Stochastic disturbance rejection in model predictive control by randomized algorithms

In this paper we consider model predictive control with stochastic disturbances and input constraints. We present an algorithm which can solve this problem approximately but with arbitrary high accuracy. The optimization at each time step is a closed loop optimization and therefore takes into account the effect of disturbances over the horizon in the optimization. Via an example it is shown that this gives a clear improvement of performance although at the expense of a large computational effort

Optimal control of linear, stochastic systems with state and input constraints

In this paper we extend the work presented in our previous papers (2001) where we considered optimal control of a linear, discrete time system subject to input constraints and stochastic disturbances. Here we basically look at the same problem but we additionally consider state constraints. We discuss several approaches for incorporating state constraints in a stochastic optimal control problem. We consider in particular a soft-constraint on the state constraints where constraint violation is punished by a hefty penalty in the cost function. Because of the stochastic nature of the problem, the penalty on the state constraint violation can not be made arbitrary high. We derive a condition on the growth of the state violation cost that has to be satisfied for the optimization problem to be solvable. This condition gives a link between the problem that we consider and the well known $H_\infty$ control problem

D-region differential-phase measurements and ionization variability studies

Measurements of electron densities in the D region are made by the partial-reflection differential-absorption and differential-phase techniques. The differential-phase data are obtained by a hard-wired phase-measuring system. Electron-sensity profiles obtained by the two techniques on six occasions are plotted and compared. Electron-density profiles obtained at the same time on 30 occasions during the years 1975 through 1977 are averaged to form a single profile for each technique. The effect of varying the assumed collision-frequency profile on these averaged profiles is studied. Time series of D-region electron-sensity data obtained by 3.4 minute intervals on six days during the summer of 1977 are examined for wave-like disturbances and tidal oscillations

Investigation of the winds and electron concentration variability in the D region of the ionosphere by the partial-reflection radar technique

The development and first observations of the partial-reflection drifts experiment at Urbana, Illinois (40 N) are described. The winds data from the drifts experiment are compared with electron concentration data obtained by the differential-absorption technique to study the possible meteorological causes of the winter anomaly in the mesosphere at midlatitudes. winds data obtained by the meteor-radar experiment at Urbana are also compared with electron concentration data measured at Urban. A significant correlation is shown is both cases between southward winds and increasing electron concentration measured at the same location during winter. The possibility of stratospheric/mesospheric coupling is investigated by comparing satellite-measured 0.4 mbar geopotential data with mesospheric electron concentration data. No significant coupling was observed. The winds measured at Saskatoon, Saskatchewan (52 N) are compared with the electron concentrations measured at Urban, yielding constant fixed relationship, but significant correlations for short segments of the winter. A significant coherence is observed at discrete frequencies during segments of the winter

\u3cem\u3ePlasmodium falciparum\u3c/em\u3e SSB Tetramer Wraps Single-Stranded DNA with Similar Topology but Opposite Polarity to \u3cem\u3eE. coli\u3c/em\u3e SSB

Single-stranded DNA binding (SSB) proteins play central roles in genome maintenance in all organisms. Plasmodium falciparum, the causative agent of malaria, encodes an SSB protein that localizes to the apicoplast and likely functions in the replication and maintenance of its genome. P. falciparum SSB (Pf-SSB) shares a high degree of sequence homology with bacterial SSB proteins but differs in the composition of its C-terminus, which interacts with more than a dozen other proteins in Escherichia coli SSB (Ec-SSB). Using sedimentation methods, we show that Pf-SSB forms a stable homo-tetramer alone and when bound to single-stranded DNA (ssDNA). We also present a crystal structure at 2.1 Å resolution of the Pf-SSB tetramer bound to two (dT)35 molecules. The Pf-SSB tetramer is structurally similar to the Ec-SSB tetramer, and ssDNA wraps completely around the tetramer with a “baseball seam” topology that is similar to Ec-SSB in its “65 binding mode”. However, the polarity of the ssDNA wrapping around Pf-SSB is opposite to that observed for Ec-SSB. The interactions between the bases in the DNA and the amino acid side chains also differ from those observed in the Ec-SSB–DNA structure, suggesting that other differences may exist in the DNA binding properties of these structurally similar proteins

Training medical specialists in communication with patients with medically unexplained physical symptoms

Introduction In secondary care about 50% of newly referred patients to outpatient clinics of Neurology, Gynecology, Rheumatology or Internal Medicine present medically unexplained physical symptoms (MUPS). Medical specialists consider patients with symptoms without underlying pathology difficult to deal with, especially when patients have invalidating symptoms. Specialists sometimes don’t understand patients’ expectations and face patients, who are not willing to accept their findings and definition of MUPS. Moreover, medical specialists feel less competent in their consultations with MUPS patients compared to patients with explained symptoms. MUPS patients in specialist care sometimes don’t feel understood, anxious and unsatisfied when expectations are not met. Contest between patients' expertise, resting on their knowledge of their symptoms and doctors' authority, based on the normal findings of tests and investigations often contribute to problems in MUPS-consultations. Providing medical specialists with MUPS-focused knowledge and communication skills could make them more comfortable and effective in consultations, which could improve patient health and reduce costs. Methods We performed a systematic review on MUPS-focused communication and the effects on patient health and use of care. We used the Intervention Mapping (IM) framework to systematically apply theories, empirical evidence and practice perspectives in developing a MUPS-focused communication training in specialist care. We designed a multi-center cluster-randomized trial and tested the effectiveness of this training model on doctors’ communication skills by videotaped consultations using a MUPS-focused version of the Four Habits Coding Scheme. We assessed the quality of specialists’ reply letters to the general practitioners about MUPS patients on eight digital items and studied outcomes on patient health and costs by validated patient questionnaires (Whitely Index; 4DSQ; VAS; SF-36; TiCP). Doctors evaluated the usefulness of the training program by self-report questionnaires. Results We found limited research on MUPS-focused communication in specialist care. Patient outcomes and use of care were positively influenced by perceiving patients’ expectations correctly, explaining the nature of MUPS with additional information, explaining normal test results prior to investigation and a positive doctor-patient interaction. With the IM approach we developed an evidence-based, 14-hour communication training for medical specialists and residents in which they were taught to explore biopsychosocial aspects of patient’s symptoms, explain MUPS understandably, reassure patients effectively and to write appropriate reply letters to the general practitioner about MUPS patients. 123 doctors (40% medical specialists and 60% residents) and 478 MUPS patients from eleven specialties were included in the trial; 98 doctors completed the study with one or more videotaped consultation and reply letter. The training improved doctor’s exploring and information-giving skills in MUPS consultations. Specialists more often mentioned and answered patients questions in their reply letter to the general practitioner. Evalu

Finite-time behavior of inner systems

In this paper, we investigate how nonminimum phase characteristics of a dynamical system affect its controllability and tracking properties. For the class of linear time-invariant dynamical systems, these characteristics are determined by transmission zeros of the inner factor of the system transfer function. The relation between nonminimum phase zeros and Hankel singular values of inner systems is studied and it is shown how the singular value structure of a suitably defined operator provides relevant insight about system invertibility and achievable tracking performance. The results are used to solve various tracking problems both on finite as well as on infinite time horizons. A typical receding horizon control scheme is considered and new conditions are derived to guarantee stabilizability of a receding horizon controller