11,993 research outputs found
Visualization of hydrogen injection in a scramjet engine by simultaneous PLIF imaging and laser holographic imaging
Flowfield characterization has been accomplished for several fuel injector configurations using simultaneous planar laser induced fluorescence (PLIF) and laser holographic imaging (LHI). The experiments were carried out in the GASL-NASA HYPULSE real gas expansion tube facility, a pulsed facility with steady test times of about 350 microsec. The tests were done at simulated Mach numbers 13.5 and 17. The focus of this paper is on the measurement technologies used and their application in a research facility. The HYPULSE facility, the models used for the experiments, and the setup for the LHI and PLIF measurements are described. Measurement challenges and solutions are discussed. Results are presented for experiments with several fuel injector configurations and several equivalence ratios
Swain Committee Report
Letter addressed to the Secretary of the Navy, the Honorable Josephus H. Daniels, from the Committee appointed by the President of the Society for the Promotion of Engineering Education, to visit the U.S. Naval Academy in Annapolis, MD. The purpose was to evaluate the work of the Post Graduate School. The committee recommended enlarging the enrollment of the Post Graduate School and providing for appropriate funding for buildings, equipment and curricula
Final Report: National Science Foundation Remote Sensing Workshop. Held at Purdue University February 28, 29, March 1, 1984
It was the purpose of this workshop to examine the potential for further advancement of the science of remote sensing, and to define directions which the Engineering aspects of remote sensing research could not take in order to maximize the scientific and technological return
The Cerebellum: A Neural System for the Study of Reinforcement Learning
In its strictest application, the term “reinforcement learning” refers to a computational approach to learning in which an agent (often a machine) interacts with a mutable environment to maximize reward through trial and error. The approach borrows essentials from several fields, most notably Computer Science, Behavioral Neuroscience, and Psychology. At the most basic level, a neural system capable of mediating reinforcement learning must be able to acquire sensory information about the external environment and internal milieu (either directly or through connectivities with other brain regions), must be able to select a behavior to be executed, and must be capable of providing evaluative feedback about the success of that behavior. Given that Psychology informs us that reinforcers, both positive and negative, are stimuli or consequences that increase the probability that the immediately antecedent behavior will be repeated and that reinforcer strength or viability is modulated by the organism's past experience with the reinforcer, its affect, and even the state of its muscles (e.g., eyes open or closed); it is the case that any neural system that supports reinforcement learning must also be sensitive to these same considerations. Once learning is established, such a neural system must finally be able to maintain continued response expression and prevent response drift. In this report, we examine both historical and recent evidence that the cerebellum satisfies all of these requirements. While we report evidence from a variety of learning paradigms, the majority of our discussion will focus on classical conditioning of the rabbit eye blink response as an ideal model system for the study of reinforcement and reinforcement learning
Quantum interference in optical fields and atomic radiation
We discuss the connection between quantum interference effects in optical
beams and radiation fields emitted from atomic systems. We illustrate this
connection by a study of the first- and second-order correlation functions of
optical fields and atomic dipole moments. We explore the role of correlations
between the emitting systems and present examples of practical methods to
implement two systems with non-orthogonal dipole moments. We also derive
general conditions for quantum interference in a two-atom system and for a
control of spontaneous emission. The relation between population trapping and
dark states is also discussed. Moreover, we present quantum dressed-atom models
of cancellation of spontaneous emission, amplification on dark transitions,
fluorescence quenching and coherent population trapping.Comment: To be published in Journal of Modern Optics Special Issue on Quantum
Interferenc
A depression before a bump in the highest energy cosmic ray spectrum
We re-examine the interaction of ultra high energy nuclei with the microwave
background radiation. We find that the giant dipole resonance leaves a new
signature in the differential energy spectrum of iron sources located around 3
Mpc: A depression before the bump which is followed by the expected cutoff.Comment: revisited version, 5 pages RevTex, 5 figure
Transmission spectroscopy of the sodium 'D' doublet in WASP-17b with the VLT
The detection of increased sodium absorption during primary transit implies
the presence of an atmosphere around an extrasolar planet, and enables us to
infer the structure of this atmosphere. Sodium has only been detected in the
atmospheres of two planets to date - HD189733b and HD209458b. WASP-17b is the
least dense planet currently known. It has a radius approximately twice that of
Jupiter and orbits an F6-type star. The transit signal is expected to be about
five times larger than that observed in HD209458b. We obtained 24 spectra with
the GIRAFFE spectrograph on the VLT, eight during transit. The integrated flux
in the sodium doublet at wavelengths 5889.95 and 5895.92 {\AA} was measured at
bandwidths 0.75, 1.5, 3.0, 4.0, 5.0, and 6.0 {\AA}. We find a transit depth of
0.55 \pm 0.13 per cent at 1.5 {\AA}. This suggests that, like HD209458b,
WASP-17b has an atmosphere depleted in sodium compared to models for a
cloud-free atmosphere with solar sodium abundance. We observe a sharp cut-off
in sodium absorption between 3.0 and 4.0 {\AA} which may indicate a layer of
clouds high in the atmosphere.Comment: Amended for typographic conventions following publicatio
Optimal squeezing, pure states, and amplification of squeezing in resonance fluorescence
It is shown that 100% squeezed output can be produced in the resonance
fluorescence from a coherently driven two-level atom interacting with a
squeezed vacuum. This is only possible for squeezed input, and is
associated with a pure atomic state, i.e., a completely polarized state. The
quadrature for which optimal squeezing occurs depends on the squeezing phase
the Rabi frequency and the atomic detuning . Pure
states are described for arbitrary not just or as in
previous work. For small values of there may be a greater degree of
squeezing in the output field than the input - i.e., we have squeezing
amplification.Comment: 6 pages & 7 figures, Submitted to Phys. Rev.
The Implications of M Dwarf Flares on the Detection and Characterization of Exoplanets at Infrared Wavelengths
We present the results of an observational campaign which obtained high time
cadence, high precision, simultaneous optical and IR photometric observations
of three M dwarf flare stars for 47 hours. The campaign was designed to
characterize the behavior of energetic flare events, which routinely occur on M
dwarfs, at IR wavelengths to milli-magnitude precision, and quantify to what
extent such events might influence current and future efforts to detect and
characterize extrasolar planets surrounding these stars. We detected and
characterized four highly energetic optical flares having U-band total energies
of ~7.8x10^30 to ~1.3x10^32 ergs, and found no corresponding response in the J,
H, or Ks bandpasses at the precision of our data. For active dM3e stars, we
find that a ~1.3x10^32 erg U-band flare (delta Umax ~1.5 mag) will induce <8.3
(J), <8.5 (H), and <11.7 (Ks) milli-mags of a response. A flare of this energy
or greater should occur less than once per 18 hours. For active dM4.5e stars,
we find that a ~5.1x10^31 erg U-band flare (delta Umax ~1.6 mag) will induce
<7.8 (J), <8.8 (H), and <5.1 (Ks) milli-mags of a response. A flare of this
energy or greater should occur less than once per 10 hours. No evidence of
stellar variability not associated with discrete flare events was observed at
the level of ~3.9 milli-mags over 1 hour time-scales and at the level of ~5.6
milli-mags over 7.5 hour time-scales. We therefore demonstrate that most M
dwarf stellar activity and flares will not influence IR detection and
characterization studies of M dwarf exoplanets above the level of ~5-11
milli-mags, depending on the filter and spectral type. We speculate that the
most energetic megaflares on M dwarfs, which occur at rates of once per month,
are likely to be easily detected in IR observations with sensitivity of tens of
milli-mags.Comment: Accepted in Astronomical Journal, 17 pages, 6 figure
Time evolution of the Rabi Hamiltonian from the unexcited vacuum
The Rabi Hamiltonian describes a single mode of electromagnetic radiation
interacting with a two-level atom. Using the coupled cluster method, we
investigate the time evolution of this system from an initially empty field
mode and an unexcited atom. We give results for the atomic inversion and field
occupation, and find that the virtual processes cause the field to be squeezed.
No anti-bunching occurs.Comment: 25 pages, 8 figures, RevTe
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