1,284 research outputs found
Active management of multi-service networks.
Future multiservice networks will be extremely large and complex. Novel management solutions will be required to keep the management costs reasonable. Active networking enables management to be delegated to network users as a large set of independent small scale management systems. A novel architecture for an active network based management solution for multiservice networking is presented
Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses
Flow patterns generated by medusan swimmers such as
jellyfish are known to differ according the morphology of
the various animal species. Oblate medusae have been
previously observed to generate vortex ring structures
during the propulsive cycle. Owing to the inherent
physical coupling between locomotor and feeding
structures in these animals, the dynamics of vortex ring
formation must be robustly tuned to facilitate effective
functioning of both systems. To understand how this is
achieved, we employed dye visualization techniques on
scyphomedusae (Aurelia aurita) observed swimming in
their natural marine habitat. The flow created during each
propulsive cycle consists of a toroidal starting vortex
formed during the power swimming stroke, followed by a
stopping vortex of opposite rotational sense generated
during the recovery stroke. These two vortices merge in a
laterally oriented vortex superstructure that induces flow
both toward the subumbrellar feeding surfaces and
downstream. The lateral vortex motif discovered here
appears to be critical to the dual function of the medusa
bell as a flow source for feeding and propulsion.
Furthermore, vortices in the animal wake have a greater
volume and closer spacing than predicted by prevailing
models of medusan swimming. These effects are shown to
be advantageous for feeding and swimming performance,
and are an important consequence of vortex interactions
that have been previously neglected
Experimental Study of Heat Convection From Stationary and Oscillating Circular Cylinder in Cross Flow
An experimental study is made on the processes of heat transfer from the surface of a
forced oscillating cylinder in a crossflow. A range of oscillation amplitude (A/D
=0.1,0.2), forced oscillation frequency (0<St_c<1), and Reynolds number (Re=550,
1100, 3500) is covered in water (Pr=6). Besides the increase at the natural vortex
shedding frequency, large increases in the heat transfer are found at certain superharmonics.
By using Digital Particle Image Velocimetry/Thermometry (DPIV/T), the increase
in the heat transfer rate is found to correlate inversely with the distance at which
vortices roll-up behind the cylinder, i.e., the distance decreases when the heat transfer
increases. The cause of the increase is found to be the removal of the stagnant and low
heat convecting fluid at the base of the cylinder during the roll-up of the vortices
Estimation of elastic and viscous properties of the left ventricle based on annulus plane harmonic behavior
Assessment of left ventricular (LV) function
with an emphasis on contractility has been a challenge
in cardiac mechanics during the recent decades. The LV
function is usually described by the LV pressurevolume
(P-V) diagram. The standard P-V diagrams are
easy to interpret but difficult to obtain and require
invasive instrumentation for measuring the
corresponding volume and pressure data. In the present
study, we introduce a technique that can estimate the
viscoelastic properties of the LV based on harmonic
behavior of the ventricular chamber and it can be
applied non-invasively as well. The estimation technique
is based on modeling the actual long axis displacement
of the mitral annulus plane toward the cardiac base as a
linear damped oscillator with time-varying coefficients.
The time-varying parameters of the model were
estimated by a standard Recursive Linear Least
Squares (RLLS) technique. LV stiffness at end-systole
and end diastole was in the range of 61.86-136.00
dyne/g.cm and 1.25-21.02 dyne/g.cm, respectively. The
only input used in this model was the long axis
displacement of the annulus plane, which can also be
obtained non-invasively using tissue Doppler or MR
imaging
Experimental Study of Heat Convection From Stationary and Oscillating Circular Cylinder in Cross Flow
Wicking of a liquid bridge connected to a moving porous surface
We study the coupled problem of a liquid bridge connected to a porous surface and an impermeable surface, where the gap between the surfaces is an externally controlled function of time. The relative motion between the surfaces influences the pressure distribution and geometry of the liquid bridge, thus affecting the shape of liquid penetration into the porous material. Utilizing the lubrication approximation and Darcy’s phenomenological law, we obtain an implicit integral relation between the relative motion between the surfaces and the shape of liquid penetration. A method to control the shape of liquid penetration is suggested and illustrated for the case of conical penetration shapes with an arbitrary cone opening angle. We obtain explicit analytic expressions for the case of constant relative speed of the surfaces as well as for the relative motion between the surfaces required to create conical penetration shapes. Our theoretical results are compared with experiments and reasonable agreement between the analytical and experimental data is observed
Chaos in Shear Flows
Almost 25 years ago Lorenz published his seminal
study on the existence of a strange attractor in the phase
space of a severely truncated model system arising from
the hydrodynamical equations describing two-dimensional
convection. Nearly a century ago Poincare
published his famous treatise Les Methodes Noovelles
de la Mecaniaue Celeste (1892) in which the possible
complexity of behavior in nonintegrable, conservative
systems was first envisioned. Both these works address
an age old puzzle: How do apparently stochastic outputs
arise from an entirely deterministic system subject to
non-stochastic inputs
Flow Velocity Measurement by Image Processing of Optically Activated Tracers
A computerized flow visualization technique
capable of quantifying the flow field automatically
has been developed. This technique uses afterglowing effect of optically activated phosphorescent
particles to retrieve vectorial information on each
trace. By using this information, in conjunction
with computer image processing, the flow field of a
free surface transient vortex was investigated
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