无人机联合D2D应急通信网络的性能分析

无人机与D2D(Device-to-Device)通信技术相结合可以作为应急通信网络的可行选项之一。受限于频谱资源,无人机与D2D用户往往采用共享频谱技术,这会导致网络中干扰链路增多,影响网络的通信性能。为此,将无人机配备定向天线以降低干扰的影响。为量化分析其对网络的具体影响,利用随机几何理论,对D2D通信与无人机通信共存的网络进行系统建模,推导了D2D用户成功传输概率的精确表达式以及无人机通信用户成功传输概率的上下界理论表达式,讨论了无人机密度以及天线阵子数等关键参数对系统性能的影响。仿真结果表明,相比全向天线,无人机配备定向天线可以有效地提高网络性能,且存在一个最优的无人机密度,使无人机通信用户的成功传输概率最大化。     

基于三维空间模型的毫米波蜂窝网络覆盖概率分析

毫米波蜂窝网络通常在二维空间下建模和性能分析.二维模型适合基站分布稀疏的郊区,但是并不适合城市环境下密集蜂窝网络的性能分析.基于随机几何理论提出三维空间模型.该模型假设基站分布为三维泊松点过程;阻碍模型为视距(line of sight,LOS)球模型;信道为Nakagami-m衰落信道;收发端使用大规模天线阵列获得最大的波束成形增益.基于该模型,给出了三维空间下目标用户和最近基站距离的概率密度函数,推导出目标用户的平均覆盖概率,通过蒙特卡洛仿真实验与二维模型的性能进行了对比,分析了路径损耗、蜂窝半径、天线的波束宽度和天线增益等参数变化对平均覆盖概率的影响.实验结果表明,在密集的城市环境下,三维模型对毫米波蜂窝网络的性能分析更加精确.     

同信道干扰下中继选择网络的性能

使用端到端等效信干噪比的累积分布函数表达式,推导了瑞利衰落信道上同信道干扰下中继选择网络分别在M进制相移键控调制下的平均误符号率闭合表达式、M进制正交幅度调制下的平均误符号率的近似表达式和信道容量上界表达式。数值计算和仿真结果表明:高信干噪比时,M进制相移键控调制的平均误符号率理论结果与仿真结果相吻合,M进制正交幅度调制的平均误符号率的近似表达式具有较高的精度;中继的数目越多,信道容量的仿真结果与其理论上界越紧。     

基于机会调度的上行认知中继蜂窝网络中断性能研究

对基于机会调度的上行两跳认知放大中继蜂窝网络的中断性能进行研究,导出了该系统的中断概率封闭表达式和高信噪比下的中断概率近似表达式。该系统中有多个源节点,研究表明,通过选择最优的次用户进行信息传输,系统中断性能可得到改善。仿真验证了理论推导的正确性。     

多跳分集系统优化功率分配方案

针对协同通信中广泛使用的等功率分配(EPA)方案性能往往不是最优问题,采用理论推导和仿真的方法找出了最优功率分配方案.推导了在高信噪比条件下解码转发(DF)多跳分集网络的中断概率近似表达式和分集度,选取此表达式为代价函数,提出一种适合于DF多跳分集系统的近似最优功率分配方案.仿真结果验证了理论分析的正确性,在DF多跳分集系统中采取此近似最优功率分配方案(AOPA)要优于等功率分配(EPA)方案.与等功率分配(EPA)方案相比,此近似最优功率分配方案(AOPA)能更有效地提高系统的性能.     

无人机辅助的蜂窝数据流量卸载及保密传输方案

为解决传统蜂窝网络中边缘用户上行通信链路质量较差且容易遭到窃听的问题,提出了一种移动无人机辅助的流量卸载和保密传输方案。首先根据空地视距信道特性,建立了基于接收信号强度阈值的信道接入机制,解决了用户传输模式选择问题;其次,根据空地信道接入时延、无人机飞行高度和速度,确定了任意时刻无人机链路的覆盖范围;然后,利用随机几何理论,给出了平均可达速率解析式和安全容量评估方法;最后,通过仿真实验验证所提方案和理论结果的有效性,并给出关键参数的最优化配置方案。仿真结果表明,与传统蜂窝网络相比,所提出的基于移动无人机的组网方案能够在保证用户公平性的基础上,使网络上行通信速率提高约40%,安全容量提高约70%。     

生物组织光传播的理论研究

从光的传输理论出发,利用漫射近似方程,推导出当无限细脉冲光及连续光束垂直入射到生物组织表面时,生物组织表面漫反射光随空间及时间变化的解析表达式。详细分析了组织光学特性参数与组织表面漫反射挑分布之间的关系,为生物组织光学特性参数的无损测量提供了理论根据。     

频域时间反转多用户系统的信干噪比和误比特率分析

为了更有效地将时间反转技术应用到正交频分复用系统中,推导了多天线频域时间反转预编码多用户系统的平均信干噪比和误比特率的表达式。通过推导信号功率均值的表达式和用户间干扰信号功率均值的近似表达式,得到用户的平均接收信干噪比的近似表达式,进而得到二进制相移键控调制下的平均误比特率的一个下界和近似表达式。仿真结果表明,推导的平均信干噪比的近似值与仿真结果很接近,近似BER值与仿真得到的平均BER值较为接近;通过增大速率回退因子和天线数,可明显提高平均信干噪比,降低误比特率。     

某无人机撞网回收系统动力学仿真

以某无人机撞网回收系统为例,基于LS-DYNA软件,提出了柔性带、阻尼器等关键部件的建模方法,建立了系统有限元仿真模型,进行了不同入网位置的动力学仿真计算,并用试验验证了仿真模型的准确性.仿真和试验结果表明:本文建立的无人机撞网回收系统模型具有较好的工程适用性,提出的动力学建模仿真方法具有一定的通用性.     

IP级拓扑新生与消亡节点的特征

针对IP级拓扑新生与消亡节点特征进行研究,基于CAIDA项目授权的海量数据,结合复杂网络的研究理论和方法,对IP级Internet拓扑新生与消亡节点的度分布、幂律特性等特征量,以及IP级新生连接进行统计分析及演化分析.结果表明,新生与消亡节点近似符合幂律分布,新生节点不倾向于与新生节点相连,而倾向于与网络中已存在的节点相连,且连接数为1的可能性较大.新生连接不符合优先连接性质,富者更富理论在动态上的表现不显著,高度节点的影响力在连接产生时不高.新生节点连接数目具有稳定性及普适性,这为Internet建模提供有效依据.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

橡胶颗粒沥青混合料低温抗裂性试验研究

以AC-13级配为基础,将橡胶颗粒代替部分集料掺入混合料中,以低温弯曲试验为评价方法对不同橡胶颗粒掺量下沥青混合料的低温抗裂性进行研究,并引入应变能密度值对混合料的低温抗裂性进行综合评价.试验结果表明:橡胶颗粒沥青混合料试件的破坏微应变均超过2 300,满足冬寒区的技术指标;无论是否掺加橡胶颗粒,随着温度的下降,沥青混合料破坏时的最大弯拉强度增大,弯拉应变降低,劲度模量增大;弯曲应变能密度在胶粒掺量为1%左右时具有较大的弯曲应变能密度值,此时橡胶颗粒沥青混合料具有较好的低温抗裂性.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

Quantitative trait loci （QTLs） for quality traits related to protein and starch in wheat

Quality traits in wheat （Triticum aestirum L.） were studied by quantitative trait locus （QTL） analysis in a recombinant inbred line （RIL） population, a set of 131 lines derived from Chuan 35050 × Shannong 483 cross （ChSh）. Grains from RILs were assayed for 21 quality traits related to protein and starch. A total of 35 putative QTLs for 19 traits with a single QTL explaining 7.99-40.52% of phenotypic variations were detected on 10 chromosomes, 1D, 2A, 2D, 3B, 3D, 5A, 6A, 6B, 6D, and 7B. The additive effects of 30 QTLs were positive, contributed by Chuan 35050, the remaining 5 QTLs were negative with the additive effect contributed by Shannong 483. For protein traits, 15 QTLs were obtained and most of them were located on chromosomes 1 D, 3B and 6D, while 20 QTLs for starch traits were detected and most of them were located on chromosomes 3D, 6B and 7B. Only 7 QTLs for protein and starch traits were co-located in three regions on chromosomes 1D, 2A and 2D. These protein and starch trait QTLs showed a distinct distribution pattern in certain regions and chromosomes. Twenty-two QTLs were clustered in 6 regions of 5 chromosomes. Two QTL clusters for protein traits were located on chromosomes 1D and 3B, respectively, three clusters for starch traits on chromosomes 3D, 6B and 7B, and one cluster including protein and starch traits on chromosome 1D.     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.