3,909 research outputs found
Satellite microwave sensing of oceanic cloud liquid water: application to the earth radiation budget and climate
March 1995.Sponsored by NASA Graduate Student Fellowship in Global Change Research NGT-30046.Sponsored by NASA Research NAG-8-981.Sponsored by NOAA NA37RJ0202
Price Competition, Fluctuations, and Welfare Guarantees
In various markets where sellers compete in price, price oscillations are
observed rather than convergence to equilibrium. Such fluctuations have been
empirically observed in the retail market for gasoline, in airline pricing and
in the online sale of consumer goods. Motivated by this, we study a model of
price competition in which an equilibrium rarely exists. We seek to analyze the
welfare, despite the nonexistence of an equilibrium, and present welfare
guarantees as a function of the market power of the sellers.
We first study best response dynamics in markets with sellers that provide a
homogeneous good, and show that except for a modest number of initial rounds,
the welfare is guaranteed to be high. We consider two variations: in the first
the sellers have full information about the valuation of the buyer. Here we
show that if there are items available across all sellers and is
the maximum number of items controlled by any given seller, the ratio of the
optimal welfare to the achieved welfare will be at most
. As the market power of the largest seller
diminishes, the welfare becomes closer to optimal. In the second variation we
consider an extended model where sellers have uncertainty about the buyer's
valuation. Here we similarly show that the welfare improves as the market power
of the largest seller decreases, yet with a worse ratio of
. The exponential gap in welfare between the two
variations quantifies the value of accurately learning the buyer valuation.
Finally, we show that extending our results to heterogeneous goods in general
is not possible. Even for the simple class of -additive valuations, there
exists a setting where the welfare approximates the optimal welfare within any
non-zero factor only for fraction of the time, where is the number
of sellers
Horava-Lifshitz gravity: tighter constraints for the Kehagias-Sfetsos solution from new solar system data
We analytically work out the perturbation induced by the Kehagias-Sfetsos
(KS) space-time solution of the Horava-Lifshitz (HL) modified gravity at long
distances on the two-body range for a pair of test particles A and B orbiting
the same mass M. We apply our results to the most recently obtained
range-residuals \delta\rho for some planets of the solar system (Mercury, Mars,
Saturn) ranged from the Earth to effectively constrain the dimensionsless KS
parameter \psi_0 for the Sun. We obtain \psi_0 >= 7.2 x 10^-10 (Mercury),
\psi_0 >= 9 x 10^-12 (Mars), \psi_0 >= 1.7 x 10^-12 (Saturn). Such lower bounds
are tighter than other ones existing in literature by several orders of
magnitude. We also preliminarily obtain \psi_0 >= 8 x 10^-10 for the system
constituted by the S2 star orbiting the Supermassive Black Hole (SBH) in the
center of the Galaxy.Comment: LaTex2e, 15 pages, 1 table, 3 figures, 31 references. Version
matching the one at press in International Journal of Modern Physics D
(IJMPD
Nimbus-7 observations of the effect of clouds on the earth's radiation budget
August 1990.Includes bibliographical references.Outgoing longwave (LW) flux and shortwave (SW) albedo data obtained from narrow field-of-view scanner measurements aboard the Nimbus-7 satellite are used along with coincident cloudiness data to estimate the effect of clouds on the earth's radiation budget (ERB). A simple technique is described to obtain clear sky albedos and LW fluxes using daily Nimbus-7 ERB and total cloud amount data. The analysis is done for the following four seasons: June-August 1979, September-November 1979, December-February 1980, and March-May 1980. When compared with the recent results from the Earth Radiation Budget Experiment (ERBE) the Nimbus-7 derived clear sky LW and SW fluxes are about 5-6 Wm-2 too low and 3-4 Wm-2 too high, respectively, most likely resulting from cloud contamination. The concept of cloud radiative forcing, referred to in this study as cloud effect, can provide a quantitative measure of the impact of clouds on the ERB. It is defined as the difference between the clear sky flux and the cloudy sky flux at the top of the atmosphere. The SW cloud effect is shown to be negative over most of the earth and is greatest in the midlatitudes in areas of stratus clouds and storm tracks. The LW cloud effect, on the other hand, is primarily positive and most significant in the tropics. The net cloud effect is found to be negative over most of the earth, with a near cancellation of the SW and LW effects in the tropics and a significant negative effect in the midlatitudes. Moreover, it is shown that the net cloud effect, when globally averaged, is negative and varies with season. A comparison of the Nimbus-7 derived LW and SW cloud effects to those obtained from ERBE shows, on average, a 5-6 Wm-2 bias resulting from cloud contamination of the Nimbus-7 clear sky fluxes.This research was supported by the Cooperative Institute for Research in the Atmosphere through the National Park Service Grant #DOC-NOAA-NA85RAH5045 and NASA Grant #NAG-1-865
Three-dimensional viscous flow analysis inside a turbine volute
A three-dimensional numerical method has been developed to analyze the complex flow field inside a turbine volute. Comparisons are made between solutions with different boundary conditions
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