1,135 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
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
Double oxidation scheme for tunnel junction fabrication
The authors report a method to achieve Al–AlOx–Al tunnel junctions with high specific resistance in a controlled manner using a double oxidation technique. The technique is based on the standard method for oxidation repeated on an additional Al layer. The tunnel junctions were characterized with standard methods, such as comparison of room temperature resistance with liquid helium resistance and the authors found them to be of comparable quality to junctions fabricated with standard single oxidation. Fitting with the Simmons model suggests that both the barrier width and barrier height are consistent with those obtained in a single oxidation step. The junction specific capacitance was determined at low temperature to be 68fF/μm2. These junctions, employed in low temperature measurements and applications, demonstrate expected and stable conductance characteristics. The double oxidation method is straightforward to implement in a basic setup for tunnel junction fabrication.Peer reviewe
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
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.
The Chronology of Corded Ware Culture in Finland - Reviewing New Data
This paper reviews radiocarbon dates from the Late Neolithic Corded Ware Culture (CWC) contexts in Finland. The authors have recently published new CWC radiocarbon dates as a part of their multi-site geochemical provenance investigation of CWC pottery recovered from archaeological contexts in Finland, Sweden, and Estonia. In this paper, the new and old radiocarbon dates are modelled using a Bayesian phase model to identify outliers in the data set and elaborate the new dates within the wider picture of the CWC absolute chronology of the study area. Timeframe 2900–2200 calBC is suggested for the CWC in Finland.Peer reviewe
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
Does Social Presence or the Potential for Interaction reduce Social Gaze in Online Social Scenarios? Introducing the "Live Lab" paradigm.
Research has shown that people’s gaze is biased away from faces in the real-world but
towards them when they are viewed onscreen. Non-equivalent stimulus conditions may have
represented a confound in this research however, as participants viewed onscreen stimuli as
pre-recordings where interaction was not possible, compared to real-world stimuli which
were viewed in real-time where interaction was possible. We assessed the independent
contributions of online social presence and ability for interaction on social gaze by
developing the “live lab” paradigm. Participants in three groups (N = 132) viewed a
confederate either as a) a live webcam stream where interaction was not possible (one-way),
b) a live webcam stream where an interaction was possible (two-way) or c) as a prerecording.
Potential for interaction, rather than online social presence, was the primary
influence on gaze behaviour: Participants in the pre-recorded and one-way conditions looked
more to the face than those in the two-way condition, particularly when the confederate made
“eye contact”. Fixation durations to the face were shorter when the scene was viewed live,
particularly during a bid for eye contact
Our findings support the dual function of gaze, but suggest that online social presence alone
is not sufficient to activate social norms of civil inattention. Implications for the
reinterpretation of previous research are discussed
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