The 0.1–100 keV spectrum and variability of Mrk 421 in a high state     

A. Malizia  M. Capalbi  F. Fiore  P. Giommi  G. Gandolfi  A. Tesseri  L. A. Antonelli  R. C. Butler  G. Celidonio  A. Coletta  L. Di Ciolo  J. M. Muller  L. Piro  S. Rebecchi  D. Ricci  R. Ricci  M. Smith  V. Torroni 《Monthly notices of the Royal Astronomical Society》2000,312(1):123-129

The results of a BeppoSAX target of opportunity (TOO) observation of the BL Lac object Mrk 421 during a high-intensity state are reported and compared with monitoring X-ray data collected with the BeppoSAX Wide Field Cameras (WFC) and the RXTE All Sky Monitor (ASM). The 0.1–100 keV spectrum of Mrk 421 shows continuous convex curvature that can be interpreted as the high-energy end of the synchrotron emission. The source shows significant short-term temporal and spectral variability, which can be interpreted in terms of synchrotron cooling. The comparison of our results with those of previous observations when the source was a factor 3–5 fainter shows evidence for strong spectral variability, with the maximum of the synchrotron power shifting to higher energy during high states. This behaviour suggests an increase in the number of energetic electrons during high states.  相似文献   

Comparison of polynomial chaos and Gaussian process surrogates for uncertainty quantification and correlation estimation of spatially distributed open-channel steady flows   总被引：1，自引：1，他引：0  

Pamphile?T.?RoyEmail authorView author&#;s OrcID profile  Nabil?El Mo?ayd  Sophie?Ricci  Jean-Christophe?Jouhaud  Nicole?Goutal  Matthias?De Lozzo  Mélanie?C.?Rochoux 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(6):1723-1741

Data assimilation is widely used to improve flood forecasting capability, especially through parameter inference requiring statistical information on the uncertain input parameters (upstream discharge, friction coefficient) as well as on the variability of the water level and its sensitivity with respect to the inputs. For particle filter or ensemble Kalman filter, stochastically estimating probability density function and covariance matrices from a Monte Carlo random sampling requires a large ensemble of model evaluations, limiting their use in real-time application. To tackle this issue, fast surrogate models based on polynomial chaos and Gaussian process can be used to represent the spatially distributed water level in place of solving the shallow water equations. This study investigates the use of these surrogates to estimate probability density functions and covariance matrices at a reduced computational cost and without the loss of accuracy, in the perspective of ensemble-based data assimilation. This study focuses on 1-D steady state flow simulated with MASCARET over the Garonne River (South-West France). Results show that both surrogates feature similar performance to the Monte-Carlo random sampling, but for a much smaller computational budget; a few MASCARET simulations (on the order of 10–100) are sufficient to accurately retrieve covariance matrices and probability density functions all along the river, even where the flow dynamic is more complex due to heterogeneous bathymetry. This paves the way for the design of surrogate strategies suitable for representing unsteady open-channel flows in data assimilation.  相似文献   

Radiological hazards of coal and ash samples collected from Xi’an coal-fired power plants of China   总被引：1，自引：0，他引：1  

Xinwei Lu  Loretta Y. Li  Fengling Wang  Lijun Wang  Xu Zhang 《Environmental Earth Sciences》2012,66(7):1925-1932

The natural radiological characteristics and their respective annual effective dose (AED) rates, produced by ²²⁶Ra, ²³²Th and ⁴⁰K in coal, fly ash and bottom ash from two large coal-fired power plants (CFPPs) of Xi’an were determined by means of γ-ray spectrometry. The average activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in all ash samples (fly ash and bottom ash samples) from the two CFPPs were 67.6, 74.3 and 225.3 Bq kg⁻¹, respectively. The results are compared with data from other locations. To evaluate the radiological hazards of the natural radioactivity, the radium equivalent activity (Ra_eq), air absorbed dose rate (D), AED and external hazard index (H _ex) are compared with internationally accepted values. Ra_eq and H _ex of all samples except three fly ash samples were less than the limits of 370 Bq kg⁻¹ and unity, respectively. The average D and AED for ash samples were 86.8 nGy h⁻¹ and 0.11 mSv y⁻¹, respectively, which exceed the world average and Xi’an average values.  相似文献   

The Canada–UK Deep Submillimetre Survey – VIII. Source identifications in the 3-hour field     

Dave Clements  Steve Eales  Kris Wojciechowski  Tracy Webb  Simon Lilly  Loretta Dunne  Rob Ivison  Henry McCracken  Min Yun  Ashley James  Mark Brodwin  Olivier Le Fèvre  Walter Gear 《Monthly notices of the Royal Astronomical Society》2004,351(2):447-465

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A census of metals at high and low redshift and the connection between submillimetre sources and spheroid formation     

Loretta Dunne  Stephen A. Eales  M. G. Edmunds 《Monthly notices of the Royal Astronomical Society》2003,341(2):589-598

Deep surveys in many wavebands have shown that the rate at which stars were forming was at least a factor of 10 higher at redshifts >1 than today. Heavy elements ('metals') are produced by stars, and the star formation history deduced by these surveys implies that a significant fraction of all metals in the Universe today should already exist at   z ∼ 2–3  . However, only 10 per cent of the total metals expected to exist at this redshift have so far been accounted for (in damped Lyman α absorbers and the Lyman forest). In this paper, we use the results of submillimetre surveys of the local and high-redshift Universe to show that there was much more dust in galaxies in the past. We find that a large proportion of the missing metals are traced by this dust, bringing the metals implied from the star formation history and observations into agreement. We also show that the observed distribution of dust masses at high redshift can be reproduced remarkably well by a simple model for the evolution of dust in spheroids, suggesting that the descendants of the dusty galaxies found in deep submillimetre surveys are the relatively dust-free spiral bulges and ellipticals in the Universe today.  相似文献   

The SCUBA Local Universe Galaxy Survey – III. Dust along the Hubble sequence     

Catherine Vlahakis †  Loretta Dunne  Stephen Eales 《Monthly notices of the Royal Astronomical Society》2005,364(4):1253-1285

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Effect of salt of various concentrations on liquid limit,and hydraulic conductivity of different soil-bentonite mixtures   总被引：1，自引：0，他引：1  

Anil Kumar Mishra  Masami Ohtsubo  Loretta Y. Li  Takahiro Higashi  Junboum Park 《Environmental Geology》2009,57(5):1145-1153

Effect of the various concentrations of NaCl and CaCl₂ on the four different soil-bentonite mixtures has been evaluated. The results show that the liquid limit of the mixtures decreases with an increase in the salt concentration. Liquid limit decreased significantly with an increase in CaCl₂ concentration from 0 to 0.1 N. However, a further increase in the concentration did not produce any significant decrease in liquid limit. A quite opposite trend was observed for the NaCl solution. An increase in NaCl concentration from 0 to 0.1 N did not produce any major decrease in the liquid limit, but a further increase in concentration from 0.1 to 1 N decreased the liquid limit significantly. Consolidation tests were carried out on the mixtures to evaluate the effect of mineralogical composition of the bentonite on the hydraulic conductivity (k) of the mixture in the presence of various salts concentrations. The k for any mixtures was found to be decreasing with decrease in the salt concentration. At relatively low concentration, Ca²⁺ had more effect on the k in comparison to the same concentration of Na⁺. However, at 1 N of NaCl and CaCl₂ almost an equal value of k was observed. A comparison of the performance of four bentonites showed that the mixture with bentonite having highest exchangeable sodium percentage (ESP) exhibited the lowest k when permeated with de-ionized (DI) water, however, k increased with an increase in the salt concentration. Similarly, mixture with a bentonite of lower ESP exhibited a higher k with DI water but with the increase in the salt concentration alteration in the k, compared to all other mixtures, was relatively less.  相似文献   

The extragalactic radio-source population at 95 GHz     

Elaine M. Sadler  Roberto Ricci  Ronald D. Ekers  Robert J. Sault  Carole A. Jackson  Gianfranco De Zotti 《Monthly notices of the Royal Astronomical Society》2008,385(3):1656-1672

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Water quality assessment of Wei River, China using fuzzy synthetic evaluation   总被引：5，自引：1，他引：4  

Xinwei Lu  Loretta Y. Li  Kai Lei  Lijun Wang  Yuxiang Zhai  Meng Zhai 《Environmental Earth Sciences》2010,60(8):1693-1699

Wei River is the major source of water for the urban residents, industrial production and agricultural activities in the central Shaanxi plain of China. Water quality of the Wei River was determined by collecting water samples from 25 locations along the Baoji Xi’an reach and analyzing for pH, EC, BOD₅, DO, COD, F, Se, As, and Hg. Fuzzy synthetic evaluation with the entropy method for weight determination was used to assess the water quality of the river. Results indicate that the water quality of 23 sampling sites fall into the fifth grade (bad level), whereas two sampling sites are in the fourth grade (poor level). The comparison of this method with the typical fuzzy synthetic evaluation shows that it is effective in water quality assessment. The assessment results indicate that the Wei River is heavily polluted at most of the sampling locations, with mercury as the major pollutant. Strict enforcement of the regulations for domestic and industrial wastewater discharges is vital to avoid damage to the water environment and to protect human and ecological health.  相似文献   

First Mass-resolved Measurement of High-Energy Cosmic-Ray Antiprotons     

Bergström D  Boezio M  Carlson P  Francke T  Grinstein S  Khalchukov F  Suffert M  Hof M  Kremer J  Menn W  Simon M  Stephens SA  Ambriola ML  Bellotti R  Cafagna F  Ciacio F  Circella M  De Marzo C  Finetti N  Papini P  Piccardi S  Spillantini P  Bartalucci S  Ricci M  Casolino M  De Pascale MP  Morselli A  Picozza P  Sparvoli R  Bonvicini V  Schiavon P  Vacchi A  Zampa N  Mitchell JW  Ormes JF  Streitmatter RE  Bravar U  Stochaj SJ 《The Astrophysical journal》2000,534(2):L177-L180

We report new results for the cosmic-ray antiproton-to-proton ratio from 3 to 50 GeV at the top of the atmosphere. These results represent the first measurements, on an event-by-event basis, of mass-resolved antiprotons above 18 GeV. The results were obtained with the NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas-RICH (Ring-Imaging Cerenkov) counter and a silicon-tungsten imaging calorimeter. The RICH detector was the first ever flown that is capable of identifying charge-one particles at energies above 5 GeV. The spectrometer was flown on 1998 May 28-29 from Fort Sumner, New Mexico. The measured p&d1;/p ratio is in agreement with a pure secondary interstellar production.  相似文献