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961.
K. Slezakova M. C. Pereira M. A. Reis M. C. Alvim-Ferraz 《Journal of Atmospheric Chemistry》2007,58(1):55-68
Epidemiological studies initially considered the impact of total solid particles on human health, but according to the acquired
knowledge about the worse effect of smaller particles, those studies turned to consider the impact of PM10. However, for the last decade PM2.5 began to be more important, once as they are smaller they can penetrate deeper in the lungs, being possible their trapping
in alveoli and worse effects on human health. Therefore, more information on PM2.5 should be provided namely concerning the levels and elemental composition. Considering the relevance of traffic on the emission
of particles of small sizes, this work included the detailed characterization of PM10 and PM2.5, sampled at two sites directly influenced by traffic, as well as at two reference sites, aiming a further evaluation of the
influence of PM10 and PM2.5 on public health. The specific objectives were to study the influence of traffic emission on PM10 and PM2.5 characteristics, considering concentration, size distribution and elemental composition. PM10 and PM2.5 samples were collected using low-volume samplers; the element analyses were performed by particle induced X-ray emission
(PIXE). At the sites influenced by traffic emissions PM10 and PM2.5 concentrations were 7–9 and 6–7 times higher than at the background sites. The presence of 17 elements (Mg, Al, Si, P, S,
Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn and Pb) was determined in both PM fractions; particle metal contents were 3–44 and
3–27 times higher for PM10 and PM2.5, respectively, than at the backgrounds sites. The elements originated mostly from anthropogenic activities (S, K, V, Mn,
Ni, Zn and Pb) were predominantly present in PM2.5, while the elements mostly originated from crust (Mg, Al, Si and Ca) predominantly occurred in PM2.5–10. The results also showed that in coastal areas sea salt spray is an important source of particles, influencing PM concentration
and distributions (PM10 increased by 46%, PM2.5/PM10 decreased by 26%), as well as PM compositions (Cl in PM10 was 11 times higher). 相似文献
962.
963.
S.W. Allen G.B. Taylor P.E.J. Nulsen R.M. Johnstone L.P. David S. Ettori A.C. Fabian W. Forman C. Jones B. McNamara 《Monthly notices of the Royal Astronomical Society》2001,324(4):842-858
We examine the properties of the X-ray gas in the central regions of the distant ( z =0.46) , X-ray luminous cluster of galaxies surrounding the powerful radio source 3C 295, using observations made with the Chandra Observatory . Between radii of 50 and 500 kpc, the cluster gas is approximately isothermal with an emission-weighted temperature, kT ∼5 keV . Within the central 50-kpc radius this value drops to kT ∼3.7 keV . The spectral and imaging Chandra data indicate the presence of a cooling flow within the central 50-kpc radius of the cluster, with a mass deposition rate of approximately 280 M⊙ yr−1 . We estimate an age for the cooling flow of 1–2 Gyr , which is approximately 1000 times older than the central radio source. We find no evidence in the X-ray spectra or images for significant heating of the X-ray gas by the radio source. We report the detection of an edge-like absorption feature in the spectrum for the central 50-kpc region, which may be caused by oxygen-enriched dust grains. The implied mass in metals seen in absorption could have been accumulated by the cooling flow over its lifetime. Combining the results on the X-ray gas density profile with radio measurements of the Faraday rotation measure in 3C 295, we estimate the magnetic field strength in the region of the cluster core to be B ∼12 μG . 相似文献
964.
Martin A. Zwaan † 《Monthly notices of the Royal Astronomical Society》2001,325(3):1142-1148
Five galaxy groups with properties similar to those of the Local Group have been surveyed for H i clouds with the Arecibo Telescope. In total 300 pointings have been observed on grids of approximately 2.5×1.5 Mpc2 centred on the groups. The 4.5 σ detection limit on the minimal detectable H i masses is approximately 7×106 M⊙ ( H 0 =65 km s−1 Mpc−1 ) . All detections could be attributed to optical galaxies; no significant detections of H i clouds have been made. This null result leads to the conclusion that the total H i mass of intragroup clouds must be less than 10 per cent of the total H i mass of galaxy groups and less than 0.05 per cent of the dynamical mass. The recent hypothesis that Galactic high-velocity clouds are Local Group satellite galaxies is highly inconsistent with these observations. 相似文献
965.
H.C. Thomas L. Dunne M.S. Clemens P. Alexander S. Eales D.A. Green 《Monthly notices of the Royal Astronomical Society》2002,329(4):747-758
We present matched-resolution VLA H i and SCUBA 850-μm maps of 20 IRAS -bright galaxies. Of the galaxies observed, two were not detected in H i and two were detected in absorption. The H i distributions of the galaxies have a range of morphologies. Some of the systems appear H i deficient in the central regions which could be due to a high conversion rate of H i into molecules or H i absorption. In contrast to the H i , the 850-μm emission has a smooth distribution which is concentrated towards the optical centre of each galaxy. We also find evidence for 850-μm emission extending to the periphery of the optical disc in some of the galaxies. Finally, we note that the relative lack of 850-μm emission when compared with H i does not necessarily mean that the atomic gas and dust do not have similar mass distributions. 相似文献
966.
Hard X-ray states and radio emission in GRS 1915+105 总被引:1,自引:0,他引:1
M.Klein-Wolt R. P.Fender G. G.Pooley T.Belloni S.Migliari E. H.Morgan M.van der Klis 《Monthly notices of the Royal Astronomical Society》2002,331(3):745-764
We compare simultaneous Ryle Telescope radio and Rossi X-Ray Timing Explorer X-ray observations of the galactic microquasar GRS 1915+105, using the classification of the X-ray behaviour in terms of three states as previously established. We find a strong (one-to-one) relation between radio oscillation events and series of spectrally hard states in the X-ray light curves, if the hard states are longer than ∼100 s and are 'well separated' from each other. In all other cases the source shows either low-level or high-level radio emission, but no radio oscillation events. During intervals when the source stays in the hard spectral state for periods of days to months, the radio behaviour is quite different; during some of these intervals a quasi-continuous jet is formed with an almost flat synchrotron spectrum extending to at least the near-infrared. Based on the similarities between the oscillation profiles at different wavelengths, we suggest a scenario which can explain most of the complex X-ray:radio behaviour of GRS 1915+105. We compare this behaviour with that of other black hole sources, and challenge previous reports of a relation between spectrally soft X-ray states and the radio emission. 相似文献
967.
Henry Florence Bockelée-Morvan Dominique Crovisier Jacques Wink Jörn 《Earth, Moon, and Planets》2002,90(1-4):57-60
CO was observed on March 11, 1997 in comet Hale–Bopp with theIRAM Plateau de Bure interferometer. The maps show evidence for
asymmetrical patterns, due to the Existence of CO jets. Analysis of the spectra and their velocity shifts shows that there
is a spiral CO jet rotating in a plane almost perpendicular to the sky plane.This is the first time that rotating jets are
observed for parent molecules.We have developed a 3-D model simulating rotating spiral jets of CO gas.We present here the
comparison between the observations and our model. 相似文献
968.
Shan-Jie Qian A. Kraus Xi-Zhen Zhang T. P. Krichbaum A. Witzel J. A. Zensus National Astronomical Observatories Chinese Academy of Sciences Beijing Max-Planck-Institut fur Radioastronomie Auf dem Hugel Bonn Germany 《中国天文和天体物理学报》2002,2(4):325-346
We present a detailed analysis of multi-frequency observations of linear polarization in the intraday variable quasar 0917+624 (z = 1.44). The observations were made in May 1989 at five frequencies (1.4, 2.7, 5.0, 8.3 and 15GHz) with the VLA and the Effelsberg 100 m-telescope and in December 1988 at two frequencies (2.7 and 5.0 GHz) with the latter. It is shown that the relationship between the variations of the polarized and total flux density is highly wavelength dependent, and the multi-frequency polarization behavior may be essential for investigating the mechanisms causing these variations. It is shown that the variations observed at 20 cm can be interpreted in terms of refractive interstellar scintillation. However, after subtracting the variation due to scintillation, three 'features' emerged in the light-curve of the polarized flux density, indicating an additional variable component. Interestingly, these features are shown to be correlated with the variations at 2-6 cm, thus indicating that thes 相似文献
969.
Fifty-three spectrograms in the optical region (3700–7300 Å) with the spectral resolution ~8 Å have been obtained for the Seyfert nucleus of the galaxy NGC 3227 with the 6-m telescope on January 1977, while the nucleus was in the historically important epoch of its extreme maximum brightness. Width of the slit was 1″, length of the box during the spectra measurements was 1.5″. Data obtained by us and those compiled from literature showed that profiles of the Balmer lines Hα, Hβ and Hγ are different, evidencing that the gas emitting these lines is highly self-absorbed. It was shown that narrow components of the profiles revealed by Rubin and Ford kept their positions (radial velocities) over 25 years. The components showed intensity variations compared to the central one from minimum to maximum of the nucleus brightness. The same variations were observed by us earlier in the emission line profiles of the NGC 7469 nucleus spectrum. Narrow profile components can reflect long-lived flows or jets in the broad line region (BLR). Obtained facts evidenced that long-lived gas streams and flows causing narrow components of broad line profiles presented not only when BLR of accretion disc is strong but when BLR of accretion disc declined. Blue bump at radial velocity of ?5000 km/s in Hγ profile was revealed in spectra of high states of the nucleus, which disappeared in low state. One of the interpretations of this event can be in the framework of a model of one-sided or two-sided gas ejection during the high state of the nucleus, positive radial velocities of which being screened out by a circumnuclear disk. 相似文献
970.