28,657 research outputs found
True high-order VCO-based ADC
A novel approach to use a voltage-controlled oscillator (VCO) as the first integrator of a high-order continuous-time delta-sigma modulator (CT-DSM) is presented. In the proposed architecture, the VCO is combined with a digital up-down counter to implement the first integrator of the CT-DSM. Thus, the first integrator is digital-friendly and hence can maximally benefit from technological scaling
Finite-Size Scaling of Vector and Axial Current Correlators
Using quenched chiral perturbation theory, we compute the long-distance
behaviour of two-point functions of flavour non-singlet axial and vector
currents in a finite volume, for small quark masses, and at a fixed gauge-field
topology. We also present the corresponding predictions for the unquenched
theory at fixed topology. These results can in principle be used to measure the
low-energy constants of the chiral Lagrangian, from lattice simulations in
volumes much smaller than one pion Compton wavelength. We show that quenching
has a dramatic effect on the vector correlator, which is argued to vanish to
all orders, while the axial correlator appears to be a robust observable only
moderately sensitive to quenching.Comment: version to appear in NP
BhaBAR: Big Halpha kinematical sample of BARred spiral galaxies - I. Fabry-Perot Observations of 21 galaxies
The Halpha gas kinematics of twenty-one representative barred spiral galaxies
belonging to the BHaBAR sample is presented. The galaxies were observed with
FaNTOmM, a Fabry-Perot integral-field spectrometer, on three different
telescopes. The 3D data cubes were processed through a robust pipeline with the
aim of providing the most homogeneous and accurate dataset possible useful for
further analysis. The data cubes were spatially binned to a constant
signal-to-noise ratio, typically around 7. Maps of the monochromatic Halpha
emission line and of the velocity field were generated and the kinematical
parameters were derived for the whole sample using tilted-ring models. The
photometrical and kinematical parameters (position angle of the major axis,
inclination, systemic velocity and kinematical centre) are in relative good
agreement, except maybe for the later-type spirals.Comment: 34 pages, 25 figures, accepted for publication in MNRAS. To obtain a
higher resolution version, go to
ftp://ftp.astro.umontreal.ca/outgoing/olivier/bhabar.pdf or to
http://www.astro.umontreal.ca/fantomm/bhabar
A comparison of optical and radar measurements of mesospheric winds and tides
Optical measurements of mesospheric winds by FabryâPerot spectrometers, FPSs, at Mawson, 67.6°S 62.9°E, and Davis, 68.6°S 78.0°E, Antarctica are compared with similar measurements obtained using a spacedâantenna MF radar at Davis. The FPSs observed the OH emission. Different analysis procedures, used to determine the mean wind, and amplitude and phase of the semidiurnal tide, have been compared. At these latitudes the diurnal tide is weak and the semiâdiurnal tide, although highly variable in amplitude, is usually the dominant periodicity. When comparing the amplitude and phase of the semidiurnal tide good agreement is obtained between measurements by the two instruments
A nucleon in a tiny box
We use Chiral Perturbation Theory to compute the nucleon mass-shift due to
finite volume and temperature effects. Our results are valid up to
next-to-leading order in the "\eps-regime" (mL ~ m\beta << 1) as well as in the
"p-regime" (mL ~ m\beta >> 1). Based on the two leading orders, we discuss the
convergence of the expansion as a function of the lattice size and quark
masses. This result can be used to extrapolate lattice results obtained from
lattice sizes smaller than the pion cloud, avoiding the numerical simulation of
physics under theoretical control. An extraction of the low-energy coefficient
c_3 of the chiral Lagrangean from lattice simulations at small volumes and a
``magic'' ratio \beta=1.22262 L might be possible.Comment: 7 figures, numerical examples and discussion changed. Minor misprints
corrected. Version accepted by Phys Rev
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