4,712 research outputs found
Tracking control with adaption of kites
A novel tracking paradigm for flying geometric trajectories using tethered
kites is presented. It is shown how the differential-geometric notion of
turning angle can be used as a one-dimensional representation of the kite
trajectory, and how this leads to a single-input single-output (SISO) tracking
problem. Based on this principle a Lyapunov-based nonlinear adaptive controller
is developed that only needs control derivatives of the kite aerodynamic model.
The resulting controller is validated using simulations with a point-mass kite
model.Comment: 20 pages, 12 figure
Grid-enabling FIRST: Speeding up simulation applications using WinGrid
The vision of grid computing is to make computational power, storage capacity, data and applications available to users as readily as electricity and other utilities. Grid infrastructures and applications have traditionally been geared towards dedicated, centralized, high performance clusters running on UNIX flavour operating systems (commonly referred to as cluster-based grid computing). This can be contrasted with desktop-based grid computing which refers to the aggregation of non-dedicated, de-centralized, commodity PCs connected through a network and running (mostly) the Microsoft Windowstrade operating system. Large scale adoption of such Windowstrade-based grid infrastructure may be facilitated via grid-enabling existing Windows applications. This paper presents the WinGridtrade approach to grid enabling existing Windowstrade based commercial-off-the-shelf (COTS) simulation packages (CSPs). Through the use of a case study developed in conjunction with Ford Motor Company, the paper demonstrates how experimentation with the CSP Witnesstrade and FIRST can achieve a linear speedup when WinGridtrade is used to harness idle PC computing resources. This, combined with the lessons learned from the case study, has encouraged us to develop the Web service extensions to WinGridtrade. It is hoped that this would facilitate wider acceptance of WinGridtrade among enterprises having stringent security policies in place
Norm discontinuity and spectral properties of Ornstein-Uhlenbeck semigroups
Let be a real Banach space. We study the Ornstein-Uhlenbeck semigroup
associated with the Ornstein-Uhlenbeck operator Here is a positive symmetric operator from
to and is the generator of a -semigroup on . Under
the assumption that admits an invariant measure we prove that if
is eventually compact and the spectrum of its generator is nonempty, then \n
P(t)-P(s)\n_{L^1(E,\mu)} = 2 for all with . This result
is new even when . We also study the behaviour of in the space
. We show that if there exists such that \n
P(t)-P(s)\n_{BUC(E)} = 2 for all with . Moreover,
under a nondegeneracy assumption or a strong Feller assumption, the following
dichotomy holds: either \n P(t)- P(s)\n_{BUC(E)} = 2 for all , \
, or is the direct sum of a nilpotent semigroup and a
finite-dimensional periodic semigroup. Finally we investigate the spectrum of
in the spaces and .Comment: 14 pages; to appear in J. Evolution Equation
The stochastic Weiss conjecture for bounded analytic semigroups
Suppose -A admits a bounded H-infinity calculus of angle less than pi/2 on a
Banach space E with Pisier's property (alpha), let B be a bounded linear
operator from a Hilbert space H into the extrapolation space E_{-1} of E with
respect to A, and let W_H denote an H-cylindrical Brownian motion. Let
gamma(H,E) denote the space of all gamma-radonifying operators from H to E. We
prove that the following assertions are equivalent:
(i) the stochastic Cauchy problem dU(t) = AU(t)dt + BdW_H(t) admits an
invariant measure on E;
(ii) (-A)^{-1/2} B belongs to gamma(H,E);
(iii) the Gaussian sum \sum_{n\in\mathbb{Z}} \gamma_n 2^{n/2} R(2^n,A)B
converges in gamma(H,E) in probability.
This solves the stochastic Weiss conjecture proposed recently by the second
and third named authors.Comment: 17 pages; submitted for publicatio
L^2-Theory for non-symmetric Ornstein-Uhlenbeck semigroups on domains
We present some new results on analytic Ornstein-Uhlenbeck semigroups and use
them to extend recent work of Da Prato and Lunardi for Ornstein-Uhlenbeck
semigroups on open domains O to the non-symmetric case. Denoting the generator
of the semigroup by L_O, we obtain sufficient conditions in order that the
domain Dom(\sqrt{-L_O}) be a first order Sobolev space.Comment: 23 pages, revised version, to appear in J. Evol. Eq. The main change
is a correction in Theorem 5.5: the second assertion has been withdrawn due
to a gap in the original proo
On Factorization, Interconnection and Reduction of Collocated Port-Hamiltonian Systems
Based on a geometric interpretation of nonlinear balanced reduction some implications of this approach are analyzed in the case of collocated port-Hamiltonian systems which have a certain balance in its structure. Furthermore, additional examples of reduction for this class of systems are presented.
Multiuser Detection Assisted Time- and Frequency-Domain Spread Multicarrier Code-Division Multiple-Access
In this contribution, we study a reduced-complexity multiuser detection aided multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) scheme, which employs both time (T)-domain and frequency (F)-domain spreading. We investigate the achievable detection performance in the context of synchronous TF-domain spread MC DS-CDMA when communicating over an additive white Gaussian noise (AWGN) channel. Five detection schemes are investigated, which include the single-user correlation based detector, the joint TF-domain decorrelating multiuser detector (MUD), the joint TF-domain MMSEMUD, the separate TF-domain decorrelating/MMSE MUD, and the separate TF-domain MMSE/decorrelating MUD. Our simulation results show that the separate TF-domain MUD schemes are capable of achieving a similar bit error rate (BER) performance to that of the significantly more complex joint TF-domain MUD schemes. Index Terms—Code-division multiple-access (CDMA), decorrelating, frequency-domain spreading, joint detection, minimum mean square error (MMSE), multicarrier (MC), multiuser detection, separate detection, time-domain spreading
Contacts and contracts: Cross-level network dynamics in the development of an aircraft material
In this paper, we investigate how interorganizational networks and interpersonal networks interact over time. We present a retrospective longitudinal case study of the network system that developed a novel aircraft material and analyze changeepisodes from a structurationist perspective. We identify five types of episodes in which interpersonal and interorganizational networks interact (persistence, prospecting, consolidation, reconfiguration, and dissolution) and analyze conditionsfor these episodes and sequences among them. Our findings advance a cross-level perspective on embeddedness and show how individuals may draw on relational and structural embeddedness as distributed resources. The multiple levels of embeddedness impact network dynamics by introducing converging and diverging dialectics, thereby limiting path dependence and proactive network orchestration
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