A Survey and Evaluation of High Energy Liquid Chemical Propulsion Systems

This report presents the results of a study to develop a procedure for evaluating liquid propellants in order (a) to select the most appropriate propellant (from among those under development) for each of several applications on each of the various missions in the NASA program, or (b) to select new propellants (from among those being proposed) for initiation or continuation of research and development. The analysis begins with a consideration of requirements--either for the specific application or for the various classes of applications. The known characteristics of the propellant or propellants to be evaluated are then put into a convenient form for evaluation. The next step is to determine whether or not there are requirements that simply cannot be met by the propellant. If the propellant passes this test, an optimum vehicle configuration using the propellant (and meeting all requirements) is estimated. (The configuration should be optimized with respect to the total resource consumption for all aspects of the mission, including R&D, production, logistics, and operation.) The total resource consumption for this configuration is then compared with that for similar configurations using other propellants (and meeting all requirements equally well). If all factors have been properly taken into account, this comparison of resource consumption will complete the evaluation. Such an evaluation may be performed several times, in increasing detail and with correspondingly increasing accuracy, as an R&D program proceeds, and the accuracy of the data as well as the cost of the next step in the program increase. The procedure is superior to those in common use in that it minimizes both the amount of analytical work and the number of points at which subjective value judgments are made

Small linear wind tunnel saltation experiments: Some experiences

Since the wind tunnels proposed to be used for the Space Station Planetology Experiments are of a rather limited size, some experience and techniques used for saltation experiments in a small linear wind tunnel may be of interest. Three experiments will be presented. The first concerns a length effect of saltation mass flux in which the size of the wind tunnel exaggerates the physical process taking place. The second experiment concerns a nonoptical technique that does not interfere with flow and by which momentum flux to the floor may be measured. The technique may also be used to calculate saltation flux (using appropriate assumptions). The third experiment concerns the use of the momentum equation to estimate momentum fluxes by difference

Trading institutions and price discovery: the cash and futures markets for crude oil

We provide substantial evidence that the futures market for West Texas Intermediate crude oil increased the short-term volatility of the cash price of crude oil. We show that the variability of prices increased using both published posted prices and transaction prices for producers. This increased volatility in the price of crude oil may reflect information aggregated into the price, an increase the variance of shocks to the price of crude oil, or noise in the futures price that affects the cash price. We present evidence from experiments consistent with the interpretation that information aggregation not feasible in a posted-price market can explain at least part of the increase in variance. This evidence supports the proposition that information not previously aggregated into the cash price for crude oil is at least part of the reason for the greater variability of the cash price after the opening of the futures market and provides at least one example in which a futures market increased the volatility of the cash market, and prices became more efficient.

Can Public Debt Enhance Democracy?

This Essay draws on historical and current examples to examine the extent to which public creditors can enhance democracy by monitoring public officials in a manner that compensates for the failures of the government debtor\u27s constituents to monitor public officials. Creditors and constituents may share significant interests, depending on the structure of security arrangements for public debt and the identity of the debtors. Where interests overlap, the capacity of creditors to overcome collective action problems suffered by constituents may transform creditors into surrogates for constituents. Whether creditors are willing to play this role, however, may depend on the existence of alternatives to creditor monitoring, such as diversification and market constraints on default. The Essay concludes with an examination of the plausible scope of creditor monitoring in contemporary settings of sovereign and state and local debt

Feasibility study of an Integrated Program for Aerospace vehicle Design (IPAD). Volume 2: The design process

The extent to which IPAD is to support the design process is identified. Case studies of representative aerospace products were developed as models to characterize the design process and to provide design requirements for the IPAD computing system

VII. The Grape-Vine Typhlocybids of the Mesilla Valley, N. M.

Volume: 7Start Page: 14End Page: 1

Tropically convex constraint satisfaction

A semilinear relation S is max-closed if it is preserved by taking the componentwise maximum. The constraint satisfaction problem for max-closed semilinear constraints is at least as hard as determining the winner in Mean Payoff Games, a notorious problem of open computational complexity. Mean Payoff Games are known to be in the intersection of NP and co-NP, which is not known for max-closed semilinear constraints. Semilinear relations that are max-closed and additionally closed under translations have been called tropically convex in the literature. One of our main results is a new duality for open tropically convex relations, which puts the CSP for tropically convex semilinaer constraints in general into NP intersected co-NP. This extends the corresponding complexity result for scheduling under and-or precedence constraints, or equivalently the max-atoms problem. To this end, we present a characterization of max-closed semilinear relations in terms of syntactically restricted first-order logic, and another characterization in terms of a finite set of relations L that allow primitive positive definitions of all other relations in the class. We also present a subclass of max-closed constraints where the CSP is in P; this class generalizes the class of max-closed constraints over finite domains, and the feasibility problem for max-closed linear inequalities. Finally, we show that the class of max-closed semilinear constraints is maximal in the sense that as soon as a single relation that is not max-closed is added to L, the CSP becomes NP-hard.Comment: 29 pages, 2 figure

: P

International audienceThe GANIL facility consists of three successive cyclotrons. The tuning of these cyclotrons and of the transfer beam lines isachieved in about 24 hours. Reducing this setting time would enable to increase the time allocated to physics experiments.New tools are realized for automatic beam tuning. These tools are expected to make the tuning easier, shorter and morereproducible