What is Erased in the Quantum Erasure?

In this paper, we re-examine a series of gedanken welcher Weg (WW) experiments introduced by Scully, Englert and Walther that contain the essential ideas underlying the quantum eraser. For this purpose we use the Bohm model which gives a sharp picture of the behaviour of the atoms involved in these experiments. This model supports the thesis that interference disappears in such WW experiments, even though the centre of mass wave function remains coherent throughout the experiment. It also shows exactly what it means to say ‘that the interference can be restored by manipulating the WW detectors long after the atoms have passed’. It does not support Wheeler’s notion that ‘the past is undefined and undefinable without the observation (in the present)’.     

超细Sr2CeO4 粉体微乳液-高温法制备条件的正交试验及其发光性能研究

本文首先利用正交试验确定了微乳液-高温法合成蓝色发光Sr₂CeO₄超细粉体的最佳制备条件。接着研究了最佳条件下制备的Sr₂CeO₄超细粉体的性能。场发射扫描电镜(FE-SEM)显示，在850 ℃、900 ℃、1 000 ℃或者更高温度下退火4 h制备的粉体的形状分别呈球状、梭状和球状，平均粒径分别在100 nm左右和1 μm以内。X射线粉末衍射数据分析表明，该超细粉体属于正交晶系。室温下的光致发光光谱显示，该粉体的激发光谱有3个激发峰，主峰分别位于262 nm、281 nm和341 nm，而其发射光谱只呈现出1个发射峰，主峰位于约470 nm。与高温固相制备方法相比，微乳液-高温法可以在较低温度下制备出超细的粉体，而且它不但在262 nm处出现了一个新的激发峰，主激发峰和发射峰的位置也分别蓝移了大约30 nm和12 nm。     

Importance of the isopropylidene terminal of geranylgeranyl group for the formation of tetraether lipid in methanogenic archaea

Labeling experiments using several deuterated lipids were pursued to study the biosynthesis of macrocyclic isoprenoidal lipids of thermophilic methanogenic archaea, Methanothermobacter thermautotrophicus. The isopropylidene terminal of geranylgeranyl group of monomeric precursor appeared to be important for the CC bond formation at the hydrophobic end in the macrocyclic lipids. A mechanism involving a radical trigger at the allylic methyl group is proposed for this CC bond formation.     

On retroactive occurrence and twin events in quantum mechanics

Bohr's well-known claim that only a registered phenomenon is a true phenomenon is further elaborated into occurrence in the past: If ideal occurrence of an eventP ((1–P)) is a state at a timet _i makes another eventQ ((1–Q))certain at a later timet _f, and, finallyU is the evolution operator fromt _i tot _f, then, it is proved that the final collapsed stateQ(U U ⁺)Q/TrQU U ⁺, which comes about in ideal occurrence ofQ att _f,equals the initial collapsed stateU(P P/TrP)U ⁺, which evolves from the state resulting from the ideal occurrence ofP in att _i. Utilizing the latter state is called theretroactive apparent ideal occurrence (RAIO) ofP in. A number of consequences, including the general notion of twin events (the case whent _f=t _i, andU=1) is derived. It is pointed out that RAIO is relevant in second-kind quantum measurement, in Wheeler's delayed-choice experiments in second-kind (or conditional) quantum preparators.     

物理演示实验教学在高素质新型军事人才培养中的作用

培养高素质新型军事人才是国防科技大学的核心任务之一.物理演示实验以直观、形象地演示物理现象为课程特色,可有效提高学员对物理规律、物理本质的直观认识和深刻理解,并引起学员的深入思考,在教学实践中可促进学员科学素质、综合能力和创新能力的提高.     

爆轰试验中高速摄影控制及闪光装置改进

研究爆轰试验高速摄影中,闪光灯和摄影机快门失灵引起试验失败问题,提出对试验操控装置和闪光灯电源改进措施。首先,在实验操控上增加防止仅雷管起爆的逻辑控制,并采用集中控制,分布检测设计;其次,在闪光氙灯电源中,采用伪火花开关和多节LC（电感-电容）脉冲形成线技术,解决氙灯存在的自闪、不引燃和光强不均。此外,还解决了装置研制中遇到的电磁干扰、同步引燃等问题。通过改进,有效地防止了爆轰试验中高速摄影光学影像丢失情况和底片曝光不均匀现象,介绍了主要元件、线路和系统、实验结果及研制过程。     

转移基板材质对Si衬底GaN基LED芯片性能的影响

在Si衬底上生长了GaN基LED外延材料,分别转移到新的硅基板和铜基板上,制备了垂直结构蓝光LED芯片。研究了这两种基板GaN基LED芯片的光电性能。在切割成单个芯片之前,对大量尺寸为(300μm×300μm)的这两种芯片分别通高达1 A的大电流在测试台上加速老化1 h。结果显示,铜基板Si衬底GaN基LED芯片有更大的饱和电流,光输出效率更高,工作电压随驱动电流的变化不大,光输出在老化过程中衰减更小。铜基板芯片比硅基板芯片可靠性更高,在大功率半导体照明器件中前景诱人。     

Experimental study on age and gender differences in microscopic movement characteristics of students

Campus security has aroused many concerns from the whole society. Stampede is one of the most frequent and influential accidents in campus. Studies on pedestrian dynamics especially focusing on students are essential for campus security, which are helpful to improve facility design and emergency evacuation strategy. In this paper, primary and middle school students were recruited to participate in the single-file experiments. The microscopic movement characteristics,including walking speed, headway, gait characteristics(step length, step frequency and swaying amplitude) and their relations were investigated. Age and gender differences in the headway-speed diagram and space requirements were analyzed by statistical tests. The results indicated that the impacts of age and gender were significant. There were three stages for the influence of gender on the headway-speed diagram for both age groups. The impacts on students' space requirements were consistent for different age and gender groups. But the impacts of age and gender on free-flow speed were affected by each other. Due to the connection of walking speed and gait characteristics, the comparisons of gait characteristics between different ages and genders were performed to understand the corresponding differences in speed more deeply. The results showed that differences in step length and swaying amplitude between males and females were significant for both age groups. The effect of gender on step frequency was significant for primary students. But for middle school students,whether gender had significant impact on step frequency was not clear here because of the large P-value. Besides, the influence of age on gait characteristics changed with gender.     

在线社交网络控制实验的现状与展望

在线社交网络已发展成为一个独特的电子生态系统,其应用深刻影响着人们生活的方方面面。由于在线社交网络特性复杂,分析在线社交网络形成和变化中的规律成为当前计算机科学、社会学和物理学的一项挑战。传统上,在线社交网络实证研究主要采用计算机辅助的被动数据获取和分析方式。近年来,在真实大规模在线社交网络上直接进行控制实验从而主动获取数据并开展分析研究的方式广受关注。评述了这一领域的研究进展,包括：社交网络控制实验的主要研究模式;控制实验方法在社交网络结构、信息传播、行为和心理学等领域取得的主要成果以及主要实验工具的适用条件和局限性。最后,展望了人工智能技术在社交网络控制实验中的应用潜力,分析了智能算法对降低实验成本和提高实验效率的作用。