Characterizing and approximating eigenvalue sets of symmetric interval matrices

We consider the eigenvalue problem for the case where the input matrix is symmetric and its entries perturb in some given intervals. We present a characterization of some of the exact boundary points, which allows us to introduce an inner approximation algorithm, that in many case estimates exact bounds. To our knowledge, this is the first algorithm that is able to guaran- tee exactness. We illustrate our approach by several examples and numerical experiments

Bolivia’s fiscal rules: dynamic stochastic general equilibrium model approach

Changes in fiscal revenues in Bolivia allow us to assess its impact on the fiscal budget and spending policy. Based on a Dynamic Stochastic General Equilibrium Model (DSGE) using stylized facts for small open economy, we’re looking for a simulation of fundamentals’ responses or effects against different fiscal rules applied. In these sense we use two rules: first, where taxes adjust according to the debt level and government expenditures; and second, balanced budget where taxes adjust every time in order to maintain the equilibrium in budget. Our results show that after the fiscal shock hits the economy, the first fiscal rule has mayor stabilization effects on the price level than the second one, around 50%.Government expenditure, fiscal rule, pass - through, rule - of – thumb households

Preparation and characterization of slush hydrogen and nitrogen gels

Slush hydrogen and nitrogen gels for rocket propellant

Quality determination of liquid-solid hydrogen mixtures

Quality determinations of liquid-solid hydrogen mixtures from mass fraction of vapor pumped off in freeze-thaw proces

A computational model for a regenerator

This paper concerns a numerical model of a regenerator running at very low temperatures. The model consists of the usual three equations for a compressible fluid with an additional equation for a matrix temperature. The main difficulty with the model is the very low Mach number (approximately 1.E-3). The divergence of the velocity is not small, the pressure divergence is small, and the pressure fluctuation in time is not small. An asymptotic expansion based on the bounded derivative method of Kreiss is used to give a reduced model which eliminates acoustic waves. The velocity is then determined by a two-point boundary value problem which does not contain a time derivative. The solution obtained from the reduced system is compared with the numerical solution of the original system

A cryocooler for applications requiring low magnetic and mechanical interference

A very low-power, low-interference Stirling cryocooler is being developed based on principles and techniques described in several previous publications over the last four years. It differs in several important details from those built previously. It uses a tapered displacer based upon an analytical optimization procedure. The displacer is driven by an auxiliary piston and cylinder (rather than by mechanical linkage) using some of the working fluid itself to provide the driving force. This provides smooth, vibration-free motion, and, more importantly, allows complete mechanical and spatial separation of the cryostat from the pressure-wave generator. Either of two different pressure-wave generators can be used. One is a non-contaminating, unlubricated ceramic piston and cylinder. The other is a compressed-air-operated rubber diaphragm with motor-driven valves to cycle the pressure between appropriate limits

Cryogenic Propellant Scavenging

A detailed description of a computer model that has been developed for assessing the feasibility of low g cryogen propellant scavenging from the space shuttle External Tank (ET) is given. Either pump-assisted or pressure-induced propellant transfer may be selected. The program will accept a wide range of input variables, including the fuel to be transferred (LOX or LH2), heat leaks, tank temperatures, and piping and equipment specifications. The model has been parametrically analyzed to determine initial design specification for the system