2,679 research outputs found
Thermal evolution of hybrid stars within the framework of a nonlocal Nambu--Jona-Lasinio model
We study the thermal evolution of neutron stars containing deconfined quark
matter in their core. Such objects are generally referred to as quark-hybrid
stars. The confined hadronic matter in their core is described in the framework
of non-linear relativistic nuclear field theory. For the quark phase we use a
non-local extension of the SU(3) Nambu Jona-Lasinio model with vector
interactions. The Gibbs condition is used to model phase equilibrium between
confined hadronic matter and deconfined quark matter. Our study indicates that
high-mass neutron stars may contain between 35 and 40 % deconfined quark-hybrid
matter in their cores. Neutron stars with canonical masses of around would not contain deconfined quark matter. The central proton
fractions of the stars are found to be high, enabling them to cool rapidly.
Very good agreement with the temperature evolution established for the neutron
star in Cassiopeia A (Cas A) is obtained for one of our models (based on the
popular NL3 nuclear parametrization), if the protons in the core of our stellar
models are strongly paired, the repulsion among the quarks is mildly repulsive,
and the mass of Cas A has a canonical value of .Comment: 10 pages, 7 figure
Push-Over Analysis of RC Frame with Corroded Rebar
As known, the Italian building heritage largely consists of reinforced concrete frames designed before the '80s, which are, in many cases, built in the absence of specific anti-seismic criteria. Moreover, many of them, today, are characterized by bad structural conditions. Moreover, the problem of the structural conditions of the existing buildings, and their residual strength capacity, is often linked to the deterioration induced by the corrosive phenomena, which end up having a big impact on steel rebar mechanical properties. In this work, in order to investigate the influence of corrosion-damage on seismic response of existing reinforced concrete structures, a study has been carried out by analysing the non-linear behaviour of a reinforced concrete frame. The strength deterioration and reduction of the cross-section of steel rebar have been investigated and taken into account in the numerical analysis. This work shows the way in which the corrosion levels affected the push-over response, and the numerical results have been deeply analysed
Improvement of interation in and properties of PMMA-MWNT nanocomposites through microwave assisted acid treatment of MWNT
Soluble derivatives of multi-walled carbon nanotubes (MWNT) embedded in a poly(methylmethacrylate) (PMMA) matrix forming thick, homogeneous and transparent nanocomposites, were prepared and characterized. A new photo-assisted method using microwaves, to purify the MWNTs from amorphous carbon and synthesis catalyst clusters, was tested in a sulphonitric mix. This method shortened the processing time compared to other methods. Pristine and functionalized MWNTs were introduced into the MMA, then in situ photo-polymerized. Transmission electron microscopy (TEM) and X-ray diffractometry (XRD), as well as Fourier-transform infrared (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy were used to monitor the effects of the treatment on the different components. The thermal properties of the composites were determined through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The short, microwave treated and polyethylene glycol (PEG) functionalized MWNTs showed the best dispersion in and interaction with PMMA, and had the most significant influence on the thermal properties of this polymer
Increasing the Capacity of Existing Bridges by Using Unbonded Prestressing Technology: A Case Study
External posttensioning or unbonded prestressing was found to be a powerful tool for retrofitting and for increasing the life
extension of existing structures. Since the 1950s, this technique of reinforcement was applied with success to bridge structures
in many countries, and was found to provide an efficient and economic solution for a wide range of bridge types and conditions.
Unbonded prestressing is defined as a system in which the post-tensioning tendons or bars are located outside the concrete crosssection
and the prestressing forces are transmitted to the girder through the end anchorages, deviators, or saddles. In response to
the demand for a faster and more efficient transportation system, there was a steady increase in the weight and volume of traffic
throughout the world. Besides increases in legal vehicle loads, the overloading of vehicles is a common problem and it must also
be considered when designing or assessing bridges. As a result, many bridges are now required to carry loads significantly greater
than their original design loads; and their deck results still deteriorated by cracking of concrete, corrosion of rebars, snapping of
tendons, and so forth. In the following, a case study about a railway bridge retrofitted by external posttensioning technique will be
illustrated
Macro-micro relationship in nanostructured functional composites
This paper examines the results of the characterization of two functional composites: Poly(methyl methacrylate)
(PMMA)-Ce:YAG (yttrium aluminium garnet doped with cerium) and PMMA-cobalt hexacyanoferrate (CoHCF). The
composites were prepared as possible emitters in the fields of lighting thermal sensors. The prepared composites were characterized
using transmission electron microscopy (TEM), nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric
analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) analyses to study
the correlation between micro and macro characteristics. We found that the molecular interactions of the two different
fillers with the matrix were localized in different sites of the polymer chains. Moreover, the composites showed an
increased thermal strength and stiffness, in particular the PMMA-Ce:YAG composite
Frontal Polymerization and Geopolymerization, the First Example: Organic-Inorganic Hybrid Materials
This work shows the first example of frontal geopolymerization, obtained in the same reactor in which the frontal polymerization of 1,6 hexanediolodiaacrylate occurs at the same time; the simultaneous frontal polymerization allows to obtain an organic-inorganic hybrid material in a single step and in a short time (a few minutes), thanks to the exothermicity of the two reactions which are mutually self-supporting. This technique represents the only way to obtain hybrid organic polymer-geopolymer mate-rials: using the classical polymerization (prolonged heating) the reaction is explosive due to the formation of gaseous products, while the polymerization at room temperature, due to the very long times, leads to a phase separation
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