Metallicity estimates for A-, F-, and G-type stars from the Edinburgh–Cape Blue Object Survey     

T. C. Beers  S. Rossi  D. O'Donoghue  D. Kilkenny  R. S. Stobie  C. Koen  R. Wilhelm 《Monthly notices of the Royal Astronomical Society》2001,320(4):451-464

The Edinburgh–Cape Blue Object Survey is an ongoing project to identify and analyse a large sample of hot stars selected initially on the basis of photographic colours (down to a magnitude limit     over the entire high-Galactic-latitude southern sky, and then studied with broad-band UBV photometry and medium-resolution spectroscopy. Due to unavoidable errors in the initial candidate selection, stars that are likely metal-deficient dwarfs and giants of the halo and thick-disc populations are inadvertently included, yet are of interest in their own right. In this paper we discuss a total of 206 candidate metal-deficient dwarfs, subgiants, giants, and horizontal-branch stars with photoelectric colours redder than     and with available spectroscopy. Radial velocities, accurate to ∼10–15 km s⁻¹, are presented for all of these stars. Spectroscopic metallicity estimates for these stars are obtained using a recently recalibrated relation between Ca  ii K-line strength and     colour. The identification of metal-poor stars from this colour-selection technique is remarkably efficient, and competitive with previous survey methods. An additional sample of 186 EC stars with photoelectric colours in the range     composed primarily of field horizontal-branch stars and other, higher gravity, A- and B-type stars, is also analysed. Estimates of the physical parameters T _eff, log  g , and [Fe/H] are obtained for cooler members of this subsample, and a number of candidate RR Lyrae variables are identified.  相似文献   

Oscillatory propagation of an ionization-shock front     

K. V. Krasnobaev 《Astronomy Letters》2001,27(2):91-94

Based on numerical simulations, we show that the oscillatory propagation of a plane-parallel ionization-shock front is possible for a typical dependence of the interstellar-medium cooling function on density and temperature. In this case, the oscillation amplitude of the shock position in the presence of an ionization front can be several times larger than its value for a single shock wave. The variations in neutral and ionized gas velocities attributable to oscillations are comparable in order of magnitude and agree with the random velocities observed in H II regions.  相似文献   

Taxonomic reexamination of the genus Chirolophis in China waters     

刘静  田明诚尤锋 《中国海洋湖沼学报》2005,23(2):199-203

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新显色剂1-(2-咪唑偶氮)-2-萘酚-4-磺酸分光光度法测定铜     

潘富友  张孙玮 《岩矿测试》1992,(4)

新显色剂1-(2-咪唑偶氮)-2-萘酚-4-磺酸在pH 3的介质中光度法测定Cu的摩尔吸光系数为1.94×10~4 L.mol~(-1).cm~(-1),络合物的组成为1:1,最大吸收在530nm,对比度△λ为120nm,表观稳定常数为6.96×10~6,Cu~(2+)在0～0.8μg/ml范围内遵守比尔定律,方法已用于镁介金及铁矿石中Cu的测定。  相似文献   

Secular trends in mean tidal range around the British Isles and along the adjacent European coastline   总被引：2，自引：0，他引：2  

P. L. Woodworth  S. M. Shaw  D. L. Blackman 《Geophysical Journal International》1991,104(3):593-609

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Use of Pitzer Equations to Examine the Formation of Mercury(II) Hydroxide and Chloride Complexes in NaClO<Subscript>4</Subscript> Media     

Melchor González-Dávila  J. Magdalena Santana-Casiano  Frank J. Millero 《Aquatic Geochemistry》2007,13(4):339-355

The thermodynamic stability constants for the hydrolysis and formation of mercury (Hg²⁺) chloride complexes have been used to calculate the activity coefficients for Hg(OH) _n ^(2–n)+ and HgCl _n ^(2–n)+ complexes using the Pitzer specific interaction model. These values have been used to determine the Pitzer parameters for the hydroxide and chloro complexes and C _ML). The values of and have been determined for the neutral complexes (Hg(OH)₂ and HgCl₂). The resultant parameters yield calculated values for the measured values of log to  ±0.01 from I  =  0.1 to 3 m at 25°C. Since the activity coefficients of and are in reasonable agreement with the values for Pb(II), we have estimated the effect of temperature on the chloride constants for Hg(II) from 0 to 300°C and I = 0–6 m using the Pitzer parameters for complexes. The resulting parameters can be used to examine the speciation of Hg(II) with Cl⁻ in natural waters over a wide range of conditions.  相似文献   

Hydrogen peroxide production in marine bathing waters: Implications for fecal indicator bacteria mortality     

Clark CD  De Bruyn WJ  Jakubowski SD  Grant SB 《Marine pollution bulletin》2008,56(3):397-401

Hydrogen peroxide concentrations [H(2)O(2)] have been measured over the last two decades in multiple studies in surface waters in coastal, estuarine and oceanic systems. Diurnal cycles consistent with a photochemical production process have frequently being observed, with [H(2)O(2)] increasing by two orders of magnitude over the course of the day, from low nM levels in the early morning to 10(2)nM in late afternoon. Production rates range from <10 for off-shore ocean waters to 20-60nMh(-1) for near-shore coastal and estuarine environments. Slow night-time loss rates (<10nMh(-1)) have been attributed to biological and particle mediated processes. Diurnal cycles have also frequently been observed in fecal indicator bacteria (FIB) levels in surf zone waters monitored for microbial water quality. Measured peak peroxide concentrations in surface coastal seawaters are too low to directly cause FIB mortality based on laboratory studies, but likely contribute to oxidative stress and diurnal cycling. Peroxide levels in the surf zone may be increased by additional peroxide production mechanisms such as deposition, sediments and stressed marine biota, further enhancing impacts on FIB in marine bathing waters.  相似文献   

Isotopically anomalous neon in meteoritic nanodiamonds: Formation during type II supernova explosions     

A. V. Fisenko  L. F. Semenova 《Astronomy Letters》2008,34(9):598-607

We hypothesize the formation of neon associated with isotopically anomalous xenon (Xe-HL) in meteoritic nanodiamonds and designated as Ne-X through the mixing of the Ne-HL and Ne-S subcomponents. The Ne-HL subcomponent is neon from the helium (He/C) zone of a type II supernova or a mixture of neon from this zone and its hydrogen zone, while the Ne-S subcomponent is spallation neon formed during a supernova explosion in nuclear spallation reactions induced by high-energy protons. Based on this hypothesis and the presumed abundances of neon isotopes in the zones of a high-mass (25M _⊙) supernova after its explosion, we have calculated the abundances of neon components in nanodiamond separates and its grain-size fractions. Our calculations have shown the following. (1) The main source of Ne-HL is neon from the helium zone of the supernova; as a result, the ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios for Ne-X are 0.26 ± 0.03 and 0.19 ± 0.04, respectively. The isotopic composition of Ne-X is identical to that for Ne-A2 if Ne-HL is produced by the mixing of neon from the helium and hydrogen zones in proportion 1: 1.06. (2) In meteoritic nanodiamonds, the main neon abundance is determined by neon of the P3 component (Ne-P3). Ne-P3 is retained during thermal metamorphism, because it is sited in traps of the crystal lattice of diamond with a high energy of its activation. (3) The Ne-X/Ne-P3 ratio increases with nanodiamond grain size; as a result, there is no need to invoke an additional neon component (Ne-P6) to interpret the data on neon in meteoritic nanodiamonds.  相似文献   

一次早春多单体冰雹分析   总被引：2，自引：1，他引：1  

金飞胜  黄飞羽  方素青  查光英 《气象科技》2010,38(5):577-580

利用常规气象资料、NCEP再分析资料,结合黄山多普勒雷达观测资料,对2009年2月发生在黄山地区一次冰雹天气个例发生发展过程进行分析。结果显示:①此次降雹是由于高空急流引发的,有一次积云合并过程,具有多雷暴单体的基本特征。②冰雹发生在早春2月,具有明显的季节特征,组合反射率也很高,但由于空气柱气温较低,垂直液态水含量相比初夏的冰雹要小,-20℃高度相比初夏低1～2km。  相似文献   

Application of oxidative stress indices in natural populations of Perna viridis as biomarker of environmental pollution   总被引：2，自引：0，他引：2  

Jena KB  Verlecar XN  Chainy GB 《Marine pollution bulletin》2009,58(1):107-113

Oxidative stress indices were measured in gills and digestive glands of Perna viridis collected from three coastal locations in Goa i.e., Bambolim, Marmugao Harbour and Malim. In addition to lipid peroxidation, the activities of antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione S-transferase and two non-enzymatic antioxidants (ascorbic acid and reduced glutathione) were investigated in order to understand their variation with respect to pollution status of the sampling locations. We observed a significant increase in lipid peroxidation and antioxidant enzymes of both the tissues at Mormugao Harbour and Malim, suggesting that the animals at these two locations are at higher level of oxidative stress as compared to those at Bambolim. Conversely, low levels of non-enzymatic antioxidants such as ascorbic acid and reduced glutathione, observed at Mormugao Harbour and Malim indicate that the animals may use these compounds to counteract stress in the tissues. This study shows that changes in lipid peroxidation, superoxide dismutase, catalase, glutathione reductase, glutathione S-transferase and reduced glutathione in tissues of P. viridis can be used as molecular biomarkers in environmental monitoring programs.  相似文献