2,192 research outputs found
Entropy involved in fidelity of DNA replication
Information has an entropic character which can be analyzed within the
Statistical Theory in molecular systems. R. Landauer and C.H. Bennett showed
that a logical copy can be carried out in the limit of no dissipation if the
computation is performed sufficiently slowly. Structural and recent
single-molecule assays have provided dynamic details of polymerase machinery
with insight into information processing. We introduce a rigorous
characterization of Shannon Information in biomolecular systems and apply it to
DNA replication in the limit of no dissipation. Specifically, we devise an
equilibrium pathway in DNA replication to determine the entropy generated in
copying the information from a DNA template in the absence of friction. Both
the initial state, the free nucleotides randomly distributed in certain
concentrations, and the final state, a polymerized strand, are mesoscopic
equilibrium states for the nucleotide distribution. We use empirical stacking
free energies to calculate the probabilities of incorporation of the
nucleotides. The copied strand is, to first order of approximation, a state of
independent and non-indentically distributed random variables for which the
nucleotide that is incorporated by the polymerase at each step is dictated by
the template strand, and to second order of approximation, a state of
non-uniformly distributed random variables with nearest-neighbor interactions
for which the recognition of secondary structure by the polymerase in the
resultant double-stranded polymer determines the entropy of the replicated
strand. Two incorporation mechanisms arise naturally and their biological
meanings are explained. It is known that replication occurs far from
equilibrium and therefore the Shannon entropy here derived represents an upper
bound for replication to take place. Likewise, this entropy sets a universal
lower bound for the copying fidelity in replication.Comment: 25 pages, 5 figure
Rotor detection in atrial fibrillation
Atrial fibrillation (AF) is one of the most common arrhythmias in the clinical
practice. Catheter ablation method was developed more than 20 years ago as
an approach to terminate this rhythm disorder. Since its outbreak, this technique
obtained international acceptance among the clinicians, and technological advances
in this field increased its safety while reducing the procedure duration. However,
there is no perfect AF treatment procedure described yet, since the understanding
of the driving and sustaining AF mechanisms remains poor, with pulmonary vein
isolation being the most common ablation strategy.
Several theories try to explain the initiating and maintenance mechanisms of
the AF, ranging from multiple wavelets propagating at random in the atria to
ectopic focus fired from the pulmonary veins. Alternatively, spatiotemporal stable
sources (rotors) have been proposed as the maintenance mechanism of AF. The
most representative characteristic of a rotor is the re-entry spiral-like propagation
pattern that the electrical wavefront exhibits as it propagates. The assessment of
its presence and posterior ablation of the sites where rotors anchor might improve
the success of AF ablation.
Technical solutions emerged focusing on the rotor assessment problem. They
base their methods on the reconstruction of the atrial activity using multi-electrode
catheters and phase maps, in which they detect singularity points, the sites where
rotors spin. The ablation of these sites showed promising results, but the difficulty
to reproduce the results by other authors increased the controversy on this technique.
In this Thesis we address the rotor detection problem in the time domain
as opposed to current methods based on the phase domain of the signals.
We develop a new method to identify local activation times (LATs) in unipolar
electrograms (EGMs) recorded with multi-electrode catheters. We propose a new
filtering scheme to enhance the activation component of the EGM while considerably
reducing the presence of noise in the signal. This signal processing method
reects the real activity of the tissue in contact with the electrode. It opposes the
Hilbert transform (HT) used to extract the phase component of the signal, that
do not correlate well with the temporal activations. With the EGM LATs we perform
a spatial interpolation translating the electrode positions of the catheter into
a regular 2D grid. This way we generate isochronal maps revealing the electrical
wavefronts in the atrium. What is more, this step guarantees compatibility with
multi-electrode catheters, not restricting the method to specific models. With the
isochronal maps, we develop a new rotor detection algorithm based on the optical
flow of the wavefront dynamics, and a rotation pattern match. Additionally, we
develop a new method based on Granger's causality to estimate the directionality
of the wavefronts, that provides an additional indicator for rotational patterns.
We validate the methods using in silico and real AF signals.
We implement these methods into a system that can assess the presence of
rotational activation sites in the atrium. Our system is able to operate in realtime
with multi-electrode catheters of different topologies in contact with the atrial
wall. We integrate signal acquisition and processing in our system, allowing direct
acquisition of the signals without requiring signal exportation from a recording
device, which delays the clinical procedure. We address the computational time
handicap by designing parallelizable signal processing steps. We employ multi-core
processors and GPU based code to distribute the computations and minimize the
processing times, achieving near real-time results.
The results presented in this Thesis provide a new technical solution to detect
the presence of rotational activity (rotors) in AF patients in real-time. Although
the presence of rotational activity is itself controversial, we individually validate
each of the steps of the procedure and obtain evidence of the presence of rotational
activity in AF patients. The system has been also found useful to characterize the
atrial sites where rotational activity was found in terms of spatial and voltage
distribution. The results of this Thesis provide a new alternative to existing methods
based on phase analysis and open a new research line in the detection of the
mechanisms sustaining AF.La fibrilación auricular (FA) es una de las arritmias más comunes en la práctica
clínica. Para tratar de terminar esta fibrilación en pacientes se desarrollo el método
de ablación con catéter hace ya más de 20 años. Desde su puesta en marchar esta
técnica ha ido ganando aceptación internacional por parte de la comunidad médica,
y los avances tecnológicos desarrollados en esta línea han aumentado la seguridad
y disminuido la duración del procedimiento. Sin embargo todavía no existe un
tratamiento perfecto para tratar la FA, debido en parte a que el conocimiento de
los mecanismos que inician y sostienen la fibrilación son limitados. Como método
de ablación el aislamiento de las venas pulmonares prevalece como el más empleado
en la práctica, pero se hace necesario el desarrollo de nuevos métodos para hacer
frente al problema de la FA.
Distintas teorías tratan de explicar los mecanismos de inicio y mantenimiento
de la FA, desde unas basadas en la propagación de múltiples frentes de onda aleatorios
en las aurículas, hasta las que basan su hipótesis en focos ectópicos disparados
principalmente desde las venas pulmonares, entre otras teorías. Recientemente,
una de estas teorías basada en fuentes espacio-temporalmente estables (rotores) se
propuso como mecanismo de mantenimiento de la FA. La característica más representativa
de un rotor es su patrón de reentrada en forma de espiral que realiza
el frente de onda eléctrico en el tejido auricular. La evaluación de la presencia de
rotores y la posterior de los sitios en los que se encuentren puede mejorar el éxito
de la ablación en pacientes con FA.
En vista de esta tendencia por la búsqueda de rotores se desarrollaron soluciones
técnicas para la evaluación de zonas que alberguen actividad rotacional.
Sus técnicas se basan en la reconstrucción de la actividad auricular empleando
catéteres multi-electrodo y detectando puntos de singularidad en mapas de phase,
esto es la posición en la aurícula en la que el rotor gira. La ablación de estos puntos
mostró resultados prometedores, pero la dificultad por replicar los resultados
por parte de otros autores incremento la controversia con respecto a esta técnica.
En esta Tesis abordamos el problema de la detección de rotores en el dominio del
tiempo, oponiéndonos a las técnicas actuales basadas en el dominio de la fase de
las señales.
Para ello hemos desarrollado un nuevo para identificar tiempos de activación
local en electrogramas unipolares registrados con catéteres multi-electrodo. Para
ello proponemos un nuevo método de filtrado para realzar la activación del electrograma
reduciendo considerablemente la presencia de ruido en la señal. Con
este procesado de la señal extraemos y reflejamos la actividad real del tejido en
contacto con el electrodo. Al mismo tiempo nos oponemos a la transformada de
Hilbert empleada para calcular la componente de fase de la señal, que es sabido
no tiene una buena correlación con las activaciones temporales. Con los electrogramas
y los tiempos de activación locales aplicamos una interpolación espacial
logrando trasladar la posición de los electrodos en el catéter a una rejilla regular
en 2D. Mediante este paso generamos mapas isócronos que reconstruyen los
frentes de onda eléctricos que se propagan en la aurícula. Además, la interpolación
nos permite garantizar una compatibilidad con otros catéteres multi-electrodos,
no restringiendo el uso de nuestro método a modelos específicos. Con los mapas
isócronos hemos desarrollado un nuevo algoritmo de detección de rotores basado
en el flujo óptico de la dinámica del frente de onda que hacemos coincidir con un
patrón de rotación. Adicionalmente hemos desarrollado un nuevo método basad
en la causalidad propuesta por Granger para estimar la dirección de los frentes de
propagación, que sirve como indicador adicional para encontrar patrones de activación rotacional. Hemos validado todos y cada uno de los métodos empleando
señales in silico así como señales reales de pacientes con FA.
En la parte de aplicación, hemos implementado los métodos en un sistema
que evalúa la presencia de actividad rotacional en la aurícula. Nuestro sistema
opera en tiempo real siendo compatible con catéteres multi-electrodo de diferentes
topologías asegurando contacto con la pared auricular. Para evitar sobreextender
el procedimiento clínico, hemos integrado las partes de adquisición y procesado
de señal conjuntamente, lo que nos permite un registro de las señales directo sin
viii
necesidad de requerir un exportado adicional desde un sistema de registro. Para
hacer frente al objetivo de presentar los resultados en tiempo real hemos diseñado
todos los pasos de procesado de señal para que sean paralelizables. Para ello
empleamos procesadores multinúcleo y código para ejecutar en tarjetas gráficas
(GPUs) para distribuir las computaciones y minimizar el tiempo de procesado,
logrando resultados en quasi tiempo real. Hemos empleado el sistema de detección
de rotores para estudiar la distribución espacial y de voltaje de los sitios que
muestran actividad rotacional en la aurícula. Aunque la presencia de actividad
rotacional es en sí misma controvertida, hemos validad individualmente todos y
cada uno de los pasos descritos obteniendo evidencia de la presencia de actividad
rotacional en pacientes con FA.Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Pablo Laguna Lasaosa.- Secretario: Pablo Martínez Olmos.- Vocal: Batiste Andreu Martínez Climen
Techno-Economic Analysis of Rural 4th Generation Biomass District Heating
Biomass heating networks provide renewable heat using low carbon energy sources.
They can be powerful tools for economy decarbonization. Heating networks can increase heating
efficiency in districts and small size municipalities, using more efficient thermal generation
technologies, with higher efficiencies and with more efficient emissions abatement technologies.
This paper analyzes the application of a biomass fourth generation district heating, 4GDH
(4th Generation Biomass District Heating), in a rural municipality. The heating network is designed
to supply 77 residential buildings and eight public buildings, to replace the current individual diesel
boilers and electrical heating systems. The development of the new fourth district heating generation
implies the challenge of combining using low or very low temperatures in the distribution network
pipes and delivery temperatures in existing facilities buildings. In this work biomass district heating
designs based on third and fourth generation district heating network criteria are evaluated in terms
of design conditions, operating ranges, effect of variable temperature operation, energy efficiency
and investment and operating costs. The Internal Rate of Return of the different options ranges
from 6.55% for a design based on the third generation network to 7.46% for a design based on the
fourth generation network, with a 25 years investment horizon. The results and analyses of this
work show the interest and challenges for the next low temperature DH generation for the rural area
under analysis
Field trials of an improved cost-effective device for detecting peridomestic populations of Triatoma infestans (Hemiptera: Reduviidae) in rural Argentina
An improved device for detecting peridomestic Triatoma infestans consisting of one-liter recycled Tetra Brik milk boxes with a central structure was tested using a matched-pair study design in two rural areas in Argentina. In Olta (La Rioja), the boxes were installed beneath the thatched roofs and on the vertical wooden posts of each peridomestic structure. After a 5-month exposure, at least one of the recovered boxes detected 88% of the 24 T. infestans-positive sites, and 86% of the 7 negative sites by timed manual collections at baseline. In Amamá (Santiago del Estero), the boxes were paired with the best performing prototype tested before (shelter unit). After 3 months, some evidence of infestation was detected in 89% (boxes) and 79% (shelters) of 18-19 sites positive by timed collections, whereas 19% and 16% of 32 negative sites were positive, respectively. Neither device differed significantly in the qualitative or quantitative collection of every sign of infestation. The installation site did not modify significantly the boxes' sampling efficiency in both study areas. As the total cost of each box was half as expensive as each shelter unit, the boxes are thus the most cost-effective and easy-to-use tool for detecting peridomestic T. infestans currently available.Fil: Vazquez Prokopec, Gonzalo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; ArgentinaFil: Ceballos, Leonardo A.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; ArgentinaFil: Salomón, Oscar Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Dirección Nacional de Institutos de Investigación. Administración Nacional de Laboratorios e Institutos de Salud. Centro Nacional de Diagnóstico e Investigaciones Endemo-epidémicas; ArgentinaFil: Gurtler, Ricardo Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentin
The role of sodium phosphate cotransporters in ectopic calcification
Phosphate plays a critical role in many vital cellular processes. Deviations from normal serum phosphate levels, including alterations in the extracellular phosphate/pyrophosphate ratio, can cause severe consequences, such as ectopic calcification. Cellular phosphate levels are tightly controlled by sodium phosphate cotransporters, underscoring their importance in cellular physiology. The role of sodium phosphate cotransporters in ectopic calcification requires further elucidation, taking into account their important role in the control of intracellular phosphate levels and the synthesis of ATP, the main source of extracellular pyrophosphate (a potent endogenous inhibitor of calcification). In this review, we discuss the roles of phosphate and pyrophosphate homeostasis in ectopic calcification, with a specific focus on phosphate transporters. We concentrate on the five known sodium-dependent phosphate transporters and review their localisation and regulation by external factors, and the effects observed in knockout studies and in naturally occurring mutations
Effect of isolation conditions on structural properties and surface behavior of soy-whey proteins
In this study, the impact of isolation conditions on structural and surface properties at the air/water interface of soy-whey proteins (SWP) was assessed. SWP were obtained by precipitation of soy-whey (at pH 4.5 or 8.0) with acetone or ammonium sulfate. Despite the fact that all SWP samples exhibited similar electrophoretic patterns, they showed different protein content (from 54.2 to 98.2% w/w). When precipitation was performed at pH 4.5, SWP samples evidenced a decrease of protein solubility (SP) and thermal stability, while the precipitation with acetone promoted the enrichment in polysaccharides and minerals. For all samples, intrinsic fluorescence, surface hydrophobicity and Fourier transform infrared (FTIR) studies revealed structural changes correlated to protein unfolding and aggregation processes. However, the surface behavior can be predicted from these studies mainly due to differences in surface hydrophobicity and the differential contribution of insoluble aggregates. The heating of SWP samples enhanced the surface activity, regardless of the pH of the raw material and the isolation method. These results can be useful as a reference research and as a starting point for industrial exploitation of proteins from soy wastewater.Fil: Ingrassia, Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Sobral, Pablo Antonio. Universidad Nacional de La Plata. Facultad de Ciencias Exactas; ArgentinaFil: Risso, Patricia Hilda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Palazolo, Gonzalo Gastón. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Investigación en Funcionalidad y Tecnología de Alimentos; ArgentinaFil: Wagner, Jorge Ricardo. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Investigación en Funcionalidad y Tecnología de Alimentos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Purification and biological characterization of halocin H1 from Haloferax mediterranei M2a
The production of halocins, bacteriocin-like proteins of ecological significance, is a frequent characteristic of species from the family Halobacteriaceae. Halocin H1, produced by Haloferax mediterranei strain M2a, is a single 31-kDa polypeptide. Its purification was achieved by combining two chromatographic systems: Sepharose 4B linked to bacitracin followed by hydroxylapatite Bio-gel HTP. Halocin H1 required concentrations of NaCl higher than 1.5 M to maintain its activity. Haoarchaeal strains showed a differential degree of sensitivity to the action of this halocin
- …