针对underlay认知无线电中时频重叠正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)信号的信噪比(Signal to Noise Ratio,SNR)难以估计的问题,提出了一种基于循环自相关特性的时频重叠OFDM信噪比盲估计方法.该方法提取...针对underlay认知无线电中时频重叠正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)信号的信噪比(Signal to Noise Ratio,SNR)难以估计的问题,提出了一种基于循环自相关特性的时频重叠OFDM信噪比盲估计方法.该方法提取接收信号的循环自相关函数截面中的离散谱线估计出分量信号的总功率,并结合时延和循环频率均为零时的离散谱线估计出时频重叠OFDM信号的信噪比.仿真结果表明,在无需先验信息的情况下,当SNR大于-7d B时,所提方法估计的均方误差小于0.1,并且对分量信号的功率比和频谱重叠率具有稳健性.展开更多
Heusler Co2FeSi films with a uniaxial magnetic anisotropy and high ferromagnetic resonance frequency fr were deposited by an oblique sputtering technique on Ru underlayers with various thicknesses tRufrom 0 nm to 5 nm...Heusler Co2FeSi films with a uniaxial magnetic anisotropy and high ferromagnetic resonance frequency fr were deposited by an oblique sputtering technique on Ru underlayers with various thicknesses tRufrom 0 nm to 5 nm.It is revealed that the Ru underlayers reduce the grain size of Co2FeSi,dramatically enhance the magnetic anisotropy field HK induced by the internal stress from 242 Oe(1 Oe=79.5775 A·m^-1)to 582 Oe with an increment ratio of 2.4,while a low damping coefficient remains.The result of damping implies that the continuous interface between Ru and Co2FeSi induces a large in-plane anisotropic field without introducing additional external damping.As a result,excellent high-frequency soft magnetic properties with fr up to 6.69 GHz are achieved.展开更多
Hematite is regarded as a promising photoanode for photoelectrochemical(PEC) water splitting.However,the charge recombination occurred at the interface of FTO/hematite strictly limits the PEC performance of hematite.H...Hematite is regarded as a promising photoanode for photoelectrochemical(PEC) water splitting.However,the charge recombination occurred at the interface of FTO/hematite strictly limits the PEC performance of hematite.Herein,we reported a Ti3C2 MXene underlayer modified hematite(Ti-Fe2O3) photoanode via a simple drop-casting followed by hydrothermal and annealing processes.Owing to the bifunctional role of Ti3C2 MXene underlayer in improving the interfacial properties of FTO/hematite and providing Ti source for the construction of Fe2 TiO5/Fe2O3 heterostructure in hematite nanostructure,the bulk and interfacial charge transfer dynamics of hematite are significantly enhanced,and consequently enhancing the PEC performance.Compared with the pristine hematite,the as-prepared Ti-Fe2O3 photoanode shows an increased photocurrent density from 0.80 mA/cm^(2) to 1.30 mA/cm^(2) at 1.23 V vs.RHE.Moreover,a further promoted PEC performance including a dramatically increased photocurrent density of 2.49 mA/cm^(2) at1.23 V vs.RHE and an obviously lowered onset potential is achieved for the Ti-Fe2O3 sample after the subsequent surface F-treatment and the loading of FeNiOOH cocatalyst.Such results suggest that the introduction of Ti3C2 MXene underlayer is a facile but effective approach to improve the PEC water splitting activity of hematite.展开更多
Three kinds of oxide underlayers, namely Si02, ZnO and Al2O3, were deposited prior to the sputtering of Sr-ferrite films, respectively, in order to induce the optimum grain morphology and the texture of the films. A S...Three kinds of oxide underlayers, namely Si02, ZnO and Al2O3, were deposited prior to the sputtering of Sr-ferrite films, respectively, in order to induce the optimum grain morphology and the texture of the films. A Sr-ferrite film with an easy axis in-plane orientation was induced by SiO2 underlayer. In contrast, it prefers to be perpendicular to film plane for the cases of ZnO and Al2O3 underlayers. The optimum magnetic properties of the former film along film plane are: 4πMr=1.7 kG, iHc=5.35 kOe, and Sq=0.59, which are mainly dominated by the exchange coupling effect, determined by Wohlfarth's remanence analysis, among grains. While those for the films with an easy axis perpendicular to film plane can be as high as 4πMr=3.72 kG, iHc=6.42 kOe, and Sq=0.82, which are mainly dominated by the magnetostatic interaction among grains.展开更多
The Device-to-Device(D2D)communication underlaying cellular networks is considered in this study.The D2D transmitter in the D2D mode can directly transmit messages to a receiver,but it may interfere with the transmiss...The Device-to-Device(D2D)communication underlaying cellular networks is considered in this study.The D2D transmitter in the D2D mode can directly transmit messages to a receiver,but it may interfere with the transmission of another cellular user who shares the same uplink channel.The transmitter can also operate in a cellular mode in which no interference to another cellular user occurs.We propose a mode selection scheme that aims to minimize the transmission power of the D2D transmitter subject to constraints on the minimum required data rate and maximum interference to other cellular users.The proposed scheme is based on bounds for transmission power and is less complex than the optimal scheme.Furthermore,it requires only a few statistics and does not need a fading channel distribution.The performance of the scheme is close to optimum when the number of Base Station(BS)antennas is large,and the mean absolute deviation of the fading terms is small.We verify this with numerical results of the Rician and Rayleigh fading channels by assuming that the BS antennas are independent.The simulation results for the two correlated BS antennas are presented herein.展开更多
In order to improve the physical layer security of the device-to-device(D2D)cellular network,we propose a collaborative scheme for the transmit antenna selection and the optimal D2D pair establishment based on deep le...In order to improve the physical layer security of the device-to-device(D2D)cellular network,we propose a collaborative scheme for the transmit antenna selection and the optimal D2D pair establishment based on deep learning.Due to the mobility of users,using the current channel state information to select a transmit antenna or establish a D2D pair for the next time slot cannot ensure secure communication.Therefore,in this paper,we utilize the Echo State Network(ESN)to select the transmit antenna and the Long Short-Term Memory(LSTM)to establish the D2D pair.The simulation results show that the LSTMbased and ESN-based collaboration scheme can effectively improve the security capacity of the cellular network with D2D and increase the life of the base station.展开更多
The γ'-Fe4N films on Cu underlayers are deposited on the glass and Si substrates by dc magnetron reactive sputtering. The effects of Cu underlayer on the structure, morphology and magnetic properties of the γ'-Fe4...The γ'-Fe4N films on Cu underlayers are deposited on the glass and Si substrates by dc magnetron reactive sputtering. The effects of Cu underlayer on the structure, morphology and magnetic properties of the γ'-Fe4N films are studied. The single-phase γ'-Fe4N films with Cu underlayers on the glass substrate are obtained, while the mixture of Fe and γ'-Fe4N is observed on the Si substrate. In comparison with the films without Cu underlayers, the grains of the films with Cu underlayers exhibit a non-uniform size distribution and give rise to a rougher surface. The magnetic measurements indicate that the γ'-Fe4N films show a good soft ferromagnetic behavior. The enhanced coercivity in the films with Cu underlayers is observed due to the deterioration of the crystallographic structure as well as the rougher surface.展开更多
Between 2005 and 2015,the Brazilian real estate market experienced strong growth,driven by the stable scenario of the Brazilian economy and policies to encourage real estate credit.With this demand,the companies of th...Between 2005 and 2015,the Brazilian real estate market experienced strong growth,driven by the stable scenario of the Brazilian economy and policies to encourage real estate credit.With this demand,the companies of the sector sought to be more competitive in the market.One of the measures adopted is the search for more efficient executive processes.While the traditional manual methodology for underlayment predominates in the country’s construction sites,a self-levelling underlayment presents a tendency towards mechanization of executive construction procedures.This paper aims to present a case study of a residential construction in Rio de Janeiro,which used self-levelling underlayment technology.Comparisons regarding cost and productivity of both methodologies were made to evaluate the viability of the self-levelling underlayment in future construction sites.Data obtained from other constructions were used to estimate the productivity and cost of the traditional underlayment levelling.The results demonstrate that the use of self-levelling underlayment has potential to be widespread and used in the constructions in Brazil.展开更多
Effects of Cu underlayer on the structure of Fe50Mn50 films were studied. Samples with a structure of Fe50Mn50(200 nm)/ Cu(tCu) were prepared by magnetron sputtering on thermally oxidized silicon substrates at room ...Effects of Cu underlayer on the structure of Fe50Mn50 films were studied. Samples with a structure of Fe50Mn50(200 nm)/ Cu(tCu) were prepared by magnetron sputtering on thermally oxidized silicon substrates at room temperature. The thickness of Cu underlayer varied from 0 to 60 nm in the intervals of 10 nm. High-vacuum annealing treatments, at different temperatures of 200, 300 and 400 ℃ for 1 h, respectively, on the Fe50Mn50(200 nm)/ Cu(20 nm) thin films were performed. The surface morphologies and textures of the samples were measured by field emission scan electronic microscope (FE-SEM) and X-ray diffraction(XRD). Energy dispersive X-ray spectroscopy (EDX) and Auger electron spectroscopy(AES) were used to analyze the compositional distribution. It is found that Cu underlayer has an obvious induce effect on (111) orientation of Fe50Mn50 thin films. The induce effects of Cu on (111) orientation of Fe50Mn50 changed with the increase of Cu layer thickness and the best effect was obtained at the Cu layer thickness of 20 nm. High-vacuum annealing treatments cause the migration of Mn atoms towards surface of the film and interface between Cu layer and substrate. With the increasing annealing temperature, migration of Mn atoms is more obvious, which leads to a Fe-riched Fe-Mn alloy film.展开更多
国家新型基础设施建设给各运营商带来了新的发展契机,纷纷布局以云网融合为特征的数据中心建设。本文重点分析运营商如何打造云网一体化网络服务提供点(Point of Presence,POP),满足不同客户差异化的入云或云间组网需求,实现云网能力端...国家新型基础设施建设给各运营商带来了新的发展契机,纷纷布局以云网融合为特征的数据中心建设。本文重点分析运营商如何打造云网一体化网络服务提供点(Point of Presence,POP),满足不同客户差异化的入云或云间组网需求,实现云网能力端到端快速贯通,云资源池快速规模化部署,缩短云资源池或数据中心接入网络的建设和开通周期。展开更多
The structure and morphology of A1 interdigital transducers as a function of Ni underlayer thickness were studied. The A1 (111) texture intensity increases first and then decreases as Ni underlayer thickness increas...The structure and morphology of A1 interdigital transducers as a function of Ni underlayer thickness were studied. The A1 (111) texture intensity increases first and then decreases as Ni underlayer thickness increases. 6-nm Ni underlayer results in the strongest A1 (111) texture with flattest surface, which exhibits almost 10 times longer life in electromigration measurement than those without Ni underlayer. 1.5 GHz surface acoustic wave filters fabri- cated with A1 film on 6-nm Ni underlayer also have improved power durability compared with those without Ni underlayer from 29.0 to 32.5 dBm. It is observed that those fine grains in the 6-nm Ni underlayer greatly enhance A1 (111) texture. Together with increased adhesion force, strong A1 (111) texture accounts for the improved resistance to electromigration and acoustomigration via the reduction of gains boundaries, resistivity, and fine grains at the interface, which is promising for high power surface acoustic wave filters.展开更多
The performance of a device-to-device(D2D)underlay communication system is limited by the co-channel interference between cellular users(CUs)and D2D devices.To address this challenge,a reconfigurable intelligent surfa...The performance of a device-to-device(D2D)underlay communication system is limited by the co-channel interference between cellular users(CUs)and D2D devices.To address this challenge,a reconfigurable intelligent surface(RIS)aided D2D underlay system is studied in this paper.A two-timescale optimization scheme is proposed to reduce the required channel training and feedback overhead,where transmit beamforming at the base station(BS)and power control at the D2D transmitters are adapted to instantaneous effective channel state information(CSI);and the RIS phase shifts are adapted to slow-varying channel mean.Based on the two-timescale optimization scheme,we aim to maximize the D2D ergodic weighted sum-rate(WSR)subject to a given outage probability constrained signal-to-interference-plus-noise ratio(SINR)target for each CU.The two-timescale problem is decoupled into two sub-problems,and the two sub-problems are solved iteratively.Numerical results verified that the two-timescale based optimization performs better than two baselines,and also demonstrated a favourable trade-off between system performance and CSI overhead.展开更多
Secure data transmission in future high-capacity high-coverage multi-tier hierarchical networks, for which cognitive radio (CR) has emerged as an essential recipe, is of utmost importance. This paper investigates th...Secure data transmission in future high-capacity high-coverage multi-tier hierarchical networks, for which cognitive radio (CR) has emerged as an essential recipe, is of utmost importance. This paper investigates the secrecy outage performance of selection combining (SC) in CR networks (CRNs) over Rayleigh fading channels. In a single-input multiple-output (SIMO) wiretap channel, a secondary user transmits confidential messages to another secondary user, which is equipped with n B (nB ≥1) antennas. Meanwhile, a passive eavesdropper, which is equipped with nE (n E ≥1) antennas, intends to overhear the messages. Both the legal receiver and the eavesdropper adopt SC scheme to process the received multiple signals. The secondary transmitter uses the underlay strategy to guarantee the quality of service of the primary user without spectrum sensing. Compared to the work proposed by Maged Elkashlan et al. in Ref. [ 1 ], we present an alternative method to derive the closed-form expression for the secrecy outage probability (SOP) and develop a simplified SOP when the maximal transmit power at the secondary user is sufficiently high. Our results reveal the impact of the primary network on the secondary network with a multi-antenna wiretap channel and simulations are conducted to validate the accuracy of our proposed analytical models.展开更多
Due to their unique thermal, electronic and mechanical properties, carbon nanotubes (CNTs) have aroused various attentions of many researchers. Among all the techniques to fabricate CNTs, plasma enhanced chemical va...Due to their unique thermal, electronic and mechanical properties, carbon nanotubes (CNTs) have aroused various attentions of many researchers. Among all the techniques to fabricate CNTs, plasma enhanced chemical vapor deposition (PECVD) has been extensively developed as one growth technique to produce verticallyaligned car bon nanotubes (VACNTs). Though CNTs show a trend to be integrated into nanoelectromechanical system (NEMS), CNT growth still remains a mysterious technology. This paper attempts to reveal the effects of substrates and un derlayers to CNT synthesis. We tried five different substrates by substituting intrinsic Si with high resistivity ones and byincreasing the thickness of SiO2 insulativity layer. And also, we demonstrated an innovative way of adjusting CNT den sity by changing the thickness of Cu underlayer.展开更多
We have fabricated Ni0.81Fe0.19 films with (Ni0.81Fe0.19)1-xCrx films as underlayers by dc magnetron sputtering, the results show that larger anisotropic magnetoresistance (△R/R) values of Ni0.81Fe0.19 films are obse...We have fabricated Ni0.81Fe0.19 films with (Ni0.81Fe0.19)1-xCrx films as underlayers by dc magnetron sputtering, the results show that larger anisotropic magnetoresistance (△R/R) values of Ni0.81Fe0.19 films are observed using the underlayers with Cr concentration of ~36 at.% at an optimum underlayer thickness of ~4.4 nm, the maximum AMR value is 3.35%. The results of atomic force microscope (AFM) and X-ray diffraction (XRD) show that the △R/R enhancement is attributed to the formation of large average grain size and the strong(111) texture in the Ni0.81Fe0.19 films.展开更多
文摘针对underlay认知无线电中时频重叠正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)信号的信噪比(Signal to Noise Ratio,SNR)难以估计的问题,提出了一种基于循环自相关特性的时频重叠OFDM信噪比盲估计方法.该方法提取接收信号的循环自相关函数截面中的离散谱线估计出分量信号的总功率,并结合时延和循环频率均为零时的离散谱线估计出时频重叠OFDM信号的信噪比.仿真结果表明,在无需先验信息的情况下,当SNR大于-7d B时,所提方法估计的均方误差小于0.1,并且对分量信号的功率比和频谱重叠率具有稳健性.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674187 and 51871127)the Fund from the Technology on Electronic Test&Measurement Laboratory(Grant No.6142001180103)。
文摘Heusler Co2FeSi films with a uniaxial magnetic anisotropy and high ferromagnetic resonance frequency fr were deposited by an oblique sputtering technique on Ru underlayers with various thicknesses tRufrom 0 nm to 5 nm.It is revealed that the Ru underlayers reduce the grain size of Co2FeSi,dramatically enhance the magnetic anisotropy field HK induced by the internal stress from 242 Oe(1 Oe=79.5775 A·m^-1)to 582 Oe with an increment ratio of 2.4,while a low damping coefficient remains.The result of damping implies that the continuous interface between Ru and Co2FeSi induces a large in-plane anisotropic field without introducing additional external damping.As a result,excellent high-frequency soft magnetic properties with fr up to 6.69 GHz are achieved.
基金the support from the high-performance computing platform of Jiangsu UniversityThe Jiangsu University Foundation (18JDG019)+3 种基金the Postdoctoral Foundation of Jiangsu Province (2018K072C)Six Talent Peak Project of Jiangsu Province (XLC-158)the China Postdoctoral Science Foundation (2019M651727, 2019M651719)the National Natural Science Foundation of China (21808090, 51902139, U1932211) financially supported this work。
文摘Hematite is regarded as a promising photoanode for photoelectrochemical(PEC) water splitting.However,the charge recombination occurred at the interface of FTO/hematite strictly limits the PEC performance of hematite.Herein,we reported a Ti3C2 MXene underlayer modified hematite(Ti-Fe2O3) photoanode via a simple drop-casting followed by hydrothermal and annealing processes.Owing to the bifunctional role of Ti3C2 MXene underlayer in improving the interfacial properties of FTO/hematite and providing Ti source for the construction of Fe2 TiO5/Fe2O3 heterostructure in hematite nanostructure,the bulk and interfacial charge transfer dynamics of hematite are significantly enhanced,and consequently enhancing the PEC performance.Compared with the pristine hematite,the as-prepared Ti-Fe2O3 photoanode shows an increased photocurrent density from 0.80 mA/cm^(2) to 1.30 mA/cm^(2) at 1.23 V vs.RHE.Moreover,a further promoted PEC performance including a dramatically increased photocurrent density of 2.49 mA/cm^(2) at1.23 V vs.RHE and an obviously lowered onset potential is achieved for the Ti-Fe2O3 sample after the subsequent surface F-treatment and the loading of FeNiOOH cocatalyst.Such results suggest that the introduction of Ti3C2 MXene underlayer is a facile but effective approach to improve the PEC water splitting activity of hematite.
文摘Three kinds of oxide underlayers, namely Si02, ZnO and Al2O3, were deposited prior to the sputtering of Sr-ferrite films, respectively, in order to induce the optimum grain morphology and the texture of the films. A Sr-ferrite film with an easy axis in-plane orientation was induced by SiO2 underlayer. In contrast, it prefers to be perpendicular to film plane for the cases of ZnO and Al2O3 underlayers. The optimum magnetic properties of the former film along film plane are: 4πMr=1.7 kG, iHc=5.35 kOe, and Sq=0.59, which are mainly dominated by the exchange coupling effect, determined by Wohlfarth's remanence analysis, among grains. While those for the films with an easy axis perpendicular to film plane can be as high as 4πMr=3.72 kG, iHc=6.42 kOe, and Sq=0.82, which are mainly dominated by the magnetostatic interaction among grains.
基金This work was supported by Kasetsart University Research and Development Institute(KURDI)under the FY2016 Kasetsart University research grant,and the Royal Golden Jubilee Ph.D.program.
文摘The Device-to-Device(D2D)communication underlaying cellular networks is considered in this study.The D2D transmitter in the D2D mode can directly transmit messages to a receiver,but it may interfere with the transmission of another cellular user who shares the same uplink channel.The transmitter can also operate in a cellular mode in which no interference to another cellular user occurs.We propose a mode selection scheme that aims to minimize the transmission power of the D2D transmitter subject to constraints on the minimum required data rate and maximum interference to other cellular users.The proposed scheme is based on bounds for transmission power and is less complex than the optimal scheme.Furthermore,it requires only a few statistics and does not need a fading channel distribution.The performance of the scheme is close to optimum when the number of Base Station(BS)antennas is large,and the mean absolute deviation of the fading terms is small.We verify this with numerical results of the Rician and Rayleigh fading channels by assuming that the BS antennas are independent.The simulation results for the two correlated BS antennas are presented herein.
基金supported in part by the Aerospace Science and Technology Innovation Fund of China Aerospace Science and Technology Corporationin part by the Shanghai Aerospace Science and Technology Innovation Fund (No. SAST2018045, SAST2016034, SAST2017049)+1 种基金in part by the China Fundamental Research Fund for the Central Universities (No. 3102018QD096)in part by the Seed Foundation of Innovation and Creation for Graduate Students in Northwestern Polytechnical University (No. ZZ2019024)
文摘In order to improve the physical layer security of the device-to-device(D2D)cellular network,we propose a collaborative scheme for the transmit antenna selection and the optimal D2D pair establishment based on deep learning.Due to the mobility of users,using the current channel state information to select a transmit antenna or establish a D2D pair for the next time slot cannot ensure secure communication.Therefore,in this paper,we utilize the Echo State Network(ESN)to select the transmit antenna and the Long Short-Term Memory(LSTM)to establish the D2D pair.The simulation results show that the LSTMbased and ESN-based collaboration scheme can effectively improve the security capacity of the cellular network with D2D and increase the life of the base station.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61434002,61204097,11274214 and 51301099the National High-Tech Research and Development Program of China under Grant No 2014AA032904+1 种基金the Chang Jiang Scholars and Innovative Team Development Plan by the Ministry of Education under Grant No IRT1156the Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant Nos 20121404130001 and 20121404120003
文摘The γ'-Fe4N films on Cu underlayers are deposited on the glass and Si substrates by dc magnetron reactive sputtering. The effects of Cu underlayer on the structure, morphology and magnetic properties of the γ'-Fe4N films are studied. The single-phase γ'-Fe4N films with Cu underlayers on the glass substrate are obtained, while the mixture of Fe and γ'-Fe4N is observed on the Si substrate. In comparison with the films without Cu underlayers, the grains of the films with Cu underlayers exhibit a non-uniform size distribution and give rise to a rougher surface. The magnetic measurements indicate that the γ'-Fe4N films show a good soft ferromagnetic behavior. The enhanced coercivity in the films with Cu underlayers is observed due to the deterioration of the crystallographic structure as well as the rougher surface.
文摘Between 2005 and 2015,the Brazilian real estate market experienced strong growth,driven by the stable scenario of the Brazilian economy and policies to encourage real estate credit.With this demand,the companies of the sector sought to be more competitive in the market.One of the measures adopted is the search for more efficient executive processes.While the traditional manual methodology for underlayment predominates in the country’s construction sites,a self-levelling underlayment presents a tendency towards mechanization of executive construction procedures.This paper aims to present a case study of a residential construction in Rio de Janeiro,which used self-levelling underlayment technology.Comparisons regarding cost and productivity of both methodologies were made to evaluate the viability of the self-levelling underlayment in future construction sites.Data obtained from other constructions were used to estimate the productivity and cost of the traditional underlayment levelling.The results demonstrate that the use of self-levelling underlayment has potential to be widespread and used in the constructions in Brazil.
基金Project(19974005) supported by the National Natural Science Foundation of China
文摘Effects of Cu underlayer on the structure of Fe50Mn50 films were studied. Samples with a structure of Fe50Mn50(200 nm)/ Cu(tCu) were prepared by magnetron sputtering on thermally oxidized silicon substrates at room temperature. The thickness of Cu underlayer varied from 0 to 60 nm in the intervals of 10 nm. High-vacuum annealing treatments, at different temperatures of 200, 300 and 400 ℃ for 1 h, respectively, on the Fe50Mn50(200 nm)/ Cu(20 nm) thin films were performed. The surface morphologies and textures of the samples were measured by field emission scan electronic microscope (FE-SEM) and X-ray diffraction(XRD). Energy dispersive X-ray spectroscopy (EDX) and Auger electron spectroscopy(AES) were used to analyze the compositional distribution. It is found that Cu underlayer has an obvious induce effect on (111) orientation of Fe50Mn50 thin films. The induce effects of Cu on (111) orientation of Fe50Mn50 changed with the increase of Cu layer thickness and the best effect was obtained at the Cu layer thickness of 20 nm. High-vacuum annealing treatments cause the migration of Mn atoms towards surface of the film and interface between Cu layer and substrate. With the increasing annealing temperature, migration of Mn atoms is more obvious, which leads to a Fe-riched Fe-Mn alloy film.
文摘国家新型基础设施建设给各运营商带来了新的发展契机,纷纷布局以云网融合为特征的数据中心建设。本文重点分析运营商如何打造云网一体化网络服务提供点(Point of Presence,POP),满足不同客户差异化的入云或云间组网需求,实现云网能力端到端快速贯通,云资源池快速规模化部署,缩短云资源池或数据中心接入网络的建设和开通周期。
基金financially supported by the National Key Research and Development Program of China(No. 2016YFB0402700)Beijing Science and Technology Project (No. D171100004617001).
文摘The structure and morphology of A1 interdigital transducers as a function of Ni underlayer thickness were studied. The A1 (111) texture intensity increases first and then decreases as Ni underlayer thickness increases. 6-nm Ni underlayer results in the strongest A1 (111) texture with flattest surface, which exhibits almost 10 times longer life in electromigration measurement than those without Ni underlayer. 1.5 GHz surface acoustic wave filters fabri- cated with A1 film on 6-nm Ni underlayer also have improved power durability compared with those without Ni underlayer from 29.0 to 32.5 dBm. It is observed that those fine grains in the 6-nm Ni underlayer greatly enhance A1 (111) texture. Together with increased adhesion force, strong A1 (111) texture accounts for the improved resistance to electromigration and acoustomigration via the reduction of gains boundaries, resistivity, and fine grains at the interface, which is promising for high power surface acoustic wave filters.
基金This work was supported in part by National Natural Science Foundation of China(No.62071090)in part by General Research Funding(Project number 14208107)from Research Grants Council of Hong Kong.The associate editor coordinating the review of this paper and approving it for publication was R.Wang.
文摘The performance of a device-to-device(D2D)underlay communication system is limited by the co-channel interference between cellular users(CUs)and D2D devices.To address this challenge,a reconfigurable intelligent surface(RIS)aided D2D underlay system is studied in this paper.A two-timescale optimization scheme is proposed to reduce the required channel training and feedback overhead,where transmit beamforming at the base station(BS)and power control at the D2D transmitters are adapted to instantaneous effective channel state information(CSI);and the RIS phase shifts are adapted to slow-varying channel mean.Based on the two-timescale optimization scheme,we aim to maximize the D2D ergodic weighted sum-rate(WSR)subject to a given outage probability constrained signal-to-interference-plus-noise ratio(SINR)target for each CU.The two-timescale problem is decoupled into two sub-problems,and the two sub-problems are solved iteratively.Numerical results verified that the two-timescale based optimization performs better than two baselines,and also demonstrated a favourable trade-off between system performance and CSI overhead.
基金supported in part by the National Science Foundation (61401372, 61531016)Research Fund for the Doctoral Program of Higher Education of China(20130182120017)+1 种基金Natural Science Foundation of CQ CSTC(cstc2013jcyj A40040)the Fundamental Research Funds for the Central Universities (XDJK2015B023, XDJK2016A011)
文摘Secure data transmission in future high-capacity high-coverage multi-tier hierarchical networks, for which cognitive radio (CR) has emerged as an essential recipe, is of utmost importance. This paper investigates the secrecy outage performance of selection combining (SC) in CR networks (CRNs) over Rayleigh fading channels. In a single-input multiple-output (SIMO) wiretap channel, a secondary user transmits confidential messages to another secondary user, which is equipped with n B (nB ≥1) antennas. Meanwhile, a passive eavesdropper, which is equipped with nE (n E ≥1) antennas, intends to overhear the messages. Both the legal receiver and the eavesdropper adopt SC scheme to process the received multiple signals. The secondary transmitter uses the underlay strategy to guarantee the quality of service of the primary user without spectrum sensing. Compared to the work proposed by Maged Elkashlan et al. in Ref. [ 1 ], we present an alternative method to derive the closed-form expression for the secrecy outage probability (SOP) and develop a simplified SOP when the maximal transmit power at the secondary user is sufficiently high. Our results reveal the impact of the primary network on the secondary network with a multi-antenna wiretap channel and simulations are conducted to validate the accuracy of our proposed analytical models.
基金supported by EU programs "Nanotec","Mercure","Nanocom","Nano-RF" and "Nanotherm", the SSF program"Scalable Nanomaterials and Solution Processable Thermoelectric Generators", and also Contract No.EM11-0002a part of the Sustainable Production Initiative and the Production Area of Advance at Chalmerssupported by the Shanghai Science and Technology Program(Grant No.12JC1403900) and NSFC(Grant No.51272153)
文摘Due to their unique thermal, electronic and mechanical properties, carbon nanotubes (CNTs) have aroused various attentions of many researchers. Among all the techniques to fabricate CNTs, plasma enhanced chemical vapor deposition (PECVD) has been extensively developed as one growth technique to produce verticallyaligned car bon nanotubes (VACNTs). Though CNTs show a trend to be integrated into nanoelectromechanical system (NEMS), CNT growth still remains a mysterious technology. This paper attempts to reveal the effects of substrates and un derlayers to CNT synthesis. We tried five different substrates by substituting intrinsic Si with high resistivity ones and byincreasing the thickness of SiO2 insulativity layer. And also, we demonstrated an innovative way of adjusting CNT den sity by changing the thickness of Cu underlayer.
基金This work was supported by the National Natural Science Foundation of China(Grant No.19890310)the Beijing Natural Science Foundation of China(Grant No.201 2011).
文摘We have fabricated Ni0.81Fe0.19 films with (Ni0.81Fe0.19)1-xCrx films as underlayers by dc magnetron sputtering, the results show that larger anisotropic magnetoresistance (△R/R) values of Ni0.81Fe0.19 films are observed using the underlayers with Cr concentration of ~36 at.% at an optimum underlayer thickness of ~4.4 nm, the maximum AMR value is 3.35%. The results of atomic force microscope (AFM) and X-ray diffraction (XRD) show that the △R/R enhancement is attributed to the formation of large average grain size and the strong(111) texture in the Ni0.81Fe0.19 films.