2,143 research outputs found
Undulatory swimming in shear-thinning fluids: Experiments with C. elegans
The swimming behaviour of microorganisms can be strongly influenced by the
rheology of their fluid environment. In this manuscript, we experimentally
investigate the effects of shear-thinning viscosity on the swimming behaviour
of an undulatory swimmer, the nematode Caenorhabditis elegans. Tracking methods
are used to measure the swimmer's kinematic data (including propulsion speed)
and velocity fields. We find that shear-thinning viscosity modifies the
velocity fields produced by the swimming nematode but does not modify the
nematode's speed and beating kinematics. Velocimetry data show significant
enhancement in local vorticity and circulation and an increase in fluid
velocity near the nematode's tail compared to Newtonian fluids of similar
effective viscosity. These findings are compared to recent theoretical and
numerical results
Radio Polarization of the Young High-Magnetic-Field Pulsar PSR J1119-6127
We have investigated the radio polarization properties of PSR J1119-6127, a
recently discovered young radio pulsar with a large magnetic field. Using
pulsar-gated radio imaging data taken at a center frequency of 2496 MHz with
the Australia Telescope Compact Array, we have determined a rotation measure
for the pulsar of +842 +/- 23 rad m^-2. These data, combined with archival
polarimetry data taken at a center frequency of 1366 MHz with the Parkes
telescope, were used to determine the polarization characteristics of PSR
J1119-6127 at both frequencies. The pulsar has a fractional linear polarization
of ~75% and ~55% at 1366 and 2496 MHz, respectively, and the profile consists
of a single, wide component. This pulse morphology and high degree of linear
polarization are in agreement with previously noticed trends for young pulsars
(e.g., PSR J1513-5908). A rotating-vector (RV) model fit of the position angle
(PA) of linear polarization over pulse phase using the Parkes data suggests
that the radio emission comes from the leading edge of a conal beam. We discuss
PSR J1119-6127 in the context of a recent theoretical model of pulsar spin-down
which can in principle be tested with polarization and timing data from this
pulsar. Geometric constraints from the RV fit are currently insufficient to
test this model with statistical significance, but additional data may allow
such a test in the future.Comment: 9 pages, including 6 figures and 1 table. Accepted for publication in
Ap
Chiral sedimentation of extended objects in viscous media
We study theoretically the chirality of a generic rigid object's
sedimentation in a fluid under gravity in the low Reynolds number regime. We
represent the object as a collection of small Stokes spheres or stokeslets, and
the gravitational force as a constant point force applied at an arbitrary point
of the object. For a generic configuration of stokeslets and forcing point, the
motion takes a simple form in the nearly free draining limit where the
stokeslet radius is arbitrarily small. In this case, the internal hydrodynamic
interactions between stokeslets are weak, and the object follows a helical path
while rotating at a constant angular velocity about a fixed axis. This
is independent of initial orientation, and thus constitutes a chiral
response for the object. Even though there can be no such chiral response in
the absence of hydrodynamic interactions between the stokeslets, the angular
velocity obtains a fixed, nonzero limit as the stokeslet radius approaches
zero. We characterize empirically how depends on the placement of the
stokeslets, concentrating on three-stokeslet objects with the external force
applied far from the stokeslets. Objects with the largest are aligned
along the forcing direction. In this case, the limiting varies as the
inverse square of the minimum distance between stokeslets. We illustrate the
prevalence of this robust chiral motion with experiments on small macroscopic
objects of arbitrary shape.Comment: 35 pages, 10 figures; Section VII.A redone and other edits made for
clarity. Accepted by Phys. Rev.
Multidimensional Data Visual Exploration by Interactive Information Segments
Visualization techniques provide an outstanding role in KDD process for data analysis and mining. However, one image does not always convey successfully the inherent information from high dimensionality, very large databases. In this paper we introduce VSIS (Visual Set of Information Segments), an interactive tool to visually explore multidimensional, very large, numerical data. Within the supervised learning, our proposal approaches the problem of classification by searching of meaningful intervals belonging to the most relevant attributes. These intervals are displayed as multi–colored bars in which the degree of impurity with respect to the class membership can be easily perceived. Such bars can be re–explored interactively with new values of user–defined parameters. A case study of applying VSIS to some UCI repository data sets shows the usefulness of our tool in supporting the exploration of multidimensional and very large data
Anisotropic elasticity in confocal studies of colloidal crystals
We consider the theory of fluctuations of a colloidal solid observed in a
confocal slice. For a cubic crystal we study the evolution of the projected
elastic properties as a function of the anisotropy of the crystal using
numerical methods based on the fast Fourier transform. In certain situations of
high symmetry we find exact analytic results for the projected fluctuations.Comment: 6 pages, 7 figure
Effects of Autonomy on Worker Performance
Having autonomy can produce positive effects on an individual’s well-being as well as overall job-satisfaction. Research has shown that background music influences listener attention and is associated with the listeners fondness of the music (Huang & Shih, 2011). This study investigates the effects that autonomy may also have on performance levels in the workplace. Specifically, the effects of listening to music of preference and the effects it has on attention, concentration, and enjoyment of task. In this study worker autonomy is operationally defined as preferred genre of music. Performance will be measured by participants score on a recall task that mimics a medical scenario where a healthcare worker would have to recall specific patient information. We hypothesize that participants autonomy preferred background music will have a positive effect on worker performance. If the predicted results are found, this research could be beneficial to companies that are considering implementing new policies to encourage autonomy and in turn produce greater success in the workplace
Reversible Motion In a Contact Line
When a body of liquid sits on a surface, an irregular border between the wet and dry regions of the surface exists, called the contact line. Driving this contact line back and forth repeatedly can change its shape.We use a syringe pump to cyclically infuse and withdraw a predetermined volume of water, and take photos of the contact line after each cycle. Comparing these images to each other determines if the contact line is returning to the same shape. We find that below a critical value of infused volume, after many cycles the contact line reaches a steady state in which it always returns to the same shape. Above that value the shape fluctuates in the steady state. This suggests a transition similar to that seen in other systems like particle suspensions and solids
Fluid-Induced Propulsion of Rigid Particles in Wormlike Micellar Solutions
In the absence of inertia, a reciprocal swimmer achieves no net motion in a
viscous Newtonian fluid. Here, we investigate the ability of a reciprocally
actuated particle to translate through a complex fluid that possesses a network
using tracking methods and birefringence imaging. A geometrically polar
particle, a rod with a bead on one end, is reciprocally rotated using magnetic
fields. The particle is immersed in a wormlike micellar (WLM) solution that is
known to be susceptible to the formation of shear bands and other localized
structures due to shear-induced remodeling of its microstructure. Results show
that the nonlinearities present in this WLM solution break time-reversal
symmetry under certain conditions, and enable propulsion of an artificial
"swimmer." We find three regimes dependent on the Deborah number (De): net
motion towards the bead-end of the particle at low De, net motion towards the
rod-end of the particle at intermediate De, and no appreciable propulsion at
high De. At low De, where the particle time-scale is longer then the fluid
relaxation time, we believe that propulsion is caused by an imbalance in the
fluid first normal stress differences between the two ends of the particle
(bead and rod). At De~1, however, we observe the emergence of a region of
network anisotropy near the rod using birefringence imaging. This anisotropy
suggests alignment of the micellar network, which is "locked in" due to the
shorter time-scale of the particle relative to the fluid
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