Rational representations and controller synthesis of L2 behaviors

This paper considers linear dynamical systems restricted to square integrable trajectories. Following the behavioral formalism, a number of relevant classes of linear and shift-invariant L2systems are defined. It is shown that rational functions, analytic in specific half-spaces of the complex plane, prove most useful for representing such systems. For various classes of L2 systems, this paper provides a complete characterization of system equivalence in terms of rational kernel representations of L2 systems. In addition, a complete solution is given for the problem when selected (non-manifest) variables of an L2 system can be completely eliminated from their behavior. This elimination theorem has considerable independent interest in general modeling problems. It is shown that the elimination result is key in the solution of the problem for realizing an arbitrary L2 system as the interconnection of a given L2 system and a to-be-synthesized L2 system. In the context of control, this problem amounts to characterizing the existence and parameterization of all controllers that, after interconnection with a given plant, constitute a desired controlled system

A model reduction strategy preserving disturbance decoupling properties

In this paper, we address the problem of model reduction with control relevant approximation criteria. We focus on a reduction strategy in which the feasibility to design a controller that completely decouples disturbances from to-be-controlled variables in a system is left invariant. The main result of this paper provides a model reduction strategy with the property that disturbance decoupling is possible for the full order system if and only if this is possible for the reduced order system. In addition, controllers that achieve disturbance decoupling for the reduced order system can be implemented on the full order system with guaranteed disturbance decoupling properties

A model reduction scheme with preserved optimal performance

This paper addresses a problem in control relevant model reduction. More specifically, a model reduction scheme is proposed that preserves the disturbance decoupling property of the to-be-reduced plant. It is shown that optimal feedback laws designed for the reduced system will actually be optimal for the non-reduced system. Moreover, a characterization is given for the minimal reduction order for which this property can be established. This can be extended to the design of observers for complex systems. The results are illustrated by a simulation example

Reduced-order observer design using a Lagrangian model

This paper considers the problem of reduced-order observer design. A design procedure is proposed in which the impulse response of the observer is treated as the solution of a general optimization problem. Using principles from variational analysis, the corresponding Lagrangian system is reduced so as to yield observers of reduced-order. Using this approach, two different observer design problems are discussed and compared on an industrial example

Cavity-enhanced photoionization of an ultracold rubidium beam for application in focused ion beams

A two-step photoionization strategy of an ultracold rubidium beam for application in a focused ion beam instrument is analyzed and implemented. In this strategy the atomic beam is partly selected with an aperture after which the transmitted atoms are ionized in the overlap of a tightly cylindrically focused excitation laser beam and an ionization laser beam whose power is enhanced in a build-up cavity. The advantage of this strategy, as compared to without the use of a build-up cavity, is that higher ionization degrees can be reached at higher currents. Optical Bloch equations including the photoionization process are used to calculate what ionization degree and ionization position distribution can be reached. Furthermore, the ionization strategy is tested on an ultracold beam of $^{85}$Rb atoms. The beam current is measured as a function of the excitation and ionization laser beam intensity and the selection aperture size. Although details are different, the global trends of the measurements agree well with the calculation. With a selection aperture diameter of 52 $\mu$m, a current of $\left(170\pm4\right)$ pA is measured, which according to calculations is 63% of the current equivalent of the transmitted atomic flux. Taking into account the ionization degree the ion beam peak reduced brightness is estimated at $1\times10^7$ A/(m$^2\,$sr$\,$eV).Comment: 13 pages, 9 figure

Mesothelial cells in tissue repair and fibrosis

Mesothelial cells are fundamental to the maintenance of serosal integrity and homeostasis and play a critical role in normal serosal repair following injury. However, when normal repair mechanisms breakdown, mesothelial cells take on a profibrotic role, secreting inflammatory, and profibrotic mediators, differentiating and migrating into the injured tissues where they contribute to fibrogenesis. The development of new molecular and cell tracking techniques has made it possible to examine the origin of fibrotic cells within damaged tissues and to elucidate the roles they play in inflammation and fibrosis. In addition to secreting proinflammatory mediators and contributing to both coagulation and fibrinolysis, mesothelial cells undergo mesothelial-to-mesenchymal transition, a process analogous to epithelial-to-mesenchymal transition, and become fibrogenic cells. Fibrogenic mesothelial cells have now been identified in tissues where they have not previously been thought to occur, such as within the parenchyma of the fibrotic lung. These findings show a direct role for mesothelial cells in fibrogenesis and open therapeutic strategies to prevent or reverse the fibrotic process

Direct magneto-optical compression of an effusive atomic beam for high-resolution focused ion beam application

An atomic rubidium beam formed in a 70 mm long two-dimensional magneto-optical trap (2D MOT), directly loaded from a collimated Knudsen source, is analyzed using laser-induced fluorescence. The longitudinal velocity distribution, the transverse temperature and the flux of the atomic beam are reported. The equivalent transverse reduced brightness of an ion beam with similar properties as the atomic beam is calculated because the beam is developed to be photoionized and applied in a focused ion beam. In a single two-dimensional magneto-optical trapping step an equivalent transverse reduced brightness of $(1.0\substack{+0.8-0.4})$ $\times 10^6$ A/(m$^2$ sr eV) was achieved with a beam flux equivalent to $(0.6\substack{+0.3-0.2})$ nA. The temperature of the beam is further reduced with an optical molasses after the 2D MOT. This increased the equivalent brightness to $(6\substack{+5-2})$$\times 10^6$ A/(m$^2$ sr eV). For currents below 10 pA, for which disorder-induced heating can be suppressed, this number is also a good estimate of the ion beam brightness that can be expected. Such an ion beam brightness would be a six times improvement over the liquid metal ion source and could improve the resolution in focused ion beam nanofabrication.Comment: 10 pages, 8 figures, 1 tabl

Genetic partitioning of interleukin-6 signalling in mice dissociates Stat3 from Smad3-mediated lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal disease that is unresponsive to current therapies and characterized by excessive collagen deposition and subsequent fibrosis. While inflammatory cytokines, including interleukin (IL)-6, are elevated in IPF, the molecular mechanisms that underlie this disease are incompletely understood, although the development of fibrosis is believed to depend on canonical transforming growth factor (TGF)-β signalling. We examined bleomycin-induced inflammation and fibrosis in mice carrying a mutation in the shared IL-6 family receptor gp130. Using genetic complementation, we directly correlate the extent of IL-6-mediated, excessive Stat3 activity with inflammatory infiltrates in the lung and the severity of fibrosis in corresponding gp130757F mice. The extent of fibrosis was attenuated in B lymphocyte-deficient gp130757F;µMT−/− compound mutant mice, but fibrosis still occurred in their Smad3−/− counterparts consistent with the capacity of excessive Stat3 activity to induce collagen 1α1 gene transcription independently of canonical TGF-β/Smad3 signalling. These findings are of therapeutic relevance, since we confirmed abundant STAT3 activation in fibrotic lungs from IPF patients and showed that genetic reduction of Stat3 protected mice from bleomycin-induced lung fibrosis

On the elimination of latent variables in L2 behaviors

Abstract-This paper considers the problem to eliminate latent variables from models in the class of linear shift-invariant L2 systems. Models in this class are assumed to relate manifest and latent variables by means of rational operators. The question is addressed when the induced manifest behavior of such a model again admits a representation as the L2 kernel of a rational operator. Necessary and sufficient conditions for eliminability in this class are given and are compared with earlier obtained results for classical C ∞ behaviors. We also provide an explicit state space algorithm for the construction of the induced manifest behavior, which is a result from the obtained relation between elimination of variables and disturbance decoupling problems. I. INTRODUCTION This paper deals with the question to completely eliminate latent variables from a model description in which manifest and latent variables are related. For general models, manifest variables are thought of as distinguished variables that are relevant for the purpose of the model, whereas latent variables are auxiliary variables that serve to represent the model. Models derived from first principles are usually represented in terms of equations that relate both manifest and latent variables. The partial or complete elimination of latent variables from a general model representation that relates manifest and latent variables is of evident interest from a general modeling point of view. It amounts to characterizing and removing the redundancy in the latent variables of the model representation. We believe that the behavioral approach is, actually, the most natural framework for studying this question. This means that we view systems as sets of trajectories that evolve over time. Earlier work on the elimination problem in continuous time and infinitely smooth linear systems has been studied i