9,291 research outputs found
Characterization of SINR Region for Multiple Interfering Multicast in Power-Controlled Systems
This paper considers a wireless communication network consisting of multiple
interfering multicast sessions. Different from a unicast system where each
transmitter has only one receiver, in a multicast system, each transmitter has
multiple receivers. It is a well known result for wireless unicast systems that
the feasibility of an signal-to-interference-plus-noise power ratio (SINR)
without power constraint is decided by the Perron-Frobenius eigenvalue of a
nonnegative matrix. We generalize this result and propose necessary and
sufficient conditions for the feasibility of an SINR in a wireless multicast
system with and without power constraint. The feasible SINR region as well as
its geometric properties are studied. Besides, an iterative algorithm is
proposed which can efficiently check the feasibility condition and compute the
boundary points of the feasible SINR region.Comment: 25 pages, 4 figures, submitted to IEEE Trans. Inform. Theor
On the Rapid Spin-down and Low Luminosity Pulsed Emission from AE Aquarii
AE Aqr is an unusual close binary system with a very short white dwarf spin
period, a high spin-down rate, a relatively low quiescent luminosity, and clear
pulse signals. The exact nature of the large spin-down power has not been well
explained mainly due to the fact that the observed luminosities in various
energy ranges are much lower than the spin-down power. We consider an
unconventional picture of AE Aqr in which an accreting white dwarf, modeled as
a magnetic dipole whose axis is misaligned with the spin axis, is rapidly
spun-down via gravitational radiation emission and therefore the spin-down
power is not directly connected to any observable electromagnetic emission.Comment: 25 pages and one PS figure, Submitted to Ap
The effects of the carrier interaction and electric fields on subband structures of selectively--doped semiconductor quantum wells
We investigate the ground--state electronic properties of the symmetrically--
doped semiconductor quantum well in the presence of a homogeneous electric
field. In this paper we examined the effect of the electric field and carrier
interaction on the subband structure as a function of the field strength and
carrier concentration. The many--body effects are evaluated using a local
density functional exchange--correlation potential. We find that the electron
subband energy is reduced as the magnitude of the electric field is increased,
but it is increased as the surface carrier density is increased. However, the
separation of the electron subband energies is reduced for the increase in both
the electric field and surface carrier density. On the other hand, the energy
separation of the hole subbands is increased as the carrier density and field
strength are increased. Effect of the exchange--correlation potential on the
subband structure is found negligibly small in this calculation. The subband
energies are reduced slightly, increasing their separations little in the
presence of the local exchange--correlation potential.Comment: 17 pages, revtex, 11 figures(available on request
Forecasting the detectability of known radial velocity planets with the upcoming CHEOPS mission
The Characterizing Exoplanets Satellite (CHEOPS) mission is planned for
launch next year with a major objective being to search for transits of known
RV planets, particularly those orbiting bright stars. Since the radial velocity
method is only sensitive to planetary mass, the radii, transit depths and
transit signal-to-noise values of each RV planet are, a-priori, unknown. Using
an empirically calibrated probabilistic mass-radius relation, forecaster (Chen
& Kipping 2017a), we address this by predicting a catalog of homogeneous
credible intervals for these three keys terms for 468 planets discovered via
radial velocities. Of these, we find that the vast majority should be
detectable with CHEOPS, including terrestrial bodies, if they have the correct
geometric alignment. In particular, we predict that 22 mini-Neptunes and 82
Neptune-sized planets would be suitable for detection and that more than 80% of
these will have apparent magnitude of V < 10, making them highly suitable for
follow-up characterization work. Our work aims to assist the CHEOPS team in
scheduling efforts and highlights the great value of quantifiable,
statistically robust estimates for upcoming exoplanetary missions.Comment: Accepted to MNRAS, results available at
https://github.com/CoolWorlds/cheopsforecast
From Semi-supervised to Almost-unsupervised Speech Recognition with Very-low Resource by Jointly Learning Phonetic Structures from Audio and Text Embeddings
Producing a large amount of annotated speech data for training ASR systems
remains difficult for more than 95% of languages all over the world which are
low-resourced. However, we note human babies start to learn the language by the
sounds (or phonetic structures) of a small number of exemplar words, and
"generalize" such knowledge to other words without hearing a large amount of
data. We initiate some preliminary work in this direction. Audio Word2Vec is
used to learn the phonetic structures from spoken words (signal segments),
while another autoencoder is used to learn the phonetic structures from text
words. The relationships among the above two can be learned jointly, or
separately after the above two are well trained. This relationship can be used
in speech recognition with very low resource. In the initial experiments on the
TIMIT dataset, only 2.1 hours of speech data (in which 2500 spoken words were
annotated and the rest unlabeled) gave a word error rate of 44.6%, and this
number can be reduced to 34.2% if 4.1 hr of speech data (in which 20000 spoken
words were annotated) were given. These results are not satisfactory, but a
good starting point
Improved Audio Embeddings by Adjacency-Based Clustering with Applications in Spoken Term Detection
Embedding audio signal segments into vectors with fixed dimensionality is
attractive because all following processing will be easier and more efficient,
for example modeling, classifying or indexing. Audio Word2Vec previously
proposed was shown to be able to represent audio segments for spoken words as
such vectors carrying information about the phonetic structures of the signal
segments. However, each linguistic unit (word, syllable, phoneme in text form)
corresponds to unlimited number of audio segments with vector representations
inevitably spread over the embedding space, which causes some confusion. It is
therefore desired to better cluster the audio embeddings such that those
corresponding to the same linguistic unit can be more compactly distributed. In
this paper, inspired by Siamese networks, we propose some approaches to achieve
the above goal. This includes identifying positive and negative pairs from
unlabeled data for Siamese style training, disentangling acoustic factors such
as speaker characteristics from the audio embedding, handling unbalanced data
distribution, and having the embedding processes learn from the adjacency
relationships among data points. All these can be done in an unsupervised way.
Improved performance was obtained in preliminary experiments on the LibriSpeech
data set, including clustering characteristics analysis and applications of
spoken term detection
Towards Unsupervised Automatic Speech Recognition Trained by Unaligned Speech and Text only
Automatic speech recognition (ASR) has been widely researched with supervised
approaches, while many low-resourced languages lack audio-text aligned data,
and supervised methods cannot be applied on them.
In this work, we propose a framework to achieve unsupervised ASR on a read
English speech dataset, where audio and text are unaligned. In the first stage,
each word-level audio segment in the utterances is represented by a vector
representation extracted by a sequence-of-sequence autoencoder, in which
phonetic information and speaker information are disentangled.
Secondly, semantic embeddings of audio segments are trained from the vector
representations using a skip-gram model. Last but not the least, an
unsupervised method is utilized to transform semantic embeddings of audio
segments to text embedding space, and finally the transformed embeddings are
mapped to words.
With the above framework, we are towards unsupervised ASR trained by
unaligned text and speech only.Comment: Code is released:
https://github.com/grtzsohalf/Towards-Unsupervised-AS
Information-Theoretic Caching: Sequential Coding for Computing
Under the paradigm of caching, partial data is delivered before the actual
requests of users are known. In this paper, this problem is modeled as a
canonical distributed source coding problem with side information, where the
side information represents the users' requests. For the single-user case, a
single-letter characterization of the optimal rate region is established, and
for several important special cases, closed-form solutions are given, including
the scenario of uniformly distributed user requests. In this case, it is shown
that the optimal caching strategy is closely related to total correlation and
Wyner's common information. Using the insight gained from the single-user case,
three two-user scenarios admitting single-letter characterization are
considered, which draw connections to existing source coding problems in the
literature: the Gray--Wyner system and distributed successive refinement.
Finally, the model studied by Maddah-Ali and Niesen is rephrased to make a
comparison with the considered information-theoretic model. Although the two
caching models have a similar behavior for the single-user case, it is shown
through a two-user example that the two caching models behave differently in
general.Comment: submitted to IEEE Trans. Inf. Theory and presented in part at ISIT
201
Estimating Supermassive Black Hole Mass Through Radio/X-Ray Luminosity Relation of X-Ray Bright Galactic Nuclei
It has been suggested that optically thin and geometrically thick accretion
flows are responsible for the observed radio/X-ray luminosity relation of the
X-ray bright galactic nuclei. If this is the case then central supermassive
black hole masses can be estimated directly from measurements of the core radio
luminosity and the X-ray luminosity, provided that properties of such accretion
flows are known. Calculated ratios of the luminosities are presented in cases
of the standard ADAF model and modified ADAF models, in which a truncation of
inner parts of the flows and winds causing a reduction of the infalling matter
are included. We compare the observed ratio of the luminosities with
predictions from models of optically thin accretion flows. We also discuss the
possible effects of the convection in ADAFs. We confirm that the supermassive
black hole (SMBH) mass estimate is possible with the radio/X-ray luminosity
relation due to ADAF models in the absence of a radio jet. We find that
observational data are insufficient to distinguish the standard ADAF model from
its modified models. However, the ADAF model with convection is inconsistent
with observations, unless microphysics parameters are to be substantially
changed. High resolution radio observations are required to avoid the
contamination of other components, such as, a jet component. Otherwise, the
SMBH mass is inclined to be over-estimated.Comment: 19 pages, 3 ps figures, Submitted to ApJ
Observations of Spectral and Time Variabilities from MCG-2-58-22
We present results from analysis of the X-ray archive data of MCG-2-58-22,
acquired with ROSAT from 1991 to 1993 and with ASCA from 1993 to 1997. By
analyzing light curves, we find that MCG-2-58-22 shows a clear time variability
in X-ray flux. The time scales of the variations range widely from about 1000 s
to more than years. Among the variations, a flare-like event overlaid on the
gradual flux decrease from 1979 to 1993 is detected. We also find clear time
variability of the spectra in the energy range of 0.1 - 2.0 keV. However, the
flux variation does not influences on their spectra in the energy range of 2 -
10 keV. The implications of these observational results are discussed in terms
of a supermassive black hole model and accretion flow dynamics near the central
black hole.Comment: 27 pages and 9 figures, submitted to Ap
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