A Type IV Radio Burst Associated with Type III Burst,Pulsation and Spike Emissions     

Wang  M.  Xie  R.X.  Duan  C.C.  Yan  Y.H.  Sych  R.A.  Altyntsev  A.T. 《Solar physics》2003,212(2):407-424

A type IV radio burst accompanied by several normal- and reverse-drifting type III bursts, multiple long-term quasi-periodic pulsations and spikes was observed with the radio spectrometers (1.0–2.0 and 2.6–3.8 GHz) at National Astronomical Observatories of China (NAOC) on 23 September 1998. In combination with the images of Siberian Solar Radio Telescope (SSRT) of Russia, the complex and multiple magnetic structures inferred from the radio bursts reveal the existence of both large-scale and small-scale magnetic structures. This event suggests that the geometries of coronal magnetic fields contain multiple discrete electron acceleration/injection sites at different heights, and extended open and closed magnetic field lines. It can be shown that the energetic electrons gain access to open, diverging and closed field lines thus producing different types of radio bursts. From the characteristics of position, polarization, dispersion and displacement of the sources, the model of the type IV event is supported, which involves synchrotron emission from the electrons confined by the rapid scattering through the interaction of hydromagnetic wave with particles.  相似文献   

Optical colors of 56 near-Earth objects: trends with size and orbit     

C.L Dandy  A Fitzsimmons 《Icarus》2003,163(2):363-373

We present the results of BVRIZ photometry of 56 near-Earth objects (NEOs) obtained with the 1-m Jacobus Kapteyn telescope on La Palma during 2000 and 2001. Our sample includes many NEOs with particularly deep 1-μm pyroxene/olivine absorption bands, similar to Q-type asteroids. We also classify three NEOs with particularly blue colors. No D-type asteroids were found, placing an upper limit of ∼2% on the fraction of the NEO population originating in the outer main belt or the Trojan clouds. The ratio of dark to bright objects in our sample was found to be 0.40, significantly higher than current theoretical predictions. As well as classifying the NEOs, we have investigated color trends with size and orbit. We see a general trend for larger silicate objects to have shallower absorption bands but find no significant difference in the distribution of taxonomic classes at small and large sizes. Our data clearly show that different taxonomic classes tend to occupy different regions of (a, e) space. By comparing our data with current model predictions for NEO dynamical evolution we see that Q-, R-, and V-type NEOs tend to have orbits associated with “fast track” delivery from the main belt, whereas S-type NEOs tend to have orbits associated with “slow track” delivery. This outcome would be expected if space weathering occurs on time scales of >10⁶ years.  相似文献   

Reliability assessment of granular filters in embankment dams     

Roberto Mínguez  Fernando Delgado  Ignacio Escuder  Manuel G. de Membrillera 《国际地质力学数值与分析法杂志》2006,30(10):1019-1037

Empirical criteria have been used successfully to design filters of most embankment large dam projects throughout the world. However, these empirical rules are only applicable to a particular range of soils tested in laboratory and do not take into account the variability of the base material and filter particle sizes. In addition, it is widely accepted that the safety of fill dams is mainly dependent on the reliability of their filter performance. The work herein presented consists in a new general method for assessing the probability of fulfilling any empirical filter design criteria accounting for base and filter heterogeneity by means of first‐order reliability methods (FORM), so that reliability indexes and probabilities of fulfilling any particular criteria are obtained. This method will allow engineers to estimate the safety of existing filters in terms of probability of fulfilling their design criteria and might also be used as a decision tool on sampling needs and material size tolerances during construction. In addition, sensitivity analysis makes possible to analyse how reliabilities are influenced by different sources of input data. Finally, in case of a portfolio risk assessment, this method will allow engineers to compare the safety of several existing dams in order to prioritize safety investments and it is expected to be a very useful tool to evaluate probabilities of failure due to internal erosion. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Middle-ear stiffness of the bottlenose dolphin tursiops truncatus     

Miller  B.S. Zosuls  A.L. Ketten  D.R. Mountain  D.C. 《Oceanic Engineering, IEEE Journal of》2006,31(1):87-94

Previous research on the cetacean auditory system has consisted mostly of behavioral studies on a limited number of species. Little quantitative physiologic data exists on cetacean hearing. The frequency range of hearing varies greatly across different mammalian species. Differences among species correlate with differences in the middle-ear transfer function. Middle-ear transfer functions depend on the mechanical stiffness of the middle ear and the cochlear input impedance. The purpose of this study was to measure the middle-ear stiffness for the bottlenose dolphin (Tursiops truncatus), a species specialized for underwater high-frequency hearing and echolocation. Middle-ear stiffness was measured with a force probe that applied a known displacement to the stapes and measured the restoring force. The average middle-ear stiffness in ten dolphin ears was 1.37 N//spl mu/m, which is considerably higher than that reported for most terrestrial mammals. The relationship between middle-ear stiffness and low-frequency hearing cutoff in Tursiops was shown to be comparable to that of terrestrial mammals.  相似文献   

Opening angles, Lorentz factors and confinement of X-ray binary jets     

J. C. A. Miller-Jones  R. P. Fender  E. Nakar 《Monthly notices of the Royal Astronomical Society》2006,367(4):1432-1440

We present a collation of the available data on the opening angles of jets in X-ray binaries, which in most cases are small (≲10°). Under the assumption of no confinement, we calculate the Lorentz factors required to produce such small opening angles via the transverse relativistic Doppler effect. The derived Lorentz factors, which are in most cases lower limits, are found to be large, with a mean >10, comparable to those estimated for active galactic nuclei (AGN) and much higher than the commonly assumed values for X-ray binaries of 2–5. Jet power constraints do not, in most cases, rule out such high Lorentz factors. The upper limits on the opening angles show no evidence for smaller Lorentz factors in the steady jets of Cygnus X-1 and GRS 1915+105. In those sources in which deceleration has been observed (notably  XTE J1550−564  and Cygnus X-3), some confinement of the jets must be occurring, and we briefly discuss possible confinement mechanisms. It is however possible that all the jets could be confined, in which case the requirement for high bulk Lorentz factors can be relaxed.  相似文献   

Photoevaporation of protoplanetary discs – I. Hydrodynamic models     

R. D. Alexander  C. J. Clarke  J. E. Pringle 《Monthly notices of the Royal Astronomical Society》2006,369(1):216-228

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The HNCO ring in the Sgr B2 region     

Y.C. Minh  W.M. Irvine   《New Astronomy》2006,11(8):594-599

The large-scale structure associated with the 2′N HNCO peak in Sgr B2 [Minh, Y.C., Haikala, L., Hjalmarson, Å., Irvine, W.M., 1998. ApJ 498, 261 (Paper I)] has been investigated. A ring-like morphology of the HNCO emission has been found; this structure may be colliding with the Principal Cloud of Sgr B2. This “HNCO Ring” appears to be centered at (l,b) = (0.7°,−0.07°), with a radius of 5 pc and a total mass of 1.0 × 10⁵ to 1.6 × 10⁶ M. The expansion velocity of the Ring is estimated to be 30–40 km s⁻¹, which gives an expansion time scale of 1.5 × 10⁵ year. The morphology suggests that collision between the Ring and the Principal Cloud may be triggering the massive star formation in the Sgr B2 cloud sequentially, with the latest star formation taking place at the 2′N position. The chemistry related to HNCO is not certain yet, but if it forms mainly via reaction with the evaporated OCN⁻ from icy grain mantles, the observed enhancement of the HNCO abundance can be understood as resulting from shocks associated with the collision between the Principal Cloud and the expanding HNCO Ring.  相似文献   

Radiation exposure and Mission Strategies for Interplanetary Manned Missions (REMSIM)   总被引：1，自引：0，他引：1  

C. Cougnet  N. B. Crosby  S. Eckersley  C. Foullon  V. Guarnieri  S. Guatelli  D. Heynderickx  A. Holmes-Siedle  C. Lobascio  S. Masiello  P. Nieminen  G. Parisi  P. Parodi  M. A. Perino  M. G. Pia  R. Rampini  P. Spillantini  V. Tamburini  E. Tracino 《Earth, Moon, and Planets》2004,94(3-4):279-285

Cosmic radiation is an important problem for human interplanetary missions. The “Radiation Exposure and Mission Strategies for Interplanetary Manned Missions–REMSIM” study is summarised here. They are related to current strategies and countermeasures to ensure the protection of astronauts from radiation during interplanetary missions, with specific reference to: radiation environment and its variability; radiation effects on the crew; transfer trajectories and associated fluences; vehicle and surface habitat concepts; passive and active shielding concepts; space weather monitoring and warning systems.  相似文献   

Erratum: Towards cosmological concordance on galactic scales     

Frank C. van den Bosch  H. J. Mo  Xiaohu Yang 《Monthly notices of the Royal Astronomical Society》2004,348(2):736-736

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The D-CIXS X-ray mapping spectrometer on SMART-1     

M Grande  R BrowningN Waltham  D ParkerS.K Dunkin  B KentB Kellett  C.H PerryB Swinyard  A PerryJ Feraday  C HoweG McBride  K PhillipsJ Huovelin  P MuhliP.J Hakala  O VilhuJ Laukkanen  N ThomasD Hughes  H AlleyneM Grady  R LundinS Barabash  D BakerP.E Clark  C.D MurrayJ Guest  I CasanovaL.C d'Uston  S MauriceB Foing  D.J Heather  V FernandesK Muinonen  S.S RussellA Christou  C OwenP Charles  H KoskinenM Kato  K SipilaS Nenonen  M HolmstromN Bhandari  R ElphicD Lawrence 《Planetary and Space Science》2003,51(6):427-433

The D-CIXS Compact X-ray Spectrometer will provide high quality spectroscopic mapping of the Moon, the primary science target of the ESA SMART-1 mission. D-CIXS consists of a high throughput spectrometer, which will perform spatially localised X-ray fluorescence spectroscopy. It will also carry a solar monitor, to provide the direct calibration needed to produce a global map of absolute lunar elemental abundances, the first time this has been done. Thus it will achieve ground breaking science within a resource envelope far smaller than previously thought possible for this type of instrument, by exploiting two new technologies, swept charge devices and micro-structure collimators. The new technology does not require cold running, with its associated overheads to the spacecraft. At the same time it will demonstrate a radically novel approach to building a type of instrument essential for the BepiColombo mission and potential future planetary science targets.  相似文献