On the parallax of WD 0346++246: a halo white dwarf candidate     

N. C. Hambly  S. J. Smartt  S. T. Hodgkin  R. F. Jameson  S. N. Kemp  W. R. J. Rolleston  I. A. Steele 《Monthly notices of the Royal Astronomical Society》1999,309(4):L33-L36

We present a parallax measurement for the very cool degenerate WD 0346+246, the serendipitous discovery of which was reported by Hambly et al. We find an absolute parallax of 36±5 mas, yielding a distance estimate of 28±4 pc. The resulting absolute visual magnitude of the object is M _V =16.8±0.3, making it the second-lowest luminosity white dwarf currently known. We use the distance estimate and measured proper motion to show that the object has kinematics consistent with membership of the Galactic halo. WD 0346+246 is therefore by far the coolest and least luminous of only a handful of plausible halo white dwarf candidates. As such, the object has relevance to the ongoing debate concerning the results of microlensing experiments and the nature of any baryonic dark matter component to the Galactic halo residing in stellar remnants.  相似文献   

A spatially resolved 'inside-out' outburst of IP Pegasi     

N. A. Webb  T. Naylor  Z. Ioannou  W. J. Worraker  J. Stull  A. Allan  R. Fried  N. D. James  D. Strange 《Monthly notices of the Royal Astronomical Society》1999,310(2):407-413

We present a comprehensive photometric data set taken over the entire outburst of the eclipsing dwarf nova IP Peg in 1997 September/October. Analysis of the light curves taken over the long rise to the peak-of-outburst shows conclusively that the outburst started near the centre of the disc and moved outwards. This is the first data set that spatially resolves such an outburst. The data set is consistent with the idea that long rise times are indicative of such 'inside-out' outbursts. We show how the thickness and the radius of the disc, along with the mass transfer rate, change over the whole outburst. In addition, we show evidence of the secondary and the irradiation thereof. We discuss the possibility of spiral shocks in the disc; however, we find no conclusive evidence of their existence in this data set.  相似文献   

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

M. A. Barstow  I. Hubeny  J. B. Holberg 《Monthly notices of the Royal Astronomical Society》1999,307(4):884-894

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.  相似文献   

Commuting activity spaces of married women in a suburb of the Tokyo metropolitan area     

Masaki Kawase 《GeoJournal》1999,48(3):217-222

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中国对虾淋巴器官中球形病毒的电镜观察     

汝少国  姜明  李永祺  贾翠红  丛日山  王悦 《海洋科学》1999,23(5):44-48

应用光镜和电镜对中国对虾淋巴器官的显微结构和超微结构进行观察,结果表明,淋巴器官的盲管主要由内皮细胞和基质细胞构成,细胞间隙内充满着大量的以颗粒细胞为主的血细胞,  相似文献   

芒果苷对高脂肪/高果糖饮食诱导大鼠代谢综合征的影响          下载免费PDF全文

史小四  梁兴  骞秀芳 《应用海洋学学报》2023,39(10):183

目的：探讨芒果苷对高脂肪/高果糖饮食诱导大鼠代谢综合征（MS）的影响。方法：将60只大鼠随机分为正常组,模型组,阳性对照组,芒果苷高、中、低剂量组,每组各10只。每天饲喂17%脂肪/17%果糖饲料+20%果糖水,构建MS模型,造模8周。造模成功后阳性对照组灌胃二甲双胍50mg/kg,芒果苷高、中、低剂量组分别灌胃40、20、10mg/kg,正常组和模型组灌胃等体积0.5%羧甲基纤维素钠,连续给药8周。观察各组的体质量、内脏脂肪质量、脂体比及血清总胆固醇、三酰甘油、空腹血糖、胰岛素水平、胰岛素抵抗指数（IRI）、脂肪细胞因子（脂联素、抵抗素）水平。结果：与模型组比较,芒果苷高、中、低剂量组的体质量、内脏脂肪质量、脂体比、血清总胆固醇、三酰甘油、空腹血糖、胰岛素及抵抗素水平下降（P<0.01）,芒果苷高、中剂量组IRI降低（P<0.05）。结论：芒果苷通过调控糖脂代谢、脂肪细胞因子、脂肪堆积、胰岛素抵抗等途径干预大鼠MS的病理进程。  相似文献   

二温式RT-PCR检测对虾Taura综合征病毒的研究   总被引：16，自引：1，他引：15  

庞耀珊  谢芝勋  何竞铭  邓显文  莫友群 《海洋科学》2004,28(2):54-57

设计了一对能扩增大小为231bp对虾Taura综合征病毒(TSV)某段基因的特异性引物,优化建立了能快速检测TSV的二温式RT-PCR。特异性和敏感性试验结果表明。二温式RT-PCR能对3个试验用TSV毒株的RNA进行扩增,并得到与预期大小一致的231bp的扩增产物,而其它3种对虾病原则无相同大小的特异性扩增产物出现;RT-PCR最低能检测到1pg的TSV RNA。应用RT-PCR对320份分别来自广西沿海不同对虾养殖场的对虾样品进行检测,结果共有85份检出TSV。说明TSV在广西沿海地区养殖对虾中已呈现出区域性流行趋势。同时也显示了RT-PCR在TSV临床检测中具有较高的实用性。  相似文献   

长白山火山活动发展阶段及火山灾害评价     

于宏斌  吕忠良  常永祥  姚廷才 《吉林地质》2004,23(4):34-37,73

长白山地区火山活动划分二个发展阶段：以点一线形式喷发形成的广阔玄武岩台地阶段一焊缝构造发展阶段;中心式大规模喷发形成的锥状火山机构一焊点构造发展阶段,长白山地区乃至吉林东部地区中一新生代以来抬升平均速率81m／Ma及白头山一泉阳一露水河一带中生代以来存在一个火山坳陷盆地。  相似文献   

Heterosis and heritability estimates for the survival of the Pacific white shrimp (Litopenaeus vannamei) under the commercial scale ponds     

LU Xi  LUAN Sheng  CAO Baoxiang  SUI Juan  DAI Ping  MENG Xianhong  LUO Kun  KONG Jie 《海洋学报(英文版)》2017,36(2):62-68

The aim of the present study is to detect the potential of the base population from diallel crosses of eight introduced strains of the Pacific white shrimp(Litopenaeus vannamei) for improving the yield. Heterosis and heritability were estimated for pond survival at commercial farm conditions for the base population that included 207 full-sib families from a nested mating design by artificial insemination. Among all the hybrids,the heterosis ranged from –11.37%(UA1×UA2) to 20.53%(UA3×SIN) with an average of 0.953%. The results showed that more than half of the hybrids(51.85%) have negative heterosis for survival rate, but most of the hybrids with positive heterosis have high estimates. The high proportion of negative heterosis for survival rate reminders us that the survival trait also should be considered in the crossbreeding program to avoid yield decrease. However, high positive heterosis manifested in most of the hybrids for survival indicates the usefulness of these hybrids for improving the survival to obtain higher yield by crossbreeding in this breeding program. The heritability estimate for pond survival was 0.092±0.043 when genetic groups were included in the pedigree, and it was significantly different from zero(P0.05). The results from this study also indicated that significant improvement for survival is possible through selection in L. vannamei.  相似文献   

Movement patterns of an endangered fishery species,Lithognathus lithognathus (Sparidae), and the role of no-take marine protected areas as a management tool     

RH Bennett  PD Cowley  A-R Childs  CG Attwood  L Swart  TF Næsje 《African Journal of Marine Science》2017,39(4):475-489

Understanding movement behaviour is essential for effective management of fishery species. Dart tags were used to study coastal movement patterns of white steenbras Lithognathus lithognathus, an overexploited seabream (Sparidae) in South Africa. In total, 6 962 fish (190–1 080 mm fork length) were tagged throughout the species’ distributional range, in four long-term fish-tagging programmes. The predominant behaviour recorded was residency, with relatively short-ranging movements. More than 60% of the 351 recaptured fish were recaptured within 1 km of their tagging site, some of which were at liberty in excess of three years. Most of the juveniles (93.9%), subadults (71.7%) and adults (64.0%) were recaptured within 10 km. Occasional long-distance movements of up to 800 km were recorded. Recapture distances were positively, but weakly, correlated with fish fork length (n = 257 fish measured at recapture; r² = 0.166, p < 0.001). Low levels of connectivity among coastal areas suggest that large-scale annual spawning migrations, as previously hypothesised for this species, are unlikely, which raises the possibility of multiple spawning sites. Seventy-seven percent of L. lithognathus tagged within three marine protected areas (MPAs) were recaptured within the same MPA, suggesting that area closures provide protection for L. lithognathus through the post-estuarine juvenile, subadult and adult life stages. We confirm that the country’s current network of coastal MPAs plays a vital role in sustaining this species, and suggest that additional closures, or otherwise substantial reductions in catch rates, are necessary for the species’ recovery.  相似文献