1,223 research outputs found
Landing impact studies of a 0.3-scale model air cushion landing system for a Navy fighter airplane
An experimental study was conducted in order to determine the landing-impact behavior of a 0.3-scale, dynamically (but not physically) similar model of a high-density Navy fighter equipped with an air cushion landing system. The model was tested over a range of landing contact attitudes at high forward speeds and sink rates on a specialized test fixture at the Langley aircraft landing loads and traction facility. The investigation indicated that vertical acceleration at landing impact was highly dependent on the pitch angle at ground contact, the higher acceleration of approximately 5g occurring near zero body-pitch attitude. A limited number of low-speed taxi tests were made in order to determine model stability characteristics. The model was found to have good pitch-damping characteristics but stability in roll was marginal
Phase Equilibrium in the 1-Butene-Water System and Correlation of Hydrocarbon-Water Solubility Data
Letter from T. W. Leland, Educational Director, American Institute of Accountants, to the Librarian [of Other Firms], Re: Pamphlet Entitled, Public Accounting as a Career .
Experimental and analytical dynamic flow characteristics of an axial-flow fan from an air cushion landing system model
An investigation was conducted to compare the steady-state and dynamic flow characteristics of an axial-flow fan which had been used previously as the air supply fan for some model air cushion landing system studies. Steady-state flow characteristics were determined in the standard manner by using differential orifice pressures for the flow regime from free flow to zero flow. In this same regime, a correlative technique was established so that fan inlet and outlet pressures could be used to measure dynamic flow as created by a rotating damper. Dynamic tests at damper frequencies up to 5 Hz showed very different flow characteristics when compared with steady-state flow, particularly with respect to peak pressures and the pressure-flow relationship at fan stall and unstall. A generalized, rational mathematical fan model was developed based on physical fan parameters and a steady-state flow characteristic. The model showed good correlation with experimental tests at damper frequencies up to 5 Hz
Short-range cluster spin glass near optimal superconductivity in BaFeNiAs
High-temperature superconductivity in iron pnictides occurs when electrons
are doped into their antiferromagnetic (AF) parent compounds. In addition to
inducing superconductivity, electron-doping also changes the static
commensurate AF order in the undoped parent compounds into short-range
incommensurate AF order near optimal superconductivity. Here we use neutron
scattering to demonstrate that the incommensurate AF order in
BaFeNiAs is not a spin-density-wave arising from the
itinerant electrons in nested Fermi surfaces, but consistent with a cluster
spin glass in the matrix of the superconducting phase. Therefore, optimal
superconductivity in iron pnictides coexists and competes with a mesoscopically
separated cluster spin glass phase, much different from the homogeneous
coexisting AF and superconducting phases in the underdoped regime.Comment: 4 figure
Spin Waves in Detwinned BaFeAs
Understanding magnetic interactions in the parent compounds of
high-temperature superconductors forms the basis for determining their role for
the mechanism of superconductivity. For parent compounds of iron pnictide
superconductors such as FeAs ( Ba, Ca, Sr), although spin
excitations have been mapped out throughout the entire Brillouin zone (BZ),
measurements were carried out on twinned samples and did not allow for a
conclusive determination of the spin dynamics. Here we use inelastic neutron
scattering to completely map out spin excitations of 100\% detwinned
BaFeAs. By comparing observed spectra with theoretical calculations, we
conclude that the spin excitations can be well described by an itinerant model
with important contributions from electronic correlations.Comment: 6 pages, 4 figures, with supplemental materia
GT2006-90778 A DESIGN TO INCREASE THE STATIC STIFFNESS OF HOLE PATTERN STATOR GAS SEALS
ABSTRACT An analysis is presented which shows that a deep groove located at about 60% along the axial length from the inlet will approximately double the static stiffness of a holepattern-stator, annular gas seal. Test results for a seal using this geometry generally confirm the correctness of this prediction. The groove also produces an increase in leakage by about 4% and a modest decrease in effective damping. INTRODUCTION Injection compressors require comparatively long annular seals with high pressure drops that have a significant impact on rotordynamics. The balance-piston seal for straightthrough compressors usually absorbs the full head rise of the machine. For back-to-back machines, the division-wall seal normally takes about one half of the machine's head rise but deals with higher density gas. Annular seals using smooth rotors and honeycomb (HC) stators have been used since the 1960s in some petrochemical compressors. Conventional aluminum labyrinths were replaced because of the corrosion resistance of a stainless steel honeycomb material. HC surfaces are normally made from high-temperature stainless steels that have been developed as abradable surfaces for tooth-on-rotor labyrinths in aircraft gas turbines. This material is unforgiving in a rubbing condition. In addition, long lead times are frequently involved in securing a custom-manufactured honeycomb seal for a compressor. In response to these circumstances, Yu and Childs [1] tested three aluminum hole-pattern (HP) stator seals. The seal with a hole-area density of 60% performed as well as previously tested honeycomb-stator seals. Moore et al
Delays in IP routers, a Markov model
Delays in routers are an important component of end-to-end delay and therefore have a significant impact on quality of service. While the other component, the propagation time, is easy to predict as the distance divided by the speed of light inside the link, the queueing delays of packets inside routers depend on the current, usually dynamically changing congestion and on the stochastic features of the flows. We use a Markov model taking into account the distribution of the size of packets and self-similarity of incoming flows to investigate their impact on the queueing delays and their dynamics
Large Scale Cross-Correlations in Internet Traffic
The Internet is a complex network of interconnected routers and the existence
of collective behavior such as congestion suggests that the correlations
between different connections play a crucial role. It is thus critical to
measure and quantify these correlations. We use methods of random matrix theory
(RMT) to analyze the cross-correlation matrix C of information flow changes of
650 connections between 26 routers of the French scientific network `Renater'.
We find that C has the universal properties of the Gaussian orthogonal ensemble
of random matrices: The distribution of eigenvalues--up to a rescaling which
exhibits a typical correlation time of the order 10 minutes--and the spacing
distribution follow the predictions of RMT. There are some deviations for large
eigenvalues which contain network-specific information and which identify
genuine correlations between connections. The study of the most correlated
connections reveals the existence of `active centers' which are exchanging
information with a large number of routers thereby inducing correlations
between the corresponding connections. These strong correlations could be a
reason for the observed self-similarity in the WWW traffic.Comment: 7 pages, 6 figures, final versio
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