Haematopoietic stem cells do not transdifferentiate into cardiac myocytes in myocardial infarcts

The mammalian heart has a very limited regenerative capacity and, hence, heals by scar formation. Recent reports suggest that haematopoietic stem cells can transdifferentiate into unexpected phenotypes such as skeletal muscle, hepatocytes, epithelial cells, neurons, endothelial cells and cardiomyocytes, in response to tissue injury or placement in a new environment. Furthermore, transplanted human hearts contain myocytes derived from extra-cardiac progenitor cells, which may have originated from bone marrow. Although most studies suggest that transdifferentiation is extremely rare under physiological conditions, extensive regeneration of myocardial infarcts was reported recently after direct stem cell injection, prompting several clinical trials. Here, we used both cardiomyocyte-restricted and ubiquitously expressed reporter transgenes to track the fate of haematopoietic stem cells after 145 transplants into normal and injured adult mouse hearts. No transdifferentiation into cardiomyocytes was detectable when using these genetic techniques to follow cell fate, and stem-cell-engrafted hearts showed no overt increase in cardiomyocytes compared to sham-engrafted hearts. These results indicate that haematopoietic stem cells do not readily acquire a cardiac phenotype, and raise a cautionary note for clinical studies of infarct repair.     

Lensless imaging of magnetic nanostructures by X-ray spectro-holography

Our knowledge of the structure of matter is largely based on X-ray diffraction studies of periodic structures and the successful transformation (inversion) of the diffraction patterns into real-space atomic maps. But the determination of non-periodic nanoscale structures by X-rays is much more difficult. Inversion of the measured diffuse X-ray intensity patterns suffers from the intrinsic loss of phase information, and direct imaging methods are limited in resolution by the available X-ray optics. Here we demonstrate a versatile technique for imaging nanostructures, based on the use of resonantly tuned soft X-rays for scattering contrast and the direct Fourier inversion of a holographically formed interference pattern. Our implementation places the sample behind a lithographically manufactured mask with a micrometre-sized sample aperture and a nanometre-sized hole that defines a reference beam. As an example, we have used the resonant X-ray magnetic circular dichroism effect to image the random magnetic domain structure in a Co/Pt multilayer film with a spatial resolution of 50 nm. Our technique, which is a form of Fourier transform holography, is transferable to a wide variety of specimens, appears scalable to diffraction-limited resolution, and is well suited for ultrafast single-shot imaging with coherent X-ray free-electron laser sources.     

Vacuum Rabi splitting with a single quantum dot in a photonic crystal nanocavity

Cavity quantum electrodynamics (QED) systems allow the study of a variety of fundamental quantum-optics phenomena, such as entanglement, quantum decoherence and the quantum-classical boundary. Such systems also provide test beds for quantum information science. Nearly all strongly coupled cavity QED experiments have used a single atom in a high-quality-factor (high-Q) cavity. Here we report the experimental realization of a strongly coupled system in the solid state: a single quantum dot embedded in the spacer of a nanocavity, showing vacuum-field Rabi splitting exceeding the decoherence linewidths of both the nanocavity and the quantum dot. This requires a small-volume cavity and an atomic-like two-level system. The photonic crystal slab nanocavity--which traps photons when a defect is introduced inside the two-dimensional photonic bandgap by leaving out one or more holes--has both high Q and small modal volume V, as required for strong light-matter interactions. The quantum dot has two discrete energy levels with a transition dipole moment much larger than that of an atom, and it is fixed in the nanocavity during growth.     

The native architecture of a photosynthetic membrane

In photosynthesis, the harvesting of solar energy and its subsequent conversion into a stable charge separation are dependent upon an interconnected macromolecular network of membrane-associated chlorophyll-protein complexes. Although the detailed structure of each complex has been determined, the size and organization of this network are unknown. Here we show the use of atomic force microscopy to directly reveal a native bacterial photosynthetic membrane. This first view of any multi-component membrane shows the relative positions and associations of the photosynthetic complexes and reveals crucial new features of the organization of the network: we found that the membrane is divided into specialized domains each with a different network organization and in which one type of complex predominates. Two types of organization were found for the peripheral light-harvesting LH2 complex. In the first, groups of 10-20 molecules of LH2 form light-capture domains that interconnect linear arrays of dimers of core reaction centre (RC)-light-harvesting 1 (RC-LH1-PufX) complexes; in the second they were found outside these arrays in larger clusters. The LH1 complex is ideally positioned to function as an energy collection hub, temporarily storing it before transfer to the RC where photochemistry occurs: the elegant economy of the photosynthetic membrane is demonstrated by the close packing of these linear arrays, which are often only separated by narrow 'energy conduits' of LH2 just two or three complexes wide.     

The induction of Sinorhizobium meliloti C4-dicarboxylate transport system （Dct） is regulated by oxygen concentration

The Sinorhizobium meliloti C4-dicarboxylate transport （Dct） system is essential for symbiotic nitrogen fixation. The dctA gene, encoding the C4-dicarboxylate permease, is expressed in both free living and symbiotic cells. But in free living cells expression of dctD and dctB is absolutely required for the expression of dctA. In this study, in order to investigate the effect of oxygen concentration on the induction of Dct system, E. coli DH5a strain which carries the plasmid-encoded dctABD operon was used in tube assays. It was found that the specific induction of Dct system oc- curred only at a certain depth under the surface of M63-0.6% agar media, suggesting that Dct system could respond to oxygen concentration during succinate-induced expression. Furthermore, when measured at different oxygen concentrations, the highest expression level was observed at oxygen concentration of 2%. Thus, we predict that in addition to dicarboxylates, the induction of Dct system may also regulated by oxygen concentration.     

湍流反应流的计算模型

本书是剑桥大学出版社出版的《化学工程》系列丛书之一。此书全面论述湍流反应流计算模型的进展，评介各种技术的优缺点，重点叙述实用模型的公式化，而不是解的数值方法，介绍在单点和单时间的联合概率密度函数（PDF）基础上发展理论框架，并证明：所有常用的湍流反应流的模型都可以用化学项和焓的联合概率密度函数的公式表示，包括基于对化学源项直接闭合的模型和迁移PDF法，为了完整起见，还介绍了湍流理论和湍流标量迁移理论。     

1994～2003年图书馆参考咨询工作研究概况

为了揭示近10年来我国图书馆参考咨询工作研究的基本概貌和发展趋势，时1994年～2003年我国图书馆参考咨询工作研究论文的外部特征和内容特征进行了统计分析，得出了我国传统参考咨询工作正在向网络参考咨询服务方向发展的结论。     

我国青贮玉米的研究现状及市场前景

青贮玉米作为饲料玉米既能大幅度地提高饲料产量，同时具有较高的营养价值，在国民经济和人民生活中占有越来越重要的地位。在借鉴欧美等发达国家对青贮玉米研究成果的基础上，分析了我国发展青贮玉米的优势和潜力，提出了青贮玉米的育种策略、育种目标和主要用于家畜饲养业的有效利用途径。     

纳米碳对DMcT-PAn正极材料电化学性能的影响

研究了纳米碳对DMcT-PAn正极材料的电化学性能的影响.实验结果表明:DMcT-PAn正极材料的电化学氧化还原电流随着纳米碳含量的增加而增大;纳米碳使聚苯胺(PAn)膜的第2个氧化还原峰(位于0～0.2 V)电位发生正移,而微米级碳的存在使得PAn膜的氧化还原电位发生负移,因此,纳米碳主要是影响复合材料中聚苯胺的电化学性能;同时,在纳米碳的作用下,DMcT-PAn的电化学反应阻抗变小,复合膜的电化学容量增加,说明纳米碳对DMcT-PAn电化学反应有电催化作用;当纳米碳质量分数为8%～15%时,含碳复合膜的电化学容量比本征DMcT-PAn膜的电化学容量高,电化学反应阻抗Ret较低;纳米碳可有效改善DMcT-PAn正极材料的电化学性能.