7,178 research outputs found
A low-delay 8 Kb/s backward-adaptive CELP coder
Code excited linear prediction coding is an efficient technique for compressing speech sequences. Communications quality of speech can be obtained at bit rates below 8 Kb/s. However, relatively large coding delays are necessary to buffer the input speech in order to perform the LPC analysis. A low delay 8 Kb/s CELP coder is introduced in which the short term predictor is based on past synthesized speech. A new distortion measure that improves the tracking of the formant filter is discussed. Formal listening tests showed that the performance of the backward adaptive coder is almost as good as the conventional CELP coder
Fluctuation diagnostics of the electron self-energy: Origin of the pseudogap physics
We demonstrate how to identify which physical processes dominate the
low-energy spectral functions of correlated electron systems. We obtain an
unambiguous classification through an analysis of the equation of motion for
the electron self-energy in its charge, spin and particle-particle
representations. Our procedure is then employed to clarify the controversial
physics responsible for the appearance of the pseudogap in correlated systems.
We illustrate our method by examining the attractive and repulsive Hubbard
model in two-dimensions. In the latter, spin fluctuations are identified as the
origin of the pseudogap, and we also explain why wave pairing fluctuations
play a marginal role in suppressing the low-energy spectral weight, independent
of their actual strength.Comment: 6 pages, 2 figures + 4 pages supplementar
In vivo nuclear magnetic resonance imaging
A number of physiological changes have been demonstrated in bone, muscle and blood after exposure of humans and animals to microgravity. Determining mechanisms and the development of effective countermeasures for long duration space missions is an important NASA goal. The advent of tomographic nuclear magnetic resonance imaging (NMR or MRI) gives NASA a way to greatly extend early studies of this phenomena in ways not previously possible; NMR is also noninvasive and safe. NMR provides both superb anatomical images for volume assessments of individual organs and quantification of chemical/physical changes induced in the examined tissues. The feasibility of NMR as a tool for human physiological research as it is affected by microgravity is demonstrated. The animal studies employed the rear limb suspended rat as a model of mucle atrophy that results from microgravity. And bedrest of normal male subjects was used to simulate the effects of microgravity on bone and muscle
Modelling of the scandium abundance evolution in AmFm stars
Scandium is a key element of the Am star phenomenon since its surface
under-abundance is one of the criteria that characterise such stars. Thanks to
the availability of a sufficiently complete set of theoretical atomic data for
this element, reliable radiative accelerations for Sc can now be computed,
which allows its behaviour under the action of atomic diffusion to be modelled.
We explore the required conditions, in terms of mixing processes or mass loss,
for our models to reproduce the observed surface abundances of Sc in Am stars.
The models are computed with the Toulouse-Geneva evolution code, which uses the
parametric single-valued parameter method for the calculation of radiative
accelerations. Fingering mixing is included, using a prescription that comes
from 3D hydrodynamical simulations. Other parameter-dependent turbulent mixing
processes are also considered. A global mass loss is also implemented. When no
mass loss is considered, the observed abundances of Sc are rather in favour of
the models whose superficial layers are fully mixed down to the iron
accumulation zone, although other mixing prescriptions are also able to
reproduce the observations for the most massive model presented here (). The models including mass loss with rates in the range of
/yr are compatible with some of the observations,
while other observations suggest that the mass-loss rate could be lower. The
constraints brought by the modelling of Sc are consistent with those derived
using other chemical elements.Comment: 9 pages, 7 figure
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