216 research outputs found
Instantaneous frequency and amplitude of complex signals based on quaternion Fourier transform
The ideas of instantaneous amplitude and phase are well understood for
signals with real-valued samples, based on the analytic signal which is a
complex signal with one-sided Fourier transform. We extend these ideas to
signals with complex-valued samples, using a quaternion-valued equivalent of
the analytic signal obtained from a one-sided quaternion Fourier transform
which we refer to as the hypercomplex representation of the complex signal. We
present the necessary properties of the quaternion Fourier transform,
particularly its symmetries in the frequency domain and formulae for
convolution and the quaternion Fourier transform of the Hilbert transform. The
hypercomplex representation may be interpreted as an ordered pair of complex
signals or as a quaternion signal. We discuss its derivation and properties and
show that its quaternion Fourier transform is one-sided. It is shown how to
derive from the hypercomplex representation a complex envelope and a phase.
A classical result in the case of real signals is that an amplitude modulated
signal may be analysed into its envelope and carrier using the analytic signal
provided that the modulating signal has frequency content not overlapping with
that of the carrier. We show that this idea extends to the complex case,
provided that the complex signal modulates an orthonormal complex exponential.
Orthonormal complex modulation can be represented mathematically by a polar
representation of quaternions previously derived by the authors. As in the
classical case, there is a restriction of non-overlapping frequency content
between the modulating complex signal and the orthonormal complex exponential.
We show that, under these conditions, modulation in the time domain is
equivalent to a frequency shift in the quaternion Fourier domain. Examples are
presented to demonstrate these concepts
GLRT-based array receivers for the detection of a known signal with unknown parameters corrupted by noncircular interferences
H-band observations of the Chandra Deep Field South
We report preliminary results of our H-band survey of the Chandra Deep Field
South (CDFS). The observations were made using SofI on the NTT, and cover 0.027
square degrees with a 50% completeness limit of H = 20.5, and 0.17 square
degrees with a 50% completeness limit of H =19.8. We used SExtractor to extract
sources from our fields. In total we have detected 4819 objects. Star-galaxy
separation was performed using the SExtractor parameter ``stellarity index''.
All objects with an index of 0.5 or lower were classified as galaxies.
According to this criterion, 80 % of our detections are galaxies. We then
compare our results with previous observations of the CDFS. Our astrometric
solutions are in good agreement with the Las Campanas Infrared Survey (LCIRS),
the COMBO-17 and the ESO-EIS surveys. The photometry of our catalog compares
satisfactorily with the results of the LCIRS, as well as with the GOODS data.
Galaxy number counts are presented and compared with the LCIRS results. The
present data are intended to complement the recent and future multi-wavelenghth
observations of the CDFS and will be used, in conjuction with additional
multiband photometry, to find counterparts of the upcoming mid-infrared surveys
with SIRTF.Comment: 7 figures, submitted to Astronomy and Astrophysics, catalogue
available at http://www.mpe.mpg.de/~dmr/table1.da
Povodom puštanja u pogon nove Gradske mljekare u Zagrebu
Dne 2. kolovoza 1952. godine u 8 sati svečano je puštena u pogon nova Centralna Gradska Mljekara u Zagrebu na Žitnjaku. Svečanom činu otvorenja mljekare prisustvovali su u ime Međunarodne organizacije za pomoć djeci Unicef-a gg. Julius Perstein, šef glavnog centra Unicef-a u Parizu, G. I. R. Cooper, šef odjela za izgradnju mljekara u Evropi i na Bliskom Istoku, gdja Helen Glassey, šef misije za Jugoslaviju i g. J. L. Vinck, član Unicefa u Parizu
Electronic case report forms and electronic data capture within clinical trials and pharmacoepidemiology
Emergence of New Norovirus Variants on Spring Cruise Ships and Prediction of Winter Epidemics
A reporting system could provide early warning
Recommended from our members
Monitoring one-electron photo-oxidation of guanine in DNA crystals using ultrafast infrared spectroscopy
To understand the molecular origins of diseases caused by ultraviolet and visible light, and also to develop photodynamic therapy, it is important to resolve the mechanism of photoinduced DNA damage. Damage to DNA bound to a photosensitizer molecule frequently proceeds by one-electron photo-oxidation of guanine, but the precise dynamics of this process are sensitive to the location and the orientation of the photosensitizer, which are very difficult to define in solution. To overcome this, ultrafast time-resolved infrared (TRIR) spectroscopy was performed on photoexcited ruthenium polypyridyl–DNA crystals, the atomic structure of which was determined by X-ray crystallography. By combining the X-ray and TRIR data we are able to define both the geometry of the reaction site and the rates of individual steps in a reversible photoinduced electron-transfer process. This allows us to propose an individual guanine as the reaction site and, intriguingly, reveals that the dynamics in the crystal state are quite similar to those observed in the solvent medium
Multistage Quadrature Sigma-Delta Modulators for Reconfigurable Multi-Band Analog-Digital Interface in Cognitive Radio Devices
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