6,542 research outputs found
Native state of natural proteins optimizes local entropy
The differing ability of polypeptide conformations to act as the native state of proteins has long been rationalized in terms of differing kinetic accessibility or thermodynamic stability. Building on the successful applications of physical concepts and sampling algorithms recently introduced in the study of disordered systems, in particular artificial neural networks, we quantitatively explore how well a quantity known as the local entropy describes the native state of model proteins. In lattice models and all-atom representations of proteins, we are able to efficiently sample high local entropy states and to provide a proof of concept of enhanced stability and folding rate. Our methods are based on simple and general statistical-mechanics arguments, and thus we expect that they are of very general use
From Display to Labelled Proofs for Tense Logics
We introduce an effective translation from proofs in the display calculus to proofs in the labelled calculus in the context of tense logics. We identify the labelled calculus proofs in the image of this translation as those built from labelled sequents whose underlying directed graph possesses certain properties. For the basic normal tense logic Kt, the image is shown to be the set of all proofs in the labelled calculus G3Kt
Asymmetrical copper root pruning may improve root traits for reforesting steep and/or windy sites
Our research demonstrates that plant material can be produced in the nursery with asymmetrical root systems, which may have utility for reforestation of difficult planting sites characterized by steep slopes and/or windy conditions. Such a root system can be generated using chemical root pruning by applying cupric carbonate (Cu) that can arrest the development of, or cause mortality to, root apical meristems resulting in the formation of new lateral roots with an overall increase in the biomass, length, and volume of the root system. Our objective was to investigate the effect of chemical root pruning on the morphological and architectural traits of adventitious roots produced by poplar cuttings (Populus nigra L.) grown in containers coated with Cu in various symmetrical (Side, Bottom, Side + Bottom) and asymmetrical (half side + half bottom) patterns. After six weeks, roots of the cuttings were extracted from different container depths (Top, Middle, and Bottom) and portions (non-coated, Cu-coated), and analyzed. The root systems reacted to all coating patterns by increasing length, biomass, volume, and average diameters, but magnitude of increase was further affected by depth. In particular, root growth was unaffected at the Top of the container, and length was the highest at the Bottom depth. The Middle depth had a significant increment in both biomass and volume. Also, the root population increased in diameter as a possible response to Cu exposure. Interestingly, in the asymmetrically coated containers this depth response in the non-coated portions was of higher magnitude than in the Cu-coated portions
Electricity from Wood: A Wood Quality and Energy Efficiency Approach to Small Scale Pyro-gasification
AbstractThe global demand for renewable energy in the last years is facing innovations like the co-generation of electricity and heat from wooden industrial residues and biomass. Wood gasification is a very promising technique for conversion of wood chemical energy into thermal energy and into electricity. A new generation of small scale, moderately priced and easy to install pyro-gasification plants became available on the market, being an opportunity for the SMEs. These systems are also characterized by a remarkable operational easiness and great versatility in the type of used biomass, which can range from industrial residues (sawdust, wood chips...) to biomass of forestry and non-forestry origin. This study performed an extensive testing of a small size pyro-gasification plant capable of producing 30kW of electricity and 30kW of thermal energy, both net to enter in the network of GSE (Energy Services Manager) via the feed-in tariff and in a small district heating network or other uses. The process of pyro-gasification is analyzed in its entirety by a characterization of input biomass, pyro-gasification process monitoring, analysis of the quality of the produced syngas, characterization of residues due to the process (washing water smoke, charcoal...) and verification of the total efficiency. The electric efficiency of the system, from hardwood to syngas to electricity is quantified in being 12%
Integrated stratigraphy and astrochronology of the Messinian GSSP at Oued Akrech (Atlantic Morocco)
A much improved high-resolution integrated stratigraphy (calcareous plankton biostratigraphy, magnetostratigraphy,
cyclostratigraphy) is presented for the classic section of Oued Akrech (Atlantic Morocco) straddling the
Tortonian^Messinian boundary. Magnetobiostratigraphic correlations with time-equivalent and astronomically dated
sections in the Mediterranean indicate that cyclic alternations of indurated light beige coloured marls and softer, more
clayey and reddish coloured marls are dominantly precession-controlled. Characteristic sedimentary cycle patterns, in
particular those reflecting precession^obliquity interference, allow for one possible tuning, thus providing accurate
astronomical ages for cycles, calcareous plankton events and magnetic reversals. The tuning further indicates that the
reddish layers are the equivalent of sapropels in the Mediterranean. The Messinian Global boundary Stratotype Section
and Point (GSSP) has recently been formally defined at the base of the reddish layer of cycle No. 15 in section Oued
Akrech. This level coincides closely with the first regular occurrence of the Globorotalia miotumida group and is
astronomically dated at 7.251 Ma. The global correlation potential is guaranteed by the straightforward calibration of
the Oued Akrech magnetostratigraphy to the geomagnetic polarity time scale, locating the GSSP within C3Br.1r. In the
marine realm the calcareous nannofossil genus Amaurolithus provides a series of extremely useful events to delimit the
boundary on a global scale. The astronomical tuning guarantees a direct first-order calibration of the Messinian GSSP
to the standard geological time scale once, as anticipated, the late Miocene part of the astronomical time scale has been
incorporated
Region-Based Classification of PolSAR Data Using Radial Basis Kernel Functions With Stochastic Distances
Region-based classification of PolSAR data can be effectively performed by
seeking for the assignment that minimizes a distance between prototypes and
segments. Silva et al (2013) used stochastic distances between complex
multivariate Wishart models which, differently from other measures, are
computationally tractable. In this work we assess the robustness of such
approach with respect to errors in the training stage, and propose an extension
that alleviates such problems. We introduce robustness in the process by
incorporating a combination of radial basis kernel functions and stochastic
distances with Support Vector Machines (SVM). We consider several stochastic
distances between Wishart: Bhatacharyya, Kullback-Leibler, Chi-Square,
R\'{e}nyi, and Hellinger. We perform two case studies with PolSAR images, both
simulated and from actual sensors, and different classification scenarios to
compare the performance of Minimum Distance and SVM classification frameworks.
With this, we model the situation of imperfect training samples. We show that
SVM with the proposed kernel functions achieves better performance with respect
to Minimum Distance, at the expense of more computational resources and the
need of parameter tuning. Code and data are provided for reproducibility.Comment: Accepted for publication in the International Journal of Digital
Eart
Genetic diversity and introgression by AFLP analisys in Phaseolus vulgaris L.
Phaseolus vulgaris L. is an economically important species whose origin is in the America continent where domestication took place and diverged in Mesoamerican and Andean gene pools.
After Columbus’s voyage common bean was introduced into the Iberian Peninsula from which this species spread into the European countries and around the world. In this study investigate the extent of diversity of European germplasm compared to the American germplasm and to define the level
of introgression between the European Mesoamerican and Andean gene pools are investigated. 68 accessions representative of Mesoamerican and Andean American gene pools and 241 accessions from 24 different countries belonging to an European bean core collection were analysed for three
morphologic quantitative (length, height and width ) and 4 qualitative (shape, lighter colour, darker colour and coat pattern of seed) seed characters and for 4 AFLP primer combinations: E-AGT/MGAC, E-AGT/M-GTA, E-ACC/M-AGA and E-ACC/M-ATG. A total of 138 polymorphic bands were scored among the 309 accessions analysed.
The European and the Mesoamerican gene pools had a number of common and very common AFLP polymorphic bands higher than the American and the Andean gene pools. The European
accessions moreover were used for Structure and cpSSR analysis to identify pure and introgressed lines. These groups were compared for morphological traits and AFLP profiles. Results showed significative differences among diverse groups for morphological traits and for AFLP band frequencies, even though the diversity index were the same (He = 0.23).
Hypothesis of introgression among American and European, Mesoamerican and Andean gene pools are discussed
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