18,215 research outputs found
Thermal activation energy of 3D vortex matter in NaFe1-xCoxAs (x=0.01, 0.03 and 0.07) single crystals
We report on the thermally activated flux flow dependency on the doping
dependent mixed state in NaFe1-xCoxAs (x=0.01, 0.03, and 0.07) crystals using
the magnetoresistivity in the case of B//c-axis and B//ab-plane. It was found
clearly that irrespective of the doping ratio, magnetoresistivity showed a
distinct tail just above the Tc, offset associated with the thermally activated
flux flow (TAFF) in our crystals. Furthermore, in TAFF region the temperature
dependence of the activation energy follows the relation U(T, B)=U_0 (B)
(1-T/T_c )^q with q=1.5 in all studied crystals. The magnetic field dependence
of the activation energy follows a power law of U_0 (B)~B^(-{\alpha}) where the
exponent {\alpha} is changed from a low value to a high value at a crossover
field of B=~2T, indicating the transition from collective to plastic pinning in
the crystals. Finally, it is suggested that the 3D vortex phase is the dominant
phase in the low-temperature region as compared to the TAFF region in our
series samples
Effect of Imperceptible Vibratory Noise Applied to Wrist Skin On Fingertip Touch Evoked Potentials – An EEG Study
Random vibration applied to skin can change the sense of touch. Specifically, low amplitude white-noise vibration can improve fingertip touch perception. In fact, fingertip touch sensation can improve even when imperceptible random vibration is applied to other remote upper extremity areas such as wrist, dorsum of the hand, or forearm. As such, vibration can be used to manipulate sensory feedback and improve dexterity, particularly during neurological rehabilitation. Nonetheless, the neurological bases for remote vibration enhanced sensory feedback are yet poorly understood. This study examined how imperceptible random vibration applied to the wrist changes cortical activity for fingertip sensation. We measured somatosensory evoked potentials to assess peak-to-peak response to light touch of the index fingertip with applied wrist vibration versus without. We observed increased peak-to-peak somatosensory evoked potentials with wrist vibration, especially with increased amplitude of the later component for the somatosensory, motor, and premotor cortex with wrist vibration. These findings corroborate an enhanced cortical-level sensory response motivated by vibration. It is possible that the cortical modulation observed here is the result of the establishment of transient networks for improved perception
Non-Gaussian errors of baryonic acoustic oscillations
We revisit the uncertainty in baryon acoustic oscillation (BAO) forecasts and
data analyses. In particular, we study how much the uncertainties on both the
measured mean dilation scale and the associated error bar are affected by the
non-Gaussianity of the non-linear density field. We examine two possible
impacts of non-Gaussian analysis: (1) we derive the distance estimators from
Gaussian theory, but use 1000 N-Body simulations to measure the actual errors,
and compare this to the Gaussian prediction, and (2) we compute new optimal
estimators, which requires the inverse of the non-Gaussian covariance matrix of
the matter power spectrum. Obtaining an accurate and precise inversion is
challenging, and we opted for a noise reduction technique applied on the
covariance matrices. By measuring the bootstrap error on the inverted matrix,
this work quantifies for the first time the significance of the non-Gaussian
error corrections on the BAO dilation scale. We find that the variance (error
squared) on distance measurements can deviate by up to 12% between both
estimators, an effect that requires a large number of simulations to be
resolved. We next apply a reconstruction algorithm to recover some of the BAO
signal that had been smeared by non-linear evolution, and we rerun the
analysis. We find that after reconstruction, the rms error on the distance
measurement improves by a factor of ~1.7 at low redshift (consistent with
previous results), and the variance ({\sigma}^2) shows a change of up to 18%
between optimal and sub-optimal cases (note, however, that these discrepancies
may depend in detail on the procedure used to isolate the BAO signal). We
finally discuss the impact of this work on current data analyses.Comment: 13 pages, 11 figures, MNRAS accepte
Epitaxial growth and the magnetic properties of orthorhombic YTiO3 thin films
High-quality YTiO3 thin films were grown on LaAlO3 (110) substrates at low
oxygen pressures (<10-8 Torr) using pulsed laser deposition. The in-plane
asymmetric atomic arrangements at the substrate surface allowed us to grow
epitaxial YTiO3 thin films, which have an orthorhombic crystal structure with
quite different a- and b-axes lattice constants. The YTiO3 film exhibited a
clear ferromagnetic transition at 30 K with a saturation magnetization of about
0.7 uB/Ti. The magnetic easy axis was found to be along the [1-10] direction of
the substrate, which differs from the single crystal easy axis direction, i.e.,
[001].Comment: 14 pages, 4 figure
Anisotropic sub-Doppler laser cooling in dysprosium magneto-optical traps
Magneto-optical traps (MOTs) of Er and Dy have recently been shown to exhibit
population-wide sub-Doppler cooling due to their near degeneracy of excited and
ground state Lande g factors. We discuss here an additional, unusual intra-MOT
sub-Doppler cooling mechanism that appears when the total Dy MOT cooling laser
intensity and magnetic quadrupole gradient increase beyond critical values.
Specifically, anisotropically sub-Doppler-cooled cores appear, and their
orientation with respect to the quadrupole axis flips at a critical ratio of
the MOT laser intensity along the quadrupole axis versus that in the plane of
symmetry. This phenomenon can be traced to a loss of the velocity-selective
resonance at zero velocity in the cooling force along directions in which the
atomic polarization is oriented by the quadrupole field. We present data
characterizing this anisotropic laser cooling phenomenon and discuss a
qualitative model for its origin based on the extraordinarily large Dy magnetic
moment and Dy's near degenerate g factors.Comment: 4 pages, 5 figure
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