The BeppoSAX High Energy Large Area Survey (HELLAS) – III. Testing synthesis models for the X-ray background     

A. Comastri  F. Fiore  C. Vignali  G. Matt  G.C. Perola  F. La Franca 《Monthly notices of the Royal Astronomical Society》2001,327(3):781-787

The BeppoSAX High Energy Large Area Survey (HELLAS) has surveyed several tens of deg² of the sky in the     band down to a flux of about     . The source surface density of     at the survey limit corresponds to a resolved fraction of the     X-ray background (XRB) of the order of     per cent. The extrapolation of the HELLAS     towards fainter fluxes with a Euclidean slope is consistent with the first XMM–Newton measurements, in the same energy band, which are a factor of 20 times more sensitive. The source counts in the hardest band so far surveyed by X-ray satellites are used to constrain XRB models. It is shown that in order to reproduce the     counts over the range of fluxes covered by BeppoSAX and XMM–Newton a large fraction of highly absorbed     , luminous     active galactic nuclei is needed. A sizeable number of more heavily obscured, Compton-thick, objects cannot be ruled out but they are not required by the present data. The model predicts an absorption distribution consistent with that found from the hardness ratios analysis of the so far identified HELLAS sources. Interestingly enough, there is evidence of a decoupling between X-ray absorption and optical reddening indicators, especially at high redshifts/luminosities where several broad-line quasars show hardness ratios typical of absorbed power-law models with     .  相似文献   

Comparison of ozone vertical distributions measured by different techniques at mesospheric altitudes     

N. Monnanteuil  J. De La Noe  P. Marche 《Planetary and Space Science》1983,31(7):809-810

A comparison is done between the ozone vertical profiles obtained by a microwave technique at the Bordeaux Observatory and by a short Umkehr method at the Chiran station of the Observatoire de Haute-Provence, on 19 June 1981. There is a good agreement between the results obtained by both methods in spite of the distance between both sites.  相似文献   

Three Reflection Telescopes for Wide Field Space Astronomy. First Results from a 30 cm Prototype and Prospects     

Roberto Viotti  Cesare D. La Padula  Domenico Nanni  Agostino Vignato 《Astrophysics and Space Science》2001,276(1):81-88

We present the basic concepts of the two-mirror, three-reflection optical system (2MTRT), and discuss the important benefits of such a system for space projects: wide ( 2^°) correctedand unvignetted FOV, without the use of refractive optics for thefield correction, planarity of the focal surface for an optimizedinstallation of wide area detectors, easy telescope adjustement, small volume and little mass.We also report the results of optical tests made with a 30 cm prototype,equipped with a 2k × 2k CCD camera, and give examples of scientific programmes which can be performed from space and in hostile terrestrial sites such as the Antarctic Plateau.  相似文献   

Coastal Impacts of the March 11th Tohoku, Japan Tsunami in the Galapagos Islands     

Patrick Lynett  Robert Weiss  Willington Renteria  Giorgio De La Torre Morales  Sangyoung Son  Maria Elizabeth Martin Arcos  Breanyn Tiel MacInnes 《Pure and Applied Geophysics》2013,170(6-8):1189-1206

On March 11, 2011 at 5:46:23 UTC (March 10 11:46:23 PM Galapagos Local Time), the M_w 9.0 Great East Japan Earthquake occurred near the Tohoku region off the east coast of Japan, spawning a Pacific-wide tsunami. Approximately 12,000 km away, the Galapagos Islands experienced moderate tsunami impacts, including flooding, structural damage, and strong currents. In this paper, we present observations and measurements of the tsunami effects in the Galapagos, focusing on the four largest islands in the archipelago; (from west to east) Isabela, Santiagio, Santa Cruz, and San Cristobal. Access to the tsunami affected areas was one of the largest challenges of the field survey. Aside from approximately ten sandy beaches open to tourists, all other shoreline locations are restricted to anyone without a research permit; open cooperation with the Galapagos National Park provided the survey team complete access to the Islands coastlines. Survey locations were guided by numerical simulations of the tsunami performed prior to the field work. This numerical guidance accurately predicted the regions of highest impact, as well as regions of relatively low impact. Tide-corrected maximum tsunami heights were generally in the range of 3–4 m with the highest runup of 6 m measured in a small pocket beach on Isla Isabela. Puerto Ayora, on Santa Cruz Island, the largest harbor in the Galapagos experienced significant flooding and damage to structures located at the shoreline. A current meter moored inside the harbor recorded relatively weak tsunami currents of less than 0.3 m/s (0.6 knot) during the event. Comparisons with detailed numerical simulations suggest that these low current speed observations are most likely the result of data averaging at 20-min intervals and that maximum instantaneous current speeds were considerably larger. Currents in the Canal de Itabaca, a natural waterway between Santa Cruz Island and a smaller island offshore, were strong enough to displace multiple 5.5-ton navigation buoys. Numerical simulations indicate that currents in the Canal de Itabaca exceeded 4 m/s (~8 knots), a very large flow speed for a navigational waterway.  相似文献   

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   

Geochemical influence of waste trench no. 22T at Chernobyl Pilot Site at the aquifer: Long-term trends,governing processes,and implications for radionuclide migration     

D. Bugai  E. Tkachenko  N. Van Meir  C. Simonucci  A. Martin-Garin  C. Roux  C. Le Gal La Salle  Yu. Kubko 《Applied Geochemistry》2012

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Groundwater residence time downgradient of Trench No. 22 at the Chernobyl Pilot Site: Constraints on hydrogeological aquifer functioning     

C. Le Gal La Salle  L. Aquilina  E. Fourre  P. Jean-Baptiste  J.-L. Michelot  C. Roux  D. Bugai  T. Labasque  C. Simonucci  N. Van Meir  A. Noret  S. Bassot  A. Dapoigny  D. Baumier  P. Verdoux  D. Stammose  J. Lancelot 《Applied Geochemistry》2012

Following the explosion of reactor 4 at the Chernobyl power plant in northern Ukraine in 1986, contaminated soil and vegetation were buried in shallow trenches dug directly on-site in an Aeolian sand deposit. These trenches are sources of radionuclide (RN) pollution. The objective of the present study is to provide constraints for the Chernobyl flow and RN transport models by characterising groundwater residence time. A radiochronometer ³H/³He method (t_1/2 = 12.3 a) and anthropogenic tracers including CFC and SF₆ are investigated along with the water mass natural tracers Na, Cl, ¹⁸O and ²H.  相似文献   

Geodetic techniques applied to the study of the Etna volcano area (Italy)     

Santo La Delfa  Monia Negusini  Sabrina Di Martino  Giuseppe Patanè 《International Journal of Earth Sciences》2012,101(4):1065-1075

Volcanic behaviour of Mt. Etna is due to the complex interaction between both the local and the regional stress field involving the eastern Sicily. Eruptions could trigger (be triggered?) during crust extension and/or compression, which are strictly linked with the dynamics of the lower mantle. In this study, very long baseline interferometry (VLBI) space geodesy technique has been used in order to study Etna volcano’s activity by means of the crustal deformations between Noto and Matera (located on the African and the Eurasian Plates, respectively). By analysing VLBI data, we obtained the behaviour of the baseline which crosses the Etnean area, from 1990 December to 2003 March, representing the time variations of the distance between the two geodetic stations; the linear trend of the baseline shows a general increasing, pointing out an extension of the crust between them. A detailed analysis of the Noto-Matera baseline allows the identification of three parts of the VLBI curve in the considered period. In the first part of the curve (from 20/12/90 to 09/02/94), VLBI data are rather poor and therefore no reliable consideration about correlation between crust movements and volcanic and seismicity activity has been made. In the second part of the curve (from 09/02/94 to 04/09/00), VLBI data are more frequent and show slightly fluctuations in the distance. Increasing in the extension and compression were observed in the central and in the final part of this period. In the third period (from 04/09/00 to 25/03/03), VLBI data are very sparse even if the time series was quite long; therefore, to fill gaps in the information, we analysed global positioning system (GPS) data. GPS technique performs continuous observations, and we were able to highlight both extensions and compressions in detail. Comparisons between the trend of Noto-Matera baseline length variations, volcanic activity and seismicity in the Etna area show the complexity of the development over time and space of the phenomenology determined by a deep cause which can be traced, in our opinion, to the interaction between the asthenospheric mantle, deep crust and surface crust. Therefore, we state that crustal distension and compression are determined by the lower pulsating mantle.  相似文献   

Porosity and mineralogy evolution during the decay process involved in the Chellah monument stones     

Abderrahim Samaouali  Larbi Laânab  Mohamed Boukalouch  Yves Geraud 《Environmental Earth Sciences》2010,59(6):1171-1181

The objective of this work is to study the decay process involved in the historical Roman Chellah located in the Rabat city (Morocco). This monument is made up of porous calcarenite stone. Several samples, taken from altered and unaltered blocks, were analyzed by the water saturation, the mercury intrusion porosimetry techniques and using the scanning electron microscopy coupled to energy dispersive X-ray spectrometer (SEM–EDX). To perform a reliable chemical analysis, some samples were also analyzed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The mercury porosimetry results show a bimodal porous network for this porous material, the deterioration process of these stones involved an increase in porous volume of about 2%. The lowest porosity observed in the unaltered block is connected to the presence of sparitic cement which causes a partial inter-granular porosity clogging. The highest porosity of the deteriorated block without crust is due to the increase in inter-granular space. SEM photographs of the unaltered sample show the presence of the porous primary grains, of ovoid forms and millimeter-length sizes, and of the secondary grains, of rhombohedric forms and micro size. Porosity is essentially located between the primary grains and can be completely clogged by secondary precipitations. Various forms of deterioration are observed on the altered samples such as the dissolution of the secondary grains edges, wells of dissolution and also the presence of argillaceous residues on the surface. This last was also detected by the ICP-AES and EDX analysis which show an increase of the silicon and aluminum contents toward the surface.  相似文献