Feedback methods for inverse simulation of dynamic models for engineering systems applications

Inverse simulation is a form of inverse modelling in which computer simulation methods are used to find the time histories of input variables that, for a given model, match a set of required output responses. Conventional inverse simulation methods for dynamic models are computationally intensive and can present difficulties for high-speed applications. This paper includes a review of established methods of inverse simulation,giving some emphasis to iterative techniques that were first developed for aeronautical applications. It goes on to discuss the application of a different approach which is based on feedback principles. This feedback method is suitable for a wide range of linear and nonlinear dynamic models and involves two distinct stages. The first stage involves design of a feedback loop around the given simulation model and, in the second stage, that closed-loop system is used for inversion of the model. Issues of robustness within closed-loop systems used in inverse simulation are not significant as there are no plant uncertainties or external disturbances. Thus the process is simpler than that required for the development of a control system of equivalent complexity. Engineering applications of this feedback approach to inverse simulation are described through case studies that put particular emphasis on nonlinear and multi-input multi-output models

Energy Loss from Reconnection with a Vortex Mesh

Experiments in superfluid 4He show that at low temperatures, energy dissipation from moving vortices is many orders of magnitude larger than expected from mutual friction. Here we investigate other mechanisms for energy loss by a computational study of a vortex that moves through and reconnects with a mesh of small vortices pinned to the container wall. We find that such reconnections enhance energy loss from the moving vortex by a factor of up to 100 beyond that with no mesh. The enhancement occurs through two different mechanisms, both involving the Kelvin oscillations generated along the vortex by the reconnections. At relatively high temperatures the Kelvin waves increase the vortex motion, leading to more energy loss through mutual friction. As the temperature decreases, the vortex oscillations generate additional reconnection events between the moving vortex and the wall, which decrease the energy of the moving vortex by transfering portions of its length to the pinned mesh on the wall.Comment: 9 pages, 10 figure

Analisis Perbandingan Pendapatan Petani Kopi Ateng Yang Menjual Dalam Bentuk Gelondong Merah (Cherry Red) Dengan Kopi Biji

Penelitian ini bertujuan untuk menganalisis perbedaan antara pendapatan USAhatani kopi Ateng yang dijual dalam bentuk gelondong merah (cherry red) dengan kopi biji dan untuk menganalisis nilai tambah (value added) yang diperoleh petani yang menjual kopi Ateng dalam bentuk kopi biji di Desa Bangun Das Mariah, Kecamatan Panei, Kabupaten Simalungun. Penentuan daerah penelitian secara purposive. Metode pengambilan sampel dengan metode snowball sampling sebanyak 30 sampel untuk masing-masing petani yang menjual kopi dalam bentuk gelondong merah (cherry red) dan kopi biji. Metode analisis data yang digunakan dalam penelitian ini adalah analisis uji beda model independent sample T-test, analisis nilai tambah (value added)metode Hayami. Hasil penelitian menunjukkan bahwa ada perbedaan nyata antara pendapatan USAhatani kopi Ateng yang dijual dalam bentuk gelondong merah (cherry red) dengan yang dijual dalam bentuk kopi biji, dimana pendapatan USAhatani yang dijual dalam bentuk kopi biji lebih tinggi (dua kali lebih besar) dari pendapatan USAhatani yang dijual dalam bentuk gelondong merah (cherry red) per hektar dalam 1 tahun. Nilai tambah yang diperoleh petani yang menjual kopi dalam bentuk biji yaitu sebesar Rp.1.101,47/Kg

Resonant Processes in a Frozen Gas

We present a theory of resonant processes in a frozen gas of atoms interacting via dipole-dipole potentials that vary as $r^{-3}$, where $r$ is the interatomic separation. We supply an exact result for a single atom in a given state interacting resonantly with a random gas of atoms in a different state. The time development of the transition process is calculated both on- and off-resonance, and the linewidth with respect to detuning is obtained as a function of time $t$. We introduce a random spin Hamiltonian to model a dense system of resonators and show how it reduces to the previous model in the limit of a sparse system. We derive approximate equations for the average effective spin, and we use them to model the behavior seen in the experiments of Anderson et al. and Lowell et al. The approach to equilibrium is found to be proportional to $\exp (-\sqrt{\gamma_{eq}t}$), where the constant $\gamma _{eq}$ is explicitly related to the system's parameters.Comment: 30 pages, 6 figure

Magnetic vortex-antivortex crystals generated by spin-polarized current

We study vortex pattern formation in thin ferromagnetic films under the action of strong spin-polarized currents. Considering the currents which are polarized along the normal of the film plane, we determine the critical current above which the film goes to a saturated state with all magnetic moments being perpendicular to the film plane. We show that stable square vortex-antivortex superlattices (\emph{vortex crystals}) appears slightly below the critical current. The melting of the vortex crystal occurs with current further decreasing. A mechanism of current-induced periodic vortex-antivortex lattice formation is proposed. Micromagnetic simulations confirm our analytical results with a high accuracy.Comment: 12 pages, 11 figure

Light scattering and phase behavior of Lysozyme-PEG mixtures

Measurements of liquid-liquid phase transition temperatures (cloud points) of mixtures of a protein (lysozyme) and a polymer, poly(ethylene glycol) (PEG) show that the addition of low molecular weight PEG stabilizes the mixture whereas high molecular weight PEG was destabilizing. We demonstrate that this behavior is inconsistent with an entropic depletion interaction between lysozyme and PEG and suggest that an energetic attraction between lysozyme and PEG is responsible. In order to independently characterize the lysozyme/PEG interactions, light scattering experiments on the same mixtures were performed to measure second and third virial coefficients. These measurements indicate that PEG induces repulsion between lysozyme molecules, contrary to the depletion prediction. Furthermore, it is shown that third virial terms must be included in the mixture's free energy in order to qualitatively capture our cloud point and light scattering data. The light scattering results were consistent with the cloud point measurements and indicate that attractions do exist between lysozyme and PEG.Comment: 5 pages, 2 figures, 1 tabl

Inelastic scattering of protons from 6,8^{6,8}He and 7,11^{7,11}Li in a folding model approach

The proton-inelastic scattering from $^{6,8}$He and $^{7,11}$Li nuclei are studied in a folding model approach. A finite-range, momentum, density and isospin dependent nucleon-nucleon interaction (SBM) is folded with realistic density distributions of the above nuclei. The renormalization factors N$_R$ and N$_I$ on the real and volume imaginary part of the folded potentials are obtained by analyzing the respective elastic scattering data and kept unaltered for the inelastic analysis at the same energy. The form factors are generated by taking derivatives of the folded potentials and therefore required renormalizations. The $\beta$ values are extracted by fitting the p + $^{6,8}$He,$^{7,11}$Li inelastic angular distributions. The present analysis of p + $^8$He inelastic scattering to the 3.57 MeV excited state, including unpublished forward angle data (RIKEN) confirms L = 2 transition. Similar analysis of the p + $^6$He inelastic scattering angular distribution leading to the 1.8 MeV (L = 2) excited state fails to satisfactorily reproduce the data.Comment: one LaTeX file, five PostScript figure

Wernicke's Encephalopathy: 'plus ca change, plus c'est la meme chose'

Aims: To develop clinical guidelines to identify individuals who misuse alcohol and are at risk of developing Wernicke's Encephalopathy (WE). Method: Non-systematic literature review of studies which includes a careful clinical record of the development of signs and symptoms of thiamine deficiency and in which the diagnosis of WE has been confirmed at autopsy. Results: The review of the clinical findings in cases of WE, diagnosed at autopsy, shows a consistent pattern of signs and symptoms. The pattern appears to be similar regardless of whether the thiamine deficiency is related to nutritional problems alone or associated with alcohol misuse. Conclusions: The assessment of the degree of thiamine deficiency and the diagnosis of WE remain a clinical evaluation, and guidelines are suggested to help the clinician. Since neurotoxicity due to the metabolism of excessive alcohol in patients with chronic and severe alcohol dependence may be an important factor in determining long-term outcome of treatment, this must form part of the overall evaluation

Incorporation of tetrahedral ferric iron in hydrous ringwoodite

Hydrous Fo_{91} ringwoodite crystals were synthesized at 20 GPa and high-temperature conditions using a multi-anvil press. Recovered crystals were analyzed using electron microprobe analysis, Raman spectroscopy, infrared spectroscopy, synchrotron Mössbauer spectroscopy, single-crystal X-ray diffraction, and single-crystal Laue neutron diffraction, to carefully characterize the chemistry and crystallography of the samples. Analysis of the combined data sets provides evidence for the presence of tetrahedrally coordinated ferric iron and multiple hydrogen incorporation mechanisms within these blue-colored iron-bearing ringwoodite crystals. Tetrahedral ferric iron is coupled with cation disorder of silicon onto the octahedrally coordinated site. Cation disorder in mantle ringwoodite minerals may be promoted in the presence of water, which could have implications for current models of seismic velocities within the transition zone. Additionally, the presence of tetrahedrally coordinated ferric iron may cause the blue color of many ringwoodite and other high-pressure crystals