17,479 research outputs found
On the dragging of light by a rotating medium
When light is passing through a rotating medium the optical polarization is rotated. Recently, it has been reasoned that this rotation applies also to the transmitted image. We examine these two phenomena by extending an analysis of Player (Player 1976 Proc. R. Soc. A 349, 441-445) to general electromagnetic fields. We find that in this more general case, the wave equation inside the rotating medium has to be amended by a term which is connected to the orbital angular momentum (OAM) of the light. We show that optical spin and OAM account for the rotation of the polarization and the rotation of the transmitted image, respectively
Evaluation of non-intrusive flow measurement techniques for a re-entry flight experiment
This study evaluates various non-intrusive techniques for the measurement of the flow field on the windward side of the Space Shuttle orbiter or a similar reentry vehicle. Included are linear (Rayleigh, Raman, Mie, Laser Doppler Velocimetry, Resonant Doppler Velocimetry) and nonlinear (Coherent Anti-Stokes Raman, Laser-Induced Fluorescence) light scattering, electron-beam fluorescence, thermal emission, and mass spectroscopy. Flow-field properties were taken from a nonequilibrium flow model by Shinn, Moss, and Simmonds at the NASA Langley Research Center. Conclusions are, when possible, based on quantitative scaling of known laboratory results to the conditions projected. Detailed discussion with researchers in the field contributed further to these conclusions and provided valuable insights regarding the experimental feasibility of each of the techniques
Non-intrusive flow measurements on a reentry vehicle
This study evaluates the utility of various non-intrusive techniques for the measurement of the flow field on the windward side of the Space Shuttle or a similar re-entry vehicle. Included are linear (Rayleigh, Raman, Mie, Laser Doppler Velocimetry, Resonant Doppler Velocimetry) and nonlinear (Coherent Anti-Stokes Raman, Laser Induced Fluorescence) light scattering, electron beam fluorescence, thermal emission and mass spectroscopy. Flow field properties are taken from a nonequilibrium flow model by Shinn, Moss and Simmonds at NASA Langley. Conclusions are, when possible, based on quantitative scaling of known laboratory results to the conditions projected. Detailed discussion with researchers in the field contributed further to these conclusions and provided valuable insights regarding the experimental feasibility of each of the techniques
State-of-the-Art: the quality of case study research in innovation management
The practice of innovation management is developing fast. As new concepts emerge, exploratory studies are needed and case study research is often appropriate. To investigate the usage and quality of case study research in innovation management, all of the articles published in five top journals over 20 years (1997–2016) were reviewed. Case study research accounted for 818 of the published articles in this period (12%) and an evaluation template (termed case study evaluation template: CASET) was developed to objectively assess these articles against 10 quality criteria. It was found that the quality of case study research has often been low, although it has improved over time. Similarly, quality was found to fluctuate both within and between the different innovation journals. This indicates that the peer review process for case study research is not as robust as it should be. The assessment of individual articles using the evaluation template found significant deficiencies. Many articles: did not justify why case study research was appropriate; did not apply theoretical sampling criteria; were not transparent on how conclusions were drawn from the data; did not consider validity and reliability adequately; and did not go beyond description in their interpretation. However, the evaluation template also identified 23 “exemplary studies,” which clearly addressed nearly every criterion. Such exemplary studies provide innovation management researchers with “benchmark” reading, which can help shape their own research. This article makes four contributions to the innovation management discipline. First, the evaluation template and exemplary studies can help innovation researchers improve the quality of their case study research. Second, clear recommendations are given for how reviewers can use the template to make the peer review process more consistent and robust. Third, journal editors are encouraged to consider the implications of the findings for their particular journal. Fourth, the article should stimulate a long overdue debate on methodology in innovation management research, including the use of case study research
Compressed sensing with near-field THz radiation
We demonstrate a form of near-field terahertz (THz) imaging that is compatible with compressed sensing algorithms. By spatially photomodulating THz pulses using a set of shaped binary optical patterns and employing a 6-μm-thick silicon wafer, we are able to reconstruct THz images of an object placed on the exit interface of the wafer. A single-element detector is used to measure the electric field amplitude of transmitted THz radiation for each projected pattern, with the ultra-thin wafer allowing us to access the THz evanescent near fields to achieve a spatial resolution of ∼9 μm∼9 μm
Testing the existence of optical linear polarization in young brown dwarfs
Linear polarization can be used as a probe of the existence of atmospheric
condensates in ultracool dwarfs. Models predict that the observed linear
polarization increases withthe degree of oblateness, which is inversely
proportional to the surface gravity. We aimed to test the existence of optical
linear polarization in a sample of bright young brown dwarfs, with spectral
types between M6 and L2, observable from the Calar Alto Observatory, and
cataloged previously as low gravity objects using spectroscopy. Linear
polarimetric images were collected in I and R-band using CAFOS at the 2.2 m
telescope in Calar Alto Observatory (Spain). The flux ratio method was employed
to determine the linear polarization degrees. With a confidence of 3,
our data indicate that all targets have a linear polarimetry degree in average
below 0.69% in the I-band, and below 1.0% in the R-band, at the time they were
observed. We detected significant (i.e. P/ 3) linear polarization
for the young M6 dwarf 2MASS J04221413+1530525 in the R-band, with a degree of
= 0.81 0.17 %.Comment: Accepted for publication in MNRA
Adaptive foveated single-pixel imaging with dynamic super-sampling
As an alternative to conventional multi-pixel cameras, single-pixel cameras
enable images to be recorded using a single detector that measures the
correlations between the scene and a set of patterns. However, to fully sample
a scene in this way requires at least the same number of correlation
measurements as there are pixels in the reconstructed image. Therefore
single-pixel imaging systems typically exhibit low frame-rates. To mitigate
this, a range of compressive sensing techniques have been developed which rely
on a priori knowledge of the scene to reconstruct images from an under-sampled
set of measurements. In this work we take a different approach and adopt a
strategy inspired by the foveated vision systems found in the animal kingdom -
a framework that exploits the spatio-temporal redundancy present in many
dynamic scenes. In our single-pixel imaging system a high-resolution foveal
region follows motion within the scene, but unlike a simple zoom, every frame
delivers new spatial information from across the entire field-of-view. Using
this approach we demonstrate a four-fold reduction in the time taken to record
the detail of rapidly evolving features, whilst simultaneously accumulating
detail of more slowly evolving regions over several consecutive frames. This
tiered super-sampling technique enables the reconstruction of video streams in
which both the resolution and the effective exposure-time spatially vary and
adapt dynamically in response to the evolution of the scene. The methods
described here can complement existing compressive sensing approaches and may
be applied to enhance a variety of computational imagers that rely on
sequential correlation measurements.Comment: 13 pages, 5 figure
Experimental Study of Parametric Autoresonance in Faraday Waves
The excitation of large amplitude nonlinear waves is achieved via parametric
autoresonance of Faraday waves. We experimentally demonstrate that phase
locking to low amplitude driving can generate persistent high-amplitude growth
of nonlinear waves in a dissipative system. The experiments presented are in
excellent agreement with theory.Comment: 4 pages, 4 eps figures, to appear in Phys. Rev. Let
- …