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91.
Very much like the ubiquitous quantum interference of a single particle with itself, quantum interference of two independent, but indistinguishable, particles is also possible. For a single particle, the interference is between the amplitudes of the particle's wavefunctions, whereas the interference between two particles is a direct result of quantum exchange statistics. Such interference is observed only in the joint probability of finding the particles in two separated detectors, after they were injected from two spatially separated and independent sources. Experimental realizations of two-particle interferometers have been proposed; in these proposals it was shown that such correlations are a direct signature of quantum entanglement between the spatial degrees of freedom of the two particles ('orbital entanglement'), even though they do not interact with each other. In optics, experiments using indistinguishable pairs of photons encountered difficulties in generating pairs of independent photons and synchronizing their arrival times; thus they have concentrated on detecting bunching of photons (bosons) by coincidence measurements. Similar experiments with electrons are rather scarce. Cross-correlation measurements between partitioned currents, emanating from one source, yielded similar information to that obtained from auto-correlation (shot noise) measurements. The proposal of ref. 3 is an electronic analogue to the historical Hanbury Brown and Twiss experiment with classical light. It is based on the electronic Mach-Zehnder interferometer that uses edge channels in the quantum Hall effect regime. Here we implement such an interferometer. We partitioned two independent and mutually incoherent electron beams into two trajectories, so that the combined four trajectories enclosed an Aharonov-Bohm flux. Although individual currents and their fluctuations (shot noise measured by auto-correlation) were found to be independent of the Aharonov-Bohm flux, the cross-correlation between current fluctuations at two opposite points across the device exhibited strong Aharonov-Bohm oscillations, suggesting orbital entanglement between the two electron beams. 相似文献
92.
针对汽车碰撞乘员约束系统优化设计中多参数和非线性问题,提出了基于径向基函数代理模型的优化设计方法,通过LS-DYNA分析软件建立正面碰撞乘员约束系统的仿真模型并对其进行验证.基于该模型选取对响应影响较大的设计变量作为优化变量,在LS-OPT中选择径向基函数构建代理模型,采用空间填充试验方法进行试验设计,运用自适应模拟退火算法进行优化求解.优化结果表明:人体综合损伤WIC值相比初始设计值降低了28.2%,实现了对设计目标的优化. 相似文献
93.
高分子材料时常被用在提高农业生产力,最近亦有许多研究将其应用在喷植植生工程的土壤改良上,使土壤团粒化及进而降低土壤侵蚀,在草种未发芽时达到水土保持的功效.聚乙烯醇(PVA)是广泛使用的高分子土壤改良剂之一,本研究使用扫描式电子显微镜(SEM)、红外线光谱仪(FT-IR)来分析土壤中PVA薄膜的受热降解的变化,研究结果显示PVA受热会产生降解,未来可视环境的差异选用不同的植生草种. 相似文献
94.
甘蔗提取物的抗氧化性能 总被引:1,自引:1,他引:0
膳食中的抗氧化剂有助于保护人体组织和细胞免受自由基的危害.目前,已有多种天然提取物制剂被用作膳食补充剂.文中比较了美国零售市场中4种甘蔗制品和1种玉米浆制品的组成和抗氧化能力,发现5种制品的抗氧化能力均与颜色密切相关.通过分析经不同澄清工艺并经真空浓缩的两种甘蔗汁的抗氧化能力,发现石灰澄清和纯碱澄清均不会造成抗氧化能力的显著降低.文中还对不同方法脱色后制品的抗氧化能力进行了比较. 相似文献
95.
提出一种基于力的类同传播聚类方法AFAPC.依据万有引力定律,根据数据间的相互引力,并在数据组成的网络中交替传递类同信息,计算出数据的聚类和对应的聚类中心.实验结果表明,AFAPC能在更短的时间内,取得与类同传播聚类算法APC相媲美的聚类效果. 相似文献
96.
建立了C2H2-2.5O2-Ar混合气体爆轰临界管径的测试系统,其中高压电火花作为起爆源.首先分别测定了C2H2-2.5O2,C2H2-2.5O2-50%Ar,C2H2-2.5O2-70%Ar三种混合气体在不同初始压力下的爆轰临界管径.结果表明:随着氩气稀释浓度的提高,在管道直径相同的条件下,可形成球形爆轰的临界压力增加,表明物质的爆轰敏感性降低.进一步探究各种物质临界管径与爆轰胞格的关系,得到了三种物质临界管径与胞格宽度的比例系数.最后分析了三种物质的临界管径和直接起爆的临界能量的关联性,并与Lee表面积能量模型对比,实验结果与理论模型基本吻合,得出C2H2-2.5O2-Ar混合气体爆轰临界管径与临界起爆能量之间的关系为Ec=16-1πρ0v2CJIdc3. 相似文献
97.
空时码应用最广泛的是空时分组码(space-time block code,STBC)和垂直分层空时码(vertical bell layered space-time code, VBLAST),因为STBC信号具有时间上的相关特性,所以在求高阶循环累积量时,该信号有一个特殊的循环频率,而VBLAST信号没有此特性。提出了一种基于循环稳定特性的STBC多载波码分多址(multicarrier code division multiple access,MC-CDMA)信号识别算法。该方法先根据信号系统的基带物理结构和信号模型来建立信号相关函数的选择标准,然后估计出这些相关函数对应的四阶累积量,接着把四阶循环累积量跟信道的参数结合起来建立一个循环统计量,最后把这个循环统计量与检测门限进行比较,实现信号识别。计算机模拟仿真表明,该算法能在较低的输入信噪比条件下良好地工作。 相似文献
98.
Shin J Bossenz M Chung Y Ma H Byron M Taniguchi-Ishigaki N Zhu X Jiao B Hall LL Green MR Jones SN Hermans-Borgmeyer I Lawrence JB Bach I 《Nature》2010,467(7318):977-981
Two forms of X-chromosome inactivation (XCI) ensure the selective silencing of female sex chromosomes during mouse embryogenesis. Imprinted XCI begins with the detection of Xist RNA expression on the paternal X?chromosome (Xp) at about the four-cell stage of embryonic development. In the embryonic tissues of the inner cell mass, a random form of XCI occurs in blastocysts that inactivates either Xp or the maternal X?chromosome (Xm). Both forms of XCI require the non-coding Xist RNA that coats the inactive X?chromosome from which it is expressed. Xist has crucial functions in the silencing of X-linked genes, including Rnf12 (refs 3, 4) encoding the ubiquitin ligase RLIM (RING finger LIM-domain-interacting protein). Here we show, by targeting a conditional knockout of Rnf12 to oocytes where RLIM accumulates to high levels, that the maternal transmission of the mutant X?chromosome (Δm) leads to lethality in female embryos as a result of defective imprinted XCI. We provide evidence that in Δm female embryos the initial formation of Xist clouds and Xp silencing are inhibited. In contrast, embryonic stem cells lacking RLIM are able to form Xist clouds and silence at least some X-linked genes during random XCI. These results assign crucial functions to the maternal deposit of Rnf12/RLIM for the initiation of imprinted XCI. 相似文献
99.
Cell transformation by the superoxide-generating oxidase Mox1. 总被引:65,自引:0,他引:65
Y A Suh R S Arnold B Lassegue J Shi X Xu D Sorescu A B Chung K K Griendling J D Lambeth 《Nature》1999,401(6748):79-82
Reactive oxygen species (ROS) generated in some non-phagocytic cells are implicated in mitogenic signalling and cancer. Many cancer cells show increased production of ROS, and normal cells exposed to hydrogen peroxide or superoxide show increased proliferation and express growth-related genes. ROS are generated in response to growth factors, and may affect cell growth, for example in vascular smooth-muscle cells. Increased ROS in Ras-transformed fibroblasts correlates with increased mitogenic rate. Here we describe the cloning of mox1, which encodes a homologue of the catalytic subunit of the superoxide-generating NADPH oxidase of phagocytes, gp91phox. mox1 messenger RNA is expressed in colon, prostate, uterus and vascular smooth muscle, but not in peripheral blood leukocytes. In smooth-muscle cells, platelet-derived growth factor induces mox1 mRNA production, while antisense mox1 mRNA decreases superoxide generation and serum-stimulated growth. Overexpression of mox1 in NIH3T3 cells increases superoxide generation and cell growth. Cells expressing mox1 have a transformed appearance, show anchorage-independent growth and produce tumours in athymic mice. These data link ROS production by Mox1 to growth control in non-phagocytic cells. 相似文献
100.
In this paper we show that optimal trading results can be achieved if we can forecast a key summary statistic of future prices. Consider the following optimization problem. Let the return ri (over time i=1, 2, ..., n) for the ith day be given and the investor has to make investment decision di on the ith day with di=1 representing a ‘long' position and di=0 a ‘neutral' position. The investment return is given by r=Σni=1ridi−cΣn+1i=1∣di−di−1∣, where c is the transaction cost. The mathematical programming problem of choosing d1, ..., dn to maximize r under a given transaction cost c is shown to have an analytic solution, which is a function of a key summary statistic called the largest change before reversal. The largest change before reversal is recommended to be used as an output in a neural network for the generation of trading signals. When neural network forecasting is applied to a dataset of Hang Seng Index Futures Contract traded in Hong Kong, it is shown that forecasting the largest change before reversal outperforms the k‐step‐ahead forecast in achieving higher trading profits. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献