Threshold for initiation of motion of unimodal and bimodal sediments     

Shaileshkumar B.PATEL  Prem Lal PATEL  Prakash Devidas POREY 《国际泥沙研究》2013,28(1):24-33

Experimental data,obtained from previous studies,on Critical Tractive Stress(CTS) of non-uniform sediments, have been used to verify the adequacy of existing relationships for CTS of non-uniform bimodal sediments.Keeping in view the performance of such relationships,a new relationship for computation of dimensionless CTS of individual size fraction of non-uniform unimodal and bimodal sediments has been proposed in the form of power law.The coefficient and exponent of the proposed power law have been empirically correlated with sediment characteristics for available sediment data.The proposed relationship has been validated with independent flume and field data to assess their applicability for unimodal and bimodal sediments.  相似文献   

工程水准复测垂直形变分析     

韩勇  塔拉 《华北地震科学》2013,(3):23-28

利用京沪高铁京津段的八期工程水准复测资料,绘制了2007年3月-2011年3月间的京津地区垂直形变图,并对京津沿线地区近期垂直形变趋势进行了分析研究.研究结果表明,2009年3月至2011年3月期间,不同地点出现了正速率变化,与以往对于这一区域负速率变化的地面沉降规律形成了一个“反向”变化,显示出区域应力场受外部干扰和影响后的变化特征.为分析研究首都圈地区今后一段时间的地壳垂直形变趋势提供依据.  相似文献   

Climatic cycles inferred from the aminostratigraphy and aminochronology of Quaternary dunes and palaeosols from the eastern islands of the Canary Archipelago     

J. E. Ortiz  T. Torres  Y. Yanes  C. Castillo  J. De La Nuez  M. Ibez  M. R. Alonso 《第四纪科学杂志》2006,21(3):287-306

Aminochronological and aminostratigraphical methods have been used to study the Quaternary aeolian deposits from the islands located east of the Canary Archipelago (Fuerteventura and Lanzarote islands and La Graciosa, Montaña Clara and Alegranza islets). The extent of racemisation/epimerisation of four amino acids (isoleucine, aspartic acid, phenylalanine and glutamic acid) was measured in land snail shells of the genus Theba. The age calculation algorithms of these amino acids have been determined to permit the numerical dating of these deposits. Eight Aminozones, each defining dune/palaeosol‐formation episodes, have been distinguished and dated at 48.6 ± 6.4, 42.5 ± 6.0, 37.8 ± 4.6, 29.4 ± 4.8, 22.4 ± 4.5, 14.9 ± 3.6, 11.0 ± 4.0 and 5.4 ± 1.1 ka BP, the first five of them defining cycles of 5–7 ka. The alternation of palaeosols and aeolian deposits, which are related to abrupt transitions from humid to arid conditions, are the reflection of globally induced changes in North Africa palaeoenvironmental conditions linked to the effect of African palaeomonsoons on the trade winds and the Saharan Air Layer. Probably these aeolian cycles, with a recurrence period of 5–7 ka, are the expression of multiples of the ～2.4 ka solar‐cycle. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The European Large Area ISO Survey – IX. The 90-μm luminosity function from the Final Analysis sample     

Stephen Serjeant †  Alberto Carramiñana †  Eduardo Gonzáles-Solares  Phillipe Héraudeau  Raúl Mújica †  Ismael Perez-Fournon  Nicola Sedgwick †  Michael Rowan-Robinson  Alberto Franceschini  Thomas Babbedge  Carlos del Burgo  Paolo Ciliegi  reas Efstathiou  Fabio La Franca  Carlotta Gruppioni  David Hughes  Carlo Lari  Seb Oliver  Francesca Pozzi  Manfred Stickel  Mattia Vaccari 《Monthly notices of the Royal Astronomical Society》2004,355(3):813-818

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The radio–mid-infrared correlation and the contribution of 15-μm galaxies to the 1.4-GHz source counts     

C. Gruppioni  F. Pozzi  G. Zamorani  P. Ciliegi  C. Lari  E. Calabrese  F. La Franca  I. Matute 《Monthly notices of the Royal Astronomical Society》2003,341(1):L1-L6

The radio counterparts to the 15-μm sources in the European Large Area ISO Survey southern fields are identified in 1.4-GHz maps down to ∼80 μJy. The radio–mid-infrared correlation is investigated and derived for the first time at these flux densities for a sample of this size. Our results show that radio and mid-infrared (MIR) luminosities correlate almost as well as radio and far-infrared (FIR), at least up to   z ≃ 0.6  . Using the derived relation and its spread together with the observed 15-μm counts, we have estimated the expected contribution of the 15-μm extragalactic populations to the radio source counts and the role of MIR starburst galaxies in the well-known 1.4-GHz source excess observed at sub-mJy levels. Our analysis demonstrates that IR emitting starburst galaxies do not contribute significantly to the 1.4-GHz counts for strong sources, but start to become a significant fraction of the radio source population at flux densities ≲0.5–0.8 mJy. They are expected to be responsible for more than 60 per cent of the observed radio counts at ≲0.05 mJy. These results are in agreement with the existing results on optical identifications of faint radio sources.  相似文献   

The redshift-space two-point correlation function of ELAIS-S1 galaxies     

V. D'Elia  E. Branchini  F. La Franca  V. Baccetti  I. Matute  F. Pozzi  C. Gruppioni 《Monthly notices of the Royal Astronomical Society》2005,359(3):1077-1082

We investigate the clustering properties of galaxies in the recently completed ELAIS-S1 redshift survey through their spatial two-point autocorrelation function. We used a subsample of the ELAIS-S1 catalogue covering approximately 4 deg² and consisting of 148 objects selected at 15 μm with a flux >0.5 mJy and a redshift   z < 0.5  . We detected a positive signal in the correlation function that in the range of separations  1–10  h ⁻¹ Mpc  is well approximated by a power law with a slope  γ= 1.4 ± 0.25  and a correlation length   s ₀= 5.4 ± 1.2  h ⁻¹ Mpc  , at the 90 per cent significance level. This result is in good agreement with the redshift-space correlation function measured in more local samples of mid-infrared-selected galaxies such as the IRAS Point Source Catalog (PSC z ) redshift survey. This suggests a lack of significant clustering evolution of infrared-selected objects out to   z = 0.5  that is further confirmed by the consistency found between the correlation functions measured in a local  ( z < 0.2)  and a distant  (0.2 < z < 0.5)  subsample of ELAIS-S1 galaxies. We also confirm that optically selected galaxies in the local redshift surveys, especially those of the SDSS sample, are significantly more clustered than infrared objects.  相似文献   

Decadal prediction skill in the ocean with surface nudging in the IPSL-CM5A-LR climate model     

Juliette Mignot  Javier García-Serrano  Didier Swingedouw  Agathe Germe  Sébastien Nguyen  Pablo Ortega  Eric Guilyardi  Sulagna Ray 《Climate Dynamics》2016,47(3-4):1225-1246

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Mapping the earthquake-induced landslide hazard around the main oil pipeline network of the Agri Valley (Basilicata,southern Italy) by means of two GIS-based modelling approaches     

Flavio Borfecchia  Gerardo De Canio  Luigi De Cecco  Alessandro Giocoli  Sergio Grauso  Luigi La Porta  Sandro Martini  Maurizio Pollino  Ivan Roselli  Alessandro Zini 《Natural Hazards》2016,80(2):759-773

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40Ar/39Ar and U–Pb SHRIMP dating of Aptian tuff cones in the Aisén Basin,Central Patagonian Cordillera     

M. Suárez  A. Demant  R. De La Cruz  C.M. Fanning 《Journal of South American Earth Sciences》2010,29(3):731-737

Surtseyan tuff cones of the Baño Nuevo Volcanic Complex erupted in shallow marine water during the waning stage of the Aisén Basin, the northern part of the Austral Basin of the Central Patagonian Cordillera. This volcanic complex was emplaced within the Hauterivian to early Aptian Apeleg Formation, the youngest sedimentary unit of this basin, whilst the sediments were still wet. Three new Ar/Ar dates (amphibole) and one U–Pb SHRIMP date (zircon) from this complex yielded concordant early Aptian ages of 122–121 Ma. These data agree with the contact relationships between the Apeleg Formation and the tuff cones. These dates also agree with those of early Aptian ammonites collected from the Apeleg Formation 100 km south of the study area, which represent the youngest fossils identified in this unit. Aptian to Albian subaerial volcanic rocks of the Divisadero Group, paraconformably overlie the Apeleg Formation. The emplacement of the Baño Nuevo Volcanic Complex pre-dates the disappearance of the Aisén Basin.  相似文献   

Variability and spectral energy distributions of low-luminosity active galactic nuclei: a simultaneous X-ray/UV look with Swift     

E. Pian  P. Romano  D. Maoz  A. Cucchiara  C. Pagani  V. La Parola 《Monthly notices of the Royal Astronomical Society》2010,401(1):677-686

We have observed four low-luminosity active galactic nuclei (AGNs) classified as type 1 Low-Ionization Nuclear Emission-Line Regions (LINERs) with the X-Ray Telescope (XRT) and the Ultraviolet–Optical Telescope (UVOT) onboard Swift , in an attempt to clarify the main powering mechanism of this class of nearby sources. Among our targets, we detect X-ray variability in NGC 3998 for the first time. The light curves of this object reveal variations of up to 30 per cent amplitude in half a day, with no significant spectral variability on this time-scale. We also observe a decrease of ∼30 per cent over 9 d, with significant spectral softening. Moreover, the X-ray flux is ∼40 per cent lower than observed in previous years. Variability is detected in M81 as well, at levels comparable to those reported previously: a flux increase in the hard X-rays (1–10 keV) of 30 per cent in ∼3 h and variations by up to a factor of 2 within a few years. This X-ray behaviour is similar to that of higher luminosity, Seyfert-type objects. Using previous high-angular-resolution imaging data from the Hubble Space Telescope ( HST ), we evaluate the diffuse UV emission due to the host galaxy and isolate the nuclear flux in our UVOT observations. All sources are detected in the UV band, at levels similar to those of the previous observations with HST . The XRT (0.2–10 keV) spectra are well described by single power laws and the UV-to-X-ray flux ratios are again consistent with those of Seyferts and radio-loud AGNs of higher luminosity. The similarity in X-ray variability and broad-band energy distributions suggests the presence of similar accretion and radiation processes in low- and high-luminosity AGNs.  相似文献