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41.
J. Hildebrandt A. Krüger I.M. Chertok V.V. Fomichev R.V. Gorgutsa 《Solar physics》1998,181(2):337-349
Usually the gyrosynchrotron emission of microwave bursts from electron populations with a power-law (PL) energy distribution has been considered under the assumption that the spectral index of the distribution is constant over a wide range of energies. Meanwhile, there is strong evidence, in particular from hard X-ray and -ray, but also from cm/mm wavelength radio observations, that in many solar flare events the spectrum of the emitting electrons is characterized by a significant hardening at energies above 100–500 keV. We present some examples of calculated microwave burst spectra at cm/mm wavelengths taking into account the above evidence. It is shown that a break in the energy spectrum of the PL electrons can indeed result in a spectral hardening sometimes observed in microwave bursts at frequencies above 10–30 GHz. 相似文献
42.
Niranjan D. Chatterjee Ralf Krüger Gerd Haller Walter Olbricht 《Contributions to Mineralogy and Petrology》1998,133(1-2):149-168
An internally consistent thermodynamic dataset has been derived for 148 endmember phases (145 solids and 3 fluids) comprising
the elements Li, Na, K, Be, Mg, Ca, Ti, Cr, Mn, Fe, Zn, Al, Si, C, H, and O. This has been achieved by simultaneous treatment
of phase property (like standard enthalpy of formation, standard entropy, molar heat capacity, molar volume, thermal expansivity,
bulk modulus etc.) and reaction reversal data by the Bayesian method. The theory underlying the approach, and the computational
methods involved, are briefly outlined. (For the benefit of readers unfamiliar with inference statistics, the basic concepts
of the Bayes method are also presented in such a way that they can be grasped intuitively.) Although not yet addressed, this
method can be extended to refine the thermodynamic mixing properties of crystalline solutions. The sources of the input data,
culled from the literature, are summarized in the Appendix. The resulting database is succinctly documented in this paper.
It includes the enthalpies of formation and entropies, their uncertainties, and the correlation among them. The database allows
calculation of P-T, T-X
CO2, P-X
CO2, and T-f
O2 sections, with error propagation into the computed phase diagrams on a routine basis. A user-friendly computer program has
been written to generate such phase diagrams. It is public domain software. The software and the thermodynamic database (which
includes a complete documentation of the thermodynamic data above and beyond those listed (Table 2, here) may be downloaded from the web site
http://homepage.ruhr-uni-bochum.de/niranjan.chatterjee/Index.htm. Examples of computed phase diagrams are given to illustrate
the quality of the data and the capabilities of the software.
Received: 11 March 1998 / Accepted: 11 June 1998 相似文献
43.
Fred W. Krüger 《GeoJournal》1998,46(2):79-87
Namibia and Botswana differ from other sub-Saharan nations in their record of stable political performance. However, both
countries have to face increasing social problems. In the case of Namibia these are still mainly related to the process of
post-apartheid national reconciliation and identity building, in the case of Botswana they refer to issues of growing tribal
tensions and of a gradual interior restructuring of society. This paper analyzes the various patterns of social transformation
in the two countries and examines in what ways state-society relations are different from other African nations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
44.
We report on dust measurements obtained during the seventh orbit of the Galileo spacecraft about Jupiter. The most prominent
features observed are highly time variable dust streams recorded throughout the Jovian system. The impact rate varied by more
than an order of magnitude with a 5 and 10 hour periodicity, which shows a correlation with Galileo's position relative to
the Jovian magnetic field. This behavior can be qualitatively explained by strong coupling of nanometer-sized dust to the
Jovian magnetic field. In addition to the 5 and 10 h periodicities, a longer period which is compatible with Io's orbital
period is evident in the dust impact rate. This feature indicates that Io most likely is the source of the dust streams. During
a close (3,095 km altitude) flyby at Ganymede on 5 April 1997 an enhanced rate of dust impacts has been observed, which suggests
that Ganymede is a source of ejecta particles. Within a distance of about 25 RJ(Jupiter radius, RJ= 71,492 km) from Jupiter impacts of micrometer-sized particles have been recorded which could be particles on bound orbits
about Jupiter.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
45.
Marek J. Kukula James S. Dunlop David H. Hughes & Steve Rawlings 《Monthly notices of the Royal Astronomical Society》1998,297(2):366-382
Although radio-quiet quasars (RQQs) constitute ≳ 90 per cent of optically identified quasar samples, their radio properties are only poorly understood. In this paper we present the results of a multi-frequency VLA study of 27 low-redshift RQQs. We detect radio emission from 20 objects, half of which are unresolved (≤ 0.24 arcsec). In cases where significant structure can be resolved, double, triple and linear radio sources on scales of a few kpc are found. The radio emission (typically) has a steep spectrum (α ∼ 0.7, where S ∝ ν−α ), and high brightness temperatures ( T B ≥ 105 K) are measured in some of the radio components. The RQQs form a natural extension to the radio luminosity–absolute magnitude distribution of nearby Seyfert 1s. We conclude that a significant fraction of the radio emission in RQQs originates in a compact nuclear source directly associated with the quasar. There are no significant differences between the radio properties of RQQs with elliptical hosts and those in disc galaxies within the current sample. 相似文献
46.
Igor V. Igumenshchev Marek A. Abramowicz & Igor D. Novikov 《Monthly notices of the Royal Astronomical Society》1998,298(4):1069-1078
We numerically construct slim, global, vertically integrated models of optically thin, transonic accretion discs around black holes, assuming a regularity condition at the sonic radius and boundary conditions at the outer radius of the disc and near the black hole. In agreement with several previous studies, we find two branches of shock-free solutions, in which the cooling is dominated either by advection or by local radiation. We also confirm that the part of the accretion flow where advection dominates is in some circumstances limited in size: it does not extend beyond a certain outer limiting radius. New results found in our paper concern the location of the limiting radius and the properties of the flow near to it. In particular, we find that beyond the limiting radius the advective-dominated solutions match on to Shapiro, Lightman &38; Eardley (SLE) discs through a smooth transition region. Therefore, the full global solutions are shock-free and unlimited in size. There is no need to postulate an extra physical effect (e.g. evaporation) for triggering the ADAF–SLE transition. It occurs as a result of standard accretion processes described by the classic slim disc equations. 相似文献
47.
S. J. Reid M. Rex P. Von Der Gathen I. Fløisand F. Stordal G. D. Carver A. Beck E. Reimer R. Krüger-Carstensen L. L. De Haan G. Braathen V. Dorokhov H. Fast E. Kyrö M. Gil Z. Lityñska M. Molyneux G. Murphy F. O'Connor F. Ravegnani C. Varotsos J. Wenger C. Zerefos 《Journal of Atmospheric Chemistry》1998,30(1):187-207
In this paper, we show that the rate of ozone loss in both polar and mid-latitudes, derived from ozonesonde and satellite data, has almost the same vertical distribution (although opposite sense) to that of ozone laminae abundance. Ozone laminae appear in the lower stratosphere soon after the polar vortex is established in autumn, increase in number throughout the winter and reach a maximum abundance in late winter or spring. We indicate a possible coupling between mid-winter, sudden stratospheric warmings (when the vortex is weakened or disrupted) and the abundance of ozone laminae using a 23-year record of ozonesonde data from the World Ozone Data Center in Canada combined with monthly-mean January polar temperatures at 30 hPa.Results are presented from an experiment conducted during the winter of 1994/95, in phase II of the Second European Stratospheric And Mid-latitude Experiment (SESAME), in which 93 ozone-enhanced laminae of polar origin observed by ozonesondes at different time and locations are linked by diabatic trajectories, enabling them to be probed twice or more. It is shown that, in general, ozone concentrations inside laminae fall progressively with time, mixing irreversibly with mid-latitude air on time-scales of a few weeks. A particular set of laminae which advected across Europe during mid February 1995 are examined in detail. These laminae were observed almost simultaneously at seven ozonesonde stations, providing information on their spatial scales. The development of these laminae has been modelled using the Contour Advection algorithm of Norton (1994), adding support to the concept that many laminae are extrusions of vortex air. Finally, a photochemical trajectory model is used to show that, if the air in the laminae is chemically activated, it will impact on mid-latitude ozone concentrations. An estimate is made of the potential number of ozone molecules lost each winter via this mechanism. 相似文献
48.
From wind profile and wave measurements performed during the JONSWAP II experiment, relations between the dimensionless profile slope and the significant wave height are derived. It is shown that the wind profile is distorted by the waves especially in the vicinity of the water surface. The wave influence on the profile seems to be restricted to heights below about three wave heights. Above this level, the dimensionless profile slope is an approximately constant value corresponding to a drag coefficient of about 1.15 × 10–3. 相似文献
49.
P. Eberhardt J. Geiss H. Graf N. Grögler U. Krähenbühl H. Schwaller A. Stettler 《Geochimica et cosmochimica acta》1974,38(1):97-120
The noble gases He, Ne, Ar, Kr and Xe and also K and Ba were measured in the Apollo 11 igneous rocks 10017 and 10071, and in an ilmenite and two feldspar concentrates separated from rock 10071. Whole rock K/Ar ages of rocks 10017 and 10071 are (2350 ± 60) × 106 yr and (2880 ± 60) × 106 yr, respectively. The two feldspar concentrates of rock 10071 have distinctly higher ages: (3260 ± 60) × 106 yr and (3350 ± 70) × 106 yr. These ages are still 10 per cent lower than the Rb/Sr age obtained by Papanastassiouet al. (1970) and some Ar40 diffusion loss must have occurred even in the relatively coarse-grained feldspar.The relative abundance patterns of spallation Ne, Ar, Kr and Xe are in agreement with the ratios predicted from meteoritic production rates. However, diffusion loss of spallation He3 is evident in the whole rock samples, and even more in the feldspar concentrates. The ilmenite shows little or no diffusion loss. The isotopic composition of spallation Kr and Xe is similar to the one observed in meteorites. Small, systematic differences in the spallation Kr spectra of rocks 10017 and 10071 are due to variations in the irradiation hardness (shielding). The Kr spallation spectra in the mineral concentrates are different from the whole rock spectra and also show individual variations, reflecting the differences in target element composition. The relative abundance of cosmic ray produced Xe131 differs by nearly 50 per cent in the two rocks. The other Xe isotopes show no variations of similar magnitude. The origin of the Xe131 yield variability is discussed.Kr81 was measured in all the samples investigated. The Kr81/Kr exposure ages of rocks 10017 and 10071 are (480 ± 25) × 106 yr and (350 ± 15) × 106 yr, respectively. Exposure ages derived from spallation Ne21, Ar38, Kr83 and Xe126 are essentially in agreement with the Kr81/Kr ages. The age of rock 10071 might be somewhat low because of a possible recent exposure of our sample to solar flare particles. 相似文献
50.
Faults with a well-defined strike direction that precisely coincides with the southern rift fault system occur in the study
area in southern Tenerife. This fault system was generated contemporaneously with a chain of cinder cones ~948 ka. Open fractures
in ignimbrites (~668 ka) and fossil beach deposits (~42 ka) of the El Médano area suggest that the rift-associated fault system
was seismically active in the aftermath of the initial volcanic activity (~948 ka) and is probably still active. A second
fault system striking perpendicular to the rift-related faults probably originates from a Holocene paleoearthquake of moderate
intensity. Earthquake-induced ground effects in fossil beach deposits within the study area are consistent with seismically
induced ground effects of several recent and well-documented earthquakes, as well as gravitational sliding triggered by an
intense earthquake in the Nicoya Peninsula of Costa Rica in 1990. Both, the rift-associated and the earthquake-induced fault
system, initially produced open fractures that were occupied by plants and subsequently stabilized by cementation, forming
conspicuous sediment structures in fossil beach deposits of the El Médano site in southern Tenerife. 相似文献