2,952 research outputs found
On the Self-Consistent Response of Stellar Systems to Gravitational Shocks
We study the reaction of a globular star cluster to a time-varying tidal
perturbation (gravitational shock) using self-consistent N-body simulations and
address two questions. First, to what extent is the cluster interior protected
by adiabatic invariants. Second, how much further energy change does the
postshock evolution of the cluster potential produce and how much does it
affect the dispersion of stellar energies. We introduce the adiabatic
correction} as ratio of the energy change, , to its value in the impulse
approximation. When the potential is kept fixed, the numerical results for the
adiabatic correction for stars with orbital frequency \omega can be
approximated as (1 + \omega^2 \tau^2)^{-\gamma}. For shocks with the
characteristic duration of the order the half-mass dynamical time of the
cluster, \tau < t_{dyn,h}, the exponent \gamma = 5/2. For more prolonged
shocks, \tau > 4 t_{dyn,h}, the adiabatic correction is shallower, \gamma =
3/2. When we allow for self-gravity and potential oscillations which follow the
shock, the energy of stars in the core changes significantly, while the total
energy of the system is conserved. Paradoxically, the postshock potential
fluctuations reduce the total amount of energy dispersion, . The effect
is small but real and is due to the postshock energy change being statistically
anti-correlated with the shock induced heating. These results are to be applied
to Fokker-Planck models of the evolution of globular clusters.Comment: 20 pages; ApJ 513 (in press
Secure Digital Signal Transmission by Multistep Parameter Modulation and Alternative Driving of Transmitter Variables
The idea of secure communication of digital signals via chaos synchronization
has been plagued by the possibility of attractor reconstruction by
eavesdroppers as pointed out by Perez and Cerdeira. In this Letter, we wish to
present a very simple mechanism by which this problem can be overcome, wherein
the signal is transmitted via a multistep parameter modulation combined with
alternative driving of different transmitter variables, which makes the
attractor reconstruction impossible. The method is illustrated by means of the
Lorenz system and Chua's circuit as examples.Comment: 15 pages, RevTeX, 6 eps figures, To appear in Int. J. Bifurcation and
Chaos (July 2001
Deccan volcanism and K-T boundary signatures
The Deccan Traps in the Indian subcontinent represent one of the most extensive flood basalt provinces in the world. These basalts occur mainly as flat-lying, subaerially erupted tholeiitic lava flows, some of which are traceable for distances of more than 100 km. Offshore drilling and geophysical surveys indicate that a part of the Deccan subsided or was downfaulted to the west beneath the Arabian Sea. The presence of 1 to 5 m thick intertrappean sediments deposited by lakes and rivers indicates periods of quiescence between eruptions. The occurrence of numerous red bole beds among the flows suggests intense weathering of flow tops between eruptive intervals. Although the causative relationship of the Cretaceous-Tertiary (K-T) biotic extinctions to Deccan volcanism is debatable, the fact that the main Deccan eruptions straddle the K-T event appears beyond doubt from the recent Ar-40/Ar-39 ages of various Deccan flows. This temporal relationship of the K-T event with Deccan volcanism makes the petrochemical signatures of the entire Deccan sequence (basalt flows, intercalated intertrappean sediments, infratrappean Lameta beds (with dinosaur fossils), and the bole beds) pertinent to studies of the K-T event. The results of ongoing study is presented
AN EVALUATION OF AN ECONOMIC STRATEGY FOR PREVENTING WATER POLLUTION USING A PHOSPHORUS CONSISTENT TRANSPORTATION MODEL: A CASE OF BROILER LITTER MANAGEMENT
We calculated the profitability of using broiler litter as a source of plant nutrient using a phosphorus consistent litter application rule. We found that each ton of litter can be transferred cost effectively up to 164 miles from the production facilities. The minimum cost phosphorus consistent transportation model developed to meet the nutrient needs of 29 counties in North Alabama revealed that not all the litter can be utilized in the region. The total cost for nutrient supply increased when transportation of litter from heavily surplus counties were prioritized. The effect of chemical fertilizer price change minimally affected the total litter use.Environmental Economics and Policy,
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