45,177 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
Crystal Structures of Influenza A Virus Matrix Protein M1: Variations on a Theme
Matrix protein 1 (M1) of the influenza A virus plays multiple roles in virion assembly and infection. Interest in the pH dependence of M1\u27s multiple functions led us to study the effect of subtle pH changes on M1 structure, resulting in the elucidation of a unique low-pH crystal structure of the N1-165-domain of A/WSN/33 (H1N1) M1 that has never been reported. Although the 2.2 Å crystal structure of M1 N-terminus shows a dimer with the two monomers interacting in a face-to-face fashion at low pH as observed earlier, a 44° rotation of the second monomer has led to a significantly different dimer interface that possibly affects dimer stability. More importantly, while one of the monomers is fully defined, the N-terminal half of the second monomer shows considerable disorder that appears inherent in the protein and is potentially physiologically relevant. Such disorder has not been observed in any other previously reported structure at either low or high pH conditions, despite similar crystallization pH conditions. By comparing our novel N1-165-domain structure with other low-pH or neutral-pH M1 structures, it appears that M1 can energetically access different monomer and dimer conformations, as well as oligomeric states, with varying degree of similarities. The study reported here provides further insights into M1 oligomerization that may be essential for viral propagation and infectivity
The equation of state for two-dimensional hard-sphere gases: Hard-sphere gases as ideal gases with multi-core boundaries
The equation of state for a two-dimensional hard-sphere gas is difficult to
calculate by usual methods. In this paper we develop an approach for
calculating the equation of state of hard-sphere gases, both for two- and
three-dimensional cases. By regarding a hard-sphere gas as an ideal gas
confined in a container with a multi-core (excluded sphere) boundary, we treat
the hard-sphere interaction in an interacting gas as the boundary effect on an
ideal quantum gas; this enables us to treat an interacting gas as an ideal one.
We calculate the equation of state for a three-dimensional hard-sphere gas with
spin , and compare it with the results obtained by other methods. By this
approach the equation of state for a two-dimensional hard-sphere gas can be
calculated directly.Comment: 9 pages, 1 figur
Synthesizing tungsten oxide nanowires by a thermal evaporation method
Tungsten oxide W18 O49 nanowires with diameters of 10-20 nm were synthesized with high yield by thermal evaporation in a tube furnace. By heating tungsten trioxide powder at 900 °C in vacuum (5× 10-3 torr), W18 O49 nanowires with diameters of 10-20 nm and lengths up to micrometers were produced with high yield on the Au-coated Si substrates located in the low temperature zone (550-600 °C) of the furnace. The morphology, composition, and crystal structure of the nanowires were characterized by various methods. The conditions and the mechanism of W18 O49 nanowire growth are discussed. © 2007 American Institute of Physics.published_or_final_versio
Quantum model for magnetic multivalued recording in coupled multilayers
In this paper, we discuss the possibilities of realizing the magnetic
multi-valued (MMV) recording in a magnetic coupled multilayer. The hysteresis
loop of a double-layer system is studied analytically, and the conditions for
achieving the MMV recording are given. The conditions are studied from
different respects, and the phase diagrams for the anisotropic parameters are
given in the end.Comment: 8 pages, LaTex formatted, 7 figures (those who are interested please
contact the authors requring the figures) Submitted to Physal Review B.
Email: [email protected]
Symmetry-breaking skyrmion states in fractional quantum Hall systems
We calculate in an analyical fashion the energies and net spins of skyrmions
in fractional quantum Hall systems, based on the suggestion that skyrmion
states are spontaneously and symmetry-breaking states. The
quasihole-skyrmion state with a charge around = 1/3, where the
ground state is known as a spin-polarized ferromagnetic state, is found to
exist even in high magnetic fields up to about 7 T for GaAs samples.Comment: There is conceptual change. To appear in Phys. Rev.
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