9,814 research outputs found
Control of Cavity-Induced Drag Using Steady Jets
Separated shear layer oscillations in open cavities can
induce drag, noise and vibration. This issue has many
aerospace applications such as Landing gears and control
surfaces [1]. Recently, phase-cancellation [1] and offinstability
frequency excitation [2] & [3] approaches have
been incorporated in different open-loop and feedback control
systems. Despite the high control performance of these
systems, further enhancement is still possible.
In this study, steady jets, as shown in fig. 1, are forced
through 2mm, two-dimensional slots at the leading and trailing
edges of the cavity. In order to study the performance of this
novel approach, different cases will be examined, including:
jet combination (blowing from cavity leading edge, suction
from cavity leading edge and blowing-suction), jet angle
(parallel or deflected jet) and jet-to-free stream velocity
factor /.
Computer model for simulating the long-term dynamics of annual weeds under different cultivation practices
A model is being developed which describes the population dynamics of annual weeds and how it is affected by crop rotation, cultivation practices and weed control. The model aims to predict the development of a certain weed species in order to plan crop rotation and cultivation practices to minimize the risk of proliferation. The model does not predict the exact number of weeds expected to be found in a certain year or crop, but rather the general development over a number of years. The model includes documented knowledge, as well as informal expert knowledge, on seed survival in the soil, seed placement in soil after tillage, seed germination with respect to placement in soil, time of year and tillage, weed development in response to crop competitiveness and seed production of the weeds. The model is at present only accounting for the development of one weed species at a time, and only a few weed species are parameterised. However, the model can easily be extended with more weed species, crops and cultivation practices. Model predictions should match what knowledgeable weed scientists already know, perhaps with a little new insight
Bulk and surface magnetoinductive breathers in binary metamaterials
We study theoretically the existence of bulk and surface discrete breathers
in a one-dimensional magnetic metamaterial comprised of a periodic binary array
of split-ring resonators. The two types of resonators differ in the size of
their slits and this leads to different resonant frequencies. In the framework
of the rotating-wave approximation (RWA) we construct several types of breather
excitations for both the energy-conserved and the dissipative-driven systems by
continuation of trivial breather solutions from the anticontinuous limit to
finite couplings. Numerically-exact computations that integrate the full model
equations confirm the quality of the RWA results. Moreover, it is demonstrated
that discrete breathers can spontaneously appear in the dissipative-driven
system as a results of a fundamental instability.Comment: 10 pages, 16 figure
Theory of Bubble Nucleation and Cooperativity in DNA Melting
The onset of intermediate states (denaturation bubbles) and their role during
the melting transition of DNA are studied using the Peyrard-Bishop-Daxuois
model by Monte Carlo simulations with no adjustable parameters. Comparison is
made with previously published experimental results finding excellent
agreement. Melting curves, critical DNA segment length for stability of bubbles
and the possibility of a two states transition are studied.Comment: 4 figures. Accepted for publication in Physical Review Letter
Magnetoinductive breathers in magnetic metamaterials
The existence and stability of discrete breathers (DBs) in one-dimensional
and two-dimensional magnetic metamaterials (MMs), which consist of periodic
arrangem ents (arrays) of split-ring resonators (SRRs), is investigated
numerically. We consider different configurations of the SRR arrays, which are
related to the relative orientation of the SRRs in the MM, both in one and two
spatial dimensions. In the latter case we also consider anisotropic MMs. Using
standard numerical methods we construct several types of linearly stable
breather excitations both in Hamiltonian and dissipative MMs (dissipative
breathers). The study of stability in both cases is performed using standard
Floquet analysi s. In both cases we found that the increase of dimensionality
from one to two spatial dimensions does not destroy the DBs, which may also
exist in the case of moderate anisotropy (in two dimensions). In dissipative
MMs, the dynamics is governed by a power balance between the mainly Ohmic
dissipation and driving by an alternating magnetic field. In that case it is
demonstrated that DB excitation locally alters the magnetic response of MMs
from paramagnetic to diamagnetic. Moreover, when the frequency of the applied
field approaches the SRR resonance frequency, the magnetic response of the MM
in the region of the DB excitation may even become negative (extreme
diamagnetic).Comment: 12 pages 15 figure
Extreme events in discrete nonlinear lattices
We perform statistical analysis on discrete nonlinear waves generated though
modulational instability in the context of the Salerno model that interpolates
between the intergable Ablowitz-Ladik (AL) equation and the nonintegrable
discrete nonlinear Schrodinger (DNLS) equation. We focus on extreme events in
the form of discrete rogue or freak waves that may arise as a result of rapid
coalescence of discrete breathers or other nonlinear interaction processes. We
find power law dependence in the wave amplitude distribution accompanied by an
enhanced probability for freak events close to the integrable limit of the
equation. A characteristic peak in the extreme event probability appears that
is attributed to the onset of interaction of the discrete solitons of the AL
equation and the accompanied transition from the local to the global
stochasticity monitored through the positive Lyapunov exponent of a nonlinear
map.Comment: 5 pages, 4 figures; reference added, figure 2 correcte
Probing the mechanical unzipping of DNA
A study of the micromechanical unzipping of DNA in the framework of the
Peyrard-Bishop-Dauxois model is presented. We introduce a Monte Carlo technique
that allows accurate determination of the dependence of the unzipping forces on
unzipping speed and temperature. Our findings agree quantitatively with
experimental results for homogeneous DNA, and for -phage DNA we
reproduce the recently obtained experimental force-temperature phase diagram.
Finally, we argue that there may be fundamental differences between {\em in
vivo} and {\em in vitro} DNA unzipping
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