Performance-limit criteria for the design of fast-response servo-actuation systems

Analysis of a typical nonlinear electrohydraulic servo-model establishes the dynamic-performance capabilities of servo-actuation systems

Propulsion control and control theory: A new research focus

Technological developments necessary for the implementation of advanced digital control concepts for aircraft propulsion are identified and discussed. Developments associated with the replacement analog controllers with digital control systems, sensors and actuators, and control modes and software are reported

Dynamic performance analysis of a fuel-control valve for use in airbreathing engine research

Dynamic performance analysis of fast-response fuel control valve for air breathing engine researc

A digital computer propulsion control facility: Description of capabilities and summary of experimental program results

Flight weight digital computers are being used today to carry out many of the propulsion system control functions previously delegated exclusively to hydromechanical controllers. An operational digital computer facility for propulsion control mode studies has been used successfully in several experimental programs. This paper describes the system and some of the results concerned with engine control, inlet control, and inlet engine integrated control. Analytical designs for the digital propulsion control modes include both classical and modern/optimal techniques

Control technology for future aircraft propulsion systems

The need for a more sophisticated engine control system is discussed. The improvements in better thrust-to-weight ratios demand the manipulation of more control inputs. New technological solutions to the engine control problem are practiced. The digital electronic engine control (DEEC) system is a step in the evolution to digital electronic engine control. Technology issues are addressed to ensure a growth in confidence in sophisticated electronic controls for aircraft turbine engines. The need of a control system architecture which permits propulsion controls to be functionally integrated with other aircraft systems is established. Areas of technology studied include: (1) control design methodology; (2) improved modeling and simulation methods; and (3) implementation technologies. Objectives, results and future thrusts are summarized

Flight evaluation of modifications to a digital electronic engine control system in an F-15 airplane

The third phase of a flight evaluation of a digital electronic engine control system in an F-15 has recently been completed. It was found that digital electronic engine control software logic changes and augmentor hardware improvements resulted in significant improvements in engine operation. For intermediate to maximum power throttle transients, an increase in altitude capability of up to 8000 ft was found, and for idle to maximum transients, an increase of up to 4000 ft was found. A nozzle instability noted in earlier flight testing was investigated on a test engine at NASA Lewis Research Center, a digital electronic engine control software logic change was developed and evaluated, and no instability occurred in the Phase 3 flight evaluation. The backup control airstart modification was evaluated, and gave an improvement of airstart capability by reducing the minimum airspeed for successful airstarts by 50 to 75 knots

Accurate evaluation of the interstitial KKR-Green function

It is shown that the Brillouin zone integral for the interstitial KKR-Green function can be evaluated accurately by taking proper care of the free-electron singularities in the integrand. The proposed method combines two recently developed methods, a supermatrix method and a subtraction method. This combination appears to provide a major improvement compared with an earlier proposal based on the subtraction method only. By this the barrier preventing the study of important interstitial-like defects, such as an electromigrating atom halfway along its jump path, can be considered as being razed.Comment: 23 pages, RevTe

Negative spatial regulation of the lineage specific CyIIIa actin gene in the sea urchin embryo

The CyIIIa·CAT fusion gene was injected into Strongylocentrotus purpuratus eggs, together with excess ligated competitor sequences representing subregions of the CyIIIa regulatory domain. In this construct, the chloramphenicol acetyltransferase (CAT) reporter gene is placed under the control of the 2300 nucleotide upstream regulatory domain of the lineage-specific CyIIIa cytoskeletal actin gene. CAT mRNA was detected by in situ hybridization in serial sections of pluteus stage embryos derived from the injected eggs. When carrier DNA lacking competitor CyIIIa fragments was coinjected with CyIIIa.CAT, CAT mRNA was observed exclusively in aboral ectoderm cells, i.e. the territory in which the CyIIIa gene itself is normally expressed (as also reported by us previously). The same result was obtained when five of seven different competitor subfragments bearing sites of DNA-protein interaction were coinjected. However, coinjection of excess quantities of either of two widely separated, nonhomologous fragments of the CyIIIa regulatory domain produced a dramatic ectopic expression of CAT mRNA in the recipient embryos. CAT mRNA was observed in gut, mesenchyme cells and oral ectoderm in these embryos. We conclude that these fragments contain regulatory sites that negatively control spatial expression of the CyIIIa gene

Skew Category Algebras Associated with Partially Defined Dynamical Systems

We introduce partially defined dynamical systems defined on a topological space. To each such system we associate a functor $s$ from a category $G$ to \Top^{\op} and show that it defines what we call a skew category algebra $A \rtimes^{\sigma} G$. We study the connection between topological freeness of $s$ and, on the one hand, ideal properties of $A \rtimes^{\sigma} G$ and, on the other hand, maximal commutativity of $A$ in $A \rtimes^{\sigma} G$. In particular, we show that if $G$ is a groupoid and for each e \in \ob(G) the group of all morphisms $e \rightarrow e$ is countable and the topological space $s(e)$ is Tychonoff and Baire, then the following assertions are equivalent: (i) $s$ is topologically free; (ii) $A$ has the ideal intersection property, that is if $I$ is a nonzero ideal of $A \rtimes^{\sigma} G$, then $I \cap A \neq \{0\}$; (iii) the ring $A$ is a maximal abelian complex subalgebra of $A \rtimes^{\sigma} G$. Thereby, we generalize a result by Svensson, Silvestrov and de Jeu from the additive group of integers to a large class of groupoids.Comment: 16 pages. This article is an improvement of, and hereby a replacement for, version 1 (arXiv:1006.4776v1) entitled "Category Dynamical Systems and Skew Category Algebras

Charge injection instability in perfect insulators

We show that in a macroscopic perfect insulator, charge injection at a field-enhancing defect is associated with an instability of the insulating state or with bistability of the insulating and the charged state. The effect of a nonlinear carrier mobility is emphasized. The formation of the charged state is governed by two different processes with clearly separated time scales. First, due to a fast growth of a charge-injection mode, a localized charge cloud forms near the injecting defect (or contact). Charge injection stops when the field enhancement is screened below criticality. Secondly, the charge slowly redistributes in the bulk. The linear instability mechanism and the final charged steady state are discussed for a simple model and for cylindrical and spherical geometries. The theory explains an experimentally observed increase of the critical electric field with decreasing size of the injecting contact. Numerical results are presented for dc and ac biased insulators.Comment: Revtex, 7pages, 4 ps figure