Self-Driven Synchronous Rectification System With Input Voltage Tracking for Converters With a Symmetrically Driven Transformer

Synchronous rectification (SR) is mandatory to achieve good efficiencies with low output voltages. If a transformer is driven asymmetrically without dead times, the self-driven SR (SDSR) is a very interesting solution. However, if the transformer is driven symmetrically, the synchronous rectifiers are off during the dead times, and as a consequence, the efficiency is lowered. This paper deals with the optimization of an SDSR system that keeps the rectifiers on even during the dead times. The input voltage is tracked, and the information is used to adapt the gate to the source voltage of the synchronous rectifiers and improve the efficiency. The system has been implemented in a prototype, and the results have been compared with the ones obtained in the same prototype without SDSR.     

Optimization of Thienopyrrole‐Based Finger‐Loop Inhibitors of the Hepatitis C Virus NS5B Polymerase

Infections caused by the hepatitis C virus (HCV) are a significant world health problem for which novel therapies are in urgent demand. The NS5B polymerase of HCV is responsible for the replication of viral RNA and has been a prime target in the search for novel treatment options. We had discovered allosteric finger‐loop inhibitors based on a thieno[3,2‐b]pyrrole scaffold as an alternative to the related indole inhibitors. Optimization of the thienopyrrole series led to several N‐acetamides with submicromolar potency in the cell‐based replicon assay, but they lacked oral bioavailability in rats. By linking the N4‐position to the ortho‐position of the C5‐aryl group, we were able to identify the tetracyclic thienopyrrole 40 , which displayed a favorable pharmacokinetic profile in rats and dogs and is equipotent with recently disclosed finger‐loop inhibitors based on an indole scaffold.     

GMI sensitive element based on commercial Vitrovac amorphous ribbon

A very high giant magnetoimpedance (GMI) up to 420% and sensitivities up to 60%/Oe have been achieved in commercial Vitrovac^® 6025 Co₆₇Fe₄Mo_1.5Si_16.5B₁₁ amorphous ribbons. A relatively low frequency range of 0.5–10 MHz and driving current intensities between 1.5 and 15 mA in combination with high sensitivities, low GMI hysteresis with respect to external magnetic field make this material very attractive for low field sensing processes. Special treatments under load without heating result in additional stability and favorable noise to signal ratio. We explain these outstanding GMI properties taking into account extra uniform magnetization processes and longitudinal magnetic anisotropy. The complex study of the magnetic and GMI properties shows, that equilibrium of various parameters of GMI medium is an additional guarantee of stable functionality.     

Gravitational fields as generalized string models

We show that Einstein’s main equations for stationary axisymmetric fields in vacuum are equivalent to the equations of motion for bosonic strings moving in a special nonflat background. This new representation is based on the analysis of generalized harmonic maps in which the metric of the target space explicitly depends on the parametrization of the base space. It is shown that this representation is valid for any gravitational field which possesses two commuting Killing vector fields. We introduce the concept of dimensional extension which allows us to consider this type of gravitational fields as strings embedded in D-dimensional nonflat backgrounds, even in the limiting case where the Killing vector fields are hypersurface-orthogonal.     

Autoregressive processes with data-driven regime switching

Abstract.  We develop a switching-regime vector autoregressive model in which changes in regimes are governed by an underlying Markov process. In contrast to the typical hidden Markov approach, we allow the transition probabilities of the underlying Markov process to depend on past values of the time series and exogenous variables. Such processes have potential applications in finance and neuroscience. In the latter, the brain activity at time t (measured by electroencephalograms) will be modelled as a function of both its past values as well as exogenous variables (such as visual or somatosensory stimuli). In this article, we establish stationarity, geometric ergodicity and existence of moments for these processes under suitable conditions on the parameters of the model. Such properties are important for understanding the stability properties of the model as well as for deriving the asymptotic behaviour of various statistics and model parameter estimators.     

A system simulating representation change phenomena while problem solving

This paper deals with a computer programme offering a valid simulation of cognitive human processes related to representation changes while problem solving. An introductory and brief recollection of preceding contributions by psychologists, cognitive scientists and AI researchers provides the necessary background and motivation for our work. A relevant trend of the present research concerns the formal mathematical study of representation phenomena, including precisions about isomorphic and homomorphic representation changes. In order to simplify problem resolution processes, the implemented system performs certain representation changes, by making use of specific procedures which assign and modify a certain relevance value to every attribute involved in the problem representation, on behalf of their respective importance so as to actually solve the problem. The paper includes a full account of mathematical definitions and propositions involved in this system.     

A Groebner bases-based approach to backward reasoning in rule based expert systems

The aim of this paper is to present theoretically a new algebraic method for detecting potentially dangerous states in a Rule Based Expert System whose knowledge is represented by propositional Boolean logic. Given a dangerous state which does not happen at present, our method is able to detect a possible input fact such that, if it also occurred, the dangerous situation really would happen. This method, inspired by automatic discovery of geometric theorems, is based on calculating just one reduced Groebner basis of a polynomial ideal representing the system’s knowledge. An implementation in the computer algebra system Maple is included.