3,632 research outputs found
Generalization of a 3-D resonator model for the simulation of spherical enclosures
A rectangular enclosure has such an even distribution of resonances that it
can be accurately and efficiently modelled using a feedback delay network.
Conversely, a non rectangular shape such as a sphere has a distribution of
resonances that challenges the construction of an efficient model. This work
proposes an extension of the already known feedback delay network structure to
model the resonant properties of a sphere. A specific frequency distribution of
resonances can be approximated, up to a certain frequency, by inserting an
allpass filter of moderate order after each delay line of a feedback delay
network. The structure used for rectangular boxes is therefore augmented with a
set of allpass filters allowing parametric control over the enclosure size and
the boundary properties. This work was motivated by informal listening tests
which have shown that it is possible to identify a basic shape just from the
distribution of its audible resonances.Comment: 39 pages, 16 figures, 6 tables. Accepted for publication in Applied
Signal Processin
Three-dimensional interferometric, spectrometric, and planetary views of Procyon
We used a new realistic 3D radiative-hydrodynamical model atmosphere of
Procyon generated with the Stagger Code and synthetic spectra computed with the
radiative transfer code Optim3D to re-analyze interferometric and spectroscopic
data from the optical to the infrared of Procyon. We compute intensity maps in
two optical filters centered at 500 and 800 nm (MARK III) and one infrared
filter centered at 2200 nm (VINCI). We constructed stellar disk images
accounting for the center-to-limb variations and used them to derive visibility
amplitudes and closure phases. We provide 3D limb-darkening coefficients in the
optical as well as in the infrared. We show that visibility curves and closure
phases show clear deviations from circular symmetry from the 3rd lobe on. These
deviations are detectable with current interferometers using closure phases. We
derive new angular diameters at different wavelengths with two independent
methods based on 3D simulations. We find a diameter_Vinci = 5.390 \pm 0.03 mas
that this is confirmed by an independent asteroseismic estimation. The
resulting Teff is 6591 K, which is consistent with the infrared flux method
determinations. We find also a value of the surface gravity log g = 4.01 \pm
0.03 that is larger by 0.05 dex from literature values. Spectrophotometric
comparisons with observations provide very good agreement with the spectral
energy distribution and photometric colors, allowing us to conclude that the
thermal gradient of the simulation matches fairly well Procyon. Finally, we
show that the granulation pattern of a planet hosting Procyon-like star has a
non-negligible impact on the detection of hot Jupiters in the infrared using
interferometry closure phases. It is then crucial to have a comprehensive
knowledge of the host star to directly detect and characterize hot Jupiters. In
this respect, RHD simulations are very important to reach this aim.Comment: Accepted for publication on Astronomy and Astrophysics, 14 pages, 12
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Three-dimensional fluorescent microscopy via simultaneous illumination and detection at multiple planes.
The conventional optical microscope is an inherently two-dimensional (2D) imaging tool. The objective lens, eyepiece and image sensor are all designed to capture light emitted from a 2D 'object plane'. Existing technologies, such as confocal or light sheet fluorescence microscopy have to utilize mechanical scanning, a time-multiplexing process, to capture a 3D image. In this paper, we present a 3D optical microscopy method based upon simultaneously illuminating and detecting multiple focal planes. This is implemented by adding two diffractive optical elements to modify the illumination and detection optics. We demonstrate that the image quality of this technique is comparable to conventional light sheet fluorescent microscopy with the advantage of the simultaneous imaging of multiple axial planes and reduced number of scans required to image the whole sample volume
Light-sheet microscopy: a tutorial
This paper is intended to give a comprehensive review of light-sheet (LS) microscopy from an optics perspective. As such, emphasis is placed on the advantages that LS microscope configurations present, given the degree of freedom gained by uncoupling the excitation and detection arms. The new imaging properties are first highlighted in terms of optical parameters and how these have enabled several biomedical applications. Then, the basics are presented for understanding how a LS microscope works. This is followed by a presentation of a tutorial for LS microscope designs, each working at different resolutions and for different applications. Then, based on a numerical Fourier analysis and given the multiple possibilities for generating the LS in the microscope (using Gaussian, Bessel, and Airy beams in the linear and nonlinear regimes), a systematic comparison of their optical performance is presented. Finally, based on advances in optics and photonics, the novel optical implementations possible in a LS microscope are highlighted.Peer ReviewedPostprint (published version
Particle tracking stereomicroscopy in optical tweezers: control of trap shape
We present an optical system capable of generating stereoscopic images to track trapped particles in three dimensions. Two-dimensional particle tracking on each image yields three dimensional position information. Our approach allows the use of a high numerical aperture (NA= 1.3) objective and large separation angle, such that particles can be tracked axially with resolution of 3nm at 340Hz. Spatial Light Modulators (SLMs), the diffractive elements used to steer and split laser beams in Holographic Optical Tweezers, are also capable of more general operations. We use one here to vary the ratio of lateral to axial trap stiffness by changing the shape of the beam at the back aperture of the microscope objective. Beams which concentrate their optical power at the extremes of the back aperture give rise to much more efficient axial trapping. The flexibility of using an SLM allows us to create multiple traps with different shapes
Sub-nanometer free electrons with topological charge
The holographic mask technique is used to create freely moving electrons with
quantized angular momentum. With electron optical elements they can be focused
to vortices with diameters below the nanometer range. The understanding of
these vortex beams is important for many applications. Here we present a theory
of focused free electron vortices. The agreement with experimental data is
excellent. As an immediate application, fundamental experimental parameters
like spherical aberration and partial coherence are determined.Comment: 4 pages, 5 figure
Reconstructing the Thermal Sunyaev-Zel'dovich Effect in 3D
The thermal Sunyaev-Zel'dovich (tSZ) effect measures the line-of-sight
projection of the thermal pressure of free electrons and lacks any redshift
information. By cross correlating the tSZ effect with an external cosmological
tracer we can recover a good fraction of this lost information. Weak lensing
(WL) is thought to provide an unbiased probe of the dark Universe, with many WL
surveys having sky coverage that overlaps with tSZ surveys. Generalising the
tomographic approach, we advocate the use of the spherical Fourier-Bessel (sFB)
expansion to perform an analysis of the cross-correlation between the projected
(2D) tSZ Compton -parameter maps and 3D weak lensing convergence maps. We
use redshift dependent linear biasing and the halo model as a tool to
investigate the tSZ-WL cross-correlations in 3D. We use the Press-Schechter
(PS) and the Sheth-Tormen (ST) mass-functions in our calculations, finding that
the results are quite sensitive to detailed modelling. We provide detailed
analysis of surveys with photometric and spectroscopic redshifts. The
signal-to-noise (S/N) of the cross-spectra for
individual 3D modes, defined by the radial and tangential wave numbers
, remains comparable to, but below, unity though optimal binning is
expected to improve this. The results presented can be generalised to analyse
other CMB secondaries, such as the kinetic Sunyaev-Zel'dovich (kSZ) effect.Comment: 27 pages, 12 Figures. Published in MNRA
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