179,933 research outputs found
The Impact of User Effects on the Performance of Dual Receive Antenna Diversity Systems in Flat Rayleigh Fading Channels
In this paper we study the impact of user effects on the performance of receive antenna diversity systems in flat Rayleigh fading channels. Three diversity combining techniques are compared: maximal ratio combining (MRC), equal gain combining (EGC), and selection combining (SC). User effects are considered in two scenarios: 1) body loss (the reduction of effective antenna gain due to user effects) on a single antenna, and 2) equal body loss on both antennas. The system performance is assessed in terms of mean SNR, link reliability, bit error rate of BPSK, diversity order and ergodic capacity. Our results show that body loss on a single antenna has limited (bounded) impact on system performance. In comparison, body loss on both antennas has unlimited (unbounded) impact and can severely degrade system performance. Our results also show that with increasing body loss on a single antenna the performance of EGC drops faster than that of MRC and SC. When body loss on a single antenna is larger than a certain level, EGC is not a âsub-optimalâ method anymore and has worse performance than SC
A broadband microwave Corbino spectrometer at He temperatures and high magnetic fields
We present the technical details of a broadband microwave spectrometer for
measuring the complex conductance of thin films covering the range from 50 MHz
up to 16 GHz in the temperature range 300 mK to 6 K and at applied magnetic
fields up to 8 Tesla. We measure the complex reflection from a sample
terminating a coaxial transmission line and calibrate the signals with three
standards with known reflection coefficients. Thermal isolation of the heat
load from the inner conductor is accomplished by including a section of NbTi
superconducting cable (transition temperature around 8 9 K) and hermetic
seal glass bead adapters. This enables us to stabilize the base temperature of
the sample stage at 300 mK. However, the inclusion of this superconducting
cable complicates the calibration procedure. We document the effects of the
superconducting cable on our calibration procedure and the effects of applied
magnetic fields and how we control the temperature with great repeatability for
each measurement. We have successfully extracted reliable data in this
frequency, temperature and field range for thin superconducting films and
highly resistive graphene samples
Taste or Addiction?: Using Play Logs to Infer Song Selection Motivation
Online music services are increasing in popularity. They enable us to analyze
people's music listening behavior based on play logs. Although it is known that
people listen to music based on topic (e.g., rock or jazz), we assume that when
a user is addicted to an artist, s/he chooses the artist's songs regardless of
topic. Based on this assumption, in this paper, we propose a probabilistic
model to analyze people's music listening behavior. Our main contributions are
three-fold. First, to the best of our knowledge, this is the first study
modeling music listening behavior by taking into account the influence of
addiction to artists. Second, by using real-world datasets of play logs, we
showed the effectiveness of our proposed model. Third, we carried out
qualitative experiments and showed that taking addiction into account enables
us to analyze music listening behavior from a new viewpoint in terms of how
people listen to music according to the time of day, how an artist's songs are
listened to by people, etc. We also discuss the possibility of applying the
analysis results to applications such as artist similarity computation and song
recommendation.Comment: Accepted by The 21st Pacific-Asia Conference on Knowledge Discovery
and Data Mining (PAKDD 2017
Resonant versus anti-resonant tunneling at carbon nanotube A-B-A heterostructures
Narrow antiresonances going to zero transmission are found to occur for
general (2n,0)(n,n)(2n,0) carbon nanotube heterostructures, whereas the
complementary configuration, (n,n)(2n,0)(n,n), displays simple resonant
tunneling behaviour. We compute examples for different cases, and give a simple
explanation for the appearance of antiresonances in one case but not in the
other. Conditions and ranges for the occurence of these different behaviors are
stated. The phenomenon of anti-resonant tunneling, which has passed unnoticed
in previous studies of nanotube heterostructures, adds up to the rich set of
behaviors available to nanotube based quantum effect devices.Comment: Published in phys. stat. sol. (b); 6 pages, 4 figure
Pulsar-black hole binaries: prospects for new gravity tests with future radio telescopes
The anticipated discovery of a pulsar in orbit with a black hole is expected
to provide a unique laboratory for black hole physics and gravity. In this
context, the next generation of radio telescopes, like the Five-hundred-metre
Aperture Spherical radio Telescope (FAST) and the Square Kilometre Array (SKA),
with their unprecedented sensitivity, will play a key role. In this paper, we
investigate the capability of future radio telescopes to probe the spacetime of
a black hole and test gravity theories, by timing a pulsar orbiting a
stellar-mass-black-hole (SBH). Based on mock data simulations, we show that a
few years of timing observations of a sufficiently compact pulsar-SBH (PSR-SBH)
system with future radio telescopes would allow precise measurements of the
black hole mass and spin. A measurement precision of one per cent can be
expected for the spin. Measuring the quadrupole moment of the black hole,
needed to test GR's no-hair theorem, requires extreme system configurations
with compact orbits and a large SBH mass. Additionally, we show that a PSR-SBH
system can lead to greatly improved constraints on alternative gravity theories
even if they predict black holes (practically) identical to GR's. This is
demonstrated for a specific class of scalar-tensor theories. Finally, we
investigate the requirements for searching for PSR-SBH systems. It is shown
that the high sensitivity of the next generation of radio telescopes is key for
discovering compact PSR-SBH systems, as it will allow for sufficiently short
survey integration times.Comment: 20 pages, 11 figures, 1 table, accepted for publication in MNRA
Interface states and anomalous quantum oscillations in graphene hybrid structures
One- and two-layer graphene have recently been shown to feature new physical
phenomena such as unconventional quantum Hall effects and prospects of
supporting a non-silicon technological platform using epitaxial graphene. While
both one- and two-layer graphene have been studied extensively, continuous
sheets of graphene possessing both parts have not yet been explored. Here we
report a study of such graphene hybrid structures. In a bulk hybrid featuring
two large-area one- and two-layer graphene and an interface between them, two
sets of Landau levels and features related to the interface were found. In edge
hybrids featuring a large two-layer graphene with narrow one-layer graphene
edges, we observed an anomalous suppression in quantum oscillation amplitude
due to the locking of one- and two-layer graphene Fermi energies and emergent
chiral interface states. These findings demonstrate the importance of these
hybrid structures whose unique interface states and related phenomena deserve
further studies.Comment: 4 pages, 4 figure
Brane Formation and Cosmological Constraint on the Number of Extra Dimensions
Special relativity is generalized to extra dimensions and quantized energy
levels of particles are obtained. By calculating the probability of particles'
motion in extra dimensions at high temperature of the early universe, it is
proposed that the branes may have not existed since the very beginning of the
universe, but formed later. Meanwhile, before the formation, particles of the
universe may have filled in the whole bulk, not just on the branes. This
scenario differs from that in the standard big bang cosmology in which all
particles are assumed to be in the 4D spacetime. So, in brane models, whether
our universe began from a 4D big bang singularity is questionable. A
cosmological constraint on the number of extra dimensions is also given which
favors .Comment: 11 pages, no figures. To appear in IJT
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