高腐蚀率钢筋混凝土梁抗弯性能研究

对4根未腐蚀和16根腐蚀钢筋混凝土梁进行抗弯试验,研究重复荷载下高腐蚀率对钢筋混凝土梁变形、裂缝、承载力及破坏机理的影响。提出重复荷载下受腐蚀钢筋混凝土梁承载力计算公式。同时拟合出钢筋腐蚀率对钢筋混凝土受弯开裂的影响,并提出受腐蚀梁在重复荷载下的开裂荷载计算公式。     

夏热冬冷地区节能减排、适宜居住绿色农宅设计策略研究——浙江省桐庐县分水镇为例

为研究降低农村建筑能耗,提高居住舒适度的适宜性绿色农宅设计策略,特选取夏热冬冷地区具有代表性的浙江桐庐分水镇百岁坊村农宅为研究对象。根据现场测量、调研,运用spss软件对调查问卷进行统计,分析农民居住现状、生活方式与能耗。根据地形、气候,提出具有当地农村特色的、结合节能各项措施的建筑设计方案。经ecotect日照、pkpm节能软件验证,该方案节约能耗78.56%,居住适宜,具有推广价值。     

频谱分析仪中小数环的一点改进

本文介绍了在AV4033频谱分析仪中小数环的的原理及各部分的功能。为了解决环路工作过程中不稳定,容易失锁的问题,在环路滤波器前端电阻上并联一个补偿电容,并提供了获取电容值的算法。采用该方法后,明显提高了小数环路的增益,促进了环路的捕捉与锁定。     

Mutual interference considered power allocation in OFDM-based cognitive networks: the multiple SUs case

Power allocation for secondary users (SUs) in cognitive networks is an important issue to ensure the SUs’ quality of service. When the mutual interference between the primary users (PUs) and the SUs is taken into consideration, it is wanted to achieve the conflict-free power allocation while synchronously maximizing the capacity of the secondary network. In this paper, the optimal power allocation problem is considered in orthogonal frequency division multiplexing cognitive networks. The single SU case is primarily formulated as a constrained optimization problem. On this basis, the multiple SUs case is then studied and simulated in detail. During the analysis, the mutual interference among the PUs and the SUs is comprehensively formulated as the restrictions on the SU’s transmission power and the optimization problems are finally resolved by iterative water-filling algorithms. Consequently, the proposed power allocation scheme restrains the interference to the primary network, as well as maximizing the capacity of the secondary network. Specifying the multiple-SUs case, simulation results are exhibited in a simplified scenario to confirm the efficiency of the proposed water-filling algorithm, and the influence of the mutual interference on the power allocation and the system capacity is further illustrated.     

Transfer of GaN-Based Light-Emitting Diodes From Silicon Growth Substrate to Copper

III-nitride light-emitting diodes (LEDs) grown on Si (111) substrates have the potential of low-cost manufacturing for solid-state lighting and display, by taking advantage of the well-developed IC technologies of silicon. In this letter, LEDs grown on silicon substrates were transferred onto copper substrates, to maximize light extraction and heat dissipation. On Si substrates, $hbox{300} times hbox{300} muhbox{m}^{2}$ multiple quantum well InGaN LEDs were first grown and processed. The top surface of the fabricated devices was then temporarily bonded to a sapphire wafer and the Si substrate was chemically etched. Ti/Al/Ti/Au layers were deposited on the backside of LEDs. An 80-$muhbox{m}$ -thick copper layer was electroplated and the temporary bonding was removed, resulting in LEDs on copper substrate. The optical output power of LEDs on copper increased by $sim$ 70% as compared to that of the LEDs on silicon. The improved performance was attributed to the removal of the light-absorbing Si substrate and the good thermal conductivity of copper.      

基于无场线电子扫描开放式磁粒子成像系统设计

磁粒子成像是一种全新的人体内动态靶向影像学方法,但当前磁粒子成像系统以封闭式磁场扫描结构为主,严重限制了其临床应用范围。设计了一种开放式电子扫描窄带磁粒子成像系统,在分析了超顺磁粒子谐波磁化响应的基础上,通过对线圈表面耦合磁场的计算及电流控制利用8个梯度线圈形成了基于无场线的开放式空间定位磁场,成像区域30 mm×30 mm;以单边激励线圈产生20.7 kHz激励磁场,处于高频激励磁场及定位磁场中的超顺磁纳米粒子示踪剂产生具有丰富谐波成分的可定位超顺磁磁化信号,使用高信噪比Gradiometer线圈检测其3次谐波信号形成电压云图图像;通过预测量的系统函数矩阵利用非负最小二乘法对电压云图进行重建,形成示踪剂浓度分布云图。成像实验结果表明,系统在开放式成像区域内探测灵敏度20μg Fe,图像重建空间分辨率2 mm,成像速度1 fps,达到了较好的开放式成像效果,系统也是国内首台全自主研发的开放式磁粒子成像系统。     

腐植酸番茄专用底肥在黄瓜上后效作用试验研究

在辽宁普天同乐肥业有限公司试验基地温室,进行了普天同乐腐植酸番茄专用底肥在秀月黄瓜上后效作用的对比试验。试验结果表明,在本试验条件下比对照增产6.83%～12.53%,其中第6处理比对照增产12.53%,增产较高,后效作用达5%显著水平,经济效益显著。     

我国城市交通问题成因及解决对策初探——基于经济学角度的思考

在理清交通问题的概念的基础上,借助经济学上总供给与总需求理论,分析交通问题产生的原因,最后给出可能的解决方案。     

城市化进程的思考

<正>土耳其著名诗人纳齐姆·希克梅特说"人的一生有两样东西不会忘记,那就是母亲的面孔和城市的面孔"。所谓城市面孔,如果说文化就是表情的话那么建筑就是它的轮廓,成千上万的城市面孔中,大多数只是城域文化差别的体现。     

掺高模量树脂类改性剂的沥青混合料路用性能研究

对在北京施工的掺加了高模量树脂类改性剂(以下简称"路强剂")沥青混合料与普通混合料进行了马歇尔参数特性、高温抗车辙能力、水稳定性对比试验,分析了路强剂对沥青混合料路用性能的影响,阐述了掺加路强剂混合料生产过程质量控制要点及手段。