190 research outputs found
Linear parameter-varying model to design control laws for an artificial pancreas
The contribution of this work is the generation of a control-oriented model for insulin-glucose dynamic regulation in type 1 diabetes mellitus (T1DM). The novelty of this model is that it includes the time-varying nature, and the inter-patient variability of the glucose-control problem. In addition, the model is well suited for well-known and standard controller synthesis procedures. The outcome is an average linear parameter-varying (LPV) model that captures the dynamics from the insulin delivery input to the glucose concentration output constructed based on the UVA/Padova metabolic simulator. Finally, a system-oriented reinterpretation of the classical ad-hoc 1800 rule is applied to adapt the model's gain. The effectiveness of this approach is quantified both in open- and closed-loop. The first one by computing the root mean square error (RMSE) between the glucose deviation predicted by the proposed model and the UVA/Padova one. The second measure is determined by using the Îœ-gap as a metric to determine distance, in terms of closed-loop performance, between both models. For comparison purposes, both open- (RMSE) and closed-loop (Îœ-gap metric) quality indicators are also computed for other control-oriented models previously presented. This model allows the design of LPV controllers in a straightforward way, considering its affine dependence on the time-varying parameter, which can be computed in real-time. Illustrative simulations are included. In addition, the presented modeling strategy was employed in the design of an artificial pancreas (AP) control law that successfully withstood rigorous testing using the UVA/Padova simulator, and that was subsequently deployed in a clinical trial campaign where five adults remained in closed-loop for 36 h. This was the first ever fully closed-loop clinical AP trial in Argentina, and the modeling strategy presented here is considered instrumental in resulting in a very successful clinical outcome.Fil: Colmegna, Patricio HernĂĄn. Universidad Nacional de Quilmes. Departamento de Ciencia y TecnologĂa; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: SĂĄnchez Peña, Ricardo S.. Instituto TecnolĂłgico de Buenos Aires; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Gondhalekar, R.. Harvard University; Estados Unido
MPC of constrained discrete-time linear periodic systems â A framework for asynchronous control: Strong feasibility, stability and optimality via periodic invariance
State-feedback model predictive control (MPC) of discrete-time linear periodic systems with time-dependent state and input dimensions is considered. The states and inputs are subject to periodically time-dependent, hard, convex, polyhedral constraints. First, periodic controlled and positively invariant sets are characterized, and a method to determine the maximum periodic controlled and positively invariant sets is derived. The proposed periodic controlled invariant sets are then employed in the design of least-restrictive strongly feasible reference-tracking MPC problems. The proposed periodic positively invariant sets are employed in combination with well-known results on optimal unconstrained periodic linear-quadratic regulation (LQR) to yield constrained periodic LQR control laws that are stabilizing and optimal. One motivation for systems with time-dependent dimensions is efficient control law synthesis for discrete-time systems with asynchronous inputs, for which a novel modeling framework resulting in low dimensional models is proposed. The presented methods are applied to a multirate nano-positioning system
Superconducting rebalance acceleration and rate sensor
The goal of this program is the development of a high precision multisensor based on a high T(sub c) superconducting proof mass. The design of a prototype is currently underway. Key technical issues appear resolvable. High temperature superconductors have complicated, hysteretic flux dynamics but the forces on them can be linearly controlled for small displacements. Current data suggests that the forces on the superconductors decay over a short time frame and then stabilize, though very long term data is not available. The hysteretic force characteristics are substantial for large scale excursions, but do not appear to be an issue for the very small displacements required in this device. Sufficient forces can be exerted for non-contact suspension of a centimeter sized proof mass in a vacuum sealed nitrogen jacket cryostat. High frequency capacitive sensing using stripline technology will yield adequate position resolution for 0.1 micro-g measurements at 100 Hz. Overall, a reasonable cost, but very high accuracy, system is feasible with this technology
Electrostatically suspended and sensed micro-mechanical rate gyroscope
The goal of this work is development of fully electrostatically suspended and rebalancing angular rate sensing micro-gyroscope fabricated according to standard VLSI techniques. Fabrication of test structures is proceeding. Off chip electronics for the electrostatic sensing and driving circuits has been tested. The prototype device will be assembled in a hybrid construction including the FET input stages of the sensors
Fine-structure diagnostics of neutral carbon toward HE 0515-4414
New high-resolution high signal-to-noise spectra of the damped Lyman
(DLA) system toward the quasi-stellar object HE 0515-4414 reveal
absorption lines of the multiplets 2 and 3 in \ion{C}{i}. The resonance lines
are seen in two components with total column densities of
and , respectively. The comparision of theoretical
calculations of the relative fine-structure population with the ratios of the
observed column densities suggests that the \ion{C}{i} absorbing medium is
either very dense or exposed to very intense UV radiation. The upper limit on
the local UV energy density is 100 times the galactic UV energy density, while
the upper limit on the \ion{H}{i} number density is 110 cm. The
excitation temperatures of the ground state fine-structure levels of
and K, respectively, are consistent with the temperature-redshift
relation predicted by the standard Friedmann cosmology. The cosmic microwave
background radiation (CMBR) is only a minor source of the observed
fine-structure excitation.Comment: 5 pages, 5 figures, uses A&A macro package, gzipped tar archive,
accepted by A&
The Local Interstellar Ultraviolet Radiation Field
I have used the Hipparcos Input Catalog, together with Kurucz model stellar
atmospheres, and information on the strength of the interstellar extinction, to
create a model of the expected intensity and spectral distribution of the local
interstellar ultraviolet radiation field, under various assumptions concerning
the albedo a of the interstellar grains. (This ultraviolet radiation field is
of particular interest because of the fact that ultraviolet radiation is
capable of profoundly affecting the chemistry of the interstellar medium.) By
comparing my models with the observations, I am able to conclude that the
albedo a of the interstellar grains in the far ultraviolet is very low, perhaps
a = 0.1. I also advance arguments that my present determination of this albedo
is much more reliable than any of the many previous (and conflicting)
ultraviolet interstellar grain albedo determinations. Beyond this, I show that
the ultraviolet background radiation that is observed at high galactic
latitudes must be extragalactic in origin, as it cannot be backscatter of the
interstellar radiation field.Comment: Astrophysical Journal, in press; 9 figures + 16 text page
Forces on Dust Grains Exposed to Anisotropic Interstellar Radiation Fields
Grains exposed to anisotropic radiation fields are subjected to forces due to
the asymmetric photon-stimulated ejection of particles. These forces act in
addition to the ``radiation pressure'' due to absorption and scattering. Here
we model the forces due to photoelectron emission and the photodesorption of
adatoms. The ``photoelectric'' force depends on the ambient conditions relevant
to grain charging. We find that it is comparable to the radiation pressure when
the grain potential is relatively low and the radiation spectrum is relatively
hard. The calculation of the ``photodesorption'' force is highly uncertain,
since the surface physics and chemsitry of grain materials are poorly
understood at present. For our simple yet plausible model, the photodesorption
force dominates the radiation pressure for grains with size >~0.1 micron
exposed to starlight from OB stars. We find that the anisotropy of the
interstellar radiation field is ~10% in the visible and ultraviolet. We
estimate size-dependent drift speeds for grains in the cold and warm neutral
media and find that micron-sized grains could potentially be moved across a
diffuse cloud during its lifetime.Comment: LaTeX(41 pages, 19 figures), submitted to Ap
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