Cold tolerance of two Antarctic terrestrial arthropods

Summary Two Antarctic arthropods,Alaskozetes antarcticus (Acari) andCryptopygus antarcticus (Collembola) possess the ability to supercool to –30°C, but the realisation of this potential is dependent on starvation. The mite contains glycerol in a concentration of about 1% fresh weight.Acknowledgments. We thank the British Antarctic Survey, Cambridge and the Zoological Institute. University of Oslo for support and reasearch facilities, and the Natural Environment Research Council for a research grant (GR. 3/2797). We are grateful to Ms I. Tambs-Lyche for technical assistance.     

用原噬菌体诱导法检测30种化学物质的潜在遗传毒性

应用原噬菌体诱导法检测了包括农药、食品添加剂和化妆品等30种不同化学物质的遗传毒性,并用S9和S14模拟代谢系统.在S9存在时,有17种化学物质能诱导原噬菌体的释放;在S14存在时,只有10种化学物质能诱导原噬菌体的释放;如果不加S9和S14,有15种化学物质有这种作用.测得结果为阳性的化学物质中有些是已知的潜在诱变剂和致癌剂(NTG、黄曲霉毒素B_1)或抗癌药(丝裂霉素C、阿糖胞苷和消瘤芥).     

Forecasting with an econometric model: The issue of judgemental adjustment

The paper outlines the current state of forecasting with an econometric model. After briefly distinguishing econometric techniques from other statistical approaches and arguing the advantages of this approach the paper concentrates on the issue of judgemental adjustments to models for forecasting purposes. Two types of adjustment are distinguished and the conditions under which each is justified are stated. Guidance in the use of adjustment is offered through a review of considerations in an actual forecasting situation.     

The effect of ligand on the kinetics of the sulfhydryl groups of human hemoglobin with p-mercuribenzoate

The rate of reaction of PMB with the masked sulfhydryls of human hemoglobin derivatives correlates well with the extent of dissociation for various ligands. It is suggested that the alpha1beta2 dimer of hemoglobin participates in the slow step of the reaction with PMB.     

Three-dimensional atomic-scale structure of size-selected gold nanoclusters

An unambiguous determination of the three-dimensional structure of nanoparticles is challenging. Electron tomography requires a series of images taken for many different specimen orientations. This approach is ideal for stable and stationary structures. But ultrasmall nanoparticles are intrinsically structurally unstable and may interact with the incident electron beam, constraining the electron beam density that can be used and the duration of the observation. Here we use aberration-corrected scanning transmission electron microscopy, coupled with simple imaging simulation, to determine with atomic resolution the size, three-dimensional shape, orientation and atomic arrangement of size-selected gold nanoclusters that are preformed in the gas phase and soft-landed on an amorphous carbon substrate. The structures of gold nanoclusters containing 3096 atoms can be identified with either Ino-decahedral, cuboctahedral or icosahedral geometries. Comparison with theoretical modelling of the system suggests that the structures are consistent with energetic considerations. The discovery that nanoscale gold particles function as active and selective catalysts for a variety of important chemical reactions has provoked much research interest in recent years. We believe that the detailed structure information we provide will help to unravel the role of these nanoclusters in size- and structure-specific catalytic reactions. We note that the technique will be of use in investigations of other supported ultrasmall metal cluster systems.     

个体与整体、主体与客体的互涉——论李金发诗中的多维象征

受象征主义的影响,李金发走上了象征主义的道路,他的诗歌中有着多维意象:象征主体(诗人和诗中的抒情主人公)和象征客体(被表现和被用来表现、象征的对象)之间的意合神涉,象征的个体与整体之间的契合互涉。     

CO self-shielding as the origin of oxygen isotope anomalies in the early solar nebula

The abundances of oxygen isotopes in the most refractory mineral phases (calcium-aluminium-rich inclusions, CAIs) in meteorites have hitherto defied explanation. Most processes fractionate isotopes by nuclear mass; that is, 18O is twice as fractionated as 17O, relative to 16O. In CAIs 17O and 18O are nearly equally fractionated, implying a fundamentally different mechanism. The CAI data were originally interpreted as evidence for supernova input of pure 16O into the solar nebula, but the lack of a similar isotope trend in other elements argues against this explanation. A symmetry-dependent fractionation mechanism may have occurred in the inner solar nebula, but experimental evidence is lacking. Isotope-selective photodissociation of CO in the innermost solar nebula might explain the CAI data, but the high temperatures in this region would have rapidly erased the signature. Here we report time-dependent calculations of CO photodissociation in the cooler surface region of a turbulent nebula. If the surface were irradiated by a far-ultraviolet flux approximately 10(3) times that of the local interstellar medium (for example, owing to an O or B star within approximately 1 pc of the protosun), then substantial fractionation of the oxygen isotopes was possible on a timescale of approximately 10(5) years. We predict that similarly irradiated protoplanetary disks will have H2O enriched in 17O and 18O by several tens of per cent relative to CO.     

Differentiation of the asteroid Ceres as revealed by its shape

The accretion of bodies in the asteroid belt was halted nearly 4.6 billion years ago by the gravitational influence of the newly formed giant planet Jupiter. The asteroid belt therefore preserves a record of both this earliest epoch of Solar System formation and variation of conditions within the solar nebula. Spectral features in reflected sunlight indicate that some asteroids have experienced sufficient thermal evolution to differentiate into layered structures. The second most massive asteroid--4 Vesta--has differentiated to a crust, mantle and core. 1 Ceres, the largest and most massive asteroid, has in contrast been presumed to be homogeneous, in part because of its low density, low albedo and relatively featureless visible reflectance spectrum, similar to carbonaceous meteorites that have suffered minimal thermal processing. Here we show that Ceres has a shape and smoothness indicative of a gravitationally relaxed object. Its shape is significantly less flattened than that expected for a homogeneous object, but is consistent with a central mass concentration indicative of differentiation. Possible interior configurations include water-ice-rich mantles over a rocky core.