366,681 research outputs found
Effect of inverse magnetic catalysis on conserved charge fluctuations in hadron resonance gas model
The effect of inverse magnetic catalysis (IMC) has been observed on the
conserved charge fluctuations and the correlations along the chemical
freeze-out curve in a hadron resonance gas model. The fluctuations and the
correlations have been compared with and without charge conservations. The
charge conservation plays an important role in the calculation of the
fluctuations at nonzero magnetic field and for the fluctuations in the strange
charge at zero magnetic field. The charge conservation diminishes the
correlations and , but enhances the correlation
. The baryonic fluctuations (2nd order) at
increases more than two times compared to at higher . The
fluctuations have been compared at nonzero magnetic field along the freeze-out
curve i.e along fitted parameters of the chemical freeze-out temperature and
chemical potentials, with the fluctuations at nonzero magnetic field along the
freeze-out curve with the IMC effect, and the results are very different with
the IMC effect. This is clearly seen in the products of different moments
and of net-kaon distribution.Comment: 12 pages,10 figures, Accepted by Phys. Rev.
An Adaptive Locally Connected Neuron Model: Focusing Neuron
This paper presents a new artificial neuron model capable of learning its
receptive field in the topological domain of inputs. The model provides
adaptive and differentiable local connectivity (plasticity) applicable to any
domain. It requires no other tool than the backpropagation algorithm to learn
its parameters which control the receptive field locations and apertures. This
research explores whether this ability makes the neuron focus on informative
inputs and yields any advantage over fully connected neurons. The experiments
include tests of focusing neuron networks of one or two hidden layers on
synthetic and well-known image recognition data sets. The results demonstrated
that the focusing neurons can move their receptive fields towards more
informative inputs. In the simple two-hidden layer networks, the focusing
layers outperformed the dense layers in the classification of the 2D spatial
data sets. Moreover, the focusing networks performed better than the dense
networks even when 70 of the weights were pruned. The tests on
convolutional networks revealed that using focusing layers instead of dense
layers for the classification of convolutional features may work better in some
data sets.Comment: 45 pages, a national patent filed, submitted to Turkish Patent
Office, No: -2017/17601, Date: 09.11.201
The SBF Survey of Galaxy Distances. II. Local and Large-Scale Flows
We present analysis of local large scale flows using the Surface Brightness
Fluctuation (SBF) Survey for the distances to 300 early-type galaxies. Our
models of the distribution function of mean velocity and velocity dispersion at
each point in space include a uniform thermal velocity dispersion and spherical
attractors whose position, amplitude, and radial shape are free to vary. Our
fitting procedure performs a maximum likelihood fit of the model to the
observations. We obtain a Hubble constant of Ho = 77 +/- 4 +/- 7 km/s/Mpc, but
a uniform Hubble flow is not acceptable fit to the data. Inclusion of two
attractors, one of whose fit location coincides with the Virgo cluster and the
other whose fit location is slightly beyond the Centaurus clusters nearly
explain the peculiar velocities, but the quality of the fit can be further
improved by the addition of a quadrupole correction to the Hubble flow.
Although the dipole and quadrupole may be genuine manifestations of more
distant density fluctuations, we find evidence that they are more likely due to
non-spherical attractors. We find no evidence for bulk flows which include our
entire survey volume (R < 3000 km/s); our volume is at rest with respect to the
CMB. The fits to the attractors both have isothermal radial profiles (v ~ 1/r)
over a range of overdensity between about 10 and 1, but fall off more steeply
at larger radius. The best fit value for the small scale, cosmic thermal
velocity is 180 +/- 14 km/s.Comment: 37 pages, AASTeX Latex, including 30 Postscript figures, submitted to
Astrophysical Journal, July 2, 199
A Comparative Study of Magnetic Fields in the Solar Photosphere and Chromosphere at Equatorial and Polar Latitudes
Besides their own intrinsic interest, correct interpretation of solar surface
magnetic field observations is crucial to our ability to describe the global
magnetic structure of the solar atmosphere. Photospheric magnetograms are often
used as lower boundary conditions in models of the corona, but not data from
the nearly force-free chromosphere. National Solar Observatory's (NSO) Synoptic
Optical Long-term Investigations of the Sun VSM (Vector Spectromagnetograph)
produces full-disk line-of-sight magnetic flux images deriving from both
photospheric and chromospheric layers on a daily basis. In this paper, we
investigate key properties of the magnetic field in these two layers using more
than five years of VSM data. We find from near-equatorial measurements that the
east-west inclination angle of most photospheric fields is less than about
12{\deg}, while chromospheric fields expand in all directions to a significant
degree. Using a simple stereoscopic inversion, we find evidence that
photospheric polar fields are also nearly radial but that during 2008 the
chromospheric field in the south pole was expanding superradially. We obtain a
spatially resolved polar photospheric flux distribution up to 80{\deg} latitude
whose strength increases poleward approximately as cosine(colatitude) to the
power 9-10. This distribution would give a polar field strength of 5-6 G. We
briefly discuss implications for future synoptic map construction and modeling
The influence of push-off timing in a robotic ankle-foot prosthesis on the energetics and mechanics of walking
Background: Robotic ankle-foot prostheses that provide net positive push-off work can reduce the metabolic rate of walking for individuals with amputation, but benefits might be sensitive to push-off timing. Simple walking models suggest that preemptive push-off reduces center-of-mass work, possibly reducing metabolic rate. Studies with bilateral exoskeletons have found that push-off beginning before leading leg contact minimizes metabolic rate, but timing was not varied independently from push-off work, and the effects of push-off timing on biomechanics were not measured. Most lower-limb amputations are unilateral, which could also affect optimal timing. The goal of this study was to vary the timing of positive prosthesis push-off work in isolation and measure the effects on energetics, mechanics and muscle activity.
Methods: We tested 10 able-bodied participants walking on a treadmill at 1.25 m.s(-1). Participants wore a tethered ankle-foot prosthesis emulator on one leg using a rigid boot adapter. We programmed the prosthesis to apply torque bursts that began between 46% and 56% of stride in different conditions. We iteratively adjusted torque magnitude to maintain constant net positive push-off work.
Results: When push-off began at or after leading leg contact, metabolic rate was about 10% lower than in a condition with Spring-like prosthesis behavior. When push-off began before leading leg contact, metabolic rate was not different from the Spring-like condition. Early push-off led to increased prosthesis-side vastus medialis and biceps femoris activity during push-off and increased variability in step length and prosthesis loading during push-off. Prosthesis push-off timing had no influence on intact-side leg center-of-mass collision work.
Conclusions: Prosthesis push-off timing, isolated from push-off work, strongly affected metabolic rate, with optimal timing at or after intact-side heel contact. Increased thigh muscle activation and increased human variability appear to have caused the lack of reduction in metabolic rate when push-off was provided too early. Optimal timing with respect to opposite heel contact was not different from normal walking, but the trends in metabolic rate and center-of-mass mechanics were not consistent with simple model predictions. Optimal push-off timing should also be characterized for individuals with amputation, since meaningful benefits might be realized with improved timing
The Fine-Structure of the Net-Circular Polarization in a Sunspot Penumbra
We present novel evidence for a fine structure observed in the net-circular
polarization (NCP) of a sunspot penumbra based on spectropolarimetric
measurements utilizing the Zeeman sensitive FeI 630.2 nm line. For the first
time we detect a filamentary organized fine structure of the NCP on spatial
scales that are similar to the inhomogeneities found in the penumbral flow
field. We also observe an additional property of the visible NCP, a
zero-crossing of the NCP in the outer parts of the center-side penumbra, which
has not been recognized before. In order to interprete the observations we
solve the radiative transfer equations for polarized light in a model penumbra
with embedded magnetic flux tubes. We demonstrate that the observed
zero-crossing of the NCP can be explained by an increased magnetic field
strength inside magnetic flux tubes in the outer penumbra combined with a
decreased magnetic field strength in the background field. Our results strongly
support the concept of the uncombed penumbra
Emergence of Bloch oscillations in one-dimensional systems
Electrons in periodic potentials exhibit oscillatory motion in presence of an
electric field. Such oscillations are known as Bloch oscillations. In this
article we theoretically investigate the emergence of Bloch oscillations for
systems where the electric field is confined to a finite region, like in
typical electronic devices. We use a one-dimensional tight-binding model within
the single-band approximation to numerically study the dynamics of electrons
after a sudden switching-on of the electric field. We find a transition from a
regime with direct current to Bloch oscillations when increasing the system
size or decreasing the field strength. We propose a pump-probe scheme to
observe the oscillations by measuring the accumulated charge as a function of
the pulse-length
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