The pre-main-sequence star HD 34282: a very short-period δ Scuti-type pulsator     

P. J. Amado  A. Moya  J. C. Suárez  S. Martín-Ruiz  R. Garrido  E. Rodríguez  C. Catala  M. J. Goupil 《Monthly notices of the Royal Astronomical Society》2004,352(2):L11-L15

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Discovery of unusual pulsations in the cool, evolved Am stars HD 98851 and HD 102480     

Santosh Joshi  V. Girish  Ram Sagar  D. W. Kurtz  P. Martinez  Brijesh Kumar  S. Seetha  B. N. Ashoka  A. Zhou 《Monthly notices of the Royal Astronomical Society》2003,344(2):431-438

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原油中硫代金刚烷的分析鉴定和地球化学应用     

陈中红  张平  柴智  隋明阳 《地球科学与环境学报》2020,(2):143-158

硫代金刚烷在原油中普遍存在,其独特的分子结构和形成过程使其在石油工业中具有广泛应用。对目前在硫代金刚烷分析鉴别、成因机制、热稳定性和在油气领域应用等方面的研究进展及存在问题进行了系统总结。结果表明:目前原油中硫代金刚烷主要包括烃源岩生烃演化和热化学硫酸盐还原(TSR)作用两种成因机制,其中烃源岩生烃演化可形成原油中初始含量的硫代金刚烷,TSR作用可进一步生成大量的硫代金刚烷;硫代金刚烷的笼数越高热稳定性越高,在高成熟时可以发生热裂解作用;硫代金刚烷随TSR作用增强而不断富集,是TSR作用可靠的分子标志物;硫代金刚烷的δ^34S值通过TSR作用来改变,能够反映TSR作用的成因类型;在未遭受TSR作用的前提下,原油中硫代金刚烷的初始含量和δ^34S值代表着原始烃源岩的特征,可以应用于原油族群的划分。从目前的研究现状来看,硫代金刚烷的具体成因机制和详细的热稳定性界限还不甚明确;应用硫代金刚烷的含量来判识TSR作用时,要结合硫同位素和其他指标参数等结果才最为可靠;硫代金刚烷目前主要应用于TSR作用判识研究,在油-油对比和油-源对比方面的研究尚待进一步加强。  相似文献   

Climate shifts vs. edaphic humidity and the difficulty of palaeoreconstructions – a malacological study on stable isotopes in Quaternary dune sequences of Fuerteventura     

Christiane Richter  Christopher-Bastian Roettig  Daniel Wolf  Andreas Gärtner  Thomas Kolb  Dominik Faust 《第四纪科学杂志》2021,36(3):426-440

Dune palaeosurface sequences on the Eastern Canary Islands were investigated for stable isotope records in gastropod shells of the genus Theba. Due to the ecology of the taxon and the special oceanic insularity of the study site, we assume that δ¹⁸O_shell signals in our case mainly reflect shifts in δ¹⁸O signals of sea surface water. We found that a rapid decrease in δ¹⁸O_shell signals is associated with significant changes in gastropod associations. We suggest that these faunal changes were caused by strong (hot) winds at the end of glacial phases, that were described previously by Moreno et al. In addition, we assume that rapid declines in δ¹⁸O_shell signals due to marine transgressions were followed by geomorphologically stable phases, dominated by dust enrichment. Such palaeosurfaces correlate with maxima of gastropod biodiversity and with more negative δ¹³C_shell signals indicating a higher proportion of C3 plants. Based on our results, we also assume that these silty palaeosurfaces were associated with increased soil moisture conditions due to a higher water storage capacity of the finer substrate, independent of climatic moisture conditions.  相似文献   

河套灌区耕地-荒地-海子系统间不同类型水分运移转化          下载免费PDF全文

王国帅  史海滨  李仙岳  闫建文  郭珈玮  李正中 《水科学进展》2021,31(6):832-842

为了探明耕地-荒地-海子系统中不同类型水分的运移转化规律,在2018-2019年典型时期对系统内具有代表性的采样点进行水样采集,分析了不同时期内不同水体的δ¹⁸O变化特征,并利用二端元混合模型和土壤水动力学方法计算了不同类型水分转化贡献率。结果发现：①在灌溉期,82%的灌溉水储存于1 m土体中,18%的灌溉水通过渗漏补给了耕地地下水,渠系灌溉水通过地下侧向径流给耕地地下水贡献了76%。②灌溉水和降雨对耕地地下水平均贡献率为94%和6%;耕地地下水和降雨对荒地地下水的平均贡献率为71%和29%;荒地地下水和降雨对海子的平均贡献率为43%和57%。③渠系灌溉水通过侧向径流贡献给耕地地下水的水量基本全部迁移给了荒地地下水,地下水迁移转化是由渠系水侧向径流触发的。④灌后5 d,耕荒地交界土层0~40 cm存在饱和-非饱和侧向补给;灌后15 d和30 d,耕地和耕荒地交界处的地下水向根区40~60 cm、土层80 cm以及100 cm补给水分;灌后30 d,耕地中的灌溉水水分消失。⑤在非灌溉期,荒地地下水和海子耗水较多,应给海子补给水分。  相似文献   

2005 Photometric observations and multiple frequencies of the <Emphasis Type="Italic">δ</Emphasis> Scuti variable V350 Peg     

F. Ekmekçi  S. Topal 《Astrophysics and Space Science》2009,321(2):101-107

We present the V light curves of δ Scuti type variable V350 Peg, obtained between August and October 2005 at the Ankara University Observatory (AUG) and the TüBíTAK National Observatory (TUG). By application of multiple-frequency analyses using Period04 to 7878 photometric V measurements (which are consist of our 747 V data and 7131 V data obtained at Monegrillo Observatory) of V350 Peg, a five-frequency solution was found to be fitted well to the data. In accordance with the computed Q values for V350 Peg, it was found that this star has probably radial mode with l=0 and g-mode oscillations.  相似文献   

29 frequencies for the δ Scuti variable BI CMi: the 1997–2000 multisite campaigns     

M. Breger  R. Garrido  G. Handler  M.A. Wood  R.R. Shobbrook  K.M. Bischof  F. Rodler  R. O. Gray  A. Stankov  P. Martinez  D. O'Donoghue  R. Szabó  W. Zima  A. B. Kaye  C. Barban  U. Heiter 《Monthly notices of the Royal Astronomical Society》2002,329(3):531-542

A multisite campaign of BI CMi was carried out with excellent frequency resolution and high photometric accuracy from 1997 to 2000, including two long observing seasons. 29 pulsation frequencies could be extracted from the 1024 h (177 nights) of photometry used. The detected frequencies include 20 pulsation modes in the main pulsation frequency range from 4.8 to 13.0 cycle d⁻¹ (55 to 150 μHz), eight linear combinations of these frequencies, and a very low frequency at 1.66 cycle d⁻¹. Since the value of the low frequency at 1.66 cycle d⁻¹ cannot be identified with a linear combination of other frequencies, g-mode pulsation is suspected, but rotational modulation of abundance spots cannot be ruled out. BI CMi, which is situated near the cool edge of the classical instability strip, may be both a δ Scuti and a γ Doradus star. Another outstanding property of BI CMi is the presence of a number of close frequency pairs in the power spectrum with separations as small as 0.01 cycle d⁻¹.
A rotational velocity of     was determined from a high-dispersion spectrum. From phase differences, the dominant modes can be identified with ℓ values from 0 to 2. The spectral type and evolutionary status of BI CMi are examined.  相似文献   

Period analysis of theδ Scuti star HD93044     

Zong-Li Liu 《Astrophysics and Space Science》1993,210(1-2):197-200

HD93044 was observed electrophotometricaly on April 21, May 1, 2 and 4, 1991 at Xinglong Station of Beijing Astronomical Observatory. Combining the data with Li Zhiping's data together and a period analysis was completed using a program which consists of a combination of Fourier transforms of prewhitened data and the multifrequency least squares of brightness residuals (LSR). Three pulsation frequencies (11.90809, 16.79553, 22.44827 cycles per day) with visual amplitudes between 0.0056 and 0.0203 mag were found. The solution fits the observations to +0.0071 mag which is equal to the mean square deviation of observations. The first frequency (11.90809 cycles per day) must be the right value of the fundamental frequency of HD93044.  相似文献   

Late Holocene environmental reconstruction using cave sediments from Belize     

Jason S. Polk  Philip E. van Beynen  Philip P. Reeder 《Quaternary Research》2007,68(1):53-63

Cave sediments collected from Reflection Cave on the Vaca Plateau, Belize show variations in the δ¹³C values of their fulvic acids (FAs), which indicate periods of vegetation change caused by climatic and Maya influences during the late Holocene. The δ¹³C values range from − 27.11‰ to − 21.52‰, a shift of ∼ 5.59‰, which suggests fluctuating contributions of C₃ and C₄ plants throughout the last 2.5 ka, with C₄ plant input reflecting periods of Maya agriculture. Maya activity in the study area occurred at different intensities from ∼ 2600 cal yr BP until ∼ 1500 cal yr BP, after which agricultural practices waned as the Maya depopulated the area. These changes in plant assemblages were in response to changes in available water resources, with increased aridity leading to the eventual abandonment of agricultural areas. The Ix Chel archaeological site, located in the study area, is a highland site that would have been among the first agricultural settlements to be affected during periods of aridity. During these periods, minimal water resources would have been available in this highly karstified, well-drained area, and supplemental groundwater extraction would have been difficult due to the extreme depth of the water table.  相似文献   

The oxygen isotopic composition and temperature of Southern Ocean bottom waters during the last glacial maximum     

Mitchell J Malone  Jonathan B Martin  Ulysses S Ninnemann  Timothy S White 《Earth and Planetary Science Letters》2004,222(1):275-283

We provide two new determinations of the oxygen isotopic composition of seawater during the last glacial maximum (LGM). High-resolution oxygen isotopic measurements were made on interstitial waters from Ocean Drilling Program (ODP) Sites 1168 and 1170 in the southeast Indian Ocean sector of the Southern Ocean. We use a diffusion-advection numerical model to calculate the glacial-interglacial change in bottom-water δ¹⁸O_sw from the pore water δ¹⁸O profiles; the first such determinations from this part of the oceans. Statistical analyses of the model runs indicate that Circumpolar Deep Water (CDW) δ¹⁸O_sw changed by 1.0-1.1±0.15‰ since the last glacial maximum (LGM). Our results are consistent with a previous calculation from a South Atlantic Southern Ocean location (ODP Site 1093) also situated within CDW. The new values determined in this study, together with previous estimates, are converging on a global average Δδ¹⁸O_sw of 1.0-1.1‰.Using the calculated bottom-water δ¹⁸O_sw, we have extracted the temperature component from the benthic foraminiferal δ¹⁸O record at Sites 1168 and 1170. Since the LGM, bottom waters at these two sites warmed by 2.6 and 1.9°C, respectively. The absolute temperature estimates for the LGM (−0.5°C [Θ=−0.6°C] at Site 1168 and −0.2°C [Θ=−0.4°C] at Site 1170) are slightly warmer than those reported from previous studies using the same technique, but are consistent with more homogenous deep-ocean temperatures during the LGM relative to the modern.  相似文献