13,832 research outputs found
A methodological proposal to investigate the long term storage of pollutants in freshwater sediment biofilms and their response to environmental disturbances.
This research will review novel methodologies for understanding the behaviour of microbial communities and their role in pollution storage. Freshwater sediments are inhabited by attached microbial communities (biofilms) which are responsible for the majority of a river's metabolic activity. Biofilms thus provide valuable information on the environmental quality of the river and its surrounding areas. Despite remediation of freshwater sediments, biofilms can still store large quantities of pollutants. Biofilms have the exceptional capacity to adjust to new conditions including natural and anthropogenic environmental disturbances. Gaining a more comprehensive understanding of biofilm behaviour is therefore fundamental to developing improved management strategies. The initial focus of this research will be in the River Doe Lea in North East Derbyshire. The River Doe Lea extends 18km from the South at its source near Tibshelf, to the North at its discharge at the River Rother. In the 1990s the River was famed for having the highest level of dioxins in the world, 27 times higher than the second most polluted. The acute cause of this was a single pollutant event, however the river has also been subjected to long term anthropogenic pollution through industry, agriculture, transport (railways, M1) and wastewater pollution. While previous studies by the Environment Agency have focused on the flow, chemical, biological and ecological quality of the river, no research has been conducted into the role and behaviour of biofilms
Robust active magnetic dearing control using stabilizing dynamical compensators
The robust control of active magnetic bearings, based on a linearised interval model, is considered. Through robust stability analysis, all the first-order robust stabilizing dynamical compensators for the interval system are obtained. Disturbance attenuation and minimum control effort are also addressed. The approach is applied to a high-speed flywheel supported by two active and two passive magnetic bearings. Simulation and experimental results both show that it is simple, effective, and robust
Robust magnetic bearing control using stabilizing dynamical compensators
Abstract—This paper considers the robust control of an active radial magnetic bearing system, having a homopolar, external rotor topology, which is used to support an annular fiber composite flywheel rim. A first-order dynamical compensator, which uses only position feedback information, is used for control, its design being based on a linearized one-dimensional second-order model which is treated as an interval system in order to cope with parameter uncertainties. Through robust stability analysis, a parameterization of all first-order robustly stabilizing dynamical compensators for the interval system is initially obtained. Then, by appropriate selection of the free parameters in the robust controller, the H2 norm of the disturbance-output transfer function is made arbitrarily small over the system parameter intervals, and the norm of the input–output transfer function is made arbitrarily close to a lower bound. Simulation and experimental
results demonstrate both stability and performance robustness of the developed controller
Influence of uniaxial tensile stress on the mechanical and piezoelectric properties of short-period ferroelectric superlattice
Tetragonal ferroelectric/ferroelectric BaTiO3/PbTiO3 superlattice under
uniaxial tensile stress along the c axis is investigated from first principles.
We show that the calculated ideal tensile strength is 6.85 GPa and that the
superlattice under the loading of uniaxial tensile stress becomes soft along
the nonpolar axes. We also find that the appropriately applied uniaxial tensile
stress can significantly enhance the piezoelectricity for the superlattice,
with piezoelectric coefficient d33 increasing from the ground state value by a
factor of about 8, reaching 678.42 pC/N. The underlying mechanism for the
enhancement of piezoelectricity is discussed
Generally Covariant Conservative Energy-Momentum for Gravitational Anyons
We obtain a generally covariant conservation law of energy-momentum for
gravitational anyons by the general displacement transform. The energy-momentum
currents have also superpotentials and are therefore identically conserved. It
is shown that for Deser's solution and Clement's solution, the energy vanishes.
The reasonableness of the definition of energy-momentum may be confirmed by the
solution for pure Einstein gravity which is a limit of vanishing Chern-Simons
coulping of gravitational anyons.Comment: 12 pages, Latex, no figure
Topological Bose-Mott Insulators in a One-Dimensional Optical Superlattice
We study topological properties of the Bose-Hubbard model with repulsive
interactions in a one-dimensional optical superlattice. We find that the Mott
insulator states of the single-component (two-component) Bose-Hubbard model
under fractional fillings are topological insulators characterized by a nonzero
charge (or spin) Chern number with nontrivial edge states. For ultracold atomic
experiments, we show that the topological Chern number can be detected through
measuring the density profiles of the bosonic atoms in a harmonic trap.Comment: 5 pages, published versio
Robust Quantum State Transfer in Random Unpolarized Spin Chains
We propose and analyze a new approach for quantum state transfer between
remote spin qubits. Specifically, we demonstrate that coherent quantum coupling
between remote qubits can be achieved via certain classes of random,
unpolarized (infinite temperature) spin chains. Our method is robust to
coupling strength disorder and does not require manipulation or control over
individual spins. In principle, it can be used to attain perfect state transfer
over arbitrarily long range via purely Hamiltonian evolution and may be
particularly applicable in a solid-state quantum information processor. As an
example, we demonstrate that it can be used to attain strong coherent coupling
between Nitrogen-Vacancy centers separated by micrometer distances at room
temperature. Realistic imperfections and decoherence effects are analyzed.Comment: 4 pages, 2 figures. V2: Modified discussion of disorder, added
references - final version as published in Phys. Rev. Let
The extraction of nuclear sea quark distribution and energy loss effect in Drell-Yan experiment
The next-to-leading order and leading order analysis are performed on the
differential cross section ratio from Drell-Yan process. It is found that the
effect of next-to-leading order corrections can be negligible on the
differential cross section ratios as a function of the quark momentum fraction
in the beam proton and the target nuclei for the current Fermilab and future
lower beam proton energy. The nuclear Drell-Yan reaction is an ideal tool to
study the energy loss of the fast quark moving through cold nuclei. In the
leading order analysis, the theoretical results with quark energy loss are in
good agreement with the Fermilab E866 experimental data on the Drell-Yan
differential cross section ratios as a function of the momentum fraction of the
target parton. It is shown that the quark energy loss effect has significant
impact on the Drell-Yan differential cross section ratios. The nuclear
Drell-Yan experiment at current Fermilab and future lower energy proton beam
can not provide us with more information on the nuclear sea quark distribution.Comment: 17 pages, 4 figure
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