Single mimivirus particles intercepted and imaged with an X-ray laser

X-ray lasers offer new capabilities in understanding the structure of biological systems, complex materials and matter under extreme conditions. Very short and extremely bright, coherent X-ray pulses can be used to outrun key damage processes and obtain a single diffraction pattern from a large macromolecule, a virus or a cell before the sample explodes and turns into plasma. The continuous diffraction pattern of non-crystalline objects permits oversampling and direct phase retrieval. Here we show that high-quality diffraction data can be obtained with a single X-ray pulse from a non-crystalline biological sample, a single mimivirus particle, which was injected into the pulsed beam of a hard-X-ray free-electron laser, the Linac Coherent Light Source. Calculations indicate that the energy deposited into the virus by the pulse heated the particle to over 100,000?K after the pulse had left the sample. The reconstructed exit wavefront (image) yielded 32-nm full-period resolution in a single exposure and showed no measurable damage. The reconstruction indicates inhomogeneous arrangement of dense material inside the virion. We expect that significantly higher resolutions will be achieved in such experiments with shorter and brighter photon pulses focused to a smaller area. The resolution in such experiments can be further extended for samples available in multiple identical copies.     

核磁共振内标法测定苏丹红I对照品的含量

本文建立了用核磁共振内标法快速、准确地测定苏丹红I对照品含量的方法。采用Varian公司600 MHz核磁共振仪,在氘代氯仿为溶剂、苯甲酸为内标、 25℃条件下采集苏丹红I和苯甲酸混合物的核磁共振氢谱。以苏丹红I中化学位移在δ 8.51和苯甲酸中化学位移在δ 8.13的质子信号峰为定量峰,测得3批苏丹红I的质量分数分别为99.47 %,99.34 %和99.51%。结果表明,在没有对照品的情况下,核磁共振内标法可用于苏丹红I对照品的含量测定和质量控制,同时也能够为其他化学对照品的含量测定提供参考。     

Recruitment of entomopathogenic nematodes by insect-damaged maize roots

Plants under attack by arthropod herbivores often emit volatile compounds from their leaves that attract natural enemies of the herbivores. Here we report the first identification of an insect-induced belowground plant signal, (E)-beta-caryophyllene, which strongly attracts an entomopathogenic nematode. Maize roots release this sesquiterpene in response to feeding by larvae of the beetle Diabrotica virgifera virgifera, a maize pest that is currently invading Europe. Most North American maize lines do not release (E)-beta-caryophyllene, whereas European lines and the wild maize ancestor, teosinte, readily do so in response to D. v. virgifera attack. This difference was consistent with striking differences in the attractiveness of representative lines in the laboratory. Field experiments showed a fivefold higher nematode infection rate of D. v. virgifera larvae on a maize variety that produces the signal than on a variety that does not, whereas spiking the soil near the latter variety with authentic (E)-beta-caryophyllene decreased the emergence of adult D. v. virgifera to less than half. North American maize lines must have lost the signal during the breeding process. Development of new varieties that release the attractant in adequate amounts should help enhance the efficacy of nematodes as biological control agents against root pests like D. v. virgifera.     

Solution-processed silicon films and transistors

The use of solution processes-as opposed to conventional vacuum processes and vapour-phase deposition-for the fabrication of electronic devices has received considerable attention for a wide range of applications, with a view to reducing processing costs. In particular, the ability to print semiconductor devices using liquid-phase materials could prove essential for some envisaged applications, such as large-area flexible displays. Recent research in this area has largely been focused on organic semiconductors, some of which have mobilities comparable to that of amorphous silicon (a-Si); but issues of reliability remain. Solution processing of metal chalcogenide semiconductors to fabricate stable and high-performance transistors has also been reported. This class of materials is being explored as a possible substitute for silicon, given the complex and expensive manufacturing processes required to fabricate devices from the latter. However, if high-quality silicon films could be prepared by a solution process, this situation might change drastically. Here we demonstrate the solution processing of silicon thin-film transistors (TFTs) using a silane-based liquid precursor. Using this precursor, we have prepared polycrystalline silicon (poly-Si) films by both spin-coating and ink-jet printing, from which we fabricate TFTs with mobilities of 108 cm2 V(-1) s(-1) and 6.5 cm2 V(-1) s(-1), respectively. Although the processing conditions have yet to be optimized, these mobilities are already greater than those that have been achieved in solution-processed organic TFTs, and they exceed those of a-Si TFTs (< or = 1 cm2 V(-1) s(-1)).