3,317 research outputs found
Steric-effect-induced enhancement of electrical-double-layer overlapping phenomena\ud
In this paper, we demonstrate that nontrivial interactions between steric effect and electrical-double-layer (EDL) overlap phenomena may augment the effective extent of EDL overlap in narrow fluidic confinements to a significant extent by virtue of rendering the channel centerline potential tending to the ζ potential in a limiting sense as the steric effect progressively intensifies. Such a behavior may result in a virtually uniform (undiminished) magnitude of the EDL potential across the entire channel height and may cause lowering of the total charge within the EDL.\ud
\u
A Conformal Mapping Based Fractional Order Approach for Sub-optimal Tuning of PID Controllers with Guaranteed Dominant Pole Placement
A novel conformal mapping based Fractional Order (FO) methodology is
developed in this paper for tuning existing classical (Integer Order)
Proportional Integral Derivative (PID) controllers especially for sluggish and
oscillatory second order systems. The conventional pole placement tuning via
Linear Quadratic Regulator (LQR) method is extended for open loop oscillatory
systems as well. The locations of the open loop zeros of a fractional order PID
(FOPID or PI{\lambda}D{\mu}) controller have been approximated in this paper
vis-\`a-vis a LQR tuned conventional integer order PID controller, to achieve
equivalent integer order PID control system. This approach eases the
implementation of analog/digital realization of a FOPID controller with its
integer order counterpart along with the advantages of fractional order
controller preserved. It is shown here in the paper that decrease in the
integro-differential operators of the FOPID/PI{\lambda}D{\mu} controller pushes
the open loop zeros of the equivalent PID controller towards greater damping
regions which gives a trajectory of the controller zeros and dominant closed
loop poles. This trajectory is termed as "M-curve". This phenomena is used to
design a two-stage tuning algorithm which reduces the existing PID controller's
effort in a significant manner compared to that with a single stage LQR based
pole placement method at a desired closed loop damping and frequency.Comment: 23 pages, 7 figures, in press; Communications in Nonlinear Science
and Numerical Simulations, 201
Landauer formula for phonon heat conduction: relation between energy transmittance and transmission coefficient
The heat current across a quantum harmonic system connected to reservoirs at
different temperatures is given by the Landauer formula, in terms of an
integral over phonon frequencies \omega, of the energy transmittance T(\omega).
There are several different ways to derive this formula, for example using the
Keldysh approach or the Langevin equation approach. The energy transmittance
T({\omega}) is usually expressed in terms of nonequilibrium phonon Green's
function and it is expected that it is related to the transmission coefficient
{\tau}({\omega}) of plane waves across the system. In this paper, for a
one-dimensional set-up of a finite harmonic chain connected to reservoirs which
are also semi-infinite harmonic chains, we present a simple and direct
demonstration of the relation between T({\omega}) and {\tau}({\omega}). Our
approach is easily extendable to the case where both system and reservoirs are
in higher dimensions and have arbitrary geometries, in which case the meaning
of {\tau} and its relation to T are more non-trivial.Comment: 17 pages, 1 figur
- …