4,067 research outputs found
Broadband DOA estimation using Convolutional neural networks trained with noise signals
A convolution neural network (CNN) based classification method for broadband
DOA estimation is proposed, where the phase component of the short-time Fourier
transform coefficients of the received microphone signals are directly fed into
the CNN and the features required for DOA estimation are learnt during
training. Since only the phase component of the input is used, the CNN can be
trained with synthesized noise signals, thereby making the preparation of the
training data set easier compared to using speech signals. Through experimental
evaluation, the ability of the proposed noise trained CNN framework to
generalize to speech sources is demonstrated. In addition, the robustness of
the system to noise, small perturbations in microphone positions, as well as
its ability to adapt to different acoustic conditions is investigated using
experiments with simulated and real data.Comment: Published in Proceedings of IEEE Workshop on Applications of Signal
Processing to Audio and Acoustics (WASPAA) 201
A S=1/2 vanadium-based geometrically frustrated spinel system Li2ZnV3O8
We report the synthesis and characterization of Li2ZnV3O8, which is a new
Zn-doped LiV2O4 system containing only tetravalent vanadium. A Curie-Weiss
susceptibility with a Curie-Weiss temperature of CW ~214 K suggests the
presence of strong antiferromagnetic correlations in this system. We have
observed a splitting between the zero-field cooled ZFC and field cooled FC
susceptibility curves below 6 K. A peak is present in the ZFC curve around 3.5
K suggestive of spin-freezing . Similarly, a broad hump is also seen in the
inferred magnetic heat capacity around 9 K. The consequent entropy change is
only about 8% of the value expected for an ordered S = 1=2 system. This
reduction indicates continued presence of large disorder in the system in spite
of the large CW, which might result from strong geometric frustration in
the system. We did not find any temperature T dependence in our 7Li nuclear
magnetic resonance NMR shift down to 6 K (an abrupt change in the shift takes
place below 6 K) though considerable T-dependence has been found in literature
for LiV2O4- undoped or with other Zn/Ti contents. Consistent with the above
observation, the 7Li nuclear spin-lattice relaxation rate 1/T1 is relatively
small and nearly T-independent except a small increase close to the freezing
temperature, once again, small compared to undoped or 10% Zn or 20% Ti-doped
LiV2O4.Comment: 7 pages, 8 figures, accepted in JPCM (Journal of Physics condensed
matter
Optical Modulation in the X-Ray Binary 4U 1543-624 Revisited
The X-ray binary 4U 1543624 has been provisionally identified as an
ultracompact system with an orbital period of 18~min. We have carried
out time-resolved optical imaging of the binary to verify the ultra-short
orbital period. Using 140\,min of high-cadence -band photometry we recover
the previously-seen sinusoidal modulation and determine a period
\,min. In addition, we also see a 7.0\,mag\,min linear decay, likely related to variations in the
source's accretion activity. Assuming that the sinusoidal modulation arises
from X-ray heating of the inner face of the companion star, we estimate a
distance of 6.0--6.7\,kpc and an inclination angle of
34--61 (90\% confidence) for the binary. Given the
stability of the modulation we can confirm that the modulation is orbital in
origin and 4U 1543624 is an ultracompact X-ray binary.Comment: 6 pages, 3 figures, accepted for publication in Publications of the
Astronomical Society of Australia (PASA
Selection of Dominant Characteristic Modes
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.The theory of characteristic modes is a popular
physics based deterministic approach which has found several recent
applications in the fields of radiator design, electromagnetic
interference modelling and radiated emission analysis. The modal
theory is based on the approximation of the total induced current
in an electromagnetic structure in terms of a weighted sum of
multiple characteristic current modes. The resultant outgoing
field is also a weighted summation of the characteristic field
patterns. Henceforth, a proper modal measure is an essential
requirement to identify the modes which play a dominant role
for a frequency of interest. The existing literature of significance
measures restricts itself for ideal lossless structures only. This
paper explores the pros and cons of the existing measures and
correspondingly suggests suitable alternatives for both radiating
and scattering applications. An example is presented in order
to illustrate the proposed modal method for approximating the
shielding response of a slotted geometry
Unattainable extended spacetime regions in conformal gravity
The Janis-Newman-Winicour metric is a solution of Einstein's gravity
minimally coupled to a real massless scalar field. The -metric is
instead a vacuum solution of Einstein's gravity. These spacetimes have no
horizon and possess a naked singularity at a finite value of the radial
coordinate, where curvature invariants diverge and the spacetimes are
geodetically incomplete. In this paper, we reconsider these solutions in the
framework of conformal gravity and we show that it is possible to solve the
spacetime singularities with a suitable choice of the conformal factor. Now
curvature invariants remain finite over the whole spacetime. Massive particles
never reach the previous singular surface and massless particles can never do
it with a finite value of their affine parameter. Our results support the
conjecture according to which conformal gravity can fix the singularity problem
that plagues Einstein's gravity.Comment: 1+10 pages, 2 figures. v2: refereed versio
Keck Measurement of the XTE J2123-058 Radial Velocity Curve
We measured the radial velocity curve of the companion of the neutron star
X-ray transient XTE J2123-058. Its semi-amplitude (K_2) of 298.5 +/- 6.9 km/s
is the highest value that has been measured for any neutron star LMXB. The high
value for K_2 is, in part, due to the high binary inclination of the system but
may also indicate a high neutron star mass. The mass function (f_2) of 0.684
+/- 0.047 solar masses, along with our constraints on the companion's spectral
type (K5V-K9V) and previous constraints on the inclination, gives a likely
range of neutron star masses from 1.2 to 1.8 solar masses. We also derive a
source distance of 8.5 +/- 2.5 kpc, indicating that XTE J2123-058 is unusually
far, 5.0 +/- 1.5 kpc, from the Galactic plane. Our measurement of the systemic
radial velocity is -94.5 +/- 5.5 km/s, which is significantly different from
what would be observed if this object corotates with the disk of the Galaxy.Comment: 4 pages, accepted by ApJ Letters after minor revision
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