Modeling and Analysis of OFDMA-NOMA-RA Protocol Considering Imperfect SIC in Multi-User Uplink WLANs

To address the problems of network congestion and spectrum resources shortage in multi-user large-scale scenarios,this paper proposes a twice random access OFDMA-NOMA-RA protocol combining the advantages of orthogonal frequency division multiple access(OFDMA)and non-orthogonal multiple access(NOMA).The idea of this protocol is that OFMDA is used to divide the entire frequency field into multiple orthogonal resource units(RUs),and NOMA is used on each RU to enable more users to access the channel and improve spectrum efficiency.Based on the protocol designed in this paper,in the case of imperfect successive interference cancellation(SIC),the probability of successful competition subchannels and the outage probability are derived for two scenarios:Users occupy the subchannel individually and users share the subchannel.Moreover,when two users share the channel,the decoding order of the users and the corresponding probabilities are considered.Then,the system throughput is obtained.To achieve better outage performance in the system,the optimal power allocation algorithm is proposed in this paper,which enables the optimal power allocation strategy to be obtained.Numerical results show that the larger the imperfect SIC coefficient,the worse the outage performance of weak users.Compared with pure OFDMA and NOMA,OFDMA-NOMA-RA always maintains an advantage when the imperfect SIC coefficient is less than a specific value.

Contents and Distribution of Petroleum Hydrocarbons (PHC) in Jiaozhou Bay Waters

Based on data from the investigation in Jiaozhou bay waters in 1979, the distribution, pollution source and seasonal variation of PHC in Jiaozhou Bay are analyzed. It is showed that in Jiaozhou bay PHC contents arrived the national Category Ⅱof the water quality standard during this year. In summer in the bay the pollution of PHC was heavy, while relatively light in spring. In the coastal waters in the east and the northeast of the bay, the PHC contents in spring surpassed the national Category Ⅱ, and surpassed the national Category Ⅲ. In the coastal waters, in the northeast of the bay, the change of the PHC contents formed the grads: the contents presented the falling trend from the big one to the small, which unveiled that the PHC souce in the bay mainly came from the discharge of the industrial waste water and living sewage.

Effect of pH, milling time, and Isobam content on porous silicon nitride ceramics prepared by gel casting

As a non-toxic copolymer of isobutylene and maleic anhydride,Isobam is successfully used as a dispersant and a gelling agent for fabricating porous Si_(3)N_(4) ceramics by gel casting.The dispersity and rheological properties of the Si_(3)N_(4) slurry are influenced by the pH,milling time,and Isobam content which varies from 0.1 wt.%to 0.6 wt.%,and these factors are investigated.The slurry with 40 vol.%solid content and milled for 4 h has a high zeta potential at pH 12(adjusted by Tetramethyl ammonium hydroxide(TMAH)),which means that the particles are well dispersed.The mechanisms of TMAH are electrostatic repulsion and steric hindrance.The viscosity of the slurry increases with the increase of Isobam content.After pressureless sintering at 1700℃ for 2 h,a uniform unique interlocking microstructure of rod-like β-Si_(3)N_(4) grains is observed,which may improve the flexural strength of the ceramics by intergranular fracture and particle pullout of β-Si_(3)N_(4) grains.The density and porosity of the samples fluctuate negligibly with the increase of Isobam content,and the Si_(3)N_(4) ceramic with 0.1 wt.% Isobam exhibits the highest bending strength of 251.6 MPa among all samples.

Effects of Different Processing Methods on Chlorogenic Acid Content in Fructus Gardeniae

[ Objective] This study aimed to compare the effects of different processing methods on the content of chlorogenie acid in Fructus Garden/ae. [ Method] The chromatographic separation was performed on an Inersil ODS-2 C18 column （250 mm× 4.6 mm, 5 μm） with acetonitrile -0. 1% acetic acid solution （ 12： 88, V/V） as the mobile phase under conditions of tlow rate 1.0 mb/min, detection wavelength 327 ran, column temperature 25℃. [ Result J With a range of 0.42-2.52 μg/i.d, ehlorogenic acid concentration exhibited a good linear relationship with peak area （n =6, R =0. 999 9）. The average recovery rate was 100. 83%, RSD was 1.30%. [Conclusion] The established method is eonveniem, rapid and accurate with good repeatability, which can be used to effectively control the quality of different orocessed oroduets of Fructus C.ardeniae.

Effect of C/N Ratio on DHA Production by Schizochytrium sp.JN-3 and Its Pilot-scale Fermentation

[ Objective] This study aimed to explore the effect of C/N ratio on DHA production by Schizochytrium sp. , and the results were verified by pilot-scale fermentation. [ Method] Effect of C/N ratio on DHA production by Schizochytrium sp. JN-3 was explored. The industrial fermentation potential of Schizochytrium sp. JN-3 was investigated by pilot-scale fermentation in a 200 L fermentation tank. [ Result] Results of fermentation in a 7 L fermentation tank showed that the maximum biomass and total lipid content were 34.3 and 20.1 g/L, respectively, when C/N ratio was 10 ; the maximum DHA yield was 46.9% when C/N ratio was 20. When pilot-scale fermentation was conducted in a 200 L fermentation tank, the biomass was 30. 2 g/L, total lipid content was 18.4 g/L, accounting for 63.2% of the dry weight of cells; DHA content was 7.4 g/L, accounting for 40. 2% of the total lipid content. [ Condasion ] Schizochytrlum sp. JN-3 has good industrial fermentation notential.

Thermodynamics aided design of hBN-capsulated diboride powders from novel nitrate precursors for high entropy ceramics

Hexagonal BN-coated powders have been widely used in various engineering sectors,however,their pro-ductions are restricted by the complexity of gas-solid reactions.In this study,guided by thermodynamics,a novel approach to synthesize Layer-structured hexagonal BN(hBN)-coated high entropy diboride pow-ders in vacuum was developed,using metal salt Zr(NO_(3))4·5H_(2)O,HfCl_(4),NbC_(15),TaC_(15),C_(16)H_(36)O_(4)Ti,boric acid,and sucrose as raw materials.By adjusting the ratio of carbon to metal source(C/M),powders only consisting of two boride solid solutions and hBN were finally obtained,under an optimal process-ing condition of C/M=5.5 and synthesis temperature of 1400 ℃.Parts of hBN were found to coat on high-entropy metal diborides ceramic(HEB)particles,corresponding formation mechanism for core-shell structured powders was investigated,together with the liquid precursor assisted boro/carbothermal re-duction process.Starting from as-synthesized core-shell powders,(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B2-11 vol%hBN ceramics were densified at 1900 ℃ under 50 MPa without holding,with a high relative density of 97.3%.

Formation mechanisms of Ti_(3)(Si,Al)C_(2)/Al_(2)O_(3) composites from Ti_(3)AlC_(2) and SiO via low-temperature sintering

Ti_(3)SiC_(2)/Al_(2)O_(3) composites have attracted attention due to their excellent mechanical and electromagnetic properties,but the high temperatures(≥1400℃)required for the densification of aluminum oxide(Al_(2)O_(3))leads to the decomposition of Ti_(3)SiC_(2).To address this issue,Ti_(3)(Si_(x)Al_(1−x))C2/Al_(2)O_(3)(x represents the Si content)composites were synthesized for the first time via hot-pressing(HP)sintering and current-assisted sintering(CAS)of mixed Ti_(3)AlC_(2) and silicon monoxide(SiO)powders at 1300 and 1200℃,respectively.Both approaches produced composites with x values greater than 0.9,indicating that the compositions of the prepared composites were similar to those of Ti_(3)SiC_(2)/Al_(2)O_(3) composites.The synthetic mechanism involved substitution and continuous interdiffusion of Al and Si atoms.The composite prepared by CAS at 1200℃ was compacted,whereas the composite prepared by HP had a low density.The low-temperature densification mechanism is attributed to the combined effects of amorphous SiO,liquid Al,and the high heating rates for CAS.The flexural strength and hardness of the composite prepared by CAS were also comparable to those of compacted Ti_(3)SiC_(2)/Al_(2)O_(3) composites.