Cosmological evolution of the Fanaroff–Riley type II source population     

Yang Wang  Christian R. Kaiser 《Monthly notices of the Royal Astronomical Society》2008,388(2):677-696

By combining a model for the evolution of the radio luminosity of an individual source with the radio luminosity function, we perform a multidimensional Monte Carlo simulation to investigate the cosmological evolution of the Fanaroff–Riley type II (FR II) radio galaxy population by generating large artificial samples. The properties of FR II sources are required to evolve with redshift in the artificial samples to fit the observations. Either the maximum jet age or the maximum density of the jet environment or both evolve with redshift. We also study the distribution of FR II source properties as a function of redshift. From currently available data we cannot constrain the shape of the distribution of environment density or age, but jet power is found to follow a power-law distribution with an exponent of approximately −2. This power-law slope does not change with redshift out to   z = 0.6  . We also find the distribution of the pressure in the lobes of FR II sources to evolve with redshift up to   z ∼ 1.2  .  相似文献   

SuperWASP-N extrasolar planet candidates from fields 06^h < RA < 16^h     

S. R. Kane  W. I. Clarkson  R. G. West  D. M. Wilson  D. J. Christian  A. Collier Cameron  B. Enoch  T. A. Lister  R. A. Street  A. Evans  A. Fitzsimmons  C. A. Haswell  C. Hellier  S. T. Hodgkin  K. Horne  J. Irwin  F. P. Keenan  A. J. Norton  J. Osborne  N. R. Parley  D. L. Pollacco  R. Ryans  I. Skillen  P. J. Wheatley 《Monthly notices of the Royal Astronomical Society》2008,384(3):1097-1108

The Wide Angle Search for Planets (WASP) survey currently operates two installations, designated SuperWASP-N and SuperWASP-S, located in the Northern and Southern hemispheres, respectively. These installations are designed to provide high time-resolution photometry for the purpose of detecting transiting extrasolar planets, asteroids, and transient events. Here, we present results from a transit-hunting observing campaign using SuperWASP-N covering a right ascension (RA) range of 06^h < RA < 16^h. This paper represents the fifth and final in the series of transit candidates released from the 2004 observing season. In total, 729 335 stars from 33 fields were monitored with 130 566 having sufficient precision to be scanned for transit signatures. Using a robust transit detection algorithm and selection criteria, six stars were found to have events consistent with the signature of a transiting extrasolar planet based on the photometry, including the known transiting planet XO-1b. These transit candidates are presented here along with discussion of follow-up observations and the expected number of candidates in relation to the overall observing strategy.  相似文献   

Polycyclic aromatic hydrocarbons and amino acids in meteorites and ice samples from LaPaz Icefield,Antarctica     

Oliver BOTTA  Zita MARTINS  Christian EMMENEGGER  Jason P. DWORKIN  Daniel P. GLAVIN  Ralph P. HARVEY  Renato ZENOBI  Jeffrey L. BADA  Pascale EHRENFREUND 《Meteoritics & planetary science》2008,43(9):1465-1480

Abstract— –We have analyzed ice samples and meteorites from the LaPaz region of Antarctica to investigate the composition of polycyclic aromatic hydrocarbons (PAHs) and amino acids with the goal to understand whether or not there is a compositional relationship between the two reservoirs. Four LL5 ordinary chondrites (OCs) and one CK carbonaceous chondrite were collected as part of the 2003/2004 ANSMET season. Ice samples collected from directly underneath the meteorites were extracted. In addition, exhaust particles from the snowmobiles used during the expedition were collected to investigate possible contributions from this source. The meteorite samples, the particulate matter and solid‐state extracts of the ice samples and the exhaust filters were subjected to two‐step laser mass spectrometry (L2MS) to investigate the PAH composition. For amino acids analysis, the meteorites were extracted with water and acid hydrolyzed, and the extracts were analyzed with offline OPA/NAC derivatization combined with liquid chromatography with UV fluorescence detection and time of flight mass spectrometry (LC‐FD/ToF‐MS). PAHs in the particulate matter of the ice were found to be qualitatively similar to the meteorite samples, indicating that micron‐sized grains of the meteorite may be embedded in the ice samples. The concentration levels of dissolved PAHs in all the ice samples were found to be below the detection limit of the L2MS. The PAH composition of the snowmobile exhaust is significantly different to the one in particulate matter, making it an unlikely source of contamination for Antarctic meteorites. The amino acids glycine, β‐alanine and γ‐amino‐n‐butyric acid that were detected at concentrations of 3 to 19 parts per billion (ppb) are probably indigenous to the Antarctic meteorites. Some of the LaPaz ice samples were also found to contain amino acids at concentration levels of 1 to 33 parts per trillion (ppt), in particular α‐aminoisobutyric acid (AIB), an abundant non‐protein amino acid of extraterrestrial origin found in some carbonaceous chondrites. We hypothesize that this amino acid could have been extracted from Antarctic micrometeorites and the particulate matter of the meteorites during the concentration procedure of the ice samples.  相似文献   

New impact‐melt rock from the Roter Kamm impact structure,Namibia: Further constraints on impact age,melt rock chemistry,and projectile composition     

Lutz HECHT  W. Uwe REIMOLD  Sarah SHERLOCK  Roald TAGLE  Christian KOEBERL  Ralf‐Thomas SCHMITT 《Meteoritics & planetary science》2008,43(7):1201-1218

Abstract— A new locality of in situ massive impact‐melt rock was discovered on the south‐southwestern rim of the Roter Kamm impact structure. While the sub‐samples from this new locality are relatively homogeneous at the hand specimen scale, and despite being from a nearby location, they do not have the same composition of the only previously analyzed impact‐melt rock sample from Roter Kamm. Both Roter Kamm impact‐melt rock samples analyzed to date, as well as several suevite samples, exhibit a granitic‐granodioritic precursor composition. Micro‐chemical analyses of glassy matrix and Al‐rich orthopyroxene microphenocrysts demonstrate rapid cooling and chemical disequilibrium at small scales. Platinum‐group element abundances and ratios indicate an ordinary chondritic composition for the Roter Kamm impactor. Laser argon dating of two sub‐samples did not reproduce the previously obtained age of 3.7 ± 0.3 (1s?) for this impact event, based on ⁴⁰Ar/³⁹Ar dating of a single vesicular impact‐melt rock. Instead, we obtained ages between 3.9 and 6.3 Ma, with an inverse isochron age of 4.7 ± 0.3 Ma for one analyzed sub‐sample and 5.1 ± 0.4 Ma for the other. Clearly a post‐5 Ma impact at Roter Kamm remains indicated, but further analytical work is required to better constrain the currently best estimate of 4–5 Ma. Both impactor and age constraints are clearly obstructed by the inherent microscopic heterogeneity and disequilibrium melting and cooling processes demonstrated in the present study.  相似文献   

On the potential of plant species invasion influencing bio‐geomorphologic landscape formation in salt marshes          下载免费PDF全文

Christian Schwarz  Tom Ysebaert  Wouter Vandenbruwaene  Stijn Temmerman  LiQuan Zhang  Peter M. J. Herman 《地球表面变化过程与地形》2016,41(14):2047-2057

Species invasions are known to change biotic and abiotic ecosystem characteristics such as community structure, cycling of materials and dynamics of rivers. However, their ability to alter interactions between biotic and abiotic ecosystem components, in particular bio‐geomorphic feedbacks and the resulting landscape configuration in tidal wetlands, such as tidal channels have not yet been demonstrated. We studied the impact of altered bio‐geomorphic feedbacks on geomorphologic features (i.e. tidal wetland channels), by comparing proxies for channel network geometry (unchanneled flow lengths, fractal dimension) over time between non‐invaded and invaded salt marsh habitats. The non‐invaded habitats (the south of eastern Chongming Island, Yangtze estuary, China) show little change in network geometry over time with a tendency for an increased drainage density. The invaded site (salt marshes in the north of eastern Chongming Island invaded by the exotic plant species Spartina alterniflora) showed a decreasing tendency in channel drainage density throughout and after the species invasion. This suggests that species invasions might not only affect biotic ecosystem characteristics, but also their ability to change bio‐geomorphic feedback loops, potentially leading to changes in existing geomorphologic features and therefore landscape configuration. Our results further suggest that the species invasion also altered sediment composition. Based on observations we propose a mechanism explaining the change in channel drainage density by an alteration in plant properties. The physical and physiological characteristics of the invading species Spartina alterniflora clearly differ from the native species Scirpus mariqueter, inducing different bio‐geomorphic feedback loops leading to the observed change in salt marsh channel configuration. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Impacts of human activities on recharge in a multilayered semiarid aquifer (Campo de Cartagena,SE Spain)   总被引：1，自引：0，他引：1       下载免费PDF全文

Paul Baudron  Florent Barbecot  José Luis García Aróstegui  Christian Leduc  Yves Travi  David Martinez‐Vicente 《水文研究》2014,28(4):2223-2236

The development of intense agriculture in semiarid areas modifies intensity and spatial distribution of groundwater recharge by summing irrigation return flow to limited rainfall infiltration. Environmental tracers provide key information, but their interpretation is complicated by more complex groundwater flow patterns. In multilayered aquifers, the real origin of the groundwater samples is hard to assess because of local mixing processes occurring inside long‐screened boreholes. We use environmental tracers (¹⁴C, ¹³C, ²H, ¹⁸O, ³H) to investigate the long‐term evolution of recharge in the five‐layer Campo de Cartagena aquifer in South‐Eastern Spain, in addition to high‐resolution temperature loggings to identify the depth of origin of groundwater. Despite the complex background, this methodology allowed a reliable interpretation of the geochemistry and provided a better understanding of the groundwater flow patterns. The tritium method did not give good quantitative results because of the high variability of the recharge signal but remained an excellent indicator of recent recharge. Nonetheless, both pre‐anthropization and post‐anthropization recharge regime could be identified and quantified by radiocarbon. Before the development of agriculture, recharge varied from 17 mm.year^‐1 at the mountain ranges to 6 mm.year^‐1 in the plain, whereas the mean annual rainfall is about 300 mm. In response to the increase of agricultural activity, recharge fluxes to the plain were amplified and nowadays reach up to 210 mm.year^‐1 in irrigated areas. These values are strengthened by global water budget and local unsaturated zone studies. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Generation of accelerograms compatible with design specifications using information theory     

Anas Batou  Christian Soize 《Bulletin of Earthquake Engineering》2014,12(2):769-794

This paper deals with the generation of seismic accelerograms which are compatible with a given response spectrum and other design specifications. The time sampling of the stochastic accelerogram yields a time series represented by a random vector in high dimension. The probability density function of this random vector is constructed using the maximum entropy (MaxEnt) principle under constraints defined by the available information (design specifications). In this paper, an adapted algorithm is proposed to identify the Lagrange multipliers introduced in the MaxEnt principle to take into account the constraints. This algorithm is based on (1) the minimization of an appropriate convex functional and (2) the construction of the probability distribution defined as the invariant measure of an Itô stochastic differential equation in order to estimate the integrals in high dimension of the problem. The constraints related to a seismic accelerogram are developed explicitly. This methodology is validated through an application for which the available information is related to the variance of each component of the random vector representing the accelerogram, statistics on the response spectrum, on the peak ground acceleration, on the cumulative absolute velocity and on the end-values for the velocity and for the displacement.  相似文献   

WASP-10b: a 3M_J, gas-giant planet transiting a late-type K star     

D. J. Christian  N. P. Gibson  E. K. Simpson  R. A. Street  I. Skillen  D. Pollacco  A. Collier Cameron  Y. C. Joshi  F. P. Keenan  H. C. Stempels  C. A. Haswell  K. Horne  D. R. Anderson  S. Bentley  F. Bouchy  W. I. Clarkson  B. Enoch  L. Hebb  G. Hébrard  C. Hellier  J. Irwin  S. R. Kane  T. A. Lister  B. Loeillet  P. Maxted  M. Mayor  I. McDonald  C. Moutou  A. J. Norton  N. Parley  F. Pont  D. Queloz  R. Ryans  B. Smalley  A. M. S. Smith  I. Todd  S. Udry  R. G. West  P. J. Wheatley  D. M. Wilson 《Monthly notices of the Royal Astronomical Society》2009,392(4):1585-1590

We report the discovery of WASP-10b, a new transiting extrasolar planet (ESP) discovered by the Wide Angle Search for Planets (WASP) Consortium and confirmed using Nordic Optical Telescope FIbre-fed Echelle Spectrograph and SOPHIE radial velocity data. A 3.09-d period, 29 mmag transit depth and 2.36 h duration are derived for WASP-10b using WASP and high-precision photometric observations. Simultaneous fitting to the photometric and radial velocity data using a Markov Chain Monte Carlo procedure leads to a planet radius of  1.28 R _J   , a mass of  2.96 M _J   and eccentricity of ≈0.06. WASP-10b is one of the more massive transiting ESPs, and we compare its characteristics to the current sample of transiting ESP, where there is currently little information for masses greater than ≈  2 M _J   and non-zero eccentricities. WASP-10's host star, GSC 2752−00114 (USNO-B1.0 1214−0586164) is among the fainter stars in the WASP sample, with   V = 12.7  and a spectral type of K5. This result shows promise for future late-type dwarf star surveys.  相似文献   

WASP-14b: 7.3 M_J transiting planet in an eccentric orbit     

Y. C. Joshi  D. Pollacco  A. Collier Cameron  I. Skillen  E. Simpson  I. Steele  R. A. Street  H. C. Stempels  D. J. Christian  L. Hebb  F. Bouchy  N. P. Gibson  G. Hébrard  F. P. Keenan  B. Loeillet  J. Meaburn  C. Moutou  B. Smalley  I. Todd  R. G. West  D. R. Anderson  S. Bentley  B. Enoch  C. A. Haswell  C. Hellier  K. Horne  J. Irwin  T. A. Lister  I. McDonald  P. Maxted  M. Mayor  A. J. Norton  N. Parley  C. Perrier  F. Pont  D. Queloz  R. Ryans  A. M. S. Smith  S. Udry  P. J. Wheatley  D. M. Wilson 《Monthly notices of the Royal Astronomical Society》2009,392(4):1532-1538

We report the discovery of a 7.3 M _J exoplanet WASP-14b, one of the most massive transiting exoplanets observed to date. The planet orbits the 10th-magnitude F5V star USNO-B1 11118−0262485 with a period of 2.243 752 d and orbital eccentricity   e = 0.09  . A simultaneous fit of the transit light curve and radial velocity measurements yields a planetary mass of 7.3 ± 0.5 M _J and a radius of 1.28 ± 0.08 R _J. This leads to a mean density of about 4.6 g cm⁻³ making it the densest transiting exoplanets yet found at an orbital period less than 3 d. We estimate this system to be at a distance of  160 ± 20  pc. Spectral analysis of the host star reveals a temperature of  6475 ± 100 K, log  g = 4.07  cm s⁻² and   v sin  i = 4.9 ± 1.0  km s⁻¹, and also a high lithium abundance,  log  N (Li) = 2.84 ± 0.05  . The stellar density, effective temperature and rotation rate suggest an age for the system of about 0.5–1.0 Gyr.  相似文献   

Comparison of two gas-phase chemical kinetic mechanisms of ozone formation over Europe     

Youngseob Kim  Karine Sartelet  Christian Seigneur 《Journal of Atmospheric Chemistry》2009,62(2):89-119

Two recent gas-phase chemical kinetic mechanisms for tropospheric ozone formation, one based on the lumped-structure approach (CB05) and the other based on the lumped-molecule approach (RACM2), are compared for simulations of ozone over Europe. The host air quality model is POLAIR3D of the Polyphemus modeling platform. A one-month period (15 July to 15 August 2001) is simulated. Model performance is satisfactory with both mechanisms. Overall, the two mechanisms give similar results with a domain-averaged difference of 3 ppb and a mean fractional absolute difference of 5% (values averaged over the month for the daily 8-h average maximum ozone concentrations). This difference results from different treatments in the two mechanisms for both inorganic and organic chemistry. Differences in the treatment of the inorganic chemistry are due mainly to differences in the kinetics of two reactions: NO + O₃ \(\longrightarrow\) NO₂ + O₂ and NO + HO₂ \(\longrightarrow\) NO₂ + OH. These differences lead to a domain-averaged difference in ozone concentration of 5%, with RACM2 kinetics being more conducive to ozone formation. Differences in the treatment of organic chemistry lead to a domain-averaged difference in ozone concentration of 3%, with CB05 chemistry being more conducive to ozone formation. This average difference results in part from compensating effects among various VOC classes and some significant differences are identified at specific locations (the coastline of northern Africa and eastern Europe: 9%) and for specific organic classes (aldehydes, biogenic alkenes and aromatics). Differences in the treatment of the organic chemistry result from various aspects. For some VOC classes, such as aldehydes and biogenic alkenes, the more detailed explicit treatments using more model species in RACM2 lead to either greater or lower reactivity depending on the assumptions made for the oxidation products. For other VOC species, such as aromatics, the assumptions made about the major chemical oxidation pathways (aromatic alcohol formation in CB05 vs. ring opening in RACM2) affect the ozone formation significantly. Reconciliation of different chemical kinetic mechanisms will require experimental data to reduce current uncertainties in the kinetic (e.g., NO oxidation) and mechanistic (e.g., aromatics oxidation) representations of major chemical pathways.  相似文献