基于用户QoE的室内可见光通信系统接入策略

在可见光通信网络室内场景中,针对用户难以选择合适的发光二极管进行接入从而实现高质量流量服务的问题,以用户为中心,引入系统性能指标:用户体验质量(QoE).以QoE概率覆盖模型为基础,提出基于用户QoE优化的贪婪接入算法.通过MATLAB进行仿真,将贪婪接入算法与就近接入方法在用户数量、覆盖概率、接入阈值、接收视角等方面...     

Reactive scheduling of multiple EOSs under cloud uncertainties: model and algorithms

Most earth observation satellites(EOSs)are low-orbit satellites equipped with optical sensors that cannot see through clouds.Hence,cloud coverage,high dynamics,and cloud uncertainties are important issues in the scheduling of EOSs.The proactive-reactive scheduling framework has been proven to be effective and efficient for the uncertain scheduling problem and has been extensively employed.Numerous studies have been conducted on methods for the proactive scheduling of EOSs,including expectation,chance-constrained,and robust optimization models and the relevant solution algorithms.This study focuses on the reactive scheduling of EOSs under cloud uncertainties.First,using an example,we describe the reactive scheduling problem in detail,clarifying its significance and key issues.Considering the two key objectives of observation profits and scheduling stability,we construct a multi-objective optimization mathematical model.Then,we obtain the possible disruptions of EOS scheduling during execution under cloud uncertainties,adopting an event-driven policy for the reactive scheduling.For the different disruptions,different reactive scheduling algorithms are designed.Finally,numerous simulation experiments are conducted to verify the feasibility and effectiveness of the proposed reactive scheduling algorithms.The experimental results show that the reactive scheduling algorithms can both improve observation profits and reduce system perturbations.     

Compressive sensing based multiuser detector for massive MBM MIMO uplink

Media based modulation(MBM)is expected to be a prominent modulation scheme,which has access to the high data rate by using radio frequency(RF)mirrors and fewer transmit antennas.Associated with multiuser multiple input multiple output(MIMO),the MBM scheme achieves better performance than other conventional multiuser MIMO schemes.In this paper,the massive MIMO uplink is considered and a conjunctive MBM transmission scheme for each user is employed.This conjunctive MBM transmission scheme gathers aggregate MBM signals in multiple continuous time slots,which exploits the structured sparsity of these aggregate MBM signals.Under this kind of scenario,a multiuser detector with low complexity based on the compressive sensing(CS)theory to gain better detection performance is proposed.This detector is developed from the greedy sparse recovery technique compressive sampling matching pursuit(CoSaMP)and exploits not only the inherently distributed sparsity of MBM signals but also the structured sparsity of multiple aggregate MBM signals.By exploiting these sparsity,the proposed CoSaMP based multiuser detector achieves reliable detection with low complexity.Simulation results demonstrate that the proposed CoSaMP based multiuser detector achieves better detection performance compared with the conventional methods.     

多金属氧酸盐纳米纤维催化O2氧化5-HMF

2,5-二甲基呋喃(DFF)是一种用途广泛的化合物,可作为前体用于合成各种高附加值产品,可通过氧化5-羟甲基糠醛(HMF)得到.然而,5-羟甲基糠醛的有氧氧化有不同的途径,从而会产生DFF,2,5-呋喃甲酸(FDCA)或马来酸酐(MA)等产物.迄今为止,均相和非均相金属催化剂均被作为氧化剂用于对HMF氧化为DFF的研究.特别是含钒的多金属氧酸盐(POMs)被发现可以氧化HMF生产DFF,MA等一系列产品.本文通过采用静电纺丝和表面活性剂成孔技术合成了介孔纳米纤维H_5PMo_(10)V_2O_(40)/meso-Zr O_2(f)并通过IR,~(31)P MAS NMR,XRD,SEM,TEM,N_2吸附-脱附测试对其进行了表征.H_5PMo_(10)V_2O_(40)/meso-Zr O_2(f)纳米纤维,其在氧气作为氧化剂氧化5-羟甲基糠醛(5-HMF)到2,5-二甲酰基呋喃(DFF)反应中表现出高的催化活性和产物的选择性,源于复合催化剂良好的氧化还原性、Lewis酸中心、Br?nsted酸中心及纳米纤维高的比表面积.     

有阀线性压缩机驱动液氦温区闭式JT制冷机性能

线性压缩机驱动的液氦温区闭式JT(Joule-Thomson)节流制冷系统,是实现深空探测目标的核心技术.为进一步探究闭式JT循环的压缩机工况影响和制冷温度变化情况,搭建了预冷型液氦温区闭式JT节流制冷机实验台.实验中,采用单向阀组与传统线性压缩机结合,获取JT循环所需直流流动氦气工质并提供节流所需大压比.考虑单级有阀线性压缩机压力能力,选取10 K左右预冷温度,测试了不同压缩机工况特性及节流孔的压力流量特性.通过调节活塞位移和压缩机运行频率,可以获得3.91 K的最低温度.该闭式循环JT制冷机在4.09 K稳定工况下可以获得10.8 mW的最大制冷量,为后续多级压缩和更低温区的闭式系统提供可靠的研究基础.     

消解温度对石墨消解—ICP-MS法同时测定结果的影响

本次实验采用电感耦合等离子体质谱法(ICP-MS),使用石墨消解仪消解滤膜,探讨消解温度对同时测定铬、锰、铁、镍、铜、锌、砷、硒、镉、锑、铅的影响。结果表明:在160℃时消解是同时测定铬、锰、铁、镍、铜、锌、砷、硒、镉、锑、铅的最佳条件。     

成都市冬季PM_(2.5)污染特征及溯源分析

本研究利用2019年成都锦城湖监测点PM_(2.5)的监测数据,研究成都市冬季PM_(2.5)的污染特征及其与气象要素之间的关系,并利用后向轨迹模型进行颗粒物溯源及追踪分析。结果表明:成都市环境空气PM_(2.5)平均质量浓度为53 g/m~3,达到国家空气质量二级标准;PM_(2.5)质量与温度呈显著正相关性,与风速呈负相关性,与湿度呈负相关性,与气压呈显著负相关性;成都市冬季气团主要来自东北方向,来自东南偏南方向的PM_(2.5)及其前体物对成都市PM_(2.5)质量浓度贡献最大。     

基于Max(N,D)策略的MG1排队系统的稳态指标

考虑一个由N策略和D策略同时控制的MG1排队系统.当顾客的到达个数至少为N个同时等待顾客的服务时间之和大于某非负实数D时,空闲的服务台重新开始服务顾客(称此服务启动策略为Max(N,D)策略).在此策略下,由于闲期到达顾客的服务时间是条件相依的,故队长的随机分解不再成立.通过将顾客分成两类,并借助拉普拉斯变换和概率分析,研究了该排队系统的稳态队长分布、稳态闲期和忙期分布、稳态服务时间积压量分布以及顾客的稳态逗留时间分布.数值算例分析了N、D和Max(N,D)策略对稳态平均队长的影响.在数值上获得了系统稳态费用最小的最优策略临界值,并比较了N、D、Max(N,D)和Min(N,D)策略的优越性.     

当前线粒体DNA研究及在法医学中的应用

线粒体DNA是人类第二套基因组DNA,它具有母系遗传、拷贝数多、异质性、进化速度快、突变率高等特点。正由于其上述特点,目前国内外对线粒体DNA的研究也越来越多,疾病相关性、线粒体核质基因相互作用、群体遗传学、法医学等方面的研究也都在积极地开展,线粒体DNA分析技术也不断地得到改进,虽然其检测在法医学领域仍然存在许多问题,但法医个人认定和母系遗传亲属的确定的前景还是乐观的。     

分布式声传感器井中背景噪声统计特性分析

分布式声传感器技术(DAS: Distributed Acoustic Sensor)是一种新近提出的高精度勘探数据采集方法,受制于复杂背景噪声的影响,DAS记录处理水平有待进一步提高.针对上述问题,采用基于替代序列的时间序列平稳性检验方法和Lilliefors检验法对DAS记录中复杂背景噪声的平稳性和高斯性进行研究....