6,891 research outputs found
Mechanical Evidence of the Orbital Angular Momentum to Energy Ratio of Vortex Beams
We measure, in a single experiment, both the radiation pressure and the torque due to a wide variety of
propagating acoustic vortex beams. The results validate, for the first time directly, the theoretically
predicted ratio of the orbital angular momentum to linear momentum in a propagating beam. We
experimentally determine this ratio using simultaneous measurements of both the levitation force and
the torque on an acoustic absorber exerted by a broad range of helical ultrasonic beams produced by a
1000-element matrix transducer array. In general, beams with helical phase fronts have been shown to
contain orbital angular momentum as the result of the azimuthal component of the Poynting vector around
the propagation axis. Theory predicts that for both optical and acoustic helical beams the ratio of the
angular momentum current of the beam to the power should be given by the ratio of the beamβs
topological charge to its angular frequency. This direct experimental observation that the ratio of the
torque to power does convincingly match the expected value (given by the topological charge to angular
frequency ratio of the beam) is a fundamental result
Combustion of hydrogen injected into a supersonic airstream (the SHIP computer program)
The mathematical and physical basis of the SHIP computer program which embodies a finite-difference, implicit numerical procedure for the computation of hydrogen injected into a supersonic airstream at an angle ranging from normal to parallel to the airstream main flow direction is described. The physical hypotheses built into the program include: a two-equation turbulence model, and a chemical equilibrium model for the hydrogen-oxygen reaction. Typical results for equilibrium combustion are presented and exhibit qualitatively plausible behavior. The computer time required for a given case is approximately 1 minute on a CDC 7600 machine. A discussion of the assumption of parabolic flow in the injection region is given which suggests that improvement in calculation in this region could be obtained by use of the partially parabolic procedure of Pratap and Spalding. It is concluded that the technique described herein provides the basis for an efficient and reliable means for predicting the effects of hydrogen injection into supersonic airstreams and of its subsequent combustion
Fast localized wavefront correction using area-mapped phase-shift interferometry
We propose an innovative method for localized wavefront correction based on area-mapped phase-shift (AMPS) interferometry. In this Letter, we present the theory and then experimentally compare it with a previously demonstrated method based on spot-optimized phase-stepping (SOPS) interferometry. We found that AMPS outperforms SOPS interferometry in terms of speed by threefold, although in noisy environments the improvements may be larger. AMPS yielded similar point-spread functions (PSF) as SOPS for moderate system-induced aberrations, but yielded a slightly less ideal PSF for larger aberrations. The method described in this Letter may prove crucial for applications where the phase-stepping solution does not have sufficient speed
Recent Decisions
Comments on recent decisions by Joseph C. Spalding, R. Emmett Fitzgerald, Howard G. Burke, Andrew V. Giorgi, Richard F. Welter, Edward L. Burke, Frank A. Howard, Robert C. Enburg, Carl F. Eiberger, William L. Kirchner, Jr., and William J. Hurley
Video recording true single-photon double-slit interference
As normally used, no commercially available camera has a low-enough dark
noise to directly produce video recordings of double-slit interference at the
photon-by-photon level, because readout noise significantly contaminates or
overwhelms the signal. In this work, noise levels are significantly reduced by
turning on the camera only when the presence of a photon has been heralded by
the arrival, at an independent detector, of a time-correlated photon produced
via parametric down-conversion. This triggering scheme provides the improvement
required for direct video imaging of Young's double-slit experiment with single
photons, allowing clarified versions of this foundational demonstration.
Further, we introduce variations on this experiment aimed at promoting
discussion of the role spatial coherence plays in such a measurement. We also
emphasize complementary aspects of single-photon measurement, where imaging
yields (transverse) position information, while diffraction yields the
transverse momentum, and highlight the roles of transverse position and
momentum correlations between down-converted photons, including examples of
"ghost" imaging and diffraction. The videos can be accessed at
http://sun.iwu.edu/~gspaldin/SinglePhotonVideos.html online.Comment: 7 pages, 8 figure
Π€ΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΠΏΠΎΠ½ΠΈΠΌΠ°Π½ΠΈΡ ΠΈ ΡΠΏΠΎΡΡΠ΅Π±Π»Π΅Π½ΠΈΡ Π³Π»ΡΠ±ΠΈΠ½Π½ΡΡ ΡΠΈΠ½ΡΠ°ΠΊΡΠΈΡΠ΅ΡΠΊΠΈΡ ΠΊΠΎΠ½ΡΡΡΡΠΊΡΠΈΠΉ Ρ Π΄Π΅ΡΠ΅ΠΉ Ρ ΡΠ°ΡΡΡΡΠΎΠΉΡΡΠ²Π°ΠΌΠΈ Π°ΡΡΠΈΡΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠΏΠ΅ΠΊΡΡΠ°
Π Ρ
ΠΎΠ΄Π΅ Π°Π½Π°Π»ΠΈΠ·Π° Π½Π°ΡΡΠ½ΡΡ
ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠΉ Π±ΡΠ»ΠΎ Π²ΡΡΠ²Π»Π΅Π½ΠΎ, ΡΡΠΎ Π΄Π΅ΡΠΈ Ρ ΡΠ°ΡΡΡΡΠΎΠΉΡΡΠ²Π°ΠΌΠΈ Π°ΡΡΠΈΡΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠΏΠ΅ΠΊΡΡΠ° ΠΈΡΠΏΡΡΡΠ²Π°ΡΡ ΡΡΡΠ΄Π½ΠΎΡΡΠΈ Π² ΡΠΏΠΎΠ½ΡΠ°Π½Π½ΠΎΠΌ ΠΎΠ²Π»Π°Π΄Π΅Π½ΠΈΠΈ ΡΡΠ°Π·ΠΎΠ²ΠΎΠΉ ΡΠ΅ΡΡΡ. ΠΠ°Π±Π»ΡΠ΄Π΅Π½ΠΈΡ ΠΏΠΎΠΊΠ°Π·Π°Π»ΠΈ, ΡΡΠΎ ΡΡΠ°Π΄ΠΈΡΠΈΠΎΠ½Π½ΡΠ΅ ΠΌΠ΅ΡΠΎΠ΄Ρ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π³Π»ΡΠ±ΠΈΠ½Π½ΡΡ
ΡΠΈΠ½ΡΠ°ΠΊΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΊΠΎΠ½ΡΡΡΡΠΊΡΠΈΠΉ Π² ΡΠ²ΠΎΡΠΌ ΠΏΠ΅ΡΠ²ΠΎΠ·Π΄Π°Π½Π½ΠΎΠΌ Π²ΠΈΠ΄Π΅ ΡΠ²Π»ΡΡΡΡΡ Π½Π΅ ΡΠΎΠ²ΡΠ΅ΠΌ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΡΠΌ ΠΌΠ΅ΡΠΎΠ΄ΠΎΠΌ Π² ΡΠ°Π±ΠΎΡΠ΅ Ρ Π΄Π΅ΡΡΠΌΠΈ Ρ Π°ΡΡΠΈΠ·ΠΌΠΎΠΌ. ΠΡΠΎΠ²Π΅Π΄Π΅Π½Π½ΡΠΉ ΡΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½Ρ Π΄ΠΎΠΊΠ°Π·Π°Π», ΡΡΠΎ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠ΅ ΡΡΠ°Π΄ΠΈΡΠΈΠΎΠ½Π½ΠΎΠΉ ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠΈ ΠΏΠΎ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΠΏΠΎΠ½ΠΈΠΌΠ°Π½ΠΈΡ ΠΈ ΡΠΏΠΎΡΡΠ΅Π±Π»Π΅Π½ΠΈΡ Π³Π»ΡΠ±ΠΈΠ½Π½ΡΡ
ΡΠΈΠ½ΡΠ°ΠΊΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΊΠΎΠ½ΡΡΡΡΠΊΡΠΈΠΉ Π±ΡΠ΄Π΅Ρ Π±ΠΎΠ»Π΅Π΅ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎ Π΄Π»Ρ ΠΎΠ±ΡΡΠ΅Π½ΠΈΡ Π΄Π΅ΡΠ΅ΠΉ Ρ ΡΠ°ΡΡΡΡΠΎΠΉΡΡΠ²Π°ΠΌΠΈ Π°ΡΡΠΈΡΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠΏΠ΅ΠΊΡΡΠ° ΠΏΡΠΈ ΡΡΠ»ΠΎΠ²ΠΈΠΈ, ΡΡΠΎ ΠΎΠ½Π° Π±ΡΠ΄Π΅Ρ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½Π° Π² ΡΠΎΡΠ΅ΡΠ°Π½ΠΈΠΈ Ρ ΠΌΠ΅ΡΠΎΠ΄Π°ΠΌΠΈ ΠΏΡΠΈΠΊΠ»Π°Π΄Π½ΠΎΠ³ΠΎ Π°Π½Π°Π»ΠΈΠ·Π° ΠΏΠΎΠ²Π΅Π΄Π΅Π½ΠΈΡ
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