69 research outputs found
Non-Markovian polymer reaction kinetics
Describing the kinetics of polymer reactions, such as the formation of loops
and hairpins in nucleic acids or polypeptides, is complicated by the structural
dynamics of their chains. Although both intramolecular reactions, such as
cyclization, and intermolecular reactions have been studied extensively, both
experimentally and theoretically, there is to date no exact explicit analytical
treatment of transport-limited polymer reaction kinetics, even in the case of
the simplest (Rouse) model of monomers connected by linear springs. We
introduce a new analytical approach to calculate the mean reaction time of
polymer reactions that encompasses the non-Markovian dynamics of monomer
motion. This requires that the conformational statistics of the polymer at the
very instant of reaction be determined, which provides, as a by-product, new
information on the reaction path. We show that the typical reactive
conformation of the polymer is more extended than the equilibrium conformation,
which leads to reaction times significantly shorter than predicted by the
existing classical Markovian theory.Comment: Main text (7 pages, 5 figures) + Supplemantary Information (13 pages,
2 figures
Theory and design of InGaAsBi mid-infrared semiconductor lasers: type-I quantum wells for emission beyond 3 m on InP substrates
We present a theoretical analysis and optimisation of the properties and
performance of mid-infrared semiconductor lasers based on the dilute bismide
alloy InGaAsBi, grown on conventional (001) InP
substrates. The ability to independently vary the epitaxial strain and emission
wavelength in this quaternary alloy provides significant scope for band
structure engineering. Our calculations demonstrate that structures based on
compressively strained InGaAsBi quantum wells (QWs)
can readily achieve emission wavelengths in the 3 -- 5 m range, and that
these QWs have large type-I band offsets. As such, these structures have the
potential to overcome a number of limitations commonly associated with this
application-rich but technologically challenging wavelength range. By
considering structures having (i) fixed QW thickness and variable strain, and
(ii) fixed strain and variable QW thickness, we quantify key trends in the
properties and performance as functions of the alloy composition, structural
properties, and emission wavelength, and on this basis identify routes towards
the realisation of optimised devices for practical applications. Our analysis
suggests that simple laser structures -- incorporating
InGaAsBi QWs and unstrained ternary
InGaAs barriers -- which are compatible with established
epitaxial growth, provide a route to realising InP-based mid-infrared diode
lasers.Comment: Submitted versio
Bacterial lipopolysaccharide stimulates the thyrotropin-dependent thyroglobulin gene expression at the transcriptional level by involving the transcription factors thyroid transcription factor-1 and paired box domain transcription factor 8
16 pages, 11 figures.The bacterial lipopolysaccharide (LPS) is a biological activator that induces expression of multiple genes in several cell types. LPS has been proposed as an etiopathogenic agent in autoimmune diseases. However, whether LPS affects the expression of autoantigens has not been explored. Thyroglobulin (TG) is a key protein in thyroid hormonogenesis and one of the major thyroid autoantigens. This study aimed to analyze the action of LPS on TG gene expression in Fisher rat thyroid cell line FRTL-5 thyroid cells. We demonstrate that LPS increases the TSH-induced TG protein and mRNA level. Evidence that the effect of LPS is exerted at the transcriptional level was obtained by transfecting the minimal TG promoter. The C element of the TG promoter, which contains sequences for paired box domain transcription factor 8 (Pax8) and thyroid transcription factor (TTF)-1 binding, is essential for full TG promoter expression under TSH stimulation. The transcriptional activity of a construct containing five tandem repeats of the C site is increased by LPS, indicating a possible involvement of the C site in the LPS-induced TG gene transcription. We demonstrate that the TG promoter mutated at the Pax8 or TTF-1 binding element in the C site does not respond to LPS. In band shift assays, binding of Pax8 and TTF-1 to the C site is increased by LPS. The Pax8 and TTF-1 mRNA and protein levels are augmented by LPS. The half-lives of TG, Pax8, and TTF-1 are increased in endotoxin-treated cells. Our results reveal the ability of LPS to stimulate the expression of TG, a finding of potential pathophysiological implication.This work was supported by the Consejo Nacional de Investigaciones
Científicas y Técnicas, by the Secretaría de Ciencia y Tecnología de la
Universidad Nacional de Córdoba, by the Agencia Córdoba Ciencia, by
the Agencia Nacional de Promoción Científica y Tecnológica (Argentina),
by Ministerio de Educación y Ciencia, Grant Biología Fundamental
2004-03169, and by Fondo de Investigaciones Sanitarias of the Instituto
de Salud Carlos III, Grant RCMN-C03/08 (Spain).Peer reviewe
Influence of topographical features on the surface appearance measurement of injection moulded components
Adding textures to surfaces is known to improve the external appearance of injection moulded components. However, when high surface quality is required, normally a paint coating is applied on top of the moulded textured surface. In this work, an alternative to painting for obtaining high quality surfaces is proposed, following an environmental-friendly process and having low production cost. Three different surface textures obtained by injection moulding have been characterized and compared with a painted one. Alternative topographical parameters such as the absolute functional height (AFH), the functional height distribution (FHD), texture slope (TS) or texture aperture angle (TAA) besides to the traditional roughness parameters such as the arithmetical mean height (Sa) and the root mean square height (Sq) have been utilized to characterize the random surface textures. The relationships between these parameters and the surface quality appearance represented by gloss and reflectivity contrast have been established using a new total appearance measurement (TAM) apparatus. It was found that by applying secondary operation on the textured mould cavity, such as adding micro roughness features or coatings, equal apparent quality to the ones obtained by painting can be reached
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