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41.
W. -H. Ip 《Astrophysics and Space Science》1974,31(1):57-79
The problem of planetary accretion in a jet stream is studied using the model developed by Alfvén and Arrhenius. We find that there are basically three types of planetary accretion: namely, fast process
c
<
i
, slow process
c
~
i
and delayed process
c
>
i
where
c
is the characteristic time of the occurrence of catastrophic accretion and
i
the time-scale of mass injection to the planetary system (3×108 yr). These different time scales of accretion are found to be closely related to the primordial thermal profiles and equatorial inclinations of the planets. Finally, Venus' retrograde rotational spin is shown to be a possible result of accretion process in a jet stream. 相似文献
42.
43.
Joachim Müller Sven Simon Yung-Ching Wang Uwe Motschmann Daniel Heyner Josef Schüle Wing-Huen Ip Gero Kleindienst Gavin J. Pringle 《Icarus》2012,218(1):666-687
During the first and second Mercury flyby the MESSENGER spacecraft detected a dawn side double-current sheet inside the Hermean magnetosphere that was labeled the “double magnetopause” (Slavin, J.A. et al. [2008]. Science 321, 85). This double current sheet confines a region of decreased magnetic field that is referred to as Mercury’s “dayside boundary layer” (Anderson, M., Slavin, J., Horth, H. [2011]. Planet. Space Sci.). Up to the present day the double current sheet, the boundary layer and the key processes leading to their formation are not well understood. In order to advance the understanding of this region we have carried out self-consistent plasma simulations of the Hermean magnetosphere by means of the hybrid simulation code A.I.K.E.F. (Müller, J., Simon, S., Motschmann, U., Schüle, J., Glassmeier, K., Pringle, G.J. [2011]. Comput. Phys. Commun. 182, 946–966). Magnetic field and plasma results are in excellent agreement with the MESSENGER observations. In contrast to former speculations our results prove this double current sheet may exist in a pure solar wind hydrogen plasma, i.e. in the absence of any exospheric ions like sodium. Both currents are similar in orientation but the outer is stronger in intensity. While the outer current sheet can be considered the “classical” magnetopause, the inner current sheet between the magnetopause and Mercury’s surface reveals to be sustained by a diamagnetic current that originates from proton pressure gradients at Mercury’s inner magnetosphere. The pressure gradients in turn exist due to protons that are trapped on closed magnetic field lines and mirrored between north and south pole. Both, the dayside and nightside diamagnetic decreases that have been observed during the MESSENGER mission show to be direct consequences of this diamagnetic current that we label Mercury’s “boundary-layer-current“. 相似文献
44.
This paper juxtaposes the actual areas of settlement and settlement activities of Chinese migrants in Brisbane’s southern
suburbs since the mid-1980s, with the concomitant, ‘government planned’ construction of the city’s Chinatown as an ‘exotic,’
‘ethnic,’ and ‘cosmopolitan’ landmark. It argues that while the latter, as with Chinatowns in other Australian and world cities,
has continued to appropriate the symbols of so-called ‘Chineseness’ to sell the locale to non-Chinese, the former, in recalling
the notion of ‘ethnoburbia,’ significantly evinces actual Chinese migrants’ agency and role in place-making. In the process,
these migrants have not only established a local, ethnically meaningful environment, but also challenged the still current
metonymic Western image of the Chinese as preferring life in ‘ethnic’ urban enclaves that had its origin from early Chinese
settlement and fundamentally detached from the lives of other ethnic groups per se. Indeed greater recognition and comprehension of such locales may go a long way to illustrate that many Chinese living in
Australia today do not fit the territorial, place-based identity often associated with them in the imagination of mainstream
society. 相似文献
45.
The newly detected oxygen atmosphere of Europa is modeled by invoking charged particle sputtering with H2O and O2molecules as the main ejecta. The magnetospheric corotating ions could provide the required source strength (∼3 × 1026sec−1) of O2molecules if a fraction (∼20%) of the exospheric ions were recycled to Europa's surface where they produce additional sputtering product. Two exospheric components are expected to form: an extended corona with a size of a few satellite radii which is composed of sputtered molecules in ballistic motion, and a thermal population with a surface density of 108–109cm−3and a scale height of about 20 km. The electron impact ionization of this exosphere would lead to an Io-like interaction with the jovian magnetosphere with a field-aligned Birkeland current of about 5 × 105A. 相似文献
46.
W.-H. Ip 《Planetary and Space Science》1979,27(2):121-125
If the structure of the magnetic field and electric current in the cometary type I tail can be represented by an electric current circuit, disruption of the cross-tail current system may lead to a current discharging through the cometary ionosphere, and the dissipation of the magnetic energy stored in the tail. From the point of view of energy budget, a tail-aligned magnetic field on the order of 10γ will be sufficient to produce a strong ionization effect of the cometary atmosphere. 相似文献
47.
Very often, inexact, uncertain, or vague hydrological data are encountered in water researches. Statistical and fuzzy set theories are applied to deal with hydrological uncertainty problems. In this paper, the basic concept of the rough set theory is introduced and its application to hydrological data is illustrated. The proposed method is applied to water environment and environment quality evaluation of the Hang Jiang River, a major branch of the Yangtze River, in China. Our numerical applications suggest that the rough set theory is a useful tool for analysis of inexact, uncertain, or vague hydrological data. 相似文献
48.
49.
50.
The issue of water shortage and related eco-environmental degradation in North China is one of the major emerging problems
in China. Precipitation is the most key factor for water resources. Based on the historical flood/dryness grade dataset during
the period of 1470–2000 obtained from 25 gauging stations in North China, the multi-scale variability and trends are analyzed
by means of power spectral and continuous wavelet transform. It is found that the precipitation is characterized by obvious
seasonal changes, quasi biennial oscillations, inter-annual 4–7 year component and inter-decadal 19-year periodicity. The
MK test results showe that step changes occurred around 1914 and 1964 in the annual precipitation. As for the historical flood/dryness
grade time series, it is characterized by 4∼5 year ENSO mode inter-annual oscillation, quasi-10 year inter-decadal variability,
quasi-24 year component and 50–80 year centurial periodicity. However, the scales of these variations have decreased significantly
since the 1970s. The trend for precipitation change in North China has been negative for last 30 years. Further research shows
that North China will continue to become dryer until 2015 and may change to a wetter regime after 2020. These findings should
be helpful for future decision-making to ensure sustainable water resource management in North China. 相似文献