正交频分复用系统自适应位加载算法综述

对单用户正交频分复用系统中几种常见的位加载算法包括贪婪算法、Chow算法、Fischer算法以及基于信噪比门限的简单分块加载算法进行了论述,对各个算法的复杂度和性能进行了比较和系统分析。分析得出:贪婪算法复杂度最高、发射功率最低;Chow算法使得系统的性能余量最大化;Fisher算法具有最优的误比特率性能;简单分块加载算法减少系统信令开销且具有更低的复杂度。

单桩承载力深位加载法的试验研究

一、深位加载法简介 传统的静载荷测试法虽然被各国工程界、学术界公认为确定单桩承载力的最直观、最可靠的办法,但静载荷试验的装置一直停留在压重平台或锚桩反力架两种形式,试验费时、费钱,成为桩基础领域面临的一大困惑.

沪通长江大桥静载试验车辆编组及加载轮位分析

沪通长江大桥主航道桥为双塔三索面钢桁梁公铁两用斜拉桥,主跨度1092 m,主塔高330 m,采用三片主桁的箱桁组合结构,每个主桁节点均设有横联。主梁上弦公路面采用正交异性整体钢桥面板,主梁下弦铁路面采用与弦杆焊接的整体钢箱作为桥面。由于主跨跨度和桥梁总长均超过实际列车及到发线的长度,依据现行规范活载按无限长度加载不合理。设计活载的加载标准、实际试验车辆编组和加载轮位均与传统方式有区别。依据我国铁路活载标准和客货运铁路活载现状、到发线长度与牵引定数并结合结构的影响线,本文主要研究在不同控制断面下如何确定铁路层车辆编组和加载轮位,采用配载、微调加载车辆和移动加载轮位的方式使试验荷载效率基本满足规范的要求。

基于MIDAS的钢桁梁检测静载轮位模型优化

铁路钢桁梁桥静载试验中,利用Midas建立仿真模型,并提取杆件的最不利荷载轮位及其影响线,在这一过程中,发现最不利荷载轮位中所有试验编组的集中荷载均未通过桁梁节点的问题,通过分析其问题原因,优化Midas模型,解决了静载试验加载轮位错误的问题,提取出合理影响线,通过现场测试对比实测值与理论值,验证结果良好。

多载波通信系统的实用功率分配算法

本文利用多载波通信系统的误码率、比特位数与信噪比之间的关系提出了性能良好的快速表查询法 .在噪声干扰 ,信道衰减和一定频段上功率谱密度对子信道最大传输位数限制的条件下 ,得到了一种实用的离散多音频多载波通信系统的功率分配和数据位加载算法 .在系统初始化过程中 ,该算法使系统能在满足各种约束条件下达到最优功率分配和数据位加载 ,比其他算法具有更高的计算效率和更大的系统性能裕量 .在信道特性变化时 ,该算法使系统在不增加硬件的情况下能进行快速跟踪和自适应位交换 .

一种基于64位机器的32位指针优化方法

在64位机器上,存储器一般以64位的虚地址进行访问,所有的指针变量也以8字节进行存储和使用。介绍一种在64位机器上采取32位地址进行计算和访存的编译优化方法,这种优化的目的是针对64位机器上大量使用指针数据的课题,采取32位寻址可以减少指针变量占用内存和cache空间,从而大大提高了该类课题的运行效率。

Effects of Supports and Promoters on in situ Hydrogenation of o-Cresol over Ni-based Catalysts

We investigated the effects of supports （CMK-3, SiO2ZrO2, MgO, Al2O3） and promoters （Cu, Ce, Fe） on textual properties of Ni based catalysts. o-Cresol was used as a probe to test the activity of these catalysts under the condition of 230 ℃ and nitrogen pres-sure of 0.1 MPa. The catalysts were characterized by X-ray diffraction, H2 temperature programmed reduction ammonium programmed desorption, and N2 adsorption-desorption isotherms. The results showed that the catalytic performance of Ni/CMK-3 （the conversion of o-cresol reached 45.4%） was significantly better than the other three kinds of supports. The modification of Ni/CMK-3 was also investigated and over 60% conversion of o-cresol was obtained after the addition of Ce （64.6%）and Cu （66.8%） in Ni/CMK-3, whereas the addition of Fe led to a decrease of conversion. In the meantime, Cu changed the products dis-tribution. The appearance of toluene indicated that another pathway existed in the reaction.Accompanied by the ascension of conversion in both sides, side effects also occurred and got more serious. The apparent order of activity for all the tested catalysts was NiCe/CMK-3〉NiCu/CMK-3〉Ni/CMK-3〉NiFe/CMK-3〉Ni/Al2O3Ni/SiO2ZrO2〉Ni/MgO. The reac-tion pathway, involving three routes, was also mentioned in this study.

数字存储示波器中DSP的自举方法

分析了TMS320VC5409芯片自举加载器(Bootloader)的工作原理和自举(Bootload)的实现方法。根据某数字存储示波器(Digital storage oscilloscope,DSO)系统结构的特殊性,分别通过16位数据段传输法和"二次下载法"实现了其DSP控制核心的16位并行加载自举,并对两种方法的优缺点和适用范围进行了讨论。

Field measurement of strain response for typical asphalt pavement

In order to reveal the changing law of the mechanical response of asphalt pavements under the action of vehicle load and provide references for the design of durable pavements,three typical asphalt pavement structures with flexible base(S1),combined base(S2),and semi-rigid base(S3)were selected to perform field strain tests under static and dynamic load using the fiber Bragg grating optical sensing technology.The changing characteristics of the strain field along the horizontal and depth directions of pavements were analyzed.The results indicate that the most unfavorable asphalt pavement layers were the upper-middle surface layer and the lower base layer.In addition,the most unfavorable loading positions on the surface layer and the base layer were the center of wheel load and the gap center between two wheels,respectively.The most unfavorable layer of the surface layers gradually moved from the lower layer to the upper layer with the increase of base layer modulus.The power function relationships between structural layer strain and vehicle speed were revealed.The semi-rigid base asphalt pavement was the most durable pavement type,since its strain value was lower compared to those of the other structures.

Relationship between loading angle and displacing angle in steel bolt shearing

When subjected to shear loading condition,a steel rock bolt will become bent in the field close to the loading point in situ.The bolt is deformed as the joint displacement increases,which can mobilize a normal load and a shear load on the bolt accordingly.In this work,the relationship analysis between the displacing angle and loading angle is carried out.By considering elastic andplastic states of rock bolt during shearing,the rotation of bolt extremity can be calculated analytically.Thus,the loading angle isobtained from displacing angle.The verification of analytical results and laboratory results from reference research implies that theanalytical method is correct and working.In terms of in-situ condition,the direction of the load acting on steel bolt can be predictedwell according to the direction of the deformed rock bolt with respect to original bolt axis.

Vertical displacement loading tides and self-attraction and loading tides in the Bohai, Yellow, and East China Seas

The loading tides are calculated by means of the Green's function method based on a high-resolution regional ocean tide model, the TOPO7.0 global ocean tide model, and the Gutenberg-Bullen A Earth model. The results show that the maximal amplitude of M2 vertical displacement loading (VDL) tide in the Bohai, Yellow, and East China Seas exceeding 28mm appears 150km off the Zhejiang coast; the second maximum exceeding 20mm appears in Inchon Bay; and the third maximum exceeding 14mm is located in the northeast of the North Yellow Sea. The maximal amplitudes of S2 VDL tide at the above three locations exceed 10, 8, and 4mm, respectively. The maximal amplitudes of the K1 and O1 VDL tides, exceeding 13 and 10 mm respectively, appear near the central and north Ryukyu Islands; the amplitudes tend to decease toward the inward areas. The phases of semidiurnal VDL tides are basically opposite to those of corresponding ocean tides. The phases of diurnal VDL tides are basically opposite to those of corresponding ocean tides in the most part of the East China Sea and the eastern part of the South Yellow Sea. This anti-phase relationship generally does not hold in the rest parts of the Bohai and Yellow Seas. The distribution patterns of self-attraction and loading (SAL) tides are very similar to those of VDL tides. The SAL tides have amplitudes about 1.2-1.7 times of the corresponding VDL tides and their phases are basically opposite to the corresponding VDL tides. The maximal amplitude of M2 SAL tide also appears off the Zhejiang coast, with a magnitude exceeding 42mm.

Longitudinal resistance performance of granular ballast beds under cyclic symmetric displacement loading

The longitudinal resistance performance of a granular ballast bed under cyclic symmetric displacement loading was studied based on a full-scale test model of ballast track structures. The change law of the longitudinal resistance characteristics of the ballast bed under variable displacement amplitudes was analyzed. The results show that： the resistance-displacement curves of a granular ballast bed are a set of closed hysteretic curves, indicating obvious energy consumption; a granular ballast bed softens gradually during the cyclic process with constant displacement amplitude, and the residual deformation rate increases nonlinearly with increasing cycle number; the peak value of the longitudinal resistance of lines decreases with increasing cycle number; the cyclic softening of a granular ballast bed is dependent on the displacement amplitude-the higher the displacement, the more severe the cyclic softening will become; after cyclic displacement loading is applied several times, the longitudinal resistance of the bed will degenerate obviously, and the higher the displacement amplitude, the higher the longitudinal resistance attenuation rate of the ballast bed will become.

Experimental and analytical studies on the deformability of a precast RC shear wall involving bolted connections

To study the deformability and ductility of an innovative precast shear wall joined by bolted connections,experimental tests were conducted on two test walls under monotonic and cyclic loading,respectively;subsequently,theoretical analysis was performed on the deformation performance of the shear wall assembly.The test results confirmed the favorable deformability and ductility of the specimens.The top displacement of the shear wall assembly was analytically decomposed into several constituent parts,the theoretical formulae of which were subsequently deduced.The compositional analysis demonstrated that the top displacement of the test wall was primarily induced by the elastic deformation of the upper wall panel(UWP),the relative slippages within the bolted connections,and the flexural deformation within the plastic region of the UWP,while the constituent part contributed by the deformation in the connecting steel frame can be neglected.

A dislocation-based model for cyclic plastic response of lath martensitic steels

Softening behavior of lath martensitic steels is related to the coarsening of laths and dislocation evolution during cyclic deformation.Involving the physical mechanism,we developed a dislocation-based model to study the cyclic plastic response for lath martensitic steels.For a block,we proposed an interfacial dislocation evolution model to physically present the interaction between mobile dislocations in the block and interfacial dislocations by considering the coarsening mechanism of the laths.Moreover,the evolution behavior of backstress caused by dislocation pile up at the block boundary has been considered.Then,a hierarchical model based on the elastic-viscoplastic self-consistent(EVPSC)theory is developed,which can realize the scale transition among representative volume element(RVE),prior austenite grains(PAGs)and blocks.According to the proposed model,the effective mechanical responses including the cyclic hysteretic loop and peak stress at different cycles for lath martensitic steel have been theoretically predicted and investigated.