1,126 research outputs found
Free-flight model investigation of a vertical-attitude VTOL fighter with twin vertical tails
Free-flight tests were conducted in the Langley full-scale tunnel to determine the stability and control characteristics of a vertical-attitude VTOL fighter having twin vertical tails and a pivoted fuselage forebody (nose-cockpit) arrangement. The flight tests included hovering flights and transition flights from hover to conventional forward flight. Static force tests were also made to aid in the analysis of the flight tests. The model exhibited satisfactory stability and control characteristics, and the transition from hovering flight to conventional forward flight was relatively smooth and straightforward
Free-flight model investigation of a vertical-attitude VTOL fighter
Tests were made in the Langley full-scale tunnel and included a study of the stability and control characteristics of delta- and swept-wing configurations from hovering through the transition to normal forward flight. Static force tests were also conducted to aid in the analysis of the flight tests. With conventional artificial rate stabilization, very smooth transitions could be made consistently with relatively little difficulty. Because of the lower apparent damping and a tendency to diverge in yaw, however, the swept-wing configuration was considered to be much more difficult to fly than the delta-wing configuration. With rate dampers off, both configurations were very difficult to control and the control power needed for satisfactory flights was substantially higher than with the rate dampers operating
Back-reaction of perturbation wave packets on gray solitons
Within the Bogoliubov-de Gennes linearization theory of quantum or classical
perturbations around a background solution to the one-dimensional nonlinear
Schr\"odinger equation, we study the back-reaction of wave packet perturbations
on a gray soliton background. From our recently published exact solutions, we
determine that a wave packet effectively jumps ahead as it passes through a
soliton, emerging with a wavelength-dependent forward translation in comparison
to its motion in absence of the soliton. From this and from the full theory's
exact momentum conservation, we deduce that post-Bogoliubov back-reaction must
include a commensurate forward advance by the soliton itself. We quantify this
effect with a simple theory, and confirm that it agrees with full numerical
solution of the classical nonlinear Schr\"odinger equation. We briefly discuss
the implications of this effect for quantum behavior of solitons in
quasi-condensed dilute gases at finite temperature.Comment: 12 pages, 2 figure
Sonic analog of gravitational black holes in Bose-Einstein condensates
It is shown that, in dilute-gas Bose-Einstein condensates, there exist both
dynamically stable and unstable configurations which, in the hydrodynamic
limit, exhibit a behavior resembling that of gravitational black holes. The
dynamical instabilities involve creation of quasiparticle pairs in positive and
negative energy states, as in the well-known suggested mechanism for black hole
evaporation. We propose a scheme to generate a stable sonic black hole in a
ring trap.Comment: RevTeX 3.1, 1 figure, 4 page
Low-speed stability and control wind-tunnel investigations of effects of spanwise blowing on fighter flight characteristics at high angles of attack
The effects of spanwise blowing on two configurations representative of current fighter airplanes were investigated. The two configurations differed only in wing planform, with one incorporating a trapezoidal wing and the other a 60 delta wing. Emphasis was on determining the lateral-directional characteristics, particularly in the stall/departure angle-of-attack range; however, the effects of spanwise blowing on the longitudinal aerodynamics were also determined. The-tunnel tests included measurement of static force and forced-oscillation aerodynamic data, visualization of the airflow changes created by the spanwise blowing, and free-flight model tests. The effects of blowing rate, chordwise location of the blowing ports, asymmetric blowing, and blowing on the conventional aerodynamic control characteristics were investigated. In the angle-of-attack regions in which the spanwise blowing substantially improved the wing upper-surface flow field (i.e., provided reattachment of the flow aft of the leading-edge vortex), improvements in both static and dynamic lateral-directional stability were observed. Blowing effects on stability could be proverse or adverse depending on blowing rate, blowing port loaction, and wing planform. Free-flight model tests of the trapezoidal wing confirmed the beneficial effects of spanwise blowing measured in the static and dynamic force tests
Stereosat: A proposed private sector/government joint venture in remote sensing from space
Stereosat, a free flying Sun synchronous satellite whose purpose is to obtain worldwide cloud-free stereoscopic images of the Earth's land masses, is proposed as a joint private sector/government venture. A number of potential organization models are identified. The legal, economic, and institutional issues which could impact the continuum of potential joint private sector/government institutional structures are examined
Static force tests of a model of a twin-jet fighter airplane for angles of attack from minus 10 deg to 110 deg and sideslip angles from minus 40 deg to 40 deg
Static force tests of model of twin jet fighter aircraft at various angles of attack and sideslip angles to obtain data for theoretical spin studie
Hip-Hop Hamlet: Hybrid Interpretive Discourse in a Suburban High School English Class
This study investigates the collaborative composing processes of a group of five high school seniors who constructed interpretations of each of the five acts of Shakespeare’s Hamlet through the medium of spoken word performances. The group composing processes were analyzed to identify how the students drew on conventions from the spoken word tradition to phrase and perform their interpretations. Findings indicate that across the five spoken word performances, the retelling of the Hamlet narrative involved a set of decisions that were both constrained and afforded by the rap medium. The students’ discussion of how to rewrite the story in the condensed poetic form of a rap required them to clarify events from Shakespeare’s version and both summarize them and interpret them both in their discussion and in their own text. Their interpretive work involved the incorporation of a variety of rap and other pop culture conventions such that their deliberation regarding word choice and accompanying performative elements necessitated careful consideration of the meaning that they found in Shakespeare’s version of the story, itself an adaptation from extant cultural narratives. The study concludes with a consideration of their spoken word interpretations as comprising a hybrid discourse that enabled exploratory interpretive talk that contributed to their understanding of the drama through the collaborative composition of their own representational text
Decoherence and Recoherence in Model Quantum Systems
We discuss the various manifestations of quantum decoherence in the forms of
dephasing, entanglement with the environment, and revelation of "which-path"
information. As a specific example, we consider an electron interference
experiment. The coupling of the coherent electrons to the quantized
electromagnetic field illustrates all of these versions of decoherence. This
decoherence has two equivalent interpretations, in terms of photon emission or
in terms of Aharonov-Bohm phase fluctuations. We consider the case when the
coherent electrons are coupled to photons in a squeezed vacuum state. The
time-averaged result is increased decoherence. However, if only electrons which
are emitted during selected periods are counted, the decoherence can be
suppressed below the level for the photon vacuum. This is the phenomenon of
recoherence. This effect is closely related to the quantum violations of the
weak energy condition, and is restricted by similar inequalities. We give some
estimates of the magnitude of the recoherence effect and discuss prospects for
observing it in an electron interferometry experiment.Comment: 8 pages, 3 figures, talk presented at the 7th Friedmann Seminar, Joao
Pessoa, Brazil, July 200
Ultra-heavy cosmic rays: Theoretical implications of recent observations
Extreme ultraheavy cosmic ray observations (Z greater or equal 70) are compared with r-process models. A detailed cosmic ray propagation calculation is used to transform the calculated source distributions to those observed at the earth. The r-process production abundances are calculated using different mass formulae and beta-rate formulae; an empirical estimate based on the observed solar system abundances is used also. There is the continued strong indication of an r-process dominance in the extreme ultra-heavy cosmic rays. However it is shown that the observed high actinide/Pt ratio in the cosmic rays cannot be fit with the same r-process calculation which also fits the solar system material. This result suggests that the cosmic rays probably undergo some preferential acceleration in addition to the apparent general enrichment in heavy (r-process) material. As estimate also is made of the expected relative abundance of superheavy elements in the cosmic rays if the anomalous heavy xenon in carbonaceous chondrites is due to a fissioning superheavy element
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