13,495 research outputs found
Digitizing signals - a short tutorial guide
Converting the analogue signal, as captured from a patient, into digital format is known as digitizing, or analogue to digital conversion. This is a vital first step in for digital signal processing. The acquisition of high-quality data requires appropriate choices of system and parameters (sampling rate, anti-alias filter, amplification, number of ‘bits’). Thus tutorial aims to provide a practical guide to making these choices, and explains the underlying principles (rather than the mathematical theory and proofs) and potential pitfalls. Illustrative examples from different physiological signals are provided
Resonance, multiple diffusion and critical tunneling for Gaussian lasers
We present a detailed study of the gaussian laser propagation through a
dielectric system composed by two right angle prisms. We investigate the
transition between the spatial coherence limit, which exhibits wave-like
properties and for which the resonance phenomenon can be seen, and the
decoherence limit, which exhibits particle-like properties and for which the
multiple diffusion occurs. We also analyze the tunneling at critical angles. In
our numerical analysis, we shall use BK7 and Fused Silica prisms and a gaussian
He-Ne laser with a wavelength of 632.8 nm and beam waists of 2 mm and 200
micron.Comment: 18 pages, 3 tables, 5 figure
The use of the stationary phase method as a mathematical tool to determine the path of optical beams
We use the stationary phase method to determine the path of optical beams
which propagate through a dielectric block. In the presence of partial internal
reflection, we recover the geometrical result obtained by using the Snell law.
For total internal reflection, the stationary phase method overreaches the
Snell law predicting the Goos-Haenchen shift.Comment: 11 pages, 2 figure
Shedding Light on Diatom Photonics by means of Digital Holography
Diatoms are among the dominant phytoplankters in the worl's ocean, and their
external silica investments, resembling artificial photonics crystal, are
expected to play an active role in light manipulation. Digital holography
allowed studying the interaction with light of Coscinodiscus wailesii cell wall
reconstructing the light confinement inside the cell cytoplasm, condition that
is hardly accessible via standard microscopy. The full characterization of the
propagated beam, in terms of quantitative phase and intensity, removed a
long-standing ambiguity about the origin of the light. The data were discussed
in the light of living cell behavior in response to their environment
RBF approximation of large datasets by partition of unity and local stabilization
We present an algorithm to approximate large dataset by Radial Basis Function
(RBF) techniques. The method couples a fast domain decomposition procedure with a
localized stabilization method. The resulting algorithm can efficiently deal with large
problems and it is robust with respect to the typical instability of kernel methods
Graphene tests of Klein phenomena
Graphene is characterized by chiral electronic excitations. As such it
provides a perfect testing ground for the production of Klein pairs
(electron/holes). If confirmed, the standard results for barrier phenomena must
be reconsidered with, as a byproduct, the accumulation within the barrier of
holes.Comment: 8 page
Van der Waals Coefficients of Atoms and Molecules from a Simple Approximation for the Polarizability
A simple and computationally efficient scheme to calculate approximate
imaginary-frequency dependent polarizability, hence asymptotic van der Waals
coefficient, within density functional theory is proposed. The dynamical
dipolar polarizabilities of atoms and molecules are calculated starting from
the Thomas-Fermi-von Weizs\"acker (TFvW) approximation for the
independent-electron kinetic energy functional. The van der Waals coefficients
for a number of closed-shell ions and a few molecules are hence calculated and
compared with available values obtained by fully first-principles calculations.
The success in these test cases shows the potential of the proposed TFvW
approximate response function in capturing the essence of long range
correlations and may give useful information for constructing a functional
which naturally includes van der Waals interactions.Comment: 6 pages, 4 figures. To appear in Phys. Rev.
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