Radiation-induced defects in quartz. III. Single-crystal EPR,ENDOR and ESEEM study of a peroxy radical

The X- and W-band single-crystal electron paramagnetic resonance spectra of an electron-irradiated natural quartz permit quantitative analysis of a ²⁹Si hyperfine structure (A ~12.6 MHz) and an ²⁷Al hyperfine structure (A ≤ 0.8 MHz) for a previously reported hole-like center. The ²⁹Si hyperfine structure arises from interaction with two equivalent Si atoms and is characterized by the direction of the unique A axis close to a Si–O bond direction. The ²⁷Al hyperfine structure, confirmed by pulsed electron nuclear double resonance and electron spin echo envelope modulation spectra, is characterized by the unique A axis approximately along a twofold symmetry axis. These ²⁹Si and ²⁷Al hyperfine data, together with published theoretical results on peroxy radicals in SiO₂ as well as our own density functional theory (DFT) calculations on model peroxy centers, suggest this hole-like center to have the unpaired spin on a pair of oxygen atoms linked to two symmetrically equivalent Si atoms and a substitutional Al³⁺ ion across the c-axis channel, a first peroxy radical in quartz. The nuclear quadrupole matrix P also suggests that the Al³⁺ ion corresponds closely to the diamagnetic precursor to the [AlO₄]⁰ center. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Multi-band Solar Full-disk Extreme Ultraviolet Imager

Solar Extreme Ultraviolet (EUV) imaging observation is an important measure for the researches of solar activities and coronal plasma physics. But the traditional EUV imager and spectrograph can hardly achieve simultaneously the high spectral resolution and wide field-of-view of solar imaging. This paper has designed a new type of solar EUV multi-band imager, by adopting a kind of slitless grating and grazing incidence structure, it can realize the solar full-disk imaging of high spectral and spatial resolution. The field-of-view of the imager can be as broad as 47′. The spectral resolution is 2×10^?3nm per pixel, and the spatial resolution is 1.4′ per pixel. The temporal resolution of the solar full-disk is better than 60 s. The analysis of the solar full-disk spectral image and system response shows that the imager can observe the morphological evolutions of various solar activities, and can provide more comprehensive data for the researches of solar physics and space weather forecast.     

Is LkHα 264 like a young, extremely active Sun?

We combine calibrated International Ultraviolet Explorer ( IUE ) archive data and new low-resolution optical data for the T Tauri star LkH α 264 covering the region from 1200 to 7000 Å. The UV continuum is well fitted by the combination of a blackbody at 4300 K plus hydrogenic free–free and free–bound emission from a dense plasma at 3.5×10⁴ K plus the emission by a second blackbody. This last component is at T ≈8700 K and covers about 4 per cent of the stellar surface. We interpret this last component to be the result of emission from one or various hotspots. The interesting result is that this combined emission also fits the observed optical continuum well. We conclude that this star is an analogue of the Sun, however displaying a much higher level of activity.     

Evidence for the stratification of Fe in the photosphere of G191-B2B

The presence of heavy elements in the atmospheres of the hottest H-rich DA white dwarfs has been the subject of considerable interest. While theoretical calculations can demonstrate that radiative forces, counteracting the effects of gravitational settling, can explain the detections of individual species, the predicted abundances do not accord well with observation. However, accurate abundance measurements can only be based on a thorough understanding of the physical structure of the white dwarf photospheres, which has proved elusive. Recently, the availability of new non-local thermodynamic equilibrium model atmospheres with improved atomic data has allowed self-consistent analysis of the extreme ultraviolet (EUV), far UV and optical spectra of the prototypical object G191-B2B. Even so, the predicted and observed stellar fluxes remain in serious disagreement at the shortest wavelengths (below ≈190 Å), while the inferred abundances remain largely unaltered. We show here that the complete spectrum of G191-B2B can be explained by a model atmosphere where Fe is stratified, with increasing abundance at greater depth. This abundance profile may explain the difficulties in matching observed photospheric abundances, usually obtained by analyses using homogeneous model atmospheres, to the detailed radiative levitation predictions, particularly as the latter are only strictly valid for regions deeper than where the EUV/far UV lines and continua are formed. Furthermore, the relative depletion of Fe in the outer layers of the atmosphere may be evidence for radiatively driven mass-loss in G191-B2B.     

广州市紫外线辐射资料分析与预报模型的建立

通过对广州市2004～2006年紫外线辐射资料的统计分析,初步揭示紫外线辐射强度季节性变化的规律,同时结合数值预报产品,用多元回归方法建立预报模型.     

含铁绿柱石的改色机制研究

含铁绿柱石经γ射线辐照或特定温度热处理,可因铁价态的改变引起颜色发生相应变化。处理前后的吸收光谱和顺磁共振谱研究表明,辐作用使隧道位的Ｆｅ＾２＋氧化Ｆｅ％３＋,八一位上的Ｆｅ＾３＋还原为Ｆｅ＾２＋,热处理使隧道位及八面体位Ｆｅ＾３＋均还原为Ｆｅ＾２＋。     

Application of an optical nitrate profiler to high- and low-turbidity coastal shelf waters

Here, we report the results of high-resolution nitrate measurements using an optical nitrate profiler(in situ ultraviolet spectrophotometer, ISUS) along transect across a high-turbidity shelf(East China Sea) and a lowturbidity shelf(Chukchi Sea). The ISUS-measured nitrate concentrations closely reproduced the results measured by conventional bottle methods in low-turbidity waters. However, for high-turbidity waters of the East China Sea(salinity<30), a correction factor of 1.19 was required t...     

紫外线诱导太平洋牡蛎雄核发育的研究

为诱导太平洋牡蛎雄核发育单倍体 ,本文研究利用紫外线诱导太平洋牡蛎雄核发育的条件。结果表明 :在强度为2 .8mW·cm-2 ·s-1的紫外线 (2 5 4nm)下分别照射 0 ,10 ,15 ,2 0 ,2 5 ,3 0 ,3 5 ,40 ,5 0 ,60 ,70和 80s后 ,照射 3 0s的卵子能够保持较高的受精率 (73 .5 % ) ;该处理组的D形幼虫发生率为 0。染色体检查结果显示此时单倍体率最高 (4 7.8% )。证明在强度为2 .8mW·cm-2 ·s-1的紫外线下照射 3 0s是获得雄核发育单倍体的适宜条件。研究还表明受精率和D形幼虫发生率随照射时间的增加而下降 ,遗传失活的卵子与正常精子受精后其胚胎发育至D形幼虫前期停止。实验中各处理组均出现非整倍体。原因可能由于紫外线对卵子染色体遗传失活的作用程度不同以及光线对DNA的修复作用。     

紫外辐射对鱼类及水生无脊椎动物影响的研究进展

全球性的气候变化严重地威胁着自然生态环境间的平衡。在影响生态系统功能的诸多因素中,太阳紫外辐射的增强逐渐成为最受关注的全球性环境问题之一。太阳紫外辐射对地球生物的生命过程有着举足轻重的影响。生物体一旦吸收了高能量的紫外辐射,则可对其各种生理过程产生影响,打破内稳态,尤其是紫外辐射对DNA的损伤作用,是诱导一系列生物效应的主要原因。本文综述了近年来与鱼类及水生无脊椎动物有关的紫外辐射研究。从紫外辐射对生物不同发育时期的影响、生物对紫外线响应方式、紫外辐射与其他因素复合影响三个层面进行总结。通过总结紫外辐射对鱼类及水生无脊椎动物的影响,可为预测紫外辐射在水生生态系统中的作用提供助力,为海洋生物对环境变化的生理响应研究提供参考。