794 research outputs found
Crystallization Kinetics of Colloidal Spheres under Stationary Shear Flow
A systematic experimental study of dispersions of charged colloidal spheres
is presented on the effect of steady shear flow on nucleation and
crystal-growth rates. In addition, the non-equilibrium phase diagram as far as
the melting line is concerned is measured. Shear flow is found to strongly
affect induction times, crystal growth rates and the location of the melting
line. The main findings are that (i) the crystal growth rate for a given
concentration exhibits a maximum as a function of the shear rate, (ii) contrary
to the monotonous increase of the growth rate with increasing concentration in
the absence of flow, a maximum of the crystal growth rate as a function of
concentration is observed for sheared systems, and (iii) the induction time for
a given concentration exhibits a maximum as a function of the shear rate. These
findings will be partly explained on a qualitative level.Comment: 17 pages, 10 figures, accepted in Langmui
Emergence of a negative charging energy in a metallic dot capacitively coupled to a superconducting island
We consider the hybrid setup formed by a metallic dot, capacitively coupled
to a superconducting island S connected to a bulk superconductor by a Josephson
junction. Charge fluctuations in S act as a dynamical gate and overscreen the
electronic repulsion in the metallic dot, producing an attractive interaction
between two additional electrons. As the offset charge of the metallic dot is
increased, the dot charging curve shows positive steps () followed by
negative ones () signaling the occurrence of a negative differential
capacitance. A proposal for experimental detection is given, and potential
applications in nanoelectronics are mentioned.Comment: Revised version, 4 pages, 4 figure
Primary tunnel junction thermometry
We describe the concept and experimental demonstration of primary thermometry
based on a four probe measurement of a single tunnel junction embedded within
four arrays of junctions. We show that in this configuration random sample
specific and environment-related errors can be avoided. This method relates
temperature directly to Boltzmann constant, which will form the basis of the
definition of temperature and realization of official temperature scales in the
future
Supersaturated dispersions of rod-like viruses with added attraction
The kinetics of isotropic-nematic (I-N) and nematic-isotropic (N-I) phase
transitions in dispersions of rod-like {\it fd}-viruses are studied.
Concentration quenches were applied using pressure jumps in combination with
polarization microscopy, birefringence and turbidity measurements. The full
biphasic region could be accessed, resulting in the construction of a first
experimental analogue of the bifurcation diagram. The N-I spinodal points for
dispersions of rods with varying concentrations of depletion agents (dextran)
were obtained from orientation quenches, using cessation of shear flow in
combination with small angle light scattering. We found that the location of
the N-I spinodal point is independent of the attraction, which was confirmed by
theoretical calculations. Surprisingly, the experiments showed that also the
absolute induction time, the critical nucleus and the growth rate are
insensitive of the attraction, when the concentration is scaled to the distance
to the phase boundaries.Comment: 13 pages, 14 figures. accepted in Phsical Review
Spin-precession-assisted supercurrent in a superconducting quantum point contact coupled to a single-molecule magnet
The supercurrent of a quantum point contact coupled to a nanomagnet strongly
depends on the dynamics of the nanomagnet's spin. We employ a fully microscopic
model to calculate the transport properties of a junction coupled to a spin
whose dynamics is modeled as Larmor precession brought about by an external
magnetic field and find that the dynamics affects the charge and spin currents
by inducing transitions between the continuum states below the superconducting
gap edge and the Andreev levels. This redistribution of the quasiparticles
leads to a non-equilibrium population of the Andreev levels and an enhancement
of the supercurrent which is visible as a modified current-phase relation as
well as a non-monotonous critical current as function of temperature. The
non-monotonous behavior is accompanied by a corresponding change in
spin-transfer torques acting on the precessing spin and leads to the
possibility of using temperature as a means to tune the back-action on the
spin.Comment: 11 pages, 5 figure
Respiratory Modulation in Permanent Atrial Fibrillation
Several studies have shown that the autonomic nervous system (ANS) can induce changes during atrial fibrillation (AF). There is currently a lack of methods for quantifying ANS induced variations during AF. The purpose of this study is to quantify respiratory induced modulation in the f-wave frequency trend. Following qrst-cancellation, the local f-wave frequency is estimated by fitting a harmonic f-wave model signal and a quality index (SQI) is computed based on the model fit. The resulting frequency trend is filtered using a narrow bandpass filter with a center frequency corresponding to the local respiration rate. The magnitude of the respiratory induced f-wave frequency modulation is estimated by the envelope of the filtered frequency trend. The performance of the method is validated using simulations and the method is applied to analyze ECG data from eight patients with permanent AF recorded during 0.125 Hz frequency controlled respiration before and after the full vagal blockade, respectively. Results from simulated data show the magnitude of the respiratory induced f-wave frequency modulation can be estimated with an error of less than = 0.005Hz if the SQI is above 0.45. The signal quality was sufficient for analysis in 7 out of 8 patients. In 4 patients the magnitude decreased and in 3 patients there was no change
Nematic-Isotropic Spinodal Decomposition Kinetics of Rod-like Viruses
We investigate spinodal decomposition kinetics of an initially nematic
dispersion of rod-like viruses (fd virus). Quench experiments are performed
from a flow-stabilized homogeneous nematic state at high shear rate into the
two-phase isotropic-nematic coexistence region at zero shear rate. We present
experimental evidence that spinodal decomposition is driven by orientational
diffusion, in accordance with a very recent theory.Comment: 17 pages, 6 figures, accepted in Phys. Rev.
Design and development of a low-cost mask-type eye tracker to collect quality fixation measurements in the sport domain
The aim of the study was to build a low-cost mask-type eye tracker with accuracy and precision levels similar to those reported for commercial eye tracking devices. To this end, head-mounted hardware was designed and developed, while open-source software was modified for digital image capture, manipulation, and fixation analysis. An image recognition application was also included with different lighting scenarios. Moreover, parallax and viewing perspective errors were controlled to ensure the quality of data collection. The device was wireless and lightweight (99 g) to allow for natural movement and avoid participant discomfort. After calibration of a 9-target monocular grid, spatial accuracy and precision of the eye tracker was evaluated by 30 participants, at four different lighting setups, both before and after a climbing task. Validity tests showed high levels of accuracy in all conditions as evidenced by a systematic error for a 13-target grid of <0.5°. The reliability tests also showed consistent measurements with no differences in accuracy recorded between participants, lighting conditions, and visual behaviors for the pre- versus post-climbing task. These results suggest that the present eye tracker reports spatial accuracy similar to other commercial systems with levels of high quality. Altogether, this innovative user interface is suitable for research purposes and/or performance analysis in physical activity and sport-related activities. Also, features of this mask-type eye tracking system make it a suitable perceptual user interface to investigate human–computer interactions in a large number of other research fields including psychology, education, marketing, transportation, and medicine
Transport and magnetization dynamics in a superconductor/single-molecule magnet/superconductor junction
We study dc-transport and magnetization dynamics in a junction of arbitrary
transparency consisting of two spin-singlet superconducting leads connected via
a single classical spin precessing at the frequency . The presence of
the spin in the junction provides different transmission amplitudes for spin-up
and spin-down quasiparticles as well as a time-dependent spin-flip transmission
term. For a phase biased junction, we show that a steady-state superconducting
charge current flows through the junction and that an out-of-equilibrium
circularly polarized spin current, of frequency , is emitted in the
leads. Detailed understanding of the charge and spin currents is obtained in
the entire parameter range. In the adiabatic regime,
where is the superconducting gap, and for high transparencies of the
junction, a strong suppression of the current takes place around \vp \approx
0 due to an abrupt change in the occupation of the Andreev bound-states. At
higher values of the phase and/or precession frequency, extended
(quasi-particle like) states compete with the bound-states in order to carry
the current. Well below the superconducting transition, these results are shown
to be weakly affected by the back-action of the spin current on the dynamics of
the precessing spin. Indeed, we show that the Gilbert damping due to the
quasi-particle spin current is strongly suppressed at low-temperatures, which
goes along with a shift of the precession frequency due to the condensate. The
results obtained may be of interest for on-going experiments in the field of
molecular spintronics.Comment: 19 pages, 13 figures (v3) Minor modifications per referee's comments.
No change in results. (v2) 2 authors added, 1 reference added (Ref. 25), no
change in the text and result
Collective diffusion in charge-stabilized suspensions: Concentration and salt effects
The authors present a joint experimental-theoretical study of collective diffusion properties in aqueous suspensions of charge-stabilized fluorinated latex spheres. Small-angle x-ray scattering and x-ray photon correlation spectroscopy have been used to explore the concentration and ionic-strength dependence of the static and short-time dynamic properties including the hydrodynamic function H (q), the wave-number-dependent collective diffusion coefficient D (q), and the intermediate scattering function over the entire accessible range. They show that all experimental data can be quantitatively described and explained by means of a recently developed accelerated Stokesian dynamics simulation method, in combination with a modified hydrodynamic many-body theory. In particular, the behavior of H (q) for de-ionized and dense suspensions can be attributed to the influence of many-body hydrodynamics, without any need for postulating hydrodynamic screening to be present, as it was done in earlier work. Upper and lower boundaries are provided for the peak height of the hydrodynamic function and for the short-time self-diffusion coefficient over the entire range of added salt concentrations.Fil: Gapinski, J.. A. Mickiewicz University; PoloniaFil: Patkowski, A.. A. Mickiewicz University; PoloniaFil: Banchio, Adolfo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Holmqvist, P.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Meier, Guillermo Enrique. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Lettinga, M.P.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Nägele, G.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; Alemani
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