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201.
It is shown that a two-dimensional lower-hybrid wave structure can parametrically trigger the growth of VLF and ULF noises in a plasma. Analytical expressions for the increment and threshold of the instability are obtained. Application of our work to the auroral zones of the topside ionosphere is discussed. 相似文献
202.
Rabindra Nath Das 《Astrophysics and Space Science》1979,61(1):169-173
The application of the Wiener-Hopf technique to the coupled linear integral equation ofX- andY-equations gives rise to the Fredholm equations with simpler kernels.X-equation is expressed in terms ofY-equation and vice-versa. These are unique in representation with respect to coupled linear constraints. 相似文献
203.
204.
205.
R. K. Das A. K. Shrivastava B. Ishwar 《Celestial Mechanics and Dynamical Astronomy》1988,45(4):387-393
The differential equations of motion of the elliptic restricted problem of three bodies with decreasing mass are derived. The mass of the infinitesimal body varies with time. We have applied Jeans' law and the space-time transformation of Meshcherskii. In this problem the space-time transformation is applicable only in the special case whenn=1,k=0,q=1/2. We have applied Nechvile's transformation for the elliptic problem. We find that the equations of motion of our problem differ from that of constant mass only by a small perturbing force. 相似文献
206.
Sumit R. Das 《Journal of Astrophysics and Astronomy》1999,20(3-4):131-148
We review some of the progress in understanding the statistical basis of black hole thermodynamics in string theory. The emphasis
is on the “derivation” of Hawking radiation from the unitary decay of near extremal D-brane states. We also review recent
progress in understanding Schwarzschild black holes by relating them to D-brane black holes via “boosts” in M-theory. 相似文献
207.
208.
We have taken a plasma model of ionosphere which is quite different from the earlier model employed by several workers to study the whistler as a diagnostic technique in the ionosphere. In contrast to the earlier model, we have considered an ionosphere that includes negative ionic species and due to which the mathematical technique loses the basic assumptions chosen earlier to derive the group travel time. We have shown that the negative ion has a significant role and without its contribution, the method to diagnose the ionospheric parameters may lead to an error. We have discussed also how to uset()=
0
h
dh/v
g
as a diagnostic tool in determining the ionospheric parameters. 相似文献
209.
In this work, we have simulated orbits of a particle moving in gravitational field of the Sun-Jupiter system. The effect of
solar radiation pressure, including Poynting Robertson drag, on the evolution of particle orbits in phase space have been
studied for different values of the parameter β
1 (the ratio of radiation to gravitational force) and initial conditions. Characteristics of various computed trajectories
have been studied using wavelet transform (WT), Fourier transform (FT) and Poincare surface of section method. We use wavelet
analysis to identify transitions of a trajectory in time-frequency plane and further apply it to classify it as regular or
chaotic in phase space. Unlike the Fourier transform method (FT), we observe that the wavelet transform (WT) also provides
a basis to identify ‘sticky’ trajectories in the present dynamical system. 相似文献
210.
Experimental calibration of lake-sediment spectral reflectance to chlorophyll a concentrations: methodology and paleolimnological validation 总被引:1,自引:0,他引:1
Alexander P. Wolfe Rolf D. Vinebrooke Neal Michelutti Benoit Rivard Biplob Das 《Journal of Paleolimnology》2006,36(1):91-100
Chlorophyll a preserved in lake sediments reflects, in part, past primary production. This study assesses the spectral properties of sedimentary
chlorophyll a using visible-near infrared reflectance (VNIR) spectroscopy, with the objective of establishing a new, non-destructive paleolimnological
proxy. Reflectance spectra were determined from a dilution series (n = 10) involving incremental additions of pulverized modern algae to a lake sediment matrix of low organic content. This enabled
an assessment of the development of sediment reflectance spectra in relation to different sediment chlorophyll a concentrations, and subsequent regression of spectral features against measured concentrations of chlorophyll a and derivatives obtained by high performance liquid chromatography (HPLC). The experiment demonstrates that ubiquitous troughs
in sediment reflectance near 675 nm are attributable to chlorophyll a and derivative compounds. A significant correlation (r
2 = 0.98, P < 0.01) was obtained between the area of the reflectance trough in the 650–700 nm interval and summed concentrations of chlorophyll
a, all derivative isomers, and degradational pheopigments. A simple linear inference model derived from this experiment was
applied to a down-core sequence of VNIR spectra from a productive prairie lake (Alberta, Canada), where it produced inferred
sediment chlorophyll a concentrations in concordance with HPLC measurements. Although a larger training set is desirable to further refine the inference
model, the analyses reported here demonstrate that reflectance spectroscopy provides a rapid, semi-quantitative method for
assessing the chlorophyll a content of lake sediments. 相似文献