排序方式： 共有25条查询结果，搜索用时 453 毫秒
1.
2.
Valentí Bosch-Ramon 《Astrophysics and Space Science》2007,309(1-4):321-331
Microquasar (MQ) jets are sites of particle acceleration and synchrotron emission. Such synchrotron radiation has been detected
coming from jet regions of different spatial scales, which for the instruments at work nowadays appear as compact radio cores,
slightly resolvedradio jets, or (very) extended structures (e.g. Mirabel and Rodríguez, 1999; Fender, 2001; Corbel et al., 2002). Because of the presence of relativistic particles and dense photon, magnetic and matter fields, these outflows are also
the best candidates to generate the very high-energy (VHE) gamma-rays detected coming from two of these objects, LS 5039 and
LS I +61 303 (Aharonian, 2005; Aharonian et al., 2006a; and Albert, 2006, respectively), and may be contributing significantly to the X-rays emitted from the MQ core (e.g. Markoff et al., 2001; Bosch-Ramon et al., 2005a). In addition, beside electromagnetic radiation, jets at different scales are producing some amount of leptonic and hadronic
cosmic rays (CR), and evidences of neutrino production in these objects may be eventually found. In this work, we review on
the different physical processes that may be at work in or related to MQ jets. The jet regions capable to produce significant
amounts of emission at different wavelengths have been reduced to the jet base, the jet at scales of the order of the size
of the system orbital semi-major axis, the jet middle scales (the resolved radio jets), and the jet termination point. The
surroundings of the jet could be sites of multiwavelength emission as well, deserving also an insight. We focus on those scenarios,
either hadronic or leptonic, in which it seems more plausible to generate both photons from radio to VHE and high-energy neutrinos.
We briefly comment as well on the relevance of MQ as possible contributors to the galactic CR in the GeV–PeV range. 相似文献
3.
Diego F. Torres Shu Zhang Olaf Reimer Xavier Barcons Amalia Corral Valentí Bosch-Ramon Josep M. Paredes Gustavo E. Romero Jin Qu Werner Collmar Volker Schönfelder Yousaf Butt 《Astrophysics and Space Science》2007,309(1-4):17-21
The COMPTEL unidentified source GRO J 1411-64 was observed by INTEGRAL and XMM-Newton in 2005. The Circinus Galaxy is the
only source detected within the 4σ location error of GRO J1411-64, but in here excluded as the possible counterpart. At soft X-rays, 22 reliable and statistically
significant sources (likelihood >10) were extracted and analyzed from XMM-Newton data. Only one of these sources, XMMU J141255.6-635932,
is spectrally compatible with GRO J1411-64 although the fact the soft X-ray observations do not cover the full extent of the
COMPTEL source position uncertainty make an association hard to quantify and thus risky. At the best location of the source,
detections at hard X-rays show only upper limits, which, together with MeV results obtained by COMPTEL suggest the existence
of a peak in power output located somewhere between 300–700 keV for the so-called low state. Such a spectrum resembles those
in blazars or microquasars, and might suggest at work by the models accordingly. However, an analysis using a microquasar
model consisting on a magnetized conical jet filled with relativistic electrons, shows that it is hard to comply with all
observational constrains. This fact and the non-detection at hard X-rays introduce an a-posteriori question mark upon the
physical reality of this source, what is discussed here. 相似文献
4.
Valentí Bosch-Ramon Gustavo E. Romero Josep M. Paredes 《Astrophysics and Space Science》2005,297(1-4):119-129
Population studies of EGRET gamma-ray sources indicate that there is a distinctive population of bright sources at low galactic
latitudes. The sources have a distribution consistent with that of young galactic objects, with a concentration toward the
inner spiral arms. There is a subgroup that displays strong variability with timescales from days to months. Following an
earlier suggestion by Kaufman Bernadó et al. (2002), we explore the possibility that these sources could be high-mass microquasars.
Detailed models for the gamma-ray emission that include inverse Compton interactions of electrons in the relativistic jets
and photons from all local fields (stellar UV photons, synchrotron photons, soft X-ray photons from the accretion disk, and
hard X-ray photons from a corona) are presented. We conclude that microquasars are excellent candidates for the parent population
of the subgroup of variable low-latitude EGRET sources. 相似文献
5.
Valentín Bujarrabal 《Astrophysics and Space Science》2008,313(1-3):209-214
Planetary nebulae (PNe) are formed in a very fast process. In just about 1000 years, the nebula evolves from a spherical and
slowly expanding AGB envelope to a PN, with usually axial symmetry and high axial velocities. Molecular lines are known to
probe most of the nebular material in young PNe and protoplanetary nebulae (PPNe), and are therefore very useful to study
such an impressive evolution. Many quantitative results on these objects have been so obtained, including general structure,
total mass and density distribution, kinetic temperatures, velocity fields, etc. Existing observations probe both the gas
accelerated by post-AGB shocks and the quiescent components. But the study of crucial regions to understand PN formation (recently
shocked shells, regions heated by the stellar UV and inner rotating disks) requires observations at higher frequency and with
better spatial resolution.
相似文献
6.
Valentí Rull José A. López-Sáez Teresa Vegas-Vilarrúbia 《Journal of Paleolimnology》2008,40(1):399-411
This paper evaluates the potential usefulness of non-pollen palynomorphs or NPPs (microfossils other than pollen and spores
present in palynological preparations) contained in lake sediments in the paleolimnological reconstruction of high altitude
environments (>4,000 m) from the Venezuelan Andes. A synthetic, quantitative approach is employed, instead of the classical
analytical and mostly qualitative approach commonly used so far for NPPs. The main sources of variation are the Pediastrum–Botryococcus alternation and the relationship between these two algae and animal remains such as Acari legs, postabdomina of Cladocera,
mandibles of other invertebrates, and an unknown type called LVA-1. Other significant microfossils are remains of Rivularia-type and turbellarian oocytes, including Gyratrix. The sequence initiates around 15,000 calibrated years before present (cal BP) with the deglaciation of the lake catchment,
high water levels and still cold climates. A phase of lower lake levels was recorded between about 12,000 and 6,000 cal BP.
Temperatures increased by around 9,000 and 7,000 cal BP, and then decreased until 6,000 cal BP. Since that time, both lake
levels and temperature increased again and stabilized at about 4,000 cal BP, when they reach modern-like values. These results
show a good agreement with previous studies based on pollen, diatom and oxygen isotope analyses, and provide additional paleoecological
information, as for example the possibility of a previously unrecorded Younger Dryas signal. The inclusion of quantitative
NPP analysis in routine paleolimnological studies using synthetic methods is thus recommended. Possible future improvements
are suggested, mainly those related with the development and use of NPP modern analogs. 相似文献
7.
Regional and species specific sexual reproductive patterns of three zooxanthellate scleractinian corals across the Eastern Tropical Pacific 
下载免费PDF全文
下载免费PDF全文 Jeimy D. Santiago‐Valentín Susan B. Colley Peter W. Glynn Amilcar L. Cupul‐Magaña Ramon A. López‐Pérez Fabián A. Rodríguez‐Zaragoza Francisco Benítez‐Villalobos Eric Bautista‐Guerrero Denisse A. Zavala‐Casas Alma P. Rodríguez‐Troncoso 《Marine Ecology》2018,39(2)
Sexual reproduction of zooxanthellate scleractinian corals in the Eastern Tropical Pacific (ETP) is influenced by the interactive effects of regional and local oceanographic conditions, as well as a variety of other environmental factors. Differences in spatial and temporal gamete development and reproductive patterns of three widespread scleractinian corals of this region—Pocillopora damicornis (branching colony morphology, characterized as hermaphrodite broadcaster), Pavona gigantea (massive colonies, characterized as gonochoric broadcaster/sequential co‐sexually hermaphroditic) and Porites panamensis (encrusting colonies, characterized as gonochoric brooder)—were evaluated at local and regional scales across the ETP. This area extended from the Gulf of California (24°N) to the southern coast of Ecuador (–1°S), including offshore islands, using existing data pooled from prior studies. Predictive models were employed based on environmental variables: sea surface temperature, daylight hours, diffuse attenuation co‐efficient at 490 nm and photosynthetically active radiation. Datasets were extracted from satellite images ( https://oceancolor.gsfc.nasa.gov ) and analysed using WAM_STATIST ver. 6.33® software to obtain monthly average data from each site. The spatial (region, sub‐region and site) and seasonal (wet, dry) variation in reproductive activity (% colonies with gametes) differed among the three species; significant interactions were season × sub‐region for P. damicornis, season × site (sub‐region) for P. gigantea, and season × site for P. panamensis, for which sub‐region was not considered as a factor. The predictive models also suggest that gamete production/maturation of P. damicornis and P. gigantea is influenced by local differences in sea surface temperature and daylight hours. Porites panamensis was not correlated with any environmental variable examined. Variations in local and regional reproductive developmental patterns are likely an acclimatization response by each species imposed by the timing and duration of local stressor events. This analysis has provided insights into the diverse local and regional physical drivers that affect species responses and acclimatization in sexual reproduction across the ETP. 相似文献
8.
9.
Frank M. Rieger Valentí Bosch-Ramon Peter Duffy 《Astrophysics and Space Science》2007,309(1-4):119-125
We consider the acceleration of energetic particles by Fermi processes (i.e., diffusive shock acceleration, second order Fermi
acceleration, and gradual shear acceleration) in relativistic astrophysical jets, with particular attention given to recent
progress in the field of viscous shear acceleration. We analyze the associated acceleration timescales and the resulting particle
distributions, and discuss the relevance of these processes for the acceleration of charged particles in the jets of AGN,
GRBs and microquasars, showing that multi-component powerlaw-type particle distributions are likely to occur. 相似文献
10.
Delineating coastal groundwater discharge processes in a wetland area by means of electrical resistivity imaging, 224Ra and 222Rn 下载免费PDF全文
下载免费PDF全文 Mario Zarroca Rogelio Linares Valentí Rodellas Jordi Garcia‐Orellana Carles Roqué Joan Bach Pere Masqué 《水文研究》2014,28(4):2382-2395
Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra‐enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra‐rich groundwater have induced high activities of Ra isotopes and 222Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (224Ra, 222Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater‐fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献