57,502 research outputs found
Robust observer for uncertain linear quantum systems
In the theory of quantum dynamical filtering, one of the biggest issues is
that the underlying system dynamics represented by a quantum stochastic
differential equation must be known exactly in order that the corresponding
filter provides an optimal performance; however, this assumption is generally
unrealistic. Therefore, in this paper, we consider a class of linear quantum
systems subjected to time-varying norm-bounded parametric uncertainties and
then propose a robust observer such that the variance of the estimation error
is guaranteed to be within a certain bound. Although in the linear case much of
classical control theory can be applied to quantum systems, the quantum robust
observer obtained in this paper does not have a classical analogue due to the
system's specific structure with respect to the uncertainties. Moreover, by
considering a typical quantum control problem, we show that the proposed robust
observer is fairly robust against a parametric uncertainty of the system even
when the other estimators--the optimal Kalman filter and risk-sensitive
observer--fail in the estimation.Comment: 11 pages, 1 figur
Dynamic microscopic structures and dielectric response in the cubic-to-tetragonal phase transition for BaTiO3 studied by first-principles molecular dynamics simulation
The dynamic structures of the cubic and tetragonal phase in BaTiO3 and its
dielectric response above the cubic-to-tetragonal phase transition temperature
(Tp) are studied by first-principles molecular dynamics (MD) simulation. It's
shown that the phase transition is due to the condensation of one of the
transverse correlations. Calculation of the phonon properties for both the
cubic and tetragonal phase shows a saturation of the soft mode frequency near
60 cm-1 near Tp and advocates its order-disorder nature. Our first-principles
calculation leads directly to a two modes feature of the dielectric function
above Tp [Phys. Rev. B 28, 6097 (1983)], which well explains the long time
controversies between experiments and theories
Covert Ephemeral Communication in Named Data Networking
In the last decade, there has been a growing realization that the current
Internet Protocol is reaching the limits of its senescence. This has prompted
several research efforts that aim to design potential next-generation Internet
architectures. Named Data Networking (NDN), an instantiation of the
content-centric approach to networking, is one such effort. In contrast with
IP, NDN routers maintain a significant amount of user-driven state. In this
paper we investigate how to use this state for covert ephemeral communication
(CEC). CEC allows two or more parties to covertly exchange ephemeral messages,
i.e., messages that become unavailable after a certain amount of time. Our
techniques rely only on network-layer, rather than application-layer, services.
This makes our protocols robust, and communication difficult to uncover. We
show that users can build high-bandwidth CECs exploiting features unique to
NDN: in-network caches, routers' forwarding state and name matching rules. We
assess feasibility and performance of proposed cover channels using a local
setup and the official NDN testbed
Sequential Adaptive Detection for In-Situ Transmission Electron Microscopy (TEM)
We develop new efficient online algorithms for detecting transient sparse
signals in TEM video sequences, by adopting the recently developed framework
for sequential detection jointly with online convex optimization [1]. We cast
the problem as detecting an unknown sparse mean shift of Gaussian observations,
and develop adaptive CUSUM and adaptive SSRS procedures, which are based on
likelihood ratio statistics with post-change mean vector being online maximum
likelihood estimators with . We demonstrate the meritorious performance
of our algorithms for TEM imaging using real data
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