BiLSTM-based SP scheme outperforms the LSTM-oriented SP scheme in terms of both accuracy and learning speed.

The genus Paenibacillus was originally recognized based on the 16S rRNA gene phylogeny. Recently, a standardized bacterial taxonomy approach based on a genome phylogeny has substantially revised the classification of Paenibacillus, dividing it into 23 genera. However, the metabolic differences among these groups remain undescribed. Here, genomes of 41 Paenibacillus strains comprising 25 species were sequenced, and a comparative genomic analysis was performed considering these and 187 publicly available Paenibacillus genomes to understand their phylogeny and metabolic differences. Phylogenetic analysis indicated that Paenibacillus clustered into 10 subgroups. Core genome and pan-genome analyses revealed similar functional categories among the different Paenibacillus subgroups; however, each group tended to harbor specific gene families. A large proportion of genes in the subgroups A, E, and G are related to carbohydrate metabolism. Among them, genes related to the glycoside hydrolase family were most abundant. Metabolic reconstruction of the newly sequenced genomes showed that the Embden-Meyerhof-Parnas pathway, pentose phosphate pathway, and citric acid cycle are central pathways of carbohydrate metabolism in Paenibacillus. Further, the genomes of the subgroups A and G lack genes involved in glyoxylate cycle and D-galacturonate degradation, respectively. The current study revealed the metabolic diversity of Paenibacillus subgroups assigned based on a genomic phylogeny and could inform the taxonomy of Paenibacillus. KEY POINTS: • Paenibacillus clustered into 10 subgroups. • Genomic content variation and metabolic diversity in the subgroup A, E, and G were described. • Carbohydrate transport and metabolism is important for Paenibacillus survival.

Mg2Si1−xSnx-based compounds have been recognized as promising thermoelectric materials owing to their high figure-of-merit ZTs, abundance of raw constituent elements and nontoxicity. However, further improvement in the thermoelectric performance in this type of material is still constrained by the high thermal conductivity. In this work, we prepared a series of representative Mg2Si0.4−xSn0.6Sbx (x = 0, 0.0075, 0.008, 0.009, 0.01, 0.011) samples via the alkaline earth metal reduction method through a combination of ball milling and spark plasma sintering (SPS) processes. The samples featured many dislocations at the grain boundaries and plenty of nanoscale-coherent Mg2Si–Mg2Sn spinodal phases; both of which can effectively scatter heat-carrying phonons and have nearly no impact on the carrier transport. Meanwhile, Sb-doping can efficiently optimize the carrier concentration and significantly suppress the bipolar effects. As a result, a maximal ZT of 1.42 at 723 K and engineering (ZT)eng of 0.7 are achieved at the optimal Sb-doping level of x = 0.01. This result indicates that the alkaline earth metal reduction method could be an effective route to engineer phonon transport and improve the thermoelectric performance in Mg2Si1−xSnx-based materials.

Distributions of branched glycerol dialkyl glycerol tetraether (brGDGT) lipids are sensitive to environmental parameters, which enables their use in paleoenvironmental studies. In particular, the degree of methylation of brGDGTs (MBT and MBT′) and the cyclization ratio of brGDGTs (CBT) are often used to estimate changes in temperature in paleoclimate studies. Application of these proxies requires reliable and precise calibrations to temperature. However, available calibrations of brGDGT proxies to temperature have large calibration errors in arid areas which suggests that other environmental variables influence brGDGT distributions in these areas. Here we analyze brGDGT distributions in soils from the Tibetan Plateau, an arid/semi-arid region with gradients in vegetation cover (forest, grassland, and desert) to examine: (1) the applicability of MBT′/CBT calibrations to reconstruct mean annual air temperature (MAAT); and (2) the effects of vegetation cover on temperature calibrations. We show that temperatures reconstructed using the global soil MBT′/CBT calibrations are warmer than instrumentally observed temperature, and that the calibrations are significantly influenced by the presence or absence of vegetation. Excluding sample sites without vegetation (bare soil) from temperature calibrations substantially improves the correlation between observed and reconstructed temperatures. Within the vegetated soils, we reanalyzed published global soil calibration datasets, including results of analyses that either did or did not separate 5- and 6-methyl brGDGT isomers, and find that the correlation between MBT′5Me and MBT′ and temperature varies for different vegetation types (grass and forest) and that the error of temperature calibrations is reduced if calibrations are separated by the type of vegetative cover (grass or forest). We test these new calibrations in sequences from the Lantian and Mangshan loess of the Chinese Loess Plateau and find that reconstructed temperatures from both modern and Last Glacial Maximum sediments are more consistent with other reconstructions and climate model simulations when vegetation-specific calibrations are applied to the brGDGT data. The results indicate that changes in vegetation should be taken into consideration when applying brGDGT proxies to reconstruct past changes in climate.

Purpose Long noncoding RNA PVT1 is dysregulated in some human tumors and has been found to increase the risk of tumor progression and poor prognosis. This study aimed to reanalyze the effect of PVT1 on tumorous prognosis. Materials and methods The effect of PVT1 on metastasis and survival were analyzed by univariate logistic regression and Cox proportional hazards model for 32 types of cancer in the Cancer Genome Atlas database (TCGA), and the relationship between PVT1 level and expression of relative genes was assessed by Pearson correlation analysis. RevMan5.3 and STATA14.0 were used to estimate pooled effects of PVT1 on cancer prognosis with data from TCGA and published studies. Results In TCGA data, high PVT1 expression tended to increase the risk of TNM progression and decreased the overall survival (OS) time in most of cancers. The pooled effect of PVT1 on TNM (pooled-OR=1.46, 95% CI: 1.29–1.65) and OS (pooled HR=1.32, 95% CI: 1.22–1.43), calculated from 37 and 48 cohorts, identified that high PVT1 expression promoted the metastasis and poor prognosis of cancer. Furthermore, the pooled ORs of 2.77 (95% CI: 1.65–4.66), 4.32 (95% CI: 1.99–9.36), 1.35 (95% CI: 1.01–1.80), 1.62 (95% CI: 1.21–2.18) and 1.48 (95% CI: 1.02–2.15) provided evidence that PVT1 played a role in lymph node metastasis, depth of invasion, distant metastasis, differentiation and lymphatic invasion; while the expression of 24 identified target genes was significantly associated with PVT1 level, and high PVT1 expression dependently decreased the OS time under the influence of co-expression genes (OR=1.29, 95% CI: 1.25–1.32) in high-throughput RNA sequencing merging data. In addition, the expression of PVT1 could be upregulated by smoking, with the pooled OR being 1.09 (95% CI 1.01–1.16). Conclusion PVT1 is a dependent biomarker for tumorous prognosis surveillance. However, the reference value of PVT1 needs further study.

Owing to cavitation inside the nozzle, spray breakup, and complex flow fields in the cylinder of a spark ignition engine, a certain degree of cycle-to-cycle variation (CCV) remains in different spray cycles under the same operating conditions, thereby affecting the spark ignition engine significantly. Therefore, the effect of cross-flow on the cyclic variation of the spray characteristics is investigated in this work. The CCV of fuel spray characteristics is evaluated via the statistical analysis of 30 repeated experiments under atmospheric pressure. First, the coefficient of variation (COV) is used to assess variations in the spray penetration, area, and optical thickness. Moreover, the effects of injection pressure and cross-flow velocity on the statistical characteristics of the spray are analyzed at the end of injection (EOI). Finally, a dimensionless “Ins number”, which is defined as the parameter of any spray characteristic at a certain time divided by the average experimental value, is proposed to evaluate the spray variation characteristics under cross-flow conditions. Therefore, when the absolute value of the Ins number approaches 1, the CCV of the spray characteristic parameters is low. Results show that the COV of the spray penetration is the largest in the initial stage of injection and then decreases gradually. Meanwhile, the COV of the vertical penetration can be categorized into two stages. Furthermore, it is discovered that the variation in the horizontal penetration is enhanced by the cross-flow and injection pressure at the EOI. In addition, in terms of the COV of the optical thickness, the variation on the windward side is greater, and the cross-flow enhanced the variation in the spray tip region. Most of the Ins numbers of the spray characteristics range from 0.9 to 1.1 (±10%) in this study, and they can provide data support for improving the accuracy of empirical prediction equations and models.

Satellite communication systems (SCS) operating on frequency bands above 10GHz are sensitive to atmosphere physical phenomena, especially rain attenuation. To evaluate impairments in satellite performance, stochastic dynamic modeling (SDM) is considered as an effective way to predict real-time satellite channel fading caused by rain. This article carries out a survey of SDM using stochastic differential equations (SDEs) currently in the literature. Special attention is given to the different input characteristics of each model to satisfy specific local conditions. Future research directions in SDM are also suggested in this paper.

Large quantities of carbon are stored in alpine grassland of the Tibetan Plateau, which is extremely sensitive to climate change. However, it remains unclear whether soil organic matter (SOM) in different layers responds to climate change analogously, and whether microbial communities play vital roles in SOM turnover of topsoil. In this study we measured and collected SOM turnover by the 14C method in alpine grassland to test climatic effects on SOM turnover in soil profiles. Edaphic properties and microbial communities in the northwestern Qinghai Lake were investigated to explore microbial influence on SOM turnover. SOM turnover in surface soil (0–10 cm) was more sensitive to precipitation than that in subsurface layers (10–40 cm). Precipitation also imposed stronger effects on the composition of microbial communities in the surface layer than that in deeper soil. At the 5–10 cm depth, the SOM turnover rate was positively associated with the bacteria/fungi biomass ratio and the relative abundance of Acidobacteria, both of which are related to precipitation. Partial correlation analysis suggested that increased precipitation could accelerate the SOM turnover rate in topsoil by structuring soil microbial communities. Conversely, carbon stored in deep soil would be barely affected by climate change. Our results provide valuable insights into the dynamics and storage of SOM in alpine grasslands under future climate scenarios.

The oxygen and hydrogen isotopic compositions of gypsum hydration water can be useful for determining the isotopic composition of the original brine from which gypsum precipitated. However, relatively few long-term and continuous records of the stable isotope geochemistry of gypsum hydration water in arid regions have been reported. We measured the 8180 and SD of primary gypsum hydration water from a 938.5 m-long deep core (SG-1) in the western Qaidam Basin to study the mechanisms that contributed to gypsum formation and to reconstruct potential paleoclimatic change. The measured delta O-18 and delta D ranged from - 4.21%o to 8.69%o and from - 72.77%o to 49.73%o, respectively. The linear relationship between delta O-18 and delta D indicates that meteoric water was the original source of the gypsum hydration water. The gradient of 5.39 for the delta O-18 and SD plots is lower than that of global meteoric water, suggesting that paleo-lakewater evaporated and became a CaSO4-rich brine leading to gypsum deposition. The evaporation/precipitation (E/P) ratio played an important role in determining delta O-18 and SD. The oscillations noted in the delta O-18 and SD of the gypsum hydration water imply that: (a) there was a long-term and stepwise aridification after similar to 2.2 Ma in the western Qaidam Basin; and (b) there were three increasingly dry phases at 2.2-1.2 Ma, 1.2-0.6 Ma, and 0.6-0.1 Ma, with two cold and dry events at similar to 1 Ma and similar to 0.6 Ma. Global cooling, especially during the Mid Pleistocene Climate Transition event (MPT), may have been the primary cause of the aridification recorded in core SG-1 in the Asian inland.

Distributed satellite cluster (DSC) consisted of number of formation flying satellites is hot research topic in the space information network. In this paper, a collaborative beamforming algorithm is proposed to enhance transceiver capability of the DSC by forming a virtual large aperture array (VLAA) based on random antenna array theory. According to the location information characteristic of the formation flying satellites in a DSC, the array manifold vector of the VLAA can be divided into two parts: one is the random term associated with the satellite perturbation; the other is the fixed term related to the design of the formation. The random term is analyzed by the random antenna array theory. Furthermore, we also formulate an optimization problem to meet the requirement of a fixed electromagnetic wave transceiver task by a optimal formation of the DSC based on mixed integer programming (MIP). Simulation results showed that the proposed algorithm can obtain an optimal formation of a DSC to enhance electromagnetic wave transceiver capability and extend the collaborative beamforming technology to the research field of space information network.

Internet of Things (IoT) has become an essential part of the coming 5th generation (5G). As a powerful supplementation, satellite systems can extend terrestrial IoT network to a full-time global network. In order to effectively allocate relatively limited on-board resources for meeting massive access demand, global traffic model needs to be studied. In this paper, we analyze the characteristics of satellite-based IoT devices based on corresponding geographic properties and applications. Such characteristics combining with specific LEOSCS design lead to the global traffic model of LEOS-based IoT network. Simulations results are also presented for different satellites in the system.

Global warming accompanied by precipitation changes impacts soil carbon sequestration. A three-year field manipulation experiment with warming (+2 °C above ambient temperature) and increased precipitation (+15% and +30% above ambient precipitation) was conducted in an alpine grassland to investigate the response of soil organic matter (SOM) to future climate change on the Qinghai-Tibet Plateau (QTP). Labile-fraction SOM (LF-SOM) fingerprints were characterized by pyrolysis-gas chromatography/tandem-mass spectrometry (Py-GC–MS/MS), and organic compounds in LF-SOM were used as indicators to quantify the contributions of vegetation input and microbial degradation to LF-SOM transformation. Increased precipitation promoted LF-SOM accumulation, which were mainly due to the positive effect of increased precipitation on vegetation productivity. Plant-derived compounds in LF-SOM (including lignin, long-chain alkyl compounds, polysaccharides and phenols) were more sensitive to increasing soil moisture than microbial-derived (including short-chain alkyl compounds, N compounds and chitin) and aromatic-derived compounds (including aromatics and polyaromatics). In contrast, warming alone intensified the effect of drought on the alpine grassland, which had negative effects on both vegetation and microorganisms and reduced LF-SOM. Warming plus increased precipitation not only alleviated the water loss caused by warming but also increased soil temperature, which was more favorable for the growth of microorganisms. This was reflected in the increase in microbial-derived compounds in LF-SOM with increasing soil temperature, which contributed to LF-SOM degradation. Aromatic-derived compounds, as refractory compounds in soil, showed no significant response to either warming or increased precipitation treatments. Acidobacteria (approximately 25%) and Actinobacteria (approximately 20%), as the dominant soil bacterial communities in the alpine grassland, were significantly correlated with plant-derived compounds. At the same time, there were significant correlations between Proteobacteria and microbial-derived compounds, as well as between Firmicutes and aromatic-derived compounds (relative abundance). Under future climate change, microbial activity will increase as temperature increases, which will promote LF-SOM degradation only if precipitation also increases.

The accuracy of the frequency difference of arrival (FDOA) estimation of signal location with the traditional cross ambiguity function (CAF) method is limited by the spectral resolution of CAF. This paper proposes a cross ambiguity function interpolation (CAFI) method, which uses linear interpolation of the phase difference of adjacent CAF values between frequency bins around CAF peak to estimate the FDOA. Theoretical analysis and Monte Carlo simulation results show that the accuracy of the proposed CAFI for FDOA estimation method has been significantly improved and it is close to Cramer-Rao Lower Bound (CRLB). In the case of a signal-to-noise ratio(SNR) of 5 dB and a data length of 128, the FDOA's estimated Root Mean Square Error (RMSE) is reduced to 5% of the conventional CAF direct result, and the estimation accuracy is improved by 20 times.

Impacts of atmospheric nitrogen (N) deposition on soil carbon (C) dynamics are highly variable, and the underlying mechanisms remain unclear. This limits our ability to predict soil responses to climate change. Labile-fraction soil organic matter (LF-SOM), which is the earliest-responding indicator of soil changes, was examined to investigate SOM dynamics on a Tibetan alpine steppe in response to N addition at six levels (0, 10, 20, 40, 80 and 160 kg⋅N⋅ha−1⋅yr−1) after 2 and 5 years. LF-SOM fingerprints (pyrolysis-gas chromatography/tandem-mass spectrometry) combined with microbial community data (high-throughput sequencing) were used to explore LF-SOM responses to N addition and their drivers. LF-SOM showed accumulation (N10–N20) and decomposition (N40–N160) in the 2nd year of N addition but only decomposition (N10–N160) in the 5th year. Organic compounds in LF-SOM showed high sensitivity (90% significant correlations with the N level) but low resistance (0.38 resistance index) and low sensitivity (no significant correlation) but high resistance (0.48) to the N level in the 2nd year and 5th year, respectively. Abiotic and biotic factors showed higher sensitivity to the N level in the 2nd year (more than 70% significant correlations) than in the 5th year (approximately 20% significant correlations), and biotic factors showed higher resistance (0.83) to the N level in the 5th year than in the 2nd year (0.73). Abiotic factors, mainly the soil C/N balance, were the primary drivers of LF-SOM transformation in the 2nd year, while biotic factors, primarily microbes, were the main drivers of LF-SOM decomposition in the 5th year. Our study demonstrated that the variable impacts of N deposition on LF-SOM transformation depended on shifts in the responses of abiotic and biotic factors to N accumulation. This understanding is significant for predicting terrestrial ecosystem functions under future N deposition.

Cavitation in nozzle orifices plays an important role on atomization and spray. In the industrial manufacturing, the processing method, especially the fluid grinding technology seriously affects the geometry of the orifice, such as the inlet rounding and roughness of inner orifice, which may result in the cavitation and turbulence of the internal flow. Therefore, the effect of grinding nozzle orifice on fuel spray was studied in this paper. Two mini-sac injectors with the same single orifice were used to compared. One was electrical discharge machining (EDM) nozzle orifice with Hydro-Erosive (HE) Grinding, and the other was EDM orifice without grinding. The spray experiments were conducted in the constant volume chamber. Firstly, the discharged coefficient (Cd) was calculated by controlling the injection duration and quantity. Secondly, non-evaporating characteristics were obtained through Mie scattering method. The spray tip penetration, spray area, spray cone angle and spray angle were defined and analyzed. Then, evaporating behaviors were characterized by laser absorption scattering (LAS) measurement as well as vapor mass and evaporation ratio. Finally, microscopic behaviors of near-nozzle spray and droplets were compared with the help of particle image analysis (PIA) technology. Results showed that owing to the cavitation without grinding process, Cd decreased sharply, leading to less spray area and angle. But the evaporation was promoted by the cavitation and turbulence. More vapor mass and evaporation ratio can be obtained without HE Grinding. Furthermore, droplet size becomes smaller without grinding due to the better atomization by turbulence. However, the mean velocity decreases sharply, and the coefficient of variation (COV) increases without grinding, which should be considered carefully in the injector design.

With the rapid development of communication technology, satellite communication has been very popular in our life. However, due to the openness of satellite communication channel, the communication security has been a hot topic. The large signal masking technology is a potential solution to improve the safety of satellite communications in recent years. To achieve this technique, an efficient and reliable signal separation method must be supplemented at the receiver. Based on existing methods, there are problems of low accuracy of parameter estimation and complex estimation process. The improved scheme introduces the Amplitude and Phase Estimation(APES) based parameter estimation procedure, and proposes a new scheme consisting of APES algorithm, Costas loop and Least Mean Square (LMS) adaptive filter. Compared with existing methods, the simulation results show that the proposed method can achieve mask signal separation successfully, and can achieve better separation performance.

High amounts of deposited nitrogen (N) dramatically influence the stability and functions of alpine ecosystems by changing soil microbial community functions, but the mechanism is still unclear. To investigate the impacts of increased N deposition on microbial community functions, a 2-year multilevel N addition (0, 10, 20, 40, 80 and 160 kg N ha−1 year−1) field experiment was set up in an alpine steppe on the Tibetan Plateau. Soil microbial functional genes (GeoChip 4.6), together with soil enzyme activity, soil organic compounds and environmental variables, were used to explore the response of microbial community functions to N additions. The results showed that the N addition rate of 40 kg N ha−1 year−1 was the critical value for soil microbial functional genes in this alpine steppe. A small amount of added N (≤40 kg N ha−1 year−1) had no significant effects on the abundance of microbial functional genes, while high amounts of added N (>40 kg N ha−1 year−1) significantly increased the abundance of soil organic carbon degradation genes. Additionally, the abundance of microbial functional genes associated with NH4+, including ammonification, N fixation and assimilatory nitrate reduction pathways, was significantly increased under high N additions. Further, high N additions also increased soil organic phosphorus utilization, which was indicated by the increase in the abundance of phytase genes and alkaline phosphatase activity. Plant richness, soil NO2−/NH4+ and WSOC/WSON were significantly correlated with the abundance of microbial functional genes, which drove the changes in microbial community functions under N additions. These findings help us to predict that increased N deposition in the future may alter soil microbial functional structure, which will lead to changes in microbially-mediated biogeochemical dynamics in alpine steppes on the Tibetan Plateau and will have extraordinary impacts on microbial C, N and P cycles.

Internet of Things (IoT) is one of the evolutionary directions of the Internet. This paper focuses on the low earth orbit (LEO) satellite constellation-based IoT services for their irreplaceable functions. In many cases, IoT devices are distributed in remote areas (e.g., desert, ocean, and forest) in some special applications, they are placed in some extreme topography, where are unable to have direct terrestrial network accesses and can only be covered by satellite. Comparing with the traditional geostationary earth orbit (GEO) systems, LEO satellite constellation has the advantages of low propagation delay, small propagation loss and global coverage. Furthermore, revision of existing IoT protocol are necessary to enhance the compatibility of the LEO satellite constellation-based IoT with terrestrial IoT systems. In this paper, we provide an overview of the architecture of the LEO satellite constellation-based IoT including the following topics: LEO satellite constellation structure, efficient spectrum allocation, heterogeneous networks compatibility, and access and routing protocols.

A Gram-stain-negative, non-motile, light-pink-pigmented, aerobic, rod-shaped bacterium, designated V5RDT, was isolated from soil of Damxung county in the Qinghai-Tibetan Plateau. Strain V5RDT grew luxuriously at 10 °C, at pH 9.0 and in the presence of 1 % NaCl (w/v). Phylogenetic analysis of 16S rRNA gene sequences placed strain V5RDT in the genus Pedobacter and found that it was most closely related to Pedobacter alluvionis DSM 19624T (97.3 %), Pedobacter ginsenosidimutans JCM 16721T (96.84 %), Pedobacter agri DSM 19486T (96.28 %), Pedobacter roseus JCM 13399T (96.22 %), Pedobacter sandarakinus KCTC 12559T (95.92 %) and Pedobacter borealis DSM 19626T (95.85 %). The G+C content of the genomic DNA of the type strain V5RDT was 37.40 mol%. DNA–DNA relatedness for the type strain V5RDT with respect to its closest phylogenetic relative, P . alluvionis DSM 19624T, was 62.5±1.7 %. The polar lipid profile of the strain consisted of phosphatidylethanolamine, one unidentified aminolipid, one unidentified glycolipid and two unidentified polar lipids. Menaquinone MK-7 was the predominant respiratory quinone, and summed feature 3 (comprising C16 : 1 ω7c and/or C16 : 1 ω6c), iso-C15 : 0 and iso-C17 : 0 3-OH were the major fatty acids. With respect to phenotypic characteristics, biochemical properties and phylogenetic inference, strain V5RDT represents a novel species of the genus Pedobacter , for which the name Pedobacter psychrotolerans sp. nov is proposed. The type strain is V5RDT (=CGMCC 1.15644T=DSM 103236T).

A Gram-staining-negative, non-motile, orange-coloured and rod-shaped aerobic bacterium, designated W18RDT, was isolated from the alpine meadow soil of the Tibetan plateau. Phylogenetic analysis based on 16S rRNA gene sequences positioned strain W18RDT as a representative of a novel species under the genus Sphingomonas which was most closely related to Sphingomonas fennica DSM 13665T with a sequence similarity level of 97.14 %. Meanwhile, it also had a high level of sequence similarity with Sphingomonas laterariae DSM 25432T (96.51 %), Sphingomonas haloaromaticamans CGMCC 1.10206T (96.43 %) and Sphingomonas formosensis DSM 24164T (96.26 %). The G+C content of the genomic DNA of the type strain W18RDT was 66.4mol%. DNA-DNA relatedness for the type strain W18RDT with respect to its closest phylogenetic relative Sphingomonas. fennica DSM 13665Twas 21.54±1.2 %. Major cellular fatty acids in strain W18RDT were C16 : 1ω7c and/or C16 : 1ω6c (48.12 %), C18 : 1ω7c and/or C18 : 1ω6c (21.98 %) and C14 : 0 2-OH (14.93 %), with ubiquinone-10 (Q-10) as the predominant respiratory quinone. The polar lipid profile of the strain consisted of phosphatidylethanolamine, phosphatidylglycerol, sphingoglycolipid, phosphatidylcholine, diphosphatidylglycerol and two unknown lipids. Based on the evidence from a combination of phenotypic, taxonomic and phylogenetic analyses, strain W18RDT represents a novel species of the genus Sphingomonas, for which the name Sphingomonas prati sp. nov. is proposed. The type strain is W18RDT (=CGMCC 1.15645T=DSM 103336T).

Soil microorganisms play an important role in regulating the feedback of Alpine steppe ecosystems to future climate change. However, the interaction effect of warming and increasing precipitation on soil microorganisms remains unclear, in the face of an ongoing warmer and wetter climate on the Tibetan Plateau. In this study, we investigate the multi-factorial effects on soil microbial diversity, community structure, and microbial interactions in a three-year climate change experiment established in an Alpine steppe on the Tibetan Plateau, involving warming (+2 °C), +15% increasing precipitation and +30% increasing precipitation. Compared to warming, warming plus increasing precipitation alleviated the decrease in microbial diversity, and increased the dissimilarities in microbial community structures, largely influenced by water and substrate availability. We further observed differences in moisture increased the differences in microbial diversity and dissimilarities in microbial community structures across different precipitation levels under ambient temperature. Interestingly, warming plus increasing precipitation could create more ecological niches for microbial species to coexist but may lessen the strength of microbial interactions in contrast to increasing precipitation alone. Collectively, our findings indicate that microbial responses to future climate change in Alpine steppe soils will be more complex than those under single-climate-factor conditions.

Alpine grasslands provide essential ecosystem functions and services, yet they are increasingly subject to anthropogenic perturbations. Northwest Yunnan (NWY) is one of the most popular tourist destinations in China, and alpine grasslands of NWY are particularly susceptible to human recreational activities such as hiker trampling. However, studies that explicitly evaluate the effects of trampling disturbance on alpine communities of NWY are very limited, let alone research testing the responses of these communities to trampling from a functional trait perspective. The present research is performed in alpine grasslands within and outside of a core nature conservation area of Shangri-La, NWY of China, to study species- and community-level responses of alpine communities to simulated trampling through a functional trait-based approach. The results showed that although species-specific differences existed, alpine plants generally showed rapid morphological changes in response to trampling disturbance. At the community level, trampling disturbance caused strong shifts in taxonomy-based diversity metrics (e.g., species richness, Simpson’s index and Shannon’s index) and functional trait-based diversity metrics (e.g., functional richness, functional evenness, functional divergence, and community-weighted mean trait values). Specifically, increased trampling intensity led to a decrease in taxonomic diversity. Meanwhile, functional richness decreased, while functional evenness and functional divergence increased with an increase in trampling intensity. Also, characteristics of alpine community traits had changed towards those with shorter height, reduced leaf size and lower LDMC, and such strong shifts in taxonomic and functional diversity might further affect the functioning and value of alpine grasslands. Therefore, the protection of high-altitude natural grasslands with high sensitivity and vulnerability is urgent, especially as they are increasingly experiencing multiple environmental and climatic stressors nowadays.