The lepton asymmetry: the last chance for a critical-density cosmology?     

Julien Lesgourgues  rew R. Liddle 《Monthly notices of the Royal Astronomical Society》2001,327(4):1307-1312

We use a wide range of observations to constrain cosmological models possessing a significant asymmetry in the lepton sector, which offer perhaps the best chance of reconciling a critical-density Universe with current observations. The simplest case, with massless neutrinos, fails to fit many experimental data and does not lead to an acceptable model. If the neutrinos have mass of order 1 eV (which is favoured by some neutrino observations), then models can be implemented which prove a good fit to the microwave anisotropies and large-scale structure data. However, taking into account the latest microwave anisotropy results, especially those from BOOMERANG, we show that the model can no longer accommodate the observed baryon fraction in clusters. Together with the observed acceleration of the present Universe, this puts considerable pressure on such critical-density models.  相似文献   

Star formation in a multi-phase interstellar medium     

Adrianne Slyz  Julien Devriendt  Greg Bryan  Joseph Silk 《Astrophysics and Space Science》2003,284(2):833-836

This contribution reports on our first efforts to simulate a multiphase interstellar medium on a kiloparsec scale in three dimensions with the stars and gas modeled self-consistently. Starting from inhomogenous initial conditions, our closed box simulations follow the gas as it cools and collapses under its own self-gravity to form stars which eventually return material and energy back through supernovae explosions and winds. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

系统聚类方法在房地产周期分析中的应用   总被引：1，自引：0，他引：1  

罗乐  张欣莉 《成都信息工程学院学报》2006,21(4):598-601

选取了9项房地产经济波动指标，经过相关性分析，确定房地产经济综合指标体系，并运用聚类分析方法对我国房地产经济波动进行了分析，为进一步分析研究我国房地产周期提供了方法和手段。  相似文献   

Preliminary results on VLT K-band imaging observations of GRB host galaxies     

E. Le Floc’h  I. F. Mirabel  P. -A. Duc 《Journal of Astrophysics and Astronomy》2002,23(1-2):119-122

We have obtainedK-band imaging observations of Gamma-Ray Burst (GRB) host galaxies with the near-infrared spectro-imager ISAAC installed on the Very Large Telescope at Paranal (Chile). The derivedK magnitudes, combined with other photometric data taken from the literature, are used to investigate theR-K colors of GRB hosts. We do not find any extremely reddened starbursts in our sample, despite the capability of GRBs to trace star formation even in dusty regions. The observedR-K colors are on the contrary typical of irregular and spiral blue galaxies at high redshift.  相似文献   

改进Canny算法的图像边缘增强方法     

李靖  王慧  闫科  阎晓东  杨乐 《测绘科学技术学报》2021,38(4):398-403

边缘检测是图像特征提取的关键技术之一.为强化所提取的边缘特征,设计一种联合Otsu算法和多尺度细节增强的策略对传统Canny算法进行改进.首先针对高斯滤波模糊图像细节的不足,利用多尺度细节增强算法对遥感图像进行处理,增强图像的细节信息,降低高斯算法的影响;然后针对传统Canny算法的人为选择阈值带来的不足,利用Otsu算法进行自适应阈值选择,以提高算法的适应性.实验证明,在主观视觉效果以及客观评价指标下,所设计的改进方法对于不同场景的图像边缘特征增强都具备良好的效果.  相似文献   

When Daily Sunspot Births Become Positively Correlated     

Alexander Shapoval  Jean-Louis Le Mouël  Mikhail Shnirman  Vincent Courtillot 《Solar physics》2015,290(10):2709-2717

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The amino acid and hydrocarbon contents of the Paris meteorite: Insights into the most primitive CM chondrite          下载免费PDF全文

Zita Martins  Paola Modica  Brigitte Zanda  Louis Le Sergeant d'Hendecourt 《Meteoritics & planetary science》2015,50(5):926-943

The Paris meteorite is one of the most primitive carbonaceous chondrites. It is reported to be the least aqueously altered CM chondrite, and to have experienced only weak thermal metamorphism. We have analyzed for the first time the amino acid and hydrocarbon contents of this pristine meteorite by gas chromatography–mass spectrometry (GC–MS). When plotting the relative amino acids abundances of several CM chondrites according to the increasing hydrothermal scale (petrologic subtypes), from the CM2.7/2.8 Paris to the CM2.0 MET 01070, Paris has the lowest relative abundance of β‐alanine/glycine (0.15), which fits with the relative abundances of β‐alanine/glycine increasing with increasing aqueous alteration for CM chondrites. These results confirm the influence of aqueous alteration on the amino acid abundances and distribution. The amino acid analysis shows that the isovaline detected in this meteorite is racemic (d /l  = 0.99 ± 0.08; l ‐enantiomer excess = 0.35 ± 0.5%; corrected d /l  = 1.03; corrected l ‐enantiomer excess = ?1.4 ± 2.6%). The identified hydrocarbons show that Paris has n‐alkanes ranging from C₁₆ to C₂₅ and 3‐ to 5‐ring nonalkylated polycyclic aromatic hydrocarbons (PAHs). The lack of alkylated PAHs in Paris seems to be also related to this low degree of aqueous alteration on its parent body. The extraterrestrial hydrocarbon content, suggested by the absence of any biomarker, may well have a presolar origin. The chemistry of the Paris meteorite may thus be closely related to the early stages of the solar nebula with a contribution from interstellar (molecular cloud) precursors.  相似文献   

Distribution of Olivine and Pyroxene Derived from Clementine Data in Crater Copernicus     

刘福江  杨荣  章颖  乔乐  王顺  杨阳  王小攀 《中国地质大学学报(英文版)》2011,(5)

In order to derive the distribution of olivine and pyroxene in Crater Copernicus,we compute two band ratios(950/750 and 2 000/1 500 nm) ,percent content of elements(Al%,Ca%,Mg%,FeO%) and maturity(Is/FeO) based on Clementine UVVIS and NIR image data.The central peaks of Copernicus,which are known to be olivine-rich or pyroxene-rich,are chosen as ground truth and ROIs used to derive the distribution of olivine and pyroxene with a decision tree and spectral angle mapper(SAM) .Additionally,we compared previous ...  相似文献   

Seasonality of European warming: Influence of the tropics     

E. M. Blanter  J.-L. Le Mouél  M. G. Shnirman  V. Courtillot 《Doklady Earth Sciences》2011,440(1):1316-1319

This paper describes seasonal peculiarities of modern climate warming in the European region. It is shown that warming scenarios considerably differ in cold and warm periods of the year. The warming is accompanied with growth and considerable change in the phase of the yearly cycle in solarity data. A strong half-year cycle is recognized in seasonal variation of long-term trends over the last few years. Peculiarities of climate change in Europe and the increased influence of the tropics are discussed in view of the results obtained.  相似文献   

The first ML scale for North of Vietnam     

Le Minh Nguyen  Ting-Li Lin  Yih-Min Wu  Bor-Shouh Huang  Chien-Hsin Chang  Win-Gee Huang  Tu Son Le  Van Toan Dinh 《Journal of Asian Earth Sciences》2011,40(1):279-286

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