Experimental extraction of an entangled photon pair from two identically decohered pairs

Entanglement is considered to be one of the most important resources in quantum information processing schemes, including teleportation, dense coding and entanglement-based quantum key distribution. Because entanglement cannot be generated by classical communication between distant parties, distribution of entangled particles between them is necessary. During the distribution process, entanglement between the particles is degraded by the decoherence and dissipation processes that result from unavoidable coupling with the environment. Entanglement distillation and concentration schemes are therefore needed to extract pairs with a higher degree of entanglement from these less-entangled pairs; this is accomplished using local operations and classical communication. Here we report an experimental demonstration of extraction of a polarization-entangled photon pair from two decohered photon pairs. Two polarization-entangled photon pairs are generated by spontaneous parametric down-conversion and then distributed through a channel that induces identical phase fluctuations to both pairs; this ensures that no entanglement is available as long as each pair is manipulated individually. Then, through collective local operations and classical communication we extract from the two decohered pairs a photon pair that is observed to be polarization-entangled.     

小圈条最大容量时的气孔直径

本文通过分析计算，导出了小圈条最大容量时的气孔直径d0，有助于新机设计和老机改造时参考。     

b-nucleic acid,and the initial step of deoxyribonucleic acid-degradation by deoxyribonuclease I

Zusammenfassung Feulgen fand, dass die Degradation der Desoxyribonukleinsäure durch Pankreatin keine Mononucleotide bildete, jedoch auf der Stufe der Oligonucleotide (b-Nukleinsäure) blieb. In dieser Mitteilung wird die b-Säure mit dem ersten Degradationsprodukt identifiziert, welches aus Nukleinsäure unter Einwirkung von DNase 1 gebildet wird, und der Verlauf der Nukleinsäure-Degradation wird ausführlich verfolgt.     

Role of active oxygen species in diethyldithiocarbamate-induced gastric ulcer in the rat

Summary Diethyldithiocarbamate, an inhibitor of Cu,Zn-superoxide dismutase, was recently found to be ulcerogenic in the rat stomach, and active oxygen species were found to be responsible for its ulcerogenicity. To clarify which active oxygen species play a role in ulcerogenesis, the effects of various scavengers and iron-chelators were studied. As superoxide dismutase and catalase reduced the ulcerogenesis induced by diethyldithiocarbamate, the superoxide radical and hydrogen peroxide were considered to play a pathogenic role in this ulcer model.     

航天器的稳定自旋对双程多普勒追踪测量的影响

多普革追踪是航天器测量的主要手段之一,在通过对绕月轨道变化的观测来精确测定月球引力场球协函数高阶项的研究中,要求在数十秒采样间隔内得的多普勒频率漂移精度要达到１ＭＨｚ,然而,由于采用了自转稳定姿态控制模式,航天器的旋转会对多普勒测量产生影响,介绍了这种影响以及消除这种影响的方法。     

Crystal structure of a stable dimer reveals the molecular basis of serpin polymerization

Repeating intermolecular protein association by means of beta-sheet expansion is the mechanism underlying a multitude of diseases including Alzheimer's, Huntington's and Parkinson's and the prion encephalopathies. A family of proteins, known as the serpins, also forms large stable multimers by ordered beta-sheet linkages leading to intracellular accretion and disease. These 'serpinopathies' include early-onset dementia caused by mutations in neuroserpin, liver cirrhosis and emphysema caused by mutations in alpha(1)-antitrypsin (alpha(1)AT), and thrombosis caused by mutations in antithrombin. Serpin structure and function are quite well understood, and the family has therefore become a model system for understanding the beta-sheet expansion disorders collectively known as the conformational diseases. To develop strategies to prevent and reverse these disorders, it is necessary to determine the structural basis of the intermolecular linkage and of the pathogenic monomeric state. Here we report the crystallographic structure of a stable serpin dimer which reveals a domain swap of more than 50 residues, including two long antiparallel beta-strands inserting in the centre of the principal beta-sheet of the neighbouring monomer. This structure explains the extreme stability of serpin polymers, the molecular basis of their rapid propagation, and provides critical new insights into the structural changes which initiate irreversible beta-sheet expansion.     

基于洛毕达极限法则的机构奇异位置运动分析

提出了运用洛毕达极限法则分析机构通过死点或切换点的角速度或速比的新方法，并具体应用于具有切换点的GRASHOF neutral机构和GALLOWAY机构的运动分析，计算分析和实验结果证明：这两种特殊的平面双曲槽机构的运动周期是原动曲柄旋转二整周，而并非通常的一整周，发现当CALLOWAY机构的相对杆长差取很小值时，机构能输出具有超长近似停歇期和反向自锁特性的间歇运动，具有实用价值。     

31P-NMR study on nucleotides and intracellular pH of hereditary spherocytes

Summary As determined by³¹p-NMR spectroscopy, intracellarar pH of hereditary spherocytes was lower (pH 6.7–6.9) than that of normal red cells. The level of adenosine diphosphate in hereditary spherocytes was found to be persistently high. The metabolism of nucleotides and other phosphoryl compounds in human red blood cells have been studied in detail by³¹p-NMR spectroscopy^1–3. However, to our knowledge, there seems to be no report describing the result of³¹p-NMR spectroscopy on red blood cells from hereditary spherocytosis.