Energy dissipation and equivalent damping of RC columns subjected to biaxial bending: an investigation based in experimental results

The cyclic behaviour of reinforced concrete columns have been object of many experimental studies in the recent past years. However, the experimental studies on the biaxial response of RC columns are still limited. In this paper are presented the main results of an experimental study of 24 full-scale rectangular building columns tested for different loading paths under uniaxial and biaxial conditions. The experimental results are presented and discussed in terms of global behaviour, particularly focusing on the stiffness and strength degradation due to the increasing cyclic demand, and energy dissipation evolution. The equivalent viscous damping was estimated based on the experimental results of the RC columns tested under biaxial loading and empirical expressions are proposed

Quark-hybrid matter in the cores of massive neutron stars

Using a nonlocal extension of the SU(3) Nambu-Jona Lasinio model, which reproduces several of the key features of Quantum Chromodynamics, we show that mixed phases of deconfined quarks and confined hadrons (quark-hybrid matter) may exist in the cores of neutron stars as massive as around 2.1 M_Sun. The radii of these objects are found to be in the canonical range of $\sim 12-13$ km. According to our study, the transition to pure quark matter does not occur in stable neutron stars, but is shifted to neutron stars which are unstable against radial oscillations. The implications of our study for the recently discovered, massive neutron star PSR J1614-2230, whose gravitational mass is $1.97 \pm 0.04 M_Sun$, are that this neutron star may contain an extended region of quark-hybrid matter at it center, but no pure quark matter.Comment: 13 pages, 3 figure

Quark deconfinement in high-mass neutron stars

In this paper, we explore whether or not quark deconfinement may occur in high-mass neutron stars such as J1614-2230 (1.97 \pm 0.04 M_Sun) and J0348+0432 (2.01 \pm 0.04 M_Sun). Our study is based on a non-local extension of the SU(3) Nambu Jona-Lasinio (n3NJL) model with repulsive vector interactions among the quarks. This model goes beyond the frequently used local version of the Nambu Jona-Lasinio (NJL) model by accounting for several key features of QCD which are not part of the local model. Confined hadronic matter is treated in the framework of non-linear relativistic mean field theory. We find that both the local as well as the non-local NJL model predict the existence of extended regions of mixed quark-hadron (quark-hybrid) matter in high-mass neutron stars with masses of 2.1 to 2.4 M_Sun. Pure quark matter in the cores of neutron stars is obtained for certain parametrizations of the hadronic lagrangian and choices of the vector repulsion among quarks. The radii of high-mass neutron stars with quark-hybrid matter and/or pure quark matter cores in their centers are found to lie in the canonical range of 12 to 13 km.Comment: 31 pages, 17 figures, PRC accepted versio

Correlating the interstellar magnetic field with protostellar jets and its sources

This article combines new CCD polarimetric data with previous information about protostellar objects in a search for correlations involving the interstellar magnetic field. Specifically, we carried out an optical polarimetric study of a sample of 28 fields of 10 X 10 arcmin^2 located in the neighborhood of protostellar jets and randomly spread over the Galaxy. The polarimetry of a large number of field stars is used to estimate both the average and dispersion of the interstellar magnetic field (ISMF) direction in each region. The results of the applied statistical tests are as follows. Concerning the alignment between the jet direction and the interstellar magnetic field, the whole sample does not show alignment. There is, however, a statistically significant alignment for objects of Classes 0 and I. Regarding the interstellar magnetic field dispersion, our sample presents values slightly larger for regions containing T Tauri objects than for those harboring younger protostars. Moreover the ISMF dispersion in regions containing high-mass objects tends to be larger than in those including only low-mass protostars. In our sample, the mean interstellar polarization as a function of the average interstellar extinction in a region reaches a maximum value around 3% for A(V) = 5, after which it decreases. Our data also show a clear correlation of the mean value of the interstellar polarization with the dispersion of the interstellar magnetic field: the larger the dispersion, the smaller the polarization. Based on a comparison of our and previous results, we suggest that the dispersion in regions forming stars is larger than in quiescent regions.Comment: ApJ accepte

Vacuum fluctuations of a scalar field near a reflecting boundary and their effects on the motion of a test particle

The contribution from quantum vacuum fluctuations of a real massless scalar field to the motion of a test particle that interacts with the field in the presence of a perfectly reflecting flat boundary is here investigated. There is no quantum induced dispersions on the motion of the particle when it is alone in the empty space. However, when a reflecting wall is introduced, dispersions occur with magnitude dependent on how fast the system evolves between the two scenarios. A possible way of implementing this process would be by means of an idealized sudden switching, for which the transition occurs instantaneously. Although the sudden process is a simple and mathematically convenient idealization it brings some divergences to the results, particularly at a time corresponding to a round trip of a light signal between the particle and the wall. It is shown that the use of smooth switching functions, besides regularizing such divergences, enables us to better understand the behavior of the quantum dispersions induced on the motion of the particle. Furthermore, the action of modifying the vacuum state of the system leads to a change in the particle energy that depends on how fast the transition between these states is implemented. Possible implications of these results to the similar case of an electric charge near a perfectly conducting wall are discussed.Comment: 17 pages, 8 figure

Complements in modular and semimodular lattices

We study the relations between the complements of a and b when a is covered by b on finite upper-semimodular lattices and when a < b on modular lattices. We give some results that generalize the well known properties of complements in distibutive lattices. From there, we derive a property of semisimple R-modules.info:eu-repo/semantics/publishedVersio

Enhancing Context Specifications for Dependable Adaptive Systems: A Data Mining Approach

Context: Adaptive systems are expected to cater for various operational contexts by having multiple strategies in achieving their objectives and the logic for matching strategies to an actual context. The prediction of relevant contexts at design time is paramount for dependability. With the current trend on using data mining to support the requirements engineering process, this task of understanding context for adaptive system at design time can benefit from such techniques as well. Objective: The objective is to provide a method to refine the specification of contextual variables and their relation to strategies for dependability. This refinement shall detect dependencies between such variables, priorities in monitoring them, and decide on their relevance in choosing the right strategy in a decision tree. Method: Our requirements-driven approach adopts the contextual goal modelling structure in addition to the operationalization values of sensed information to map contexts to the system’s behaviour. We propose a design time analysis process using a subset of data mining algorithms to extract a list of relevant contexts and their related variables, tasks, and/or goals. Results: We experimentally evaluated our proposal on a Body Sensor Network system (BSN), simulating 12 resources that could lead to a variability space of 4096 possible context conditions. Our approach was able to elicit subtle contexts that would significantly affect the service provided to assisted patients and relations between contexts, assisting the decision on their need, and priority in monitoring. Conclusion: The use of some data mining techniques can mitigate the lack of precise definition of contexts and their relation to system strategies for dependability. Our method is practical and supportive to traditional requirements specification methods, which typically require intense human intervention

Direct Diode Lasers for Industrial Laser Cutting: A Performance Comparison with Conventional Fiber and CO2 Technologies

AbstractThe direct use of diode lasers for cutting sheet metal has high potential to decrease operational costs, but, currently, implementation in industrial environments is constrained by beam quality. In this paper the performance of a novel direct diode laser (DDL) with increased beam quality is documented for both fusion and flame cutting and compared to conventional CO2 and fiber laser sources. Experimental tests were carried out for steel and aluminium based on a Design of Experiments approach. Furthermore, an analytical model, focusing on the absorption of lasers in metals, is described here, which predicts and clarifies performance variation. Although the observed laser beam quality is still lower than the other studied technologies, industrially relevant cutting speeds, with acceptable surface quality, are achievable with DDL, as validated by our result

The role of structural evolution on the quantum conductance behavior of gold nanowires during stretching

Gold nanowires generated by mechanical stretching have been shown to adopt only three kinds of configurations where their atomic arrangements adjust such that either the [100], [111] or [110] zone axes lie parallel to the elongation direction. We have analyzed the relationship between structural rearrangements and electronic transport behavior during the elongation of Au nanowires for each of the three possibilities. We have used two independent experiments to tackle this problem, high resolution transmission high resolution electron microscopy to observe the atomic structure and a mechanically controlled break junction to measure the transport properties. We have estimated the conductance of nanowires using a theoretical method based on the extended H\"uckel theory that takes into account the atom species and their positions. Aided by these calculations, we have consistently connected both sets of experimental results and modeled the evolution process of gold nanowires whose conductance lies within the first and third conductance quanta. We have also presented evidence that carbon acts as a contaminant, lowering the conductance of one-atom-thick wires.Comment: 10 page

Quantum Conductance in Silver Nanowires: correlation between atomic structure and transport properties

We have analyzed the atomic arrangements and quantum conductance of silver nanowires generated by mechanical elongation. The surface properties of Ag induce unexpected structural properties, as for example, predominance of high aspect ratio rod-like wires. The structural behavior was used to understand the Ag quantum conductance data and the proposed correlation was confirmed by means of theoretical calculations. These results emphasize that the conductance of metal point contacts is determined by the preferred atomic structures and, that atomistic descriptions are essential to interpret the quantum transport behavior of metal nanostructures.Comment: 4 pages, 4 figure