Fast delivery of meteorites to Earth after a major asteroid collision

Very large collisions in the asteroid belt could lead temporarily to a substantial increase in the rate of impacts of meteorites on Earth. Orbital simulations predict that fragments from such events may arrive considerably faster than the typical transit times of meteorites falling today, because in some large impacts part of the debris is transferred directly into a resonant orbit with Jupiter. Such an efficient meteorite delivery track, however, has not been verified. Here we report high-sensitivity measurements of noble gases produced by cosmic rays in chromite grains from a unique suite of fossil meteorites preserved in approximately 480 million year old sediments. The transfer times deduced from the noble gases are as short as approximately 10(5) years, and they increase with stratigraphic height in agreement with the estimated duration of sedimentation. These data provide powerful evidence that this unusual meteorite occurrence was the result of a long-lasting rain of meteorites following the destruction of an asteroid, and show that at least one strong resonance in the main asteroid belt can deliver material into the inner Solar System within the short timescales suggested by dynamical models.     

Effect and fate of intravenously administered porphobilin in rats

Summary It rats after i.v. prophobilin, blood pressure and pulse rate remained stable, the animals were calm and moved freely with no symptoms or signs of nervous effect. Prophobilin was rapidly excreted in the urine.     

半胱氨酸亚金铵的合成、理化性质及电镀金应用

以半胱氨酸为配体合成一种新型亚金配合物NH4Au(Cys)2,对该配合物进行元素分析、红外光谱、紫外光谱、热失重分析和导电性测量等理化性质研究;以该亚金配合物为金源开展相关的电镀金工艺探索,并通过四因素三水平的正交试验获得其最佳条件参数;采用扫描电子显微镜(SEM)和X线衍射(XRD)对镀金层的表面质量进行探讨。研究结果表明:该目标产物的分子式为NH4Au(Cys)2·2H2O,该配合物中以半胱氨酸的巯基和金配位为成健特征,在170℃以下热稳定性较好,该亚金配合物是一个典型的离子化合物。在电流密度为200~300 A/m2,p H为10.5~12.0,温度为35~45℃,金质量浓度为15~25 g/L的电镀工艺条件下,得到粒度为0.5~1.0μm的单质金,且主要沿着(111)面进行生长。     

随机纳米碳管网络及其渗流性质

数值模拟了实验上构造纳米碳管网络的溶液沉积方法.与一般的随机网络模型不同,将碳管的长度计算在内,而且考虑了不同的空间相交位形.数值模拟发现网络的度分布为高斯分布,平均集聚系数约为0.11.当网络中碳管平均面密度取值在σ0=179 200根/cm2附近时,网络系综达到渗流.在临界点附近,网络的连通概率p、两极之间电导G、...     

用模糊综合评判法评价变电所所址

变电所选址是电力系统规划的一个重要环节。但与变电所所址有关的因素错综复杂,很难仅凭经验就能确定最佳所址。本文采用模糊综合评判方法对备选所址进行评判,确定其优先次序。在模糊综合评判中,各因素的权重分配对结果起决定性作用,用层次分析法确定与所址密切相关的各个因素相对总体目标而言的权重,使得权重的确定更科学。算例表明该方法是可行的。     

十六位微机教学实验系统分析与改进

本文在分析CCT－88／51／98教学实验系统监控程序的基础上，对该教学实验系统监控程序中存在的问题作出了一些改进。     

用脸谱图对太子河本溪市区段河流沉积物中重金属污染进行评价的研究

本文将沉积学原理及国际上新发展的两种重金属污染评价方法与多变量的图表示法——脸谱图相结合,对太子河本溪市区段河道沉积物中重金属的污染状况及潜在生态危害进行了综合性的评价研究。从脸谱图上可以直观地看出各采样点重金属的污染情况和潜在生态危害程度。从研究结果可以看出,太子河本溪市区段河道沉积物中重金属的污染是很严重的。     

寻找四元域上n维线性空间中n/2维自对偶子空间的方法

本文讨论F4上n维线性空间的k维子空间W，这些子空间都有特定的自同构群(实际上是典型群GLn(F4)的一个子群)，根据群中元素形式的不同可将子空间W分为两类，并对寻找n维空间中形如这两类的n／2维自对偶子空间提供了一种采用降低维数寻找的方法。     

Fehlerkorrekturen bei stereologischen Messungen an menschlichen Plazenten:2. Die Schnittstauchung

Summary Irreversible compression of the sections, due to cutting on the microtome, which may attain up to 20% in thin paraffin sections, does not influence stereological measurings of volume per cm³ of human placental villi. The measured villous surface, however, must be corrected by multiplication with 1/(1+q/2), whereq means the percentage of compression, expressed as decimal fraction.

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Arbeit mit Unterstützung durch die Deutsche Forschungs-gemeinschaft.     

Climbing the Jaynes-Cummings ladder and observing its nonlinearity in a cavity QED system

The field of cavity quantum electrodynamics (QED), traditionally studied in atomic systems, has gained new momentum by recent reports of quantum optical experiments with solid-state semiconducting and superconducting systems. In cavity QED, the observation of the vacuum Rabi mode splitting is used to investigate the nature of matter-light interaction at a quantum-mechanical level. However, this effect can, at least in principle, be explained classically as the normal mode splitting of two coupled linear oscillators. It has been suggested that an observation of the scaling of the resonant atom-photon coupling strength in the Jaynes-Cummings energy ladder with the square root of photon number n is sufficient to prove that the system is quantum mechanical in nature. Here we report a direct spectroscopic observation of this characteristic quantum nonlinearity. Measuring the photonic degree of freedom of the coupled system, our measurements provide unambiguous spectroscopic evidence for the quantum nature of the resonant atom-field interaction in cavity QED. We explore atom-photon superposition states involving up to two photons, using a spectroscopic pump and probe technique. The experiments have been performed in a circuit QED set-up, in which very strong coupling is realized by the large dipole coupling strength and the long coherence time of a superconducting qubit embedded in a high-quality on-chip microwave cavity. Circuit QED systems also provide a natural quantum interface between flying qubits (photons) and stationary qubits for applications in quantum information processing and communication.