29,123 research outputs found
Finite-horizon H∞ control for discrete time-varying systems with randomly occurring nonlinearities and fading measurements
This technical note deals with the H∞ control problem for a class of discrete time-varying nonlinear systems with both randomly occurring nonlinearities and fading measurements over a finite-horizon. The system measurements are transmitted through fading channels described by a modified stochastic Rice fading model. The purpose of the addressed problem is to design a set of time-varying controllers such that, in the presence of channel fading and randomly occurring nonlinearities, the H∞ performance is guaranteed over a given finite-horizon. The model transformation technique is first employed to simplify the addressed problem, and then the stochastic analysis in combination with the completing squares method are carried out to obtain necessary and sufficient conditions of an auxiliary index which is closely related to the finite-horizon H∞ performance. Moreover, the time-varying controller parameters are characterized via solving coupled backward recursive Riccati difference equations (RDEs). A simulation example is utilized to illustrate the usefulness of the proposed controller design scheme
Weight function for the quantum affine algebra
We give a precise expression for the universal weight function of the quantum
affine algebra . The calculations use the technique of
projecting products of Drinfeld currents on the intersections of Borel
subalgebras.Comment: 28 page
Overall properties of the Gaia DR1 reference frame
We compare quasar positions of the auxiliary quasar solution with ICRF2
sources using different samples and evaluate the influence on the {\it Gaia}
DR1 reference frame owing to the Galactic aberration effect over the
J2000.0-J20015.0 period. Then we estimate the global rotation between TGAS with
{\it Tycho}-2 proper motion systems to investigate the property of the {\it
Gaia} DR1 reference frame. Finally, the Galactic kinematics analysis using the
K-M giant proper motions is performed to understand the property of {\it Gaia}
DR1 reference frame. The positional comparison between the auxiliary quasar
solution and ICRF2 shows negligible orientation and validates the declination
bias of \mas~in {\it Gaia} quasar positions with respect to ICRF2.
Galactic aberration effect is thought to cause an offset \mas~of
the axis direction of {\it Gaia} DR1 reference frame. The global rotation
between TGAS and {\it Tycho}-2 proper motion systems, obtained by different
samples, shows a much smaller value than the claimed value \masyr. For
the Galactic kinematics analysis of the TGAS K-M giants, we find possible
non-zero Galactic rotation components beyond the classical Oort constants: the
rigid part \masyr~and the differential part
\masyr~around the axis of Galactic
coordinates, which indicates possible residual rotation in {\it Gaia} DR1
reference frame or problems in the current Galactic kinematical model.Comment: 6 pages, 1 figure. Accepted for publication in A&
Physical implementation of holonomic quantum computation in decoherence-free subspaces with trapped ions
We propose a feasible scheme to achieve holonomic quantum computation in a
decoherence-free subspace (DFS) with trapped ions. By the application of
appropriate bichromatic laser fields on the designated ions, we are able to
construct two noncommutable single-qubit gates and one controlled-phase gate
using the holonomic scenario in the encoded DFS.Comment: 4 pages, 3 figures. To appear in Phys. Rev. A 74 (2006
A Survey on Multisensor Fusion and Consensus Filtering for Sensor Networks
Multisensor fusion and consensus filtering are two fascinating subjects in the research of sensor networks. In this survey, we will cover both classic results and recent advances developed in these two topics. First, we recall some important results in the development ofmultisensor fusion technology. Particularly, we pay great attention to the fusion with unknown correlations, which ubiquitously exist in most of distributed filtering problems. Next, we give a systematic review on several widely used consensus filtering approaches. Furthermore, some latest progress on multisensor fusion and consensus filtering is also presented. Finally,
conclusions are drawn and several potential future research directions are outlined.the Royal Society of the UK, the National Natural Science Foundation of China under Grants 61329301, 61374039, 61304010, 11301118, and 61573246, the Hujiang Foundation of China under Grants C14002
and D15009, the Alexander von Humboldt Foundation of Germany, and the Innovation Fund Project for Graduate Student of Shanghai under Grant JWCXSL140
Internal stress wave measurements in solids subjected to lithotripter pulses
Semiconductor strain gauges were used to measure the internal strain along the axes of spherical and disk plaster specimens when subjected to lithotripter shock pulses. The pulses were produced by one of two lithotripters. The first source generates spherically diverging shock waves of peak pressure approximately 1 MPa at the surface of the specimen. For this source, the incident and first reflected pressure (P) waves in both sphere and disk specimens were identified. In addition, waves reflected by the disk circumference were found to contribute significantly to the strain fields along the disk axis. Experimental results compared favorably to a ray theory analysis of a spherically diverging shock wave striking either concretion. For the sphere, pressure contours for the incident P wave and caustic lines were determined theoretically for an incident spherical shock wave. These caustic lines indicate the location of the highest stresses within the sphere and therefore the areas where damage may occur. Results were also presented for a second source that uses an ellipsoidal reflector to generate a 30-MPa focused shock wave, more closely approximating the wave fields of a clinical extracorporeal lithotripter
Magnetic Reconnection resulting from Flux Emergence: Implications for Jet Formation in the lower solar atmosphere?
We aim at investigating the formation of jet-like features in the lower solar
atmosphere, e.g. chromosphere and transition region, as a result of magnetic
reconnection. Magnetic reconnection as occurring at chromospheric and
transition regions densities and triggered by magnetic flux emergence is
studied using a 2.5D MHD code. The initial atmosphere is static and isothermal,
with a temperature of 20,000 K. The initial magnetic field is uniform and
vertical. Two physical environments with different magnetic field strength (25
G and 50 G) are presented. In each case, two sub-cases are discussed, where the
environments have different initial mass density. In the case where we have a
weaker magnetic field (25 G) and higher plasma density (
cm), valid for the typical quiet Sun chromosphere, a plasma jet would be
observed with a temperature of 2--3 K and a velocity as high as
40 km/s. The opposite case of a medium with a lower electron density
( cm), i.e. more typical for the transition region,
and a stronger magnetic field of 50 G, up-flows with line-of-sight velocities
as high as 90 km/s and temperatures of 6 10 K, i.e. upper
transition region -- low coronal temperatures, are produced. Only in the latter
case, the low corona Fe IX 171 \AA\ shows a response in the jet which is
comparable to the O V increase. The results show that magnetic reconnection can
be an efficient mechanism to drive plasma outflows in the chromosphere and
transition region. The model can reproduce characteristics, such as temperature
and velocity for a range of jet features like a fibril, a spicule, an hot X-ray
jet or a transition region jet by changing either the magnetic field strength
or the electron density, i.e. where in the atmosphere the reconnection occurs.Comment: 11 pages, 13 figures, 2 table
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