12,104 research outputs found
Dispersion enhancement and damping by buoyancy driven flows in 2D networks of capillaries
The influence of a small relative density difference on the displacement of
two miscible liquids is studied experimentally in transparent 2D networks of
micro channels. Both stable displacements in which the denser fluid enters at
the bottom of the cell and displaces the lighter one and unstable displacements
in which the lighter fluid is injected at the bottom and displaces the denser
one are realized. Except at the lowest mean flow velocity U, the average
of the relative concentration satisfies a convection-dispersion
equation. The dispersion coefficient is studied as function of the relative
magnitude of fluid velocity and of the velocity of buoyancy driven fluid
motion. A model is suggested and its applicability to previous results obtained
in 3D media is discussed
Spectral interferometric polarised coherent anti-Stokes Raman spectroscopy
We have developed an interferometric implementation of coherent anti-Stokes
Raman scattering (CARS) which enables broadband coherent Raman spectroscopy
free from non-resonant background (NRB), with a signal strength proportional to
concentration. Spectra encode mode symmetry information into the amplitude
response which can be directly compared to polarised spontaneous Raman spectra.
The method requires only passive polarisation optics and is suitable for a wide
range of laser linewidths and pulse durationsComment: 5 pages, 3 figures, submitted to PR
Pulse shaping with birefringent crystals: a tool for quantum metrology
A method for time differentiation based on a Babinet-Soleil-Bravais
compensator is introduced. The complex transfer function of the device is
measured using polarization spectral interferometry. Time differentiation of
both the pulse field and pulse envelope are demonstrated over a spectral width
of about 100 THz with a measured overlap with the objective mode greater than
99.8%. This pulse shaping technique is shown to be perfectly suited to time
metrology at the quantum limit
Tomorrow's Metamaterials: Manipulation of Electromagnetic Waves in Space, Time and Spacetime
Metamaterials represent one of the most vibrant fields of modern science and
technology. They are generally dispersive structures in the direct and
reciprocal space and time domains. Upon this consideration, I overview here a
number of metamaterial innovations developed by colleagues and myself in the
holistic framework of space and time dispersion engineering. Moreover, I
provide some thoughts regarding the future perspectives of the area
Study of radar pulse compression for high resolution satellite altimetry
Pulse compression techniques are studied which are applicable to a satellite altimeter having a topographic resolution of + 10 cm. A systematic design procedure is used to determine the system parameters. The performance of an optimum, maximum likelihood processor is analysed, which provides the basis for modifying the standard split-gate tracker to achieve improved performance. Bandwidth considerations lead to the recommendation of a full deramp STRETCH pulse compression technique followed by an analog filter bank to separate range returns. The implementation of the recommended technique is examined
Characterizing Exoplanets in the Visible and Infrared: A Spectrometer Concept for the EChO Space Mission
Transit-spectroscopy of exoplanets is one of the key observational techniques
to characterize the extrasolar planet and its atmosphere. The observational
challenges of these measurements require dedicated instrumentation and only the
space environment allows an undisturbed access to earth-like atmospheric
features such as water or carbon-dioxide. Therefore, several exoplanet-specific
space missions are currently being studied. One of them is EChO, the Exoplanet
Characterization Observatory, which is part of ESA's Cosmic Vision 2015-2025
program, and which is one of four candidates for the M3 launch slot in 2024. In
this paper we present the results of our assessment study of the EChO
spectrometer, the only science instrument onboard this spacecraft. The
instrument is a multi-channel all-reflective dispersive spectrometer, covering
the wavelength range from 400 nm to 16 microns simultaneously with a moderately
low spectral resolution. We illustrate how the key technical challenge of the
EChO mission - the high photometric stability - influences the choice of
spectrometer concept and drives fundamentally the instrument design. First
performance evaluations underline the fitness of the elaborated design solution
for the needs of the EChO mission.Comment: 20 pages, 8 figures, accepted for publication in the Journal of
Astronomical Instrumentatio
Application of weighted average velocity (WAVe) method to determine Vs,30
AbstractThe weighted average velocity (WAVe) method was recently proposed as an alternative inversion algorithm for obtaining shear-wave velocity (Vs) profiles from Rayleigh wave dispersion curves. In this paper, the WAVe method is discussed in relation to its accuracy in estimating the average shear-wave velocity to 30m (Vs,30) and to other depths (Vs,z). Values for Vs,30 are used in building codes to determine ground-type classes for seismic design. Five case studies, representing typical shear-wave velocity (Vs) profiles, are presented. The Vs profiles obtained using the WAVe method and those obtained using more rigorous inversion methods were quantitatively compared based on Vs,30 as well as Vs, z. The comparison showed that the WAVe method yielded similar Vs profiles and Vs,30 leading to same ground type for seismic design
A Study of DAS delays and their Impact on the Wireless Channels with Application to Indoor Localization
This research evaluates the Distributed Antenna Systems (DAS) introduced delays and their effects on the indoor channel in simulcast situations where the effect of delays is most prevalent. Different simulcast cases that form the basic building blocks are analyzed to form an understanding of the problem. Two case studies of important indoor environments are presented. Importance of improving ray tracing simulations to include propagation and DAS delays is highlighted.
The paper also introduces a DAS element representation and delay mapping model and explores techniques of engineering DAS delays to optimize location estimation by ranging and RF fingerprinting to achieve E911 mandated accuracy.
A brief description is introduced for a Software Defined Radio (SDR) implementation of a Correlation Channel Sounder and the possible application of channel sounding for indoor DAS. The paper suggests procedures to produce a full DAS delay profile and ways to optimize it for location estimation
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