公路路基施工的压实控制探讨

随着我国国民经济的发展,各地区互通交流运输日益增多,公路作为人们出行最基础的选择,这就促进公路行业的迅猛发展,使得公路运输范围越来越广,线路越来越长,而国家政府在公路建设投入也越来越多。近些年,公路事业得到了飞速发展,同时拉动了国家经济发展,也为人们出行带来了极大方便,但是其路基压实情况令人堪忧,在实际使用过程存在的问题也日益增多。本文简析公路路基压实施工特性及压实质量的影响因素,进而提出公路路基压实质量控制措施的对策。

公众参与在城市公园规划设计中的作用

一、公众参与对城市公园设计的限定作用1．场地调查阶段确定服务对象。根据公园的性质和服务半径．设计者与公众一起确定公园的服务对象。参与设计的公众是不同层次的人（年龄、职业、收入等），他们的需求各不相同，所在的社会群体不同。对公园的需求也不同，公园建设的好坏与他们有直接的关系，所以，公众要对自己负责。

Simulating resonance-mediated two-photon absorption enhancement in rare-earth ions by a rectangle phase modulation

Improving the up-conversion luminescence efficiency crucial in several related application areas. In this work, of rare-earth ions via the multi-photon absorption process is we theoretically propose a feasible scheme to enhance the resonance-mediated two-photon absorption in Er3＋ ions by shaping the femtosecond laser field with a rectangle phase modulation. Our theoretical results show that the resonance-mediated two-photon absorption can be decomposed into the on-resonant and near-resonant parts, and the on-resonant part mainly comes from the contribution of laser central frequency components, while the near-resonant part mainly results from the excitation of low and high laser frequency components. So, the rectangle phase modulation can induce a constructive interference between the two parts by properly designing the modulation depth and width, and finally realizes the resonance-mediated two-photon absorption enhancement. More- over, our results also show that the enhancement efficiency of resonance-mediated two-photon absorption depends on the laser pulse width （or laser spectral bandwidth）, final state transition frequency, and intermediate and final state absorption bandwidths. The enhancement efficiency modulation can be attributed to the relative weight manipulation of on-resonant and near-resonant two-photon absorption in the whole excitation process. This study presents a clear physical insight for the quantum control of resonance-mediated two-photon absorption in the rare-earth ions, and there will be an important significance for improving the up-conversion luminescence efficiency of rare-earth ions.

激光强度对Dy^(3+)离子掺杂玻璃上转换发光控制的影响（英文）

稀土离子上转换发光是理解多光子激发过程和上转换发光机制的重要基础研究.用方波调制飞秒脉冲作为激发光源,理论、实验研究了Dy^(3+)掺杂玻璃的上转换发光调控,结果表明在较高、较低激光强度下上转换发光具有不同的控制效率.通过考虑高阶多光子吸收过程进一步研究了其物理控制机制,即上转换发光多光子吸收包括双光子和四光子吸收过程.在整个激发过程中,四光子吸收的相对权重随着激光强度增加而增加,由于双光子和四光子跃迁路径的相消干涉,上转换发光在不同激光强度下表现出不同的控制行为。在高激光强度下,观测稀土离子高阶多光子吸收过程为理解多光子吸收上转换发光机制提供了清晰的图像,并为调控上转换发光提供了新的方法。

浅谈沥青混凝土路面施工工艺

沥青混凝土施工过程中很容易产生材料离析和温度离析,材料离析是混合料粗细集料和沥青含量的不均匀的体现,温度离析是指混合料在运输、摊铺、压实过程中各部位的温度不同而引起沥青混合料的性能不同。

Radio-frequency compressed electron pulse-width characterization by cross-correlation between electron bunches and laser-induced plasma

A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal evolution of 2-dimensional transverse profile of ultrafast electron bunches repelled by the formed transient electric field of laser-induced plasma on a silver needle is investigated, and the pulse-width can be obtained by analyzing these time-dependent images.This approach can characterize radio-frequency compressed ultrafast electron bunches with picosecond or sub-picosecond timescale and up to 105 electron numbers.

Compressing ultrafast electron pulse by radio frequency cavity

An ultrafast electron diffraction technique with both high temporal and spatial resolution has been shown to be a powerful tool to observe the material transient structural change on an atomic scale.The space charge forces in a multi-electron bunch will greatly broaden the electron pulse width,and therefore limit the temporal resolution of the high brightness electron pulse.Here in this work,we design an ultrafast electron diffraction system,and utilize a radio frequency cavity to realize the ultrafast electron pulse compression.We experimentally demonstrate that the stretched electron pulse width of14.98 ps with an electron energy of 40 keV and the electron number of 1.0 ×10;can be maximally compressed to about0.61 ps for single-pulse measurement and 2.48 ps for multi-pulse measurement by using a 3.2-GHz radiofrequency cavity.We also theoretically and experimentally analyze the parameters influencing the electron pulse compression efficiency for single-and multi-pulse measurements by considering radiofrequency field time jitter,electron pulse time jitter and their relative time jitter.We suggest that increasing the electron energy or shortening the distance between the compression cavity and the streak cavity can further improve the electron pulse compression efficiency.These experimental and theoretical results are very helpful for designing the ultrafast electron diffraction experiment equipment and compressing the ultrafast electron pulse width in a future study.

单曝光偏振映射超快成像

单曝光超快光学成像可以捕捉发生在纳秒时间尺度内的瞬态场景,尤其是对于泵浦探测技术无能为力的不可逆或难以重复的场景更具优势.为了打破传统CCD或CMOS相机的数据读出速度限制,单曝光超快成像技术通常将时间信息转换到波长、空间或空间频域等来进行超快探测.本文作者开发了一种新型时间-偏振映射的超快成像技术(PUMP),首先利用石英旋光晶体产生具有时变偏振角的超短激光脉冲照明动态场景,然后通过偏振滤波阵列对不同时刻信息进行快照曝光,最后结合迭代去卷积算法,实现了将时域信息转换到偏振维度的超快成像.此外,作者利用该新型超快成像系统实时观测了氧化铟锡薄膜的超快激光烧蚀动力学过程,验证了其在超快探测中的出色性能.该技术的发展有望进一步推动超快光学成像在基础和应用科学研究领域的应用.

超快电子衍射技术及其应用

时间和空间上实时观测原子运动对于自然科学研究有着非常重大的意义,而超快电子衍射(UED)技术同时具备飞秒激光脉冲的高时间分辨特性和电子衍射技术的高空间特性,可以为实时观测原子级分辨尺度物质的结构变化提供一种有效工具.本文综述了超快电子衍射技术的发展历史、实验方法以及相关应用,并且展望了超快电子衍射技术未来的发展.