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Quantum mechanics, through the Heisenberg uncertainty principle, imposes limits on the precision of measurement. Conventional measurement techniques typically fail to reach these limits. Conventional bounds to the precision of measurements such as the shot noise limit or the standard quantum limit are not as fundamental as the Heisenberg limits and can be beaten using quantum strategies that employ "quantum tricks" such as squeezing and entanglement. 相似文献
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The possibility of arbitrarily "adding" and "subtracting" single photons to and from a light field may give access to a complete engineering of quantum states and to fundamental quantum phenomena. We experimentally implemented simple alternated sequences of photon creation and annihilation on a thermal field and used quantum tomography to verify the peculiar character of the resulting light states. In particular, as the final states depend on the order in which the two actions are performed, we directly observed the noncommutativity of the creation and annihilation operators, one of the cardinal concepts of quantum mechanics, at the basis of the quantum behavior of light. These results represent a step toward the full quantum control of a field and may provide new resources for quantum information protocols. 相似文献
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Seife C 《Science (New York, N.Y.)》2000,289(5484):1447a-1448a
A physicist has used the laws of thermodynamics, information, relativity, and quantum mechanics to figure out the ultimate physical limits on the speed of a computer. His calculations show that, in principle, a kilogram of matter in a liter-sized container could be an "ultimate laptop" more than a trillion trillion trillion times as powerful as today's fastest supercomputer--if it could be turned into a black hole. 相似文献
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Wagner K Janousek J Delaubert V Zou H Harb C Treps N Morizur JF Lam PK Bachor HA 《Science (New York, N.Y.)》2008,321(5888):541-543
Position and momentum were the first pair of conjugate observables explicitly used to illustrate the intricacy of quantum mechanics. We have extended position and momentum entanglement to bright optical beams. Applications in optical metrology and interferometry require the continuous measurement of laser beams, with the accuracy fundamentally limited by the uncertainty principle. Techniques based on spatial entanglement of the beams could overcome this limit, and high-quality entanglement is required. We report a value of 0.51 for inseparability and 0.62 for the Einstein-Podolsky-Rosen criterion, both normalized to a classical limit of 1. These results are a conclusive optical demonstration of macroscopic position and momentum quantum entanglement and also confirm that the resources for spatial multimode protocols are available. 相似文献
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The basic concepts for direct and catalyzed photodissociation of water have been summarized. Water dissociation in closed-cycle processes based on endothermic photochemical reactions offers a potential solution to the solar energy conversion problem. Transition metal complexes, whose excited state chemistry is extremely rich (23, 24) although mostly unexplored, are, in principle, suitable "catalysts" for cycles of this type. The most interesting cycles are those involving metal hydrido complexes or binuclear complexes in which the two metal atoms are bound into a macrocyclic ligand. Systematic investigations of the photochemistry of transition metal complexes with the aim of designing suitable systems for solar energy conversion have long-range promise and merit further consideration. 相似文献
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Signal-processing machines at the postsynaptic density 总被引：1，自引：0，他引：1
Kennedy MB 《Science (New York, N.Y.)》2000,290(5492):750-754
Dendrites of individual neurons in the vertebrate central nervous system are contacted by thousands of synaptic terminals relaying information about the environment. The postsynaptic membrane at each synaptic terminal is the first place where information is processed as it converges on the dendrite. At the postsynaptic membrane of excitatory synapses, neurotransmitter receptors are attached to large protein "signaling machines" that delicately regulate the strength of synaptic transmission. These machines are visible in the electron microscope and are called the postsynaptic density. By changing synaptic strength in response to neural activity, the postsynaptic density contributes to information processing and the formation of memories. 相似文献
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Ｇｒａｃｉｅ（格雷斯）与Ｂｒｕｎｏ（希鲁诺）是美味猕猴桃的两个优良品种。近年来国内有些果树学家和猕猴桃生产者将这两个品种混称为“布鲁诺”。经我们通过形态学的观察，证实Ｇｒａｃｉｅ与Ｂｒｕｎｏ在花、果、叶等形态方面均有明显差异，这些差异可作为鉴别该两品种的科学依据。 相似文献
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老子《道德经》洋洋五千言,把社会人生等问题置于宇宙发展演变的历史长河中对照思考,历来被人们称为“哲理诗”。对其中的生态智慧及“道”和“无为”的概念进行解读,挖掘其中的文化意蕴,可以帮助我们探索人与自然的矛盾运动规律。 相似文献
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The typical scales for plant and fungal movements vary over many orders of magnitude in time and length, but they are ultimately based on hydraulics and mechanics. We show that quantification of the length and time scales involved in plant and fungal motions leads to a natural classification, whose physical basis can be understood through an analysis of the mechanics of water transport through an elastic tissue. Our study also suggests a design principle for nonmuscular hydraulically actuated structures: Rapid actuation requires either small size or the enhancement of motion on large scales via elastic instabilities. 相似文献
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基于“卓越工程师”培养的土建类理论力学教学改革研究 总被引：1，自引：0，他引：1
理论力学是土木工程系的主干课程,是后续课程材料力学、结构力学的基础,在整个土木工程系课程结构中占有相当重要的地位。针对于教育部提出的“卓越工程师教育培养计划”,为培养高质量工程技术人才,有必要对土木工程专业理论力学进行有效的教学改革。结合课题组已有的教学经验,从教学理念、教学内容、教学手段、教学模式和实践性教学活动几个方面提出了详尽的改革措施。 相似文献
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振动式深松中耕作业机的振源部件设计及有限元分析 总被引：2，自引：0，他引：2
文章介绍了振动式深松中耕作业机的总体结构及工作原理,阐述了关键部件—振源部件设计过程,对振源部件从动轴部装受力分析给出了基于MATLAB的求解图形表达,提出其数学解析表达式,并对其进行了有限元分析。研究表明,振源部件的设计满足结构和强度要求,为机具的设计提供了理论基础。 相似文献
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从理论力学的角度,提出合碰撞冲量和撞击中心相重合的观点,建议以调节门铰的位置及在拍门下部增减“调节质量”或微移拍门下部某一横梁的方法达到仅在止水橡皮兼作缓冲的条件下,拍门关闭时门铰处理论上不产生碰撞反力的目的,供拍门设计时参考。 相似文献
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分析了木材主切削力与花旗松和曲柳的顺纹抗压强度、横纹抗压强度、弯曲强度以及剪切强度等木材力学性质之间的相关关系。结果表明，木材主切削力与各木材力学性质之间存在线形关系，但其相关关系随着相对于纤维方向的切削方向、树种、切削厚度和切削角度等因素的变化而有所不同，有的相差较大。相对而言，木材主切削力与木材密度之间的相关关系略好于木材切削力与木材的力学性质之间的相关关系。 相似文献
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作为社会批判理论,霍耐特从人与人之间应该平等的规范承诺出发,以其承认理论为基础,认为物化是一个社会病理学概念。它是对主体间交往过程中承认遗忘的描述,以“承认遗忘”赋予物化新的内涵。与霍耐特分析视角不同,马克思的劳动异化理论批判的是“资本逻辑”,是运用人的自由全面发展理论对资本主义社会生产活动中必然发生的主客异化关系进行批判分析。二者虽然都使用了“异化”与“物化”相近的概念,实质上有着不同的语境、所指和理论内涵。由于同为社会批判理论,然而也有着相同的理论特性与实践诉求。 相似文献
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不同初植密度人工兴安落叶松木材物理力学性质比较 总被引：1，自引：0，他引：1
以东北林业大学帽儿山实验林场老山实验站的人工兴安落叶松林为例．对３种不同初植密度 Ｌ２１（１． ５ ｍ × ２． ０ｍ）、 Ｌ２２（３． ０ ｍ × ３． ０ ｍ）、 Ｌ２３（２． ５ ｍ× ２． ５ ｍ）林分的人工落叶松木材物理力学性质性向变异进行比较研 究。结果表明：①生长速率．晚材率、以及气干时径向、弦向和体积干缩率均表现为：Ｌ２３＞Ｌ２１＞Ｌ２２；全干时径 向、弦向和体积干缩率均表现为：Ｌ２３＞Ｌ２２＞Ｌ２１。②生长速率、生长轮宽度、晚材率３项指标差异不显著、生长 轮密度和干缩率则表现为差异十分显著。③力学性质指标中．抗弯强度、顺纹抗压强度、横纹局部抗压和横纹全部抗 压强度差异显著．而且抗弯弹性模量、顺纹抗压强度、横纹局部抗压和横纹全部抗压强度的平均值表现为： Ｌ２３＞Ｌ２２ ＞Ｌ２１。采用综合坐标法分析．Ｌ２３林分树木生长速度较快．晚材比重大．主要力学性质好．木材材质较好． 相似文献
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曾小五 《湖南农业大学学报(自然科学版)》2008,(6)
"忠"和"恕"是两种直接相关但又互不相同的心理过程,在孔子的伦理思想中,它们也代表着两类密切关联但又彼此区别的道德原则。通过对这两个概念的剖析,我们可以揭示出孔子道德哲学的内在理路。这就是:"人之道"(即仁与义)的实现从根本上讲是人自然本性的实践化;人的自然本性对于作为人的行为动机的情感而言,就是人的心理或情感居于一种最内在、最本然的状态(即忠);只有当我们回归并持守这种最内在、最本然的心理情感状态时,才会在生活实践中自然流露出对事物的公正之心和同情之心(即恕)等确定性的道德情感;我们既可以依公正之心确立 相似文献