228 research outputs found
FPGA-Based Low-Power Speech Recognition with Recurrent Neural Networks
In this paper, a neural network based real-time speech recognition (SR)
system is developed using an FPGA for very low-power operation. The implemented
system employs two recurrent neural networks (RNNs); one is a
speech-to-character RNN for acoustic modeling (AM) and the other is for
character-level language modeling (LM). The system also employs a statistical
word-level LM to improve the recognition accuracy. The results of the AM, the
character-level LM, and the word-level LM are combined using a fairly simple
N-best search algorithm instead of the hidden Markov model (HMM) based network.
The RNNs are implemented using massively parallel processing elements (PEs) for
low latency and high throughput. The weights are quantized to 6 bits to store
all of them in the on-chip memory of an FPGA. The proposed algorithm is
implemented on a Xilinx XC7Z045, and the system can operate much faster than
real-time.Comment: Accepted to SiPS 201
Radiative transfer in disc galaxies V. The accuracy of the KB approximation
We investigate the accuracy of an approximate radiative transfer technique
that was first proposed by Kylafis & Bahcall (hereafter the KB approximation)
and has been popular in modelling dusty late-type galaxies. We compare
realistic galaxy models calculated with the KB approximation with those of a
three-dimensional Monte Carlo radiative transfer code SKIRT. The SKIRT code
fully takes into account of the contribution of multiple scattering whereas the
KB approximation calculates only single scattered intensity and multiple
scattering components are approximated. We find that the KB approximation gives
fairly accurate results if optically thin, face-on galaxies are considered.
However, for highly inclined () and/or optically thick
(central face-on optical depth ) galaxy models, the approximation can
give rise to substantial errors, sometimes, up to . Moreover, it
is also found that the KB approximation is not always physical, sometimes
producing infinite intensities at lines of sight with high optical depth in
edge-on galaxy models. There is no "simple recipe" to correct the errors of the
KB approximation that is universally applicable to any galaxy models.
Therefore, it is recommended that the full radiative transfer calculation be
used, even though it's slower than the KB approximation.Comment: 10 pages, 6 figures, accepted for publication in MNRA
Photometric defocus observations of transiting extrasolar planets
We have carried out photometric follow-up observations of bright transiting
extrasolar planets using the CbNUOJ 0.6m telescope. We have tested the
possibility of obtaining high photometric precision by applying the telescope
defocus technique allowing the use of several hundred seconds in exposure time
for a single measurement. We demonstrate that this technique is capable of
obtaining a root-mean-square scatter of order sub-millimagnitude over several
hours for a V 10 host star typical for transiting planets detected from
ground-based survey facilities. We compare our results with transit
observations with the telescope operated in in-focus mode. High photometric
precision is obtained due to the collection of a larger amount of photons
resulting in a higher signal compared to other random and systematic noise
sources. Accurate telescope tracking is likely to further contribute to
lowering systematic noise by probing the same pixels on the CCD. Furthermore, a
longer exposure time helps reducing the effect of scintillation noise which
otherwise has a significant effect for small-aperture telescopes operated in
in-focus mode. Finally we present the results of modelling four light-curves
for which a root-mean-square scatter of 0.70 to 2.3 milli-magnitudes have been
achieved.Comment: 12 pages, 11 figures, 5 tables. Submitted to Journal of Astronomy and
Space Sciences (JASS
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