Measuring intense rotation and dissipation in turbulent flows

Turbulent flows are highly intermittent--for example, they exhibit intense bursts of vorticity and strain. Kolmogorov theory describes such behaviour in the form of energy cascades from large to small spatial and temporal scales, where energy is dissipated as heat. But the causes of high intermittency in turbulence, which show non-gaussian statistics, are not well understood. Such intermittency can be important, for example, for enhancing the mixing of chemicals, by producing sharp drops in local pressure that can induce cavitation (damaging mechanical components and biological organisms), and by causing intense vortices in atmospheric flows. Here we present observations of the three components of velocity and all nine velocity gradients within a small volume, which allow us to determine simultaneously the dissipation (a measure of strain) and enstrophy (a measure of rotational energy) of a turbulent flow. Combining the statistics of all measurements and the evolution of individual bursts, we find that a typical sequence for intense events begins with rapid strain growth, followed by rising vorticity and a final sudden decline in stretching. We suggest two mechanisms which can produce these characteristics, depending whether they are due to the advection of coherent structures through our observed volume or caused locally.     

Plants lacking the main light-harvesting complex retain photosystem II macro-organization

Photosystem II (PSII) is a key component of photosynthesis, the process of converting sunlight into the chemical energy of life. In plant cells, it forms a unique oligomeric macrostructure in membranes of the chloroplasts. Several light-harvesting antenna complexes are organized precisely in the PSII macrostructure-the major trimeric complexes (LHCII) that bind 70% of PSII chlorophyll and three minor monomeric complexes-which together form PSII supercomplexes. The antenna complexes are essential for collecting sunlight and regulating photosynthesis, but the relationship between these functions and their molecular architecture is unresolved. Here we report that antisense Arabidopsis plants lacking the proteins that form LHCII trimers have PSII supercomplexes with almost identical abundance and structure to those found in wild-type plants. The place of LHCII is taken by a normally minor and monomeric complex, CP26, which is synthesized in large amounts and organized into trimers. Trimerization is clearly not a specific attribute of LHCII. Our results highlight the importance of the PSII macrostructure: in the absence of one of its main components, another protein is recruited to allow it to assemble and function.     

Millennial-scale storminess variability in the northeastern United States during the Holocene epoch

For the purpose of detecting the effects of human activities on climate change, it is important to document natural change in past climate. In this context, it has proved particularly difficult to study the variability in the occurrence of extreme climate events, such as storms with exceptional rainfall. Previous investigations have established storm chronologies using sediment cores from single lakes, but such studies can be susceptible to local environmental bias. Here we date terrigenous inwash layers in cores from 13 lakes, which show that the frequency of storm-related floods in the northeastern United States has varied in regular cycles during the past 13,000 years (13 kyr), with a characteristic period of about 3 kyr. Our data show four peaks in storminess during the past 14 kyr, approximately 2.6, 5.8, 9.1 and 11.9 kyr ago. This pattern is consistent with long-term changes in the average sign of the Arctic Oscillation, suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of Holocene climate variability in North America and Europe.     

Scotopic colour vision in nocturnal hawkmoths

Humans are colour-blind at night, and it has been assumed that this is true of all animals. But colour vision is as useful for discriminating objects at night as it is during the day. Here we show, through behavioural experiments, that the nocturnal hawkmoth Deilephila elpenor uses colour vision to discriminate coloured stimuli at intensities corresponding to dim starlight (0.0001 cd x m(-2)). It can do this even if the illumination colour changes, thereby showing colour constancy-a property of true colour vision systems. In identical conditions humans are completely colour-blind. Our calculations show that the possession of three photoreceptor classes reduces the absolute sensitivity of the eye, which indicates that colour vision has a high ecological relevance in nocturnal moths. In addition, the photoreceptors of a single ommatidium absorb too few photons for reliable discrimination, indicating that spatial and/or temporal summation must occur for colour vision to be possible. Taken together, our results show that colour vision occurs at nocturnal intensities in a biologically relevant context.     

潜器应急上浮系统方案样机海试成功

“潜器应急上浮系统方案样机”是中船总军工部下达的“七五”预研课题,由我院管理工程系系统工程研究室承担研制。本装置主要在潜器失事或超过工作深度而又无法上浮时使用,启动本装置后能在5—8秒钟内提供额外浮力,使潜器上浮而达到自救。整个方案样机—潜器应急上浮系统共分燃气发生器及其附件;快速冷却装置;可折叠气袋;控制点火系统四个部分。该样机的研制工作主要分三个阶段进行。第一阶段是方案原理设计与试验阶段;第二阶段是方案样机设计、加工、试验阶段;第三阶段是海试阶段。     

Mutations in ABCC6 cause pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a heritable disorder of the connective tissue. PXE patients frequently experience visual field loss and skin lesions, and occasionally cardiovascular complications. Histopathological findings reveal calcification of the elastic fibres and abnormalities of the collagen fibrils. Most PXE patients are sporadic, but autosomal recessive and dominant inheritance are also observed. We previously localized the PXE gene to chromosome 16p13.1 (refs 8,9) and constructed a physical map. Here we describe homozygosity mapping in five PXE families and the detection of deletions or mutations in ABCC6 (formerly MRP6) associated with all genetic forms of PXE in seven patients or families.