一种新颖的宽频带无线局域网天线设计

本文提出一种结构简单的、宽带双频、共面波导馈电的单极子天线,本天线采用50欧姆的SMA接头对其进行馈电,印刷集成在一个22×35mm2的介质基板上,覆盖了无线局域网(WLAN)的2.4-,5.2-,5.8-GHz三个频带,并且具有良好的阻抗匹配特性。此天线的低谐振模式在VSWR<2时的阻抗带宽为320MHz(2.38到2.70GHz),满足了2.4-GHz WLAN工作频段(2.400-2.484GHz);此外,天线的高谐振模式在VSWR<2时的阻抗带宽为2.480GHz(3.580到6.060GHz),包含了5.2-GHz的HIPERLAN频段(5.150到5.350GHz)和5.8-GHz的WLAN频段(5.725到5.852GHz)。     

Comment on “A Note on the Two-Spring Tomlinson Model”

A recent note by Lu et al. presented a theoretical study of atomic friction using a two-spring Tomlinson model. In this comment, we argue that the conclusion of the note can be understood in a simple manner, and that the discussion of the criterion for the onset of stick-slip is unnecessarily complicated and potentially misleading.     

变截面连续刚构桥的线形监控

对于挂篮悬臂施工的预应力混凝土连续刚构桥来说,主梁的成桥线形主要取决于施工过程的控制。变截面连续刚构桥的建成要经历一个较长而复杂的施工过程,结构体系也会随着施工过程发生变化。为确保合理线形,需设置准确的预拱度和具备完善的线形监测体系。对设置预拱度的影响因素进行了分析,并利用有限元分析软件MIDAS CIVIL建立了涪江一桥的分析模型。结合合川区涪江一桥的现场监控实践,对线形监控成果进行了分析。     

土石坝坝坡模型振动台破坏试验的数值验证

 在土石坝坝坡模型振动台破坏试验基础上,采用数值分析方法,对坝坡的动力特性、稳定性以及加筋抗震措施的性能进行研究。采用动力弹塑性分析方法,对坝坡模型振动台试验进行数值仿真,通过类比计算工况,比较、分析坝坡的破坏过程及其破坏性态以及永久位移的变化规律;同时,采用拟静力方法对坝坡的稳定性进行分析,通过设定滑裂面参数,比较滑裂面的深浅,分析加筋对坝坡稳定性的影响,并与试验结果进行对比验证。结果表明：对模型进行的数值模拟和模型试验所得到的结果较为一致,表明坝顶是薄弱部分,破坏首先从坝顶附近开始,减缓坝坡或坝坡加筋均可减小坝坡的永久位移,但加筋能提高坝坡的整体稳定性,能有效控制坝坡的浅层滑动,且不增加大坝填筑量,与缓坡比较有较强的优势。该研究结果可为大坝的加筋抗震措施设计提供依据。     

Microstructural changes during creep of a high chromium steel

This article paper deals with creep deformation of a high-chromium steel, X-20. Creep tests were performed at three temperatures, 500 °, 550 °, and 600 °, under various loads. Some of the tests terminated in rupture, while others were interrupted and examined by optical micro-scopy and scanning electron microscopy (SEM). It was found that at the onset of tertiary creep, the creep rate begins to decrease for a certain period of time and a “step” appears on the creep curve. Study of the microstructure revealed that at the beginning of the step, the martensite needles start to rotate toward the tensile axis, and at the end of the step most of the needles are parallel to this direction. Hot-rolled pieces of the steel confirmed this observation; after rolling to a reduction of 35 pct, all the martensite needles lie parallel to the rolling direction and, therefore, the step was not observed. We offer an explanation for the step on the creep curve based on the rotation of the martensite.     

铜基复合材料的摩擦磨损性能研究现状

铜基复合材料具有优异的性能及广泛的应用,而随着其应用的愈加广泛,对其摩擦磨损性能的要求也愈加严格。综述了国内外颗粒增强、石墨自润滑、纤维增强和碳纳米管增强铜基复合材料的摩擦磨损性能,并简述了目前铜基复合材料存在的一些问题及展望。     

对苯二异氰酸酯型TPU的动态力学分析

考察了异氰酸酯、多元醇和扩链剂种类对对苯二异氰酸酯(PPDI)型热塑性聚氨酯弹性体(TPU)机械性能和动态力学性能的影响.结果表明,PPDI型TPU的耐热和内生热性能均优于MDI体系,软段分子结构的不同会影响TPU的热稳定性,HQEE可提高材料的耐热性能.     

外源褪黑素对杏果实采后黑斑病的调控作用

为探究外源褪黑素对杏果实采后黑斑病的影响,以“赛买提”杏为试验材料,采用不同浓度的褪黑素（50,100,200μmol/L）在0.05 MPa条件下减压处理2 min,常压状态下浸泡8 min。以蒸馏水处理为对照组,自然晾干表面水分,在温度（0±1）℃,相对湿度90%～95%条件下放置48 h后,损伤接种交链格孢菌于相同条件下贮藏。定期测定杏果实接种发病率和病斑直径,苯丙氨酸解氨酶（PAL）、肉桂酸-4-羟化酶（C4H）、4-香豆酸辅酶A连接酶（4CL）、多酚氧化酶（PPO）、肉桂醇脱氢酶（CAD）活力及总酚、类黄酮、木质素含量。结果表明：外源褪黑素处理显著降低了杏果实接种发病率和病斑直径的上升。在贮藏42 d时,不同浓度的褪黑素处理组（50,100,200μmol/L）的病斑直径分别为8.41,7.20,8.01 mm,比对照组病斑直径低5.68%,19.32%,9.45%(P<0.05),接种发病率分别比对照组低10.00%,21.11%,12.22%(P<0.05),100μmol/L褪黑素处理组抑制杏果实交链格孢菌生长效果最佳。褪黑素处理可提高杏果实PAL、C4H、...     

Circ_0011129 Encapsulated by the Small Extracellular Vesicles Derived from Human Stem Cells Ameliorate Skin Photoaging

Photoaging is not only the main cause of skin aging caused by exogenous factors, it is also related to a variety of skin diseases and even malignant tumors. Excessive and repeated exposure to ultraviolet radiation, especially UVA induces oxidative stress, DNA damage, inflammation, and collagen and elastin degeneration, ultimately leads to skin photoaging, manifested by skin redness, coarse wrinkles, and pigmentation even skin cancer. There has been a large demand of effective prevention and medications but approaches in the current management of photoaging are very limited. In the previous study, we found that a non-coding circular RNA circ_0011129 acts as a miR-6732-5p adsorption sponge to inhibit the reduction of type I collagen and the denaturation and accumulation of elastin in UVA-induced HDF cells photoaging model. However, in vivo instability and efficient delivery to the target cell of circRNA is a major challenge for its clinical application. Therefore, improving its stability and delivery efficiency are desired. In this study, we proposed a strategy of delivering circ_0011129 with small extracellular vesicles (sEVs) from human adipose-derived stem cells (hADSCs) to intervene in the photoaging process. The results showed that sEVs from hADSCs in 3D bioreactor culture (3D-sEVs) can prevent photoaging. Consequently, by overexpressing circ_0011129 in hADSCs, we successfully loaded it into 3D-sEVs (3D-circ-sEVs) and its protective effect was better. Our studies provide a novel approach to preventing skin photoaging, which has important clinical significance and application value for the development of non-coding RNA drugs to treat skin photoaging. We first screened out hADSCs-derived sEVs with excellent anti-oxidant effects. We then compared the sEVs collected from traditional 2D culture with 3D bioreactor culture. By miRNA-seq and GEO data analysis, we found that miRNAs in 3D-sEVs were enriched in cell activities related to apoptosis, cellular senescence, and inflammation. Subsequently, we prepared circ_0011129-loaded 3D-sEVs (3D-circ-sEVs) by overexpressing it in hADSCs for the treatment of photoaging in vitro. We proved that 3D-circ-sEVs can interfere with the process of cell photoaging and protect cells from UVA radiation damage, as well as in a H2O2-induced oxidative stress model.     

基于人类听觉的伪随机序列的信息隐藏技术

提出了一种在话音传递中,蒙蔽人类听觉的信息隐藏模型。给出了数字音频信号中信息隐藏的伪随机序列生成算法。利用此算法对隐蔽信息先加密,再对数字音频信号进行分段处理,并选出部分段做离散余弦变换(DCT),最后依据人类的听觉系统选择DCT域中高频系数进行量化完成加密的隐蔽信息嵌入。实验结果表明,在提高鲁棒性的同时,还大大增加了安全性,就是在外界发现数字音频含有隐藏信息的情况下,在不知道密钥的情况下,还是很难提取隐蔽信息。