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

Coupled cavities for enhancing the cross-phase modulation in electromagnetically induced transparency

We propose an optical double-cavity resonator whose response to a signal is similar to that of an Electromagnetically Induced Transparency (EIT) medium. A combination of such a device with a four-level EIT medium can serve for achieving large cross-Kerr modulation of a probe field by a signal field. This would offer the possibility of building a quantum logic gate based on photonic qubits. We discuss the technical requirements that are necessary for realizing a probe-photon phase shift of Pi caused by a single-photon signal. The main difficulty is the requirement of an ultra-low reflectivity beamsplitter and to operate a sufficiently dense cool EIT medium in a cavity.Comment: 10 pages, 5 figures, REVTeX, to appear in Phys. Rev. A (v2 - minor changes in discussion of experimental conditions

Temperature Variation of Ultra Slow Light in a Cold Gas

A model is developed to explain the temperature dependence of the group velocity as observed in the experiments of Hau et al (Nature {\bf397}, 594 (1999)). The group velocity is quite sensitive to the change in the spatial density. The inhomogeneity in the density and its temperature dependence are primarily responsible for the observed behavior.Comment: 12 pages, 4 figure

From Storage and Retrieval of Pulses to Adiabatons

We investigate whether it is possible to store and retrieve the intense probe pulse from a $\Lambda$-type homogeneous medium of cold atoms. Through numerical simulations we show that it is possible to store and retrieve the probe pulse which are not necessarily weak. As the intensity of the probe pulse increases, the retrieved pulse remains a replica of the original pulse, however there is overall broadening and loss of the intensity. These effects can be understood in terms of the dependence of absorption on the intensity of the probe. We include the dynamics of the control field, which becomes especially important as the intensity of the probe pulse increases. We use the theory of adiabatons [Grobe {\it et al.} Phys. Rev. Lett. {\bf 73}, 3183 (1994)] to understand the storage and retrieval of light pulses at moderate powers.Comment: 15 pages, 7 figures, typed in RevTe

Incidence and control of bovine gastrointestinal nematodes in the East of the Province of La Pampa, Argentina

A cross-sectional survey including 350 stocking farms and bovine establishments that operate the full cycle (FC) as well as fattening operations (IN) was carried out in the East of the Province of La Pampa to record cases of verminous gastroenteritis (VGE) as well as control and management practices applied by the farmers.Farms were stratified by herd size into three categories: more than 900 (G), 900-500 (M) and 500-300 (P) bovines. Samples from each category were collected at random. 33% of the farmers surveyed indicated that their animals had been affected by clinical cases of VGE with morbidity and mortality rates between 11.2% and 0.42%, respectively. More cases of VEG (P<0.004, X2 8.33) occurred in herds on FC establishments (37%) that on fattening farms (IN) (21%); the relative risk (RR) was 1.77 (95%; IC 1.18 – 2.74) but no differences were noted between categories. Ninety-four percent of the farmers use avermectins alone (AVM) (71%) or combined with benzimidazole (BZD, 20%) or levamisole (3%); 6% use BZD alone. The percentage of use of other drugs in addition to AVM increases (P<0.005, X2 7.80) with larger herds (G: 32%, M: 21%, P: 15%). Of the treatments, 95.2% include avermectins alone in injectable form (82.6%) or combined with oral (16.5%) or intraruminal (0.9%) forms. Approximately 2.42 treatments per year are performed and are more prevalent (P<0.01) in G and IN farms (2.7 treatments). 35% of the farmers deworm twice a year, in the fall (between March and July) and in late winter-spring (between August and October-), 16% deworm only once (between February and April) and 12% twice (between late summer and early winter). 18% of the farmers (G: 24%, M: 18%; P: 13%) prevent VGE losses by administering treatment at a specific time of the year. 60% of the farmers consult the veterinarian although only 29% perform an egg count (hpg) although differences (P<0.001) between herd sizes were noted: G: 41%, M: 26%; P 19%. 12% (FC 10%; IN 16%). 12% of the farmers (FC 10%; IN 16%) perform a follow-up of parasite infections with an egg count and administer treatment based on this monitoring and the recommendation of a veterinarian. 94% of those surveyed indicated that VGE alone (55%) or in conjunction with other pathologies were a major problem and 30% said it was the main health problem. The study shows the economic importance of GIPs for the competitiveness of the systems in the region. The use of a significant quantity of anthelmintics, mainly avermectins, and a low participation of veterinarians in planning the controls were observed. A trend indicating that large farms and fattening operations assign more importance to control, use of anthelmintics and participation of professionals was noted

Phase Coherence and Control of Stored Photonic Information

We report the demonstration of phase coherence and control for the recently developed "light storage" technique. Specifically, we use a pulsed magnetic field to vary the phase of atomic spin excitations which result from the deceleration and storing of a light pulse in warm Rb vapor. We then convert the spin excitations back into light and detect the resultant phase shift in an optical interferometric measurement. The coherent storage of photon states in matter is essential for the practical realization of many basic concepts in quantum information processing.Comment: 5 pages, 3 figures. Submitted to Phys. Rev. Let

Slow Light in Doppler Broadened Two level Systems

We show that the propagation of light in a Doppler broadened medium can be slowed down considerably eventhough such medium exhibits very flat dispersion. The slowing down is achieved by the application of a saturating counter propagating beam that produces a hole in the inhomogeneous line shape. In atomic vapors, we calculate group indices of the order of 10^3. The calculations include all coherence effects.Comment: 6 pages, 5 figure

A Knob for Changing Light Propagation from Subluminal to Superluminal

We show how the application of a coupling field connecting the two lower metastable states of a lambda-system can produce a variety of new results on the propagation of a weak electromagnetic pulse. In principle the light propagation can be changed from subluminal to superluminal. The negative group index results from the regions of anomalous dispersion and gain in susceptibility.Comment: 6 pages,5 figures, typed in RevTeX, accepted in Phys. Rev.

Low-light-level nonlinear optics with slow light

Electromagnetically induced transparency in an optically thick, cold medium creates a unique system where pulse-propagation velocities may be orders of magnitude less than $c$ and optical nonlinearities become exceedingly large. As a result, nonlinear processes may be efficient at low-light levels. Using an atomic system with three, independent channels, we demonstrate a quantum interference switch where a laser pulse with an energy density of $\sim23$ photons per $\lambda^2/(2\pi)$ causes a 1/e absorption of a second pulse.Comment: to be published in PR

Ultrarelativistic electron-hole pairing in graphene bilayer

We consider ground state of electron-hole graphene bilayer composed of two independently doped graphene layers when a condensate of spatially separated electron-hole pairs is formed. In the weak coupling regime the pairing affects only conduction band of electron-doped layer and valence band of hole-doped layer, thus the ground state is similar to ordinary BCS condensate. At strong coupling, an ultrarelativistic character of electron dynamics reveals and the bands which are remote from Fermi surfaces (valence band of electron-doped layer and conduction band of hole-doped layer) are also affected by the pairing. The analysis of instability of unpaired state shows that s-wave pairing with band-diagonal condensate structure, described by two gaps, is preferable. A relative phase of the gaps is fixed, however at weak coupling this fixation diminishes allowing gapped and soliton-like excitations. The coupled self-consistent gap equations for these two gaps are solved at zero temperature in the constant-gap approximation and in the approximation of separable potential. It is shown that, if characteristic width of the pairing region is of the order of magnitude of chemical potential, then the value of the gap in the spectrum is not much different from the BCS estimation. However, if the pairing region is wider, then the gap value can be much larger and depends exponentially on its energy width.Comment: 13 pages with 8 figures; accepted to Eur. Phys. J.