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91.
We have studied the dynamical properties of convective overstability and Kelvin-Helmholtz instability in a vertical magnetic field with a downdraft. The Kelvin-Helmholtz instability and overstability produce the upward downward propagating Alfvén waves depending upon the magnitudes of the kinematic viscosity coefficient (eddy viscosity) ν, and thermometric conductivity κ. It is found that the instability may be driven by the density stratification and the effect of the eddy viscosity is to make the system stable. We discuss also the interaction of the overstability inx<0 and the downdraft inx>0, and the overstability at a vertical boundary of the field. 相似文献
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94.
K. S. Krishna Swamy 《Astrophysics and Space Science》1972,16(1):75-80
The profile of the absorption feature at 2200 Å has been calculated for model grains of graphite, graphite core-dirty ice mantle and silicate. They are compared with the observed profile obtained by Bless and Savage from a number of early type stars. We have also shown that it is unlikely that the radiation damage of silicates in Interstellar Space can also contribute to the absorption feature at 2200 Å. Lastly, we have discussed briefly how one can meet the objections that have been raised on the silicate model. 相似文献
95.
The oscillations observed recently in the transient X-ray source A1118-61 are attributed to variations in the magnetic activity of a rotating white dwarf similar to the 11-year solar activity cycle. The transient nature, in analogy with the sun, is attributed to the variation in the strength of the cycle.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975. 相似文献
96.
Regional tourism and South-South economic cooperation 总被引:1,自引:0,他引:1
Krishna B. Ghimire 《The Geographical journal》2000,167(2):99-110
Regional tourism within developing countries is a growing phenomenon. Yet this aspect has been largely neglected in social science research as well as tourism planning. This paper highlights the general nature, scale and economic significance of regional tourism in three leading regions in Asia, Africa and Latin America. The topic is especially timely as economic self-reliance and cooperation are increasingly reiterated in the context of the emergence of regional groupings. A key question addressed is whether regional tourism development represents any new and viable prospects for regional economic improvement and partnership, especially compared to international tourism centred on attracting visitors from industrialized countries. Based on a critical assessment of the experiences of three regional blocs (ASEAN – the Association of South-East Asian Nations; SADC – the Southern African Development Community; and Mercosur – a common market comprising Argentina, Brazil, Paraguay and Uruguay, with Chile being an associated member), the paper suggests that a basic appreciation of the prospects of regional tourism is not enough to produce perceptible benefits. Regional tourism development is occurring in a haphazard manner, with little attention to managing existing socio-economic inequalities and centre-periphery relations. The paper is based primarily on the review of secondary literature readily available to the author combined with a few documents obtained directly from different regional organizations or through Internet search. A small amount of material, especially concerning emerging tourism trends and outcomes, is drawn from a research project on national mass tourism in developing countries coordinated by the author at the United Nations Research Institute for Social Development, Geneva. 相似文献
97.
We quantify the correlation between earthquakes and use the same to distinguish between relevant causally connected earthquakes.
Our correlation metric is a variation on the one introduced by Baiesi and Paczuski (Phys Rev E 69:066,106, 2004). A network of earthquakes is constructed, which is time-ordered and with links between the more correlated ones. Data pertaining
to the California region has been used in the study. Recurrences to earthquakes are identified employing correlation thresholds
to demarcate the most meaningful ones in each cluster. The distribution of recurrence lengths and recurrence times are analyzed
subsequently to extract information about the complex dynamics. We find that the unimodal feature of recurrence lengths helps
to associate typical rupture lengths with different magnitude earthquakes. The out-degree of the network shows a hub structure
rooted on the large magnitude earthquakes. In-degree distribution is seen to be dependent on the density of events in the
neighborhood. Power laws are also obtained with recurrence time distribution agreeing with the Omori law. 相似文献
98.
The role of biofilm proteins in modulating cyprid metamorphosis is not well understood. In the present investigation this possibility was explored by disrupting biofilm proteins using commercially available protease. The influence of natural biofilm and artificial biofilms of Aeromonas salmonicida salmonicida and Bacillus brevis and their culture supernatants and exopolysaccharides obtained under different nutritional conditions was evaluated. Natural biofilm facilitated cyprid metamorphosis in Balanus amphitrite, whereas monospecies biofilms did not. The treatment of biofilms with protease resulted in a decline in metamorphosis, except in B. brevis, where although metamorphosis was negated initially, it increased with the protease concentration and observation days. As the response of cyprids to exopolysaccharides produced by A. salmonicida salmonicida was dependent on protein concentration, protease treatment resulted in a decrease in metamorphosis, whereas in case of B. brevis biofilms, protease hydrolysis products could be important in providing settlement cues. Thus, biofilm bacterial components play an important role in the cyprid metamorphosis of Balanus amphitrite. 相似文献
99.
Sanjay Bhatnagar Gopal Krishna & L. Wisotzki 《Monthly notices of the Royal Astronomical Society》1998,299(2):L25-L28
By considering the propagation of low-amplitude magnetohydrodynamic waves in partially ionized plasmas, it is shown that the ion-neutral drift (ambipolar diffusion) induced by the waves can have specific effects on the molecular chemistry of cold material. The chemistry occurring in gas swept by Alfvén waves is described and it is shown that this leads to spatial variations in the deuterium fractionation ratios of, for example, HCO+ and N2 H+ , on spatial scales of a few hundredths of a parsec, depending upon the fractional ionization of the ambient medium. The possibility of detecting interstellar Alfvén waves by molecular spectroscopy and their effect of producing small-scale chemical abundance gradients in molecular clouds are briefly discussed. 相似文献
100.
The observed variation of reddening as function of the heliocentric distance and the spatial variation of reddening within the coma of Comet West in the visual wavelength range have been considered to infer the properties of the cometary dust grains. The relevant model incorporates the variation in the size distribution function as well as the composition of the spherical grains. The real part of the complex index of refraction (m = m – im) is chosen such thatm = 1.6. The imaginary part is required to vary from m = 0.2 to 0.05 over the wavelength range 0.4 to 0.7 m. This choice of refractive index corresponds to dirty silicate grains. As a by-product, the model also satisfies the observed polarization and albedo for the Comet West. 相似文献