2,728 research outputs found
F100 multivariable control synthesis program: A review of full scale engine altitude tests
The benefits of linear quadratic regulator synthesis methods in designing a multivariable engine control capable of operating an engine throughout its flight envelope were demonstrated. The entire multivariable control synthesis program is reviewed with particular emphasis on engine tests conducted in the NASA Lewis propulsion systems laboratory altitude facility. The multivariable control has basically a proportional plus integral, model following structure with gains scheduled as functions of flight condition. The multivariable control logic design is described, along with control computer implementation aspects. Altitude tests demonstrated that the multivariable control logic could control an engine over a wide range of test conditions. Representative transient responses are presented to demonstrate engine behavior and the functioning of the control logic
The Role of Modern Control Theory in the Design of Controls for Aircraft Turbine Engines
Accomplishments in applying Modern Control Theory to the design of controls for advanced aircraft turbine engines were reviewed. The results of successful research programs are discussed. Ongoing programs as well as planned or recommended future thrusts are also discussed
Coulomb blockade and Bloch oscillations in superconducting Ti nanowires
Quantum fluctuations in quasi-one-dimensional superconducting channels
leading to spontaneous changes of the phase of the order parameter by ,
alternatively called quantum phase slips (QPS), manifest themselves as the
finite resistance well below the critical temperature of thin superconducting
nanowires and the suppression of persistent currents in tiny superconducting
nanorings. Here we report the experimental evidence that in a current-biased
superconducting nanowire the same QPS process is responsible for the insulating
state -- the Coulomb blockade. When exposed to RF radiation, the internal Bloch
oscillations can be synchronized with the external RF drive leading to
formation of quantized current steps on the I-V characteristic. The effects
originate from the fundamental quantum duality of a Josephson junction and a
superconducting nanowire governed by QPS -- the QPS junction (QPSJ).Comment: 5 pages, 4 figure
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
Superconducting MoSi nanowires
We have fabricated disordered superconducting nanowires of molybdenium
silicide. A molybdenium nanowire is first deposited on top of silicon, and the
alloy is formed by rapid thermal annealing. The method allows tuning of the
crystal growth to optimise, e.g., the resistivity of the alloy for potential
applications in quantum phase slip devices and superconducting nanowire
single-photon detectors. The wires have effective diameters from 42 to 79 nm,
enabling the observation of crossover from conventional superconductivity to
regimes affected by thermal and quantum fluctuations. In the smallest diameter
wire and at temperatures well below the superconducting critical temperature,
we observe residual resistance and negative magnetoresistance, which can be
considered as fingerprints of quantum phase slips
The Spectral Energy Distribution of Self-gravitating Interstellar Clouds I. Spheres
We derive the spectral energy distribution (SED) of dusty, isothermal, self
gravitating, stable and spherical clouds externally heated by the ambient
interstellar radiation field. For a given radiation field and dust properties,
the radiative transfer problem is determined by the pressure of the surrounding
medium and the cloud mass expressed as a fraction of the maximum stable cloud
mass above which the clouds become gravitational unstable.
To solve the radiative transfer problem a ray-tracing code is used to
accurately derive the light distribution inside the cloud. This code considers
both non isotropic scattering on dust grains and multiple scattering events.
The dust properties inside the clouds are assumed to be the same as in the
diffuse interstellar medium in our galaxy. We analyse the effect of the
pressure, the critical mass fraction, and the ISRF on the SED and present
brightness profiles in the visible, the IR/FIR and the submm/mm regime with the
focus on the scattered emission and the thermal emission from PAH-molecules and
dust grains.Comment: accepted for publication in ApJS, May 2008, v176n1 issu
Spot activity of the RS CVn star {\sigma} Geminorum
We model the photometry of RS CVn star Geminorum to obtain new
information on the changes of the surface starspot distribution, i.e., activity
cycles, differential rotation and active longitudes. We use the previously
published Continuous Periods Search-method (CPS) to analyse V-band differential
photometry obtained between the years 1987 and 2010 with the T3 0.4 m Automated
Telescope at the Fairborn Observatory. The CPS-method divides data into short
subsets and then models the light curves with Fourier-models of variable orders
and provides estimates of the mean magnitude, amplitude, period and light curve
minima. These light curve parameters are then analysed for signs of activity
cycles, differential rotation and active longitudes. We confirm the presence of
two previously found stable active longitudes, synchronised with the orbital
period d and find eight events where the active longitudes
are disrupted. The epochs of the primary light curve minima rotate with a
shorter period d than the orbital motion. If the
variations in the photometric rotation period were to be caused by differential
rotation, this would give a differential rotation coefficient of . The presence of two slightly different periods of active regions may
indicate a superposition of two dynamo modes, one stationary in the orbital
frame and the other one propagating in the azimuthal direction. Our estimate of
the differential rotation is much higher than previous results. However,
simulations show that this can be caused by insufficient sampling in our data.Comment: 10 pages, 6 figures. Submitted to A&
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