Low Altitude Satellite Constellation for Futuristic Aerial-Ground Communications

This paper discusses the significance and prospects of low altitude small satellite aerial vehicles to ensure smooth aerial-ground communications for next-generation broadband networks.To achieve the generic goals of fifthgeneration and beyondwireless networks,the existing aerial network architecture needs to be revisited.The detailed architecture of low altitude aerial networks and the challenges in resource management have been illustrated in this paper.Moreover,we have studied the coordination between promising communication technologies and low altitude aerial networks to provide robust network coverage.We talk about the techniques that can ensure userfriendly control and monitoring of the low altitude aerial networks to bring forth wireless broadband connectivity to a new dimension.In the end,we highlight the future research directions of aerial-ground communications in terms of access technologies,machine learning,compressed sensing,and quantum communications.

Occurrence of anionic redox with absence of full oxidation to Ru^(5+) in high-energy P2-type layered oxide cathode

The anionic redox has been widely studied in layered-oxide-cathodes in attempts to achieve highenergy-density for Na-ion batteries(NIBs).It is known that an oxidation state of Mn^(4+) or Ru^(5+) is essential for the anionic reaction of O^(2-)/O~-to occur during Na^(+) de/intercalation.However,here,we report that the anionic redox can occur in Ru-based layered-oxide-cathodes before full oxidation of Ru^(4+)/Ru^(5+).Combining studies using first-principles calculation and experimental techniques reveals that further Na^(+) deintercalation from P2-Na_(0.33)[Mg_(0.33)Ru_(0.67)]O_(2) is based on anionic oxidation after 0.33 mol Na^(+) deintercalation from P2-Na_(0.67)[Mg_(0.33)Ru_(0.67)]O_(2) with cationic oxidation of Ru^(4+)/Ru^(4.5+).Especially,it is revealed that the only oxygen neighboring 2Mg/1 Ru can participate in the anionic redox during Na^(+) de/intercalation,which implies that the Na-O-Mg arrangement in the P2-Na_(0.33)[M9_(0.33)Ru_(0.67)]O_(2) structure can dramatically lower the thermodynamic stability of the anionic redox than that of cationic redox.Through the O anionic and Ru cationic reaction,P2-Na_(0.67)[Mg_(0.33)Ru_(0.67)]O_(2) exhibits not only a large specific capacity of~172 mA h g^(-1) but also excellent power-capability via facile Na^(+) diffusion and reversible structural change during charge/discharge.These findings suggest a novel strategy that can increase the activity of anionic redox by modulating the local environment around oxygen to develop high-energy-density cathode materials for NIBs.

细颗粒泥沙对离心泵工作特性影响的数值研究

基于Eulerian-Eulerian"双流体"模型观点,应用CFD软件Fluent对离心泵细颗粒泥沙固液两相流进行了数值模拟。给出了在微米量级尺度上不同粒径及10%颗粒体积浓度以内条件下离心泵固液两相流动规律,得到了相应的离心泵的外特性的变化规律并与清水单相流情形进行了对比。研究结果表明:在叶轮流道内,固相体积浓度分布极不均匀,细颗粒主要集中于流道出口处及叶轮吸力面。在所研究的工况条件下,与清水情况相比,加入某些浓度、粒径的细颗粒离心泵内的湍流黏度,湍动能都有所下降,并且分布规律与颗粒的分布相似,离心泵的扬程与效率有所提高。相同体积流量下,离心泵的扬程和效率在所研究的工况条件下随颗粒浓度和粒径的增加先增大后减小。

Interface properties and phase formation between surface coated SKD61 and aluminum alloys

The intermediate phase formation and surface protection effects between SKD61 die mold alloys and aluminum alloys were investigated during a simulated die-casting process.The surface coatings of SKD61 alloy were carried out via Si pack cementation coatings at 900 ℃ for 10 h and the ε-FeSi phase formed.When the coated SKD61 alloy was dipped in the liquid aluminum alloy(ALDC12),the surface coated SKD61 alloys showed better surface properties compared with uncoated SKD61 alloys,i.e.,the intermediate phases(FeSiAl compound) were not produced for the coated SKD61 alloy.The coating layer of ε-FeSi served as a diffusion barrier for the formation of FeSiAl compounds.

简单水热法合成石墨-CdSe复合材料及其光催化降解有机染料(英文)

A graphene-CdSe composite was synthesized by a facile hydrothermal method,and characterized by X-ray diffraction,scanning electron microscopy with energy dispersive X-ray analysis,transmission electron microscopy and UV-vis diffuse reflectance spectrophotometry.The graphene-CdSe composite efficiently catalyzed the photodegradation of methylene blue(MB),methyl orange(MO) and rhodamine B(Rh.B) in aqueous solution under UV or visible light irradiation.The graphene-CdSe composite exhibited a higher photocatalytic activity for the MB solution.

Pharmacological advantages of melatonin in immunosenescence by improving activity of T lymphocytes

Melatonin plays a critical role in regulating photoperiodic signals and has recently been shown to decrease immunosenescence with age. In this study, we examined whether melatonin activates T lymphocytes as major adaptive immune cells in in vitro and in vivo models. Splenocytes, CD4＋, and naive CD4 T lymphocytes were isolated from the spleen of BALB/c mice and the cell population patterns and mRNA profiles associated with T cell activation （CD28 and p21） and the melatonin receptor （MT1A and MT1B） were assessed. The T cell activation- related proteins Ki67 and Bcl2 were also evaluated to confirm the relationship between gene and protein levels. Our data clearly revealed that CD28, p21, MT 1 A, and MT 1B mRNA were highly expressed in the presence of melatonin. Co-culture of CD4＋ T lymphocyte and peritoneal macrophage 7 days after melatonin administration to young and aged mice significantly increased APRIL mRNA, suggesting induction or maintenance of T lymphocyte responses. We also found that the intracellular amount of Ki67 and Bcl2 proteins were significantly upregulated in aged CD4＋ T lymphocytes, suggesting enhancing T cell proliferation and ling-term maintenance of memory T cells. Taken together, we conclude that melatonin supplementation may enhance immunity in aged individuals by upregulating immunosenescence indices in association with T lymphocytes and may be an attractive pharmacological candidate for aged and immunocompromised individuals.

等离子喷涂和激光表面熔化制备Si喷涂Ti-Zr-Mo合金的抗氧化性能（英文）

由于Mo基体在热空气中不稳定,采用等离子热喷涂工艺将Si涂覆于Ti-Zr-Mo合金表面以保护Mo基体。虽然单独使用等离子热喷涂工艺能使Mo合金表面在高温下及较短时间内不被氧化,但是后续的激光表面熔化工艺能提高Si喷涂合金的抗氧化性能。对于后续激光处理样品,在随后的退火工艺中形成了钼硅化合物(主要成分为Mo Si_2),且其抗氧化性能得到进一步改善。另外,研究了Si喷涂样品在3.5%Na Cl溶液中的腐蚀行为,然而经激光表面熔化工艺处理样品的耐腐蚀性能与未经激光表面熔化处理样品的耐腐蚀性能无明显差异。

Effects of casting speed on microstructure and segregation of electromagnetically stirred Aluminum alloy in continuous casting process

Recently, a semi-solid metal processing has been acknowledged as a cost-effective technique to be able to manufacture high quality product for the transportation industry. In this study a hypo-eutectic Al alloy was fabricated by means of an electromagnetic stirrer in continuous casting process and the microstructural change during solidification due to a fluid flow by electromagnetic stirring was examined. Due to the forced fluid flow during solidification a dendritic phase of primary α phase of Al alloy was turned into a globular phase, which can make the Al alloy get a thixotropic behavior in the semi-solid region. In order to establish the quantitative relationship between microstructure and the process parameters, the morphology shape, a silicon distribution and a size of primary α phase were observed according to casting speed in continuous casting machine. The primary α phase was turned into the degenerate dendrites approaching a spherical configuration with increasing casting speed. The fine-grained and equiaxed microstructure appeared at higher casting speed. A segregation behavior of Si element was declined with increasing casting speed and a very uniform distribution of Si element was observed on the billet at a casting speed of 600 mm·min-1. A thickness of the solidifying shell of the billet was shortened with increasing the casting speed.

Characterization of plasma electrolytic oxide formed on AZ91 Mg alloy in KMnO_4 electrolyte

The aim of this work is to investigate microstructure,corrosion resistance characteristics and nanohardness of the oxide layer on AZ91 Mg alloy by applying different voltage with KMnO4 contained solution.There are lots of closed pores that are filled with another oxide compound compared with the typical surface morphology with pore coated until 350 V of coating voltage.The thickness of oxide layer increases with increasing coating voltage.The oxide layer formed on AZ91 Mg alloy in electrolyte with potassium permanganate consists of MgO and Mn2O3.Corrosion potential of the oxide layer on AZ91 Mg alloy obtained at different plasma electrolytic oxidation(PEO) reaction stages increases with increasing coating voltage.The corrosion resistance of AZ91 Mg alloy depends on the existence of the manganese oxide in the oxide layer.The inner barrier layer composed of the MgO and Mn2O3 may serve as diffusion barrier to enhance the corrosion resistance and may partially explain the excellent anti-corrosion performance in corrosion test.Nanohardness values increase with increasing coating voltage.The increase in the nanohardness may be due to the effect of manganese oxide in the oxide layer on AZ91 Mg alloy coated from electrolyte containing KMnO4.

Thermal performance analysis of borehole size effect on geothermal heat exchanger

Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy.The thermal performance was affected by many different design parameters,such as configuration type and borehole size of geothermal heat exchanger.These eventually determined the operation and cost efficiency of the geothermal heat exchanger system.The main purpose of this work was to assess the thermal performance of geothermal heat exchanger with variation of borehole sizes and numbers of U-tubes inside a borehole.For this,a thermal response test rig was established with line-source theory.The thermal response test was performed with in-line variable input heat source.Effective thermal conductivity and thermal resistance were obtained from the measured data.From the measurement,the effective thermal conductivity is found to have similar values for twopair type(4 U-tubes)and three-pair type(6 U-tubes)borehole heat exchanger systems indicating similar heat transfer ability.Meanwhile,the thermal resistance shows lower value for the three-pair type compared to the two-pair type.Measured data based resistance have lower value compared to computed result from design programs.Overall comparison finds better thermal performance for the three-pair type,however,fluctuating temperature variation indicates complex flow behavior inside the borehole and requires further study on flow characteristics.

稀硫酸溶液清洗电镀铜晶种(英文)

采用稀硫酸溶液清洗以除去在铜晶种表面形成的氧化物。将通过溅射沉积在Ti/Si(100)薄片上生成的铜晶种暴露在空气中来生长原生铜氧化物。用稀硫酸溶液和TS-40A碱性清洗剂除去原生铜氧化物。先用TS-40A碱性清洗剂预处理以除去铜晶种表面的有机物,再用稀硫酸溶液除去铜氧化物(Cu2O和CuO)以及有机物和Cu(OH)2。

Optimization of post-warranty sequential inspection for second-hand products

This paper considers an optimal sequential inspection schedule for a second-hand product after that the free nonrenewable warranty is expired. The length of warranty is prespecified and during the warranty period, the product is minimally repaired by the dealer when it fails. Following the expiration of the non-renewing warranty, the product is inspected and upgraded sequentially a fixed number of times at the expenses of the customer.At each inspection, the failure rate of the product is reduced proportionally so that the product is upgraded. The product is assumed to deteriorate as it ages and the replacement of the product occurs when a fixed number of inspections are rendered. In addition,the intervals between two successive inspections are assumed to decrease monotonically. The main objective of this paper is to determine the optimal improvement level to upgrade the product at each inspection so that the expected maintenance cost during the life cycle of the product is minimized from the perspective of the customer. Under the given cost structures, we derive an explicit formula to obtain the expected maintenance cost incurred during the life cycle of the product and discuss the method to find the optimal level of the improvement analytically in case the failure times follow the Weibull distribution. Numerical results are analyzed to observe the impact of relevant parameters on the optimal solution.

Combustion Characteristics of Solid Refuse Fuels from Different Waste Sources

In the production(as co-fuel or alone)of solid refuse fuel(SRF),knowledge about the characteristics of the raw materials is required for an ecofriendly and effective combustion process.SRFs are commonly produced by drying combustible waste and removing incombustible matter,resulting in a higher combustibility as compared to the original waste.However,the characteristics of SRFs may highly vary depending on where and from which materials they were produced.Thus,we investigated the characteristics of various SRFs using thermogravimetric analysis(TGA).As a TGA sample is commonly small,on the scale of milligrams,and,unlike homogeneous fuels,SRFs are heterogeneous,individual SRF samples analysed with this method may not represent the bulk material,and sample properties may vary significantly between batches.Therefore,we further performed combustion experiments using a small-scale combustor and sample sizes from 1 to 10 g.To optimise SRF combustor design and determine the SRF characteristics,proximate,elemental,heating value,TG,and differential thermogravimetric analyses were conducted,and weight losses and gas concentrations at different temperatures were measured upon combustion.The lower heating values of the three analysed SRFs were 20,976,16,873,and 19,762 kJ/kg,and their Cl contents were 0.89,0.95,and 1.27 wt.%(legal criterion[Cl]<2.0 wt.%).TGA and small combustor experiments showed that complete weight loss was achieved below 500°C.However,CO was detected until 620°C.

Moth-eye Structured Polydimethylsiloxane Films for High-Efficiency Perovskite Solar Cells

Large-area polydimethylsiloxane(PDMS)films with variably sized moth-eye structures were fabricated to improve the efficiency of perovskite solar cells.An approach that incorporated photolithography,bilayer PDMS deposition and replication was used in the fabrication process.By simply attaching the moth-eye PDMS films to the transparent substrates of perovskite solar cells,the optical properties of the devices could be tuned by changing the size of the moth-eye structures.The device with 300-nm moth-eye PDMS films greatly enhanced power conversion efficiency of ~21 % due to the antireflective effect of the moth-eye structure.Furthermore,beautiful coloration was observed on the 1000-nm moth-eye PDMS films through optical interference caused by the diffraction grating effect.Our results imply that moth-eye PDMS films can greatly enhance the efficiency of perovskite solar cells and building-integrated photovoltaics.

Tensor based non-photo realistic rendering for Korean architectural images

Existing pen and ink sketch technologies can be applied to general images, but they could not produce optimal output for images of traditional architecture, because most images consist of exquisite straight lined patterns in traditional architecture, such as root tiles and window bars. The lines of roofs and eaves need to be described delicately to express pen and ink sketch most effectively. Therefore, by proposing a method to create white noise for light and shade of input images, to extract input vector directions from the white noise, and to determine the direction and length of stroke, a new expression technique is proposed for pen and ink sketch that could best reflect the characteristics of traditional architecture.

基于Zone Master的混合无线网络的链路稳定性研究

在无线网络环境中,因拓扑结构的变化,而产生节点间的链路不断断链、路径不断重置,给网络带来过多的控制信息等问题。为了能够有效的解决链路断链、重置问题,该研究提出以Zone Master为中心节点的混合型无线网络链路稳定性策略,通过优化Zone Master的相邻节点探索、路径探索、路径管理,提高了在多样的无线网络环境下网络链路的稳定性。

铸造Mg-2%Ca合金的拉伸蠕变和抗腐蚀性能(英文)

对分别添加Zn和Al的Mg-2%Ca合金的拉伸蠕变和抗腐蚀性能进行比较。结果表明:添加Zn比添加Al能更加显著地提高Mg-2%Ca合金在170°C下的蠕变性能。然而,添加Al对提高合金的耐腐蚀性能更为有效。由于添加Zn的合金的凝固区间更为宽大,因此,为了生产高质量的铸件产品,对铸造工艺的控制要求更加严格。

Mg-Al Alloys Manufactured by Casting and Hot Working Process

Mechanical properties of Mg-Al based alloys at different fabrication state,namely as-cast,hot rolled,and annealed,were investigated to develop the alloys that are suitable for the casting/hot working process.Exper- imental results indicated that the castability such as hot cracking resistance tends to improve with increasing the aluminum content.However,the elongation at elevated temperatures was observed to decrease as the AI content increases,implying difficulties in hot forming.A small amount of Zr additions could significantly enhance the room temperature mechanical properties of hot-rolled Mg-6%Al-1%Zn alloy.The tendency of remarkable grain coarsening at high temperatures was effectively reduced by the Zr additions.TEM analyses suggested that very fine Al-3Zr precipitates formed in the Zr-added alloy are responsible for the obtained results.

Piezoresistive Prediction of CNTs-Embedded Cement Composites via Machine Learning Approaches

Conductive cementitious composites are innovated materials that have improved electrical conductivity compared to general types of cement,and are expected to be used in a variety of future infrastructures with unique functionalities such as self-heating,electromagnetic shielding,and piezoelectricity.In the present study,machine learning methods that have been recently applied in various fields were proposed for the prediction of piezoelectric characteristics of carbon nanotubes(CNTs)-incorporated cement composites.Data on the resistivity change of CNTs/cement composites according to various water/binder ratios,loading types,and CNT content were considered as training values.These data were applied to numerous machine learning techniques including linear regression,decision tree,support vector machine,deep belief network,Gaussian process regression,genetic algorithm,bagging ensemble,random forest ensemble,boosting ensemble,long short-term memory,and gated recurrent units to estimate the time-independent and-dependent electrical properties of conductive cementitious composites.By comparing and analyzing the computed results of the proposed methods,an optimal algorithm suitable for application to CNTs-embedded cementitious composites was derived.

Characteristic analysis of bleeding effect on standing column well (SCW) type geothermal heat exchanger

Thermal performance is the most important factor in the development of a borehole heat exchanger utilizing geothermal energy.The thermal performance is affected by many different design parameters and different operating conditions such as bleeding.This eventually determines the operation and cost efficiency of the borehole heat exchanger system.The thermal performance of an open standing column well (SCW) type geothermal heat exchanger was assessed under the influence of bleeding.For this,a thermal response test rig was established with line-source theory.The test rig also had a bleeding function by releasing fluid while taking additional underground water through the heat exchanger.The thermal response test was performed with an additional constant input heat source.Effective thermal conductivity and thermal resistance were obtained from the measured data.From the measurement,the effective thermal conductivity is found to have 1.47 times higher value when bleeding is applied.The thermal resistance also increases by 1.58 times compared to a non-bleeding case.This trend indicates enhanced heat transfer in the SCW type heat exchanger with a bleeding function.Bleeding,therefore,could be an effective method of achieving a high heat transfer rate in the SCW type heat exchanger with sufficient underground water supply.