Strategies for sequential prediction of stationary time series

We present simple procedures for the prediction of a real valued sequence. The algorithms are based on a combinationof several simple predictors. We show that if the sequence is a realization of a bounded stationary and ergodic random process then the average of squared errors converges, almost surely, to that of the optimum, given by the Bayes predictor. We offer an analog result for the prediction of stationary gaussian processes.

Sistema d'adquisició de temperatures de 2 canals via R.F.

Poder mesurar i enregistrar diferents tipus de magnituds com pressió, força, temperatura etc. s’ha convertit en una necessitat per moltes aplicacions actuals. Aquestes magnituds poden tenir procedències molt diverses, tals com l’entorn, o poden ser generades per sistemes mecànics, elèctrics, etc. Per tal de poder adquirir aquestes magnituds, s’utilitzen els sistemes d’adquisició de dades. Aquests sistemes, prenen mostres analògiques del món real, i les transformen en dades digitals que poden ser manipulades per un sistema electrònic. Pràcticament qualsevol magnitud es pot mesurar utilitzant el sensor adient. Una magnitud molt utilitzada en sistemes d’adquisició de dades, és la temperatura. Els sistemes d’adquisició de temperatures estan molt generalitzats, i podem trobar-los com a sistemes, on l’objectiu és mostrar les dades adquirides, o podem trobar-los formant part de sistemes de control, aportant uns inputs necessaris per el seu correcte funcionament, garantir-ne l’estabilitat, seguretat etc. Aquest projecte, promogut per l’empresa Elausa, s’encarregarà d’adquirir, el senyal d’entrada de 2 Termoparells. Aquests mesuraran temperatures de circuits electrònics, que es trobaran dintre la càmera climàtica de Elausa, sotmesos a diferents condicions de temperatura, per tal de rebre l’homologació del circuit. El sistema haurà de poder mostrar les dades adquirides en temps real, i emmagatzemar-les en un PC que estarà ubicat en una oficina, situada a uns 30 m de distància de la sala on es farà el test. El sistema constarà d’un circuit electrònic que adquirirà, i condicionarà el senyal de sortida dels termoparells, per adaptar-lo a la tensió d’entrada d’un convertidor analògic digital, del microcontrolador integrat en aquesta placa. Seguidament aquesta informació, s’enviarà a través d’un mòdul transmissor de radiofreqüència, cap al PC on es visualitzaran les dades adquirides. Els objectius plantejats són els següents: - Dissenyar el circuit electrònic d’adquisició i condicionament del senyal. - Dissenyar, fabricar i muntar el circuit imprès de la placa d’adquisició. - Realitzar el programa de control del microcontrolador. - Realitzar el programa per presentar i desar les dades en un PC. - El sistema ha d’adquirir 2 temperatures, a través de Termoparells amb un rang d’entrada de -40ºC a +240ºC - S’ha de transmetre les dades via R.F. Els resultats del projecte han estat satisfactoris i s’han complert els objectius plantejats.

A reusable smart interface for gas sensor resistance measurement

The advances of the semiconductor industry enable microelectromechanical systems sensors, signal conditioning logic and network access to be integrated into a smart sensor node. In this framework, a mixed-mode interface circuit for monolithically integrated gas sensor arrays was developed with high-level design techniques. This interface system includes analog electronics for inspection of up to four sensor arrays and digital logic for smart control and data communication. Although different design methodologies were used in the conception of the complete circuit, high-level synthesis tools and methodologies were crucial in speeding up the whole design cycle, enhancing reusability for future applications and producing a flexible and robust component.

Continuous phase shift of sinusoidal signals using injection locked oscillators

This work presents an alternative to generate continuous phase shift of sinusoidal signals based on the use of super harmonic injection locked oscillators (ILO). The proposed circuit is a second harmonic ILO with varactor diodes as tuning elements. In the locking state, by changing the varactor bias, a phase shift instead of a frequency shift is observed at the oscillator output. By combining two of these circuits, relative phases up to 90 could be achieved. Two prototypes of the circuit have been implemented and tested, a hybrid version working in the range of 200-300 MHz and a multichip module (MCM) version covering the 900¿1000 MHz band.

A current-mode interface circuit for a piezoresistive pressure sensor

An interfacing circuit for piezoresistive pressure sensors based on CMOS current conveyors is presented. The main advantages of the proposed interfacing circuit include the use of a single piezoresistor, the capability of offset compensation, and a versatile current-mode configuration, with current output and current or voltage input. Experimental tests confirm linear relation of output voltage versus piezoresistance variation.

Higher-order colored-noise effects in multivariable systems

We extend the partial resummation technique of Fokker-Planck terms for multivariable stochastic differential equations with colored noise. As an example, a model system of a Brownian particle with colored noise is studied. We prove that the asymmetric behavior found in analog simulations is due to higher-order terms which are left out in that technique. On the contrary, the systematic ¿-expansion approach can explain the analog results.

Passage times for the decay of an unstable state triggered by colored noise

We study the decay of an unstable state in the presence of colored noise by calculating the moment generating function of the passage-time distribution. The problems of the independence of the initial condition in this non-Markovian process and that of nonlinear effects are addressed. Our results are compared with recent analog simulations.

Bistability driven by Gaussian colored noise: First-passage times

Herein we present a calculation of the mean first-passage time for a bistable one-dimensional system driven by Gaussian colored noise of strength D and correlation time ¿c. We obtain quantitative agreement with experimental analog-computer simulations of this system. We disagree with some of the conclusions reached by previous investigators. In particular, we demonstrate that all available approximations that lead to a state-dependent diffusion coefficient lead to the same result for small D¿c.

Front propagation in the A+B->2A reaction under subdiffusion

We consider an irreversible autocatalytic conversion reaction A+B->2A under subdiffusion described by continuous-time random walks. The reactants transformations take place independently of their motion and are described by constant rates. The analog of this reaction in the case of normal diffusion is described by the Fisher-Kolmogorov-Petrovskii-Piskunov equation leading to the existence of a nonzero minimal front propagation velocity, which is really attained by the front in its stable motion. We show that for subdiffusion, this minimal propagation velocity is zero, which suggests propagation failure.

A minimal i-motif stabilized by minor groove G:T:G:T tetrads

The repetitive DNA sequences found at telomeres and centromeres play a crucial role in the structure and function of eukaryotic chromosomes. This role may be related to the tendency observed in many repetitive DNAs to adopt non-canonical structures. Although there is an increasing recognition of the importance of DNA quadruplexes in chromosome biology, the co-existence of different quadruplex-forming elements in the same DNA structure is still a matter of debate. Here we report the structural study of the oligonucleotide d(TCGTTTCGT) and its cyclic analog d. Both sequences form dimeric quadruplex structures consisting of a minimal i-motif capped, at both ends, by a slipped minor groove-aligned G:T:G:T tetrad. These mini i-motifs, which do not exhibit the characteristic CD spectra of other i-motif structures, can be observed at neutral pH, although they are more stable under acidic conditions. This finding is particularly relevant since these oligonucleotide sequences do not contain contiguous cytosines. Importantly, these structures resemble the loop moiety adopted by an 11-nucleotide fragment of the conserved centromeric protein B (CENP-B) box motif, which is the binding site for the CENP-B.

Positional stability of holographic optical traps

The potential of digital holography for complex manipulation of micron-sized particles with optical tweezers has been clearly demonstrated. By contrast, its use in quantitative experiments has been rather limited, partly due to fluctuations introduced by the spatial light modulator (SLM) that displays the kinoforms. This is an important issue when high temporal or spatial stability is a concern. We have investigated the performance of both an analog-addressed and a digitally-addressed SLM, measuring the phase fluctuations of the modulated beam and evaluating the resulting positional stability of a holographic trap. We show that, despite imparting a more unstable modulation to the wavefront, our digitally-addressed SLM generates optical traps in the sample plane stable enough for most applications. We further show that traps produced by the analog-addressed SLM exhibit a superior pointing stability, better than 1 nm, which is comparable to that of non-holographic tweezers. These results suggest a means to implement precision force measurement experiments with holographic optical tweezers (HOTs).

A minimal i-motif stabilized by minor groove G:T:G:T tetrads

The repetitive DNA sequences found at telomeres and centromeres play a crucial role in the structure and function of eukaryotic chromosomes. This role may be related to the tendency observed in many repetitive DNAs to adopt non-canonical structures. Although there is an increasing recognition of the importance of DNA quadruplexes in chromosome biology, the co-existence of different quadruplex-forming elements in the same DNA structure is still a matter of debate. Here we report the structural study of the oligonucleotide d(TCGTTTCGT) and its cyclic analog d. Both sequences form dimeric quadruplex structures consisting of a minimal i-motif capped, at both ends, by a slipped minor groove-aligned G:T:G:T tetrad. These mini i-motifs, which do not exhibit the characteristic CD spectra of other i-motif structures, can be observed at neutral pH, although they are more stable under acidic conditions. This finding is particularly relevant since these oligonucleotide sequences do not contain contiguous cytosines. Importantly, these structures resemble the loop moiety adopted by an 11-nucleotide fragment of the conserved centromeric protein B (CENP-B) box motif, which is the binding site for the CENP-B.

Comments on "On resistor-induced thermal noise in linear circuits"

Correspondència referida a l'article de R. Giannetti, publicat ibid. vol.49 p.87-88

Disseny d’un circuit analògic reconfigurable

En l’actualitat, l’electrònica digital s’està apoderant de la majoria de camps de desenvolupament, ja que ofereix un gran ventall de possibilitats que permeten fer front a gran quantitat de problemàtiques. Poc a Poc s’ha anat prescindint el màxim possible de l’electrònica analògica i en el seu lloc s’han utilitzat sistemes microprocessats, PLDs o qualsevol altre dispositiu digital, que proporciona beneficis enlluernadors davant la fatigosa tasca d’implementar una solució analògica.Tot i aquesta tendència, és inevitable la utilització de l’electrònica analògica, ja que el mon que ens envolta és l’entorn en el que han de proporcionar servei els diferents dissenys que es realitzen, i aquest entorn no és discret sinó continu. Partint d’aquest punt ben conegut hem de ser conscients que com a mínim els filtres d’entrada i sortida de senyal juntament amb els convertidors D/A A/D mai desapareixeran.Així doncs, aquests circuits analògics, de la mateixa forma que els digitals, han de sercomprovats un cop dissenyats, és en aquest apartat on el nostre projecte desenvoluparà un paper protagonista, ja que serà la eina que ha de permetre obtenir les diferents senyals característiques d’un determinat circuit, per posteriorment realitzar els tests que determinaran si es compleix el rang de correcte funcionament, i en cas de no complir, poder concretar quin paràmetre és el causant del defecte

Ultra-Deep Pyrosequencing Detects Conserved Genomic Sites and Quantifies Linkage of Drug-Resistant Amino Acid Changes in the Hepatitis B Virus Genome

Selection of amino acid substitutions associated with resistance to nucleos(t)ide-analog (NA) therapy in the hepatitis B virus (HBV) reverse transcriptase (RT) and their combination in a single viral genome complicates treatment of chronic HBV infection and may affect the overlapping surface coding region. In this study, the variability of an overlapping polymerase-surface region, critical for NA resistance, is investigated before treatment and under antiviral therapy, with assessment of NA-resistant amino acid changes simultaneously occurring in the same genome (linkage analysis) and their influence on the surface coding region.