Identification of input-output LPV models

This chapter presents an overview of the available methods for identifying input-output LPV models both in discrete time and continuous time with the main focus on noise modeling issues. First, a least-squares approach and an instrumental variable method are presented for dealing with LPV-ARX models. Then, a refined instrumental variable approach is discussed to address more sophisticated noise models like Box-Jenkins in the LPV context. This latter approach is also introduced in continuous time and efficient solutions are proposed for both the problem of time-derivative approximation and the issue of continuous-time modeling of the noise

Direct identification of continuous-time LPV models

Controllers in the linear parameter-varying (LPV) framework are commonly designed in continuous time (CT) requiring accurate and low-order CT models of the system. Nonetheless, most of the methods dedicated to the identification of LPV systems are addressed in the discrete-time setting. In practice when discretizing models which are naturally expressed in CT, the dependency on the scheduling variables becomes non-trivial and over-parameterized. Consequently, direct identification of CT-LPV systems in an input-output setting is investigated. To provide consistent model parameter estimates in this setting, a refined instrumental variable approach is proposed. The statistical properties of this approach are demonstrated through a Monte Carlo simulation example

Exciton-magnon transitions in the frustrated chromium antiferromagnets CuCrO2, alpha-CaCr2O4, CdCr2O4, and ZnCr2O4

We report on optical transmission spectroscopy of the Cr-based frustrated triangular antiferromagnets CuCrO2 and alpha-CaCr2O4, and the spinels CdCr2O4 and ZnCr2O4 in the near-infrared to visible-light frequency range. We explore the possibility to search for spin correlations far above the magnetic ordering temperature and for anomalies in the magnon lifetime in the magnetically ordered state by probing exciton-magnon sidebands of the spin-forbidden crystal-field transitions of the Cr3+ ions (spin S = 3/2). In CuCrO2 and alpha-CaCr2O4 the appearance of fine structures below T_N is assigned to magnon sidebands by comparison with neutron scattering results. The temperature dependence of the line width of the most intense sidebands in both compounds can be described by an Arrhenius law. For CuCrO2 the sideband associated with the 4A2 -> 2T2 transition can be observed even above T_N. Its line width does not show a kink at the magnetic ordering temperature and can alternatively be described by a Z2 vortex scenario proposed previously for similar materials. The exciton-magnon features in alpha-CaCr2O4 are more complex due to the orthorhombic distortion. While for CdCr2O4 magnon sidebands are identified below T_N and one sideband excitation is found to persist across the magnetic ordering transition, only a weak fine structure related to magnetic ordering has been observed in ZnCr2O4.Comment: 14 pages, 10 figures, all comments are welcome and appreciated, accepted for publication in PR

Transient Local Bone Remodeling Effects of rhBMP-2 in an Ovine Interbody Spine Fusion Model

Background: Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a powerful osteoinductive morphogen capable of stimulating the migration of mesenchymal stem cells (MSCs) to the site of implantation and inducing the proliferation and differentiation of these MSCs into osteoblasts. Vertebral end-plate and vertebral body resorption has been reported after interbody fusion with high doses of rhBMP-2. In this study, we investigated the effects of 2 rhBMP-2 doses on peri-implant bone resorption and bone remodeling at 7 time points in an end-plate-sparing ovine interbody fusion model. Methods: Twenty-one female sheep underwent an end-plate-sparing discectomy followed by interbody fusion at L2-L3 and L4-L5 using a custom polyetheretherketone (PEEK) interbody fusion device. The PEEK interbody device was filled with 1 of 2 different doses of rhBMP-2 on an absorbable collagen sponge (ACS): 0.13 mg (1·) or 0.90 mg (7·). Bone remodeling and interbody fusion were assessed via high-resolution radiography and histological analyses at 1, 2, 3, 4, 8, 12, and 20 weeks postoperatively. Results: Peri-implant bone resorption peaked between 3 and 8 weeks in both the 1· and the 7· rhBMP-2/ACS-dose group. Osteoclastic activity and corresponding peri-implant bone resorption was dose-dependent, with moderate-tomarked resorption at the 7·-dose level and less resorption at the 1·-dose level. Both dose (p \u3c 0.0007) and time (p \u3c 0.0025) affected bone resorption significantly. Transient bone-resorption areas were fully healed by 12 weeks. Osseous bridging was seen at all but 1 spinal level at 12 and at 20 weeks. Conclusions: In the ovine end-plate-sparing interbody fusion model, rhBMP-2 dose-dependent osteoclastic resorption is a transient phenomenon that peaks at 4 weeks postoperatively. Clinical Relevance: Using the U.S. Food and Drug Administration (FDA)-approved rhBMP-2 concentration and matching the volume of rhBMP-2/ACS with the volume of desired bone formation within the interbody construct may limit the occurrence of transient bone resorption

Continuum models of focused electron beam induced processing

© 2015 Toth et al. Focused electron beam induced processing (FEBIP) is a suite of direct-write, high resolution techniques that enable fabrication and editing of nanostructured materials inside scanning electron microscopes and other focused electron beam (FEB) systems. Here we detail continuum techniques that are used to model FEBIP, and release software that can be used to simulate a wide range of processes reported in the FEBIP literature. These include: (i) etching and deposition performed using precursors that interact with a surface through physisorption and activated chemisorption, (ii) gas mixtures used to perform simultaneous focused electron beam induced etching and deposition (FEBIE and FEBID), and (iii) etch processes that proceed through multiple reaction pathways and generate a number of reaction products at the substrate surface. We also review and release software for Monte Carlo modeling of the precursor gas flux which is needed as an input parameter for continuum FEBIP models

Hall Effect in the coma of 67P/Churyumov-Gerasimenko

Magnetohydrodynamics simulations have been carried out in studying the solar wind and cometary plasma interactions for decades. Various plasma boundaries have been simulated and compared well with observations for comet 1P/Halley. The Rosetta mission, which studies comet 67P/Churyumov-Gerasimenko, challenges our understanding of the solar wind and comet interactions. The Rosetta Plasma Consortium observed regions of very weak magnetic field outside the predicted diamagnetic cavity. In this paper, we simulate the inner coma with the Hall magnetohydrodynamics equations and show that the Hall effect is important in the inner coma environment. The magnetic field topology becomes complex and magnetic reconnection occurs on the dayside when the Hall effect is taken into account. The magnetic reconnection on the dayside can generate weak magnetic filed regions outside the global diamagnetic cavity, which may explain the Rosetta Plasma Consortium observations. We conclude that the substantial change in the inner coma environment is due to the fact that the ion inertial length (or gyro radius) is not much smaller than the size of the diamagnetic cavity.Comment: 23 pages, 6 figur

Molecular Line Observations of the Small Protostellar Group L1251B

We present molecular line observations of L1251B, a small group of pre- and protostellar objects, and its immediate environment in the dense C18O core L1251E. These data are complementary to near-infrared, submillimeter and millimeter continuum observations reported by Lee et al. (2006, ApJ, 648, 491; Paper I). The single-dish data of L1251B described here show very complex kinematics including infall, rotation and outflow motions, and the interferometer data reveal these in greater detail. Interferometer data of N2H+ 1-0 suggest a very rapidly rotating flattened envelope between two young stellar objects, IRS1 and IRS2. Also, interferometer data of CO 2-1 resolve the outflow associated with L1251B seen in single-dish maps into a few narrow and compact components. Furthermore, the high resolution data support recent theoretical studies of molecular depletions and enhancements that accompany the formation of protostars within dense cores. Beyond L1251B, single-dish data are also presented of a dense core located ~150" to the east that, in Paper I, was detected at 850 micron but has no associated point sources at near- and mid-infrared wavelengths. The relative brightness between molecules, which have different chemical timescales, suggests it is less chemically evolved than L1251B. This core may be a site for future star formation, however, since line profiles of HCO+, CS, and HCN show asymmetry with a stronger blue peak, which is interpreted as an infall signature.Comment: 46 pages, 18 figures. Accepted for publication in Ap

Accelerating relativistic reference frames in Minkowski space-time

We study accelerating relativistic reference frames in Minkowski space-time under the harmonic gauge. It is well-known that the harmonic gauge imposes constraints on the components of the metric tensor and also on the functional form of admissible coordinate transformations. These two sets of constraints are equivalent and represent the dual nature of the harmonic gauge. We explore this duality and show that the harmonic gauge allows presenting an accelerated metric in an elegant form that depends only on two harmonic potentials. It also allows reconstruction of the spatial structure of the post-Galilean coordinate transformation functions relating inertial and accelerating frames. The remaining temporal dependence of these functions together with corresponding equations of motion are determined from dynamical conditions, obtained by constructing the relativistic proper reference frame of an accelerated test particle. In this frame, the effect of external forces acting on the observer is balanced by the fictitious frame-reaction force that is needed to keep the test particle at rest with respect to the frame, conserving its relativistic linear momentum. We find that this approach is sufficient to determine all the terms of the coordinate transformation. The same method is then used to develop the inverse transformations. The resulting post-Galilean coordinate transformations extend the Poincar\'e group on the case of accelerating observers. We present and discuss the resulting coordinate transformations, relativistic equations of motion, and the structure of the metric tensors corresponding to the relativistic reference frames involved.Comment: revtex4, 21 page

Observations of the bright radio sources in the North Celestial Pole region at the RATAN-600 radio telescope

A survey of the North Celestial Pole region using the RATAN-600 radio telescope at five frequencies in the range 2.3 to 21.7 GHz is described. Sources were chosen from the NVSS catalogue. The flux densities of 171 sources in the Declination range +75 to +88 are presented; typical flux density errors are 5-10 percent including calibration errors. About 20 percent of the sources have flat spectra or a flat component.Comment: 21 pages, 7 figures; to be published in Astronomy and Astrophysics (without last figure with the spectra of the observed sources