840 research outputs found
Self-assembly and DNA binding of the blocking factor in X chromosome inactivation
No full textX chromosome inactivation (XCI) is the phenomenon occurring in female mammals whereby dosage compensation of
X-linked genes is obtained by transcriptional silencing of one of their two X chromosomes, randomly chosen during
early embryo development. The earliest steps of random X-inactivation, involving counting of the X chromosomes and
choice of the active and inactive X, are still not understood. To explain "counting and choice," the longstanding
hypothesis is that a molecular complex, a "blocking factor" (BF), exists. The BF is present in a single copy and can
randomly bind to just one X per cell which is protected from inactivation, as the second X is inactivated by default. In
such a picture, the missing crucial step is to explain how the molecular complex is self-assembled, why only one is
formed, and how it binds only one X. We answer these questions within the framework of a schematic Statistical
Physics model, investigated by Monte Carlo computer simulations. We show that a single complex is assembled as a
result of a thermodynamic process relying on a phase transition occurring in the system which spontaneously breaks
the symmetry between the X’s. We discuss, then, the BF interaction with X chromosomes. The thermodynamics of the
mechanism that directs the two chromosomes to opposite fates could be, thus, clarified. The insights on the selfassembling
and X binding properties of the BF are used to derive a quantitative scenario of biological implications
describing current experimental evidences on "counting and choice.
Analisi dinamiche non lineari a supporto della valutazione della vulnerabilità e delle ipotesi di intervento di miglioramento sismico dei Laboratori del Polo Scientifico-Tecnologico di Ferrara
No full textLa memoria riporta i principali risultati delle analisi condotte su due edifici dell’Università di Ferrara aventi struttura prefabbricata in c.a. Con riferimento ai valori di progetto delle proprietà dei materiali, il coefficiente di sicurezza ottenuto per i laboratori di Ingegneria da analisi in campo elastico lineare è pari a 0.53. Per il laboratorio di Fisica il coefficiente risulta 0.57 se si tiene conto di massa e rigidezza dei pannelli di tamponamento, ma si riduce a 0.42 trascurando tale contributo. La vulnerabilità è associata a modalità di collasso dei pilastri per pressoflessione. Gli interventi di miglioramento sismico analizzati con modelli lineari sono stati validati per mezzo di analisi dinamiche non lineari che fanno uso di formulazioni a plasticità diffusa. La modellazione in campo non lineare si dimostra un importante strumento per la definizione degli interventi su edifici prefabbricati non progettati per resistere alle azioni sismiche
Localizzazione istochimica di mucosostanze nell'apparato digerente di Oncorhynchus mykiss. Tecniche di allevamento ecocompatibile
No full textSearching for additional functions of fish hemoglobins: evidence of multiple quaternary structures and exogeneous coordination states
No full textAll fish hemoglobins (Hb) show a high auto-oxidation rate, and some fish Hbs are endowed with Root effect (drastic drop of cooperativity at acidic pH). Differently from temperate fish Hbs, at physiological pH Antarctic fish Hbs (AFHbs) in the ferric state show both an aquomet form and two distinct hemichromes within a R / T intermediate quaternary structure (1). Interestingly, AFHbs exhibit a peroxidase activity higher than that observed for mammalian and temperate fish Hbs, thus suggesting that a partial hemichrome state in tetrameric Hbs does not protect them from peroxidation as previously proposed (2). At acidic pH, a combined EPR / x-ray crystallography approach has revealed, only for Root-effect AFHbs, significant amount of pentacoordinated (5C) high-spin Fe(III) species.(3) Furthermore, along the oxidation pathway, a combined x-ray crystallography / Resonance Raman spectroscopy of AFHbs has revealed a hybrid valence state [α(O2)/β(Fe3+, pentacoordinate)].(4) This valence hybrid states prompted us to test a FeSOD activity, that is as low as human Hb. A combined x-ray crystallography / FT-IR study has revealed at least two coordination states of the carbomonoxy form of AFHbs, one corresponding to a His assisted CO binding (band III at 1951 cm-1), and another to a not-His assisted CO binding (band IV at 1968 cm-1). The band IV, typical of both temperate fish (carp and trout) Hbs and AFHbs, assigned to the second CO coordination state, justifies the high auto-oxidation rate of fish Hbs. Furthermore, this novel CO coordination in AFHb occurs within a R-T intermediate quaternary structure. These findings provide an alternative structural explanation of the Root effect, in terms of a three state model .(5) This work was financially supported by PNRA (Italian National Programme for Antarctic Research) 1. Vergara, A., Franzese, M., Merlino, A., Vitagliano, L., di Prisco, G., Verde, C., Lee, H. C., Peisach, J., and Mazzarella, L. (2007) Biophys. J. 93, 2822-2829 2. Feng, L., Zhou, S., Gu, L., Gell, D., Mackay, J., Weiss, M., Gow, A., and Shi, Y. (2005) Nature 435, 697-701 3. Vergara, A., Franzese, M., Merlino, A., Bonomi, G., Verde, C., di Prisco, G., Lee, H., Peisach, J., and Mazzarella, L. . submitted. 4. Vitagliano, L., Vergara, A., Bonomi, G., Merlino, A., Smulevich, G., Howes, B., di Prisco, G., Verde, C., and Mazzarella, L., submitted. 5. Edelstein, S. J. (1996) J. Mol. Biol. 256, 737-74
A new FRC solution for a partially prefabricated industrial deck
No full textA new prefabricated deck is introduced in an industrial building to propose a viable alternative to the
classical TT deck with a R/C top slab cast in place. The solution is characterized by a bearing capacity
of 10 kN/m2, a main span of 14 m or more, an adjustable spacing in the orthogonal direction, FRC
plates simply supported on the prestressed beams used as predalles, 4 cm thick, and a FRC top slab
cast-in-place, 8 cm thick designed according to a continuous slab resting on the simply-supported
beams. The proposed deck is a structural solution that tries to fit different issues like construction
speed, transport cost reduction, structural optimization, high fire resistance (R120) and quality
performance. All elements are made from SFRC with varying amounts of steel fibres. This paper
firstly presents the concept of linearization to adequately select the necessary amount of fibres for the
concrete mixtures used to cast the beams, predalles and top slab. Secondly, the results of the structural
tests on four beams and two predalles are presented. The current design issues are highlighted and the
validity of MC2010 equations in the case of multi-phase casting is verified. Two specific design
situations for the precast beams are investigated: the shear behaviour at the support, where shear
reinforcement is provided and prestressing action is only partially active, and far from the support,
where only fibres are active, but the prestressing action is fully diffused and the web area is reduced
due to holes allowing the passage of ducts and channels. Finally, a study is performed of the structural
response of the composite system consisting of beams, predalles and a top slab cast-in-place
Curve empiriche di vulnerabilità per gli edifici prefabbricati colpiti dai terremoti emiliani del 2012
No full textLa sequenza sismica emiliana del 2012 ha investito un’area fortemente industrializzata comprendente alcune migliaia di edifici prefabbricati in c.a. A causa della mancanza di una specifica progettazione nei confronti delle azioni simiche, molti di tali edifici hanno riportato gravi danni. Lo studio riguarda un inventario preliminare dei danni riportati da 1133 edifici. L’entità dei danni è stata messa in relazione con la distanza epicentrale e la Pseudo-Accelerazione Spettrale (PSA) corrispondente al periodo di 1 s. In particolare, il 90% degli edifici gravemente danneggiati presenta distanza epicentrale inferiore a 14 km e ha risentito di una PSA maggiore di 0.13g. È poi significativo osservare come per il 10% degli edifici senza danni la distanza epicentrale risulti inferiore a 9 km e la massima PSA risentita sia superiore a 0.21g
A sectional approach for the bending creep of FRC based on uniaxial tension creep tests
No full textThe creep behavior of FRC elements remains an important obstacle to use FRC in structural applications. Owing to the residual post-cracking strength properties of FRC, creep deformations play an important role in the cracked sections and influence durability and SLS requirements of structural elements. Therefore, it is of high importance to take creep deformations into account in the design phase. In this paper, the results of an experimental campaign involving both bending tests and uniaxial tensile creep tests on polymeric FRC are presented. In the bending tests, a notched FRC beam is subjected to loading-unloading cycles while the deformations over the cracked section were recorded. The uniaxial tensile creep tests were performed on precracked FRC samples to quantify time-dependent crack growth. The bending behavior of FRC can be accurately predicted by the uniaxial constitutive model of Model Code 2010 in the loading phase assuming a plane section approach. For the unloading phases, a bilinear deformation distribution is assumed and a scalar damage evolution function is fitted by an inverse analysis algorithm. The results of the sectional analysis compared favorably with the experimentally observed data. Finally, a sectional analysis approach is developed and presented in which bending creep deformations are calculated using the uniaxial creep compliances. The initial stress and deformation distribution in the cracked section is predicted by the inverse analysis. The results show that the bending creep deformations of FRC can be quite large, and creep coefficients as high at 7 are observed within 120 days. However, it should be noted that the creep algorithm does not (yet) take into account additional cracking in time, and as such, the predicted creep deformations are a lower limit of what can be expected in reality. More research is needed to upgrade the algorithm to allow predictions including the time-dependent cracking behavior
La giustizia ambientale in Italia. Una riflessione introduttiva
No full textLa giustizia ambientale è un concetto non ancora del tutto condiviso in letteratura, nonostante una storia non proprio recente. L’indeterminatezza si deve probabilmente al fatto che esso si compone di altri concetti già complessi, come giustizia (sociale) e ambiente, per cui la possibilità di farne un principio ispiratore dell’agenda e della pratica politica dipende da come si sceglie di definirlo. Il contributo ha l’obiettivo di introdurre la discussione sulla utilità dello studio della giustizia ambientale in Italia nella convinzione che, pur con modalità diverse rispetto agli Stati Uniti, esso possa essere estremamente fruttuoso. Una sua migliore comprensione ed una verifica di contesto nel caso italiano potrebbero infatti contribuire sia allo sforzo complessivo di ridefinire il quadro teorico nel quale iscrivere il rapporto società/ambiente, di cui si sente il bisogno, in particolare in geografia, sia nel determinare l’evoluzione degli orientamenti politici e operativi
A multi-scale finite element analysis and sectional design approach for the creep of polymeric frc
No full textThis paper presents the experimental, numerical and analytical results of a multi-scale investigation into the uniaxial tensile creep behavior of polymeric fiber reinforced concrete (FRC). In an extensive experimental program, the short-term and creep behavior of individual fibers, the fiber-matrix interface and the composite material are investigated. The short-term and creep properties are used to calibrate the material models of a finite element model with discrete fibers, which allows to determine the creep of polymeric FRC under tensile loading. A Monte-Carlo analysis is performed to assess the influence of the fiber dispersion and sustained load level on the time-dependent crack widening. Finally, the numerical results are used in a sectional approach that allows to translate the uniaxial tensile creep behavior into a flexural creep prediction. The proposed methodology can be readily implemented into design codes, to allow for the creep deformation of cracked FRC to be taken into account
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