4,642 research outputs found
Interior feedback stabilization of wave equations with dynamic boundary delay
In this paper we consider an interior stabilization problem for the wave
equation with dynamic boundary delay.We prove some stability results under the
choice of damping operator. The proof of the main result is based on a
frequency domain method and combines a contradiction argument with the
multiplier technique to carry out a special analysis for the resolvent
Delays, Inaccuracies and Anticipation in Microscopic Traffic Models
We generalize a wide class of time-continuous microscopic traffic models to
include essential aspects of driver behaviour not captured by these models.
Specifically, we consider (i) finite reaction times, (ii) estimation errors,
(iii) looking several vehicles ahead (spatial anticipation), and (iv) temporal
anticipation. The estimation errors are modelled as stochastic Wiener processes
and lead to time-correlated fluctuations of the acceleration.
We show that the destabilizing effects of reaction times and estimation
errors can essentially be compensated for by spatial and temporal anticipation,
that is, the combination of stabilizing and destabilizing effects results in
the same qualitative macroscopic dynamics as that of the respectively
underlying simple car-following model. In many cases, this justifies the use of
simplified, physics-oriented models with a few parameters only. Although the
qualitative dynamics is unchanged, multi-anticipation increase both spatial and
temporal scales of stop-and-go waves and other complex patterns of congested
traffic in agreement with real traffic data. Remarkably, the anticipation
allows accident-free smooth driving in complex traffic situations even if
reaction times exceed typical time headways.Comment: Major revision of the model and the simulations. Particularly, the
number of model parameters has been reduce
A New Formulation of the Initial Value Problem for Nonlocal Theories
There are a number of reasons to entertain the possibility that locality is
violated on microscopic scales, for example through the presence of an infinite
series of higher derivatives in the fundamental equations of motion. This type
of nonlocality leads to improved UV behaviour, novel cosmological dynamics and
is a generic prediction of string theory. On the other hand, fundamentally
nonlocal models are fraught with complications, including instabilities and
complications in setting up the initial value problem. We study the structure
of the initial value problem in an interesting class of nonlocal models. We
advocate a novel new formulation wherein the Cauchy surface is "smeared out"
over the underlying scale of nonlocality, so that the the usual notion of
initial data at t=0 is replaced with an "initial function" defined over -M^{-1}
\leq t \leq 0 where M is the underlying scale of nonlocality. Focusing on some
specific examples from string theory and cosmology, we show that this
mathematical re-formulation has surprising implications for the well-known
stability problem. For D-brane decay in a linear dilaton background, we are
able to show that the unstable directions in phase space cannot be accessed
starting from a physically sensible initial function. Previous examples of
unstable solutions in this model therefore correspond to unphysical initial
conditions, an observation which is obfuscated in the old formulation of the
initial value problem. We also discuss implication of this approach for
nonlocal cosmological models.Comment: 36 pages, 9 figures. Accepted for publication in Nuclear Physics
Suppression of axial-torsional vibrations in drilling system described by neutral-type delay differential equations
Vibrations in deep drilling systems lead to efficiency deterioration and may even cause the system failure. In this paper, a controller is designed aiming at mitigation of these vibrations, which is based on a neutral-type time delay model that represents distributed axial and torsional dynamics. First, the stability of the associated linearized dynamics is analyzed using a spectral approach. Furthermore, the open-loop system is shown to be stabilizable by state feedback which supports subsequent controller design. An optimization-based continuous pole placement technique has been employed to design a stabilizing controller, which mitigates steady-state drill-string vibrations. The effectiveness of the controller is shown in a representative case study
Single-file pedestrian dynamics: a review of agent-following models
Single-file dynamics has been studied intensively, both experimentally and
theoretically. It shows interesting collective effects, such as stop-and-go
waves, which are validation cornerstones for any agent-based modeling approach
of traffic systems. Many models have been proposed, e.g. in the form of
car-following models for vehicular traffic. These approaches can be adapted for
pedestrian streams. In this study, we delve deeper into these models, with
particular attention on their interconnections. We do this by scrutinizing the
influence of different parameters, including relaxation times, anticipation
time, and reaction time. Specifically, we analyze the inherent fundamental
problems with force-based models, a classical approach in pedestrian dynamics.
Furthermore, we categorize car-following models into stimulus-response and
optimal velocity models, highlighting their historical and conceptual
differences. These classes can further be subdivided considering the conceptual
definitions of the models, e.g. first-order vs. second-order models, or
stochastic vs. deterministic models with and without noise. Our analysis shows
how car-following models originally developed for vehicular traffic can provide
new insights into pedestrian behavior. The focus on single-file motion, which
is similar to single-lane vehicular traffic, allows for a detailed examination
of the relevant interactions between pedestrians.Comment: 35 pages, 10 Figures; chapter accepted for publication in Crowd
Dynamics (vol. 4
Suppression of axial-torsional vibrations in drilling system described by neutral-type delay differential equations
Vibrations in deep drilling systems lead to efficiency deterioration and may even cause the system failure. In this paper, a controller is designed aiming at mitigation of these vibrations, which is based on a neutral-type time delay model that represents distributed axial and torsional dynamics. First, the stability of the associated linearized dynamics is analyzed using a spectral approach. Furthermore, the open-loop system is shown to be stabilizable by state feedback which supports subsequent controller design. An optimization-based continuous pole placement technique has been employed to design a stabilizing controller, which mitigates steady-state drill-string vibrations. The effectiveness of the controller is shown in a representative case study
Delay-dependent exponential stability of neutral stochastic delay systems (vol 54, pg 147, 2009)
In the above titled paper originally published in vol. 54, no. 1, pp. 147-152) of IEEE Transactions on Automatic Control, there were some typographical errors in inequalities. Corrections are presented here
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