1,721,190 research outputs found
Numerical Stochastic Perturbation Theory around instantons
No full textNumerical Stochastic Perturbation Theory (NSPT) has over the years proved to be a valuable tool, in particular being able to reach unprecedented orders for Lattice Gauge Theories, whose perturbative expansions are notoriously cumbersome. One of the key features of the method is the possibility to expand around non-trivial vacua. While this idea has been around for a while, and it has been implemented in the case of the (non-trivial) background of the Schrödinger functional, NSPT expansions around instantons have not yet been fully worked out. Here we present computations for the double well potential in quantum mechanics. We compute a few orders of the expansion of the ground-state energy splitting in the one-instanton sector. We discuss how (already) known two-loop results are reproduced and present the current status of higher-order computations
Taming NSPT fluctuations in O(N) Non-Linear Sigma Model: simulations in the large N regime
No full textThe Non-Linear Sigma Model (NLSM) is an example of a field theory on a target space exhibiting intricate geometry. One remarkable characteristic of the NLSM is asymptotic freedom, which triggers interest in perturbative calculations. In the lattice formulation of NLSM, one would naturally rely on Numerical Stochastic Perturbation Theory (NSPT) to conduct high-order computations. However, when dealing with low-dimensional systems, NSPT reveals increasing statistical fluctuations with higher and higher orders. This of course does not come as a surprise and one is ready to live with this, as long as the noise is not going to completely kill the signal, which unfortunately in some models does take place. We investigate how, in the O(N) context, this behaviour strongly depends on N. As expected, larger N values make higher-order computations feasible
NSPT for O(N) non-linear sigma model: the larger N the better
No full textThe O(N) non-linear sigma model (NLSM) is an example of field theory on a target space with nontrivial geometry. One interesting feature of NLSM is asymptotic freedom, which makes perturbative calculations interesting. Given the successes in Lattice Gauge Theories, Numerical Stochastic Perturbation Theory (NSPT) is a natural candidate for performing high-order computations also in the case of NLSM. However, in low-dimensional systems NSPT is known to display statistical fluctuations substantially increasing for increasing orders. In this work, we explore how for O(N) NLSM this behaviour is strongly dependent on N. As largely expected on general grounds, the larger is N, the larger is the order at which a NSPT computation can be effectively performed
Espressione batterica di un gene artificiale per la produzione di CRM197 e derivati
No full textLa presente invenzione si riferisce al campo della produzione di proteine d’interesse farmacologico mediante sequenze geniche artificiali, dette sequenze inserite in vettori d’espressione, sovraespressione delle corrispondenti proteine in microorganismi trasformati con detti vettori d’espressione e metodo di isolamento delle proteine espresse; in particolare si riferisce alla costruzione di un gene artificiale codificante il CRM197 intero e i suoi derivati, all’ espressione di CRM197 e dei suoi derivati in Escherichia coli e ad un metodo di isolamento e purificazione della proteina CRM197
Living polynucleotides formed by the spontaneous aggregation of dilauroylphosphonucleosides
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Proteome analysis of Escherichia coli W3110 expressing an heterologous sigma factor
No full textThe recombinant plasmid pASK18 carries a Streptomyces DNA fragment which includes an open reading frame, designated psfS (putative sigma factor, Streptomyces), as its putative product showed a high degree of similarity with RNA polymerase sigma factors. Previous results showed that PsfS causes transcription initiation within the bgl operon promoter-silencer region in Escherichia coli K12. In this study a proteomic approach has been applied in order to perform a comparative analysis of E. coli K12 W3110 wild-type, W3110 (pASK18) and a W3110 Bgl+ spontaneous mutant. Either by qualitative or quantitative analysis, no significant difference was observed between the proteomes of W3110 and its Bgl+ derivative, while W3110 (pASK18) showed an altered profile by both analyses. Fourteen out of the 37 protein spots showing a different expression level in E. coli W3110 harboring pASK18 were identified by peptide mass fingerprinting. Among the proteins identified, thiol peroxidase (Tpx) was the only one up-regulated. The possible involvement of bgl and tpx in the survival of the pathogen E. coli during infection is discussed
On the Surface Properties of Waterborne Fluorinated Coating Polymers
No full textIn the present work the results of a study concerning the surface properties of coating materials obtained from fluorinated latices are reported. Better understanding is required regarding the influence of polymer structure, latex composition, and morphology on the surface properties of the resulting films. For this purpose, two commercial fluorinated waterborne polymer dispersions were compared with a model fluorinated acrylic latex purposely synthesized. The surface properties of mold samples, prepared from either the whole solid matter contained in the latices (dried latex) or the purified polymer, were determined by simple contract angle measurements. Two series of homologous liquids, namely H-bonding alcohols and apolar hydrocarbons, were employed for determining the critical surface tension gamma(c) according to the method of Zisman. The results of the surface characterization indicate that the degree of fluorination plays a minor role in these materials, suggesting that the threshold above which the polymer surface is virtually saturated by CF2 or CF3 groups might have been largely exceeded. On the other hand, the effectiveness of the hydrophobic fluorinated coating resulted substantially unaffected by the presence of amphiphilic low molecular weight additives, such as surfactants and wetting agents, which can actually contribute to the reduction of the surface energy of these materials upon suitable thermal treatment
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