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281.
Xiaoning Pan 《Icarus》2004,172(2):521-525
Hydrogen peroxide (H2O2) is one of the minor constituents of the water ice covered surfaces of the jovian satellites Europa, Ganymede, and Callisto. Here we demonstrate that H2O2 production may be initiated by the dissociative electron attachment (DEA) of low-energy electrons (LEEs) to water molecules. Electronic excitation or ionization by electrons also contributes to H2O2 formation at higher electron energies. Finally, we show that hydroperoxyl (HO2) radicals could be formed on the surfaces of icy satellites by LEE impact. 相似文献
282.
We have found that 0.8 MeV proton irradiation of crystalline H2O-ice results in temperature dependent amorphization. The H2O-ice's phase was determined using the near infrared spectrum from 1.0 μm (10,000 cm−1) to 2.5 μm (4000 cm−1). In crystalline H2O-ice, the 1.65-μm (6061 cm−1) band is strong while it is nearly absent in the amorphous spectrum [Schmitt, B., Quirico, E., Trotta, F., Grundy, W.M., 1998. In: Schmitt, B., de Bergh, C., Festou, M. (Eds.), Solar System Ices. Kluwer Academic, Norwell, MA, 1998, pp. 199-240]. In this experiment, at low temperatures (9, 25, and 40 K), irradiation of crystalline H2O-ice produced the amorphous H2O-ice's spectrum. However, at 50 K, some crystalline absorptions persisted after irradiation and at 70 and 100 K the crystalline spectrum showed only slight changes after irradiation. Our results agree with previous H2O-ice irradiation studies examining the crystalline peaks near 44 and 62 μm by Moore and Hudson [Moore, M.H., Hudson, R.L., 1992. Astrophys. J. 401, 353-360] and near 3.07 μm by Strazzulla et al. [Strazzulla, G., Baratta, G.A., Leto, G., Foti, G., 1992. Europhys. Lett. 18, 517-522] and by Leto and Baratta [Leto, G., Baratta, G.A., 2003. Astron. Astrophys. 397, 7-13]. We present a method of measuring band areas to quantify the phase and radiation dose of icy Solar System surfaces. 相似文献
283.
“The investigation into the possible effects of cosmic rays on living organisms will also offer great interest.” – Victor F. Hess, Nobel Lecture, December 12, 1936High-energy radiation bursts are commonplace in our Universe. From nearby solar flares to distant gamma ray bursts, a variety of physical processes accelerate charged particles to a wide range of energies, which subsequently reach the Earth. Such particles contribute to a number of physical processes occurring in the Earth system. A large fraction of the energy of charged particles gets deposited in the atmosphere, ionizing it, causing changes in its chemistry and affecting the global electric circuit. Remaining secondary particles contribute to the background dose of cosmic rays on the surface and parts of the subsurface region. Life has evolved over the past ∼3 billion years in presence of this background radiation, which itself has varied considerably during the period [1], [2], [3]. As demonstrated by the Miller–Urey experiment, lightning plays a very important role in the formation of complex organic molecules, which are the building blocks of more complex structures forming life. There is growing evidence of increase in the lightning rate with increasing flux of charged particles. Is there a connection between enhanced rate of cosmic rays and the origin of life? Cosmic ray secondaries are also known to damage DNA and cause mutations, leading to cancer and other diseases. It is now possible to compute radiation doses from secondary particles, in particular muons and neutrons. Have the variations in cosmic ray flux affected the evolution of life on earth? We describe the mechanisms of cosmic rays affecting terrestrial life and review the potential implications of the variation of high-energy astrophysical radiation on the history of life on earth. 相似文献
284.
285.
Jorge A. Combi Juan F. Albacete Colombo Gustavo E. Romero Paula Benaglia 《Astrophysics and Space Science》2007,309(1-4):395-399
We report hard X-ray emission of the non-thermal supernova remnant G337.2+0.1. The source presents centrally filled and diffuse
X-ray emission. A spectral study confirms that the column density of the central part of the object is about N
H∼5.9(±1.5)×1022 cm−2 and its X-ray spectrum is well represented by a single power-law with a photon index Γ=0.96±0.56. Detailed spectral analysis indicates that the outer region is highly absorbed and quite softer than the inner
region. Characteristics already observed in other well-known X-ray plerions. Based on the gathered information, we confirm
the SNR nature of G337.2+0.1, and suggest that the central region of the source is a pulsar wind nebula (PWN), originated
by an energetic though yet undetected pulsar. 相似文献
286.
We discuss the possibility of observing ultra high energy cosmic ray sources in high energy gamma rays. Protons propagating
away from their accelerators produce secondary electrons during interactions with cosmic microwave background photons. These
electrons start an electromagnetic cascade that results in a broad band gamma ray emission. We show that in a magnetized Universe
(B≳10−12 G) such emission is likely to be too extended to be detected above the diffuse background. A more promising possibility comes
from the detection of synchrotron photons from the extremely energetic secondary electrons. Although this emission is produced
in a rather extended region of size ∼10 Mpc, it is expected to be point-like and detectable at GeV energies if the intergalactic
magnetic field is at the nanogauss level.
相似文献
287.
The electrical conductivity and electrical charge on the aerosols in atmosphere of Titan are computed for altitudes between 0 and 400 km. Ionization of methane and nitrogen due to galactic cosmic rays (GCR) is important at night where these ions are converted to ion clusters such as CH+5CH4, C7H+7, C4H+7, and H4C7N+. The ubiquitous aerosols observed also play an important role in determining the charge distribution in the atmosphere. Because polycyclic aromatic hydrocarbons (PAHs) are expected in Titan's atmosphere and have been observed in the laboratory and found to be electrophilic, we consider the formation of negative ions. During the night, the very smallest molecular complexes accept free electrons to form negative ions. This results in a large reduction of the electron abundance both in the region between 150 and 350 km over that predicted when such aerosols are not considered. During the day time, ionization by photoemission from aerosols irradiated by solar ultraviolet (UV) radiation overwhelms the GCR-produced ionization. The presence of hydrocarbon and nitrile minor constituents substantially reduces the UV flux in the wavelength band from the cutoff of CH4 at 155 to 200 nm. These aerosols have such a low ionization potential that the bulk of the solar radiation at longer wavelengths is energetic enough to produce a photoionization rate sufficient to create an ionosphere even without galactic cosmic ray (GCR) bombardment. At altitudes below 60 km, the electron and positive ion abundances are influenced by the three-body recombination of ions and electrons. The addition of this reaction significantly reduces the predicted electron abundance over that previously predicted. Our calculations for the dayside show that the peaks of the charge distributions move to larger values as the altitude increases. This variation is the result of the increased UV flux present at the highest altitudes. Clearly, the situation is quite different than that for the night where the peak of the distribution for a particular size is nearly constant with altitude when negative ions are not present. The presence of very small aerosol particles (embryos) may cause the peak of the distribution to decrease from about 8 negative charges to as little as one negative charge or even zero charge. This dependence on altitude will require models of the aerosol formation to change their algorithms to better represent the effect of charged aerosols as a function of altitude. In particular, the charge state will be much higher than previously predicted and it will not be constant with altitude during the day time. Charging of aerosol particles, whether on the dayside or nightside, has a major influence on both the electron abundance and electrical conductivity. The predicted conductivities are within the measurement range of the HASI PWA instrument over most but not all, of the altitude range sampled. 相似文献
288.
“重庆雾害”课题组 《成都信息工程学院学报》1992,(2)
本文将所建立的重庆雾一维模式简化移植到微机上,主要进行辐射雾的形成时间和浓雾预报。模式在386机上作12小时预报计需机时25分钟。通过对1990年11月~1991年2月24次的个例计算,预报成功率达70%,雾形成时间平均误差为1.7小时。 相似文献
289.
The Kepler problem including radiation pressure and drag is treated. The equation of the orbit is derived and the scalar and vector integrals of motion are obtained by direct operation on the vector form of the equation of motion. 相似文献
290.
《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(4):203-211
Direct solar radiation integrated over one year is a function of latitude and time of year, and topographic slope , aspect and shadowing control the local distribution. Recently, several spatial models have been developed which estimate the radiation balance based on digital elevation models, taking into account aspect, slope and shadowing effects. For the periglacial realm, these models are integrated both in models estimating possible occurrence of mountain permafrost and in studies of active layer dynamics. In this article our aim is to assess and discuss sensitivity and validations of the radiation balance model SRAD, in comparison with two other topographic-based radiation models. The study site and field data are from Finse, Southern Norway. 相似文献