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 $n$ items available across all sellers and $n_{\max}$ 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 $\log(\frac{n}{n-n_{\max}+1})+1$. 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 $\frac{n}{n-n_{\max}+1}$. 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 $k$-additive valuations, there exists a setting where the welfare approximates the optimal welfare within any non-zero factor only for $O(1/s)$ fraction of the time, where $s$ 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