9,252 research outputs found
Tunable Unidirectional Sound Propagation through a Sonic-Crystal-Based Acoustic Diode
Nonreciprocal wave propagation typically requires strong nonlinear materials to break time reversal symmetry. Here, we utilized a
sonic-crystal-based acoustic diode that had broken spatial inversion
symmetry and experimentally realized sound unidirectional transmission
in this acoustic diode. These novel phenomena are attributed to
different mode transitions as well as their associated different energy
conversion efficiencies among different diffraction orders at two sides
of the diode. This nonreciprocal sound transmission could be
systematically controlled by simply mechanically rotating the square
rods of the sonic crystal. Different from nonreciprocity due to the
nonlinear acoustic effect and broken time reversal symmetry, this new
model leads to a one-way effect with higher efficiency, broader
bandwidth, and much less power consumption, showing promising
applications in various sound devices
Effects of tidally enhanced stellar wind on the horizontal branch morphology of globular clusters
Metallicity is the first parameter to influence the horizontal branch (HB)
morphology of globular clusters (GCs). It has been found, however, that some
other parameters may also play an important role in affecting the morphology.
While the nature of these important parameters remains unclear, they are
believed to be likely correlated with wind mass-loss of red giants, since this
mass loss determines their subsequent locations on the HB. Unfortunately, the
mass loss during the red giant stages of the stellar evolution is poorly
understood at present. The stellar winds of red giants may be tidally enhanced
by companion stars if they are in binary systems. We investigate evolutionary
consequences of red giants in binaries by including tidally enhanced stellar
winds, and examine the effects on the HB morphology of GCs. We find that red,
blue, and extreme horizontal branch stars are all produced under the effects of
tidally enhanced stellar wind without any additional assumptions on the
mass-loss dispersion. Furthermore, the horizontal branch morphology is found to
be insensitive to the tidal enhancement parameter, Bw. We compare our
theoretical results with the observed horizontal branch morphology of globular
cluster NGC 2808, and find that the basic morphology of the horizontal branch
can be well reproduced. The number of blue horizontal branch stars in our
calculations, however, is lower than that of NGC 2808.Comment: 7 pages, 4 figures, 2 tables, accepted for publication in Astronomy &
Astrophysic
Reducing the Tension Between the BICEP2 and the Planck Measurements: A Complete Exploration of the Parameter Space
A large inflationary tensor-to-scalar ratio is reported by the BICEP2 team based on their B-mode
polarization detection, which is outside of the confidence level of the
Planck best fit model. We explore several possible ways to reduce the tension
between the two by considering a model in which ,
, and the neutrino parameters and
are set as free parameters. Using the Markov Chain
Monte Carlo (MCMC) technique to survey the complete parameter space with and
without the BICEP2 data, we find that the resulting constraints on
are consistent with each other and the apparent tension
seems to be relaxed. Further detailed investigations on those fittings suggest
that probably plays the most important role in reducing the
tension. We also find that the results obtained from fitting without adopting
the consistency relation do not deviate much from the consistency relation.
With available Planck, WMAP, BICEP2 and BAO datasets all together, we obtain
, ,
, and
; if the consistency relation is
adopted, we get .Comment: 8 pages, 4 figures, submitted to PL
The neural basis of responsibility attribution in decision-making
Social responsibility links personal behavior with societal expectations and plays a key role in affecting an agent's emotional state following a decision. However, the neural basis of responsibility attribution remains unclear. In two previous event-related brain potential (ERP) studies we found that personal responsibility modulated outcome evaluation in gambling tasks. Here we conducted a functional magnetic resonance imaging (fMRI) study to identify particular brain regions that mediate responsibility attribution. In a context involving team cooperation, participants completed a task with their teammates and on each trial received feedback about team success and individual success sequentially. We found that brain activity differed between conditions involving team success vs. team failure. Further, different brain regions were associated with reinforcement of behavior by social praise vs. monetary reward. Specifically, right temporoparietal junction (RTPJ) was associated with social pride whereas dorsal striatum and dorsal anterior cingulate cortex (ACC) were related to reinforcement of behaviors leading to personal gain. The present study provides evidence that the RTPJ is an important region for determining whether self-generated behaviors are deserving of praise in a social context
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