Unified computer codes: Properties data for low cost nozzle materials

The development of the analytic capability to predict the thermal ablation response of promising low cost materials for rocket nozzles is presented

Liquid Sloshing in 45 Deg Sector Compartmented Cylindrical Tanks

Liquid sloshing in 45-deg sector compartmented cylindrical tank

Divergent nematic susceptibility in an iron arsenide superconductor

Within the Landau paradigm of continuous phase transitions, ordered states of matter are characterized by a broken symmetry. Although the broken symmetry is usually evident, determining the driving force behind the phase transition is often a more subtle matter due to coupling between otherwise distinct order parameters. In this paper we show how measurement of the divergent nematic susceptibility of an iron pnictide superconductor unambiguously distinguishes an electronic nematic phase transition from a simple ferroelastic distortion. These measurements also reveal an electronic nematic quantum phase transition at the composition with optimal superconducting transition temperature.Comment: 8 pages, 8 figure

Computer model of catalytic combustion/Stirling engine heater head

The basic Acurex HET code was modified to analyze specific problems for Stirling engine heater head applications. Specifically, the code can model: an adiabatic catalytic monolith reactor, an externally cooled catalytic cylindrical reactor/flat plate reactor, a coannular tube radiatively cooled reactor, and a monolithic reactor radiating to upstream and downstream heat exchangers

XMM-Newton Detection of Hot Gas in the Eskimo Nebula: Shocked Stellar Wind or Collimated Outflows?

The Eskimo Nebula (NGC 2392) is a double-shell planetary nebula (PN) known for the exceptionally large expansion velocity of its inner shell, ~90 km/s, and the existence of a fast bipolar outflow with a line-of-sight expansion velocity approaching 200 km/s. We have obtained XMM-Newton observations of the Eskimo and detected diffuse X-ray emission within its inner shell. The X-ray spectra suggest thin plasma emission with a temperature of ~2x10^6 K and an X-ray luminosity of L_X = (2.6+/-1.0)x10^31 (d/1150 pc)^2 ergs/s, where d is the distance in parsecs. The diffuse X-ray emission shows noticeably different spatial distributions between the 0.2-0.65 keV and 0.65-2.0 keV bands. High-resolution X-ray images of the Eskimo are needed to determine whether its diffuse X-ray emission originates from shocked fast wind or bipolar outflows.Comment: 4 pages, 2 figures, accepted in Astronomy and Astrophysics Letter

An improved closed-loop stability related measure for finite-precision digital controller realizations

The pole-sensitivity approach is employed to investigate the stability issue of the discrete-time control system, where a digital controller, implemented with finite word length (FWL), is used. A new stability related measure is derived, which is more accurate in estimating the closed-loop stability robustness of an FWL implemented controller than some existing measures for the pole-sensitivity analysis. This improved stability measure thus provides a better criterion to find the optimal realizations for a generic controller structure that includes output-feedback and observer-based controllers. A numerical example is used to verify the theoretical analysis and to illustrate the design procedure

An improved closed-loop stability related measure for finite-precision digital controller realizations

The pole-sensitivity approach is employed to investigate the stability issue of the discrete-time control system, where a digital controller, implemented with finite word length (FWL), is used. A new stability related measure is derived, which is more accurate in estimating the closed-loop stability robustness of an FWL implemented controller than some existing measures for the pole-sensitivity analysis. This improved stability measure thus provides a better criterion to find the optimal realizations for a generic controller structure that includes output-feedback and observer-based controllers. A numerical example is used to verify the theoretical analysis and to illustrate the design procedure

Homotopy-coherent algebra via Segal conditions

Many homotopy-coherent algebraic structures can be described by Segal-type limit conditions determined by an “algebraic pattern”, by which we mean an ∞-category equipped with a factorization system and a collection of “elementary” objects. Examples of structures that occur as such “Segal O-spaces” for an algebraic pattern Oinclude ∞-categories, (∞, n)-categories, ∞-operads (including symmetric, non-symmetric, cyclic, and modular ones), ∞-properads, and algebras for a (symmetric) ∞-operad in spaces.In the first part of this paper we set up a general framework for algebraic patterns and their associated Segal objects, in-cluding conditions under which the latter are preserved by left and right Kan extensions. In particular, we obtain necessary and sufficient conditions on a pattern Ofor free Segal O-spaces to be described by an explicit colimit formula, in which case we say that Ois “extendable”. In the second part of the paper we explore the relationship be-tween extendable algebraic patterns and polynomial monads, by which we mean cartesian monads on presheaf ∞-categories that are accessible and preserve weakly contractible limits. We first show that the free Segal O-space monad for an extendable pattern Ois always polynomial. Next, we prove an ∞-categorical version of Weber’s Nerve Theorem for polynomial monads, and use this to define a canonical extendable pattern from any polynomial monad, whose Segal spaces are equivalent to the algebras of the monad. These constructions yield functors between polynomial monads and extendable algebraic patterns, and we show that these exhibit full sub-categories of “saturated” algebraic patterns and “complete” polynomial monads as localizations, and moreover restrict to an equivalence between the ∞-categories of saturated patterns and complete polynomial monads