395 research outputs found
Polarized Spectroscopy Studies of Single Molecules of Porphycenes
Using ambient atmosphere instead of pure nitrogen environment enabled efficient recording of room temperature fluorescence from single molecules of porphycenes, chromophores with a high triplet formation efficiency. Double hydrogen transfer between two chemically identical trans tautomers has been demonstrated for parent porphycene and three alkyl derivatives by the analysis of spatial patterns of the emission obtained after raster scanning the sample excited with an appropriately polarized laser beam. Because of tautomerization, fluorescence in porphycenes is due to two nearly orthogonal transition dipole moments. This property allows the spatial orientation of the single molecule chromophores to be determined using radially and azimuthally polarized laser beams as excitation sources
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Review of Unbiased FIR Filters, Smoothers, and Predictors for Polynomial Signals
Extracting an estimate of a slowly varying signal corrupted by noise is a common task. Examples can be found in industrial, scientific and biomedical instrumentation. Depending on the nature of the application the signal estimate is allowed to be a delayed estimate of the original signal or, in the other extreme, no delay is tolerated. These cases are commonly referred to as filtering, prediction, and smoothing depending on the amount of advance or lag between the input data set and the output data set. In this review paper we provide a comprehensive set of design and analysis tools for designing unbiased FIR filters, predictors, and smoothers for slowly varying signals, i.e. signals that can be modeled by low order polynomials. Explicit expressions of parameters needed in practical implementations are given. Real life examples are provided including cases where the method is extended to signals that are piecewise slowly varying. A critical view on recursive implementations of the algorithms is provided
Watermarking applications of Krawtchouk-Sobolev type orthogonal moments
In this contribution, we consider the sequence {Hn(x; q)}n≥0 of monic polynomials orthogonal with respect to a Sobolev-type inner product involving forward difference operators For the first time in the literature, we apply the non-standard properties of {Hn(x; q)}n≥0 in a watermarking problem. Several differences are found in this watermarking application for the non-standard cases (when j > 0) with respect to the standard classical Krawtchouk case λ = µ = 0.Universidad de Alcal
Physical Properties of Giant Molecular Clouds in the Large Magellanic Cloud
The Magellanic Mopra Assessment (MAGMA) is a high angular resolution CO
mapping survey of giant molecular clouds (GMCs) in the Large and Small
Magellanic Clouds using the Mopra Telescope. Here we report on the basic
physical properties of 125 GMCs in the LMC that have been surveyed to date. The
observed clouds exhibit scaling relations that are similar to those determined
for Galactic GMCs, although LMC clouds have narrower linewidths and lower CO
luminosities than Galactic clouds of a similar size. The average mass surface
density of the LMC clouds is 50 Msol/pc2, approximately half that of GMCs in
the inner Milky Way. We compare the properties of GMCs with and without signs
of massive star formation, finding that non-star-forming GMCs have lower peak
CO brightness than star-forming GMCs. We compare the properties of GMCs with
estimates for local interstellar conditions: specifically, we investigate the
HI column density, radiation field, stellar mass surface density and the
external pressure. Very few cloud properties demonstrate a clear dependence on
the environment; the exceptions are significant positive correlations between
i) the HI column density and the GMC velocity dispersion, ii) the stellar mass
surface density and the average peak CO brightness, and iii) the stellar mass
surface density and the CO surface brightness. The molecular mass surface
density of GMCs without signs of massive star formation shows no dependence on
the local radiation field, which is inconsistent with the
photoionization-regulated star formation theory proposed by McKee (1989). We
find some evidence that the mass surface density of the MAGMA clouds increases
with the interstellar pressure, as proposed by Elmegreen (1989), but the
detailed predictions of this model are not fulfilled once estimates for the
local radiation field, metallicity and GMC envelope mass are taken into
account.Comment: 28 pages, 10 figures, accepted by MNRA
Towards a Better Understanding of OPD Limitations for Higher Sensitivity and Contrast at the VLTI
Precise control of the optical path differences (OPD) in the Very Large
Telescope Interferometer (VLTI) was critical for the characterization of the
black hole at the center of our Galaxy - leading to the 2020 Nobel prize in
physics. There is now significant effort to push these OPD limits even further,
in-particular achieving 100nm OPD RMS on the 8m unit telescopes (UT's) to allow
higher contrast and sensitivity at the VLTI. This work calculated the
theoretical atmospheric OPD limit of the VLTI as 5nm and 15nm RMS, with current
levels around 200nm and 100nm RMS for the UT and 1.8m auxillary telescopes
(AT's) respectively, when using bright targets in good atmospheric conditions.
We find experimental evidence for the power law theoretically
predicted from the effect of telescope filtering in the case of the ATs which
is not currently observed for the UT's. Fitting a series of vibrating mirrors
modelled as dampened harmonic oscillators, we were able to model the UT OPD PSD
of the gravity fringe tracker to RMSE up to 100Hz, which could
adequately explain a hidden power law on the UTs. Vibration
frequencies in the range of 60-90Hz and also 40-50Hz were found to generally
dominate the closed loop OPD residuals of Gravity. Cross correlating
accelerometer with Gravity data, it was found that strong contributions in the
40-50Hz range are coming from the M1-M3 mirrors, while a significant portion of
power from the 60-100Hz contributions are likely coming from between the
M4-M10. From the vibrating mirror model it was shown that achieving sub 100nm
OPD RMS for particular baselines (that have OPD200nm RMS) required
removing nearly all vibration sources below 100Hz
Digital Filters and Signal Processing
Digital filters, together with signal processing, are being employed in the new technologies and information systems, and are implemented in different areas and applications. Digital filters and signal processing are used with no costs and they can be adapted to different cases with great flexibility and reliability. This book presents advanced developments in digital filters and signal process methods covering different cases studies. They present the main essence of the subject, with the principal approaches to the most recent mathematical models that are being employed worldwide
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